99 research outputs found
Mesons as qbar-q Bound States from Euclidean 2-Point Correlators in the Bethe-Salpeter Approach
We investigate the 2-point correlation function for the vector current. The
gluons provide dressings for both the quark self energy as well as the vector
vertex function, which are described consistently by the rainbow
Dyson-Schwinger equation and the inhomogeneous ladder Bethe-Salpeter equation.
The form of the gluon propagator at low momenta is modeled by a 2-parameter
ansatz fitting the weak pion decay constant. The quarks are confined in the
sense that the quark propagator does not have a pole at timelike momenta. We
determine the ground state mass in the vector channel from the Euclidean time
Fourier transform of the correlator, which has an exponential falloff at large
times. The ground state mass lies around 590 MeV and is almost independent of
the model form for the gluon propagator. This method allows us to stay in
Euclidean space and to avoid analytic continuation of the quark or gluon
propagators into the timelike region.Comment: 21 pages (REVTEX), 8 Postscript figure
Characterisation of Potential Landing Sites for the European Space Agency's Lunar Lander Project
This article describes the characterization activities of the landing sites
currently envisaged for the Lunar Lander mission of the European Space Agency.
These sites have been identified in the South Pole Region (-85{\deg} to
-90{\deg} latitude) based on favourable illumination conditions, which make it
possible to have a long-duration mission with conventional power and thermal
control subsystems, capable of enduring relatively short periods of darkness
(in the order of tens of hours), instead of utilising Radioisotope Heating
Units. The illumination conditions are simulated at the potential landing sites
based on topographic data from the Lunar Orbiter Laser Altimeter (LOLA), using
three independent tools. Risk assessment of the identified sites is also being
performed through independent studies. Long baseline slopes are assessed based
on LOLA, while craters and boulders are detected both visually and using
computer tools in Lunar Reconnaissance Orbiter Camera (LROC) images, down to a
size of less than 2 m, and size-frequency distributions are generated. Shadow
hazards are also assessed via LROC images. The preliminary results show that
areas with quasi-continuous illumination of several months exist, but their
size is small (few hundred metres); the duration of the illumination period
drops quickly to less than one month outside the areas, and some areas present
gaps with short illumination periods. Concerning hazard distributions, 50 m
slopes are found to be shallow (few degrees) based on LOLA, whereas at the
scale of the lander footprint (~5 m) they are mostly dominated by craters,
expected to be mature (from geological context) and shallow (~11{\deg}). The
preliminary conclusion is that the environment at the prospective landing sites
is within the capabilities of the Lander design
Survey of nucleon electromagnetic form factors
A dressed-quark core contribution to nucleon electromagnetic form factors is
calculated. It is defined by the solution of a Poincare' covariant Faddeev
equation in which dressed-quarks provide the elementary degree of freedom and
correlations between them are expressed via diquarks. The nucleon-photon vertex
involves a single parameter; i.e., a diquark charge radius. It is argued to be
commensurate with the pion's charge radius. A comprehensive analysis and
explanation of the form factors is built upon this foundation. A particular
feature of the study is a separation of form factor contributions into those
from different diagram types and correlation sectors, and subsequently a
flavour separation for each of these. Amongst the extensive body of results
that one could highlight are: r_1^{n,u}>r_1^{n,d}, owing to the presence of
axial-vector quark-quark correlations; and for both the neutron and proton the
ratio of Sachs electric and magnetic form factors possesses a zero.Comment: 43 pages, 17 figures, 12 tables, 5 appendice
About Bianchi I with VSL
In this paper we study how to attack, through different techniques, a perfect
fluid Bianchi I model with variable G,c and Lambda, but taking into account the
effects of a -variable into the curvature tensor. We study the model under
the assumption,div(T)=0. These tactics are: Lie groups method (LM), imposing a
particular symmetry, self-similarity (SS), matter collineations (MC) and
kinematical self-similarity (KSS). We compare both tactics since they are quite
similar (symmetry principles). We arrive to the conclusion that the LM is too
restrictive and brings us to get only the flat FRW solution. The SS, MC and KSS
approaches bring us to obtain all the quantities depending on \int c(t)dt.
