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排序方式: 共有906条查询结果,搜索用时 15 毫秒
1.
Due to their small size, mammalian oocytes and embryos pose unique problems during preparation for transmission electron microscopy. This paper outlines a method which combines protein embedding with centrifugation to locate the specimens on the face of a Beem capsule mould. This method facilitates both the processing of oocytes with minimal loss and rapid location of the specimens within the block for simultaneous sectioning, staining and examination. 相似文献
2.
The possibility that progesterone or estradiol may regulate expression of G protein in the rat myometrium during the course of pregnancy has been investigated using 1) immunoblot analysis of Gi2 alpha, Gi3 alpha, and Gq alpha subunits and 2) hybridization blot analysis of subunit mRNA. Eighteen hours after administration, estradiol had significantly increased the levels of both Gi2 alpha subunit and Gi2 alpha mRNA (by 40% and 32%, respectively). In control pregnant rats, we observed similar changes at the end of pregnancy, when myometrial concentrations of estradiol had increased, i.e., a 41% increase in immunoreactive Gi2 alpha subunit that correlated with a parallel 45% increase in mRNA levels. In contrast, levels of immunoreactive Gi3 alpha subunit and mRNA, which decreased with advancing gestation, were not influenced by estradiol or progesterone administration. Progesterone administration resulted 30 h later in a significantly decreased level of Gq alpha immunoreactivity (32%) and Gq alpha mRNA (30%). In control rats, Gq alpha protein and mRNA were also significantly lower at midpregnancy under progesterone dominance vs. term. At this stage, a twofold increase in Gq alpha subunit correlated with a 40% increase in mRNA levels. These results demonstrate that myometrial Gi2 alpha and Gq alpha subunits are physiological targets for estradiol and progesterone, respectively, in vivo. Alterations of these G protein levels are discussed in relation to their mediating effects on adenylyl cyclase activity or the phospholipase C pathway during the course of pregnancy. 相似文献
3.
Pooi Yuen Kam 《Communications, IEEE Transactions on》1994,42(12):3119-3128
Consider the classic problem of evaluating the probability that one Rician random variable exceeds another, possibly correlated, Rician random variable. This probability is given by Stein (1964) in terms of the Marcum's Q-function, which requires numerical integration on the computer for its evaluation. To facilitate application in many digital communication problems, we derive here tight upper and lower bounds on this probability. The bounds are motivated by a classic result in communication theory, namely, the error probability performance of binary orthogonal signaling over the Gaussian channel with unknown carrier phase. Various applications of the bounds are reported, including the evaluation of the bit error probabilities of MDPSK and MPSK with differential detection and generalized differential detection, respectively. The bounds prove to be tight in all cases. Further applications will be reported in the future 相似文献
4.
A numerical simulation model for random large amplitude vibration control of composite plate using piezoelectric material is presented. The H∞ control design is employed to suppress the large amplitude vibrations of composites plates under random loading. The numerical simulation model is developed and based on the finite element method. The finite element governing equation includes fully coupled structural and electrical nodal degrees of freedom, and consider the von Karman large amplitude vibration. The modal reduction method using the structural modes is adopted to reduce the finite element equations into a set of modal equations with fewer degrees of freedom. The modal equations are then employed for controller design and time domain simulation. In the simulations without control, the value of the linear mode to the nonlinear deflection is quantified; and the minimum number of linear modes needed for accurate model is obtained. In the simulations with control, it is shown that the truncated modes, which are neglected in the control design, deteriorate the controller performance. Generally, the vibration reduction level is not monotonically increasing with the size of the piezoelectric actuator. The optimal piezoelectric actuator size depends on the excitation level. For higher excitation level, optimal actuator size is larger. The H∞ controller based on the linear finite element formulation gives better vibration reduction for small amplitude vibration, but it still gives reasonable performance for large amplitude vibration provided that the piezoelectric actuator is big and powerful enough. 相似文献
5.
In this paper, we present an asymptotic performance analysis of three subspace-based methods for direction of arrival (DOA) estimation-the ESPRIT algorithm using second order statistics, the higher order ESPRIT algorithm using fourth-order cumulants, and the virtual ESPRIT (VESPA) algorithm using fourth-order cumulants. We examine the least-squares version of these algorithms, derive the expressions for the asymptotic variance of the estimated DOAs, and use specific examples to compare the relative performance of the algorithms. Finally, we present Monte Carlo simulations to validate the theoretical analysis 相似文献
6.
