39,537 research outputs found
Building stock dynamics and its impacts on materials and energy demand in China
China hosts a large amount of building stocks, which is nearly 50 billion square meters. Moreover, annual new construction is growing fast, representing half of the world's total. The trend is expected to continue through the year 2050. Impressive demand for new residential and commercial construction, relative shorter average building lifetime, and higher material intensities have driven massive domestic production of energy intensive building materials such as cement and steel. This paper developed a bottom-up building stock turnover model to project the growths, retrofits and retirements of China's residential and commercial building floor space from 2010 to 2050. It also applied typical material intensities and energy intensities to estimate building materials demand and energy consumed to produce these building materials. By conducting scenario analyses of building lifetime, it identified significant potentials of building materials and energy demand conservation. This study underscored the importance of addressing building material efficiency, improving building lifetime and quality, and promoting compact urban development to reduce energy and environment consequences in China
Positivity of High Density Effective Theory
We show that the effective field theory of low energy modes in dense QCD has
positive Euclidean path integral measure. The complexity of the measure of QCD
at finite chemical potential can be ascribed to modes which are irrelevant to
the dynamics at sufficiently high density. Rigorous inequalities follow at
asymptotic density. Lattice simulation of dense QCD should be possible using
the quark determinant calculated in the effective theory.Comment: 10 pages, Revised version, to appear in Rapid Communications of
Physical Review
Effects of Domain Wall on Electronic Transport Properties in Mesoscopic Wire of Metallic Ferromagnets
We study the effect of the domain wall on electronic transport properties in
wire of ferromagnetic 3 transition metals based on the linear response
theory. We considered the exchange interaction between the conduction electron
and the magnetization, taking into account the scattering by impurities as
well. The effective electron-wall interaction is derived by use of a local
gauge transformation in the spin space. This interaction is treated
perturbatively to the second order. The conductivity contribution within the
classical (Boltzmann) transport theory turns out to be negligiblly small in
bulk magnets, due to a large thickness of the wall compared with the fermi
wavelength. It can be, however, significant in ballistic nanocontacts, as
indicated in recent experiments. We also discuss the quantum correction in
disordered case where the quantum coherence among electrons becomes important.
In such case of weak localization the wall can contribute to a decrease of
resistivity by causing dephasing. At lower temperature this effect grows and
can win over the classical contribution, in particular in wire of diameter
, being the inelastic diffusion
length. Conductance change of the quantum origin caused by the motion of the
wall is also discussed.Comment: 30 pages, 4 figures. Detailed paper of Phys. Rev. Lett. 78, 3773
(1997). Submitted to J. Phys. Soc. Jp
Fractional Quantum Hall Effect in Topological Flat Bands with Chern Number Two
Recent theoretical works have demonstrated various robust Abelian and
non-Abelian fractional topological phases in lattice models with topological
flat bands carrying Chern number C=1. Here we study hard-core bosons and
interacting fermions in a three-band triangular-lattice model with the lowest
topological flat band of Chern number C=2. We find convincing numerical
evidence of bosonic fractional quantum Hall effect at the filling
characterized by three-fold quasi-degeneracy of ground states on a torus, a
fractional Chern number for each ground state, a robust spectrum gap, and a gap
in quasihole excitation spectrum. We also observe numerical evidence of a
robust fermionic fractional quantum Hall effect for spinless fermions at the
filling with short-range interactions.Comment: 5 pages, 7 figures, with Supplementary Materia
Effects of selective dilution on the magnetic properties of La_{0.7}Sr_{0.3}Mn_{1-x}M'_xO_3 (M' = Al, Ti)
The magnetic lattice of mixed-valence Mn ions in
LaSrMnO is selectively diluted by partial substitution of
Al or Ti for Mn. The ferromagnetic transition temperature and
the saturation magnetization both decrease with substitution. By
presenting the data in terms of selective dilution, in the
low-doping region is found to follow the relation
, where refers to
the undiluted system and is the dilution concentration defined
as or for Al or Ti,
respectively. The scaling behavior of can be
analyzed in the framework of the molecular-field theory and still valid when Mn
is substituted by both Al and Ti. The results are discussed with respect to the
contributions from ferromagnetic double exchange and other possible
antiferromagnetic superexchange interactions coexisting in the material.Comment: Revtex4, 4 pages, 4 figures, 2006 Halong Conference Repor
Non-Abelian Quantum Hall Effect in Topological Flat Bands
Inspired by recent theoretical discovery of robust fractional topological
phases without a magnetic field, we search for the non-Abelian quantum Hall
effect (NA-QHE) in lattice models with topological flat bands (TFBs). Through
extensive numerical studies on the Haldane model with three-body hard-core
bosons loaded into a TFB, we find convincing numerical evidence of a stable
bosonic NA-QHE, with the characteristic three-fold quasi-degeneracy of
ground states on a torus, a quantized Chern number, and a robust spectrum gap.
Moreover, the spectrum for two-quasihole states also shows a finite energy gap,
with the number of states in the lower energy sector satisfying the same
counting rule as the Moore-Read Pfaffian state.Comment: 5 pages, 7 figure
Topology of the polarization field in ferroelectric nanowires from first principles
The behaviour of the cross-sectional polarization field is explored for thin
nanowires of barium titanate from first-principles calculations. Topological
defects of different winding numbers have been obtained, beyond the known
textures in ferroelectric nanostructures. They result from the inward
accommodation of the polarization patterns imposed at the surface of the wire
by surface and edge effects. Close to a topological defect the polarization
field orients out of the basal plane in some cases, maintaining a close to
constant magnitude, whereas it virtually vanishes in other cases.Comment: 4 pages, 3 figure
Induced Magnetic moments in three-dimensional gauge theories with external magnetic fields
We study the appearance of induced parity-violating magnetic moment, in the
presence of external magnetic fields, for even-number of fermion species
coupled to dynamical fields in three dimensions. Specifically, we use a
SU(2)xU(1) gauge model for dynamical gauge symmetry breaking, which is also
proposed recently as a field theoretical model for high-temperature
superconductors. By decomposing the fermionic degrees of freedom in terms of
Landau levels, we show that, in the effective theory with the lowest Landau
levels, a parity-violating magnetic moment interaction is induced by the higher
Landau levels when the fermions are massive. The possible relevance of this
result for a recently observed phenomenon in high-temperature superconductors
is also discussed.Comment: 15 pages revtex, one figure incorporated, References added no other
change
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