1,377 research outputs found
Characterization of quantum angular-momentum fluctuations via principal components
We elaborate an approach to quantum fluctuations of angular momentum based on
the diagonalization of the covariance matrix in two versions: real symmetric
and complex Hermitian. At difference with previous approaches this is SU(2)
invariant and avoids any difficulty caused by nontrivial commutators.
Meaningful uncertainty relations are derived which are nontrivial even for
vanishing mean angular momentum. We apply this approach to some relevant
states.Comment: 10 pages, Two column. New section II and some clarifying comment
MOTION OF A LARGE OBJECT IN A 2D BUBBLING FLUIDIZED BED
The motion of a large object in a bubbling fluidized bed is experimentally studied using digital image analysis. A wide range of fluidized bed applications involves the motion of large objects within the bed, such objects being reactants, catalysts, agglomerates, etc.
The experiments were run in a 2D bubbling fluidized bed with glass spheres as bed material. The object motion is measured using tracking techniques, while independent measurements of the dense phase velocity (using PIV) and bubble velocity were carried out. The effect of the excess gas velocity on the object motion was also analyzed.
It is generally accepted that objects with densities in a range around the bed density will describe sinking-rising cycles throughout the whole bed, where the sinking motion is similar to that of the dense phase, and the rising motion is composed of a number of sudden jerks or jumps, as a result of the raising effect of passing bubbles. This work characterized the circulation patterns of an object with a density similar to that of the bed material, but much larger in size. A comparison between the object rising motion and the local bubble motion provided evidence for the study of the bubble ability to raise the object, depending on the bubble velocity and size. A comparison between the object sinking motion and the dense phase motion served to analyze the minor effect of buoyancy forces over the object sinking motion. Finally, the combined effects of the maximum attained depth and the number of jerks in the circulation time is studied, with some insight in the multiple-jerks phenomenon
Throughflow Velocity Crossing the Dome of Erupting Bubbles in 2-D Fluidized Beds
A new non-intrusive method for measuring the throughflow velocity crossing the dome of erupting bubbles in freely bubbling 2-D fluidized beds is presented. Using a high speed video-camera, the dome acceleration, drag force and throughflow velocity profiles are obtained for different experiments, varying the superficial gas velocity. The acceleration profiles show greater values in the dome zone where the gravity component is negligible. The drag force and the throughflow velocity profiles show a uniform value in the central region of the dome (40 deg \u3c \u3c 140 deg) and the total throughflow increases with the superficial gas velocity
Hydrodynamic Characteristics of a Fluidized Bed with Rotating Distributor
The performance of a novel rotating distributor fluidized bed is presented. The pressure drop and the standard deviation of pressure fluctuations, Ïp, were used to find the minimum fluidization velocity, Umf, and to characterize the quality of fluidization at different rotational speeds of the distributor plate. Experiments were conducted in the freely bubbling regime in a 0.19 m i.d. fluidized bed, operating with Group B particles according to Geldartâs classification. A decrease in Umf is observed when the rotational speed increases. Frequency analysis of pressure fluctuations shows that fluidization can be controlled by the adjustable rotational speed, at several excess gas velocities
Wigner Functions on a Lattice
The Wigner functions on the one dimensional lattice are studied. Contrary to
the previous claim in literature, Wigner functions exist on the lattice with
any number of sites, whether it is even or odd. There are infinitely many
solutions satisfying the conditions which reasonable Wigner functions should
respect. After presenting a heuristic method to obtain Wigner functions, we
give the general form of the solutions. Quantum mechanical expectation values
in terms of Wigner functions are also discussed.Comment: 11 pages, no figures, REVTE
Discrete Wigner functions and the phase space representation of quantum teleportation
We present a phase space description of the process of quantum teleportation
for a system with an dimensional space of states. For this purpose we
define a discrete Wigner function which is a minor variation of previously
existing ones. This function is useful to represent composite quantum system in
phase space and to analyze situations where entanglement between subsystems is
relevant (dimensionality of the space of states of each subsystem is
arbitrary). We also describe how a direct tomographic measurement of this
Wigner function can be performed.Comment: 8 pages, 1 figure, to appear in Phys Rev
Collision-model-based approach to non-Markovian quantum dynamics
We present a theoretical framework to tackle quantum non-Markovian dynamics
