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52.
C.H. Chu C.I. Hung Y.H. Wang M.P. Houng 《Photonics Technology Letters, IEEE》1997,9(9):1262-1264
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. 相似文献
53.
PURPOSE: To summarize the pathologic diagnoses of a large number of surgically-obtained specimens over an extended time period in a single ophthalmic pathology laboratory. METHODS: We analyzed the records of 24,444 surgically obtained specimens accessioned in the L.F. Montgomery Ophthalmic Pathology Laboratory, Emory University, Atlanta, GA between May 1941 and December 1995. Age, sex, topography, clinical procedure, and histologic diagnosis were entered into a database using the modified SNOMED coding system. The diagnosis of the surgically enucleated eyes were analyzed with respect to years of enucleation. RESULTS: The most common topographic area associated with a histologic diagnosis was the cornea (39.3%), followed by lens (16.0%), vitreous (12.0%), uvea (9.8%), eyelids (8.0%), conjunctiva (7.7%), retina (7.7%), and orbit (2.1%). The relative proportion of vitreous specimens has continuously increased and became the most common surgical specimen in 1995. The most common underlying disease of surgically enucleated eyes is trauma (40.9%), followed by ocular neoplasia (24.2%), 'surgical' diseases of the cornea, lens and retina including glaucoma (17.3%), vascular diseases (6.7%), and inflammatory conditions (6.7%). The relative frequency of trauma and ocular inflammation as a cause of enucleation decreased significantly (p < 0.05) over the time of the study period while the relative proportion of ocular neoplastic processes increased (p < 0.0001). CONCLUSIONS: The availability of new surgical techniques has caused a change in the relative frequencies of different ocular specimens submitted for histologic examination. 相似文献
54.
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 相似文献
55.
Wesley W. Chu Ph.D. Ion T. leong Ph.D. Ricky K. Taira Ph.D. 《The VLDB Journal The International Journal on Very Large Data Bases》1994,3(4):445-477
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. 相似文献
56.
Wenlin HE Qishan ZANG+ Zhongguang WANG State Key Laboratory for Fatigue Fracture of Materials 《材料科学技术学报》1993,9(2):107-110
The distributions of plastic strain near grain boundaries induced by fatigue loading were investigatedby the fiducial grid method in pure aluminum specimens, and the resulted grain boundary sliding(GBS) was systematically analysed. The results show that the strain field near a grain boundary isnonuniform. GBS is restricted by the junction of grain boundaries and causes discontinuities of bothdisplacement and strain. A peak value of shear strain was created in short-range area across the grainboundary. GBS plays an important role in cyclic softening and secondary hardening. The control fac-tor of GBS is the relative orientation between two grains and the macro orientation of the grainboundary rather than the ∑ value of the boundary. 相似文献
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TK40 6H侧钻短半径水平井是西北石油局在塔河油田利用已钻无产能直井井眼侧钻钻水平井而布署的第一批短半径水平井 ,也是国内目前已钻的最深的短半径水平井 ,设计侧钻造斜井深在 5 30 0m以下 ,施工难度大 ,该批短半径水平井的钻成并获得良好的产能 ,使国内水平井钻井技术迈上了新的台阶。本文主要从该油田短半径水平井钻井的技术难点入手 ,对TK40 6H侧钻短半径水平井的设计和施工进行了分析和阐述 ,并通过主要工艺技术分析 ,阐明了技术实施的着眼点和配套的技术措施 相似文献
59.
采用X射线荧光、X射线衍射、金相显微镜和扫描电镜等分析方法 ,通过对微波管陶瓷材料的理化分析 ,对俄罗斯陶瓷及其金属化技术进行了研究 ,并对化学成分和显微结构对性能的影响作了初步的讨论。 相似文献
60.