25,063 research outputs found
Nonexponential decay of an unstable quantum system: Small--value s-wave decay
We study the decay process of an unstable quantum system, especially the
deviation from the exponential decay law. We show that the exponential period
no longer exists in the case of the s-wave decay with small value, where
the value is the difference between the energy of the initially prepared
state and the minimum energy of the continuous eigenstates in the system. We
also derive the quantitative condition that this kind of decay process takes
place and discuss what kind of system is suitable to observe the decay.Comment: 17 pages, 6 figure
The Quantum-Classical Crossover in the Adiabatic Response of Chaotic Systems
The autocorrelation function of the force acting on a slow classical system,
resulting from interaction with a fast quantum system is calculated following
Berry-Robbins and Jarzynski within the leading order correction to the
adiabatic approximation. The time integral of the autocorrelation function is
proportional to the rate of dissipation. The fast quantum system is assumed to
be chaotic in the classical limit for each configuration of the slow system. An
analytic formula is obtained for the finite time integral of the correlation
function, in the framework of random matrix theory (RMT), for a specific
dependence on the adiabatically varying parameter. Extension to a wider class
of RMT models is discussed. For the Gaussian unitary and symplectic ensembles
for long times the time integral of the correlation function vanishes or falls
off as a Gaussian with a characteristic time that is proportional to the
Heisenberg time, depending on the details of the model. The fall off is
inversely proportional to time for the Gaussian orthogonal ensemble. The
correlation function is found to be dominated by the nearest neighbor level
spacings. It was calculated for a variety of nearest neighbor level spacing
distributions, including ones that do not originate from RMT ensembles. The
various approximate formulas obtained are tested numerically in RMT. The
results shed light on the quantum to classical crossover for chaotic systems.
The implications on the possibility to experimentally observe deterministic
friction are discussed.Comment: 26 pages, including 6 figure
Coagulation by Random Velocity Fields as a Kramers Problem
We analyse the motion of a system of particles suspended in a fluid which has
a random velocity field. There are coagulating and non-coagulating phases. We
show that the phase transition is related to a Kramers problem, and use this to
determine the phase diagram, as a function of the dimensionless inertia of the
particles, epsilon, and a measure of the relative intensities of potential and
solenoidal components of the velocity field, Gamma. We find that the phase line
is described by a function which is non-analytic at epsilon=0, and which is
related to escape over a barrier in the Kramers problem. We discuss the
physical realisations of this phase transition.Comment: 4 pages, 3 figure
Theory of Self-organized Criticality for Problems with Extremal Dynamics
We introduce a general theoretical scheme for a class of phenomena
characterized by an extremal dynamics and quenched disorder. The approach is
based on a transformation of the quenched dynamics into a stochastic one with
cognitive memory and on other concepts which permit a mathematical
characterization of the self-organized nature of the avalanche type dynamics.
In addition it is possible to compute the relevant critical exponents directly
from the microscopic model. A specific application to Invasion Percolation is
presented but the approach can be easily extended to various other problems.Comment: 11 pages Latex (revtex), 3 postscript figures included. Submitted to
Europhys. Let
Radiation and shielding study for the International Ultraviolet Explorer
Technical advisory services to ensure integrity of parts and material exposed to energetic particle radiation for the IUE scientific instruments, spacecraft, and subsystems are provided. A significant potential for interference, degradation, or failure for unprotected or sensitive items was found. Vulnerable items were identified, and appropriate tests, changes, and shields were defined
Gravitational lensing statistics with extragalactic surveys. II. Analysis of the Jodrell Bank-VLA Astrometric Survey
We present constraints on the cosmological constant from
gravitational lensing statistics of the Jodrell Bank-VLA Astrometric Survey
(JVAS). Although this is the largest gravitational lens survey which has been
analysed, cosmological constraints are only comparable to those from optical
surveys. This is due to the fact that the median source redshifts of JVAS are
lower, which leads to both relatively fewer lenses in the survey and a weaker
dependence on the cosmological parameters. Although more approximations have to
be made than is the case for optical surveys, the consistency of the results
with those from optical gravitational lens surveys and other cosmological tests
indicate that this is not a major source of uncertainty in the results.
However, joint constraints from a combination of radio and optical data are
much tighter. Thus, a similar analysis of the much larger Cosmic Lens All-Sky
Survey should provide even tighter constraints on the cosmological constant,
especially when combined with data from optical lens surveys.
