The effect of mass on frequency

Two experiments are described where an apparent decrease in frequency was detected when the optical path was in the vicinity of a mass. In the first experiment the 21-centimeter absorption line from Taurus A was observed near occultation by the sun. In the second experiment the frequency of a portable cesium clock was compared with the frequency of a similar clock which transmits its signals from Cape Fear, North Carolina. A decrease of frequency of the received signals as a function of the distance between the two clocks was apparent. Several relevant observations (the red shift of lines from the sun, the Mossbauer determination of the gravitational red shift, and the cosmological red shif) are discussed in view of the present results. confirmation.     

Trapped ions, laser cooling, and better clocks

Ions that are stored in electromagnetic "traps" provid the basis for extremely high resolution spectroscopy. By using lasers, the kinetic energy of the ions can be cooled to millikelvin temperatures, thereby suppressing Doppler frequency shifts. Potential accuracies of frequency standards and clocks based on such experiments are anticipated to be better than one part in 10(15).     

One-Pass水下管道检测系统在定向钻穿越管段中的优化应用

为保证穿越河流管段的正常运行,需要定期检测管道埋深.针对定向钻穿越大埋深管道检测过程中电磁信号不稳定导致检测结果不准确的问题,通过改变不同埋深穿越管段的电磁信号校准方法,对One-Pass水下管道检测系统进行优化,提高其在定向钻穿越管道检测中的检测精度.结果表明:利用优化后的电磁信号校准数据计算得到的结果与实际情况的符...     

Extraterrestrial intelligence: an observational approach

The microwave region of the electromagnetic spectrum, a plausible regime for signals from extraterrestrial intelligences, is largely unexplored. With new technology, particularly in data processing and low-noise reception, surveys can be conducted over broad regions of frequency and space with existing antennas at flux densities plausible for interstellar signals. An all-sky, broad-band survey lasting perhaps 5 years can be structured so that even negative results would establish significant boundaries on the regime in which such signals may be found. The technology and techniques developed and much of the data acquired would be applicable to radio astronomy and deep-space communications.     

控制昆虫和螨类滞育的光周期钟的研究进展

综述了控制昆虫和螨类滞育的光周期钟的研究方法与研究进展。光周期钟的模型有许多种,但基本可分为昼夜节律振荡器机制和非昼夜沙漏机制两种。光周期钟的研究内容主要包括24h昼夜循环的光周期反应、非24h昼夜循环的光周期反应、24h昼夜循环的夜间干扰试验、共鸣试验、Bünsow试验和对称骨干双稳定试验。对当前昆虫和螨类光周期时间测量机制的争议进行了评论。     

6MF-30便携式风力灭火机气动噪声分析

便携式风力灭火机是我国用于森林消防的重要设备,然而,其噪声会严重影响操作人员的生理和心理健康。本文采用FLUENT气动噪声场仿真和噪声测试试验相结合的方法,确定风力灭火机的主要气动噪声源,同时提出灭火机降噪优化的设计建议。结果表明:二维模型和大涡模拟(配合FW-H方程)结合的方法可以用于风力灭火机气动噪声的仿真,但在仿真过程中需考虑消声器的影响;风力灭火机主要气动噪声源为叶轮和涡舌,风筒噪声对其总噪声贡献较小;建议增加导流器等,以降低风力灭火机工作过程中操作人员的耳旁噪声。      

便携式风力灭火机的人机工程学评价

为研究便携式风力灭火机的振动、噪声和质量对操作人员生理和心理负荷的影响,通过试验对便携式风力灭火机(国产6MF-30和日本产HB2302)的把手振动和耳旁噪声进行测试,选取心率和反应时间对便携式风力灭火机进行人机工程学评价。结果表明:6MF-30的振动加速度、耳旁噪声、心率增加比、反应时间均大于HB2302;风力灭火机的耳旁噪声随着振动加速度的增加而增加,振动和噪声共同作用于操作人员,难以区分开,因此,将振动和噪声的综合作用视为一个影响因子,取得了较好的分析效果;质量和振动-噪声对心率增加比有显著影响,对反应时间没有显著影响,质量对心率的影响要大于振动-噪声。建议重新对6MF-30进行设计,重点考虑质量和减振降噪,发动机选择功率适中且质量轻的,前把手选择塑料作为主要材料。      

