Flexible media — recent developments from the tribology point of view

With the increase in the recording density of hard disk systems, the demand on the increase in the data recording capacity of tape drive systems as back-up systems is increasing. One of the advantages of the tape drive systems is high volumetric recording density, which is obtained by high areal recording density and thin tapes. The areal recording density can be increased by introducing high performance tapes, such as metal evaporated tapes, with superior magnetic characteristics and smooth magnetic surface to reduce the spacing loss. However, a smoother surface often produces a higher friction coefficient, which could cause tape damage by rotary heads and unstable tape runnability in the tape drives. Adoption of MR heads to tape drive systems is also effective in increasing the areal recording density. However, the wear allowance of the MR heads (shield type) is much smaller than that of the inductive heads. Thinner tapes show lower mechanical stiffness in general, which could cause damage to tape edges easily during tape transportation. In the second or later generation of tape drive systems, a thinner tape is often introduced. These thinner tapes should also have the interchangeability of the original thickness tape. New materials for a base film, such as PEN (polyethylene naphthalate) or aramid in which the elastic moduli are larger than those of PET, are required for thinner tapes. It was found that these side effects by the increase in the volumetric recording density can be improved by tribology. The tribological improvements from the drive design side is very important, as well as from the tape design side.     

改进的任意基FFT整序算法

本文提出了一种改进的适合于任意基ＦＦＴ变换的整序算法,改进整序算法采用循环嵌套结构,减少了运算量,实验结果表明,改进整序算法的运算时间较其它整序算法少。     

A NEW METHOD OF DOPPLER CENTROID ESTIMATION FOR SPACEBORNE SAR-AMPLITUDE CORRELATION METHOD

The linear relationship between Doppler centroid and range walking in spaceborne SAR data is analyzed, and a new method to estimate Doppler centroid is proposed, which is so called amplitude correlation method. Compared with clutter-lock method which is widely used now, the new method has much less computation burden and is able to give higher estimation accuracy for a quasi-homogeneous scene or a non-homogeneous scene. This is clearly verified by the experimental results of estimating Doppler centroid for SEASAT-A raw data.     

BER Performance of Frequency Domain Differential Demodulation OFDM in Flat Fading Channel

A closed form expression for the bit error rate (BER) performance of frequency domaindifferential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fadingchannel is derived.The performance is evaluated by computer simulation and compared with the timedomain differential demodulation(TDDD).The results indicate that the performance of FDDD is betterthan that of TDDD,and the lower band of BER in the former is lower than that of the latter.     

基于Dueling DQN的临近空间飞行器再入轨迹规划

针对临近空间飞行器再入段禁飞区规避制导问题,构建了临近空间飞行器再入过程横侧向制导的马尔可夫决策过程（Markov decision process,MDP）模型。基于竞争深度Q网络（dueling deep Q network,Dueling DQN）,设计了横侧向制导律及满足射程需求与禁飞区规避需求的再入过程奖励函数。经仿真验证,该横侧向制导律能够通过改变倾侧角符号实现禁飞区规避,并导引飞行器到达目标区域,具备较高精度,验证了方法的有效性。     

高速异步主轴电机的热分析与冷却结构设计

高速主轴电机是电主轴的关键核心部件,电机发热直接影响电主轴的加工精度和运行可靠性。以一台10万转主轴异步电机为例,对高速异步主轴电动机进行深入的热分析,设计高效的散热冷却结构,确保主轴电机的可靠平稳运行。确定主轴电机的主要热源,研究转子转速、转子表面粗糙度对主轴电机风摩损耗的影响规律;考虑旋转磁场和谐波对铁耗计算的影响,采用齿轭分区的有限元法提高仿真精度,分析电机铁耗的分布规律。基于流体力学对电机进行3D热仿真,对比主流的周向螺旋型和轴向Z字型两种冷却结构的冷却效果,确定高效的冷却结构设计方案,并进一步采用转子铁心开空气槽的设计方案,增加转子铁心与转轴之间的热阻,提高电机的散热能力,确保电机的转轴温升在安全范围内,最后校核转子结构的机械强度,保证主轴电机运行的可靠性。     

SAR stereo imaging algorithm based on Capon spectrum estimation

This letter presents a novel approach for the Synthetic Aperture Radar （SAR） stereo imaging based on the Capon spectrum estimation technique. In order to deal with nonuniform sampling space and lead to super resolution in the elevation direction, Capon approach is used to focus the SAR data on a certain height. Results obtained on simulated data demonstrate the feasibility of the Capon based algorithm. Compared with the classical Fast Fourier Transform （FFT）, the Capon based algorithm shows better resolution quality.     

