The studies of the interband electron transition energy in multiple Hg1-xCdxTe/Hg1-yCdyTe quantum wells (MQWs) at room temperature were carried out. The MQWs were grown on the (013) GaAs substrate by ...molecular beam epitaxy, with the layer composition and thickness being measured by the in-situ ellipsometric parameters measurement at the nanometer level. The Hg1-xCdxTe barrier composition and width were x = 0.69 and 30 nm, respectively. The Hg1-yCdyTe well composition was y = 0.06–0.10, and the width varied in the range of 2.7–13 nm. The experimental data of the interband electron transition energy were determined by the absorption spectral analysis. The calculation of the interband electron transition energy was carried out on the basis of the four-band Kane model. A good agreement between the experimental and calculated data was obtained. It was shown that MQWs may be used as a photosensitive material for creating infrared optoelectronic devices operating in different modes in the range of 3–10 μm at room temperature.
The authors examined the effect of solid-state modification of titanium dioxide powder with the nanoparticles of zirconia and silica on the composition, structure, and diffuse reflectance spectra ...(ρλ) of the powder and on their alteration (Δρλ) under influence of solar spectrum quanta. It was established that when the concentration of SiO2 nanoparticles is 3 wt% and ZrO2 is 5 wt%, the reflectance coefficient undergoes a 10% decrease in visible spectrum and increases by 9.5% in the near-IR region. After the irradiation of non-modified and modified powders with intensity three times higher than solar irradiation, the wide absorption bands appeared in Δρλ spectra with the peaks at 420 nm and 800–1200 nm. With increasing the irradiation time from 5 to 40 h, the bands’ intensity increases as well. It was established that photostability of modified powders is two times higher than that of non-modified powders. Modification with SiO2 nanoparticles provides a more significant effect in comparison with ZrO2 nanoparticles.
•Modifying TiO2 powder leads to 10% reflectance decrease in the visible region and to 9.5% increase in the near-IR region.•Irradiating with solar spectrum quanta leads to the formation of absorption bands in the visible and near-IR regions.•The efficiency of modification (in terms of photostability) with ZrO2 and SiO2 nanoparticles equals 2.25 and 2.97 times.
α‐Ribose‐1‐phosphate (Rib‐p) and 2‐deoxy‐α‐ribose‐1‐phosphate (dRib‐p) are key intermediates in nucleoside metabolism and are important starting compounds for the enzymatic synthesis of various ...modified nucleosides. To date, chemical and enzymatic methods allowed the preparation of these compounds in rather low yields (11–37 %). This prevents their widespread use for the enzymatic synthesis of biologically active and practically important nucleosides. Here we propose to use 7‐methyl‐2′‐deoxyguanosine (7‐Me‐dGuo) and 7‐methylguanosine (7‐Me‐Guo) for the preparation of dRib‐p and Rib‐p. In this paper, we present the effective preparation of Rib‐p and dRib‐p starting from readily prepared 7‐methylguanosine derivatives via their irreversible enzymatic phosphorolysis in the presence of purine nucleoside phosphorylase. Rib‐p and dRib‐P are obtained in nearly quantitative yields (HPLC analysis) and 74–96 % yields after their isolation and purification, which is much higher than previously reported.
We present a novel enzymatic method for the preparation of Rib‐p and dRib‐p starting from 7‐Me‐Guo and 7‐Me‐dGuo. Practically irreversible phosphorolysis of 7‐Me‐Guo and 7‐Me‐dGuo in the presence of PNP ensures the quantitative transformation of starting nucleosides to anomerically pure α‐Rib‐p and α‐dRib‐p. Rib‐p and dRib‐p are obtained with 74–96 % yields after isolation and purification.
