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排序方式: 共有979条查询结果,搜索用时 33 毫秒
31.
Michael R. Dörfel Bert Jüttler Bernd Simeon 《Computer Methods in Applied Mechanics and Engineering》2010,199(5-8):264-275
Isogeometric analysis based on non-uniform rational B-splines (NURBS) as basis functions preserves the exact geometry but suffers from the drawback of a rectangular grid of control points in the parameter space, which renders a purely local refinement impossible. This paper demonstrates how this difficulty can be overcome by using T-splines instead. T-splines allow the introduction of so-called T-junctions, which are related to hanging nodes in the standard FEM. Obeying a few straightforward rules, rectangular patches in the parameter space of the T-splines can be subdivided and thus a local refinement becomes feasible while still preserving the exact geometry. Furthermore, it is shown how state-of-the-art a posteriori error estimation techniques can be combined with refinement by T-splines. Numerical examples underline the potential of isogeometric analysis with T-splines and give hints for further developments. 相似文献
32.
Bert W. Leung Author Vitae Author Vitae Duncan S. Wong Author Vitae 《Pattern recognition》2009,42(5):929-940
Hou [Visual cryptography for color images, Pattern Recognition 36 (2003) 1619-1629] proposed a four-share visual cryptography scheme for color images. The scheme splits a dithered eight-color secret image into four shares: the black mask and other three shares. It was claimed that without knowing the black mask, no information about the secret image can be obtained even if all the other three shares are known. In this paper, we show that this may be true for a few specific two-color secret images only. In all other cases, however, security cannot be guaranteed. We show that an attacker can compromise a randomly chosen two-color secret image from any two of the other three shares with probability by completely recovering the shape and pattern of the secret image. The advantage will increase to if all the three shares are known. If the secret image has three or four colors, we show that the attacker can compromise it with probability and , respectively. Finally, we show that our technique can be extended to compromising secret images with more than four colors. 相似文献
33.
34.
When multimedia information is transported over a packet-switched network, the quality of presentation can be degraded due
to network delay variation or jitter. This paper presents a dejittering scheme that can be used in the transport of MPEG-4
and MPEG-2 video to absorb any introduced network jitter, thus preserving the presentation quality of transported media streams.
The dejittering scheme is based on the statistical approximation of delay variation in the arrival times of video packets
carrying encoded clock reference values and a filtering and re-stamping mechanism. In addition, a brief overview of the MPEG-4
system is presented. 相似文献
35.
36.
In sports and board games, when an opponent cheats, the other players typically greet it with disdain, anger, and disengagement. However, work has yet to fully address the role of the computer cheating in video games. In this study, participants played either a cheating or a non-cheating version of a modified open-source tower-defense game. Results indicate that when a computer competitor cheats, players perceive the opponent as being more human. Cheating also increases player aggravation and presence, but does not affect enjoyment of the experience. Additionally, players that firmly believed that their opponent was controlled by the computer exhibited significantly less state hostility compared to players that were less certain of the nature of their competitor. Game designers can integrate subtle levels of cheating into computer opponents without any real negative responses from the players. The results indicate that minor levels of cheating might also increase player engagement with video games. 相似文献
37.
Bert Schlatterer und Ekkehard Weiset 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1982,175(6):392-398
Zusammenfassung Es wird über Sulfonamidbefunde in Nieren und Muskulatur geschlachteter Tiere (36 Rinder, 3 Schweine) berichtet. Gewebeproben wurden vor und nach der Gewebefraktionierung mit einem durch Trimethoprim modifizierten Hemmstofftest (Teststamm:Bac. subtilis BGA) auf Hemmaktivität sowie mit einer dünnschichtchromatographischen Methode (DC) auf Sulfonamide untersucht. Als Indikatorreakti on für die Darstellung der Sulfonamide diente deren Derivatisierung mit Fluorescamin (Fluram) nach zweidimensionaler Trennung. Insgesamt wurden 11 verschiedene Sulfonamide identifiziert. An Hand von Dosis-Wirkungsbeziehungen wurde gezeigt, daß das mit Trimethoprim modifizierte Testsystem mit Ausnahme der enteral angewandten und kaum absorbierbaren Substanzen allen sonst untersuchten Sulfonamiden gegenüber mittel- bis hochgradig sensitiv ist. Hierbei liegt die minimale Hemmkonzentration im Agarlochtest (50 l) zwischen 10 und 25 Nanogramm je Sulfonamid. Der Vergleich der Ergebnisse von mikrobiologischem Test und chemischer Analyse zeigte bei dem vorliegenden Untersuchungsmaterial, daß knapp 30% der mit dem modifizierten Hemmstofftest positiv reagierenden Nierenproben aufgrund des DC-Befundes nicht als sulfonamidhaltig anzusehen waren, während umgekehrt bei den Muskelproben nahezu 30% der mit Hilfe der DC als sulfonamidhaltig erkannten Proben durch den mikrobiologischen Test nicht erfaßt wurden.
