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  • 1
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    Collisions of matter-wave solitons (2014)
    Springer Nature
    Details
    Publication Date: 2014-11-29
    Description: Nature Physics 10, 918 (2014). doi:10.1038/nphys3135 Authors: Jason H. V. Nguyen, Paul Dyke, De Luo, Boris A. Malomed & Randall G. Hulet Solitons are localized wave disturbances that propagate without changing shape, a result of a nonlinear interaction that compensates for wave packet dispersion. Individual solitons may collide, but a defining feature is that they pass through one another and emerge from the collision unaltered in shape, amplitude, or velocity, but with a new trajectory reflecting a discontinuous jump. This remarkable property is mathematically a consequence of the underlying integrability of the one-dimensional (1D) equations, such as the nonlinear Schrödinger equation, that describe solitons in a variety of wave contexts, including matter waves. Here we explore the nature of soliton collisions using Bose–Einstein condensates of atoms with attractive interactions confined to a quasi-1D waveguide. Using real-time imaging, we show that a collision between solitons is a complex event that differs markedly depending on the relative phase between the solitons. By controlling the strength of the nonlinearity we shed light on these fundamental features of soliton collisional dynamics, and explore the implications of collisions in the proximity of the crossover between one and three dimensions where the loss of integrability may precipitate catastrophic collapse.
    Print ISSN: 1745-2473
    Electronic ISSN: 1745-2481
    Topics: Physics
    Published by Springer Nature
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  • 2
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    Prospects for Doppler cooling of three-electronic-level molecules (2011)
    American Physical Society (APS)
    Details
    Publication Date: 2011-05-05
    Description: Author(s): J. H. V. Nguyen and B. Odom Analogous to the extension of laser cooling techniques from two-level to three-level atoms, Doppler cooling of molecules with an intermediate electronic state is considered. In particular, we use a rate-equation approach to simulate cooling of SiO^{+} , in which population buildup in the intermediat... [Phys. Rev. A 83, 053404] Published Wed May 04, 2011
    Keywords: Atomic and molecular processes in external fields, including interactions with strong fields and short pulses
    Print ISSN: 1050-2947
    Electronic ISSN: 1094-1622
    Topics: Physics
    Published by American Physical Society (APS)
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  • 3
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    Structural analysis of the essential self-cleaving type III secretion proteins EscU and SpaS (2008)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2008-05-03
    Description: During infection by Gram-negative pathogenic bacteria, the type III secretion system (T3SS) is assembled to allow for the direct transmission of bacterial virulence effectors into the host cell. The T3SS system is characterized by a series of prominent multi-component rings in the inner and outer bacterial membranes, as well as a translocation pore in the host cell membrane. These are all connected by a series of polymerized tubes that act as the direct conduit for the T3SS proteins to pass through to the host cell. During assembly of the T3SS, as well as the evolutionarily related flagellar apparatus, a post-translational cleavage event within the inner membrane proteins EscU/FlhB is required to promote a secretion-competent state. These proteins have long been proposed to act as a part of a molecular switch, which would regulate the appropriate chronological secretion of the various T3SS apparatus components during assembly and subsequently the transported virulence effectors. Here we show that a surface type II beta-turn in the Escherichia coli protein EscU undergoes auto-cleavage by a mechanism involving cyclization of a strictly conserved asparagine residue. Structural and in vivo analysis of point and deletion mutations illustrates the subtle conformational effects of auto-cleavage in modulating the molecular features of a highly conserved surface region of EscU, a potential point of interaction with other T3SS components at the inner membrane. In addition, this work provides new structural insight into the distinct conformational requirements for a large class of self-cleaving reactions involving asparagine cyclization.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zarivach, Raz -- Deng, Wanyin -- Vuckovic, Marija -- Felise, Heather B -- Nguyen, Hai V -- Miller, Samuel I -- Finlay, B Brett -- Strynadka, Natalie C J -- 5R01 AI030479/AI/NIAID NIH HHS/ -- R01 AI030479/AI/NIAID NIH HHS/ -- U54 AI057141/AI/NIAID NIH HHS/ -- England -- Nature. 2008 May 1;453(7191):124-7. doi: 10.1038/nature06832.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biochemistry and Molecular Biology, and the Center for Blood Research, University of British Columbia, 2350 Health Sciences Mall, Vancouver, British Columbia V6T 1Z3, Canada.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18451864" target="_blank"〉PubMed〈/a〉
