The effects of generating pulsed radiation by a long spark discharge are important for the development of lightning models and applications related to lightning protection. In experiments with a Marx ...generator simulating a lightning discharge, we detected the radiation in the form of a single ultrawideband electromagnetic pulse (UWB EMP) about 200 ps in duration, and rising time about 100 ps. UWB EMP generation occurs during the breakdown of a “rod–rod” 4 m long gap. Pulses of almost unipolar shape are observed in more than half of all positive discharges. EMP emission occurs before the main stage, and corresponds to the start of the upward leader from a grounded electrode. In negative discharges, pulses are also observed, but less frequently and with a smaller amplitude. The UWB EMPs, given their large amplitude (more than 100 V/m at a distance of 90 m from the discharge), can be considered as possible new lightning damage factors.
Plain Language Summary
A Marx generator with an operating voltage of several megavolts is used to simulate a lightning stroke of a grounded object. The generation of a short electromagnetic pulse (several hundreds of picoseconds long) has been detected during a breakdown of a long air gap using special electromagnetic probes. Such a pulse is observed in the majority of positive discharges in the “rod–rod” gap. Subnanosecond pulse can be regarded as possible new damage factor of lightning strokes.
Key Points
Marx generator allows studying generation of ultra‐wideband electromagnetic pulses (EMPs) by long spark discharges that model lightning
Single EMP about 200 ps duration is generated by 4‐m long spark discharge in a rod‐rod geometry
Pulses of almost unipolar shape with up to 200 V/m amplitude are observed at 90 m distance from more than half of all positive discharges
We consider dark matter consisting of long-living particles with masses 10
7
GeV ≲
M
≲10
16
GeV decaying through hadronic channel as a source of high-energy neutrino. Using recent data on high-energy ...neutrino from IceCube and Pierre Auger experiments, we derive the upper-limits on neutrino flux from dark matter decay and constraints on dark matter parameter space. For the dark matter masses of order 10
8
GeV the constraints derived are slightly stronger than those obtained for the same dark matter model using the highenergy gamma-ray limits.
The single-walled carbon nanotube-based thin films with a thickness from 11 ± 3 to 157 ± 18 nm have been formed using vacuum filtration. The thermal conductivity of the thin films as a function of ...thickness and temperature up to 450 K has been studied by the 3ω technique. It has been found that, in the region of 49 nm, the supplied heat from a gold strip started propagating with the high efficiency to the thin film plane. The thermal conductivity of the thin films with a thickness of 49 ± 8 nm was measured using the 3ω technique for bulk samples. It has been found that the thermal conductivity of the single-walled carbon nanotube-based thin films strongly depends on their thickness and temperature. The thermal conductivity sharply (by a factor of ~60) increases with an increase in thickness from 11 ± 3 to 65 ± 4 nm. In addition, it has been observed that the thermal conductivity of the thin film with a thickness of 157 ± 18 nm rapidly decreases from 211 ± 11 to 27.5 ± 1.4 W m
–1
K
–1
at 300 and 450 K, respectively.
•Pb50Se50-xTex have been fabricated by Plasma-enhanced chemical vapor deposition technique.•The morphology of PbSeTe thin films strongly depends as on the composition.•High thermoelectric ...characteristics of PbSeTe thin films are demonstrated.•Strong influence of the composition of the PbSeTe films on the thermoelectric properties.
Ternary chalcogenide PbSeTe thin films with sufficient excess of tellurium over the stoichiometry Pb50Se50-xTex have been fabricated by Plasma-enhanced chemical vapor deposition technique. High-pure elemental lead, tellurium, and selenium were the starting materials, that were supplied by the flow of high-pure argon into the 40 MHz inductively-coupled non-equilibrium plasma discharge at low pressure 13 Pa. Argon also served as the plasma-feed gas. The structural properties and chemical composition of the films were characterized by scanning electron microscope and X-ray diffraction analysis, respectively. The dependence of the Seebeck coefficient, resistivity and thermoelectric power factor on structural properties and composition were investigated. The influence of film composition on thermoelectric characteristics was studied.
