11,509 research outputs found
Avalanches in mean-field models and the Barkhausen noise in spin-glasses
We obtain a general formula for the distribution of sizes of "static
avalanches", or shocks, in generic mean-field glasses with
replica-symmetry-breaking saddle points. For the Sherrington-Kirkpatrick (SK)
spin-glass it yields the density rho(S) of the sizes of magnetization jumps S
along the equilibrium magnetization curve at zero temperature. Continuous
replica-symmetry breaking allows for a power-law behavior rho(S) ~ 1/(S)^tau
with exponent tau=1 for SK, related to the criticality (marginal stability) of
the spin-glass phase. All scales of the ultrametric phase space are implicated
in jump events. Similar results are obtained for the sizes S of static jumps of
pinned elastic systems, or of shocks in Burgers turbulence in large dimension.
In all cases with a one-step solution, rho(S) ~ S exp(-A S^2). A simple
interpretation relating droplets to shocks, and a scaling theory for the
equilibrium analog of Barkhausen noise in finite-dimensional spin glasses are
discussed.Comment: 6 pages, 1 figur
Critical Exponents of the pure and random-field Ising models
We show that current estimates of the critical exponents of the
three-dimensional random-field Ising model are in agreement with the exponents
of the pure Ising system in dimension 3 - theta where theta is the exponent
that governs the hyperscaling violation in the random case.Comment: 9 pages, 4 encapsulated Postscript figures, REVTeX 3.
Phase Diagram and Crossover Phases of Topologically Ordered Graphene Zigzag Nanoribbons: Role of Localization Effects
We computed the phase diagram of the zigzag graphene nanoribbons as a
function of on-site repulsion, doping, and disorder strength. The topologically
ordered phase undergoes topological phase transitions into crossover phases,
which are new disordered phases with a nonuniversal topological entanglement
entropy with significant variance. The topological order is destroyed by
competition between localization effects and on-site repulsion. We found that
strong on-site repulsion and/or doping weakens the nonlocal correlations
between the opposite zigzag edges. In one of the crossover phases, both
fractional charges and spin-charge separation were absent;
however, charge-transfer correlations between the zigzag edges were possible.
Another crossover phase contains fractional charges, but no
charge transfer correlations. In low-doped zigzag ribbons the interplay between
electron localization and on-site repulsion contributes to the spatial
separation of quasi-degenerate gap-edge states and protects the charge
fractionalization against quantum fluctuations. In all these effects, mixed
chiral gap-edge states play an important role. The properties of nontopological
strongly disordered and strongly repulsive phases are also observed. Each phase
of the phase diagram has a different zigzag-edge structure
The Globular Cluster System of M60 (NGC 4649). I. CFHT MOS Spectroscopy and Database
We present the measurement of radial velocities for globular clusters in M60,
giant elliptical galaxy in the Virgo cluster. Target globular cluster
candidates were selected using the Washington photometry based on the deep
16\arcmin \times 16\arcmin images taken at the KPNO 4m and using the
photometry derived from the HST/WFPC2 archive images. The spectra of the target
objects were obtained using the Multi-Object Spectrograph (MOS) at the
Canada-France-Hawaii Telescope (CFHT). We have measured the radial velocity for
111 objects in the field of M60: 93 globular clusters (72 blue globular
clusters with and 21 red globular clusters with
), 11 foreground stars, 6 small galaxies, and the nucleus of
M60. The measured velocities of the 93 globular clusters range from
km s to km s, with a mean value of
km s, which is in good agreement with the velocity of the nucleus of M60
( km s). Combining our results with data in the
literature, we present a master catalog of radial velocities for 121 globular
clusters in M60. The velocity dispersion of the globular clusters in the master
catalog is found to be km s for the entire sample,
km s for 83 blue globular clusters, and
km s for 38 red globular clusters.Comment: 29 pages, 8 figures. To appear in Ap
Combination of selenium and green tea improves the efficacy of chemoprevention in a rat colorectal cancer model by modulating genetic and epigenetic biomarkers
Dietary supplementation of selenium and green tea holds promise in cancer prevention. In this study, we evaluated the
efficacies of selenium and green tea administered individually and in combination against colorectal cancer in an
azoxymethane (AOM)-induced rat colonic carcinogenesis model and determined the underlying mechanisms of the
protection. Four-week old Sprague-Dawley male rats were fed with diets containing 0.5% green tea extract, 1ppm selenium
