Neural-network-based classification of Space Acceleration Measurement Systems (SAMS) data via supervised learning

This paper illustrates the applicability of neural networks in classifying events using Space Acceleration Measurement System (SAMS) data. Computer programs have been written in the MATLAB environment for the following purposes: automatic retrieval of SAMS data from NASA CDROM disks, computation of power spectral densities for SAMS data and construction of input patterns for the training of a multi-layer neural network (MNN). The MNN has been trained using the backpropagation learning algorithm and the SAMS data collected on the STS-50 Space Shuttle mission for three crew exercise events. It is found that the trained MNN is highly successful in classifying events. In addition, the performance of MNN is found to be better than that of the nearest neighbor classifier.     

Pyrolysis-gas chromatography/mass spectrometry analyses of biological particulates collected during recent space shuttle missions

Biological particulates collected on air filters during shuttle missions (STS-40 and STS-42) were identified using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). A method was developed for identifying the atmospheric particles and their sources through the analysis of standard materials and the selection of "marker" compounds specific to the particle type. Pyrolysis spectra of biological standards were compared with those of airborne particles collected during two space shuttle missions; marker compounds present in the shuttle particle spectra were matched with those of the standards to identify the source of particles. Particles of 0,5--1-mm diameter and weighing as little as 40 micrograms could be identified using this technique. The Py-GC/MS method identified rat food and soilless plant-growth media as two sources of particles collected from the shuttle atmosphere during flight.     

Monitoring space shuttle air quality using the Jet Propulsion Laboratory electronic nose

A miniature electronic nose (ENose) has been designed and built at the Jet Propulsion Laboratory (JPL), Pasadena, CA, and was designed to detect, identify, and quantify ten common contaminants and relative humidity changes. The sensing array includes 32 sensing films made from polymer carbon-black composites. Event identification and quantification were done using the Levenberg-Marquart nonlinear least squares method. After successful ground training, this ENose was used in a demonstration experiment aboard STS-95 (October-November, 1998), in which the ENose was operated continuously for six days and recorded the sensors' response to the air in the mid-deck. Air samples were collected daily and analyzed independently after the flight. Changes in shuttle-cabin humidity were detected and quantified by the JPL ENose; neither the ENose nor the air samples detected any of the contaminants on the target list. The device is microgravity insensitive.     

Results of nDOSE and HiDOSE Experiments for Dosimetric Evaluation During STS-134 Mission

HiDOSE (Heavy ion DOSimetry Experiment) and nDOSE (neutron DOSimetry Experiment) experiments conducted as a part of BIOKIS (Biokon in Space) payload were designed to measure the dose equivalent due to charged particles and to neutron field, on the entire energy range, during STS-134 mission. Given the complexity of the radiation field in space environment, dose measurements should be considered an asset of any space mission, and for this reason HiDOSE and nDOSE experiments represent an important contribution to the radiation environment assessment during this mission, a short duration flight. The results of these experiments, obtained using Thermo Luminescence Dosimeters (TLDs) to evaluate the charged particles dosimetry and neutron bubbles dosimeters and stack bismuth track dosimeters for neutron dosimetry, indicate that the dose equivalent rate due to space radiation exposure during the STS-134 mission is in accordance with the results obtained from long duration flights.     

Adsorption properties of C10E8 at water/ hexane interface investigated onboard STS-107, by the FAST facility

The dynamic adsorption properties of a non-ionic surfactant C₁₀E₈ at the water-hexane interface have been investigated in microgravity using FAST (Facility for Adsorption and Surface Tension studies) onboard the Shuttle STS-107. To obtain a complete characterisation of such model system, the Capillary Pressure tensiometer implemented in the facility has been used with different experimental methodologies allowing different aspects of adsorption dynamics to be investigated. Theoretical models specifically developed have been used for the data interpretation allowing the characterisation of the adsorption mechanisms.     

Green Nanocoatings Prepared by Crosslinking Self-Assembled Fatty Acids on Metals

Self-assembled monolayers (SAMs) are an important element of modern nanotechnology and surface functionalization. However, their application is still limited because they are easily removed from the surface of the object in corrosive environments. Crosslinking would make SAMs more resistant to the corrosive environment they are exposed to. In this work, how to strongly crosslink SAMs made of non-toxic and biodegradable fatty acids on metal surfaces using ionizing radiation has been demonstrated for the first time. The crosslinked nanocoatings are stable over time and have significantly improved properties compared to SAMs. Thus, crosslinking opens up the possibility of using SAMS in a variety of different systems and on different materials for surface functionalization to achieve stable and durable surface properties such as biocompatibility or selective reactivity.     

