344 research outputs found
Gravitational Collapse of Null Radiation and a String fluid
We consider the end state of collapsing null radiation with a string fluid.
It is shown that, if diffusive transport is assumed for the string, that a
naked singularity can form (at least locally). The model has the advantage of
not being asymptotically flat. We also analyse the case of a radiation-string
two-fluid and show that a locally naked singularity can result in the collapse
of such matter. We contrast this model with that of strange quark matter.Comment: RevTeX 4.0 (8 pages - no figures). submitted to Phys Rev D. Some
changes to abstract, introduction and conclusion - references update
Evidence of electronic phase arrest and glassy ferromagnetic behaviour in (Nd0.4Gd0.3)Sr0.3MnO3 manganite : Comparative study between bulk and nanometric samples
The effect of doping of rare earth Gd 3+ ion replacing Nd 3+ in
Nd0.7Sr0.3MnO3 is investigated in details. Measurements of resistivity,
magnetoresistance, magnetization, linear and non linear ac magnetic
susceptibility on chemically synthesized (Nd0.7-xGdx)Sr0.3MnO3 shows various
interesting features with doping level x=0.3. Comparative study has been
carried out between a bulk and a nanometric sample (grain size ~ 60 nm)
synthesized from the same as prepared powder to maintain identical
stoichiometry. Resistivity of the samples shows strong dependence on the
magnetic field - temperature history. The magnetoresistance of the samples also
show strong irreversibility with respect to sweeping of the field between
highest positive and negative values. Moreover, resistivity is found to
increase with time after field cooling and then switching off the field. All
these phenomena have been attributed to phase separation effect and arrest of
phases in the samples. Furthermore, the bulk sample displays a spin glass like
behaviour as evident from frequency dependence of linear ac magnetic
susceptibility and critical divergence of the nonlinear ac magnetic
susceptibility. The experimentally obtained characteristic time t after
dynamical scaling analysis of the frequency dependence of the ac susceptibility
is found to be t=10-17 s which implies that the system is different from a
canonical spin glass. An unusual frequency dependence of the second harmonic of
ac susceptibility around the magnetic transition temperature led us to
designate the magnetic state of the sample to be glassy ferromagnetic. On
reduction of grain size low field magnetoresistance and phase arrest phenomena
are found to enhance but the glassy state is observed to be destabilized in the
nanometric sample.Comment: To be published in the Journal of Physics:Condensed Matte
Photon redshift and the appearance of a naked singularity
In this paper we analyze the redshift as observed by an external observer
receiving photons which terminate in the past at the naked singularity formed
in a Tolman-Bondi dust collapse. Within the context of models considered here
it is shown that photons emitted from a weak curvature naked singularity are
always finitely redshifted to an external observer. Certain cases of strong
curvature naked singularities, including the self-similar one, where the
photons are infinitely redshifted are also pointed out.Comment: Latex file, 14 pages, no figures, one change in the reference.
Accepted for publication in Phys. Rev.
Nanocrystalline Pentaerythritoltetranitrate using Sol-Gel Process
The secondary explosives developed with reduced particle size tend to be more insensitive for mechanical stimuli and may release energy with faster rate and gaining more importance nowadays. Therefore, aiming to reduce the particle size of one of the popular explosives, viz., pentaerythritoltetranitrate (PETN) to the nanometer range, a method for preparation of nanocrystalline PETN in the silica (SiO2) gel matrix using sol-gel process has been demonstrated. The PETN-SiO2 xerogels were prepared containing PETN content ranging from 50 per cent to 90 per cent (w/w) and the xerogels were characterised using different techniques. An exothermic peak at around 185 oC preceded by an endotherm in thermal analysis accompanied with weight loss in the temperature range from 150 oC to 200 oC  for the xerogel confirmed the presence of PETN in xerogel. Infrared spectra of xerogels showed peaks at around 1285 cm-1 and 1700 cm-1 assigned to O-NO2 and C-O bond representing PETN. Small angle x-ray scattering measurements on xerogels indicated that PETN entered in the pores of silica matrix. Transmission electron microscopy revealed that cystalline PETN   with particle size of around 15 nm dispersed in silica xerogel. The specific surface area for the PETN-SiO2 (90:10) xerogels was found to be 75 m2/g.Defence Science Journal, 2011, 61(6), pp.534-539, DOI:http://dx.doi.org/10.14429/dsj.61.59
MOLECULAR CHARACTERIZATION OF DIFFERENT ADVANCED WHEAT VARIETAL LINES USING SDS-PAGE ELECTROPHORESIS DATA OF SEED STORAGE PROTEINS
ABSTRACT The present study was undertaken to evaluate the genetic diversity in gluten subunits and protein content in seed endosperm of wheat for nutritional grading of 17 advanced varietal lines of wheat using SDS-PAGE, which is useful for agricultural development regarding quality food stuffs and breeding purposes. After calculating the standard factor in spectrophotometer for unit absorbance at 595 nm and the amount of protein were calculated. The wheat lines PZ-TS-5, PZ-TS-4 and PZ-TS-9 contained maximum amount of HMW-Gs proteins as compared to rest of the lines. By comparing with the six bands of the standard marker, band numbers 4 were common in all 17 wheat lines, but the other bands showed variation. Most frequent HMW protein bands had mole. Wt. 29.03 KDa marker band, while, in LMW protein bands most frequent bands were among the 14 KDa marker band. In cluster analysis, the above mentioned 3 wheat lines grouped in the same cluster showed that they were originated from the same parental line and genetically less diverged
Classical and Quantum Interaction of the Dipole
A unified and fully relativistic treatment of the interaction of the electric
and magnetic dipole moments of a particle with the electromagnetic field is
given. New forces on the particle due to the combined effect of electric and
magnetic dipoles are obtained. Four new experiments are proposed, three of
which would observe topological phase shifts.Comment: 10 pages, Latex/Revtex. Some minor errors have been correcte
Magnesia-Based Cements: A Journey of 150 Years, and Cements for the Future?
This review examines the detailed chemical insights that have been generated through 150 years of work worldwide on magnesium-based inorganic cements, with a focus on both scientific and patent literature. Magnesium carbonate, phosphate, silicate-hydrate, and oxysalt (both chloride and sulfate) cements are all assessed. Many such cements are ideally suited to specialist applications in precast construction, road repair, and other fields including nuclear waste immobilization. The majority of MgO-based cements are more costly to produce than Portland cement because of the relatively high cost of reactive sources of MgO and do not have a sufficiently high internal pH to passivate mild steel reinforcing bars. This precludes MgO-based cements from providing a large-scale replacement for Portland cement in the production of steel-reinforced concretes for civil engineering applications, despite the potential for CO2 emissions reductions offered by some such systems. Nonetheless, in uses that do not require steel reinforcement, and in locations where the MgO can be sourced at a competitive price, a detailed understanding of these systems enables their specification, design, and selection as advanced engineering materials with a strongly defined chemical basis
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