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  • American Institute of Physics (AIP)  (17)
  • American Geophysical Union  (9)
  • 2020-2022  (3)
  • 2000-2004  (23)
  • 1
    Electronic Resource
    Electronic Resource
    Backward mode detection of laser-induced wide-band ultrasonic transients with optoacoustic transducer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 2003-2014 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time-resolved piezoelectric detection of wide-band ultrasonic transients induced by laser pulses in absorbing medium was studied. An optoacoustic transducer was developed for measuring the profiles of ultrasonic transients propagating in backward direction out of the laser-irradiated medium. For this purpose, an optical fiber for delivery of laser pulses to the surface of absorbing medium and a wide-band lithium niobate acoustic transducer were incorporated in one compact system, optoacoustic front surface transducer (OAFST). The transducer possesses temporal resolution (rise time) of 3.5 ns, low effective thermal noise pressure (10 Pa), and high sensitivity of piezoelectric detection (10 μV/Pa) over the ultrasonic frequency range from 1 to 100 MHz. Nd:YAG laser pulses at 355 nm were employed to generate distribution of acoustic sources in water solutions of potassium chromate with various concentrations. A temporal course of ultrasonic transients launched into an optically and acoustically transparent medium, coupled to the absorbing medium, was studied. Ultrasonic profiles experimentally measured at the site of laser irradiation were compared with profiles calculated using theoretical model. Experimental curves were in a good agreement with theoretical profiles. The backward detection mode permitted accurate reconstruction of the axial distribution of heat deposition in the laser-irradiated homogeneous or layered medium from the measured profiles. OAFST may become a useful modality for optoacoustic imaging in biological tissues and nondestructive evaluation of industrial materials. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372127
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  • 2
    Electronic Resource
    Electronic Resource
    Miniband formation in a quantum dot crystal (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5509-5515 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We analyze the carrier energy band structure in a three-dimensional regimented array of semiconductor quantum dots using an envelope function approximation. The coupling among quantum dots leads to a splitting of the quantized carrier energy levels of single dots and formation of three-dimensional minibands. By changing the size of quantum dots, interdot distances, barrier height, and regimentation, one can control the electronic band structure of this artificial quantum dot crystal. Results of simulations carried out for simple cubic and tetragonal quantum dot crystal show that the carrier density of states, effective mass tensor and other properties are different from those of bulk and quantum well superlattices. It has also been established that the properties of artificial crystal are more sensitive to the dot regimentation rather then to the dot shape. The proposed engineering of three-dimensional mini bands in quantum dot crystals allows one to fine-tune electronic and optical properties of such nanostructures. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1366662
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  • 3
    Electronic Resource
    Electronic Resource
    Formation of Ge nanoislands using a scanning tunneling microscope (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1397-1400 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Germanium islands were grown on a sample surface by accumulating atoms from the surrounding area through directional surface diffusion initiated by the electric field of a scanning tunneling microscope (STM). The Ge islands grew with a constant rate determined by the tip–sample bias voltage. The parameters of tip–sample interaction were estimated from the kinetic data for island growth by using a scaling relationship among the growth rate, the dipole moment of atoms on surfaces, and the tip–sample bias voltage. The results show that continuous atom transfer with a STM occurs with a rate significantly higher for Ge than for Si. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373829
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  • 4
    Electronic Resource
    Electronic Resource
    Finite-correlation-time effects in the kinematic dynamo problem (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4937-4953 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Most of the theoretical results on the kinematic amplification of small-scale magnetic fluctuations by turbulence have been confined to the model of white-noise-like (δ-correlated in time) advecting turbulent velocity field. In this work, the statistics of the passive magnetic field in the diffusion-free regime are considered for the case when the advecting flow is finite-time correlated. A new method is developed that allows one to systematically construct the correlation-time expansion for statistical characteristics of the field such as its probability density function or the complete set of its moments. The expansion is valid provided the velocity correlation time is smaller than the characteristic growth time of the magnetic fluctuations. This expansion is carried out up to first order in the general case of a d-dimensional arbitrarily compressible advecting flow. The growth rates for all moments of the magnetic-field strength are derived. The effect of the first-order corrections due to the finite correlation time is to reduce these growth rates. It is shown that introducing a finite correlation time leads to the loss of the small-scale statistical universality, which was present in the limit of the δ-correlated velocity field. Namely, the shape of the velocity time-correlation profile and the large-scale spatial structure of the flow become important. The latter is a new effect, that implies, in particular, that the approximation of a locally-linear shear flow does not fully capture the effect of nonvanishing correlation time. Physical applications of this theory include the small-scale kinematic dynamo in the interstellar medium and protogalactic plasmas. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1404383
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  • 5
    Electronic Resource
    Electronic Resource
    Thermal and nonthermal regimes of gliding arc discharge in air flow (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 1632-1641 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Gliding discharges comprising both equilibrium and nonequilibrium plasma conditions offer high energy efficiency and selectivity for chemical processes. Prevailing parameters satisfying nonequilibrium plasma conditions at relatively high power levels should be well understood and characterized. In the present work, gliding discharges formed between diverging electrodes in air flow were studied experimentally over a wide range of gas velocities and power levels. Depending on the system parameters the following discharge regimes were observed: low power nonequilibrium discharge; thermal quasiequilibrium discharge; and gliding discharge with equilibrium to nonequilibrium transition. The effect of system parameters on discharge characteristics is analyzed. The equilibrium to nonequilibrium transition was experimentally observed as a change of voltage increase rate with discharge length growth. The local electric field, defined as dV/dl, increased up to three times, indicating the change of plasma conditions. However, previously reported phenomenon of length explosion was not supported by our experimental data. The co-existence of equilibrium and nonequilibrium phases is also discussed in the frame of phenomenological theory, assuming formation of a growing nonequilibrium fragment inside the gliding discharge channel. It was found that high flow velocities provide intensive cooling, an increase of electric field, and a decrease of gas temperature, promoting equilibrium to nonequilibrium transition at high power levels. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372071
