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  • 1
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present an analysis describing how the Casimir effect can deflect a thin microfabricated rectangular membrane strip and possibly collapse it into a flat, parallel, fixed surface nearby. In the presence of the attractive parallel-plate Casimir force between the fixed surface and the membrane strip, the otherwise flat strip deflects into a curved shape, for which the derivation of an exact expression of the Casimir force is nontrivial and has not been carried out to date. We propose and adopt a local value approach for ascertaining the strength of the Casimir force between a flat surface and a slightly curved rectangular surface, such as the strip considered here. Justifications for this approach are discussed with reference to publications by other authors. The strength of the Casimir force, strongly dependent on the separation between the surfaces, increases with the deflection of the membrane, and can bring about the collapse of the strip into the fixed surface (stiction). Widely used in microelectromechanical systems both for its relative ease of fabrication and usefulness, the strip is a structure often plagued by stiction during or after the microfabrication process—especially surface micromachining. Our analysis makes no assumptions about the final or the intermediate shapes of the deflecting strip. Thus, in contrast to the usual methods of treating this type of problem, it disposes of the need for an ansatz or a series expansion of the solution to the differential equations. All but the very last step in the derivation of the main result are analytical, revealing some of the underlying physics. A dimensionless constant, Kc, is extracted which relates the deflection at the center of the strip to physical and geometrical parameters of the system. These parameters can be controlled in microfabrication. They are the separation w0 between the fixed surface and the strip in the absence of deflection, the thickness h, length L, and Young's modulus of elasticity (of the strip), and a measure of the dielectric permittivities of the strip, the fixed surface, and the filler fluid between them. It is shown that for some systems (Kc〉0.245), with the Casimir force being the only operative external force on the strip, a collapsed strip is inevitable. Numerical estimates can be made to determine if a given strip will collapse into a nearby surface due to the Casimir force alone, thus revealing the absolute minimum requirements on the geometrical dimensions for a stable (stiction-free) system. For those systems which do exhibit a stiction-free stable equilibrium state, the deflection at the middle of the strip is always found to be smaller than 0.48w0. This analysis is expected to be most accurately descriptive for strips with large aspect ratio (L/h) and small modulus of elasticity which also happen to be those most susceptible to stiction. Guidelines and examples are given to help estimate which structures meet these criteria for some technologically important materials, including metal and polymer thin films. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 3409-3418 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements were made of the capacitance and the conductance of several capacitor structures with a copper phthalocyanine (CuPc) dielectric at different voltages and in the frequency range of 102–106 Hz. A thermally evaporated CuPc film about 1300 A(ring) thick was fabricated in a parallel-plate capacitor between gold and aluminum electrodes (Al||CuPc||Au). Two distributions of relaxation times are observed in this frequency range. At low frequencies voltage-dependent polarization (possibly interfacial polarization) appears to be the dominant mechanism of current conduction. At high frequencies a relatively voltage-independent hopping within and/or between molecules appears to be dominant. The CuPc remains polarized for a long time. Measurements were also made of the capacitance-voltage (C-V) characteristic of a Al||CuPc||SiO2||Si capacitor at 104, 105, and 106 Hz for different scanning rates. The basic features of the device's C-V characteristics are discussed.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 2019-07-12
    Description: Three techniques, flow modulation, filament modulation, and reactive-filter modulation developed to obtain selective response to hydrazine or to methyl hydrazines from photoionization detector. Implemented in portable selective hydrazine detectors, useful where continuous or rapid, repetitive quantitative measurements of concentrations of vapors of these toxic substances required. Measure concentration of gaseous hydrazines in presence of other gases like cyclohexane, chlorofluorocarbons, and ammonia. Produce modulated signal, amplitude and phase indicating amount of hydrazine, monomethyl hydrazine, or 1,1-dimethyl hydrazine present in mixture. Used with such other detectors as electrochemical cells.
    Keywords: PHYSICAL SCIENCES
    Type: KSC-11520 , NASA Tech Briefs (ISSN 0145-319X); 16; 11; P. 74
    Format: text
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  • 5
    Publication Date: 2019-07-10
    Description: This report summarizes the accomplishments during a three year research project to investigate the use of surfaces, particularly in microelectromechanical systems (MEMS), to exploit quantum vacuum forces. During this project, we developed AFM instrumentation to repeatably measure Casimir forces in the nanoNewton range at 10 6 torr, designed an experiment to measure attractive and repulsive quantum vacuum forces, developed a QED based theory of Casimir forces that includes non-ideal material properties for rectangular cavities and for multilayer slabs, developed theoretical models for a variety of microdevices utilizing vacuum forces, applied vacuum physics to a gedanken spacecraft, and investigated a new material with a negative index of refraction.