based on a microscopic collision model (CM), where the bath consists of a large
collection of initially uncorrelated ancillas. Unlike standard memoryless CMs,
we endow the bath with memory by introducing inter-ancillary collisions between
next system-ancilla interactions. Our model interpolates between a fully
Markovian dynamics and the continuous interaction of the system with a single
ancilla, i.e., a strongly non-Markovian process. We show that in the continuos
limit one can derive a general master equation, which while keeping such
features is guaranteed to describe an unconditionally completely positive and
trace-preserving dynamics. We apply our theory to an atom in a dissipative
cavity for a Lorentzian spectral density of bath modes, a dynamics which can be
exactly solved. The predicted evolution shows a significant improvement in
approaching the exact solution with respect to two well-known memory-kernel
master equations.Comment: 5+1 pages, 2 figure
Strategies to tailor the architecture of dual Ag/Fe-oxide nano-heterocrystalsâinterfacial and morphology effects on the magnetic behavior
Bifunctional nanostructured architectures have shown appealing properties, since a single entity can combine the diverse properties of its individual constituents. Particularly, by growing Fe-oxide domains over Ag nanoparticles, the plasmonic and superparamagnetic properties can be combined in a single particle. Beyond the multifunctionality of this system, there are several properties that emerge from intrinsic factors, such as: interface and/or morphology. In this study, we present the synthesis protocols to obtain two sets of heterocrystals, each one with different morphology: dimer and flower-like. In addition, the magnetization behavior of these hybrid nano-heterocrystals is investigated and discussed. These nanomaterials were built by a seed assisted heterogeneous nucleation process, carried out in organic solvents of high boiling point, using the same batch of silver nanoparticles with a mean size of 6ânm as seeds, and tuning the electron-donor capacity of the reaction environment at the thermal decomposition of the iron precursor. Ag/Fe3O4 heterocrystals with dimer and flower-like morphologies were obtained. The synthesis protocols for generating these types of nanomaterials are discussed step-by-step. Structural and morphological properties were determined by transmission electron microscopy, x-ray diffraction and x-ray absorption fine structure. DC magnetization results suggest that the silver/magnetite coupling generates an increase of the blocking temperature in comparison to those obtained from pure magnetite. This behavior could be linked to a possible increase in the magnetic anisotropy produced by an additional disorder at the AgâFe3O4 interface. The higher interface area of the Ag/Fe3O4 heterocrystals with flower-like architecture leads to a higher blocking temperature and a stronger magnetic anisotropy. These results are supported by AC susceptibility data.Fil: Tancredi Gentili, Pablo. Universidad de Buenos Aires. Facultad de IngenierĂa. Departamento de FĂsica. Laboratorio de SĂłlidos Amorfos; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de TecnologĂas y Ciencias de la IngenierĂa "Hilario FernĂĄndez Long". Universidad de Buenos Aires. Facultad de IngenierĂa. Instituto de TecnologĂas y Ciencias de la IngenierĂa "Hilario FernĂĄndez Long"; ArgentinaFil: Moscoso Londoño, Oscar. Universidad AutĂłnoma de Manizales; Colombia. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidade Estadual de Campinas; BrasilFil: Rivas Rojas, Patricia Carolina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de TecnologĂas y Ciencias de la IngenierĂa "Hilario FernĂĄndez Long". Universidad de Buenos Aires. Facultad de IngenierĂa. Instituto de TecnologĂas y Ciencias de la IngenierĂa "Hilario FernĂĄndez Long"; Argentina. Universidad de Buenos Aires. Facultad de IngenierĂa. Departamento de FĂsica. Laboratorio de SĂłlidos Amorfos; ArgentinaFil: Wolff, U.. Leibniz Institute for Solid State and Materials Research; AlemaniaFil: Socolovsky, Leandro MartĂn. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad TecnolĂłgica Nacional. Facultad Regional Santa Cruz. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Nacional de la Patagonia Austral. Centro de Investigaciones y Transferencia de Santa Cruz; ArgentinaFil: Knobel, M.. Universidade Estadual de Campinas; BrasilFil: Muraca, D.. Universidade Estadual de Campinas; Brasi
Quantum computers in phase space
We represent both the states and the evolution of a quantum computer in phase
space using the discrete Wigner function. We study properties of the phase
space representation of quantum algorithms: apart from analyzing important
examples, such as the Fourier Transform and Grover's search, we examine the
conditions for the existence of a direct correspondence between quantum and
classical evolutions in phase space. Finally, we describe how to directly
measure the Wigner function in a given phase space point by means of a
tomographic method that, itself, can be interpreted as a simple quantum
algorithm.Comment: 16 pages, 7 figures, to appear in Phys Rev
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