246 research outputs found
Behavior of the current in the asymmetric quantum multibaker map
Recently, a new mechanism leading to purely quantum directed transport in the
asymmetric multibaker map has been presented. Here, we show a comprehensive
characterization of the finite asymptotic current behavior with respect to the
value, the shape of the initial conditions, and the features of the
spectrum. We have considered different degrees of asymmetry in these studies
and we have also analyzed the classical and quantum phase space distributions
for short times in order to understand the mechanisms behind the generation of
the directed current.Comment: 8 pages, 8 figure
Localization of resonance eigenfunctions on quantum repellers
We introduce a new phase space representation for open quantum systems. This
is a very powerful tool to help advance in the study of the morphology of their
eigenstates. We apply it to two different versions of a paradigmatic model, the
baker map. This allows to show that the long-lived resonances are strongly
scarred along the shortest periodic orbits that belong to the classical
repeller. Moreover, the shape of the short-lived eigenstates is also analyzed.
Finally, we apply an antiunitary symmetry measure to the resonances that
permits to quantify their localization on the repeller.Comment: 4 pages, 4 figure
Decoherence induced by a chaotic environment: A quantum walker with a complex coin
We study the differences between the process of decoherence induced by
chaotic and regular environments. For this we analyze a family of simple models
wich contain both regular and chaotic environments. In all cases the system of
interest is a "quantum walker", i.e. a quantum particle that can move on a
lattice with a finite number of sites. The walker interacts with an environment
wich has a D dimensional Hilbert space. The results we obtain suggest that
regular and chaotic environments are not distinguishable from each other in a
(short) timescale t*, wich scales with the dimensionality of the environment as
t*~log(D). Howeber, chaotic environments continue to be effective over
exponentially longer timescales while regular environments tend to reach
saturation much sooner. We present both numerical and analytical results
supporting this conclusion. The family of chaotic evolutions we consider
includes the so-called quantum multi-baker-map as a particular case.Comment: 7 pages, 8 figure
On the environmental stability of quantum chaotic ratchets
The transitory and stationary behavior of a quantum chaotic ratchet
consisting of a biharmonic potential under the effect of different drivings in
contact with a thermal environment is studied. For weak forcing and finite
, we identify a strong dependence of the current on the structure of the
chaotic region. Moreover, we have determined the robustness of the current
against thermal fluctuations in the very weak coupling regime. In the case of
strong forcing, the current is determined by the shape of a chaotic attractor.
In both cases the temperature quickly stabilizes the ratchet, but in the latter
it also destroys the asymmetry responsible for the current generation. Finally,
applications to isomerization reactions are discussed.Comment: 6 pages, 5 figure
Classical transients and the support of open quantum maps
The basic ingredients in a semiclassical theory are the classical invariant
objects serving as a support for the quantization. Recent studies, mainly
obtained on quantum maps, have led to the commonly accepted belief that it is
the classical repeller -- the set of non escaping orbits in the future and past
evolution -- the object that suitably plays this role in open scattering
systems. In this paper we present numerical evidence warning that this may not
always be the case. For this purpose we study recently introduced families of
tribaker maps [L. Ermann, G.G. Carlo, J.M. Pedrosa, and M. Saraceno, Phys. Rev.
E {\bf 85}, 066204 (2012)], which share the same asymptotic properties but
differ in their short time behavior. We have found that although the eigenvalue
distribution of the evolution operator of these maps follows the fractal Weyl
law prediction, the theory of short periodic orbits for open maps fails to
describe the resonance eigenfunctions of some of them. This is a strong
indication that new elements must be included in the semiclassical description
of open quantum systems.Comment: 7 pages, 9 figure
Using the Hadamard and related transforms for simplifying the spectrum of the quantum baker's map
We rationalize the somewhat surprising efficacy of the Hadamard transform in
simplifying the eigenstates of the quantum baker's map, a paradigmatic model of
quantum chaos. This allows us to construct closely related, but new, transforms
that do significantly better, thus nearly solving for many states of the
quantum baker's map. These new transforms, which combine the standard Fourier
and Hadamard transforms in an interesting manner, are constructed from
eigenvectors of the shift permutation operator that are also simultaneous
eigenvectors of bit-flip (parity) and possess bit-reversal (time-reversal)
symmetry.Comment: Version to appear in J. Phys. A. Added discussions; modified title;
corrected minor error
Relativistic graphene ratchet on semidisk Galton board
Using extensive Monte Carlo simulations we study numerically and analytically
a photogalvanic effect, or ratchet, of directed electron transport induced by a
microwave radiation on a semidisk Galton board of antidots in graphene. A
comparison between usual two-dimensional electron gas (2DEG) and electrons in
graphene shows that ratchet currents are comparable at very low temperatures.