    Keywords: Spacecraft Propulsion and Power
    Type: NASA/CR-2004-213311 , E-14771
    Format: application/pdf
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  • 6
    Publication Date: 2013-12-23
    Description: We report the discovery of four transiting F-M binary systems with companions between 0.1 and 0.2 M in mass by the HATSouth survey. These systems have been characterized via a global analysis of the HATSouth discovery data, combined with high-resolution radial velocities and accurate transit photometry observations. We determined the masses and radii of the component stars using a combination of two methods: isochrone fitting of spectroscopic primary star parameters and equating spectroscopic primary star rotation velocity with spin–orbit synchronization. These new very low mass companions are HATS550-016B ( $0.110_{-0.006}^{+0.005}\,\mathrm{M}_{\odot }$ , $0.147_{-0.004}^{+0.003}\,\mathrm{R}_{\odot }$ ), HATS551-019B ( $0.17_{-0.01}^{+0.01}\,\mathrm{M}_{\odot }$ , $0.18_{-0.01}^{+0.01}\,\mathrm{R}_{\odot }$ ), HATS551-021B ( $0.132_{-0.005}^{+0.014}\,\mathrm{M}_{\odot }$ , $0.154_{-0.008}^{+0.006}\,\mathrm{R}_{\odot }$ ) and HATS553-001B ( $0.20_{-0.02}^{+0.01}\,\mathrm{M}_{\odot }$ , $0.22_{-0.01}^{+0.01}\,\mathrm{R}_{\odot }$ ). We examine our sample in the context of the radius anomaly for fully convective low-mass stars. Combining our sample with the 13 other well-studied very low mass stars, we find a tentative 5 per cent systematic deviation between the measured radii and theoretical isochrone models.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 7
    Publication Date: 2011-10-14
    Description: The comparison of related genomes has emerged as a powerful lens for genome interpretation. Here we report the sequencing and comparative analysis of 29 eutherian genomes. We confirm that at least 5.5% of the human genome has undergone purifying selection, and locate constrained elements covering approximately 4.2% of the genome. We use evolutionary signatures and comparisons with experimental data sets to suggest candidate functions for approximately 60% of constrained bases. These elements reveal a small number of new coding exons, candidate stop codon readthrough events and over 10,000 regions of overlapping synonymous constraint within protein-coding exons. We find 220 candidate RNA structural families, and nearly a million elements overlapping potential promoter, enhancer and insulator regions. We report specific amino acid residues that have undergone positive selection, 280,000 non-coding elements exapted from mobile elements and more than 1,000 primate- and human-accelerated elements. Overlap with disease-associated variants indicates that our findings will be relevant for studies of human biology, health and disease.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3207357/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3207357/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lindblad-Toh, Kerstin -- Garber, Manuel -- Zuk, Or -- Lin, Michael F -- Parker, Brian J -- Washietl, Stefan -- Kheradpour, Pouya -- Ernst, Jason -- Jordan, Gregory -- Mauceli, Evan -- Ward, Lucas D -- Lowe, Craig B -- Holloway, Alisha K -- Clamp, Michele -- Gnerre, Sante -- Alfoldi, Jessica -- Beal, Kathryn -- Chang, Jean -- Clawson, Hiram -- Cuff, James -- Di Palma, Federica -- Fitzgerald, Stephen -- Flicek, Paul -- Guttman, Mitchell -- Hubisz, Melissa J -- Jaffe, David B -- Jungreis, Irwin -- Kent, W James -- Kostka, Dennis -- Lara, Marcia -- Martins, Andre L -- Massingham, Tim -- Moltke, Ida -- Raney, Brian J -- Rasmussen, Matthew D -- Robinson, Jim -- Stark, Alexander -- Vilella, Albert J -- Wen, Jiayu -- Xie, Xiaohui -- Zody, Michael C -- Broad Institute Sequencing Platform and Whole Genome Assembly Team -- Baldwin, Jen -- Bloom, Toby -- Chin, Chee Whye -- Heiman, Dave -- Nicol, Robert -- Nusbaum, Chad -- Young, Sarah -- Wilkinson, Jane -- Worley, Kim C -- Kovar, Christie L -- Muzny, Donna M -- Gibbs, Richard A -- Baylor College of Medicine Human Genome Sequencing Center Sequencing Team -- Cree, Andrew -- Dihn, Huyen H -- Fowler, Gerald -- Jhangiani, Shalili -- Joshi, Vandita -- Lee, Sandra -- Lewis, Lora R -- Nazareth, Lynne V -- Okwuonu, Geoffrey -- Santibanez, Jireh -- Warren, Wesley C -- Mardis, Elaine R -- Weinstock, George M -- Wilson, Richard K -- Genome Institute at Washington University -- Delehaunty, Kim -- Dooling, David -- Fronik, Catrina -- Fulton, Lucinda -- Fulton, Bob -- Graves, Tina -- Minx, Patrick -- Sodergren, Erica -- Birney, Ewan -- Margulies, Elliott H -- Herrero, Javier -- Green, Eric D -- Haussler, David -- Siepel, Adam -- Goldman, Nick -- Pollard, Katherine S -- Pedersen, Jakob S -- Lander, Eric S -- Kellis, Manolis -- 095908/Wellcome Trust/United Kingdom -- GM82901/GM/NIGMS NIH HHS/ -- R01 HG003474/HG/NHGRI NIH HHS/ -- R01 HG004037/HG/NHGRI NIH HHS/ -- U54 HG003067/HG/NHGRI NIH HHS/ -- U54 HG003067-09/HG/NHGRI NIH HHS/ -- U54 HG003273/HG/NHGRI NIH HHS/ -- Howard Hughes Medical Institute/ -- England -- Nature. 2011 Oct 12;478(7370):476-82. doi: 10.1038/nature10530.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Broad Institute of Harvard and Massachusetts Institute of Technology, 7 Cambridge Center, Cambridge, Massachusetts 02142, USA. kersli@broadinstitute.org〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21993624" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Disease ; *Evolution, Molecular ; Exons/genetics ; Genome/*genetics ; Genome, Human/*genetics ; Genomics ; Health ; Humans ; Mammals/*genetics ; Molecular Sequence Annotation ; Phylogeny ; RNA/classification/genetics ; Selection, Genetic/genetics ; Sequence Alignment ; Sequence Analysis, DNA
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 8
    Publication Date: 2014-11-15
    Description: The 30-Hz rotation rate of the Crab pulsar has been monitored at Jodrell Bank Observatory since 1984 and by other observatories before then. Since 1968, the rotation rate has decreased by about 0.5 Hz, interrupted only by sporadic and small spin-up events (glitches). 24 of these events have been observed, including a significant concentration of 15 occurring over an interval of 11 yr following MJD 50000. The monotonic decrease of the slowdown rate is partially reversed at glitches. This reversal comprises a step and an asymptotic exponential with a 320-d time constant, as determined in the three best-isolated glitches. The cumulative effect of all glitches is to reduce the decrease in slowdown rate by about 6 per cent. Overall, a low mean braking index of 2.342(1) is measured for the whole period, compared with values close to 2.5 in intervals between glitches. Removing the effects of individual glitches reveals an underlying power-law slowdown with the same braking index of 2.5. We interpret this value in terms of a braking torque due to a dipolar magnetic field in which the inclination angle between the dipole and rotation axes is increasing. There may also be further effects due to a monopolar particle wind or infalling supernova debris.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 9
    Publication Date: 2013-10-30
    Description: Author(s): L. E. Hintzsche, C. M. Fang, M. Marsman, G. Jordan, M. W. P. E. Lamers, A. W. Weeber, and G. Kresse We present an ab initio density functional theory study of the dominant defects in hydrogenated amorphous silicon nitrides covering different stoichiometries, the influence of hydrogen, and the influence of the annealing history. Whereas nitrogen (N) lone pair states dominate the valence band edge i... [Phys. Rev. B 88, 155204] Published Tue Oct 29, 2013
    Keywords: Semiconductors I: bulk
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
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  • 10
    Publication Date: 2012-12-15
    Description: Author(s): L. E. Hintzsche, C. M. Fang, T. Watts, M. Marsman, G. Jordan, M. W. P. E. Lamers, A. W. Weeber, and G. Kresse We present ab initio density functional theory studies for stoichiometric as well as nonstoichiometric amorphous silicon nitride, varying the stoichiometry between Si 3 N 4.5 and Si 3 N 3 . Stoichiometric amorphous Si 3 N 4 possesses the same local structure as crystalline Si 3 N 4 , with Si being fourfold coordi... [Phys. Rev. B 86, 235204] Published Fri Dec 14, 2012
    Keywords: Semiconductors I: bulk
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
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