Classical and quantum many-body description of bremsstrahlung in dense matter (Landau - Pomeranchuk - Migdal effect)

Some considerations about the importance of coherence effects for bremsstrahlung processes in non--equilibrium dense matter (Landau - Pomeranchuk - Migdal - effect) are presented. They are of particular relevance for the application to photon - and di-lepton production from high energy nuclear collisions, to gluon radiation in QCD transport, or parton kinetics and to neutrino and axion radiation from supernova explosion and from hot neutron stars. The soft behavior of the bremsstrahlung from a source described by classical transport models is discussed and pocket correction formulas for the in-matter radiation cross sections are suggested in terms of standard transport coefficients. The radiation rates are also discussed within a non--equilibrium quantum field theory (Schwinger - Kadanoff - Baym - Keldysh) formulation. A classification of diagrams and corresponding resummation in physically meaningful terms is proposed, which considers the finite damping width of all source particles in matter. This way each diagram in this expansion is already free from the infra--red divergences. Both, the correct quasi--particle and quasi--classical limits are recovered from this subset of graphs. Explicit results are given for dense matter in thermal equilibrium. The diagrammatic description may suggest a formulation of a transport theory that includes the propagation of off--shell particles in non--equilibrium dense matter.Comment: 50 pages, submitted to Ann. Phys. (N. Y.); diagrams coded as tex-macros; 5 figures available at: ftp://tpri6b.gsi.de/pub/knoll/ap-95-fig.uu; paper as postscript file (compressed and uuencoded) available at: ftp://tpri6b.gsi.de/pub/knoll/ap-95.p

NON-EQUILIBRIUM DESCRIPTION OF BREMSSTRAHLUNG IN DENSE MATTER (Landau - Pomeranchuk - Migdal Effect)

The soft behavior of the bremsstrahlung from a source is discussed in terms of classical transport models and within a non--equilibrium quantum field theory (Schwinger - Kadanoff - Baym - Keldysh) formulation.Comment: 8 pages, latex, no figures (diagrams in latex

Soft Modes, Resonances and Quantum Transport

Effects of the propagation of particles, which have a finite life-time and an according width in their mass spectrum, are discussed in the context of transport description. First, the importance of coherence effects (Landau-Pomeranchuk-Migdal effect) on production and absorption of field quanta in non-equilibrium dense matter is considered. It is shown that classical diffusion and Langevin results correspond to re-summation of certain field-theory diagrams formulated in terms of full non-equilibrium Green's functions. Then the general properties of broad resonances in dense and hot systems are discussed in the framework of a self-consistent and conserving Phi-derivable method of Baym at the examples of the rho-meson in hadronic matter and the pion in dilute nuclear matter. Further we address the problem of a transport description that properly accounts for the damping width of the particles. The Phi-derivable method generalized to the real-time contour provides a self-consistent and conserving kinetic scheme. We derive a generalized expression for the non-equilibrium kinetic entropy flow, which includes corrections from fluctuations and mass-width effects. In special cases an H-theorem is proved. Memory effects in collision terms give contributions to the kinetic entropy flow that in the Fermi-liquid case recover the famous bosonic type T^3 ln T correction to the specific heat of liquid Helium-3. At the example of the pion-condensate phase transition in dense nuclear matter we demonstrate important part played by the width effects within the quantum transport.Comment: submitted to Phys. At. Nucl. (Rus.), the volume dedicated to the memory of A.B. Migdal. 31 pages, 5 figure

Evaluation of initial collector field performance at the Langley Solar Building Test Facility

The thermal performance of the solar collector field for the NASA Langley Solar Building Test Facility is given for October 1976 through January 1977. A 1,180 square meter solar collector field with seven collector designs helped to provide hot water for the building heating system and absorption air conditioner. The collectors were arranged in 12 rows with nominally 51 collectors per row. Heat transfer rates for each row were calculated and recorded along with sensor, insolation, and weather data every five minutes using a minicomputer. The agreement between the experimental and predicted collector efficiencies was generally within five percentage points

Design, development and test of shuttle/Centaur G-prime cryogenic tankage thermal protection systems