    Keywords: Asparagine/chemistry/metabolism ; Circular Dichroism ; Crystallography, X-Ray ; Cyclization ; Enteropathogenic Escherichia coli/*chemistry/*metabolism/pathogenicity ; Escherichia coli Proteins/*chemistry/genetics/*metabolism ; Models, Chemical ; Models, Molecular ; Protein Structure, Tertiary ; Salmonella typhimurium/genetics/metabolism ; Virulence Factors/metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of monomer architecture on the shear properties of molecularly thin polymer melts (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2346-2351 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effective viscosity and shear behavior of ultrathin films of two structurally different perfluoropolyether fluids have been investigated. The materials used were Fomblin Z, a linear random copolymer of fluoroethylene oxide and fluoromethylene oxide, and Fomblin Y, a branched random copolymer with fluoropropylene oxide and fluoromethylene oxide monomer units. The shearing experiments were conducted with the fluids confined between molecularly smooth surfaces at shear rates ranging from 200 to 4×103 s−1. It was found that when the thickness of the fluid films decreases from 10 to 2 nm, both perfluoropolyethers exhibited a sharp increase in viscosity, from bulk values to "surface viscosity'' values that are many orders of magnitude larger. With increasing shear rates, the Z-type fluid showed a gradual decrease in the shear stress indicating an apparent ordering of the molecules due to the applied shear forces. On the other hand, with the Y-type copolymer, the shear stresses were significantly lower and were proportional to the shear rate resembling Newtonian fluids. The results are explained in terms of the differences in the molecular architecture of the fluids and suggest a close relation between the molecular structure of the polymer melt near a solid wall and its frictional and lubricating properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459906
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  • 5
    Electronic Resource
    Electronic Resource
    Continental Climatic Variations between 130,000 and 90,000 Years BP (1970)
    [s.l.] : Nature Publishing Group
    Nature 226 (1970), S. 631-633 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Corals, which may be dated back to about 500,000 yr BP by the uranium desequilibrium method, may be used to determine dates outside the range of 14C measurements. These corals also reflect sea level variations associated with temperature. Variations of foraminiferal associations5 or their isotopic ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/226631a0
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  • 6
    Electronic Resource
    Electronic Resource
    Real time spectroscopic ellipsometry characterization of the nucleation of diamond by filament-assisted chemical vapor deposition (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5287-5289 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The recently developed technique of real time spectroscopic ellipsometry (SE) has been applied to characterize the nucleation of diamond on c-Si by W filament-assisted chemical vapor deposition, leading to improved control over the process. Specifically, techniques are developed which minimize W contamination at the diamond/substrate interface; calibrations are performed which determine the temperature of the top ∼250 A(ring) of the substrate under growth conditions; and alterations in gas flow conditions are implemented in response to diamond growth for a reduced induction time. With these procedures in place, real time SE provides the induction time, nucleation density, and mass thickness, and is in quantitative agreement with ex situ scanning electron microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350544
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  • 7
    Electronic Resource
    Electronic Resource