Ha W. Gambin V. Bank S. Wistey M. Yuen H. Seongsin Kim Harris J.S. Jr. 《Quantum Electronics, IEEE Journal of》2002,38(9):1260-1267
The boom in fiber-optic communications has caused a high demand for GaAs-based lasers in the 1.3-1.6-μm range. This has led to the introduction of small amounts of nitrogen into InGaAs to reduce the bandgap sufficiently, resulting in a new material that is lattice matched to GaAs. More recently, the addition of Sb has allowed further reduction of the bandgap, leading to the first demonstration of 1.5-μm GaAs-based lasers by the authors. Additional work has focused on the use of GaAs, GaNAs, and now GaNAsSb barriers as cladding for GaInNAsSb quantum wells. We present the results of photoluminescence, as well as in-plane lasers studies, made with these combinations of materials. With GaNAs or GaNAsSb barriers, the blue shift due to post-growth annealing is suppressed, and longer wavelength laser emission is achieved. Long wavelength luminescence out to 1.6 μm from GaInNAsSb quantum wells, with GaNAsSb barriers, was observed. In-plane lasers from these samples yielded lasers operating out to 1.49 μm, a minimum threshold current density of 500 A/cm2 per quantum well, a maximum differential quantum efficiency of 75%, and pulsed power up to 350 mW at room temperature 相似文献
7.
AIM: To examine the association of Epstein-Barr virus (EBV) with carcinoma of the ear. METHODS: Five non-keratinising squamous cell carcinomas and two undifferentiated carcinomas of the ear were examined. In situ hybridisation was used to localised EBV-encoded RNAs (EBER). Immunohistochemical methods to detect LMP-1 and EBNA2 were performed in the EBER positive cases. RESULTS: Two cases were EBER positive, including one non-keratinising and one undifferentiated carcinoma. Both showed identical morphology to those arising from the nasopharynx, with abundant lymphoid stroma. They were both negative for LMP-1 and EBNA2. CONCLUSIONS: EBV associated carcinoma with the morphology of lymphoepithelioma can also arise from the middle ear. 相似文献
8.
The effect of Pseudomonas aeruginosa infection on clinical parameters in steady-state bronchiectasis
PL Ho KN Chan MS Ip WK Lam CS Ho KY Yuen KW Tsang 《Canadian Metallurgical Quarterly》1998,114(6):1594-1598
STUDY OBJECTIVE: To investigate the effect of Pseudomonas aeruginosa infection on clinical parameters in Chinese patients with noncystic fibrosis and steady-state bronchiectasis. DESIGN: Prospective, cross-sectional clinicomicrobiological study with informed consent. SETTING: Consecutive outpatient recruitment from a specialist bronchiectasis respiratory clinic. PATIENTS: Outpatients (n = 100; 62 women; 55.1+/-16.7 years old; FEV1/FVC 1.4+/-0.7/2.1+/-0.9 L), who had stable respiratory symptoms for more than 3 weeks. MEASUREMENTS AND RESULTS: Respiratory pathogens isolated from the sputum were: Pseudomonas aeruginosa (33), Haemophilus influenzae (10), Moraxella catarrhalis (2), other Gram-negative bacilli (5), Streptococcus pneumoniae (6), Staphylococcus aureus (5), mycobacteria (3), and yeast (1). Clinical parameters in patients with positive isolation of P aeruginosa were compared with those without the organism in the sputum culture (non-P aeruginosa). In the P aeruginosa group, the FEV1/FVC ratio and sputum volume were lower (p < 0.005) and higher (p < 0.0001), respectively, than those of the non-P aeruginosa group. The FEV1/FVC ratio (< 60%) and sputum volume (grading > 5) were independently associated with a positive sputum isolation of P aeruginosa with odds ratios of 3.1 (confidence interval [CI] 1.2 to 8.4; p < 0.01) and 4.7 (CI 1.6 to 13.3; p < 0.001), respectively. CONCLUSIONS: P aeruginosa is the predominant respiratory pathogen isolated in the sputum of Chinese patients with steady-state bronchiectasis, and its isolation is associated with high sputum output (> or = 75th quartile) and moderately severe airflow obstruction (FEV1/FVC < 60%). 相似文献
9.
A study of the properties of ink-jet printed cotton fabric following low-temperature plasma treatment 总被引:1,自引:0,他引:1
This paper studies the effect of low-temperature plasma treatment on an ink-jet printed cotton fabric. Due to the specific printing and conductivity requirements for ink-jet printing, not all conventional printing chemicals, such as sodium alginate and urea, used for cotton fabric can be directly incorporated into the ink formulation. As a result, the cotton fabric requires pretreatment with the printing chemicals prior to the stage of ink-jet printing. Cotton is pretreated with the printing chemicals by means of a coating method. The aim of this paper was to study the possibility and effectiveness of applying low-temperature plasma treatment to enhance the performance of pretreatment paste containing sodium alginate so as to improve the properties of the ink-jet printed cotton fabric. Experimental results revealed that a low-temperature plasma pretreatment coupled with the ink-jet printing technique could improve the final printed properties of cotton fabric. 相似文献
10.
十四醇聚氧化烯烃醚琥珀酸单酯磺酸盐的表面活性研究 总被引:6,自引:0,他引:6
合成了一系列十四醇聚氧乙烯醚和聚氧丙烯醚琥珀酸单酯磺酸盐,比较了其临界胶束浓度、润湿力、起泡力等表面活性 相似文献