Ion milling-assisted study of defect structure of HgCdTe films grown by liquid phase epitaxy

Ion milling, as a tool for “stirring” defects in HgCdTe by injecting high concentration of interstitial mercury atoms, was used for studying films grown by liquid phase epitaxy (LPE) on CdZnTe substrates. The films appeared to have very low residual donor concentration (∼10¹⁴ cm⁻³), yet, similar to the material grown by molecular beam epitaxy, contained Te-related neutral defects, which the milling activated electrically. It is shown that ion milling has a stronger effect on HgCdTe defect structure than thermal treatment, and yet eventually brings the material to an “equilibrium” state with defect concentration lower than that after low-temperature annealing.     

Optical breakdown threshold in the electron-thermal model of defect generation

An investigation is made of the conditions for the nucleation of optical breakdown in transparent material when recombination-stimulated defect-formation reactions occur in it. It is shown that a positive feedback between the conduction electron concentration and point defects activates defect formation even if the medium is not heated. Under real conditions, where heating of the medium by the light is important, lowering of the activation barrier by thermal defect generation aided by conduction electrons results in optical breakdown of the medium at light intensities much lower than predicted in the classical “semiconductor” or “thermochemical” models of thermal breakdown. The analysis confirms that optical breakdown of transparent condensed media is due to electron-aided defect formation reactions over a broad range of illumination conditions. Zh. Tekh. Fiz. 67, 48–53 (May 1997)     

Reconstruction of size and depth of simulated defects in austenitic steel plate using pulsed infrared thermography

In this paper the size and depth (distance from the tested surface) of defects in austenitic steel were estimated using pulse infrared thermography. The thermal contrast calculated from the surface distribution of the temperature is dependent on both these parameters. Thus, two independent experimental methods of defect size and depth determination were proposed. The defect size was estimated on the basis of surface distribution of the time derivative of the temperature, whereas the defect depth was assessed from the dependence of surface thermal contrast vs. cooling time.     

Energetic and thermal performance of high-gain diode-side-pumped Nd:YAG rods

We investigated the energetic and thermal performance of a diode-side-pumped Nd:YAG rod laser with up to 50 W power deposited as excess heat into a 3-mm-diameter, 10-cm-length rod. The rod design produces an extremely flat gain profile resulting in “textbook” expressions of thermal lensing and birefringence. Thermal and energetic measurements are compared to corresponding “textbook” theoretical expressions. Discrepancies between various published thermo-mechanical YAG parameters are resolved by a self-consistent set of measured and calculated data for rod thermal lens focal lengths, birefringence depolarization and ratio of heat to stored energy (χ). Measured thermal and energetic performance under lasing and nonlasing conditions are presented, which agree with published theoretical expressions and measurements. Compensation of rod thermal lensing with simple spherical concave lenses is demonstrated. In addition various methods for compensating birefringence depolarization are theoretically and experimentally analyzed and compared. Received: 19 July 1999 / Revised version: 22 October 1999 / Published online: 23 February 2000     

A new method for determination of satellite orbits by transfer

The original idea of a new method for determination of satellite orbits by transfer is from Two-Way Satellite Time and Frequency Transfer (TWSTFT). The original method is called “determination of satellite orbit by transfer”. The method is not only for determination of satellite orbit but also for the time transfer with high accuracy and precision. The advantage is that the accuracy and the precision for determination of satellite orbit are very high and the new method is favorable for various applications. The combination of various signals disseminated and received forms various modes of satellite orbit determinations. If receivers at stations receive the own station-disseminated signals via a satellite transponder, it forms an orbit determination mode called “receiving the own station-disseminated signals mode”. If receivers at all stations receive the signals disseminated from the master station via satellite transponders, it forms an orbit determination mode called “receiving the master station-disseminated signals mode”. If all of receivers at stations receive all stations-disseminated signals via satellite transponders, it forms an orbit determination mode called “receiving all stations-disseminated signals mode”. Also there are other combinations of signals for satellite orbit determination. For different orbit determination modes with different signal combinations, their rigorous formulae of processing are hereby presented in this paper. The accurate and the precise satellite orbit determination for both of the modes, “receiving the own station-disseminated signals mode” and “receiving the master station-disseminated signals mode” is attempted. It shows that the accuracy and precision for both of modes are nearly the same, the ranging accuracy is better than 1 cm, and the observation residuals of satellite orbit determination are better than 9 cm in the observation duration of 1 day. Supported by the National Basic Research and Development Program of China (Grant No. 2007CB815503100453001)     

