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  • 11
    Electronic Resource
    Electronic Resource
    Percolating cermet thin-film thermistors between 50 mK–300 K and 0–20 T (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4760-4762 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cermet thin-film resistors consisting of roughly 50-A(ring) Pt or Mo particles in Al2O3 at compositions just below the percolation transition provide a number of useful features for thermometry. These include: continuous sensitivity from at least 50 mK to 300 K, adjustable temperature dependence, low heat capacity, small size, excellent stability, and a saturable magnetoresistance. The fabrication, microstructure, and temperature dependence of the resistance and magnetoresistance of these materials are described. We find poor agreement with existing theories of conduction in granular materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341192
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  • 12
    Electronic Resource
    Electronic Resource
    Macroscopic quantum tunneling in single domain magnetic particles (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 4234-4236 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Since the 1950's there have been a number of experimental observations involving small single domain (SD) magnetic particles ((approximately-less-than)200 A(ring) diameter) which have been attributed to what we'd today call "macroscopic quantum tunneling'' (MQT) of the magnetization in its switching from one easy axis direction to another. A comprehensive study of this phenomenon is not only of great interest for the sake of fundamental physics: It is of utmost practical importance in that MQT sets a limit on the lifetime of information storage on magnetic tapes and films. In this paper we present a brief summary of some of the latest results of our theoretical and experimental studies of this phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340216
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  • 13
    Electronic Resource
    Electronic Resource
    High magnetic field corrections to resistance thermometers at low temperatures (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 2026-2030 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a reliable method to account for the magnetoresistance of resistance sensors which are used as thermometers in many low temperature (T≤20 K) experiments carried out in high magnetic fields (to 31 T). To apply the method, a set of isothermal magnetoresistance data, and a zero magnetic field temperature calibration are first necessary. A simple algorithm, which uses this data set, can then be applied to compute the temperature from the measured resistance at any field. The method is particularly useful for temperature dependent measurements at fixed field, or where, in cases where the temperature may change unpredictably during a change in magnetic field. We apply this method to the treatment of data in two separate experiments with the two different thermometers, RuO2 (below 1 K) and Cernox (above 1 K) sensors, respectively. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149705
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  • 14
    Electronic Resource
    Electronic Resource
    Uniaxial stress method for delicate crystals: Application to Shubnikov–de Haas and superconductivity studies in organic conductors (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1061-1064 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method to measure the resistance of fragile single crystals under high uniaxial stress is reported. To compensate for its natural brittleness, the crystal is embedded in epoxy, whose shape is optimized to sustain the stress. This method was used to study the magnetoresistance of (BEDT-TTF)2KHg(SCN)4 at low temperatures and high magnetic fields and the superconducting transition temperature of (BEDT-TTF)2Cu(NCS)2 under uniaxial stress perpendicular to the planes of BEDT-TTF molecules. The results obtained indicate a high degree of homogeneity of the stress in the crystal and comparison with previous hydrostatic pressure measurements reveal the true uniaxial nature of the stress applied. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146046
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  • 15
    Electronic Resource
    Electronic Resource
    Tunnel diode oscillator application to high sensitivity de Haas–van Alphen and superconducting critical field studies of anisotropic organic conductors (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 3248-3251 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report the first application of a tunnel diode circuit to investigate the de Haas–van Alphen effect and superconducting critical field values in small single crystal organic conductors. The materials of interest are in the family of charge transfer salts (BEDT-TTF)2X, where X is one of a number of anion structures. Small (≤1 mm3) oriented single crystal samples were placed inside the inductance coil of the LC tank circuit of the oscillator, and measurements were carried out at low temperatures and in high magnetic fields. We observe a marked improvement over previous magnetic methods for the determination of both de Haas–val Alphen signals and for critical field studies. The method is applicable where such information is required for very small samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144336
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  • 16
    Electronic Resource
    Electronic Resource
    New opportunities in science, materials, and biological systems in the low-gravity (magnetic levitation) environment (invited) (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6194-6199 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We discuss new opportunities that present themselves with the advent of very high magnetic field resistive magnets with appreciable central bore access. A detailed description of the parameters of the magnetic force environment for the case of diamagnetic materials in a water-cooled Bitter-type resistive magnet is provided for the reader who may have an interest in low-gravity experiments. We discuss emerging research activities involving novel uses of magnetic forces in high field resistive magnets at the National High Magnetic Field Laboratory. Particular attention is given to the area of diamagnetic materials that allow a low or "zero" gravity state, i.e., magnetic levitation. These include studies involving plant growth, protein crystallization, and dynamics of single particles and granular materials. In the latter case, unique aspects of the magnetic force environment allow low gravity experiments on particulates that cannot be performed on the Space Shuttle due to the lack of a weak confining potential in space. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372653
