27 research outputs found
Modal analysis of gravitational instabilities in nearly Keplerian, counter-rotating collisionless discs
We present a modal analysis of instabilities of counter-rotating,
self-gravitating collisionless stellar discs, using the recently introduced
modified WKB formulation of spiral density waves for collisionless systems
(Gulati \& Saini). The discs are assumed to be axisymmetric and in coplanar
orbits around a massive object at the common center of the discs. The mass in
both discs is assumed to be much smaller than the mass of the central object.
For each disc, the disc particles are assumed to be in near circular orbits.
The two discs are coupled to each other gravitationally. The perturbed dynamics
of the discs evolves on the order of the precession time scale of the discs,
which is much longer than the Keplerian time scale. We present results for the
azimuthal wave number and , for the full range of disc mass ratio
between the prograde and retrograde discs. The eigenspectra are in general
complex, therefore all eigenmodes are unstable. Eigenfunctions are radially
more compact for as compared to . Pattern speed of eigenmodes is
always prograde with respect to the more massive disc. The growth rate of
unstable modes increases with increasing mass fraction in the retrograde disc,
and decreases with ; therefore instability is likely to play the
dominant role in the dynamics of such systems.Comment: 24 pages, 8 figures, 1 tabl
Slow pressure modes in thin accretion discs
Thin accretion discs around massive compact objects can support slow pressure
modes of oscillations in the linear regime that have azimuthal wavenumber
. We consider finite, flat discs composed of barotropic fluid for various
surface density profiles and demonstrate--through WKB analysis and numerical
solution of the eigenvalue problem--that these modes are stable and have
spatial scales comparable to the size of the disc. We show that the eigenvalue
equation can be mapped to a Schr\"odinger-like equation. Analysis of this
equation shows that all eigenmodes have discrete spectra. We find that all the
models we have considered support negative frequency eigenmodes; however, the
positive eigenfrequency modes are only present in power law discs, albeit for
physically uninteresting values of the power law index and barotropic
index .Comment: 9 pages, 7 figures, 1 table, accepted in MNRAS for pulicatio
MATHCAD Geometrie Benutzerhandbuch
Copy held by FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
INTERNET ADDICTION AND LEVEL OF ANXIETY AMONG SCHOOL STUDENTS
Internet Addiction is a rising problem among the Indian school students. The purpose of this research
was to find out the extent of internet addiction among higher secondary level school students and the anxiety of higher secondary level school students having different levels of internet addiction. The research was
conducted on 600 students of CBSE schools in Bhopal. The information was collected by Internet Addiction
Scale and General Anxiety Scale. The findings revealed that 10% had normal level of internet addiction,
56% had mild level of internet addiction, 33% had moderate level of internet addiction and just 1% had severe level of internet addiction, the lower the level of internet addiction the lower will be the anxiety of the
higher secondary level school students and girls are found to have significantly higher anxiety than boys
Unstable m=1 modes of counter-rotating Keplerian discs
We study the linear m= 1 counter-rotating instability in a two-component, nearly Keplerian disc. Our goal is to understand these slow modes in discs orbiting massive black holes in galactic nuclei. They are of interest not only because they are of large spatial scale and can hence dominate observations but also because they can be growing modes that are readily excited by accretion events. Self-gravity being non-local, the eigenvalue problem results in a pair of coupled integral equations, which we derive for a two-component softened gravity disc. We solve this integral eigenvalue problem numerically for various values of mass fraction in the counter-rotating component. The eigenvalues are in general complex, being real only in the absence of the counter-rotating component, or imaginary when both components have identical surface density profiles. Our main results are as follows: (i) the pattern speed appears to be non-negative, with the growth (or damping) rate being larger for larger values of the pattern speed; (ii) for a given value of the pattern speed, the growth (or damping) rate increases as the mass in the counter-rotating component increases; (iii) the number of nodes of the eigenfunctions decreases with increasing pattern speed and growth rate. Observations of lopsided brightness distributions would then be dominated by modes with the least number of nodes, which also possess the largest pattern speeds and growth rates
Enhanced biomass and steviol glycosides in Stevia rebaudiana treated with phosphate-solubilizing bacteria and rock phosphate
Biofertilizers offer alternative means to promoting
cultivation of medicinal plants less dependent on
chemical fertilizers. Present study was aimed at evaluating
the potential of phosphate-solubilizing bacteria (PSB)
Burkholderia gladioli MTCC 10216, B. gladioli MTCC
10217, Enterobacter aerogenes MTCC 10208 and Serratia
marcescens MTCC 10238 for utilizing Mussoorie rock
phosphate (MRP) to enhance plant growth, and stevioside
(ST) and rebaudioside-A (R-A) contents of Stevia rebaudiana.
The solubilization of MRP by PSB strains varied
from 1.4 to 15.2 lg ml-1, with the highest solubilization
by Enterobacter aerogenes 10208. The PSB treatment
increased the growth and ST and R-A contents of plants.
Plant growth and stevioside contents were more pronounced
with plants treated with a mixture of strains and
grown in MRP amended soil compared to the unamended
soil. The increment in shoot length (47.8%), root length
(17.4%), leaf dry weight (164%), stem dry weight (116%),
total shoot biomass (136%) resulted in enhanced productivity
of ST (291%) and R-A (575%) in plants inoculated
with mixture of PSB as compared to the uninoculated
plants. The soils of PSB treated plants contained more
available P than the soils of uninoculated plants (increase
of 86–576%). PSB inoculated plants also recorded higher P
content (64–273% increase) compared to uninoculated
plants. The PSB strains differed in the extent of rhizosphere
colonization, carbon source utilization pattern and whole
cell fatty acids methyl esters compositio
Isolation and identification of phosphate solubilizing bacteria able to enhance the growth and aloin-A biosynthesis of Aloe barbadensis Miller
Aloe barbadensis in soil containing tricalcium phosphate (TCP). PSB were identified based on 16S rRNA
gene sequencing as Pseudomonas synxantha, Burkholderia gladioli, Enterobacter hormaechei and Serratia
marcescens. These PSB solubilized 25–340 μg ml−1 of TCP into the liquid phase. The treatment of plants
with individual PSB or mixture of these increased soil available P, P uptake in plants and plant growth.
The increase in aloin-A content due to higher plant biomass and unit biomass production was 673%, 294%,
276%, 119% and 108% in plants treated with a PSB consortium, P. synxantha, S. marcescens, B. gladioli, and
E. hormaechei in TCP amended soil, respectivel