A beam reversal experiment for the estimation of microwave powershifts in an optically pumped Cs beam frequency standard

The characteristics of microwave-power-dependent frequency shifts of an optically pumped Cs frequency standard are reported. The general features of the shifts are in good agreement with simple theoretical predictions. The shift is quite symmetrical in beam reversal, and the standard deviation of the difference between the observed and predicted shift is about 6×10-14     

Implementation of intra-cavity beam shaping technique to enhance pump efficiency

In this work we propose an implementation of a new intra-cavity beam shaping technique to vary the intensity distribution of the fundamental mode in a resonator cavity while maintaining a constant intensity distribution at the output. This method can be useful for fitting a transversal intensity profile of the required mode with a pump beam profile in the region of the active medium to increase mode discrimination.     

Synthetic transmit beam technique in an aberrating environment

Parallel beamforming is a commonly used method for increasing the frame rate in ultrasound imaging systems. By receiving in several directions for each transmission, the frame rate is increased. However, this method also introduces blocklike artifacts in the B-mode image, due to the reception offsets when compared with the transmission direction. The synthetic transmit beam technique (STB) has been previously proposed as a compensation technique when addressing these artifacts. Previous work by Hergum et al. investigated the performance of this method in regard to the case of 2 parallel beams in tissue mimicking phantoms without aberrations. This study is a continuation of that work in which this method is tested in an aberrating environment using 4 parallel beams. Several quantitative and qualitative performance aspects of this method have been investigated such as lateral shift invariance, beam-to-beam correlation fluctuations, speckle- tracking performance, improvements from higher order STB interpolation and beam profile shape preservation, as well as perceived image quality improvements. The results were obtained from simulations, in vivo measurements, and in vitro measurements. The results showed that aberration amplified the image artifacts for regular parallel beamforming, which resulted in more shift variance, lower beam-to-beam correlation, higher speckle- tracking error, and more variation in beam profile shape. Compared with regular parallel beamforming, STB resulted in a significantly better image quality and a higher score in all measuring methods. The improvements from using STB were largest in cases involving aberration. Using STB, the variation in beam-to-beam correlation was reduced from 30% to 1%, and the standard deviation of the speckle-tracking error was reduced from 8% to 1.5%.     

Ion beam sputtering coatings on large substrates: toward an improvement of the mechanical and optical performances

Large mirrors (?350 mm) having extremely low optical loss (absorption, scattering, wavefront) were coated for the VIRGO interferometer. The new generation of mirrors needs to have a better wavefront and lower mechanical loss. To improve the component wavefront, the corrective coating technique was used. By doping the tantalum pentoxide layers, we improved, for the first time to our knowledge, the multilayer mechanical loss. The first results are discussed.     

Improvement of the beam lifetime by applying an rf electric kick field in the compact storage ring

The lifetime of the stored electron beam in the compact storage ring AURORA is governed by the Touchek effect. It has been shown that it is appreciably increased by applying a vertical rf kick field to the electron beam without giving harmful effect to the beam stability. Interferometric measurement of the radiation beam profile showed an increase in the beam size, indicating the reduction of the Touchek effect. Application of the field with increase in power has induced collective excitation of the betatron oscillation.     

Increasing the accuracy of laser beam diameter measurement

A procedure for determining the diameter of a focused laser beam based on the measurement of laser damage to a thin film is described. This method has several advantages over the spatial methods of using calibrated diaphragms and the measurement of relative power density distribution with subapertures.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 23–24, June, 1995.     

Evolution of competitive priorities towards performance improvement: a meta-analysis

Competitive priorities are critical operational dimensions that a business process must possess to satisfy its internal and external customers. The process of defining competitive priorities is evolving and changing over time according to a new business paradigm. Therefore, it is the right time to revisit the critical dimensions of competitive priority. The purpose of this study is threefold: (1) to identify and revise the critical dimensions of competitive priority; (2) to assess the quality of competitive priority measures across studies based on different criteria; (3) to confirm the relationship between several competitive priorities and organisational performance. The results show the different effects that competitive priorities have on organisational performance. Cost and quality priorities show evidence of strong effect size compared to the others.     

Photoelasticity—-An improvement in the sandwich technique

The development of the sandwich technique in photoelasticity necessitates a suitable cement. The results of experiments using cyanoacrylate IS 12 in cementing Perspex and Araldite are compared with the results of experiments using resorcinol formaldehyde. These show that cyanoacry/ate is much superior in strength and that it has other properties suitable for the purpose.     

