1,974 research outputs found
Self-energy corrections to anisotropic Fermi surfaces
The electron-electron interactions affect the low-energy excitations of an
electronic system and induce deformations of the Fermi surface. These effects
are especially important in anisotropic materials with strong correlations,
such as copper oxides superconductors or ruthenates. Here we analyze the
deformations produced by electronic correlations in the Fermi surface of
anisotropic two-dimensional systems, treating the regular and singular regions
of the Fermi surface on the same footing. Simple analytical expressions are
obtained for the corrections, based on local features of the Fermi surface. It
is shown that, even for weak local interactions, the behavior of the
self-energy is non trivial, showing a momentum dependence and a self-consistent
interplay with the Fermi surface topology. Results are compared to experimental
observations and to other theoretical results.Comment: 13 pages, 10 figure
Validity of effective material parameters for optical fishnet metamaterials
Although optical metamaterials that show artificial magnetism are mesoscopic
systems, they are frequently described in terms of effective material
parameters. But due to intrinsic nonlocal (or spatially dispersive) effects it
may be anticipated that this approach is usually only a crude approximation and
is physically meaningless. In order to study the limitations regarding the
assignment of effective material parameters, we present a technique to retrieve
the frequency-dependent elements of the effective permittivity and permeability
tensors for arbitrary angles of incidence and apply the method exemplarily to
the fishnet metamaterial. It turns out that for the fishnet metamaterial,
genuine effective material parameters can only be introduced if quite stringent
constraints are imposed on the wavelength/unit cell size ratio. Unfortunately
they are only met far away from the resonances that induce a magnetic response
required for many envisioned applications of such a fishnet metamaterial. Our
work clearly indicates that the mesoscopic nature and the related spatial
dispersion of contemporary optical metamaterials that show artificial magnetism
prohibits the meaningful introduction of conventional effective material
parameters
Hydrogen or Soot?: Partial Oxidation of High-boiling Hydrocarbon Wastes
This paper is focused on researching the influence of process parameters of partial oxidation, such as quality of hydrocarbon raw materials that differ in their stock properties (especially boiling point and viscosity) on the composition of output gas (selectivity of the process), and also on the formation extent of soot which could be used as an excellent and valued sorbent CHEZACARB® and/or filler in the rubber industry, e.g. for automotive tires. The effects of steam flow rate and the oxygen to raw material feed rate ratio is discussed as well. In addition, sensitivity of POX product composition depending
on properties of different raw materials and reaction conditions were analysed in this study
Deformation of anisotropic Fermi surfaces due to electron-electron interactions
We analyze the deformations of the Fermi surface induced by electron-electron
interactions in anisotropic two dimensional systems. We use perturbation theory
to treat, on the same footing, the regular and singular regions of the Fermi
surface. It is shown that, even for weak local coupling, the self-energy
presents a nontrivial behavior showing momentum dependence and interplay with
the Fermi surface shape. Our scheme gives simple analytical expressions based
on local features of the Fermi surface.Comment: 7 pages, 3 figure
Atom made from charged elementary black hole
It is believed that there may have been a large number of black holes formed
in the very early universe. These would have quantised masses. A charged
``elementary black hole'' (with the minimum possible mass) can capture
electrons, protons and other charged particles to form a ``black hole atom''.
We find the spectrum of such an object with a view to laboratory and
astronomical observation of them, and estimate the lifetime of the bound
states. There is no limit to the charge of the black hole, which gives us the
possibility of observing Z>137 bound states and transitions at the lower
continuum. Negatively charged black holes can capture protons. For Z>1, the
orbiting protons will coalesce to form a nucleus (after beta-decay of some
protons to neutrons), with a stability curve different to that of free nuclei.
In this system there is also the distinct possibility of single quark capture.
This leads to the formation of a coloured black hole that plays the role of an
extremely heavy quark interacting strongly with the other two quarks. Finally
we consider atoms formed with much larger black holes.Comment: 22 pages, 4 figure
Isospin-mixing corrections for fp-shell Fermi transitions
Isospin-mixing corrections for superallowed Fermi transitions in {\it
fp}-shell nuclei are computed within the framework of the shell model. The
study includes three nuclei that are part of the set of nine accurately
measured transitions as well as five cases that are expected to be measured in
the future at radioactive-beam facilities. We also include some new
calculations for C. With the isospin-mixing corrections applied to the
nine accurately measured values, the conserved-vector-current hypothesis
and the unitarity condition of the Cabbibo-Kobayashi-Maskawa (CKM) matrix are
tested.Comment: 13 pages plus five tables. revtex macro
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