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  • 1
    Electronic Resource
    Electronic Resource
    A modified dual-slope method for heat capacity measurements of condensable gases (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3841-3845 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high resolution nonadiabatic method for measuring the heat capacity (CP) of bulk samples of condensable gases in the range of 7.5–70 K is described. In this method CP is evaluated by directly comparing the heating and cooling rates of the sample temperature for two algebraically independent heat pulse sequences without explicit use of the thermal conductance between sample and thermal bath. A fully automated calorimeter for rapid measurement of CP of molecular solids utilizing this technique is presented. The technique along with the automated calorimeter with a provision to apply external electric and magnetic fields is particularly useful for the study of continuous phase transitions in molecular solids as well as field induced changes in the heat capacity. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290040
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  • 2
    Electronic Resource
    Electronic Resource
    Very high sensitivity ac capacitance bridge for the dielectric study of molecular solids at low temperatures (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 4055-4058 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An ac capacitance bridge with excellent stability and two parts per billion resolution in the real part of the dielectric constant at temperatures ranging from 4.2 to 80 K and in the audio frequency range (0.2–20 kHz) is reported. The method uses commercially available components as well as few homemade cables and capacitors. Construction details and data on the resolution are presented. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150035
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  • 3
    Electronic Resource
    Electronic Resource
    Ultralow power low noise ultrahigh frequency magnetic resonance spectrometer (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 157-162 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a simple marginal oscillator that operates at ultralow power dissipation (≥20 μW at 750 MHz) for use in ultrasensitive low noise magnetic resonance detection at very low temperatures. We have operated the circuit down to 0.6 K with the sample maintained below 20 mK and in magnetic fields up to 4.0 T. The samples are maintained at mK temperatures by physically separating the sample from the rf coil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142980
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  • 4
    Electronic Resource
    Electronic Resource
    Measurements of the nuclear spin-lattice relaxation times in BCC3He for high magnetic fields, high molar volumes, and low temperatures (1985)
    Springer
    Journal of low temperature physics 59 (1985), S. 45-81 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Experimental studies of the nuclear spin-lattice relaxation times in BCC helium three are reported for high molar volumes and low temperatures close to the minimum in the melting curve. The results show the existence of a new relaxation mechanism at low temperatures with an approximately linear temperature dependence (T 1 ∝T −1). An analysis of the vacancy-induced relaxation shows that both the vacancy formation energy and the vacancy mobility decrease dramatically as a function of density on approaching the maximum possible molar volume (minimum density) of the solid. A possible interpretation of both the new relaxation mechanism and the vacancy properties is outlined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00681504
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  • 5
    Electronic Resource
    Electronic Resource
    The Orientational Ordering of Molecular Hydrogen in 2D (2000)
    Springer
    Journal of low temperature physics 120 (2000), S. 89-106 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The orientational ordering of ortho-hydrogen molecules on a triangular lattice is calculated as a function of ortho concentration using the method of restricted traces. The calculated temperatures for the transitions from the disordered phase to the long range pinwheel ordered phase show a strong concentration dependence with a critical concentration X c=73% below which the long range ordering is not realized in this model. The results are consistent with recent NMR studies of ortho-para hydrogen mixtures adsorbed as a commensurate $$\sqrt 3 $$ × $$\sqrt 3 $$ structure on hexagonal boron nitride for which X c=69±4%. The values of the observed transition temperatures can only be understood if there is a large renormalization of the effective quadrupolar interaction constant in 2D.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004660919750
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  • 6
    Electronic Resource
    Electronic Resource
    Spectral inhomogeneity of nuclear spin-lattice relaxation in orientationally ordered solid hydrogen (1986)
    Springer
    Journal of low temperature physics 65 (1986), S. 1-11 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The results of calculations of the nuclear spin-lattice relaxation time of orientationally ordered ortho-hydrogen molecules for the case of the local ordering in the orientational “glass” phase of ortho-para-hydrogen mixtures are given. A strong dependence on the position of the NMR isochromat in the line shape is found and this is in good agreement with the experimental results of the Duke group, provided that the cross-relaxation is taken into account. The relaxation is found to deviate considerably from an exponential recovery.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00685399
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  • 7
    Electronic Resource
    Electronic Resource
    Coupling of the Nuclear Spin Alignment of Quadrupolar Nuclei to 3He at Interfaces (1998)
    Springer
    Journal of low temperature physics 113 (1998), S. 323-328 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Measurements of the relaxation of nuclear spin alignments have been carried out using NQR spin echo studies of powdered antimony in contact with liquid 3 He. This system differs from previous studies of the relaxation and magnetization coupling of 3 He at surfaces because the magnetizations 〈 S z 〉≃ 0. The spin alignments 〈 S z 2 〉 are the relevant dynamical variables. The analysis of the experimental results shows that the coupling of the nuclear spin alignment of the antimony nuclei to the magnetization of the 3 He nuclei is determined by the spectral density of the fluctuations of the spin-spin dipolar couplings at the interface. This power density is attributed to the zero-point motions (atom-atom and atom-vacancy exchange) of the 3 He atoms on the surface of the metal particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022558919066
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  • 8
    Electronic Resource
    Electronic Resource
    The Orientational Ordering in Dilute Solid N2–Ar Mixtures (1998)
    Springer
    Journal of low temperature physics 111 (1998), S. 365-370 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract NMR studies have been carried out to determine the nature of the orientational ordering of N 2 in dilute solid N 2–Ar mixtures. The orientational ordering for cubic lattices (x(N 2)≍50%) was compared to that observed for the hexagonal lattice structures for 57 〈 x(N 2) 〈 75%. The NMR line shapes for the cubic structures were found to be sharply defined and could only be explained in terms of a narrow distribution of order parameters. This is in contrast to the quadrupolar glass state with a very broad order parameter distribution observed for the hexagonal structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022287720183
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  • 9
    Electronic Resource
    Electronic Resource
    Experimental studies of hydrogen on boron nitride: I. Adsorption isotherms of HD (1995)
    Springer
    Journal of low temperature physics 100 (1995), S. 535-549 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report the results of measurements of adsorption isotherms of deuterium hydride (HD) adsorbed onto boron nitride. From this data we derive both the two-dimensional critical point temperatures (using Larher's method) and the heat of adsorption for the first few layers of this system. These results are compared with similar measurements of HD adsorbed onto graphite and MgO. While substantial substeps within some adlayer steps are evident in the adsorption isotherms of HD on graphite and MgO and have been shown to indicate a two-dimensional liquid-solid transition within the layer, no substep is evident at the level of one percent of a step level for HD adsorbed onto BN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00751524
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  • 10
    Electronic Resource
    Electronic Resource
    Experimental studies of hydrogen on boron nitride: II. NMR studies of orientational ordering of H2 (1995)
    Springer
    Journal of low temperature physics 100 (1995), S. 551-574 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report the results of NMR studies of thin films of hydrogen adsorbed on hexagonal boron nitride. Orientational ordering is observed below 1 K but the ordering is not complete, and a clear two-component ordering is observed. Molecules are either (i) almost completely ordered with local order parameters σ = 〈1 − 3/2Jz 2〉 clustered close to a maximum value of a σ ≅0.94 (comparable to the values for long range ordering in bulk samples at high ortho concentrations), and (ii) a large fraction of the molecules that remain nearly disordered with σ ⩽ 0.25. The degree of Orientational ordering depends on the number of hydrogen layers and on the ortho-hydrogen concentration, and these studies indicate that ordering occurs principally in the first four layers closest to the substrate, with weaker Orientational ordering in the outer layers near the free surface even at temperatures as low as 210 mK.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00751525
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