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Show moreBackground of the invention: Polysilicon is one of the most widely used structural materials for microelectromechanical systems and devices. However, when deposited by low-pressure chemical vapor deposition (LPCVD) techniques, polysilicon films typically display high residual stresses and often stress gradients as well. These stresses, particularly when compressive, may cause released devices to bend and buckle, altering their original shapes and degrading their performances. While tensile stresses may promote planarity in doubly clamped designs, such stresses also increase stiffness and cause deformation of asymmetric features. Zero-stress polysilicon thin film structures would be optimal for many applications. Prior artisans have attempted to produce thin silicon films with reduced stress levels. U.S. Pat. No. 5,753,134 entitled "Method for Producing a Layer With Reduced Mechanical Stresses" to Biebl, is directed to a method for producing a silicon layer having a reduced overall stress value, the layer being composed of two silicon sublayers. The first sublayer and the second sublayer are matched to one another such that the stresses in the two layers substantially compensate each other, and in effect, cancel each other out. However, Biebl requires that one or more auxiliary layers of silicon dioxide be provided between the sublayers. Those auxiliary layers require additional manufacturing or processing operations. Although satisfactory in some respects, a need still exists for an improved multi-layer polysilicon assembly and technique for forming, and particularly for an assembly that does not require the use of intermediate or auxiliary layers. In addition, a disadvantage often associated with polysilicon films deposited by chemical vapor deposition techniques, pertains to the resulting relatively rough surface of the deposited film. Although approaches are known for producing films having relatively smooth finishes, typically, additional processing steps are necessary or critical process control schemes must be implemented. Accordingly, a need remains for a technique for producing films and multi-layer assemblies of such films having relatively smooth surfaces. Summary of the invention: The present invention achieves the foregoing objectives and provides in a first aspect, a multi-layer thin film assembly comprising a first thin film including polysilicon, and a second thin film also comprising polysilicon. The first thin film has a devitrified microstructure and an internal tensile stress. The second thin film has a predominantly columnar microstructure and an internal compressive stress. The first and second thin films are disposed immediately adjacent to one another to form the multi-layer assembly, thereby avoiding the use of an intermediate layer between the first and second thin films. In addition, the resulting films have exceptionally smooth surfaces.
http://www.google.com/patents?vid=USPAT6268068
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Show moreField of the invention: This invention relates to a novel DNA sequence, and derivatives thereof, useful in the screening of compounds that are agonistic or antagonistic to seronergic receptor activity. Background: The enormous phenotypic diversity of neural cell types implies a corresponding complexity of gene-specific transcription factor combinations required to regulate thousands of genes in the appropriate stage and cell type-specific manner (He, X., and Rosenfeld, M. G., "Mechanisms of complex transcriptional regulation: implications for brain development" Neuron 7:183-196, 1991; Mandel, G., and McKinnon, D, "Molecular basis of neural-specific gene expression" Annu. Rev. Neurosci. 16:323-345, 1993; Struhl, K., "Mechanisms for diversity in gene expression patterns" Neuron 7:177-181, 1991). Indeed, several members of different transcription factor classes, such as homeodomain, zinc-finger and basic helix-loop-helix proteins, function to regulate neural cell-type identity in specific regions of both the vertebrate and invertebrate nervous systems. Many of these genes are expressed early in neural development, which suggests they play a critical role in neurogenesis and neuronal patterning (Tanabe, Y., and Jessell, T. M., "Diversity and pattern in the developing spinal cord" Science 274:1115-1124, 1996). However, an understanding of the functional interplay between different transcription factors and the neural genes they regulate is just beginning to emerge. Little is known about the identity and specific functions of transcription factors which operate particular differentiation programs involved in the appearance and maintenance of specific neural cell phenotypes. The central serotonin (5-HT) neurotransmitter system consists of a relatively small population of morphologically diverse neurons whose cell bodies are present largely within the limits of the midbrain/hindbrain raphe nuclei and particular regions of the reticular formation (Steinbusch, H. W. M., Neuroscience 6:557-618, 1981). Although there are only about 20,000 serotonergic neurons in the rat brain the extensive axonal projection system arising from these neurons bears a tremendous number of collateral branches so that the 5-HT system densely innervates nearly all regions of the central nervous system (Halliday, G., Harding, A., and Paxinos, G. (1995) in the rat nervous system (Paxinos, G. ed), 2nd Ed., pp. 929-974, Academic Press, San Diego; Jacobs, B. L., and Azmitia, E. C., Physiological Reviews 72:165-220, 1992). Given its widespread distribution it is not surprising that 5-HT has been implicated in the control of numerous neural systems which mediate such functions as cognition, aggression, and perception (Heninger, G. R., Proc. Natl. Acad. Sci. USA 94:4823-4824, 1997). Abnormal function of the central 5-HT system has been implicated in several psychiatric maladies such as depression, anxiety, and eating disorders.
http://www.google.com/patents?vid=USPAT6268216
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