[en] For over a decade, ultrathin superconducting films have been developed for the detection of single photons at optical or near infrared frequencies, with competitive performances in terms of quantum efficiency, speed, and low dark count rate. In order to avoid the requirement of helium refrigeration, we consider here the use of high temperature materials, known to achieve very fast responsiveness to laser irradiation. We excite thin filaments of the cuprate YBa₂Cu₃O₇ by rectangular pulses of supercritical current so as to produce either a phase-slip centre (PSC) or a normal hot spot (HS), according to the temperature and the current amplitude selected. That procedure provides information about the maximum bias current to be used in a particle detector, about the return current back to the quiescent state after excitation, and about the rate of growth and decay of a HS. We also measure the time of PSC nucleation. A unique feature of that approach is to provide the rate of heat transfer between the film and its substrate at whatever temperature, in the superconducting state, in the practical conditions of operation. (orig.)

[en] The current–voltage ( J-E ) isotherms of single crystal FeSe_0.5Te_0.5 sample have been measured at several temperatures near the transition temperature (T_c) and under applied magnetic fields (H). A power law ( E ∼ J^β ) has been used to fit the data and evaluate the activation energy U_o (T) using β = U_o/k_BT. At low current density (J << J_c), the initial behaviour is associated with thermally activated flux Flow ( TAFF ) while at J >> J_c vortex flux flow ( FF ) behavior is expected. The effects of applied magnetic field on FF and TAFF also been investigated. We found that U_o( FF ) was reduced with by about an order of magnitude in magnetic fields as low as ∼1.5 Tesla-the reduction in U_o( TAFF ) is even faster than in U_o( FF )-hence reflecting the low pinning nature (defects, vacancies etc.) of FeSe_0.5Te_0.5 superconductor. (paper)

[en] High transition temperature (high-Tc) superconductivity arises in cuprate materials when sufficient holes or electrons are doped into the CuO₂ layers of their antiferromagnetic (AF) insulating parent compounds. While hole doping immediately turns the material superconducting, mere electron doping is not enough to induce superconductivity in some of the cuprates which need to be annealed in a low oxygen environment in order to induce superconductivity. In this work we analyse STM spectra on an electron doped superconductor, Pr_1−xLaCe_xCuO_4±δ(PLCCO), and show that compared to their hole doped counterparts, these electron-doped materials show a significant in-plane elastic scattering component. Since the copper deficiencies are intrinsic to PLCCO these could be the main source of the high in-plane scattering rate

[en] Multi-metallic nanoparticles (NPs) can offer dynamic and tunable localized surface plasmon resonance (LSPR) properties that are suitable for various catalysis, sensing and energy harvesting applications due to the wide range of tunability and applicability. In this work, the systematic fabrication and improved LSPR characteristics of multi-metallic alloy NP arrays are demonstrated based on the solid-state dewetting (SSD) of multi-layers of Ag/Pt/Au/Pd on sapphire (0001). The evolution of surface NPs in terms of configurational and elemental specifications yields vary strong and dynamic LSPR bands in the UV and VIS wavelengths based on the excitation of various plasmonic modes, i.e. dipolar (DR), quadrupolar (QR), multipolar (MR) and higher order (HO) bands, which is further exploited by the finite difference time domain simulations. Through the systematic control of multi-layer thickness, layer ratio and growth conditions, various nanostructures such as voided nanoclusters, network-like NPs and isolated semispherical NPs are obtained, which are unique in terms of morphology and elemental composition at each stage of dewetting process. The growth mechanism of multi-metallic alloy NP arrays is proposed based on the temperature driven thermal diffusion, alloying, Rayleigh-like instability and energy minimization mechanisms. Due to the subsequent sublimation of Ag atoms at above 650 °C, a sharp alteration in the elemental and morphological characteristics is demonstrated. In specific, the high percentage of Ag alloy NPs exhibits strong LSPR bands and gradually weakened along with the Ag sublimation. At the same time, however, the alloy or mono-metallic NPs without Ag still demonstrate much stronger LSPR bands as compared to the monometallic NPs by the SSD of pure films. (paper)

[en] Interest in Radio-based detection schemes for ultra-high energy cosmic rays (UHECR) has surged in recent years, owing to the potentially very low cost/detection ratio. The method of radio-frequency (RF) scatter has been proposed as potentially the most economical detection technology. Though the first dedicated experiment to employ this method, the Telescope Array RADAR experiment (TARA) reported no signal, efforts to develop more robust and sensitive trigger techniques continue. This paper details the development of a time-domain firmware trigger that exploits characteristics of the expected scattered signal from an UHECR extensive-air shower (EAS). The improved sensitivity of this trigger is discussed, as well as implementation in two separate field deployments from 2016 to 2017.