At 95% confidence, our lower and upper limits on ,
using the JVAS lensing statistics information alone, are respectively -2.69 and
0.68. For a flat universe, these correspond to lower and upper limits on
\lambda_{0} of respectively -0.85 and 0.84. Using the combination of JVAS
lensing statistics and lensing statistics from the literature as discussed in
Quast & Helbig (Paper I) the corresponding values are
-1.78 and 0.27. For a flat universe, these correspond to lower and upper limits
on of respectively -0.39 and 0.64.Comment: LaTeX, 9 pages, 18 PostScript files in 6 figures. Paper version
available on request. Data available from
http://gladia.astro.rug.nl:8000/ceres/data_from_papers/papers.htm
Brownian Motion Model of Quantization Ambiguity and Universality in Chaotic Systems
We examine spectral equilibration of quantum chaotic spectra to universal
statistics, in the context of the Brownian motion model. Two competing time
scales, proportional and inversely proportional to the classical relaxation
time, jointly govern the equilibration process. Multiplicity of quantum systems
having the same semiclassical limit is not sufficient to obtain equilibration
of any spectral modes in two-dimensional systems, while in three-dimensional
systems equilibration for some spectral modes is possible if the classical
relaxation rate is slow. Connections are made with upper bounds on
semiclassical accuracy and with fidelity decay in the presence of a weak
perturbation.Comment: 13 pages, 6 figures, submitted to Phys Rev
Membrane Type 1 Matrix Metalloproteinase Regulates Monocyte Migration and Collagen Destruction in Tuberculosis
Tuberculosis (TB) remains a global pandemic and drug resistance is rising. Multicellular granuloma formation is the pathological hallmark of Mycobacterium tuberculosis infection. The membrane type 1 matrix metalloproteinase (MT1-MMP or MMP-14) is a collagenase that is key in leukocyte migration and collagen destruction. In patients with TB, induced sputum MT1-MMP mRNA levels were increased 5.1-fold compared with matched controls and correlated positively with extent of lung infiltration on chest radiographs (r = 0.483; p < 0.05). M. tuberculosis infection of primary human monocytes increased MT1-MMP surface expression 31.7-fold and gene expression 24.5-fold. M. tuberculosis-infected monocytes degraded collagen matrix in an MT1-MMP-dependent manner, and MT1-MMP neutralization decreased collagen degradation by 73%. In human TB granulomas, MT1-MMP immunoreactivity was observed in macrophages throughout the granuloma. Monocyte-monocyte networks caused a 17.5-fold increase in MT1-MMP surface expression dependent on p38 MAPK and G protein-coupled receptor-dependent signaling. Monocytes migrating toward agarose beads impregnated with conditioned media from M. tuberculosis-infected monocytes expressed MT1-MMP. Neutralization of MT1-MMP activity decreased this M. tuberculosis network-dependent monocyte migration by 44%. Taken together, we demonstrate that MT1-MMP is central to two key elements of TB pathogenesis, causing collagen degradation and regulating monocyte migration
Feelings of dual-insecurity among European workers: A multi-level analysis
This article analyses European Social Survey data for 22 countries. We assess the relationship between feelings of employment and income insecurity (dual-insecurity) among workers and national flexicurity policies in the areas of lifelong learning, active labour market policy, modern social security systems and flexible and reliable contractual arrangements. We find that dual-insecurity feelings are lower in countries that score better on most flexicurity polices, but these effects are in all cases outweighed by levels of GDP per capita. Thus feelings of insecurity are reduced more by the affluence of a country than by its social policies. However, affluence is strongly correlated with the policy efforts designed to reduce insecurity, especially active labour market policies and life-long learning, two policy areas that are threatened with cuts as a result of austerity
CMB observations with the Jodrell Bank - IAC interferometer at 33 GHz
The paper presents the first results obtained with the Jodrell Bank - IAC
two-element 33 GHz interferometer. The instrument was designed to measure the
level of the Cosmic Microwave Background (CMB) fluctuations at angular scales
of 1 - 2 degrees. The observations analyzed here were taken in a strip of the
sky at Dec = +41 deg with an element separation of 16.7 lambda, which gives a
maximum sensitivity to ~1.6 deg structures on the sky. The data processing and
calibration of the instrument are described. The sensitivity achieved in each
of the two channels is 7 micro K per resolution element. A reconstruction of
the sky at Dec = +41 deg using a maximum entropy method shows the presence of
structure at a high level of significance. A likelihood analysis, assuming a
flat CMB spatial power spectrum, gives a best estimate of the level of CMB
fluctuations of Delta Tl = 43 (+13,-12) micro K for the range l = 109 +/- 19;
the main uncertainty in this result arises from sample variance. We consider
that the contamination from the Galaxy is small. These results represent a new
determination of the CMB power spectrum on angular scales where previous
results show a large scatter; our new results are in agreement with the
theoretical predictions of the standard inflationary cold dark matter models.Comment: 11 pages, 11 figures. Web site at
http://www.jb.man.ac.uk/research/cmb/ Accepted for publication in MNRA
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