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ScienceWeek
SCIENCEWEEK NEWS BRIEFS
MATHEMATICS AND COMPLEX SYSTEMS
R. Foote (19 October 2007)
Science 318 (5849), 410-412. [DOI: 10.1126/science.1141754]
Contemporary researchers strive to understand complex physical phenomena that involve many constituents, may be influenced by numerous forces, and may exhibit unexpected or emergent behavior. Often such "complex systems" are macroscopic manifestations of other systems that exhibit their own complex behavior and obey more elemental laws. This article proposes that areas of mathematics, even ones based on simple axiomatic foundations, have discernible layers, entirely unexpected "macroscopic" outcomes, and both mathematical and physical ramifications profoundly beyond their historical beginnings. In a larger sense, the study of mathematics itself, which is increasingly surpassing the capacity of researchers to verify "by hand," may be the ultimate complex system.
Book Sources:
complex systems
theoretical physics
history of mathematics
GENOME BIOLOGY: Paired-End Mapping Reveals Extensive Structural Variation in the Human Genome
J. O. Korbel et al. (19 October 2007)
Science 318 (5849), 420-426. [DOI: 10.1126/science.1149504]
Structural variation of the genome involves kilobase- to megabase-sized deletions, duplications, insertions, inversions, and complex combinations of rearrangements. We introduce high-throughput and massive paired-end mapping (PEM), a large-scale genome-sequencing method to identify structural variants (SVs) ~3 kilobases (kb) or larger that combines the rescue and capture of paired ends of 3-kb fragments, massive 454 sequencing, and a computational approach to map DNA reads onto a reference genome. PEM was used to map SVs in an African and in a putatively European individual and identified shared and divergent SVs relative to the reference genome. Overall, we fine-mapped more than 1000 SVs and documented that the number of SVs among humans is much larger than initially hypothesized; many of the SVs potentially affect gene function. The breakpoint junction sequences of more than 200 SVs were determined with a novel pooling strategy and computational analysis. Our analysis provided insights into the mechanisms of SV formation in humans.
Book Sources:
human genome
DNA
molecular biology
PALEOCLIMATOLOGY: Southern Hemisphere and Deep-Sea Warming Led Deglacial Atmospheric CO2 Rise and Tropical Warming
L. Stott, A. Timmermann, and R. Thunell (19 October 2007)
Science 318 (5849), 435-438. [DOI: 10.1126/science.1143791]
Establishing what caused Earth's largest climatic changes in the past requires a precise knowledge of both the forcing and the regional responses. We determined the chronology of high- and low-latitude climate change at the last glacial termination by radiocarbon dating benthic and planktonic foraminiferal stable isotope and magnesium/calcium records from a marine core collected in the western tropical Pacific. Deep-sea temperatures warmed by ~2°C between 19 and 17 thousand years before the present (ky B.P.), leading the rise in atmospheric CO2 and tropical–surface-ocean warming by ~1000 years. The cause of this deglacial deep-water warming does not lie within the tropics, nor can its early onset between 19 and 17 ky B.P. be attributed to CO2 forcing. Increasing austral-spring insolation combined with sea-ice albedo feedbacks appear to be the key factors responsible for this warming.
Book Sources:
climate science
glaciers
geophysics
SOCIOBIOLOGY: Wasp Gene Expression Supports an Evolutionary Link Between Maternal Behavior and Eusociality
A. L. Toth et al. (19 October 2007)
Science 318 (5849), 441-444. [DOI: 10.1126/science.1146647]
The presence of workers that forgo reproduction and care for their siblings is a defining feature of eusociality and a major challenge for evolutionary theory. It has been proposed that worker behavior evolved from maternal care behavior. We explored this idea by studying gene expression in the primitively eusocial wasp Polistes metricus. Because little genomic information existed for this species, we used 454 sequencing to generate 391,157 brain complementary DNA reads, resulting in robust hits to 3017 genes from the honey bee genome, from which we identified and assayed orthologs of 32 honey bee behaviorally related genes. Wasp brain gene expression in workers was more similar to that in foundresses, which show maternal care, than to that in queens and gynes, which do not. Insulin-related genes were among the differentially regulated genes, suggesting that the evolution of eusociality involved major nutritional and reproductive pathways.
