The Coaxial Shunt for Measurement of Current Pulses of Artificial Lightning with the Amplitude up to ±220 kA

The improved construction of the coaxial shunt SC-300M intended for measurement of decaying sine and aperiodic pulses of artificial lightning current with amplitudes up to ±220 kA is described. The results of tests of the instrument shunt in the high-current discharging circuit of power high-voltage generator of lightning current (g.l.c.) under pulsed A-component with the first amplitude -198 kA corresponding to time ≈35 µs and an action integral of the simulated pulse of current of lightning discharge equal to ≈2.38 × 10⁶ J/Ω are presented. The quantity of electricity under single action on the shunt by a current pulse of artificial lightning with logarithmic decrement of oscillations ≈2.06 that passed through the current-carrying elements of its construction was ≈-9.9 C. It was shown that, simultaneously with registration of pulsed A-component of lightning current, the shunt, owing to using of a matching voltage divider at the end of its cable communication line, allows also to measure normalized amplitude-time parameters of aperiodic shortened long-term C*-component of artificial lightning current (-568 A; ≈5 ms;τ_C* ≈18 ms; -16 C) that was being formed in the discharging circuit of the generator.     

Calculation of mean velocity and discharge using water surface velocity in small streams

Calculation of mean velocity and discharge are very important for demands such as water management, water supply, irrigation and flood control. This paper presents to determine the mean velocity and discharge in small streams using based water surface velocity. For this purpose, flow measurements were carried out at four different cross-sections at eighteen field measurements in central Turkey. The mean velocities (U_m) were calculated using velocity–area method. (U_m) and water surface velocities (u_ws) at these stations exhibited a linear distribution as U_m=0.552u_ws which has R²=0.99 determination coefficient. It was observed that this constant was smaller than the literature value 0.85. The advantage of this ratio is that it does not change in T/R (T; width of cross-section, R; hydraulic radius) and Froude numbers for the small streams. Using this constant, mean velocities (U_mcal) and discharges (Q_mcal) for all measurements can be calculated. The average relative error between measured and calculated discharges (Q−Q_mcal) was found to be 4.08%. The results presented that this method can be utilized to determine the mean velocity and discharge in small streams successfully.     

Elastohydrodynamic analysis of a cylindrical journal bearing with a flexible bearing shell

The effect of the elastic deformation of a bearing shell was considered in the determination of the performance characteristics of a hydrodynamic journal bearing. The finite element method with an iteration scheme was employed to solve the Reynolds equation governing flow in the clearance space and the three-dimensional linear elasticity equations representing the displacement vector field in the bearing shell. For design convenience a nondimensional deformation coefficient ψ relating μ, E_m, U₀ , C, R_j and tis defined. The performance characteristics were obtained in terms of load-carrying capacity, fluid flow, power loss and attitude angle for an aspect ratio $\text{L}\text{D = 1}$, eccentricity ? = 0.6 and for a wide range of deformation coefficients. The results are compared for bearing materials having Poisson's ratio v equal to 0.3 and 0.4.     

Thermal imaging system based on a high-temperature superconductor

A laboratory prototype of an infrared imaging system is described. Its operating principle is based on the formation of an area on the surface of a patterned high-temperature superconducting (HTSC) film, which is sensitive to external radiation and its displacement by local heating. The basic parameters of the activated pixel zone were measured: dimensions A ≈ (95 × 95) μm², detectivity D* = 1.3 × 10⁸ cm Hz^1/2/W, and the time constant τ = 6 ms. The considered pixel-by-pixel data readout procedure and the bolometric nature of the detector sensitivity open the possibility of utilizing the imaging system over a broad spectral range.     

Method for increasing quality of the cathode surface of a vacuum gap

A method for controlled processing of the cathode surface in vacuum has been developed. The control is effected in a steady-state regime by monitoring the amplification factor of the electric-field strength at cathode microinhomogeneities. High-voltage pulses of nanosecond durations with amplitudes ensuring a breakdown delay time equal to the duration of the applied pulse, t_d = t_p, are used to affect the surface. This method allows the surface quality to be substantially improved after application of a minimum number of pulses. The application of five pulses at t_p = 10 ns with amplitudes ensuring the condition t_d = t_p to stainless-steel electrodes results in a decrease in the field-amplification factor by a factor exceeding 5 (from 136 to 26) and in an increase in the emission area by more than four orders of magnitude (from 4.6 × 10^?19 to 10^?14 m²).     