However, a large mean free path in graphene should allow to have a strong
ratchet transport at room temperatures. Also in graphene the ratchet transport
emerges even for unpolarized radiation. These properties open promising
possibilities for room temperature graphene based sensitive photogalvanic
detectors of microwave and terahertz radiation.Comment: 4 pages, 4 figures. Research done at Quantware
http://www.quantware.ups-tlse.fr/. More detailed analysis is give
Non-inhibitory levels of oxygen during cultivation increase freeze-drying stress tolerance in Limosilactobacillus reuteri DSM 17938
The physiological effects of oxygen on Limosilactobacillus reuteri DSM 17938 during cultivation and the ensuing properties of the freeze-dried probiotic product was investigated. On-line flow cytometry and k-means clustering gating was used to follow growth and viability in real time during cultivation. The bacterium tolerated aeration at 500 ml/min, with a growth rate of 0.74 ± 0.13 h-1 which demonstrated that low levels of oxygen did not influence the growth kinetics of the bacterium. Modulation of the redox metabolism was, however, seen already at non-inhibitory oxygen levels by 1.5-fold higher production of acetate and 1.5-fold lower ethanol production. A significantly higher survival rate in the freeze-dried product was observed for cells cultivated in presence of oxygen compared to absence of oxygen (61.8 ± 2.4 % vs 11.5 ± 4.3 %), coinciding with a higher degree of unsaturated fatty acids (UFA:SFA ratio of 10 for air sparged vs 3.59 for N2 sparged conditions.). Oxygen also resulted in improved bile tolerance and boosted 5’nucleotidase activity (370 U/L vs 240 U/L in N2 sparged conditions) but lower tolerance to acidic conditions compared bacteria grown under complete anaerobic conditions which survived up to 90 min of exposure at pH 2. Overall, our results indicate the controlled supply of oxygen during production may be used as means for probiotic activity optimisation of L. reuteri DSM 17938
Distribution of resonances in the quantum open baker map
We study relevant features of the spectrum of the quantum open baker map. The
opening consists of a cut along the momentum direction of the 2-torus phase
space, modelling an open chaotic cavity. We study briefly the classical forward
trapped set and analyze the corresponding quantum nonunitary evolution
operator. The distribution of eigenvalues depends strongly on the location of
the escape region with respect to the central discontinuity of this map. This
introduces new ingredients to the association among the classical escape and
quantum decay rates. Finally, we could verify that the validity of the fractal
Weyl law holds in all cases.Comment: 6 pages, 7 figures, accepted for publication in Phys. Rev.
An inflammation-targeting hydrogel for local drug delivery in inflammatory bowel disease
There is a clinical need for new, more effective treatments for chronic and debilitating inflammatory bowel disease (IBD), including Crohn’s disease and ulcerative colitis. Targeting drugs selectively to the inflamed intestine may improve therapeutic outcomes and minimize systemic toxicity. We report the development of an inflammation-targeting hydrogel (IT-hydrogel) that acts as a drug delivery system to the inflamed colon. Hydrogel microfibers were generated from ascorbyl palmitate, an amphiphile that is generally recognized as safe (GRAS) by the U.S. Food and Drug Administration. IT-hydrogel microfibers loaded with the anti-inflammatory corticosteroid dexamethasone (Dex) were stable, released drug only upon enzymatic digestion, and demonstrated preferential adhesion to inflamed epithelial surfaces in vitro and in two mouse colitis models in vivo. Dex-loaded IT-hydrogel enemas, but not free Dex enemas, administered every other day to mice with colitis resulted in a significant reduction in inflammation and were associated with lower Dex peak serum concentrations and, thus, less systemic drug exposure. Ex vivo analysis of colon tissue samples from patients with ulcerative colitis demonstrated that IT-hydrogel microfibers adhered preferentially to mucosa from inflamed lesions compared with histologically normal sites. The IT-hydrogel drug delivery platform represents a promising approach for targeted enema-based therapies in patients with colonic IBD
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