141 research outputs found
Dynamics of Motility-Induced clusters: coarsening beyond Ostwald ripening
We study the dynamics of clusters of Active Brownian Disks generated by
Motility-Induced Phase Separation, by applying an algorithm that we devised to
track cluster trajectories. We identify an aggregation mechanism that goes
beyond Ostwald ripening but also yields . Active clusters of mass
self-propel with enhanced diffusivity Pe. Their fast
motion drives aggregation into large fractal structures, which are patchworks
of diverse hexatic orders, and coexist with regular, orientationally uniform,
smaller ones. To bring out the impact of activity, we perform a comparative
study of a passive system that evidences major differences with the active
case.Comment: 6 pages, 5 figures, S
Quantum Tunneling in Nuclear Fusion
Recent theoretical advances in the study of heavy ion fusion reactions below
the Coulomb barrier are reviewed. Particular emphasis is given to new ways of
analyzing data, such as studying barrier distributions; new approaches to
channel coupling, such as the path integral and Green function formalisms; and
alternative methods to describe nuclear structure effects, such as those using
the Interacting Boson Model. The roles of nucleon transfer, asymmetry effects,
higher-order couplings, and shape-phase transitions are elucidated. The current
status of the fusion of unstable nuclei and very massive systems are briefly
discussed.Comment: To appear in the January 1998 issue of Reviews of Modern Physics. 13
Figures (postscript file for Figure 6 is not available; a hard copy can be
requested from the authors). Full text and figures are also available at
http://nucth.physics.wisc.edu/preprints
Elovl5 is required for proper action potential conduction along peripheral myelinated fibers
Elovl5 elongates fatty acids with 18 carbon atoms and in cooperation with other enzymes guarantees the normal levels of very long‐chain fatty acids, which are necessary for a proper membrane structure. Action potential conduction along myelinated axons depends on structural integrity of myelin, which is maintained by a correct amount of fatty acids and a proper interaction between fatty acids and myelin proteins. We hypothesized that in Elovl5 (−/−) mice, the lack of elongation of Elovl5 substrates might cause alterations of myelin structure. The analysis of myelin ultrastructure showed an enlarged periodicity with reduced G‐ratio across all axonal diameters. We hypothesized that the structural alteration of myelin might affect the conduction of action potentials. The sciatic nerve conduction velocity was significantly reduced without change in the amplitude of the nerve compound potential, suggesting a myelin defect without a concomitant axonal degeneration. Since Elovl5 is important in attaining normal amounts of polyunsaturated fatty acids, which are the principal component of myelin, we performed a lipidomic analysis of peripheral nerves of Elovl5‐deficient mice. The results revealed an unbalance, with reduction of fatty acids longer than 18 carbon atoms relative to shorter ones. In addition, the ratio of saturated to unsaturated fatty acids was strongly increased. These findings point out the essential role of Elovl5 in the peripheral nervous system in supporting the normal structure of myelin, which is the key element for a proper conduction of electrical signals along myelinated nerves
Effects of membrane depolarization and changes in extracellular [K+] on the Ca2+ transients of fast skeletal muscle fibers. Implications for muscle fatigue
Repetitive activation of skeletal muscle fibers leads to a reduced transmembrane K+ gradient. The resulting membrane depolarization has been proposed to play a major role in the onset of muscle fatigue. Nevertheless, raising the extracellular K+ (\documentclass[12pt]{minimal}
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\begin{document}\end{document}) to 10 mM potentiates twitch force of rested amphibian and mammalian fibers. We used a double Vaseline gap method to simultaneously record action potentials (AP) and Ca2+ transients from rested frog fibers activated by single and tetanic stimulation (10 pulses, 100 Hz) at various \documentclass[12pt]{minimal}
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\begin{document}\end{document} and membrane potentials. Depolarization resulting from current injection or raised \documentclass[12pt]{minimal}
