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ScienceWeek
SCIENCEWEEK
ScienceWeek - October 11, 2002 Vol. 6 Number 41
An Online Research Digest Published Weekly Since 1997
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Concepts are games we play with our heads; methods are games we
play with our hands, which at times are so handy they can be
played without a head. -- Frank E. Egler
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Section 1
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1. On Phagocyte Discrimination of Normal vs. Damaged Self Cells
2. On Germ Cell Migration
3. Organization and Modularity in Metabolic Networks
4. Quantum Brownian Motion: Quantum and Classical Correlations
5. On Water Structure
6. On Charge Inversion in Polymers
7. Neuropsychiatric Symptoms in Dementia and Cognitive
Impairment
8. On Adolescent Depression
9. On Kidney Transplantation from Donors Without a Heartbeat
10. On Plastic Deformation of Crystals
11. On the Thickness of Wetting Layers
12. Helical Rosette Chiroptical Nanotubes
13. ScienceWeek Notices and Subscription Information
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Section 2
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1. ON PHAGOCYTE DISCRIMINATION OF NORMAL VS. DAMAGED SELF CELLS
S. Brown et al (Center for Inflammation Research, UK) discuss
phagocytic discrimination, the authors making the following
points:
1) Macrophage recognition and ingestion of "self" cells
undergoing apoptosis in vivo protects tissues from the toxic
contents of dying cells and modulates macrophage regulation of
inflammatory and immune responses(1,2). However, the complex
molecular mechanisms mediating macrophage discrimination between
viable and apoptotic cells are poorly understood(2,3). In
particular, little is known of why viable nucleated cells are
not engulfed by macrophages.
2) CD31 is a member of the immunoglobulin superfamily of
transmembrane cell-surface adhesion and signaling molecules that
is expressed by both leukocytes and macrophages(4). Homophilic
interaction of leukocyte CD31 with endothelial CD31 regulates
leukocyte motility and active movement across endothelial cell
surfaces away from the initial site of binding, directing
leukocytes towards intercellular junctions.
3) To reveal active repulsion of viable cells and to seek
specific capture or "tethering" of apoptotic cells, the authors
adapted a flow-chamber system(5) and studied macrophage binding
of viable and apoptotic leukocytes under conditions of flow. The
authors report they found that homophilic ligation of the cell
surface CD31 on viable leukocytes promoted their active,
temperature-dependent detachment under low shear, whereas such
CD31-mediated detachment was disabled in apoptotic leukocytes,
promoting tight binding and macrophage ingestion of dying cells.
The authors propose that CD31 (also known as
platelet-endothelial cell adhesion molecule-1, PECAM-1) is an
example of a cell-surface molecule that prevents phagocyte
ingestion of closely apposed viable cells by transmitting
"detachment" signals, and which changes function on apoptosis,
promoting tethering of dying cells to phagocytes.
References (abridged):
1. Kerr, J. F., Wyllie, A. H. & Currie, A. R. Apoptosis: a basic
biological phenomenon with wide-ranging implications in tissue
kinetics. Br. J. Cancer 26, 239-257 (1972)
2. Savill, J. & Fadok, V. Corpse clearance defines the meaning
of cell death. Nature 407, 784-788 (2000)
3. Green, D. R. & Beere, H. M. Apoptosis. Mostly dead. Nature
412, 133-135 (2001)
4. Newman, P. J. The biology of PECAM-1. J. Clin. Invest. 99,
3-8 (1997)
5. Sakariassen, K. S., Aarts, P. A., de Groot, P. G., Houdijk,
W. P. & Sixma, J. J. A perfusion chamber developed to
investigate platelet interaction in flowing blood with human
vessel wall cells, their extracellular matrix, and purified
components. J. Lab. Clin. Med. 102, 522-535 (1983)
Nature 2002 418:200
Web Links: phagocytes macrophages
Related Background Brief:
CROSS-TALK BETWEEN CELL ADHESION MOLECULES REGULATES THE
MIGRATION VELOCITY OF NEUTROPHILS. Although the adhesive
mechanisms underlying the capture and immobilization of
circulating neutrophils in inflamed blood vessels have been well
described, factors controlling the subsequent migration of
neutrophils over and through the blood vessel endothelium are
poorly understood. Directional rearrangement of the actin
cytoskeleton within the neutrophil, along with modulation of
integrin-mediated adhesion, are necessary for neutrophil
migration. Signals from chemotactic agents and from the adhesive
substrate may regulate these processes, but little is known
about their relative importance or their mode of integration.
The authors examined the kinetics of neutrophil migration after
formyl tripeptide or platelet-activating factor was perfused
over neutrophils that were already rolling on the adhesion
molecule P-selectin, which was presented either on the surface
of immobilized platelets or in purified form coated on glass
capillaries. Upon activation, neutrophils stopped rolling,
spread and began to migrate; each of these processes was
dependent on beta2 integrin (CD11b/CD18). The rate of migration
increased over a period of about 8 minutes and was modulated
directly by both the P-selectin and the CD31 surface receptors.
Antibody blockade of either CD31 or P-selectin on platelets
resulted in a reduction in the velocity of migration, and
simultaneous blockade of both receptors reduced velocity
further. Purified CD31 and P-selectin (but not a control
adhesion molecule, ICAM-1) increased migration velocity in a
concentration-dependent and additive manner that reconstituted
the migratory behavior observed on platelets. The authors
suggest these studies show that binding of ligands to CD31
and/or P-selectin modifies the rate of integrin-supported
neutrophil migration. This novel example of "cross-talk" between
surface receptors suggests that cell adhesion molecules might
generally transduce accessory signals between adjacent cells to
modify their migratory responses to chemotactic signals. G.E.
Rainger et al: Current Biology 1997 7:316.
Related Background Brief:
CONSTITUTIVE DEATH OF PLATELETS LEADING TO SCAVENGER
RECEPTOR-MEDIATED PHAGOCYTOSIS. A CASPASE-INDEPENDENT CELL
CLEARANCE PROGRAM. Apoptosis is a physiological program for the
deletion of cells in which caspases govern events leading to
safe clearance by phagocytes. However, a growing weight of
evidence now suggests that not all forms of programmed cell
death are caspase-dependent. The authors report a complete and
constitutive but caspase-independent program for the specific
phagocytic clearance of intact effete platelets, anucleated
blood cells of critical importance in health and disease.
Platelets aged in vitro not only exhibited increased expression
of pro-apoptotic Bak and Bax but also evidenced constitutive
diminution of function such as decreased aggregation to ADP,
which was accelerated by culture in the absence of plasma. This
abrogation of cell function in plasma-deprived platelets was
associated with morphological and biochemical features similar
to those of granulocyte apoptosis, that is, cytoplasmic
condensation, plasma membrane changes including exposure of
phosphatidylserine and the granule protein P-selectin, and
recognition by phagocyte scavenger receptors. However, and in
contrast with constitutive death of other inflammatory blood
cells by apoptosis, these events were not affected by caspase
inhibitors, nor was there evidence of caspase-3 activation
either by hydrolysis of analog peptide substrates or Western
blot analysis, serving to emphasize that neither programmed cell
death nor clearance by phagocytes need involve caspases. S.B.
Brown et al: J Biol Chem 2000 275:5987.
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2. ON GERM CELL MIGRATION
H.-Arno J. Mueller (Heinrich-Heine University, DE) discusses
germ cell migration, the author making the following points:
1) Fertilized eggs of metazoan organisms undergo a series of
rapid cleavage divisions, which give rise to two distinct cell
types: the somatic cells and the germ cells [1] . During
morphogenesis of the gonad, the germ cells migrate through the
interior of the embryo to the somatic gonadal tissues. Germ
cells have to overcome many hurdles during their migration: they
need to cross an epithelial monolayer; they migrate
directionally between tissues; and they have to recognize and
firmly attach to target tissues. Systematic genetic screens in
Drosophila are providing insights into the pathways that control
the directional migration of germ cells [2,3] . An involved
novel gene, called "slow as molasses" (slam), has now been
identified which is exceptional in that this gene is active
before germ cell migration -- during the establishment of the
somatic cells [4,5].
2) In Drosophila, fertilization is followed by 13 rapid mitotic
cycles without cytokinesis; most of the resulting nuclei migrate
to the cortical cytoplasm by cycle 9. The germ cells are the
first cells to be formed. During cycle 9, the germ cells pinch
off in a particular posterior cortical region of the egg
containing the germ plasm. At interphase of cycle 14,
cytokinesis of the somatic cells proceeds in a process called
"cellularization". The germ cells are attached to a posterior
region of the blastoderm epithelium, the part that will give
rise to the distal tip of the posterior midgut primordium. When
the midgut primordium has invaginated during gastrulation, the
germ cells begin their migration [1] . The germ cells first
migrate through the posterior midgut epithelium to its basal
side, where they move along the basal surface of the midgut into
the lateral mesoderm. In the mesoderm, the germ cells split up
into two bilateral groups and then associate with the gonadal
mesoderm. Later the gonadal mesoderm and the germ cells coalesce
to establish the embryonic gonad.
3) What tells the germ cells when to start moving, where to move
and when to stop? The analysis of three genes provided strong
evidence that the directional migration of the germ cells is
governed by attractive and repulsive cues.
References (abridged):
1. Starz-Gaiano M. and Lehmann R. (2001) Moving towards the next
generation. Mech. Dev., 105:5-18.
2. Brohier H.T., Moore L.A., vanDoren M., Newman S. and Lehmann
R. (1998) zfh-1 is required for germ cell migration and gonadal
mesoderm development in Drosophila Development, 125:655-666.
3. Moore L.A., Brohier H.T., vanDoren M., Lunsford L.B. and
Lehmann R. (1998) Identification of genes controlling germ cell
migration and embryonic gonad formation in Drosophila
Development, 125:667-678.
4. Stein J.A., Brohier H.T., Moore L.A. and Lehmann R. (2002)
slow as molasses is required for polarized membrane growth and
germ cell migration in Drosophila Development, 129:3925-3934.
5. Lecuit T., Samanta R. and Wieschaus E. (2002) slam encodes a
developmental regulator of polarized membrane growth during
cleavage of the Drosophila embryo. Dev. Cell, 2:425-436.
