39,534 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
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
Facile synthesis of Co-N4-doped mesoporous carbon for oxygen reduction reaction
The oxygen reduction reaction (ORR) is a critical factor in fuel cells that has attracted significant research attention. Non-precious metal catalysts have improved the ORR activity considerably, but they still exhibit poorer ORR performance than commercial Pt-based catalysts. In this study, Co-N-4-doped mesoporous carbon (Co-N-4-MC) was prepared for the ORR using cobalt-azides as the Co-N-4-containing precursor, and ordered mesoporous silica SBA-15 as a template for achieving mesoporous structures. The Co-N-4-MC electrode exhibited remarkable ORR activity in an alkaline medium (a half-wave potential of -0.15 V vs. MMO, only similar to 19 mV deviation from the commercial Pt/C catalyst), high selectivity (electron-transfer number similar to 4) and excellent electrochemical stability (similar to 8 mV negative shift of the half-wave potential after 1000 cycles). The good performance of the Co-N-4- MC electrode was attributed to the synergetic effects of N-4, C and Co. In particular, the existence of graphitic pores in the Co-N-4-MC catalyst facilitated the diffusion of O-2 to the catalytic active sites, which benefited the progression of the ORR on the Co-N-4-MC catalyst. (C) 2017 The Electrochemical Society
Discrete Anomaly and Dynamical Mass in 2+1 dimensional Model
We note that in (2+1)-dimensional gauge theories with even number of massless
fermions, there is anomalous symmetry if theory is regularized in a
parity-invariant way. We then consider a parity invariant
model, which induces a mutual Chern-Simons term in the effective action due to
anomaly. The effect of the discrete anomaly is studied in the induced
spin and in the dynamical fermion mass.Comment: 14 pages, latex, two figures (available upon request
Mass Terms in Effective Theories of High Density Quark Matter
We study the structure of mass terms in the effective theory for
quasi-particles in QCD at high baryon density. To next-to-leading order in the
expansion we find two types of mass terms, chirality conserving
two-fermion operators and chirality violating four-fermion operators. In the
effective chiral theory for Goldstone modes in the color-flavor-locked (CFL)
phase the former terms correspond to effective chemical potentials, while the
latter lead to Lorentz invariant mass terms. We compute the masses of Goldstone
bosons in the CFL phase, confirming earlier results by Son and Stephanov as
well as Bedaque and Sch\"afer. We show that to leading order in the coupling
constant there is no anti-particle gap contribution to the mass of
Goldstone modes, and that our results are independent of the choice of gauge.Comment: 22 pages, 4 figure
The High Energy Telescope on EXIST
The Energetic X-ray Imaging Survey Telescope (EXIST) is a proposed next
generation multi-wavelength survey mission. The primary instrument is a High
Energy telescope (HET) that conducts the deepest survey for Gamma-ray Bursts
(GRBs), obscured-accreting and dormant Supermassive Black Holes and Transients
of all varieties for immediate followup studies by the two secondary
instruments: a Soft X-ray Imager (SXI) and an Optical/Infrared Telescope (IRT).
EXIST will explore the early Universe using high redshift GRBs as cosmic probes
and survey black holes on all scales. The HET is a coded aperture telescope
employing a large array of imaging CZT detectors (4.5 m^2, 0.6 mm pixel) and a
hybrid Tungsten mask. We review the current HET concept which follows an
intensive design revision by the HET imaging working group and the recent
engineering studies in the Instrument and Mission Design Lab at the Goddard
Space Flight Center. The HET will locate GRBs and transients quickly (<10-30
sec) and accurately (< 20") for rapid (< 1-3 min) onboard followup soft X-ray
and optical/IR (0.3-2.2 micron) imaging and spectroscopy. The broad energy band
(5-600 keV) and the wide field of view (~90 deg x 70 deg at 10% coding
fraction) are optimal for capturing GRBs, obscured AGNs and rare transients.
The continuous scan of the entire sky every 3 hours will establish a
finely-sampled long-term history of many X-ray sources, opening up new
possibilities for variability studies.Comment: 10 pages, 6 figures, 3 tables, SPIE conference proceedings (UV,
X-ray, and Gamma-Ray Space Instrumentation for Astronomy XVI, 7435-9
Flavor symmetry breaking effects on SU(3) Skyrmion
We study the massive SU(3) Skyrmion model to investigate the flavor symmetry
breaking (FSB) effects on the static properties of the strange baryons in the
framework of the rigid rotator quantization scheme combined with the improved
Dirac quantization one. Both the chiral symmetry breaking pion mass and FSB
kinetic terms are shown to improve the ratio of the strange-light to
light-light interaction strengths and that of the strange-strange to
light-light.Comment: 12 pages, latex, no 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
- …