Activity

We calculate heat transfer between a 2D sheet (e.g. graphene) and a dielectric in presence of the gate voltage. The gate potential induces surface charge densities on the sheet and dielectric which results in coupling between an electric field and the surface displacements and, as a consequence, to an additional contributions to the radiative heat transfer. The electrostatic and van der Waals interactions between the surface displacement result in the phonon heat transfer which we calculate taking into account the nonlocality of these interactions. The numerical calculations are presented for heat transfer between graphene and a SiO2 substrate. © 2020 IOP Publishing Ltd.Recent experiments have given evidence that for elemental Nd, Tb, and Dy the application of sufficient pressure pushes their magnetic ordering temperatures to anomalously high values. Pr metal has the dhcp structure and is trivalent with the 4f2configuration. Its singlet ground state suppresses magnetic order from the 15 K anticipated from de Gennes scaling to 50 mK. Four-point electrical resistivity measurements were carried out on Pr for temperatures 1.5 – 295 K under pressures to 48 GPa. Although no clear evidence for magnetic order (or superconductivity) is observed above 1.5 K, the temperature dependence of the resistivity gives evidence that Pr may enter a dense Kondo state above 10 GPa. © 2020 IOP Publishing Ltd.Recently RuB2was shown to be a possible two-gap, type-I superconductor. Temperature dependent heat capacity measurements revealed a two-gap superconducting ground state while magnetic field dependent magnetization measurements indicated surprising type-I superconductivity with a very low experimental critical fieldHc∼ 120 Oe. In this paper, we report direct spectroscopic evidence of two superconducting energy gaps in RuB2. We have measured scanning tunnelling spectra exhibiting signature of two gaps on different grains of polycrystalline RuB2, possibly originating from multiple bands. Analysis of the temperature dependent tunnelling spectra revealed that the gaps from different bands evolve differently with temperature before disappearing simultaneously at a singleTc. Interestingly, our experiments also reveal that the gaps in quasiparticle density of states survive up to magnetic fields much higher than the bulkHcand they evolve smoothly with field, unlike what is expected for a type-I superconductor, indicating the existence of a “mixed state”. © 2020 IOP Publishing Ltd.Femtosecond transient absorption measurements have been performed to study the pump wavelength- and fluence-dependent hot carrier relaxation dynamics in monolayer MoS2. The relaxation process of the photoinduced carriers monitored within hundreds of femtoseconds after photoexcitation is demonstrated to be achieved through the carrier-phonon scattering mechanism. It is observed that an efficient hot-phonon effect can slow down the relaxation rate by around three times with the injected carrier density changing from 1×1012to 3×1013cm-2. A pronounced increase in the hot carrier relaxation time with decreasing temperature is further detected, which is attributed to the decreased phonon occupancy at lower temperature. © 2020 IOP Publishing Ltd.Accurate segmentation of organs-at-risk (OARs) is necessary for adaptive head and neck (H&N) cancer treatment planning but manual delineation is tedious, slow, and inconsistent. A Self-Channel-and-Spatial-Attention neural network (SCSA-Net) is developed for H&N OARs segmentation on CT images. To simultaneously ease the training and improve the segmentation performance, the proposed SCSA-Net utilizes the self-attention ability of the network. this website Spatial and channel-wise attention learning mechanisms are both employed to adaptively force the network to emphasize on the meaningful features and weaken the irrelevant features simultaneously. The proposed network was first evaluated on a public dataset, which includes 48 patients, then on a separate serial CT dataset, which contains ten patients who received weekly diagnostic fan-beam CT scans. On the second dataset, the accuracy of using SCSA-Net to track the parotid and submandibular gland volume changes during radiotherapy treatment was quantified. Dice similarity the volume changes of individual patients are highly consistent between the automated and manual segmentation (Pearson’s Correlation 0.97-0.99). The proposed SCSA-Net is computationally efficient to perform segmentation (~2 seconds/CT). © 2020 Institute of Physics and Engineering in Medicine.The high dose and dose-per-pulse rates (up to 130 mGy/pulse) produced by some Intraoperative Radiation Therapy (IORT) accelerators pose specific dosimetric problems due to the high density of electric charge per pulse produced in the ionization chamber cavity. In particular, the correction factor for ion recombination, kscalculated with the two-voltage method is significantly overestimated and three alternative models have been proposed in the literature allowing for the presence of a free-electron component. However, at present there is no general consensus on the best model to assess the ion recombination correction and controversy remains on the uncertainty associated with ks. In the present work we adopted a Monte Carlo approach to assess the combined standard uncertainty associated with the ion recombination correction in plane-parallel chambers used in high dose-per-pulse electron beam dosimetry. The uncertainty associated with kswas calculated for the following plane-parallel ionization chambers Scanditronix/Wellhofer Parallel Plate Chamber PPC05 and PPC40, PTW Advanced Markus Model N34045 and PTW Roos Model 34001. Input variables for MC calculations were derived from experimental data at 28 and 73 mGy/pulse. Taken together, the results of this study indicate that the three ion recombination models do not overlap within their standard uncertainties, indicating that an additional type-B uncertainty component would be necessary to take into account possible differences between the models. Our results indicate that the combined relative standard uncertainty in ksshould be calculated as the sum in quadrature of a (type-A) MC based uncertainty component and a (type-B) uncertainty contribution evaluated assuming a uniform distribution between ksvalues obtained from the two extreme models. © 2020 Institute of Physics and Engineering in Medicine.