Transition of the lubricated wear of carbon steel

To study the transition of the lubricated wear of 0.53% C steel in the steady state, wear tests were carried out by rubbing the annular surfaces of two cylindrical test pieces in machine oil with no additives. The ratio of mating areas was varied to approach actual contact conditions. Three regions of variation in the coefficient of friction with contact load were determined. Fatigue wear, characterized by a friction coefficient μ ≈ 0.05 and a specific wear rate ω_s ≈ 0.005 × 10^?6 mm³ N^?1 m^?1, occurs in the first region.A transition from fatigue wear to adhesive wear, with μ ≈ 0.05?0.12 and ω_s ≈ (0.005?0.05) × 10^?6 mm³ N^?1 m^?1, takes place gradually within a specific load range. Finally, adhesive wear predominates above the load level that marks the end of the transition. The same behaviour was analysed through stepwise loading tests. The onset of transition and seizure occurs at constant mean surface temperatures. However, the end of transition is also affected by factors other than temperature. The results are compared with the transitions reported by the International Research Group on Wear of Engineering Materials of the Organization for Economic Cooperation and Development.     

Using magnetic hysteresis for testing electroconductive objects in pulsed magnetic fields

The distributions of the electric voltage U(t) that is read from an induction magnetic head as it scans a discrete magnetic medium with residual magnetic field records that were obtained under the action of a pulsed magnetic field with different-polarity surges on a magnetic medium with a tested object are given. The onset of ordered distributions of the residual magnetic fields on the magnetic medium due to the sequential action on it by pulses of the magnetic field is called the hysteresis interference of a pulsed magnetic field (HI). The scheme of an experimental device for studying propagations of pulsed magnetic fields and methods of testing objects made of electroconductive and magnetic materials, which increase the accuracy of the determination of their specific conductivity σ, permeability μ, distribution uniformity of σ and μ, thickness, and parameters of continuous defects in them, are described.     

The role of cementite in the formation of magnetic hysteresis properties of plastically deformed high-carbon steels: I. Magnetic properties and structural state of cementite

Magnetic properties of cementite after strong plastic deformations and subsequent annealing in a broad range of temperatures are studied. The plastically deformed cementite is shown to exist in a soft (H _c ≈ 80 A/cm) state; the annealed cementite, in a hard (H _c ≈ 240 A/cm) state. The nature of the cementite’s soft and hard states is discussed. The field dependence of the cementite’s magnetostriction is measured. The longitudinal magnetostriction of the polycrystalline cementite’s saturated state is shown to be negative and approximately four times smaller than iron’s magnetostriction in the saturated state.     

On the dual spherical motions—ISur les mouvements spheriques duaux (lére partie)

In this paper it is shown that if the axes of curvature of the ruled surfaces $\text{U}{}_1\text{(t)}$ in the moving and fixed spaces intersect each other perpendicularly then the dralls (or distribution parameter) of the ruled surfaces, which are generated by the geodesic trihedron U₁, U₂, U₃s of a dual curve $\text{U}{}_1\text{(t)}$, satify the A. Mannheim and R. Hamilton's formulae. Furthermore, the “explicit characterization” of the spherical curve of striction is given in terms of U₃-surface and the skewness of distribution of the generator of U₁-surface.     

Registration of picosecond CO<Subscript>2</Subscript> laser pulses by means of two-stage parametric transformation in nonlinear crystals

A technique for registering the temporal structure of picosecond pulses of CO₂ laser radiation with an energy of 1.5–4.5 μJ at a wavelength of 10.27 μm using two-stage parametric transformation of IR radiation frequency into visible light under pumping of nonlinear crystals by Nd:YAG-laser radiation in a Q-switched mode is described. A GaSe nonlinear crystal was used at the first stage of transformation (10.27 μm + 1.064 μm → 0.964 μm). Radiation was further transformed (1.064 μm + 0.960 μm → 0.506 μm) by using the same pumping in an α-HIO₃ nonlinear crystal. For the first time, no additional optical elements were present between the stages of the frequency transformer in the proposed optical scheme. The transformed radiation was registered with a Hamamatsu Temporal Disperser C1587 streak camera in a region of the photocathode maximum spectral sensitivity of ～0.5 μm with a temporal resolution of up to 2 ps. The minimum recorded pulse duration of the CO₂ laser was ～45 ps.     

