17,810 research outputs found
Exchange and spin Jahn-Teller distortions for a triangular cluster of spin-1/2
We study the effects of magnetoelastic coupling on the degenerate ground
state of the spin-1/2 antiferromagnetic Heisenberg model for the regular
triangular spin cluster. Static displacement of spins spontaneously lifts the
degeneracy of the ground state through the distance dependence of exchange
coupling, i.e., a spin Jahn-Teller mechanism takes place. On the other hand,
dynamical displacement does not lift the degeneracy, though the cluster
distorts spontaneously. The energy decrease obtained by dynamical theory is
twice as large as that obtained by static theory because of quantum
fluctuation.Comment: 4 pages, 1 figure. Accepted by JPSJ. Clarified some setences.
Corrected typo
Effective Theory Approach to the Skyrme model and Application to Pentaquarks
The Skyrme model is reconsidered from an effective theory point of view. From
the most general chiral Lagrangian up to including terms of order ,
and (), new interactions, which have never
been considered before, appear upon collective coordinate quantization. We
obtain the parameter set best fitted to the observed low-lying baryon masses,
by performing the second order perturbative calculations with respect to
. We calculate the masses and the decay widths of the other members
of (mainly) anti-decuplet pentaquark states. The formula for the decay widths
is reconsidered and its baryon mass dependence is clarified.Comment: 65 pages, 1 figure. Revised version:the complete second order
perturbative calculations performed and two appendices adde
Two loop finiteness of Higgs mass and potential in the gauge-Higgs unification
The zero mode of an extra-dimensional component of gauge potentials serves as
a 4D Higgs field in the gauge-Higgs unification. We examine QED on and determine the mass and potential of a 4D Higgs field (the
component) at the two loop level with gauge invariant reguralization. It is
seen that the mass is free from divergences and independent of the
renormalization scheme.Comment: 18 pages, 1 figur
Charge 4/3 leptons in cosmic rays
A cosmic ray counter telescope has been operated at zenith angles of 0, 40, 44, and 60 degs in order to look for charge 4/3 particles. A few million clean single cosmic rays of each zenith angle are analyzed
Preparation of Neutron-activated Xenon for Liquid Xenon Detector Calibration
We report the preparation of neutron-activated xenon for the calibration of
liquid xenon (LXe) detectors. Gamma rays from the decay of xenon metastable
states, produced by fast neutron activation, were detected and their activities
measured in a LXe scintillation detector. Following a five-day activation of
natural xenon gas with a Cf-252 (4 x 10^5 n/s) source, the activities of two
gamma ray lines at 164 keV and 236 keV, from Xe-131m and Xe-129m metastable
states, were measured at about 95 and 130 Bq/kg, respectively. We also observed
three additional lines at 35 keV, 100 keV and 275 keV, which decay away within
a few days. No long-lifetime activity was observed after the neutron
activation.Comment: to be published in NIM A, corrected typos in Table 1 and Fig.6 of the
previous versio
Biomass Gasification for the Co-Production of Fischer-Tropsch Liquids and Electricity
This report examines the co-production of Fischer-Tropsch (F-T) liquids and electricity using biomass gasification. F-T liquids and electricity derived from biomass gasification appear as attractive alternatives for meeting energy needs in the medium-term. Biomassbased electricity generation constitutes an attractive option for the introduction of renewable energy resources and the gasification technology could offer an efficient, flexible and clean option for electricity production, as compared to conventional combustion-based plants. On the other hand, F-T liquids could have applications in the transportation sector, enabling the use of advanced internal combustion engines while being compatible with today's fuel delivery infrastructure. However, they still have to undergo substantial cost reductions in order to become competitive in the energy markets. Our analysis illustrates that a sales strategy for the co-product electricity could substantially contribute to improve the economics of F-T liquids.
The biomass gasification could act as a facilitating technology for the development of integrated and flexible bioenergy strategies, since it allows the production or coproduction of, among others, electricity, hydrogen and clean liquid fuels. Biomassbased "energyplexes" would have an inherent flexibility that could be an important asset in liberalized energy markets.
We also illustrate the costs and energy consumption associated with long-distance bioenergy transport to Japan using two scenarios where forest residues produced in North America and energy crops produced in Latin America are transported to Japan via ship. A variety of supply chains were compared, including transport in the forms of logs, bales, chips, pellets and F-T liquids. Early conversion of biomass to F-T liquids in advance of long-distance transport via ship appears as a favorable option on economic and energy-consumption grounds
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