5,375 research outputs found
Modeling The X-ray Timing Properties Of Cygnus X-1 As Caused By Waves Propagating In A Transition Disk
We show that waves propagating in a transition disk can explain the short
term temporal behavior of Cygnus X-1. In the transition disk model the spectrum
is produced by saturated Comptonization within the inner region of the
accretion disk where the temperature varies rapidly with radius. Recently, the
spectrum from such a disk has been shown to fit the average broad band spectrum
of this source better than that predicted by the soft-photon Comptonization
model. Here, we consider a simple model where waves are propagating
cylindrically symmetrical ly in the transition disk with a uniform propagation
speed (). We show that this model can qualitatively explain (a) the
variation of the power spectral density (PSD) with energy, (b) the hard lags as
a function of frequency and (c) the hard lags as a function of energy for
various frequencies. Thus the transition disk model can explain the average
spectrum and the short term temporal behavior of Cygnus X-1.Comment: accepted for publication in APJ letter
Modulational instability of ion-acoustic wave packets in quantum pair-ion plasmas
Amplitude modulation of quantum ion-acoustic waves (QIAWs) in a quantum
electron-pair-ion plasma is studied. It is shown that the quantum coupling
parameter (being the ratio of the plasmonic energy density to the Fermi
energy) is ultimate responsible for the modulational stability of QIAW packets,
without which the wave becomes modulational unstable. New regimes for the
modulational stability (MS) and instability (MI) are obtained in terms of
and the positive to negative ion density ratio . The growth rate of MI
is obtained, the maximum value of which increases with and decreases
with . The results could be important for understanding the origin of
modulated QIAW packets in the environments of dense astrophysical objects,
laboratory negative ion plasmas as well as for the next generation laser solid
density plasma experiments.Comment: 4 pages, 2 figures (to appear in Astrophysics and Space Science
A QUALITATIVE CHOICE ANALYSIS OF FACTORS INFLUENCING POST-CRP LAND USE DECISIONS
The future use of Conservation Reserve Program (CRP) lands is an important agricultural policy issue. To examine the effects of factors that influence landowners' post-contract use of CRP lands, a survey of Texas High Plains CRP contract holders was conducted in 1992. This study analyzes the results of the survey using a qualitative choice model. It was found that the presence of a livestock enterprise in the current contract holder's operation increases the probability of these acres remaining in the established cover. Contract holders who value the commodity base have an increased probability of returning their acres to crop production.Agricultural policy, Conservation Reserve Program, Ordered probit model, Land Economics/Use,
Tunneling between Dilute GaAs Hole Layers
We report interlayer tunneling measurements between very dilute
two-dimensional GaAs hole layers. Surprisingly, the shape and
temperature-dependence of the tunneling spectrum can be explained with a Fermi
liquid-based tunneling model, but the peak amplitude is much larger than
expected from the available hole band parameters. Data as a function of
parallel magnetic field reveal additional anomalous features, including a
recurrence of a zero-bias tunneling peak at very large fields. In a
perpendicular magnetic field, we observe a robust and narrow tunneling peak at
total filling factor , signaling the formation of a bilayer quantum
Hall ferromagnet.Comment: Revised to include additional data, new discussion
Role of terms of trade in Indian agricultural growth: a national and state level analysis
Using time series data, this paper analyses the relative contributions of terms of trade and non-price variables in explaining agricultural growth in recent decades in India. Agricultural growth is largely explained by expansion of irrigation, (which in the model is also a proxy for HYVs and other capital investments), and, until the 1970s, by increases in the net cultivated area. Agricultural output is inelastic, and is becoming increasingly more so over time. The terms of trade was not an important factor in explaining past growth. Even during the late 1960s and early 1970s when the terms of trade improved by 18 percent for agriculture, they only accounted for 15 percent of the growth in output. Increases in agricultural output are also found to worsen the terms of trade for agriculture, despite government attempts to control prices. The results highlight the importance of further investments in agricultural research, extension, irrigation and other supply-enhancing inputs if the ongoing policy reforms in India are to translate into more rapid and sustained agricultural growth.Agricultural productivity India., Terms of trade India., Investment of public funds India.,
