International comparison GT-RF 75-A 14: attenuation (6,10,20,40 dB)at 300 MHz in 75 Ω coaxial line

This is the first comparison between national standard devices in which attenuation values up to 40 dB at a frequency of 300 MHz in the 75 Ω coaxial line have been compared. Five national laboratories of metrology, from the UK, Finland, Canada, The Netherlands, and the Federal Republic of Germany (pilot laboratory), participated. The transfer standards were two fixed attenuators with an attenuation of 6 and 20 dB, and two switchable attenuators with 10 and 40 dB steps. The maximum difference between any two results for the more stable fixed attenuators is 0.009 dB at an attenuation of 6 dB and 0.016 dB at 20 dB attenuation. For three of the five participants, the deviation between mean values was not larger than 0.0004 dB for an attenuation of 6 dB and not larger than 0.0013 dB for one of 20 dB     

International comparison GT-RF 78-1: high attenuation (60 dB, 100dB) at 30 MHz in 50 Ω coaxial line

A worldwide comparison of national standard devices in which high attenuation values (up to 100 dB) at the frequency of 30 MHz have been compared is reported. Eleven national laboratories of metrology from the Netherlands, France, Italy, the United Kingdom, Sweden, Poland, Hungary, Australia, the People's Republic of China, the USSR, and the Federal Republic of Germany participated. The transfer standards were two fixed attenuators with an attenuation of about 60 dB and 100 dB and one switchable attenuator with 100 dB. The maximum difference between any two results is 0.064 dB at an attenuation of 60 dB and 0.125 at 100 dB. For a considerable number of laboratories, the deviation between mean values was not larger than 0.001 dB for a 60-dB attenuation step, and not larger than 0.005 dB for a 100-dB attenuation step     

烟用甜味接装纸三氯蔗糖甜味稳定性影响因素研究

目的 考察烟用甜味接装纸中影响三氯蔗糖的稳定性的因素,为制备出更稳定的甜味接装纸提供参考。方法 通过模拟卷烟过程中,卷烟机的辊子与接装纸的摩擦,以及烫金温度对甜味接装纸甜味稳定性的影响来探究影响甜味接装纸甜味稳定性的原因,同时,通过调整光油的性质和品牌、甜味剂用量、扫描电镜探究光油对三氯蔗糖甜味接装纸甜味稳定性的影响。结果 水性光油的衰减周期为75 d,衰减率最大为78.64%,醇性光油为溶剂的甜味接装纸衰减周期大于105 d,衰减率最大值为15.34%,立美特光油作溶剂比使用其他品牌光油在甜味剂衰减上要更加缓慢,最大衰减率为16.70%。以醇性光油作为溶剂时,甜味剂用量为12 kg/t的甜味与水性光油为溶剂时的甜味剂用量为8 kg/t的甜味接装纸甜味相近。结论 温度是造成以水性光油为溶剂的甜味接装纸甜味损失的重要原因,烘箱法可以作为一种快速检测甜味接装纸甜味衰变过程的检测方法。醇性光油为溶剂的甜味接装纸具有很好的稳定性,通过表征分析,醇性光油将甜味剂包裹,唾液不断将包裹住的甜味剂不断释放,甜味渐渐明显。     

Liquid-crystal-deflector based variable fiber-optic attenuator

A compact, low-component-count, no-moving-parts variable optical attenuator (VOA) is demonstrated for the first time by means of beam spoiling that is implemented via an electrically reconfigurable nonpixelated nematic liquid-crystal deflector. The VOA design features an in-line alignment polarization-insensitive design that does not use bulky polarization splitting and combining optics. The proof-of-concept VOA at 1550 nm demonstrates a 30-dB attenuation range, a 2.5-dB insertion loss, a < or = 0.8-dB polarization-dependent loss, and a 1-s maximum attenuation reset time. The VOA design can counter performance-reducing environmental effects such as excess-loss increases due to temperature variations.     

Possible Sound Mode Conversion in “Superfluid 4He-97% Open Aerogel” System

We have studied the acoustic properties of liquid helium filled in various aerogels. The longitudinal ultrasound velocity and attenuation were measured at the frequency of 10 MHz with aerogels that had porosity from 92 to 97%. The mode intermediate between first and fourth sound was observed. The attenuation of this mode decreased with decreasing temperature for dense aerogels. However, an attenuation maximum was observed around 1.6 K for 97% open aerogel at various liquid pressures. In the present work, we discuss the possibility of the sound modes conversion between first, second sound in superfluid and aerogel sound mode in this composite system.     

