148 research outputs found
Bethe--Salpeter equation in QCD
We extend to regular QCD the derivation of a confining
Bethe--Salpeter equation previously given for the simplest model of scalar QCD
in which quarks are treated as spinless particles. We start from the same
assumptions on the Wilson loop integral already adopted in the derivation of a
semirelativistic heavy quark potential. We show that, by standard
approximations, an effective meson squared mass operator can be obtained from
our BS kernel and that, from this, by expansion the
corresponding Wilson loop potential can be reobtained, spin--dependent and
velocity--dependent terms included. We also show that, on the contrary,
neglecting spin--dependent terms, relativistic flux tube model is reproduced.Comment: 23 pages, revte
Dynamic Ordering and Transverse Depinning of a Driven Elastic String in a Disordered Media
We examine the dynamics of an elastic string interacting with quenched
disorder driven perpendicular and parallel to the string. We show that the
string is the most disordered at the depinning transition but with increasing
drive partial ordering is regained. For low drives the noise power is high and
we observe a 1/f^2 noise signature crossing over to a white noise character
with low power at higher drives. For the parallel driven moving string there is
a finite transverse critical depinning force with the depinning transition
occuring by the formation of running kinks.Comment: 4 pages, 4 postscript figure
Practice Considerations for Adapting In-Person Groups to Telerehabilitation
The Coronavirus-2019 (COVID-19) pandemic has shifted research and healthcare system priorities, stimulating literature on implementation and evaluation of telerehabilitation for a variety of patient populations. While there is substantial literature on individual telerehabilitation, evidence about group telerehabilitation remains limited despite its increasing use by rehabilitation providers. Therefore, the purpose of this manuscript is to describe our expert team’s consensus on practice considerations for adapting in-person group rehabilitation to group telerehabilitation to provide rapid guidance during a pandemic and create a foundation for sustainability of group telerehabilitation beyond the pandemic’s end.
 
V-I characteristics in the vicinity of order-disorder transition in vortex matter
The shape of the V-I characteristics leading to a peak in the differential
resistance r_d=dV/dI in the vicinity of the order-disorder transition in NbSe2
is investigated. r_d is large when measured by dc current. However, for a small
Iac on a dc bias r_d decreases rapidly with frequency, even at a few Hz, and
displays a large out-of-phase signal. In contrast, the ac response increases
with frequency in the absence of dc bias. These surprisingly opposite phenomena
and the peak in r_d are shown to result from a dynamic coexistence of two
vortex matter phases rather than from the commonly assumed plastic depinning.Comment: 12 pages 4 figures. Accepted for publication in PRB rapi
Transverse phase-locking in fully frustrated Josephson junction arrays: a new type of fractional giant steps
We study, analytically and numerically, phase locking of driven vortex
lattices in fully-frustrated Josephson junction arrays at zero temperature. We
consider the case when an ac current is applied {\it perpendicular} to a dc
current. We observe phase locking, steps in the current-voltage
characteristics, with a dependence on external ac-drive amplitude and frequency
qualitatively different from the Shapiro steps, observed when the ac and dc
currents are applied in parallel. Further, the critical current increases with
increasing transverse ac-drive amplitude, while it decreases for longitudinal
ac-drive. The critical current and the phase-locked current step width,
increase quadratically with (small) amplitudes of the ac-drive. For larger
amplitudes of the transverse ac-signal, we find windows where the critical
current is hysteretic, and windows where phase locking is suppressed due to
dynamical instabilities. We characterize the dynamical states around the
phase-locking interference condition in the curve with voltage noise,
Lyapunov exponents and Poincar\'e sections. We find that zero temperature
phase-locking behavior in large fully frustrated arrays is well described by an
effective four plaquette model.Comment: 12 pages, 11 figure
Effects of columnar disorder on flux-lattice melting in high-temperature superconductors
The effect of columnar pins on the flux-lines melting transition in
high-temperature superconductors is studied using Path Integral Monte Carlo
simulations. We highlight the similarities and differences in the effects of
columnar disorder on the melting transition in YBaCuO
(YBCO) and the highly anisotropic BiSrCaCuO (BSCCO) at
magnetic fields such that the mean separation between flux-lines is smaller
than the penetration length. For pure systems, a first order transition from a
flux-line solid to a liquid phase is seen as the temperature is increased. When
adding columnar defects to the system, the transition temperature is not
affected in both materials as long as the strength of an individual columnar
defect (expressed as a flux-line defect interaction) is less than a certain
threshold for a given density of randomly distributed columnar pins. This
threshold strength is lower for YBCO than for BSCCO. For higher strengths the
transition line is shifted for both materials towards higher temperatures, and
the sharp jump in energy, characteristic of a first order transition, gives way
to a smoother and gradual rise of the energy, characteristic of a second order
transition. Also, when columnar defects are present, the vortex solid phase is
replaced by a pinned Bose glass phase and this is manifested by a marked
decrease in translational order and orientational order as measured by the
appropriate structure factors. For BSCCO, we report an unusual rise of the
translational order and the hexatic order just before the melting transition.
