402 research outputs found
Time-dependent numerical renormalization group method for multiple quenches: towards exact results for the long time limit of thermodynamic observables and spectral functions
We develop an alternative time-dependent numerical renormalization group
(TDNRG) formalism for multiple quenches and implement it to study the response
of a quantum impurity system to a general pulse. Within this approach, we
reduce the contribution of the NRG approximation to numerical errors in the
time evolution of observables by a formulation that avoids the use of the
generalized overlap matrix elements in our previous multiple-quench TDNRG
formalism [Nghiem {\em et al.,} Phys. Rev. B {\bf 89}, 075118 (2014); Phys.
Rev. B {\bf 90}, 035129 (2014)]. We demonstrate that the formalism yields a
smaller cumulative error in the trace of the projected density matrix as a
function of time and a smaller discontinuity of local observables between
quenches than in our previous approach. Moreover, by increasing the switch-on
time, the time between the first and last quench of the discretized pulse, the
long-time limit of observables systematically converges to its expected value
in the final state, i.e., the more adiabatic the switching, the more accurately
is the long-time limit recovered. The present formalism can be
straightforwardly extended to infinite switch-on times. We show that this
yields highly accurate results for the long-time limit of both thermodynamic
observables and spectral functions, and overcomes the significant errors within
the single quench formalism [Anders {\em et al.}, Phys. Rev. Lett. {\bf 95},
196801 (2005); Nghiem {\em et al.}, Phys. Rev. Lett. {\bf 119}, 156601 (2017)].
This improvement provides a first step towards an accurate description of
nonequilibrium steady states of quantum impurity systems, e.g., within the
scattering states NRG approach [Anders, Phys. Rev. Lett. {\bf 101}, 066804
(2008)].Comment: 15 pages and 10 figures; Additional figures and references added;
typos fixed; references fixe
Sixty GHz IMPATT diode development
The objective of this program is to develop 60 GHz GaAs IMPATT Diodes suitable for communications applications. The performance goal of the 60 GHz IMPATT is 1W CW output power with a conversion efficiency of 15 percent and 10 year life time. During the course of the program, double drift (DD) GaAs IMPATT Diodes have been developed resulting in the state of the art performance at V band frequencies. A CW output power of 1.12 W was demonstrated at 51.9 GHz with 9.7 percent efficiency. The best conversion efficiency achieved was 15.3 percent. V band DD GaAs IMPATTs were developed using both small signal and large signal analyses. GaAs wafers of DD flat, DD hybrid, and DD Read profiles using molecular beam epitaxy (MBE) were developed with excellent doping profile control. Wafer evaluation was routinely made by the capacitance versus voltage (C-V) measurement. Ion mass spectrometry (SIMS) analysis was also used for more detailed profile evaluation
Confinement effect on solar thermal heating process of TiN solutions
We propose a theoretical approach to describe quantitatively the heating
process in aqueous solutions of dispersed TiN nanoparticles under solar
illumination. The temperature gradients of solution with different
concentrations of TiN nanoparticles are calculated when confinement effects of
the container on the solar absorption are taken into account. We find that the
average penetration of solar radiation into the solution is significantly
reduced with increasing the nanoparticle concentration. At high concentrations,
our numerical results show that photons are localized near the surface of the
solution. Moreover, the heat energy balance equation at the vapor-liquid
interface is used to describe the solar steam generation. The theoretical time
dependence of temperature rise and vaporization weight losses is consistent
with experiments. Our calculations give strong evidence that the substantially
localized heating near the vapor-liquid interface is the main reason for the
more efficient steam generation process by floating plasmonic membranes when
compared to randomly dispersed nanoparticles. The validated theoretical model
suggests that our approach can be applied towards new predictions and other
experimental data descriptions.Comment: 6 pages, 3 figures, accepted for publication in PCC
Polarimetric scattering from layered media with multiple species of scatterers