    Simultaneous real-time spectroscopic ellipsometry and reflectance for monitoring thin-film preparation (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3489-3500 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An expansion of the capabilities of high-speed, multichannel spectroscopic ellipsometry (SE) is described that involves simultaneous measurement of the reflectance spectrum along with the two spectra in the ellipsometric angles (ψ, Δ). Previously, a novel rotating-polarizer spectroscopic ellipsometer has been perfected that employs a photodiode array detector for high-speed acquisition of (ψ, Δ) spectra, designed for real-time studies of thin-film growth. For a polarizer angular rotation frequency of ω0, the (ψ, Δ) values at a given photon energy are deduced from the 2ω0 Fourier components of the detector irradiance, normalized by the dc component. A third parameter, the weighted reflectance RA, can be obtained from the dc component and from a calibration based on the known optical properties of the substrate measured prior to film growth. With (ω0/2π)=12.5 Hz, three-parameter data sets, [ψ(hν), Δ(hν), RA(hν); 1.5≤hν≤4.5 eV], can be acquired with a time resolution as short as 40 ms. Although RA provides complementary information to (ψ, Δ), it has yet to be exploited in conjunction with real-time SE until this study. A resilient analysis approach, based on mathematical inversion and least-squares fitting of the real-time three-parameter data sets, is designed to yield the film dielectric functions and thicknesses independently at each time during the early stages of thin-film growth. The three-parameter approach has been applied successfully in studies of amorphous silicon (a-Si:H) thin films prepared by plasma-enhanced chemical vapor deposition, and aluminum and silver films prepared by physical vapor deposition. For the a-Si:H films, RA(hν) exhibits deviations as large as ∼3% from that predicted in modeling (ψ, Δ) alone. The deviations result from light scattering by plasma particulates, and we show how additional information can be extracted from the spectral dependence of the scattering loss.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144527
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  • 8
    Electronic Resource
    Electronic Resource
    Spectroscopic ellipsometry on the millisecond time scale for real-time investigations of thin-film and surface phenomena (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 3842-3848 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Submonolayer sensitivity to thin-film nucleation and growth in real time on the millisecond scale has been achieved with a unique rotating polarizer multichannel ellipsometer. Continuous spectra in the ellipsometry angles {ψ(hv),Δ(hv)} consisting of ∼50 points from hv=1.5 to 4.3 eV have been obtained with acquisition and repetition times as short as 16 and 32 ms, respectively. As an example of the instrument capabilities, we present results for hydrogenated amorphous silicon (a-Si:H) growth on c-Si by plasma-enhanced chemical vapor deposition at a rate of 400 A(ring)/min. In this example, the acquisition and repetition times are both 64 ms, and at this speed a precision in (ψ,Δ) of ∼0.02–0.03° is obtained under optimum conditions. We observe a-Si:H nucleation in the first 2 s of deposition, and detect relaxation of nucleation-induced surface roughness with submonolayer sensitivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143280
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  • 9
    Electronic Resource
    Electronic Resource
    Preparation of ultrathin microcrystalline silicon layers by atomic hydrogen etching of amorphous silicon and end-point detection by real time spectroellipsometry (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 3335-3337 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The etching of hydrogenated amorphous silicon (a-Si:H) in thermally generated atomic hydrogen has been investigated in detail, utilizing real time spectroellipsometry for characterization and end-point detection. When properly controlled, etching can yield ultrathin microcrystalline Si (μc-Si:H) films of relatively high density on virtually any substrate material. These films are unique in that their microstructure is established by the crystallization of the near-surface a-Si:H, rather than by the nucleation of crystallites on the substrate, as occurs for plasma-enhanced chemical vapor-deposited μc-Si:H films. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113024
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  • 10
    Electronic Resource
    Electronic Resource
    In situ determination of dielectric functions and optical gap of ultrathin amorphous silicon by real time spectroscopic ellipsometry (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2543-2545 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed techniques to determine the near-infrared to near-ultraviolet dielectric function and optical gap of ultrathin amorphous silicon [a-Si:(H)] using real-time spectroscopic ellipsometry during preparation and processing. The techniques have been applied to ∼50 A(ring) a-Si:H films prepared by plasma-enhanced chemical vapor deposition, and to ∼250 A(ring) pure a-Si chemically modified by atomic H exposure. For the latter, the time evolution of the bonded H content can be estimated along with the evolution of the gap.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105947
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