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Murphy K Harris AD Diukova A Evans CJ Lythgoe DJ Zelaya F Wise RG 《Magnetic resonance imaging》2011,29(10):1382-1389
Pulsed arterial spin labeling (PASL) is an increasingly common technique for noninvasively measuring cerebral blood flow (CBF) and has previously been shown to have good repeatability. It is likely to find a place in clinical trials and in particular the investigation of pharmaceutical agents active in the central nervous system. We aimed to estimate the sample sizes necessary to detect regional changes in CBF in common types of clinical trial design including (a) between groups, (b) a two-period crossover and (3) within-session single dosing. Whole brain CBF data were acquired at 3 T in two independent groups of healthy volunteers at rest; one of the groups underwent a repeat scan. Using these data, we were able to estimate between-groups, between-session and within-session variability along with regional mean estimates of CBF. We assessed the number of PASL tag-control image pairs that was needed to provide stable regional estimates of CBF and variability of regional CBF across groups. Forty tag-control image pairs, which take approximately 3 min to acquire using a single inversion label delay time, were adequate for providing stable CBF estimates at the group level. Power calculations based on the variance estimates of regional CBF measurements suggest that comparatively small cohorts are adequate. For example, detecting a 15% change in CBF, depending on the region of interest, requires from 7-15 subjects per group in a crossover design, 6-10 subjects in a within-session design and 20-41 subjects in a between-groups design. Such sample sizes make feasible the use of such CBF measurements in clinical trials of drugs. 相似文献
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Light causes an aggregation of the melanosomes in the melanophores of isolated dark adapted Xenopus tadpole tails. Dose response curves for 6 wavelengths of light were measured, and using a standard response, an action spectrum was derived that can be fitted to a porphyropsin absorbance curve. 相似文献
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A new, vectorial approach to fast correlation attacks on binary memoryless combiners is proposed. Instead of individual input sequences or their linear combinations, the new attack is targeting subsets of input sequences as a whole thus exploiting the full correlation between the chosen subset and the output sequence. In particular, the set of all the input sequences can be chosen as the target. The attack is based on a novel iterative probabilistic algorithm which is also applicable to general memoryless combiners over finite fields or finite rings. To illustrate the effectiveness of the introduced approach, experimental results obtained for random balanced combining functions are presentedMost of this work was done while he was with Rome CryptoDesign Center, Gemplus, Italy 相似文献
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The motion of a holonomic scleronomic non-conservative mechanicalsystem with minimal dissipation is considered. As applicationsof the theory several problems are studied in detail. 相似文献
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A Mukherjee M Dasgupta DJ Hinde CR Morton AC Berriman RD Butt JO Newton H Timmers 《Pramana》2001,57(1):195-198
Fusion cross-sections for the 7Li + 12C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy
evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their
contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections
due to the breakup of 7Li may not be significant for 7Li + 12C reaction at energies around the barrier. 相似文献