32,663 research outputs found
Field-aligned electric currents and their measurement by the incoherent backscatter technique
Field aligned electric currents flow in the magnetosphere in many situations of fundamental geophysical interest. It is shown here that the incoherent backscatter technique can be used to measure these currents when the plasma line can be observed. The technique provides a ground based means of measuring these currents which complements the rocket and satellite ones
Hedge funds, credit risk transfer and financial stability.
Over the past decade, central bankers and financial institution supervisors have sharpened their focus on the increasingly important role that private pools of investment funds play in global financial markets. The growth in these pools has contributed significantly to market efficiency and financial stability by expanding liquidity in many financial markets, improving price discovery, and, ultimately, lowering the costs of capital. Private investment pools and the alternative investment strategies they pursue have contributed to a signifi cant expansion of the global markets and have helped accelerate the evolution in traded credit products such as credit derivatives, collateralized debt obligations, and the securitization of an increasing array of traditionally illiquid assets. However, because of the lack of transparency and an established regime of supervision of these investment vehicles, policymakers and supervisors have become concerned about customer protection and the potential for systemic risk. This paper discusses some of the key issues confronting supervisors in light of the recent growth of private investment pools and the rapid developments in the area of credit risk transfer, with a particular focus on the implications of these trends regarding systemic risk and financial stability.
The Flow of a Viscous Compressible Fluid Through a Very Narrow Gap
The effect of compressibility on the pressure distribution
in the narrow gap between a rotating cylinder and a plane in a viscous fluid was studied by Taylor and Saffman [1] during an investigation of the centripetal pump effect discovered by Reiner [2]
Shocks in asymmetric simple exclusion processes of interacting particles
In this paper, we study shocks and related transitions in asymmetric simple
exclusion processes of particles with nearest neighbor interactions. We
consider two kinds of inter-particle interactions. In one case, the
particle-hole symmetry is broken due to the interaction. In the other case,
particles have an effective repulsion due to which the particle-current-density
drops down near the half filling. These interacting particles move on a one
dimensional lattice which is open at both the ends with injection of particles
at one end and withdrawal of particles at the other. In addition to this, there
are possibilities of attachments or detachments of particles to or from the
lattice with certain rates. The hydrodynamic equation that involves the exact
particle current-density of the particle conserving system and additional terms
taking care of the attachment-detachment kinetics is studied using the
techniques of boundary layer analysis.Comment: 10 pages, 8 figure
The evolution of the star forming sequence in hierarchical galaxy formation models
It has been argued that the specific star formation rates of star forming
galaxies inferred from observational data decline more rapidly below z = 2 than
is predicted by hierarchical galaxy formation models. We present a detailed
analysis of this problem by comparing predictions from the GALFORM
semi-analytic model with an extensive compilation of data on the average star
formation rates of star-forming galaxies. We also use this data to infer the
form of the stellar mass assembly histories of star forming galaxies. Our
analysis reveals that the currently available data favour a scenario where the
stellar mass assembly histories of star forming galaxies rise at early times
and then fall towards the present day. In contrast, our model predicts stellar
mass assembly histories that are almost flat below z = 2 for star forming
galaxies, such that the predicted star formation rates can be offset with
respect to the observational data by factors of up to 2-3. This disagreement
can be explained by the level of coevolution between stellar and halo mass
assembly that exists in contemporary galaxy formation models. In turn, this
arises because the standard implementations of star formation and supernova
feedback used in the models result in the efficiencies of these process
remaining approximately constant over the lifetime of a given star forming
galaxy. We demonstrate how a modification to the timescale for gas ejected by
feedback to be reincorporated into galaxy haloes can help to reconcile the
model predictions with the data.Comment: 30 Pages, 16 Figures, MNRAS accepte
