9,824 research outputs found
A novel system architecture for real-time low-level vision
A novel system architecture that exploits the spatial locality in memory access that is found in most low-level vision algorithms is presented. A real-time feature selection system is used to exemplify the underlying ideas, and an implementation based on commercially available Field Programmable Gate Arrays (FPGAâs) and synchronous SRAM memory devices is proposed. The peak memory access rate of a system based on this architecture is estimated at 2.88 G-Bytes/s, which represents a four to five times improvement with respect to existing reconfigurable computers
Capturing the phase diagram of (2+1)-dimensional CDT using a balls-in-boxes model
We study the phase diagram of a one-dimensional balls-in-boxes (BIB) model
that has been proposed as an effective model for the spatial-volume dynamics of
(2+1)-dimensional causal dynamical triangulations (CDT). The latter is a
statistical model of random geometries and a candidate for a nonperturbative
formulation of quantum gravity, and it is known to have an interesting phase
diagram, in particular including a phase of extended geometry with classical
properties. Our results corroborate a previous analysis suggesting that a
particular type of potential is needed in the BIB model in order to reproduce
the droplet condensation typical of the extended phase of CDT. Since such a
potential can be obtained by a minisuperspace reduction of a (2+1)-dimensional
gravity theory of the Ho\v{r}ava-Lifshitz type, our result strengthens the link
between CDT and Ho\v{r}ava-Lifshitz gravity.Comment: 21 pages, 7 figure
Dynamics of quantum correlations in colored environments
We address the dynamics of entanglement and quantum discord for two non
interacting qubits initially prepared in a maximally entangled state and then
subjected to a classical colored noise, i.e. coupled with an external
environment characterized by a noise spectrum of the form . More
specifically, we address systems where the Gaussian approximation fails, i.e.
the sole knowledge of the spectrum is not enough to determine the dynamics of
quantum correlations. We thus investigate the dynamics for two different
configurations of the environment: in the first case the noise spectrum is due
to the interaction of each qubit with a single bistable fluctuator with an
undetermined switching rate, whereas in the second case we consider a
collection of classical fluctuators with fixed switching rates. In both cases
we found analytical expressions for the time dependence of entanglement and
quantum discord, which may be also extended to a collection of flcutuators with
random switching rates. The environmental noise is introduced by means of
stochastic time-dependent terms in the Hamiltonian and this allows us to
describe the effects of both separate and common environments. We show that the
non-Gaussian character of the noise may lead to significant effects, e.g.
environments with the same power spectrum, but different configurations, give
raise to opposite behavior for the quantum correlations. In particular,
depending on the characteristics of the environmental noise considered, both
entanglement and discord display either a monotonic decay or the phenomena of
sudden death and revivals. Our results show that the microscopic structure of
environment, besides its noise spectrum, is relevant for the dynamics of
quantum correlations, and may be a valid starting point for the engineering of
non-Gaussian colored environments.Comment: 8 pages, 3 figure
Silent Reading before Oral Reading on the IRI: Implication for Diagnosis and Instruction
The purpose of this study was to test the effect of silent pre-reading on the number of oral reading errors a student makes on an IRI. Twenty children read passages silently and then orally read passages without pre-reading. The results supported the null hypothesis that there would be no statistically significant difference on oral reading performances for disabled second and fourth graders. Implications for diagnosis and instruction are discussed
On simultaneous diagonalization of one Hermitian and one symmetric form
AbstractIt is remarked that if A, B Ï” Mn(C), A = At, and BÌ = Bt, B positive definite, there exists a nonsingular matrix U such that (1) ĆȘtBU = I and (2) UtAU is a diagonal matrix with nonnegative entries. Some related actions of the real orthogonal group and equations involving the unitary group are studied
Spatial structures and dynamics of kinetically constrained models for glasses
Kob and Andersen's simple lattice models for the dynamics of structural
glasses are analyzed. Although the particles have only hard core interactions,
the imposed constraint that they cannot move if surrounded by too many others
causes slow dynamics. On Bethe lattices a dynamical transition to a partially
frozen phase occurs. In finite dimensions there exist rare mobile elements that
destroy the transition. At low vacancy density, , the spacing, ,
between mobile elements diverges exponentially or faster in . Within the
mobile elements, the dynamics is intrinsically cooperative and the
characteristic time scale diverges faster than any power of (although
slower than ). The tagged-particle diffusion coefficient vanishes roughly
as .Comment: 4 pages. Accepted for pub. in Phys. Rev. Let
Experimental estimation of quantum discord for polarization qubit and the use of fidelity to assess quantum correlations
We address the experimental determination of entropic quantum discord for
systems made of a pair of polarization qubits. We compare results from full and
partial tomography and found that the two determinations are statistically
compatible, with partial tomography leading to a smaller value of discord for
depolarized states. Despite the fact that our states are well described, in
terms of fidelity, by families of depolarized or phase-damped states, their
entropic discord may be largely different from that predicted for these classes
of states, such that no reliable estimation procedure beyond tomography may be
effectively implemented. Our results, together with the lack of an analytic
formula for the entropic discord of a generic two-qubit state, demonstrate that
the estimation of quantum discord is an intrinsically noisy procedure. Besides,
we question the use of fidelity as a figure of merit to assess quantum
correlations
Combinatorial Hopf algebra of superclass functions of type
We provide a Hopf algebra structure on the space of superclass functions on
the unipotent upper triangular group of type D over a finite field based on a
supercharacter theory constructed by Andr\'e and Neto. Also, we make further
comments with respect to types B and C. Type A was explores by M. Aguiar et. al
(2010), thus this paper is a contribution to understand combinatorially the
supercharacter theory of the other classical Lie types.Comment: Last section modified. Recent development added and correction with
respect to previous version state
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