as selenium-enriched milk protein, or combination of 1ppm selenium and 0.5% green tea extract. Animals received 2 AOM
(15 mg/kg) treatments to induce colonic oncogenesis. Rats were killed 8 or 30 wk later after the last AOM to examine the
effect of dietary intervention on aberrant crypt foci (ACF) formation or tumor development. On sacrifice, colons were
examined for ACF and tumors, the mRNA levels of SFRP5 and Cyclin D1, and the proteins levels of ß-catenin, COX-2, Ki-67,
DNMT1 and acetyl histone H3. The combination of selenium and green tea resulted in a significant additive inhibition of
large ACF formation, this effect was greater than either selenium or green tea alone, P,0.01; the combination also had a
significant additive inhibition effect on all tumor endpoints, the effect of the combination diet on tumor incidence,
multiplicity and size was greater than selenium or green tea alone, P,0.01. Rats fed the combination diet showed marked
reduction of DNMT1 expression and induction of histone H3 acetylation, which were accompanied by restoration of SFRP5
mRNA in normal-appearing colonic crypts. The combination diet also significantly reduced ß-catenin nuclear translocation,
Cyclin D1 expression and cell proliferation. These data show, for the first time, that combination of selenium and green tea is
more effective in suppressing colorectal oncogenesis than either agent alone. The preventive effect is associated with
regulation of genetic and epigenetic biomarkers implicated in colonic carcinogenesis
Colorectal cancer linkage on chromosomes 4q21, 8q13, 12q24, and 15q22
A substantial proportion of familial colorectal cancer (CRC) is not a consequence of known susceptibility loci, such as mismatch repair (MMR) genes, supporting the existence of additional loci. To identify novel CRC loci, we conducted a genome-wide linkage scan in 356 white families with no evidence of defective MMR (i.e., no loss of tumor expression of MMR proteins, no microsatellite instability (MSI)-high tumors, or no evidence of linkage to MMR genes). Families were ascertained via the Colon Cancer Family Registry multi-site NCI-supported consortium (Colon CFR), the City of Hope Comprehensive Cancer Center, and Memorial University of Newfoundland. A total of 1,612 individuals (average 5.0 per family including 2.2 affected) were genotyped using genome-wide single nucleotide polymorphism linkage arrays; parametric and non-parametric linkage analysis used MERLIN in a priori-defined family groups. Five lod scores greater than 3.0 were observed assuming heterogeneity. The greatest were among families with mean age of diagnosis less than 50 years at 4q21.1 (dominant HLOD = 4.51, α = 0.84, 145.40 cM, rs10518142) and among all families at 12q24.32 (dominant HLOD = 3.60, α = 0.48, 285.15 cM, rs952093). Among families with four or more affected individuals and among clinic-based families, a common peak was observed at 15q22.31 (101.40 cM, rs1477798; dominant HLOD = 3.07, α = 0.29; dominant HLOD = 3.03, α = 0.32, respectively). Analysis of families with only two affected individuals yielded a peak at 8q13.2 (recessive HLOD = 3.02, α = 0.51, 132.52 cM, rs1319036). These previously unreported linkage peaks demonstrate the continued utility of family-based data in complex traits and suggest that new CRC risk alleles remain to be elucidated. © 2012 Cicek et al
H2CO and CH3OH maps of the Orion Bar photodissociation region
A previous analysis of methanol and formaldehyde towards the Orion Bar
concluded that the two molecular species may trace different physical
components, methanol the clumpy material, and formaldehyde the interclump
medium. To verify this hypothesis, we performed multi-line mapping observations
of the two molecules to study their spatial distributions. The observations
were performed with the IRAM-30m telescope at 218 and 241 GHz, with an angular
resolution of ~11''. Additional data for H2CO from the Plateau de Bure array
are also discussed. The data were analysed using an LVG approach.
Both molecules are detected in our single-dish data. Our data show that CH3OH
peaks towards the clumps of the Bar, but its intensity decreases below the
detection threshold in the interclump material. When averaging over a large
region of the interclump medium, the strongest CH3OH line is detected with a
peak intensity of ~0.06K. Formaldehyde also peaks on the clumps, but it is also
detected in the interclump gas. We verified that the weak intensity of CH3OH in
the interclump medium is not caused by the different excitation conditions of
the interclump material, but reflects a decrease in the column density of
methanol. The abundance of CH3OH relative to H2CO decreases by at least one
order of magnitude from the dense clumps to the interclump medium.Comment: 11 pages, accepted for publication in A&
Spatial models with covariates improve estimates of peat depth in blanket peatlands.
