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  • 1
    Electronic Resource
    Electronic Resource
    Theoretical aspects of higher-order truncations in solid-state nuclear magnetic resonance (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 8947-8960 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recent experimental developments of high-resolution NMR in solids (for example, double rotation and dynamic-angle spinning) address the reduction of second-order line broadening effects, particularly in systems involving quadrupolar nuclei such as 23Na, 17O, 27Al, and 14N. However, some aspects of the theoretical description of these systems have not been clearly understood; in particular, the various procedures available to truncate the interactions give incompatible results. We present a general framework, based on static perturbative methods, which provides a natural procedure to derive the correct Hamiltonian for higher-order effects in irreducible tensor form. Applications of this method to coherent averaging techniques (sample motion or radio-frequency irradiation) are described and compared to previous treatments based on average Hamiltonian theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463321
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  • 2
    Electronic Resource
    Electronic Resource
    Optimization procedure for the cooling of liquid 3He by adiabatic demagnetization of praseodymium nickel (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 437-443 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The construction and performance of a single stage nuclear demagnetization apparatus utilizing 0.267 mole of praseodymium nickel material is described. An optimization procedure to minimize entropy production during the demagnetization of the hyperfine enhanced material has been developed which enabled the cryostat to cool a liquid-3He sample to a temperature of 350 μK. The effects of measured heat leaks and inferred eddy-current heating are accounted for satisfactorily in a model of this procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138319
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  • 3
    Electronic Resource
    Electronic Resource
    Coherent isotropic averaging in zero-field nuclear magnetic resonance. II. Cubic sequences and time-reversal of spin couplings (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 3982-3997 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a special case of the theory of coherent isotropic averaging in zero-field NMR, given in part I of this work. In a zero external field, combinations of the magnetic-field pulses restricted to π/2 rotations along the three coordinate axes can selectively average internal spin Hamiltonians while preserving the intrinsic invariance of the spectrum with respect to the sample orientation. Compared with the general case, the limits of the allowed scaling factors of first- and second-rank interactions are slightly reduced. For instance, time reversal is possible for second-rank tensors with a −1/5 scaling factor, instead of −1/4 in general. Finite pulse compensations are analyzed and experimental illustrations are given for two optimum time-reversal sequences. The cubic sequences, though less efficient than the icosahedral sequences, are technically more feasible and may be used in zero-field experiments such as decoupling (by rank or nuclear species), time reversal or multipolar experiments (the zero-field equivalent of multiple-quantum NMR). © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469585
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  • 4
    Electronic Resource
    Electronic Resource
    Coherent isotropic averaging in zero-field nuclear magnetic resonance. I. General theory and icosahedral sequences (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 3966-3981 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a general theory of coherent isotropic averaging in nuclear magnetic resonance (NMR). In a zero external field, magnetic-field pulses can selectively average the internal spin Hamiltonians, while preserving the intrinsic invariance of the spectrum with respect to the sample orientation. The theory predicts the limits of the scaling factors for tensor interactions of different ranks. Time reversal is found to be possible for first- and second-rank tensors with scaling factors of −1/3 and −1/4, respectively. Explicit sequences, based on icosahedral symmetry, are given for a number of optimal scaling factors. To illustrate the theory, an experiment is also presented in the special case of rank-selective decoupling. As in high-field NMR, applications can be expected from the introduction of coherent averaging schemes for zero-field techniques: for example, decouplings (by rank or nuclear species), time reversal, and multipolar experiments (zero-field analog of multiple-quantum NMR). © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469584
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  • 5
    Electronic Resource
    Electronic Resource
    Novel “ship-in-the-bottle” type catalyst: evidence for encapsulation of 12-tungstophosphoric acid in the supercage of synthetic faujasite (1996)
    Springer
    Catalysis letters 39 (1996), S. 27-31 
    Details
    ISSN: 1572-879X
    Keywords: heteropolyacid in zeolite ; faujasite with H3PW12O40 ; encapsulation of H3PW12O40 in faujasite ; m-xylene conversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new type of “ship-in-the-bottle” catalyst has been obtained by encapsulation of heteropolyacid H3PW12O40 in the supercage of faujasite. As shown by XRD and IR, the structure of zeolite Y after encapsulation is retained.31P MAS NMR reveals that the signal at −14.4 ppm, assigned to the Keggin unit, is in the case of the encapsulated catalyst much broader than the line observed for a sample containing the heteropolyacid adsorbed on the zeolite. The broadening is due to interaction between phosphorus and aluminium from zeolite. Highly active catalysts are formed by encapsulation, as exemplified here by strongly increased activity and modified selectivity in isomerization and disproportionation ofm-xylene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00813725
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  • 6
    Electronic Resource
    Electronic Resource
    Heterogenization of 12-tungstophosphoric acid on stabilized zeolite Y (2000)
    Springer
    Topics in catalysis 11-12 (2000), S. 391-400 
    Details
    ISSN: 1572-9028
    Keywords: 12-tungstophosphoric acid ; dealuminated faujasite ; 31P MAS NMR ; 29Si MAS NMR ; 27Al MAS NMR ; m-xylene transformation ; liquid-phase oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 12-tungstophosphoric acid (PW12) has been supported on dealuminated zeolite Y, containing a secondary pore system with the predominant pore radii of 15 Å. The interaction between the heteropolyacid and the zeolite matrix has been studied using 29Si, 27Al and 31P MAS NMR. Distribution of two types of the Keggin anions, strongly and weakly interacting with the support, has been estimated quantitatively. Increased acidic properties of the PW12/zeolite Y system were demonstrated by a change in the selectivity pattern of m-xylene transformations in the gas phase (significantly increased dealkylation and transalkylation paths at the expense of isomerization). Redox properties were evaluated in oxidation reactions with H2O2 in the liquid phase. It has been shown that the PW12/zeolite Y catalysts can selectively oxidize a number of organic compounds at relatively low temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1027213512038
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  • 7
    Electronic Resource
    Electronic Resource
    A comparison of the3He melting curve,T c(P) curve, and the susceptibility of lanthanum-diluted cerium magnesium nitrate below 50 mK (1985)
    Springer
    Journal of low temperature physics 60 (1985), S. 57-72 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The ac susceptibility of lanthanum-diluted cerium magnesium nitrate has been compared to the temperature scales as derived from the (P, T) relation determined by Halperin and that was measured recently by Greywall. It is found that the susceptibility does not obey a simple Curie-Weiss law over the temperature range between 1 and 50 mK. The results of these calibrations are also used to determine the temperatures for the second-order phase transitions into the superfluid phases of3He at several pressures. TheseT c(P) values are compared to results of earlier experiments that used thermometry based on the susceptibility of platinum as well as other thermometry techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00681653
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