541 research outputs found
Radar Cross-section Measurement Techniques
Radar cross-section (RCS) is an important study parameter for defence applications specially dealing with airborne weapon system. The RCS parameter guides the detection range for a target and is therefore studied to understand the effectiveness of a weapon system. It is not only important to understand the RCS characteristics of a target but also to look into the diagnostic mode of study where factors contributing to a particular RCS values are studied. This further opens up subject like RCS suppression and stealth. The paper discusses the RCS principle, control, and need of measurements. Classification of RCS in terms of popular usage is explained with detailed theory of RF imaging and inverse synthetic aperture radar (ISAR). The various types of RCS measurement ranges are explained with brief discussion on outdoor RCS measurement range. The RCS calibration plays a critical role in referencing the measurement to absolute values and has been described.The RCS facility at Reseach Centre Imarat, Hyderabad, is explained with some details of different activities that are carried out including RAM evaluation, scale model testing, and diagnostic imaging.Defence Science Journal, 2010, 60(2), pp.204-212, DOI:http://dx.doi.org/10.14429/dsj.60.34
Bell's theorem as a signature of nonlocality: a classical counterexample
For a system composed of two particles Bell's theorem asserts that averages
of physical quantities determined from local variables must conform to a family
of inequalities. In this work we show that a classical model containing a local
probabilistic interaction in the measurement process can lead to a violation of
the Bell inequalities. We first introduce two-particle phase-space
distributions in classical mechanics constructed to be the analogs of quantum
mechanical angular momentum eigenstates. These distributions are then employed
in four schemes characterized by different types of detectors measuring the
angular momenta. When the model includes an interaction between the detector
and the measured particle leading to ensemble dependencies, the relevant Bell
inequalities are violated if total angular momentum is required to be
conserved. The violation is explained by identifying assumptions made in the
derivation of Bell's theorem that are not fulfilled by the model. These
assumptions will be argued to be too restrictive to see in the violation of the
Bell inequalities a faithful signature of nonlocality.Comment: Extended manuscript. Significant change
Manual of seed handling in genebanks
This manual and its accompanying self-learning module provide detailed procedural guidlines and lessons for staff who do not have the opportinity to attend courses on seed conservation and genebank management. It focuses on seed handling procedures and does not cover documentation, collecting or characterization procedures in great detail. The manual discusses and presents some of the common procedures in handling seeds in genebanks. These steps include germplasm acquisition and registration; seed cleaning; seed moisture content determination and drying; seed quality testing which includes viability testing; health testing, and testing for inadvertent introduction of transgenes; seed packaging and storage; germplasm distribution; and the last one is germplasm monitoring and regeneration. At the end of the manual one finds annex on international policies and frameworks influencing access to and exchange of germplasm; serological methods for detecting plant pathogens; glossary; and specialized equipment for gene banks. And the module is a stand-alone self -learning tool organised into units and lessons and it is intended to be used in conjuction with the manual. Each lesson includes learning objectives, a description of procedures; learning checks to assess understanding, problem scenarios for applying learning to a pratctical situation and lesson summaries. In addition each lesson contains a glossary of commonly used genebank terms, references to further reading, and detailed photographs to illustrate the steps in seed-handling procedure
Risk factors of sleep-disordered breathing among Public Transport Drivers of Kochi, India
Introduction: Sleep-disordered breathing (SDB) appears to be a major occupational health concern among transport drivers as it increases the chance of road traffic crashes. The study aimed to determine the prevalent risk factors of sleep-disordered breathing in public transport drivers of Kochi, India.
Methods: A descriptive cross-sectional study was performed among 50 public transport drivers who satisfied the inclusion criteria and were categorized as high and low-risk groups using the STOP-BANG questionnaire. Physical examination recorded Neck circumference, waist-hip ratio, body mass index, blood pressure, and facial profile. Excessive daytime sleepiness was evaluated using the Epworth sleepiness scale. Mann Whitney and Chi-square tests were used to test for significance. Logistic regression was also done by including the significant variables.
Results: The high risk (n= 27) and low-risk groups (n=23) were identified. Among the high-risk group; age, body mass index, neck circumference, blood pressure, snoring and tiredness showed statistically significant results (p<0.05) when compared to the low-risk group. Excessive daytime sleepiness was present among 29.6% of high-risk subjects. Logistic regression confirmed that age (OR=1.176; p=0.001) and body mass index (OR=1.348; p=0.050) were independent predictors of developing a high risk of SDB.