Ion neutralisation in secondary ion mass spectrometry

Experiments are described which allow the characteristic velocity of ion neutralisation, A/a, to be measured independent of the secondary ion energy by varying the angle of ion emission and hence the velocity component perpendicular to the surface. The A/a parameter is found to be energu dependent, increasing from ≈1×10⁶ cm/s at low ion energy, to ≈3.5×10⁶ cm/s at 200 eV.     

Results of measurements of ion energy losses in the range βγ ≈ 0.01–0.06 in thin absorbers

Results of measurements of ion energy losses in the insufficiently known range βγ = 0.01–0.06 in thin (～2 μg/cm²) absorbers are presented. For this purpose, the energy losses and time-of-flight of ions have been measured simultaneously using low-pressure avalanche gas-filled detectors at P ≈ 1 Torr. These measurements have been complemented with ion residual energy measurements using a semiconductor detector. The energy of ions with βγ ≈ 0.01–0.03 has been reconstructed using the time-of-flight measurements. The ΔE(E) dependence for ⁴He, Be, C, and O ions is presented.     

A study on the spray characteristics of a piezo pintle-type injector for DI gasoline engines

We studied the spray flow initiated from a piezo pintle-type injector for DI gasoline engines in an environment supplied by a constant volume vessel by means of laser diagnostics. To fully grasp the effects of the characteristic parameters, including designed spray angle, needle lift, injection pressure (P _inj ) and ambient pressure (P _b ), on the spray atomization and mixture preparation, particle image velocimetry (PIV) and phase Doppler anemometry (PDA) are used in the experiment, respectively. The gas perpendicularly enters into the outer periphery of the conical spray injected through the pintle-type injector activated by piezo, which creates two large-scale vortices: the vortex A and vortex B. The velocity standard deviation of the spray field is introduced to analyze the gas flow motion in the vicinity of nozzle. The droplet information of spray field is also recorded by PDA in variable boundary conditions. The time dividing method is used to study the droplet characteristics in four parts of spray. The injector with 98° designed spray angle has smaller droplet mean diameter (D10 and D32), due to a larger spray distribution. When the droplet velocity of the spray field is close to 0 m/s, the D10 and D32 hold at around 10 μm and 20 μm, respectively, in atmospheric pressure condition, which are about 20 μm and 40 μm, respectively, at ambient pressure of 1.1 MPa.     

Optimization of processing parameters for double-ridged rectangular tube rotary draw bending based on grey relational analysis

The rotary draw bending of double-ridged rectangular tube is a complex nonlinear physical process with multifactors coupling effects. Processing parameters, especially clearances and friction coefficients between tube and various dies, have a significant effect on the forming quality of the double-ridged rectangular tube in rotary draw bending. If the values of these processing parameters are inappropriate, some defects including cross-sectional deformation, wall thinning, and wall thickening easily occur in the bending process of double-ridged rectangular tube. So optimization of these processing parameters is of great importance to control these defects. Based on the grey relational analysis method combined with the orthogonal experimental design and finite element simulation, a grey relational analysis model was established for the rotary draw bending process of double-ridged rectangular H96 brass tube. With the model, optimization of clearances and friction coefficients between tube and various dies was implemented with consideration of interactive effects of the above defects. The results show that (1) the main factors influencing cross-sectional deformation, wall thickening, and wall thinning are tube–mandrel clearance Δc _m, tube-bending die clearance Δc _b, and tube–mandrel clearance Δc _m, respectively. (2) The optimal values of clearances Δc _m, Δc _p, Δc _w, and Δc _b and friction coefficients μ_m, μ_p, μ_w, and μ_b of tube–mandrel, tube–pressure die, tube–wiper die, and tube-bending die are 0.15, 0.2, 0.2, 0.2, 0.02, 0.3, 0.06 and 0.17 mm, respectively. Furthermore, the verification for the optimal values of these processing parameters was carried out, and the double-ridged rectangular H96 bent tube obtained by using the optimal values of these processing parameters has the minimum values of cross-sectional deformation, wall thinning, and wall thickening and can satisfy the national aviation industry standards.     

