The use of new resonance integrals for determining the parameters of the epithermal neutron spectrum

A simple method for determining parameters α and b in the presentation of the epithermal neutron spectrum in the form of φ_epi(E) = b/E ^{1 + α} using expansion of function φ_epi(E) in Taylor series with respect to parameter α is described. The problem of determining the parameters is reduced to finding a solution to a system of algebraic equations. The approximation used describes the spectrum with an adequate accuracy up to energies of ～1–50 keV, depending on value α ～ 0.2?0.1, with the help of the first two or three expansion terms (resonance integrals), respectively. The first two resonance integrals for reactions ¹⁹⁷Au(n, γ)¹⁹⁸Au and ⁵⁵Mn(n, γ)⁵⁶Mn are estimated. The measured rates of the appropriate reactions and the values of parameters α and b for the case of an assembly with a graphite moderator are presented.     

Fast design of the QP-based optimal trajectory for a motion simulator

The main difficulty in realizing a motion simulator comes from the constraints on its workspace. The so-called washout filter prevents a simulator from being driven to go off its pre-determined boundaries and generate excessive torques. By noting that the existing washout filters are conservative and more aggressive motions may be accommodated, this paper presents a novel approach that fully exploits the simulator workspace and thereby reproduces the real-world sensations with high fidelity. The washout filter converts the real-world input trajectory as a realizable one that satisfies the spatial and dynamic constraints while minimizing the sensation error and fidelity between the motions experienced in the real world and on the motion simulator. The control objective is to reduce the computational burdens by using the QP algorithm. The proposed approach formulates the task of designing a washout filter as a quadratic programming (QP). The direct approach to the solution of the QP often results in a computational burden that amounts toO(N ³) flops andO(N ²) storage space (N=10⁴ ～ 10⁵, typically). By judiciously exploiting the Toeplitz structures of the underlying matrices, an orders-of-magnitude faster algorithm is obtained to reduce the computational burdens toO(Nlog₂ N) flops andO(N) storage space. The extensive simulation studies on the Eclipse-II motion simulator at Seoul National University assure that the QP-based fast algorithm outperforms the existing ones in reproducing the real-world sensations.     

Big data analysis of a mini three-axis CNC machine tool based on the tuning operation of controller parameters

The characteristic responses of a mini three-axis computer numerical control (CNC) machine tool based on the controller tuning operation were investigated for big data estimation. The major tuning parameters included the position control gains K _p, the position feed-forward control gains K _f, the speed control gains K _v, and the gain ratios K _g of the position and speed control values in manufacturing industries. K _p gains of 10, 30, 50, 80, 100, 200, 300, and 400 rad/s, K _f gains of 0, 30, 50, 60, 80, and 100 %, K _v gains of 30, 50, 70, 100, 300, 900, 2000, and 3000 rad/s, and K _g ratios of (1:1), (3:1), (5:1), and (7:1) were analyzed for smart productivity. The results show that the settling times at different K _p values were almost constant when the K _p gain was over 200 rad/s. The maximum overshoots, when the feed-forward gain is over 60 %, almost increased with increasing feed-forward gains. However, the overshoot of the three-axis CNC machine tool decreased as the K _v gain increased until the K _v gain reached 70 rad/s. The settling times at a constant K _g ratio decreased with an increase in the K _p and K _v gains. The characteristic responses of the tuning operations were enabled with connectivity to a cloud network to share the big data, to support decision making, and to adjust operations in real time.     

Quantitative proximate X-ray analysis of loose raw materials based on detection of diffraction and characteristic radiation

A method of rapid X-ray analysis is proposed. The content of the method is that the ratio I _d/I _i ^A is measured in two channels of a γ spectrometer, one of which is configured for the diffraction maximum of the determined phase (I _d) and the other measures the intensity of the spectral line of secondary element A (I _i ^A ), the atomic number of which is the same as that of the material of the X-ray tube anode. Results of the X-ray analysis of chromite and molybdenum are presented. The test rate was 7 min per test. The maximum deviation from the content of MoS₂ was 0.4% in standard specimens with concentrations of 24–29% and that of Fe and Cr₂O₃ was 0.3% for concentrations of 14–19%.     

