余弦形负载超声变幅杆的设计与研究

研究余弦形负载超声变幅杆特性。求解了加负载时四种超声变幅杆的输入阻抗,得到加负载时输入阻抗和Mbius变换参数的统一算式。当变幅杆的输入抗分量为零时,计算了余弦形负载变幅杆的纵向振动共振频率方程和放大系数。由输入阻抗的表达式讨论了此类变幅杆的工作稳定性条件和相对阻抗相等点。结果表明由两种方法计算的共振频率方程是相同的;余弦形变幅杆的各种参量和方程与负载阻抗紧密相关;有负载力阻时1/4波长变幅杆的放大系数要比1/2波长变幅杆显著的多,和杆两端特性阻抗的几何平均值成正比,而与负载力组成反比。     

不同温度和温周期下白茨粗角萤叶甲的实验生命表

本文分析了七级恒温和五组变温条件下白茨粗角萤叶甲(Diorhabda rybakowi Weise)的种群生长,组建了生命表.得知不同恒温与幼期存活率的关系呈二次曲线型变化;变温对幼期存活率的影响受其变幅大小的影响,23—31℃的变温有利于该虫的世代存活.成虫寿命和产卵量随试验温度上升分别呈现“S”形下降和二次曲线趋势;变温下成虫寿命延长,产卵量明显增高.采用Weibull函数模型能很好地模拟试验温度和温周期条件下种群世代死亡率的变化.在19—35℃恒温下,种群周限增长率可用二次曲线方程表示.在17.8—37.8℃种群生长为增长趋势.在变温下,种群周限增长率和变温的变幅呈负相关.在平均温度为27℃、变幅为25.1℃时,种群生长保持稳定.     

镇江内江湿地不同演替阶段植物群落小气候日动态

2005年5月,选择镇江内江湿地具有代表性的裸地、虉草群落和芦苇群落,分别代表植被群落的不同演替阶段,测定不同群落、不同层次的光照强度、气温、土温和空气相对湿度,研究其植物群落小气候的日动态.结果表明,随演替由裸地到虉草群落到芦苇群落进行,群落内光照强度、气温和土壤温度均明显降低,日变幅减小.其中,日均光照强度由1 204.7 μmol·m^-2·s^-1降至141.28 μmol·m^-2·s^-1,日均变幅由1 126μmol·m^-2·s^-1降至265 μmol·m^-2·s^-1;日均气温由32.2 ℃降至24.9 ℃,日均变幅由12.75 ℃降至4.8 ℃;日均土温由21.83 ℃降至19.47 ℃,日均变幅由4.5 ℃降至2.1 ℃.群落内空气相对湿度明显升高(由58.95%增至87.3%）,变幅减小(由29.75%降至5.15%）.生境具有早期的开放性和后期的封闭性,小气候环境朝着更为阴、凉、湿的环境变化,且波动性减弱,稳定性增强.各群落内的光强、气温、湿度及土温之间均存在一定相关,但不同演替阶段各因子间相关程度各异.     

低能量心脏除颤的实验研究

本研究用22只犬建立实验模型。除颤脉冲采用非周期性衰减波,通过四种不同的除颤电极系统向心脏发放:1.双极导管电极;2.多极导管电极;3.导管—杯状心外膜电极;4.导管一体表电极。共除颤151次,成功133次,其中小于30J(焦耳)的成功除颤93次。上述各种电极在除颤能量小于30J时以导管—杯状心外膜电极的除颤成功率为最高,达84.5％。测量9只犬的导管除颤电极心肌阻抗值为431±117(?)(欧姆)。研制了一种多道除颤信号的A/D、D/A接口,在微型计算机上进行了除颤脉冲的波形分析和除颤能量的计算等试验。     

钾离子对心房T波(Ta波)的影响

在离体灌流的豚鼠心脏的心表面心电图上,进行了钾离子(K~ )对了 Ta 波影响的研究。提高灌流液中的 K~ 浓度(由6增到8、10和14毫当量/升)后,在28例实验中有26例(92.9%)的 Ta 波出现了明显的变化:(1)Ta 波的振幅显著增高;(2)Ta 波的上升支急剧加速;(3)P—aTa(由 P 波开始到 Ta 波顶点)的时间明显缩短。因而,Ta 波的形态由正常时升、降支基本对称的“帐篷形”,变为上升支十分陡峻而下降支非常迟缓的“锐角形”。降低灌流液中的 K~ 浓度(由6.0降到3.0和1.2毫当量/升)时,总共20例实验也都出现了 Ta 波的明显变化:(1)全部了 Ta 波(100%)的振幅都显著降低;(2)16例(80%)Ta 波的上升支变缓,使 P—aTa 的时间明显延长。因而,Ta 波的形态变得低平和迟缓。通过分析认为,灌流液中 K~ 浓度的变化,影响了心房肌复极化期间 K~ 的外流,可能是引起上述 Ta 波变化的原因。     