Current Biology 2002 12:R612
Web Links: germ cell migration Drosophila embryo
Related Background Brief:
ZFH-1 IS REQUIRED FOR GERM CELL MIGRATION AND GONADAL MESODERM
DEVELOPMENT IN DROSOPHILA. In Drosophila as well as in many
vertebrate systems, germ cells form extra-embryonically and
migrate into the embryo before navigating toward gonadal
mesodermal cells. How the gonadal mesoderm attracts migratory
germ cells is not understood in any system. The authors report
they have taken a genetic approach to identify genes required
for germ cell migration in Drosophila. The authors describe the
role of zfh-1 in germ cell migration to the gonadal mesoderm. In
zfh-1 mutant embryos, the initial association of germ cells and
gonadal mesoderm is blocked. Loss of zfh-1 activity disrupts the
development of two distinct mesodermal populations: the caudal
visceral mesoderm and the gonadal mesoderm. The authors
demonstrate that the caudal visceral mesoderm facilitates the
migration of germ cells from the endoderm to the mesoderm. Zfh-1
is also expressed in the gonadal mesoderm throughout the
development of this tissue. Ectopic expression of Zfh-1 is
sufficient to induce additional gonadal mesodermal cells and to
alter the temporal course of gene expression within these cells.
Finally, through analysis of a tinman zfh-1 double mutant, the
authors show that zfh-1 acts in conjunction with tinman, another
homeodomain protein, in the specification of lateral mesodermal
derivatives, including the gonadal mesoderm. H.T. Broihier et
al: Development 1998 125:655.
Related Background Brief:
IDENTIFICATION OF GENES CONTROLLING GERM CELL MIGRATION AND
EMBRYONIC GONAD FORMATION IN DROSOPHILA. Gonadogenesis in the
Drosophila embryo is a complex process involving numerous
cellular migratory steps and cell-cell interactions. The
mechanisms guiding germ cells to move through, recognize and
adhere to specific cell types are poorly understood. In order to
identify genes that are required for these processes, the
authors conducted an extensive mutagenesis of the third
chromosome and screened for mutations disrupting germ cell
migration at any point in embryonic development. Phenotypic
analysis of these mutants demonstrates that germ cell migration
can be broken down into discrete developmental steps, with each
step requiring a specific set of genes. Many of these genes are
involved in the development of gonadal mesoderm, the tissue that
associates with germ cells to form the embryonic gonad.
Moreover, mutations that were isolated affecting embryonic
patterning as well as germ cell migration suggest that the
origin of gonadal mesoderm lies within the eve domain of the
developing mesoderm. L.A. Moore et al: Development 1998 125:667.
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3. ON ORGANIZATION AND MODULARITY IN METABOLIC NETWORKS
E. Ravasz et al ( University of Notre Dame, US) discuss
metabolic networks, the authors making the following points:
1) The identification and characterization of system-level
features of biological organization is a key issue of
post-genomic biology (1-3). The concept of modularity assumes
that cellular functionality can be seamlessly partitioned into a
collection of modules. Each module is a discrete entity of
several elementary components and performs an identifiable task,
separable from the functions of other modules (1,4,5). Spatially
and chemically isolated molecular machines or protein complexes
(such as ribosomes and flagella) are prominent examples of such
functional units, but more extended modules, such as those
achieving their isolation through the initial binding of a
signaling molecule, are also apparent.
2) Simultaneously, it is recognized that the thousands of
components of a living cell are dynamically interconnected, so
that the cell's functional properties are ultimately encoded
into a complex intracellular web of molecular interactions (2).
This is perhaps most evident with cellular metabolism, a fully
connected biochemical network in which hundreds of metabolic
substrates are densely integrated through biochemical reactions.
Within this network, however, modular organization (i.e., clear
boundaries between subnetworks) is not immediately apparent.
Indeed, recent studies have demonstrated that the probability
that a substrate can react with (k) other substrates [the degree
distribution P(k) of a metabolic network] decays as a power law
in all organisms, suggesting that metabolic networks have a
scale-free topology. A distinguishing feature of such scale-free
networks is the existence of a few highly connected nodes (e.g.,
pyruvate or coenzyme A), which participate in a very large
number of metabolic reactions. With a large number of links,
these hubs integrate all substrates into a single, integrated
web in which the existence of fully separated modules is
prohibited by definition.
3) In summary: Spatially or chemically isolated functional
modules composed of several cellular components and carrying
discrete functions are considered fundamental building blocks of
cellular organization, but their presence in highly integrated
biochemical networks lacks quantitative support. The authors
demonstrate that the metabolic networks of 43 distinct organisms
are organized into many small, highly connected topologic
modules that combine in a hierarchical manner into larger, less
cohesive units, with their number and degree of clustering
following a power law. Within Escherichia coli, the uncovered
hierarchical modularity closely overlaps with known metabolic
functions. The identified network architecture may be generic to
system-level cellular organization.
References (abridged):
1. L. H. Hartwell, J. J. Hopfield, S. Leibler, A. W. Murray,
Nature 402, C47 (1999)
2. H. Kitano, Science 295, 1662 (2002)
3. Y. I. Wolf, G. Karev, E. V. Koonin, Bioessays 24, 105 (2002)
4. D. A. Lauffenburger, Proc. Natl. Acad. Sci. U.S.A. 97, 5031
(2000)
5. C. V. Rao and A. P. Arkin, Annu. Rev. Biomed. Eng. 3, 391
(2001)
Science 2002 297:1551
Web Links: metabolic networks systems biology
Related Background Brief:
CONTROL MOTIFS FOR INTRACELLULAR REGULATORY NETWORKS. A number
of technological innovations are yielding unprecedented data on
the networks of biochemical, genetic, and biophysical reactions
that underlie cellular behavior and failure. These networks are
composed of hundreds to thousands of chemical species and
structures, interacting via nonlinear and possibly stochastic
physical processes. A central goal of modern biology is to
optimally use the data on these networks to understand how their
design leads to the observed cellular behaviors and failures.
Ultimately, this knowledge should enable cellular engineers to
redesign cellular processes to meet industrial needs (such as
optimal natural product synthesis), aid in choosing the most
effective targets for pharmaceuticals, and tailor treatment for
individual genotypes. The size and complexity of these networks
and the inevitable lack of complete data, however, makes
reaching these goals extremely difficult. If it proves possible
to modularize these networks into functional subnetworks, then
these smaller networks may be amenable to direct analysis and
might serve as regulatory motifs. These motifs, recurring
elements of control, may help to deduce the structure and
function of partially known networks and form the basis for
fulfilling the goals described above. The authors review a
number of approaches to identifying and analyzing control motifs
in intracellular networks. C.V. Rao and A.P. Arkin: Annu Rev
Biomed Eng 2001 3:391.
Related Background Brief:
NETWORK MOTIFS IN THE TRANSCRIPTIONAL REGULATION NETWORK OF
ESCHERICHIA COLI. Little is known about the design principles of
transcriptional regulation networks that control gene expression
in cells. Recent advances in data collection and analysis,
however, are generating unprecedented amounts of information
about gene regulation networks. To understand these complex
wiring diagrams, the authors sought to break down such networks
into basic building blocks. The authors generalize the notion of
motifs, widely used for sequence analysis, to the level of
networks. The authors define "network motifs" as patterns of
interconnections that recur in many different parts of a network
at frequencies much higher than those found in randomized
networks. The authors applied new algorithms for systematically
detecting network motifs to one of the best-characterized
regulation networks, that of direct transcriptional interactions
in Escherichia coli. The authors report they find that much of
the network is composed of repeated appearances of three highly
significant motifs. Each network motif has a specific function
in determining gene expression, such as generating temporal
expression programs and governing the responses to fluctuating
external signals. The motif structure also allows an easily
interpretable view of the entire known transcriptional network
of the organism. The authors suggest this approach may help
define the basic computational elements of other biological
networks. S.S. Shen-Orr et al: Nat Genet 2002 31:64.
Related Background:
CELL BIOLOGY: FUNCTIONAL MODULES IN BIOLOGICAL ORGANIZATION
The term "phenomenology" has a variety of meanings, but in this
report we are concerned with only one meaning of the term: we
take the term "phenomenology" to refer to a scientific approach
that focuses on explanations based on formal relationships among
observed entities or processes, as opposed to an approach
("reductionist") that focuses on explanations based on analysis
of the fundamental constituents of such entities or processes.
Using the terms in this way, we have the following examples: a)
Thermodynamics is a phenomenological approach to the behavior of
a gas; statistical mechanics is a reductionist approach to the
behavior of a gas. b) Mendelian genetics is a phenomenological
approach to the inheritance of traits; molecular genetics is a
reductionist approach to the inheritance of traits. One can
think of similar dichotomies in almost every field in science.
The term "reductionist" has had an unfortunate history in
biology, where it has been used to characterize the idea that
any biological entity or process can be "explained" in terms of
the laws of physics and chemistry. Certainly, the behavior of
every entity or process in the natural world is ultimately
totally dependent on the laws of physics and chemistry (which
leads to the idea that the behavior can "in principle" be
derived ["explained"] from such laws), but the actual practical
possibility of any explanations of the behavior of observable
entities or processes in terms of the laws of physics and
chemistry depends on the current state of our knowledge
concerning both the observables and the fundamental laws. In the
practice of science, it can be argued that it does not matter
much which approach is used, phenomenological or reductionist,
provided the approach produces results that are useful, or which
help in understanding the behavior of the entity or process, or
which suggest new and intriguing questions. Beyond this, the
discussion properly belongs in the domain of philosophy and not
science.
The above preamble is necessary in the context of the present
report, since the report concerns a recent article in which a
group of authors (2 molecular biologists, a biophysicist, and a
physiologist) call for a more "phenomenological" approach to
cell biology, an interesting idea, since cell biology is not one
of those areas of biology where such appeals are common. During
the last 50 years, in fact, cell biology has experienced a
remarkable flowering based on the application of fundamental
biochemistry, biophysics, and molecular biology to entities and
processes recognizable at the cellular level (i.e., micron-scale
objects).
L.H. Hartwell et al (4 authors at 3 installations, US) present
an essay calling for a transition from molecular to "modular"
cell biology, the authors making the following points:
1) The authors begin their essay with the following statement:
"Although living systems obey the laws of physics and chemistry,
the notion of function or purpose differentiates biology from
other natural sciences. Organisms exist to reproduce, whereas,
outside religious belief, rocks and stars have no purpose.
Selection for function has produced the living cell, with a
unique set of properties that distinguish it from inanimate
systems of interacting molecules."
2) The authors propose that a major challenge for science in the
21st century is to develop an integrated understanding of how
biological cells and organisms survive and reproduce. The
authors suggest that cell biology is in transition from a
science that was preoccupied with assigning functions to
individual proteins or genes, to a science that is now
attempting to cope with the complex sets of molecules that
interact to form "functional modules".
3) The authors define a "functional module" as a discrete entity
whose function is separable from those of other modules. This
separation depends on chemical isolation, which can originate
from spatial localization or from chemical specificity. For
example, a ribosome, the module that synthesizes proteins,
concentrates the reactions involved in making a polypeptide into
a single particle, thus spatially isolating its function.
Modules can be insulated from or connected to each other. The
authors suggest that in the future, the higher-level properties
of cells, such as their ability to integrate information from
multiple sources, will be described by the pattern of
connections among their functional modules.
