Positron-annihilation study of oxygen-deficient YBa2Cu3Ox (6.3

CQ Tang  BR Li  A Chen 《Canadian Metallurgical Quarterly》1990,42(13):8078-8080

The effect of scene elevation on the coherence of wide-angle crossing-node SAR pairs

The interference between two radar images, acquired from approximately the same location, has a number of uses. In particular, the literature abounds with examples of coherent change detection (CCD) and interferometric synthetic aperture radar (InSAR) uses that, respectively, enable the detection of small changes and the extraction of terrain elevation. In almost all of these examples, collections have been deliberately constrained so that they have almost identical collection geometries. Details of the variation in geometry have been analyzed extensively but generally only with respect to variation in the mean grazing angle. Much of this variation is due to the angular variation in the scene reflectivity; however, when collection geometries differ in other respects, the reduction in performance cannot be entirely explained by angular variations alone. This paper identifies a source of performance degradation when the collection geometries are different for scenes containing local relief. The error is due to approximations during image formation that both the collection geometry and the terrain are flat. The effect of these errors is derived as a blurring kernel to the true scene. The impact of the blurring is then assessed in the interferometric case and broken into common and differential blurring terms to facilitate the impact of some special cases and to explain why the parallel-pass geometry works as well as it does even though the true three-dimensional nature of the collection and the ground are ignored.     

Comparison of technetium-99m-ECD to Xenon-133 SPECT in normal controls and in patients with mild to moderate regional cerebral blood flow abnormalities

Technetium-99m-1,1-ethyl cysteinate dimer (ECD) has been proposed as a "chemical microsphere" for SPECT measurement of regional cerebral blood flow (rCBF). However, its distribution has not yet been compared in humans to an established rCBF measure. Therefore, we compared the uptake and distribution of ECD with rCBF measured by 133Xe SPECT in subjects with mild to moderate flow abnormalities and in normal volunteers. Blood and urine chemistries and vital signs were unchanged from pre-ECD values up to seven days postinjection. Profile plots demonstrated pattern agreement between rCBF ratios (133Xe) and ECD count density ratios. A significant correlation of rCBF ratios to ECD count density ratios was observed (r = 0.77), with a slope of 0.64 and intercept of 0.36. To explore whether or not the relationship between rCBF and ECD was dependent on absolute flow, ECD region of interest data were expressed in units of ml/min/100 g by equating global CBF (133Xe) and ECD global count density. A closer correlation (r = 0.88) was found for these data than for the count ratio data. The slope was closer to one (m = 0.83) and the intercept was closer to zero (b = 8.2). Also, a significant correlation was observed between ECD-derived rCBF and 133Xe rCBF in the lesion area (r = 0.92) for patients with well-demarcated rCBF lesions. The slope (0.80) suggested a slight underestimation of lesion flow by ECD. Finally, ECD clearance from cortical gray matter ROIs derived from high-resolution scans from 1 to 4 hr postinjection was slow (2.4%/hr). In summary, ECD is a safe and effective marker of regional cerebral perfusion. The distribution of ECD is linearly related to rCBF measured by 133Xe SPECT, although our data suggest a mild underestimation of flow at the high end of the normal range.     

Hypermnesia for pictures and words: Testing the recall level hypothesis.

Five experiments with 150 undergraduates examined the hypothesis that hypermnesia (improved recall across repeated tests) can be predicted from cumulative recall levels. Contrary to this view, Exp I demonstrated that when the cumulative recall levels for pictures and words were equated, pictures still produced a larger hypermnesic effect. Results of Exps II and III show that varying test length (and thus recall level) had no effect on the magnitude of the hypermnesic effect. In Exp IV, Ss studied a categorized word list and then received 1 21-min test or 3 7-min tests. Results suggest that (a) similar retrieval processes are used in these 2 conditions and (b) hypermnesia in the repeated test paradigm results from Ss generating covert cues to aid item recovery across tests. Overall findings suggest that although hypermnesia is related to cumulative recall levels, various other factors (e.g., item type) modulate the magnitude of the hypermnesia by affecting item accessibility across tests. It is argued that changes in item accessibility across tests, caused by learning during testing, play a major role in producing hypermnesia in both episodic and semantic memory tasks. (43 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ribosome binding to mitochondria is regulated by GTP and the transit peptide

The association between ribosomes and the pore proteins at the endoplasmic reticulum membrane is important to co-translational translocation. To determine if a similar association occurs between the ribosome and mitochondrial membrane protein(s) during protein import in higher eukaryotes, we examined ribosome-mitochondria binding. By using spectral measurements, analysis of mitochondrial associated RNA, and electron microscopy, we demonstrated that ribosomes stably bind to purified rat liver mitochondria in vitro. Binding of ribosomes to mitochondria was markedly reduced by GTP and nearly abolished by the non-hydrolyzable GTP analogue, guanosine-5'-[thio]-triphosphate (GTPgammaS), but was only modestly reduced by GDP or ATP and unaffected by CTP. The initial rate of GTP hydrolysis by mitochondria was increased by ribosomes, whereas the rate of ATP hydrolysis by mitochondria was not affected. Ribosomes programmed with mRNA for 92 amino acids of the N terminus of mitochondrial malate dehydrogenase bound to mitochondria, but unlike unprogrammed rat liver ribosomes, neither GTP nor GDP disrupted binding; however, GTPgammaS did. These data show that receptors specific for ribosomes are present on the mitochondrial membrane, and a GTP-dependent process mediates this binding. The presence of a nascent chain alters these binding characteristics. These findings support the hypothesis that a co-translational translocation pathway exists for import of proteins into mitochondria.