Geophysical media are usually heterogeneous and contain multiple species of scatterers. In this paper a model is presented to calculate effective permittivities and polarimetric backscattering coefficients of multispecies-layered media. The same physical description is consistently used in the derivation of both permittivities and scattering coefficients. The strong permittivity fluctuation theory is extended to account for the multiple species of scatterers with a general ellipsoidal shape whose orientations are randomly distributed. Under the distorted Born approximation, polarimetric scattering coefficients are obtained. These calculations are applicable to the special cases of spheroidal and spherical scatterers. The model is used to study effects of scatterer shapes and multispecies mixtures on polarimetric signatures of heterogeneous media. The multispecies model accounts for moisture content in scattering media such as snowpack in an ice sheet. The results indicate a high sensitivity of backscatter to moisture with a stronger dependence for drier snow and ice grain size is important to the backscatter. For frost-covered saline ice, model results for bare ice are compared with measured data at C band and then the frost flower formation is simulated with a layer of fanlike ice crystals including brine infiltration over a rough interface. The results with the frost cover suggest a significant increase in scattering coefficients and a polarimetric signature closer to isotropic characteristics compared to the thin saline ice case
Oscillations in Procyon A: First results from a multi-site campaign
Procyon A is a bright F5IV star in a binary system. Although the distance,
mass and angular diameter of this star are all known with high precision, the
exact evolutionary state is still unclear. Evolutionary tracks with different
ages and different mass fractions of hydrogen in the core pass, within the
errors, through the observed position of Procyon A in the Hertzsprung-Russell
diagram. For more than 15 years several different groups have studied the
solar-like oscillations in Procyon A to determine its evolutionary state.
Although several studies independently detected power excess in the
periodogram, there is no agreement on the actual oscillation frequencies yet.
This is probably due to either insufficient high-quality data (i.e., aliasing)
or due to intrinsic properties of the star (i.e., short mode lifetimes). Now a
spectroscopic multi-site campaign using 10 telescopes world-wide (minimizing
aliasing effects) with a total time span of nearly 4 weeks (increase the
frequency resolution) is performed to identify frequencies in this star and
finally determine its properties and evolutionary state.Comment: 7 pages, 4 figures to be published in the proceedings of HELAS II
International Conference: Helioseismology, Asteroseismology and MHD
Connections published in the Journal of Physics: Conference Series. High
resolution colour figures can be provided on reques
LVM-Med: Learning Large-Scale Self-Supervised Vision Models for Medical Imaging via Second-order Graph Matching
Obtaining large pre-trained models that can be fine-tuned to new tasks with
limited annotated samples has remained an open challenge for medical imaging
data. While pre-trained deep networks on ImageNet and vision-language
foundation models trained on web-scale data are prevailing approaches, their
effectiveness on medical tasks is limited due to the significant domain shift
between natural and medical images. To bridge this gap, we introduce LVM-Med,
the first family of deep networks trained on large-scale medical datasets. We
have collected approximately 1.3 million medical images from 55 publicly
available datasets, covering a large number of organs and modalities such as
CT, MRI, X-ray, and Ultrasound. We benchmark several state-of-the-art
self-supervised algorithms on this dataset and propose a novel self-supervised
contrastive learning algorithm using a graph-matching formulation. The proposed
approach makes three contributions: (i) it integrates prior pair-wise image
similarity metrics based on local and global information; (ii) it captures the
structural constraints of feature embeddings through a loss function
constructed via a combinatorial graph-matching objective; and (iii) it can be
trained efficiently end-to-end using modern gradient-estimation techniques for
black-box solvers. We thoroughly evaluate the proposed LVM-Med on 15 downstream
medical tasks ranging from segmentation and classification to object detection,
and both for the in and out-of-distribution settings. LVM-Med empirically
outperforms a number of state-of-the-art supervised, self-supervised, and
foundation models. For challenging tasks such as Brain Tumor Classification or
Diabetic Retinopathy Grading, LVM-Med improves previous vision-language models
