Superconductivity in nearly single-phase Bi-Pb-Sr-Ca-Cu-O samples with different nominal compositions

The preparation conditions, phase composition, and superconducting properties of Bi-Pb-Sr-Ca-Cu oxide materials from different nominal compositions have been investigated. Nearly single-phase samples from Bi₂Pb_0.4Sr₂Ca₃Cu₄O _y , as well as from the proposed compositions Bi_1.8Pb_0.4Sr₂Ca₃Cu₄O _y and Bi_1.8Pb_0.4Sr₂Ca_2.5Cu_3.5O _y were obtained by a solid-state reaction in air. Samples with the third nominal composition showed the best superconducting properties (T _on=111 K and zero resistance atT ₀=103 K). A possible mechanism for the 2223 phase formation in the three investigated compositions has been discussed.     

Data-dependent sampling of two-dimensional signals

Samples taken at scattered points of a finite-support two-dimensional signal can be interpolated to recover an approximation of the original signal. Given a bound on the number of samples, where should they be placed to enable the most accurate reconstruction? Or, given an error bound for the reconstruction, what is the minimum number of samples required, and where should they be placed? In this paper we introduce search schemes that provide good candidate solutions to these problems, for digital signals. Natural Neighbour Interpolation is used in iterative sample removal and movement processes to obtain sparse sample patterns. For pictures and Digital Elevation Models, fewer samples are required if the interpolant is onlyC ⁰ continuous at the data sites, than if it isC ¹. Retained samples lie on the ridges and valleys of the laplacian.     

纳米电子器件中的噪声及其应用研究

对多种纳米材料和纳米器件的噪声进行了比较详细的研究,对纳米器件中几种常用的噪声测量方法进行了探讨。讨论了利用噪声(主要是散粒噪声)进行介观电学机制探测的方法,并提出了用于解决单电子晶体管中背景电荷噪声的有效方法,揭示了双势垒共振隧穿二极管在负微分电阻区的散粒噪声大于Poisson值的本质。     

激光喷丸强化变形镁合金的疲劳寿命数值分析

以ABAQUS和MSC.fatigue软件为平台, 建立了激光喷丸强化前后试样疲劳寿命及薄弱位置预测的有限元分析模型。为研究材料强度对激光喷丸强化效果的影响, 以AZ31B和ZK60两种不同强度变形镁合金为对象, 对激光喷丸强化后的残余应力和塑性变形进行了分析, 并预测了喷丸前后的疲劳寿命, 两种材料的疲劳寿命增益分别为112.04%和181.2%。结果表明, 高强度材料激光喷丸强化效果优于低强度材料。     

皮秒拍瓦激光的参数测量系统可靠性分析

皮秒参数测量系统用于提供皮秒拍瓦激光系统的各项状态参数,协助激光系统达到预期的技术指标。针对皮秒拍瓦激光系统的技术指标,皮秒参数测量系统将提供压缩脉冲的能量、脉宽、远场、信噪比等参数。为了判断参数测量系统的工作性能,采用均方根(RMS)误差来描述测量系统的可靠性。经过实验测试,能量测量单元的测量范围为10～1000J,标定实验数据的RMS误差为2.2%。脉宽测量单元的时间测量范围为0.5～18.0ps,时间分辨率为0.07ps,测试数据的RMS误差为3%。远场测量单元的空间测量范围为150倍衍射极限(DL),空间分辨率为0.3倍DL,测试数据的RMS误差为0.15%。信噪比测量单元的时间测量范围为30ps,时间分辨率为0.3ps,动态范围为106。基于拍瓦实验提供的测试数据表明,皮秒参数测量系统能够稳定可靠地提供以上参数的实时测试数据,实现拍瓦装置的运行状态诊断功能。     

Chromium determination in food by slurry sampling graphite furnace atomic absorption spectrometry using classical and permanent modifiers

A simple method, using permanent modifiers, has been developed for chromium (Cr) determination in food of plant origin by the slurry sampling graphite furnace atomic absorption spectrometry. In particular comparison of the action of Mg(NO₃)₂, iridium (Ir)/niobium (Nb) and iridium (Ir)/tungsten (W) was examined. Finally, for chromium determination in food, the mixture of 2 μg of Ir with 10 μg of Nb was used as permanent modifier. The analytical procedure was optimised carefully on the basis of the data from pyrolysis and atomisation temperature curves studies. The results obtained for four certified reference materials using external calibration with aqueous standards were in good agreement with the certified values. The precision and accuracy of Cr determination by the described method were also acceptable: the RSD were lower than 10% and recoveries for CRMs were in the range of 95-103%. The characteristic mass for chromium was determined to be 3.9 pg and the detection limit for the optimised procedure at the 0.75% (w/v) slurry concentration - 86.6 ng g⁻¹.     

