1,278 research outputs found
The s-wave pion-nucleus optical potential
We calculate the s-wave part of the pion-nucleus optical potential using a
unitarized chiral approach that has been previously used to simultaneously
describe pionic hydrogen and deuterium data as well as low energy pi N
scattering in the vacuum. This energy dependent model allows for additional
isoscalar parts in the potential from multiple rescattering. We consider Pauli
blocking and pion polarization in an asymmetric nuclear matter environment.
Also, higher order corrections of the pi N amplitude are included. The model
can accommodate the repulsion required by phenomenological fits, though the
theoretical uncertainties are bigger than previously thought. At the same time,
we also find an enhancement of the isovector part compatible with empirical
determinations.Comment: 31 pages, 27 figure
Charge fluctuations and electric mass in a hot meson gas
Net-Charge fluctuations in a hadron gas are studied using an effective
hadronic interaction. The emphasis of this work is to investigate the
corrections of hadronic interactions to the charge fluctuations of a
non-interacting resonance gas. Several methods, such as loop, density and
virial expansions are employed. The calculations are also extended to SU(3) and
some resummation schemes are considered. Although the various corrections are
sizable individually, they cancel to a large extent. As a consequence we find
that charge fluctuations are rather well described by the free resonance gas.Comment: 32 pages, 18 figure
Helicity Amplitudes of the Lambda(1670) and two Lambda(1405) as dynamically generated resonances
We determine the helicity amplitudes A_1/2 and radiative decay widths in the
transition Lambda(1670) to gamma Y (Y=Lambda or Sigma^0). The Lambda(1670) is
treated as a dynamically generated resonance in meson-baryon chiral dynamics.
We obtain the radiative decay widths of the Lambda(1670) to gamma Lambda as 3
\pm 2 keV and to gamma Sigma^0 as 120 \pm 50 keV. Also, the Q^2 dependence of
the helicity amplitudes A_1/2 is calculated. We find that the K Xi component in
the Lambda(1670) structure, mainly responsible for the dynamical generation of
this resonance, is also responsible for the significant suppression of the
decay ratio Gamma_{gamma Lambda}/Gamma_{gamma Sigma^0}. A measurement of the
ratio would, thus, provide direct access to the nature of the Lambda(1670). To
compare the result for the Lambda(1670), we calculate the helicity amplitudes
A_1/2 for the two states of the Lambda(1405). Also, the analytic continuation
of Feynman parameterized integrals of more complicated loop amplitudes to the
complex plane is developed which allows for an internally consistent evaluation
of A_1/2.Comment: 15 pages, 8 figure
Engagement in a virtual learning environment predicts academic achievement in research methods modules: A longitudinal study combining behavioral and self-reported data
The use of virtual learning environments (VLE) has grown exponentially in the past years. Research indicates that students’ online learning behavior predicts their academic performance and that students’ academic emotions can play a key role in this process. However, few studies have attempted to investigate the effectiveness of VLE activities in learning achievement within psychology education. In this longitudinal study, we analyzed the relationship between students’ activity in a VLE, their attendance, academic emotions, and module grades at a face-to-face-based university in the United Kingdom. Data were collected over 1 year across two research methods modules, each of which is compulsory for a psychology degree. VLE and attendance data from 210 students were gathered for the first-year module, with 152 students continuing to the second year. The data were cross-referenced with students’ module grades, alongside self-reported emotion data for a subset of students. The results showed that overall VLE activity and the use of specific online tools such as optional online tests and lecture recording were important predictors of academic achievement. While some significant relationships between emotions and student’s learning behavior and achievement were found, these correlations were relatively small and not consistent throughout the year. These findings have potential implications for curriculum design, particularly by making psychology educators aware of the usefulness of VLE activities and tools from the onset of students’ research methods learning journey
Topos quantum theory with short posets
Topos quantum mechanics, developed by Isham et. al., creates a topos of
presheaves over the poset V(N) of abelian von Neumann subalgebras of the von
Neumann algebra N of bounded operators associated to a physical system, and
established several results, including: (a) a connection between the
Kochen-Specker theorem and the non-existence of a global section of the
