8,168 research outputs found
Computation of Kolmogorov's Constant in Magnetohydrodynamic Turbulence
In this paper we calculate Kolmogorov's constant for magnetohydrodynamic
turbulence to one loop order in perturbation theory using the direct
interaction approximation technique of Kraichnan. We have computed the
constants for various , i.e., fluid to magnetic energy ratios
when the normalized cross helicity is zero. We find that increases from
1.47 to 4.12 as we go from fully fluid case to a situation when , then it decreases to 3.55 in a fully magnetic limit .
When , we find that .Comment: Latex, 10 pages, no figures, To appear in Euro. Phys. Lett., 199
Nonlinear electrostatic oscillations in a cold magnetized electron-positron plasma
We study the spatio-temporal evolution of the nonlinear electrostatic
oscillations in a cold magnetized electron-positron (e-p) plasma using both
analytics and simulations. Using a perturbative method we demonstrate that the
nonlinear solutions change significantly when a pure electrostatic mode is
excited at the linear level instead of a mixed upper-hybrid and zero-frequency
mode that is considered in a recent study. The pure electrostatic oscillations
undergo phase mixing nonlinearly. However, the presence of the magnetic field
significantly delays the phase-mixing compared to that observed in the
corresponding unmagnetized plasma. Using 1D PIC simulations we then analyze the
damping of the primary modes of the pure oscillations in detail and infer the
dependence of the phase-mixing time on the magnetic field and the amplitude of
the oscillations. The results are remarkably different from those found for the
mixed upper-hybrid mode mentioned above. Exploiting the symmetry of the e-p
plasma we then explain a generalized symmetry of our non-linear solutions. The
symmetry allows us to construct a unique nonlinear solution up to the second
order which does not show any signature of phase mixing but results in a
nonlinear wave traveling at upper-hybrid frequency. Our investigations have
relevance for laboratory/astrophysical e-p plasmas
Interval structure of the Pieri formula for Grothendieck polynomials
We give a combinatorial interpretation of a Pieri formula for double
Grothendieck polynomials in terms of an interval of the Bruhat order. Another
description had been given by Lenart and Postnikov in terms of chain
enumerations. We use Lascoux's interpretation of a product of Grothendieck
polynomials as a product of two kinds of generators of the 0-Hecke algebra, or
sorting operators. In this way we obtain a direct proof of the result of Lenart
and Postnikov and then prove that the set of permutations occuring in the
result is actually an interval of the Bruhat order.Comment: 27 page
Premature Coronary Artery Disease and Familial Hypercholesterolemia: Need for Early Diagnosis and Cascade Screening in the Indian Population
Cardiovascular disease (CVD) is the leading cause of death in India, accounting for 28% of mortality. The average age of onset of CVD is younger (below 55 years) among Indians than in other populations. This may be due to bad lifestyle, genetic factors, or both. Hypertension, smoking, diabetes, and physical inactivity have been identified as modifiable risk factors for heart disease. Hypercholesterolemia is the most common and treatable cause of heart disease. Genetic factors that lead to hypercholesterolemia have not been fully studied in India. Familial Hypercholesterolemia results from mutations in the LDL receptor, ApoB, PCSK9, and ApoE genes. There is an urgent need to screen subjects with premature CAD and their relatives in India for the presence of FH, identify the mutations that lead to high cholesterol, and carry out cascade screening in the at-risk relatives. Those harbouring mutations in the above genes can be treated to lower the cholesterol levels, prevent early CVD, and avoid death. A programme based on these lines has been initiated in Delhi
Emergence of small-scale magnetic flux in the quiet Sun
We study the evolution of a small-scale emerging flux region (EFR) in the
quiet Sun, from its emergence to its decay. We track processes and phenomena
across all atmospheric layers, explore their interrelations and compare our
findings with recent numerical modelling studies. We used imaging, spectral and
spectropolarimetric observations from space-borne and ground-based instruments.
The EFR appears next to the chromospheric network and shows all characteristics
predicted by numerical simulations. The total magnetic flux of the EFR exhibits
distinct evolutionary phases, namely an initial subtle increase, a fast
increase and expansion of the region area, a more gradual increase, and a slow
decay. During the initial stages, bright points coalesce, forming clusters of
positive- and negative-polarity in a largely bipolar configuration. During the
fast expansion, flux tubes make their way to the chromosphere, producing
pressure-driven absorption fronts, visible as blueshifted chromospheric
features. The connectivity of the quiet-Sun network gradually changes and part
of the existing network forms new connections with the EFR. A few minutes after
the bipole has reached its maximum magnetic flux, it brightens in soft X-rays
forming a coronal bright point, exhibiting episodic brightenings on top of a
long smooth increase. These coronal brightenings are also associated with
surge-like chromospheric features, which can be attributed to reconnection with
adjacent small-scale magnetic fields and the ambient magnetic field. The
emergence of magnetic flux even at the smallest scales can be the driver of a
series of energetic phenomena visible at various atmospheric heights and
temperature regimes. Multi-wavelength observations reveal a wealth of
mechanisms which produce diverse observable effects during the different
evolutionary stages of these small-scale structures.Comment: Accepted for publication in Astronomy & Astrophysics 14 pages, 14
figure
Biochemical genetic polymorphism in Indian mackerel (Rastrelliger kanagurta)
Six enzymes glucose 6 phosphate dehydrogenase (G6PD), xanthene de hydrogenase (XDH), alcohol dehydrogenase
(ADH), peroxidase (PO), lactate dehydrogenase (LDH) and isocitric dehydrogenase (lDH) were examined to discover the
genetic variation in Indian mackerel through polyacrylamide gel electrophoresis. A significant difference in allelic frequency at XDH locus was observed between the eachin and Thotapally populations. Thotapally stocks exhibited a significant
deviation (P< 0.05) from Hardy weinberg equillibrium. The proportion of polymorphic Joci was 0.777. The coefficient of
identity and the genetic distance estimated were 0.9262 and 0.076 respectively
Biochemical genetic polymorphism in the Indian mackerel Rastrelliger kanagurta from Mangalore region
Electrophoresis is the modern and most
popular technique used for studying the genetic
variability within and among the populations of
plants and animals. Genetically controlled tissue
enzymes are the most suitable parameters for
genetic variability studies. In the present study
Polyacrylamide Gel Electrophoresis was used to
study the genetic variability in Indian mackerel
A comparative DFT study of electronic properties of 2H-, 4H- and 6H-SiC(0001) and SiC(000-1) clean surfaces: Significance of the surface Stark effect
Electric field, uniform within the slab, emerging due to Fermi level pinning
at its both sides is analyzed using DFT simulations of the SiC surface slabs of
different thickness. It is shown that for thicker slab the field is nonuniform
and this fact is related to the surface state charge. Using the electron
density and potential profiles it is proved that for high precision simulations
it is necessary to take into account enough number of the Si-C layers. We show
that using 12 diatomic layers leads to satisfactory results. It is also
demonstrated that the change of the opposite side slab termination, both by
different type of atoms or by their location, can be used to adjust electric
field within the slab, creating a tool for simulation of surface properties,
depending on the doping in the bulk of semiconductor. Using these simulations
it was found that, depending on the electric field, the energy of the surface
states changes in a different way than energy of the bulk states. This
criterion can be used to distinguish Shockley and Tamm surface states. The
electronic properties, i.e. energy and type of surface states of the three
clean surfaces: 2H-, 4H-, 6H-SiC(0001), and SiC() are analyzed and
compared using field dependent DFT simulations.Comment: 18 pages, 10 figures, 4 table
- …