13,933 research outputs found
Interacting spinor and scalar fields in Bianchi type-I Universe filled with viscous fluid: exact and numerical solutions
We consider a self-consistent system of spinor and scalar fields within the
framework of a Bianchi type I gravitational field filled with viscous fluid in
presence of a term. Exact self-consistent solutions to the
corresponding spinor, scalar and BI gravitational field equations are obtained
in terms of , where is the volume scale of BI universe. System of
equations for and \ve, where \ve is the energy of the viscous fluid,
is deduced. Some special cases allowing exact solutions are thoroughly studied.Comment: 18 pages, 6 figure
Investigation of Superconducting Gap Structure in HfIrSi using muon spin relaxation/rotation
Appearance of strong spin-orbit coupling (SOC) is apparent in ternary
equiatomic compounds with 5-electrons due to the large atomic radii of
transition metals. SOC plays a significant role in the emergence of
unconventional superconductivity. Here we examined the superconducting state of
HfIrSi using magnetization, specific heat, zero and transverse-field (ZF/TF)
muon spin relaxation/rotation (SR) measurements. Superconductivity is
observed at = 3.6 K as revealed by specific heat and
magnetization measurements. From the TFSR analysis it is clear that
superfluid density well described by an isotropic BCS type -wave gap
structure. Furthermore, from TFSR data we have also estimated the
superconducting carrier density = 6.6 10m,
London penetration depth = 259.59 nm and effective mass
= 1.57 . Our zero-field muon spin relaxation data indicate no
clear sign of spontaneous internal field below , which implies
that the time-reversal symmetry is preserved in HfIrSi. Theoretical
investigation suggests Hf and Ir atoms hybridize strongly along the -axis of
the lattice, which is responsible for the strong three-dimensionality of this
system which screens the Coulomb interaction. As a result despite the presence
of correlated -electrons in this system, the correlation effect is weakened,
promoting electron-phonon coupling to gain importance.Comment: 8 pages, 4 figure
Probing the superconducting ground state of ZrIrSi: A SR study
The superconducting ground state of newly reported ZrIrSi is probed by means
of SR technique along with resistivity measurement. The occurrence of
superconductivity at = 1.7 K is confirmed by resistivity
measurement. ZF-SR study revealed that below , there is no
spontaneous magnetic field in the superconducting state, indicates TRS is
preserved in case of ZrIrSi. From TF-SR measurement, we have estimated the
superfluid density as a function of temperature, which is described by an
isotropic wave model with a superconducting gap
= 5.1, indicates the presence of strong
spin-orbit coupling. {\it Ab-initio} electronic structure calculation indicates
that there are four bands passing through the Fermi level, forming four Fermi
surface pockets. We find that the low-energy bands are dominated by the
-orbitals of transition metal Zr, with substantially lesser weight from the
-orbitals of the Ir-atoms.Comment: 6 pages, 4 figure
Scalar field in cosmology: Potential for isotropization and inflation
The important role of scalar field in cosmology was noticed by a number of
authors. Due to the fact that the scalar field possesses zero spin, it was
basically considered in isotropic cosmological models. If considered in an
anisotropic model, the linear scalar field does not lead to isotropization of
expansion process. One needs to introduce scalar field with nonlinear potential
for the isotropization process to take place. In this paper the general form of
scalar field potentials leading to the asymptotic isotropization in case of
Bianchi type-I cosmological model, and inflationary regime in case of isotropic
space-time is obtained. In doing so we solved both direct and inverse problem,
where by direct problem we mean to find metric functions and scalar field for
the given potential, whereas, the inverse problem means to find the potential
and scalar field for the given metric function. The scalar field potentials
leading to the inflation and isotropization were found both for harmonic and
proper synchronic time.Comment: 10 page
A new approach to the analysis of a noncommutative Chern-Simons theory
A novel approach to the analysis of a noncommutative Chern--Simons gauge
theory with matter coupled in the adjoint representation has been discussed.
