1,556 research outputs found
Exchange Monte Carlo Method and Application to Spin Glass Simulations
We propose an efficient Monte Carlo algorithm for simulating a
``hardly-relaxing" system, in which many replicas with different temperatures
are simultaneously simulated and a virtual process exchanging configurations of
these replica is introduced. This exchange process is expected to let the
system at low temperatures escape from a local minimum. By using this algorithm
the three-dimensional Ising spin glass model is studied. The ergodicity
time in this method is found much smaller than that of the multi-canonical
method. In particular the time correlation function almost follows an
exponential decay whose relaxation time is comparable to the ergodicity time at
low temperatures. It suggests that the system relaxes very rapidly through the
exchange process even in the low temperature phase.Comment: 10 pages + uuencoded 5 Postscript figures, REVTe
Stochastic Collapse and Decoherence of a Non-Dissipative Forced Harmonic Oscillator
Careful monitoring of harmonically bound (or as a limiting case, free) masses
is the basis of current and future gravitational wave detectors, and of
nanomechanical devices designed to access the quantum regime. We analyze the
effects of stochastic localization models for state vector reduction, and of
related models for environmental decoherence, on such systems, focusing our
analysis on the non-dissipative forced harmonic oscillator, and its free mass
limit. We derive an explicit formula for the time evolution of the expectation
of a general operator in the presence of stochastic reduction or
environmentally induced decoherence, for both the non-dissipative harmonic
oscillator and the free mass. In the case of the oscillator, we also give a
formula for the time evolution of the matrix element of the stochastic
expectation density matrix between general coherent states. We show that the
stochastic expectation of the variance of a Hermitian operator in any
unraveling of the stochastic process is bounded by the variance computed from
the stochastic expectation of the density matrix, and we develop a formal
perturbation theory for calculating expectation values of operators within any
unraveling. Applying our results to current gravitational wave interferometer
detectors and nanomechanical systems, we conclude that the deviations from
quantum mechanics predicted by the continuous spontaneous localization (CSL)
model of state vector reduction are at least five orders of magnitude below the
relevant standard quantum limits for these experiments. The proposed LISA
gravitational wave detector will be two orders of magnitude away from the
capability of observing an effect.Comment: TeX; 34 page
Analysis of chromosome positions in the interphase nucleus of Chinese hamster cells by laser-UV-microirradiation experiments
Unsynchronized cells of an essentially diploid strain of female Chinese hamster cells derived from lung tissue (CHL) were laser-UV-microirradiated (=257 nm) in the nucleus either at its central part or at its periphery. After 7â9 h postincubation with 0.5 mM caffeine, chromosome preparations were made in situ. Twenty-one and 29 metaphase spreads, respectively, with partial chromosome shattering (PCS) obtained after micro-irradiation at these two nuclear sites, were Q-banded and analyzed in detail. A positive correlation was observed between the frequency of damage of chromosomes and both their DNA content and length at metaphase. No significant difference was observed between the frequencies of damage obtained for individual chromosomes at either site of microirradiation. The frequency of joint damage of homologous chromosomes was low as compared to nonhomologous ones. Considerable variation was noted in different cells in the combinations of jointly shattered chromosomes. Evidence which justifies an interpretation of these data in terms of an interphase arrangement of chromosome territories is discussed. Our data strongly argue against somatic pairing as a regular event, and suggest a considerable variability of chromosome positions in different nuclei. However, present data do not exclude the possibility of certain non-random chromosomal arrangements in CHL-nuclei. The interphase chromosome distribution revealed by these experiments is compared with centromere-centromere, centromere-center and angle analyses of metaphase spreads and the relationship between interphase and metaphase arrangements of chromosomes is discussed
Recommended from our members
Size distribution, mass concentration, chemical and mineralogical composition and derived optical parameters of the boundary layer aerosol at Tinfou, Morocco, during SAMUM 2006
During the SAMUM 2006 field campaign in southern Morocco, physical and chemical properties of desert aerosols
were measured. Mass concentrations ranging from 30ÎŒgmâ3 for PM2.5 under desert background conditions up to
300 000ÎŒgmâ3 for total suspended particles (TSP) during moderate dust storms were measured. TSP dust concentrations
are correlated with the local wind speed, whereasPM10 andPM2.5 concentrations are determined by advection from
distant sources. Size distributions were measured for particles with diameter between 20 nm and 500ÎŒm (parametrizations
are given). Two major regimes of the size spectrum can be distinguished. For particles smaller than 500 nm
diameter, the distributions show maxima around 80 nm, widely unaffected of varying meteorological and dust emission
conditions. For particles larger than 500 nm, the range of variation may be up to one order of magnitude and up to
three orders of magnitude for particles larger than 10ÎŒm. The mineralogical composition of aerosol bulk samples was
measured by X-ray powder diffraction. Major constituents of the aerosol are quartz, potassium feldspar, plagioclase,
calcite, hematite and the clay minerals illite, kaolinite and chlorite. A small temporal variability of the bulk mineralogical
composition was encountered. The chemical composition of approximately 74 000 particles was determined by
electron microscopic single particle analysis. Three size regimes are identified: for smaller than 500 nm in diameter, the
aerosol consists of sulphates and mineral dust. For larger than 500 nm up to 50ÎŒm, mineral dust dominates, consisting
mainly of silicates, andâto a lesser extentâcarbonates and quartz. For diameters larger than 50ÎŒm, approximately
half of the particles consist of quartz. Time series of the elemental composition show a moderate temporal variability
of the major compounds. Calcium-dominated particles are enhanced during advection from a prominent dust source in
Northern Africa (Chott El Djerid and surroundings). The particle aspect ratio was measured for all analysed particles.
