530 research outputs found
Quantum Correlations and Coherence in Spin-1 Heisenberg Chains
We explore quantum and classical correlations along with coherence in the
ground states of spin-1 Heisenberg chains, namely the one-dimensional XXZ model
and the one-dimensional bilinear biquadratic model, with the techniques of
density matrix renormalization group theory. Exploiting the tools of quantum
information theory, that is, by studying quantum discord, quantum mutual
information and three recently introduced coherence measures in the reduced
density matrix of two nearest neighbor spins in the bulk, we investigate the
quantum phase transitions and special symmetry points in these models. We point
out the relative strengths and weaknesses of correlation and coherence measures
as figures of merit to witness the quantum phase transitions and symmetry
points in the considered spin-1 Heisenberg chains. In particular, we
demonstrate that as none of the studied measures can detect the infinite order
Kosterlitz-Thouless transition in the XXZ model, they appear to be able to
signal the existence of the same type of transition in the biliear biquadratic
model. However, we argue that what is actually detected by the measures here is
the SU(3) symmetry point of the model rather than the infinite order quantum
phase transition. Moreover, we show in the XXZ model that examining even single
site coherence can be sufficient to spotlight the second-order phase transition
and the SU(2) symmetry point.Comment: 8 pages. 5 figure
Sustainable development aspects of biodiesel production and application in Brazil
Concerns about climate change effects have prompted many countries to search for solutions to reduce fossil fuel consumption. In the last few years biodiesel production has gained world attention, as it is seen as a sustainable and renewable energy source. Biodiesel is a natural substitute for diesel oil, and can be obtained from different oleaginous plants. However, there are worries about devastation of forests and biodiversity-rich areas to produce biodiesel. Even considering biodiesel as a promising solution, the impacts of its production must be carefully evaluated. This work examines the Brazilian scenario for biodiesel production and use as an automotive fuel. Native and adapted oleaginous in many Brazilian regions and their potentiality for biodiesel production are presented. Experimental results of hydrocarbons (HC), carbon monoxide (CO), and carbon dioxide (CO2) emissions from a diesel power generator fuelled by blends of diesel oil and castor oil or soybean biodiesel are also presented
Further developments on biodiesel production and applications in brazil
Environmental concerns have motivated many countries to search for solutions to reduce fossil fuel consumption. In the last few years, biodiesel has attracted attention as a possible sustainable and renewable energy source to substitute diesel oil. Biodiesel can be produced from different oleaginous plants, but there are worries about food competition and forests and biodiversity-rich areas devastation to produce biodiesel. Even considering biodiesel as a promising solution, its production impacts must be carefully evaluated. This work examines the Brazilian prospects for biodiesel production and use as an engine fuel for automotive propulsion and power generation. The potential for biodiesel production of many native and adapted oleaginous plants in Brazilian territory is discussed. Experimental results of hydrocarbons, carbon monoxide, and carbon dioxide emis-sions from a diesel power generator fuelled by blends of diesel oil and castor oil or soybean biodiesel are also presented
Cough and dyspnea during bronchoconstriction: comparison of different stimuli
Abstract
Background
Bronchial challenge tests are used to evaluate bronchial responsiveness in diagnosis and follow-up of asthmatic patients. Challenge induced cough has increasingly been recognized as a valuable diagnostic tool. Various stimuli and protocols have been employed. The aim of this study was to compare cough and dyspnea intensity induced by different stimuli.
Methods
Twenty asthmatic patients underwent challenge tests with methacholine, bradykinin and exercise. Cough was counted during challenge tests. Dyspnea was assessed by modified Borg scale and visual analogue scale. Statistical comparisons were performed by linear mixed-effects model.
Results
For cough evaluation, bradykinin was the most potent trigger (p < 0.01). In terms of dyspnea measured by Borg scale, there were no differences among stimuli (p > 0.05). By visual analogue scale, bradykinin induced more dyspnea than other stimuli (p ≤ 0.04).
Conclusion
Bradykinin seems to be the most suitable stimulus for bronchial challenge tests intended for measuring cough in association with bronchoconstriction
Experimental implementation of a NMR entanglement witness
Entanglement witnesses (EW) allow the detection of entanglement in a quantum
system, from the measurement of some few observables. They do not require the
complete determination of the quantum state, which is regarded as a main
advantage. On this paper it is experimentally analyzed an entanglement witness
recently proposed in the context of Nuclear Magnetic Resonance (NMR)
experiments to test it in some Bell-diagonal states. We also propose some
optimal entanglement witness for Bell-diagonal states. The efficiency of the
two types of EW's are compared to a measure of entanglement with tomographic
cost, the generalized robustness of entanglement. It is used a GRAPE algorithm
to produce an entangled state which is out of the detection region of the EW
for Bell-diagonal states. Upon relaxation, the results show that there is a
region in which both EW fails, whereas the generalized robustness still shows
entanglement, but with the entanglement witness proposed here with a better
performance
Schmidt balls around the identity
Robustness measures as introduced by Vidal and Tarrach [PRA, 59, 141-155]
quantify the extent to which entangled states remain entangled under mixing.
Analogously, we introduce here the Schmidt robustness and the random Schmidt
robustness. The latter notion is closely related to the construction of Schmidt
balls around the identity. We analyse the situation for pure states and provide
non-trivial upper and lower bounds. Upper bounds to the random Schmidt-2
robustness allow us to construct a particularly simple distillability
criterion. We present two conjectures, the first one is related to the radius
of inner balls around the identity in the convex set of Schmidt number
n-states. We also conjecture a class of optimal Schmidt witnesses for pure
states.Comment: 7 pages, 1 figur
Optimal measurement bases for Bell-tests based on the CH-inequality
The Hardy test of nonlocality can be seen as a particular case of the Bell
tests based on the Clauser-Horne (CH) inequality. Here we stress this
connection when we analyze the relation between the CH-inequality violation,
its threshold detection efficiency, and the measurement settings adopted in the
test. It is well known that the threshold efficiencies decrease when one
considers partially entangled states and that the use of these states,
unfortunately, generates a reduction in the CH violation. Nevertheless, these
quantities are both dependent on the measurement settings considered, and in
this paper we show that there are measurement bases which allow for an optimal
situation in this trade-off relation. These bases are given as a generalization
of the Hardy measurement bases, and they will be relevant for future Bell tests
relying on pairs of entangled qubits.Comment: 8 pages, 6 figure
Quantifying Quantum Correlations in Fermionic Systems using Witness Operators
We present a method to quantify quantum correlations in arbitrary systems of
indistinguishable fermions using witness operators. The method associates the
problem of finding the optimal entan- glement witness of a state with a class
of problems known as semidefinite programs (SDPs), which can be solved
efficiently with arbitrary accuracy. Based on these optimal witnesses, we
introduce a measure of quantum correlations which has an interpretation
analogous to the Generalized Robust- ness of entanglement. We also extend the
notion of quantum discord to the case of indistinguishable fermions, and
propose a geometric quantifier, which is compared to our entanglement measure.
Our numerical results show a remarkable equivalence between the proposed
Generalized Robustness and the Schliemann concurrence, which are equal for pure
states. For mixed states, the Schliemann con- currence presents itself as an
upper bound for the Generalized Robustness. The quantum discord is also found
to be an upper bound for the entanglement.Comment: 7 pages, 6 figures, Accepted for publication in Quantum Information
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