1,611 research outputs found
Reviving the Macrobrachium rosenbergii (de Man) fishery in Vembanad Lake, India
In Vembanad Lake and its confluent rivers (Kerala, India), the catches of Macrobrachium rosenbergii (de Man) were reported to have dwindled to a mere 39 t in the 1980s from average landings of 300 t during the 1960s. This decline is due to the impact of a number of human interventions affecting the ecosystem and, hence, the stocks of M. rosenbergii. Monitoring of landings in 1994-1995 and 1995-1996 indicates an improvement in catches. This paper discusses the reasons for the decline and revival in stocks and suggestions for their replenishment
Observability of Dark Matter Substructure with Pulsar Timing Correlations
Dark matter substructure on small scales is currently weakly constrained, and
its study may shed light on the nature of the dark matter. In this work we
study the gravitational effects of dark matter substructure on measured pulsar
phases in pulsar timing arrays (PTAs). Due to the stability of pulse phases
observed over several years, dark matter substructure around the Earth-pulsar
system can imprint discernible signatures in gravitational Doppler and Shapiro
delays. We compute pulsar phase correlations induced by general dark matter
substructure, and project constraints for a few models such as monochromatic
primordial black holes (PBHs), and Cold Dark Matter (CDM)-like NFW subhalos.
This work extends our previous analysis, which focused on static or single
transiting events, to a stochastic analysis of multiple transiting events. We
find that stochastic correlations, in a PTA similar to the Square Kilometer
Array (SKA), are uniquely powerful to constrain subhalos as light as , with concentrations as low as that predicted by standard
CDM.Comment: 45 pages, 12 figure
Antisite Disorder-induced Exchange Bias Effect in Multiferroic Y2CoMnO6
Exchange bias effect in the ferromagnetic double perovskite compound
YCoMnO, which is also a multiferroic, is reported. The exchange bias,
observed below 8~K, is explained as arising due to the interface effect between
the ferromagnetic and antiferromagnetic clusters created by {\it antisite}
disorder in this material. Below 8~K, prominent ferromagnetic hysteresis with
metamagnetic "steps" and significant coercive field, 10~kOe are
observed in this compound which has a 75~K. A model based on
growth of ferromagnetic domains overcoming the elastic energy of structurally
pinned magnetic interfaces, which closely resembles martensitic-like
transitions, is adapted to explain the observed effects. The role of {\it
antisite} disorder in creating the domain structure leading to exchange bias
effect is highlighted in the present work.Comment: 4 pages two-column, 4 figures, accepted to Appl. Phys. Let
Spin Freezing in the Spin Liquid Compound FeAl2O4
Spin freezing in the -site spinel FeAlO which is a spin liquid
candidate is studied using remnant magnetization and nonlinear magnetic
susceptibility and isofield cooling and heating protocols. The remnant
magnetization behavior of FeAlO differs significantly from that of a
canonical spin glass which is also supported by analysis of the nonlinear
magnetic susceptibility term . Through the power-law analysis of
, a spin-freezing temperature, = 11.40.9~K and critical
exponent, = 1.480.59 are obtained. Cole-Cole analysis of magnetic
susceptibility shows the presence of broad spin relaxation times in
FeAlO, however, the irreversible dc susceptibility plot discourages an
interpretation based on conventional spin glass features. The magnetization
measured using the cooling-and-heating-in-unequal-fields protocol brings more
insight to the magnetic nature of this frustrated magnet and reveals
unconventional glassy behaviour. Combining our results, we arrive at the
conclusion that the present sample of FeAlO consists of a majority spin
liquid phase with "glassy" regions embedded.Comment: 5 pages, 6 figs, 2-column, Accepted to Phys. Rev.
Pulsar Timing Probes of Primordial Black Holes and Subhalos
Pulsars act as accurate clocks, sensitive to gravitational redshift and
acceleration induced by transiting clumps of matter. We study the sensitivity
of pulsar timing arrays (PTAs) to single transiting compact objects, focusing
on primordial black holes and compact subhalos in the mass range from to well above . We find that the Square Kilometer
Array can constrain such objects to be a subdominant component of the dark
matter over this entire mass range, with sensitivity to a dark matter
sub-component reaching the sub-percent level over significant parts of this
range. We also find that PTAs offer an opportunity to probe substantially less
dense objects than lensing because of the large effective radius over which
such objects can be observed, and we quantify the subhalo concentration
parameters which can be constrained.Comment: 18 pages, 6 figure
Double-phase transition and giant positive magnetoresistance in the quasi-skutterudite GdIrSn
The magnetic, thermodynamic and electrical/thermal transport properties of
the caged-structure quasi-skutterudite GdIrSn are
re-investigated. The magnetization , specific heat and the
resistivity reveal a double-phase transition -- at 10~K
and at 8.8~K -- which was not observed in the previous report on
this compound. The antiferromagnetic transition is also visible in the thermal
transport data, thereby suggesting a close connection between the electronic
and lattice degrees of freedom in this Sn-based quasi-skutterudite. The
temperature dependence of is analyzed in terms of a power-law for
resistivity pertinent to Fermi liquid picture. Giant, positive
magnetoresistance (MR) 80 is observed in GdIrSn at
2~K with the application of 9~T. The giant MR and the double magnetic
transition can be attributed to the quasi-cages and layered antiferromagnetic
structure of GdIrSn vulnerable to structural distortions and/or
dipolar or spin-reorientation effects. The giant value of MR observed in this
class of 3:4:13 type alloys, especially in a Gd-compound, is the highlight of
this work.Comment: 20 pages single column, 7 figures, 1 table; Accepted to J. Appl.
Phys., 201
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