Its size dependence reflects that of the chemical composition. For larger than 500 nm particle diameter, a median aspect
ratio of 1.6 is measured. Towards smaller particles, it decreases to about 1.3 (parametrizations are given). From the
chemical/mineralogical composition, the aerosol complex refractive index was determined for several wavelengths
from ultraviolet to near-infrared. Both real and imaginary parts show lower values for particles smaller than 500 nm in
diameter (1.55â2.8 Ă 10â3i at 530 nm) and slightly higher values for larger particles (1.57â3.7 Ă 10â3i at 530 nm)
Multiple-scattering effects on incoherent neutron scattering in glasses and viscous liquids
Incoherent neutron scattering experiments are simulated for simple dynamic
models: a glass (with a smooth distribution of harmonic vibrations) and a
viscous liquid (described by schematic mode-coupling equations). In most
situations multiple scattering has little influence upon spectral
distributions, but it completely distorts the wavenumber-dependent amplitudes.
This explains an anomaly observed in recent experiments
Immunocytochemical localization of a large intrinsic membrane protein to the incisures and margins of frog rod outer segment disks.
Qweak: A Precision Measurement of the Proton's Weak Charge
The Qweak experiment at Jefferson Lab aims to make a 4% measurement of the
parity-violating asymmetry in elastic scattering at very low of a
longitudinally polarized electron beam on a proton target. The experiment will
measure the weak charge of the proton, and thus the weak mixing angle at low
energy scale, providing a precision test of the Standard Model. Since the value
of the weak mixing angle is approximately 1/4, the weak charge of the proton
is suppressed in the Standard Model, making it
especially sensitive to the value of the mixing angle and also to possible new
physics. The experiment is approved to run at JLab, and the construction plan
calls for the hardware to be ready to install in Hall C in 2007. The
theoretical context of the experiment and the status of its design are
discussed.Comment: 5 pages, 2 figures, LaTeX2e, to be published in CIPANP 2003
proceeding
Search for Millicharged Particles at SLAC
Particles with electric charge q < 10^(-3)e and masses in the range 1--100
MeV/c^2 are not excluded by present experiments. An experiment uniquely suited
to the production and detection of such "millicharged" particles has been
carried out at SLAC. This experiment is sensitive to the infrequent excitation
and ionization of matter expected from the passage of such a particle. Analysis
of the data rules out a region of mass and charge, establishing, for example, a
95%-confidence upper limit on electric charge of 4.1X10^(-5)e for millicharged
particles of mass 1 MeV/c^2 and 5.8X10^(-4)e for mass 100 MeV/c^2.Comment: 4 pages, REVTeX, multicol, 3 figures. Minor typo corrected. Submitted
to Physical Review Letter
Baryonic systems with charm and bottom in the bound state soliton model
The binding energies of baryonic systems (BS) with baryon number and
4 possessing heavy flavor, charm and bottom, are estimated within the rigid
oscillator version of the bound state approach to chiral soliton models. Two
tendencies are noted: the binding energy increases with increasing mass of the
flavor and with increasing . Therefore, the charmed or bottomed baryonic
systems have more chances to be bound than strange baryonic systems discussed
previously. The flavor symmetry breaking in decay constants is considered
which is especially important for baryonic systems with bottom quantum numbers.
Generally, for heavy flavors the scale of the binding energies of BS depends on
the scale of flavor symmetry violation in .Comment: 9 pages, no figures. Modified version of a talk presented at the
International Workshop JHF98 on Science at Japan Hadron Facility (KEK,
Tsukuba, March 4-7, 1998). Some statements concerning the case of very heavy
quark flavor are changed and several misprints are remove
- âŠ