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  • 17
    Electronic Resource
    Electronic Resource
    Specific heat measurements of pressure-induced reentrant superconductivity in Eu0.9Ho0.1Mo6S8 (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1886-1891 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Specific heat measurements of Eu0.9Ho0.1Mo6S8 were performed using an ac calorimetry technique under the extreme conditions of low temperature, high magnetic field, and hydrostatic pressure. The title compound is a Chevrel phase material, which is paramagnetic at ambient pressure, becomes superconducting for pressures above 7 kbar, and has a reentrant upper critical field [dHc2(T)/dT≥0, as T→0 K]. Evidence that this material also has a high magnetic field-induced superconducting phase at low temperatures (H≥5 T, T≤1 K) was previously reported. The present ac calorimetry study carried out for 0.15≤T≤6 K, 0≤H≤20 T, and P(approximately-equal-to)8 kbar, shows a sharp superconducting transition for T≤1 K in the specific heat, which broadens at higher fields and temperatures. The results are analyzed to obtain a reentrant phase diagram in agreement with previous transport work, but direct evidence for the high field-induced phase was not found. The mechanism for the field and temperature dependence of the superconductivity of Eu0.9Ho0.1Mo6S8 is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353176
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  • 18
    Electronic Resource
    Electronic Resource
    The role of added polymer in dilute lamellar surfactant phases (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 5467-5480 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study theoretically the effect of adding polymer to the dilute lamellar phase of surfactant solutions. The polymer, assumed semidilute and in a good solvent, is taken to have a repulsive or attractive interaction with surfactant bilayers, but has no other effect on their properties. Such polymers can mediate an attractive or repulsive interaction between bilayers which we combine with pre-existing interactions (the Helfrich repulsion, van der Waals, and hydration) using a simple additive model. The polymeric contribution to the free energy is estimated using a blob model (for nonadsorbing chains) and the Cahn–de Gennes scaling functional (for adsorbing chains). Phase diagrams for the system are obtained under various conditions. For a lamellar phase which is bound (i.e., which cannot be indefinitely diluted) as a result of van der Waals forces, nonadsorbing polymer is completely expelled as a semidilute solution, leading to a compression of the lamellar stack. Adsorbing polymer can enter the phase, also tending to cause a slight reduction in the maximum layer spacing. For an unbound lamellar phase controlled by Helfrich forces, nonadsorbing polymer is expelled if the bilayers are stiff, but for flexible enough layers, a significant amount of polymer can be solubilized. At too high a volume fraction of polymer, part of the polymer is expelled as a solution, whereas at high surfactant fractions, a phase separation arises between two lamellar phases (one containing polymer, the other not). For the case of adsorbing chains, small amounts of added polymer cause the system to become bound with expulsion of excess solvent. For large amounts of added polymer, the unbound behavior is recovered, whereas for intermediate polymer content, phase equilibria involve either two lamellar phases (each containing polymer), or one such phase coexisting with a polymer solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465964
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  • 19
    Electronic Resource
    Electronic Resource
    Sheath superheat transmission due to redeposition of thermally emitted material (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2565-2570 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A self-consistent three-dimensional numerical analysis using the newly developed BPHI-3D code was performed for the Debye/magnetic tokamak-type oblique incidence magnetic field sheath, with near-surface ionization and transport of thermally emitted surface material. The analysis uses Monte Carlo, kinetic treatment for deuterium–tritium and impurity ions/neutrals, Boltzmann/guiding-center electrons, and particle-in-cell time-independent Poisson solver. For typical predicted fusion edge plasma conditions for a liquid lithium divertor most evaporated lithium atoms—from a ∼1 cm2 overheated spot–are ionized in the ∼1 mm-wide magnetic sheath. These ions are strongly redeposited due to the sheath electric field. While this redeposition minimizes core plasma contamination, it increases the peak heat flux to the surface. A runaway situation is then possible due to superheating/evaporation positive feedback. Carbon may behave likewise as seen in code results obtained for a TORE SUPRA [Aymar et al., Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1989)] carbon limiter. A semianalytic formula for sheath parameters as a function of emitted surface material flux is developed and verified with the code. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874097
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  • 20
    Electronic Resource
    Electronic Resource
    Analysis of the tokamak sheath region with in-sheath ionization and transport of surface emitted particles (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3607-3613 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A self-consistent numerical analysis has been performed of the oblique incidence magnetic field tokamak sheath, with in-sheath ionization and transport of surface desorbed and reflected hydrogen molecules and atoms, and sputtered and evaporated surface atoms. The analysis uses the newly developed bphi Monte Carlo/cloud-in-cell kinetic code together with particle–surface interaction models. For typical plasma boundary conditions (Te=100 eV, ne=1×1020 m−3), nearly all desorbed hydrogen molecules are ionized in the sheath; this lowers sheath potential by up to 30% and increases heat transmission by up to 150%. Backscattered hydrogen, and elastic collisions between primary ions and hydrogen molecules, in contrast, have a negligible effect on sheath parameters. The magnetic sheath region has a significant effect on sputtered tungsten atoms, resulting in high local redeposition, but is not itself changed by the sputtering. Ionization of thermally evaporated surface atoms (from overheating) can increase sheath heat transmission significantly, a process which may contribute to surface hot-spot formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870896
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