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21.
Poly(A)+ mRNA was isolated from leaves of potato plants (Solanum tuberosum L. cv. Desiree) according to standard protocols. This poly(A)+ mRNA was injected via glass microcapillaries into oocytes that were surgically removed from the African clawed toad Xenopus laevis. As a control, oocytes were either injected with H2O or remained untreated. Three days after injection the oocytes were analyzed by two electrode voltage clamping. Current voltage analysis revealed that a K+ channel from potato was functionally expressed in injected oocytes. The identity of this K+ channel was confirmed by its substrate specificity and a shift in the reversal potential. In particular, when the outside K+ concentration was increased the reversal potential of poly(A)+ injected oocytes shifted to more positive values. Furthermore, K+ outward currents declined when the outside K+ concentration was raised from 0.1 to 100 mM. Inward currents increased with an elevation of the K+ concentration. Several pharmaceuticals were tested for their potential to block this K+ channel. As a result, the channel was completely blocked by BaCl2. A three state reaction kinetic model was used to simulate the currents through the K+ transport protein as function of the extracellular K+ concentration. In particular, the simulation revealed current voltage relations that exactly matched the measured ones. Saturation of current voltage curves emerged from the simulation as a consequence of high extracellular potassium concentration.  相似文献   
22.
OBJECTIVE: To characterize the existence and role of transforming growth factor-beta (TGF-beta) in otitis media with effusion (OME). STUDY DESIGN: Retrospective. METHODS: The levels of two major TGF-beta isoforms, TGF-beta1 and TGF-beta2, in the middle ear effusions (MEEs) of 44 children were evaluated using enzyme-linked immunospecific assays (ELISAs). Forty-eight MEEs were separated into three clinically relevant groups (i.e., serous, mucoid, and purulent), and TGF-beta levels were correlated with clinical parameters of disease for these MEEs. RESULTS: Both TGF-beta1 and TGF-beta2 were present in the samples. Mean levels of TGF-beta1 (920.36 +/- 437.75 pg/mg total protein) were generally 100-fold greater than those of TGF-beta2 (9.65 +/- 11.19 pg/mg total protein). TGF-beta1 levels were elevated in association with a history of previous tympanostomy tube placements (TTPs) (P = .029) and mucoid effusions (P = .042). TGF-beta2 levels were elevated in association with a history of previous TTPs (P = .100) and chronic (i.e., serous or mucoid) effusions (P = .003). CONCLUSIONS: TGF-beta1 is present in the MEEs of children with OME. Furthermore, TGF-beta1 and TGF-beta2 levels were elevated differentially in the presence of chronic disease indicators in OME, suggesting that these isoforms may have differing roles in the inflammatory processes that characterize OME.  相似文献   
23.
Lithium naphthalene reacts with acetic acid to give α-anion of lithium acetate. The reaction of this anion with various ketones gives the corresponding β-hydroxy-acids in good yield.  相似文献   
24.
Photocatalytic activities for water decomposition were examined for photocatalysts using hexa- and octa-titanates and TiO2(B) with different tunnel space in the structure. Using RuO2 as promoter, M2Ti6O13 (M = Li, Na, K, Rb) showed the stoichiometric production of Hz and O2 except for Li, whereas H2Ti8O17 and TiO2(B) had very low activity producing only hydrogen as a product. The effects of promoters on Na2Ti6O13 showed that the activity increased in the order of RuO2 > RuO2 + IrO2 > IrO2 > RuO2 + Pt > MnO2. These effects along with other related ones are discussed: it emerges that the presence of the tunnels is important for the achievement of high photocatalytic activity.  相似文献   
25.
The structure-activity relationship of eclosion hormone from the silkworm, Bombyx mori, was analyzed. First, the probable active residues in silkworm eclosion hormone and also tobacco hornworm eclosion hormone were predicted by the average distance map method. To examine the contributions of those residues to the activity of silkworm eclosion hormone, Gly-substituted mutants for those predicted residues were produced by site-directed mutagenesis and their activities were evaluated by a bioassay. Finally, Glu12, Met24 and Phe25 were estimated to be the crucial residues for the eclosion hormone activity. The possibility of the development of a blocker of an eclosion hormone receptor on the basis of the present work is also discussed.   相似文献   
26.
A tripod parallel mechanism consists of three links of fixed length and a rigid platform, and these are connected by revolute joints. The platform can achieve sixdegrees-of-freedom (6-DOF) motion by the coordinated movement of the bottom ends of the three links on a horizontal plane. This mechanism has advantages over the more common six extendible parallel manipulators. It has a much larger work space and a simple structure. In this article, we show that the vector analysis for this tripod parallel mechanism and the derivation of the positions of the three bottom ends of the links in an arbitrary attitude of platform can be found by inverse kinematics and the conditions of geometrical constraint. Then, by a numerical simulation, the trajectories of the bottom ends of the three links are shown.  相似文献   
27.
Oriented poly-p-phenylene sulphide (PPS) films (thickness 12 and 75 m) and PPS powder were carbonized/graphitized after stabilizing by oxidation, in order to examine the effect of sulphur on graphitizability of the resulting carbons. The films and the powder resulted in carbons with a high and a low graphitizability respectively. An in-plane oriented structure of the PPS film was the most predominant factor to lead to a high graphitizability, and sulphur in the precursor did not lower the graphitizability when it was subjected to solid-phase carbonization. These phenomena are discussed on the basis of analytical data.  相似文献   
28.
29.
We have investigated the normal-state conduction of superconducting Sr2RuO4 (Tc 1K), which is isostructural to La2–xSrxCuO4. The resistivity of single crystals shows a crossover at TM130K from 3D metallic conduction at lower temperatures to 2D one at higher temperatures. Concerning the temperature dependence of the out-of-plane resistivity, we present a systematic interpretation based on competition between the life time of the quasiparticles and the time for the quasiparticles to travel between the adjacent RuO2 planes.  相似文献   
30.
A robust automatic crack detection method from noisy concrete surfaces   总被引:2,自引:0,他引:2  
In maintenance of concrete structures, crack detection is important for the inspection and diagnosis of concrete structures. However, it is difficult to detect cracks automatically. In this paper, we propose a robust automatic crack-detection method from noisy concrete surface images. The proposed method includes two preprocessing steps and two detection steps. The first preprocessing step is a subtraction process using the median filter to remove slight variations like shadings from concrete surface images; only an original image is used in the preprocessing. In the second preprocessing step, a multi-scale line filter with the Hessian matrix is used both to emphasize cracks against blebs or stains and to adapt the width variation of cracks. After the preprocessing, probabilistic relaxation is used to detect cracks coarsely and to prevent noises. It is unnecessary to optimize any parameters in probabilistic relaxation. Finally, using the results from the relaxation process, a locally adaptive thresholding is performed to detect cracks more finely. We evaluate robustness and accuracy of the proposed method quantitatively using 60 actual noisy concrete surface images.  相似文献   
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