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  • Oxford University Press  (23)
  • Cell Press  (12)
  • American Institute of Physics (AIP)  (9)
  • 1995-1999  (44)
  • 1998  (19)
  • 1997  (25)
  • 1
    Electronic Resource
    Electronic Resource
    The stability of advanced operational regimes on the Tokamak Fusion Test Reactor : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1589-1595 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of the Tokamak Fusion Test Reactor [D. Meade and the TFTR Group, in Plasma Physics and Controlled Nuclear Fusion Research, Washington, D.C., 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. I, pp. 9–24], as defined by the maximum fusion power production, has been limited, not by confinement, but by stability to pressure-driven modes. Two classes of current profile modification have been investigated to overcome this limit. A new technique has been developed to increase the internal inductance of low-q (q(approximate)4), high-current (Ip〉2MA) plasmas. As was the case at higher edge q, the disruptive β limit has been found to increase roughly linearly with the internal inductance, li. Plasmas with hollow current profiles, i.e., reversed shear, are also predicted and experimentally observed to have increased stability in the negative shear region to ballooning and kink modes. However, performance of these plasmas is still limited by pressure-driven modes in the normal shear region. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872290
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  • 2
    Electronic Resource
    Electronic Resource
    First results of collective scattering on JET (invited) : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 275-280 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The fast ion and α-particle diagnostic at JET is based on collective Thomson scattering of high power millimeter-wave radiation. The principal aim of the diagnostic will be the measurement of the spatially resolved velocity distribution of fast α particles when tritium is introduced in JET plasmas, although several other applications are foreseen. The diagnostic uses a 140 GHz, 500 kW, gyrotron as the source of probing radiation and a heterodyne detection system. The diagnostic came into operation during the last JET operational campaign. First measurements were made of the thermal and mildly suprathermal (induced by ion cyclotron resonance heating) ion feature. The results confirmed expectations, indicating that the diagnostic should give the predicted performance for observation of α-particle populations in the DT phase. The signal-to-noise ratio is limited by the noise on the background radiation (electron cyclotron emission), which has a minimum around 140 GHz only when JET is operated at B∼3.4 T. To further improve the S/N and to make the diagnostic suitable for operation at higher field, which is now being considered for some of the DT plasmas, a viewing dump will be installed before the DT phase. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147822
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of growth interruption on the properties of InGaAs/InAlAs quantum well structures (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 338-340 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of the growth interruption time during the growth of InGaAs/InAlAs quantum well structures is shown to have a significant effect on both the interband transitions, as determined by photoreflectance, and the electrical properties of the as-grown structure. The results show that, for increasing growth interruption time, the quantum well heterointerfaces become more abrupt and the carrier mobility increases, thereby demonstrating that long interruption times are preferable for the growth of high quality rectangular quantum well structures. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120729
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  • 4
    Electronic Resource
    Electronic Resource
    Terahertz pulse-induced switching of a quantum-well optical amplifier (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3872-3874 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate theoretically that an intense half-cycle terahertz pulse can be used conjunctively with a quantum-well optical amplifier to form the basis of an efficient ultrahigh-speed optical switch. Our procedure implies terahertz and subterahertz switching and recovery rates, respectively. Constraints and practicalities are discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122921
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  • 5
    Electronic Resource
    Electronic Resource
    NMR excitation of quadrupolar order using adiabatic demagnetization in the rotating frame (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 876-889 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Adiabatic demagnetization and remagnetization in the rotating frame (ADRF and ARRF) are shown to be practical and efficient techniques for exciting and observing quadrupolar order, T2,0, in NMR of quadrupolar nuclei such as 2H or 23Na. A detailed theoretical description of ADRF and ARRF of spin I=1 and 3/2 nuclei, based on the well-known vector model of NMR, is presented and used to derive analytically a variety of pulse shapes for ADRF and ARRF. This theory is also used to calculate the state of the spin I=1 and 3/2 density operators following an ADRF or ARRF pulse and it is shown that the desired coherence transfer processes have the maximum amplitudes allowed by the well-known "universal bound" theorem. In principle, therefore, ADRF is shown to be superior as a method of exciting quadrupolar order to the Jeener-Broekaert experiment since the latter fails to excite the maximum T2,0 amplitude for spin I=3/2 nuclei. The performance of ADRF is investigated using computer calculations and simulations and the conditions under which it yields broadband (i.e., non-oscillatory) excitation of quadrupolar order are derived. Using both 2H (I=1) and 23Na (I=3/2) NMR of liquid crystalline and biological samples, ADRF and ARRF are demonstrated experimentally. The predicted broadband excitation behavior is observed for both ADRF and ARRF, whereas both the Jeener-Broekaert and double-quantum filtration experiments show excitation profiles that oscillate sinusoidally as a function of either the quadrupolar splitting parameter, ωQ, or the duration of the pulse sequence, τ. Finally, a more general discussion of ADRF and ARRF of quadrupolar nuclei is presented and it is shown that the maximum coherence transfer amplitudes are achieved for nuclei of any spin quantum number I. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475451
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  • 6
    Electronic Resource
    Electronic Resource