Manufacturing and mechanical characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/β-TCP/TiO<Subscript>2</Subscript> biocomposite as a potential bone substitute

This paper focuses on the mechanical characterization of a bioceramic based on commercial alumina (Al₂O₃) mixed with synthesized tricalcium phosphate (β-TCP) and commercial titania powder (TiO₂). The effect of β-TCP and TiO₂ addition on the mechanical performance was investigated. After a sintering process at 1600 °C for 1 h, various mechanical properties of the samples have been studied, such as compressive strength, flexural strength, tensile strength, elastic modulus, and fracture toughness. The measurements of the elastic modulus (E) and the tensile strength (σ _t ) were conducted using the modified Brazilian test while the compressive strength (σ _c ) was determined through a compression test. Also, semi-circular bending (SCB) specimens were used to evaluate the flexural strength (σ _f ) and the opening mode fracture toughness (K _IC). From the main results, it was found that the best mechanical performance is obtained with the addition of 10 wt.% TCP and 5 wt.% TiO₂. Alumina/10 wt.% tricalcium phosphate/5 wt.% titania composites displayed the highest values of mechanical properties and a good combination of compressive strength (σ _c ?≈?352 MPa), flexural strength (σ _f ?≈?98 MPa), tensile strength (σ _t ?≈?86.65 MPa), and fracture toughness (K _IC?≈?13 MPa m^1/2).     

Lubricity of High Water Content Aqueous Gels

Aqueous gels such as biopolymer gels, mucus, and high water content hydrogels are often qualitatively described as lubricious. In hydrogels, mesh size, ξ, has been found to be a controlling parameter in friction coefficient. In the tribology of aqueous gels, we suggest that the Weissenberg number (Wi) is a useful parameter to define different regimes, and following the original formulations in rheology, Wi is given by the polymer relaxation time (ηξ³/k_BT) multiplied by the shear rate due to fluid shear through a single mesh (V/ξ): Wi?=?ηVξ²/k_BT. At sliding speeds below a Weissenberg number of approximately 0.1, Wi?<?0.1, the friction coefficient is velocity-independent and scales with mesh size to the ??1 power, µ ∝ ξ^?1. De Gennes’ scaling concepts for elastic modulus, E, give a dependence on polymer mesh size to the ??3 power, E ∝ ξ^?3, and following Hertzian contact analysis, the contact area is found to depend on the mesh size squared, A ∝ ξ². Combining these concepts, the shear stress, τ, and therefore the lubricity of aqueous gels, is predicted to be highly dependent on the mesh size, τ ∝ ξ^?3. Studies aimed at elucidating the fundamental mechanism of lubricity in biopolymer gels, mucus, and hydrogels have wrestled with comparisons across mesh size, which can be extremely difficult to accurately quantify. Using scaling concepts relating polymer mesh size to water content reveals that shear stress decreases rapidly with increasing water content, and plots of shear stress as a function of swollen water content are suggested as a useful method to compare aqueous gels of unknown mesh size. As a lower bound, these data are compared against estimates of fluid shear stress for free and bound water flowing through a mesh size estimated by the water content of the gels. The results indicate that the strong dependence on lubricity is likely due to a synergistic combination of a low viscosity solvent (water) coupled to a system that has a decreasing friction coefficient, modulus, and the resulting contact pressure with increasing water content. Although the permeability, K, of aqueous gels increases dramatically with water content (and mesh size), K ? ξ²/η, the stronger decrease of the elastic modulus and subsequent decrease in contact pressure due to an increase in the contact length, predicts that the draining time under contact, t, actually increases strongly with increasing water content and mesh size, t ∝ ξ². Consistent with the finding of extremely high water content aqueous gels on the surfaces of biological tissues, these high water content gels are predicted to be optimal for lubrication as they are both highly lubricious and robust at resisting draining and sustaining hydration.     