The possibility of modifying the properties of a (Ga,Mn)As layer on the surface of a quantum-size InGaAs/GaAs-structure by laser annealing with the conservation of its emitting properties is studied. ...To perform these studies by a combination of the methods of MOC-hydride epitaxy and pulsed laser deposition, the structures have been prepared with four quantum wells InGaAs/GaAs (indium contents from 0.08 to 0.25) located at various distances from the (Ga,Mn)As layer. The radiation energy density of an LPX-200 pulsed excimer laser was varied during the experiments from 200 to 360 mJ/cm
2
, and the depth of the laser action was determined from the changes in the photoluminescence spectra of the quantum wells. The results are described using the laser annealing model based on the solution of the problem of heat propagation in a one-dimensional GaAs system, taking into account a (Ga,Mn)As layer on the surface. The changes in the structural and galvanomagnetic properties of the samples under action of laser irradiation are analyzed. It is shown that the pulsed laser irradiation with the laser radiation energy density 250–300 mJ/cm
2
enable one to conserve the emitting properties of the active region (quantum wells InGaAs/GaAs) disposed at the distances 10–12 nm from the (Ga,Mn)As layer and to modify the ferromagnetic properties of the (Ga,Mn)As semiconductor, namely, to increase the ferromagnet–paramagnet phase transition temperature to values no lower than 120 K. The results are promising for the development of the technology of devices of spin optoelectronics.
The results of studies of the time-resolved photoluminescence in semiconductor heterostructures containing two noninteracting InGaAs quantum wells in a GaAs matrix are reported. One of the quantum ...wells was undoped, and the other was uniformly doped with chromium atoms (InGaAs:Cr). It was shown that the introduction of Cr had a profound effect on the recombination lifetime of charge carriers in quantum wells. The change in the photoluminescence intensity after excitation cannot be described by a monoexponential decay function, which is attributed to a change in the built-in electric field of the surface barrier in the quantum wells because of screening by photoexcited charge carriers.
•Ferromagnetic (Ga,Mn)As layers were obtained by pulsed laser deposition and annealing.•Results of X-ray diffraction, TEM and the magnetization study are presented.•Decomposition of MnAs inclusions ...is observed after laser annealing of thin (Ga,Mn)As layer.•The Curie temperature increased to 105–110 K in the annealed thin (Ga,Mn)As layer.
We have investigated the layers of the (Ga,Mn)As diluted magnetic semiconductor with the thickness in the range of 150 – 400 nm, which have been formed by the combination of the methods of a pulsed laser deposition and a post-growth pulsed laser annealing. It has been found that the laser annealing has a significant effect on the structural, magnetic, and electrical properties of the thinnest (∼150 nm) (Ga,Mn)As layer. For this layer the additional activation of the Mn impurity, the Curie temperature increase and the dissolution of the second phase MnAs clusters have been observed. The results of model calculations of heat spread in (Ga,Mn)As layer have shown that in thicker layers a MnAs melting point temperature is not achievable (for the chosen conditions of pulsed laser annealing) in the entire layer.
A series of experiments was carried out at the P critical facility of National Research Center Kurchatov Institute to study neutron characteristics of VVER type water-uranium compositions that ...contain fuel rods enriched up to 6.5% of
235
U and absorbers on the basis of erbium oxide (Er
2
O
3
). The geometry and composition of fuel assemblies were chosen to obtain the experimental data which are of use for validating codes used for examination and design of extended VVER cycles with a uranium-erbium fuel. The experimental facility and compositions of implemented fuel assemblies are described, and the main experimental results are presented.
The possibilities of doping carbon layers grown by pulsed laser deposition with transition-metal impurities are analyzed. The composition and optical and electrical parameters of structures on GaAs ...and Si/SiO
2
substrates are studied. It is shown that the introduction of such atoms as Fe ones modifies the magnetic properties of layers, which are responsible for nonlinear magnetic-field dependences of the Hall effect at temperatures of up to 300 K.
We examine the role of the large-scale anisotropy of the high-energy cosmic ray distribution in a search for the heavy decaying dark matter (DM) signal. Using recent anisotropy measurements from the ...extensive air shower (EAS) observatories, we constrain the lifetime of the DM particles with masses 10
7
≤
M
X
≤ 10
16
GeV. These constraints appear to be weaker than that obtained with the high-energy gamma-ray limits. We also estimate the desired precision level for the anisotropy measurements to discern the decaying DM signal marginally allowed by the gamma-ray limits and discuss the prospects of the DM search with the modern EAS facilities.
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