超声参量对制备原油乳化液的影响

采用原油配制了原油质量分数为5%的油水混合液,通过实验探究了超声辐射功率、辐射时间、间歇比、脉冲重复周期等因素对超声乳化效果的影响.实验结果表明,制备低含油原油乳化液的最佳超声参数为:超声辐射功率400W、辐射时间5min;间歇比和脉冲重复周期对原油乳化效果影响较小.     

超声对蛋白质盐析作用的研究

在蛋白质（牛血清白蛋白）-水胶体溶液中加入无机盐，利用蛋白质盐析的原理粗分离蛋白质是常用的生物分离技术。本文试图利用超声强化蛋白质盐析分离过程。讨论了声场参数，即频率、声强、超声辐射时间对该过程的影响。实验表明超声处理牛血清白蛋白时，20kHz超声辐照比无超声处理可缩短了近4．5小时的静置时间，20kHz超声处理可得到约90％的最高蛋白质收率；不同超声频率下有不同的最佳声压值，频率较低时的盐析效果较好；超声辐照并非时间越长越好，超声辐照2min时，牛血清白蛋白的收率最大。由此证明超声技术可加速盐析后的蛋白质沉降速度。     

L波段微波脉冲对微型计算机的辐照效应实验

 在L波段使用1.3 GHz载波频率的微波脉冲辐照微型计算机主板，通过改变脉冲宽度、重复频率和脉冲串长度等参数，实验研究了微波脉冲辐照导致微型计算机失去响应的功率阈值的变化规律，讨论了L波段微波脉冲辐射的积累效应。实验结果表明：当微波脉冲宽度增加时，微波功率阈值下降；当微波脉冲重复频率升高时，微波功率阈值呈下降趋势；在固定重复频率的条件下，微波脉冲数目的增加也会导致微波功率阈值的下降；微波脉冲功率阈值始终小于连续波微波的功率阈值。当微波脉冲间隔时间较长或者脉冲宽度较宽时，微波功率阈值由单个微波脉冲的参数确定，与脉冲重复频率没有明显关系。利用假设的微波脉冲辐射积累效应，可以定性解释和分析微波脉冲辐照微型计算机实验中功率阈值变化的趋势。     

室内脉冲声场中声强的测量研究

采用多次重复发射的声源配合装置在缓慢转动平台上的接收传声器所组成的测量系统(简称为RRS),它等效于多个完全匹配的传声器组成的圆型阵列.文中着重阐述了借助此技术测量房间内脉冲声场中声强的时间与空间分布特性.阐明了以RRS测量入射脉冲声强的理论基础,分别对离散的脉冲声场及扩散声场提出了测量声强的定量关系式,对实验结果及应用作了分析与讨论.     

超声吸收体物理参数对红外热成像测量高强度聚焦超声声场的影响

超声吸收体的物理参数对利用水听器和红外热成像技术的高强度聚焦超声(High-Intensity Focused Ultrasound,HIFU)声场测量结果具有重要影响。为了探索超声吸收体的物理参数(密度、声速、衰减系数、热扩散系数、定压比热容)对测量结果的影响规律,本文根据层状模型计算出相同声源功率输出时不同物理参数对应的超声吸收体内部声场和热场,利用有限差分法计算出超声吸收体表面在辐照过程中的温度变化;利用基于水听器和红外热成像技术的聚焦声场测量方法测量出焦域内不同位置上声场特征值(轴线声强和-6 dB声束宽度),与通过理论计算得到的声源在纯水中声场特征值进行比较,分析了不同物理参数对测量结果的影响。超声吸收体的声、热学参数中除了声速外,其它物理参数的变化引起声场特征值的测量造成最大相对差异率小于15%。因为声波传播速度的改变会导致超声吸收体内部热场分布变化,使测量结果与理论计算值有较大偏差,其中-6 dB声束宽度和轴线声强最大相对差异率为95.37%和69.97%。因此在选择超声吸收体的声、热学参数时应重点关注声波在吸收体内声速的影响。超声吸收体的声学参数与水的声学参数相近时,可以在焦域内获得较好的测量结果。      

