4,526 research outputs found
byr2, a Schizosaccharomyces pombe gene encoding a protein kinase capable of partial suppression of the ras1 mutant phenotype
Schizosaccharomyces pombe contains a single gene, ras1, which is a homolog of the mammalian RAS genes. ras1 is required for conjugation, sporulation, and normal cell shape. ras1 has been previously identified as ste5. We report here a gene we call byr2 that can encode a predicted protein kinase and can partially suppress defects in ras1 mutants. ras1 mutant strains expressing high levels of byr2 can sporulate competently but are still defective in conjugation and abnormally round. byr2 mutants are viable and have normal shape but are absolutely defective in conjugation and sporulation. byr2 is probably identical to ste8. In many respects, byr2 resembles the byr1 gene, another suppressor of the ras1 mutation, which has been identified previously as ste1. Our data indicate that if ras1, byr2, and byr1 act along the same pathway, then the site of action for byr2 is between the sites for ras1 and byr1
Spin Glass Phase Transition on Scale-Free Networks
We study the Ising spin glass model on scale-free networks generated by the
static model using the replica method. Based on the replica-symmetric solution,
we derive the phase diagram consisting of the paramagnetic (P), ferromagnetic
(F), and spin glass (SG) phases as well as the Almeida-Thouless line as
functions of the degree exponent , the mean degree , and the
fraction of ferromagnetic interactions . To reflect the inhomogeneity of
vertices, we modify the magnetization and the spin glass order parameter
with vertex-weights. The transition temperature () between the
P-F (P-SG) phases and the critical behaviors of the order parameters are found
analytically. When , and are infinite, and the
system is in the F phase or the mixed phase for , while it is in the
SG phase at . and decay as power-laws with increasing
temperature with different -dependent exponents. When ,
the and are finite and related to the percolation threshold. The
critical exponents associated with and depend on for () at the P-F (P-SG) boundary.Comment: Phys. Rev. E in pres
Slowly driven sandpile formation with granular mixtures
We introduce a one-dimensional sandpile model with different particle types and an infinitesimal driving rate. The parameters for the model are the N^2 critical slopes for one type of particle on top of another. The model is trivial when N=1, but for N=2 we observe four broad classes of sandpile structure in different regions of the parameter space. We describe and explain the behaviour of each of these classes, giving quantitative analysis wherever possible. The behaviour of sandpiles with N>2 essentially consists of combinations of these four classes. We investigate the model's robustness and highlight the key areas that any experiment designed to reproduce these results should focus on
Subclinical psychosis syndromes in the general population: results from a large-scale epidemiological survey among residents of the canton of Zurich, Switzerland
Aims. Prevalence and covariates of subclinical psychosis have gained increased interest in the context of early identification and treatment of persons at risk for psychosis. Methods. We analysed 9829 adults representative of the general population within the canton of Zurich, Switzerland. Two psychosis syndromes, derived from the SCL-90-R, were applied: 'schizotypal signs' and 'schizophrenia nuclear symptoms'. Results. Only a few subjects (13.2%) reported no schizotypal signs. While 33.2% of subjects indicated mild signs, only a small proportion (3.7%) reported severe signs. A very common outcome was no 'schizophrenia nuclear symptoms' (70.6%). Although 13.5% of the participants reported mild symptoms, severe nuclear symptoms were very rare (0.5%). Because these two syndromes were only moderately correlated (r = 0.43), we were able to establish sufficiently distinct symptom clusters. Schizotypal signs were more closely connected to distress than was schizophrenia nuclear symptoms, even though their distribution types were similar. Both syndromes were associated with several covariates, such as alcohol and tobacco use, being unmarried, low education level, psychopathological distress and low subjective well-being. Conclusions. Subclinical psychosis symptoms are quite frequent in the general population but, for the most part, are not very pronounced. In particular, our data support the notion of a continuous Wald distribution of psychotic symptoms in the general population. Our findings have enabled us to confirm the usefulness of these syndromes as previously assessed in other independent community samples. Both can appropriately be associated with well-known risk factors of schizophrenia
Gas phase production of NHD2 in L134N
We show analytically that large abundances of NH2D and NHD2 can be produced
by gas phase chemistry in the interiors of cold dense clouds. The calculated
fractionation ratios are in good agreement with the values that have been
previously determined in L134N and suggest that triply-deuterated ammonia could
be detectable in dark clouds. Grain surface reactions may lead to similar NH2D
and NHD2 enhancements but, we argue, are unlikely to contribute to the
