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11.
Prevalent visualization tools exploit gray value distribution in images through modified histogram equalization and matching technique, referred to as the window width/window level-based method, to improve visibility and enhance diagnostic value. The window width/window level tool is extensively used in magnetic resonance (MR) images to highlight tissue boundaries during image interpretation. However, the identification of different regions and distinct boundaries between them based on gray-level distribution and displayed intensity levels is extremely difficult because of the large dynamic range of tissue intensities inherent in MR images. We propose a soft-segmentation visualization scheme to generate pixel partitions from the histogram of MR image data using a connectionist approach and then generate selective visual depictions of pixel partitions using pseudo color based on an appropriate fuzzy membership function. By applying the display scheme in clinical examples in this study, we could demonstrate additional overlapping regions between distinct tissue types in healthy and diseased areas (in the brain) that could help improve the tissue characterization ability of MR images. 相似文献
12.
To test a developed reconstruction algorithm for cone beam geometry, whether it is transmission or emission tomography, one
needs projection data. Generally, mathematical phantoms are generated in three dimensions and the projection for all rotation
angles is calculated. For non-symmetric objects, the process is cumbersome and computation intensive. This paper describes
a simple methodology for the generation of projection data for cone beam geometry for both transmission and emission tomographies
by knowing the object’s attenuation and/or source spatial distribution details as input. The object details such as internal
geometrical distribution are nowhere involved in the projection data calculation. This simple approach uses the pixilated
object matrix values in terms of the matrix indices and spatial geometrical coordinates. The projection data of some typical
phantoms (generated using this approach) are reconstructed using standard FDK algorithm and Novikov’s inversion formula. Correlation
between the original and reconstructed images has been calculated to compare the image quality. 相似文献
13.
We have studied the collective behaviour of a one-dimensional ring of cells for conditions when the individual uncoupled cells
show stable, bistable and oscillatory dynamics. We show that the global dynamics of this model multicellular system depends
on the system size, coupling strength and the intrinsic dynamics of the cells. The intrinsic variability in dynamics of the
constituent cells are suppressed to stable dynamics, or modified to intermittency under different conditions. This simple
model study reveals that cell–cell communication, system size and intrinsic cellular dynamics can lead to evolution of collective
dynamics in structured multicellular biological systems that is significantly different from its constituent single-cell behaviour. 相似文献
14.
The following article describes a concise synthesis of a collection of 4,5-dihydro-1H-benzo[e][1,4]diazepines fused to a hydantoin ring. Molecular complexity and biological relevance are high and structures are generated in a mere three steps, employing the Ugi reaction to assemble diversity reagents. The protocol represents a novel UDC (Ugi-deprotect-cyclize) strategy employed in the Ugi-5-component CO2-mediated condensation, followed by further cyclization under basic conditions, to afford the fused hydantoin. Mechanistic caveats, dependent on the aldehydes of choice will be revealed and a facile oxidation of the final products to imidazolidenetriones is briefly discussed. 相似文献
15.
The oxidation of 34 organic sulphides hy 2,2′-hipyridinium chlorochromate (BPCC) resulted in the formation of the corresponding
sulphoxides. The reaction is first order with respect to both BPCC and the sulphide, and is catalysed by hydrogen ions. The
hydrogen-ion dependence has the form:k
obs = a+b[H+]. The oxidation was studied in 19 different organic solvents. An analysis of the solvent effect by Swain’s equation showed
that the both cation-and anion-solvating powers of the solvents play important roles. The rates of oxidation meta- andp-substituted phenyl methyl sulphides were correlated with Charton’s LDR equation. The rates of theo-compounds showed excellent correlation with the LDRS equation. Oxidation of thep-compounds is more susceptible to the delocalizationeffect. Oxidation of themcompounds exhibited a greater dependence on the field effect. In the oxidation of theo-compounds, the contribution of delocalized effect is slightly more than that of the field effect. The oxidation of alkyl
phenyl sulphides is subject to both polar and steric effects of the alkyl groups. Polar reaction constants are negative, indicating
an electron-deficient sulphur centre in the rate-determining step. A mechanism involving formation of a sulphurane intermediate
in the slow step has been proposed. 相似文献
16.
17.
Hatch A Hansmann G Murthy SK 《Langmuir : the ACS journal of surfaces and colloids》2011,27(7):4257-4264
Microfluidic adhesion-based cell separation systems are of interest in clinical and biological applications where small sample volumes must be processed efficiently and rapidly. While the ability to capture rare cells from complex suspensions such as blood using microfluidic systems has been demonstrated, few methods exist for rapid and nondestructive release of the bound cells. Such detachment is critical for applications in tissue engineering and cell-based therapeutics in contrast with diagnostics wherein immunohistochemical, proteomic, and genomic analyses can be carried out by simply lysing captured cells. This paper demonstrates how the incorporation of four-arm amine-terminated poly(ethylene glycol) (PEG) molecules along with antibodies within alginate hydrogels can enhance the ability of the hydrogels to capture endothelial progenitor cells (EPCs) from whole human blood. The hydrogel coatings are applied conformally onto pillar structures within microfluidic channels and their dissolution with a chelator allows for effective recovery of EPCs following capture. 相似文献
18.
19.
Synthesis of 3-(′, 1′-dimethylallyl)herniarin and 3-(′, 1′-dimethylallyl)desmothosyherniarin has been carried out by a versatile route. 相似文献
20.
We present a fully polynomial time approximation scheme (FPTAS) for optimizing a very general class of non-linear functions of low rank over a polytope. Our approximation scheme relies on constructing an approximate Pareto-optimal front of the linear functions which constitute the given low-rank function. In contrast to existing results in the literature, our approximation scheme does not require the assumption of quasi-concavity on the objective function. For the special case of quasi-concave function minimization, we give an alternative FPTAS, which always returns a solution which is an extreme point of the polytope. Our technique can also be used to obtain an FPTAS for combinatorial optimization problems with non-linear objective functions, for example when the objective is a product of a fixed number of linear functions. We also show that it is not possible to approximate the minimum of a general concave function over the unit hypercube to within any factor, unless P = NP. We prove this by showing a similar hardness of approximation result for supermodular function minimization, a result that may be of independent interest. 相似文献