    Spectroscopy and dynamics of rare gas-spherical top complexes. III. The infrared spectrum of the ν3 band of Ne–SiH4 ( j=1←1 and j=2←1 transitions) (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2738-2751 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The infrared spectrum of the rare gas-spherical top complex Ne–SiH4 has been recorded in a supersonic jet in the region of the SiH4 ν3 triply degenerate stretching vibration at ∼2189 cm−1. The Ne–SiH4 spectrum is complex with no obvious regular band structure; a previous paper has reported the assignment and analysis of bands correlating with the SiH4 R(0) (K=0←0, K=1←0) and P(1) (K=0←0, K=0←1) transitions. This paper concludes the study of Ne–SiH4, with the assignment and analysis of bands correlating with the SiH4 Q(1) (K=0←0, K=1←0, K=0←1, K=1←1) and R(1) (K=0←0, K=1←0, K=1←1, K=2←1) transitions. This was facilitated by a twofold approach: The bands were identified by the use of a theoretical intermolecular potential, with potential parameters determined by reference to the two bands previously fitted; and the relative magnitudes of the Coriolis interactions between the K sublevels within the bands determined by explicit calculation of the Coriolis matrix elements. Having fitted the bands to appropriate energy-level expressions, an effective anisotropic potential for the internal rotation of the SiH4 molecule within the complex was fitted to the total of 15 observed band origins. With a fixed R approximation, the V3 anisotropic term was found to be ∼30 cm−1, approximately one-third that of Ar–SiH4, reflecting the freer rotation of the SiH4 molecule when complexed with the less polarizable Ne atom. However, the overall quality of the fit was an order of magnitude worse than that for Ar–SiH4, indicating increased importance of the radial dependence of the Ne–SiH4 potential compared to that of Ar–SiH4. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474700
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  • 7
    Electronic Resource
    Electronic Resource
    Comparison between the optical limiting behavior of chloroaluminum phthalocyanine and a cyanine dye (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5905-5912 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The picosecond optical limiting characteristics of the optical limiting dyes hexamethylindotricarbocyanine iodide (HITCI) and chloroaluminum phthalocyanine (CAP) are compared and contrasted at 532 nm. From single pulse transmittance experiments, HITCI is shown to possess a serious limitation in its optical limiting behavior, where the regime of induced absorption becomes one of induced transmission for high irradiances. CAP, on the other hand, although possessing a smaller ratio of the excited-state to ground-state absorption cross-section, continues to exhibit optical limiting over a much broader dynamic range. From cross-polarized time-resolved excitation-probe measurements, HITCI exhibits a sharp negative spike around zero delay which originates from orientational coherent grating effects, while CAP does not exhibit any spike. These nonlinearities are explained theoretically as a complex interplay between a series of excited manifolds for the dyes and the radiation properties of the interacting laser pulse. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364377
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  • 8
    Electronic Resource
    Electronic Resource
    Bounds on spin dynamics and the design of multiple-pulse NMR experiments (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 2105-2117 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The "universal bound on spin dynamics'' proposed by Sørensen is examined in detail and shown to be of great assistance in the design of novel multiple-pulse NMR experiments. The efficiency of coherence transfer between all possible states of a spin system, including populations, single-quantum coherences, and multiple-quantum coherences, is investigated. Examples are drawn from coherence transfer processes in quadrupolar coupled spin I=1 and 3/2 nuclei and weakly J coupled systems of two and three spin I=1/2 nuclei. It is found that many of the most commonly used NMR pulse sequences fail to achieve the maximum coherence transfer efficiency when applied to spin I=3/2 or to three spin I=1/2 nuclei. However, it is shown that, with knowledge of the universal bound, novel multiple-pulse NMR experiments that achieve optimal efficiency can be easily derived using computer optimization. The application of the universal bound to two-step coherence transfer experiments presents a number of conceptual difficulties. In particular, examples are presented where the product of the universal bounds on the two individual coherence transfer coefficients is larger than the universal bound on the overall transfer from the initial to the final state. These difficulties are resolved and explained in terms of the presence of a "residue'' that is created together with the intermediate state. The universal bound is used to examine the conditions under which the effect of this residue can be suppressed and the constraints that this places on the design of optimal multi-step coherence transfer NMR experiments. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473783
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  • 9
    Electronic Resource
    Electronic Resource
    A deuterium nuclear magnetic resonance investigation of the symmetry and orientational order of the nematic phase of 4-[3,4,5-tris(4-dodecyloxybenzyloxy)benzoyloxy]-4′- (4-dodecyloxybenzoyloxy)-1,1′-biphenyl. A biaxial nematic? (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 9252-9263 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The first compound for which the previously predicted biaxial nematic phase was claimed is 4-[3,4,5-tris(4-dodecyloxybenzyloxy)benzoyloxy]-4′-(4-dodecyloxybenzoyloxy)-1,1′-biphenyl (I). This assignment was based on the observation of the optical texture and the x-ray diffraction pattern. To confirm this identification of the biaxial nematic phase, we have studied the deuterium nuclear magnetic resonance (NMR) spectra of nonuniformly aligned samples with the deuterons located specifically in the mesogen itself or in the disklike solute, hexamethylbenzene-d18, dissolved in the mesogen. These experiments allow us to determine the biaxiality in the partially averaged quadrupolar tensor. For both systems, the biaxiality parameter is found to be zero within the experimental error which is estimated to be less than ±0.08 for the pure mesogen and ±0.06 for the solute. The orientational order parameters determined from the quadrupolar splitting change discontinuously at the nematic-isotropic transition thus confirming the first order character of the transition and in accord with the uniaxial symmetry of the nematic phase. The order parameters determined for the two groups of equivalent deuterons in the specifically deuteriated oxymethylene links allow us to comment on the conformations of these links. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475318
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  • 10
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    Lectin histochemistry — a concise practical handbook (1997)
    Cell Press
    Details
    Publication Date: 1997-08-01
    Print ISSN: 0968-0004
    Electronic ISSN: 1362-4326
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Published by Cell Press
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