基于Kalman滤波的UWB的TOA估计

提出了一种基于卡尔曼滤波的TOA估计算法,充分利用了卡尔曼滤波的预测功能,以预测值为中心对接收信号进行加窗处理,对此窗口内的接收信号作主成份分析得到测量值,然后对预测值进行修正.实验结果表明,与传统的TOA估计算法相比,该算法不仅使信噪比提高了约8～12 dB、均方误差降低了3～4个数量级,而且更便于实时实现.     

电磁场对鲫血清4种生化指标的影响研究

为研究电磁场对鱼类生理的影响,试验中将体质量为(103±2)g的40尾鲫Carassius auratus幼鱼分组放置在相同水温(10℃±1℃)、不同电磁场强度(0、0.5、1.0、1.5、2.0 mT的恒定磁场)下培养,并对每组鱼血清中的碱性磷酸酶(AKP)、乙酰胆碱酯酶(AChE)、溶菌酶(LZM)活性和蛋白含量进行测定,试验周期为10 d,电磁场环境由亥姆霍兹线圈产生。结果表明:从试验第2天开始,电磁场试验组AKP活性明显低于对照组(P0.05);电磁场试验组AChE活性在2~10 d内逐渐减弱,并最终下降至初始活性的85.98%~95.47%;试验结束时,电磁场试验组LZM活性显著低于对照组(P0.05),蛋白含量较初始水平降低了24.61%。研究表明,电磁场对鲫血清4种生化指标的影响基本为抑制作用,说明多数外界环境的变化对鱼体本身会造成不利影响。     

基于微波反射法的冬笋探测器设计

针对目前我国冬笋采收只能依靠传统人工经验法,没有合适的探测设备的问题,根据高频电磁波作用下冬笋与土壤的介电特性差异导致反射系数显著不同的原理,设计基于微波反射法的冬笋探测器。该探测器通过2块贴片天线向土壤发射并接收电磁波信号;构建基于卷积神经网络的回波序列检测模型,用于所设计冬笋探测器接收回波信号的分类,利用回波信号的电磁波衰减强度判断土壤内是否有冬笋存在。试验结果表明,本研究提出的回波序列检测模型通过冬笋探测器回波信号判断土壤内有无冬笋的准确率为79.08%,漏警率为21.47%,虚警率为20.37%,与支持向量机以及频谱阈值法相比,回波序列检测模型在冬笋探测的准确率、虚警率、漏警率方面均为最优。该探测器能对地下冬笋位置进行预测,可提高冬笋采收效率。     

动态应变采集系统的设计

动态应变采集系统是通过便携式微机向单片机发送命令,由单片机根据频率,量程,数量等参数控制采集工作的进行。便携式微机用于对所得数据作进一步处理。该系统可方便的用于设备的可靠性验证,故障分析等。     

串联型罗仑兹混沌遮掩保密通信电路

设计了一种串联型罗仑兹混沌数字信号保密通信电路系统．该系统利用串联同步罗仑兹混沌电路进行信号混沌遮掩保密通信，在发送端和接收端之间只需传送一个叠加有传送信息的混沌信号即可实现高质量保密传送信息．模拟实验表明，在一定条件下传送数字信号时接收端可无失真地恢复所传信号．     

排列码算法应用于加密移动硬盘的研究

作为一种通信接口规范,通用串行总线(USB)因其具有传输速度快、可靠性高、使用灵活等优点被广泛应用在PC外设和便携式系统中。本文研究了将排列码算法应用于加密USB移动硬盘系统的设计方案,提出采用ALTERA公司的Maxplus II设计此算法的专门功能部件来提高数据传输加密/解密速度,解决了数据传输过程中的加密/解密速度慢的瓶颈问题,实现了一种具有加密功能且传输速度快的USB移动硬盘系统。     

Sr lattice clock at 1 x 10(-16) fractional uncertainty by remote optical evaluation with a Ca clock

Optical atomic clocks promise timekeeping at the highest precision and accuracy, owing to their high operating frequencies. Rigorous evaluations of these clocks require direct comparisons between them. We have realized a high-performance remote comparison of optical clocks over kilometer-scale urban distances, a key step for development, dissemination, and application of these optical standards. Through this remote comparison and a proper design of lattice-confined neutral atoms for clock operation, we evaluate the uncertainty of a strontium (Sr) optical lattice clock at the 1 x 10(-16) fractional level, surpassing the current best evaluations of cesium (Cs) primary standards. We also report on the observation of density-dependent effects in the spin-polarized fermionic sample and discuss the current limiting effect of blackbody radiation-induced frequency shifts.     

