不同水产品中有色和无色孔雀石绿的降解动力学研究

目的 研究不同水产品基质中有色和无色孔雀石绿的降解规律。方法 样品经提取净化后, 用HPLC进行检测, 结果用SPSS软件、降解动力学软件进行分析。结果 三种基质中有色和无色孔雀石绿降解反应均符合准一级反应动力学。在10、50、100 μg/kg三个添加水平下, 三种基质中有色孔雀石绿平均降解率分别为57.9%、48.0%、23.0%, 无色孔雀石绿平均降解率分别为46.6%、43.4%、19.8%。添加浓度为50 μg/kg的鲤鱼基质, 采用自然解冻时有色和无色孔雀石绿降解速率常数分别为K(50 μg/kg)=0.00338 d?1, K(50 μg/kg)=0.00268 d-1, 采用微波解冻方式时有色和无色孔雀石绿降解速率常数分别为K(50 μg/kg)=0.00359 d?1, K(50 μg/kg)=0.00321 d?1。实际样品中无色孔雀石绿降解速率常数K(111.2 μg/kg无色, 鲤鱼)=0.000614 d?1, K(50 μg/kg无色, 鲤鱼)=0.00125 d?1。结论 有色孔雀石绿较无色孔雀石绿降解快, 低浓度比高浓度降解快; 两种解冻方式对有色和无色孔雀石绿降解影响较小; 实际样品中无色孔雀石绿降解速率常数均比空白基质中添加无色孔雀石绿降解慢。     

Biometric technology overview

1 Introduction Biometrics are drawing much attention since the 9/11 incident not only for anti-terrorism issues, but also for being a powerful authentication method to verify the identity of a person so as to restrict access to sensitive areas or systems. In their daily lives, people face many situations where there is a need to verify their personal identity by means of cards, passwords, or personal identification numbers (PIN), etc. Due to the limitations of these traditional techniques bas…     

Experimental Wettability Study of Lead-Free Solder on Cu Substrates Using Varying Flux and Temperature

The selection of soldering flux plays a critical role in promoting wetting and product reliability of printed circuit board assemblies. In this study, the effects of fluxes on the wetting characteristics of the Sn-3.0Ag-0.5Cu solder alloy on Cu substrates was researched by using various flux systems at different soldering temperatures. Because of the distinct characteristic of the lead-free solder—poor wettability—three kinds of fluxes [no-clean flux with high solid content (NCF), rosin mildly activated flux (RMA) and water-soluble flux (WSF)] were chosen for the wetting experiments. The wetting time and force were the evaluating indicators. The experimental observations indicated that the wettability clearly depended on the soldering temperature and flux system when using the same solder. Furthermore, the corrosion potential of flux residues was measured by surface insulation resistance (SIR) testing. Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to determine the contents of the flux residues and corrosion products.     

取定s的严格d-正则随机(3,2s)-SAT问题的可满足临界

3-CNF公式的随机难解实例生成对于揭示3-SAT问题的难解实质和设计满足性测试的有效算法有着重要意义.对于整数k>2和s>0,如果在一个k-CNF公式中每个变量正负出现次数均为s,则称该公式是严格正则（k,2s）-CNF公式.受严格正则（k,2s）-CNF公式的结构特征启发,提出每个变量正负出现次数之差的绝对值均为d的严格d-正则（k,2s）-CNF公式,并使用新提出的SDRRK2S模型生成严格d-正则随机（k,2s）-CNF公式.取定整数5<s<11,模拟实验显示,严格d-正则随机（3,2s）-SAT问题存在SAT-UNSAT相变现象和HARD-EASY相变现象.因此,立足于3-CNF公式的随机难解实例生成,研究了严格d-正则随机（3,2s）-SAT问题在s取定时的可满足临界.通过构造一个特殊随机实验和使用一阶矩方法,得到了严格d-正则随机（3,2s）-SAT问题在s取定时可满足临界值的一个下界.模拟实验结果验证了理论证明所得下界的正确性.     

Sparse kernel minimum squared error using Householder transformation and givens rotation

Two obvious limitations exist for baseline kernel minimum squared error (KMSE): lack of sparseness of the solution and the ill-posed problem. Previous sparse methods for KMSE have overcome the second limitation using a regularization strategy, which introduces an increase in the computational cost to determine the regularization parameter. Hence, in this paper, a constructive sparse algorithm for KMSE (CS-KMSE) and its improved version (ICS-KMSE) are proposed which will simultaneously address the two limitations described above. CS-KMSE chooses the training samples that incur the largest reductions on the objective function as the significant nodes on the basis of the Householder transformation. In contrast with CS-KMSE, there is an additional replacement mechanism using Givens rotation in ICS-KMSE, which results in ICS-KMSE giving better performance than CS-KMSE in terms of sparseness. CS-KMSE and ICS-KMSE do not require the regularization parameter at all before they begin to choose significant nodes, which is beneficial since it saves on the model selection time. More importantly, CS-KMSE and ICS-KMSE terminate their procedures with an early stopping strategy that acts as an implicit regularization term, which avoids overfitting and curbs the sparse level on the solution of the baseline KMSE. Finally, in comparison with other algorithms, both ICS-KMSE and CS-KMSE have superior sparseness, and extensive comparisons confirm their effectiveness and feasibility.     