南海北部浅海声场起伏及统计特性

水下声场的时间积分声强和峰值声强是声呐检测中的重要物理量,而海洋中的内波等动力学过程会造成声场强度的起伏。对南海北部浅海内波环境下定点声起伏实验数据分析,结合数值仿真,总结了试验海域近海底发射和近海底接收条件下内波引起接收信号强度起伏的统计特性.分析结果表明:接收信号的时间积分声强起伏小于峰值声强起伏;时间积分声强与峰值声强起伏的概率分布与对数正态分布较为接近.时间积分声强和峰值声强起伏大小与信号的频率有关,同一收发距离,中心频率650 Hz信号的声强起伏较中心频率310 Hz和375 Hz信号的声强起伏更为剧烈。对于同一频率,当海底较平坦时,声强起伏的闪烁指数随传播距离的增加而增大;当水深随传播距离逐渐变深时,声强起伏规律受内波和水深变化共同影响而更为复杂,闪烁指数先随传播距离增加而增大,之后又随传播距离的增加而逐渐变小.      

不同条件的声波对果蝇行为影响的实验研究

利用声波不同频率、声强及作用时间3个因子,研究了声波辐照对果蝇行为的影响。通过正交实验得出声波对果蝇行为影响的主次因素及最优水平搭配,并按照最优水平搭配进行了验证实验。实验结果表明:(1)果蝇在声波辐照下,其行为会做出趋避反应、觅食被抑制。(2)本次正交实验的声波辐照因子中,声压级和频率是主要因素。(3)按最优水平搭配因子声波辐照果蝇,果蝇有显著的趋避行为反应,有效趋避率达到22.48%。     

重频激光作用下碳纤维/环氧树脂复合材料热损伤规律

 运用热化学分析、扫描电子显微技术等手段,分析了碳纤维增强环氧树脂基复合材料在ms量级重频激光辐照下的损伤形式,研究了峰值功率密度、辐照时间、重复频率和脉冲宽度等对复合材料烧蚀规律的影响。研究结果表明：在激光辐照过程中,复合材料树脂基体在300 ℃开始裂解;由于裂解气体的保护作用,碳纤维不发生氧化,而是在汽化点（3 300 ℃）汽化烧蚀;复合材料热烧蚀率随峰值功率密度和重复频率提高而增大,随辐照时间增加而减小,最终均趋于定值;增加脉冲宽度可以提高辐照区峰值温度,降低碳纤维损伤的功率密度阈值。     

γ脉宽对电子器件瞬时辐照效应的影响

 采用了2种γ脉冲辐射源,在脉冲宽度分别约为20,50,150 ns,剂量率为10⁶～10⁹ Gy(Si)·s^-1下,对5种不同类型的电子器件进行了辐照试验并对其辐照响应进行了分析,比较了不同脉冲宽度条件下辐照响应的差异。实验结果表明：脉冲宽度是影响瞬时辐照效应的重要因素,γ脉冲宽度越宽,辐照响应越强,分离器件比集成电路受脉宽的影响更明显。     

长脉冲激光辐照下环氧树脂的热烧蚀规律

 研究了树脂基复合材料中常用的E-51环氧树脂在ms级脉冲激光辐照下热烧蚀率及质量烧蚀率的变化规律,分析了脉冲激光的辐照时间、峰值功率密度、重复频率以及脉宽对烧蚀率的影响。研究结果表明：随辐照时间的增加热烧蚀率逐渐增大,但辐照一定时间后,热烧蚀率趋于稳定;峰值功率密度的增加能明显提高热烧蚀率,但随峰值功率密度的增加,热烧蚀率的增幅减小直至趋于一定值;热烧蚀率不随脉冲激光重复频率和脉宽的变化而改变,当峰值功率密度一定时,热烧蚀率一定,质量烧蚀率与频率和脉宽成正比。     

Thresholds for cavitation produced in water by pulsed ultrasound

The threshold for transient cavitation produced in water by pulsed ultrasound was measured as a function of pulse duration and pulse repetition frequency at both 0.98 and 2.30 MHz. The cavitation events were detected with a passive acoustic technique which relies upon the scattering of the irradiation field by the bubble clouds associated with the events. The results indicate that the threshold is independent of pulse duration and acoustic frequency for pulses longer than approximately 10 acoustic cycles. The threshold increases for shorter pulses. The cavitation events are likely to be associated with bubble clouds rather than single bubbles.     

