Creep crack growth analysis using <Emphasis Type="Italic">C</Emphasis><Subscript><Emphasis Type="Italic">t</Emphasis></Subscript>-parameter for internal circumferential and external axial surface cracks in a pressurized cylinder

Creep crack growth at elevated temperatures is a critical consideration in estimating the remaining life of high temperature structural components and in deciding their inspection interval. In this study, creep crack growth analyses for external radial-axial and internal radial-circumferential surface cracks in a pressurized cylinder were conducted by an analytical method. The effect of crack depth and crack length on the variations in C _t and remaining life predictions were investigated for surface cracks with various initial aspect ratios. It was observed that the remaining life of an internal radial-circumferential surface crack was approximately 53 times longer than that of an external radial-axial surface crack for the same crack size and loading conditions with 316 stainless steel material. It was also observed that the variations in remaining life, crack propagations, and the C _t values were considerably sensitive to the crack location and crack depth. Convergence of crack aspect ratio was not observed when the crack depth ratio was increased. Since the method is independent of material properties and location of the crack geometries, it can be extended to various material properties and various locations of the surface crack geometries.     

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.     

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).     

Nonparametric estimation of a probability density function and its derivatives. <Emphasis Type="Italic">C</Emphasis>-approach

Nonparametric (kernel) estimation of a probability density function f(x) for a sample of finite size is considered using the C-approach. The smoothness parameter β of the estimated probability density is introduced. For the case β > 2, it is shown that the convergence of the density estimate f _n (x) to the function f(x) can be improved by using alternating-sign weight functions (higher-order weight functions). Estimation of the derivatives of a function is briefly considered using the same approach.     

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.     

Nonparametric estimation of a density and its derivatives: The <Emphasis Type="Italic">L</Emphasis><Subscript>2</Subscript>-approach

The nonparametric estimates of a density and its derivatives are considered within the scope of the L ₂-approach. New sets of weight functions with a bounded support are proposed for constructing admissible (unimprovable in the space metric L ₂(?∞, ∞)) estimates of the density itself and its derivatives to the third order, inclusive.     

Molecular beam epitaxy of BaF<Subscript>2</Subscript>/CaF<Subscript>2</Subscript> buffer layers on the Si(100) substrate for monolithic photoreceivers

This paper describes the study of the surface morphology of BaF2 epitaxial films grown by means of molecular beam epitaxy in various growth regimes on a CaF₂/Si(100) surface, which is performed by means of atomic force microscopy. The CaF₂ layers were obtained on a Si(100) substrate in a low-temperature growth regime (T _s = 500 °C). The technological regimes of growth of BaF₂ continuous films with a smooth surface on CaF₂/Si(100), suitable as buffer layers for the subsequent growth of PbSnTe layers or other semiconductors, such as A₄B₆, and solid solutions based on them.     

Multi-color space threshold segmentation and self-learning <Emphasis Type="Italic">k</Emphasis>-NN algorithm for surge test EUT status identification

The identification of targets varies in different surge tests. A multi-color space threshold segmentation and self-learning k-nearest neighbor algorithm (k-NN) for equipment under test status identification was proposed after using feature matching to identify equipment status had to train new patterns every time before testing. First, color space (L*a*b*, hue saturation lightness (HSL), hue saturation value (HSV)) to segment was selected according to the high luminance points ratio and white luminance points ratio of the image. Second, the unknown class sample S _r was classified by the k-NN algorithm with training set T _z according to the feature vector, which was formed from number of pixels, eccentricity ratio, compactness ratio, and Euler’s numbers. Last, while the classification confidence coefficient equaled k, made S _r as one sample of pre-training set T _z ′. The training set T _z increased to T _z+1 by T _z ′ if T _z ′ was saturated. In nine series of illuminant, indicator light, screen, and disturbances samples (a total of 21600 frames), the algorithm had a 98.65%identification accuracy, also selected five groups of samples to enlarge the training set from T ₀ to T ₅ by itself.     

Spectroscopy of Single AlInAs Quantum Dots

A system of quantum dots based on Al _x In_1?xAs/Al _y Ga_1?yAs solid solutions is investigated. The use of Al _x In_1?xAs wide-gap solid solutions as the basis of quantum dots substantially extends the spectral emission range to the short-wavelength region, including the wavelength region near 770 nm, which is of interest for the development of aerospace systems of quantum cryptography. The optical characteristics of Al _x In_1?xAs single quantum dots grown by the Stranski–Krastanov mechanism were studied by cryogenic microphotoluminescence. The statistics of the emission of single quantum dot excitons was studied using a Hanbury Brown–Twiss interferometer. The pair photon correlation function indicates the sub-Poissonian nature of the emission statistics, which directly confirms the possibility of developing single-photon emitters based on Al _x In_1?xAs quantum dots. The fine structure of quantum dot exciton states was investigated at wavelengths near 770 nm. The splitting of the exciton states is found to be similar to the natural width of exciton lines, which is of great interest for the development of entangled photon pair emitters based on Al _x In_1?xAs quantum dots.     

