305 research outputs found
Superconducting gap and pair breaking in CeRu2 studied by point contacts
The superconducting gap in a CeRu single crystal is investigated by
point contacts. BCS-like behavior of the gap in the temperature range
below TT, where T is the critical temperature, is
established, indicating the presence of a gapless superconductivity region
(between T and T). The pair-breaking effect of paramagnetic
impurities, supposedly Ce ions, is taken into consideration using the
Scalski-Betbeder-Matibet-Weiss approach based on Abrikosov-Gorkov theory. It
allows us to recalculate the superconducting order parameter (in the presence of paramagnetic impurities) and the gap (in
the pure case) for the single crystal and for the previously studied
polycrystalline CeRu. The value 2(0)2 meV, with
2(0)kT3.75, is found in both cases,
indicating that CeRu is a ``moderate'' strong-coupling superconductor.Comment: 4 pages incl. 3 figs., publ. in Fiz. Nizk. Temp.
(http://fnte.ilt.kharkov.ua/list.html
Quasiparticle Density of States of Clean and Dirty s-Wave Superconductors in the Vortex State
The quasiparticle density of states (DOS) in the vortex state has been probed
by specific heat measurements under magnetic fields (H) for clean and dirty
s-wave superconductors, Y(Ni1-xPtx)2B2C and Nb1-xTaxSe2. We find that the
quasiparticle DOS per vortex is appreciably H-dependent in the clean-limit
superconductors, while it is H-independent in the dirty superconductors as
expected from a conventional rigid normal electron core picture. We discuss
possible origins for our observations in terms of the shrinking of the vortex
core radius with increasing H.Comment: 5 pages, 4 figures, to appear in J. Phys. Soc. Jpn. Vol. 68 No.
Validation and reconstruction of flow meter data in the Barcelona water distribution network
12 páginas, 16 figuras, 1 tabla.-- El PDF es la versión pre-print.-- et al.This paper presents a signal analysis methodology to validate (detect) and reconstruct the missing and false data of a large set of flow meters in the telecontrol system of a water distribution network. The proposed methodology is based on two time-scale forecasting models: a daily model based on a ARIMA time series, while the 10-min model is based on distributing the daily flow using a 10-min demand pattern. The demand patterns have been determined using two methods: correlation analysis and an unsupervised fuzzy logic classification, named LAMDA algorithm. Finally, the proposed methodology has been applied to the Barcelona water distribution network, providing very good results.This work is part of a applied research project granted by ADASA and AGBAR companies. The authors also wish to thank the support received by the Research Commission of the Generalitat of Catalunya (Group SAC Ref. 2009 SGR 1491) and by CICYT (Ref. HYFA DPI2008-01996 and WATMAN DPI2009-13744) of Spanish Ministry of Education.Peer reviewe
Validation and reconstruction of flow meter data in the Barcelona water distribution network
This paper presents a signal analysis methodology to validate (detect) and reconstruct the missing and false data of a large set of flow meters in the telecontrol system of a water distribution network. The proposed methodology is based on two time-scale forecasting models: a daily model based on a ARIMA time series, while the 10-min model is based on distributing the daily flow using a 10-min demand pattern. The demand patterns have been determined using two methods: correlation analysis and an unsupervised fuzzy logic classification, named LAMDA algorithm. Finally, the proposed methodology has been applied to the Barcelona water distribution network, providing very good results.Peer ReviewedPostprint (author’s final draft
Positive and negative pressure effects on the magnetic ordering and the Kondo effect in the compound Ce2RhSi3
The competition between magnetic ordering and the Kondo effect in Ce2RhSi3,
ordering antiferromagnetically at 7 K, is investigated by the measurements of
magnetization, heat capacity and electrical resistivity on the solid solutions,
Ce(2-x)La(x)RhSi3, Ce(2-y)Y(y)RhSi3, and Ce2RhSi(3-z)Ge(z), as well as by high
pressure studies on this compound. The trends in the Kondo and Neel temperature
variations among these alloys are compared to infer the roles of unit-cell
volume and electronic structure changes. On the basis of the results, we infer
that this compound lies at the peak of Doniach-magnetic-phase-diagram. The high
pressure electrical resistivity data indicate that the quantum critical point
for this compound is in the vicinity of 4 GPa
Assessment of Narrow-Body Transport Airplane Evacuation by Numerical Simulation
This paper presents the results obtained with a new agent-based computer model that can simulate the evacuation
of narrow-body transport airplanes in the conditions prescribed by the airworthiness regulations for certification.
