53,571 research outputs found
X-ray absorption branching ratio in actinides: LDA+DMFT approach
To investigate the x-ray absorption (XAS) branching ratio from the core 4d to
valence 5f states, we set up a theoretical framework by using a combination of
density functional theory in the local density approximation and Dynamical Mean
Field Theory (LDA+DMFT), and apply it to several actinides. The results of the
LDA+DMFT reduces to the band limit for itinerant systems and to the atomic
limit for localized f electrons, meaning a spectrum of 5f itinerancy can be
investigated. Our results provides a consistent and unified view of the XAS
branching ratio for all elemental actinides, and is in good overall agreement
with experiments.Comment: 6 pages, 4 figure
Hydrologic significance of lineaments in central Tennessee
There are no author-identified significant results in this report
Classical Sphaleron Rate on Fine Lattices
We measure the sphaleron rate for hot, classical Yang-Mills theory on the
lattice, in order to study its dependence on lattice spacing. By using a
topological definition of Chern-Simons number and going to extremely fine
lattices (up to beta=32, or lattice spacing a = 1 / (8 g^2 T)) we demonstrate
nontrivial scaling. The topological susceptibility, converted to physical
units, falls with lattice spacing on fine lattices in a way which is consistent
with linear dependence on (the Arnold-Son-Yaffe scaling relation) and
strongly disfavors a nonzero continuum limit. We also explain some unusual
behavior of the rate in small volumes, reported by Ambjorn and Krasnitz.Comment: 14 pages, includes 5 figure
Theory of superradiant scattering of laser light from Bose-Einstein condensates
In a recent MIT experiment, a new form of superradiant Rayleigh scattering
was observed in Bose-Einstein condensates. We present a detailed theory of this
phenomena in which the directional dependence of the scattering rate and
condensate depletion lead to mode competition which is ultimately responsible
for superradiance. The nonlinear response of the system is highly sensitive to
initial quantum fluctuations which cause large run to run variations in the
observed superradiant pulses.Comment: Updated version with new figures,a numerical simulation with
realistic experimental parameters is now included. Featured in September 1999
Physics Today, in Search and Discovery sectio
A pseudo-potential analog for zero-range photoassociation and Feshbach resonance
A zero-range approach to atom-molecule coupling is developed in analogy to
the Fermi-Huang pseudo-potential treatment of atom-atom interactions. It is
shown by explicit comparison to an exactly-solvable finite-range model that
replacing the molecular bound-state wavefunction with a regularized
delta-function can reproduce the exact scattering amplitude in the
long-wavelength limit. Using this approach we find an analytical solution to
the two-channel Feshbach resonance problem for two atoms in a spherical
harmonic trap
S matrix of collective field theory
By applying the Lehmann-Symanzik-Zimmermann (LSZ) reduction formalism, we
study the S matrix of collective field theory in which fermi energy is larger
than the height of potential. We consider the spatially symmetric and
antisymmetric boundary conditions. The difference is that S matrices are
proportional to momenta of external particles in antisymmetric boundary
condition, while they are proportional to energies in symmetric boundary
condition. To the order of , we find simple formulas for the S matrix
of general potential. As an application, we calculate the S matrix of a case
which has been conjectured to describe a "naked singularity".Comment: 19 page, LaTe
Gravitational-wave phasing for low-eccentricity inspiralling compact binaries to 3PN order
[abridged] Although gravitational radiation causes inspiralling compact
binaries to circularize, a variety of astrophysical scenarios suggest that
binaries might have small but nonnegligible orbital eccentricities when they
enter the low-frequency bands of ground and space-based gravitational-wave
detectors. If not accounted for, even a small orbital eccentricity can cause a
potentially significant systematic error in the mass parameters of an
inspiralling binary. Gravitational-wave search templates typically rely on the
quasi-circular approximation, which provides relatively simple expressions for
the gravitational-wave phase to 3.5 post-Newtonian (PN) order. The
quasi-Keplerian formalism provides an elegant but complex description of the
post-Newtonian corrections to the orbits and waveforms of inspiralling binaries
with any eccentricity. Here we specialize the quasi-Keplerian formalism to
binaries with low eccentricity. In this limit the non-periodic contribution to
the gravitational-wave phasing can be expressed explicitly as simple functions
of frequency or time, with little additional complexity beyond the well-known
formulas for circular binaries. These eccentric phase corrections are computed
to 3PN order and to leading order in the eccentricity for the standard PN
approximants. For a variety of systems these eccentricity corrections cause
significant corrections to the number of gravitational wave cycles that sweep
through a detector's frequency band. This is evaluated using several measures,
including a modification of the useful cycles. We also evaluate the role of
periodic terms that enter the phasing and discuss how they can be incorporated
into some of the PN approximants. While the eccentric extension of the PN
approximants is our main objective, this work collects a variety of results
that may be of interest to others modeling eccentric relativistic binaries.Comment: 49 pages, 4 figures. Submitted to Phys. Rev. D. Supplementary
materials available at
http://link.aps.org/supplemental/10.1103/PhysRevD.93.124061. V2: minor
updates to match published versio
Local Density of the Bose Glass Phase
We study the Bose-Hubbard model in the presence of on-site disorder in the
canonical ensemble and conclude that the local density of the Bose glass phase
behaves differently at incommensurate filling than it does at commensurate one.
Scaling of the superfluid density at incommensurate filling of and
on-site interaction predicts a superfluid-Bose glass transition at
disorder strength of . At this filling the local density
distribution shows skew behavior with increasing disorder strength.
Multifractal analysis also suggests a multifractal behavior resembling that of
the Anderson localization. Percolation analysis points to a phase transition of
percolating non-integer filled sites around the same value of disorder. Our
findings support the scenario of percolating superfluid clusters enhancing
Anderson localization near the superfluid-Bose glass transition. On the other
hand, the behavior of the commensurate filled system is rather different. Close
to the tip of the Mott lobe () we find a Mott insulator-Bose
glass transition at disorder strength of . An analysis of
the local density distribution shows Gaussian like behavior for a wide range of
disorders above and below the transition.Comment: 12 pages, 14 figure
Microstructural analysis of solar cell welds
Parallel-gap resistance welding of silicon solar cells with copper interconnects results in complex microstructural variations that depend on the welding variables. At relatively low heat input solid-state welds are produced. At medium heat the Ag-Cu eutectic forms resulting in a braze joint. High heat produces a fusion weld with complete melting of the silver layer on the silicon solar cell. If the silicon is also melted, cracking occurs in the silicon cell below the weld nugget. These determinations were made using light microscopy, microprobe, and scanning electron microscopy analyses
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