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  • 1
    Publikationsdatum: 2013-11-15
    Beschreibung: The stability of a two-dimensional surfactant-free (gas-liquid) foam in a gravitational field is considered. The foam is assumed to have low liquid fraction, so the gas phase can be divided into approximately polygonal bubbles separated by thin liquid films. These free films drain toward accumulations of liquid at the bubble vertices, the Plateau borders, and eventually rupture due to van der Waals intermolecular attractions; this drives foam coarsening through the coalescence of neighbouring bubbles. In particular, we demonstrate how gravitational effects strongly modify the shape of the Plateau border interfaces and enhance the drainage flow in the liquid films, driving non-uniform thinning with exponential decay of the minimum film thickness, significantly faster than the power-law thinning predicted when gravitational effects are negligible. ©2013 Cambridge University Press.
    Print ISSN: 0022-1120
    Digitale ISSN: 1469-7645
    Thema: Maschinenbau , Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2000-01-01
    Beschreibung: In the western Grand Canyon, fluvial terraces and pediment surfaces, both associated with a Pleistocene basalt flow, document Quaternary aggradation and downcutting by the Colorado River, illuminate the river's response to overload and the end of overload, and allow calibration of soil-carbonate stages and determination of downcutting rates. Four downcutting–aggradation cycles are present. Each begins with erosion of older deposits to form a new river channel in which a characteristic suite of deposits is laid down. The current cycle (I) started ∼700 yr B.P. The oldest (IV) includes the 603,000 ± 8000 to 524,000 ± 7000 yr Black Ledge basalt flow, emplaced when the river channel was ∼30 m higher than it is now. The flow is overlain by basalt–cobble gravel and basalt sand. Soils reach the stage V level of carbonate development. Calibrated ages for soil stages are Stage V, ∼525,000 yr; stage IV,
    Print ISSN: 0033-5894
    Digitale ISSN: 1096-0287
    Thema: Geographie , Geologie und Paläontologie
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2010-08-18
    Beschreibung: An ultra-thin viscous film on a substrate is susceptible to rupture instabilities driven by van der Waals attractions. When a unidirectional wind shear is applied to the free surface, the rupture instability in two dimensions is suppressed when exceeds a critical value c and is replaced by a permanent finite-amplitude structure, an intermolecular-capillary wave, that travels at approximately the speed of the surface. For small amplitudes, the wave is governed by the Kuramoto-Sivashinsky equation. If three-dimensional disturbances are allowed, the shear is decoupled from disturbances perpendicular to the flow, and line rupture would occur. In this case, replacing the unidirectional shear with a shear whose direction rotates with angular speed, suppresses the rupture if 2c. For the most dangerous wavenumber, c 102 dyn cm 2 at 1 rad s1 for a film with physical properties similar to water at a thickness of 100 nm. © 2010 Cambridge University Press.
    Print ISSN: 0022-1120
    Digitale ISSN: 1469-7645
    Thema: Maschinenbau , Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2022-10-26
    Beschreibung: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Priscu, J. C., Kalin, J., Winans, J., Campbell, T., Siegfried, M. R., Skidmore, M., Dore, J. E., Leventer, A., Harwood, D. M., Duling, D., Zook, R., Burnett, J., Gibson, D., Krula, E., Mironov, A., McManis, J., Roberts, G., Rosenheim, B. E., Christner, B. C., Kasic, K., Fricker, H. A., Lyons, W. B., Barker, J., Bowling, M., Collins, B., Davis, C., Gagnon, A., Gardner, C., Gustafson, C., Kim, O-S., Li, W., Michaud, A., Patterson, M. O., Tranter, M., Ryan Venturelli, R., Trista Vick-Majors, T., & Elsworth, C. Scientific access into Mercer Subglacial Lake: scientific objectives, drilling operations and initial observations. Annals of Glaciology, 62(85–86), (2021): 340–352, https://doi.org/10.1017/aog.2021.10.
    Beschreibung: The Subglacial Antarctic Lakes Scientific Access (SALSA) Project accessed Mercer Subglacial Lake using environmentally clean hot-water drilling to examine interactions among ice, water, sediment, rock, microbes and carbon reservoirs within the lake water column and underlying sediments. A ~0.4 m diameter borehole was melted through 1087 m of ice and maintained over ~10 days, allowing observation of ice properties and collection of water and sediment with various tools. Over this period, SALSA collected: 60 L of lake water and 10 L of deep borehole water; microbes 〉0.2 μm in diameter from in situ filtration of ~100 L of lake water; 10 multicores 0.32–0.49 m long; 1.0 and 1.76 m long gravity cores; three conductivity–temperature–depth profiles of borehole and lake water; five discrete depth current meter measurements in the lake and images of ice, the lake water–ice interface and lake sediments. Temperature and conductivity data showed the hydrodynamic character of water mixing between the borehole and lake after entry. Models simulating melting of the ~6 m thick basal accreted ice layer imply that debris fall-out through the ~15 m water column to the lake sediments from borehole melting had little effect on the stratigraphy of surficial sediment cores.
