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51.
Kurt Strobl 《Electrical Engineering (Archiv fur Elektrotechnik)》1939,33(2):100-107
Zusammenfassung Stroboskopische Bilder entstehen nur, wenn die Rückstrahlfähigkeit (oder Lichtdurchlässigkeit) des bewegten Körpers und die Zeitfunktion der Helligkeit gleichfrequente Komponenten haben. Form und Kontrast des stroboskopischen Bildes lassen sich berechnen, wenn Rückstrahlfähigkeit und Helligkeit in ihrer Kurvenform gegeben sind. Der Versuch bestätigt die Richtigkeit der Gleichungen und zeigt, daß die Empfindlichkeit des Auges für das Auftreten stroboskopischer Bilder sehr hoch ist. 相似文献
52.
53.
Case hardening is the most important heat treatment process for highly stressed components in engines, gear boxes, machines, etc. Nevertheless some disadvantages prevail, e.g. distortion due to oil quenching, internal oxidation and limited temper resistance up to 200°C in combination with standard case hardening steel grades such as 16MnCr5. In the past efforts were made to remove at least some of the disadvantages mentioned above. The only way to achieve tempering restistance beyond 300°C is swapping to significantly higher alloyed and therefore more expensive case hardening steels (e.g. 15NiMoCr10). Rübig was confronted with numerous customer inquiries regarding possiblities to increase temper restistance by means of case hardening in combination with standard case hardening steel grades like 16MnCr5. As a resul of HighCarb the case hardening steel grade 16MnCr5 yields a surface hardness after tempering at 300°C of approx. 60.5 HRC. An additional benefit is, that HighCarb-treated parts show a very fine grain, no discernible retained austenite (by means of light microscopy) and very little internal oxidation. 相似文献
54.
A. HoffmannG. Strobl 《Polymer》2003,44(19):5803-5809
We developed a procedure for a direct evaluation of light scattering patterns registered during an isothermal crystallization of s-polypropylene. Analysis is based on the determination of three parameters of the scattering curve for both, polarized and depolarized measuring conditions: (i) the forward scattering intensity I(q→0) (ii) the width Δq of the intensity distribution (iii) the integral intensity in the registration plane, Q2. We derive equations for these parameters and relate them to the size and the inner structure of the hedrites which develop in s-polypropylene during a crystallization. 相似文献
55.
Application of artificial neural networks for classifying lake eutrophication status 总被引:1,自引:0,他引:1
Several artificial neural network architectures were ‘trained’ on data from the Eastern Lake Survey – Phase I of the Environmental Protection Agency's National Surface Water Survey in order to investigate which physical–chemical parameters are possibly of greatest importance in determining the eutrophication status of lakes. From the 110 available lake parameters in the Survey, 60 were chosen as input to the neural networks. The traditional eutrophication classification scheme of Vollenweider was used for comparative purposes. The various artificial neural network simulations showed that, in addition to total phosphorus and inorganic nitrogen, turbidity, specific conductance, lake elevation and hydrogen ion concentration were identified as the most significant parameters affecting the classification of lakes in regard to their eutrophication status. These results suggest a conceivable association between these parameters and lake eutrophication, thereby indicating a need for further study on these relationships. A model simulation utilizing an unsupervised neural network did not provide much insight into the lake eutrophication status, but did show that the available physical–chemical lake data could be categorized according to physical region, thereby providing an indication that the lake data used in this study were region‐dependent. 相似文献
56.
Classification trees are a popular tool in applied statistics because their heuristic search approach based on impurity reduction is easy to understand and the interpretation of the output is straightforward. However, all standard algorithms suffer from a major problem: variable selection based on standard impurity measures as the Gini Index is biased. The bias is such that, e.g., splitting variables with a high amount of missing values—even if missing completely at random (MCAR)—are artificially preferred. A new split selection criterion that avoids variable selection bias is introduced. The exact distribution of the maximally selected Gini gain is derived by means of a combinatorial approach and the resulting p-value is suggested as an unbiased split selection criterion in recursive partitioning algorithms. The efficiency of the method is demonstrated in simulation studies and a real data study from veterinary gynecology in the context of binary classification and continuous predictor variables with different numbers of missing values. The proposed method is extendible to categorical and ordinal predictor variables and to other split selection criteria such as the cross-entropy. 相似文献
57.
