417 research outputs found
Universal Scaling Laws for Shear Induced Dilation in Frictional Granular Media
Compressed frictional granular matter cannot flow without dilation. Upon
forced shearing to generate flow, the amount of dilation may depend on the
initial preparation and a host of material variables. On the basis of both
experiments and numerical simulations we show that as a result of training by
repeated compression-decompression cycles the amount of dilation induced by
shearing the system depends only on the shear rate and on the (pre-shearing)
packing fraction. Relating the rheological response to structural properties
allows us to derive a scaling law for the amount of dilation after cycles
of compression-decompression. The resulting scaling law has a universal
exponent that for trained systems is independent of the inter-granules force
laws, friction parameters and strain rate. The amplitude of the scaling law is
analytically computable, and it depends only on the shear rate and the
asymptotic packing fraction.Comment: 8 pages, 10 figures, Published Versio
Heat conduction in the disordered harmonic chain revisited
A general formulation is developed to study heat conduction in disordered
harmonic chains with arbitrary heat baths that satisfy the
fluctuation-dissipation theorem. A simple formal expression for the heat
current J is obtained, from which its asymptotic system-size (N) dependence is
extracted. It is shown that the ``thermal conductivity'' depends not just on
the system itself but also on the spectral properties of the fluctuation and
noise used to model the heat baths. As special cases of our heat baths we
recover earlier results which reported that for fixed boundaries , while for free boundaries . For other choices we
find that one can get other power laws including the ``Fourier behaviour'' .Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev. Let
Identification of Differentially Expressed Proteins in Murine Embryonic and Postnatal Cortical Neural Progenitors
BACKGROUND: The central nervous system (CNS) develops from a heterogeneous pool of neural stem and progenitor cells (NSPC), the underlying differences among which are poorly understood. The study of NSPC would be greatly facilitated by the identification of additional proteins that mediate their function and that would distinguish amongst different progenitor populations. METHODOLOGY/PRINCIPAL FINDINGS: To identify membrane and membrane-associated proteins expressed by NSPC, we used a proteomics approach to profile NSPC cultured as neurospheres (NS) isolated from the murine cortex during a period of neurogenesis (embryonic day 11.5, E11.5), as compared to NSPC isolated at a peak of gliogenesis (postnatal day 1, P0) and to differentiated E11.5 NS. 54 proteins were identified with high expression in E11.5 NS, including the TrkC receptor, several heterotrimeric G proteins, and the Neogenin receptor. 24 proteins were identified with similar expression in E11.5 and P0 NS over differentiated E11.5 NS, and 13 proteins were identified with high expression specifically in P0 NS compared to E11.5 NS. To illustrate the potential relevance of these identified proteins to neural stem cell biology, the function of Neogenin was further studied. Using Fluorescence Activated Cell Sorting (FACS) analysis, expression of Neogenin was associated with a self-renewing population present in both E11.5 and adult subventricular zone (SVZ) NS but not in P0 NS. E11.5 NS expressed a putative Neogenin ligand, RGMa, and underwent apoptosis when exposed to a ligand-blocking antibody. CONCLUSIONS/SIGNIFICANCE: There are fundamental differences between the continuously self-renewing and more limited progenitors of the developing cortex. We identified a subset of differentially expressed proteins that serve not only as a set of functionally important proteins, but as a useful set of markers for the subsequent analysis of NSPC. Neogenin is associated with the continuously self-renewing and neurogenic cells present in E11.5 cortical and adult SVZ NS, and the Neogenin/RGMa receptor/ligand pair may regulate cell survival during development
Persistent expression of Ia antigen and viral genome in visna-maedi virus-induced inflammatory cells. Possible role of lentivirus-induced interferon.