Data recording system of a dispersion interferometer based on a CO<Subscript>2</Subscript> laser

The data recording system of a multichannel double-pass dispersion interferometer based on a CO₂ laser is described. This system has been designed to record the linear density of plasmas in a real-time mode with a time discreteness of 4 μs and resolution 〈N _e L〉 ～ 0.34 × 10¹³ cm^?2 (N _e is the electron component of the plasma density, and L is the plasma size in the wave propagation direction) in the range of linear density variations of up to 10¹⁷ cm^?2. The system is built from unified recording modules that use fast ADCs to record the shape of photodetector and modulator signals and FPGA-based digital units of dataflow processing to form results of measurements. The single-channel recording module of the dispersion interferometer has been tested under actual experimental conditions of the GDL gas-dynamic trap and the TEXTOR tokamak (Julich, Germany).     

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.     

Effect of Oxygen on the Self-formation of Carbonaceous Tribo-layer with Carbon Nitride Coatings under a Nitrogen Atmosphere

The ball-on-disk friction and wear tests of CN _X coatings (CN _X /CN _X ) were conducted under a nitrogen atmosphere with controlled relative humidity (RH) (3.4–40.0%RH) and oxygen concentration (100–21 × 10⁴ ppm) in this study. We found that the specific wear rate of CN _X coating on ball (W _b), which could give stable and low friction coefficient (<0.05), was below 3.0 × 10^?8 mm³/Nm. Average friction coefficients (µ _a) and W _b of CN _X /CN _X increased (µ _a: 0.02–0.33, W _b: 1.6 × 10^?8–2.4 × 10^?7 mm³/Nm) with increasing oxygen concentration (230–211,000 ppm) as well as RH (4.7–21.1%RH) under a nitrogen atmosphere. However, the W _b remained low value below 2.3 × 10^?8 mm³/Nm regardless of oxygen concentration (100–207,000 ppm) of a nitrogen atmosphere (3.4–3.9%RH) when CN _X -coated balls were slid against a hydrogenated CN _X (CN _X :H) coatings (CN _X /CN _X :H). Besides, the CN _X /CN _X :H achieved low and stable friction coefficient below 0.05 under a nitrogen atmosphere (10,000 ppmO₂) regardless of increasing RH up to 20%RH. Raman analysis indicated that the structure of carbon on the top surface of CN _X coating was changed from as-deposited CN _X coating in the case of low friction coefficient (<0.05). Furthermore, TOF-SIMS analysis provided the evidence that the carbon derived from CN _X -coated disk was considered to diffuse into the ball surface, and it mixed with the carbon derived from CN _X -coated ball on the wear scar, which formed the chemically bonded carbon tribo-layer. Low friction coefficient (<0.05) with CN _X coatings under a nitrogen atmosphere was achieved due to self-formation of the carbon tribo-layer.     

Measurements of the solidification point of the GKGh-136 silicone liquid

Two methods for measuring solidification point T _S of the GKGh-136 silicone liquid are described. T _S ≌ 125 K is determined by the first method from specific features of the temperature dependence of the resistance of an organic quasi-2D conductor in a GKGh-136 droplet with a size of ～1 mm. T _S ≌ 130 K is assessed by the second method from the occurrence of a specific feature in the temperature dependence of the resistance of the GKGh-136 and fine-dispersed graphite mixture, which is caused by desorption of helium in the sample volume during warming-up >T _S .     

