10,191 research outputs found
Vortex-glass transition in superconducting Nb/Cu superlattices
Nb/Cu superconducting superlattices have been fabricated by dc magnetron
sputtering. This system shows a vortex glass transition with critical exponents
similar to high temperatures superconductors exponents. The transition
dymensionality is governed by the superconducting coupling regime. The vortex
glass transition shows a pure two dimensional behavior in decoupled
superlattices and a quasi-two dimensional behavior in the superlattice coupling
regime.Comment: 9 pages, 3 figure
Analysis of SPDEs Arising in Path Sampling Part I: The Gaussian Case
In many applications it is important to be able to sample paths of SDEs
conditional on observations of various kinds. This paper studies SPDEs which
solve such sampling problems. The SPDE may be viewed as an infinite dimensional
analogue of the Langevin SDE used in finite dimensional sampling. Here the
theory is developed for conditioned Gaussian processes for which the resulting
SPDE is linear. Applications include the Kalman-Bucy filter/smoother. A
companion paper studies the nonlinear case, building on the linear analysis
provided here
Optical-fiber source of polarization-entangled photon pairs in the 1550nm telecom band
We present a fiber based source of polarization-entangled photon pairs that
is well suited for quantum communication applications in the 1550nm band of
standard fiber-optic telecommunications. Polarization entanglement is created
by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed
orthogonally-polarized pump pulses and subsequently removing the time
distinguishability by passing the parametrically scattered signal-idler photon
pairs through a piece of birefringent fiber. Coincidence detection of the
signal-idler photons yields biphoton interference with visibility greater than
90%, while no interference is observed in direct detection of either the signal
or the idler photons. All four Bell states can be prepared with our setup and
we demonstrate violations of CHSH form of Bell's inequalities by up to 10
standard deviations of measurement uncertainty.Comment: 12 pages, 4 figures, to be submitted to Phys. Rev. Lett. See also
paper QTuB4 in QELS'03 Technical Digest (OSA, Washington, D.C., 2003). This
is a more complete versio
Aluminium-oxide wires for superconducting high kinetic inductance circuits
We investigate thin films of conducting aluminium-oxide, also known as
granular aluminium, as a material for superconducting high quality, high
kinetic inductance circuits. The films are deposited by an optimised reactive
DC magnetron sputter process and characterised using microwave measurement
techniques at milli-Kelvin temperatures. We show that, by precise control of
the reactive sputter conditions, a high room temperature sheet resistance and
therefore high kinetic inductance at low temperatures can be obtained. For a
coplanar waveguide resonator with 1.5\,k sheet resistance and a kinetic
inductance fraction close to unity, we measure a quality factor in the order of
700\,000 at 20\,mK. Furthermore, we observe a sheet resistance reduction by
gentle heat treatment in air. This behaviour is exploited to study the kinetic
inductance change using the microwave response of a coplanar wave guide
resonator. We find the correlation between the kinetic inductance and the sheet
resistance to be in good agreement with theoretical expectations.Comment: 16 pages, 7 figure
Common beans in Africa and their constraints
Beans are grown in Africa in a wide range of environments, mainly in the cool highlands of central and tropical eastern Africa, leading to a diversity of cropping systems and agronomic constraints to production. Beans are cultivated for large-scale production or home consumption either in monoculture or in association. The main constraints to production are poor agronomic practices, soil infertility, lack of improved cv., water stress, weed competition, and diseases and pests. Main diseases affecting bean crops in Africa include viral diseases (BCMV, SBMV, BGMV, and BYMV), bacterial diseases (bacterial wilt and bacterial brown spot), and fungal diseases (angular leaf spot, anthracnose, rust, Ascochyta blight, and floury leaf spot). Suggestions for disease management are given, highlighting the use of integrated control. Estimates of annual production per region and crop losses due to pathogens are given in table form. (CIAT)El frijol se cultiva en Africa en un amplio rango de ambientes, principalmente en las areas montanosas templadas de las regiones central y oriental tropical de Africa, lo cual supone diversos sistemas de cultivo y limitaciones agronomicas a la produccion. El frijol se cultiva para produccion en gran escala o para consumo domestico, sea en monocultivo o en asociacion. Las principales limitaciones a la produccion son practicas agronomicas inadecuadas, infertilidad del suelo, falta de cv. mejorados, estres hidrico, competencia de malezas y plagas y enfermedades. Las principales enfermedades que afectan el cultivo del frijol en Africa son las de tipo viral (BCMV, SBMV, BGMV y BYMV), las bacterianas (anublo bacteriano y mancha parda bacteriana) y las fungicas (mancha angular, antracnosis, roya, anublo por Ascochyta y mancha harinosa). Se dan sugerencias para manejo de enfermedades, destacando el uso de control integrado. Se incluyen en forma de tabla estimativos de produccion anual por region y perdidas de cosecha por patogenos. (CIAT
Parallel Algorithm and Dynamic Exponent for Diffusion-limited Aggregation
A parallel algorithm for ``diffusion-limited aggregation'' (DLA) is described
and analyzed from the perspective of computational complexity. The dynamic
exponent z of the algorithm is defined with respect to the probabilistic
parallel random-access machine (PRAM) model of parallel computation according
to , where L is the cluster size, T is the running time, and the
algorithm uses a number of processors polynomial in L\@. It is argued that
z=D-D_2/2, where D is the fractal dimension and D_2 is the second generalized
dimension. Simulations of DLA are carried out to measure D_2 and to test
scaling assumptions employed in the complexity analysis of the parallel
algorithm. It is plausible that the parallel algorithm attains the minimum
possible value of the dynamic exponent in which case z characterizes the
intrinsic history dependence of DLA.Comment: 24 pages Revtex and 2 figures. A major improvement to the algorithm
and smaller dynamic exponent in this versio
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