Book Sources:
evolution
sociobiology
insect societies
CANCER BIOLOGY: Network Analysis of Oncogenic Ras Activation in Cancer
E. C. Stites et al.(19 October 2007)
Science 318 (5849), 463-467. [DOI: 10.1126/science.1144642]
To investigate the unregulated Ras activation associated with cancer, we developed and validated a mathematical model of Ras signaling. The model-based predictions and associated experiments help explain why only one of two classes of activating Ras point mutations with in vitro transformation potential is commonly found in cancers. Model-based analysis of these mutants uncovered a systems-level process that contributes to total Ras activation in cells. This predicted behavior was supported by experimental observations. We also used the model to identify a strategy in which a drug could cause stronger inhibition on the cancerous Ras network than on the wild-type network. This system-level analysis of the oncogenic Ras network provides new insights and potential therapeutic strategies.
Book Sources:
cancer biology
cancer genes
tumor biology
EVOLUTION: Natural Selection, Not Chance, Paints the Desert Landscape
E. Pennisi (19 October 2007)
Natural Selection, Not Chance, Paints the Desert Landscape
Two evolutionary biologists have found that the color patterns in a flower called desert snow, which for 60 years have been attributed to genetic drift, are actually the result of natural selection.
Science 318 (5849), 376. [DOI: 10.1126/science.318.5849.376]
Book Sources:
evolution
natural selection
desert botany
ARCHAEOLOGY: Coastal Artifacts Suggest Early Beginnings for Modern Behavior
A. Gibbons (19 October 2007)
An international team of researchers reports in this week's issue of Nature that artifacts found in a coastal cave indicate that some key elements of modern human behavior were in place by 164,000 years ago, pushing back the appearance of some of these activities by 25,000 to 40,000 years.
Science 318 (5849), 377a. [DOI: 10.1126/science.318.5849.377a]
Book Sources:
human evolution
anthropology
archeology
ASTRONOMY: Space Sighting Suggests Stardust Doesn't Have to Come From Stars
G. Schilling (19 October 2007)
Astronomers have spotted the telltale spectroscopic fingerprints of microscopic rubies and sapphires in space near a supermassive black hole, which may help explain the abundance of dust particles in the very early universe.
Science 318 (5849), 379a. [DOI: 10.1126/science.318.5849.379a]
Book Sources:
early universe
black holes
cosmology
astrophysics
Nature: Published online 17 October 2007 doi:10.1038/news.2007.173
Embryo Screening Does Not Improve Pregnancy Success
Brendan Maher
Do you get more babies if you screen embryos for abnormal numbers of chromosomes? Maybe not.Do you get more babies if you screen embryos for abnormal numbers of chromosomes? Maybe not.Getty
Two major societies in reproductive medicine have announced that screening for general genetic flaws in ‘test-tube’ embryos before they are implanted in the womb does not improve the chances of having a healthy baby, and so should not be promoted. The declaration sparked heated debate at the American Society for Reproductive Medicine (ASRM) annual meeting in Washington DC yesterday.
The ASRM and the Society for Assisted Reproductive Technology (SART) used the meeting to update their policy recommendations for both preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS).
In PGD, doctors examine embryo DNA for specific genetic signatures, usually in cases in which one or both parents have a genetic disorder or are known carriers. More controversially, it is also used when parents wish to have a child that can provide suitable bone marrow for transplantation into a sick sibling. It has generally been deemed effective.
Book Sources:
pregnancy
embryo screening
reproductive medicine
Neurobiology: Faulty Transmission
Neuron 56, 58-65 (2007) doi:10.1016/j.neuron.2007.08.018
Researchers have found that a protein implicated in the autism-spectrum disorder 'Rett syndrome' regulates the formation of certain neuronal connections.
Loss of the protein MeCP2 causes Rett syndrome, but gene duplications that double protein levels also produce autism-like characteristics and seizures. A likely cause of these disorders is an imbalance between excitation and inhibition in the brain. Hsiao-Tuan Chao, Huda Zoghbi and Christian Rosenmund at Baylor College of Medicine in Houston, Texas, found that when mice lack MeCP2, neurons that transmit the amino acid glutamate in the hippocampus showed 46% less transmission. And mice that produced twice the normal level of MeCP2 exhibited twofold higher neuronal transmission.