In this study we investigated the pathogenesis of the lymphoproliferative response in the chronic-active visna maedi virus-induced inflammatory lesions. Viral RNA expression was confined to macrophages, but only in tissues showing inflammatory lesions. A persistent and high level of Ia antigen expression was seen in macrophage-like cells in the inflammatory lesions, and the amounts of viral RNA and Ia expression were closely correlated. A small subpopulation of macrophages contained both viral RNA and Ia antigen, and these were found in greatest number in the lung. In vitro experiments showed that a lentivirus-induced interferon (LV-IFN) could induce Ia antigens in normal sheep spleen and lymph node cells as well as in a transformed sheep macrophage cell line. Ia antigen expression in macrophages was transient in the absence of a continuing IFN stimulus and persisted for at least 2 wk in the presence of LV-IFN. LV-IFN also restricted viral replication in macrophages. It is suggested that LV-IFN induced by the inflammatory cells in visna-maedi lesions may induce Ia antigen expression in macrophages, thereby indirectly causing the lymphoproliferative response and restricted virus replication
Controlling the energy flow in nonlinear lattices: a model for a thermal rectifier
We address the problem of heat conduction in 1-D nonlinear chains; we show
that, acting on the parameter which controls the strength of the on site
potential inside a segment of the chain, we induce a transition from conducting
to insulating behavior in the whole system. Quite remarkably, the same
transition can be observed by increasing the temperatures of the thermal baths
at both ends of the chain by the same amount. The control of heat conduction by
nonlinearity opens the possibility to propose new devices such as a thermal
rectifier.Comment: 4 pages with figures included. Phys. Rev. Lett., to be published
(Ref. [10] corrected
Macrophage Bridging Conduit Trafficking of HIV-1 Through the Endoplasmic Reticulum and Golgi Network
Metabolic drift in the aging brain.
Brain function is highly dependent upon controlled energy metabolism whose loss heralds cognitive impairments. This is particularly notable in the aged individuals and in age-related neurodegenerative diseases. However, how metabolic homeostasis is disrupted in the aging brain is still poorly understood. Here we performed global, metabolomic and proteomic analyses across different anatomical regions of mouse brain at different stages of its adult lifespan. Interestingly, while severe proteomic imbalance was absent, global-untargeted metabolomics revealed an energymetabolic drift or significant imbalance in core metabolite levels in aged mouse brains. Metabolic imbalance was characterized by compromised cellular energy status (NAD decline, increased AMP/ATP, purine/pyrimidine accumulation) and significantly altered oxidative phosphorylation and nucleotide biosynthesis and degradation. The central energy metabolic drift suggests a failure of the cellular machinery to restore metabostasis (metabolite homeostasis) in the aged brain and therefore an inability to respond properly to external stimuli, likely driving the alterations in signaling activity and thus in neuronal function and communication
Simulation of heat transport in low-dimensional oscillator lattices
The study of heat transport in low-dimensional oscillator lattices presents a
formidable challenge. Theoretical efforts have been made trying to reveal the
underlying mechanism of diversified heat transport behaviors. In lack of a
unified rigorous treatment, approximate theories often may embody controversial
predictions. It is therefore of ultimate importance that one can rely on
numerical simulations in the investigation of heat transfer processes in
low-dimensional lattices. The simulation of heat transport using the
non-equilibrium heat bath method and the Green-Kubo method will be introduced.
It is found that one-dimensional (1D), two-dimensional (2D) and
three-dimensional (3D) momentum-conserving nonlinear lattices display power-law
divergent, logarithmic divergent and constant thermal conductivities,
respectively. Next, a novel diffusion method is also introduced. The heat
diffusion theory connects the energy diffusion and heat conduction in a
straightforward manner. This enables one to use the diffusion method to
investigate the objective of heat transport. In addition, it contains
fundamental information about the heat transport process which cannot readily
be gathered otherwise.Comment: Article published in: Thermal transport in low dimensions: From
statistical physics to nanoscale heat transfer, S. Lepri, ed. Lecture Notes
in Physics, vol. 921, pp. 239 - 274, Springer-Verlag, Berlin, Heidelberg, New
York (2016
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