10,209 research outputs found
Geostationary earth climate sensor: Scientific utility and feasibility, phase A
The possibility of accurate broad band radiation budget measurements from a GEO platform will provide a unique opportunity for viewing radiation processes in the atmosphere-ocean system. The CSU/TRW team has prepared a Phase 1 instrument design study demonstrating that measurements of radiation budget are practical from geosynchronous orbit with proven technology. This instrument concept is the Geostationary Earth Climate Sensor (GECS). A range of resolutions down to 20 km at the top of the atmosphere are possible, depending upon the scientific goals of the experiment. These tradeoffs of resolution and measurement repeat cycles are examined for scientific utility. The design of a flexible instrument is shown to be possible to meet the two goals: long-term, systematic monitoring of the diurnal cycles of radiation budget; and high time and space resolution studies of regional radiation features
b-Initiated processes at the LHC: a reappraisal
Several key processes at the LHC in the standard model and beyond that
involve quarks, such as single-top, Higgs, and weak vector boson associated
production, can be described in QCD either in a 4-flavor or 5-flavor scheme. In
the former, quarks appear only in the final state and are typically
considered massive. In 5-flavor schemes, calculations include quarks in the
initial state, are simpler and allow the resummation of possibly large initial
state logarithms of the type into the
parton distribution function (PDF), being the typical scale of the
hard process. In this work we critically reconsider the rationale for using
5-flavor improved schemes at the LHC. Our motivation stems from the observation
that the effects of initial state logs are rarely very large in hadron
collisions: 4-flavor computations are pertubatively well behaved and a
substantial agreement between predictions in the two schemes is found. We
identify two distinct reasons that explain this behaviour, i.e., the
resummation of the initial state logarithms into the -PDF is relevant only
at large Bjorken and the possibly large ratios 's are
always accompanied by universal phase space suppression factors. Our study
paves the way to using both schemes for the same process so to exploit their
complementary advantages for different observables, such as employing a
5-flavor scheme to accurately predict the total cross section at NNLO and the
corresponding 4-flavor computation at NLO for fully exclusive studies.Comment: Fixed typo in Eq. (A.10) and few typos in Eq. (C.2) and (C.3
Mid-Infrared Photometry and Spectra of Three High Mass Protostellar Candidates at IRAS 18151-1208 and IRAS 20343+4129
We present arcsecond-scale mid-ir photometry (in the 10.5 micron N band and
at 24.8 microns), and low resolution spectra in the N band (R~100) of a
candidate high mass protostellar object (HMPO) in IRAS 18151-1208 and of two
HMPO candidates in IRAS 20343+4129, IRS 1 and IRS 3. In addition we present
high resolution mid-ir spectra (R~80000) of the two HMPO candidates in IRAS
20343+4129. These data are fitted with simple models to estimate the masses of
gas and dust associated with the mid-ir emitting clumps, the column densities
of overlying absorbing dust and gas, the luminosities of the HMPO candidates,
and the likely spectral type of the HMPO candidate for which [Ne II] 12.8
micron emission was detected (IRAS 20343+4129 IRS 3). We suggest that IRAS
18151-1208 is a pre-ultracompact HII region HMPO, IRAS 20343+4129 IRS 1 is an
embedded young stellar object with the luminosity of a B3 star, and IRAS
20343+4129 IRS 3 is a B2 ZAMS star that has formed an ultracompact HII region
and disrupted its natal envelope.Comment: 40 pages, 8 figures, 3 tables. Accepted for publication in
Astrophysical Journal (Part 1
Single-top t-channel hadroproduction in the four-flavour scheme with POWHEG and aMC@NLO
We present results for the QCD next-to-leading order (NLO) calculation of
single-top t-channel production in the 4-flavour scheme, interfaced to Parton
Shower (PS) Monte Carlo programs according to the POWHEG and MC@NLO methods.