4) The authors point out that the number of cellular functional
modules that have been analyzed in detail is very small, and
each of these efforts has required intensive study. The authors
suggest that biologists need to study more functions at the
modular level and develop methods that make it easier to
determine the relationship of inputs to outputs of modules,
their biochemical connectivity, and the states of key
intermediates within them.
5) The authors suggest that the best test of our understanding
of cells will be to make quantitative predictions about their
behavior and test them. This will require detailed simulations
of the biochemical processes occurring within the modules. "But
making predictions is not synonymous with understanding. We need
to develop simplifying, higher-level models and find general
principles that will allow us to grasp and manipulate the
functions of biological modules."
6) The authors summarize their essay: "Cellular functions, such
as signal transmission, are carried out by 'modules' made up of
many species of interacting molecules. Understanding how modules
work has depended on combining phenomenological analysis with
molecular studies. General principles that govern the structure
and behavior of modules may be discovered with help from
synthetic sciences such as engineering and computer science,
from stronger interactions between experiment and theory in cell
biology, and from an appreciation of evolutionary constraints."
Editor's note: The essential idea here can be presented as
follows: Consider a computer, a machine with a "purpose" -- to
compute. A computer operates on its inputs in specific ways to
produce specific outputs. A "flow diagram" of computer dynamics
is a phenomenological description of the behavior of the
machine. A complete "wiring diagram" of electrical entities and
events in the machine is a reductionist description of the
behavior of the machine. (Of course, from the perspective of
quantum mechanics, the wiring diagram is itself
phenomenological.) Suppose we are given a machine and know
nothing about it except that it operates on inputs to produce
outputs. If our problem is to predict the behavior of the
machine in response to particular inputs, there will come a time
when a flow diagram, albeit "phenomenological", will be of
immense value in understanding how the machine works. What the
authors propose is that much of the future of cell biology will
lie in the construction of the equivalent of detailed and
predictive flow diagrams for the internal operations of
biological cells.
Nature 1999 402supp:C47
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4. QUANTUM BROWNIAN MOTION: QUANTUM AND CLASSICAL CORRELATIONS
J. Eisert and M. B. Plenio (Imperial College London, UK) discuss
Brownian motion, the authors making the following points:
1) No quantum system is completely isolated from its
environment. This basic yet fundamental observation has been one
of the key insights allowing an appropriate understanding of the
dynamical emergence of classical properties in quantum systems.
Not all initial states are equally fragile under the interaction
of a distinguished quantum system with its environment, and a
relatively robust set of so-called preferred or pointer states
is selected dynamically, a process typically referred to as
environment-induced superselection ("einselection") or simply
decoherence. This process is thought to play an important role
in the transition from quantum to classical [1,2].
2) The most frequently employed model in investigations of
einselection is the quantum Brownian motion model [3,4]. In this
model one considers a distinguished quantum oscillator which is
linearly coupled via the position operators to an environment
consisting of many harmonic oscillators. Initially, the state of
the system of interest and its environment are assumed to be
uncorrelated, and the state of the environment is taken to be
the canonical (Gibbs) state with respect to some temperature.
The typical argument is that starting from the initial
situation, the product state of the composite quantum system
turns into a correlated state due to the interaction. If one
considers the reduced state of the distinguished system, one
finds that it undergoes dissipation and decoherence. In the
context of quantum Brownian motion, it is often argued that
entanglement is unavoidable.
3) The aim of the authors is to revisit the question of the
creation of entanglement in quantum Brownian motion with recent
powerful methods from quantum information theory [5]. The
analysis is split into two parts. In the first part the authors
demonstrate that surprisingly, quantum Brownian motion does not
necessarily create entanglement between the distinguished system
and its environment. The joint state of the system and its
environment may be separable at all times, that is, not
entangled: All correlations are merely classical in the sense
that one could prepare the same state by mixing product states,
which can in turn be prepared by implementing local quantum
operations only. The second part of the analysis is concerned
with the question whether there exist initial states of the
distinguished oscillator for which the joint state becomes
immediately entangled. This question is answered positively, and
it is demonstrated that all pure Gaussian states have this
property, regardless of the initial temperature of the
environment.
4) In summary: The authors investigate the entanglement
properties of the joint state of a distinguished quantum system
and its environment in the quantum Brownian motion model. This
model is a frequent starting point for investigations of
environment-induced superselection. Using recent methods from
quantum information theory, the authors show that there exists a
large class of initial states for which no entanglement will be
created at all times between the system of salient interest and
the environment. If the distinguished system has been initially
prepared in a pure Gaussian state, then entanglement is created
immediately, regardless of the temperature of the environment
and the nonvanishing coupling.
References (abridged):
1. D. Giulini et at, Decoherence and the Appearance of a
Classical World in Quantum Theory (Springer, Heidelberg, 1996);
H. P. Breuer and F. Petruccione, The Theory of Open Quantum
Systems (Oxford University Press, Oxford, 2002).
2. W.H. Zurek, Phys. Today 44, No. 10, 36 (1991); D. Guilini, C.
Kiefer, and H. D. Zeh, Phys. Lett. A 199, 291 (1995); J.
Halliwell and A. Zoupas, Phys. Rev. D 52, 7294 (1995); WG.Unruh
and W.H. Zurek, ibid. 40, 1071 (1989); J.R. Anglin, J.P. Paz,
and W.H. Zurek, Phys. Rev. A 55, 4041 (1997).
3. A. 0. Caldeira and A. J. Leggett, Physica (Amsterdam) 121A,
587 (1983).
4. F. Haake and R. Reibold, Phys. Rev. A 32, 2462 (1985); P.
Riseborough, P. Hanggi, and U. Weiss, ibid. 31, 471 (1985); B.
L. Hu, J. P. Paz, and Y. Zhang, Phys. Rev. D 45, 2843 (1992); R.
Karrlein and H. Grabert, Phys. Rev. E 55, 153 (1997); P.
Talkner, Ann. Phys. (N.Y.) 167, 390 (1986).
5. R. F. Werner, Quantum Information, Springer Tracts in Modern
Physics Vol. 173 (Springer, Heidelberg, 2001).
Phys. Rev. Lett. 2002 89:137902
Web Links: quantum Brownian motion quantum decoherence
Related Background:
ENTANGLEMENT, DECOHERENCE, AND THE QUANTUM-CLASSICAL BOUNDARY
Quantum mechanical entanglement is a phenomenon that has caught
the imagination of the public as one of the more bizarre
consequences of fundamental physical theory. Entanglement is
unique to quantum mechanics, and involves a relationship (a
"superposition of states") between the possible quantum states
of two entities such that when the possible states of one entity
collapse to a single state as a result of suddenly imposed
boundary conditions, a similar and related collapse occurs in
the possible states of the entangled entity no matter where or
how far away the entangled entity is located. Entanglement
arises from the wave function equation of quantum mechanics,
which has an array of possible function solutions rather than a
single function solution, with each possible solution describing
a set of possible probabilistic quantum states of the physical
system under consideration. Upon fixation of the appropriate
boundary conditions, the array of possible solutions collapses
into a single solution. For many quantum mechanical physical
systems, the fixation of boundary conditions is a theoretical
and fundamental consequence of some interaction of the physical
system with something outside that system, e.g., an interaction
with the measuring device of an observer.
In this context, two entities that are described by the same
array of possible solutions to the wave function equation are
said to be "coherent", and when events decouple these entities,
the consequence is said to be "decoherence". As a physical
phenomenon, entanglement was discussed many years ago, most
particularly following the publication in 1935 of the often
quoted Einstein-Podolsky-Rosen paper (Phys Rev 1935 47:777).
These discussions have been in the form of "gedanken" (thought)
experiments involving two quantum-mechanical entangled entities.
More recently, however, there have been laboratory constructions
of actual quantum mechanical systems exhibiting such
entanglement phenomena, and the reportage of these laboratory
arrangements by the media have engaged the public fancy.
Essential here is that any purely verbal account of quantum
mechanical phenomena is severely limited by the constraint that
the properties of quantum mechanical systems can be precisely
described only by the equations relevant for those systems, and
all other descriptions usually introduce serious ambiguities.
Serge Haroche (Ecole Normale Superieure Paris, FR) reviews
quantum mechanical entanglement, decoherence, and the question
of the boundary between the physics of quantum phenomena and the
physics of classical phenomena. Haroche makes the following
points:
1) In quantum mechanics, a particle can be delocalized
(simultaneously occupy various probable positions in space), can
be simultaneously in several energy states, and can even have
several different identities at once. This apparent "weirdness"
behavior is encoded in the wave function of the particle.
2) Recent decades have witnessed a rash of experiments designed
to test whether nature exhibits implausible nonlocality. In such
experiments, the wave function of a pair of particles flying
apart from each other is entangled into a non-separable
superposition of states. The quantum formalism asserts that
detecting one of the particles has an immediate effect on the
other, even if they are very far apart, even far enough apart to
be out of interaction range. The experiments clearly demonstrate
that the state of one particle is always correlated to the
result of the measurement performed on the other particle, and
in just the strange way predicted by quantum mechanics.
3) An important question is: Why and how does quantum weirdness
disappear (decoherence) in large systems? In the last 15 years,
entirely solvable models of decoherence have been presented by
various authors (e.g., Leggett, Joos, Omnes, Zeh, Zurek), these
models based on the distinction in large objects between a few
relevant macroscopic observables (e.g., position or momentum)
and an "environment" described by a huge number of variables,
such as positions and velocities of air molecules, number of
black-body radiation photons, etc. The idea of these models,
essentially, is that the environment is "watching" the path
followed by the system (i.e., interacting with the system), and
thus effectively suppressing interference effects and quantum
weirdness, and the result of this process is that for
macroscopic systems only classical physics obtains.
4) In mesoscopic systems, which are systems between macroscopic
and microscopic dimensions, decoherence may occur slowly enough
to be observed. Until recently, this could only be imagined in a
gedanken experiment, but technological advances have now made
such experiments real, and these experiments have opened this
field to practical investigation.
Physics Today 1999 July
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5. ON WATER STRUCTURE
T. Head-Gordon and G. Hura (University of California Berkeley,
US) discuss water structure, the authors making the following
points:
1) The fundamental unit of water structure is the hydrogen bond.
In ice I a given water molecule is hydrogen bonded to four water
neighbors in a tetrahedral structure that gives rise to a
crystal made up of connected hexagonal rings. In the case of
crystalline materials such as ice I, X-rays and neutrons are
scattered by atomic centers at discrete angles represented as
sinusoidal (Fourier) components of the electron density and
nuclear scattering potential of the specimen, respectively. The
scattering angle is determined by the spatial period of the
Fourier component that is responsible for the scattering. The
spatial period of each Fourier component of the electron density
is determined by the lengths of the unit cell vectors of the
crystal.