These changes were primarily due to alterations in the number of connections — known as synapses — between neurons, the researchers found. The results suggest that MeCP2 regulates synapse formation during early development.
Book Sources:
neuroscience
neurobiology
synaptic transmission
Mechanics: A Defiant Droplet
Phys. Rev. Lett. 99, 44501 (2007)
How can water travel uphill? Simple, say Philippe Brunet and colleagues from the University of Bristol, UK: place a droplet on a sloping plate and shake the plate up and down.
As the plate descends, the droplet gets taller, with a larger contact angle on the upper than the lower edge (pictured, below). This tends to push it up the slope. The effect should cancel out over a complete oscillation cycle, but it doesn't owing to a combination of factors: fore- and aft-symmetry breaking due to the slope, and nonlinear friction between the droplet and the surface.
Above a certain vibration amplitude and frequency all drops will climb. This might be used to transport liquids in microfluidic networks.
Book Sources:
physics
physics mechanics
physics surfaces
Astronomy: Superlative Supernova
Astrophys. J. Lett. 668, L99-L102 (2007)
Astronomers have found the most luminous supernova yet.
Named 2005ap, it lies 4.7 billion light years away and burst with a peak magnitude roughly eight times as bright as the Milky Way. Discovered just before this peak in March 2005, the supernova faded after three weeks. It was about twice as bright as the previous bar-setter, discovered by the leader of the current team, Robert Quimby, a postdoctoral researcher at the California Institute of Technology in Pasadena and leader of the Texas Supernova Search.
The authors speculate that this supernova's record-setting luminosity may have come from an exploding red giant's shock wave hitting and lighting up a shell of material around the star.
Book Sources:
astrophysics
supernova
astronomy
Microbiology: Life on the Rocks
Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0708183104 (2007)
Exactly how some microorganisms live in glacial ice has been something of a mystery. Previous research identified two habitats in which they could obtain water and energy — the surface of trapped mineral grains and liquid veins at ice boundaries. Some life is tuned to these niches, but microbes unable to survive in them have nevertheless been found in glacial ice, meaning another habitat is probably present.
Buford Price and Robert Rohde, at the University of California, Berkeley, may have identified this missing habitat. They calculated that enough molecules such as carbon dioxide, oxygen, nitrogen and methane can diffuse through ice to sustain life.
By scanning ice cores with laser fluorimeters they detected protein spikes, some of which were indicative of single isolated cells, in just such habitats.
Book Sources:
microbiology
glaciers
extreme environments
Astrochemistry: Salty Stars
Astrophys. J. 668, L131-L134 (2007)
Researchers in the United States have found a dash of the unexpected in oxygen-rich stars.
Lucy Ziurys and her colleagues at the University of Arizona in Tucson used the Submillimeter Telescope on Mount Graham and the 12 Meter Telescope on Kitt Peak, both operated by the Arizona Radio Observatory, to observe two red-giant stars that have shells dominated by oxygen. By analysing the recorded spectra, the team determined that the shells contain NaCl, which has previously been observed only in carbon-rich red giants.
The findings suggest that oxygen-rich stars, like their carbon-rich cousins, may be home to the complex types of chemistry that create molecular precursors to life.
Book Sources:
astronomy
astrochemistry
origin of life
Biochemistry: Keeping the Code
Cell 131, 58-69 (2007)
Certain chemical changes, or marks, made to the histone proteins around which DNA wraps seem to tell the cell whether or not that DNA should be transcribed.
Teams led by Matthias Mann at the Max Planck Institute for Biochemistry in Martinsried, Germany, and Marc Timmers at the University Medical Centre Utrecht in the Netherlands looked for proteins that bind to one chemical mark — trimethylation of lysine 4 on the histone H3. This mark is usually associated with transcriptional activity, and they found that a component of the transcription factor TFIID bound it tightly.
Dimethylation of a nearby arginine residue inhibited this binding, and other specific marks strengthened it, lending credence to the hypothesis that a combinatorial 'histone code' determines how cells read their DNA.
Book Sources:
DNA
histones
genetic code
Plant Ecology: Grass Attack
J. Ecol. doi:10.1111/j.1365-2745.2007.01307.x (2007)
Looking for signs of biological warfare past, Carolyn Malmstrom of Michigan State University in East Lansing and her colleagues delved into herbarium specimens at two University of California sites and extracted some of the oldest plant-virus RNA ever recovered.
