On the heating modulation frequency dependence of the photopyroelectric signal in experiments for liquid thermal characterization

A pyroelectric sensor can be seen as a layered system consisted on a pyroelectric material sandwiched between two thin metal layers acting as electrical contacts for measurements of the voltage drop that can be induced by heating. This kind of sensor can be used as a detector of electromagnetic radiation but also for thermal characterization of materials using the photopyroelectric technique. In this work we perform a theoretical analysis based in the so-called thermal wave approach to show that, when this sensor is heated periodically by the absorption of intensity modulated light by one of the metalized surfaces, while the other metal surface is in contact with a liquid sample, the resulting pyroelectric voltage signal amplitude enhances respecting the one resulting from the bare sensor, for certain values of the modulation frequency. This contradicts the intuitively expectation based in the assumption that the sample provides a new channel for heat conduction, thereby decreasing the pyroelectric temperature. We will show that the back and forth propagation and the superposition of thermal waves through the metal coatings must be taken into account in order to explain the observed behavior. The proposed model was experimentally tested for water and glycerin samples, and using a polyvinylidene difluoride (PVDF) polymer film, with Ni–Cu metal electrodes, as a pyroelectric sensor.     

Cyclotron resonance masers: State of the art

Cyclotron resonance masers, gyrotrons and gyroklystrons, are dominant high-energy sources at millimeter wavelengths and still have considerable margins of power and efficiency. The present-day challenge of creating CW megawatt gyrotrons is associated with many problems, among which the output window problem is a key one. New results of the investigation of gyrotrons and gyroklystrons in Russia are reported. A state-of-the-art analysis of gyrotrons for plasma heating in fusion installations and technological applications as well as gyroklystrons for millimeter-wavelength radars is performed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 6, pp. 635–670, June, 1996.     

A guided wave technique for the characterization of highly attenuative viscoelastic materials

The measurement of the acoustic properties of highly attenuative materials such as bitumen is very difficult. One possibility is to use measurements of the extent to which filling a cylindrical waveguide with the material affects the dispersion relationship of the cylinder. Torsional modes have been excited using piezoelectric transducers placed at one end of the cylinder, while the phase velocity and attenuation spectra have been measured by means of laser scanning. At each frequency, under the hypothesis of linear viscoelasticity, the phase velocity and attenuation of the fundamental torsional mode have been calculated as a function of the bulk shear velocity and the bulk shear attenuation of the inner core at that frequency. The resulting phase velocity and guided wave attenuation contour plots have been employed for deriving the unknown shear properties from the measured velocity and attenuation of the guided wave. The monochromaticity of the approach has not required a particular frequency dependence of the material properties to be assumed. Results for bitumen are given.     

On the Thermal Stability of Tracks in Plastics and some Uses in Radiography

The eradication of alpha and fission tracks and the selective track discrimination by heat treatment have been studied in cellulose nitrate, cellulose acetate, and polycarbonate sheets. Some applications of the phenomena in alphagraphy and fissionography are presented.     

等离子体光学的研究现状与发展前景

等离子体介质由于具有极高的储能密度、无光致损伤阈值和丰富的光学特性,利用它改善光束输出性能是发展高功率激光技术的一条重要技术路线。系统介绍了近年来等离子体光学的研究现状,并论述了今后等离子体光学的发展趋势。     

Boron nitride phase diagram. State of the art

Abstract

From recent experimental data on BN thermodynamic propeties, the equilibrium phase diagram for boron nitride has been plotted, which differs from the generally accepted Bundy-Wentorfs one. At atmospheric pressure cubic boron niride has been shown to be a thermodynamically stable modification up to temperatures of 1600 K, which drastically changes the established notions of BN polymorphism, based on assumed analogy of phase diagrams for carbon and boron nitride. These studies have shown that according to the proposed equilibrium phase diagram the threshold pressure of cBN crystallization can be reduced from 4 down to 2 GPa with the supercritical fluids present, which opens new fields for developing methods for cBN low-pressure synthesis.     

