Band structures of Cu2nSnS4 and Cu2nSnSe4 from many-body methods

We calculate the band structures of kesterite and stannite Cu2ZnSnS4 and Cu2ZnSnSe4, using a state-of-the-art self-consistent GW approach. Our accurate quasiparticle states allow to discuss: the dependence of the gap on the anion displacement; the key-role of the non-locality of the exchange-correlation potential to obtain good structural parameters; the reliability of less expensive hybrid functional and GGA+U approaches. In particular, we show that even if the band gap is correctly reproduced by hybrid functionals, the band-edge corrections are in disagreement with self-consistent GW results, which has decisive implications for the positioning of the defect levels in the band gap.Comment: accepted for publication in App. Phys. Lett. (2011

Transient Thermo-Mechanical Analysis of the TPSG4 Beam Diluter

A new extraction channel is being built in the Super Proton Synchrotron (SPS) Long Straight Section 4 (LSS4) to transfer proton beams to the Large Hadron Collider (LHC) and also to the CERN Neutrino to Gran Sasso (CNGS) target. The beam is extracted in a fast mode during a single turn. For this purpose a protection of the MSE copper septum coil, in the form of a beam diluting element placed upstream, will be required to cope with the new failure modes associated with the fast extraction operation. The present analysis focuses on the thermo-mechanical behavior of the proposed TPSG4 diluter element irradiated by a fast extracted beam (up to 4.9 x 10^13 protons per 7.2 mus pulse) from the SPS. The deposited energy densities, estimated from primary and secondary particle simulations using the high-energy particle transport code FLUKA, were converted to internal heat generation rates taken as a thermal load input for the finite-element engineering analyses code ANSYS. According to the time dependence of the extracted beam, the transient solutions were obtained for coupled heat transfer, structural deformation, and shock wave problems. The results are given for the space distribution and the time evolution of temperatures and stresses in the most critical parts of the TPSG4 beam diluting element followed by the MSE copper septum coil. In the worst case of impact of the full LHC ultimate beam, the maximum temperatures remain safely below the melting point. However, the maximum equivalent stresses may slightly exceed the elastic limit in the aluminium section of the diluter. Also, the predicted maximum temperature rise in the MSE septum coil exceeds the design value

Thermal Performance of the LHC Connection Cryostat

The 16 connection cryostats for the Large Hadron Collider (LHC) being built at CERN are designed to fill the gap existing between the dispersion suppressor zones and the standard arcs of the accelerator. The first connection cryostat was cold tested down to superfluid helium temperature in August 2005, and the measured thermal performance was as expected. This paper presents the test results and a new thermal modeling of the connection cryostat based on the measurement of the thermal resistances of the braids used for thermalisation, allowing the precise determination of cool down times and equilibrium temperatures of the shielding under various conditions such as lead heating

Study of mechanical behavior on single use bags welding under gamma irradiation

Since a long time, biopharmaceutical industry utilizes more and more single use plastic bags due to its very easy use (long shelf-lives, mechanical properties), preparation, and storage properties (oxygen and water barriers). These plastic bags are composed of two welded multilayer polymer films. To ensure the function of the closure and the non-contamination from the external environment, welding must answer to several parameters according to norm (“ISO 15747,” 2018) and standard (F02 Committee, n.d.). In this present study, the behavior of weldings on Ethylene Vinyl Acetate (EVA) single use bags under gamma irradiation have been studied. Mechanical tests have been performed at several gamma irradiation doses (from 0 kGy to 270 kGy) and at different location of the bag (Figure 1). The first objective is to study the impact of gamma irradiation dose on the welding mechanical tensile behavior. The second objective is to evaluate the impact of the welding location on the welding tensile properties. Each tensile curve (Figure 2) has been decomposed in 6 characteristic points which were evaluated with Principal Component Analysis (PCA): Ultimate Tensile strength at break (UTS), Ultimate elongation or elongation at break, 1st Yield-Strength (Y1 Strength), 1st Yield-Strain (Y1 Strain), 2nd Yield-Strength (Y2 Strength), 2nd Yield-Strain (Y2 Strain). The study showed that weldings are never impacted during tensile testing: this evaluation reveals that in fine the film cracks before the welding modification. Its function of closure and bag content preservation from external environment is fully achieved whatever the gamma irradiation dose and the welding location. Only the multilayer film on both sides of the welding is altered after 100% elongation strain. The EVA bag showed no degradation up to 115 kGy whereas they become to be altered at 270 kGy. The welding location on EVA bag showed different film mechanical behavior correlated to the polymer film extrusion process orientation. Please click Additional Files below to see the full abstract

Short Term Effects of Hurricane Irma on the Phytoplankton of Lake Louise, Georgia, USA

