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131.
CT快速图像重建算法研究 总被引:4,自引:0,他引:4
快速图像重建算法一直是图像重建中的关键问题和衡量CT系统的重要指标之一。本文以扇形束结构为例,分析了各种快速重建算法的特点,并从算法结构、实现技巧及代码优化等方面论述了快速图像重建的方法.这些方法可有效地提高图像重建的速度。 相似文献
132.
Principal components analysis of evoked potentials differing between groups presents an interpretive problem, particularly in psychiatric research. Two sets of principal components and associated factor scores may appear to differ. The issue is to determine the extent to which visually differing principal components and resultant factor scores span the same factor space. Sets of evoked potentials from controls and from schizophrenics were each subjected to principal components analysis, from which factor score coefficients were computed for all subjects. This allowed determination of the extent to which (1) the two sets of basis waves were similar and (2) the factor scores resulting from the set of basis waves derived from principal components analysis of the control subjects' evoked potential data adequately represented those of the schizophrenics and vice-versa. Canonical correlation analyses indicated substantial similarities between the principal component structures (sets of basis waves). Multiple correlational analyses confirmed that the basis waves from either group spanned the other group's factor space. Factor scores from either set of basis waves were highly correlated. These results suggest that principal component structures derived from evoked potentials of a control group may be used in computing evoked potential factor scores of psychiatrically diverse populations even though the average evoked potentials of the groups may differ in several ways. 相似文献
133.
Structure of avian orthoreovirus virion by electron cryomicroscopy and image reconstruction 总被引:6,自引:0,他引:6
Among members of the genus Orthoreovirus, family Reoviridae, a group of non-enveloped viruses with genomes comprising ten segments of double-stranded RNA, only the "non-fusogenic" mammalian orthoreoviruses (MRVs) have been studied to date by electron cryomicroscopy and three-dimensional image reconstruction. In addition to MRVs, this genus comprises other species that induce syncytium formation in cultured cells, a property shared with members of the related genus Aquareovirus. To augment studies of these "fusogenic" orthoreoviruses, we used electron cryomicroscopy and image reconstruction to analyze the virions of a fusogenic avian orthoreovirus (ARV). The structure of the ARV virion, determined from data at an effective resolution of 14.6 A, showed strong similarities to that of MRVs. Of particular note, the ARV virion has its pentameric lambda-class core turret protein in a closed conformation as in MRVs, not in a more open conformation as reported for aquareovirus. Similarly, the ARV virion contains 150 copies of its monomeric sigma-class core-nodule protein as in MRVs, not 120 copies as reported for aquareovirus. On the other hand, unlike that of MRVs, the ARV virion lacks "hub-and-spokes" complexes within the solvent channels at sites of local sixfold symmetry in the incomplete T=13l outer capsid. In MRVs, these complexes are formed by C-terminal sequences in the trimeric mu-class outer-capsid protein, sequences that are genetically missing from the homologous protein of ARVs. The channel structures and C-terminal sequences of the homologous outer-capsid protein are also genetically missing from aquareoviruses. Overall, the results place ARVs between MRVs and aquareoviruses with respect to the highlighted features. 相似文献
134.
The manner of packing of the terminal DNA loci into nucleosomes and higher order structures may strongly influence their functional
interactions. Besides the structural flexibility of telomeric DNA sequences, conserved features of their chromatin including
short nucleosome phasing (157 bp) and nucleosome sliding have been described previously. To gain a complementary knowledge
of subtelomeres, we have analysed the chromatin structure of two subtelomeric tandem repeats from the plant Silene latifolia: X43.1 and 15Ssp. X43.1 shows two distinct nucleosome periodicities – 157 and 188 bp. Preferred positions of its two nucleosomes
have been mapped at both low and high resolution and the experimental results correspond to computer-predicted positions.
15Ssp is a newly-discovered sequence showing a telomere-associated position by PCR and a subtelomeric location by pulsed-field
gel electrophoresis and fluorescence in situ hybridisation. Its 159 bp sequence unit shows a tandem arrangement and the presence of micrococcal nuclease-hypersensitive
sites when either naked DNA or chromatin is digested. Use of a chemical nuclease results in a regular nucleosome ladder of
157 bp periodicity. Moreover, 15Ssp mononucleosomes show instability and absence of specific positioning, features typical
for telomeric chromatin.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
135.