An experimental setup for studying specular reflection of hard γ quanta

An experimental setup is described on which the fact of specular reflection of hard γ quanta (E _γ ≤ 5 MeV) from a smooth amorphous surface has been experimentally established. Specular reflection is observed at sliding incidence of γ quanta onto a reflecting surface at angles of a few thousandths of a degree. The setup is composed of a microtron, a system of electron transportation to a bremsstrahlung target, the bremsstrahlung target generating an intense directed flux of electron bremsstrahlung γ quanta), a guiding system forming a ribbon beam of γ radiation with a width of ～1 cm and a thickness of ≈20 μm, a reflector (a liquid mercury surface or a glass plate), and a detection system containing the counting and spectrometric detectors located at a distance of 120 m from the bremsstrahlung target. Some experimental results are presented.     

Fluorescence relaxation in 3D from diffraction-limited sources of PAGFP or sinks of EGFP created by multiphoton photoconversion

The relaxation of fluorescence from diffraction‐limited sources of photoactivatable green fluorescent protein (PAGFP) or sinks of photobleached enhanced GFP (EGFP) created by multiphoton photo‐conversion was measured in solutions of varied viscosity (η), and in live, spherical Chinese hamster ovary (CHO) cells. Fluorescence relaxation was monitored with the probing laser fixed, or rapidly scanning along a line bisected by the photoconversion site. Novel solutions to several problems that hamper the study of PAGFP diffusion after multiphoton photoconversion are presented. A theoretical model of 3D diffusion in a sphere from a source in the shape of the measured multiphoton point‐spread function was applied to the fluorescence data to estimate the apparent diffusion coefficient, D_ap. The model incorporates two novel features that make it of broad utility. First, the model includes the no‐flux boundary condition imposed by cell plasma membranes, allowing assessment of potential impact of this boundary on estimates of D_ap. Second, the model uses an inhomogeneous source term that, for the first time, allows analysis of diffusion from sources produced by multiphoton photoconversion pulses of varying duration. For diffusion in aqueous solution, indistinguishable linear relationships between D_ap and η⁻¹ were obtained for the two proteins: for PAGFP, D_aq= 89 ± 2.4 μm² s⁻¹ (mean ± 95% confidence interval), and for EGFP D_aq= 91 ± 1.8 μm² s⁻¹. In CHO cells, the application of the model yielded D_ap= 20 ± 3 μm² s⁻¹ (PAGFP) and 19 ± 2 μm² s⁻¹ (EGFP). Furthermore, the model quantitatively predicted the decline in baseline fluorescence that accompanied repeated photobleaching cycles in CHO cells expressing EGFP, supporting the hypothesis of fluorophore depletion as an alternative to the oft invoked ‘bound fraction’ explanation of the deviation of the terminal fluorescence recovery from its pre‐bleach baseline level. Nonetheless for their identical diffusive properties, advantages of PAGFP over EGFP were found, including an intrinsically higher signal/noise ratio with 488‐nm excitation, and the requirement for ∼1/200th the cumulative light energy to produce data of comparable signal/noise.     

Flow visualization of grid generated turbulence under stable thermal stratification

We demonstrated the evolution of grid turbulence under the action of a stable, linear, temperature gradient with smoke-wire method. The experiment was carried out in a large, open circuit, low speed wind tunnel 0.91×0.91 m² and 9.14 m in length specially designed for the study of stratified turbulence. The smoke was generated by heating a thin nichrome wire coated with heavy-weight oil and the facility to take the pictures was controlled by a computer for the consistant shots. The temperature gradient, formed at the entrance to the plenum chamber of the tunnel by means of an array of 72 horizontal, differentially heated elements was 0°C/m for the unstratified case and 55°C/m for the stratified case where a Brunt-Väisälä frequencyN was 1. 3s ^?1. The grid mesh sizeM was 2.54 cm and the mean velocityU was fixed at 2.8 m/s for both cases. Thus the mesh Froude numberFr _M =U/(NM) was ∞ and 84.8 for the unstratified and stratified case respectively. We show that there are distinct differences in the evolution of the flow for the stable case, especially, the vertical motion decays much more rapidly than for the neutral (unstratified) case. No evidence of internal wave motion is found from the flow visualization pictures.     