    Beschreibung: This material is based upon work supported by the US National Science Foundation, Section for Antarctic Sciences, Antarctic Integrated System Science program as part of the interdisciplinary (Subglacial Antarctic Lakes Scientific Access (SALSA): Integrated study of carbon cycling in hydrologically-active subglacial environments) project (NSF-OPP 1543537, 1543396, 1543405, 1543453 and 1543441). Ok-Sun Kim was funded by the Korean Polar Research Institute. We are particularly thankful to the SALSA traverse personnel for crucial technical and logistical support. The United States Antarctic Program enabled our fieldwork; the New York Air National Guard and Kenn Borek Air provided air support; UNAVCO provided geodetic instrument support. Hot water drilling activities, including repair and upgrade modifications of the WISSARD hot water drill system, for the SALSA project were supported by a subaward from the Ice Drilling Program of Dartmouth College (NSF-PLR 1327315) to the University of Nebraska-Lincoln. J. Lawrence assisted with manuscript preparation. Finally, we are grateful to C. Dean, the SALSA Project Manager, and R. Ricards, SALSA Project Coordinator at McMurdo Station, for their organizational skills, and B. Huber of Lamont-Doherty Earth Observatory for providing the SBE39 PT sensors and the Nortek Aquadopp current meter and assisting with interpretation of the data. B. Huber also provided helpful input on programing and calibrating the SBE19PlusV2 6112 CTD.
    Schlagwort(e): Antarctic glaciology ; Basal ice ; Biogeochemistry ; Glacial sedimentology ; Subglacial lakes
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 3345-3350 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Canonical ensemble molecular dynamics simulations were conducted for methane diffusion in AlPO4-5 in order to assess the role of the lattice motion on adsorbate diffusivity in straight pore zeolites. Both a static lattice model and a full dynamic lattice model were used at a loading of 1.5 methane/unit cell at 295 K. Although recent simulation work has asserted that there should be a difference, we show that there is little difference in the observed methane diffusivity (1.26×10−7 m2/s) and passing frequency (0.305) when a static lattice approximation is used over a full dynamic lattice (1.33×10−7 m2/s and 0.328). Furthermore, we introduce a methodology for handling lattice motion in molecular simulations by utilizing the normal vibrational modes in a harmonic crystal approximation. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 859-874 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Many systems approach equilibrium slowly along surfaces of dimension smaller than the original dimensionality. Such systems include coupled chemical kinetics and master equations. In the past the steady state approximation has been used to estimate these lower dimensional surfaces, commonly referred to as "manifolds," and thus reduce the dimensionality of the system which needs to be studied. However, the steady state approximation is often inaccurate and sometimes difficult to define unambiguously. In recent years two methods have been proposed to go beyond the steady state approximation to improve the accuracy of dimension reduction. We investigate these methods and suggest significant modifications to one of them to allow it to be used for the generation of low-dimensional manifolds in large systems. Based on the geometric investigations, two other approaches are suggested which have some advantages over these two methods for the cases studied here. All four approaches are geometric and offer advantages over methods based on the evaluation of time-dependent behavior, where phenomenological rate laws are extracted from the time-dependent behavior. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 7793-7802 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: High-resolution infrared spectra of jet-cooled allyl (CH2–CH–CH2) radical in the CH2 stretching region are obtained in a slit jet discharge spectrometer. Over 200 transitions are observed in the 3100–3140 cm−1 region, which have been rigorously assigned to "in-phase" (ν1) and "out-of-phase" (ν13) coupling of antisymmetric CH stretch excitations on each of the equivalent CH2 subunits. Origins for the two bands are determined to be 3113.98 488(89) cm−1 (ν1) and 3110.59 857(36) cm−1 (ν13), respectively. The data are reasonably well fit to semirigid asymmetric rotor behavior for the Ka≤2 levels populated in the slit jet at Trot(approximate)20 K, though not to within the experimental precision, which provides some indication of perturbations in the upper states. The sign and magnitude of the +3.4 cm−1 splitting between"in-phase" and"out-of-phase" excitations are in good qualitative agreement with a simple electrostatic model of dipole–dipole coupling between the two "local mode" CH2 groups. Due to sub-Doppler resolution (Δν(approximate)70 MHz) in the slit jet expansion, quantum-state-dependent excess broadening of the rovibrational transitions is observed, which can be ascribed to spin–rotation interactions. Based on a least squares analysis of the high-resolution line shapes, the data are consistent with a spin rotation constant of cursive-epsilonaa(approximate)−67(25) MHz. