289 research outputs found
Shape Optimization for Time-dependent Domains
In this thesis, we treat shape optimization for parabolic equations on time-dependent domains. As a theoretical foundation we extend the solution theory of parabolic boundary integral equations in the canonical Sobolev spaces from the cylindrical to the time-dependent case. The results imply existence and uniqueness of solutions. This is followed by a review of shape optimization theory on time-dependent domains, where we complement a few proofs which seem to be missing in the literature. Building on these foundations we give general formulae for shape gradients of functionals. These theoretical results are complemented by two numerical examples. The first example is concerned with a time-dependent shape detection problem, reformulated as a time-dependent shape optimization problem. The second example is a time-dependent one-phase Stefan problem in multiple dimensions, also reformulated as a shape optimization problem
Spiral phases and two-particle bound states from a systematic low-energy effective theory for magnons, electrons, and holes in an antiferromagnet
We have constructed a systematic low-energy effective theory for hole- and
electron-doped antiferromagnets, where holes reside in momentum space pockets
centered at and where electrons live in
pockets centered at or . The effective
theory is used to investigate the magnon-mediated binding between two holes or
two electrons in an otherwise undoped system. We derive the one-magnon exchange
potential from the effective theory and then solve the corresponding
two-quasiparticle Schr\"odinger equation. As a result, we find bound state wave
functions that resemble -like or -like symmetry. We also
study possible ground states of lightly doped antiferromagnets.Comment: 2 Pages; Proc. of SCES'07, Housto
Health Universities - Konzept, Relevanz und Best Practice : Mit regionaler Versorgung und interprofessioneller Bildung zu bedarfsgerechten Gesundheitsfachleuten
Das Konzept der Health Universities entstand als eine Antwort auf die Herausforderungen des Gesundheitswesens in den 1960er und 1970er Jahren. Es vereint bildungs- und versorgungspolitische Ansprüche, die schwierig unter einen Hut zu bringen sind. Wie hat sich dieses Konzept in Europa weiter entwickelt? Welche Bedeutung hat es für die Herausforderungen von heute? Dieser Bericht zeigt das Potential der Health Universities für eine bedarfsgerechte Ausbildung von Gesundheitsfachleuten zu Beginn des 21. Jahrhunderts, indem Konzept, Relevanz und Best Practice beschrieben werden
Emotions while awaiting lung transplantation : a comprehensive qualitative analysis
Patients awaiting lung transplantation are at risk of negative emotional and physical experiences. How do they talk about emotions? Semi-structured interviews were performed (15 patients). Categorical analysis focusing on emotion-related descriptions was organized into positive–negative–neutral descriptions: for primary and secondary emotions, evaluation processes, coping strategies, personal characteristics, emotion descriptions associated with physical states, (and) contexts were listed. Patients develop different strategies to maintain positive identity and attitude, while preserving significant others from extra emotional load. Results are discussed within various theoretical and research backgrounds, in emphasizing their importance in the definition of emotional support starting from the patient’s perspective
Magnon-mediated binding between holes in an antiferromagnet
Abstract.: The long-range forces between holes in an antiferromagnet are due to magnon exchange. The one-magnon exchange potential between two holes is proportional to cos(2 ϕ)/r 2 where r is the distance vector of the holes and ϕ is the angle between r and an axis of the square crystal lattice. One-magnon exchange leads to bound states of holes with antiparallel spins resembling d-wave symmetr
Thermodynamics of Two-Dimensional Ideal Ferromagnets - Three-Loop Analysis
Within the effective Lagrangian framework, we explicitly evaluate the
partition function of two-dimensional ideal ferromagnets up to three loops at
low temperatures and in the presence of a weak external magnetic field. The
low-temperature series for the free energy density, energy density, heat
capacity, entropy density, as well as the magnetization are given and their
range of validity is critically examined in view of the Mermin-Wagner theorem.
The calculation involves the renormalization and numerical evaluation of a
particular three-loop graph which is discussed in detail. Interestingly, in the
low-temperature series for the two-dimensional ideal ferromagnet, the spin-wave
interaction manifests itself in the form of logarithmic terms. In the free
energy density the leading such term is of order -- remarkably, in
the case of the three-dimensional ideal ferromagnet no logarithmic terms arise
in the low-temperature series. While the present study demonstrates that it is
straightforward to consider effects up to three-loop order in the effective
field theory framework, this precision seems to be far beyond the reach of
microscopic methods such as modified spin-wave theory.Comment: 31 pages, 2 figure
Homogeneous versus Spiral Phases of Hole-doped Antiferromagnets: A Systematic Effective Field Theory Investigation
Using the low-energy effective field theory for magnons and holes -- the
condensed matter analog of baryon chiral perturbation theory for pions and
nucleons in QCD -- we study different phases of doped antiferromagnets. We
systematically investigate configurations of the staggered magnetization that
provide a constant background field for doped holes. The most general
configuration of this type is either constant itself or it represents a spiral
in the staggered magnetization. Depending on the values of the low-energy
parameters, a homogeneous phase, a spiral phase, or an inhomogeneous phase is
energetically favored. The reduction of the staggered magnetization upon doping
is also investigated.Comment: 35 pages, 5 figure
Systematic Low-Energy Effective Field Theory for Electron-Doped Antiferromagnets
In contrast to hole-doped systems which have hole pockets centered at , in lightly electron-doped antiferromagnets
the charged quasiparticles reside in momentum space pockets centered at
or . This has important consequences for
the corresponding low-energy effective field theory of magnons and electrons
which is constructed in this paper. In particular, in contrast to the
hole-doped case, the magnon-mediated forces between two electrons depend on the
total momentum of the pair. For the one-magnon exchange
potential between two electrons at distance is proportional to ,
while in the hole case it has a dependence. The effective theory
predicts that spiral phases are absent in electron-doped antiferromagnets.Comment: 25 pages, 7 figure
Two-Hole Bound States from a Systematic Low-Energy Effective Field Theory for Magnons and Holes in an Antiferromagnet
Identifying the correct low-energy effective theory for magnons and holes in
an antiferromagnet has remained an open problem for a long time. In analogy to
the effective theory for pions and nucleons in QCD, based on a symmetry
analysis of Hubbard and t-J-type models, we construct a systematic low-energy
effective field theory for magnons and holes located inside pockets centered at
lattice momenta (\pm pi/2a,\pm pi/2a). The effective theory is based on a
nonlinear realization of the spontaneously broken spin symmetry and makes
model-independent universal predictions for the entire class of lightly doped
antiferromagnetic precursors of high-temperature superconductors. The
predictions of the effective theory are exact, order by order in a systematic
low-energy expansion. We derive the one-magnon exchange potentials between two
holes in an otherwise undoped system. Remarkably, in some cases the
corresponding two-hole Schr\"odinger equations can even be solved analytically.
The resulting bound states have d-wave characteristics. The ground state wave
function of two holes residing in different hole pockets has a d_{x^2-y^2}-like
symmetry, while for two holes in the same pocket the symmetry resembles d_{xy}.Comment: 35 pages, 11 figure
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