包覆泡沫铝钢梁动态位移的计算及影响因素

为考察运用FSI(流固耦合效应)能否考虑包覆泡沫铝对钢梁在爆炸荷载作用下最大动位移的影响及分析包覆泡沫铝衰减爆炸荷载作用下钢梁最大动位移的影响因素,运用理论及数值模拟方法分析了包覆泡沫铝钢梁在爆炸荷载作用下的动态位移变化情况。在验证理论及数值模拟结果可靠的基础上,对比理论结果与数值模拟计算结果的优缺点,并运用数值模拟分析影响包覆泡沫铝衰减钢梁在爆炸荷载作用下动位移的因素。结果表明:FSI可以考虑包覆材料对爆炸冲击波的衰减作用,但不能反映材料本身变化的影响(如材料厚度、屈服强度等);在计算包覆泡沫铝衰减爆炸荷载作用下钢梁最大动位移时,泡沫铝的厚度、屈服强度均具有最优解;增加刚性面板会放大包覆泡沫铝钢梁在爆炸荷载作用下的最大动位移。     

Propagation of inhomogeneous waves in anisotropic piezo-thermoelastic media

A mathematical model for the propagation of harmonic plane waves in an anisotropic piezo-thermoelastic medium is explained through three relations. Two of them relate the stress-induced harmonic variations in temperature and electric potential to mechanical displacement of material particles. The third is a system that defines modified Christoffel equations for wave propagation in the medium. The solution of this system is ensured by a quartic equation whose complex roots explain the existence and propagation of four attenuating waves in the medium. The effects of piezoelectricity and thermoelasticity on the wave propagation are analyzed in the discussion of special cases. An angle between propagation direction and direction of maximum attenuation defines the attenuated wave as inhomogeneous wave. The complex slowness vector for each of the four attenuated waves in the medium is resolved to calculate the phase velocity and the attenuation factor for its propagation as an inhomogeneous wave along a general direction in three-dimensional space. The variations in phase velocities and attenuation factors with propagation direction are computed, for a realistic numerical model.     

Errors and uncertainties in the measurement of ultrasonic wave attenuation and phase velocity

This paper presents an analysis of the error generation mechanisms that affect the accuracy of measurements of ultrasonic wave attenuation coefficient and phase velocity as functions of frequency. In the first stage of the analysis we show that electronic system noise, expressed in the frequency domain, maps into errors in the attenuation and the phase velocity spectra in a highly nonlinear way; the condition for minimum error is when the total measured attenuation is around 1 Neper. The maximum measurable total attenuation has a practical limit of around 6 Nepers and the minimum measurable value is around 0.1 Neper. In the second part of the paper we consider electronic noise as the primary source of measurement error; errors in attenuation result from additive noise whereas errors in phase velocity result from both additive noise and system timing jitter. Quantization noise can be neglected if the amplitude of the additive noise is comparable with the quantization step, and coherent averaging is employed. Experimental results are presented which confirm the relationship between electronic noise and measurement errors. The analytical technique is applicable to the design of ultrasonic spectrometers, formal assessment of the accuracy of ultrasonic measurements, and the optimization of signal processing procedures to achieve a specified accuracy.     

The effect of salinity and temperature on electromagnetic wave attenuation in brine

Ice slurries are typically formed from an aqueous solution of water and salt (NaCl) at 5% salinity. Ice pigs, used in many industry areas, are taken from a bulk ice slurry and used to clear waste or recover product from pipes. Ice fraction is a key property of an ice slurry, since it determines it's ‘thickness’ and therefore cleaning capacity. Electromagnetic wave interrogation has been shown to accurately predict an ice fraction to within an error of ±1.2%. The largest remaining process error comes from inherent salinity variation, which affects the electromagnetic wave attenuation significantly. Increasing electromagnetic wave attenuation with increasing salinity and the effect of temperature, shown to also increase attenuation, is quantified. Calibration methods are proposed, aiming to eliminate the unwanted effect of varying salinity. Analysis on multiple samples showed a 16% reduction in average error, and 9% reduction in maximum error when the calibration method was applied.     

