基于马尔可夫随机场的遥感图像分割和描述

讨论了基于马尔可夫随机场的遥感图像分割．根据卫星遥感图像的特点,建立了相应的基于马尔可夫随机场的图像分割模型．由此将图像分割问题转化成图像标记问题, 并进一步转化成求图像的最大后验概率估计的问题． 本文引进了一种基于博弈理论的决定性退火算法, 可以用该算法对图像进行标记, 该算法收敛于局部最大, 在实验中取得了很好的效果．     

Dexamethasone enhances CTLA-4 expression during T cell activation

T cell activation is enhanced by the costimulatory interaction of B7 on antigen-presenting cells and CD28 on T cells, resulting in long-term T cell proliferation, differentiation and production of large amounts of cytokines, such as interleukin (IL)-2. CTLA-4 is a co-stimulation receptor that shares 31% homology with CD28 and binds B7 family members with higher affinity. CTLA-4 is transiently expressed intracellularly and on the cell surface following activation of T cells. We have studied the kinetics of CTLA-4 expression and the effects of dexamethasone on CTLA-4 expression during T cell activation in cultures of mouse spleen cells stimulated by a mixture of immobilized anti-CD3 and anti-CD28 monoclonal antibodies (anti-CD3/CD28 mAb) or concanavalin A (ConA). CTLA-4 expression peaked on day 2 and returned to background levels after 7 days. Dexamethasone was found to potentiate CTLA-4 expression in a dose-dependent manner with an EC₅₀ effective concentration 50%) of about 10⁻⁸ M. In contrast, other immunosuppressive agents, such as rapamycin or cyclosporin A had no or an inhibitory effect on CTLA-4 expression, respectively. Dexamethasone also stimulated CD28 expression, but inhibited IL-2R expression during anti-CD3/CD28 mAb-induced mouse splenic T cell activation. Western blot analyses of lysates of activated mouse T cells showed that dexamethasone increased CTLA-4 protein levels twofold during anti-CD3/CD28 mAb-induced activation. Dexamethasone also enhanced CTLA-4 messenger RNA twofold as quantified by ribonuclease protection assay. The effects of dexamethasone on CTLA-4 expression were glucocorticoid-specific and completely inhibited by the glucocorticoid receptor antagonist mifepristone (RU486), indicating that the effect of dexamethasone on CTLA-4 expression is mediated through the glucocorticoid receptor. In conclusion, the immunosuppressive agent dexamethasone actually stimulates CTLA-4 expression, which is involved in downregulation of T cell activation. Received 19 May 1999; received after revision 13 July 1999; accepted 13 July 1999     

认知语言学视角下的新疆少数民族学生汉语介词习得

在新疆诸多少数民族语言中，没有介词这一词类，介词向来是新疆少数民族学生汉语学习中的难点。我们在调查的基础上，从认知语言学的角度探究新疆少数民族学生汉语介词习得问题，以有标记与无标记、总括扫描与次第扫描等概念为切入点，以认知为最终的解释，以期对学生的一些偏误现象做出合理的概括和解释。     

基于资源稀缺视角的房地产制度变迁

我国房地产的迅猛发展为我国经济的发展和人们住房的改善起到了较大的作用。然而,由于房价格上涨过快过高,造成了许多政治和经济问题。尽管国家出台了一系列的调控制度,但是这些制度效率低下,主要原因是这些制度结构不合理,缺乏实施机制。随着经济的不断发展,国内外经济环境的变化,国内其他制度如外汇、对外资开放等制度的改变,房地产制度也应该变迁。在坚持节约原则的前提下,遵循市场经济规律,房地产制度应该做如下变迁:提高个人住房按揭贷款的首付比例到80%或取消贷款、征收房地产物业税、取消预售制度。     