The model, described in detail in a former paper, has been verified with real data of narrow-body certification
demonstrations. Numerical simulations of around 20 narrow-body aircraft, representative of current designs in
various market segments, show the capabilities of the model and provide relevant information on the relationship
between cabin features and emergency evacuation. The longitudinal location of emergency exits seems to be even
more important than their size or the overall margin with respect to the prescribed number and type of exits indicated
by the airworthiness requirement
Differential-thermal analysis around and below the critical temperature Tc of various low-Tc superconductors: A comparative study
We present specific-heat data on the type-II superconductors V3Si, LuNi2B2C
and NbSe2 which were acquired with a low-temperature thermal analysis (DTA)
technique. We compare our data with available literature data on these
superconductors. In the first part we show that the DTA technique allows for
fast measurements while providing a very high resolution on the temperature
scale. Sharp features in the specific heat such as at the one at the transition
to superconductivity are resolved virtually without instrumental broadening. In
the second part we investigate the magnetic-field dependence of the specific
heats of V3Si and LuNi2B2C at a fixed temperature T=7.5K to demonstrate that
DTA techniques also allow for sufficiently precise measurements of absolute
values of cp even in the absence of a sharp phase transition. The corresponding
data for V3Si and LuNi2B2C are briefly discussed
Entropy and Spin Susceptibility of s-wave Type-II Superconductors near
A theoretical study is performed on the entropy and the spin
susceptibility near the upper critical field of s-wave
type-II superconductors with arbitrary impurity concentrations. The changes of
these quantities through may be expressed as , for example, where is the average flux density
and denotes entropy in the normal state. It is found that the
slopes and at T=0 are identical, connected
directly with the zero-energy density of states, and vary from 1.72 in the
dirty limit to in the clean limit. This mean-free-path dependence
of and at T=0 is quantitatively the same as that
of the slope for the flux-flow resistivity studied
previously. The result suggests that and near
T=0 are convex downward (upward) in the dirty (clean) limit, deviating
substantially from the linear behavior . The specific-heat
jump at also shows fairly large mean-free-path dependence.Comment: 8 pages, 5 figure
Theory of de Haas-van Alphen Effect in Type-II Superconductors
Theory of quasiparticle spectra and the de Haas-van Alphen (dHvA) oscillation
in type-II superconductors are developed based on the Bogoliubov-de Gennes
equations for vortex-lattice states. As the pair potential grows through the
superconducting transition, each degenerate Landau level in the normal state
splits into quasiparticle bands in the magnetic Brillouin zone. This brings
Landau-level broadening, which in turn leads to the extra dHvA oscillation
damping in the vortex state. We perform extensive numerical calculations for
three-dimensional systems with various gap structures. It is thereby shown that
(i) this Landau-level broadening is directly connected with the average gap at
H=0 along each Fermi-surface orbit perpendicular to the field H; (ii) the extra
dHvA oscillation attenuation is caused by the broadening around each extremal
orbit. These results imply that the dHvA experiment can be a unique probe to
detect band- and/or angle-dependent gap amplitudes. We derive an analytic
expression for the extra damping based on the second-order perturbation with
respect to the pair potential for the Luttinger-Ward thermodynamic potential.
This formula reproduces all our numerical results excellently, and is used to
estimate band-specific gap amplitudes from available data on NbSe_2, Nb_3Sn,
and YNi_2B_2C. The obtained value for YNi_2B_2C is fairly different from the
one through a specific-heat measurement, indicating presence of gap anisotropy
in this material. C programs to solve the two-dimensional Bogoliubov-de Gennes
equations are available at http://phys.sci.hokudai.ac.jp/~kita/index-e.html .Comment: 16 pages, 11 figure
Manifestation of history-dependent critical currents via dc and ac magnetization measurements in single crystals of CeRu<SUB>2</SUB> and 2H-NbSe<SUB>2</SUB>
A study of path dependent effects in single crystals of CeRu2 and 2H-NbSe2 shows that critical current density Jc of the vortex state depends on its thermomagnetic history over a very large part of (H,T) parameter space. The path dependence in Jc is absent above the peak position (i.e., H>Hp) of the peak effect region, which we believe identifies the complete loss of order in the vortex structure. The highly disordered field cooled (FC) state can be healed into a relatively ordered vortex lattice by subjecting it to a large enough change in dc field (few tens of Oe) or by shaking the field cooled state with sufficient ac field (few Oe)
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