钙、钠离子对心房 T 波(Ta 波)的影响

本文用心电图记录离体豚鼠灌流心脏。提高灌流液中钙的浓度(由2.5分别提高到4.0、6.0、8.0和10.0mEq/L),导致全部的 Ta 波振幅降低,P—aTa 间期缩短。Ta 波的形态由正常时的“帐蓬形’变为“钝角形”。然而,降低灌流液中钙的浓度(由2.5降至2.0、1.2和0mEq/L)引起的相反变化,即 Ta 波振幅增加和 P—aTa 间期延长。另一方面,降低灌流液中钠的浓度(由143分别降至133、123和113mEq/L)出现 Ta 波振幅降低,但当提高灌流液中钠浓度时,所观察标本仅50%出现 Ta 波振幅升高。这提示,豚鼠心房肌对高钠浓度不如对低钠浓度敏感。T 波的变化可能是由于钠浓度改变的结果。     

天津扉门虫属二新种记述（缘毛目：鞘居科）

本文报道了在天津市发现并鉴定的扉门虫属二新种。波缘扉门虫,Thuricola limbata sp.nov.鞘呈花瓶形,鞘口边缘呈较大波浪形.歪扉门虫,Thuricola anomola sp. nov.,鞘形不规则,中部膨大。鞘前端1/4为一歪斜的颈部。     

Logistic方程中的速度参数(μ_L)等于种群的内禀增殖率(μ_m)吗?

众所周知,在养分等环境条件不受限制时,种群增殖遵循Malthus方程,形为: dx/xdt=μ_m (1) 此处,x为种群密度;t为时间;μ_m称为内禀增殖率,意为种群不受养分等环境因素限制时的一种取决于种群内部特性的最大可能增殖比速度(或增殖率)。在养分等环境条件有限时,常引用Logistic方程,形为:     

雄蚤阳茎体的研究：角叶蚤科三种雄蚤阳茎体的观察

用光镜和扫描电镜观察鞋形共系蚤Syngenopsyllus calceatus (Rothochild)、无值大锥蚤Macrostylophora euteles (Jordan et Rothschiold)和不等单蚤Monopsyllus anisus(Rothechild)的阳茎体侧面、背面和腹面。其中三种蚤阳茎体的背、腹面和无值大锥蚤阳茎体的侧面形态结构是首次报道。鞋形共系蚤有一对明显的阳茎囊突和一对与其相连的"c-骨片", 首次报道该蚤具有前距。无值大锥蚤具一对“茄形骨片”,阳茎钩突末端分为长而宽的腹叶和短而末端尖的背叶,阳茎内突后半部分特化为“后阳茎内突”。三种蚤的钩突桩略呈牛角形,由后弯向前。三种蚤阳茎体的形态结构差异显著,指出了它们是分类上值得注意的特征。认为交配时阳茎杆只在一定范围内作定向滑动。将阳茎体从蚤体内解剖出来,并且观察其背腹面,有助于清晰、完整和准确地观察其形态结构。     

飞虱科的一些新属和新种记述

1974至1977年期间,在全国各地采集了一批飞虱标本,现发表已定名的10个新种和一个新属。模式标本分别保存于各定名人的单位。 一、长突飞虱属 Stenocranus Fieber1.红条长突飞虱 Stenocranus hongtiaus Kuoh新种(图1) 头顶中央长度为基部宽的1.4倍,向前略渐收狭,侧缘儿直,基缘波曲,两中侧脊起自基部1/3处,于头顶端部汇合成一宽隆脊,显著突出于端缘,Y形脊明显,头顶基缘与Y形脊主干长度比为1.5:1,与基     

