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  • 1
    Electronic Resource
    Electronic Resource
    Effects of solute–solvent coupling and solvent saturation on solvation dynamics of charge transfer reactions (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 859-865 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of the solute–solvent coupling on the dynamics of adiabatic charge transfer reactions is examined. A two-state description of the solute electronic configuration is implemented to adequately treat the gradual transfer of charge from the donor to acceptor as the reaction progresses. A formalism is developed for separating the solute and solvent contributions to the reaction coordinate (defined here as the difference in energy between the reactant and product states) and equations of motion are derived for these coordinates. It is found that these equations of motion are far more elaborate than the ones considered in the diabatic case (weak coupling between solute electronic states). In particular, they must reflect the effect of the solvent polarization on the solute polarization. The corresponding coupling term is missing in most treatments of charge transfer processes. To explore the coupled dynamics of the reactive trajectories we use both direct downhill simulations and a new approach which evaluates the average solvent coordinate using the linear response approximation. Our study indicates that the reactive fluctuations are characterized by both the polarization time of the solute dipole and the relaxation time (or times) of the solvent. The nature of the relevant solvent relaxation time is explored on a microscopic level for different charge configurations and different solute radii. The results demonstrate that the autocorrelation function of the solvent coordinate (which is proportional to the solvent reaction field) reflects saturation effects and depends on the solute size and charge distribution. Thus we conclude that the microscopic dynamics of the solvent can deviate from the corresponding macroscopic estimate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455719
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  • 2
    Electronic Resource
    Electronic Resource
    An all refractory NbN Josephson junction medium scale integrated circuit process (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4853-4860 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fabrication and electrical performance of an all refractory, eight mask step, NbN medium scale integrated circuit process are discussed. In situ rf sputter deposited trilayers of NbN/MgO/NbN are plasma etched to fabricate Josephson junctions. A novel low temperature, plasma enhanced chemical vapor deposited SiO2 film is used for wiring and resistor insulation. Sputter deposited molybdenum films are used for resistors. Tunnel junctions fabricated with this process have Vm=61 mV at jc=1100 A/cm2, and Vg = 5.1–5.2 mV at 4.2 K. Critical currents are uniform to within ±3% for 101 junction strings and are within ±25% over all die on 3 in. wafers. This process has been used to fabricate 8-bit single flux quantum counter circuits, squid magnetometer circuits, 870 junction strings, and arrays of 256 squids. Preliminary circuit testing indicates operation at temperatures within the range of small closed-cycle refrigerators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346145
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  • 3
    Electronic Resource
    Electronic Resource
    Predicting chaotic dispersion with Eulerian symmetry measures: Wavy Taylor-vortex flow (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 2522-2528 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a recent investigation of particle transport in numerically computed wavy Taylor-vortex flow, Rudman estimated an effective axial diffusion coefficient, Dz, to characterize the enhanced mixing due to chaotic advection [AIChE J. 44, 1015 (1998)]. We find that Dz is proportional to the product of two measures of symmetry deviation. The first is a measure of the average deviation of the flow from rotational symmetry, and the second is a measure of the average deviation from flexion-free flow (a flow where the curl of the vorticity is zero). Because these quantities are obtained directly from the velocity field, we call them Eulerian symmetry measures. Thus, we show that the macroscopic transport behavior in a flow can be quantified directly in terms of the velocity field and its gradients, and hence provides a connection between Eulerian and Lagrangian pictures of transport—a problem of fundamental and widespread interest. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1387471
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  • 4
    Electronic Resource
    Electronic Resource
    Fine structure of granular banding in two-phase rimming flow (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 2720-2723 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Solid–liquid two-phase flow inside a partially filled horizontally rotating cylinder is investigated. We document the observation of a new, secondary banding pattern developing in the flow when the solid phase comes out of suspension to accumulate as regularly spaced, circumferential bands on the inner cylinder wall. This secondary pattern, the fine structure, is superposed on the primary pattern which we previously described [O. A. M. Boote and P. J. Thomas, Phys. Fluids 11, 2020 (1999)]. The fine structure is characterized by each of the primary bands adopting a compound structure consisting of three individual, narrower secondary bands. New results on the influence of the physical properties of the solid phase on transitions between characteristic flow states are briefly discussed. It is reported that state-transition boundaries in the phase plane and the wavelength of the primary instability are insensitive to particle size and shape while there exist influences due to the particle density. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1388183
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  • 5
    Electronic Resource
    Electronic Resource
