The excitation of terahertz plasmon modes in a graphene rectangle by normally incident linearly polarized electromagnetic wave has been theoretically studied. The complete electromagnetic approach ...based on formulation of the integral equations for sought-for electromagnetic quantities has been developed. The influence of edge-field effects on excitation of plasmon modes for different polarization of the incident wave and different shapes of graphene rectangle has been studied. The absorption cross-section spectra and the charge density distributions in graphene rectangle for different plasmon modes have been studied. It has been found that the edge-field effect, which results in spreading the plasmon field beyond the geometric boundaries of graphene rectangle, leads to considerable red shifts of the plasmon mode frequencies and modifies the plasmon mode dispersion.
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•5–500kW AC plasma torches for plasma chemical technologies are developed.•Air plasma gasification of coal, wood and RDF gives 43–55% of H2+CO in product gas.•Steam in the mix with ...other gases is using as plasma forming media in plasma torch.•Conversion is ∼99%, selectivity is ∼98%, during steam-CO2 plasma reforming of CH4.
The usage of plasma as a gasifying agent is efficient in waste to energy (WTE) gasification technologies. Over 20years the IEE RAS conducted researches in the field of Electrophysics, studied the properties of electrical discharges in gases and liquids in a wide range of pressures. AC plasma torches with long life time (thousands of hours) working on air, mixtures of steam, air, CO2 and CH4 have been developed. The power of these devices varies widely from 5 to 500kW and the thermal efficiency is 90–95%. Experimental results of wood, coal and refuse derived fuel (RDF) air plasma gasification are presented. The content of H2+CO is 43–55%vol., lower heating value (LHV) of product gas up to 6.61MJ/m3 when the specific energy consumption is 1.4–2.5MJ/kg of raw material. Methane reforming with usage of multi-gas plasma torch allows production of synthesis gas with H2 and CO selectivity up to 98%, methane conversion ∼99% and yield of soot is no more than 125mg/Nm3.
Once you have missed the first button …, you'll never manage to button up
Johann Wolfgang von Goethe
Formate oxidation is a final step of methanol oxidation in methylotrophic prokaryotes and is ...important for detoxification of formate in other organisms. The structural mechanism of the formate dehydrogenase (FDH) of Pseudomonas sp. 101 has been studied for about 30 years. In the active center of FDH, the oxidation of formic acid into carbon dioxide in a NAD+-dependent way takes place. Residues that form the active center of that enzyme, as well as those that form the so-called substrate channel, are engaged in the catalytic cycle. Our study allowed to characterize a new residue, Tyr102, involved in the work of the enzyme. This residue is located in the outer neck of the substrate channel (at the beginning of the path of the substrate to the active center) and acts as a “button” which connects two enzyme domains into an active, “buttoned up” conformation. Our study of the kinetic parameters of mutant enzymes has shown that Tyr102Phe substitution leads to an approximately 80-fold increase of the Michaelis constant relative to the native enzyme, unlike Phe311Trp and Phe311Tyr substitution of neighboring residue Phe311. Our analysis of the Tyr102Phe mutant in the open conformation by X-ray crystallography has shown that its overall fold remains almost the same as that of the native enzyme. Molecular dynamics simulations of the ternary complexes of the native FDH enzyme and its Tyr102Phe mutant showed that Tyr102Phe substitution results in the loss of an interdomain hydrogen bond between the Tyr102 and Gln313 residues, which, in turn, destabilizes the closed conformation and affects the isolation of the FDH active site from water molecules. Our structural investigations have shown that Tyr102Phe replacement also leads to the destruction of interdomain contacts of Phe102 with Phe311, Pro312 residues, and decreases the stability of the Leu103-Val127 beta bridge. Phylogenetic analysis also confirmed the importance of the Tyr102 residue for enzymes from the FDH family, in which it is absolutely conserved.
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•Tyr102 is strongly conserved in the FDH family.•Tyr102Phe substitution leads to an 80-fold decrease in the Michaelis constant.•Tyr102Phe substitution decreases stability of the Leu103-Val127 beta bridge.•Tyr102Phe substitution decreases interdomain contacts.•Tyr102 is necessary for the correct transition of FDH into the closed state.
