750 research outputs found
Generalized Semimagic Squares for Digital Halftoning
Completing Aronov et al.'s study on zero-discrepancy matrices for digital
halftoning, we determine all (m, n, k, l) for which it is possible to put mn
consecutive integers on an m-by-n board (with wrap-around) so that each k-by-l
region holds the same sum. For one of the cases where this is impossible, we
give a heuristic method to find a matrix with small discrepancy.Comment: 6 pages, 6 figure
High-frequency spin valve effect in ferromagnet-semiconductor-ferromagnet structure based on precession of injected spins
New mechanism of magnetoresistance, based on tunneling-emission of spin
polarized electrons from ferromagnets (FM) into semiconductors (S) and
precession of electron spin in the semiconductor layer under external magnetic
field, is described. The FM-S-FM structure is considered, which includes very
thin heavily doped (delta-doped) layers at FM-S interfaces. At certain
parameters the structure is highly sensitive at room-temperature to variations
of the field with frequencies up to 100 GHz. The current oscillates with the
field, and its relative amplitude is determined only by the spin polarizations
of FM-S junctions at relatively large bias voltage.Comment: 5 pages, 2 figures, (v2) new plot with a dependence of current J on
magnetic field H added in Fig.2 (top panel), minor amendments in the text;
(v3) minor typos corrected. To appear in Phys. Rev. Letter
On a Possibility to Measure Thermoelectric Power in SNS Structures
Two dissimilar Josephson junctions, which are connected to a heater can act
as precise batteries. Because of the difference in thermoelectric power of
these batteries, circuit with two dissimilar batteries, under heat flow would have a net EMF around the zero-resistance
loop leading to a loop's magnetic flux oscillating in time. It is shown its
theoretical value is proportional to both the temperature difference as well as
the disparity in the thermoelectric powers of the two junctions.Comment: 5 page
Finding Pairwise Intersections Inside a Query Range
We study the following problem: preprocess a set O of objects into a data
structure that allows us to efficiently report all pairs of objects from O that
intersect inside an axis-aligned query range Q. We present data structures of
size and with query time
time, where k is the number of reported pairs, for two classes of objects in
the plane: axis-aligned rectangles and objects with small union complexity. For
the 3-dimensional case where the objects and the query range are axis-aligned
boxes in R^3, we present a data structures of size and query time . When the objects and
query are fat, we obtain query time using storage
Spin injection dependent metamagnetic transition
We define the metamagnetic phase transition of itinerant electrons controlled
by the spin injection mechanism. The current flow between a ferromagnetic metal
and a metamagnetic metal produces the non-equilibrium shift of chemical
potential for spin up and spin down electrons that acts as an effective
magnetic field driving the metamagnetic transition.Comment: 6 pages, 3 figure
Deterministic Digital Clustering of Wireless Ad Hoc Networks
We consider deterministic distributed communication in wireless ad hoc
networks of identical weak devices under the SINR model without predefined
infrastructure. Most algorithmic results in this model rely on various
additional features or capabilities, e.g., randomization, access to geographic
coordinates, power control, carrier sensing with various precision of
measurements, and/or interference cancellation. We study a pure scenario, when
no such properties are available. As a general tool, we develop a deterministic
distributed clustering algorithm. Our solution relies on a new type of
combinatorial structures (selectors), which might be of independent interest.