2) Representation of the electron density as a sum of Fourier
components is equally applicable to noncrystalline materials,
however, such as the water liquid. As a result it is still true
that the spatial period of the Fourier component can be
calculated from the measured scattering angle. As with
crystalline materials, the amplitude of each Fourier component
of the electron density is given by the square root of the
scattered intensity. Information about the vector direction of
the Fourier component is lost in scattering from liquids,
however, unlike the case of crystals.
3) In the case of liquid water, the strict adherence to
hydrogen-bonded hexagons of the ice crystal gives way to greater
translational and rotational motion of waters and a broader
distribution of hydrogen-bonded configurations, including a
variety of polygons of varying sizes and degrees of puckering or
distortion, all of which result in a more compact arrangement of
water molecules. The electron density of the liquid is now
characterized by the scattering as a diffuse water ring rather
than a discrete distribution of Fourier components. Furthermore,
the scattering intensity is peaked at a distance that remains
larger than the center-to-center distance between individual
water molecules, which is typically approximately 0.28 nm. Thus,
it is clear that the most prominent Fourier components of the
scattering density of pure liquid water have a repeat distance
that is larger than the oxygen-oxygen nearest neighbor distance.
This tells us that the fundamental scattering unit in liquid
water must be something bigger than pairs of hydrogen-bonded
water molecules. In fact, it is a measure of the highly
associated three-dimensional hydrogen-bonded network of the
water liquid. The importance of accurate experimental
information and classical and emerging ab initio simulation
methodologies is their ability to characterize this fundamental
unit of scattering to help us to understand the topology of the
hydrogen-bonded network over the full phase diagram.
References (abridged):
1. Water, a comprehensive treatise; Franks, F., Ed.; Plenum
Press: New York, 1972.
2. Dore, J. C.; Teixeira, J. Hydrogen-bonded liquids:
proceedings of the NATO Advanced Study Institute on
Hydrogen-bonded Liquids, Institut Scientifique de Cargese,
Corsica, April 3-15, 1989; Kluwer Academic Publishers:
Dordrecht,; Boston, 1991.
3. Bellissent-Funel, M. C.; Dore, J. C. Hydrogen bond networks;
Kluwer Academic Publishers: Dordrecht, Boston, 1994.
4. Franks, F. Water: A Matrix of Life, 2nd ed.; Royal Society of
Chemistry: Cambridge, 2000.
5. Stillinger, F. H. Science (USA) 1980, 209, 451-7.
Chem. Rev. 2002 102:2651
Web Links: water structure
Related Background:
LIQUID WATER: CURRENT RESEARCH PROBLEMS
In general, "ab initio" (from first principles) calculations
utilize experimental data on atomic systems to facilitate the
adjustment of parameters. The excellent performance of ab initio
techniques distinguishes them from their predecessors, the
"semiempirical" methods, with the quantitative predictions of ab
initio techniques usually falling within experimental error when
comparisons are made to experimental measurements.
Contemporary molecular dynamics simulations, which are
extrapolations of statistical mechanics and which originate in
the work of Alder and Wainright in the 1960s, are computer
simulations of molecular systems typically involving hundreds or
sometimes thousands of idealized particles interacting with
physically realistic potentials. Such molecular dynamics
simulations can provide time-dependent properties of a liquid,
but most commonly they are used to produce a set of
configurations and forces which can be averaged to give
equilibrium properties of the system.
F.N. Keutsch and R.L. Saykally (University of California
Berkeley, US) discuss current research on liquid water. The
quest to achieve an accurate description of liquid water has
produced major advances in the last two decades, but despite the
construction of hundreds of model force fields for use in
simulations, the great advances in computational technology, and
the development of powerful ab initio molecular dynamics
methods, we remain unable to accurately calculate the properties
of liquid water (e.g., heat capacity, density, dielectric
constant, compressibility) over significant ranges in various
conditions. We do not yet have a satisfactory molecular
description of how a proton moves in the liquid, we do not fully
understand the molecular nature of the surfaces of either ice or
liquid water, nor do we understand the origin of the intriguing
anomalies and singularities found in the deeply supercooled
region. Although it is clear that the hydrogen bond network and
its fluctuations and rearrangement dynamics determine the
properties of the liquid, no experimental studies exist that
reveal detailed information on a molecular level without
considerable interpretation. Moreover, the reliability of water
models for simulating solvation phenomena and biological
processes remains relatively untested. A general obstacle to
resolving these issues is that of correctly describing the
many-body or cooperative nature of the hydrogen bonding
interactions among a collection of water molecules. Theoretical
work has demonstrated that the H-bond is dominated by
electrostatic interactions, balanced by the repulsive electron
exchange, but that dispersion makes an appreciable contribution,
whereas induction (polarization) is the dominant many-body
effect. It has proven notoriously difficult to accurately
parameterize these interactions from ab initio calculations.
Proc. Nat. Acad. Sci. Sci. 2001 98:10533
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6. ON CHARGE INVERSION IN POLYMERS
T.T. Nguyen and B.I. Shklovskii (University of Minnesota, US)
discuss polymer charge inversion, the authors making the
following points:
1) The inversion of the negative charge of a DNA double helix by
its complexation with a positive polyelectrolyte (PE) is used
for gene delivery. The positive charge of a DNA-PE complex
facilitates DNA contact with a typically negative cell membrane,
making penetration into the cell hundreds of times more likely
[1]. Charge inversion of DNA-PE complexes was confirmed recently
by electrophoresis [2]. At a given concentration of long DNA
helices, when the concentration of shorter PE molecules
increases, at some critical concentration the electrophoretic
mobility of a DNA-PE complex changes sign from negative to
positive.
2) The challenging and counterintuitive phenomenon of charge
inversion of a macroion by an oppositely charged PE and other
multivalent ions has attracted significant attention [3-5].
Intuitively, one can think that, when a PE completely
neutralizes a large macroion such as the DNA double helix, new
molecules of a PE do not attach to the macroion. Indeed, the
Poisson-Boltzmann approximation for the description of screening
of a macroion by any counterions including PE does not lead to
charge inversion. Charge inversion can be explained if one takes
into account that the surface potential of an
already-neutralized macroion is locally affected by a new
approaching PE molecule or, in other words, it can be explained
if one takes into account correlations between PE molecules.
3) For quantitative consideration, the charges of a macroion are
always assumed to be uniformly smeared. This approach ignores
the interference between the structure of the macroion surface
and that of a PE and clearly is not fully satisfactory. More
importantly, it is not clear whether or not charge inversion is
an artifact of the assumption of uniformly smeared charge.
4) In summary: The authors model one strand of DNA by a
one-dimensional lattice (ODL) of negative charges and consider
the problem of inversion of its charge by a positive
polyelectrolyte (PE). In the neutral state of the ODL-PE
complex, each of the ODL charges is locally compensated by a PE
charge. When an additional PE molecule is adsorbed by ODL, its
charge gets fractionalized into monomer charges of defects
(tails and arches) on the background of the perfectly
neutralized ODL. Defects spread all over the ODL, eliminating
the self-energy of PE. For DNA this fractionalization mechanism
leads to a substantial inversion of charge, a phenomenon which
is widely used for gene delivery.
References (abridged):
1. A.V. Kabanov and V.A. Kabanov, Bioconjug. Chem. 6, 7 (1995);
Adv. Drug Delivery Rev. 30, 49 (1998).
2. V.A. Kabanov, A. A. Yaroslavov, and S.A. Sukhisvili, J.
Controlled Release 39, 173 (1996).
3. T. Wallin and P. Linse, J. Phys. Chem. 100, 17 873 (1996).
4. E.M. Mateescu, C. Jeppersen, and P. Pincus, Europhys. Lett.
46, 454 (1999).
5. S. Y. Park, R. F. Bruinsma, and W. M. Gelbart, Europhys.
Lett. 46, 493 (1999).
Phys. Rev. Lett. 2002 89:018101
Web Links: polymer polyelectrolytes
Related Background:
A NEW COLLOID STABILIZATION MECHANISM
V. Tohver et al (University of Illinois Urbana-Champaign, US)
discuss a new mechanism of *colloid stabilization. Colloidal
suspensions have widespread use in applications ranging from
advanced materials to drug delivery. By tailoring interactions
between colloidal particles, one can design stable fluids, gels,
or colloidal crystals needed for ceramics processing, coatings,
direct-write photonic devices, and pharmaceutical applications.
Long-range attractive *van der Waals forces are ubiquitous and
must be balanced by *Coulombic, steric, or other repulsive
interactions to engineer the desired degree of colloidal
stability. The authors report the discovery of a new mechanism
for regulating the stability of colloidal particles. Colloidal
microspheres with negligible charge, which *flocculate when
suspended alone in aqueous solution, undergo a remarkable
stabilizing transition upon the addition of a critical volume
fraction of highly charged nanoparticle species. *Zeta potential
analysis reveals that these microspheres exhibit an effective
charge build-up in the presence of such nanoparticle species.
*Reflectometry measurements, however, indicate that these
nanoparticle species do not adsorb on the microspheres under the
experimental conditions. The authors therefore propose that
highly charged nanoparticles segregate to regions of near
negligibly charged microspheres because of their repulsive
Coulombic interactions in solution, and that this type of
nanoparticle haloing provides a previously unreported method for
tailoring the behavior of complex fluids.
Proc. Nat. Acad. Sci. 2001 98:8950
Text Notes:
... ... *colloid: In general, a colloid is a system of particles
1 to 1000 nanometers in diameter dispersed in another phase.
... ... *van der Waals forces: (also spelled Van der Waals)
Considering molecules that have permanent dipoles, and molecules
that can have dipoles induced by the electric fields of other
molecules, there are three possible mechanisms recognized in the
formation of the van der Waals bonds: 1) the orientation effect,
in which molecules rearrange themselves in their mutual
electrical fields, the rearrangements involving reorientations
of whole molecules; 2) the static induction effect, in which
molecules that are static monopoles (ions) or dipoles may induce
a static rearrangement of the electron distribution of other
molecules; 3) the dynamic induction effect, or "dispersion"
effect, in which any molecule, polar or nonpolar, may induce in
other molecules transient electron distribution rearrangements
that are time-variant. All these mechanism involve interaction
energies, and they are "bonds" in the sense that they all
involve energetic couplings between molecules.
... ... *Coulombic force: In general, the electrical force
between two charged particles.
... ... *flocculate: In general, flocculation is the process in
which particles in a colloid aggregate into larger clumps.
... ... *Zeta potential: (electrokinetic potential) The electric
potential associated with an electrical double layer around a
colloid.
... ... *Reflectometry: In general, measurement of the optical
reflectance of a surface.