Re-evaluation of the mechanical loss factor of hydroxide-catalysis bonds and its significance for the next generation of gravitational wave detectors

New measurements of the mechanical loss factors of hydroxide-catalysis bonds have been made and these have been found to be significantly lower than previously reported. We provide the first estimate for the resulting thermal noise limitation for a practical test mass geometry for next generation gravitational wave detectors.     

The effect of Pb2+ dopant in the crystal of CsI and its application as scintillation detector: a study of alpha particles

Scintillation crystals have been used in various fields, such as high energy physics, nuclear instrumentation, radiation measurements, medical imaging, nuclear tomography, astrophysics and other fields of science and engineering. For these applications, the development of scintillation crystals with good performance is required. Scintillation crystals based on cesium iodide (CsI) matrix are matters with relatively low hygroscopicity, easy to handle and of low cost, characteristics that favor their use as radiation detectors. In this study, pure CsI crystal and lead doped CsI crystals were grown using the Bridgman vertical technique. The concentration of the lead doping element (Pb) was studied in the range of 10^?2 to 5×10^?4 M. The distribution of the doping element in the crystalline volume was determined by atomic absorption technique. The CsI:Pb crystal with nominal concentration of 10^?3 M was cut into 14 slices of 6 mm. The results show a higher concentration at the top of the crystal with a decrease in the initial phase of growth. The dopant concentration of Pb showed good uniformity from the slice 2 to the slice 12: the region is, therefore, suitable for use as a radiation detector. The luminescence emission of these crystals was measured. A predominant luminescence band near 450 nm and a single broad band around 320 nm were found with the addition of the Pb²⁺ ions in the CsI matrix. Alpha particles spectrometry measurements were carried out to evaluate the developed scintillators.The resolution of 5.6% was obtained for the CsI:Pb 5×10^?4 M crystal, when excited with alpha particles from a ²⁴¹Am source, with energy of 5.54 MeV.     

Study of Boron Distribution in Germanium Single Crystals grown from the Melt with Solid State Nuclear Track Detectors

To get information about the transport mechanisms of impurities or dopants in the liquid zone for the crucibleless zone melting method of crystal growth the boron distribution was studied in Ge-single crystals using neutron induced autoradiography on solid state nuclear track detectors. The boron distribution found for a cover-free surface of the zone was proved to be caused by non-stationary thermocapillary (Marangoni) convection. The Marangoni convection could be suppressed by a viscous oxide layer on the zone.

Zur Aufklärung der Transportvorgänge von Verunreinigungen oder Dotanden in der schmelzflüssigen Zone beim Verfahren des tiegelfreien Zonenschmelzens der Kristallzüchtung wurde die Bor-Verteilung in Germanium-Einkristallen mittels neutroneninduzierter Autoradiographic mit Festkörperspurdetektoren untersucht. Die bei bedeckungsfreier Schmelzzone gefundene B-Verteilung wird durch eine instationäre thermokapillare (Marangoni-) Konvektion verursacht. Die Marangoni-Konvektion wird durch eine viskose Oxidsrhicht auf der Schmelzzone unterdrückt.     

Calibration of power and energy meters for the far infrared/near millimeter wave spectral region

Power and energy measurments in the sub-mm/near-mm wave spectral region are assuming greater importance as experimentation and data exchange increases. Much of the information on power and energy measurements of lasers and other sources is derived from common detectors constructed for operation at visible and near infrared wavelengths. This paper reports on recent progress in attempts to provide accurate calibrations for instruments such as pyroelectrics and calorimeters in the 40 m to 3 mm spectral region.This work was supported by the Department of Energy     

Optical characterization of the silicon photodiodes for the establishment of national radiometric standards

Optical properties of the silicon photodiodes are investigated in the visible spectral regime. Non-linearity measurement standard was established by using Hamamatsu S1337-11 type windowless silicon photodiode whose non-linearity value was found to be better than 6×10⁻⁵ at photocurrent level of 10⁻⁹ to 10⁻⁴ A. Temperature effects on the spectral responsivity for S1337-11, S1337-1010BQ and S1227-1010BQ type photodiodes were analyzed between 20°C and 40°C at 488.1, 514.7 and 632.8 nm vacuum wavelengths. The spatial uniformities of the responsivity for three type photodiodes are performed with a laser beam having 1 mm diameter by using home made two-axis micro translation system. Results of the reflectance measurements for three elements of reflection-based trap detectors were compared with the predicted values obtained from Fresnel equations.     