deuteration observed in L134N.Comment: 6 pages, 2 figures, uses psfig.sty and emulateapj.sty, to appear in
Astrophysical Journal, vol 55
A coarse grained model of granular compaction and relaxation
We introduce a theoretical model for the compaction of granular materials by discrete vibrations which is expected to hold when the intensity of vibration is low. The dynamical unit is taken to be clusters of granules that belong to the same collective structure. We rigourously construct the model from first principles and show that numerical solutions compare favourably with a range of experimental results. This includes the logarithmic relaxation towards a statistical steady state, the effect of varying the intensity of vibration resulting in a so-called `annealing' curve, and the power spectrum of density fluctuations in the steady state itself. A mean-field version of the model is introduced which shares many features with the exact model and is open to quantitative analysi
Resistivity peak values at transition between fractional quantum Hall states
Experimental data available in the literature for peak values of the diagonal
resistivity in the transitions between fractional quantum Hall states are
compared with the theoretical predictions. It is found that the majority of the
peak values are close to the theoretical values for two-dimensional systems
with moderate mobilities.Comment: 3 pages, 1 figur
Rotationally invariant family of L\'evy like random matrix ensembles
We introduce a family of rotationally invariant random matrix ensembles
characterized by a parameter . While corresponds to
well-known critical ensembles, we show that describes "L\'evy
like" ensembles, characterized by power law eigenvalue densities. For the density is bounded, as in Gaussian ensembles, but
describes ensembles characterized by densities with long tails. In particular,
the model allows us to evaluate, in terms of a novel family of orthogonal
polynomials, the eigenvalue correlations for L\'evy like ensembles. These
correlations differ qualitatively from those in either the Gaussian or the
critical ensembles.Comment: 9 pages, 5 figure
Building up the Stellar Halo of the Galaxy
We study numerical simulations of satellite galaxy disruption in a potential
resembling that of the Milky Way. Our goal is to assess whether a merger origin
for the stellar halo would leave observable fossil structure in the phase-space
distribution of nearby stars. We show how mixing of disrupted satellites can be
quantified using a coarse-grained entropy. Although after 10 Gyr few obvious
asymmetries remain in the distribution of particles in configuration space,
strong correlations are still present in velocity space. We give a simple
analytic description of these effects, based on a linearised treatment in
action-angle variables, which shows how the kinematic and density structure of
the debris stream changes with time. By applying this description we find that
a single satellite of current luminosity 10^8 L_\sun disrupted 10 Gyr ago
from an orbit circulating in the inner halo (mean apocentre kpc)
would contribute about kinematically cold streams with internal
velocity dispersions below 5 km/s to the local stellar halo. If the whole
stellar halo were built by disrupted satellites, it should consist locally of
300 - 500 such streams. Clear detection of all these structures would require a
sample of a few thousand stars with 3-D velocities accurate to better than 5
km/s. Even with velocity errors several times worse than this, the expected
clumpiness should be quite evident. We apply our formalism to a group of stars
detected near the North Galactic Pole, and derive an order of magnitude
estimate for the initial properties of the progenitor system.Comment: 28 pages, 10 figures, minor changes, matches the version to appear in
MNRAS, Vol. 307, p.495-517 (August 1999
The Southern Galactic Plane Survey: The Test Region
The Southern Galactic Plane Survey (SGPS) is a project to image the HI line
emission and 1.4 GHz continuum in the fourth quadrant of the Milky Way at high
resolution using the Australia Telescope Compact Array (ATCA) and the Parkes
Radio Telescope. In this paper we describe the survey details and goals,
present lambda 21-cm continuum data, and discuss HI absorption and emission
characteristics of the SGPS Test Region (325.5 deg < l < 333.5 deg; -0.5 deg <
b < +3.5 deg). We explore the effects of massive stars on the interstellar
medium (ISM) through a study of HI shells and the HI environments of HII
regions and supernova remnants. We find an HI shell surrounding the HII region
RCW 94 which indicates that the region is embedded in a molecular cloud. We
give lower limits for the kinematic distances to SNRs G327.4+0.4 and G330.2+1.0
of 4.3 kpc and 4.9 kpc, respectively. We find evidence of interaction with the
surrounding HI for both of these remnants. We also present images of a possible
new SNR G328.6-0.0. Additionally, we have discovered two small HI shells with
no counterparts in continuum emission.Comment: 17 pages, 7 embedded EPS figures, 10 low-res jpeg figures, uses
emulateapj5.sty. Accepted for publication in the Astrophysical Journal.
Version with all full resolution figures embedded is available at
http://www.astro.umn.edu/~naomi/sgps/papers/SGPS.ps.g
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