Although ecological theory generally says that invasive species are successful outside their home ranges because they are freed from the pathogens that evolved to plague them, Malmstrom and colleagues suspect that a historical takeover of California grasslands by Eurasian grasses succeeded in part because the invaders brought viruses with them that affected the natives or changed the dynamics of an existing virus population.
They extracted barley yellow dwarf virus RNA from several specimens, including a 1917 invasive wild oat, proving that the virus was present at the time of invasion.
Book Sources:
plant ecology
botany grass
plant pathology
Cell 131, 80-92 (2007)
Visual Perception Protein
The fruitfly protein INAD had long been considered to be a scaffolding protein, organizing important visual signalling proteins that attach to it. But recent research suggests that INAD directly regulates visual perception.
Rama Ranganathan, of the University of Texas Southwestern Medical Center in Dallas, and colleagues show that, in response to light, one of five structural 'PDZ' domains of INAD transiently switches from a reduced to an oxidized state, distorting INAD's ability to bind to other molecules. This seems crucial to visually mediated reflex behaviours and for terminating visual responses.
Many scaffolding proteins contain PDZ domains, which could undergo similar conformational changes to that of INAD. Thus, rather than support components, these might serve as control centres for other signalling molecules.
Book Sources:
protein conformation
visual neuroscience
biochemical signaling
Entomology: Parallel protection
Proc. R. Soc. B doi:10.1098/rspb.2007.1039 (2007)
Research highlights
To win the game of concealment, it's often best to use the tools at hand. Several desert spiders from around the world hide by attaching sand to their bodies. Using scanning electron microscopy on moults of spiders from Africa, South America and the United States, undergraduate Rebecca Duncan and her colleagues from Lewis & Clark College in Portland, Oregon, compared two unrelated spider genera that independently evolved this ability.
The team found that both have long, thin, flexible 'hairlettes' on the bristles that cover their bodies. The researchers suggest that intermolecular forces make sand stick and keep the spiders camouflaged.
The almost indistinguishable methods for adhesion in the two genera show the power of evolution to produce similar adaptations in similar environments.
Book Sources:
entomology
spiders
insect camouflage
Current Biology, Vol 17, 1646-1656, 09 October 2007
An AMPK-FOXO Pathway Mediates Longevity Induced by a Novel Method of Dietary Restriction in C. elegans
Eric L. Greer et al.
Dietary restriction (DR) is the most effective environmental intervention to extend lifespan in a wide range of species. However, the molecular mechanisms underlying the benefits of DR on longevity are still poorly characterized. AMP-activated protein kinase (AMPK) is activated by a decrease in energy levels, raising the possibility that AMPK might mediate lifespan extension by DR. By using a novel DR assay that we developed and validated in C. elegans, we find that AMPK is required for this DR method to extend lifespan and delay age-dependent decline. We find that AMPK exerts its effects in part via the FOXO transcription factor DAF-16. FOXO/DAF-16 is necessary for the beneficial effects of this DR method on lifespan. Expression of an active version of AMPK in worms increases stress resistance and extends longevity in a FOXO/DAF-16-dependent manner. Lastly, we find that AMPK activates FOXO/DAF-16-dependent transcription and phosphorylates FOXO/DAF-16 at previously unidentified sites, suggesting a possible direct mechanism of regulation of FOXO/DAF-16 by AMPK. Our study shows that an energy-sensing AMPK-FOXO pathway mediates the lifespan extension induced by a novel method of dietary restriction in C. elegans.