Enhancing sonochemical activity in aqueous media using power-modulated pulsed ultrasound: an initial study

Relatively little is known about the effects of pulsed ultrasound on the facilitation of chemical reactivity. Previous studies have indicated that sonochemistry using pulses is generally less effective than continuous ultrasonic irradiation. However, the pulse trains employed were such that the peak power of the pulses was the same as the maximum power used in continuous irradiation. As a result, less acoustic energy was transmitted to the solutions over the same period of time. The effectiveness of ultrasound when the pulse is adjusted so that the same amount of acoustic energy is input compared to continuous irradiation over a given time has not been previously explored. In this study we have embarked on an examination of the efficacy of power-modulated pulsed (PMP) sonochemistry. Specifically, we have explored the effects of pulse type and pulse frequency on the oxidation of potassium iodide and the degradation of acid orange, a common industrial colorant. A rate increase by a factor of three was observed compared with continuous irradiation under conditions of equivalent acoustic input power.     

Generation and reception of short acoustic pulses by multilayer piezoelectric transducers

By means of the Fourier transformation, a formula is obtained for calculating the pulse response of a transducer when a square pulse of a given duration is supplied to its input and the excited “sound” is reflected from the free flat end of the acoustic line and returns to the transducer. For a frequency of 100 MHz, real lithium niobate transducers that are connected through intermediate layers to the acoustic line made of fused quartz and to a rear load with a given acoustic impedance are considered. The pulse response is calculated for the transducers with different values of the sublayer thickness, rear acoustic load, transmission line impedance, and original pulse duration. The results of the calculations are compared with the experiment.     

Acoustic Measures of Symptoms in Abductor Spasmodic Dysphonia

Speech of patients with abductor spasmodic dysphonia (ABSD) was analyzed using acoustic analyses to determine: (1) which acoustic measures differed from controls and were independent factors representing patients' voice control difficulties, and (2) whether acoustic measures related to blinded perceptual counts of the symptom frequency in the same patients. Patients' voice onset time for voiceless consonants in speech were significantly longer than the controls (p = 0.015). A principle components analysis identified three factors that accounted for 95% of the variance: the first factor included sentence and word duration, frequency shifts, and aperiodic instances; the second was phonatory breaks; and the third was voice onset time. Significant relationships with perceptual counts of symptoms were found for the measures of acoustic disruptions in sentences and sentence duration. Finally, a multiple regression demonstrated that the acoustic measures related well with the perceptual counts (r² = 0.84) with word duration most highly related and none of the other measures contributing once the effect of word duration was partialed out. The results indicate that some of the voice motor control deficits, namely aperiodicity, phonatory breaks, and frequency shifts, which occur in patients with ABSD, are similar to those previously found in adductor spasmodic dysphonia. Results also indicate that acoustic measures of intermittent disruptions in speech, voice onset time, and speech duration are closely related to the perception of symptom frequency in the disorder.     