扩散硅压力传感器双桥补偿法

本文提出关于扩散硅压力传感器误差补偿的一种新方法，重点介绍该方法对零点温度漂移、灵敏度温度漂移以及非线性的补偿。     

MAPCATI改性环氧丙烯酸双酯的合成及其紫外光固化涂料

采用自制个甲基丙烯酰氧β－丙氧甲酰氨基甲苯２－异氰酸酯（简称ＭＡＰＣＡＴＩ）中的异氰酸基与自制环氧丙烯酸双酯中羟基上的氢反应，制得了改性树脂；并以此为基料配成紫外光固化涂料。所得涂层性能优良，有应用前景。     

对高聚物薄膜栅控电晕注极的研究

本文以Teflon-FEP薄膜在常温下的空气中,加控制栅极前后进行电晕注极为例,研究了样品膜的注极效果。栅极的引入,不但能控制样品的表面电位值,而且使得样品的表面电荷分布更加均匀. 注极参数的变化将影响注极结果.实验表明:针极电压,注极时间,栅极电压,栅网孔径,针-栅间距和栅-膜间距各注极参数直接影响薄膜的表面电位值和表面电荷的分布.最后导出对Teflon-FEP薄膜的最佳注极参数,这些参数在同样条件下对其它聚合物也是适用的.     

K-rich lamellar exsolution in clinopyroxene： Constraint on the depth of peridotite source at Zhimafang

The oriented lamellar K-rich exsolutions within clinopyroxene host were recognized in garnet peridotite massif at Zhimafang in the Sulu ultrahigh pressure metamorphic terrane, eastern China. EMP and TEM analyses revealed that the composition and the index of electron diffraction for this exsolution are corresponding with phlogopite, and the shape is the lamellae with 1 μm in width and 5 to 30 μm in length. Moreover, the topotaxy is that the (001) of K-rich exsolution parallels to (I00) of the clinopyroxene host. The electron diffraction analyzing shows the exsolution is of a 1M polymorphism. The high-resolution lattice fringe image displays the stack features along [001], which only a layer mineral shows. We conclude that the clinopyroxene with IM and K-rich exsolution was probably derived from mantle depths over 240 km, thus resulting from decompressional exsolution in the initial stage of slab exhumation.     

Fingerprint representation methods based on B-Spline functions

The global characteristics of a fingerprint image such as the ridge shape and ridge topology are often ignored in most automatic fingerprint verification system.In this paper,a new representative method based on B-Spline curve is proposed to address this problem.The resultant B-Spline curves can represent the global characteristics completely and the curves are analyzable and precise.An algorithm is also proposed to extract the curves from the fingerprint image.In addition to preserve the most information of the fingerprint image,the knot-points number of the B-Spline curve is reduced to minimum in this algorithm. At the same time,the influence of the fingerprint image noise is discussed.In the end,an example is given to demonstrate the effectiveness of the representation method.     

Multiple regulatory sites in large-conductance calcium-activated potassium channels

Large conductance, Ca(2+)- and voltage-activated K(+) channels (BK) respond to two distinct physiological signals -- membrane voltage and cytosolic Ca(2+) (refs 1, 2). Channel opening is regulated by changes in Ca(2+) concentration spanning 0.5 micro M to 50 mM (refs 2-5), a range of Ca(2+) sensitivity unusual among Ca(2+)-regulated proteins. Although voltage regulation arises from mechanisms shared with other voltage-gated channels, the mechanisms of Ca(2+) regulation remain largely unknown. One potential Ca(2+)-regulatory site, termed the 'Ca(2+) bowl', has been located to the large cytosolic carboxy terminus. Here we show that a second region of the C terminus, the RCK domain (regulator of conductance for K(+) (ref. 12)), contains residues that define two additional regulatory effects of divalent cations. One site, together with the Ca(2+) bowl, accounts for all physiological regulation of BK channels by Ca(2+); the other site contributes to effects of millimolar divalent cations that may mediate physiological regulation by cytosolic Mg(2+) (refs 5, 13). Independent regulation by multiple sites explains the large concentration range over which BK channels are regulated by Ca(2+). This allows BK channels to serve a variety of physiological roles contingent on the Ca(2+) concentration to which the channels are exposed.