1,156 research outputs found
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
Streamer evolution arrest governed amplified AC breakdown strength of graphene and CNT colloids
The present article experimentally explores the concept of large improving
the AC dielectric breakdown strength of insulating mineral oils by the addition
of trace amounts of graphene or CNTs to form stable dispersions. The nano-oils
infused with these nanostructures of high electronic conductance indicate
superior AC dielectric behaviour in terms of augmented breakdown strength
compared to the base oils. Experimental observations of two grades of
synthesized graphene and CNT nano-oils show that the nanomaterials not only
improve the average breakdown voltage but also significantly improve the
reliability and survival probabilities of the oils under AC high voltage
stressing. Improvement of the tune of ~ 70-80 % in the AC breakdown voltage of
the oils has been obtained via the present concept. The present study examines
the reliability of such nano-colloids with the help of two parameter Weibull
distribution and the oils show greatly augmented electric field bearing
capacity at both standard survival probability values of 5 % and 63.3 %. The
fundamental mechanism responsible for such observed outcomes is reasoned to be
delayed streamer development and reduced streamer growth rates due to effective
electron scavenging by the nanostructures from the ionized liquid insulator. A
mathematical model based on the principles of electron scavenging is proposed
to quantify the amount of electrons scavenged by the nanostructures. The same
is then employed to predict the enhanced AC breakdown voltage and the
experimental values are found to match well with the model predictions. The
present study can have strong implications in efficient, reliable and safer
operation of real life AC power systems
Structural domain and spin ordering induced glassy magnetic phase in single layered manganite PrSrMnO
The single layered manganite PrSrMnO undergoes
structural transition from high temperature tetragonal phase to low temperature
orthorhombic phase below room temperature. The orthorhombic phase was reported
to have two structural variants with slightly different lattice parameters and
Mn-3 levels show orbital ordering within both the variants, albeit having
mutually perpendicular ordering axis. In addition to orbital ordering, the
orthorhombic variants also order antiferromagnetically with different N\'eel
temperatures. Our magnetic investigation on the polycrystalline sample of
PrSrMnO shows large thermal hysteresis indicating the
first order nature of the tetragonal to orthorhombic transition. We observe
magnetic memory, large relaxation, frequency dependent ac susceptbility and
aging effects at low temperature, which indicate spin glass like magnetic
ground state in the sample. The glassy magnetic state presumably arises from
the interfacial frustration of orthorhombic domains with orbital and spin
orderings playing crucial role toward the competing magnetic interactions.Comment: 6 pages, 4 figures, Accepted in Europhysics Letter
Incidence of Chirodiscoides caviae in Laboratory Rats-Screening, Identification and Treatment
This is a report on the incidence and treatment of the guinea pig fur mite Chirodiscoides caviae, which was so far considered as host specific, in a conventional colony of laboratory rats. Chirodiscoides caviae infestation in laboratory rats was accidentally observed during the screening of Syphacia obvelata by the peri-anal cellophane tape test (CTT). The organism was identified by comparing the morphology described by various researchers and was differentially diagnosed from other common mites of rat, Radfordia ensifera and Notoedres muris. The adult male mites (n=15) were of 330.2±13.3 μm long and the females (n=15) 495.5±25.2 μm. Later on, the entire rat colony consisting of Wistar, Sprague Dawley and Spontaneously Hypertensive Rats (SHR) and the mice colony of Balb/c and Swiss Albino were randomly sampled and screened for the presence of the mite by the cellophane tape technique. All the rat strains were found positive for C. caviae infestation, which was more concentrated towards the posterior region of the body and, collectively, the screening results of C. caviae revealed that the posterio-dorsal and peri-anal regions are most suitable for sampling-suggesting that, the infestation pattern of C. caviae in rats has similarities to that of guinea pigs. Interestingly the mice colony was found free from the infestation. The Cellophane tape test was found to be an easier method than fur examination by hair plucking and equally accurate for screening of fur mite in a colony of laboratory rats. No clinical symptoms were observed in any of the animals in the colony, which possessed infestation. The facility strictly practised physical separation of animals by species, which pointed to the only possibility of cross infestation being through indirect contact between guinea pigs and laboratory rats and thereby questioning previous reports on the mode of transmission of C. caviae. The entire colony was effectively treated with 0.2% Ivermectin spray followed by 1% spray in an interval of 2 weeks. This report is the first one, which demonstrates the guinea pig fur mite in laboratory rats. It also questions the so far documented “host specificity” and “direct contact” mode of transmission and demonstrates indirect contact as a possible mode of transmission.
Warmest Sea Surface Temperature Event in the South Eastern Arabian Sea over the Decade using Satellite and INS Sagardhwani Observations
South Eastern Arabian Sea is well known for its prolonged and warmer sea surface temperature (>30 °C) events generally known as Arabian Sea mini warm pool occurring during the pre-monsoon periods (March-May). To study the intensity and spatial extent of the warm pool, ten years (2007-2016) of satellite-derived weekly averaged SST and in-situ data measured from INS Sagardhwani are used. The analysis is done based on the precondition ‘sea surface temperature > 30 °C’ and lasts more than a week. These analysis demonstrate the existence of a strong inter-annual variability. It is also identified that the sea surface temperature in the year 2016 is the hottest over the decade with maximum spatial coverage and prolonged period of occurrence. These anomalous events are also explained in terms of variabilities of the atmospheric water vapour and wind at the sea surface
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