Testing a thermoacoustic sensor of high-power microwave pulses

We present the results of testing a new thermoacoustic sensor designed to detect microwave pulses having durations from 3 to 120 ns at wavelengths of 0.8 and 3 cm. Operation of the sensor is based on the effect of generation of acoustic signals during absorption of microwave pulses in a radiotransparent substrate–absorber–liquid layered structure . A thin nanometer-thick film deposited on a substrate is used as an absorber. Microwaves are converted to an acoustic pulse in the film and the adjacent liquid. The pulse is received by a wideband acoustic receiver and then recorded by a digital oscilloscope. It is shown that for a pulse duration of 120 ns, the shape of the signal recorded by the thermoacoustic sensor completely corresponds to the signal of a tube-diode detector of microwave pulses. The response of the thermoacoustic sensor to shorter pulses (3 and 5 ns long) is a pulse with a duration of 18 ns which is determined by a limited frequency band of the acoustic receiver.     

Long-range interaction of picosecond solitons through excitation of acoustic waves in optical fibers

We present the theory of electrostrictional interaction of soliton pulses in optical fibers. Solitons excite acoustic waves propagating in the direction transverse to the fiber axis. Scattering of optical radiation on these waves leads to a timing jitter of the optical pulses arrival time. We consider this effect as nonlinear self-scattering of light on acoustic waves. Because of the fact that a value of acoustic lifetime can reach a value of about 100 ns self-scattering on acoustic waves can be observed for a single optical pulse as well as for an optical pulse sequence as a whole. The value of single soliton self-frequency shift due to excitation of acoustic waves as a function of soliton duration have been obtained. For soliton duration _sol > 14 ps an acoustic wave soliton self-frequency shift is larger than the Raman soliton self-frequency shift.The obtained theoretical results describe well the long-range interaction of soliton pulse trains in an optical fiber. The value of bit error rate due to electrostrictional interaction of optical pulses in high bit rate, ultra long soliton communication systems have been obtained.     

Modulational interactions in magnetised piezoelectric semiconductor plasmas

Based on hydrodynamic model of plasmas an analytical investigation of frequency modulational interaction between copropagating high frequency pump and acoustic mode and consequent amplification (steady-state and transient) of the modulated waves is carried out in a magnetised piezoelectric semiconductor medium. The phenomenon of modulational amplification is treated as four wave interaction process involving cubic nonlinearity of the medium. Gain constants, threshold-pump intensities and optimum-pulse duration for the onset of modulational instabilities are estimated. The analysis has been performed in non-dispersive regime of the acoustic mode, which is one of the preconditions for achieving an appreciable initial steady-state growth of the modulated signal wave. It is found that the transient gain constant diminishes very rapidly if one chooses the pump pulse duration beyond the maximum gain point. Moreover, the desired value of the gain can be obtained by adjusting intensity and pulse duration of the pump and doping concentration of the medium concerned. Received 12 August 1999 and Received in final form 17 December 1999     

Transient changes in quartz resonators following exposure to pulse ionization

Abstract

This paper is a review of the transient effect of pulse ionization on the resonant frequency and Q of quartz resonators. A number of different samples of both natural and synthetic quartz crystals have been used. Fifth-overtone 5, 32, and 125 MHz thickness shear (AT-cut) crystal units were fabricated and studied using several different oscillator circuits, one of which was designed such that the resistance R_s (αQ ^?1) of the crystal unit at series resonance as well as frequency could be measured after pulse exposure. With the exception of one purposely altered crystal, all the resonators exhibited a negative-transient frequency offset after irradiation which thereafter anneals as a function of t ^?1/2 over nearly four decades of time. The pulse irradiation effect on Q ^?1 is most striking at 5 MHz in natural quartz units, which suffer a thirty-fold increase in acoustic absorption after exposure to 10⁴ rad. The transient increase in the acoustic absorption in natural quartz anneals within 10 seconds to a value somewhat larger than the preirradiation absorption. Theoretical models are described which account for these observations.     

The measurement of peak acoustic intensity generated by pulsed ultrasonic equipment

The peak acoustic intensity generated by pulsed ultrasonic equipment is calculated from measurement of the transmitted acoustic pulse by a calibrated, small, high frequency transducer. The average acoustic output is then computed from the intensity waveform, the beamwidth and the pulse repetition rate. Alternatively, the acoustic pulse may be measured by an uncalibrated transducer and the intensity is then computed from the average acoustic output.