153 research outputs found
Mechanical Instabilities of Biological Tubes
We study theoretically the shapes of biological tubes affected by various
pathologies. When epithelial cells grow at an uncontrolled rate, the negative
tension produced by their division provokes a buckling instability. Several
shapes are investigated : varicose, enlarged, sinusoidal or sausage-like, all
of which are found in pathologies of tracheal, renal tubes or arteries. The
final shape depends crucially on the mechanical parameters of the tissues :
Young modulus, wall-to-lumen ratio, homeostatic pressure. We argue that since
tissues must be in quasistatic mechanical equilibrium, abnormal shapes convey
information as to what causes the pathology. We calculate a phase diagram of
tubular instabilities which could be a helpful guide for investigating the
underlying genetic regulation
Particle Ratios and the QCD Critical Temperature
We show how the measured particle ratios at RHIC can be used to provide
non-trivial information about the critical temperature of the QCD phase
transition. This is obtained by including the effects of highly massive
Hagedorn resonances on statistical models, which are used to describe hadronic
yields. Hagedorn states are relevant close to and have been shown to
decrease to the KSS limit and allow for quick chemical equilibrium
times in dynamical calculations of hadrons. The inclusion of Hagedorn states
creates a dependence of the thermal fits on the Hagedorn temperature, ,
which is assumed to be equal to , and leads to an overall improvement of
thermal fits. We find that for Au+Au collisions at RHIC at
GeV the best square fit measure, , occurs at MeV and
produces a chemical freeze-out temperature of 170.4 MeV and a baryon chemical
potential of 27.8 MeV.Comment: 6 pages, 2 figures, talk presented at the International Conference on
Strangeness in Quark Matter, Buzios, Rio de Janeiro, Brazil, Sept. 27 - oct.
2, 200
Theory of the anomalous Hall effect from the Kubo formula and the Dirac equation
A model to treat the anomalous Hall effect is developed. Based on the Kubo
formalism and on the Dirac equation, this model allows the simultaneous
calculation of the skew-scattering and side-jump contributions to the anomalous
Hall conductivity. The continuity and the consistency with the
weak-relativistic limit described by the Pauli Hamiltonian is shown. For both
approaches, Dirac and Pauli, the Feynman diagrams, which lead to the
skew-scattering and the side-jump contributions, are underlined. In order to
illustrate this method, we apply it to a particular case: a ferromagnetic bulk
compound in the limit of weak-scattering and free-electrons approximation.
Explicit expressions for the anomalous Hall conductivity for both
skew-scattering and side-jump mechanisms are obtained. Within this model, the
recently predicted ''spin Hall effect'' appears naturally
Encoding of Temporal Information by Timing, Rate, and Place in Cat Auditory Cortex
A central goal in auditory neuroscience is to understand the neural coding of species-specific communication and human speech sounds. Low-rate repetitive sounds are elemental features of communication sounds, and core auditory cortical regions have been implicated in processing these information-bearing elements. Repetitive sounds could be encoded by at least three neural response properties: 1) the event-locked spike-timing precision, 2) the mean firing rate, and 3) the interspike interval (ISI). To determine how well these response aspects capture information about the repetition rate stimulus, we measured local group responses of cortical neurons in cat anterior auditory field (AAF) to click trains and calculated their mutual information based on these different codes. ISIs of the multiunit responses carried substantially higher information about low repetition rates than either spike-timing precision or firing rate. Combining firing rate and ISI codes was synergistic and captured modestly more repetition information. Spatial distribution analyses showed distinct local clustering properties for each encoding scheme for repetition information indicative of a place code. Diversity in local processing emphasis and distribution of different repetition rate codes across AAF may give rise to concurrent feed-forward processing streams that contribute differently to higher-order sound analysis
Mutations of androgen receptor gene in Brazilian patients with male pseudohermaphroditism
A Systematic Screen for Tube Morphogenesis and Branching Genes in the Drosophila Tracheal System
Many signaling proteins and transcription factors that induce and pattern organs have been identified, but relatively few of the downstream effectors that execute morphogenesis programs. Because such morphogenesis genes may function in many organs and developmental processes, mutations in them are expected to be pleiotropic and hence ignored or discarded in most standard genetic screens. Here we describe a systematic screen designed to identify all Drosophila third chromosome genes (βΌ40% of the genome) that function in development of the tracheal system, a tubular respiratory organ that provides a paradigm for branching morphogenesis. To identify potentially pleiotropic morphogenesis genes, the screen included analysis of marked clones of homozygous mutant tracheal cells in heterozygous animals, plus a secondary screen to exclude mutations in general βhouse-keepingβ genes. From a collection including more than 5,000 lethal mutations, we identified 133 mutations representing βΌ70 or more genes that subdivide the tracheal terminal branching program into six genetically separable steps, a previously established cell specification step plus five major morphogenesis and maturation steps: branching, growth, tubulogenesis, gas-filling, and maintenance. Molecular identification of 14 of the 70 genes demonstrates that they include six previously known tracheal genes, each with a novel function revealed by clonal analysis, and two well-known growth suppressors that establish an integral role for cell growth control in branching morphogenesis. The rest are new tracheal genes that function in morphogenesis and maturation, many through cytoskeletal and secretory pathways. The results suggest systematic genetic screens that include clonal analysis can elucidate the full organogenesis program and that over 200 patterning and morphogenesis genes are required to build even a relatively simple organ such as the Drosophila tracheal system
Isocyanate Formation in the Catalytic Reaction of CO + NO on Pd(111): An in Situ Infrared Spectroscopic Study at Elevated Pressures
A Highly Active and Selective Manganese Oxide Promoted Cobalt-on-Silica FischerβTropsch Catalyst
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