Analysis of sulfonamides in tissues of slaughtered animals. Comparison of results from a microbiological test and from thin layer chromatographic analysis after derivatization with fluorescamin
Summary Sulfonamide residues in kidneys and muscles of slaughtered animals (36 cattle, 3 pigs) are reported. Tissue samples were examined prior to and after separation first for inhibitory activity by an inhibition test modified by addition of trimethoprim and subsequently for sulfonamides by thin layer chromatography (TLC). Sulfonamides were demonstrated by derivatisation with fluorescamine (Fluram) after two dimensional separation. A total of 11 different sulfonamides was identified. It could be demonstrated by dosage-activity relationships that the test system modified with trimethoprim was moderately to highly sensitive to all examined sulfonamides with the exception of the enterally applied and hardly absorbable substances. In this test (agar diffusion test, 50 l per well) the minimal inhibotory concentration is between 10 and 25 ng for each of the sulfonamides. Comparing the microbiological test with the chemical analysis it could be demonstrated that nearly 30% of the kidney samples which were positive in the modified inhibition test did not contain sulfonamides according to interpretation of the TLC. On the other hand nearly 30% of the muscle samples containing sulfonamides (found by TLC) did not react to the microbiological test.相似文献
38.
Software organizations can significantly improve the quality of their output if they have a defined and documented software process, together with the appropriate techniques and tools to measure its effectiveness. Without a defined process it is impossible to measure success or focus on how development capability can be enhanced. To date, a number of software process improvement frameworks have been developed and implemented. However, most of these models have been targeted at large-scale producers. Furthermore, they have applied to companies who use traditional development techniques. Smaller companies and those operating in development areas where speed of delivery is paramount have not, as yet, had process improvement paradigms available for adoption.This study examined the software process in a small company and emerged with the recommendation of the use of the Dynamic Systems Development Method (DSDM) and the Personal Software Process (PSP) for achieving software process improvement. 相似文献
39.
Effective optimization for fuzzy model predictive control 总被引:4,自引:0,他引:4
Mollov S. Babuska R. Abonyi J. Verbruggen H.B. 《Fuzzy Systems, IEEE Transactions on》2004,12(5):661-675
This paper addresses the optimization in fuzzy model predictive control. When the prediction model is a nonlinear fuzzy model, nonconvex, time-consuming optimization is necessary, with no guarantee of finding an optimal solution. A possible way around this problem is to linearize the fuzzy model at the current operating point and use linear predictive control (i.e., quadratic programming). For long-range predictive control, however, the influence of the linearization error may significantly deteriorate the performance. In our approach, this is remedied by linearizing the fuzzy model along the predicted input and output trajectories. One can further improve the model prediction by iteratively applying the optimized control sequence to the fuzzy model and linearizing along the so obtained simulated trajectories. Four different methods for the construction of the optimization problem are proposed, making difference between the cases when a single linear model or a set of linear models are used. By choosing an appropriate method, the user can achieve a desired tradeoff between the control performance and the computational load. The proposed techniques have been tested and evaluated using two simulated industrial benchmarks: pH control in a continuous stirred tank reactor and a high-purity distillation column. 相似文献
40.
Bert Baumgaertner 《Minds and Machines》2012,22(3):213-234
One feature of vague predicates is that, as far as appearances go, they lack sharp application boundaries. I argue that we would not be able to locate boundaries even if vague predicates had sharp boundaries. I do so by developing an idealized cognitive model of a categorization faculty which has mobile and dynamic sortals (??classes??, ??concepts?? or ??categories??) and formally prove that the degree of precision with which boundaries of such sortals can be located is inversely constrained by their flexibility. Given the literature, it is plausible that we are appropriately like the model. Hence, an inability to locate sharp boundaries is not necessarily because there are none; boundaries could be sharp and it is plausible that we would nevertheless be unable to locate them. 相似文献