Coronaviruses (CoVs) pose a huge threat to public health as emerging viruses. Bat-borne CoVs are especially unpredictable in their evolution due to some unique features of bat physiology boosting the ...rate of mutations in CoVs, which is already high by itself compared to other viruses. Among bats, a meta-analysis of overall CoVs epizootiology identified a nucleic acid observed prevalence of 9.8% (95% CI 8.7-10.9%). The main objectives of our study were to conduct a qPCR screening of CoVs' prevalence in the insectivorous bat population of Fore-Caucasus and perform their characterization based on the metagenomic NGS of samples with detected CoV RNA. According to the qPCR screening, CoV RNA was detected in 5 samples, resulting in a 3.33% (95% CI 1.1-7.6%) prevalence of CoVs in bats from these studied locations. BetaCoVs reads were identified in raw metagenomic NGS data, however, detailed characterization was not possible due to relatively low RNA concentration in samples. Our results correspond to other studies, although a lower prevalence in qPCR studies was observed compared to other regions and countries. Further studies should require deeper metagenomic NGS investigation, as a supplementary method, which will allow detailed CoV characterization.
Search for heavy neutrino in K+→μ+νH decay Sadovsky, A. S.; Kurshetsov, V. F.; Filin, A. P. ...
The European physical journal. C, Particles and fields,
02/2018, Letnik:
78, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A high statistics data sample of the
K
+
→
μ
+
ν
μ
decay was accumulated by the OKA experiment in 2012. The missing mass analysis was performed to search for the decay channel
K
+
→
μ
+
ν
H
with a ...hypothetic stable heavy neutrino in the final state. The obtained missing mass spectrum does not show peaks that could be attributed to existence of stable heavy neutrinos in the mass range
(
270
<
m
ν
H
<
375
)
MeV
/
c
2
. As a result, upper limits on the branching ratio and on the value of the mixing element
|
U
μ
H
|
2
are obtained.
Abstract A high statistics data sample of the $$K^{+}\rightarrow \mu ^{+}\nu _{\mu }$$ K+→μ+νμ decay was accumulated by the OKA experiment in 2012. The missing mass analysis was performed to search ...for the decay channel $$K^{+}\rightarrow \mu ^{+}\nu _{H}$$ K+→μ+νH with a hypothetic stable heavy neutrino in the final state. The obtained missing mass spectrum does not show peaks that could be attributed to existence of stable heavy neutrinos in the mass range $$(270< m_{\nu _{H}} < 375)$$ (270<mνH<375) MeV$$/c^{2}$$ /c2 . As a result, upper limits on the branching ratio and on the value of the mixing element $$|U_{\mu H}|^{2}$$ |UμH|2 are obtained.
Abstract A high statistics data sample of the decays of $$K^+$$ K+ mesons to three charged particles was accumulated by the OKA experiment in 2012 and 2013. This allowed to select a clean sample of ...about 450 events with $$K^{+}\rightarrow \pi ^{+}\pi ^{-}\pi ^{+}\gamma $$ K+→π+π-π+γ decays with the energy of the photon in the kaon rest frame greater than 30 MeV. The measured branching fraction of the $$K^{+}\rightarrow \pi ^{+}\pi ^{-}\pi ^{+}\gamma $$ K+→π+π-π+γ , with $$E_{\gamma }^{*} > 30\ \hbox {MeV}$$ Eγ∗>30MeV is equal to $$(0.71 \pm 0.05) \times 10^{-5}$$ (0.71±0.05)×10-5 . The measured differential branching fraction over photon energy is compared with the prediction of the chiral perturbation theory to $${\mathcal {O}}(p^{4})$$ O(p4) . A search for an up-down asymmetry of the photon with respect to the hadronic system decay plane is also performed.