LONGITUDINAL IMPEDANCE OF THE SQUID GIANT AXON

Longitudinal alternating current impedance measurements have been made on the squid giant axon over the frequency range from 30 cycles per second to 200 kc. per second. Large sea water electrodes were used and the inter-electrode length was immersed in oil. The impedance at high frequency was approximately as predicted theoretically on the basis of the poorly conducting dielectric characteristics of the membrane previously determined. For the large majority of the axons, the impedance reached a maximum at a low frequency and the reactance then vanished at a frequency between 150 and 300 cycles per second. Below this frequency, the reactance was inductive, reaching a maximum and then approaching zero as the frequency was decreased. The inductive reactance is a property of the axon and requires that it contain an inductive structure. The variation of the impedance with interpolar distance indicates that the inductance is in the membrane. The impedance characteristics of the membrane as calculated from the measured longitudinal impedance of the axon may be expressed by an equivalent membrane circuit containing inductance, capacity, and resistance. For a square centimeter of membrane the capacity of 1 µf with dielectric loss is shunted by the series combination of a resistance of 400 ohms and an inductance of one-fifth henry.     

Low-frequency pulmonary impedance in rabbits and its response to inhaled methacholine.

We assessed pulmonary mechanics in six open-chest rabbits (3 young and 3 adult) by the forced oscillation technique between 0.16 and 10.64 Hz. Under control conditions, pulmonary resistance (RL) decreased markedly between 0.16 and 4 Hz, after which it became reasonably constant. Measurements of alveolar pressure from two alveolar capsules in each rabbit showed that the large decrease of RL with increasing frequency below 4 Hz was due to lung tissue rheology and that tissue resistance was close to zero above 4 Hz. Estimates of resistance and elastance, also obtained by fitting tidal ventilation data at 1 Hz to the equation of the linear single-compartment model, gave values for RL motion that were slightly higher than those obtained by forced oscillations at the same frequency, presumably because of the flow dependence of airways resistance. After treatment with increasing doses of aerosolized methacholine, RL and pulmonary elastance between 0.16 and 1.34 Hz progressively increased, as did the point at which the pulmonary reactance crossed zero (the resonant frequency). The alveolar pressure measurements showed the lung to become increasingly inhomogeneously ventilated in all six animals, whereas in the three younger rabbits lobar atelectasis developed at high methacholine concentrations and the alveolar capsules ceased to communicate with the central airways. We conclude that the low-frequency pulmonary impedance of rabbits exhibits the same qualitative features observed in other species and that it is a sensitive indicator of the changes in pulmonary mechanics occurring during bronchoconstriction.     

White noise measurement of squid axon membrane impedance.

The use of white noise techniques for system identification is illustrated by the following characterization of the subthreshold membrane impedance of the squid giant axon, space-clamped in a double sucrose gap. Power spectra were also computed. Depolarization increases the resonance, shifts the resonant frequently upward and decreases the membrane's inductive reactance. Reduced external Ca⁺⁺ increases the resonance, shifts the resonant frequency downward and increases the inductive reactance.     

Bioelectrical impedance analysis for the prediction of fat-free mass in buffalo calf

The objective of this study has been to develop a prediction equation of fat-free mass (FFM) from buffalo calves. Twenty buffaloes were fed ad libitum access at unifeed, with vitamin-mineral integration, for 14 months. Seven days before slaughtering, the animals were weighed and bioelectrical impedance measurements were collected. The data were analyzed by multiple linear regressions to evaluate the relationship between FFM and various predictor variables. Stepwise regression was used to eliminate variables that did not influence variation in the model. The value of resistance collected showed a decrease when the electrical frequency increases, while the values of reactance (Xc) increase. When using live weight (LW) and reactance at 500 and at 1000 kHz as independent variables, we obtained the best R2 Adj (0.967) and Durbin Watson statistic (2.596) that explain the prediction model (FFM = - 30.59 + 0.993LW + 0.150Xc500 - 0.123Xc1000 + 9.11). These results indicate that the use of bioelectrical impedance analysis has excellent potential as a rapid method, with minimal perturbation for the animal, to predict FFM in buffalo.     

