11,365 research outputs found
A lower bound for metric 1-median selection
Consider the problem of finding a point in an n-point metric space with the
minimum average distance to all points. We show that this problem has no
deterministic -query -approximation algorithms
Secure secret sharing in the cloud
In this paper, we show how a dealer with limited resources is possible to share the secrets to players via an untrusted cloud server without compromising the privacy of the secrets. This scheme permits a batch of two secret messages to be shared to two players in such a way that the secrets are reconstructable if and only if two of them collaborate. An individual share reveals absolutely no information about the secrets to the player. The secret messages are obfuscated by encryption and thus give no information to the cloud server. Furthermore, the scheme is compatible with the Paillier cryptosystem and other cryptosystems of the same type. In light of the recent developments in privacy-preserving watermarking technology, we further model the proposed scheme as a variant of reversible watermarking in the encrypted domain
Anomalous spin Hall effects in Dresselhaus (110) quantum wells
Anomalous spin Hall effects that belong to the intrinsic type in Dresselhaus
(110) quantum wells are discussed. For the out-of-plane spin component,
antisymmetric current-induced spin polarization induces opposite spin Hall
accumulation, even though there is no spin-orbit force due to Dresselhaus (110)
coupling. A surprising feature of this spin Hall induction is that the spin
accumulation sign does not change upon bias reversal. Contribution to the spin
Hall accumulation from the spin Hall induction and the spin deviation due to
intrinsic spin-orbit force as well as extrinsic spin scattering, can be
straightforwardly distinguished simply by reversing the bias. For the inplane
component, inclusion of a weak Rashba coupling leads to a new type of
intrinsic spin Hall effect solely due to spin-orbit-force-driven spin
separation.Comment: 6 pages, 5 figure
Source Mergers and Bubble Growth During Reionization
The recently introduced models of reionization bubbles based on extended
Press-Schechter theory (Furlanetto, Zaldarriaga & Hernquist 2004) are
generalized to include mergers of ionization sources. Sources with a recent
major merger are taken to have enhanced photon production due to star
formation, and accretion onto a central black hole if a black hole is present.
This produces a scatter in the number of ionized photons corresponding to a
halo of a given mass and a change in photon production over time for any given
halo mass. Photon production histories, bubble distributions, and ionization
histories are computed for several different parameter and recombination
assumptions; the resulting distributions interpolate between previously
calculated limiting cases.Comment: 44 pages, 11 figures, version to appear in MNRAS. Some discussion of
case with WMAP parameters and expanded explanation
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