Natural disturbances such as fires and severe storms can have profound impacts on the hydrology and ecology of inland waters, potentially altering the structure and function of the ecosystem for extended periods of time. Studies of the initial impacts are, however, uncommon. Here we report on the short-term impacts of Hurricane Irma in the structure of the phytoplankton association in Lake Louise, a small blackwater lake in southern Georgia. Irma hit the region on September 11, 2017, with tropical storm force winds. The event corresponded to a period during which we were conducting routine weekly monitoring of environmental conditions in the lake. Parameters monitored included temperature, dissolved oxygen, conductivity, and light from the surface to a depth of 6 m. Chlorophyll concentrations and the structure of the phytoplankton were also determined at 1 m intervals from the surface to a depth of 5 m. An increase in the overall abundance of phytoplankton in the upper meter of the lake and a decrease in the abundance of phytoplankton deeper in the water column were observed immediately after Hurricane Irma. These decreases were followed by a bloom involving several species of cyanobacteria beginning about four weeks after the passage of the hurricane. Signatures of the passage of the hurricane were erased in early December as cooler temperatures created isothermal conditions in the lake

How intramolecular hydrogen bonding (IHB) controls the C-ON bond homolysis in alkoxyamines

International audienceRecent amazing results (Nkolo et al., Org. Biomol. Chem., 2017, 6167) on the effect of solvents and polarity on the C-ON bond homolysis rate constants kd of alkoxyamine R1R2NOR3 led us to re-investigate the antagonistic effect of intramolecular hydrogen-bonding (IHB) on kd. Here, IHB is investigated both in the nitroxyl fragment R1R2NO and in the alkyl fragment R-3, as well as between fragments, that is, the donating group on the alkyl fragment and the accepting group on the nitroxyl fragment, and conversely. It appears that IHB between fragments (inter IHB) strikingly decreases the homolysis rate constant kd, whereas IHB within the fragment (intra IHB) moderately increases kd. For one alkoxyamine, the simultaneous occurrence of IHB within the nitroxyl fragment and between fragments is reported. The protonation effect is weaker in the presence than in the absence of IHB. A moderate solvent effect is also observed

High-vacuum-compatible high-power Faraday isolators for gravitational-wave interferometers

Faraday isolators play a key role in the operation of large-scale gravitational-wave detectors. Second-generation gravitational-wave interferometers such as the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo will use high-average-power cw lasers (up to 200 W) requiring specially designed Faraday isolators that are immune to the effects resulting from the laser beam absorption–degraded isolation ratio, thermal lensing, and thermally induced beam steering. In this paper, we present a comprehensive study of Faraday isolators designed specifically for high-performance operation in high-power gravitational-wave interferometers

DC-readout of a signal-recycled gravitational wave detector

All first-generation large-scale gravitational wave detectors are operated at the dark fringe and use a heterodyne readout employing radio frequency (RF) modulation-demodulation techniques. However, the experience in the currently running interferometers reveals several problems connected with a heterodyne readout, of which phase noise of the RF modulation is the most serious one. A homodyne detection scheme (DC-readout), using the highly stabilized and filtered carrier light as local oscillator for the readout, is considered to be a favourable alternative. Recently a DC-readout scheme was implemented on the GEO 600 detector. We describe the results of first measurements and give a comparison of the performance achieved with homodyne and heterodyne readout. The implications of the combined use of DC-readout and signal-recycling are considered.Comment: 11 page

LOFAR observations of the quiet solar corona

The quiet solar corona emits meter-wave thermal bremsstrahlung. Coronal radio emission can only propagate above that radius, $R_\omega$, where the local plasma frequency eqals the observing frequency. The radio interferometer LOw Frequency ARray (LOFAR) observes in its low band (10 -- 90 MHz) solar radio emission originating from the middle and upper corona. We present the first solar aperture synthesis imaging observations in the low band of LOFAR in 12 frequencies each separated by 5 MHz. From each of these radio maps we infer $R_\omega$, and a scale height temperature, $T$. These results can be combined into coronal density and temperature profiles. We derived radial intensity profiles from the radio images. We focus on polar directions with simpler, radial magnetic field structure. Intensity profiles were modeled by ray-tracing simulations, following wave paths through the refractive solar corona, and including free-free emission and absorption. We fitted model profiles to observations with $R_\omega$ and $T$ as fitting parameters. In the low corona, $R_\omega < 1.5$ solar radii, we find high scale height temperatures up to 2.2e6 K, much more than the brightness temperatures usually found there. But if all $R_\omega$ values are combined into a density profile, this profile can be fitted by a hydrostatic model with the same temperature, thereby confirming this with two independent methods. The density profile deviates from the hydrostatic model above 1.5 solar radii, indicating the transition into the solar wind. These results demonstrate what information can be gleaned from solar low-frequency radio images. The scale height temperatures we find are not only higher than brightness temperatures, but also than temperatures derived from coronograph or EUV data. Future observations will provide continuous frequency coverage, eliminating the need for local hydrostatic density models