International intercomparison of attenuation in fiber opticsystems: multimode fiber and LED-based comparison

The result of an international comparison of incremental attenuation steps of a multimode fiber-optics attenuator bat 850 nm is reported. In multimode systems, the measurement value varies with such measuring conditions as the light source spectrum and the spatial distribution of light at launching into the fiber. Therefore, a specially designed step attenuator was used as the transfer standard, and reference conditions were set up. The maximum differences among the mean values of the measurements were less than 0.03 dB/10 dB. The result shows the possibility of using a step attenuator as an attenuation standard in multimode fiber-optic systems under specific reference conditions     

Time-varying autoregressive spectral estimation for ultrasound attenuation in tissue characterization

In the field of biological tissue characterization, fundamental acoustic attenuation properties have been demonstrated to have diagnostic importance. Attenuation caused by scattering and absorption shifts the instantaneous spectrum to the lower frequencies. Due to the time-dependence of the spectrum, the attenuation phenomenon is a time-variant process. This downward shift may be evaluated either by the maximum energy frequency of the spectrum or by the center frequency. In order to improve, in strongly attenuating media, the results given by the short-time Fourier analysis and the short-time parametric analysis, we propose two approaches adapted to this time-variant process: an adaptive method and a time-varying method. Signals backscattered by an homogeneous medium of scatterers are modeled by a computer algorithm with attenuation values ranging from 1 to 5 dB/cm MHz and a 45 MHz transducer center frequency. Under these conditions, the preliminary results obtained with the proposed time-variant methods, compared with the classical short-time Fourier analysis and the short-time auto-regressive (AR) analysis, are superior in terms of standard deviation (SD) of the attenuation coefficient estimate. This study, based on nonstationary AR spectral estimation, promises encouraging perspectives for in vitro and in vivo applications both in weakly and highly attenuating media.     

A laboratory apparatus for determining the moisture content in capillary-porous materials by the method of super-high-frequency absorption

A test apparatus and procedure are described for determining the moisture content in capillary-porous materials by the absorption of super-high-frequency radio waves. Results are shown which have been obtained for clay and ceramics at temperatures from 300 to 373°K.Notation X thickness of wet material layer, cm - X₁ thickness of wet material layer corresponding to an attenuation N₁, cm - N₁ attenuation, dB - N_max maximum attenuation recorded on the test stand, dB - T temperature of the material, °K - W moisture content in the material, % Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1068–1071, June, 1972.     

刚性防爆墙迎爆面荷载计算方法研究

防爆墙作为一种有效的防护措施在国内外重要工程中得到了广泛应用,研究防爆墙迎爆面荷载计算方法有助于防爆墙的科学设计和合理使用。该文采用数值模拟的方法,对不同倾斜角度刚性墙迎爆面压力荷载的计算方法及不同倾角墙体的抗爆效能进行了研究。分析了冲击波在垂直墙体、迎向以及背向炸药倾斜墙体上的反射、绕流以及荷载分布规律,总结出了不同工况时墙体荷载计算方法。研究发现背向炸药倾斜的墙体与垂直墙体以及迎向炸药倾斜的墙体具有几乎相同的防护效果,但墙体所承受的荷载要低于其他两者,合理的解释了工程中存在的防爆墙后倾现象的力学机制。     

爆破载荷作用下充填体稳定条件分析

间柱回采过程中，如何确保两侧充填体稳定是一个重要的研究课题。作者对爆破载荷作用下充填体的动应力场、破坏特性、衰减规律进行了一系列试验研究，结果表明布孔参数、起爆顺序、最大一段药量等对充填体稳定均有影响     

爆破载荷作用下充填体稳定条件分析

间柱回采过程中，如何确保两侧充填体稳定是一个重要的研究课题。作者对爆破载荷作用下充填体的动应力场、破坏特性、衰减规律进行了一系列试验研究，结果表明布孔参数、起爆顺序、最大一段药量等对充填体稳定均有影响     

钻爆法原位扩建隧道的振动监测分析

为了研究城市环境下钻爆法施工对周边环境的振动影响,以福州市马尾隧道原位扩建工程为背景,在北洞钻爆扩挖过程中,对南洞衬砌结构上的振动效应进行跟踪监测。通过选取单段最大装药量、爆心距为变量,归纳整理峰值振速的规律,并采用萨道夫公式拟合空洞赋存条件下的振速衰减规律。结果表明,既有空洞对爆破振动的衰减有很大影响:以II级围岩段为例,单空洞情况下其衰减指数α为1.476,接近硬岩的上限;而双空洞情况下其衰减指数α达到1.836,已落入软岩的推荐取值范围。拟合公式可应用于赋存空洞条件下的爆破振速估算;同时建议后续南洞扩挖及类似扩建工程中,可以充分发挥既有空洞的减振效应,适当加大进尺、缩短工期、提高施工效率。     