Impedance measurement during air and He-O2 breathing before and after salbutamol in normal subjects

Total respiratory resistance and reactance from 4 to 52 Hz were determined by the method of forced pseudorandom noise oscillation in 20 normal male subjects before and after inhalation of 0.200 mg salbutamol (albuterol) and before and after the subjects were equilibrated with 80% He-20% O2. During air breathing, there was a statistically significant decrease of resistance values at lower frequencies after inhalation of salbutamol. When the subject was equilibrated with 80% He-20% O2, total respiratory resistance markedly decreased at all frequencies, and a negative frequency dependence of resistance was observed between 8 and 20 Hz. Resistance values further decreased during He-O2 breathing after inhalation of salbutamol. After inhalation of salbutamol, reactance values increased during air and He-O2 breathing. The density-dependent decrease of the real part of impedance can be explained by a decrease of turbulence in the larger airways. The bronchodilating effect of salbutamol was not influenced by a change in the physical properties of the inhaled gas. During He-O2 breathing, reactance values significantly decreased, resulting in an increase of resonant frequency due to a decrease of inductive reactance. It is concluded that an increase in the capacitance of the respiratory system must be supposed to explain the increase in reactance values after inhalation of the beta-adrenergic agonist salbutamol.     

Analytic assessment of the various bioimpedance methods used to estimate body water

Knowledge of patient fluid distribution would beuseful clinically. Both single-frequency (SF) and impedance modelingapproaches are proposed. The high intercorrelation between body watercompartments makes determining the best approach difficult. This studywas conducted to evaluate the merits of an SF approach. Mathematical simulation was performed to determine the effect of tissue change onresistance and reactance. Dilution results were reanalyzed, andresistance and parallel reactance were used to predict the intracellular water for two groups. Results indicated that the amountof intracellular and extracellular water conduction at any SF can varywith tissue change, and reactance at any SF is affected by all tissueparameters. Modeling provided a good prediction of dilutionintracellular and extracellular water, but an SF method did not.Intracellular, extracellular, and total body water were equallypredicted at all frequencies by SF resistance and parallel reactance.Extracellular and intracellular water are best measured throughmodeling, because only at the zero and infinite frequencies are theresults sensitive only to extracellular and intracellular water. At allother frequencies there are other effects.

     

Antenna impedance matching with neural networks

Impedance matching between transmission lines and antennas is an important and fundamental concept in electromagnetic theory. One definition of antenna impedance is the resistance and reactance seen at the antenna terminals or the ratio of electric to magnetic fields at the input. The primary intent of this paper is real-time compensation for changes in the driving point impedance of an antenna due to frequency deviations. In general, the driving point impedance of an antenna or antenna array is computed by numerical methods such as the method of moments or similar techniques. Some configurations do lend themselves to analytical solutions, which will be the primary focus of this work. This paper employs a neural control system to match antenna feed lines to two common antennas during frequency sweeps. In practice, impedance matching is performed off-line with Smith charts or relatively complex formulas but they rarely perform optimally over a large bandwidth. There have been very few attempts to compensate for matching errors while the transmission system is in operation and most techniques have been targeted to a relatively small range of frequencies. The approach proposed here employs three small neural networks to perform real-time impedance matching over a broad range of frequencies during transmitter operation. Double stub tuners are being explored in this paper but the approach can certainly be applied to other methodologies. The ultimate purpose of this work is the development of an inexpensive microcontroller-based system.     

Optimal Workloop Energetics of Muscle-Actuated Systems: An Impedance Matching View

Integrative approaches to studying the coupled dynamics of skeletal muscles with their loads while under neural control have focused largely on questions pertaining to the postural and dynamical stability of animals and humans. Prior studies have focused on how the central nervous system actively modulates muscle mechanical impedance to generate and stabilize motion and posture. However, the question of whether muscle impedance properties can be neurally modulated to create favorable mechanical energetics, particularly in the context of periodic tasks, remains open. Through muscle stiffness tuning, we hypothesize that a pair of antagonist muscles acting against a common load may produce significantly more power synergistically than individually when impedance matching conditions are met between muscle and load. Since neurally modulated muscle stiffness contributes to the coupled muscle-load stiffness, we further anticipate that power-optimal oscillation frequencies will occur at frequencies greater than the natural frequency of the load. These hypotheses were evaluated computationally by applying optimal control methods to a bilinear muscle model, and also evaluated through in vitro measurements on frog Plantaris longus muscles acting individually and in pairs upon a mass-spring-damper load. We find a 7-fold increase in mechanical power when antagonist muscles act synergistically compared to individually at a frequency higher than the load natural frequency. These observed behaviors are interpreted in the context of resonance tuning and the engineering notion of impedance matching. These findings suggest that the central nervous system can adopt strategies to harness inherent muscle impedance in relation to external loads to attain favorable mechanical energetics.