1,877 research outputs found
Dynamical Localization in Quasi-Periodic Driven Systems
We investigate how the time dependence of the Hamiltonian determines the
occurrence of Dynamical Localization (DL) in driven quantum systems with two
incommensurate frequencies. If both frequencies are associated to impulsive
terms, DL is permanently destroyed. In this case, we show that the evolution is
similar to a decoherent case. On the other hand, if both frequencies are
associated to smooth driving functions, DL persists although on a time scale
longer than in the periodic case. When the driving function consists of a
series of pulses of duration , we show that the localization time
increases as as the impulsive limit, , is
approached. In the intermediate case, in which only one of the frequencies is
associated to an impulsive term in the Hamiltonian, a transition from a
localized to a delocalized dynamics takes place at a certain critical value of
the strength parameter. We provide an estimate for this critical value, based
on analytical considerations. We show how, in all cases, the frequency spectrum
of the dynamical response can be used to understand the global features of the
motion. All results are numerically checked.Comment: 7 pages, 5 figures included. In this version is that Subsection III.B
and Appendix A on the quasiperiodic Fermi Accelerator has been replaced by a
reference to published wor
Quantum walk as a generalized measuring device
We show that a one-dimensional discrete time quantum walk can be used to
implement a generalized measurement in terms of positive operator value measure
(POVM) on a single qubit. More precisely, we show that for a single qubit any
set of rank 1 and rank 2 POVM elements can be generated by a properly
engineered quantum walk. In such a scenario the measurement of particle at
position x=i corresponds to a measurement of a POVM element E_i on a qubit. We
explicitly construct quantum walks implementing unambiguous state
discrimination and SIC-POVM.Comment: 6 pages, 1 figur
Los trabajadores y sus organizaciones durante los gobiernos kirchneristas
La larga década kirchnerista significó en Argentina el retorno de antiguas instituciones del mundo del trabajo, como las convenciones colectivas, de la mano del crecimiento del empleo durante buena parte del periodo 2003-2015. No obstante, el trabajo no registrado y la división entre el movimiento obrero organizado y el «otro movimiento obrero» marcaron líneas de fractura dentro del mundo de los trabajadores y pusieron en evidencia los límites de las transformaciones recientes.Fil: Abal Medina, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de General Sarmiento; Argentina. Universidad Nacional de San Martín; Argentin
Spatial search in a honeycomb network
The spatial search problem consists in minimizing the number of steps
required to find a given site in a network, under the restriction that only
oracle queries or translations to neighboring sites are allowed. In this paper,
a quantum algorithm for the spatial search problem on a honeycomb lattice with
sites and torus-like boundary conditions. The search algorithm is based on
a modified quantum walk on a hexagonal lattice and the general framework
proposed by Ambainis, Kempe and Rivosh is used to show that the time complexity
of this quantum search algorithm is .Comment: 10 pages, 2 figures; Minor typos corrected, one Reference added.
accepted in Math. Structures in Computer Science, special volume on Quantum
Computin
Extended Advancing Front Technique for the Initial Triangular Mesh Construction on a Single Coil for Radiative Heat Transfer
Radiative heat distribution inside an ethylene cracker furnace is often modeled using the finite volume and finite element methods. In both cases, meshes in the form of rectangles and triangles are needed to form the approximating points in the domain. In this paper, a new method called extended advancing Front technique (XAFT) is proposed for meshing the domain inside the cracker furnace, integrated with the deployment of sensors on the wall to obtain the required boundary values. XAFT is the extended version of standard advancing Front technique (SAFT) where the two normal cases in SAFT are extended with six cases of study for the element creation procedure in order to generate the initial mesh. The focus of this method is to construct triangular meshes with the requirements of having the location of sensors deployed along the wall as boundary nodes and to generate nodes at certain boundaries with linearly different lengths. It is also our objective to construct the triangular element iteratively without having to re-order the Front or delete the existing element. There are two contributions from the paper. First is the introduction of six extended cases for the element creation procedure, and second is the layer concept to generate edges with linearly different lengths. XAFT provides the framework for the heat to be approximated using the discrete ordinate method, which is a variant of the finite volume method. Simulation results produced using FLUENT support the findings for effectively approximating the radiation intensity and temperature values inside the furnace
Extended Advancing Front Technique for the Initial Triangular Mesh Construction on a Single Coil for Radiative Heat Transfer
Radiative heat distribution inside an ethylene cracker furnace is often modeled using the finite volume and finite element methods. In both cases, meshes in the form of rectangles and triangles are needed to form the approximating points in the domain. In this paper, a new method called extended advancing Front technique (XAFT) is proposed for meshing the domain inside the cracker furnace, integrated with the deployment of sensors on the wall to obtain the required boundary values. XAFT is the extended version of standard advancing Front technique (SAFT) where the two normal cases in SAFT are extended with six cases of study for the element creation procedure in order to generate the initial mesh. The focus of this method is to construct triangular meshes with the requirements of having the location of sensors deployed along the wall as boundary nodes and to generate nodes at certain boundaries with linearly different lengths. It is also our objective to construct the triangular element iteratively without having to re-order the Front or delete the existing element. There are two contributions from the paper. First is the introduction of six extended cases for the element creation procedure, and second is the layer concept to generate edges with linearly different lengths. XAFT provides the framework for the heat to be approximated using the discrete ordinate method, which is a variant of the finite volume method. Simulation results produced using FLUENT support the findings for effectively approximating the radiation intensity and temperature values inside the furnace
In vitro and in vivo toxicity study of compounds of natural origin: marine biotoxins
This doctoral thesis provides data on different phases necessary for a complete risk assessment of the most common marine biotoxins in Galicia: okadaic acid (OA), their derivatives the dinophysistoxins (DTXs), the azaspiracids (AZAs), and also the emerging toxin: tetrodotoxin (TTX). For this, elimination of the toxic source from the natural environment, the passage of toxins through the gastrointestinal tract, toxic effects, and oral toxicity studies are evaluated. Natural clays with smaller particle size result more efficient in eliminating dinoflagellates producing toxins. Azaspiracid-1 (AZA1) crosses the intestinal barrier in a dose-
dependent manner causing alterations in intestinal epithelial cells. In vivo studies reveal highest toxicity for DTX1 and lowest for DTX2 with respect to OA, while a relationship between the diarreal effect of OA and its neuronal action is suggested in vitro. Besides, this is the first time that oral lethal dose 50 and NOAEL (No-Observed-Adverse-Effect-Level) values for TTX are established
Quantum random walk on the line as a markovian process
We analyze in detail the discrete--time quantum walk on the line by
separating the quantum evolution equation into Markovian and interference
terms. As a result of this separation, it is possible to show analytically that
the quadratic increase in the variance of the quantum walker's position with
time is a direct consequence of the coherence of the quantum evolution. If the
evolution is decoherent, as in the classical case, the variance is shown to
increase linearly with time, as expected. Furthermore we show that this system
has an evolution operator analogous to that of a resonant quantum kicked rotor.
As this rotator may be described through a quantum computational algorithm, one
may employ this algorithm to describe the time evolution of the quantum walker.Comment: few typos corrected, 13 pages, 2 figures, to appear in Physica
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