812 research outputs found

    Thin Film Encapsulation of Radio Frequency (RF) Microelectromechanical Systems (MEMS) Switches

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    Microelectromechanical systems (MEMS) radio frequency (RF) switches have been shown to have excellent electrical performance over a wide range of frequencies. However, cost-effective packaging techniques for MEMS switches do not currently exist. This thesis involves the design of RF-optimized encapsulations consisting of dielectric and metal layers, and the creation of a novel thin film encapsulation process to fabricate the encapsulations. The RF performance of several encapsulation designs are evaluated with an analytical model, full wave electromagnetic simulation, and laboratory testing. Performance degradation due to parasitic and reflection losses due to the package is considered, and RF feed-throughs of the transmission line into and out of the package are designed and assessed. Ten different encapsulation designs were created and their RF performance was characterized in terms of insertion loss, return loss, and isolation. A switch without an encapsulation and a switch with a dielectric encapsulation were fabricated and tested by the Air Force Research Laboratory (AFRL), and the test data was used to verify the data from analytical modeling and electromagnetic simulation performed in this work. All results were used to design an optimized encapsulation. An RF MEMS switch with this encapsulation was shown to have an overall insertion loss of less than -0.15 dB at 20 GHz compared to an unencapsulated switch insertion loss of about -0.1 dB. The isolation of the switch was slightly improved with the encapsulation. The fabrication process proposed to manufacture these encapsulations uses a low temperature solder as the metal encapsulation layer. As the final step in the fabrication, the solder is brought to melting temperature and reflowed over the etch holes to form a hermetic encapsulation

    XMM-Newton and Optical Observations of Cataclysmic Variables from SDSS

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    We report on XMM-Newton and optical results for 6 cataclysmic variables that were selected from Sloan Digital Sky Survey spectra because they showed strong HeII emission lines, indicative of being candidates for containing white dwarfs with strong magnetic fields. While high X-ray background rates prevented optimum results, we are able to confirm SDSSJ233325.92+152222.1 as an intermediate polar from its strong pulse signature at 21 min and its obscured hard X-ray spectrum. Ground-based circular polarization and photometric observations were also able to confirm SDSSJ142256.31-022108.1 as a polar with a period near 4 hr. Photometry of SDSSJ083751.00+383012.5 and SDSSJ093214.82+495054.7 solidifies the orbital period of the former as 3.18 hrs and confirms the latter as a high inclination system with deep eclipses.Comment: 31 pages, 14 figures. Accepted for publication in the Astronomical Journa

    Developmental interneuron subtype deficits after targeted loss of Arx

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    Abstract Background Aristaless-related homeobox (ARX) is a paired-like homeodomain transcription factor that functions primarily as a transcriptional repressor and has been implicated in neocortical interneuron specification and migration. Given the role interneurons appear to play in numerous human conditions including those associated with ARX mutations, it is essential to understand the consequences of mutations in this gene on neocortical interneurons. Previous studies have examined the effect of germline loss of Arx, or targeted mutations in Arx, on interneuron development. We now present the effect of conditional loss of Arx on interneuron development. Results To further elucidate the role of Arx in forebrain development we performed a series of anatomical and developmental studies to determine the effect of conditional loss of Arx specifically from developing interneurons in the neocortex and hippocampus. Analysis and cell counts were performed from mouse brains using immunohistochemical and in situ hybridization assays at 4 times points across development. Our data indicate that early in development, instead of a loss of ventral precursors, there is a shift of these precursors to more ventral locations, a deficit that persists in the adult nervous system. The result of this developmental shift is a reduced number of interneurons (all subtypes) at early postnatal and later time periods. In addition, we find that X inactivation is stochastic, and occurs at the level of the neural progenitors. Conclusion These data provide further support that the role of Arx in interneuron development is to direct appropriate migration of ventral neuronal precursors into the dorsal cortex and that the loss of Arx results in a failure of interneurons to reach the cortex and thus a deficiency in interneurons.http://deepblue.lib.umich.edu/bitstream/2027.42/134595/1/12868_2016_Article_265.pd

    A Catalog of Spectroscopically Confirmed White Dwarfs from the Sloan Digital Sky Survey Data Release 4

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    We present a catalog of 9316 spectroscopically confirmed white dwarfs from the Sloan Digital Sky Survey Data Release 4. We have selected the stars through photometric cuts and spectroscopic modeling, backed up by a set of visual inspections. Roughly 6000 of the stars are new discoveries, roughly doubling the number of spectroscopically confirmed white dwarfs. We analyze the stars by performing temperature and surface gravity fits to grids of pure hydrogen and helium atmospheres. Among the rare outliers are a set of presumed helium-core DA white dwarfs with estimated masses below 0.3 Msun, including two candidates that may be the lowest masses yet found. We also present a list of 928 hot subdwarfs.Comment: Accepted by the Astrophysical Journal Supplements, 25 pages, 24 figures, LaTeX. The electronic catalog, as well as diagnostic figures and links to the spectra, is available at http://das.sdss.org/wdcat/dr4

    Recent Updates on the Melanin-Concentrating Hormone (MCH) and Its Receptor System: Lessons from MCH1R Antagonists

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    Melanin-concentrating hormone (MCH) is a 19-amino-acid cyclic peptide which was originally found to lighten skin color in fish that is highly conserved among many species. MCH interacts with two G-protein-coupled receptors, MCH1R and MCH2R, but only MCH1R is expressed in rodents. MCH is mainly synthesized in the lateral hypothalamus and zona incerta, while MCH1R is widely expressed throughout the brain. Thus, MCH signaling is implicated in the regulation of many physiological functions. The identification of MCH1R has led to the development of small-molecule MCH1R antagonists that can block MCH signaling. MCH1R antagonists are useful not only for their potential therapeutic value, but also for understanding the physiological functions of the endogenous MCH system. Here, we review the physiological functions of the MCH system which have been investigated using MCH1R antagonists such as food intake, anxiety, depression, reward, and sleep. This will help us understand the physiological functions of the MCH system and suggest some of the potential applications of MCH1R antagonists in human disorders