A Neutron Spectrometer for Experiments with Radioactive Beams on the ACCULINNA-2 Fragment Separator

A neutron spectrometer based on stilbene crystals has been developed by the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research (Dubna, Russia). The timing resolution is determined as a function of the signal amplitude (σT = 0.18 ns at an amplitude of 1 MeV in the electron equivalent). The measured energy resolution of the detecting modules for γ rays is σE/E = 4.5% at E = 1 MeV. The quality of the n–γ discrimination is investigated. It is shown that reliable discrimination is possible, beginning with a deposited energy of 100 keV in the electron equivalent, which corresponds to the kinetic energy of recoil protons of ～700 keV. The neutron spectrometer helps to significantly expand the experimental capabilities and to carry out correlation experiments with radioactive beams on the ACCULINNA-2 fragment separator at a new level of quality.     

Multichannel linear detector for x-ray spectroscopy

This paper considers a new linear multichannel x-ray detector designed on the basis of a BLPP-369M4 silicon photodiode array (2612 photodiodes, array pitch 12.5 µm, height 4 mm, and dynamic range 10⁴). The structure and characteristics of the multichannel detector are given, along with the Kα1,2, Kβ ₁, and Kβ ₅ x-ray emission lines and a K-edge absorption spectrum of metallic copper recorded on a universal URS-2I spectrometer using this detector. The resolution and the signal/noise ratio of these spectra are superior to those of spectra recorded by an SRPP-21 gas ionization counter at the same recording time. The detector has a spatial resolution of 20 µm and an x-ray detection limit to equal 1 quantum at λ = 1.54 Å. It is suitable for studying the fine structure of absorption spectra at 1–10 Å.     

Fast-response thermistors made of synthetic single-crystal diamonds

Miniature thermistors are produced from boron-doped synthetic single-crystal diamonds grown under pressure using the thermal gradient method. It is shown that heavily doped diamonds with a boron concentration of 10¹⁹ cm^?3 or higher are most suitable for this purpose. In the temperature range of 300–700 K, coefficient β = ln(R ₁/R ₂)/(1/T ₁ ? 1/T ₂) is 2500 K. The characteristic response time of temperature-sensitive elements based on crystals with dimensions of 1 × 1 × 0.3 mm is ～100 µs; i.e., they can be used in monitoring systems with a response speed of up to 10 kHz.     

Quantitative X-ray analysis for Cr–Fe binary ferroalloys by using EDXRF−WDXRF techniques

Quantitative analysis of materials is significant for its potential usage in different areas. In the present study, quantitative analysis for Fe–Cr binary ferroalloys was evaluated by using Energy Dispersive X-Ray Fluorescence (EDXRF) system and the classical α-coefficient equation. The ferroalloys were prepared from powder form of Fe and Cr elements. The ferroalloys were excited by 59.54 keV γ-rays from ²⁴¹Am annular radioactive source in EDXRF and K _α X-ray fluorescence spectra of Fe were analyzed in the binary matrices for determining analyte element Fe. Also, Wavelength Dispersive X-Ray Fluorescence (WDXRF) system was used to compare the concentrations of the analyte. The agreement was found to be quite satisfactory between the EDXRF and WDXRF (≤1.76 relative difference (%) between concentrations), and it should be noted that the classical α-coefficient equation is highly reliable approach for quantitative analysis of ferroalloys. In addition, effective atomic numbers (Z _eff ) of alloys were calculated using scattering ratio (R/C) method and fitted to concentrations obtained of alloys for fit equation.     

On the possibility of observing low-intensity spectral lines of internal conversion electrons using the MAC-1 setup

Results of upgrading of MAC-1 setup components are described. It is shown that the optimum conditions for detection of low-intensity spectral lines are ensured by the high sensitivity of the instrument to gradations of photoemulsion blackening and by the high resolution of the optoelectronic channel that forms the image of emulsion grains, in combination with the possibility of varying the spectrogram scanning modes, which has been provided by the upgrading. The upgrading of the instrument opens up new avenues for spectroscopy of internal conversion electrons if sufficient statistics is acquired in an experiment. The efficiency of the proposed procedures is demonstrated by the example of extraction of low-intensity K672.35 ¹⁶⁰Dy and K673.09 ¹⁶⁰Dy lines in a spectrogram of internal conversion electrons from erbium fractions.     