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\begin{document}\end{document} produced an increase in the resting [Ca2+]. Ca2+ transients elicited by single stimulation were potentiated by depolarization from −80 to −60 mV but markedly depressed by further depolarization. Potentiation was inversely correlated with a reduction in the amplitude, overshoot and duration of APs. Similar effects were found for the Ca2+ transients elicited by the first pulse of 100 Hz trains. Depression or block of Ca2+ transient in response to the 2nd to 10th pulses of 100 Hz trains was observed at smaller depolarizations as compared to that seen when using single stimulation. Changes in Ca2+ transients along the trains were associated with impaired or abortive APs. Raising \documentclass[12pt]{minimal}
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\begin{document}\end{document} to 10 mM potentiated Ca2+ transients elicited by single and tetanic stimulation, while raising \documentclass[12pt]{minimal}
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\begin{document}\end{document} to 15 mM markedly depressed both responses. The effects of 10 mM \documentclass[12pt]{minimal}
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\begin{document}\end{document} on Ca2+ transients, but not those of 15 mM \documentclass[12pt]{minimal}
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\begin{document}\end{document}, could be fully reversed by hyperpolarization. The results suggests that the force potentiating effects of 10 mM \documentclass[12pt]{minimal}
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\begin{document}\end{document} might be mediated by depolarization dependent changes in resting [Ca2+] and Ca2+ release, and that additional mechanisms might be involved in the effects of 15 mM \documentclass[12pt]{minimal}
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\begin{document}\end{document} on force generation
Gallium Solar Neutrino Experiments: Absorption Cross sections, Neutrino spectra, and Predicted Event Rates
Neutrino absorption cross sections for 71Ga are calculated for all solar
neutrino sources with standard energy spectra, and for laboratory sources of
51Cr and 37Ar; the calculations include, where appropriate, the thermal energy
of fusing solar ions and use improved nuclear and atomic data. The ratio, R, of
measured (in GALLEX and SAGE) to calculated 51Cr capture rate is R = 0.95 +/-
0.07 (exp)} + ^{+0.04}_{-0.03} (theory). Cross sections are also calculated for
specific neutrino energies chosen so that a spline fit determines accurately
the event rates in a gallium detector even if new physics changes the energy
spectrum of solar neutrinos. Theoretical uncertainties are estimated for cross
sections at specific energies and for standard neutrino energy spectra.
Standard energy spectra are presented for pp and CNO neutrino sources in the
appendices. Neutrino fluxes predicted by standard solar models, corrected for
diffusion, have been in the range 120 SNU to 141 SNU since 1968.Comment: 57 pages, ReVTeX file. Accepted for publication in Phys. Rev. C.
Viewgraphs and numerical tables of neutrino spectra and cross sections at
http://www.sns.ias.edu/~jn
Influence of sorbitol on mechanical and physico-chemical properties of soy protein-based bioplastics processed by injection molding
A Glial Variant of the Vesicular Monoamine Transporter Is Required To Store Histamine in the Drosophila Visual System
Unlike other monoamine neurotransmitters, the mechanism by which the brain's histamine content is regulated remains unclear. In mammals, vesicular monoamine transporters (VMATs) are expressed exclusively in neurons and mediate the storage of histamine and other monoamines. We have studied the visual system of Drosophila melanogaster in which histamine is the primary neurotransmitter released from photoreceptor cells. We report here that a novel mRNA splice variant of Drosophila VMAT (DVMAT-B) is expressed not in neurons but rather in a small subset of glia in the lamina of the fly's optic lobe. Histamine contents are reduced by mutation of dVMAT, but can be partially restored by specifically expressing DVMAT-B in glia. Our results suggest a novel role for a monoamine transporter in glia that may be relevant to histamine homeostasis in other systems
Reactive oxygen species in phagocytic leukocytes
Phagocytic leukocytes consume oxygen and generate reactive oxygen species in response to appropriate stimuli. The phagocyte NADPH oxidase, a multiprotein complex, existing in the dissociated state in resting cells becomes assembled into the functional oxidase complex upon stimulation and then generates superoxide anions. Biochemical aspects of the NADPH oxidase are briefly discussed in this review; however, the major focus relates to the contributions of various modes of microscopy to our understanding of the NADPH oxidase and the cell biology of phagocytic leukocytes
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