3,025 research outputs found
Optimization of photon storage fidelity in ordered atomic arrays
A major application for atomic ensembles consists of a quantum memory for
light, in which an optical state can be reversibly converted to a collective
atomic excitation on demand. There exists a well-known fundamental bound on the
storage error, when the ensemble is describable by a continuous medium governed
by the Maxwell-Bloch equations. The validity of this model can break down,
however, in systems such as dense, ordered atomic arrays, where strong
interference in emission can give rise to phenomena such as subradiance and
"selective" radiance. Here, we develop a general formalism that finds the
maximum storage efficiency for a collection of atoms with discrete, known
positions, and a given spatial mode in which an optical field is sent. As an
example, we apply this technique to study a finite two-dimensional square array
of atoms. We show that such a system enables a storage error that scales with
atom number like ,
and that, remarkably, an array of just atoms in principle allows
for an efficiency comparable to a disordered ensemble with optical depth of
around 600.Comment: paper is now identical to published versio
Multicomponent reaction-diffusion processes on complex networks
We study the reaction-diffusion process on uncorrelated
scale-free networks analytically. By a mean-field ansatz we derive analytical
expressions for the particle pair-correlations and the particle density.
Expressing the time evolution of the particle density in terms of the
instantaneous particle pair-correlations, we determine analytically the
`jamming' effect which arises in the case of multicomponent, pair-wise
reactions. Comparing the relevant terms within the differential equation for
the particle density, we find that the `jamming' effect diminishes in the
long-time, low-density limit. This even holds true for the hubs of the network,
despite that the hubs dynamically attract the particles.Comment: 8 pages, 6 figure
Strongly inhibited transport of a 1D Bose gas in a lattice
We report the observation of strongly damped dipole oscillations of a quantum
degenerate 1D atomic Bose gas in a combined harmonic and optical lattice
potential. Damping is significant for very shallow axial lattices (0.25 photon
recoil energies), and increases dramatically with increasing lattice depth,
such that the gas becomes nearly immobile for times an order of magnitude
longer than the single-particle tunneling time. Surprisingly, we see no
broadening of the atomic quasimomentum distribution after damped motion. Recent
theoretical work suggests that quantum fluctuations can strongly damp dipole
oscillations of 1D atomic Bose gas, providing a possible explanation for our
observations.Comment: 5 pages, 4 figure
EFFECT OF SUPERHEATING DEGREE AND PRESSURE ON EFFICIENCY OF AN ORES (ORGANIC RANKINE ENERGY STORAGE) SYSTEM
The increased share of intermittent renewable energy sources has led to the development of new energy storage solutions to mitigate the effects of the variability of energy supply. CAES (Compressed Air Energy Storage) and LAES (Liquid Air Energy Storage) are two of the main solutions for medium to large-scale systems for long-term energy storage. However, both are limited; the first requires the availability of suitable geological formations and the second requires considerable investment because of the required liquefaction process. This work aims to evaluate the thermodynamic performance of an energy storage system, called Organic Rankine Energy Storage (ORES), with a focus on the effects of pressure and superheating degree at the expander inlet on the round-trip efficiency (i.e. ratio of generated energy during energy discharge over consumed energy during energy storage) of the system. The system was evaluated for six organic fluids which were selected based on commercial maturity, environmental impacts, and safety conditions, namely R-134a, R-152a, R-142b, R-236ea, R-365mfc, and R-141b. The efficiency of the system was obtained for each of those fluids using a steady-state model approximation of the operation of the system and for pressures at the expander inlet varying from 675 kPa up to 4,300 kPa (or 95% of the critical pressure, if lower) and for superheating degrees from 0 up to 40 K. The evaluation of the system for six organic fluids as working fluid resulted in round-trip efficiencies around 70 % (comparable to both CAES and LAES when subject to similar methodologies) with higher sensitivity to pressure than to superheating degree. For all fluids, an increase of 5 K in the superheating degree resulted in an absolute decrease of 2-5% in the round-trip efficiency. Effects of pressure were more diverse, R-152b, R-134a and R-142b showed an average reduction of 10% in efficiency for each reduction of 500 kPa in pressure (in the high efficiency operation region, while R-365mfc and R-141b were much less affected, around 5% decrease in efficiency for each reduction of 500 kPa. The fluids that had the highest efficiencies and that also presented a high efficiency for a wider range of pressures were the R141b and R365mfc, which are also the fluids with the highest critical temperatures
Utilizacao de materiais flutuantes no controle da evaporacao no Tropico Semi-Arido (TSA).
Materiais flutuantes foram testados em tanques tipo Classe A, com o objetivo de reduzir as perdas por evaporacao das superficies livres d'agua. As coberturas consistiram de discos impoermaveis compostos de vermiculita, parafina e cera de carnauba (Copernicia cerifera Mart.); esferas de barro vitrificadas; esferas de barro nao vitrificadas; e discos de isopor impreganados de uma mistura de cera de carnauba mais parafina derretida. Cada tratamento cobriu 80% da superficie exposta do tanque, apresentando os seguintes resultados no controle das perdas: 54%, 60%, 50% e 61% respectivamente. A eficiencia apresentada indicou que as coberturas empregadas poderao ser viaveis
Análise global da expressão de genes Dof em videira.
Neste trabalho é caracterizada a família gênica Dof em videira (Vitis vinifera L.), a qual é composta por 25 genes. A busca por domínios conservados foi realizada utilizando-se o programa MEME suite v.4.9.0. Estudos filogenéticos foram conduzidos comparando 163 sequências Dof de videira, álamo, Arabidopsis thaliana e tomate com proteínas Dof de função conhecida previamente descritos na literatura
Preparing and probing atomic number states with an atom interferometer
We describe the controlled loading and measurement of number-squeezed states
and Poisson states of atoms in individual sites of a double well optical
lattice. These states are input to an atom interferometer that is realized by
symmetrically splitting individual lattice sites into double wells, allowing
atoms in individual sites to evolve independently. The two paths then
interfere, creating a matter-wave double-slit diffraction pattern. The time
evolution of the double-slit diffraction pattern is used to measure the number
statistics of the input state. The flexibility of our double well lattice
provides a means to detect the presence of empty lattice sites, an important
and so far unmeasured factor in determining the purity of a Mott state
- …