291 research outputs found
Optimally Dense Packings for Fully Asymptotic Coxeter Tilings by Horoballs of Different Types
The goal of this paper to determine the optimal horoball packing arrangements
and their densities for all four fully asymptotic Coxeter tilings (Coxeter
honeycombs) in hyperbolic 3-space . Centers of horoballs are
required to lie at vertices of the regular polyhedral cells constituting the
tiling. We allow horoballs of different types at the various vertices. Our
results are derived through a generalization of the projective methodology for
hyperbolic spaces. The main result states that the known B\"or\"oczky--Florian
density upper bound for "congruent horoball" packings of remains
valid for the class of fully asymptotic Coxeter tilings, even if packing
conditions are relaxed by allowing for horoballs of different types under
prescribed symmetry groups. The consequences of this remarkable result are
discussed for various Coxeter tilings.Comment: 26 pages, 10 figure
OPTIMALE KUGELPACKUNGEN FÜR DIE RAUMGRUPPEN F23, P432 UND F432
In this paper the optimal ball-packing is determined where the centres of balls form an
orbit (with trivial stabilizer) of a particular crystallographic space group. The space
groups are F23, P432, F432 which allow a unified method called the method of cones
Phase Separation of Superfluids in the Chain of Four-Component Ultracold Atoms
We investigate the competition of various exotic superfluid states in a chain
of spin-polarized ultracold fermionic atoms with hyperfine spin and
s-wave contact interactions. We show that the ground state is an exotic
inhomogeneous mixture in which two distinct superfluid phases --- spin-carrying
pairs and singlet quartets --- form alternating domains in an extended region
of the parameter space
SU(N) quantum spin models: A variational wavefunction study
The study of SU(N) quantum spin models is relevant to a variety of physical
systems including ultracold atoms in optical lattices, and also leads to
insights into novel quantum phases and phase transitions of SU(2) spin models.
We use Gutzwiller projected fermionic variational wavefunctions to explore the
phase diagram and correlation functions of SU(N) spin models in the
self-conjugate representation, with Heisenberg bilinear and biquadratic
interactions. In 1D, the variational phase diagram of the SU(4) spin chain is
constructed by examining instabilities of the Gutzwiller projected free fermion
ground state to various broken symmetries, and it agrees well with exact
results.The spin and dimer correlations of the Gutzwiller projected free
fermion state with N flavors of fermions are also in good agreement with exact
and 1/N calculations for the critical points of SU(N) spin chains. In 2D, the
variational phase diagram on the square lattice is obtained by studying
instabilities of the Gutzwiller projected pi-flux state. The variational ground
state of the pure Heisenberg model is found to exhibit long range Neel order
for N=2,4 and spin Peierls order for N > 4. For N=4 and 6, biquadratic
interactions lead to a complex phase diagram which includes an extended valence
bond crystal in both cases, as well as a stable pi-flux phase for N=6. The spin
correlations of the projected pi-flux state at N=4 are in good agreement with
1/N calculations. We find that this state also shows strongly enhanced dimer
correlations, in qualitative accord with the large-N results. We compare our
results with a recent QMC study of the SU(4) Heisenberg model.Comment: 22 pages, 7 figs, added references to arxiv versio
Medizinische probleme und physikalische grundlagen der kernreaktoren
Die Autoren berichten Uber die Forschungen mit Hilfe von Kernreaktoren auf dem Grenzgebiet der Medizin und Strahlenphysik (Reaktorphysik). Es wurden kurz ihre eigene bisherige Ergebnisse, das Ziel dieser Forschungen und einzelne Zukunftsmoglichkeiten erwahnt. Nachdem wurden in mehreren Teilen die Kernreaktoren beschrieben. 1m erstem Teil werden die allgemeinen physikalischen Grundlagen eines
Kernreaktors dargestellt. Mit Hilfe der Kernkrafte und der Bindungsenergie wird gezeigt, wieso eine Kernspaltung auftreten kann und wieso aus den nicht spaltbaren Isotopen U-238 die spaltbaren Isotope Pu-239 bzw. U-233 "erbrutet" werden konnen. -Das Zustandekommen einer Kettenreaktion,