亚表面双球孔洞的热波散射与温度分布

基于非Fourier热传导方程,采用波函数展开法,对含双球形孔洞缺陷的半无限体材料内部的热波散射与温度分布进行了研究,给出了材料内部任一点温度的解析解和表面温度分布的数值计算结果。分析了孔洞的几何参数和物理参数对金属材料表面温度分布的影响。结果表明:相对热扩散长度、入射波波数和埋藏深度对表面温度分布的影响比较大,当孔洞间距较大时,可以忽略孔洞之间的热波散射。     

Analysis of the accuracy of a neural algorithm for defect depth estimation using PCA processing from active thermography data

In the paper a neural algorithm, which uses an active thermography for defect depth estimation, is presented. Simulations of the algorithm, for three datasets representing different phases of the heat transfer process developing in the test sample were performed. The influence of the emissivity error of the test sample surface on the accuracy of defect depth estimation is discussed. The investigations were performed for test sample made of the material with low thermal diffusivity.     

Experimental study and mathematical modelling of heat transfer processes in heat accumulating media

Experimental results on reversing non-stationary heat transfer are presented for filtration of an air flow through an immobile heat accumulating medium consisting of lead (D = 2.0, 3.5, and 4.5 mm) and glass (D = 3.2 mm) balls. The studied device imitated the cyclic modes of heat regeneration in the ventilation system for domestic and office rooms. Dependency between the time of flow switching and Re number was measured. The mathematical model describing heat transfer between a gas flow and an immobile layer of balls was developed. Good correspondence between the experimental data and calculation results is observed for high Reynolds numbers. For low Re numbers the effect of heat losses is considerable, and experimental time of flow switching is shorter than the calculation one. The work was financially supported by the President of the Russian Federation (Grant No. NSh 6526.2006.3), Russian Foundation for Basic Research (Grant No. 06-08-00982), Foundation “Global energy” and Program “Energy saving of SB RAS”.     

Size determination of subsurface defect by active thermography – Simulation research

This paper presents the results of 3D numerical simulations of thermal phenomena in uniform material with subsurface defect located at some depth. The material is aimed to be tested by means of IR active thermography. The temperature field of the front surface of material tested is observed and analysed. The results of modelling are suitable for step heating as an external thermal stimulation – heat flux. The heating duration needed for accurately defect sizing is discussed. Also, an effect of two defects with different thermal properties and simultaneously occurring in the material tested is analysed.     

Acoustic wave propagation in fluid metamaterial with solid inclusions

Acoustic wave propagation in a composite of water with embedded double-layered silicone resin/silver rods is considered. Approximate values of effective dynamical constitutive parameters are obtained. Frequency ranges of simultaneous negative constitutive parameters are found. Localized surface states on the interface between metamaterial and “normal” material are found. The Doppler effect in metamaterial is considered. The presence of anomalous modes is shown.     

