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排序方式: 共有279条查询结果,搜索用时 109 毫秒
1.
René-Maxime Gracien Sarah C. Reitz Marlies Wagner Christoph Mayer Steffen Volz Stephanie-Michelle Hof Vinzenz Fleischer Amgad Droby Helmuth Steinmetz Sergiu Groppa Elke Hattingen Johannes C. Klein Ralf Deichmann 《Magma (New York, N.Y.)》2017,30(1):75-83
Objective
Proton density (PD) mapping requires correction for the receive profile (RP), which is frequently performed via bias-field correction. An alternative RP-mapping method utilizes a comparison of uncorrected PD-maps and a value ρ(T1) directly derived from T1-maps via the Fatouros equation. This may be problematic in multiple sclerosis (MS), if respective parameters are only valid for healthy brain tissue. We aimed to investigate whether the alternative method yields correct PD values in MS patients.Materials/methods
PD mapping was performed on 27 patients with relapsing-remitting MS and 27 healthy controls, utilizing both methods, yielding reference PD values (PDref, bias-field method) and PDalt (alternative method).Results
PDalt-values closely matched PDref, both for patients and controls. In contrast, ρ(T1) differed by up to 3 % from PDref, and the voxel-wise correlation between PDref and ρ(T1) was reduced in a patient subgroup with a higher degree of disability. Still, discrepancies between ρ(T1) and PDref were almost identical across different tissue types, thus translating into a scaling factor, which cancelled out during normalization to 100 % in CSF, yielding a good agreement between PDalt and PDref.Conclusion
RP correction utilizing the auxiliary parameter ρ(T1) derived via the Fatouros equation provides accurate PD results in MS patients, in spite of discrepancies between ρ(T1) and actual PD values.2.
3.
Osama Abboud Konstantin Pussep Aleksandra Kovacevic Katharina Mohr Sebastian Kaune Ralf Steinmetz 《Multimedia Systems》2011,17(3):177-197
Peer-to-Peer (P2P) techniques for multimedia streaming have been shown to be a good enhancement to the traditional client/server
methods when trying to reduce costs and increase robustness. Due to the fact that P2P systems are highly dynamic, the main
challenge that has to be addressed remains supporting the general resilience of the system. Various challenges arise when
building a resilient P2P streaming system, such as network failures and system dynamics. In this paper, we first classify
the different challenges that face P2P streaming and then present and analyze the possible countermeasures. We classify resilience
mechanisms as either core mechanisms, which are part of the system, or as cross-layer mechanisms that use information from
different communication layers, which might inflict additional costs. We analyze and present resilience mechanisms from an
engineering point of view, such that a system engineer can use our analysis as a guide to build a resilient P2P streaming
system with different mechanisms and for various application scenarios. 相似文献
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Rabbits were first given left cerebellar interpositus nucleus lesions followed by classical nictitating membrane (NM) conditioning using paired presentations of a tone conditioned stimulus (CS) and an air puff unconditioned stimulus (UCS). Multiple-unit hippocampal activity was monitored over the course of training. In rabbits with anterior interpositus lesions, the acquisition of learned responses and significant increases in training-related hippocampal activity were prevented when paired training was given to the left NM but not when training was switched to the right NM. Rabbits with lesions anterior to the interpositus or in surrounding cerebellar regions failed to show deficits in behavioral responding or hippocampal activity. These results indicate that acquisition of conditioning-related activity in the hippocampus depends on an intact interpositus nucleus of the cerebellum. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
Memorializes Irving J. Saltzman, known for his work as chair of the Department of Psychology at Indiana University. He guided the department through a time of major change in education and in psychology. He promoted an atmosphere that was particularly beneficial to new faculty at a time when the loyalty of faculty was decreasing and the professionalization of psychology was increasing. He was a tenacious proponent of his department, and led by example, saying that he could not expect others to do what he was unwilling to do himself. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
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Port Richard L.; Romano Anthony G.; Steinmetz Joseph E.; Mikhail Adel A.; Patterson Michael M. 《Canadian Metallurgical Quarterly》1986,100(5):745
Examined the effects of dorsal hippocampal lesions on retention of classical trace conditioned responses (CRs) using the rabbit nictitating membrane preparation. In Exp I, 18 New Zealand albino rabbits were trained to criteria and then lesioned either in the cortex or in the hippocampus and the cortex. Hippocampal damage had no effect on the retention of responses but produced significantly longer onset latencies. A control group of hippocampal Ss acquired CRs at least as quickly as the prelesion Ss and exhibited longer response onset latency. Exp II, with 24 Ss, evaluated the performance of hippocampal-lesioned Ss in classical trace conditioning with either a low-intensity periorbital shock or a corneal air puff as the unconditioned stimulus (UCS). Hippocampal Ss successfully acquired CRs under both conditions but exhibited an alteration of response onset that depended on the form of the UCS. Hippocampal Ss displayed shorter response onset in the air-puff condition and longer response onset in the shock condition. Cortical Ss consistently timed responses regardless of the UCS. Findings suggest that the hippocampus modulates temporal characteristics of learned behavior. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
Herbert Wilhelmi Eberhard Steinmetz Gereon Schlsser Ulrich Renz Bernd Hillemacher Frank Lange 《国际钢铁研究》1991,62(11):492-495
Zur Erfassung der Strömungsverhältnisse in Kaltmodellen bodengeblasener Stahlwerkspfannen wurden theoretische und experimentelle Untersuchungen durchgeführt. Frühere Berechnungen laminarer Strömungen, die unter stark vereinfachenden Annahmen vorgenommen wurden, zeigen nur tendenzielle Übereinstimmungen zu den mit LDA-Verfahren ermittelten Strömungsbildern. Durch die Entwicklung der Großrechneranlagen ist der Einsatz von Strömungssimulationsprogrammen möglich, mit denen auch turbulente Strömungen berechnet werden können. Der Vergleich der berechneten Geschwindigkeitsvektorfelder mit den gemessenen Vektorfeldern zeigt eine grundsätzlich übereinstimmende Darstellung der Strömungsverläufe. Jedoch werden die im Experiment an Wassermodellen beobachteten Gegenwirbel und Ablösungen der Abwärtsströmungen von der Gefäßwand rechnerisch nicht erfaßt. Nur die numerische Simulation für zähere Flüssigkeiten (Paraffinöl) zeigt eine von der Wand abgelöste Abwärtsströmung und die Ausbildung eines Gegenwirbels. Man kommt also nicht umhin, neben der mathematischen Modellierung auch praktische Versuche durchzuführen, wie man umgekehrt die physikalischen Modelle mit mathematischen begleiten sollte. 相似文献