Conclusion: mong public transport drivers in Kochi, India; older age and increased body mass index were significant contributing factors to developing sleep-disordered breathing. Obstructive sleep apnea (OSA), whether diagnosed or undiagnosed, is a major public health concern and a proven risk factor for vehicle crashes. Applicants for public transport driver's licenses should be thoroughly examined for the risk of OSA/SDB. A standardized screening protocol for OSA risk assessment should be advisable for public transport drivers to ensure road safety
Stability of the lattice formed in first-order phase transitions to matter containing strangeness in protoneutron stars
Well into the deleptonization phase of a core collapse supernova, a
first-order phase transition to matter with macroscopic strangeness content is
assumed to occur and lead to a structured lattice defined by negatively charged
strange droplets. The lattice is shown to crystallize for expected droplet
charges and separations at temperatures typically obtained during the
protoneutronstar evolution. The melting curve of the lattice for small
spherical droplets is presented. The one-component plasma model proves to be an
adequate description for the lattice in its solid phase with deformation modes
freezing out around the melting temperature. The mechanical stability against
shear stresses is such that velocities predicted for convective phenomena and
differential rotation during the Kelvin-Helmholtz cooling phase might prevent
the crystallization of the phase transition lattice. A solid lattice might be
fractured by transient convection, which could result in anisotropic neutrino
transport. The melting curve of the lattice is relevant for the mechanical
evolution of the protoneutronstar and therefore should be included in future
hydrodynamics simulations.Comment: accepted for publication in Physical Review
On the role of pressure anisotropy for relativistic stars admitting conformal motion
We investigate the spacetime of anisotropic stars admitting conformal motion.
The Einstein field equations are solved using different ansatz of the surface
tension. In this investigation, we study two cases in details with the
anisotropy as: [1] [2] where, n, and are arbitrary constants.
The solutions yield expressions of the physical quantities like pressure
gradients and the mass.Comment: 21 pages, accepted for publication in 'Astrophysics and Space
Science
Quark Hadron Phase Transition and Hybrid Stars
We investigate the properties of hybrid stars consisting of quark matter in
the core and hadron matter in outer region. The hadronic and quark matter
equations of state are calculated by using nonlinear Walecka model and chiral
colour dielectric (CCD) model respectively. We find that the phase transition
from hadron to quark matter is possible in a narrow range of the parameters of
nonlinear Walecka and CCD models. The transition is strong or weak first order
depending on the parameters used. The EOS thus obtained, is used to study the
properties of hybrid stars. We find that the calculated hybrid star properties
are similar to those of pure neutron stars.Comment: 25 pages in LaTex and 9 figures available on request, IP/BBSR/94-3
The hadron-quark phase transition in dense matter and neutron stars
We study the hadron-quark phase transition in the interior of neutron stars
(NS's). We calculate the equation of state (EOS) of hadronic matter using the
Brueckner-Bethe-Goldstone formalism with realistic two-body and three-body
forces, as well as a relativistic mean field model. For quark matter we employ
the MIT bag model constraining the bag constant by using the indications coming
from the recent experimental results obtained at the CERN SPS on the formation
of a quark-gluon plasma. We find necessary to introduce a density dependent bag
parameter, and the corresponding consistent thermodynamical formalism. We
calculate the structure of NS interiors with the EOS comprising both phases,
and we find that the NS maximum masses fall in a relatively narrow interval,
. The precise value of the
maximum mass turns out to be only weakly correlated with the value of the
energy density at the assumed transition point in nearly symmetric nuclear
matter.Comment: 25 pages, Revtex4, 16 figures included as postscrip
Warm stellar matter with deconfinement: application to compact stars
We investigate the properties of mixed stars formed by hadronic and quark
matter in -equilibrium described by appropriate equations of state (EOS)
in the framework of relativistic mean-field theory. We use the non- linear
Walecka model for the hadron matter and the MIT Bag and the Nambu-Jona-Lasinio
models for the quark matter. The phase transition to a deconfined quark phase
is investigated. In particular, we study the dependence of the onset of a mixed
phase and a pure quark phase on the hyperon couplings, quark model and
properties of the hadronic model. We calculate the strangeness fraction with
baryonic density for the different EOS. With the NJL model the strangeness
content in the mixed phase decreases. The calculations were performed for T=0
and for finite temperatures in order to describe neutron and proto-neutron
stars. The star properties are discussed. Both the Bag model and the NJL model
predict a mixed phase in the interior of the star. Maximum allowed masses for
proto-neutron stars are larger for the NJL model ( M)
than for the Bag model ( M).Comment: RevTeX,14 figures, accepted to publication in Physical Review
Cooperative Ring Exchange and Quantum Melting of Vortex Lattices in Atomic Bose-Einstein Condensates
Cooperative ring-exchange is suggested as a mechanism of quantum melting of
vortex lattices in a rapidly-rotating quasi two dimensional atomic
Bose-Einstein condensate (BEC). Using an approach pioneered by Kivelson et al.
[Phys. Rev. Lett. {\bf 56}, 873 (1986)] for the fractional quantized Hall
effect, we calculate the condition for quantum melting instability by
considering large-correlated ring exchanges in a two-dimensional Wigner crystal
of vortices in a strong `pseudomagnetic field' generated by the background
superfluid Bose particles. BEC may be profitably used to address issues of
quantum melting of a pristine Wigner solid devoid of complications of real
solids.Comment: 7 pages, 1 figure, to appear in Physical Review
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