Characterization of the Accelerometric Environment of DCMIX2/3 Experiments

A comparative analysis of the vibratory environment of the DCMIX2/3 thermodiffusion experiments is presented here by using acceleration signals coming from different sensors placed in the Destiny, Columbus and Kibo modules. The es03 sensor nearest to the experimental device and located inside the Glovebox (Destiny module) has been defined as reference. Data were downloaded from the NASA PIMS website paying special attention to the runs coinciding with disturbances such as dockings or extravehicular activities (EVAs) as they could particularly affect the International Space Station (ISS) microgravity levels. The analyses have been made minute by minute for the three acceleration components by using the Frequency Factor Index (FFI), Spectral Entropy (SEN) and Root Mean Square (RMS) values evaluated over one-third-octave frequency bands. Spearman’s rank correlation coefficient and the coherence function have been used to investigate the degree of linear correlation between the reference signal and the other ones. SEN evolution showed different patterns compared to the reference. Also, RMS values surpassing the ISS microgravity limits were detected in all sensors, mainly at low frequency bands (<?10 Hz) and prevailing on z_A direction. However the sensors located in the Destiny module better accomplished the ISS vibratory limits requirements. Finally, some degree of linear correlation at structural frequencies (<?3 Hz) has also been detected. Overall, the sensors placed in the Destiny, Columbus and Kibo modules presented different vibratory characteristics and, despite they offer valuable information of the whole environment, may not be sufficient to properly characterize DCMIX2/3 experiments.     

应力波传播对弹丸实测超高值加速度的影响

采用较为简单的力学模型和简化的边界条件,以直杆一端施加一半正弦载荷脉冲和模拟弹体冲击刚性靶为例,用理论推导和计算机仿真的方法分析应力波传播和弹体加速度的关系.并采用LS-DYNA对加速度存储测试电路系统(含其缓冲结构)的壳体上不同点的加速度分布进行了计算机仿真.研究表明,在弹体侵彻目标时,刚体的弹体质心加速度与实际值相差好几倍,数据处理时应根据具体目的分析.     

Experimental results from CEM-UT's single shot 9 MJ railgun

A 10-m-long, 90-mm bore railgun has been designed and fabricated. During the test program, a number of solid armatures and projectile packages have been tested in a 50-m-deep vertical test range. The experiments are powered by six homopolar generator (HPG) charged inductive stores, sequentially staged to provide the desired acceleration profile. Prior to testing, computer simulations are run to determine the preferred current profile and predict system performance. During projectile flight, high-speed films, X-rays, muzzle volts, and velocity/acceleration profiles are recorded along with power supply operating parameters. Postshot diagnostics include bore wear analysis and armature and target recovery. Comparisons of predicted and recorded shot performance are also made. On selected tests, an energy balance is performed to determine efficiencies of the various components. A summary of all 90-mm gun shots is presented along the critical data collected from selected tests     

Sequence-specific retention calculator. Algorithm for peptide retention prediction in ion-pair RP-HPLC: application to 300- and 100-A pore size C18 sorbents

Continued development of a new sequence-specific algorithm for peptide retention prediction in RP HPLC is reported. Our discovery of the large effect on the apparent hydrophobicity of N-terminal amino acids produced by the ion-pairing retention mechanism has led to the development of sequence-specific retention calculator (SSRCalc) algorithms. These were optimized for a set of approximately 2000 tryptic peptides confidently identified by off-line microHPLC-MALDI MS (MS/MS) (300-A pore size C18 sorbent, linear water/acetonitrile gradient, and trifluoroacetic acid as ion-pairing modifier). The latest version of the algorithm takes into account amino acid composition, position of the amino acid residues (N- and C-terminal), peptide length, overall hydrophobicity, pI, nearest-neighbor effect of charged side chains (K, R, H), and propensity to form helical structures. A correlation with R2 approximately 0.98 was obtained for the 2000-peptide optimization set. A flexible structure for the SSRC programming code allows easy adaptation to different chromatographic conditions. This was demonstrated by adapting the algorithm (approximately 0.98 R2 value) for a set of approximately 2500 peptides separated on a 100-A pore size C18 column. The SSRCalc algorithm has also been extensively tested for a number of real samples, providing solid support for protein identification and characterization; correlations in the range of 0.95-0.97 R2 value have normally been observed.     

