812 research outputs found
Marine pollution and zooplankton: some recent trends in marine pollution studies
The presence of even very minute quantities of pollutants may become harmful either due to their direct effect on zooplankton or indirectly due to the transfer of the pollutants to other trophic levels through zooplankton. The recent trend in marine pollution studies is therefore to find out the effects of very minute quantities of these pollutants on marine zooplankton and the methods of their accumulation and transfer to the organisms of higher trophic level including man. A review of laboratory and field studies concerning the effects of pollutants such as hydrocarbons, crude oil, heavy metals, pesticides and heated waste water on the survival, breeding, movement, faecal pellet production, growth and development on marine zooplankton is presented
Effect of Bovine Serum Albumin on Red Blood Cell Optical Anisotropy Probed Through the Optomechanical Response in an Optical Trap
The dynamics of trapped entities in an Optical Trap (OT) can yield information with regards to their viscoelastic response as well as optical anisotropy, if any. Detailed analysis of such dynamics correlated with parameters which affect the response can yield additional clues to the exact effect of these on the trapped entities. In this work, we illustrate this point by showing how the altered behavior of Red Blood Cells (RBC) treated with Bovine Serum Albumin (BSA) yields information about the nature of action of BSA, on which there is no current consensus in literature. We conclude from our studies that BSA treatment leads to a change in the birefringence of the RBCs, a conclusion arrived at from the altered optomechanical response of such cells in a linearly polarized Gaussian beam OT. Furthermore, we argue that the observed changes in cellular optical anisotropy may be thought of as due to changes in the curvature of the RBC membrane. We also note that BSA action could help mimic pathological conditions that result in an altered cell shape. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
An optimal network for passenger traffic
The optimal solution of an inter-city passenger transport network has been
studied using Zipf's law for the city populations and the Gravity law
describing the fluxes of inter-city passenger traffic. Assuming a fixed value
for the cost of transport per person per kilometer we observe that while the
total traffic cost decreases, the total wiring cost increases with the density
of links. As a result the total cost to maintain the traffic distribution is
optimal at a certain link density which vanishes on increasing the network
size. At a finite link density the network is scale-free. Using this model the
air-route network of India has been generated and an one-to-one comparison of
the nodal degree values with the real network has been made.Comment: 5 pages, 4 figure
A study of supercooling of the disordered vortex phase via minor hysteresis loops in 2H-NbSe_2
We report on the observation of novel features in the minor hysteresis loops
in a clean crystal of NbSe_2 which displays a peak effect. The observed
behavior can be explained in terms of a supercooling of the disordered vortex
phase while cooling the superconductor in a field. Also, the extent of spatial
order in a flux line lattice formed in ascending fields is different from (and
larger than) that in the descending fields below the peak position of the peak
effect; this is attributed to unequal degree of annealing of the state induced
by a change of field in the two cases.Comment: 5 pages of text + 6 figures, submitted to Phys. Rev.
Transcriptional regulation of PRPF31 gene expression by MSR1 repeat elements causes incomplete penetrance in retinitis pigmentosa.
PRPF31-associated retinitis pigmentosa presents a fascinating enigma: some mutation carriers are blind, while others are asymptomatic. We identify the major molecular cause of this incomplete penetrance through three cardinal features: (1) there is population variation in the number (3 or 4) of a minisatellite repeat element (MSR1) adjacent to the PRPF31 core promoter; (2) in vitro, 3-copies of the MSR1 element can repress gene transcription by 50 to 115-fold; (3) the higher-expressing 4-copy allele is not observed among symptomatic PRPF31 mutation carriers and correlates with the rate of asymptomatic carriers in different populations. Thus, a linked transcriptional modifier decreases PRPF31 gene expression that leads to haploinsufficiency. This result, taken with other identified risk alleles, allows precise genetic counseling for the first time. We also demonstrate that across the human genome, the presence of MSR1 repeats in the promoters or first introns of genes is associated with greater population variability in gene expression indicating that copy number variation of MSR1s is a generic controller of gene expression and promises to provide new insights into our understanding of gene expression regulation
Transcriptional regulation of PRPF31 gene expression by MSR1 repeat elements causes incomplete penetrance in retinitis pigmentosa.
