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Dielectric spectroscopy study of thermally-aged extruded model power cables
“Model” extruded power cables, having a much reduced geometry but using the same extrusion techniques and materials as full-sized cables, have been examined using dielectric spectroscopy techniques to study their thermal ageing effects. Cables insulated with homo-polymer XLPE and co-polymer of XLPE with micron-sized ethylene-butyl-acrylate (EBA) islands were studied by both frequency-domain and time-domain dielectric spectroscopy techniques after accelerated thermal ageing under 135°C for 60 days. In the frequency domain, a frequency response analyzer (FRA) was used to measure the frequency range from 10-4Hz to 1Hz at temperatures from 20°C to 80°C. In the time domain, a special charging/discharging current measurement system was developed to measure the frequencies from 10-1Hz to 102Hz. These techniques were chosen to cope with the extremely low dielectric losses of the model cables. The results are compared with those from new model power cables that were degassed at 80°C for 5 days. Thermal ageing was found to increase the low-frequency conductivity, permittivity and the discharging current. Both homo- and co-polymer cables have substantial increase of dielectric loss after ageing
Quantum Brayton cycle with coupled systems as working substance
We explore the quantum version of Brayton cycle with a composite system as
the working substance. The actual Brayton cycle consists of two adiabatic and
two isobaric processes. Two pressures can be defined in our isobaric process,
one corresponds to the external magnetic field (characterized by ) exerted
on the system, while the other corresponds to the coupling constant between the
subsystems (characterized by ). As a consequence, we can define two types
of quantum Brayton cycle for the composite system. We find that the subsystem
experiences a quantum Brayton cycle in one quantum Brayton cycle (characterized
by ), whereas the subsystem's cycle is of quantum Otto in another Brayton
cycle (characterized by ). The efficiency for the composite system equals
to that for the subsystem in both cases, but the work done by the total system
are usually larger than the sum of work done by the two subsystems. The other
interesting finding is that for the cycle characterized by , the subsystem
can be a refrigerator while the total system is a heat engine. The result in
the paper can be generalized to a quantum Brayton cycle with a general coupled
system as the working substance.Comment: 7 pages, 3 figures, accepted by Phys. Rev.
Spin-dependent correlation in two-dimensional electron liquids at arbitrary degeneracy and spin-polarization: CHNC approach
We apply the classical mapping technique developed recently by Dharma-wardana
and Perrot for a study of the uniform two-dimensional electron system at
arbitrary degeneracy and spin-polarization. Pair distribution functions,
structure factors, the Helmhotz free energy, and the compressibility are
calculated for a wide range of parameters. It is shown that at low temperatures
T/ T_F <0.1, T_F being the Fermi temperature, our results almost reduce to
those of zero-temperature analyses. In the region T/ T_F >= 1, the finite
temperature effects become considerable at high densities for all
spin-polarizations. We find that, in our approximation without bridge
functions, the finite temperature electron system in two dimensions remains to
be paramagnetic fluid until the Wigner crystallization density. Our results are
compared with those of three-dimensional system and indicated are the
similarities in temperature, spin-polarization, and density dependencies of
many physical properties.Comment: 8 pages, 9 figure
The Equation of State and the Hugoniot of Laser Shock-Compressed Deuterium
The equation of state and the shock Hugoniot of deuterium are calculated
using a first-principles approach, for the conditions of the recent shock
experiments. We use density functional theory within a classical mapping of the
quantum fluids [ Phys. Rev. Letters, {\bf 84}, 959 (2000) ]. The calculated
Hugoniot is close to the Path-Integral Monte Carlo (PIMC) result. We also
consider the {\it quasi-equilibrium} two-temperature case where the Deuterons
are hotter than the electrons; the resulting quasi-equilibrium Hugoniot mimics
the laser-shock data. The increased compressibility arises from hot
pairs occuring close to the zero of the electron chemical potential.Comment: Four pages; One Revtex manuscript, two postscipt figures; submitted
to PR
Correlation between the Proton Conductivity and Diffusion Coefficient of Sulfonic Acid Functionalized Chitosan and Nafion Composites via Impedance Spectroscopy Measurements
Étude de la corrosion du cuivre par microélectrochimie: Comparaison entre microélectrode et microcellule
Ce travail présente la comparaison de mesures électrochimiques réalisées à l'aide d'une microcellule et de microélectrodes conventionnelles. Des mesures de voltamétrie cyclique et d’impédances électrochimiques ont été réalisées sur des électrodes de cuivre pur, électrode classique couplée à des capillaires et microélectrodes, au potentiel de corrosion dans une solution NaCl 0,1 M, La comparaison entre ces deux types de mesure apporte des informations relatives à leurs sensibilités et limitations. En particulier, le domaine des basses fréquences du diagramme d’impédance est sensible à la géométrie de la microcellule ainsi qu'au positionnement relatif des électrodes
Face Recognition based on Facial Composite
Due to the wide range of commercial and law enforcementapplications, major advances and initiatives in the past twenty years have propelled biometrics and specifically face recognition technology into the spotlight. Face images have been used for several decades to verify identities. Now, digital face images are used in many applications, including security systems and criminal identifications, as well as computer automated face recognition. Many face recognition software packages have emerged. Most of them require high quality images, others take into account the problem of images coming from low-resolution Close Circuit TeleVision, but the problem of dealing with Facial Composites remains. We will discuss the relevance of a face recognition system using Facial Composite
The Path Integral Monte Carlo Calculation of Electronic Forces
We describe a method to evaluate electronic forces by Path Integral Monte
Carlo (PIMC). Electronic correlations, as well as thermal effects, are included
naturally in this method. For fermions, a restricted approach is used to avoid
the ``sign'' problem. The PIMC force estimator is local and has a finite
variance. We applied this method to determine the bond length of H and the
chemical reaction barrier of H+HH+H. At low
temperature, good agreement is obtained with ground state calculations. We
studied the proton-proton interaction in an electron gas as a simple model for
hydrogen impurities in metals. We calculated the force between the two protons
at two electronic densities corresponding to Na () and Al
() using a supercell with 38 electrons. The result is compared to
previous calculations. We also studied the effect of temperature on the
proton-proton interaction. At very high temperature, our result agrees with the
Debye screening of electrons. As temperature decreases, the Debye theory fails
both because of the strong degeneracy of electrons and most importantly, the
formation of electronic bound states around the protons.Comment: 18 pages, 10 figure
Collective excitations in double-layer quantum Hall systems
We study the collective excitation spectra of double-layer quantum-Hall
systems using the single mode approximation. The double-layer in-phase density
excitations are similar to those of a single-layer system. For out-of-phase
density excitations, however, both inter-Landau-level and intra-Landau-level
double-layer modes have finite dipole oscillator strengths. The oscillator
strengths at long wavelengths for the latter transitions are shifted upward by
interactions by identical amounts proportional to the interlayer Coulomb
coupling. The intra-Landau-level out-of-phase mode has a gap when the ground
state is incompressible except in the presence of spontaneous inter-layer
coherence. We compare our results with predictions based on the
Chern-Simons-Landau-Ginzburg theory for double-layer quantum Hall systems.Comment: RevTeX, 21 page
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