270 resultados para SM


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The effects of aniracetam on extracellular amino acid levels in the hippocampus of conscious gerbils, with or without transient cerebral ischemia/reperfusion, were measured by microdialysis and reverse phase-high performance liquid chromatography. Increased extracellular levels of aspartate and glutamate that were observed in the hippocampus of conscious gerbils during transient global forebrain ischemia were reversed by aniracetam. In contrast, the level of extracellular gamma-aminobutyric acid was increased, while taurine was maintained at a higher level than other amino acids by administration of aniracetam (100 mg/kg, p.o.) 60 min before ischemia. Further, in contrast to ischemic animals, administration of aniracetam (100 mg/kg, p.o.) enhanced the release of glutamate and aspartate in the normal gerbil hippocampus. The results suggest that these effects might be due to a partial calcium agonist activity of aniracetam, and that the effects of aniracetam on amino acid levels might be a mechanism of protection against delayed neuronal death in the ischemic hippocampus, thereby improving memory dysfunction induced by ischemia/reperfusion. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.

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用氧氟沙星(Ofl)和链霉素(Sm)分别处理纤细裸藻获得褪色突变株,电子显微镜观察显示细胞中存在残留质体,其中一个Ofl突变株质体有原初类囊体膜形成,而两个Sm突变株质体内有异常致密、发达的膜结构。用PCR方法检查了质体DNA的9个基因,显示所有突变株均有核糖体蛋白基因丢失,其中一个Sm突变株仍保留质体DNA的大部分基因,其余突变株质体DNA则基本丢失。通过差异显示和RT-PCR方法证明叶绿体的退化在完全黑暗异养条件下也可导致某些核基因转录的变化。

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<正> 对于豚类染色体核型,国外有过关于海豚类方面的研究,而关于淡水豚类迄今尚未见有报道。本文是对白鱀豚核型研究的初步结果。材料取自一头体长为1.97米的雄性白鱀豚“淇淇”。此豚自1980年元月12日以来一直饲养在本所的饲养池内。采用哺乳动物常规的外周血培养法,空气干燥制片,吉姆萨染色法。我们共分析9个中期相,对其中2个中期相进行了测量。根据它们的臂比按Laven命名法分为以下4组: M组,(具中着丝点染色体(Metacentric))r=1.00-1.67;SM组,(具亚中着丝点染色体(Submerce

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三种鱼的二倍体数目完全相同,均为2n=50。三种鱼的核型差异较大,尤其是双亲间的组型在形态上有明显的差异。然而杂交一代的m、sm二组染色体的组型却十分接近母体,这二组的染色体数占了全部染色体总数的88%。杂交一代染色体组型中的st和t二组染色体虽与双亲有所不同,但与双亲中这二组染色体组型的差异来比要小一些。三种鱼的中期分裂相中,未曾发现带有随体的染色体,也未发现与性别有关的异型染色体的存在。

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本文对莫桑比克罗非鱼、尼罗罗非鱼、加俐俐罗非鱼的染色体组型进行了分析研究,并绘制了它们各自的核型模式图。所有这3种罗非鱼的二倍体染色体数目都是44,即2n=44。第1对染色体最长,第2对次之,其余20对均为大小差不多的染色体。它们的核型可分为3组,SM组4对,ST组17对,T组1对。3种罗非鱼的染色体组型形态基本相似,用常规染色体染色的方法难以区分。本文还讨论了罗非鱼的核型与进化问题。

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Bleached mutants of Euglena gracilis were obtained by treatment with ofloxacin (Ofl) and streptomycin (Sm) respectively. As shown by electron microscopy, the residual plastids contain prothylakoids in an Ofl mutant, and the highly developed and tightly stacked membranous structure found in cells of two Sm, mutants. Nine genes of the plastid genome were examined with PCR, showing that ribosomal protein genes and most other plastid genes were lost in all but one Sm mutant. Using differential display and RT-PCR, it was shown that chloroplast degeneration could cause changes in transcription of certain nucleus-encoded genes during heterotrophic growth in darkness.