Features of the <Superscript>85</Superscript>Rb Spectrum in a Cell with an Antirelaxation Coating

Distortion of the spectrum of the D₁-line of ⁸⁵Rb in optical cells with an antirelaxation coating on the inner walls of the cell is studied. The spectrum shape is found to be significantly dependent on the velocity and direction of changes in the laser frequency. A physical explanation is provided for these features, which are confirmed by numerical simulations. The effect of the magnetic field on the spectrum shape is discussed.     

Peculiarities of admittance in MOS structures based on MBE-grown MCT layers

Admittance of MOS structures based on Hg_1?x Cd _x Te layers grown by molecular beam epitaxy on semi-insulating GaAs substrates is studied. Effect of anomalous generation on the Hg_1?x Cd _x Te surface in a strong electric field (≈10⁵ V/cm) is found. It is shown that the density of surface states of the MCT — SiO₂ interface depends weakly on the presence of the graded energy-gap layer and the type of semiconductor admittance.     

Method for determining critical pressure in assembling hybrid MCT focal plane arrays

A simple method is proposed for determining the critical pressure that does not destroy Cd _x Hg_1?x Te diodes in hybrid assembling. The method allows obtaining a set of data that reliably define the critical parameter (the value of force) of the flip-chip hybrid FPA process. The method was tested on Cd _x Hg_1?x Te samples (x = 0.21). It is found that the abrupt change in the electrophysical properties of the material occurs when the diameter of indium bumps increases 2 times and more during compression at a pressure of about 3 kg/mm². The obtained gage load/bump deformation dependences show that this pressure corresponds to the beginning of the region of indium strengthening on the deformation curve.     

Adatom concentration distribution on an extrawide Si(111) terrace during sublimation

The formation of an adsorption layer on the Si(111) surface during sublimation at temperatures of 1000–1100 °C and subsequent quenching at T = 750 °C is studied by methods of in situ ultrahigh-vacuum reflection electron microscopy and ex situ atomic force microscopy. The adatom concentration distribution on an extrawide (~60 μm) atomically flat terrace is determined for the first time, and the diffusion length x_s = 31±2 μm at T = 1000 °C is obtained. The analysis of the temperature dependence of the equilibrium concentration of adatoms near a monatomic step allows pioneering measurements of the energy necessary for adatom detachment from the step and attachment to the terrace E _ad ≈ 0.68 eV. Based on these results, the energy parameters for some atomic processes on the Si(111) surface are estimated.     

Cutting performance of Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/TiC micro-nanocomposite ceramic tool in dry machining of hardened steel

A type of Si₃N₄/TiC micro-nanocomposite ceramic cutting tool material was fabricated using Si₃N₄ micro-matrix with Si₃N₄ and TiC nanoparticles. Cutting performance of the Si₃N₄/TiC ceramic cutting tool in dry cutting of hardened steel was investigated in comparison with a commercial Sialon insert. Hard turning experiments were carried out at three different cutting speeds, namely 97, 114, and 156 m/min. Feed rate (f) and depth of cut (a _p) were fixed at 0.1 mm/rev and 0.2 mm, respectively. Results showed that cutting temperature increased rapidly to nearly 1000 °C with increasing cutting speed. The two types of cutting tools featured similar wear behavior. However, the Si₃N₄/TiC micro-nanocomposite ceramic cutting tool exhibited better wear resistance than the Sialon tool. Morphologies of crater and flank wear were observed with a scanning electron microscope. Results indicated that wear variation of the two types of ceramic cutting tools differed in the same conditions. Wear of the Si₃N₄/TiC micro-nanocomposite ceramic cutting tool is mainly dominated by abrasion and adhesion, whereas that of the Sialon ceramic cutting tool is dominated by abrasion, adhesion, thermal shock cracking, and flaking.     

Investigating the 1/<Emphasis Type="Italic">z</Emphasis><Superscript>2</Superscript>-filtering in tomography algorithms

The filtering of projections in tomography algorithms, which is based on the regularization of distribution 1/z ², is investigated. Numerical simulations validate that changing the filter support will substantially improve the tomograms. Comparison of the results of reconstruction by the 1/z ²-filtering algorithm and the Shepp-Logan algorithm shows that the reconstruction accuracy of the latter is worse when the number of angles of observation is small or a high noise is present in the projection data.     

