Influence of quantum capture and tunneling mechanisms on the dark current of bound-to-continuum quantum-well infrared photodetectors

We present a theoretical model for the dark current of bound-to-continuum quantum-well infrared photodetectors (QWIPs), by considering the field-induced mixing effect, tunneling rate and phonon scattering rate between bound and continuum states. Using this model, we can see clearly how these mechanisms significantly influence the Fermi levels of bound and continuum electrons, and thus, the dark current. Nonlinear temperature dependence of the dark current at low temperature is predicted and discussed in detail. The simulated dark currents exhibit good agreement with the experimental results, without use of parameter fitting techniques.     

First break refraction event picking using fuzzy logic systems

First break picking is a pattern recognition problem in seismic signal processing, one that requires much human effort and is difficult to automate. The authors' goal is to reduce the manual effort in the picking process and accurately perform the picking. Feedforward neural network first break pickers have been developed using backpropagation training algorithms applied either to an encoded version of the raw data or to derived seismic attributes which are extracted from the raw data. The authors summarize a study in which they applied a backpropagation fuzzy logic system (BPFLS) to first break picking. The authors use derived seismic attributes as features, and take lateral variations into account by using the distance to a piecewise linear guiding function as a new feature. Experimental results indicate that the BPFLS achieves about the same picking accuracy as a feedforward neural network that is also trained using a backpropagation algorithm; however, the BPFLS is trained in a much shorter time, because there is a systematic way in which the initial parameters of the BPFLS can be chosen, versus the random way in which the weights of the neural network are chosen     

A semantic modeling approach for image retrieval by content

We introduce a semantic data model to capture the hierarchical, spatial, temporal, and evolutionary semantics of images in pictorial databases. This model mimics the user's conceptual view of the image content, providing the framework and guidelines for preprocessing to extract image features. Based on the model constructs, a spatial evolutionary query language (SEQL), which provides direct image object manipulation capabilities, is presented. With semantic information captured in the model, spatial evolutionary queries are answered efficiently. Using an object-oriented platform, a prototype medical-image management system was implemented at UCLA to demonstrate the feasibility of the proposed approach.     

Trends and variations in neonatal length of in-hospital stay in Canada

The objectives of this study were to evaluate the possible mechanisms involved in prolongation of bleeding time in pre-eclamptic patients receiving a magnesium sulfate infusion to prevent convulsions. Eighteen pre-eclamptic patients near term or at term (4 cases 33 to 35 weeks; the remainder > 36 weeks) were studied. Fifteen of them received magnesium sulfate infusion; 3 did not and served as controls. Bleeding time (modified Ivy method with Surgicutt), platelet count, platelet aggregation pattern, as well as serum arachidonic acid metabolites [thromboxane B2 (TxB2) and 6-Keto-prostaglandin F1 alpha (6-Keto-PGF1 alpha)] werde done on admission to the labor floor (before magnesium infusion) and repeated at discontinuation of the infusion, 12-24 hours postpartum; the controls received the second test 24 hours postpartum. Thirteen of 15 patients receiving magnesium sulfate had an increase in bleeding time from an average of 6 minutes 31 seconds to 11 minutes 56 seconds, an 82% rise (p < 0.004). In 2 there was a decrease. Among the 3 controls the averages were 6 minutes 38 seconds and 6 minutes 3 seconds. The total magnesium given ranged from 52.5 to 145 grams. Platelet counts averaged 251,000/mm3 (range 145,000-519,000). Platelet aggregation pattern done in 11 patients and was normal and unchanged after magnesium in 10 of the patients with increased bleeding time and one control. TxB2 and 6-Keto-PGF1 alpha levels did not change significantly either after magnesium administration (688 and 135 pgm/ml, to 654 and 117) or in controls (695 and 230 pgm/ml, to 445 and 225). Likewise, the ratio of these 2 substances did not change in either group (6.3 to 6.6, and 4.2 to 2.2). There was no correlation between duration of infusion or total magnesium given and directions of small changes observed. This study confirms a prior preliminary observation that magnesium sulfate infusion, as currently used to prevent eclamptic convulsions, induces a significant prolongation of bleeding time. This effect is mediated neither by changes in platelets count or aggregation pattern, nor by changing the level or ratios of serum arachidonic acid metabolites (TxB2 and 6-Keto-PGF1 alpha). Further studies are needed to clarify the mechanism of this clinically important observation of increased bleeding following magnesium sulfate infusion.     

应用粒子动态分析仪研究水力旋流器流场

利用粒子动态分析仪(PDA),对水力旋流器内固相颗粒流场做了全面的测定,得出水力旋流器内固相颗粒的流态、浓度及粒度分布,为进一步查清水力旋流器的工作机理提供了重要理论依据。     

催化裂化汽油选择性加氢脱硫催化剂RSDS-1的开发

介绍了用于催化裂化汽油选择性加氢脱硫催化剂RSDS-1的研究开发，考察了载体、活性组元、金属原子比以及助剂对催化剂选择性的影响。研究结果表明，催化裂化汽油中烯烃的加氢饱和受扩散限制；Co—Mo组合对烯烃饱和的能力相对较弱；较高的Co／Mo原子比有利于提高催化剂选择性；助剂的加入对催化剂选择性有明显的影响；RSDS—1催化剂用于催化裂化汽油选择性脱硫，对不同原料油适应性好，脱硫率可达80％，RON损失小于2个单位，且可长周期稳定运转。     

电镀企业火警和爆鸣事故实例

列举了作者经历的18种火警和爆呜事故，为电镀企业敲响警钟，安全重于泰山。     

Technology for testing nondeterministic client/server database applications

The execution of a client/server application involving database access requires a sequence of database transaction events (or, T-events), called a transaction sequence (or, T-sequence). A client/server database application may have nondeterministic behavior in that multiple executions thereof with the same input may produce different T-sequences. We present a framework for testing all possible T-sequences of a client/server database application. We first show how to define a T-sequence in order to provide sufficient information to detect race conditions between T-events. Second, we design algorithms to change the outcomes of race conditions in order to derive race variants, which are prefixes of other T-sequences. Third, we develop a prefix-based replay technique for race variants derived from T-sequences. We prove that our framework can derive all the possible T-sequences in cases where every execution of the application terminates. A formal proof and an analysis of the proposed framework are given. We describe a prototype implementation of the framework and present experimental results obtained from it.