105,336 research outputs found
Electronic structure of strongly correlated d-wave superconductors
We study the electronic structure of a strongly correlated d-wave
superconducting state. Combining a renormalized mean field theory with direct
calculation of matrix elements, we obtain explicit analytical results for the
nodal Fermi velocity, v_F, the Fermi wave vector, k_F, and the momentum
distribution, n_k, as a function of hole doping in a Gutzwiller projected
d-wave superconductor. We calculate the energy dispersion, E_k, and spectral
weight of the Gutzwiller-Bogoliubov quasiparticles, and find that the spectral
weight associated with the quasiparticle excitation at the antinodal point
shows a non monotonic behavior as a function of doping. Results are compared to
angle resolved photoemission spectroscopy (ARPES) of the high temperature
superconductors.Comment: final version, comparison to experiments added, 4+ pages, 4 figure
Parametric analysis of diffuser requirements for high expansion ratio space engine
A supersonic diffuser ejector design computer program was developed. Using empirically modified one dimensional flow methods the diffuser ejector geometry is specified by the code. The design code results for calculations up to the end of the diffuser second throat were verified. Diffuser requirements for sea level testing of high expansion ratio space engines were defined. The feasibility of an ejector system using two commonly available turbojet engines feeding two variable area ratio ejectors was demonstrated
The origin of phase in the interference of Bose-Einstein condensates
We consider the interference of two overlapping ideal Bose-Einstein
condensates. The usual description of this phenomenon involves the introduction
of a so-called condensate wave functions having a definite phase. We
investigate the origin of this phase and the theoretical basis of treating
interference. It is possible to construct a phase state, for which the particle
number is uncertain, but phase is known. However, how one would prepare such a
state before an experiment is not obvious. We show that a phase can also arise
from experiments using condensates in Fock states, that is, having known
particle numbers. Analysis of measurements in such states also gives us a
prescription for preparing phase states. The connection of this procedure to
questions of ``spontaneously broken gauge symmetry'' and to ``hidden
variables'' is mentioned.Comment: 22 pages 4 figure
Quasi-Particles in Two-Dimensional Hubbard Model: Splitting of Spectral Weight
It is shown that the energy and momentum dependences of
the electron self-energy function are, where is some
constant, being the band energy,
and the critical exponent , which depends on the curvature of the
Fermi surface at , satisfies, . This leads to a
new type of electron liquid, which is the Fermi liquid in the limit of but for has a split
one-particle spectra as in the Tomonaga-Luttinger liquid.Comment: 8 pages (LaTeX) 4 figures available upon request will be sent by air
mail. KomabaCM-preprint-O
One-Particle Excitation of the Two-Dimensional Hubbard Model
The real part of the self-energy of interacting two-dimensional electrons has
been calculated in the t-matrix approximation. It is shown that the forward
scattering results in an anomalous term leading to the vanishing
renormalization factor of the one-particle Green function, which is a
non-perturbative effect of the interaction U. The present result is a
microscopic demonstration of the claim by Anderson based on the conventional
many-body theory. The effect of the damping of the interacting electrons, which
has been ignored in reaching above conclusion, has been briefly discussed.Comment: 7 pages, LaTeX, 1 figure, uses jpsj.sty, to be published in J. Phys.
Soc. Jpn. 66 No. 3 (1997
Recommendation Subgraphs for Web Discovery
Recommendations are central to the utility of many websites including
YouTube, Quora as well as popular e-commerce stores. Such sites typically
contain a set of recommendations on every product page that enables visitors to
easily navigate the website. Choosing an appropriate set of recommendations at
each page is one of the key features of backend engines that have been deployed
at several e-commerce sites.
Specifically at BloomReach, an engine consisting of several independent
components analyzes and optimizes its clients' websites. This paper focuses on
the structure optimizer component which improves the website navigation
experience that enables the discovery of novel content.
We begin by formalizing the concept of recommendations used for discovery. We
formulate this as a natural graph optimization problem which in its simplest
case, reduces to a bipartite matching problem. In practice, solving these
matching problems requires superlinear time and is not scalable. Also,
implementing simple algorithms is critical in practice because they are
significantly easier to maintain in production. This motivated us to analyze
three methods for solving the problem in increasing order of sophistication: a
sampling algorithm, a greedy algorithm and a more involved partitioning based
algorithm.
We first theoretically analyze the performance of these three methods on
random graph models characterizing when each method will yield a solution of
sufficient quality and the parameter ranges when more sophistication is needed.
We complement this by providing an empirical analysis of these algorithms on
simulated and real-world production data. Our results confirm that it is not
always necessary to implement complicated algorithms in the real-world and that
very good practical results can be obtained by using heuristics that are backed
by the confidence of concrete theoretical guarantees
Approaching the Problem of Time with a Combined Semiclassical-Records-Histories Scheme
I approach the Problem of Time and other foundations of Quantum Cosmology
using a combined histories, timeless and semiclassical approach. This approach
is along the lines pursued by Halliwell. It involves the timeless probabilities
for dynamical trajectories entering regions of configuration space, which are
computed within the semiclassical regime. Moreover, the objects that Halliwell
uses in this approach commute with the Hamiltonian constraint, H. This approach
has not hitherto been considered for models that also possess nontrivial linear
constraints, Lin. This paper carries this out for some concrete relational
particle models (RPM's). If there is also commutation with Lin - the Kuchar
observables condition - the constructed objects are Dirac observables.
Moreover, this paper shows that the problem of Kuchar observables is explicitly
resolved for 1- and 2-d RPM's. Then as a first route to Halliwell's approach
for nontrivial linear constraints that is also a construction of Dirac
observables, I consider theories for which Kuchar observables are formally
known, giving the relational triangle as an example. As a second route, I apply
an indirect method that generalizes both group-averaging and Barbour's best
matching. For conceptual clarity, my study involves the simpler case of
Halliwell 2003 sharp-edged window function. I leave the elsewise-improved
softened case of Halliwell 2009 for a subsequent Paper II. Finally, I provide
comments on Halliwell's approach and how well it fares as regards the various
facets of the Problem of Time and as an implementation of QM propositions.Comment: An improved version of the text, and with various further references.
25 pages, 4 figure
On the Stability and Single-Particle Properties of Bosonized Fermi Liquids
We study the stability and single-particle properties of Fermi liquids in
spatial dimensions greater than one via bosonization. For smooth non-singular
Fermi liquid interactions we obtain Shankar's renormalization- group flows and
reproduce well known results for quasi-particle lifetimes. We demonstrate by
explicit calculation that spin-charge separation does not occur when the Fermi
liquid interactions are regular. We also explore the relationship between
quantized bosonic excitations and zero sound modes and present a concise
derivation of both the spin and the charge collective mode equations. Finally
we discuss some aspects of singular Fermi liquid interactions.Comment: 13 pages plus three postscript figures appended; RevTex 3.0;
BUP-JBM-
Feasibility of Experimental Realization of Entangled Bose-Einstein Condensation
We examine the practical feasibility of the experimental realization of the
so-called entangled Bose-Einstein condensation (BEC), occurring in an entangled
state of two atoms of different species. We demonstrate that if the energy gap
remains vanishing, the entangled BEC persists as the ground state of the
concerned model in a wide parameter regime. We establish the experimental
accessibility of the isotropic point of the effective parameters, in which the
entangled BEC is the exact ground state, as well as the consistency with the
generalized Gross-Pitaevskii equations. The transition temperature is
estimated. Possible experimental implementations are discussed in detail.Comment: 6 pages, published versio
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