基于石墨烯/铟砷量子点/砷化镓异质结新型光电探测器

研究了一种石墨烯/铟砷量子点/砷化镓界面形成的异质结探测器的暗电流特性以及光电响应性质.虽然石墨烯具有很高的电子迁移率,但受限于较低的光子吸收率,使其在光电探测领域的应用受到了限制.而半导体量子点具有量子效率高,光吸收能力强等独特优点.于是利用石墨烯-砷化铟量子点-砷化镓异质结结构制备了一种新型光电探测器.并对该探测器的响应率、I-V特性曲线、暗电流特性、探测率、开关比等关键性能进行了研究.其在637 nm入射光情况下的响应率、探测率以及开关比可分别达到为17. 0 m A/W、2. 3×10~(10)cm Hz~(1/2)W~(-1)和1×10~3.而当入射光为近红外波段的940纳米时,响应率进一步增加到了207 m A/W.同时,还证实了该器件的暗电流、肖特基势垒高度和理想因子对温度的都具有较高的依赖性都较强.     

机会网络

大量具备短距离通信能力的智能设备的出现推动了无线自组网应用的迅速发展.但在许多实际应用环境中,节点移动、网络稀疏或信号衰减等各种原因通常导致形成的网络大部分时间不连通.传统的移动自组织网络传输模式要求通信源和目标节点之间存在至少一条完整的路径,因而无法在这类环境中运行.机会网络利用节点移动形成的通信机会逐跳传输消息,以"存储-携带-转发"的路由模式实现节点间通信,这种完全不同于传统网络通信模式的新兴组网方式引起了研究界极大的兴趣.首先介绍机会网络的概念和理论基础,并给出了当前机会网络的一些典型应用,然后详细阐述了机会网络研究的热点问题,包括机会转发机制、移动模型和基于机会通信的数据分发和检索等,并简要叙述了机会网络的通信中间件、协作和安全机制以及机会网络新的应用等其他研究问题,最后进行总结并展望了机会网络未来一段时间内的研究重点.     

由提升的滤波器实现的9/7 DWT系数算法改进

采用简单的移位-加操作代替结构复杂的浮点计算方法，把CDF9／7双正交小波基的提升系数化为二进制，移位-加操作计算简单，易于VLSI实现，因而能采用硬件实时处理图像信号。仿真结果表明：在同样的压缩比下，用移位-加操作重构的图像，其PSNR值只比浮点法低0．1～0．3dB，而且随着压缩比的降低，二者的PSNR值趋近于相同。     

A novel method to obtain modulus image of soft tissues using ultrasound water jet indentation: a phantom study

The alteration of tissue stiffness is generally known to be associated with pathological changes. Ultrasound indentation is one of the methods that can be used to assess the mechanical properties of the soft tissues. It uses a flat-ended ultrasound transducer to directly contact the tissue to sense tissue deformation under an applied load. This paper introduced a novel noncontact ultrasound indentation system using water jet compression. The key idea was to utilize a water jet as the indenter as well as the coupling medium for propagation of the ultrasound beam. High frequency focused ultrasound (20 MHz) was used to measure the indentation deformation at a microscopic level. It has been demonstrated that the system could effectively assess the tissue-mimic phantoms with different stiffness. Water jet coupling allows the system to conduct C-scan on soft tissues rapidly and conveniently. By applying different pressures while taking C-scan sequences, the modulus images of the phantoms could be obtained based on the applied pressure and the phantom deformation and thickness. This paper presented the preliminary results on gel phantoms. The spatial resolution, the contrast resolution of the measurements and the reproducibility of the results were also discussed.     

Extended algorithm for the design of diffractive optical elements around the focal plane

We present a multiplane algorithm for three-dimensional uniform illumination. The large-diameter diffractive optical element simulated by this algorithm homogeneously concentrates more than 86.5% of the incident energy into a 200 microm length of columnar space around the focal plane. The intensity profile in the whole space is nearly flattop, and the beam's quality measured by the root mean square is less than 20.6%. The algorithm is very useful if a great deal of tolerance is required for the installation error of the optical system or if it is used for some particular application, such as uniform illumination on an incline plane.