双声学共振腔体蜗舌降低离心式风机噪声的研究

论述了双声学共振腔体蜗舌降低离心式风机噪声的新方法,进一步提出了双声学共振腔体蜗舌的解析模型。经实验验证,当采用双声学共振腔体蜗舌时,可降低基频噪声２５２ｄＢ（Ａ）。降低一次谐波噪声１６３ｄＢ（Ａ）,总声压级下降９７ｄＢ（Ａ）,比单声学共振腔体蜗舌总声压级多下降３４ｄＢ（Ａ）,风机气动力性能基本不受影响。     

开关磁阻电机稳态特性的等效磁网络模型分析方法Ⅰ.数学模型

本文利用开关磁阻电机的等效磁网络模型,推导出了电机绕组满足的以绕组磁链为状态变量的微分方程,建立了电机稳态运行分析的数学模型。本文成功地将非线性磁参数法的思想从单相电流系统推广到了多相电流系统,对开关磁阻电机的理论研究具有重要的意义。     

Breathhold imaging of the upper abdomen using a circular polarized-array coil: comparison with standard body coil imaging

Current studies emphasize the use of array coils to decrease noise and increase the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). We applied Tl-weighted and T2-weighted standard nonbreathhold spin echo (SE) sequences and Tl-weighted FLASH, TurboFLASH, T2-weighted spin-echo time (TSE), and heavily T2-weighted half Fourier acquisition single-shot TSE (HASTE) sequences during breathhold for abdominal imaging in 15 normal volunteers. The breathhold scans were performed using both a standard coil and a circular polarized array coil. We analyzed the signal intensity (SI), SNR, and CNR of abdominal organs in all sequences. SNRs increased in all cases by an overall factor of 3 due to an 8% increase in overall Sis and a 50% decrease in noise when applying the array coil. Although the array-coil FLASH sequence performed at least as well as the respective SE sequence, the SNRs of the array-coil TurboFLASH, TSE breathhold, and HASTE sequences were generally lower. We conclude that array-coil imaging significantly improves fast imaging of the abdomen.     

3-Methyl-α-himachalene: Proposed structure for novel homosesquiterpene sex pheromone ofLutzomyia longipalpis (diptera: Psychodidae) from Jacobina,Brazil

The principal behaviorally active volatile component (ca. 90% +) of the sex pheromone glands ofLutzomyia longipalpis from Jacobina. Brazil, has been isolated and characterized as a novel homosesquiterpene with the structure 3-methyl--himachalene (C₁₆H₂₆). A minor component (ca. 10%) of the gland extract has also been identified as the sesquiterpene-himachalene (C₁₅H₂₄). This work confirms that there are at least 3 members of theL. longipalpis species complex.     

Improvements in data reduction in direct pulse heating calorimetry

This paper describes improvements introduced in data reduction in direct heating pulse specific heat experiments. In calculations of specific heat, it is necessary to calculate the first derivative of the recorded temperature data as a function of time. The error induced by different numerical differentiation techniques can represent a significant part of the overall measurement error. Thus, different digital filtering techniques, differentiation, and smoothing algorithms were applied and tested to examine their influence on the minimization of errors induced by noise, which is unavoidable in measured signals. A minimum square error criterion was applied in designing digital filters, with arbitrary prescribed magnitude characteristics. Attention was paid to applications when one or more structural phase transitions in the specimen material occur within the temperature range covered by the experiment. The cases where the frequency spectrum of induced noise overlaps with the spectrum of temperature transient signals originating from phase transitions were analyzed in detail. The effectiveness of the methods of extracting the final specific heat data from a noisy signal using different digital filtering techniques is demonstrated.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

相控式与偏磁式消弧线圈的研究

分析了相控式消弧线圈与偏磁式消弧线圈的工作原理,详细介绍了这两种消弧线圈补偿电流的特性,阐述了电网正常运行和发生单相接地故障时这两种消弧线圈的工作特性,从而得出结论:带滤波电路的相控式消弧线圈有一定的滤波作用,但由于存在滤波电路而使相控式消弧线圈的补偿效果较差;偏磁式消弧线圈既能有效滤波,又能起到很好的补偿效果。     

GPS失效时组合导航系统修正方法研究

针对采用低成本惯性元件的MEMS-IMU/GPS组合导航系统在GPS信号长时间失效后系统趋于发散的问题,在研究捷联航姿解算算法、加速计测量姿态角算法和磁传感器解算航向角算法的基础上,提出将航姿辅助修正算法引入组合导航系统中,一旦系统检测到无效信号出现,则能自动切换到辅助修正状态,使导航结果被抑制在0.5°左右;通过半实物仿真实验,证明了该方法能够有效解决GPS信号长时间失效后系统发散问题,满足了在低成本MEMS惯性元件基础上的高精度导航要求。     

磁罗盘姿态解算及误差补偿

详细介绍了磁罗盘的姿态解算原理,并分析了造成磁罗盘解算误差的主要因素,提出了基于最小二乘的36位置法,重点对其中的罗差以及制造误差中的零位误差和灵敏度误差进行了补偿修正;并用项目试验验证得出:当只进行零位误差和灵敏度误差修正时,磁罗盘的偏航角解算误差最大可达3°;而经过罗差补偿后,磁罗盘的偏航角解算误差可控制在0.5°以内;实验结果表明,经过补偿后,磁罗盘的解算精度明显提高,且成本低,使用简便,适用范围广。     

基于MAXQ3108+DS8102的三相智能电能表设计

针对目前市场上采用电磁式电流互感器作为电流传感器的三相智能电能表计量精度普遍易受外部强磁场干扰的不足,采用美信半导体公司提出的MAXQ3108+DS8102芯片组,解决方案设计了一款采用锰铜分流器作为电流传感器的三相智能电能表,解决了锰铜分流器采样电流方式下各相电压、电流信号与数据采集MCU电气隔离的技术瓶颈,并详细阐述了信号采集与测量的过程;样机测试结果表明:文中设计的三相智能电表能够有效抑制外部强磁场干扰,有功电能计量精度满足IEC62053标准中有功0.5S级相关技术指标要求。