Utility of solid phase spectrophotometry for the modified determination of trace amounts of cadmium in food samples

A modified selective, highly sensitive and accurate procedure for the determination of trace amounts of cadmium which reacts with 1-(2-benzothiazolylazo)-2-hydroxy-3-naphthoic acid (BTAHNA) to give a deep violet complex with high molar absorptivity (7.05 × 10⁶ L mol⁻¹ cm⁻¹, 3.92 × 10⁷ L mol⁻¹ cm⁻¹, 1.78 × 10⁸ L mol⁻¹ cm⁻¹, and 4.10 × 10⁸ L mol⁻¹ cm⁻¹), fixed on a Dowex 1-X8 type anion-exchange resin for 10 mL, 100 mL, 500 mL, and 1000 mL, respectively. Calibration is linear over the range 0.2-3.5 μg L⁻¹ with RSD of ?1.14% (n = 10). The detection and quantification limits were calculated. Increasing the sample volume can enhance the sensitivity. The method has been successfully applied for the determination of Cd(II) in food samples, water samples and some salts samples without interfering effect of various cations and anions.     

螺旋弹簧快速疲劳试验加载优化方法

新设计以及投产加工制造的高应力圆柱螺旋弹簧都需进行快速疲劳试验,试验时间短。要求圆柱螺旋弹簧加载频率高,使用寿命长,实际疲劳断裂主要为正断型疲劳断裂模式。金属材料扭转疲劳断裂机制图诠释了材料的疲劳断裂寿命、屈服强度、外施交变切应力振幅和疲劳断裂模式之间的关系。利用原理图表述不同试验条件下引发疲劳断裂模式发生的替代变化。缩短快速试验时间的主要方法:提高加载应力水平;最大正应力不变条件下,降低应力比值;对圆柱螺旋弹簧进行优化的二次喷丸处理等。给出快速疲劳试验的一般试验程序。     

少样本学习下的服装风格分析与评价

为提高服装风格评价的客观性,提出了利用卷积神经网络对不同品牌服装风格特征进行自动提取、识别和分类的方法,以不同品牌的服装为对象,探究其视觉风格合理表征的方法,并实现品牌服装的分类任务。建立了品牌服装数据集,该数据集包含50个品牌的服装图像,每个服装品牌30张,随机抽取36个用作训练集,剩余14个用作支持集和查询集。采用少样本学习的网络模型,Siamese网络模型、Protype网络模型、Meta baseline网络模型对品牌服装数据集进行测试,对比分析3种网络模型的实验结果。结果表明:在品牌服装图像数据较少的情况下,可以通过少样本学习方法对其进行分类,使用meta baseline网络在5-way,1-shot任务中的分类准确率高达0.9475。     

Evaluation of apple texture with contact acoustic emission detector: A study on performance of calibration models

Performance of calibration models for evaluation of apples sensory texture with contact acoustic emission detector (CAED) was studied. For model evaluation and testing, 2500 apples of 19 cultivars were harvested over two seasons. Apples were stored at normal atmosphere (NA), controlled atmosphere (CA) for different periods or were treated with 1-methylcyclopropene (1-MCP) in order to obtain a high variability of texture and fruit maturity. Apples were tested simultaneously in two distinct laboratories. The models were created and validated on averaged values from 10 fruits using simple linear regression, multiple linear regression (MLR) and principal component regression (PCR). Performance statistics of the models were expressed in terms of determination coefficient (R²), root mean square errors of cross validation (RMSECV) or prediction (RMSEP) and ratio of prediction to deviation (RPD). Firmness and total acoustic emission counts were predictors of sensory texture in the models. MLR and PCR models show better performance for prediction of sensory data than simple linear regression models however PCR models show the best results among models tested in this study. Common PCR models for several cultivars allow for successful prediction of hardness (RPD > 2.0), crispness and overall texture (1.5 < RPD < 2.0). The single-cultivar PCR models, constructed on data sets containing 26-39 averaged values, reveal significantly better performance (RPD > 2.0 for most of the cases) than the common PCR models for many varieties.