Related Background:
INTERACTION BETWEEN LIKE-CHARGED COLLOIDAL SPHERES
The interactions between *colloidal particles in electrolyte
solutions play an apparently central role in the *phase behavior
and agglomeration kinetics of colloidal dispersions. These
interactions are thus of fundamental importance for
understanding the properties of inorganic materials (e.g.,
ceramics composed of nanoparticles), foods such as milk, and
solutions of biomacromolecules such as globular proteins. After
decades of theoretical and experimental efforts, the
long-accepted theories for describing the interactions of
colloidal particles in electrolyte solutions have been
challenged by results from recent experiments. Included in this
challenge is the issue of apparent attractive electrostatic
forces between like-charged colloidal particles in an
electrolyte solution.
J. Wu et al (University of California Berkeley, US) now report
Monte Carlo simulation studies that indicate the existence of a
short-range attractive force between identical macroions in
electrolyte solutions containing divalent counterions. The
authors report strong evidence (complementing recent and related
results by others) of attraction between a pair of spherical
macroions in the presence of added salt ions for the conditions
where the interacting macroion pair is not affected by any other
macroions that may be in the solution. The authors state that
classical theories fail to describe the attractive interactions
found in their simulations, with one set of classical theories
(Derjaguin-Landau-Verwey-Overbeek) predicting only repulsive
interactions and another set of theories (Sogami-Ise) predicting
a long-range attraction that is too weak and that occurs at too
large macroion separations. The authors suggest their
simulations provide fundamental "data" for an improved theory of
colloidal interactions in electrolyte solutions.
Proc. Nat. Acad. Sci. US 22 Dec 98 95:15169
Text Notes:
... ... *colloidal particles: In general, a colloid is a system
of particles 1 to 1000 nanometers in diameter dispersed in
another phase.
... ... *phase behavior: In this context, the term "phase"
refers to any part of a system which is uniform in chemical
composition and physical properties and separated from other
homogeneous parts of the system by boundary surfaces. Also in
this context, the term "phase behavior" refers to the
equilibrium relationships between water, the dispersed colloid,
and dissolved non-colloidal electrolytes.
Related Background:
ATTRACTION BETWEEN LIKE-CHARGED SPHERES IN A CHARGED PORE
A colloid is a system of particles 1 to 1000 nanometers in
diameter dispersed in another phase, and such systems,
particularly systems of electrically charged colloids, have
important practical significance and are also of considerable
theoretical interest. The existence of long-range attractive (as
opposed to the expected repulsive) electrostatic forces between
particles of like charge is one of the current major
controversies of colloid science. The established classical
theory (Derjaguin-Landau-Vervey-Overbeek) of colloidal
interactions predicts that an isolated pair of like-charged
colloidal spheres in an electrolyte should experience a purely
repulsive *screened electrostatic (coulombic) interaction.
Direct measurements of such interactions have shown quantitative
agreement with the classical theory, but recent experiments have
provided evidence that the effective interparticle potential can
have a long-range attractive component in more concentrated
suspensions and for particles confined by charged glass walls.
This long range attraction in concentrated systems is apparently
due to multi-body interactions. Theoretical explanations have
been proposed but remain the subject of controversy.
Bowen and Sharif (University of Wales, UK) now present a
quantitative theoretical explanation of the attractive forces
between confined colloidal particles, the theory based on direct
solutions of the classical nonlinear Poisson-Boltzmann equation
for two like-charged spheres confined in a cylindrical charged
pore. The calculations show that the attraction may be explained
by the redistribution of the electric double layer of ions and
counterions in solution around the spheres, owing to the
presence of the wall. The authors suggest there is thus no need
to revise the established concepts of underlying theories of
colloidal interactions. [Editor's Note: The theoretical result
in this paper is unequivocal: the calculation shows that for the
given boundary conditions, the force between two particles of
like charge dips below zero (i.e., becomes attractive) before
returning to zero at infinite distance.]
Nature 18 Jun 98 393:663
... ... *screened: Screening is a reduction of the effective
electric field at a point, the reduction due to the space charge
of ambient charged particles of sign opposite to the source of
the field.
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7. ON NEUROPSYCHIATRIC SYMPTOMS IN DEMENTIA AND COGNITIVE
IMPAIRMENT
C.G. Lyketsos et al (Johns Hopkins University, US) discuss
dementia and mild cognitive impairment, the authors making the
following points:
1) Dementia is a serious public health problem with an
increasing prevalence because of the aging of the population.(1)
Dementia is characterized by global cognitive decline sufficient
to affect functioning.(2) It is a chronic illness with seriously
disabling effects for patients, their families, and society.(2)
Mild cognitive impairment (MCI) describes cognitive impairment
in elderly persons not of sufficient severity to qualify for a
diagnosis of dementia.(3) Individuals with MCI have complaints
of impairment in memory or other areas of cognitive functioning
usually noticeable to those around them. In addition, their
performance on memory and cognitive tests is below that expected
for their age and education. However, their day-to-day
functioning is generally preserved. Several operational
definitions for MCI have been proposed.(3,4) Mild cognitive
impairment is a chronic condition and may be a precursor to
Alzheimer-type dementia.(4) Mild cognitive impairment is often
worrisome to patients and families, and is increasingly a
presenting complaint for care.
2) Neuropsychiatric symptoms are a common accompaniment of
dementia.(5) These include agitation, depression, apathy,
delusions, hallucinations, and sleep impairment. In some cases,
they cluster into syndromes, leading to the proposal of
operational criteria for specific dementia-associated psychotic
or mood disturbances. These symptoms have serious adverse
consequences for patients and caregivers, such as greater
impairment in activities of daily living, more rapid cognitive
decline, worse quality of life, earlier institutionalization,
and greater caregiver depression. Thus, the neuropsychiatric
accompaniments of dementia are serious conditions that are
increasingly becoming a focus of attention.
3) The authors report a population-based study to estimate the
prevalence of neuropsychiatric symptoms in dementia and MCI. A
total of 3608 participants were cognitively evaluated using data
collected longitudinally over 10 years and additional data
collected in 1999-2000 in 4 US counties. Dementia and MCI were
classified using clinical criteria and adjudicated by committee
review by expert neurologists and psychiatrists. A total of 824
individuals completed the Neuropsychiatric Inventory (NPI); 362
were classified as having dementia, 320 as having MCI; and 142
did not meet criteria for MCI or dementia. From their results,
the authors conclude: Neuropsychiatric symptoms occur in the
majority of persons with dementia over the course of the
disease. These are the first population-based estimates for
neuropsychiatric symptoms in MCI, indicating a high prevalence
associated with this condition as well. The authors suggest
these symptoms have serious adverse consequences and should be
inquired about and treated as necessary.
References (abridged):
1. Brookmeyer R, Gray S, Kawas C. Projections of Alzheimer's
disease in the United States and the public health impact of
delaying disease onset. Am J Public Health. 1998;88:1337-1342.
2. Rabins PV, Lyketsos CG, Steele C. Practical Dementia Care.
New York, NY: Oxford University Press; 1999.
3. Petersen RC, Stevens JC, Ganguli M, et al. Practice
parameter: Early detection of dementia: mild cognitive
impairment (an evidence-based review). Neurology.
2001;56:1133-1142.
4. Morris JC, Storandt M, Miller JP, et al. Mild cognitive
impairment represents early-stage Alzheimer disease. Arch
Neurol. 2001;58:397-405.
5. Finkel SI, Costa e Silva J, Cohen G, et al. Behavioral and
psychological signs and symptoms of dementia. Int Psychogeriatr.
1996;8(suppl 3):497-500.
J. Am. Med. Assoc. 2002 288:1475
Web Links: dementia mild cognitive impairment
Related Background Brief:
PROJECTIONS OF ALZHEIMER'S DISEASE IN THE UNITED STATES AND THE
PUBLIC HEALTH IMPACT OF DELAYING DISEASE ONSET. The authors
report a study to project the future prevalence and incidence of
Alzheimer's disease in the US and the potential impact of
interventions to delay disease onset. The numbers of individuals
in the US with Alzheimer's disease and the numbers of newly
diagnosed cases that can be expected over the next 50 years were
estimated from a model that used age-specific incidence rates
summarized from several epidemiological studies, US mortality
rates, and US Bureau of the Census projections. RESULTS: in
1997, the prevalence of Alzheimer's disease in the US was 2.32
million (range: 1.09 to 4.58 million); of these individuals, 68%
were female. It is projected that the prevalence will nearly
quadruple in the next 50 years, by which time approximately 1 in
45 Americans will be afflicted with the disease. Currently, the
annual number of new incident cases in 360,000. If interventions
could delay onset of the disease by 2 years, after 50 years
there would be nearly 2 million fewer cases than projected; if
onset could be delayed by 1 year, there would be nearly 800,000
fewer prevalent cases. The authors conclude: As the US
population ages, Alzheimer's disease will become an enormous
public health problem. interventions that could delay disease
onset even modestly would have a major public health impact. R.
Brookmeyer et al: Am J Public Health 1998 88:1337.
Related Background Brief:
PRACTICE PARAMETER: EARLY DETECTION OF DEMENTIA: MILD COGNITIVE
IMPAIRMENT (AN EVIDENCE-BASED REVIEW). REPORT OF THE QUALITY
STANDARDS SUBCOMMITTEE OF THE AMERICAN ACADEMY OF NEUROLOGY. The
authors report a study to determine whether screening different
groups of elderly individuals in a general or specialty practice
would be beneficial in detecting dementia. Epidemiologic studies
of aging and dementia have demonstrated that the use of research
criteria for the classification of dementia has yielded three
groups of subjects: those who are demented, those who are not
demented, and a third group of individuals who cannot be
classified as normal or demented but who are cognitively
(usually memory) impaired. The authors conducted computerized
literature searches and generated a set of abstracts based on
text and index words selected to reflect the key issues to be
addressed. Articles were abstracted to determine whether there
were sufficient data to recommend the screening of asymptomatic
individuals. Other research studies were evaluated to determine
whether there was value in identifying individuals who were
memory-impaired beyond what one would expect for age but who
were not demented. Finally, screening instruments and evaluation
techniques for the identification of cognitive impairment were
reviewed. The authors report there were insufficient data to
make any recommendations regarding cognitive screening of
asymptomatic individuals. Persons with memory impairment who
were not demented were characterized in the literature as having
mild cognitive impairment. These subjects were at increased risk
for developing dementia or Alzheimer's disease (AD) when
compared with similarly aged individuals in the general
population. There were sufficient data to recommend the
evaluation and clinical monitoring of persons with mild
cognitive impairment due to their increased risk for developing
dementia. Screening instruments, e.g., Mini-Mental State
Examination, were found to be useful to the clinician for
assessing the degree of cognitive impairment, as were
neuropsychologic batteries, brief focused cognitive instruments,
and certain structured informant interviews. Increasing
attention is being paid to persons with mild cognitive
impairment for whom treatment options are being evaluated that
may alter the rate of progression to dementia. R.C. Petersen et
al: Neurology. 2001 56:1131.