PRPF31-associated retinitis pigmentosa presents a fascinating enigma: some mutation carriers are blind, while others are asymptomatic. We identify the major molecular cause of this incomplete penetrance through three cardinal features: (1) there is population variation in the number (3 or 4) of a minisatellite repeat element (MSR1) adjacent to the PRPF31 core promoter; (2) in vitro, 3-copies of the MSR1 element can repress gene transcription by 50 to 115-fold; (3) the higher-expressing 4-copy allele is not observed among symptomatic PRPF31 mutation carriers and correlates with the rate of asymptomatic carriers in different populations. Thus, a linked transcriptional modifier decreases PRPF31 gene expression that leads to haploinsufficiency. This result, taken with other identified risk alleles, allows precise genetic counseling for the first time. We also demonstrate that across the human genome, the presence of MSR1 repeats in the promoters or first introns of genes is associated with greater population variability in gene expression indicating that copy number variation of MSR1s is a generic controller of gene expression and promises to provide new insights into our understanding of gene expression regulation
History effect in inhomogeneous superconductors
A model was proposed to account for a new kind of history effect in the
transport measurement of a sample with inhomogeneous flux pinning coupled with
flux creep. The inhomogeneity of flux pinning was described in terms of
alternating weak pinning (lower jc) and strong pinning region (higher jc). The
flux creep was characterized by logarithmic barrier. Based on this model, we
numerically observed the same clockwise V-I loops as reported in references.
Moreover, we predicted behaviors of the V-I loop at different sweeping rates of
applied current dI/dt or magnetic fields Ba, etc. Electric transport
measurement was performed in Ag-sheathed Bi2-xPbxSr2Ca2Cu3Oy tapes immersed in
liquid nitrogen with and without magnetic fields. V-I loop at certain dI/dt and
Ba was observed. It is found that the area of the loop is more sensitive to
dI/dt than to Ba, which is in agreement well with our numerical results.Comment: To appear in Phys Rev B, October 1 Issu
Critical depinning force and vortex lattice order in disordered superconductors
We simulate the ordering of vortices and its effects on the critical current
in superconductors with varied vortex-vortex interaction strength and varied
pinning strengths for a two-dimensional system. For strong pinning the vortex
lattice is always disordered and the critical depinning force only weakly
increases with decreasing vortex-vortex interactions. For weak pinning the
vortex lattice is defect free until the vortex-vortex interactions have been
reduced to a low value, when defects begin to appear with a simultaneous rapid
increase in the critical depinning force. In each case the depinning force
shows a maximum for non-interacting vortices. The relative height of the peak
increases and the peak width decreases for decreasing pinning strength in
excellent agreement with experimental trends associated with the peak effect.
We show that scaling relations exist between the distance between defects in
the vortex lattice and the critical depinning force.Comment: 5 pages, 6 figure
Disordered Type-II Superconductors: A Universal Phase Diagram for Low-T Systems
A universal phase diagram for weakly pinned low-T type-II superconductors
is revisited and extended with new proposals. The low-temperature ``Bragg
glass'' phase is argued to transform first into a disordered, glassy phase upon
heating. This glassy phase, a continuation of the high-field equilibrium vortex
glass phase, then melts at higher temperatures into a liquid. This proposal
provides an explanation for the anomalies observed in the peak effect regime of
2H-NbSe and several other low-T materials which is independent of the
microscopic mechanisms of superconductivity in these systems.Comment: 23 pages, 9 figure
History effects and pinning regimes in solid vortex matter
We propose a phenomenological model that accounts for the history effects
observed in ac susceptibility measurements in YBa2Cu3O7 single crystals [Phys.
Rev. Lett. 84, 4200 (2000) and Phys. Rev. Lett. 86, 504 (2001)]. Central to the
model is the assumption that the penetrating ac magnetic field modifies the
vortex lattice mobility, trapping different robust dynamical states in
different regions of the sample. We discuss in detail on the response of the
superconductor to an ac magnetic field when the vortex lattice mobility is not
uniform inside the sample. We begin with an analytical description for a simple
geometry (slab) and then we perform numerical calculations for a strip in a
transverse magnetic field which include relaxation effects. In calculations,
the vortex system is assumed to coexist in different pinning regimes. The
vortex behavior in the regions where the induced current density j has been
always below a given threshold (j_c^>) is described by an elastic Campbell-like
regime (or a critical state regime with local high critical current density,
j_c^>). When the VS is shaken by symmetrical (e.g. sinusoidal) ac fields, the
critical current density is modified to j_c^) at
regions where vortices have been forced to oscillate by a current density
larger than j_c^>. Experimentally, an initial state with high critical current
density (j_c^>) can be obtained by zero field cooling, field cooling (with no
applied ac field) or by shaking the vortex lattice with an asymmetrical (e.g.
sawtooth) field. We compare our calculations with experimental ac
susceptibility results in YBa2Cu3O7 single crystals.Comment: 11 pages, 7 figures. To be published in PR
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