Maximally selected Chi-squared statistics and non-monotonic associations: An exact approach based on two cutpoints 总被引:1,自引:0,他引:1
Anne-Laure Boulesteix Carolin Strobl 《Computational statistics & data analysis》2007,51(12):6295-6306
Binary outcomes that depend on an ordinal predictor in a non-monotonic way are common in medical data analysis. Such patterns can be addressed in terms of cutpoints: for example, one looks for two cutpoints that define an interval in the range of the ordinal predictor for which the probability of a positive outcome is particularly high (or low). A Chi-squared test may then be performed to compare the proportions of positive outcomes in and outside this interval. However, if the two cutpoints are chosen to maximize the Chi-squared statistic, referring the obtained Chi-squared statistic to the standard Chi-squared distribution is an inappropriate approach. It is then necessary to correct the p-value for multiple comparisons by considering the distribution of the maximally selected Chi-squared statistic instead of the nominal Chi-squared distribution. The exact distribution of the Chi-squared statistic obtained with the two optimal cutpoints is derived based on combinatorial considerations. This approach is illustrated by a simulation study and an application to varicella data. 相似文献
58.
PJ Pereira ZM Wang H Rubin R Huber W Bode NM Schechter S Strobl 《Canadian Metallurgical Quarterly》1999,286(1):163-173
Human chymase (HC) is a chymotrypsin-like serine proteinase expressed by mast cells. The 2.2 A crystal structure of HC complexed to the peptidyl inhibitor, succinyl-Ala-Ala-Pro-Phe-chloromethylketone (CMK), was solved and refined to a crystallographic R-factor of 18.4 %. The HC structure exhibits the typical folding pattern of a chymotrypsin-like serine proteinase, and shows particularly similarity to rat chymase 2 (rat mast cell proteinase II) and human cathepsin G. The peptidyl-CMK inhibitor is covalently bound to the active-site residues Ser195 and His57; the peptidyl moiety juxtaposes the S1 entrance frame segment 214-217 by forming a short antiparallel beta-sheet. HC is a highly efficient angiotensin-converting enzyme. Modeling of the chymase-angiotensin I interaction guided by the geometry of the bound chloromethylketone inhibitor indicates that the extended substrate binding site contains features that may generate the dipeptidyl carboxypeptidase-like activity needed for efficient cleavage and activation of the hormone. The C-terminal carboxylate group of angiotensin I docked into the active-site cleft, with the last two residues extending beyond the active site, is perfectly localized to make a favorable hydrogen bond and salt bridge with the amide nitrogen of the Lys40-Phe41 peptide bond and with the epsilon-ammonium group of the Lys40 side-chain. This amide positioning is unique to the chymase-related proteinases, and only chymases from primates possess a Lys residue at position 40. Thus, the structure conveniently explains the preferred conversion of angiotensin I to angiotensin II by human chymase. 相似文献
59.
As almost fully automated techniques as well as expert systems obtain more and more importance in the geocoding of synthetic aperture radar (SAR) images, the solution to the problem of the identification of homologue points between the SAR image and reference system moves into the fields of pattern recognition and feature matching. Shadow regions, which appear as dark regions in the SAR image, are independent from the backscattering of the imaged terrain. Due to the multiplicity of signals, layover regions appear brighter than the surrounding regions. Hence, the phenomena of layover and shadow are stressed in the present paper. The reasons for their occurrence are studied through the digital elevation model representing the Earth's surface. An algorithm to define layover and shadow regions directly in the geometry of the digital elevation model is presented. The results are given in a so-called layover and shadow map 相似文献
60.
Referring to a general conception of coping as an adaptive reaction to a perceived is-ought discrepancy, the authors present an interdisciplinary perspective on coping processes. Based on systems theory, a psychological view is compared with a sociological perspective, focusing structural equivalencies between social and individual adaptational processes. Defensive, proactive, and accommodative reactions are discussed as 3 general modes of coping. It is argued that all of these coping reactions in both individuals and social systems have specific costs and benefits, which are particularly visible if the interaction and "interpenetration" between the coping strategies of individuals and social systems are observed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献