12,855 research outputs found
Asymptotic distributions of the signal-to-interference ratios of LMMSE detection in multiuser communications
Let ,
where are independent and identically distributed
random variables with and . Let
, and
\beta_k=p_k{\mathbf{s}}_k^T({\mathb
f{S}}_k{\mathbf{P}}_k{\mathbf{S}}_k^T+\sigma^2{\mathbf{I}})^{-1}{\math
bf{s}}_k, where and the is referred to as the
signal-to-interference ratio (SIR) of user with linear minimum mean-square
error (LMMSE) detection in wireless communications. The joint distribution of
the SIRs for a finite number of users and the empirical distribution of all
users' SIRs are both investigated in this paper when and tend to
infinity with the limit of their ratio being positive constant. Moreover, the
sum of the SIRs of all users, after subtracting a proper value, is shown to
have a Gaussian limit.Comment: Published at http://dx.doi.org/10.1214/105051606000000718 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
Two-dimensional topological superconducting phases emerged from d-wave superconductors in proximity to antiferromagnets
Motivated by the recent observations of nodeless superconductivity in the
monolayer CuO grown on the BiSrCaCuO
substrates, we study the two-dimensional superconducting (SC) phases described
by the two-dimensional - model in proximity to an antiferromagnetic (AF)
insulator. We found that (i) the nodal d-wave SC state can be driven via a
continuous transition into a nodeless d-wave pairing state by the proximity
induced AF field. (ii) The energetically favorable pairing states in the strong
field regime have extended s-wave symmetry and can be nodal or nodeless. (iii)
Between the pure d-wave and s-wave paired phases, there emerge two
topologically distinct SC phases with (i) symmetry, i.e., the weak and
strong pairing phases, and the weak pairing phase is found to be a
topological superconductor protected by valley symmetry, exhibiting robust
gapless non-chiral edge modes. These findings strongly suggest that the
high- superconductors in proximity to antiferromagnets can realize fully
gapped symmetry protected topological SC.Comment: 7 pages, 4 figures; revised versio
Set Representations of Linegraphs
Let be a graph with vertex set and edge set . A family
of nonempty sets is a set representation of
if there exists a one-to-one correspondence between the vertices in and the sets in such that if and only if S_i\cap S_j\neq \es. A set representation
is a distinct (respectively, antichain, uniform and simple) set representation
if any two sets and in have the property (respectively, , and ). Let . Two set
representations and are isomorphic if
can be obtained from by a bijection from
to . Let denote a class of set
representations of a graph . The type of is the number of equivalence
classes under the isomorphism relation. In this paper, we investigate types of
set representations for linegraphs. We determine the types for the following
categories of set representations: simple-distinct, simple-antichain,
simple-uniform and simple-distinct-uniform
Conquer the fine structure splitting of excitons in self-assembled InAs/GaAs quantum dots via combined stresses
Eliminating the fine structure splitting (FSS) of excitons in self-assembled
quantum dots (QDs) is essential to the generation of high quality entangled
photon pairs. It has been shown that the FSS has a lower bound under uniaxial
stress. In this letter, we show that the FSS of excitons in a general
self-assembled InGaAs/GaAs QD can be fully suppressed via combined stresses
along the [110] and [010] directions. The result is confirmed by atomic
empirical pseudopotential calculations. For all the QDs we studied, the FSS can
be tuned to be vanishingly small ( 0.1 eV), which is sufficient small
for high quality entangled photon emission.Comment: 4 pages, 3 figure, 1 tabl
Quantifying the Influence of Component Failure Probability on Cascading Blackout Risk
The risk of cascading blackouts greatly relies on failure probabilities of
individual components in power grids. To quantify how component failure
probabilities (CFP) influences blackout risk (BR), this paper proposes a
sample-induced semi-analytic approach to characterize the relationship between
CFP and BR. To this end, we first give a generic component failure probability
function (CoFPF) to describe CFP with varying parameters or forms. Then the
exact relationship between BR and CoFPFs is built on the abstract
Markov-sequence model of cascading outages. Leveraging a set of samples
generated by blackout simulations, we further establish a sample-induced
semi-analytic mapping between the unbiased estimation of BR and CoFPFs.
Finally, we derive an efficient algorithm that can directly calculate the
unbiased estimation of BR when the CoFPFs change. Since no additional
simulations are required, the algorithm is computationally scalable and
efficient. Numerical experiments well confirm the theory and the algorithm
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