基于遗传神经网络的履带行驶系统载荷识别方法

针对煤矿掘进机器人履带行驶系统工作环境恶劣,载荷无法直接有效获取这一工程实际问题,提出了基于遗传神经网络的振动信号载荷识别方法。构建了遗传算法(GA)优化BP(back propagation)神经网络载荷识别模型,采用路试法试验采集了履带小车的5组振动加速度数据和单组应力载荷数据,探讨路面不平度频率和驱动轮啮频等对履带车振动和应力载荷的影响规律;借助快速傅里叶变换(FFT)对原始应力载荷数据进行去噪处理,依据履带小车行驶平顺性指标,利用sym8小波函数对振动加速度信号进行5层特征提取以提高载荷识别的精度,然后将5组小波变换分解的加速度数据和滤波后的应力载荷数据分别作为GA-BP神经网络的输入和输出进行训练及验证,揭示了履带行驶系统运动过程中振动与应力载荷之间的关系。研究结果表明,路面不平度频率、驱动轮啮频及转频为小车振动的主要频率成分,路面不平度引起的振动频率为13.765 Hz,驱动轮啮频为68.25 Hz,转频为3.25 Hz。多组试验得到的BP神经网络最佳隐含层神经元数为63,GA-BP神经网络识别的应力载荷与期望应力载荷具有较高吻合度,相对误差为4.5%,验证了该方法的有效性...     

Trace Elements in Superalloys

Abstract

In this study, effects of superheated steam on cyclic crack propagation behavior of a heat resistant steel were investigated. Crack propagation experiments were carried out on NF616 (9Cr-0.5Mo-2WVNb) in pressurized superheated steam (600°C/10MPa) under cyclic loading either with or without holding time at constant load. Superheated steam environment has two opposing effects on cyclic crack growth, acceleration and retardation. A modified tarnish rupture (TR) model has been proposed to explain the crack propagation behavior. The crack propagation rate estimated based on the TR-type model well agreed with the experimental data.     

Effect of microgravity on collagenase deproteinization and EDTA decalcification of bone fragments

Undecalcified (n = 140) and decalcified (n = 11) bone fragments were treated with either collagenase (to remove collagen portion; undecalcified n = 64, decalcified n = 11) or EDTA (to remove mineral portion; n = 76) under the reduced gravity environment on US Space Shuttle mission STS-57. The fragments were initially stored in Dulbecco's phosphate buffer solution. After orbit had been established, fragments were exposed to either a neutral buffered collagenase or EDTA solution. Reactions were terminated (neutral buffered formalin for collagenase, 21% CuSO4 5H2O for EDTA) before reentry to earth's atmosphere. Differences in bone samples mass from before flight to after flight were measured. EDTA-treated sample mass was corrected for CuSO4 content. Flight and matched ground (gravitational control) sample showed similar EDTA-induced loss of mineral mass. Collagenase treatments, however, appeared to be more effective in flight samples compared to ground control samples. The flight-exposed, collagenase-treated samples showed significantly more loss of mass than did ground samples. The microgravity environment appeared to promote proteolytic reactions in bone more than the EDTA decalcification reaction.     

Application of the Mixed‐field‐environments concept in lifetime prediction of some ceramic components

In lifetime prediction, the effect of a certain use environment on the lifetime is taken into account by using an acceleration factor that is specific to that use environment. The fact that the product may be used in different countries with differing environmental conditions results in a set of acceleration factor values. Prior to this paper, the effect of multiple field environments has been taken into account by using an average value of the acceleration factors obtained for several use environments. As the magnitudes of the acceleration factors (each specific to a certain use environment) vary a lot, the use of the average value has resulted in unrealistic lifetime estimates. The unrealism related to the use of the average value can be avoided when using the mixture‐of‐distributions concept, since the true acceleration factor values, instead of an average value, can then be used. In this paper, the mixture‐of‐distributions concept is applied for the first time to evaluate the effect of multiple use environments (thermal cycling) on the lifetime of a component population. By using this concept, it is possible to evaluate all of the key figures of reliability for the whole population based on the fractions of the component population that are used in multiple, different use environments. This approach can be applied when allocating maintenance and spare parts for a product that is used worldwide. The mixture‐of‐distributions concept in lifetime prediction is demonstrated by analyzing the test results of some ceramic leadless chip carrier components. Acceleration factors in four alternative field environments are estimated by running thermo‐mechanical finite element analysis simulations. The lifetime performance of the whole component population used in certain alternative field environments is then evaluated by applying the mixture‐of‐distributions concept. Copyright © 2006 John Wiley & Sons, Ltd.     