Comparisons between the two methods, as well as with the corresponding process
in the 5-flavour scheme are presented. For the first time results for typical
kinematic distributions of the spectator-b jet are presented in an NLO+PS
approach.Comment: 16+1 pages, 8 figures, matches version accepted for publication in
JHE
Factorization and resummation of s-channel single top quark production
In this paper we study the factorization and resummation of s-channel single
top quark production in the Standard Model at both the Tevatron and the LHC. We
show that the production cross section in the threshold limit can be factorized
into a convolution of hard function, soft function and jet function via
soft-collinear-effective-theory (SCET), and resummation can be performed using
renormalization group equation in the momentum space resummation formalism. We
find that in general, the resummation effects enhance the Next-to-Leading-Order
(NLO) cross sections by about at both the Tevatron and the LHC, and
significantly reduce the factorization scale dependence of the total cross
section at the Tevatron, while at the LHC we find that the factorization scale
dependence has not been improved, compared with the NLO results.Comment: 29 pages, 7 figures; version published in JHE
Exome sequencing followed by large-scale genotyping suggests a limited role for moderately rare risk factors of strong effect in schizophrenia.
Schizophrenia is a severe psychiatric disorder with strong heritability and marked heterogeneity in symptoms, course, and treatment response. There is strong interest in identifying genetic risk factors that can help to elucidate the pathophysiology and that might result in the development of improved treatments. Linkage and genome-wide association studies (GWASs) suggest that the genetic basis of schizophrenia is heterogeneous. However, it remains unclear whether the underlying genetic variants are mostly moderately rare and can be identified by the genotyping of variants observed in sequenced cases in large follow-up cohorts or whether they will typically be much rarer and therefore more effectively identified by gene-based methods that seek to combine candidate variants. Here, we consider 166 persons who have schizophrenia or schizoaffective disorder and who have had either their genomes or their exomes sequenced to high coverage. From these data, we selected 5,155 variants that were further evaluated in an independent cohort of 2,617 cases and 1,800 controls. No single variant showed a study-wide significant association in the initial or follow-up cohorts. However, we identified a number of case-specific variants, some of which might be real risk factors for schizophrenia, and these can be readily interrogated in other data sets. Our results indicate that schizophrenia risk is unlikely to be predominantly influenced by variants just outside the range detectable by GWASs. Rather, multiple rarer genetic variants must contribute substantially to the predisposition to schizophrenia, suggesting that both very large sample sizes and gene-based association tests will be required for securely identifying genetic risk factors. © 2012 The American Society of Human Genetics
A complete one-loop description of associated tW production at LHC and an estimate of possible genuine supersymmetric effects
We compute, in the MSSM framework, the sum of the one-loop electroweak and of
the total QED radiation effects for the process , initiated by
the parton process . Combining these terms with the existing NLO
calculations of SM and SUSY QCD corrections, we analyze the overall one-loop
supersymmetric effects on the partial rates of the process, obtained by
integrating the differential cross section up to a final variable invariant
mass. We conclude that, for some choices of the SUSY parameters and for
relatively small final invariant masses, they could reach the relative ten
percent level, possibly relevant for a dedicated experimental effort at LHC.Comment: Title changed. Final version published in Eur. Phys. J.
Resonance and frequency-locking phenomena in spatially extended phytoplankton-zooplankton system with additive noise and periodic forces
In this paper, we present a spatial version of phytoplankton-zooplankton
model that includes some important factors such as external periodic forces,
noise, and diffusion processes. The spatially extended
phytoplankton-zooplankton system is from the original study by Scheffer [M
Scheffer, Fish and nutrients interplay determines algal biomass: a minimal
model, Oikos \textbf{62} (1991) 271-282]. Our results show that the spatially
extended system exhibit a resonant patterns and frequency-locking phenomena.
The system also shows that the noise and the external periodic forces play a
constructive role in the Scheffer's model: first, the noise can enhance the
oscillation of phytoplankton species' density and format a large clusters in
the space when the noise intensity is within certain interval. Second, the
external periodic forces can induce 4:1 and 1:1 frequency-locking and spatially
homogeneous oscillation phenomena to appear. Finally, the resonant patterns are
observed in the system when the spatial noises and external periodic forces are
both turned on. Moreover, we found that the 4:1 frequency-locking transform
into 1:1 frequency-locking when the noise intensity increased. In addition to
elucidating our results outside the domain of Turing instability, we provide
further analysis of Turing linear stability with the help of the numerical
calculation by using the Maple software. Significantly, oscillations are
enhanced in the system when the noise term presents. These results indicate
that the oceanic plankton bloom may partly due to interplay between the
stochastic factors and external forces instead of deterministic factors. These
results also may help us to understand the effects arising from undeniable
subject to random fluctuations in oceanic plankton bloom.Comment: Some typos errors are proof, and some strong relate references are
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