die die Grundlage einer Energiegewinnung aus der Kernspaltung ist, wird erlautert, wobei sich auf die Wechselwirkungen zwischen Atomkernen und Neutronen hingewiesen wird. 1m AnschluB daran werden die Vorgange im Kernreaktor im Einzelnen naher verfolgt. Dabei werden mehrere Moglichkeiten beschriebenk die es erlauben, die Neutronenzahl, die fur die Kettenreaktion entscheidend ist, zu erhohen. Einer allgemeinen Dbersicht uber die verschiedenen Reaktortypen und ihreu Einsatz in Forschung und Industrie schlie13t sich eine Beschreibung verschiedener deutscher Reaktoren und ihrer speziellen Eigenschaften und Vorteile an. Zum SchluB wird noch besonders auf die groBen Projekte der Entwicklung von Thorium-Brutern und von schnellen Brutern eingegangen.</p
International trade and knowledge spillovers : the case of Indonesian manufacturing
The successful industrialisation and catch-up of countries in the East Asian region gave rise to an important debate concerning the role played by technological learning and knowledge creation. This paper seeks to examine this issue for Indonesia, a second tier Newly Industrialising Country (NIC). It focuses on the relative importance of learning from imported inputs vis-à-vis other factors influencing productivity in manufacturing. The concept of learning is operationalised drawing on the literature on technology spillovers on the one hand, and the literature on catch-up à la Abramovitz, on the other. Our results indicate that knowledge spillovers have become significant contributors to labour productivity growth after the liberalisation of the Indonesian economy
Possible phases of two coupled n-component fermionic chains
A two-leg ladder with -component fermionic fields in the chains has been
considered using an analytic renormalization group method. The fixed points and
possible phases have been determined for generic filling as well as for a
half-filled system and for the case when one of the subbands is half filled. A
weak-coupling Luttinger-liquid phase and several strong-coupling gapped phases
have been found. In the Luttinger liquid phase, for the most general spin
dependence of the couplings, all modes have different velocities if the
interband scattering processes are scaled out, while doubly degenerate
modes appear if the interband scattering processes remain finite. The role of
backward-scattering, charge-transfer and umklapp processes has been analysed
using their bosonic form and the possible phases are characterized by the
number of gapless modes. As a special case the SU() symmetric Hubbard ladder
has been investigated numerically. It was found that this model does not scale
to the Luttinger liquid fixed point. Even for generic filling gaps open up in
the spectrum of the spin or charge modes, and the system is always insulator in
the presence of umklapp processes
Spatially nonuniform phases in the one-dimensional SU(n) Hubbard model for commensurate fillings
The one-dimensional repulsive SU Hubbard model is investigated
analytically by bosonization approach and numerically using the density-matrix
renormalization-group (DMRG) method for , and 5 for commensurate
fillings where and are relatively prime. It is shown that the
behavior of the system is drastically different depending on whether ,
, or , the umklapp processes are irrelevant, the model is
equivalent to an -component Luttinger liquid with central charge . When
, the charge and spin modes are decoupled, the umklapp processes open a
charge gap for finite , whereas the spin modes remain gapless and the
central charge . The translational symmetry is not broken in the ground
state for any . On the other hand, when , the charge and spin modes are
coupled, the umklapp processes open gaps in all excitation branches, and a
spatially nonuniform ground state develops. Bond-ordered dimerized, trimerized
or tetramerized phases are found depending on the filling.Comment: 10 pages, 11 figure
Neues stomatologisches verfahren : Myologische bestimmung der funktion der kaumuskulatur bzw. des M. masseters mit dem Szirmaischen myotonometer
Die Autoren haben festgestellt, daβ man mit Hilfe des Myotonometers auf Grund von Kau- bzw. Masseterfunktionsmessung auf verschiedene stomatologische Krankheiten, bzw. auf verschiedene Veranderungen schliessen
kann. Man kann feststellen, ob die Muskeln atrophisch sind oder nicht, was fur eine Prothese bei einzelnen Individuen der Funktion der Muskeln entspricht, ob eine Prothese schlecht ist, welche Verfahren fur die Orthodontie bzw. Prognathie notwendig sind und welche Medikamente eine gute stomatologische Wirkung haben. Auch die verschiedenen orthopadischen Fragen sind erleichtert.</p
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