Cold processing of green state LTCC with a CO2 laser

We report a novel “cold” self-cleaning technique for processing low temperature co-fired ceramic (LTCC) in the “green” state at high resolution and high speed, using a low power carbon dioxide laser. A particle ejection process involving both the ceramic grains and the organic binder produces material removal rates of >100 μm per pulse with lateral processing resolution of 50 μm and depth resolution comparable to ceramic grain size with no heat-effected zone or other deleterious thermal effects. The process has been used to drill microvias and to machine arbitrary shapes with high resolution. PACS 79.20.Ds; 42.62.Cf; 42.55.Lt; 81.20.Wk     

Stability of a thermal boundary layer in the presence of vibration in weightlessness environment

Several weightless experiment with supercritical fluids have shown that thermal boundary layers can be destabilized when submitted to a harmonic vibration. A study of the phenomenon is given here in a regular fluid during a sudden change of wall temperature in the presence of harmonic tangential vibrations and under weightlessness. A semi-infinite space is filled with a fluid and bounded by a flat wall oscillating in its plane. For this configuration, a state with the fluid velocity parallel to the wall is possible but this fluid motion does not influence the heat transfer. Then the propagation of thermal waves can be described by classical relations. The stability of this state is studied under the assumption of a “frozen” temperature profile. The vibration frequency is assumed to be high such that the viscous boundary layer thickness is small in comparison with the thermal boundary layer thickness. The calculations show that the instability develops when the thickness of the thermal boundary layer attains a critical value. The wavelength of the most dangerous perturbations is found to be about twice the critical thermal boundary layer thickness.     

Second sound and heat conduction of magnons in the ferromagnetic Eu-chalcogenides

The various relaxation times of the thermal magnons in the ferromagnetic Eu-chalcogenides are calculated for temperatures well below the Curie point, and the conditions for the existence of magnon second sound and magnon heat conduction are examined. It is found that for EuS the “frequency window” for magnon second sound exists around 2 MHz at temperatures of about 1 K. In the same material the magnon contribution to the static thermal conductivity should be measurable at temperatures between 1 K and 2 K. Supported in part by the Fonds National Suisse de la Recherche Scientifique.     

Determination of thermal wave reflection coefficient to better estimate defect depth using pulsed thermography

Thermography is a promising method for detecting subsurface defects, but accurate measurement of defect depth is still a big challenge because thermographic signals are typically corrupted by imaging noise and affected by 3D heat conduction. Existing methods based on numerical models are susceptible to signal noise and methods based on analytical models require rigorous assumptions that usually cannot be satisfied in practical applications. This paper presents a new method to improve the measurement accuracy of subsurface defect depth through determining the thermal wave reflection coefficient directly from observed data that is usually assumed to be pre-known. This target is achieved through introducing a new heat transfer model that includes multiple physical parameters to better describe the observed thermal behaviour in pulsed thermographic inspection. Numerical simulations are used to evaluate the performance of the proposed method against four selected state-of-the-art methods. Results show that the accuracy of depth measurement has been improved up to 10% when noise level is high and thermal wave reflection coefficients is low. The feasibility of the proposed method in real data is also validated through a case study on characterising flat-bottom holes in carbon fibre reinforced polymer (CFRP) laminates which has a wide application in various sectors of industry.     

Radiation-induced defects and their complexes in ion-irradiated thermostable dielectrics

The parameters of defects of radiation-induced and biographic types and of their complexes in boron nitride andAl ₂O₃ mono- and polycrystals after ion and thermal modification are investigated invoking the methods of optical and thermoactivation spectroscopy. The influence of electron transitions involving defect energy levels on changes in the electrophysical and optical properties of modified dielectrics is recognized. The contribution of the forbidden band width and of the material structure to changes in the properties of defect clusters with continuous spectra of energy levels and of separate radiation-induced point-type defects with local energy levels is evaluated. The stability of defects with various energy spectra under thermal, field, and photoexcitation and also after heat treatment in air is evaluated. The most probable nature of vacancy and impurity-vacancy defects and of vacancy complexes is understood. Scientific-Research Institute of High Voltages at Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 85–94, March, 2000.     