Identification of patterns of a parametrically specified class

A problem of detecting a set of functions of the F(x, α) type in signals with noise, interferences, and distortions, i.e., identifying a class of patterns, is solved. During signal processing, the amplitude and parameter α_opt of the found pattern are determined. A method for estimating the uncertainty (error) of the pattern characteristics is proposed. Numerical experiments for identifying classes of functions that demonstrate the efficiency of this approach are described.     

Single-Frequency TEA CO<Subscript>2</Subscript> Laser for Experiments on Non-Resonant Radiation Interaction with Matter

The design philosophy and output radiation parameters of single frequency TEA CO₂ laser with bleaching intracavity longitudinal modes selector (cell filled with SF₆) are described. At cavity tuning to 10P(16) line and choosing optimum SF₆ pressure in the cell the stable single frequency lasing is realized with scatter of radiation peak power in a series of “shots” less than ±7% of average value. The radiation energy density and intensity gradually tuned in the ranges 0.36–12.5 J/cm² and 2.9–100 MW/cm² correspondingly were realized in the focal plane of a lens with f = 127 mm.     

Control of the optical properties of a CaCO<Subscript>3</Subscript> crystal in problems of generating bessel vortex beams by heating

The transformation of zero-order Bessel beams to a second-order Bessel vortex beam in a c-cut CaCO₃ crystal has been studied experimentally. It has been shown that it is possible to control the beam transformation in the crystal during heating. The influence of the thermo-optic effect and the linear thermal expansion of the crystal on the transformation of the Bessel beam is explained.     

Vibration response analysis caused by rubbing between rotating blade and casing

Two types of blade-tip rubbing due to the static misalignment of the bladed-disk center and casing center and casing deformation are simulated. By applying aerodynamic load in the blade lateral/flexural direction, vibration responses due to blade-casing rubbing are analyzed under the run-up process with constant angular acceleration and the steady-state process at 10000 rev/min. The effects of some parameters, such as the static misalignment e _c, casing stiffness k _c and casing deformation n _p, on the system vibration responses are also illustrated by spectrum cascades, time-domain waveforms of displacement, normal rubbing forces, amplitude spectra and the impulse P in a single blade-casing rubbing period. The results show that blade-tip rubbing will cause amplitude amplification and harmonic resonance phenomena when the multiple frequencies (nf _r) of rotational frequency (f _r) coincide with the first three flexural dynamic frequencies of the blade (f _n1, f _n2 and f _n3). For example, the displacement amplitudes at 3f _r, 14f _r and 38f _r are large and the vibration is dominant near f _n1. In addition, the casing deformation mainly excites the dominant Blade passing frequency (BPF), which is related to the casing deformation coefficient n _p. By comparing these impulse values, for the selected parameters in this paper, the casing stiffness has a greater effect on impulse than the static misalignment and casing deformation coefficient. The impulse shows a linear increase trend with the increasing static misalignment, and it decreases under the large n _p because the contact time decreases with the increase of n _p.     

Determining electrophysical characteristics of metal-oxide-semiconductor structures from the data of voltage-capacitance analysis of the depletion region of a semiconductor surface

The oxide layer in nanotransistors with metal-oxide-semiconductor (MOS) structures may be as thin as 20Å. The physical diagnostics of such structures via conventional methods of voltage-capacitance characteristics (VFCs) is impossible without taking into account the usually disregarded effects of degeneracy and dimensional quantization of the electron gas. However, as the oxide-layer thickness decreases, these effects make an increasingly substantial contribution to capacitance C of the MOS structure not only at C?C _i (where C _i is the “oxide capacitance”) but also at C < C _i . In this study, we have developed a general method for determining the principal characteristics of MOS structures from the data of analysis of the VFCs in the region of the Schottky depletion layer. The doping level, the surface potential, the semiconductor surface charge, the voltage of “flat bands,” oxide capacitance C _i , the voltage drop across the oxide, and the sign and density of the charge fixed in it can be found at an accuracy of ?0.1% within the framework of a single experiment regardless of the oxide-layer thickness and without using fitting parameters and a priori assumptions concerning the properties of the electron gas in the accumulation and inversion layers. The stages and results of the implementation of this method are demonstrated by the results of experiments performed on an n-Si-based MOS structure with a 171.2 Å-thick oxide layer.