1,642 research outputs found
Finite-volume matrix elements of two-body states
In this talk, we present a framework for studying structural information of
resonances and bound states coupling to two-hadron scattering states. This
makes use of a recently proposed finite-volume formalism to determine a class
of observables that are experimentally inaccessible but can be accessed via
lattice QCD. In particular, we shown that finite-volume two-body matrix
elements with one current insertion can be directly related to scattering
amplitudes coupling to the external current. For two-hadron systems with
resonances or bound states, one can extract the corresponding form factors of
these from the energy-dependence of the amplitudes.Comment: 7 pages, 2 figures, Proceedings of Lattice 201
Accurate quadratic-response approximation for the self-consistent pseudopotential of semiconductor nanostructures
Quadratic-response theory is shown to provide a conceptually simple but
accurate approximation for the self-consistent one-electron potential of
semiconductor nanostructures. Numerical examples are presented for GaAs/AlAs
and InGaAs/InP (001) superlattices using the local-density approximation to
density-functional theory and norm-conserving pseudopotentials without
spin-orbit coupling. When the reference crystal is chosen to be the
virtual-crystal average of the two bulk constituents, the absolute error in the
quadratic-response potential for Gamma(15) valence electrons is about 2 meV for
GaAs/AlAs and 5 meV for InGaAs/InP. Low-order multipole expansions of the
electron density and potential response are shown to be accurate throughout a
small neighborhood of each reciprocal lattice vector, thus providing a further
simplification that is confirmed to be valid for slowly varying envelope
functions. Although the linear response is about an order of magnitude larger
than the quadratic response, the quadratic terms are important both
quantitatively (if an accuracy of better than a few tens of meV is desired) and
qualitatively (due to their different symmetry and long-range dipole effects).Comment: 16 pages, 20 figures; v2: new section on limitations of theor
Quadratic response theory for spin-orbit coupling in semiconductor heterostructures
This paper examines the properties of the self-energy operator in
lattice-matched semiconductor heterostructures, focusing on nonanalytic
behavior at small values of the crystal momentum, which gives rise to
long-range Coulomb potentials. A nonlinear response theory is developed for
nonlocal spin-dependent perturbing potentials. The ionic pseudopotential of the
heterostructure is treated as a perturbation of a bulk reference crystal, and
the self-energy is derived to second order in the perturbation. If spin-orbit
coupling is neglected outside the atomic cores, the problem can be analyzed as
if the perturbation were a local spin scalar, since the nonlocal spin-dependent
part of the pseudopotential merely renormalizes the results obtained from a
local perturbation. The spin-dependent terms in the self-energy therefore fall
into two classes: short-range potentials that are analytic in momentum space,
and long-range nonanalytic terms that arise from the screened Coulomb potential
multiplied by a spin-dependent vertex function. For an insulator at zero
temperature, it is shown that the electronic charge induced by a given
perturbation is exactly linearly proportional to the charge of the perturbing
potential. These results are used in a subsequent paper to develop a
first-principles effective-mass theory with generalized Rashba spin-orbit
coupling.Comment: 20 pages, no figures, RevTeX4; v2: final published versio
Patient Active Approaches in Osteopathic Practice: A Scoping Review
Background: In the field of manual therapies there is a growing interest in moving from passive hands-on approaches to patient active approaches. In the osteopathic field there are both active and passive methods described as integrated in the process of care. However, this prospective linkage has not been formally explored and is not well shared in the community of practice. The present review aims to appraise the relevant literature on the functioning and principles of Patient active osteopathic approaches (PAOAs) and explore a prospective model for selecting the different types of PAOA, highlighting their integration into patient management strategies. Methods: A scoping review was conducted to analyze the relevant literature on the functioning and the different principles of PAOA and to obtain a comprehensive perspective on the phenomenon. Results: The eligible articles provide insights into the mechanisms of functioning and principles of application of active approaches to be integrated with hands-on approaches. These results provide new insights into the relevance of PAOA to clinical practice. Conclusions: The proposal, emerging from the review, may promote discussions in the community of practice and provide a road map for research towards achieving an evidence-based structure for PAOA
First-principles study on the origin of large thermopower in hole-doped LaRhO3 and CuRhO2
Based on first-principles calculations, we study the origin of the large
thermopower in Ni-doped LaRhO3 and Mg-doped CuRhO2. We calculate the band