Titanium oxy-nitride films deposited on stainless steel by an ion beam assisted deposition technique

Surfaces of stainless steel SUS304 were coated with titanium oxy-nitride (TiON) films at temperatures of 400–770°C using an ion-beam assisted deposition technique constructed from an electron beam evaporator for Ti evaporation and a microwave ion source for ionizing nitrogen gas. The N ions were accelerated at energies of 0.5–2.0 keV. Most of the deposited TiON films consisted of (60–80)% TiN and (40–20)% TiO₂, and the fraction of TiO₂ increased with increasing substrate temperature. Hardness of the TiNO films varied in the range from 160 GPa to 260 GPa with increasing substrate temperature. The titanium oxy-nitride film could be deposited on stainless steel without a significant deterioration surface layer at 600°C. However, when TiNO films were deposited at temperatures higher than 700°C, the thickness of the TiNO films were significantly thinner and a thick layer containing nitride such as Cr₂N, CrFe, Fe₂N and Fe₄N was formed in a near surface region of stainless steel because more nitrogen diffused into stainless steel.     

提高光学电压互感器测量精度方法的探讨

提高光学电压互感器测量精度的方法,包括选择合适的电光晶体,利用退火法消除自然双折射的影响,利用双晶体或旋转反射法进行温度补偿以及双光路温度补偿等。由于有许多的因素影响测量结果,必须多种方法综合运用,才能达到较高的测量精度。     

Preliminary design of a Gd-NCT neutron beam based on compact D-T neutron source

Gadolinium has been recently proposed, as neutron capture agent in NCT (Neutron Capture Therapy), due to both the nuclide high neutron capture cross section, and the remarkable selective uptake inside tumour tissue that Gd-loaded compounds, can provide. When a neutron external source is supplied, different Gd nuclear reactions, and the generated Auger electrons in particular, cause a high local energy deposition, which results in a tumour cell inactivation. Preliminary micro- as well as macrodosimetric Monte Carlo computational investigations show that the tumour-to-healthy tissue biological damage ratio is in close relation to the neutron beam energy spectrum. The results points out that the optimum neutron spectrum, to be used for Gd-NCT, seems to lie in the 1 to 10 keV energy range. In order to 'tailor' such spectra, an original, accelerator-driven, neutron source and spectrum shaping assembly for hospital-based Gd-NCT are presented and preliminary results are reported.     

基于刚度匹配的汽车保险杠防撞梁改进设计

为提高某汽车保险杠防撞梁的吸能和经济性,基于刚度匹配原理对其进行改进设计.搭建有限元仿真平台,对40%偏置静压试验进行模拟分析,验证了仿真方法的有效性;考虑设计功效、制造成本与维修费用等因素,提出了包含横梁弹性变形、吸能盒塑性变形和横梁塑性变形三阶段的防撞梁合理变形模式;结合变形与刚度的关系,提出了防撞梁刚度匹配模式;以调整结构及材料参数为途径,针对原防撞梁变形不够合理的缺点进行了改进并验证.结果表明:改进后的防撞梁总吸能更多,达到吸能充分的要求;通过满足刚度匹配关系,实现了防撞梁合理变形模式.     

Regularized autoregressive analysis of intravascular ultrasound backscatter: improvement in spatial accuracy of tissue maps

Autoregressive (AR) models are qualified for analysis of stochastic, short-time data, such as intravascular ultrasound (IVUS) backscatter. Regularization is required for AR analysis of short data lengths with an aim to increase spatial accuracy of predicted plaque composition and was achieved by determining suitable AR orders for short data records. Conventional methods of determining order were compared to the use of trend in the mean square error for determining order. Radio-frequency data from 101 fibrous, 56 fibro-lipidic, 50 calcified, and 70 lipid-core regions of interest (ROIs) were collected ex vivo from 51 human coronary arteries with 30 MHz unfocused IVUS transducers. Spectra were computed for AR model orders between 3-20 for data representing ROIs of two sizes (32 and 16 samples at 100 MHz sampling frequency) and were analyzed in the 17-42 MHz bandwidth. These spectra were characterized based on eight previously identified parameters. Statistical classification schemes were computed from 75% of the data and cross-validated with the remaining 25% using matched histology. The results determined the suitable AR order numbers for the two ROI sizes. Conventional methods of determining order did not perform well. Trend in the mean square error was identified as the most suitable factor for regularization of short record lengths.     