[en] We investigate the effects of iron content on the upper critical field (H_c2) and the activation energy U(T) in thermally activated flux flow in Fe_xSe_0.5Te_0.5 near the superconducting transition temperature T_c. The variations in H_c2(T) with temperature are analyzed using Ginzburg-Landau (GL), Werthamer-Helfand-Hohenberg (WHH) models along with the empirical relation (ER). The obtained values of H_c2(0) depend strongly on the model and the criteria used to determine the transition temperature. However, the general trend is that that H_c2(0) increases with the increasing Fe content. The activation energy U(T) is maximum for x =  1 and rapidly suppressed by excess or deficiency of iron. The low values of U(T) (∼10 meV) reflect the low vortex-pinning nature (due to defects, vacancies, etc.) in the Fe_xSe_0.5Te_0.5 superconductor.

[en] Elevated choline (Cho) level has been documented on proton magnetic resonance spectroscopy (¹H MRS) in head and neck squamous cell carcinoma and therefore percentage changes in Cho levels after chemoradiotherapy may serve as a marker of residual cancer in a post-treatment mass (PTM). Forty-six patients underwent ¹H MRS before treatment and the 30 patients with a PTM underwent repeat ¹H MRS at 6 weeks post-treatment. The percentage change in Cho/creatine and Cho/water ratios were correlated with residual cancer. The mean pretreatment Cho/creatine and Cho/water ratios were 2.24 and 1.20 x 10^-3, respectively. Cho persisted in four out of nine PTMs with residual cancer. Cho was absent in five out of nine PTMs with residual cancer and 21/21 PTMs without cancer. The number of PTMs with persistent Cho was too small to allow analysis of percentage change in ratios but the presence of Cho in a PTM showed significant correlation with residual cancer (p=0.0046), producing a sensitivity, specificity, positive predictive value and negative predictive value of 44%, 100%, 100% and 81%, respectively. Therefore, the presence of Cho in a PTM may serve as a marker of residual cancer. Furthermore since so few PTMs contain Cho, a percentage change in Cho ratios may not be a useful method for monitoring treatment response. (orig.)

[en] To investigate the role of diffusion-weighted imaging (DWI) in predicting and monitoring chemoradiotherapy response in head and neck squamous cell carcinoma (HNSCC). Diffusion-weighted imaging was performed pre-treatment (n = 50), intra-treatment (n = 41) and post-treatment (n = 20). Apparent diffusion coefficient (ADC) values were correlated with locoregional failure (LF). Locoregional failure occurred in 20/50 (40%) patients. A significant correlation was found between LF and post-treatment ADC (p = 0.02) but not pre- or intra-treatment ADC. Serial change in ADC was even more significant (p = 0.00001), using a fall in ADC early (pre- to intra-treatment) or late (intra- to post-treatment) to indicate LF, achieved 100% specificity, 80% sensitivity and 90% accuracy. Single ADC measurements pre- or intra-treatment did not predict response, but ADC post-treatment was a marker for LF. Serial change in ADC was an even stronger marker, when using an early or late treatment fall in ADC to identify LF. (orig.)

[en] Construction was completed during summer 2013 on the Telescope Array RAdar (TARA) bi-static radar observatory for Ultra-High Energy Cosmic Rays (UHECR). TARA is co-located with the Telescope Array, the largest “conventional” cosmic ray detector in the Northern Hemisphere, in radio-quiet Western Utah. TARA employs an 8 MW Effective Radiated Power (ERP) VHF transmitter and smart receiver system based on a 250 MS/s data acquisition system in an effort to detect the scatter of sounding radiation by UHECR-induced atmospheric ionization. TARA seeks to demonstrate bi-static radar as a useful new remote sensing technique for UHECRs. In this report, we describe the design and performance of the TARA transmitter and receiver systems

[en] With the observation of high-energy astrophysical neutrinos by the IceCube Neutrino Observatory, interest has risen in models of PeV-mass decaying dark matter particles to explain the observed flux. We present two dedicated experimental analyses to test this hypothesis. One analysis uses 6 years of IceCube data focusing on muon neutrino 'track' events from the Northern Hemisphere, while the second analysis uses 2 years of 'cascade' events from the full sky. Known background components and the hypothetical flux from unstable dark matter are fitted to the experimental data. Since no significant excess is observed in either analysis, lower limits on the lifetime of dark matter particles are derived: we obtain the strongest constraint to date, excluding lifetimes shorter than 10²⁸ s at 90% CL for dark matter masses above 10 TeV. (orig.)