2,082 research outputs found
Unfolding the Sulcus
Sulci are localized furrows on the surface of soft materials that form by a
compression-induced instability. We unfold this instability by breaking its
natural scale and translation invariance, and compute a limiting bifurcation
diagram for sulcfication showing that it is a scale-free, sub-critical {\em
nonlinear} instability. In contrast with classical nucleation, sulcification is
{\em continuous}, occurs in purely elastic continua and is structurally stable
in the limit of vanishing surface energy. During loading, a sulcus nucleates at
a point with an upper critical strain and an essential singularity in the
linearized spectrum. On unloading, it quasi-statically shrinks to a point with
a lower critical strain, explained by breaking of scale symmetry. At
intermediate strains the system is linearly stable but nonlinearly unstable
with {\em no} energy barrier. Simple experiments confirm the existence of these
two critical strains.Comment: Main text with supporting appendix. Revised to agree with published
version. New result in the Supplementary Informatio
Economics of membrane occupancy and respiro-fermentation
The authors propose that prokaryotic metabolism is fundamentally constrained by the cytoplasmic membrane surface area available for protein expression, and show that this constraint can explain previously puzzling physiological phenomena, including respiro-fermentation
Are Particles in Advection-Dominated Accretion Flows Thermal?
We investigate the form of the momentum distribution function for protons and
electrons in an advection-dominated accretion flow (ADAF). We show that for all
accretion rates, Coulomb collisions are too inefficient to thermalize the
protons. The proton distribution function is therefore determined by the
viscous heating mechanism, which is unknown. The electrons, however, can
exchange energy quite efficiently through Coulomb collisions and the emission
and absorption of synchrotron photons. We find that for accretion rates greater
than \sim 10^{-3} of the Eddington accretion rate, the electrons have a thermal
distribution throughout the accretion flow. For lower accretion rates, the
electron distribution function is determined by the electron's source of
heating, which is primarily adiabatic compression. Using the principle of
adiabatic invariance, we show that an adiabatically compressed collisionless
gas maintains a thermal distribution until the particle energies become
relativistic. We derive a new, non-thermal, distribution function which arises
for relativistic energies and provide analytic formulae for the synchrotron
radiation from this distribution. Finally, we discuss its implications for the
emission spectra from ADAFs.Comment: 29 pages (Latex), 3 Figures. Submitted to Ap
Systematic Topology Analysis and Generation Using Degree Correlations
We present a new, systematic approach for analyzing network topologies. We
first introduce the dK-series of probability distributions specifying all
degree correlations within d-sized subgraphs of a given graph G. Increasing
values of d capture progressively more properties of G at the cost of more
complex representation of the probability distribution. Using this series, we
can quantitatively measure the distance between two graphs and construct random
graphs that accurately reproduce virtually all metrics proposed in the
literature. The nature of the dK-series implies that it will also capture any
future metrics that may be proposed. Using our approach, we construct graphs
for d=0,1,2,3 and demonstrate that these graphs reproduce, with increasing
accuracy, important properties of measured and modeled Internet topologies. We
find that the d=2 case is sufficient for most practical purposes, while d=3
essentially reconstructs the Internet AS- and router-level topologies exactly.
We hope that a systematic method to analyze and synthesize topologies offers a
significant improvement to the set of tools available to network topology and
protocol researchers.Comment: Final versio
Impact of bottom trawling on water and sediment characteristics of Cuddalore and Parangipettai coastal waters
639-646The present study was carried out to understand the impact of bottom trawling on the hydrographic, nutrient and sediment characteristics of Cuddalore and Parangipettai coastal waters during April 2014–March 2015. The present study addressed the impact of trawling on the sediment re-suspension, biochemical composition and bioavailability of organic matter in two coastal waters off Bay of Bengal. Sampling was carried out in four depth stations at 10, 20, 30, 40 m. Water and sediment samples were collected before and after trawling. The variations in total organic carbon and sediment nutrients were prominent in relation to stations and seasons. Pronounced changes were observed in water nutrients before and after trawling, while there was a minor effect on dissolved oxygen, total organic carbon and sediment nutrients. Conforming to the results, the PCA plot drawn for both the regions also revealed similar trend by the fact that the water nutrients had positive correlation with samples collected after trawling in all the stations, while dissolved oxygen, soil nutrients and total organic carbon showed negative correlation with the samples collected before trawling in all the stations
Mechanism of immunosuppression in leprosy: presence of suppressor factor(s) from macrophages of lepromatous patients
Human peripheral blood mononuclear cell proliferation induced by Mycobacterium leprae could be inhibited by the suppressor factor in the lysate of the macrophages of lepromatous leprosy patients. Macrophages from normal subjects and tuberculoid patients did not show production of a suppressor factor. Inhibition occurred only when the factor was present in the initial stages of lymphocyte culture. The factor is heat stable and nondialyzable. Proliferation induced by some mycobacteria and concanavalin A could also be blocked by the factor. Interestingly, blastogenic response by a few other antigens and phytohemagglutinin could not be inhibited by the suppressor factor. Mononuclear cells pretreated with such lysate from lepromatous macrophages for 24 h could induce suppressive activity in the cells in vitro in an autologous system. Treatment of these cells with carbonyl iron after the induction phase, to remove phagocytic cells, did not abolish their suppressive activity. The lepromatous macrophage lysate also generated suppressive activity in a T-ymphocyte-enriched population of normal subjects. These studies are interpreted to indicate that immunosuppression in lepromatous patients is produced by both macrophages and T lymphocytes. The exact phase in which either of these cells acts as a suppressor may be different. Specific suppression by macrophages to M. leprae can be an early event, and nonspecific suppression by T lymphocytes may be a later event in the course of lepromatous leprosy
Gamma-ray Emission From Advection-Dominated Accretion Flows Around Black Holes: Application to the Galactic Center
We calculate the flux and spectrum of \gamma-rays emitted by a
two-temperature advection-dominated accretion flow (ADAF) around a black hole.
The \gamma-rays are from the decay of neutral pions produced through
proton-proton collisions. We discuss both thermal and power-law distributions
of proton energies and show that the \gamma-ray spectra in the two cases are
very different. We apply the calculations to the \gamma-ray source, 2EG
J1746-2852, detected by EGRET from the direction of the Galactic Center. We
show that the flux and spectrum of this source are consistent with emission
from an ADAF around the supermassive accreting black hole Sgr A^* if the proton
distribution is a power-law. The model uses accretion parameters within the
range made likely by other considerations. If this model is correct, it
provides evidence for the presence of a two temperature plasma in Sgr A^*, and
predicts \gamma-ray fluxes from other accreting black holes which could be
observed with more sensitive detectors.Comment: 19 pages (Latex), 4 Figures. ApJ 486. Revised Tables and Figure
Catch trend of the commercial trawl fisheries of Rameswaram
The present report summarises the catch details of some of the commercially important fishes landed by the trawlers operating from Rameswaram during the years 1980 and 1981. The silverbellies, formed the major group, indicating the availability of silverbellies in large quantities throughout the year, followed by Elasmobranchs and Penaeid prawns in the landings. Quarterrwise landings of trawlnets and monthwise landings of prawns and other groups were portrayed
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