170 research outputs found
Deformations of quantum field theories on spacetimes with Killing vector fields
The recent construction and analysis of deformations of quantum field
theories by warped convolutions is extended to a class of curved spacetimes.
These spacetimes carry a family of wedge-like regions which share the essential
causal properties of the Poincare transforms of the Rindler wedge in Minkowski
space. In the setting of deformed quantum field theories, they play the role of
typical localization regions of quantum fields and observables. As a concrete
example of such a procedure, the deformation of the free Dirac field is
studied.Comment: 35 pages, 3 figure
Relativistic calculation of nuclear transparency in (e,e'p) reactions
Nuclear transparency in (e,e'p) reactions is evaluated in a fully
relativistic distorted wave impulse approximation model. The relativistic mean
field theory is used for the bound state and the Pauli reduction for the
scattering state, which is calculated from a relativistic optical potential.
Results for selected nuclei are displayed in a Q^2 range between 0.3 and 1.8
(GeV/c)^2 and compared with recent electron scattering data. For Q^2 = 0.3
(GeV/c)^2 the results are lower than data; for higher Q^2 they are in
reasonable agreement with data. The sensitivity of the model to different
prescriptions for the one-body current operator is investigated. The off-shell
ambiguities are rather large for the distorted cross sections and small for the
plane wave cross sections.Comment: 8 pages, 3 figure
Measurement of the Mass Splittings between the States
We present new measurements of photon energies and branching fractions for
the radiative transitions: Upsilon(2S)->gamma+chi_b(J=0,1,2). The masses of the
chi_b states are determined from the measured radiative photon energies. The
ratio of mass splittings between the chi_b substates,
r==(M[J=2]-M[J=1])/(M[J=1]-M[J=0]) with M the chi_b mass, provides information
on the nature of the bbbar confining potential. We find
r(1P)=0.54+/-0.02+/-0.02. This value is in conflict with the previous world
average, but more consistent with the theoretical expectation that r(1P)<r(2P);
i.e., that this mass splittings ratio is smaller for the chi_b(1P) triplet than
for the chi_b(2P) triplet.Comment: 11 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Radiative Decay Modes of the Meson
Using data recorded by the CLEO-II detector at CESR we have searched for four
radiative decay modes of the meson: ,
, , and . We
obtain 90% CL upper limits on the branching ratios of these modes of , , and
respectively.Comment: 15 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
A conceptual modeling methodology based on niches and granularity
This paper presents a methodology for conceptual modeling which is based on a new modeling primitive, the niche, and associated constructs granularity and reconciliation. A niche is an environment where entities interact for a specific purpose, playing specific roles, and according to the norms and constraints of that environment. Granularity refers to the relative level of power or influence of an entity within a niche. Reconciliation is a relationship from N entities onto one reconciled entity, and represents explicitly a situation where two or more different perspectives of the same entity have been reconciled, by negotiation, into a single consensus view. The methodology we propose provides a systematic method of designing conceptual models along with a process for normalising inappropriate relationships. Normalising is a prescriptive process for identifying and remedying inconsistencies within a model based on granularities. Drawing on a number of case studies, we show how niches and granularity make complexity easier to manage, highlight inaccuracies in a model, identify opportunities for achieving project goals, and reduce semantic heterogeneity
Bruno Touschek: particle physicist and father of the electron-positron collider
This article gives a brief outline of the life and works of the Austrian
physicist Bruno Touschek, who conceived, proposed and, 50 years ago, brought to
completion the construction of AdA, the first electron-positron storage ring.
The events which led to the approval of the AdA pro ject and the Franco-Italian
collaboration which con- firmed the feasibility of electron-positron storage
rings will be recalled. We shall illustrate Bruno Touschek's formation both as
a theoretical physicist and as an expert in particle accelerators during the
period be- tween the time he had to leave the Vienna Staat Gymnasium in 1938,
because of his Jewish origin from the maternal side, until he arrived in Italy
in the early 1950s and, in 1960, proposed to build AdA, in Frascati. The events
which led to Touschek's collaboration with Rolf Wideroe in the construction of
the first European betatron will be de- scribed. The article will make use of a
number of unpublished as well as previously unknown documents, which include an
early correspon- dence with Arnold Sommerfeld and Bruno Touschek's letters to
his family in Vienna from Italy, Germany and Great Britain. The impact of
Touschek's work on students and collaborators from University of Rome will be
illustrated through his work on QED infrared radiative corrections to high
energy e+e- experiments and the book Meccanica Statistica.Comment: To be published in EPJ
The HERMES Spectrometer
The HERMES experiment is collecting data on inclusive and semi-inclusive deep inelastic scattering of polarised positrons from polarised targets of Il, D, and He-3. These data give information on the spin structure of the nucleon. This paper describes the forward angle spectrometer built for this purpose. The spectrometer includes numerous tracking chambers (micro-strip gas chambers, drift and proportional chambers) in front of and behind a 1.3 T.m magnetic field, as well as an extensive set of detectors for particle identification (a lead-glass calorimeter, a pre-shower detector, a transition radiation detector, and a threshold Cherenkov detector). Two of the main features of the spectrometer are its good acceptance and identification of both positrons and hadrons, in particular pions. These characteristics, together with the purity of the targets, are allowing HERMES to make unique contributions to the understanding of how the spins of the quarks contribute to the spin of the nucleon. (C) 1998 Elsevier Science B.V. All rights reserved
Whole-genome sequencing reveals host factors underlying critical COVID-19
Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease
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