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An antibody phage display library against White Spot Syndrome Virus (WSSV) was constructed. After four rounds of panning against WSSV, 192 out of 480 clones displayed WSSV binding activity. One of the positive clones, designated A1, had relatively higher activity specifically binding to WSSV A1-soluble, single-chain fragment variable (scFv) antibody has an affinity constant (K-aff) of 2.02 +/- 0.42 x 10(9) M-1. Dot blot assays showed that A1-soluble scFv could detect WSSV directly from shrimp hemolymph after 24-h feeding infection by WSSV. A1 scFv has potential for the development of a cheap, simple and sensitive diagnostic kit for WSSV in the field. (C) 2003 Elsevier Science B.V. All rights reserved.

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The influence of well thickness on the electroluminescence (EL) of InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition is investigated. It is found that the peak wavelength of EL increases with the increase of well thickness when the latter is located in the range of 3.0-5.1 nm. The redshift is mainly attributed to the quantum confined Stark effect (QCSE). As a contrast, it is found that the EL intensity of InGaN/GaN MQWs increases with the increase of well thickness in spite of QCSE. The result of X-ray diffraction demonstrates that the interface become smoother with the increase of well thickness and suggests that the reduced interface roughness can be an important factor leading to the increase of EL intensity of InGaN/GaN MQWs. (C) 2009 Elsevier B.V. All rights reserved.

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To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au (5 nm/5 nm) film deposition. The surface morphology of wafers and the current-voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes

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We present the growth of GaN epilayer on Si (111) substrate with a single AlGaN interlayer sandwiched between the GaN epilayer and AlN buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an AlN buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.

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A new method to test the hole concentration of p-type GaN is proposed, which is carried out by analyzing the spectral response of p-n(+) structure GaN ultraviolet photodetector. It is shown that the spectral response of the photodetector changes considerably with reversed bias. It is found that the difference between photodetector's quantum efficiency at two wavelengths, i.e. 250 and 361 nm, varies remarkably with increasing reversed bias. According to the simulation calculation, the most characteristic change occurs at a reversed voltage under which the p-GaN layer starts to be completely depleted. Based on this effect the carrier concentration of p-GaN can be derived.

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This paper reports that Al1-xInxN epilayers were grown on GaN template by metalorganic chemical vapor deposition with an In content of 7%-20%. X-ray diffraction results indicate that all these Al1-xInxN epilayers have a relatively low density of threading dislocations. Rutherford backscattering/channeling measurements provide the exact compositional information and show that a gradual variation in composition of the Al1-xInxN epilayer happens along the growth direction. The experimental results of optical reflection clearly show the bandgap energies of Al1-xInxN epilayers. A bowing parameter of 6.5 eV is obtained from the compositional dependence of the energy gap. The cathodoluminescence peak energy of the Al1-xInxN epilayer is much lower than its bandgap, indicating a relatively large Stokes shift in the Al1-xInxN sample.

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InGaN/GaN multi-quantum-well-structure laser diodes with an array structure are successfully fabricated on sapphire substrates. The laser diode consists of four emitter stripes which share common electrodes on one laser chip. An 800-mu m-long cavity is formed by cleaving the substrate along the < 1 (1) over bar 00 >. orientation using laser scriber. The threshold current and voltage of the laser array diode are 2A and 10.5 V, respectively. A light output peak power of 12W under pulsed current injection at room temperature is achieved. We simulate the electric properties of GaN based laser diode in a co-planar structure and the results show that minimizing the difference of distances between the different ridges and the n-electrode and increasing the electrical conductivity of the n-type GaN are two effective ways to improve the uniformity of carrier distribution in emitter stripes. Two pairs of emitters on a chip are arranged to be located near the two n-electrode pads on the left and right sides, and the four stripe emitters can laser together. The laser diode shows two sharp peaks of light output at 408 and 409 nm above the threshold current. The full widths at half maximum for the parallel and perpendicular far field patterns are 8 degrees and 32 degrees, respectively.

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The leakage current of GaN Schottky barrier ultraviolet photodetectors is investigated. It is found that the photodetectors adopting undoped GaN instead of lightly Si-doped GaN as an active layer show a much lower leakage current even when they have a higher dislocation density. It is also found that the density of Ga vacancies in undoped GaN is much lower than in Si-doped GaN. The Ga vacancies may enhance tunneling and reduce effective Schottky barrier height, leading to an increase of leakage current. It suggests that when undoped GaN is used as the active layer, it is necessary to reduce the leakage current of GaN Schottky barrier ultraviolet photodetector.