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Irradiation of polyamide-6 (PA) with γ-rays reduces its resistance to subsequent IR laser radiation. The average rate of laser ablation of PA, preliminarily irradiated with γ-rays at a dose above ~300 kGy, is almost dose-invariant and is 30% higher than that of the initial unirradiated polymer. The pattern of the dose dependence of the laser ablation rate for the samples pre-irradiated with a dose of 3.24 MGy at a dose rate of 4.2 Gy/s is mixed in character, varying from the shape characteristic of the initial polymer at the initial stage to the shape typical of the maximum radiation dose in the stationary laser ablation mode. One of the products of PA laser ablation is a dispersed polymer, consisting of nano- to micrometer-sized particles, the size range of these particles shifting toward smaller values with an increase in the γ radiation dose, a trend that is explained by a decrease in melt viscosity. [ABSTRACT FROM AUTHOR]

We present the description of an automated hardware-software complex intended for measuring the 3 dB frequency of modulation and evaluation of the quantum efficiency of separate spectral components of the full spectrum of electroluminescence of light-emitting diodes, including the range of low levels of excitation. The principle of operation of this complex is based on measuring the spectrum of radiation of a light-emitting diode with the help of an OceanOptics USB2000+ spectrometer in the signal-accumulation mode in the course of transmission of current pulses with given amplitude and repetition frequency through the light-emitting diode with subsequent selection of separate spectral components from the full spectrum of radiation. We present the results of testing the hardware-software complex performed by measuring, as an example, the frequency characteristics of separate spectral components of the full electroluminescence spectrum of commercial InGaN green light-emitting diodes. The analyzed hardware-software complex can be used for the diagnostics of the quality of light-emitting heterostructures with quantum wells. [ABSTRACT FROM AUTHOR]

The implosion of combined loads consisting of an outer wire (fiber) array and inner cylindrical target was studied experimentally at the Angara-5-1 facility (3.5 MA, 100 ns) at currents of up to 3.5 MA. The experiments were carried out with 12- and 20-mm-diameter outer arrays made of 15-μm-diameter aluminum wires, composite arrays made of aluminum wires and 25-μm-diameter kapron fibers, and arrays made of kapron fibers with a 1-μm-thick aluminum coating. The number of wires varied from 10 to 40. The targets were made of agar-agar or low-density deuterated polyethylene. The parameters of the Z-pinch plasma were determined using the Angara-5-1 diagnostic complex, which included optical streak cameras, X-ray frame cameras, X-ray detectors, X-ray pinhole cameras, neutron detectors, and a mica-crystal X-ray spectrograph. It is established that the plasma compression dynamics and the formation of local plasma structures generating neutrons depend on the load configuration: the array diameter, the number of wires (fibers), and the diameter and density of the target. The most efficient compression and the highest plasma parameters (the compression ratio and plasma temperature), as well as the highest neutron yield, were achieved in experiments with 12-mm-diameter aluminum wire arrays inside which a 1-mm-diameter deuterated target with a mass density of 0.3 g/cm3 was installed As a result of collision of the bulk of the array mass with the inner target, a compact pinch with a diameter of ≈0.5 mm forms. The pinch formation is accompanied by the generation of a soft X-ray pulse. The development of MHD instabilities in the pinch plasma results in the formation of multiple hot spots (HSs) on the pinch axis with a typical size of 200–300 μm and an electron temperature of 0.4–0.7 keV. The HS formation is accompanied by emission of neutrons with a mean energy of 2.7 ± 0.2 MeV. The maximum neutron yield achieved in these experiments was 2.6 × 1010 neutrons/shot. [ABSTRACT FROM AUTHOR]

The electrophysical and noise characteristics of arrays of multiwall carbon nanotubes (MWCNTs) functionalized in various ways were studied. It is demonstrated that the as-prepared and annealed MWCNT arrays have semiconductor-type resistivities and temperature dependences of resistivity, while the arrays of annealed MWCNTs functionalized with acids have metallic properties. Low-frequency 1/f noise in the 0.2‒20 kHz range was observed for all MWCNT arrays. Simple thermal annealing raised the noise level severalfold and annealing with acid treatment resulted in noise reduction and a change in the index of power in its current dependence. The normal amplitude distribution of noise spikes transformed to a lognormal one as the density of as-prepared MWCNT arrays increased. The duration distribution of these spikes became narrower at higher densities. [ABSTRACT FROM AUTHOR]

The irradiation of a poly(vinylidene fluoride) (PVDF) plate with γ-rays up to 100 kGy leads to the breaking of the chain and the formation of unsaturated bonds but practically does not have any effect on the conformation composition of PVDF macromolecules. The main conformer, as in native PVDF, is the β form. Irradiation with an IR laser leads to a noticeable carbonization of PVDF macromolecules and is accompanied by a structural transition of polymer macromolecules from the β conformer to the α conformer. In the IR spectrum of the powdered product from laser ablation of PVDF, in addition to the absorption bands of the ablation crater, absorption bands from the parent PVDF are still present. [ABSTRACT FROM AUTHOR]

