38 research outputs found
Point-contact Andreev reflection spectroscopy of heavy-fermion-metal/superconductor junctions
Our previous point-contact Andreev reflection studies of the heavy-fermion
superconductor CeCoIn using Au tips have shown two clear features: reduced
Andreev signal and asymmetric background conductance [1]. To explore their
physical origins, we have extended our measurements to point-contact junctions
between single crystalline heavy-fermion metals and superconducting Nb tips.
Differential conductance spectra are taken on junctions with three
heavy-fermion metals, CeCoIn, CeRhIn, and YbAl, each with different
electron mass. In contrast with Au/CeCoIn junctions, Andreev signal is not
reduced and no dependence on effective mass is observed. A possible explanation
based on a two-fluid picture for heavy fermions is proposed. [1] W. K. Park et
al., Phys. Rev. B 72 052509 (2005); W. K. Park et al., Proc. SPIE-Int. Soc.
Opt. Eng. 5932 59321Q (2005); W. K. Park et al., Physica C (in press)
(cond-mat/0606535).Comment: 2 pages, 2 figures, submitted to the SCES conference, Houston, Texas,
USA, May 13-18, 200
Overscreening Diamagnetism in Cylindrical Superconductor-Normal Metal-Heterostructures
We study the linear diamagnetic response of a superconducting cylinder coated
by a normal-metal layer due to the proximity effect using the clean limit
quasiclassical Eilenberger equations. We compare the results for the
susceptibility with those for a planar geometry. Interestingly, for
the cylinder exhibits a stronger overscreening of the magnetic field, i.e., at
the interface to the superconductor it can be less than (-1/2) of the applied
field. Even for , the diamagnetism can be increased as compared to the
planar case, viz. the magnetic susceptibility becomes smaller than
-3/4. This behaviour can be explained by an intriguing spatial oscillation of
the magnetic field in the normal layer
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Catalytic multi-stage liquefaction (CMSL)
Reported herein are the details and the results of laboratory and bench scale experiments that were conducted at Hydrocarbon Technologies, Inc. under DOE Contract No. DE-AC22-93PC92147 during the period of October 1, 1992, to December 31, 1995. The program results described herein build on the previous technology base and investigating additional methods to improve the economics of producing transportation fuels from coal. This included purely physical parameters, coal treatment and variation in solvent to coal ratio, the use of syngas to replace part of the hydrogen as the reducing gas, the use of dispersed catalyst in addition to and replacing the supported catalyst, and the co-processing of coal with plastic waste material. The overall objective of this program is to produce liquid fuels from direct coal liquefaction at a cost that is competitive with conventional fuels. The report includes the results of an economic assessment of the various process strategies that were evaluated during this program. A summary of the technical/economic evaluations is given in Volume I, Section II of this report. The experimental details of the eleven run of the program are given in Volume I, Section III and Volume II of this report. The details of the technical evaluations are given in the Volume III of the report
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Vapor-liquid equilibrium of the Mg(NO/sub 3/)/sub 2/-HNO/sub 3/-H/sub 2/O system
The vapor-liquid equilibrium of the Mg(NO/sub 3/)/sub 2/-HNO/sub 3/-H/sub 2/O system in concentrations of 0 to 70 wt % Mg(NO/sub 3/)/sub 2/ and 0 to 75 wt % HNO/sub 3/ at atmospheric pressure was correlated by two approaches. One was based on a dissociation equilibrium expression in which the activities of the reacting species (HNO/sub 3/, NO/sub 3//sup -/, and H/sup +/) were approximated with mole fractions. The activity coefficients of the undissociated HNO/sub 3/ and H/sub 2/O were correlated as functions of the concentrations of magnesium nitrate and nitric acid by second-order polynomials. The average absolute difference between predicted and experimental values was 8% for the mole fraction of acid in the vapor and 8/sup 0/K for the bubble-point temperature. The second approach was to correlate the mean ionic rational activity coefficient of water with a form of the excess Gibbs energy composed of two terms. One term, a function of the ionic strength, accounts for the coulombic (ionic) interactions; the other term accounts for the non-coulombic (molecular) interactions. The average absolute difference between predicted and experimental values was 9% for the mole fraction of acid in the vapor, and 10/sup 0/K for the bubble-point temperature
Field-screening properties of proximity-coupled
In Nb/Ag layers, the induced superconductivity in Ag by Nb gives
rise to diamagnetic screening currents in the Ag layer well below
the transition temperature of the superconductor. By investigating
the position dependence of the individual diamagnetic transitions of
Nb and Ag with a gradiometer in a nearly parallel magnetic field, we
find that the screening of the Ag layer is remarkably different
compared to the Nb layer. While for the Nb layer a strong
out-of-plane contribution is observed due to the large
demagnetization factor, such a contribution is absent for the Ag
layer. This can be explained by the partial overscreening
of the magnetic field, i.e. a reduced diamagnetic response of the Ag
layer, as suggested by the theory for the clean limit
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Catalytic multi-stage liquefaction of coal. Sixth quarterly report, 1 January 1994--31 March 1994
The overall objective of this program is to produce liquid fuels from coal by direct liquefaction at a cost that is competitive with conventional fuels. Specifically, this continuous bench-scale program contains provisions to examine new ideas in areas such as low temperature pretreatments, more effective catalysts, on-line hydrotreating, new coal feedstocks, other hydrogen sources, more concentrated coal feeds and other highly responsive process improvements while assessing the design and economics of the bench-scale results. This quarterly report covers work on Laboratory Scale Studies, Continuous Bench-Scale Operations, Technical Assessment and Project Management
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Catalytic multi-stage liquefaction of coal
This quarterly report covers activities of Catalytic Multi-Stage Liquefaction of Coal dozing the period December 8--December 31, 1992, at Hydrocarbon Research, Inc. in Lawrenceville and Princeton, New Jersey. This DOE contract period is from December 8, 1992 to December 7, 1994. The overall objective of the program is to produce liquid fuels from direct coal liquefaction at a cost that is competitive with conventional fuels. Specifically, this continuous bench-scale program examine new ideas in areas such as: low temperature pretreatments, more effective catalysts, on-line hydrotreating, new coal feedstocks, other hydrogen sources, more concentrated coal feeds and other highly responsive process improvements while assessing the design and economics of bench-scale results. The quarterly report covers work on Project Management Plan, Laboratory Scale Studies, Continuous Bench-Scale Operations, Technical Assessment and Project Management/Administration
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Catalytic multi-stage liquefaction of coal twelth quarterly report for the period 1 July 1995--30 September 1995
The overall objective of this program is to produce liquid fuels from coal by direct liquefaction at a cost that is competitive with conventional fuels. Specifically, this continuous bench-scale program contains provisions to examine new ideas in areas such as: low temperature pretreatments, more effective catalysts, on-line hydrotreating, new coal feedstocks, other hydrogen sources, more concentrated coal feeds and other highly responsive process improvements while assessing the design and economics of the bench- scale results. This quarterly report covers work on Laboratory Scale Studies, Continuous Bench-Scale Operations, Technical Assessment and Project Management