Experimental study of creep of hardened Portland cement paste at variable water content

Tests of creep under axial load and torque have been made using tubular specimens of extremely small wall thickness (0.7 mm) in order to achieve sufficiently rapid moisture exchange with the environment. The changes of relative humidity and temperature in a program-controlled environmental chamber have been gradual, so as to minimize the differences in pore humidity throughout the specimen wall and the accompanying residual stresses and microcracking. A number of different humidity and temperature histories, including the drying before and during the creep test, and the humidity changes during the creep test and during the recovery, have been tested. The measurements have revealed a decline of the slope of creep curve in log-time after a sufficiently long drying period; acceleration of creep as well as recovery by both drying and wetting; a smaller and more delayed acceleration at lower humidities; a delay of this acceleration with respect to the weight loss; a similarity of these effects in axial and torsional creep; a higher recovery as well as creep at higher humidities when moisture equilibrium has been approached before loading; a higher creep acceleration by temperature increases or decreases when the humidity is below saturation, but a smaller acceleration at nearly dry state; and other effects.     

Gentamicin: effect on E. coli in space

Previous investigations have shown that liquid bacterial cultures grown in space flight were not killed as effectively by antibiotic treatments as were cultures grown on Earth. However, the cause for the decreased antibiotic effectiveness remains unknown. Possible explanations include modified cell proliferation and modified antibiotic transport in the culture medium. Escherichia coli cultures were grown in space flight (STS-69 and STS-73), with and without gentamicin, on a solid agar substrate thus eliminating fluid effects and reducing the unknowns associated with space-flight bacterial cultures in suspension. This research showed that E. coli cultures grown in flight on agar for 24 to 27 hours experienced a heightened growth compared to simultaneous controls. However, addition of gentamicin to the agar killed the bacteria such that both flight and ground control E. coli samples had similar final cell concentrations. Therefore, while the reported existence of a decrease in antibiotic effectiveness in liquid cultures remains unexplained, these data suggest that gentamicin in space flight was at least as effective as, if not more effective than, on Earth, when E. coli cells were grown on agar.     

田湾核电二期深孔台阶爆破振动监测与分析

针对田湾核电站二期工程台阶爆破引起的振动对一期工程建筑物的影响,在现场对离爆破地点最近且最敏感的核岛进行了爆破振动监测。本文对采集的数据进行了较全面的分析,得出了台阶爆破振动质点振动加速度衰减参数k、α的最佳取值;同时得出在当地条件下,爆破振动加速度与比例距离的关系、爆破振动加速度与不耦合系数的关系,并发现水平方向爆破振动加速度的峰值是垂直方向上的3～5倍。这些爆破振动监测数据与分析结果,为后期施工提供了理论和技术指导。     

田湾核电二期深孔台阶爆破振动监测与分析

针对田湾核电站二期工程台阶爆破引起的振动对一期工程建筑物的影响,在现场对离爆破地点最近且最敏感的核岛进行了爆破振动监测。本文对采集的数据进行了较全面的分析,得出了台阶爆破振动质点振动加速度衰减参数k、α的最佳取值;同时得出在当地条件下,爆破振动加速度与比例距离的关系、爆破振动加速度与不耦合系数的关系,并发现水平方向爆破振动加速度的峰值是垂直方向上的3～5倍。这些爆破振动监测数据与分析结果,为后期施工提供了理论和技术指导。     

一种基于均方比值的人致结构振动加速度响应信号筛选方法

提出了一种基于人致楼板振动响应的加速度均方根值参数,该参数是结构振动响应信号均方根值和加权均方根值的比值,该参数能够快速判断采集到的人致楼板构振动信号数据是否异常。通过人致楼板振动响应均方根值的理论推导得到了该参数的具体表达式,同时通过建立施加不同工况的人群荷载有限元楼板模型,和不同工况人群作用下楼板振动现场试验,对该参数的性质进行了论证,该参数受人群荷载的参数影响小,与结构自身的基本性质相关性大,在处理大量数据信号时,可以通过该参数对数据进行快速筛选。     

3种吡啶甲酰腙席夫碱自组装分子膜对铜的缓蚀作用

用3种自制油溶性吡啶甲酰腙席夫碱在铜表面制备自组装单分子膜(SAMS),研究了该膜在3.5%NaCl中对铜的缓蚀作用。通过极化曲线法和交流阻抗法的研究,发现在3.5%NaCl溶液中,3种吡啶甲酰腙席夫碱对铜均有良好的缓蚀效果,其中L2B的缓蚀效果最好,L4B次之,后为L3B,常温下,缓蚀率分别为91.75%,90.68%和88.27%。同时缓蚀效果受温度影响不大。交流阻抗法测试结果表明,3种酰腙化合物在自组装膜和缓蚀过程中未发生分解,同时分析表明它们都是以抑制阴极为主的混合型缓蚀剂。最后通过密度泛函理论对其缓蚀机理进行了初步探讨。