No such rise is observed in YBCO.Comment: 32 pages, 13 figures, revte
Coherent electron-phonon coupling and polaron-like transport in molecular wires
We present a technique to calculate the transport properties through
one-dimensional models of molecular wires. The calculations include inelastic
electron scattering due to electron-lattice interaction. The coupling between
the electron and the lattice is crucial to determine the transport properties
in one-dimensional systems subject to Peierls transition since it drives the
transition itself. The electron-phonon coupling is treated as a quantum
coherent process, in the sense that no random dephasing due to electron-phonon
interactions is introduced in the scattering wave functions. We show that
charge carrier injection, even in the tunneling regime, induces lattice
distortions localized around the tunneling electron. The transport in the
molecular wire is due to polaron-like propagation. We show typical examples of
the lattice distortions induced by charge injection into the wire. In the
tunneling regime, the electron transmission is strongly enhanced in comparison
with the case of elastic scattering through the undistorted molecular wire. We
also show that although lattice fluctuations modify the electron transmission
through the wire, the modifications are qualitatively different from those
obtained by the quantum electron-phonon inelastic scattering technique. Our
results should hold in principle for other one-dimensional atomic-scale wires
subject to Peierls transitions.Comment: 21 pages, 8 figures, accepted for publication in Phys. Rev. B (to
appear march 2001
Carotenoid content and reflectance of yellow and red nuptial plumages in widowbirds (Euplectes spp.)
1. Ornamental carotenoid coloration is commonly based on several different pigments with different nutritional and metabolic constraints. The identification and quantification of carotenoid pigments is therefore crucial to the understanding of signal content and signal evolution. 2. In male widowbirds (Euplectes spp.), the striking yellow and red carotenoid colours have been measured by reflectance spectrometry and studied with respect to sexual selection through male contest competition, but their biochemical mechanisms have not been analysed. 3. Here we use reflectance analysis and high performance liquid chromatography (HPLC) to describe the species-specific colours and plumage carotenoids in three widowbird species: yellow-mantled widowbird (YMW) Euplectes macrourus, red-shouldered widowbird (RSW) E. axillaris and red-collared widowbird (RCW) E. ardens. 4. YMW yellow (‘hue’ colorimetric λR50 = 522 nm) derives from the two ‘dietary yellow’ xanthophylls lutein and zeaxanthin, together with small amounts of ‘derived yellow’ pigments (3′-dehydrolutein and canary xanthophylls). 5. RCW red (λR50 = 574 nm) is achieved by the addition of low concentrations of ‘derived red ’ 4-keto-carotenoids, notably α- and β-doradexanthin and canthaxanthin. 6. RSW red (λR50 = 589 nm) is, in contrast, created by high concentrations of ‘dietary yellow ’ pigments (lutein, zeaxanthin) and ‘derived yellow ’ anhydrolutein, the latter only recently described in birds. 7. The two different mechanisms of producing red plumage are compared with other bird species and discussed with regard to costs and signal ‘honesty’
PIK3CA mutation in HPV-associated OPSCC patients receiving deintensified chemoradiation
PIK3CA is the most frequently mutated gene in human papillomavirus (HPV)-associated oropharyngeal squamous cell carcinoma (OPSCC). Prognostic implications of such mutations remain unknown. We sought to elucidate the clinical significance of PIK3CA mutations in HPV-associated OPSCC patients treated with definitive chemoradiation (CRT). Seventyseven patients with HPV-associated OPSCC were enrolled on two phase II clinical trials of deintensified CRT (60 Gy intensitymodulated radiotherapy with concurrent weekly cisplatin). Targeted next-generation sequencing was performed. Of the 77 patients, nine had disease recurrence (two regional, four distant, three regional and distant). Thirty-four patients had mutation( s) identified; 16 had PIK3CA mutations. Patients with wild-type-PIK3CA had statistically significantly higher 3-year disease-free survival than PIK3CA-mutant patients (93.4%, 95% confidence interval [CI] = 85.0% to 99.9% vs 68.8%, 95% CI = 26.7% to 89.8%; P=.004). On multivariate analysis, PIK3CA mutation was the only variable statistically significantly associated with disease recurrence (hazard ratio = 5.71, 95% CI = 1.53 to 21.3; P=.01). PIK3CA mutation is associated with worse diseasefree survival in a prospective cohort of newly diagnosed HPV-associated OPSCC patients treated with deintensified CRT
Signaling via a CD27-TRAF2-SHP-1 axis during naive T cell activation promotes memory-associated gene regulatory networks.
The interaction of the tumor necrosis factor receptor (TNFR) family member CD27 on naive CD8 <sup>+</sup> T (Tn) cells with homotrimeric CD70 on antigen-presenting cells (APCs) is necessary for T cell memory fate determination. Here, we examined CD27 signaling during Tn cell activation and differentiation. In conjunction with T cell receptor (TCR) stimulation, ligation of CD27 by a synthetic trimeric CD70 ligand triggered CD27 internalization and degradation, suggesting active regulation of this signaling axis. Internalized CD27 recruited the signaling adaptor TRAF2 and the phosphatase SHP-1, thereby modulating TCR and CD28 signals. CD27-mediated modulation of TCR signals promoted transcription factor circuits that induced memory rather than effector associated gene programs, which are induced by CD28 costimulation. CD27-costimulated chimeric antigen receptor (CAR)-engineered T cells exhibited improved tumor control compared with CD28-costimulated CAR-T cells. Thus, CD27 signaling during Tn cell activation promotes memory properties with relevance to T cell immunotherapy
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