含双圆柱亚表面缺陷板条材料的表面温度分布

基于非傅里叶热传导方程,采用复变函数法和镜像法,研究了含双圆柱亚表面缺陷板条材料热波散射的温度场,并给出了热波散射温度场的解析解。分析了入射波波数、热扩散长度、缺陷的埋藏深度以及板条材料的厚度等对板条表面温度分布的影响。温度波由调制光束在材料表面激发,缺陷表面的边界条件为绝热。该分析方法和数值结果可为工程材料结构的传热分析、热波成像和材料内部缺陷评估,以及热物理反问题研究提供参考。     

A numerical study of energy transfer mechanisms in materials following irradiation by swift heavy ions

Swift heavy ions interact with electrons in materials and this may yield permanent atomic displacements; the energy transfer mechanisms that bring electronic excitations into atomic motion are not fully understood, and are generally discussed in terms of two theories, viz. Coulomb explosion and heat exchange between excited electrons and atoms, which is limited by electron-phonon coupling. We address this problem for a “generic” material using a semi-classical numerical approach where the dynamics of the evolving electron density is calculated by using molecular dynamics simulations applied to pseudo-electrons. The forces exerted on the nuclei are then used to calculated the trajectories of the nuclei. From the temporal evolution of the atomic kinetic energy, we find that the energy transfer between the electrons and the nuclei can be divided in two parts. First, a Coulomb heating starts the motion of the atoms by giving them a radial speed; this process differs from Coulomb explosion because the atoms are not displaced over interatomic distances. Second, a thermal energy transfer, as described in linear transport theory, takes place. Our study thus confirms the domination of thermal energy exchange mechanisms over Coulomb explosion models.     

Oblique Sounding and Modeling of the Ionospheric HF Channel

We present the results of experimental studies of the distance-frequency and amplitude-frequency characteristics of the ionospheric HF channel on mid-latitude paths of oblique chirp sounding. It is shown that the maximum observed frequencies (MOFs) are subject to short-period variations with the quasi-periods from 30 min to 2 h.The amplitude of the MOF variations reaches 2 MHz and can increase up to 5–8 MHz on the Cyprus—Rostov-on-Don one-hop path in the sunrise-sunset time. It is established that the MOF fluctuations are accompanied by pronounced “cusp” features occurring in the upper rays and moving with time to the region of shorter delays, i.e., from lower to higher frequencies. The amplitude-frequency characteristics of individual propagation modes undergo deep fluctuations (up to 20–30 dB)whose quasi-period and depth depend on the frequency. It is shown that the appearance of fluctuations is caused by interference of the unresolved rays within the limits of one propagation mode. Based on the modeling, it is shown that “cusps” in oblique-sounding ionograms are due to the influence of traveling ionospheric disturbances (TIDs). The TID parameters are estimated. It is shown that conditions of the formation of “ cusps” in the distance-frequency characteristics depend on the TID amplitude, the wavelength of the disturbance wave, and the direction of its phase front with respect to the propagation path. The effect of quasi-regular frequency modulation of the Pedersen mode with a period of 250–300 kHz on the Cyprus-Rostov-on-Don chirp-sounding path is found. Altitude stratification of the ionosphere near the F-layer maximum, which is responsible for the focusing and defocusing of the Pedersen mode, is estimated. It is established that the stratification scale amounts to approximately 200–250 m. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 6, pp.455–471, June 2005.     

A Fast Algorithm for Wave Propagation from a Plane or a Cylindrical Surface

The newly developed Taylor-Interpolation-FFT (TI-FFT) algorithm dramatically increases the computational speeds for millimeter wave propagation from a planar (cylindrical) surface onto a “quasi-planar” (“quasi-cylindrical”) surface. Two different scenarios are considered in this article: the planar TI-FFT is for the computation of the wave propagation from a plane onto a “quasi-planar” surface and the cylindrical TI-FFT is for the computation of wave propagation from a cylindrical surface onto a “quasi-cylindrical” surface. Due to the use of the FFT, the TI-FFT algorithm has a computational complexity of O(N ² log₂  N ²) for an N × N computational grid, instead of N ⁴ for the direct integration method. The TI-FFT algorithm has a low sampling rate according to the Nyquist sampling theorem. The algorithm has accuracy down to −80 dB and it works particularly well for narrow-band fields and “quasi-planar” (“quasi-cylindrical”) surfaces.