DDS信号发生器在FPGA上的设计与实现

利用直接数字频率合成（Direct Digital Synthesis,DDS）技术,以现场可编程门阵列（Fieldprogrammable Gate Array,FPGA）芯片为载体,设计了一个信号发生器.该信号发生器能够产生频率、相位和幅度可调的周期信号.同时,DDS技术自身具有频率和相位调节功能,无需额外硬件调节电路.利用数模转换器基准电压可调特性设计实现了信号幅度调节.     

基于声发射信号信息熵的木材损伤断裂过程研究

为获得木材在弯曲破坏过程中的声发射（acoustic emission,AE）信号特征,从AE信号的随机性出发,利用AE信号信息熵辨识木材的损伤过程,并研究木材在不同损伤断裂水平下的AE信号分布特性。首先,对气干状态的榉木和樟子松试件进行三点弯曲试验,并通过谐振频率为150 kHz的AE传感器采集原始AE信号,采样频率设置为500 kHz。然后,采用小波变换重构AE信号波形,依据无AE发生时的信号幅值确定AE阈值,统计每秒内超过阈值的次数并作为AE活动计数,再以活动计数为随机变量定义AE信息熵。最后,依据信息熵值确定应变能释放的转折点,并结合三点弯曲试验的载荷-时间曲线,将木材损伤断裂过程划分为线性变形、非线性变形、宏观断裂3个阶段。以10 ms为间隔分析并统计AE信号的频率,获得木材弯曲破坏过程的AE信号频率分布情况,从而揭示不同损伤阶段的AE信号特征。结果表明,线性变形阶段,AE信号表现为低幅值、低频率,主要集中在30~55 kHz频段内;非线性变形和宏观断裂阶段,AE信号中既存在大量的30~55 kHz低频信号成分,又存在100~110 kHz和115~130 kHz的高频信号。研究提出的基于AE活动数信息熵能够准确反映应变能释放的集中程度,为木材损伤断裂水平评价提供了客观依据。     

灌注根超声脉冲检测法和判据的研究

本文论述了钴孔灌注桩超声脉中检测法的原理、仪器和方法.分析了当超声脉冲穿过缺陷区时其传播时间、幅值(或衰减)以及接收信号波形所呈现的变化.提出了基于"声时—深度"曲线的缺陷定量判据.即声时差值与斜率乘积判据.该判据能估算缺陷的性质和大小.而且,若将该判据与"幅值—深度"曲线综合运用,则可提高检测和判断结果的精度.     

基于高SBS阈值的HNLF产生高重复频率超短光脉冲

基于光纤中的四波混频(FWM)产生高重复频率超短光脉冲的原理,并为抑制光纤中的受激Brillouin散射(SBS),采用非均匀掺杂高SBS阈值非线性光纤,通过FWM对双拍频信号进行整形压缩,实验上获得了100GHz的高重复率超短光脉冲序列,进而分析了入纤功率对输出光脉冲的影响。     

马的水合氯醛麻醉脑电图观察

本文叙述了马的不同剂量水合氯醛静脉注射麻醉脑电图。水合氯醛剂量为4—6克/每100公斤体重,脑电图呈现口节律减弱,水合氯醛剂量为8克/每100公斤体重,脑电图呈现高波幅、长周期、混合型慢节律α——δ节律,有时呈现典型睡眠波形——Sigma节律;水合氯醛剂量为12克/每100公斤体重,脑电图呈现节律好、波形规律、波幅较低慢节律——θ节律。水合氯醛麻醉脑电图能够成功地提供客观控制麻醉深度的指标。     

任意波形电源的设计

世界许多国家的反倾销法中都设立了市场经济地位标准,其中欧盟、美国的市场经济地位标准(简称欧标、美标)最具代表性和典型性。欧标与美标的核心内容都与会计标准息息相关。揭示欧标与美标的实质,有助于提高我国涉案企业的反倾销会计应诉水平。     

脉冲电场对水稻纹枯菌的杀灭效果

探讨了脉冲电场杀菌的机理,仿真分析了培养液中脉冲电场的分布情况,仿真结果表明：进入培养液内脉冲电场时域波形的脉宽都有不同程度的变窄;脉冲上升沿越陡峭,进入培养液内部的脉冲电场峰值越高,穿透性越好。对脉冲电场水稻纹枯菌杀灭效果进行了试验研究,在同轴型处理室中分别以不同幅值的电磁脉冲（频率为2.5 Hz）和不同的作用时间对10-4稀释的水稻纹枯菌菌液进行处理,试验结果表明：当电磁脉冲的幅值较低时,可以通过延长灭菌的时间来提高灭菌效果;而幅值较高时,则脉冲幅值为灭菌效果的主要影响因素,延长灭菌时间的意义不大。     

Information delivery and the sensory evoked potential

The waveform of evoked responses recorded from human scalp is not determined solely by the physical eliciting stimulus, but also varies as a function of the effective information provided by the stimulus. There is a positive component whose latency is determined by the point in time at which ambiguity is reduced, and whose shape and amplitude are influenced by whether it is the presence or absence of an external event which delivers the information.     

