A system for controlled microwave heating of small samples.

A system for the controlled thawing and heating of small samples in a waveguide is described. A means of maintaining constant absorbed power within the sample over a wide range of sample parameters is a major feature of the system. Provision for sensing the melting point of immersed samples is include. Samples are continuously rotated to improve heating uniformity.     

高校课堂教学现状分析及学生创新素质培养

以重庆市部分高校进行的关于教学方面的问卷调查为基础,分析了当前高校课堂教学中存在的一系列问题,提出了工科课堂教学应以创新素质培养为重点,应从教学环境、教学方式、教学内容、考核方式等方面对课堂教学模式进行改革.     

Microwave sintering process model.

In order to simulate and optimize the microwave sintering of a silicon nitride and tungsten carbide/cobalt toolbits process, a microwave sintering process model has been built. A cylindrical sintering furnace was used containing a heat insulating layer, a susceptor layer, and an alumina tube containing the green toolbit parts between parallel, electrically conductive, graphite plates. Dielectric and absorption properties of the silicon nitride green parts, the tungsten carbide/cobalt green parts, and an oxidizable susceptor material were measured using perturbation and waveguide transmission methods. Microwave absorption data were measured over a temperature range from 20 degrees C to 800 degrees C. These data were then used in the microwave process model which assumed plane wave propagation along the radial direction and included the microwave reflection at each interface between the materials and the microwave absorption in the bulk materials. Heat transfer between the components inside the cylindrical sintering furnace was also included in the model. The simulated heating process data for both silicon nitride and tungsten carbide/cobalt samples closely follow the experimental data. By varying the physical parameters of the sintering furnace model, such as the thickness of the susceptor layer, the thickness of the allumina tube wall, the sample load volume and the graphite plate mass, the model data predicts their effects which are helpful in optimizing those parameters in the industrial sintering process.     

Single-frequency relative Q measurements using perturbation theory

Traditionally, Q measurement requires a nonzero frequency bandwidth or time period. Contrasted to this, the principle of a new single-frequency relative Q measurement method is developed. It is found that Q is directly or inversely proportional to the normalized input resonant resistance if a moderate perturbation condition is satisfied. Theoretical proof and experimental verification of the single-frequency method's validity are presented. Consequently, a relative and, often used in dielectric measurements, can be measured using a much simpler measurement system. Moreover, error analysis shows that, in making a relative Q measurement, the error in the single-frequency method is smaller than that in the traditional bandpass method when using a reflectometer     

A Finite Element Approach to Modeling Abrasive Wear Modes

Machine components operating in sandy environments will wear because of the abrasive interaction with sand particles. In this work, a method is derived to predict the amount of wear caused by such abrasive action, in order to improve the maintenance concept of the components. A finite element model is used to simulate various tips scratching a smooth surface. The model is verified by comparing the obtained results with a set of experiments performed earlier (M. Woldman, et al., 2013, Wear, 301(1–2), pp 76–81).     

New results for coaxial re-entrant cavity with partially dielectricfilled gap

Resonant frequencies, Q-factor and electromagnetic field intensity are presented for a set of varied parameters of a coaxial re-entrant cavity with a gap partially filled with a dielectric. The cavity is analyzed using the mode matching technique. The numerical results are found to be in good agreement with experimental data. Based on the numerical results, a scheme for mode identification is proposed and the mode transition is discussed. Furthermore, the equivalent gap capacitances are obtained and compared with the results from an existing formula which has been modified for the dielectric loaded gap     

Generation and transmission of FM and π/4 DQPSK signals atmicrowave frequencies using harmonic generation and optoelectronicmixing in Mach-Zehnder modulators

A novel method of using the harmonic generation and optoelectronic mixing properties of Mach-Zehnder modulators to generate modulated subcarrier signals at high-order harmonics of the input signals is presented. The method permits the simultaneous transmission over optical fiber of a modulated and an unmodulated signal, both at high-order harmonic frequencies of the input signals, for the purpose of transmitting both a local oscillator tone and the modulated signal required at a base station for microcellular applications. We present the theory of operation and demonstrate the validity of the concept with a narrow band single-tone FM experiment as well as a 20-Mb/s π/4 DQPSK experiment     

Fertility after conservative and radical surgery for tubal pregnancy

A retrospective cohort study was set up to evaluate the effectiveness of conservative and radical surgery for tubal pregnancy towards subsequent fertility. Consecutive patients undergoing conservative or radical surgery for tubal pregnancy between January 1990 and August 1993 in two university hospitals were included in the study. Outcome measures were spontaneous intrauterine pregnancy (IUP) and repeat ectopic pregnancy (EP). Of the 135 patients analysed, 56 underwent conservative surgery and 79 underwent radical surgery. Patients treated with conservative surgery achieved a higher 3-year cumulative pregnancy rate than those treated radically (P < 0.001, log-rank test). In patients treated conservatively, there was only one spontaneous IUP in the period between 18 months and 3 years after the tubal pregnancy. In contrast, patients treated radically continued to conceive in this period. Multivariate analysis showed a fecundity rate ratio (FRR) of 1.9 [95% confidence interval (CI): 0.91 to 3.8] for IUP after conservative surgery in the first 18 months of follow-up. In patients with a history of bilateral tubal disease the FRR was 3.1 (95% CI: 0.76 to 12), whereas in patients without a history of bilateral tubal disease the FRR was 1.4 (95% CI: 0.13 to 16). The FRR for repeat EP was 2.4 (95% CI: 0.57 to 11). Our data indicate a beneficial effect of conservative surgery towards subsequent fertility that was not, however, statistically significant in the multivariate analysis. In view of these inconclusive data and the importance of this major health problem, randomized studies are required to assess whether conservative surgery really improves the fertility prospects of patients with tubal pregnancy.     

Numerical analysis of a movable dielectric gap in coaxialresonators for dielectric measurements

For the purpose of improving dielectric measurements, a movable dielectric gap in coaxial resonators is analyzed using numerical simulations. The obtained field distributions, loading factors, and resonant frequency shifts for different gap positions are presented and discussed     

利多卡因和左旋布比卡因对大鼠臂丛神经功能的影响

目的探讨利多卡因和左旋布比卡因对大鼠臂丛神经功能的影响。方法将54只SD大鼠按随机数字表法分为9组,每组6只：随机选取大鼠的一侧,生理盐水对照组（NS组）于腋鞘内注入生理盐水1mL,利多卡因L1-L4组于腋鞘内分别注入0.25%、0.50%、1.00%、2.00%利多卡因1mL,左旋布比卡因Z1-Z4组于腋鞘内分别注入0.25%、0.50%、1.00%、2.00%左旋布比卡因1mL。给药5d后,检测9组大鼠臂丛神经动作电位（AP）最大振幅、神经传导速度（NCV）的变化。结果与NS组相比,L2-L4组、Z3-Z4组臂丛神经AP的最大振幅降低,NCV减慢（P〈0.05）;组内比较：随着药物浓度递增,L2-L4组、Z3-Z4组臂丛神经AP的最大振幅降低,NCV减慢（P〈0.05）;相同浓度利多卡因和左旋布比卡因比较：利多卡因组臂丛神经AP的最大振幅降低,NCV减慢（P〈0.05）。结论相同浓度利多卡因对臂丛神经功能的损害较左旋布比卡因更大。