335 research outputs found
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Survey of Biomass Resource Assessments and Assessment Capabilities in APEC Economies
This survey of biomass resource assessments and assessment capabilities in Asia-Pacific Economic Cooperation (APEC) economies considered various sources: academic and government publications, media reports, and personal communication with contacts in member economies
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Future of Liquid Biofuels for APEC Economies
This project was initiated by APEC Energy Working Group (EWG) to maximize the energy sector's contribution to the region's economic and social well-being through activities in five areas of strategic importance including liquid biofuels production and development
Renormalization group and 1/N expansion for 3-dimensional Ginzburg-Landau-Wilson models
A renormalization-group scheme is developed for the 3-dimensional
O()-symmetric Ginzburg-Landau-Wilson model, which is consistent with the
use of a 1/N expansion as a systematic method of approximation. It is motivated
by an application to the critical properties of superconductors, reported in a
separate paper. Within this scheme, the infrared stable fixed point controlling
critical behaviour appears at , where is the inverse of
the quartic coupling constant, and an efficient renormalization procedure
consists in the minimal subtraction of ultraviolet divergences at . This
scheme is implemented at next-to-leading order, and the standard results for
critical exponents calculated by other means are recovered. An apparently novel
result of this non-perturbative method of approximation is that corrections to
scaling (or confluent singularities) do not, as in perturbative analyses,
appear as simple power series in the variable . At least in
three dimensions, the power series are modified by powers of .Comment: 20 pages; 5 figure
Critical-point scaling function for the specific heat of a Ginzburg-Landau superconductor
If the zero-field transition in high temperature superconductors such as
YBa_2Cu_3O_7-\delta is a critical point in the universality class of the
3-dimensional XY model, then the general theory of critical phenomena predicts
the existence of a critical region in which thermodynamic functions have a
characteristic scaling form. We report the first attempt to calculate the
universal scaling function associated with the specific heat, for which
experimental data have become available in recent years. Scaling behaviour is
extracted from a renormalization-group analysis, and the 1/N expansion is
adopted as a means of approximation. The estimated scaling function is
qualitatively similar to that observed experimentally, and also to the
lowest-Landau-level scaling function used by some authors to provide an
alternative interpretation of the same data. Unfortunately, the 1/N expansion
is not sufficiently reliable at small values of N for a quantitative fit to be
feasible.Comment: 20 pages; 4 figure
Alternative liquid fuels
Meeting: Energy Research Priorities Seminar, 9 Aug. 1983, Ottawa, ON, C
3D Lowest Landau Level Theory Applied to YBCO Magnetization and Specific Heat Data: Implications for the Critical Behavior in the H-T Plane
We study the applicability of magnetization and specific heat equations
derived from a lowest-Landau-level (LLL) calculation, to the high-temperature
superconducting (HTSC) materials of the YBaCuO (YBCO)
family. We find that significant information about these materials can be
obtained from this analysis, even though the three-dimensional LLL functions
are not quite as successful in describing them as the corresponding
two-dimensional functions are in describing data for the more anisotropic HTSC
Bi- and Tl-based materials. The results discussed include scaling fits, an
alternative explanation for data claimed as evidence for a second order flux
lattice melting transition, and reasons why 3DXY scaling may have less
significance than previously believed. We also demonstrate how 3DXY scaling
does not describe the specific heat data of YBCO samples in the critical
region. Throughout the paper, the importance of checking the actual scaling
functions, not merely scaling behavior, is stressed.Comment: RevTeX; 10 double-columned pages with 7 figures embedded. (A total of
10 postscript files for the figures.) Submitted to Physical Review
Critical Dynamics of a Vortex Loop Model for the Superconducting Transition
We calculate analytically the dynamic critical exponent measured in
Monte Carlo simulations for a vortex loop model of the superconducting
transition, and account for the simulation results. In the weak screening
limit, where magnetic fluctuations are neglected, the dynamic exponent is found
to be . In the perfect screening limit, . We relate
to the actual value of observable in experiments and find that , consistent with some experimental results
Extreme Type-II Superconductors in a Magnetic Field: A Theory of Critical Fluctuations
A theory of critical fluctuations in extreme type-II superconductors
subjected to a finite but weak external magnetic field is presented. It is
shown that the standard Ginzburg-Landau representation of this problem can be
recast, with help of a novel mapping, as a theory of a new "superconductor", in
an effective magnetic field whose overall value is zero, consisting of the
original uniform field and a set of neutralizing unit fluxes attached to
fluctuating vortex lines. The long distance behavior is related to
the anisotropic gauge theory in which the original magnetic field plays the
role of "charge". The consequences of this "gauge theory" scenario for the
critical behavior in high temperature superconductors are explored in detail,
with particular emphasis on questions of 3D XY vs. Landau level scaling,
physical nature of the vortex "line liquid" and the true normal state, and
fluctuation thermodynamics and transport. A "minimal" set of requirements for
the theory of vortex-lattice melting in the critical region is also proposed
and discussed.Comment: 28 RevTeX pages, 4 .ps figures; appendix A added, additional
references, streamlined Secs. IV and V in response to referees' comment
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