Specific Features of Excitation and Propagation of Longitudinal and Transverse Subsurface Waves in Solids: II. Effects of Some Boundary Conditions on Formation of Acoustic Fields

Modification of boundary conditions for propagation of transverse and longitudinal subsurface waves by covering a specimen's boundary surface with a layer of liquid may significantly affect amplitude P _A and the form and directivity characteristic (DC) of a subsurface wave (SW) source in a near-surface zone even in the case when the ratio of acoustic impedances of coupling media is m₁₂≈0.1. Dependences of the wave amplitude and the DC of probes of transverse and longitudinal SWs on geometric parameters of a rectangular protrusion located on the surface of the inspected solid body and on the wave frequency are established. The DC of a transverse-SW source has two global maxima located in the volume of the raised area and beneath it. These maxima are due to superposition of the fields belonging to the principal ST mode and to an additional mode transformed on the protrusion's edge. The studies performed have shown an increase in the sensitivity to flaws located beneath the extension of the coupling surface's plane in the protrusion's volume or above it.     

Hydrodynamic drag versus roughness for rotating disks

Stylus measurements of the microroughness of rotating disks and their significant correlation with hydrodynamic drag measurements were studied. The roughest disks (R_a ≈ 16 μm) were found to have drag coefficients about 30% greater than those of the smoothest disks (R_a ≈ 0.14 μm). For a Reynolds' number of 1.5 × 10⁶, the following empirical relationship between the drag coefficient C, the average roughness R_a and a parameter designated the peak count wavelength λ_pc was obtained:

$\text{C=}\text{bR}{}_{\mathrm{a}}\text{λ}{}_{\mathrm{pc}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{+ C}{}_{\mathrm{o}}$

where .Other surface parameters and functions were measured in addition to R_a and λ_pc; however, it seems that knowledge of an amplitude-sensitive parameter and a wavelength-sensitive parameter is adequate for characterizing increases in the drag of rotating disks due to surface roughness. R_a is the preferred amplitude-sensitive parameter because it is the most widely used. We propose λ_pc as the wavelength parameter because it is sensitive to the larger profile features rather than to the fine structure.However, there is a need for all workers in the field to standardize on measuring the same parameters so that the results of one group can be easily related to the work of other groups.     

Growing HgTe/Cd<Subscript>0.735</Subscript>Hg<Subscript>0.265</Subscript>Te quantum wells by molecular beam epitaxy

HgTe/Cd_0.735Hg_0.265Te nanostructures with HgTe quantum wells 16.2 and 21.0 nm thick are grown without additional doping on (013)CdTe/ZnTe/GaAs substrates by the method of molecular beam epitaxy. The compositions and thicknesses of the wide-gap layer and quantum well in the course of growth are performed by means of ellipsometry. The accuracy is Δx ? ±0.002 mole fractions of cadmium telluride in determining the composition and Δd ? 0.5 nm in determining the thickness of the wide-gap layer and quantum well. The central fragments of the wide-gap layers ≈ 10 nm thick are additionally doped by indium for a ～ 10¹⁵ cm^?3 volume concentration of charge carriers to be reached. Galvanomagnetic research in a wide range of magnetic field intensities at liquid helium temperatures reveals dimensional quantization levels and the presence of a two-dimensional electron gas in grown nanostructures. High mobility of the two-dimensional electron gas μ _e is obtained: 2 · 10⁵ and 5 · 10⁵ cm²/V · s for electron densities N _s equal to 1.5 · 10¹¹ and 3.5 · 10¹¹ cm^?2, respectively.