2,526 research outputs found
Qubit-portraits of qudit states and quantum correlations
The machinery of qubit-portraits of qudit states, recently presented, is
consider here in more details in order to characterize the presence of quantum
correlations in bipartite qudit states. In the tomographic representation of
quantum mechanics, Bell-like inequalities are interpreted as peculiar
properties of a family of classical joint probability distributions which
describe the quantum state of two qudits. By means of the qubit-portraits
machinery a semigroup of stochastic matrices can be associated to a given
quantum state. The violation of the CHSH inequalities is discussed in this
framework with some examples, we found that quantum correlations in qutrit
isotropic states can be detected by the suggested method while it cannot in the
case of qutrit Werner states.Comment: 12 pages, 4 figure
Effects of a home-based contingency program on improving academic performance of disadvantaged middle school youths
Research has demonstrated various ways of improving academic performance of students in public-school classrooms (e.g., Barrish, Saunders, & Wolf, 1969), some of which may be clinically effective but not practical within present school systems. A more practical method is the use of a program involving home-based contingencies. Home-based contingencies simply means that: When children are reinforced by their parents for their appropriate behavior and performance at school, school behavior and performance will improve (Broughton, Barton, & Owen;. 1981). The current study employed a program including home-based contingencies modeled after one created by Shumaker, Hovell, and Sherman (1977), and tested the program\u27s effect on academic performance of disadvantaged middle school youths. The independent variable was the home-based contingency component of the program, and the dependent variables were daily report cards, grades, truancy, attendance, and archival data reflecting previous grades, truancy, and attendance. Results indicated that the home-based contingency program significantly increased appropriate school behavior (t(25) = 13.85, p\u3c0.00), but, did not have any substantial impact on grades (t(2) = 1.53, p\u3e0.08), truancy, or attendance
Entanglement frustration in multimode Gaussian states
Bipartite entanglement between two parties of a composite quantum system can
be quantified in terms of the purity of one party and there always exists a
pure state of the total system that maximizes it (and minimizes purity). When
many different bipartitions are considered, the requirement that purity be
minimal for all bipartitions gives rise to the phenomenon of entanglement
frustration. This feature, observed in quantum systems with both discrete and
continuous variables, can be studied by means of a suitable cost function whose
minimizers are the maximally multipartite-entangled states (MMES). In this
paper we extend the analysis of multipartite entanglement frustration of
Gaussian states in multimode bosonic systems. We derive bounds on the
frustration, under the constraint of finite mean energy, in the low and high
energy limit.Comment: 4 pages, 2 figures. Contribution to "Folding and Unfolding:
Interactions from Geometry. Workshop in honour of Giuseppe Marmo's 65th
birthday", 8-12 June 2011, Ischia (NA) Ital
Dorsoventral patterning of the Xenopus eye involves differential temporal changes in the response of optic stalk and retinal progenitors to Hh signalling
Background: Hedgehog (Hh) signals are instrumental to the dorsoventral patterning of the vertebrate eye, promoting optic stalk and ventral retinal fates and repressing dorsal retinal identity. There has been limited analysis, however, of the critical window during which Hh molecules control eye polarity and of the temporal changes in the responsiveness of eye cells to these signals.
Results: In this study, we used pharmacological and molecular tools to perform stage-specific manipulations of Hh signalling in the developing Xenopus eye. In gain-of-function experiments, most of the eye was sensitive to ventralization when the Hh pathway was activated starting from gastrula/neurula stages. During optic vesicle stages, the dorsal eye became resistant to Hh-dependent ventralization, but this pathway could partially upregulate optic stalk markers within the retina. In loss-of-function assays, inhibition of Hh signalling starting from neurula stages caused expansion of the dorsal retina at the expense of the ventral retina and the optic stalk, while the effects of Hh inhibition during optic vesicle stages were limited to the reduction of optic stalk size.
Conclusions: Our results suggest the existence of two competence windows during which the Hh pathway differentially controls patterning of the eye region. In the first window, between the neural plate and the optic vesicle stages, Hh signalling exerts a global influence on eye dorsoventral polarity, contributing to the specification of optic stalk, ventral retina and dorsal retinal domains. In the second window, between optic vesicle and optic cup stages, this pathway plays a more limited role in the maintenance of the optic stalk domain. We speculate that this temporal regulation is important to coordinate dorsoventral patterning with morphogenesis and differentiation processes during eye development
Invariant measures on multimode quantum Gaussian states
We derive the invariant measure on the manifold of multimode quantum Gaussian
states, induced by the Haar measure on the group of Gaussian unitary
transformations. To this end, by introducing a bipartition of the system in two
disjoint subsystems, we use a parameterization highlighting the role of
nonlocal degrees of freedom -- the symplectic eigenvalues -- which characterize
quantum entanglement across the given bipartition. A finite measure is then
obtained by imposing a physically motivated energy constraint. By averaging
over the local degrees of freedom we finally derive the invariant distribution
of the symplectic eigenvalues in some cases of particular interest for
applications in quantum optics and quantum information.Comment: 17 pages, comments are welcome. v2: presentation improved and typos
corrected. Close to the published versio
On the classical capacity of quantum Gaussian channels
The set of quantum Gaussian channels acting on one bosonic mode can be
classified according to the action of the group of Gaussian unitaries. We look
for bounds on the classical capacity for channels belonging to such a
classification. Lower bounds can be efficiently calculated by restricting to
Gaussian encodings, for which we provide analytical expressions.Comment: 10 pages, IOP style. v2: minor corrections, close to the published
versio
Memory effects in attenuation and amplification quantum processes
With increasing communication rates via quantum channels, memory effects
become unavoidable whenever the use rate of the channel is comparable to the
typical relaxation time of the channel environment. We introduce a model of a
bosonic memory channel, describing correlated noise effects in quantum-optical
processes via attenuating or amplifying media. To study such a channel model,
we make use of a proper set of collective field variables, which allows us to
unravel the memory effects, mapping the n-fold concatenation of the memory
channel to a unitarily equivalent, direct product of n single-mode bosonic
channels. We hence estimate the channel capacities by relying on known results
for the memoryless setting. Our findings show that the model is characterized
by two different regimes, in which the cross correlations induced by the noise
among different channel uses are either exponentially enhanced or exponentially
reduced.Comment: 10 pages, 7 figures, close to the published versio
Persistence Steenrod modules
It has long been envisioned that the strength of the barcode invariant offiltered cellular complexes could be increased using cohomology operations.Leveraging recent advances in the computation of Steenrod squares, we introducea new family of computable invariants on mod 2 persistent cohomology termed-barcodes. We present a complete algorithmic pipeline for theircomputation and illustrate their real-world applicability using the space ofconformations of the cyclo-octane molecule.<br
Synoptic/planetary-scale interactions and blocking over the North Atlantic Ocean
One segment of work in the past year focused on the diagnosis of a major blocking anticyclone and its interacting synoptic scale circulations that occurred during January 1979 over the North Atlantic Ocean. Another segment focused on the diagnosis of a second explosive cyclone development that occurred over the southeastern United States during the time of block formation. The diagnoses were accomplished using the diagnostic relationship known as the Zwack-Okossi (Z-O) development equation. Results indicate that in both cyclone cases the development occurred as a result of the favorable influence of positive vorticity advection, warm air advection, and latent heat release and ceased when one or more of these influences diminished. The advantages of the Z-O equation are described
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