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 943-952 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The initial dissociative chemisorption probability, S0, of O2 on Ir(111) has been investigated with molecular beam techniques and electron energy loss spectroscopy (EELS). The adsorption process on the clean surface occurs by distinct dynamical mechanisms. At incident kinetic energies, Ei, of 0.1 eV and below, the dissociative chemisorption probability decreases with increasing kinetic energy, indicating the dominance of a trapping-mediated mechanism. A decrease in the value of S0 with increasing surface temperature, Ts, is also characteristic of this regime. This temperature dependence reflects the participation of a physically adsorbed state and molecularly chemisorbed state in the dissociation scheme. Additionally, the dependence of S0 on incident angle, θi, in the low kinetic energy regime exhibits near normal energy scaling. At high kinetic energy (Ei〉0.1 eV), the initial dissociative chemisorption probability rises with increasing Ei indicating that translational energy is effective in surmounting a potential barrier to adsorption. Direct access of a molecularly chemisorbed state followed by dissociation, rather than direct access of the dissociated state, is hypothesized to be the primary initial adsorption step. Several observations support this mechanism, including a temperature dependence in the high kinetic energy regime and no observed increase in oxygen saturation coverage with increasing kinetic energy. In addition, EEL spectra show that molecularly chemisorbed states of oxygen are formed on the Ir(111) surface at Ts〈70 K after exposure to a 1.36 eV beam and partial saturation of the atomic overlayer. Attempts to identify molecularly chemisorbed oxygen at low coverages were unsuccessful and limited by the experimental setup which provides cooling of the iridium crystal to only ∼68 K. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 5661-5675 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A novel high-intensity source of jet-cooled molecular radicals is described based on the combination of (i) slit supersonic expansions with (ii) pulsed electric discharges. The electrode bias configuration effectively confines the discharge to a region upstream of the supersonic expansion, which results both in efficient rotational cooling (Trot(approximate)25 K) and high radical densities (〉1014/cm3). In conjunction with direct absorption laser probe methods, this discharge source provides a general technique for high-resolution IR studies of jet-cooled radicals. Performance of the slit discharge system is demonstrated on v=1←0 rovibrational transitions in jet-cooled OH radicals, which indicate sub-Doppler linewidths (Δν(approximate)100 MHz) when probed along the slit expansion axis. The enhanced spectral resolution of the slit discharge geometry is utilized to probe the v3=1←0 asymmetric CH stretch vibration–rotation spectra of CH3 radical. Under sub-Doppler conditions, spin–rotation splittings are fully resolved and nuclear hyperfine splittings partially resolved in all of the transitions, permitting the first measure of Fermi contact interactions [af″=−65.5(9) MHz, εbb″=−354(5) MHz, af′=−65(2) MHz, εbb′=−353(2) MHz] and therefore both the sign and magnitude of spin-polarization effects for CH3 under isolated gas-phase conditions. The results permit direct comparison with high level ab initio calculations, and highlight a clear trend in spin-polarization effects between condensed and gas-phase behavior. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2873-2882 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Cadmium sulfide (CdS) layers were deposited from an aqueous solution of thiourea, cadmium sulfate, and ammonia on (100) n-InP at 60–95 °C. X-ray photoelectron spectroscopy showed that the deposition process effectively removes native oxides on InP and forms a protective layer for subsequent dielectric deposition. Surface analysis also showed that the InP surface is not P deficient following oxide deposition on CdS-treated InP. Capacitance–voltage and conductance–voltage measurements of metal–insulator–semiconductor (MIS) capacitors were used to compare samples with and without CdS films between InP and a deposited insulator. Capacitance–voltage response of CdS-treated MIS structures showed well-defined regions of accumulation, depletion, and inversion. The interface-state density at midgap was reduced from 5×1011 to 6×1010 eV−1 cm−2 with CdS treatment. Depletion-mode MIS field-effect transistors made using this new passivation technique exhibited superior device performance to that of untreated samples.
    Materialart: Digitale Medien
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