Book Sources:
longevity
C. elegans
dietary restriction
Current Biology, Vol 17, R827-R831, 09 October 2007
Adaptive radiation of cichlid fish
George F. Turner
How do new species arise? What is the genetic basis for adaptive morphological change and reproductive isolation? How can closely related species co-exist in the same place? What makes some groups diversify faster and more extensively than others? These are some of the questions that evolutionary biologists would like to answer by investigating the extraordinary tendency of cichlid fishes to diversify in tropical lakes. In addition, their diverse suite of mating and parental care strategies, and the importance of the tilapias in human nutrition through aquaculture, have placed cichlid fishes at the centre of an important confluence of research areas and led to the recent decision to fund the sequencing of a cichlid fish genome. Cichlids (pronounced SICK-lids) are a family of fishes (Cichlidae) found mainly in tropical freshwaters. Mitochondrial genome sequences have indicated that cichlids are closely related to the marine surfperches (Embiotocidae) and damselfishes (Pomacentridae), but not, as previously thought, to wrasse and parrotfishes (Labridae and related families). Many fishes have pharyngeal teeth in the throat for processing their food, but fishes of all of these families have a similar and unusually structured set of pharyngeal jaws which are believed to be particularly powerful and flexible in the processing of food items. This is thought to have allowed the oral jaws to become more specialised for food capture, as they have in the cichlids and wrasse. The natural distribution of the cichlids is centred on Africa, Latin America and Madagascar, with a few species native to south Asia and the middle east, suggesting that cichlids were already widespread throughout the great southern supercontinent Gondwana when it started to split up around 120-160 million years ago. The African cichlids have been the focus of most research, both because of their great adaptive radiations and their importance as food fish (Table 1). The African cichlids are classed into a number of ‘tribes’, of which the haplochromines are the most species-rich and ecologically diverse, and the tilapiines the most important in aquaculture and fisheries. This article has focussed on the significance of cichlid fishes in the understanding of adaptive evolution and rapid speciation. As yet, there is no clear explanation for the propensity for some groups of cichlid fishes to undergo rapid speciation and diversification in African lakes. This is hardly surprising, as investigating such a question is likely to involve comparative study across many lineages in different localities, and most of these are found in areas in which local resources for research are comparatively poor. However, many significant issues have been raised and these have proved applicable to a wider community of researchers, such as the significance of hybridisation and sympatric speciation in animals. Genome sequencing could facilitate progress in these areas, for example through the identification of correlated rapid adaptive evolution and rapid genetic change in functional gene or regulatory element sequence, in gene expression levels or through structural rearrangements such as gene duplication. It may also help sort out the phylogenetic relationships of closely related species and populations. Of course, cichlids are interesting for other reasons apart from adaptive radiation. Most species live in species-rich but resource-poor areas of the world, particularly sub-Saharan Africa. Many species are believed to be threatened or possibly extinct, in particular the open-water species of Lake Victoria, where the ecosystem has changed drastically since the introduction of predatory Nile Perch. Tilapiine cichlids are among the most important freshwater food-fishes in tropical regions — they are palatable, tolerant of poor water conditions, fast-growing and easily bred. They are now cultured extensively outside their native range. Unlike many fishes cultured in temperate regions, they are largely herbivorous, making them ecologically and economically efficient to culture. On a crowded, warming planet, tilapia culture is likely play a significant role in human economy and food security, with artificial selection, hybridisation, preservation of wild genetic diversity and genetic modification all likely to be key issues. Thus, it is expected that sequencing of an African cichlid genome can only help stimulate substantial advances in evolutionary studies, conservation biology and aquaculture.
Book Sources:
evolutionary biology
cichlid fishes
evolution adaptive radiation
Current Biology, Vol 17, R832-R833, 09 October 2007
African elephants run from the sound of disturbed bees
Lucy E. King et al.
Encroaching human development into former wildlife areas [1] is compressing African elephants into ever smaller home ranges, causing increased levels of human-elephant conflict [2]. African honeybees have been proposed as a possible deterrent to elephants [3]. We have performed a sound playback experiment to study this hypothesis. We found that a significant majority of elephants, in a sample of 18 well-known families and subgroups of varying sizes, reacted negatively — immediately walking or running away — when they heard the buzz of disturbed bees, while they ignored the control sound of natural white-noise. Whether the observed response was the result of individual conditioning or of learning by social facilitation remains to be established. Our study strongly supports the hypothesis that bees — and perhaps even their buzz alone — may be deployed to keep elephants at bay.