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8. ON ADOLESCENT DEPRESSION
D.A. Brent and B. Birmaher (University of Pittsburgh, US)
discuss adolescent depression, the authors making the following
points:
1) In children and adolescents, depression is not always
characterized by sadness, but instead by irritability, boredom,
or an inability to experience pleasure. Depression is a chronic,
recurrent, and often familial illness that frequently first
occurs in childhood or adolescence. Any child can be sad, but
depression is characterized by a persistent irritable, sad, or
bored mood and difficulty with familial relationships, school,
and work(1). In the absence of treatment, a major depressive
episode lasts an average of eight months. The risk of recurrence
is approximately 40 percent at two years and 72 percent at five
years.(2) Longer depressive episodes occur in patients who have
a dysthymic disorder (a milder, but chronic and insidious form
of depression) that gradually evolves into major depression.
More prolonged episodes are also associated with coexisting
psychiatric conditions, parental depression, and parent–child
discord.(2)
2) At least 20 percent of those with early-onset depressive
disorders (those beginning in childhood or adolescence) are at
risk for bipolar disorder, particularly if they have a family
history of bipolar disorder, psychotic symptoms, or a manic
response to antidepressant treatment.(2,3) Bipolar disorder is
characterized by depressive episodes that alternate with periods
of mania, defined by a decreased need for sleep, increased
energy, grandiosity, euphoria, and an increased propensity for
risk-taking behavior. Often in children and adolescents, mania
and depression occur as "mixed states", in which the lability of
mania is combined with depression, or there is rapid cycling
between depression and mania over a period of days or even
hours.(4)
3) Suicidal behavior is closely associated with depression. Risk
factors for suicide during a depressive episode include chronic
depression, coexisting substance abuse, impulsivity and
aggression, a history of physical or sexual abuse, same-sex
attraction and sexual activity, a personal or family history of
a suicide attempt, and access to an effective means of suicide,
such as a gun.(5) Girls are more likely to attempt suicide, and
boys to complete suicide. Among adolescents, the annual rate of
suicide attempts requiring medical attention is 2.6 percent.
Completed suicide is much rarer: among 15-to-19-year-olds, the
rates in 1998 were 14.6 per 100,000 in boys and 2.9 per 100,000
in girls.
4) Depression is present in about 1 percent of children and 5
percent of adolescents at any given time. Before puberty, boys
and girls are at equal risk for depression, whereas after the
onset of puberty, the rate of depression is about twice as high
in girls. Having a parent with a history of depression increases
a child's risk of a depressive episode by a factor of 2 to 4.7
Anxiety, particularly social phobia, may be a precursor of
depression.
References (abridged):
1. Diagnostic and statistical manual of mental disorders, 4th
ed.: DSM-IV. Washington, D.C.: American Psychiatric Association,
1994.
2. Birmaher B, Ryan ND, Williamson DE, et al. Child and
adolescent depression: a review of the past 10 years. J Am Acad
Child Adolesc Psychiatry 1996;35:1427-1439.
3. Geller B, Zimerman B, Williams M, Bolhofner K, Craney JL.
Bipolar disorder at prospective follow-up of adults who had
prepubertal major depressive disorder. Am J Psychiatry
2001;158:125-127.
4. Geller B, Zimerman B, Williams M, et al. Diagnostic
characteristics of 93 cases of a prepubertal and early
adolescent bipolar disorder phenotype by gender, puberty and
comorbid attention deficit hyperactivity disorder. J Child
Adolesc Psychopharmacol 2000;10:157-164.
5. Brent DA. Mood disorders and suicide. In: Green M, Haggerty
RJ, eds. Ambulatory pediatrics. 5th ed. Philadelphia: W.B.
Saunders, 1999:447-54.
New Engl. J. Med. 2002 347:667
Web Links: adolescent depression bipolar disorder
Related Background Brief:
CHILDHOOD AND ADOLESCENT DEPRESSION: A REVIEW OF THE PAST 10
YEARS. PART I. The authors qualitatively review the literature
of the past decade covering the epidemiology, clinical
characteristics, natural course, biology, and other correlates
of early-onset major depressive disorder (MDD) and dysthymic
disorder (DD). A computerized search for articles published
during the past 10 years was made and selected studies are
presented. RESULTS: Early-onset MDD and DD are frequent,
recurrent, and familial disorders that tend to continue into
adulthood, and they are frequently accompanied by other
psychiatric disorders. These disorders are usually associated
with poor psychosocial and academic outcome and increased risk
for substance abuse, bipolar disorder, and suicide. In addition,
DD increases the risk for MDD. There is a secular increase in
the prevalence of MDD, and it appears that MDD is occurring at
an earlier age in successive cohorts. Several genetic, familial,
demographic, psychosocial, cognitive, and biological correlates
of onset and course of early-onset depression have been
identified. Few studies, however, have examined the combined
effects of these correlates. The authors conclude: Considerable
advances have been made in our knowledge of early-onset
depression. Nevertheless, further research is needed in
understanding the pathogenesis of childhood mood disorders.
Toward this end, studies aimed at elucidating mechanisms and
interrelationships among the different domains of risk factors
are needed. B. Birmaher et al: J Am Acad Child Adolesc
Psychiatry. 1997 36:1325.
Related Background Brief:
BIPOLAR DISORDER AT PROSPECTIVE FOLLOW-UP OF ADULTS WHO HAD
PREPUBERTAL MAJOR DEPRESSIVE DISORDER. The goal of the authors
was to conduct an adult follow-up of subjects who had
participated in a study of nortriptyline for childhood
depression. The study group represented 100 (90.9%) of the
original 110 subjects and included 72 subjects who had a
prepubertal diagnosis of major depressive disorder and 28 normal
comparison subjects. Subjects were assessed with semistructured
research interviews given by research nurses who were blind to
the subjects’ original diagnoses. RESULTS: In the original
study, the mean age of the children with prepubertal major
depressive disorder was 10.3 years (SD=1.5); at adult follow-up
the mean age of these subjects was 20.7 years (SD=2.0). At
follow-up, significantly more of the subjects who had
prepubertal diagnoses of major depressive disorder (N=24
[33.3%]) than normal comparison subjects (none) had bipolar I
disorder. Subjects who had prepubertal diagnoses of major
depressive disorder also had significantly higher rates of any
bipolar disorder than normal subjects (48.6% [N=35] versus 7.1%
[N=2]), major depressive disorder (36.1% [N=26] versus 14.3%
[N=4]), substance use disorders (30.6% [N=22] versus 10.7%
[N=3]), and suicidality (22.2% [N=16] versus 3.6% [N=1]).
Parental and grandparental mania predicted bipolar I disorder
outcomes. The authors conclude: High rates of switching to mania
have implications for the treatment of depressed children. The
authors discuss the reasons for their finding a higher rate of
bipolar disorder in this outcome study than was found in the one
other adult outcome study of prepubertal major depressive
disorder. B. Geller et al: Am J Psychiatry 2001 158:125.
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9. ON KIDNEY TRANSPLANTATION FROM DONORS WITHOUT A HEARTBEAT
M. Weber et al (University of Zurich, CH) discuss kidney
transplantation, the authors making the following points:
1) The number of patients awaiting organs for transplantation
has grown dramatically during the past two decades, triggering
interest in expanding the pool of organs beyond those obtained
from brain-dead donors with a heartbeat. Alternative sources of
organs include elderly, brain-dead donors whose hearts continue
to beat, living donors, and donors without a heartbeat. A
successful program of transplantation from donors without a
heartbeat could increase the number of kidneys available for
transplantation by 30 percent.(1)
2) Death in donors without a heartbeat is defined as an
irreversible cessation of circulatory and respiratory
function,(2) whereas brain death in donors with a heartbeat is
determined according to neurologic criteria. Therefore, by
definition, a donor without a heartbeat has had a prolonged
phase of hypotension (one that lasts several minutes) followed
by cardiac arrest before organ harvesting. Insufficient
perfusion or complete lack of perfusion of such organs has long
been thought to cause irreversible damage, resulting in poor
short-term and long-term outcomes after grafting.(3) With the
exception of recent limited experience in liver
transplantation,(4) the use of organs from donors without a
heartbeat has been restricted to the kidneys, since dialysis is
available for support in case the graft does not function after
transplantation.(5)
3) The authors report they conducted a matched, single-center
study of kidney transplants obtained from donors without a
heartbeat and those from donors with a heartbeat, with a 15-year
follow-up period. Between 1985 and 2000, 122 kidney
transplantations involving donors without a heartbeat were
performed at the University of Zurich, in Switzerland. Outcomes
of these procedures were compared with those of 122
transplantations of kidneys from donors with a heartbeat. The
recipients were matched according to age, sex, number of
transplantations, and calendar period of transplantation. The
authors conclude that although the incidence of delayed graft
function is significantly higher with kidneys from donors
without a heartbeat than with kidneys from donors with a
heartbeat, there is no difference in long-term outcome between
the two types of graft.
References (abridged):
1. Sanchez-Fructuoso AI, Prats D, Torrente J, et al. Renal
transplantation from non-heart beating donors: a promising
alternative to enlarge the donor pool. J Am Soc Nephrol
2000;11:350-358.
2. Guidelines for the determination of death: report of the
medical consultants on the diagnosis of death to the President's
Commission for the Study of Ethical Problems in Medicine and
Biomedical and Behavioral Research. JAMA 1981;246:2184-2186.
3. Kahan BD, Ponticelli C. Selection and operative approaches
for donors: non-heart-beating cadaveric donors. In: Kahan BD,
Ponticelli C, eds. Principles and practice of renal
transplantation. London: Martin Dunitz, 2000:149-50.
4. D'allessandro AM, Hoffman RM, Knechtle SJ, et al. Liver
transplantation from controlled non-heart-beating donors.
Surgery 2000;128:579-588.
5. Wijnen RMH, Booster MH, Stubenitski BM, de Boer J, Heineman
E, Kootstra G. Outcome of transplantation of non-heart-beating
donor kidneys. Lancet 1995;345:1067-1070.
New Engl. J. Med. 2002 347:248
Web Links: organ transplantation
Related Background Brief:
RENAL TRANSPLANTATION FROM NON-HEART BEATING DONORS: A PROMISING
ALTERNATIVE TO ENLARGE THE DONOR POOL. The authors state the aim
of this study was to compare the survival and midterm function
of kidneys from non-heart beating donors (NHBD) with those of
kidneys from heart beating donors (HBD). From 1989 to 1998, 144
kidneys were procured from NHBD at the Hospital Clínico San
Carlos in Madrid, of which 95 were transplanted. The kidney
grafts were maintained from the moment of the diagnosis of
cardiac arrest until the time of procurement by cardiopulmonary
bypass. There was no significant difference in renal function
and the number of rejection episodes between the NHBD and HBD
transplants. The NHBD kidneys showed a 5.73-fold increase in the
incidence of delayed graft function (adjusted relative risk 95%
confidence interval, 2.82 to 11.62). One- and five-year survival
rates for NHBD grafts were 84.6 and 82.7%, respectively,
compared with 87.5 and 83.9% for HBD (P = 0.5767). Cox analysis
showed that the predictive factors for worse NHBD graft survival
were type of NHBD donor and the occurrence of corticoresistant
rejection. Ninety of the NHBD organs were procured from subjects
suffering irreversible cardiac arrest on the street who were
transferred to our center for the sole purpose of donation.