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  • 6
    Electronic Resource
    Electronic Resource
    Translational motion of a spherical bubble in an acoustic standing wave of high intensity (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 14 (2002), S. 1420-1425 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using the Lagrangian formalism, coupled equations of radial and translational motions of a spherical gas bubble in an acoustic wave field are derived. The equation of radial motion is then modified, for the purpose of allowing for effects of liquid compressibility, using Keller–Miksis' approach, and the equation of translation is added by the primary Bjerknes force and the viscous force in the form of the Levich drag. The resulting equations are solved numerically for the purpose of studying the translational motion of a bubble in a plane standing wave. It is shown that, if the acoustic pressure amplitude is high enough, a bubble driven below resonance, instead of moving to the pressure antinode as it does in a weak field, reciprocates about the pressure node plane. This result is of interest for an understanding of irregular bubble motions observed experimentally in strong acoustic fields. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1458597
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  • 7
    Electronic Resource
    Electronic Resource
    Visible photoluminescence of Ge dots embedded in Si/SiO2 matrices (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 1432-1434 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ge island formation on ultrathin SiO2 films enabled us to fabricate multilayer structures of Ge dots ∼6–7 nm in diameter and with an extremely high dot density of 2×1012 cm−2. Each dot had a boundary with the SiO2 film and a Si spacer layer. The multilayer structures exhibited photoluminescence (PL) with a maximum in the range of 2–3 eV depending on the excitation energy. The PL was associated with recombination between holes confined within Ge dots and electrons localized in the radiative defect centers at the Ge-dot/SiO2 interfaces. The results suggest that this recombination is much more effective than that at the Si/SiO2 interface and supported by the hole migration from the Si spacer layers to the Ge dots. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1451986
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  • 8
    Electronic Resource
    Electronic Resource
    Theoretical investigation of the initial reaction of the NO decomposition on the Si (100) (2×1) reconstructed surface (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 8237-8248 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have investigated theoretically the initial reaction of nitric oxide (NO) with the Si(001)(2×1) surface, followed by N and O insertion into the silicon film during the initial growth of the oxynitride film. We use quantum chemical [ab initio and density functional theory (DFT) cluster approach] and solid state physics (DFT with periodic boundary conditions) computational methods. Our study suggests a low barrier reaction path for NO decomposition on the Si(100)(2×1) reconstructed silicon surface. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1316040
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  • 9
    Electronic Resource
    Electronic Resource
    Cl+HD (v=1; J=1,2) reaction dynamics: Comparison between theory and experiment (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 670-685 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrationally state-resolved differential cross sections (DCS) and product rotational distributions have been measured for the Cl+HD(v=1, J=1)→HCl(DCl)+D(H) reaction at a mean collision energy of 0.065 eV using a photoinitiated reaction ("photoloc") technique. The effect of HD reagent rotational alignment in the Cl+HD(v=1, J=2) reaction has also been investigated. The experimental results have been compared with exact quantum mechanical and quasiclassical trajectory calculations performed on the G3 potential energy surface of Allison et al. [J. Phys. Chem. 100, 13575 (1996)]. The experimental measurements reveal that the products are predominantly backward and sideways scattered for HCl(v′=0) and HCl(v′=1), with no forward scattering at the collision energies studied, in quantitative agreement with theoretical predictions. The experimental product rotational distribution for HCl(v′=1) also shows excellent agreement with quantum-mechanical calculations, but the measured DCl+H to HCl+D branching ratio is near unity, which is at variance with the theoretical calculations that predict about 3 times larger yield of HCl+D at these collision energies. The reactivity shows a marked dependence on the direction of the HD(v=1, J=2) rotational angular momentum, and experimental measurements of this reagent alignment effect are in good agreement with theoretical predictions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480602
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  • 10
    Electronic Resource
    Electronic Resource
    Tandem time-of-flight mass spectrometer (TOF-TOF) with a quadratic-field ion mirror (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2115-2123 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A tandem time-of-flight (TOF-TOF) mass spectrometer comprised of two ion mirrors is described. The first ion mirror, which is a linear-field, single-stage mirror (MS1) with an intermediate collision cell, has been designed to provide the temporal focus necessary for the second, quadratic-field ion mirror (MS2) to function effectively. Due to the wide energy-range focusing capabilities of the quadratic field employed in the second ion mirror all the fragment ions can be collected in one spectrum without the need to step the reflecting working voltage of the MS2. The size of the active area of the microchannel plate detector used in the preliminary experiments was the limiting factor governing the collection efficiently of fragment ions. The use of the first ion mirror to provide temporal focusing of the precursor ion packet at the first focal point of the quadratic mirror used as the MS2 requires no alteration of the focusing conditions for different masses, in contrast to delayed extraction or postsource pulsed focusing. Precursor ions formed by matrix-assisted laser desorption/ionization were mass-selected with an ion gate located before the collision cell and the fragment ions were mass analyzed using the quadratic-field ion mirror. Experimental results demonstrating effective high-energy collision-induced dissociation of polymer and fullerene molecule-ions are presented. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1470229
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