The analysis is based on a recently proposed closed form Seiberg--Witten map
which is exact in the noncommutative parameter.Comment: 9 pages latex, some new results added. To be published in Modern
Physics Letters
Probiotic Effect of Lactobacillus Isolates Against Bacterial Pathogens in Fresh Water Fish
A total of 59 Lactobacillus isolates were isolated from 5 different fresh water fish such as Cat fish ( Clarias orientalis) , Hari fish (Anguilla sp), Rohu fish ( Labeo rohita), Jillabe fish (Oreochromis sp) and Gende fish ( Punitus carnaticus). Among the 59 isolates only 4 Lactobacillus isolates were selected for further study. Based on morphological and biochemical characteristics, the isolates were identified as Lactobacillus sp. The pathogen were isolated from infected cat fishes, characterized and identified as Vibrio parahaemolyticus, Aeromonas sp and Aeromonas salmonicida. The Lactobacillus isolates were screened for antagonistic activity against Aeromonas, Vibrio sp. by agar diffusion assay. Among the 4 isolates, Lactobacilli RLD2 showed significant antagonistic activity against Aeromonas and Vibrio sp alone. and was further evaluated by standard plate count assay for the viability of pathogen. The isolate was multiplied and the fish feed was supplement with Lactobacillus isolates. The results reveal that the size, weight of the fish was statically increased in comparison to that of control fish. The present study concluded that the Lactobacillus isolates could be used as probiotic bacteria in aquaculture, to manage aeromonasis
Electrons as quasi-bosons in magnetic white dwarfs
A white dwarf star achieves its equilibrium from the balancing of the
gravitational compression against the Fermi degeneracy pressure of the electron
gas. In field theory there are examples (e.g. the monopole-charge system) where
a strong magnetic field can transform a boson into a fermion or a fermion into
a boson. In some condensed matter systems (e.g. fractional quantum Hall
systems) a strong magnetic field can transform electrons into effective
fermions, or effective anyons. Based on these examples we investigate the
possibility that the strong magnetic fields of some white dwarfs may transform
some fraction of the electrons into effective bosons. This could have
consequences for the structure of highly magnetized white dwarfs. It would
alter the mass-radius relationship, and in certain instances one could envision
a scenario where a white dwarf below the Chandrasekhar limit could nevertheless
collapse into a neutron star due to a weakening of the electron degeneracy
pressure. In addition the transformation of electrons into effective bosons
could result in the electrons Bose condensing, which could speed up the cooling
rate of white dwarfs.Comment: 10 pages. To be published IJMP
Effect of synthesis conditions on formation pathways of metal organic framework (MOF-5) Crystals
Metal Organic Frameworks (MOFs) represent a class of nanoporous crystalline materials with far reaching potential in gas storage, catalysis, and medical devices. We investigated the effects of synthesis process parameters on production of MOF-5 from terephthalic acid and zinc nitrate in diethylformamide. Under favorable synthesis conditions, we systematically mapped a solid formation diagram in terms of time and temperature for both stirred and unstirred conditions. The synthesis of MOF-5 has been previously reported as a straightforward reaction progressing from precursor compounds in solution directly to the final MOF-5 solid phase product. However, we show that the solid phase formation process is far more complex, invariably transferring through metastable intermediate crystalline phases before the final MOF-5 phase is reached, providing new insights into the formation pathways of MOFs. We also identify process parameters suitable for scale-up and continuous manufacturing of high purity MOF-5
Coupled Phonons, Magnetic Excitations and Ferroelectricity in AlFeO3: Raman and First-principles Studies
We determine the nature of coupled phonons and magnetic excitations in AlFeO3
using inelastic light scattering from 5 K to 315 K covering a spectral range
from 100-2200 cm-1 and complementary first-principles density functional
theory-based calculations. A strong spin-phonon coupling and magnetic ordering
induced phonon renormalization are evident in (a) anomalous temperature
dependence of many modes with frequencies below 850 cm-1, particularly near the
magnetic transition temperature Tc ~ 250 K, (b) distinct changes in band
positions of high frequency Raman bands between 1100-1800 cm-1, in particular a
broad mode near 1250 cm-1 appears only below Tc attributed to the two-magnon
Raman scattering. We also observe weak anomalies in the mode frequencies at ~
100 K, due to a magnetically driven ferroelectric phase transition.
Understanding of these experimental observations has been possible on the basis
of first-principles calculations of phonons spectrum and their coupling with
spins
- …