Broadband Laser-Ultrasonic Spectroscopy for Quantitative Characterization of Porosity Effect on Acoustic Attenuation and Phase Velocity in CFRP Laminates

This work aims at applying the method of broadband laser-ultrasonic spectroscopy for quantitative evaluation of the effect of isolated dispersed voids and additional extended interply delaminations on the acoustic attenuation and on the phase velocity in CFRP laminates. This method is based on the laser thermoelastic generation of broadband reference pulses of longitudinal ultrasonic waves in the specially designed source of ultrasound. The high-sensitivity piezoelectric transducer is used to detect these pulses propagating normal to the fiber plies in composite specimens. The laminate specimens investigated have different total porosity levels up to 10.5 % determined by the X-ray computer tomography. The resonance peak of the attenuation coefficient and the corresponding jump of the phase velocity are observed governed by the periodic layered structure of the specimens. The absolute maximum and the frequency bandwidth of the resonance attenuation peak depend on the total porosity level formed by the predominant type of imperfections, either of isolated spheroidal voids entrapped in epoxy layers or of extended interply delaminations. With an increase of the specimen’s total porosity dispersion of the phase velocity becomes noticeable in the low-frequency band before the resonance jump. The derived empirical relations between the total porosity level and the parameters of the frequency dependencies of the ultrasonic attenuation coefficient and of the phase velocity can be used for rapid quantitative characterization of the structure of CFRP laminates subject to different fabrication conditions.     

Extending the Dynamic Range of a Spectrum Monitor Using Comparison Switching and Spectral Averaging

The dynamic range of a spectrum monitor can be extended by incoherently averaging the difference between the spectrum from the antenna and the spectrum from a comparison load. We show that it is often advantageous to increase the attenuation to the spectrum analyzer, thereby lowering the maximum signal strength at the mixer and subsequently compensating for the added noise by incoherent spectral averaging. We analyzed the case of a conventional heterodyne analyzer as well as an analyzer using direct analog-to-digital conversion (ADC) sampling.     

Design of Relaxation Oscillator Based Ultra-wideband SFQ Amplifier for Chip to Chip Interconnection

In Rapid Signal Flux Quantum (RSFQ) logic circuits, on-chip interconnects and multichip module implementations for nearby distances have already been established. However, the flexible interconnection of two distant chips is still not achieved reliably due to impedance mismatching and attenuation. In this work, we propose a circuit that allows the usage of Passive Transmission Lines (PTLs) to transfer single-flux-quantum (SFQ) pulses between two distant chips which are separated by a distance greater than 10 cm by using 50 ?? transmission lines. For this purpose, we design an SFQ amplifier circuit to deal with impedance mismatch and attenuation problems. The circuit consists of two main parts: a relaxation oscillator (RO) circuit and an impedance transformer. The RO circuit utilizes relaxation oscillations occur in the underdamped Josephson junctions. The impedance matching circuit is an 8-section Chebyshev quarter-wave transformer and it eliminates impedance mismatching problem between the amplifier circuit and PTL. We performed circuit simulations and obtained voltage amplitude of about 600 ??V at the output of the circuit. The transformer has a broadband impedance matching with a fractional bandwidth (ratio of the bandwidth of a device to its central frequency) of 1.4 and a maximum Voltage Standing Wave Ratio (VSWR, the maximum voltage divided by minimum voltage on the transmission line) of 1.5.     

碳纳米管磁化氢等离子体薄膜的微波吸收特性

为从理论上掌握有外加静磁场存在时铁催化高压歧化生成的碳纳米管中氢等离子体的微波吸收特性,根据磁离子理论和Appleton-Hartee方程,采用W.K.B近似方法,导出了碳纳米管磁化氢等离子体薄膜的微波衰减系数公式,数值计算了不同条件下碳纳米管磁化氢等离子体薄膜在0.3～30 GHz频段的微波衰减系数。研究结果表明:随着外加磁场强度的增加,Att30.00 dB/cm的频宽明显增大,吸收峰向高频方向移动.适当控制碳纳米管中等离子体的自由电子密度、电子碰撞的有效频率和外加磁场强度,能够实现碳纳米管中磁化氢等离子体薄膜对对特定微波段的强吸收.在外磁场等于0时,运用所构建的微波吸收模型得到的数值计算结果与已有的实验数据相吻合.