Measuring the galaxy power spectrum and scale-scale correlations with multiresolution-decomposed covariance -- I. method
We present a method of measuring galaxy power spectrum based on the
multiresolution analysis of the discrete wavelet transformation (DWT). Since
the DWT representation has strong capability of suppressing the off-diagonal
components of the covariance for selfsimilar clustering, the DWT covariance for
popular models of the cold dark matter cosmogony generally is diagonal, or
(scale)-diagonal in the scale range, in which the second scale-scale
correlations are weak. In this range, the DWT covariance gives a lossless
estimation of the power spectrum, which is equal to the corresponding Fourier
power spectrum banded with a logarithmical scaling. In the scale range, in
which the scale-scale correlation is significant, the accuracy of a power
spectrum detection depends on the scale-scale or band-band correlations. This
is, for a precision measurements of the power spectrum, a measurement of the
scale-scale or band-band correlations is needed. We show that the DWT
covariance can be employed to measuring both the band-power spectrum and second
order scale-scale correlation. We also present the DWT algorithm of the binning
and Poisson sampling with real observational data. We show that the alias
effect appeared in usual binning schemes can exactly be eliminated by the DWT
binning. Since Poisson process possesses diagonal covariance in the DWT
representation, the Poisson sampling and selection effects on the power
spectrum and second order scale-scale correlation detection are suppressed into
minimum. Moreover, the effect of the non-Gaussian features of the Poisson
sampling can be calculated in this frame.Comment: AAS Latex file, 44 pages, accepted for publication in Ap
Physical Bias of Galaxies From Large-Scale Hydrodynamic Simulations
We analyze a new large-scale (Mpc) numerical hydrodynamic
simulation of the popular CDM cosmological model, including in our
treatment dark matter, gas and star-formation, on the basis of standard
physical processes. The method, applied with a numerical resolution of
kpc (which is still quite coarse for following individual galaxies,
especially in dense regions), attempts to estimate where and when galaxies
form. We then compare the smoothed galaxy distribution with the smoothed mass
distribution to determine the "bias" defined as on scales large compared with the code
numerical resolution (on the basis of resolution tests given in the appendix of
this paper). We find that (holding all variables constant except the quoted
one) bias increases with decreasing scale, with increasing galactic age or
metallicity and with increasing redshift of observations. At the Mpc
fiducial comoving scale bias (for bright regions) is 1.35 at reaching to
3.6 at , both numbers being consistent with extant observations. We also
find that Mpc voids in the distribution of luminous objects are
as observed (i.e., observed voids are not an argument against CDM-like models)
and finally that the younger systems should show a colder Hubble flow than do
the early type galaxies (a testable proposition). Surprisingly, little
evolution is found in the amplitude of the smoothed galaxy-galaxy correlation
function (as a function of {\it comoving} separation). Testing this prediction
vs observations will allow a comparison between this work and that of Kauffmann
et al which is based on a different physical modelingmethod.Comment: in press, ApJ, 26 latex pages plus 7 fig
Quantum System Identification by Bayesian Analysis of Noisy Data: Beyond Hamiltonian Tomography
We consider how to characterize the dynamics of a quantum system from a
restricted set of initial states and measurements using Bayesian analysis.
Previous work has shown that Hamiltonian systems can be well estimated from
analysis of noisy data. Here we show how to generalize this approach to systems
with moderate dephasing in the eigenbasis of the Hamiltonian. We illustrate the
process for a range of three-level quantum systems. The results suggest that
the Bayesian estimation of the frequencies and dephasing rates is generally
highly accurate and the main source of errors are errors in the reconstructed
Hamiltonian basis.Comment: 6 pages, 3 figure
Bulk and surface transitions in asymmetric simple exclusion process: Impact on boundary layers
In this paper, we study boundary-induced phase transitions in a particle
non-conserving asymmetric simple exclusion process with open boundaries. Using
boundary layer analysis, we show that the key signatures of various bulk phase
transitions are present in the boundary layers of the density profiles. In
addition, we also find possibilities of surface transitions in the low- and
high- density phases. The surface transition in the low-density phase provides
a more complete description of the non-equilibrium critical point found in this
system.Comment: 9 pages including figure
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