Therefore, in order to study their behavior we impose some physical
restrictions like for example the condition q<0 (accelerating universe). In
this way we find that is a growing time function and Lambda is a decreasing
time function whose sing depends on the equation of state, w, while the
exponents of the scale factor must satisfy the conditions
and
, i.e. for all equation of state relaxing in this way the
Kasner conditions. The behavior of depends on two parameters, the equation
of state and a parameter that controls the behavior of
therefore may be growing or decreasing.We also show that through
the Lie method, there is no difference between to study the field equations
under the assumption of a var affecting to the curvature tensor which the
other one where it is not considered such effects.Nevertheless, it is essential
to consider such effects in the cases studied under the SS, MC, and KSS
hypotheses.Comment: 29 pages, Revtex4, Accepted for publication in Astrophysics & Space
Scienc
Bianchi II with time varying constants. Self-similar approach
We study a perfect fluid Bianchi II models with time varying constants under
the self-similarity approach. In the first of the studied model, we consider
that only vary and The obtained solution is more general that
the obtained one for the classical solution since it is valid for an equation
of state while in the classical solution
Taking into account the current observations, we conclude
that must be a growing time function while is a positive
decreasing function. In the second of the studied models we consider a variable
speed of light (VSL). We obtain a similar solution as in the first model
arriving to the conclusions that must be a growing time function if
is a positive decreasing function.Comment: 10 pages. RevTeX
Electromagnetic form factors of the nucleon in a covariant diquark model
We present a simple covariant constituent diquark-quark model for the
nucleon. The nucleon is assumed to be composed of a scalar diquark and a quark
which interact via a quark exchange. Starting from the Bethe-Salpeter equation,
the instantaneous approximation leads to a diquark-quark Salpeter equation. In
the Mandelstam formalism, the electromagnetic form factors of the nucleon are
calculated for momentum transfers up to q^2 = - 3 \; (\mbox{GeV/c})^2. A
remarkable description of the experimental data is obtained. Especially, the
model gives nearly the right values for the proton and (negative) neutron
charge radii, and a qualitative description of the magnetic form factors.Comment: 17 pages, revtex, 8 figures in additional fil
Predictive validity of conversion from the clinical high risk syndrome to frank psychosis
Although the clinical high risk for psychosis (CHR) paradigm has become well-established over the past two decades, one key component has received surprisingly little investigative attention: the predictive validity of the criteria for conversion or transition to frank psychosis. The current study evaluates the predictive validity of the transition to psychosis as measured by the Structured Interview for Psychosis-Risk Syndromes (SIPS) in CHR individuals. Participants included 33 SIPS converters and 399 CHR non-converters both from the North American Prodromal Longitudinal Study (NAPLS-2), as well as a sample of 67 separately ascertained first-episode psychosis (FEP) patients from the STEP program. Comparisons were made at baseline and one-year follow-up on demographic, diagnostic stability (SCID), and available measurement domains relating to severity of illness (psychotropic medication, psychosocial treatment, and resource utilization). Principal findings are: 1) a large majority of cases in both SIPS converters (n = 27/33, 81.8%) and FEP (n = 57/67, 85.1%) samples met criteria for continued psychosis at one-year follow-up; 2) follow-up prescription rates for current antipsychotic medication were higher in SIPS converters (n = 17/32, 53.1%) compared to SIPS non-converters (n = 81/397, 20.4%), and similar as compared to FEP cases (n = 39/65, 60%); and 3) at follow-up, SIPS converters had higher rates of resource utilization (psychiatric hospitalizations, day hospital admissions, and ER visits) than SIPS non-converters and were similar to FEP in most categories. The results suggest that the SIPS definition of psychosis onset carries substantial predictive validity. Limitations and future directions are discussed
The Public Repository of Xenografts enables discovery and randomized phase II-like trials in mice
More than 90% of drugs with preclinical activity fail in human trials, largely due to insufficient efficacy. We hypothesized that adequately powered trials of patient-derived xenografts (PDX) in mice could efficiently define therapeutic activity across heterogeneous tumors. To address this hypothesis, we established a large, publicly available repository of well-characterized leukemia and lymphoma PDXs that undergo orthotopic engraftment, called the Public Repository of Xenografts (PRoXe). PRoXe includes all de-identified information relevant to the primary specimens and the PDXs derived from them. Using this repository, we demonstrate that large studies of acute leukemia PDXs that mimic human randomized clinical trials can characterize drug efficacy and generate transcriptional, functional, and proteomic biomarkers in both treatment-naive and relapsed/refractory disease
Erratum: Global, regional, and national comparative risk assessment of 84 behavioural, environmental and occupational, and metabolic risks or clusters of risks for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017
Interpretation: By quantifying levels and trends in exposures to risk factors and the resulting disease burden, this assessment offers insight into where past policy and programme efforts might have been successful and highlights current priorities for public health action. Decreases in behavioural, environmental, and occupational risks have largely offset the effects of population growth and ageing, in relation to trends in absolute burden. Conversely, the combination of increasing metabolic risks and population ageing will probably continue to drive the increasing trends in non-communicable diseases at the global level, which presents both a public health challenge and opportunity. We see considerable spatiotemporal heterogeneity in levels of risk exposure and risk-attributable burden. Although levels of development underlie some of this heterogeneity, O/E ratios show risks for which countries are overperforming or underperforming relative to their level of development. As such, these ratios provide a benchmarking tool to help to focus local decision making. Our findings reinforce the importance of both risk exposure monitoring and epidemiological research to assess causal connections between risks and health outcomes, and they highlight the usefulness of the GBD study in synthesising data to draw comprehensive and robust conclusions that help to inform good policy and strategic health planning
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