A search for sub-GeV dark matter production mediated by a new vector boson A′, called a dark photon, is performed by the NA64 experiment in missing energy events from 100 GeV electron interactions in ...an active beam dump at the CERN SPS. From the analysis of the data collected in the years 2016, 2017, and 2018 with 2.84×1011 electrons on target no evidence of such a process has been found. The most stringent constraints on the A′ mixing strength with photons and the parameter space for the scalar and fermionic dark matter in the mass range ≲0.2 GeV are derived, thus demonstrating the power of the active beam dump approach for the dark matter search.
Stainless steels undergo a sharp rise in pitting corrosion rate as the potential, solution concentration, or temperature is changed only slightly. We report experiments using real-time microscopic in ...situ visualizations that resolve the nucleation and evolution of individual pits during the transition. They suggest that the sudden onset of corrosion is explained by an explosive autocatalytic growth in the number of metastable pits and that stabilization of individual pits takes place only later. This finding agrees with a theoretical approach treating the onset of pitting corrosion as a cooperative critical phenomenon resulting from interactions among metastable pits, and it extends perspectives on the control and prevention of corrosion onset.
Abstract
In this paper, we show that electron states formed in topological insulators at the interfaces topological phase–trivial phase and topological phase–vacuum may possess different properties. ...This is demonstrated on an example of heterostructures based on thick topological Hg
1−
x
Cd
x
Te films, in which the
PT
-symmetric terahertz photoconductivity is observed. It is shown that the effect originates from features of the interface topological film–trivial buffer/cap layer. The
PT
-symmetric terahertz photoconductivity is not provided by electron states formed at the interface topological film–vacuum.
We carried out a model-independent search for light scalar (s) and pseudoscalar axionlike (a) particles that couple to two photons by using the high-energy CERN SPS H4 electron beam. The new ...particles, if they exist, could be produced through the Primakoff effect in interactions of hard bremsstrahlung photons generated by 100 GeV electrons in the NA64 active dump with virtual photons provided by the nuclei of the dump. The a (s) would penetrate the downstream HCAL module, serving as a shield, and would be observed either through their a (s) → γγ decay in the rest of the HCAL detector, or as events with a large missing energy if the a (s) decays downstream of the HCAL. This method allows for the probing of the a (s) parameter space, including those from generic axion models, inaccessible to previous experiments. No evidence of such processes has been found from the analysis of the data corresponding to 2.84 × 10 11 electrons on target, allowing us to set new limits on the a(s)γγ -coupling strength for a (s) masses below 55 MeV.
The first measurement of transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190 GeV/c π^{-} beam and a transversely polarized ...ammonia target. Three azimuthal asymmetries giving access to different transverse-momentum-dependent (TMD) parton distribution functions (PDFs) are extracted using dimuon events with invariant mass between 4.3 GeV/c^{2} and 8.5 GeV/c^{2}. Within the experimental uncertainties, the observed sign of the Sivers asymmetry is found to be consistent with the fundamental prediction of quantum chromodynamics (QCD) that the Sivers TMD PDFs extracted from DY have a sign opposite to the one extracted from semi-inclusive deep-inelastic scattering (SIDIS) data. We present two other asymmetries originating from the pion Boer-Mulders TMD PDFs convoluted with either the nucleon transversity or pretzelosity TMD PDFs. A recent COMPASS SIDIS measurement was obtained at a hard scale comparable to that of these DY results. This opens the way for possible tests of fundamental QCD universality predictions.
Measurement data on methane fluxes in the palsa mire ecosystem at the border of tundra and taiga zones in northeastern European Russia are presented. It was found for the first time that an intense ...methane flux from the surface of the permafrost mound (palsa) is determined by the spring thawing of the seasonally thawed horizon in the layer of 14–25 cm. During this period, the emission was 4–20 times higher than the summer values. In lichen communities of peat mounds, the CH
4
sink prevailed during the summer-autumn period. The total methane flux in different parts of the mire in June–September varied from 0.18 to 16.5 kg CH
4
/ha. In general, the palsa mire emitted 81 kg CH
4
/ha per year to the atmosphere. The methane emission from the surface of peat mounds and hollows made up 20% and 80% of the annual flux, respectively.
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