2,588 research outputs found
Pulsed laser deposition of KNbO<sub>3</sub> thin films
The laser ablation of stationary KNbO3 single crystal targets induces a Nb enrichment of the target surface. In rotated targets this effect is observed only in those areas irradiated with low laser fluence. The composition of the plasma formed close to the target surface is congruent with the target composition; however, at further distances K-deficient films are formed due to the preferential backscattering of K in the plasma. This loss may be compensated for by using K-rich ceramic targets. Best results so far have been obtained with [K]/[Nb] = 2.85 target composition, and crystalline KNbO3 films are formed when heating the substrates to 650 °C. Films formed on (100)MgO single crystals are usually single phase and oriented with the (110) film plane parallel to the (100) substrate surface. (100)NbO may coexist with KNbO3 on (100)MgO. At substrate temperatures higher than 650 °C, niobium diffuses into MgO forming Mg4Nb2O9 and NbO, leading to K evaporation from the film. Films formed on (001) alpha-Al2O3 (sapphire) show the coexistence of (111), (110), and (001) orientations of KNbO3, and the presence of NbO2 is also observed. KNbO3 films deposited on (001)LiNbO3 crystallize with the (111) plane of the film parallel to the substrate surface. For the latter two substrates the Nb diffusion into the substrate is lower than in MgO and consequently the K concentration retained in the film is comparatively larger
Density-Matrix approach to a Strongly Coupled Two-Component Bose-Einstein Condensate
The time evolution equations for average values of population and relative
phase of a strongly coupled two component BEC is derived analytically. The two
components are two hyper-fine states coupled by an external laser that drives
fast Rabi oscillations between these states. Specifically, this derivation
incorporates the two-mode model proposed in [1] for the strongly coupled
hyper-fine states of Rb. The fast Rabi cycle is averaged out and rate equations
are derived that represents the slow dynamics of the system. These include the
collapse and revival of Rabi oscillations and their subsequent dependence on
detuning and trap displacement as reported in experiments of [1]. A proposal to
create stable vortices is also given.Comment: 11 Latex pages, 2 figures (Figure 3 was removed and the text chnaged
accordingly
Geotechnical characterization of the North Ramp of the Exploratory Studies Facility: Yucca Mountain Site Characterization Project. Volume 1, Data summary
This report presents the results of geological and geotechnical characterization of the Miocene volcanic tuff rocks of the Timber Mountain and Paintbrush groups that the tunnel boring machine will encounter during excavation of the Exploratory Studies Facility (ESF) North Ramp. The is being constructed by the DOE as part of the Yucca Mountain Project site characterization activities. The purpose of these activities is to evaluate the feasibility of locating a potential high-level nuclear waste repository on lands adjacent to the Nevada Test Site, Nye County, Nevada. This report was prepared as part of the Soil and Rock Properties Studies in accordance with the 8.3.1.14.2 Study Plan. This report is volume 1 of the data summary
Vector bundles on the projective line and finite domination of chain complexes
Finitely dominated chain complexes over a Laurent polynomial ring in one
indeterminate are characterised by vanishing of their Novikov homology. We
present an algebro-geometric approach to this result, based on extension of
chain complexes to sheaves on the projective line. We also discuss the
K-theoretical obstruction to extension.Comment: v1: 11 page
Topology of the ground state of two interacting Bose-Einstein condensates
We investigate the spatial patterns of the ground state of two interacting
Bose-Einstein condensates. We consider the general case of two different atomic
species (with different mass and in different hyperfine states) trapped in a
magnetic potential whose eigenaxes can be tilted with respect to the vertical
direction, giving rise to a non trivial gravitational sag. Despite the
complicated geometry, we show that within the Thomas-Fermi approximations and
upon appropriate coordinate transformations, the equations for the density
distributions can be put in a very simple form. Starting from this expressions
we give explicit rules to classify the different spatial topologies which can
be produced, and we discuss how the behavior of the system is influenced by the
inter-atomic scattering length. We also compare explicit examples with the full
numeric Gross-Pitaevskii calculation.Comment: RevTex4, 8 pages, 7 figure
Dynamics of two colliding Bose-Einstein condensates in an elongated magneto-static trap
We study the dynamics of two interacting Bose-Einstein condensates, by
numerically solving two coupled Gross-Pitaevskii equations at zero temperature.
We consider the case of a sudden transfer of atoms between two trapped states
with different magnetic moments: the two condensates are initially created with
the same density profile, but are trapped into different magnetic potentials,
whose minima are vertically displaced by a distance much larger than the
initial size of both condensates. Then the two condensates begin to perform
collective oscillations, undergoing a complex evolution, characterized by
collisions between the two condensates. We investigate the effects of their
mutual interaction on the center-of-mass oscillations and on the time evolution
of the aspect ratios. Our theoretical analysis provides a useful insight into
the recent experimental observations by Maddaloni et al., cond-mat/0003402.Comment: 8 pages, 7 figures, RevTe
Deformation independent open brane metrics and generalized theta parameters
We investigate the consequences of generalizing certain well established
properties of the open string metric to the conjectured open membrane and open
Dp-brane metrics. By imposing deformation independence on these metrics their
functional dependence on the background fields can be determined including the
notorious conformal factor. In analogy with the non-commutativity parameter
in the string case, we also obtain `generalized' theta
parameters which are rank q+1 antisymmetric tensors (polyvectors) for open
Dq-branes and rank 3 for the open membrane case. The expressions we obtain for
the open membrane quantities are expected to be valid for general background
field configurations, while the open D-brane quantities are only valid for one
parameter deformations. By reducing the open membrane data to five dimensions,
we show that they, modulo a subtlety with implications for the relation between
OM-theory and NCYM, correctly generate the open string and open D2-data.Comment: 24 pages, LaTe
Real time statistical field theory
We have written a {\it Mathematica} program that calculates the integrand
corresponding to any amplitude in the closed-time-path formulation of real time
statistical field theory. The program is designed so that it can be used by
someone with no previous experience with {\it Mathematica}. It performs the
contractions over the tensor indices that appear in real time statistical field
theory and gives the result in the 1-2, Keldysh or RA basis. We have used the
program to calculate the ward identity for the QED 3-point function, the QED
4-point function for two photons and two fermions, and the QED 5-point function
for three photons and two fermions. In real time statistical field theory,
there are seven 3-point functions, 15 4-point functions and 31 5-point
functions. We produce a table that gives the results for all of these
functions. In addition, we give a simple general expression for the KMS
conditions between -point green functions and vertex functions, in both the
Keldysh and RA basesComment: 25 pages, 12 figure
Response Functions in Phase Ordering Kinetics
We discuss the behavior of response functions in phase ordering kinetics
within the perturbation theory approach developed earlier. At zeroth order the
results agree with previous gaussian theory calculations. At second order the
nonequilibrium exponents \lambda and \lambda_{R} are changed but remain equal.Comment: 29 page
Inflationary models inducing non-Gaussian metric fluctuations
We construct explicit models of multi-field inflation in which the primordial
metric fluctuations do not necessarily obey Gaussian statistics. These models
are realizations of mechanisms in which non-Gaussianity is first generated by a
light scalar field and then transferred into curvature fluctuations. The
probability distribution functions of the metric perturbation at the end of
inflation are computed. This provides a guideline for designing strategies to
search for non-Gaussian signals in future CMB and large scale structure
surveys.Comment: 4 pages, 7 figure
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