The motion of the outer boundary of a quasi-spherical tungsten wire array at currents of 2−4 MA was studied experimentally. It is shown that the outer boundary shifts later than it is predicted by simulations by the heterogeneous array model. The instabilities developing at the boundary of the quasi-spherical array are similar to those occurring in a cylindrical array made of the same material. It is found that, in spite of the different time behaviors of the inductances during implosions of quasi-spherical and cylindrical arrays, the energies required to compress these arrays to ~0.4 of the initial radius differ insignificantly. [ABSTRACT FROM AUTHOR]

The article aims to reconstruct and analyze the development trends of the Russian high-tech complex in 2011–2017. The main goal is to assess the development potential of the high-tech complex in 2018–2020 taking into consideration the state defense order financing, export supplies of weapons and military equipment, as well as civil output of the defense and nuclear industries. The findings showed that until 2014 the growth rates of the defense complex approximately correspond to official data, whereas in 2016–2017 there was a turnaround as in some subsectors the real growth was significantly lower than expected. It enables us to predict that the preservation of the current economic policy in the field of defense and security may lead to a reduction in the high-tech complex output from 2020. Meanwhile, it appears that at the moment there are no macroeconomic limitations that would hinder the positive dynamics continuation of the high-tech complex development provided changes in economic policy. [ABSTRACT FROM AUTHOR]

Experiments on the acceleration of a flyer by a magnetic field make it possible to study the dynamic characteristics of matter on submicrosecond time scales. Megabar pressures at the Angara-5-1 facility are produced using the magnetic field of the current with a linear density of up to 5 MA/cm. In the previous experiments on the acceleration of a duralumin flyer, velocities of up to 10 km/s were achieved. The flyer motion was recorded by means of laser shadowgraphy. In this work, the efficiency of momentum transfer from a duralumin flyer to an initially immobile tungsten target was studied. From the kinematic parameters of the flyer motion before the impact and the motion of the flyer together with the target after the impact, the fraction of the flyer mass that transfer the momentum to the target was estimated. It is established that almost the entire mass of the flyer is involved in the impact process. [ABSTRACT FROM AUTHOR]

Abstract: The causes and mechanisms of variation in the quantum efficiency and other characteristics of InGaN/GaN heterostructures are actively investigated in various operating modes. The results are presented from an experimental study of the variation in the external quantum efficiency of low-power InGaN/GaN green light-emitting diodes with and without a quantum well in the space-charge region (SCR) of the heterostructure in the accelerated test mode. It is found that after 8 hours of testing at a temperature of 300 K in the pulse mode with a pulse amplitude of 0.5 A, a pulse duration of 100 µs, and a duty cycle of 100, the external quantum efficiency grows for all LEDs without a quantum well in the SCR and diminishes for LEDs with a quantum well throughout the range of operating currents. It is shown that at a low level of injection, the intensity of emission of light emitting diodes without a quantum well in the SCR is determined by recombination processes according to the Shockley-Read-Hall mechanism, while that of LEDs with a quantum well is determined by tunneling-recombination processes. Current training of green LEDs based on InGaN/GaN heterostructures in the forced pulse mode for 4 hours can be used as a technological operation for stabilizing their lighting characteristics, and for identifying potentially unreliable products under conditions of mass production. [ABSTRACT FROM AUTHOR]

The acceleration of a flyer by a magnetic field allows studying the dynamic characteristics of matter in submicrosecond processes. At the Angara-5-1 facility, pressure is created by a magnetic field of the current with the linear current density of up to 5 MA/cm. The velocity of up to 10 km/s was obtained in the first experiments on acceleration of a duralumin flyer 1 mm thick. Two methods are used for registration of the flyer velocity: laser shadow photography and VISAR interferometric method. This paper presents the results of experiments on determining the velocity of a flyer by the VISAR method. Particular attention is paid to the problem of suppression of spurious signals in the VISAR registration system. The first problem was electromagnetic interference emerging when the Angara-5-1 facility is activated, when megavolt voltages and megaampere currents are generated within a hundred nanoseconds. The second problem was bremstrahlung radiation emerging when magnetic self-isolation is established in vacuum transmission lines. This radiation affects the optics, fiber optic cables, and photomultipliers. The suppression of these two sources of interference ensured the reliable registration of the VISAR signals. The results obtained by the two laser methods—shadow photography and VISAR—coincide with each other and with the results of numerical simulation of flyer acceleration. The experimental results and simulation results are compared. [ABSTRACT FROM AUTHOR]

We propose an automated measuring complex for the diagnostics of the lateral homogeneity of semiconductor heterostructures by measurements and analysis of the photoelectric and optic responses to their local photoexcitation in static and dynamic modes. The electronic-mechanical and optical positioning systems guarantee the illumination of local region of the investigated structure with a minimum diameter of the spot of 14 μm and a positioning accuracy of 10 μm. It is shown that the measuring complex can be used for the diagnostics of the quality of light-emitting heterostructures, transistors, solar cells, and photodiodes. [ABSTRACT FROM AUTHOR]