80 research outputs found
The fate of high redshift massive compact galaxies in dense environments
Massive compact galaxies seem to be more common at high redshift than in the
local universe, especially in denser environments. To investigate the fate of
such massive galaxies identified at z~2 we analyse the evolution of their
properties in three cosmological hydrodynamical simulations that form
virialised galaxy groups of mass ~10^13 Msun hosting a central massive
elliptical/S0 galaxy by redshift zero. We find that at redshift ~2 the
population of galaxies with M_*> 2 10^10 Msun is diverse in terms of mass,
velocity dispersion, star formation and effective radius, containing both very
compact and relatively extended objects. In each simulation all the compact
satellite galaxies have merged into the central galaxy by redshift 0 (with the
exception of one simulation where one of such satellite galaxy survives).
Satellites of similar mass at z = 0 are all less compact than their high
redshift counterparts. They form later than the galaxies in the z = 2 sample
and enter the group potential at z < 1, when dynamical friction times are
longer than the Hubble time. Also, by z = 0 the central galaxies have increased
substantially their characteristic radius via a combination of in situ star
formation and mergers. Hence in a group environment descendants of compact
galaxies either evolve towards larger sizes or they disappear before the
present time as a result of the environment in which they evolve. Since the
group-sized halos that we consider are representative of dense environments in
the LambdaCDM cosmology, we conclude that the majority of high redshift compact
massive galaxies do not survive until today as a result of the environment.Comment: 10 pages, 4 figures, submitted to MNRA
Precision Measurement of a Particle Mass at the Linear Collider
Precision measurement of the stop mass at the ILC is done in a method based
on cross-sections measurements at two different center-of-mass energies. This
allows to minimize both the statistical and systematic errors. In the framework
of the MSSM, a light stop, compatible with electro-weak baryogenesis, is
studied in its decay into a charm jet and neutralino, the Lightest
Supersymmetric Particle(LSP), as a candidate of dark matter. This takes place
for a small stop-neutralino mass difference.Comment: 6 pages, 4 figures, 3tables,
Conference(Workshop)-LCWS/ILC2007-June,2,200
A Method for the Precision Mass Measurement of the Stop Quark at the International Linear Collider
Many supersymmetric models predict new particles within the reach of the next
generation of colliders. For an understanding of the model structure and the
mechanism(s) of symmetry breaking, it is important to know the masses of the
new particles precisely. In this article the measurement of the mass of the
scalar partner of the top quark (stop) at an e+e- collider is studied. A
relatively light stop is motivated by attempts to explain electroweak
baryogenesis and can play an important role in dark matter relic density. A
method is presented which makes use of cross-section measurements near the
pair-production threshold as well as at higher center-of-mass energies. It is
shown that this method not only increases the statistical precision, but also
greatly reduces the systematic uncertainties, which can be important. Numerical
results are presented, based on a realistic event simulation, for two signal
selection strategies: using conventional selection cuts, and using an Iterative
Discriminant Analysis (IDA). Our studies indicate that a precision of
\Delta\mstop = 0.42 GeV can be achieved, representing a major improvement
over previous studies. While the analysis of stops is particularly challenging
due to the possibility of stop hadronization, the general procedure could be
applied to the mass measurement of other particles as well. We also comment on
the potential of the IDA to discover a stop quark in this scenario, and we
revisit the accuracy of the theoretical predictions for the neutralino relic
densityComment: 41 pages, 14 figures, in JHEP forma
Two-Loop QCD Corrections to the Heavy-to-Light Quark Decay
We present an analytic expression for the two-loop QCD corrections to the
decay process b -> u W^*, where b and u are a massive and massless quark,
respectively, while W^* is an off-shell charged weak boson. Since the W-boson
can subsequently decay in a lepton anti-neutrino pair, the results of this
paper are a first step towards a fully analytic computation of differential
distributions for the semileptonic decay of a b-quark. The latter partonic
process plays a crucial role in the study of inclusive semileptonic charmless
decays of B-mesons. The three independent form factors characterizing the b W u
vertex are provided in form of a Laurent series in (d-4), where d is the
space-time dimension. The coefficients in the series are expressed in terms of
Harmonic Polylogarithms of maximal weight 4, and are functions of the invariant
mass of the leptonic decay products of the W-boson.Comment: 27 pages, 3 figures, References added, version published on JHE
Report of the 2005 Snowmass Top/QCD Working Group
This report discusses several topics in both top quark physics and QCD at an
International Linear Collider (ILC). Issues such as measurements at the
threshold, including both theoretical and machine requirements, and
the determination of electroweak top quark couplings, are reviewed. New results
concerning the potential of a 500 GeV collider for measuring
couplings and the top quark Yukawa coupling are presented. The status of higher
order QCD corrections to jet production cross sections, heavy quark form
factors, and longitudinal gauge boson scattering, needed for percent-level
studies at the ILC, are reviewed. A new study of the measurement of the
hadronic structure of the photon at a collider is presented. The
effects on top quark properties from several models of new physics, including
