78,777 research outputs found
Central limit theorem for signal-to-interference ratio of reduced rank linear receiver
Let with
independent and identically distributed complex random
variables. Write ,
and
. Define
$\beta_{km}=p_k\mathbf{s}_k^*\mathbf{A}_{km}(\mathbf {A}_{km}^*\times\
mathbf{R}_k\mathbf{A}_{km})^{-1}\mathbf{A}_{km}^*\mathbf{s}_kkN/K\to c>0$. Moreover, we provide a
central limit theorem for linear spectral statistics of eigenvalues and
eigenvectors of sample covariance matrices, which is a supplement of Theorem 2
in Bai, Miao and Pan [Ann. Probab. 35 (2007) 1532--1572]. And we also improve
Theorem 1.1 in Bai and Silverstein [Ann. Probab. 32 (2004) 553--605].Comment: Published in at http://dx.doi.org/10.1214/07-AAP477 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Conditions for Nondistortion Interrogation of Quantum System
Under some physical considerations, we present a universal formulation to
study the possibility of localizing a quantum object in a given region without
disturbing its unknown internal state. When the interaction between the object
and probe wave function takes place only once, we prove the necessary and
sufficient condition that the object's presence can be detected in an initial
state preserving way. Meanwhile, a conditioned optimal interrogation
probability is obtained.Comment: 5 pages, Revtex, 1 figures, Presentation improved, corollary 1 added.
To appear in Europhysics Letter
Domain walls in gapped graphene
The electronic properties of a particular class of domain walls in gapped
graphene are investigated. We show that they can support mid-gap states which
are localized in the vicinity of the domain wall and propagate along its
length. With a finite density of domain walls, these states can alter the
electronic properties of gapped graphene significantly. If the mid-gap band is
partially filled,the domain wall can behave like a one-dimensional metal
embedded in a semi-conductor, and could potentially be used as a single-channel
quantum wire.Comment: 4 pgs. revte
Transition Metal-Ethylene Complexes as High-Capacity Hydrogen Storage Media
From first-principles calculations, we predict that a single ethylene
molecule can form a stable complex with two transition metals (TM) such as Ti.
The resulting TM-ethylene complex then absorbs up to ten hydrogen molecules,
reaching to gravimetric storage capacity of 14 wt%. Dimerization,
polymerizations and incorporation of the TM-ethylene complexes in nanoporous
carbon materials have been also discussed. Our results are quite remarkable and
open a new approach to high-capacity hydrogen storage materials discovery.Comment: 5 pages, 4 figures, additional content, Phys. Rev. Lett. in pres
Electronic, dynamical, and thermal properties of ultra-incompressible superhard rhenium diboride: A combined first-principles and neutron scattering study
Rhenium diboride is a recently recognized ultra-incompressible superhard
material. Here we report the electronic (e), phonon (p), e-p coupling and
thermal properties of ReB from first-principles density-functional theory
(DFT) calculations and neutron scattering measurements. Our calculated elastic
constants ( = 641 GPa, = 159 GPa, = 128 GPa,
= 1037 GPa, and = 271 GPa), bulk modulus ( 350 GPa) and
hardness ( 46 GPa) are in good agreement with the reported
experimental data. The calculated phonon density of states (DOS) agrees very
well with our neutron vibrational spectroscopy result. Electronic and phonon
analysis indicates that the strong covalent B-B and Re-B bonding is the main
reason for the super incompressibility and hardness of ReB. The thermal
expansion coefficients, calculated within the quasi-harmonic approximation and
measured by neutron powder diffraction, are found to be nearly isotropic in
and directions and only slightly larger than that of diamond in terms of
magnitude. The excellent agreement found between calculations and experimental
measurements indicate that first-principles calculations capture the main
interactions in this class of superhard materials, and thus can be used to
search, predict, and design new materials with desired properties.Comment: submitted to pr
Spin-Hall and Anisotropic Magnetoresistance in Ferrimagnetic Co-Gd / Pt layers
We present the Co-Gd composition dependence of the spin-Hall
magnetoresistance (SMR) and anisotropic magnetoresistance (AMR) for
ferrimagnetic Co100-xGdx / Pt bilayers. With Gd concentration x, its magnetic
moment increasingly competes with the Co moment in the net magnetization. We
find a nearly compensated ferrimagnetic state at x = 24. The AMR changes sign
from positive to negative with increasing x, vanishing near the magnetization
compensation. On the other hand, the SMR does not vary significantly even where
the AMR vanishes. These experimental results indicate that very different
scattering mechanisms are responsible for AMR and SMR. We discuss a possible
origin for the alloy composition dependence.Comment: 31 Pages, 9 figure
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