High-power sources of ultra-wideband radiation with subnanosecond pulse lengths

Sources of high-power ultra-wideband electromagnetic pulses of nanosecond duration are described. A bipolar voltage pulse with a length of 0.5 ns and an amplitude of ～200 kV is fed to the input of a radiating system (a 16-element array antenna or a single antenna). The values of the effective radiation potential E _p R = 260 kV for a source with a single antenna and E _p R = 690 kV for a source with a 16-element antenna array were obtained at a pulse repetition frequency of 100 Hz.     

Numerical and experimental method for the prediction of the propagation life of fatigue crack on metallic materials

A prediction method for the propagation life of fatigue crack for cracked components was provided and verified in this study to predict the propagation life of fatigue cracks on components in engineering applications conveniently and directly. In the simulation aspect, a finite element (FE) model of cracked specimen was created to obtain the stress intensity factor range ΔK. The FE model was verified by comparing simulated ΔK to a formulary calculated one. The simulated ΔK could be used for studying the relationship with crack size. In the experimental aspect, the fatigue crack propagation test was conducted on three specimens. The material coefficients C and m were fitted according to Paris’ law. The load cycles with different crack depths were recorded in the testing process. The propagation life of fatigue cracks of specimen was predicted via the relationship between ΔK and crack size a according to Paris’ law. The comparison between predicted life and experimental life of specimens indicated the feasibility of the method. The proposed prediction method in this study for the propagation life of fatigue cracks can be used in engineering applications.     

A Dispersion Interferometer Based on a CO<Subscript>2</Subscript> Laser

A double-pass dispersion interferometer based on a 9.6-μm CO₂ laser with a sensitivity of 〈 n _e l〉_min ∼ 1 × 10¹³ cm⁻² and a temporal resolution of ∼50 μ s, designed to measure linear plasma density, is described. A ZnGeP₂ nonlinear crystal is used as the frequency doubler. The main advantages of the interferometer are its compactness and a low sensitivity to vibrations of optical elements. The interferometer requires no special vibration isolation. Its main components are arranged compactly on an optical bench outside the apparatus, except for a window for radiation injection and a retroreflector; these are mounted on the wall of the experimental facility's vacuum chamber. The advantages of the dispersion interferometer have been demonstrated in an experiment with a gas-dynamic trap. __________ Translated from Pribory i Tekhnika Eksperimenta, No. 5, 2005, pp. 96–106. Original Russian Text Copyright ? 2005 by Solomakhin, Bagryanskii, Voskoboinikov, Zubarev, Kvashnin, Lizunov, Maksimov, Khil'chenko.     

Experimental investigation of the preferred Strouhal number used in self-resonating pulsed waterjet

Self-resonating pulsed waterjet (SRPW) is superior to plain waterjet in many ways and is being employed in numerous applications. To further improve the performance of SRPW, the optimal value of the preferred Strouhal number (S_d), which is used to determine the chamber length of a self-resonating nozzle, was experimentally studied at inlet pressures of 10 MPa and 20 MPa. The axial pressure oscillation peak and amplitude were used to evaluate the performance of SRPW, in order to find the optimum S_d value. Results show that S_d value determines the self-resonance behavior of an organ-pipe nozzle and greatly affects the intensity of the axial pressure oscillation. Under the experimental conditions, the optimum S_d values are 0.315 and 0.278 respectively, corresponding to inlet pressures of 10 MPa and 20 MPa. Compared with the default value of 0.3 obtained from air jet experiment, the optimum S_d value at inlet pressure of 10 MPa is a little larger and oppositely a bit smaller at inlet pressure of 20 MPa. Thus, if the inlet pressure is not considered, S_d value of 0.3 is reasonable for determining the chamber length of a self-resonating nozzle for generating effective SRPW.