composite models, Little Higgs theories, and CPT violation, are studied.Comment: 39 pages, many figs; typos fixed and refs added. Contributed to the
2005 International Linear Collider Physics and Detector Workshop and 2nd ILC
Accelerator Workshop, Snowmass, Colorado, 14-27 Aug 200
Rhapsody. II. Subhalo Properties and the Impact of Tidal Stripping From a Statistical Sample of Cluster-Size Halos
We discuss the properties of subhalos in cluster-size halos, using a
high-resolution statistical sample: the Rhapsody simulations introduced in Wu
et al. (2012). We demonstrate that the criteria applied to select subhalos have
significant impact on the inferred properties of the sample, including the
scatter in the number of subhalos, the correlation between the subhalo number
and formation time, and the shape of subhalos' spatial distribution and
velocity structure. We find that the number of subhalos, when selected using
the peak maximum circular velocity in their histories (a property expected to
be closely related to the galaxy luminosity), is uncorrelated with the
formation time of the main halo. This is in contrast to the previously reported
correlation from studies where subhalos are selected by the current maximum
circular velocity; we show that this difference is a result of the tidal
stripping of the subhalos. We also find that the dominance of the main halo and
the subhalo mass fraction are strongly correlated with halo concentration and
formation history. These correlations are important to take into account when
interpreting results from cluster samples selected with different criteria. Our
sample also includes a fossil cluster, which is presented separately and placed
in the context of the rest of the sample.Comment: 15 pages, 10 figures; Paper I: arXiv:1209.3309; replaced to match
published versio
Computing for Perturbative QCD - A Snowmass White Paper
We present a study on high-performance computing and large-scale distributed
computing for perturbative QCD calculations.Comment: 21 pages, 5 table
State-of-the-art of 3D cultures (organs-on-a-chip) in safety testing and pathophysiology.
Integrated approaches using different in vitro methods in combination with bioinformatics can (i) increase the success rate and speed of drug development; (ii) improve the accuracy of toxicological risk assessment; and (iii) increase our understanding of disease. Three-dimensional (3D) cell culture models are important building blocks of this strategy which has emerged during the last years. The majority of these models are organotypic, i.e., they aim to reproduce major functions of an organ or organ system. This implies in many cases that more than one cell type forms the 3D structure, and often matrix elements play an important role. This review summarizes the state of the art concerning commonalities of the different models. For instance, the theory of mass transport/metabolite exchange in 3D systems and the special analytical requirements for test endpoints in organotypic cultures are discussed in detail. In the next part, 3D model systems for selected organs--liver, lung, skin, brain--are presented and characterized in dedicated chapters. Also, 3D approaches to the modeling of tumors are presented and discussed. All chapters give a historical background, illustrate the large variety of approaches, and highlight up- and downsides as well as specific requirements. Moreover, they refer to the application in disease modeling, drug discovery and safety assessment. Finally, consensus recommendations indicate a roadmap for the successful implementation of 3D models in routine screening. It is expected that the use of such models will accelerate progress by reducing error rates and wrong predictions from compound testing
Does psychopathology at admission predict the length of inpatient stay in psychiatry? Implications for financing psychiatric services
Background: The debate on appropriate financing systems in inpatient psychiatry is ongoing. In this context, it is important to control resource use in terms of length of stay (LOS), which is the most costly factor in inpatient care and the one that can be influenced most easily. Previous studies have shown that psychiatric diagnoses provide only limited justification for explaining variation in LOS, and it has been suggested that measures such as psychopathology might be more appropriate to predict resource use. Therefore, we investigated the relationship between LOS and psychopathological syndromes or symptoms at admission as well as other characteristics such as sociodemographic and clinical variables.
Methods: We considered routine medical data of patients admitted to the Psychiatric University Hospital Zurich in the years 2008 and 2009. Complete data on psychopathology at hospital admission were available in 3,220 inpatient episodes. A subsample of 2,939 inpatient episodes was considered in final statistical models, including psychopathology as well as complete datasets of further measures (e.g. sociodemographic, clinical, treatment-related and psychosocial variables). We used multivariate linear as well as logistic regression analysis with forward selection procedure to determine the predictors of LOS.
Results: All but two syndrome scores (mania, hostility) were positively related to the length of stay. Final statistical models showed that syndromes or symptoms explained about 5% of the variation in length of stay. The inclusion of syndromes or symptoms as well as basic treatment variables and other factors led to an explained variation of up to 25%.
Conclusions: Psychopathological syndromes and symptoms at admission and further characteristics only explained a small proportion of the length of inpatient stay. Thus, according to our sample, psychopathology might not be suitable as a primary indicator for estimating LOS and contingent costs. This might be considered in the development of future costing systems in psychiatry
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