水果分选台单片机测控系统的研究

在现有电子称重式水果分选台的基础上，对其测控系统进行了重新研制，将原有的PC机控制替代为单片机控制。在保持原有测控功能的前提下。操作更加灵活、简便，降低了设备成本。该单片机测控系统以AT89C51为核心。配以信号调理电路、A／D转换单元、信号输出电路和键盘／显示单元等几个部分。工作时，通过压敏式压力传感器采集水果重量产生的电压模拟信号，信号经放大、滤波、模数转换后，进入单片机进行运算处理，最终实现对水果的动态称重和实时分选控制。试验结果表明，该测控系统设计方案合理可行，操作简便灵活；能够预先设置分选等级。实现多种水果的分选。具有较好的通用性和灵活性。     

化学镀铜杨木单板的导电性与电磁屏蔽效能分析

为了给电热式化学镀铜地热地板研究提供参考,对化学镀铜杨木单板的导电性与电磁屏蔽效能进行测试,分 析镀层厚度与吸收损耗、反射损耗、趋肤效应的关系。结果表明:镀铜杨木单板屏蔽效能主要以反射损耗为主,属 于反射型电磁屏蔽材料;表面电阻率随镀层厚度的增加呈减小趋势,横纹方向的表面电阻率是顺纹方向的3 倍左 右;频率越高,电磁波在镀铜层中传导时的趋肤深度越小,通过计算趋肤深度确定化学镀铜层的厚度,可以节省镀 铜时间并节约成本。      

Optical clocks and relativity

Observers in relative motion or at different gravitational potentials measure disparate clock rates. These predictions of relativity have previously been observed with atomic clocks at high velocities and with large changes in elevation. We observed time dilation from relative speeds of less than 10 meters per second by comparing two optical atomic clocks connected by a 75-meter length of optical fiber. We can now also detect time dilation due to a change in height near Earth's surface of less than 1 meter. This technique may be extended to the field of geodesy, with applications in geophysics and hydrology as well as in space-based tests of fundamental physics.     

Around-the-World Atomic Clocks: Predicted Relativistic Time Gains

During October 1971, four cesium beam atomic clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein's theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicts that the flying clocks, compared with reference clocks at the U.S. Naval Observatory, should have lost 40 +/- 23 nanoseconds during the eastward trip, and should have gained 275 +/- 21 nanoseconds during the westward trip. The observed time differences are presented in the report that follows this one.     

Erratum

In the Research News article "New test of variable gravitational constant" (23 Dec., p. 1316), in the third paragraph of column two on page 1317, a minus sign was left out of an exponent. The correct value for the drift of atomic clocks relative to gravitational clocks is (0.1 +/- 0.8) x 10(-11) per year.     

Light-driven changes in energy metabolism directly entrain the cyanobacterial circadian oscillator

Circadian clocks are self-sustained biological oscillators that can be entrained by environmental cues. Although this phenomenon has been studied in many organisms, the molecular mechanisms of entrainment remain unclear. Three cyanobacterial proteins and adenosine triphosphate (ATP) are sufficient to generate oscillations in phosphorylation in vitro. We show that changes in illumination that induce a phase shift in cultured cyanobacteria also cause changes in the ratio of ATP to adenosine diphosphate (ADP). When these nucleotide changes are simulated in the in vitro oscillator, they cause phase shifts similar to those observed in vivo. Physiological concentrations of ADP inhibit kinase activity in the oscillator, and a mathematical model constrained by data shows that this effect is sufficient to quantitatively explain entrainment of the cyanobacterial circadian clock.