Using the clustering, we develop a deterministic distributed local broadcast
algorithm accomplishing this task in rounds, where
is the density of the network. To the best of our knowledge, this is
the first solution in pure scenario which is only polylog away from the
universal lower bound , valid also for scenarios with
randomization and other features. Therefore, none of these features
substantially helps in performing the local broadcast task. Using clustering,
we also build a deterministic global broadcast algorithm that terminates within
rounds, where is the diameter of the
network. This result is complemented by a lower bound , where is the path-loss parameter of the
environment. This lower bound shows that randomization or knowledge of own
location substantially help (by a factor polynomial in ) in the global
broadcast. Therefore, unlike in the case of local broadcast, some additional
model features may help in global broadcast
Theory of thermal spin-charge coupling in electronic systems
The interplay between spin transport and thermoelectricity offers several
novel ways of generating, manipulating, and detecting nonequilibrium spin in a
wide range of materials. Here we formulate a phenomenological model in the
spirit of the standard model of electrical spin injection to describe the
electronic mechanism coupling charge, spin, and heat transport and employ the
model to analyze several different geometries containing ferromagnetic (F) and
nonmagnetic (N) regions: F, F/N, and F/N/F junctions which are subject to
thermal gradients. We present analytical formulas for the spin accumulation and
spin current profiles in those junctions that are valid for both tunnel and
transparent (as well as intermediate) contacts. For F/N junctions we calculate
the thermal spin injection efficiency and the spin accumulation induced
nonequilibrium thermopower. We find conditions for countering thermal spin
effects in the N region with electrical spin injection. This compensating
effect should be particularly useful for distinguishing electronic from other
mechanisms of spin injection by thermal gradients. For F/N/F junctions we
analyze the differences in the nonequilibrium thermopower (and chemical
potentials) for parallel and antiparallel orientations of the F magnetizations,
as evidence and a quantitative measure of the spin accumulation in N.
Furthermore, we study the Peltier and spin Peltier effects in F/N and F/N/F
junctions and present analytical formulas for the heat evolution at the
interfaces of isothermal junctions.Comment: to be published in PRB (in press), 19 pages, 19 figure
Supersymmetry for disordered systems with interaction
Considering disordered electron systems we suggest a scheme that allows us to
include an electron-electron interaction into a supermatrix sigma-model. The
method is based on replacing the initial model of interacting electons by a
fully supersymmetric model. Although this replacement is not exact, it is a
good approximation for a weak short range interaction and arbitrary disorder.
The replacement makes the averaging over disorder and further manipulations
straightforward and we come to a supermatrix sigma-model containing an
interaction term. The structure of the model is rather similar to the replica
one, although the interaction term has a different form. We study the model
making perturbation theory and renormalization group calculations. We check the
renormalizability of the model in the first loop approximation and in the first
order in the interaction. In this limit we reproduce the renormalization group
equations known from earlier works. We hope that the new supermatrix
sigma-model may become a new tool for non-perturbative calculations for
disordered systems with interaction.Comment: 18 pages, 8 figures, published version with minor change
Shape Analysis of the Level Spacing Distribution around the Metal Insulator Transition in the Three Dimensional Anderson Model
We present a new method for the numerical treatment of second order phase
transitions using the level spacing distribution function . We show that
the quantities introduced originally for the shape analysis of eigenvectors can
be properly applied for the description of the eigenvalues as well. The
position of the metal--insulator transition (MIT) of the three dimensional
Anderson model and the critical exponent are evaluated. The shape analysis of
obtained numerically shows that near the MIT is clearly different
from both the Brody distribution and from Izrailev's formula, and the best
description is of the form , with
. This is in good agreement with recent analytical results.Comment: 14 pages in plain TeX, 6 figures upon reques
Subsampling in Smoothed Range Spaces
We consider smoothed versions of geometric range spaces, so an element of the
ground set (e.g. a point) can be contained in a range with a non-binary value
in . Similar notions have been considered for kernels; we extend them to
more general types of ranges. We then consider approximations of these range
spaces through -nets and -samples (aka
-approximations). We characterize when size bounds for
-samples on kernels can be extended to these more general
smoothed range spaces. We also describe new generalizations for -nets to these range spaces and show when results from binary range spaces can
carry over to these smoothed ones.Comment: This is the full version of the paper which appeared in ALT 2015. 16
pages, 3 figures. In Algorithmic Learning Theory, pp. 224-238. Springer
International Publishing, 201
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