6,470 research outputs found
Current-induced synchronized switching of magnetization
We investigate current-induced magnetization switching for a multilayer
structure that allows a reduced switching current while maintaining high
thermal stability of the magnetization. The structure consists of a
perpendicular polarizer, a perpendicular free-layer, and an additional
free-layer having in-plane magnetization. When the current runs perpendicular
to the structure, the in-plane free-layer undergoes a precession and supplies
an internal rf field to the perpendicular free-layer, resulting in a reduced
switching current for one current polarity. For the other polarity, the
in-plane free-layer almost saturates perpendicular to the plane and acts as
another perpendicular polarizer, which also reduces the switching current.Comment: 18 pages, 4 figure
Pseudogap induced by short-range spin correlations in a doped Mott insulator
We study the evolution of a Mott-Hubbard insulator into a correlated metal
upon doping in the two-dimensional Hubbard model using the Cellular Dynamical
Mean Field Theory. Short-range spin correlations create two additional bands
apart from the familiar Hubbard bands in the spectral function. Even a tiny
doping into this insulator causes a jump of the Fermi energy to one of these
additional bands and an immediate momentum dependent suppression of the
spectral weight at this Fermi energy. The pseudogap is closely tied to the
existence of these bands. This suggests a strong-coupling mechanism that arises
from short-range spin correlations and large scattering rates for the pseudogap
phenomenon seen in several cuprates.Comment: 6 pages, 6 figure
Pairing dynamics in strongly correlated superconductivity
Confirmation of the phononic origin of Cooper pair formation in
superconductors came with the demonstration that the interaction was retarded
and that the corresponding energy scales were associated with phonons. Using
cellular dynamical mean-field theory for the two-dimensional Hubbard model, we
identify such retardation effects in d-wave pairing and associate the
corresponding energy scales with short-range spin fluctuations. We find which
frequencies are relevant for pairing as a function of interaction strength and
doping and show that the disappearance of superconductivity on the overdoped
side coincides with the disappearance of the low energy feature in the
antiferromagnetic fluctuations, as observed in neutron scattering experiments.Comment: LaTeX, 8 pages, 8 figure
On the intersection of tolerance and cocomparability graphs.
It has been conjectured by Golumbic and Monma in 1984 that the intersection of tolerance and cocomparability graphs coincides with bounded tolerance graphs. Since cocomparability graphs can be efficiently recognized, a positive answer to this conjecture in the general case would enable us to efficiently distinguish between tolerance and bounded tolerance graphs, although it is NP-complete to recognize each of these classes of graphs separately. The conjecture has been proved under some – rather strong – structural assumptions on the input graph; in particular, it has been proved for complements of trees, and later extended to complements of bipartite graphs, and these are the only known results so far. Furthermore, it is known that the intersection of tolerance and cocomparability graphs is contained in the class of trapezoid graphs. In this article we prove that the above conjecture is true for every graph G, whose tolerance representation satisfies a slight assumption; note here that this assumption concerns only the given tolerance representation R of G, rather than any structural property of G. This assumption on the representation is guaranteed by a wide variety of graph classes; for example, our results immediately imply the correctness of the conjecture for complements of triangle-free graphs (which also implies the above-mentioned correctness for complements of bipartite graphs). Our proofs are algorithmic, in the sense that, given a tolerance representation R of a graph G, we describe an algorithm to transform R into a bounded tolerance representation R  ∗  of G. Furthermore, we conjecture that any minimal tolerance graph G that is not a bounded tolerance graph, has a tolerance representation with exactly one unbounded vertex. Our results imply the non-trivial result that, in order to prove the conjecture of Golumbic and Monma, it suffices to prove our conjecture. In addition, there already exists evidence in the literature that our conjecture is true
Korean Ikat
Imagine yourself without a sewing machine, broad fabric, simple paper patterns, a tape measure, or even a sharp pair of scissors. These are the beginning of folkloric clothes. The clothes for the most part are made from square and oblong pieces, put together like a jigsaw puzzle with narrow fabric lengths from hand looms. They are made of curving circles, curves and tapered seams, with no waste of materials. It all sounds very primitive, but on a closer inspection, traditional clothes are everything that most modern fashions are not. They are practical, versatile, comfortable, durable and flattering; in short, masterpieces of style. Style always begins with a simple shape, and above all, simple shapes are functional and practical. But what has function to do with fashion? Only the fact that the best known names in fashion design have established their reputations by turning their backs on functionality, concentrating on style. And where do they seek inspiration? Coco Chanel\u27s famous coats were based on the Breton fisherman\u27s blouse. Coco Chanel admits, I get many ideas from simple clothes worn by muscle workers who have nothing to do with fashion. The patterns of traditional Korean clothes are very simple and functional also. Since these patterns are already functional and change only slowly, attention is focused on the surfaces, colors, patterns and textures. The three garments designed are based on simple traditional patterns. These patterns relate beauty to simplicity in traditional design
Potential-energy (BCS) to kinetic-energy (BEC)-driven pairing in the attractive Hubbard model
The BCS-BEC crossover within the two-dimensional attractive Hubbard model is
studied by using the Cellular Dynamical Mean-Field Theory both in the normal
and superconducting ground states. Short-range spatial correlations
incorporated in this theory remove the normal-state quasiparticle peak and the
first-order transition found in the Dynamical Mean-Field Theory, rendering the
normal state crossover smooth. For smaller than the bandwidth, pairing is
driven by the potential energy, while in the opposite case it is driven by the
kinetic energy, resembling a recent optical conductivity experiment in
cuprates. Phase coherence leads to the appearance of a collective Bogoliubov
mode in the density-density correlation function and to the sharpening of the
spectral function.Comment: 5 pages, 4 figure
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