191 research outputs found
Screening magnetic fields by a superconducting disk: a simple model
We introduce a simple approach to evaluate the magnetic field distribution
around superconducting samples, based on the London equations; the elementary
variable is the vector potential. This procedure has no adjustable parameters,
only the sample geometry and the London length, , determine the
solution. The calculated field reproduces quantitatively the measured induction
field above MgB disks of different diameters, at 20K and for applied fields
lower than 0.4T. The model can be applied if the flux line penetration inside
the sample can be neglected when calculating the induction field distribution
outside the superconductor. Finally we show on a cup-shape geometry how one can
design a magnetic shield satisfying a specific constraint
Power processing unit for hall-effect thrusters on "Meteor-M №3 spacecraf"
The development results of power processing unit (PPU-M) for hall-effect thrusters on "Meteor-M №3" spacecraft are considered. The structure, weight, dimensions and main technical characteristics of the system in the paper are presented. The work peculiarity of the system is unstable input voltage of both power bus and control bus that increases the ripple voltages and currents at the input and the output and causes the additional requirements to the circuit design. A comparative analysis of the system characteristics and European analogs was carried out, and then a conclusion on the basis of available data that the characteristics of the system are not inferior to European analogs was mad
Enhanced thermoelectric performance in spark plasma textured bulk n-type BiTe2.7Se0.3 and p-type Bi0.5Sb 1.5Te3
Bulk p and n-type bismuth tellurides were prepared using spark plasma texturization method. The texture development along the uniaxial load in the 001 direction is confirmed from both x-ray diffraction analysis and electron backscattering diffraction measurements. Interestingly, those textured samples outperform the samples prepared by conventional spark plasma sintering (SPS) leading to a reduced thermal conductivity in the ab-plane. The textured samples of n-type BiTe2.7Se0.3 and p-type Bi0.5Sb 1.5Te3 showed a 42% and 33% enhancement in figure of merit at room temperature, respectively, as compared to their SPS counterparts, opening the route for applications. © 2013 AIP Publishing LLC
The decrease of the critical current of coated conductors when a perpendicular magnetic field is applied : a Josephson effect point of view
A large decrease is observed in the critical current density of YBCO coated
conductors (CC) and related compounds when a strong perpendicular magnetic
field is applied. While measurements are generally carried out at 77K only,
here we present a magnetic technique permitting to determine the critical
current per unit width of conductor (Icr/w) in a large temperature range. We
report measurements carried out on various CCs that show that, in addition to
the reduction in the critical temperature that can be attributed to the low
value of the irreversibility field near Tc, the field application results in a
large decrease of Icr/w at all temperatures. We ascribe this reduction to the
Josephson behaviour of the twin boundaries included in the YBCO layer
ОБЗОР СЕМАНТИКИ ЯЗЫКА HTML 5
HTML5 несет в себе множество изменений разного уровня и разной важности. Принципиально, ключевые изменения можно разделить на 5 блоков: семантика, мультимедиа, динамичная графика, веб-формы, JavaScript APls. В данной статье рассмотрен обзор семантики HTML5 в котором появился ряд новых семантических тегов, позволяющих более осмысленно организовывать внутреннюю структуру веб-страни
Strongly correlated properties of the thermoelectric cobalt oxide Ca3Co4O9
We have performed both in-plane resistivity, Hall effect and specific heat
measurements on the thermoelectric cobalt oxide CaCoO. Four
distinct transport regimes are found as a function of temperature,
corresponding to a low temperature insulating one up to 63 K,
a strongly correlated Fermi liquid up to 140 K, with
and , followed
by an incoherent metal with and a high temperature insulator above
T510 K . Specific heat Sommerfeld coefficient
mJ/(mol.K) confirms a rather large value of the electronic effective mass
and fulfils the Kadowaki-Woods ratio 10 . Resistivity measurements under pressure reveal a
decrease of the Fermi liquid transport coefficient A with an increase of
as a function of pressure while the product remains constant and
of order . Both thermodynamic and transport properties suggest a strong
renormalization of the quasiparticles coherence scale of order that seems
to govern also thermopower.Comment: 5 pages, 6 figures, accepted for publication in Physical Review
Screening magnetic fields by superconductors: A simple model
We introduce a simple approach to evaluate the magnetic field distribution around superconducting samples, based on the London equations; the elementary variable is the vector potential. This procedure has no
adjustable parameters, only the sample geometry and the London length
determine the solution. This approach was validated by comparing the induction field calculated to the one measured above MgB2 disks of different diameters, at 20K and for applied fields lower than 0.4T. The model can be applied if the flux line penetration inside the sample can be neglected when calculating the induction field distribution outside the superconductor. We conclude by showing on a cup-shape geometry how one can design a magnetic shield satisfying a specific constraint
Modification of the trapped field in bulk high-temperature superconductors as a result of the drilling of a pattern of artificial columnar holes
The trapped magnetic field is examined in bulk high-temperature
superconductors that are artificially drilled along their c-axis. The influence
of the hole pattern on the magnetization is studied and compared by means of
numerical models and Hall probe mapping techniques. To this aim, we consider
two bulk YBCO samples with a rectangular cross-section that are drilled each by
six holes arranged either on a rectangular lattice (sample I) or on a centered
rectangular lattice (sample II). For the numerical analysis, three different
models are considered for calculating the trapped flux: (i), a two-dimensional
(2D) Bean model neglecting demagnetizing effects and flux creep, (ii), a 2D
finite-element model neglecting demagnetizing effects but incorporating
magnetic relaxation in the form of an E-J power law, and, (iii), a 3D finite
element analysis that takes into account both the finite height of the sample
and flux creep effects. For the experimental analysis, the trapped magnetic
flux density is measured above the sample surface by Hall probe mapping
performed before and after the drilling process. The maximum trapped flux
density in the drilled samples is found to be smaller than that in the plain
samples. The smallest magnetization drop is found for sample II, with the
centered rectangular lattice. This result is confirmed by the numerical models.
In each sample, the relative drops that are calculated independently with the
three different models are in good agreement. As observed experimentally, the
magnetization drop calculated in the sample II is the smallest one and its
relative value is comparable to the measured one. By contrast, the measured
magnetization drop in sample (1) is much larger than that predicted by the
simulations, most likely because of a change of the microstructure during the
drilling process.Comment: Proceedings of EUCAS 09 conferenc
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