trained on 1 billion masks by 6-7% while using only a ResNet-50.Comment: Update Appendi
Online Monitoring of the Osiris Reactor with the Nucifer Neutrino Detector
Originally designed as a new nuclear reactor monitoring device, the Nucifer
detector has successfully detected its first neutrinos. We provide the second
shortest baseline measurement of the reactor neutrino flux. The detection of
electron antineutrinos emitted in the decay chains of the fission products,
combined with reactor core simulations, provides an new tool to assess both the
thermal power and the fissile content of the whole nuclear core and could be
used by the Inter- national Agency for Atomic Energy (IAEA) to enhance the
Safeguards of civil nuclear reactors. Deployed at only 7.2m away from the
compact Osiris research reactor core (70MW) operating at the Saclay research
centre of the French Alternative Energies and Atomic Energy Commission (CEA),
the experiment also exhibits a well-suited configuration to search for a new
short baseline oscillation. We report the first results of the Nucifer
experiment, describing the performances of the 0.85m3 detector remotely
operating at a shallow depth equivalent to 12m of water and under intense
background radiation conditions. Based on 145 (106) days of data with reactor
ON (OFF), leading to the detection of an estimated 40760 electron
antineutrinos, the mean number of detected antineutrinos is 281 +- 7(stat) +-
18(syst) electron antineutrinos/day, in agreement with the prediction 277(23)
electron antineutrinos/day. Due the the large background no conclusive results
on the existence of light sterile neutrinos could be derived, however. As a
first societal application we quantify how antineutrinos could be used for the
Plutonium Management and Disposition Agreement.Comment: 22 pages, 16 figures - Version
Avelumab in patients with previously treated metastatic Merkel cell carcinoma (JAVELIN Merkel 200): updated overall survival data after >5 years of follow-up
Background: Merkel cell carcinoma (MCC) is a rare, aggressive skin cancer that has a poor prognosis in patients with advanced disease. Avelumab [anti-programmed death-ligand 1 (PD-L1)] became the first approved treatment for patients with metastatic MCC (mMCC), based on efficacy and safety data observed in the JAVELIN Merkel 200 trial. We report long-term overall survival (OS) data after >5 years of follow-up from the cohort of patients with mMCC whose disease had progressed after one or more prior lines of chemotherapy. Patients and methods: In Part A of the single-arm, open-label, phase II JAVELIN Merkel 200 trial, patients with mMCC that had progressed following one or more prior lines of chemotherapy received avelumab 10 mg/kg by intravenous infusion every 2 weeks until confirmed disease progression, unacceptable toxicity, or withdrawal. In this analysis, long-term OS was analyzed. Results: In total, 88 patients were treated with avelumab. At data cut-off (25 September 2020), median follow-up was 65.1 months (range 60.8-74.1 months). One patient (1.1%) remained on treatment, and an additional patient (1.1%) had reinitiated avelumab after previously discontinuing treatment. Median OS was 12.6 months [95% confidence interval (CI) 7.5-17.1 months], with a 5-year OS rate of 26% (95% CI 17% to 36%). In patients with PD-L1+ versus PD-L1- tumors, median OS was 12.9 months (95% CI 8.7-29.6 months) versus 7.3 months (95% CI 3.4-14.0 months), and the 5-year OS rate was 28% (95% CI 17% to 40%) versus 19% (95% CI 5% to 40%), respectively (HR 0.67; 95% CI 0.36-1.25). Conclusion: Avelumab monotherapy resulted in meaningful long-term OS in patients with mMCC whose disease had progressed following chemotherapy. These results further support the role of avelumab as a standard of care for patients with mMCC
Rotating Higher Spin Partition Functions and Extended BMS Symmetries
We evaluate one-loop partition functions of higher-spin fields in thermal
flat space with angular potentials; this computation is performed in arbitrary
space-time dimension, and the result is a simple combination of Poincar\'e
characters. We then focus on dimension three, showing that suitable products of
one-loop partition functions coincide with vacuum characters of higher-spin
asymptotic symmetry algebras at null infinity. These are extensions of the
bms_3 algebra that emerges in pure gravity, and we propose a way to build their
unitary representations and to compute the associated characters. We also
extend our investigations to supergravity and to a class of gauge theories
involving higher-spin fermionic fields.Comment: 58 pages; clarifications and references added; version to be
published in JHE
- …