Evidence for a ubiquitous seismic discontinuity at the base of the mantle

A sharp discontinuity at the base of Earth's mantle has been suggested from seismic waveform studies; the observed travel time and amplitude variations have been interpreted as changes in the depth of a spatially intermittent discontinuity. Most of the observed variations in travel times and the spatial intermittance of the seismic triplication can be reproduced by a ubiquitous first-order discontinuity superimposed on global seismic velocity structure derived from tomography. The observations can be modeled by a solid-solid phase transition that has a 200-kilometer elevation above the core-mantle boundary under adiabatic temperatures and a Clapeyron slope of about 6 megapascal per kelvin.     

Hemolysis near a transversely oscillating wire

Erythrocyte suspensions were subjected to hydrodynamic forces generated by a partially submerged tungsten wire set into transverse oscillation at 20 kilohertz. Free hemoglobin appears in solution when the oscillation amplitude exceeds a critical threshold value. The hemolysis probably results from stresses exerted on cell by a microstreaming field established near the wire.     

Hemolysis near an ultrasonically pulsating gas bubble

A small volume of an erythrocyte suspension was subjected to the action of a manipulated gas bubble set into stable oscillation at 20 kilohertz. Release of hemoglobin occurred when the oscillation amplitude exceeded a critical threshold. Hydrodynamic stresses resulting from acoustically induced small-scale eddying motion near the bubble may be the mechanism of hemolysis.     

Trampoline effect in extreme ground motion

In earthquake hazard assessment studies, the focus is usually on horizontal ground motion. However, records from the 14 June 2008 Iwate-Miyagi earthquake in Japan, a crustal event with a moment magnitude of 6.9, revealed an unprecedented vertical surface acceleration of nearly four times gravity, more than twice its horizontal counterpart. The vertical acceleration was distinctly asymmetric; the waveform envelope was about 1.6 times as large in the upward direction as in the downward direction, which is not explained by existing models of the soil response. We present a simple model of a mass bouncing on a trampoline to account for this asymmetry and the large vertical amplitude. The finding of a hitherto-unknown mode of strong ground motion may prompt major progress in near-source shaking assessments.     

Extracranial responses to acoustic clicks in man

Electronic averaging of potentials recorded from the human scalp reveals the presence of small average responses following the presentation of click stimuli. These responses are first detectable near the subject's psychophysical threshold and vary in amplitude with click intensity. It is suggested that the short-latency components of these responses are cortical in origin.     

Development of the equine vibration arthrometry system (EVAS) for the study of equine lameness

Friction caused at different articular surfaces in horses’ joints can produce various vibration signals. In this study, we collected and analyzed the articular vibration signals in the fetlock joints of a healthy horse, an aged horse, and a horse with laminitis using the equine vibration arthrometry system (EVAS). The data obtained from the EVAS enabled the researchers to easily understand the condition of the horses’ inner joints and to differentiate between the joints of healthy limbs and those of diseased limbs with musculoskeletal disorders. Furthermore, we also developed mathematical algorithms to analyze the data from the EVAS in this study. We identified two periodic waveform cycles for each horse’s step in the time domain. The negative waveform cycle first appeared at each aged horse’s step. The root-mean-square (RMS) values of both the positive and negative waveform cycles were significantly larger at the first periodic waveform in the aged horse. In contrast, the positive waveform cycle first appeared in each healthy horse’s step and the RMS values of the positive waveform cycle were significantly larger in the healthy horse. We also measured the energy of the articular vibration signals of the healthy and aged horses in the first and second periodic waveform cycle during each horse’s step. By analyzing and comparing articular vibration signals in these horses, we were able to determine which of the horses had a musculoskeletal disorder. EVAS is a simple, convenient and non-invasive method of identifying articular problems in equine joints.     