Book Sources:
elephants
bees
animal behavior
Current Biology, Vol 17, 1669-1674, 09 October 2007
Expression Partitioning between Genes Duplicated by Polyploidy under Abiotic Stress and during Organ Development
Zhenlan Liu and Keith L. Adams
Allopolyploidy has been a prominent mode of speciation and a recurrent process during plant evolution and has contributed greatly to the large number of duplicated genes in plant genomes. Polyploidy often leads to changes in genome organization and gene expression. The expression of genes that are duplicated by polyploidy (termed homeologs) can be partitioned between the duplicates so that one copy is expressed and functions only in some organs and the other copy is expressed only in other organs, indicative of subfunctionalization. To determine how homeologous-gene expression patterns change during organ development and in response to abiotic stress conditions, we have examined expression of the alcohol dehydrogenase gene AdhA in allopolyploid cotton (Gossypium hirsutum). Expression ratios of the two homeologs vary considerably during the development of organs from seedlings and fruits. Abiotic stress treatments, including cold, dark, and water submersion, altered homeologous-gene expression. Most notably, only one copy is expressed in hypocotyls during a water-submersion treatment, and only the other copy is expressed during cold stress. These results imply that subfunctionalization of genes duplicated by polyploidy has occurred in response to abiotic stress conditions. Partitioning of duplicate gene expression in response to environmental stress may lead to duplicate gene retention during subsequent evolution.
Book Sources:
gene expression
polyploidy
developmental biology
Current Biology, Vol 17, 1692-1696, 09 October 2007
The Essential Role of Premotor Cortex in Speech Perception
Ingo G. Meister et al
Besides the involvement of superior temporal regions in processing complex speech sounds, evidence suggests that the motor system might also play a role [1, 2, 3, 4]. This suggests that the hearer might perceive speech by simulating the articulatory gestures of the speaker [5, 6]. It is still an open question whether this simulation process is necessary for speech perception. We applied repetitive transcranial magnetic stimulation to the premotor cortex to disrupt subjects' ability to perform a phonetic discrimination task. Subjects were impaired in discriminating stop consonants in noise but were unaffected in a control task that was matched in difficulty, task structure, and response characteristics. These results show that the disruption of human premotor cortex impairs speech perception, thus demonstrating an essential role of premotor cortices in perceptual processes.
Book Sources:
neuroscience
brain premotor cortex
brain speech perception
Current Biology, Vol 17, 1663-1668, 09 October 2007
The Evolutionary Origins of Human Patience: Temporal Preferences in Chimpanzees, Bonobos, and Human Adults
Alexandra G. Rosati et al.
To make adaptive choices, individuals must sometimes exhibit patience, forgoing immediate benefits to acquire more valuable future rewards [1, 2, 3]. Although humans account for future consequences when making temporal decisions [4], many animal species wait only a few seconds for delayed benefits [5, 6, 7, 8, 9, 10]. Current research thus suggests a phylogenetic gap between patient humans and impulsive, present-oriented animals [9, 11], a distinction with implications for our understanding of economic decision making [12] and the origins of human cooperation [13]. On the basis of a series of experimental results, we reject this conclusion. First, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) exhibit a degree of patience not seen in other animals tested thus far. Second, humans are less willing to wait for food rewards than are chimpanzees. Third, humans are more willing to wait for monetary rewards than for food, and show the highest degree of patience only in response to decisions about money involving low opportunity costs. These findings suggest that core components of the capacity for future-oriented decisions evolved before the human lineage diverged from apes. Moreover, the different levels of patience that humans exhibit might be driven by fundamental differences in the mechanisms representing biological versus abstract rewards.
Book Sources:
evolutionary psychology
chimpanzee behavior
bonobo behavior
Subcellular Processes
Dynamics of an idealized model of microtubule growth and catastrophe
T. Antal, P. L. Krapivsky, S. Redner, M. Mailman, and B. Chakraborty
We investigate a simple dynamical model of a microtubule that evolves by attachment of guanosine triphosphate (GTP) tubulin to its end, irreversible conversion of GTP to guanosine diphosphate (GDP) tubulin by hydrolysis, and detachment of GDP at the end of a microtubule. As a function of rates of th ... [Phys. Rev. E 76, 041907 (2007)] published Wed Oct 10, 2007.
Book Sources:
theoretical biology
cell biology
microtubules
Gravity, Black Holes and Strings
Thomas Mohaupt
We give a brief pedagogical introduction to the application of string theory to gravity and black holes. ... [AIP Conf. Proc. 939, 192 (2007)] published Fri Oct 12, 2007.