Gluon Condensates, Chiral Symmetry Breaking and Pion Wave Function
We consider here chiral symmetry breaking in quantum chromodynamics arising
from gluon condensates in vacuum. Through coherent states of gluons simulating
a mean field type of approximation, we show that the off-shell gluon
condensates of vacuum generate a mass-like contribution for the quarks, giving
rise to chiral symmetry breaking. We next note that spontaneous breaking of
global chiral symmetry links the four component quark field operator to the
pion wave function. This in turn yields many hadronic properties in the light
quark sector in agreement with experiments, leading to the conclusion that low
energy hadron properties are primarily driven by the vacuum structure of
quantum chromodynamics.Comment: 25 pages, IP/BBSR/92-76, revte
A fit to the simultaneous broadband spectrum of Cygnus X-1 using the transition disk model
We have used the transition disk model to fit the simultaneous broad band
( keV) spectrum of Cygnus X-1 from OSSE and Ginga observations. In this
model, the spectrum is produced by saturated Comptonization within the inner
region of the accretion disk, where the temperature varies rapidly with radius.
In an earlier attempt, we demonstrated the viability of this model by fitting
the data from EXOSAT, XMPC balloon and OSSE observations, though these were not
made simultaneously. Since the source is known to be variable, however, the
results of this fit were not conclusive. In addition, since only once set of
observations was used, the good agreement with the data could have been a
chance occurrence. Here, we improve considerably upon our earlier analysis by
considering four sets of simultaneous observations of Cygnus X-1, using an
empirical model to obtain the disk temperature profile. The vertical structure
is then obtained using this profile and we show that the analysis is self-
consistent. We demonstrate conclusively that the transition disk spectrum is a
better fit to the observations than that predicted by the soft photon
Comptonization model. Since the temperature profile is obtained by fitting the
data, the unknown viscosity mechanism need not be specified. The disk structure
can then be used to infer the viscosity parameter , which appears to
vary with radius and luminosity. This behavior can be understood if
depends intrinsically on the local parameters such as density, height and
temperature. However, due to uncertainties in the radiative transfer,
quantitative statements regarding the variation of cannot yet be made.Comment: 8 figures. uses aasms4.sty, accepted by ApJ (Mar 98
Mean field and Monte Carlo studies of the magnetization-reversal transition in the Ising model
Detailed mean field and Monte Carlo studies of the dynamic
magnetization-reversal transition in the Ising model in its ordered phase under
a competing external magnetic field of finite duration have been presented
here. Approximate analytical treatment of the mean field equations of motion
shows the existence of diverging length and time scales across this dynamic
transition phase boundary. These are also supported by numerical solutions of
the complete mean field equations of motion and the Monte Carlo study of the
system evolving under Glauber dynamics in both two and three dimensions.
Classical nucleation theory predicts different mechanisms of domain growth in
two regimes marked by the strength of the external field, and the nature of the
Monte Carlo phase boundary can be comprehended satisfactorily using the theory.
The order of the transition changes from a continuous to a discontinuous one as
one crosses over from coalescence regime (stronger field) to nucleation regime
(weaker field). Finite size scaling theory can be applied in the coalescence
regime, where the best fit estimates of the critical exponents are obtained for
two and three dimensions.Comment: 16 pages latex, 13 ps figures, typos corrected, references adde
Nickel Resources in India and their Exploitation
NICKEL is one of the important strategic alloying
elements : its consumption has increased considerably
after World War II and during the last few years it increased by 6U-70°,,. It is felt that the increase would have been still higher if more nickel was available. The present annual production outside the communist block has well exceeded 400 000 tons and there is every likelihood of further rise in production in the near future as new production centres are being established. The largest single producer of nickel is Canada with the world's richest deposits at Sudbury, Ontario
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