应用模糊极小极大神经网络研究了化合物复杂结构和性能(QSAR)之间的关系,用该法进行几组化合物致癌的识别,结果优于线性回归的方法,对此作出一些分析。 相似文献
136.
The clinical laboratory is regarded as a component of the medical care system extending from physician to laboratory staff and back to physician. From this concept a computer-based system of laboratory information is derived, emphasizing: (1) total laboratory responsibility for the test and its request, and (2) physician-oriented output reports. 相似文献
137.
Schaefer M 《Pflügers Archiv : European journal of physiology》2005,451(1):35-42
Mammalian homologues of the Drosophila melanogaster transient receptor potential (TRP) channels are the second largest cation channel family within the superfamily of hexahelical cation channels. Most mammalian TRP channels function as homooligomers and mediate mono- or divalent cation entry upon activation by a variety of stimuli. Because native TRP channels may be multimeric proteins of possibly complex composition, it is difficult to compare cation conductances in native tissues to those of clearly defined homomeric TRP channel complexes in living cells. Therefore, the possibility of heteromeric TRP channel assembly has been investigated in recent years by several groups. As a major conclusion of these studies, most heteromeric TRP channel complexes appear to consist of subunit combinations only within relatively narrow confines of phylogenetic subfamilies. Although the general capability of heteromer formation between closely related TRP channel subunits is now clearly established, we are only beginning to understand whether these heteromeric complexes are of physiological significance. This review summarizes the current knowledge on the promiscuity and specificity of the assembly of channel complexes composed of TRPC-, TRPV- and TRPM-subunits of mammalian TRP channels. 相似文献
138.
数值模拟鼻甲的切除对鼻腔内气体流场的影响 总被引:3,自引:0,他引:3
量化研究鼻腔结构的变化对鼻腔内气体流场分布的影响.通过CT图像对鼻腔结构进行三维重建并用有限元方法对气体流场进行数值分析.对重建的鼻腔模型的一侧,分别去掉部分中鼻甲和部分下鼻甲并用有限元方法再次进行数值分析,将得到的结果与原始模型进行比较.观察气体流场分布的变化,在两侧鼻腔的流量分布均有变化,在去掉部分鼻甲的一侧流场和气压的分布也有所改变.通过数值模拟,我们量化的显示了鼻腔结构的变化对鼻腔内气体流场分布的影响. 相似文献
139.
A fourth case of ring chromosome 7 总被引:1,自引:0,他引:1
An 8-year-old child with a ring chromosome 7 is presented, the first female and the fourth such individual to be described. The associated anomalies were rather benign: she presented with short stature, minor skeletal alterations, and normal intelligence. The only truly striking feature was the presence of multiple large, pigmented naevi, suggestive of a hamartomatous origin, but unlike those typical of any particular syndrome. Though other ring 7 patients have had naevus flammeus, and one had cafk-au-lait spots, our proband is the first with an anomaly of chromosome 7 to have such extensive lesions. These four cases of ring 7, which show great phenotypic variation, are reviewed, and the clinical presentation of the proband is also compared with that of patients suffering from terminal, interstitial and translocation-derived 7p and 7q deletions. The formation and behaviour of ring chromosomes are discussed, as are the cytogenetic factors which may influence their phenotypic expression. 相似文献
140.
A laboratory-developed analog signal processor, driven by a conventional polygraph recorder and associated signal conditioning devices, provides automatic heart beat-by-heart beat preprocessing of various cardiovascular functions for input to a laboratory-type minicomputer. The technique of preprocessing individual functions, integrated with the minicomputer system which includes an A/D converter and teletype as input-output peripherals, provides a low-cost data acquisition and reduction system for the on-line computation and analysis of cardiovascular functions in experimental research applications. Such preprocessing more efficiently uses the minicomputer's memory to handle large amounts of information since the digitized data is in the form of one data sample, per function, per heart beat. Preprocessing analog data provides a low density data format and simplified software programs that are ideally suited for the utilization of a minicomputer in this on-line application. 相似文献