structure and construct the maximally localized Wannier functions from which a
tight binding Hamiltonian is obtained. The Seebeck coefficient is calculated
within the Boltzmann's equation approach using this effective Hamiltonian. For
LaRhO3, we find that the Seebeck coefficient remains nearly constant within a
large hole concentration range, which is consistent with the experimental
observation. For CuRhO2, the overall temperature dependence of the calculated
Seebeck coefficient is in excellent agreement with the experiment. The origin
of the large thermopower is discussed.Comment: 7 pages, to be published J. Phys.: Cond. Matt., Proc. QSD 200
Long-Range Electroweak Amplitudes of Single Hadrons From Euclidean Finite-Volume Correlation Functions
A relation is presented between single-hadron long-range matrix elements defined in a finite Euclidean spacetime and the corresponding infinite-volume Minkowski amplitudes. This relation is valid in the kinematic region where any number of two-hadron states can simultaneously go on shell, so that the effects of strongly coupled intermediate channels are included. These channels can consist of nonidentical particles with arbitrary intrinsic spins. The result accommodates general Lorentz structures as well as nonzero momentum transfer for the two external currents inserted between the single-hadron states. The formalism, therefore, generalizes the work by Christ et al. [Phys. Rev. D 91, 114510 (2015)] and extends the reach of lattice quantum chromodynamics (QCD) to a wide class of new observables beyond meson mixing and rare decays. Applications include Compton scattering of the pion (πγ⋆ → [ππ;KK] → πγ⋆), kaon (Kγ⋆ → [πK; ηK] → Kγ⋆), and nucleon (Nγ⋆ → Nπ → Nγ⋆), as well as double-β decays, and radiative corrections to the single-β decay, of QCD-stable hadrons. The framework presented will further facilitate generalization of the result to studies of nuclear amplitudes involving two currents from lattice QCD
Some Remarks on the Question of Charge Densities in Stationary-Current-Carrying Conductors
Recently, some discussions arose as to the definition of charge and the value
of the density of charge in stationary-current-carrying conductors. We stress
that the problem of charge definition comes from a misunderstanding of the
usual definition. We provide some theoretical elements which suggest that
positive and negative charge densities are equal in the frame of the positive
ions.Comment: 14 pages, TeX, macro newsym.tex include
Hole dynamics in a quantum antiferromagnet beyond the retraceable path approximation
The one-hole spectral weight for two chains and two dimensional lattices is
studied numerically using a new method of analysis of the spectral function
within the Lanczos iteration scheme: the Lanczos spectra decoding method. This
technique is applied to the model for , directly in the
infinite size lattice. By a careful investigation of the first 13 Lanczos steps
and the first 26 ones for the two dimensional and the two chain cases
respectively, we get several new features of the one-hole spectral weight. A
sharp incoherent peak with a clear momentum dispersion is identified, together
with a second broad peak at higher energy. The spectral weight is finite up to
the Nagaoka energy where it vanishes in a non-analytic way. Thus the lowest
energy of one hole in a quantum antiferromagnet is degenerate with the Nagaoka
energy in the thermodynamic limit.Comment: RevTeX 3.0, SISSA preprint 156/93/CM/MB, 10 pages + postscript file
appended, contains more accurate calculations in Fig.
Ab-initio transport theory for digital ferromagnetic heterostructures
MnAs/GaAs superlattices, made by -doping GaAs with Mn, are known as
digital ferromagnetic heterostructures. Here we present a theoretical density
functional study of the electronic, magnetic and transport properties of such
heterostructures. In the absence of intrinsic donors these systems show an half
metallic density of states, with an exchange interaction much stronger than
that of a random alloy with the same Mn concentration. {\it Ab initio}
ballistic transport calculations show that the carriers with energies close to
the Fermi energy are strongly confined within a few monolayers around the MnAs
plane. This strong confinement is responsible for the large exchange coupling.
Therefore the system can be described as a two dimensional half metal with
large conductance in the MnAs plane and small conductance in the perpendicular
direction
Clustering in light nuclei in fragmentation above 1 A GeV
The relativistic invariant approach is applied to analyzing the 3.3 A GeV
Ne fragmentation in a nuclear track emulsion. New results on few-body
dissociations have been obtained from the emulsion exposures to 2.1 A GeV
N and 1.2 A GeV Be nuclei. It can be asserted that the use of the
invariant approach is an effective means of obtaining conclusions about the
behavior of systems involving a few He nuclei at a relative energy close to 1
MeV per nucleon. The first observations of fragmentation of 1.2 A GeV B
and C nuclei in emulsion are described. The presented results allow one
to justify the development of few-body aspects of nuclear astrophysics.Comment: 7 pages, 8 figures, 3 tables, Nuclear Physics in Astrophysics-2,
16-20 May, 2005 (ATOMKI), Debrecen, Hungar
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