Book Sources:
physics gravity
physics black holes
physics string theory
Quantum Black Holes: Entropy and Thermal Stability
Parthasarathi Majumdar
Arguing that black hole physics presents perhaps the most potent rationale for a quantum formulation of general relativity, the Loop Quantum Gravity approach to the problem of microcanonical black hole entropy is surveyed, emphasizing quantum corrections beyond the semiclassical Bekenstein-Hawking a ... [AIP Conf. Proc. 939, 180 (2007)] published Fri Oct 12, 2007.
Book Sources:
quantum theory
physics black holes
physics entropy
thermal physics
The role of space-time structure in effective theory and cosmology
Martin Bojowald
Quantum gravity generally gives rise to a fundamental space-time structure different from the classical continuum picture. This is incorporated in the form of states representing quantum geometry. Effective equations derived to evaluate the quantum theory by including quantum corrections in the clas ... [AIP Conf. Proc. 939, 138 (2007)] published Fri Oct 12, 2007.
Book Sources:
theoretical physics
physics spacetime
cosmology
Gravity as an emergent phenomenon: A conceptual description
T. Padmanabhan
I describe several broad features of a programme to understand gravity as an emergent, long wavelength, phenomenon (like elasticity) and discuss one concrete framework for realizing this paradigm in the backdrop of several recent results. ... [AIP Conf. Proc. 939, 114 (2007)] published Fri Oct 12, 2007.
Book Sources:
theoretical physics
physics gravity
einstein gravity
Reconstructing the Free-Energy Landscape of a Mechanically Unfolded Model Protein
Alberto Imparato, Stefano Luccioli, and Alessandro Torcini
The equilibrium free-energy landscape of an off-lattice model protein as a function of an internal (reaction) coordinate is reconstructed from out-of-equilibrium mechanical unfolding manipulations. This task is accomplished via two independent methods: by employing an extended version of the Jarzyns ... [Phys. Rev. Lett. 99, 168101 (2007)] published Mon Oct 15, 2007.
Book Sources:
protein chemistry
protein folding
protein modeling
Effects of cytoskeletal disruption on transport, structure, and rheology within mammalian cells
Daphne Weihs, Thomas G. Mason, and Michael A. Teitell
Quantification of cellular responses to stimuli is challenging. Cells respond to changing external conditions through internal structural and compositional and functional modifications, thereby altering their transport and mechanical properties. By properly interpreting particle-tracking microrheolo ... [Phys. Fluids 19, 103102 (2007)] published Wed Oct 10, 2007.
Book Sources:
cell biology
cytoskeleton
biology cell transport
Neurons And Cognition
Simple spontaneously active Hebbian learning model: Homeostasis of activity and connectivity, and consequences for learning and epileptogenesis
David Hsu, Aonan Tang, Murielle Hsu, and John M. Beggs
A spontaneously active neural system that is capable of continual learning should also be capable of homeostasis of both firing rate and connectivity. Experimental evidence suggests that both types of homeostasis exist, and that connectivity is maintained at a state that is optimal for information t ... [Phys. Rev. E 76, 041909 (2007)] published Thu Oct 11, 2007.
Book Sources:
neuroscience cognition
psychology learning theory
neuroscience epilepsy
Vulnerability of a killer whale social network to disease outbreaks
Paulo R. Guimaraes, Jr., Marcio Argollo de Menezes, Robin W. Baird, David Lusseau, Paulo Guimaraes et al.
Emerging infectious diseases are among the main threats to conservation of biological diversity. A crucial task facing epidemiologists is to predict the vulnerability of populations of endangered animals to disease outbreaks. In this context, the network structure of social interactions within anima ... [Phys. Rev. E 76, 042901 (2007)] published Tue Oct 16, 2007.
Book Sources:
biology whales
sociobiology
animal societies
A Scenario for a Natural Origin of Our Universe
Authors: Victor J. Stenger
(Submitted on 16 Oct 2007)
A mathematical model of the natural origin of our universe is presented. The model is based only on well-established physics. No claim is made that this model uniquely represents exactly how the universe came about. But the viability of a single model serves to refute any assertions that the universe cannot have come about by natural means.
Philo 9, no. 2 (2006): 93-102.
Book Sources:
general relativity
quantum cosmology
cosmology
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