spectral presheaf; (b) a version of the spectral theorem for self-adjoint
operators; (c) a connection between states of N and measures on the spectral
presheaf; and (d) a model of dynamics in terms of V(N). We consider a
modification to this approach using not the whole of the poset V(N), but only
its elements of height at most two. This produces a different topos with
different internal logic. However, the core results (a)--(d) established using
the full poset V(N) are also established for the topos over the smaller poset,
and some aspects simplify considerably. Additionally, this smaller poset has
appealing aspects reminiscent of projective geometry.Comment: 14 page
Hepatitis B subviral envelope particles use the COPII machinery for intracellular transport via selective exploitation of Sec24A and Sec23B
Hepatitis B virus (HBV) is a leading cause of liver disease. Its success as a human pathogen is related to the immense production of subviral envelope particles (SVPs) contributing to viral persistence by interfering with immune functions. To explore cellular pathways involved in SVP formation and egress, we investigated host–pathogen interactions. Yeast-based proteomics revealed Sec24A, a component of the coat protein complex II (COPII), as an interaction partner of the HBV envelope S domain. To understand how HBV co-opts COPII as a proviral machinery, we studied roles of key Sec proteins in HBV-expressing liver cells. Silencing of Sar1, Sec23, and Sec24, which promote COPII assembly concomitant with cargo loading, strongly diminished endoplasmic reticulum (ER) envelope export and SVP secretion. By analysing Sec paralog specificities, we unexpectedly found that the HBV envelope is a selective interaction partner of Sec24A and Sec23B whose functions could not be substituted by their related isoforms. In support, we found that HBV replication upregulated Sec24A and Sec23B transcription. Furthermore, HBV encountered the Sec24A/Sec23B complex via an interaction that involved the N-terminal half of Sec24A and a di-arginine motif of its S domain, mirroring a novel ER export code. Accordingly, an interference with the COPII/HBV cross-talk might display a tool to effectively inhibit SVP release
Optically trapped atom interferometry using the clock transition of large Rb-87 Bose-Einstein condensates
We present a Ramsey-type atom interferometer operating with an optically
trapped sample of 10^6 Bose-condensed Rb-87 atoms. The optical trap allows us
to couple the |F =1, mF =0>\rightarrow |F =2, mF =0> clock states using a
single photon 6.8GHz microwave transition, while state selective readout is
achieved with absorption imaging. Interference fringes with contrast
approaching 100% are observed for short evolution times. We analyse the process
of absorption imaging and show that it is possible to observe atom number
variance directly, with a signal-to-noise ratio ten times better than the
atomic projection noise limit on 10^6 condensate atoms. We discuss the
technical and fundamental noise sources that limit our current system, and
outline the improvements that can be made. Our results indicate that, with
further experimental refinements, it will be possible to produce and measure
the output of a sub-shot-noise limited, large atom number BEC-based
interferometer.
In an addendum to the original paper, we attribute our inability to observe
quantum projection noise to the stability of our microwave oscillator and
background magnetic field. Numerical simulations of the Gross-Pitaevskii
equations for our system show that dephasing due to spatial dynamics driven by
interparticle interactions account for much of the observed decay in fringe
visibility at long interrogation times. The simulations show good agreement
with the experimental data when additional technical decoherence is accounted
for, and suggest that the clock states are indeed immiscible. With smaller
samples of 5 \times 10^4 atoms, we observe a coherence time of {\tau} =
(1.0+0.5-0.3) s.Comment: 22 pages, 6 figures Addendum: 11 pages, 6 figure
Scalar mesons moving in a finite volume and the role of partial wave mixing
Phase shifts and resonance parameters can be obtained from finite-volume
lattice spectra for interacting pairs of particles, moving with nonzero total
momentum. We present a simple derivation of the method that is subsequently
applied to obtain the pi pi and pi K phase shifts in the sectors with total
isospin I=0 and I=1/2, respectively. Considering different total momenta, one
obtains extra data points for a given volume that allow for a very efficient
extraction of the resonance parameters in the infinite-volume limit.
Corrections due to the mixing of partial waves are provided. We expect that our
results will help to optimize the strategies in lattice simulations, which aim
at an accurate determination of the scattering and resonance properties.Comment: 19 pages, 12 figure
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