Implementation of an ANCF beam finite element for dynamic response optimization of elastic manipulators

Theoretical and practical aspects of an absolute nodal coordinate formulation (ANCF) beam finite element implementation are considered in the context of dynamic transient response optimization of elastic manipulators. The proposed implementation is based on the introduction of new nodal degrees of freedom, which is achieved by an adequate nonlinear mapping between the original and new degrees of freedom. This approach preserves the mechanical properties of the ANCF beam, but converts it into a conventional finite element so that its nodal degrees of freedom are initially always equal to zero and never depend explicitly on the design variables. Consequently, the sensitivity analysis formulas can be derived in the usual manner, except that the introduced nonlinear mapping has to be taken into account. Moreover, the adjusted element can also be incorporated into general finite element analysis and optimization software in the conventional way. The introduced design variables are related to the cross-section of the beam, to the shape of the (possibly) skeletal structure of the manipulator and to the drive functions. The layered cross-section approach and the design element technique are utilized to parameterize the shape of individual elements and the whole structure. A family of implicit time integration methods is adopted for the response and sensitivity analysis. Based on this assumption, the corresponding sensitivity formulas are derived. Two numerical examples illustrate the performance of the proposed element implementation.     

Measurement of light absorption by aquatic particles: improvement of the quantitative filter technique by use of an integrating sphere approach

Determination of particulate absorption in natural waters is often made by measuring the transmittance of samples on glass-fiber filters with the so-called quantitative filter technique (QFT). The accuracy of this technique is limited due to variations in the optical properties of the sample/filter composite, and due to uncertainties in the path-length amplification induced by multiple scattering inside the filter. Some variations in the optical properties of the sample/filter composite can be compensated by additional measurements of the filter's reflectance (transmittance-reflectance method [T-R] [S. Tassan and G. M. Ferrari, Limnol. Oceanogr. 40, 1358 (1995)]). We propose a different, rarely used approach, namely to measure the filter's absorptance in the center of a large integrating sphere, to avoid problems with light losses due to scattering. A comparison with other QFTs includes a sensitivity study for different error sources and determination of path-length amplification factors for each measurement technique. Measurements with a point-source integrating-cavity absorption meter were therefore used to determine the true absorption. Filter to filter variability induced a much lower error in absorptance compared to a measured transmittance. This reduced error permits more accurate determination of the usually low absorption coefficient in the near IR spectral region. The error of the T-R method was lower than that of the transmittance measurement but slightly higher than that of an absorptance measurement. The mean path-length amplification was much higher for the absorptance measurement compared to the T-R method (4.50 versus 2.45) but was found to be largely independent of wavelength and optical density. With natural samples the path-length amplification was less variable for the absorptance measurement, reducing the overall error for absorption to less than ±14%, compared to ±25% for the T-R method.     

IPMC人工肌肉的制备工艺研究与改进

研究了Nafion117质子交换膜的成膜过程与IPMC人工肌肉的制备过程.制备不同厚度的Nafion膜,在此基础上使用化学沉积法制备IPMC.制备主要分为前期预处理、主化学镀反应和次化学镀反应.由于在制备过程中膜表面产生气泡,需要高速搅拌,既要考虑到气泡快速溢出,又要使Nafion膜不与搅拌棒接触产生划痕,因此采用立式...     

On the high-energy electron beam irradiation-induced defects in Cu2SnSe3 system: an effort towards modifying the structure,microstructure, and thermoelectric transport

Journal of Materials Science: Materials in Electronics - We present report on modulating thermoelectric transport in Cu2SnSe3 system via irradiating high-energy electrons of energy of about...     

波束锐化技术在多波束测深声呐中的应用

针对常规波束形成器的分辨性能和旁瓣性能间的矛盾,研究了超波束形成器的波束特征以及空间分辨性能。通过计算机仿真验证了加权超波束形成器既有较高的空间分辨力,又有良好的旁瓣特性。通过对外场实验数据的处理,验证了该算法对于多波束测深声呐测量结果中存在的"隧道效应"假象具有明显的抑制作用。针对算法实现结构进行了优化,进一步减小了算法复杂度。利用DSP进行了算法实现,算法具有较好的实时性和工程实用性。