State of the art of prospects for investigations of luminescent solar concentrators

Kuban State University, 149 K. Libknecht Str., Krasnodar, 350640, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 3, pp. 204–209, May–June, 1995.     

Luminescence and scintillation properties of advanced Lu3Al5O12:Pr3+ single crystal scintillators

In this paper we present the luminescence and scintillation properties of Lu₃Al₅O₁₂:Pr (LuAG:Pr) single crystals with Pr³⁺ concentration of 0.13 wt %, grown by the Czochralski method. The light yield and energy resolution were measured under 662 keV γ-ray excitation. The dominant emission band peaking at 310 nm with a shoulder at 370 nm was observed in the photoluminescence spectrum. High light yield of 24,500 ph/MeV and an energy resolution of 5.3 % were obtained for a 6 × 6 × 2 mm³ LuAG:Pr sample. Light yield dependence on sample height and shaping time was measured. The estimated photofraction in pulse height spectrum and total mass attenuation coefficient at 662 keV γ-rays were also determined and compared with the theoretical ones calculated using the WinXCom program.     

面阵探测器的像点亚像素定位研究

面阵探测器可直接探测点目标图像的位置，但其定位精度受到探测器分辨率的限制。因此，亚像元精度技术得到了发展。它是利用目标像点的灰度分布特性，通过内插细分算法，确定出像点位置。可将定位精度提高1—2个数量级。本文介绍了几种实现目标像点亚像素定位的内插细分算法。对它们的计算公式、特点进行了分析，并进行了实验验证。     

核物质热力学系统的状态方程

用Bonn势和考虑强子质量Brown Rho(BR)标度规则修正,提出了改进的相对论平均场有效模型,由核物质的基态性质确定模型参数后,将该模型用来研究热密核物质系统的状态方程.     

Laser ablation of advanced ceramics and glass-ceramic materials: Reference position dependence

In this work, we present the effect produced by modifying the reference position as well as the method of machining on the results obtained when advanced ceramics and glass-ceramic materials are machined by laser ablation. A Q-switched Nd:YAG laser at its fundamental wavelength of 1064 nm with pulsewidths in the nanosecond range has been used. Morphology, depth and volume obtained by means of pulse bursts and grooves have been studied. Working within the same laser conditions, it has been shown that these values depend on the thermal, optical and mechanical features of the material processed. We have also studied the variation in the ablation yield when the position of the surface to be machined is modified. Material properties and work conditions are related to the results obtained.We have described and discussed the morphology, composition, microstructure and hardness of the materials processed.     

Sulfur composite cathode materials: comparative characterization of polyacrylonitrile precursor

The electrochemical behavior of the sulfur composite cathode material for rechargeable lithium batteries and the characteristic of the polyacrylonitrile precursor were investigated. The samples of different polyacrylonitrile precursors were characterized by thermogravimetric analysis, nuclear magnetic response, Fourier transform infrared spectrometer, and differential scanning calorimetry. The electrochemical performance of the sulfur composite cathode material made from the polyacrylonitrile precursor was also tested. The analysis showed that the molecular weight distribution and the impurity of the polyacrylonitrile precursor affected the electrochemical performance of the sulfur composite cathode material made from the precursor. The polyacrylonitrile precursor with the narrower distribution of the molecular weight and the higher structural purity of the polyacrylonitrile precursor led the better electrochemical performance of the sulfur composite cathode material made from the precursor.