基于刺探电位图谱的石蒜绵粉蚧在2种植物上的取食行为研究

利用刺探电位图谱（Electronic penetration graph, EPG）技术研究了石蒜绵粉蚧（Phenacoccus solani）在胧月（Graptopetalum paraguayense）和番茄（Lycopersicon esculentum）上的取食行为。结果表明,石蒜绵粉蚧在这2种植物上取食时,可产生A波、B波、C波、pd波、E波、E1e波以及G波等基本波型,其中,E1e波为主要的持续性取食波形;取食番茄时,E波偶发且该波内未出现典型的被动取食波（E2波）。石蒜绵粉蚧在2种植物上的取食行为差异显著,相较于后者,石蒜绵粉蚧在胧月上取食时,位点转换频率更低、穿透叶表速度更快、获取叶肉营养更多、持续性取食时间更长,且期间未出现E波而长时间发生E1e波,E1e波内出现典型的E1波和E2波（但电动势水平为零）的亚波型。本研究结果说明了石蒜绵粉蚧在2种植物上取食时产生的EPG波形与韧皮部取食型昆虫类似,但其主要取食波形为E1e波,表明石蒜绵粉蚧在多肉植物胧月上具有更强的适应性和为害风险。     

Curare and pancuronium compared: effects on previously undepressed mammalian myoneural junctions

Curare and pancuronium have multiple effects on previously undepressed rat diaphragm; these include depression of transmitter output and prolongation of the refractory period of prejunctional structures. The effect of curare on motor nerve terminals is greater than that of pancuronium. Both drugs depress postjunctional receptors; but curare, in addition, raises the threshold for the generation of muscle action potentials. In addition, these results raise questions about the validity of statistical methods used to calculate transmitter output.     

干旱区苹果园小气候特征分析

以干旱区成龄苹果园为研究对象,分析了宁夏灵武陶林园艺场果园内不同季节不同层次气象要素的时间变化特征。结果表明:日平均光照度为春季夏季秋季冬季。果园内不同季节1.5 m和3.0 m高度气温都呈现出昼高夜低型的日变化波形;晴天气温变化出现单峰型曲线,阴天出现双峰型曲线,雨天变化振幅较小,两高度间差异也较小。果园内湿度较大,不同季节1.5 m和3.0 m高度相对湿度日变化均为夜高昼低的波形曲线。从风速看,春季和冬季日变化特征最明显,日振幅也最大,夏、秋季风速相对较小。不同季节地表0 cm地温受气温变化影响最大,5 cm、10 cm次之,20 cm地温受气温变化影响最小。     

褐色橘蚜在健康与CTV植株上的EPG比较

利用刺探电位图谱（EPG）技术对褐色橘蚜Toxopter acitricida （Kirkaldy）在健康与感染CTV的植株上的取食行为进行了比较研究.结果显示,褐色橘蚜在二者上均产生8种取食波形,分别为非刺探波（np波）、路径波（A波、B波、C波）、Pd波、韧皮部分泌唾液波（E1波）、韧皮部被动吸食波（E2波）以及木质部主动吸食波（G波）.刺探过程中,二者非刺探总时间（np波）存在差异;褐色橘蚜在健康植株上的刺探次数最多且C波的总持续时间最长,与感病植株差异显著.感病植株上,E1波的次数和持续时间均显著多于健康植株.褐色橘蚜在感病植株上E2波的总持续时间为（241.33±24.12 min）,显著长于在健康植株上（160.30 ±24.63 min）的持续时间.由此可初步推断,感染CTV的植株在一定程度上会增加褐色橘蚜获毒与传毒的几率.     

加味柴胡疏肝散治疗功能性消化不良(肝郁气滞证)临床疗效观察

目的 探讨加味柴胡疏肝散治疗功能性消化不良（肝郁气滞证）的临床疗效及其对胃电图的影响。方法 选择符合纳入标准的功能性消化不良肝郁气滞证患者120例,随机分为观察组和对照组各60例,观察组服用加味柴胡疏肝散,对照组口服泮托拉唑肠溶胶囊及多潘立酮片剂,观察比较两组治疗后的临床疗效、中医证候积分变化及胃电频率与幅值的变化情况。结果 观察组总有效率91.67%,对照组总有效率78.33%,两组比较差异有统计学意义（P<0.05）;两组治疗后较治疗前中医证候积分均有所降低,且观察组优于对照组,差异有统计学意义（P<0.05）;两组治疗后空腹及餐后的胃电频率及幅值均较治疗前明显提高,且观察组优于对照组,差异有统计学意义（P<0.05）。结论 加味柴胡疏肝散治疗功能性消化不良肝郁气滞证患者疗效确切,能明显改善中医证候,提高胃电频率和幅值,增加胃动力,安全无副作用,值得临床推广。     

Habituation: occurrence at a neuromuscular junction

At the neuromuscular junctions between the motor giant axon and fast flexor muscle fibers in crayfish, stimulation at frequencies of one per minute produces a large decline in the amplitude of excitatory junctional potentials. Recovery (dishabituation) can be brought about by increases in stimulus frequency, which trigger a potentiation process; at still higher frequencies, a second form of depression intervenes. The last process appears to be due to depletion of transmitter; the first probably depends instead upon electrical changes in presynaptic terminals. Because of the interactions between the three processes, the junctions display the properties of habituation and dishabituation usually associated with complex central nervous networks.