Peatlands are spatially heterogeneous ecosystems that develop due to a complex set of autogenic physical and biogeochemical processes and allogenic factors such as the climate and topography. They are significant stocks of global soil carbon, and therefore predicting the depth of peatlands is an important part of establishing an accurate assessment of their magnitude. Yet there have been few attempts to account for both internal and external processes when predicting the depth of peatlands. Using blanket peatlands in Great Britain as a case study, we compare a linear and geostatistical (spatial) model and several sets of covariates applicable for peatlands around the world that have developed over hilly or undulating terrain. We hypothesized that the spatial model would act as a proxy for the autogenic processes in peatlands that can mediate the accumulation of peat on plateaus or shallow slopes. Our findings show that the spatial model performs better than the linear model in all cases-root mean square errors (RMSE) are lower, and 95% prediction intervals are narrower. In support of our hypothesis, the spatial model also better predicts the deeper areas of peat, and we show that its predictive performance in areas of deep peat is dependent on depth observations being spatially autocorrelated. Where they are not, the spatial model performs only slightly better than the linear model. As a result, we recommend that practitioners carrying out depth surveys fully account for the variation of topographic features in prediction locations, and that sampling approach adopted enables observations to be spatially autocorrelated
PESSTO monitoring of SN 2012hn: further heterogeneity among faint type I supernovae
We present optical and infrared monitoring data of SN 2012hn collected by the
Public ESO Spectroscopic Survey for Transient Objects (PESSTO). We show that SN
2012hn has a faint peak magnitude (MR ~ -15.7) and shows no hydrogen and no
clear evidence for helium in its spectral evolution. Instead, we detect
prominent Ca II lines at all epochs, which relates this transient to previously
described 'Ca-rich' or 'gap' transients. However, the photospheric spectra
(from -3 to +32 d with respect to peak) of SN 2012hn show a series of
absorption lines which are unique, and a red continuum that is likely intrinsic
rather than due to extinction. Lines of Ti II and Cr II are visible. This may
be a temperature effect, which could also explain the red photospheric colour.
A nebular spectrum at +150d shows prominent CaII, OI, CI and possibly MgI lines
which appear similar in strength to those displayed by core-collapse SNe. To
add to the puzzle, SN 2012hn is located at a projected distance of 6 kpc from
an E/S0 host and is not close to any obvious starforming region. Overall SN
2012hn resembles a group of faint H-poor SNe that have been discovered recently
and for which a convincing and consistent physical explanation is still
missing. They all appear to explode preferentially in remote locations offset
from a massive host galaxy with deep limits on any dwarf host galaxies,
favouring old progenitor systems. SN 2012hn adds heterogeneity to this sample
of objects. We discuss potential explosion channels including He-shell
detonations and double detonations of white dwarfs as well as peculiar
core-collapse SNe.Comment: 14 pages, 14 figures, accepted to MNRAS on 14/10/201
The supernova CSS121015:004244+132827: a clue for understanding super-luminous supernovae
We present optical photometry and spectra of the super luminous type II/IIn
supernova CSS121015:004244+132827 (z=0.2868) spanning epochs from -30 days
(rest frame) to more than 200 days after maximum. CSS121015 is one of the more
luminous supernova ever found and one of the best observed. The photometric
evolution is characterized by a relatively fast rise to maximum (~40 days in
the SN rest frame), and by a linear post-maximum decline. The light curve shows
no sign of a break to an exponential tail. A broad Halpha is first detected at
~ +40 days (rest-frame). Narrow, barely-resolved Balmer and [O III] 5007 A
lines, with decreasing strength, are visible along the entire spectral
evolution. The spectra are very similar to other super luminous supernovae
(SLSNe) with hydrogen in their spectrum, and also to SN 2005gj, sometimes
considered a type Ia interacting with H-rich CSM. The spectra are also similar
to a subsample of H-deficient SLSNe. We propose that the properties of
CSS121015 are consistent with the interaction of the ejecta with a massive,
extended, opaque shell, lost by the progenitor decades before the final
explosion, although a magnetar powered model cannot be excluded. Based on the
similarity of CSS121015 with other SLSNe (with and without H), we suggest that
the shocked-shell scenario should be seriously considered as a plausible model
for both types of SLSN.Comment: 17 pages, 10 figures and 5 tables. In press to MNRAS. This version
matches the accepted one. Main conclusions are unchange
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