99,399 research outputs found
A concentrator for static magnetic field
We propose a compact passive device as a super-concentrator to create an
extremely high uniform static magnetic field over 50T in a large
two-dimensional free space from a weak background magnetic field. Such an
amazing thing becomes possible for the first time, thanks to space-folded
transformation and metamaterials for static magnetic fields. Finite element
method (FEM) is utilized to verify the performance of the proposed device
Transforming magnets
Based on the form-invariant of Maxwell's equations under coordinate
transformations, we extend the theory of transformation optics to
transformation magneto-statics, which can design magnets through coordinate
transformations. Some novel DC magnetic field illusions created by magnets
(e.g. shirking magnets, cancelling magnets and overlapping magnets) are
designed and verified by numerical simulations. Our research will open a new
door to designing magnets and controlling DC magnetic fields
Unchanged thermopower enhancement at the semiconductor-metal transition in correlated FeSbTe
Substitution of Sb in FeSb by less than 0.5% of Te induces a transition
from a correlated semiconductor to an unconventional metal with large effective
charge carrier mass . Spanning the entire range of the semiconductor-metal
crossover, we observed an almost constant enhancement of the measured
thermopower compared to that estimated by the classical theory of electron
diffusion. Using the latter for a quantitative description one has to employ an
enhancement factor of 10-30. Our observations point to the importance of
electron-electron correlations in the thermal transport of FeSb, and
suggest a route to design thermoelectric materials for cryogenic applications.Comment: 3 pages, 3 figures, accepted for publication in Appl. Phys. Lett.
(2011
Quantum Thermalization With Couplings
We study the role of the system-bath coupling for the generalized canonical
thermalization [S. Popescu, et al., Nature Physics 2,754(2006) and S. Goldstein
et al., Phys. Rev. Lett. 96, 050403(2006)] that reduces almost all the pure
states of the "universe" [formed by a system S plus its surrounding heat bath
] to a canonical equilibrium state of S. We present an exactly solvable, but
universal model for this kinematic thermalization with an explicit
consideration about the energy shell deformation due to the interaction between
S and B. By calculating the state numbers of the "universe" and its subsystems
S and B in various deformed energy shells, it is found that, for the
overwhelming majority of the "universe" states (they are entangled at least),
the diagonal canonical typicality remains robust with respect to finite
interactions between S and B. Particularly, the kinematic decoherence is
utilized here to account for the vanishing of the off-diagonal elements of the
reduced density matrix of S. It is pointed out that the non-vanishing
off-diagonal elements due to the finiteness of bath and the stronger
system-bath interaction might offer more novelties of the quantum
thermalization.Comment: 4 pages, 2 figure
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Urban storage heat flux variability explored using satellite, meteorological and geodata
The storage heat flux (ÎQS) is the net flow of heat stored within a volume that may include the air, trees, buildings and ground. Given the difficulty of measurement of this important and large flux in urban areas, we explore the use of Earth Observation (EO) data. EO surface temperatures are used with ground-based meteorological forcing, urban morphology, land cover and land use information to estimate spatial variations of ÎQS in urban areas using the Element Surface Temperature Method (ESTM). First, we evaluate ESTM for four âsimplerâ surfaces. These have good agreement with observed values. ESTM coupled to SUEWS (an urban land surface model) is applied to three European cities (Basel, Heraklion, London), allowing EO data to enhance the exploration of the spatial variability in ÎQS. The impervious surfaces (paved and buildings) contribute most to ÎQS. Building wall area seems to explain variation of ÎQS most consistently. As the paved fraction increases up to 0.4, there is a clear increase in ÎQS. With a larger paved fraction, the fraction of buildings and wall area is lower which reduces the high values of ÎQS
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