Fabrication and flow-sensor application of flexible thermal MEMS device based on Cu on polyimide substrate

A Cu on polyimide (COP) substrate was proposed as a MEMS material, and the fabrication process for a flexible thermal MEMS sensor was developed. The COP substrate application to MEMS devices has the advantage that typical MEMS structures fabricated in a SOI wafer in the past—such as a diaphragm, a beam, a heater formed on a diaphragm—can also be easily produced in the COP substrate in the flexible fashion. These structures can be used as the sensing element in various physical sensors, such as flow, acceleration, and shear stress sensors. A flexible thermal MEMS sensor was produced by using a lift-off process and sacrificial etching of a copper layer on the COP substrate. A metal film working as a flow sensing element was formed on a thin polyimide membrane produced by the sacrificial etching. The fabricated flexible thermal MEMS sensor was used as a flow sensor, and its characteristics were evaluated. The obtained sensor output versus the flow rate curve closely matched the approximate curve derived using King’s law. The rising and falling response times obtained were 0.50 and 0.67 s, respectively.

     

Reliability of ultrasonographic measurements of bovine sole structures in relation to sole horn thickness,measured by computed tomography,and sole horn hardness

The goal of the present study was to determine the effect of sole horn thickness (SHT) and sole horn hardness (SHD) on ultrasonographic visualization of sole structures in the inner and outer claws of 150 Holstein-Friesian cows, and to evaluate different ultrasound frequencies for this purpose. Ultrasonographic views of the sole structure were considered complete when 3 echogenic lines, representing the ventral surface of the sole horn, the borders of the sole horn and soft-tissue layer, and the ventral surface of the distal phalanx, were seen. The proportion of complete ultrasonographic views of the sole structures, designated as the ultrasonographic visualization proportion (UVP), and the measurement errors of SHT were evaluated by comparing images from computed tomography (CT) and ultrasonography. The latter images were generated using 3 different probes, frequencies of 6.5 and 5.0 MHz, and 2 different ultrasound machines (#1 and #2) to assess the apex, middle, and heel regions of the claws. The UVP were 60.8 to 77.9% for the 6.5-MHz probe in ultrasound machine #1 (probe A), which were lower than those (>90%) for both the 5.0-MHz probe in ultrasound machine #1 (probe B) and the 5.0-MHz probe in ultrasound machine #2 (probe C). The UVP was significantly lower in claws with an SHD ≥50 units than in claws with an SHD <40 or 40 to <50 units (UVP: 77.1% compared with 93.7 and 91.4%, respectively) when measured with probe B. In claws with an SHT <10 mm, the UVP was significantly lower when SHD was ≥50 units compared with <40 or 40 to >50 units; the values were 69.0% versus 91.3 and 85.9%, respectively, for probe A, and 89.7% versus 100 and 100%, respectively, for probe B. When SHT were measured by either probes A or B in ultrasound machine #1, the proportions of claws in which ultrasonographic values were within a ±1 mm range compared with the values obtained by CT were 84.9 to 91.3% for CT-determined SHT <5 mm, 66.7 to 71.9% for CT-determined SHT 5 to <7 mm, 28.9 to 51.2% for CT-determined SHT 7 to <10 mm, and 6.2 to 19.7% for CT-determined SHT ≥10 mm. The data indicated that increased SHT was associated with a decrease in ultrasonographic measurement accuracy. In claws with an SHT <5 mm, the high proportion of ultrasonographic values that were accurate within a ±1 mm range suggests that this imaging modality would be useful in cows with thin soles.     

Cost-Reliability Optimal Release Policies for Software Systems

This paper extends an optimal software release problem to both cost and reliability requirements. The optimum software release time is determined both by minimizing a total average software cost and satisfying a software reliability requirement. The underlying model is software reliability growth described by a nonhomogeneous Poisson process.