Fifty-four of these kidneys were transplanted and all showed
primary function. When a strict protocol is adhered to, the
outcome of renal transplant from NHBD compares well with that
from HBD. It is believed that the high number of organs obtained
from subjects undergoing irreversible cardiac arrest on the
street might encourage the adoption of new criteria for the
management of this type of pathology with the ultimate goal of
kidney donation. A.I. Sánchez-Fructuoso et al: J Am Soc Nephrol
2000 11:350.
Related Background Brief:
LIVER TRANSPLANTATION FROM CONTROLLED NON-HEART-BEATING DONORS.
The use of organs from non-heart-beating donors (NHBDs) has been
proposed as one way to increase the donor pool. However, few
centers have transplanted livers from NHBDs. The authors report
the results of 19 liver transplants from controlled NHBDs. From
January 1993 through August 1999, 364 liver transplantations
were performed from heart-beating donors (HBDs) and 19 liver
transplantations were performed from NHBDs. Donor and recipient
characteristics, posttransplant complications, and patient and
allograft survival were compared. RESULTS: No differences in
hepatic artery, portal vein, or biliary complications were noted
between the groups. However, the rate of primary nonfunction was
higher in recipients of livers from NHBDs (10.5% vs. 1.3%; P =
.04). No difference in patient survival was seen between
recipients of NHBDs or HBDs (72.6% vs. 84.8%; P =.36); however,
allograft survival was lower in recipients who received livers
from NHBDs (53.8% vs. 80.9%; P =.007). The authors conclude that
liver transplantation from controlled NHBDs results in similar
patient survival and post-transplant complications. However,
primary nonfunction was higher and allograft survival was less
in recipients of livers from NHBDs. The authors suggest the
results of liver transplantation from controlled NHBDs are
encouraging and should continue to be cautiously pursued as one
way to help alleviate the current shortage of donor livers. A.M.
D'alessandro et al: Surgery 2000 128:579.
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10. ON PLASTIC DEFORMATION OF CRYSTALS
J. Li et al (Massachusetts Institute of Technology, US) discuss
plastic deformation of crystals, the authors making the
following points:
1) Nanometer-scale contact experiments(1-5) and simulations
demonstrate the potential to probe incipient plasticity -- the
onset of permanent deformation -- in crystals. Such studies also
point to the need for an understanding of the mechanisms
governing defect nucleation in a broad range of fields and
applications.
2) Characteristic discontinuities have been observed
consistently in the measured load–penetration depth (P–h)
response of single crystals indented to nanometer-scale
depths(1-5). Before the first discontinuity, local shear
stresses beneath the nominally sharp indenter approach the
theoretical strength of the indented crystal, indicating that
homogeneous defect nucleation is a logical starting event for
subsequent incipient (that is, early-stage) plasticity. This
hypothesis is supported by recent in situ experiments6 using the
Bragg–Nye bubble raft analogue, showing that nanoindentation of
a two-dimensional (2D) crystal indeed results in homogeneous
dislocation nucleation. However, the present level of
quantitative understanding of the mechanisms by which
contact-induced plasticity initiates and evolves in
three-dimensional (3D) crystals is still limited.
3) The authors present a fundamental framework for describing
incipient plasticity that combines results of atomistic and
finite-element modeling, theoretical concepts of structural
stability at finite strain, and experimental analysis. The
authors quantify two key features of the nucleation and
subsequent evolution of defects. A position-sensitive criterion
based on elastic stability determines the location and character
of homogeneously nucleated defects. The authors validate this
stability criterion at both the atomistic and the continuum
levels. The authors then propose a detailed interpretation of
the experimentally observed sequence of displacement bursts to
elucidate the role of secondary defect sources operating locally
at stress levels considerably smaller than the ideal strength
required for homogeneous nucleation. The authors suggest these
findings provide a self-consistent explanation of the
discontinuous elastic–plastic response in nanoindentation
measurements, and a guide to fundamental studies across many
disciplines that seek to quantify and predict the initiation and
early stages of plasticity.
References (abridged):
1. Gerberich, W. W., Venkataraman, S. K., Huang, H., Harvey, S.
E. & Kohlstedt, D. L. The injection of plasticity by millinewton
contacts. Acta Metal. Mater. 43, 1569-1576 (1995)
2. Suresh, S., Nieh, T.-G. & Choi, B. W. Nanoindentation of
copper thin films on silicon substrates. Scripta Mater. 41,
951-957 (1999)
3. Kiely, J. D., Jarausch, K. F., Houston, J. E. & Russell, P.
E. Initial stages of yield in nanoindentation. J. Mater. Res.
15, 4513-4519 (1999)
4. Gouldstone, A., Koh, H.-J., Zeng, K. Y., Giannakopoulos, A.
E. & Suresh, S. Discrete and continuous deformation during
nanoindentation of thin films. Acta Mater. 48, 2277-2295 (2000)
5. Kramer, D. E., Yoder, K. B. & Gerberich, W. W. Surface
constrained plasticity: Oxide rupture and the yield point
process. Phil. Mag. A 81, 2033-2058 (2001)
Nature 2002 418:307
Web Links: plastic deformation of crystals
Related Background Brief:
THE INJECTION OF PLASTICITY BY MILLINEWTON CONTACTS. Diamond
indentation of a surface with a thin passive film requires loads
an order of magnitude smaller for Ni[100] crystals than for Fe-3
wt% Si[100] crystals. The load bearing capacity of the Fe-3 wt%
Si can be reduced by two orders of magnitude by removing the 10
nm thick native oxide film. These phenomena can be explained by
considering the equilibrium of forces associated with tip, image
and friction stresses acting on dislocations emitted from the
indenter tip. The key ingredient to this model is the nucleation
and growth of dislocation loops at loads of only tens of
micronewtons. Three types of critical contact experiments
demonstrate that dislocations can be initiated at loads well
below those previously thought to represent elastic loading
only. W.W. Gerberich et al: Acta Metallurgica et Materialia 1995
43:1569.
Related Background Brief:
DISCRETE AND CONTINUOUS DEFORMATION DURING NANOINDENTATION OF
THIN FILMS. The authors describe nanoindentation experiments on
thin films of polycrystalline Al of known texture and different
thicknesses, and of single crystal Al of different
crystallographic orientations. Both single-crystalline and
polycrystalline films, 400-1000 nm in thickness, are found to
exhibit multiple bursts of indenter penetration displacement, h,
at approximately constant indentation loads, P. Recent results
from the nanoindentation studies of Suresh ct al. (Suresh, S.,
Nieh T.-G. and Choi, B.W., Scripta mater., 1999, 41, 951) along
with new microscopy observations of thin films of
polycrystalline Cu on Si substrates are also examined in an
attempt to extract some general trends on the discrete and
continuous deformation processes. The onset of the first
displacement burst, which is essentially independent of film
thickness, appears to occur when the computed maximum shear
stress at the indenter tip approaches the theoretical shear
strength of the metal films for all the cases examined. It is
reasoned that these displacement bursts are triggered by the
nucleation of dislocations in the thin films. A simple model to
estimate the size of the prismatic dislocation loops is
presented along with observations of deformation using
transmission electron microscopy and atomic force microscopy. It
is demonstrated that the response of the nanoindented film is
composed of purely elastic behavior with intermittent
microplasticity. The overall plastic response of the metal
films, as determined from nanoindentation, is shown to scale
with film thickness, in qualitative agreement with the trends
seen in wafer curvature or X-ray diffraction measurements. A.
Gouldstone et al: Acta Materialia 2000 48:2277.
Related Background Brief:
SURFACE CONSTRAINED PLASTICITY: OXIDE RUPTURE AND THE YIELD
POINT PROCESS. Nanoindentation of single crystals has been a
topic of several recent investigations. This is a result of
their ability to withstand near theoretical stresses without
showing signs of plastic deformation. When plasticity occurs, it
produces a yield point, a sudden discontinuous increase in
indenter displacement and decrease in contact pressure. This
study combines atomic force microscopy (AFM) with
nanoindentation to focus on the roles that oxide and asperities
play in the yield point process. Time dependent and
instantaneous yield point properties were investigated for
single crystals of tungsten and Fe-3 wt% Si in variable
temperature and variable humidity environments. AFM observations
indicate that the presence of asperities has a dramatic effect
on the time dependent yield point properties. AFM measurements
also provide evidence for plasticity in the absence of a yield
point, suggesting that dislocation nucleation can occur well
before a yield point is observed. Measurements on the dependence
of yield point load on oxide film thickness are used to develop
a fracture mechanics based model in which oxide fracture
controls the yield point process. The results suggest that
dislocation egress occurs upon oxide fracture, resulting in a
yield point. D.E. Kramer et al: Philosophical Magazine A --
Physics Of Condensed Matter Structure Defects And Mechanical
Properties 2001 81:2033.
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11. ON THE THICKNESS OF WETTING LAYERS
D. Fenistein et al (Ecole Normal Superieure Paris, FR) discuss
wetting layers, the authors making the following points:
1) When a liquid drop is placed on a substrate, two scenarios
arise depending on the contact angle. If the contact angle is
zero, the drop spreads across the surface corresponding to
complete wetting. For all other values of the contact angle, the
drop does not spread and only partial wetting of the substrate
results. The surface phase transition from partial to complete
wetting is called the wetting transition and has been
extensively studied theoretically and experimentally over the
last few decades [1,4,5].
2) Much less well understood is the behavior of wetting films
near the bulk critical point. Here the temperature dependence of
the wetting layer thickness is additionally complicated due to
effects related to the increase of the bulk correlation length
[2]. It has long been anticipated that near the bulk critical
point the influence of long-range dispersion forces diminishes
and that interfacial fluctuation effects are amplified due to
the vanishing of the surface tension [3]. However, a proper
quantitative assessment of this has not been previously
possible, leaving the behavior of wetting films near bulk
criticality a matter of some debate.
3) The authors report a study of gravity-thinned wetting layers
in binary-liquid mixtures in which they probe the critical
region much closer than in previous experiments. The authors
suggest their data unambiguously show the divergence of the film
thickness on approaching the bulk critical temperature
characterized by a critical exponent that is distinct from the
critical exponent for the bulk correlation length. Scaling
arguments are forwarded which show the observed exponent is
consistent with a crossover regime for van der Waals dominated
wetting to critical scaling of the wetting film thickness. The
authors also demonstrate the presence of an effective
short-range or fluctuation-induced correction to the leading
order direct intermolecular (van der Waals) dominated
contribution.
