437 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
Industrial Policy and Technology Diffusion: Evidence from Paper Making Machinery in Indonesia
technology diffusion, Indonesia
The role of a research and development institute in the development and diffusion of technology
In the context of late industrialisation the effective transfer and adaptation of technology is of great importance for economic development. International technology transfer is not a costless process, but requires considerable technological effort and investments in the development of technological capabilities
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
Technological inputs and productivity growth in China's high-tech industries
The relationships between investment in R&D and productivity growth at sectoral level have been well documented in the literature. So far little research has been done on this topic for China, in part due to data limitations. This paper presents an empirical study of productivity growth and R&D at sectoral level in China’s high-tech manufacturing industries. Using a version of the perpetual inventory method (PIM), new estimates have been made of the physical capital stock and the R&D stock by sector. Using a production function based on endogenous growth theory, we calculate the elasticities of output with respect to R&D stocks. The R&D stock of the electronic industry plays special role for the whole of the high-tech sector. The analysis points to spillovers from the electronic industries to other high-tech sectors. This is indicated by a significant positive influence of R&D in electronics on productivity growth in other high-tech industries.. Finally, we found that other technological inputs play a less important role in productivity growth, than the R&D stock
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
Layered Quantum Hall Insulators with Ultracold Atoms
We consider a generalization of the 2-dimensional (2D) quantum-Hall insulator
to a non-compact, non-Abelian gauge group, the Heisenberg-Weyl group. We show
that this kind of insulator is actually a layered 3D insulator with nontrivial
topology. We further show that nontrivial combinations of quantized transverse
conductivities can be engineered with the help of a staggered potential. We
investigate the robustness and topological nature of this conductivity and
connect it to the surface modes of the system. We also propose a simple
experimental realization with ultracold atoms in 3D confined to a 2D square
lattice with the third dimension being mapped to a gauge coordinate.Comment: 6 page
Mott transition and dimerization in the one-dimensional SU Hubbard model
The one-dimensional SU Hubbard model is investigated numerically for
, and 5 at half filling and filling using the density-matrix
renormalization-group (DMRG) method. The energy gaps and various quantum
information entropies are calculated. In the half-filled case, finite spin and
charge gaps are found for arbitrary positive if . Furthermore, it is
shown that the transition to the gapped phase at is of
Kosterlitz-Thouless type and is accompanied by a bond dimerization both for
even and odd . In the -filled case, the transition has similar features
as the metal-insulator transition in the half-filled SU(2) Hubbard model. The
charge gap opens exponentially slowly for , the spin sector
remains gapless, and the ground state is non-dimerized.Comment: 9 pages, 12 figure
Emergence of Quintet Superfluidity in the Chain of Partially Polarized Spin-3/2 Ultracold Atom
The system of ultracold atoms with hyperfine spin might be unstable
against the formation of quintet pairs if the interaction is attractive in the
quintet channel. We have investigated the behavior of correlation functions in
a model including only s-wave interactions at quarter filling by large-scale
density-matrix renormalization-group simulations. We show that the correlations
of quintet pairs become quasi-long-ranged, when the system is partially
polarized, leading to the emergence of various mixed superfluid phases in which
BCS-like pairs carrying different magnetic moment coexist.Comment: 4 pages, 4 figures; significantly rewritten compared to the first
versio
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
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