    Stability and chaotic advection in the eccentric Taylor problem (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1435-1435 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Theoretically, Lagrangian chaos or chaotic advection can occur by forcing a steady, two-dimensional velocity field with a time-periodic perturbation. This idea has recently been confirmed experimentally by Chaiken et al.1 and Chien et al.2 In principle, chaotic advection should also occur in a three-dimensional steady flow. To investigate this problem we constructed an eccentric Taylor–Couette apparatus with a rotating inner cylinder and a stationary outer cylinder. We obtain a 3-D steady flow in the following way. We first create a 2-D velocity field at small rotation rates of the inner cylinder by imposing a sufficiently large ecccentricity to obtain separated flow. (That is, an eddy in the region of largest gap is created by the separation of the fluid from the outer boundary and its reattachment downstream.) The inner cylinder rotation rate is then increased until Taylor vortices appear. The Taylor vortices modify the separated flow but do not destroy it. It is in this mixed Taylor vortex-separated flow regime that we carry out our studies of chaotic advection. On account of mathematical difficulties there exist few theoretical or experimental studies of stability of the flows in the eccentric geometry. We have therefore conducted numerical and laboratory experiments to identify the regions of parameter space where 3-D steady flow exists and where a transition of time dependence (i.e., 4-D flows) occurs. In our numerical work we used a commercial computational fluid dynamics program and we will report on our assessment of its accuracy in predicting the three-dimensional flow features observed in the experiments and its potential for investigating chaotic advection. In particular, we use it to find the "skeleton'' of the flow and the fluxes between the associated regions of different flow type that it defines, and compare these with experimental observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858023
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  • 6
    Electronic Resource
    Electronic Resource
    Instantaneous, quantitative measurements of molecular mixing in the axisymmetric jet near field (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 403-416 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results from a dual-tracer planar laser-induced fluorescence (PLIF) technique for making instantaneous, quantitative measurements of molecularly mixed fluid fraction are presented for an axisymmetric jet in a slow co-flow. The two-camera, two-laser technique uses PLIF of nitric oxide seeded in a nitrogen jet to mark the unmixed jet fluid fraction, while PLIF of acetone seeded into the low velocity air co-flow marks the total co-flow fluid fraction. By combining data from these two simultaneous images, quantitative measurements of molecularly mixed jet fluid fraction can be made on a pixel-by-pixel basis, while simultaneously allowing visualizations of large-structure behavior and regions of subresolution stirring. Instantaneous images of molecularly mixed jet fluid fraction and jet fluid mixing efficiency, probability density functions (PDFs) of mixed jet fluid fraction, and associated statistics are presented for Rejet=1000, 5000, 10,000, 50,000, and 100,000. For fully turbulent conditions (Rejet≥30,000), stirring at subresolution scales is detected primarily on the jet side of the mixing layer. This creates a hybrid PDF behavior (stationary on the jet side of the mixing layer, marching on the co-flow side) that is not shown by passive scalar methods at equivalent image resolution. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869888
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  • 7
    Electronic Resource
    Electronic Resource
    Attractive-mode force microscope for investigations of biomolecules under ambient conditions (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 4261-4265 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report on the design and performance of a quartz tuning-fork-based dynamic mode atomic force microscope for the imaging of biological samples under ambient conditions. The instrument uses a stiff cantilever that maintains stable oscillations at low amplitudes even in the presence of capillary and other long range forces that can overwhelm more flexible cantilevers. The performance of the microscope is demonstrated with high resolution measurements of double-stranded DNA on cleaved mica substrates using Si and Si3N4 tips. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1406927
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  • 8
    Electronic Resource
    Electronic Resource
    Iron-cored coil system for the measurement of angular distributions of charged particles (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3323-3325 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel coil system is described that enables the magnetic angle-changing technique to be used at higher energies. The system consists of coils of wire that are combined with specially shaped iron cores in such a way as to preserve localization of the magnetic field. The system extends the operational energy range of previous systems consisting of solenoids alone by a factor of 25. Measurements of the electron impact excitation of the n=2 states of helium are presented as an example of the use of the device. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287044
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  • 9
    Electronic Resource
    Electronic Resource
    Quartz tuning forks as sensors for attractive-mode force microscopy under ambient conditions (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 1712-1714 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present investigations of the frequency versus distance behavior of a quartz tuning-fork-based atomic force microscope. We show that if the amplitude of the motion A of the tip is large, then the apparent shape of the tip–surface interaction curve depends on A. For smaller amplitudes of oscillation (A(approximately-less-than)3 nm), we find that the shape of the interaction curve becomes independent of A. In this low amplitude limit, a simple relation between the observed frequency shift and the underlying interaction allows quantitative determination of tip–sample forces. Tuning fork sensors open a window for dynamic-mode force microscopy in a regime where conventional microfabricated sensors are overwhelmed by long range capillary forces. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1402960
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