References (abridged):
1. D. Bonn and D. Ross, Rep. Prog. Phys. 64, 1084 (2001).
2. S. Dietrich, Phase Transitions in Surface Films, edited by H.
Taub et al. (Plenum, New York, 1991); Phase Transitions and
Critical Phenomena, edited by C. Domb and J.L. Lebowitz
Academic, London, 1988), Vol. 12.
3. E. Brezin, B. I. Halperin, and S. Leibler, Phys. Rev. Lett.
50, 1387 (1983).
4. J.E. Rutledge and P. Taborek, Phys. Rev. Lett. 69, 937 (1992).
5. D. Bonn, H. Kellay, and G. H. Wegdam, Phys. Rev. Lett. 69,
1975 (1992); D. Bonn, E. Bertrand, J. Meunier , and R. Blossey,
Phys. Rev. Lett. 84, 4661 (2000).
Phys. Rev. Lett. 2002 89:096101
Web Links: wettability
Related Background:
ON TRIPLE-POINT WETTING ON SURFACES
In this context, the term "triple point" refers to the
temperature and pressure at which the gas, liquid, and solid
phases of a substance are in equilibrium.
A. Esztermann et al (Heinrich-Heine University, DE) discuss
surface wetting, the authors making the following points:
1) Wetting of a solid substrate exposed to a gas in
thermodynamic equilibrium is a ubiquitous phenomenon with both
fundamental aspects and important applications. Microscopically,
substrate wetting by a liquid film is caused by a strong
substrate-particle attraction mediated by van der Waals forces.
At present, an almost complete microscopic understanding of
wetting on flat solid substrates is available, predicting the
thickness of the liquid film as a function of the
substrate-particle and interparticle interactions for given
thermodynamic parameters such as temperature and pressure.
2) The following basic theoretical predictions have been
confirmed by experiment using, for example, noble gases on
different substrates: a) For fixed thermodynamic conditions, the
thickness of the wetting layer grows for increasing
substrate-particle attraction. b) Complete wetting (i.e., a
diverging thickness of the liquid layer) occurs if the
substrate-particle attraction is stronger than the interparticle
attraction and the thermodynamic conditions approach liquid-gas
coexistence.
3) The latter condition (complete wetting) can be achieved only
if the system temperature is above the triple point temperature.
For a system temperature less than the triple point temperature,
on the other hand, a solid film shows up near the sublimation
line. Various experiments have demonstrated that the width of
the solid layer always remains finite when approaching gas-solid
coexistence. It is only near the triple point that a liquid
layer on top of the solid sheet is formed, with a diverging
width as the triple point is approached. This universal behavior
is called "triple point wetting".
Phys. Rev. Lett. 2002 88:055702
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12. HELICAL ROSETTE CHIROPTICAL NANOTUBES
H. Fenniri et al (Purdue University, US) discuss nanotubes, the
authors making the following points:
1) Nonrandom symmetry breaking in supramolecular systems may be
induced by the following three general processes: (a) The
"sergeant and soldiers principle"(1), initially formulated for
covalent polymeric systems(2) to describe the inductive effect
of a small population of chiral components on the chiroptical
outcome of macromolecular systems.(3) This effect was also
recently reported as a means to transfer molecular chirality
into oligomeric(4) systems as well as in a variety of
supramolecular assemblies.(5) (b) Molecular recognition induced
chirality, a well-studied phenomenon encountered in host-guest
chemistry which ensues from the specific recognition of a chiral
guest by an achiral host and can be rationalized on the basis of
steric and electronic factors. (c) External means such as chiral
vortex forces, photoinduced electron transfer, and redox- and
photo-switches.
2) A distinct advantage of these systems over those in which
supramolecular chirality results from spontaneous resolution is
that the chiroptical outcome is predictable and reproducible. As
a result, it can be utilized in chirotechnology for the design
of sensors,(3), chiral cholesteric phases, catalysts, asymmetric
synthesis of materials with electromagnetic and optoelectronic
applications,(3a) information storage, display systems,(3b-d)
and photochromic materials, and for the design of materials with
unique chiral light-emitting and nonlinear optical properties.
3) The authors describe two supramolecular processes for the
self-assembly of helical rosette nanotubes with adjustable
chiroptical properties. The first is the result of symmetry
breaking in a preexisting racemic mixture of M- and P-helical
rosette nanotubes. The second is the result of the triggering
effect of a chiral promoter on a prochiral molecular module that
leads to the hierarchical self-assembly of the module-promoter
complex into said rosette nanotubes. In both cases, the promoter
assumes the dual role of transferring its molecular chirality,
physical, and chemical properties to the supramolecular
ensemble, and contributing to the stabilization of the resulting
nanotubular assembly.
References (abridged):
1. (a) Green, M. M.; Peterson, N. C.; Sato, T.; Teramoto, A.;
Cook, R.; Lifson, S. Science 1995, 268, 1860-1866. (b) Green, M.
M.; Reiddy, M. P.; Johnson, R. J.; Darling, G.; O'Leary, D. J.;
Wilson, G. J. Am. Chem. Soc. 1989, 111, 6452-6454.
2. (a) Rowan, A. E.; Nolte, R. J. M. Angew. Chem., Int. Ed.
1998, 37, 63-68. (b) Ferringa, B. L.; van Delden, R. A. Angew.
Chem., Int. Ed. 1999, 38, 3419-3438. (c) Yashima, E.;
Matsushima, T.; Okamoto, Y. J. Am. Chem. Soc. 1997, 119,
6345-6359.
3. (a) Akagi, K.; Piao, G.; Kaneko, S.; Sakamaki, S.; Shirakawa,
H.; Kyotani, M. Science 1998, 282, 1683-1686. (b) Feringa, B.
L.; Huck, N. P. M.; van Doren, H. A. J. Am. Chem. Soc. 1995,
117, 9929-9930. (c) Huck, N. P. M.; Jager, W. F.; de Lange, B.;
Feringa, B. L. Science 1996, 273, 1686-1688. (d) Feringa, B. L.;
Huck, N. P. M.; Schoevaars, A. M. Adv. Mater. 1996, 8, 681-684.
(e) Seebach, D.; Beck, A. K.; Heckel, A. Angew. Chem., Int. Ed.
2001, 40, 93-138. (f) Oda, R.; Huc, I.; Schmutz, M.; Candau, S.
J.; MacKintosh, F. C. Nature 1999, 399, 566-569. (g) Nakano, T.;
Okamoto, Y. Chem. Rev. 2001, 101, 4013-4038. (h) Cornelissen, J.
J. L. M.; Rowan, A. E.; Nolte, R. J. M.; Sommerdijk, N. A. J. M.
Chem. Rev. 2001, 101, 4039-4070.
4. (a) Prince, R. B.; Moore, J. S.; Brunsveld, L.; Meijer, E. W.
Chem.-Eur. J. 2001, 7, 4150-4154. (b) Hill, D. J.; Mio, M. J.;
Prince, R. B.; Hughes, T. S.; Moore, J. S. Chem. Rev. 2001, 101,
3893-4011.
5. (a) Palmans, A. R. A.; Vekemans, J. A. J. M.; Havinga, E. E.;
Meijer, E. W. Angew. Chem., Int. Ed. Engl. 1997, 36, 2648-2651.
(b) Hirschberg, K. J. H. K.; Brunsveld, L.; Ramzi, A.; Vekemans,
J. A. J. M.; Sijbesma, R. P.; Meijer, E. W. Nature 2000, 407,
167-170. (c) Brunsveld, L.; Lohmeijer, B. G. G.; Vekemans, J. A.
J. M.; Meijer, E. W. Chem. Commun. 2000, 2305-2306. (d) Prins,
L. J.; Timmmerman, P.; Reinhoudt, D. N. J. Am. Chem. Soc. 2001,
123, 10153-10163. (e) Brunsveld, L.; Meijer, E. W.; Prince, R.
B.; Moore, J. S. J. Am. Chem. Soc. 2001, 123, 7978-7984. (f)
Prins, L. J.; De Jong, F.; Timmerman, P.; Reinhoudt, D. N.
Nature 2000, 408, 181-184. (g) Brunsveld, L.; Folmer, B. J. B.;
Meijer, E. W.; Sijbesma, R. P. Chem. Rev. 2001, 101, 4071-4097.
J. Am. Chem. Soc. 2002 124:11064
Web Links: chiroptical nanotubes
Related Background Brief:
HELICAL POLYACETYLENE SYNTHESIZED WITH A CHIRAL NEMATIC REACTION
FIELD. The authors report that helical polyacetylene was
synthesized under an asymmetric reaction field consisting of
chiral nematic (N*) liquid crystals (LCs). The chiral nematic LC
was prepared by adding a chiroptical binaphthol derivative as a
chiral dopant to a mixture of two nematic LCs. Acetylene
polymerizations were carried out using the catalyst titanium
tetra-n-butoxide-triethylaluminum dissolved in the chiral
nematic LC solvent. The polyacetylene film was shown by scanning
electron microscopy to consist of clockwise or counterclockwise
helical structure of fibrils. A Cotton effect was observed in
the region of the pi --> pi* transition of the polyacetylene
chain in circular dichroism spectra. The authors suggest the
high electrical conductivities of approximately 1500 to 1800
siemens per centimeter after iodine doping and the chiral
helicity of these films may be exploited in electromagnetic and
optical applications. K. Akagi et al: Science 1998 282:1683.
Related Background Brief:
TUNING BILAYER TWIST USING CHIRAL COUNTERIONS. From seashells to
DNA, chirality is expressed at every level of biological
structures. In self-assembled structures it may emerge
cooperatively from chirality at the molecular scale. Amphiphilic
molecules, for example, can form a variety of aggregates and
mesophases that express the chirality of their constituent
molecules at a supramolecular scale of microns. Quantitative
prediction of large-scale chirality based on that at the
molecular scale remains a largely unsolved problem. Furthermore,
experimental control over the expression of chirality at the
supramolecular level is difficult to achieve: mixing of
different enantiomers usually results in phase separation. The
authors present an experimental and theoretical description of a
system in which chirality can be varied continuously and
controllably ("tuned") in micron-scale structures. The authors
report they observe the formation of twisted ribbons consisting
of bilayers of gemini surfactants (two surfactant molecules
covalently linked at their charged head groups). The authors
report they find that the degree of twist and the pitch of the
ribbons can be tuned by the introduction of opposite-handed
chiral counterions in various proportions. The authors sugges
this degree of control might be of practical value; for example,
in the use of the helical structures as templates for helical
crystallization of macromolecules. R. Oda et al: Nature 1999
399:566.
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