In slow collisions of two bare nuclei with the total charge number larger than the critical value, Zcr ≈ 173, the initially neutral vacuum can spontaneously decay into the charged vacuum and two ...positrons. Detection of the spontaneous emission of positrons would be the direct evidence of this fundamental phenomenon. However, the spontaneous emission is generally masked by the dynamical positron emission, which is induced by a strong time-dependent electric field created by the colliding nuclei. In our recent paper I. A. Maltsev et al., Phys. Rev. Lett. 123, 113401 (2019) it has been shown that the spontaneous pair production can be observed via measurements of the pair-production probabilities for a given set of nuclear trajectories. In the present paper, we have significantly advanced this study by exploring additional aspects of the process we are interested in. We calculate the positron energy spectra and find that these spectra can give a clear signature of the transition from the subcritical to the supercritical regime. It is found that focusing on a part of the positron spectrum, which accounts for the energy region where the spontaneously created positrons can contribute, allows us to get a much stronger evidence of the transition to the supercritical mode, making it very well pronounced in collisions, for example, of two uranium nuclei. The possibility of extending this study to collisions of bare nuclei with neutral atoms is also considered. The probability of a vacancy in the lowest-energy state of a quasimolecule which is formed in collisions of a bare U nucleus with neutral U and Cm atoms has been calculated. The relatively large values of this probability make such collisions suitable for observing the vacuum decay.
The main stages in the creation of the Russian segment of the MASTER network of robotic telescopes is described. This network is designed for studies of the prompt optical emission of gammaray bursts ...(GRBs; optical emission synchronous with the gamma-ray radiation) and surveys of the sky aimed at discovering uncataloged objects and photometric studies for various programs. The first results obtained by the network, during its construction and immediately after its completion in December 2010, are presented. Eighty-nine alert pointings at GRBs (in most cases, being the first ground telescopes to point at the GRBs) were made from September 2006 through July 2011. The MASTER network holds first place in the world in terms of the total number of first pointings, and currently more than half of first pointings at GRBs by ground telescopes are made by the MASTER network. Photometric light curves of GRB 091020, GRB 091127, GRB 100901A, GRB 100906A, GRB 10925A, GRB 110106A, GRB 110422A, and GRB 110530A are presented. It is especially important that prompt emission was observed for GRB 100901A and GRB 100906A, and thar GRB 091127, GRB 110422A, and GRB 110106A were observed from the first seconds in two polarizations. Very-wide-field cameras carried out synchronous observations of the prompt emission of GRB 081102, GRB 081130B, GRB 090305B, GRB 090320B, GRB 090328, and GRB 090424. Discoveries of Type Ia supernovae are ongoing (among them the brightest supernova in 2009): 2008gy, 2009nr, 2010V, and others. In all, photometry of 387 supernovae has been carried out, 43 of which were either discovered or first observed with MASTER telescopes; more than half of these are Type Ia supernovae. Photometric studies of the open clusters NGC 7129 and NGC 7142 have been conducted, leading to the discovery of 38 variable stars. Sixty-nine optical transients have been discovered.
We present the results of the prompt, early and afterglow optical observations of five γ-ray bursts (GRBs): GRB 100901A, GRB 100902A, GRB 100905A, GRB 100906A and GRB 101020A. These observations were ...made with the Mobile Astronomical System of TElescope-Robots in Russia (MASTER-II Net), the 1.5-m telescope of the Sierra Nevada Observatory and the 2.56-m Nordic Optical Telescope. For two sources, GRB 100901A and GRB 100906A, we detected optical counterparts and obtained light curves starting before the cessation of γ-ray emission, at 113 and 48 s after the trigger, respectively. Observations of GRB 100906A were conducted in two polarizing filters. Observations of the other three bursts gave the upper limits on the optical flux; their properties are briefly discussed. A more detailed analysis of GRB 100901A and GRB 100906A, supplemented by Swift data, provides the following results and indicates different origins for the prompt optical radiation in the two bursts. The light-curve patterns and spectral distributions suggest that there is a common production site for the prompt optical and high-energy emission in GRB 100901A. The results of the spectral fits for GRB 100901A in the range from optical to X-ray favour power-law energy distributions and a consistent value of the optical extinction in the host galaxy. GRB 100906A produced a smoothly peaking optical light curve, suggesting that the prompt optical radiation in this GRB originated in a front shock. This is supported by a spectral analysis. We have found that the Amati and Ghirlanda relations are satisfied for GRB 100906A. We obtain an upper limit on the value of the optical extinction on the host of GRB 100906A.
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