The thermal protection systems for the shuttle/Centaur would have had to provide fail-safe thermal protection during prelaunch, launch ascent, and on-orbit operations as well as during potential abort. The thermal protection systems selected used a helium-purged polyimide foam beneath three rediation shields for the liquid-hydrogen tank and radiation shields only for the liquid-oxygen tank (three shields on the tank sidewall and four on the aft bulkhead). A double-walled vacuum bulkhead separated the two tanks. The liquid-hydrogen tank had one 0.75-in-thick layer of foam on the forward bulkhead and two layers on the larger area sidewall. Full scale tests of the flight vehicle in a simulated shuttle cargo bay that was purged with gaseous nitrogen gave total prelaunch heating rates of 88,500 Btu/hr and 44,000 Btu/hr for the liquid-hydrogen and -oxygen tanks, respectively. Calorimeter tests on a representative sample of the liquid-hydrogen tank sidewall thermal protection system indicated that the measured unit heating rate would rapidly decrease from the prelaunch rate of approx 100 Btu/hr/sq ft to a desired rate of less than 1.3 Btu/hr/sq ft once on orbit

Soft Modes, Quantum Transport and Kinetic Entropy

The effects of the propagation of particles which have a finite life-time and an according width in their mass spectrum are discussed in the context of transport descriptions. In the first part the coupling of soft photon modes to a source of charged particles is studied in a classical model which can be solved completely in analytical terms. The solution corresponds to a re-summation of certain field theory diagrams. The general properties of broad resonances in dense finite temperature systems are discussed at the example of the $\rho$-meson in hadronic matter. The second part addresses the problem of transport descriptions which also account for the damping width of the particles. The Kadanoff--Baym equation after gradient approximation together with the $\Phi$-derivable method of Baym provides a self-consistent and conserving scheme. Memory effects appearing in collision term diagrams of higher order are discussed. We derive a generalized expression for the nonequilibrium kinetic entropy flow, which includes corrections from fluctuations and mass-width effects. In special cases an $H$-theorem is proved. Memory effects in collision terms provide contributions to the kinetic entropy flow that in the Fermi-liquid case recover the famous bosonic type $T^3 \ln T$ correction to the specific heat of liquid Helium-3.Comment: Contribution to Proc. of Int. Workshop "Kadanoff-Baym Equations - Progress and Perspectives for Many-Body Physics" Rostock (Germany), September 20-24 1999, ed. M.Bonitz, World Scientific (2000

Initial operation of a solar heating and cooling system in a full-scale solar building test facility

The Solar Building Test Facility (SBTF) was constructed to advance the technology for heating and cooling of office buildings with solar energy. Its purposes are to (1) test system components which include high-performing collectors, (2) test the performance of a complete solar heating and cooling system, (3) investigate component interactions, and (4) investigate durability, maintenance and reliability of components. The SBTF consists of a 50,000 square foot office building modified to accept solar heated water for operation of an absorption air conditioner and for the baseboard heating system. A 12,666 square foot solar collector field with a 30,000 gallon storage tank provides the solar heated water. A description of the system and the collectors selected is printed along with the objectives, test approach, expected system performance, and some preliminary results

Renormalization in Self-Consistent Approximations schemes at Finite Temperature I: Theory

Within finite temperature field theory, we show that truncated non-perturbative self-consistent Dyson resummation schemes can be renormalized with local counter-terms defined at the vacuum level. The requirements are that the underlying theory is renormalizable and that the self-consistent scheme follows Baym''s $\Phi$-derivable concept. The scheme generates both, the renormalized self-consistent equations of motion and the closed equations for the infinite set of counter terms. At the same time the corresponding 2PI-generating functional and the thermodynamical potential can be renormalized, in consistency with the equations of motion. This guarantees the standard $\Phi$-derivable properties like thermodynamic consistency and exact conservation laws also for the renormalized approximation schemes to hold. The proof uses the techniques of BPHZ-renormalization to cope with the explicit and the hidden overlapping vacuum divergences.Comment: 22 Pages 1 figure, uses RevTeX4. The Revision concerns the correction of some minor typos, a clarification concerning the real-time contour structure of renormalization parts and some comments concerning symmetries in the conclusions and outloo

A brief intervention increases fruit and vegetable intake: a comparison of two intervention sequences

Background and Purpose: To evaluate the effectiveness of two subsequent intervention components (motivational and self-regulatory components), placed in different order, to promote fruit and vegetable (FV) intake. Methods: After baseline assessment, university students (N = 205, aged 18-26 years) were allocated to two groups. One group received a motivational intervention (outcome expectancies, risk perception, and task self-efficacy) followed by a self-regulatory intervention (planning and dietary self-efficacy) after 17 days. The second group received the same intervention conditions in the opposite order. Follow-up assessments were done after another 17 days. Results: Both intervention sequences yielded gains in terms of FV intake and self-efficacy. However, this gain was only due to the self-regulatory component whereas the motivational component did not contribute to the changes. Moreover, changes in intention and self-efficacy mediated between intervention sequence and follow-up behavior, suggesting that improving these proximal predictors of FV intake was responsible for the behavioral gains. Conclusions: Findings highlight the superiority of a self-regulatory intervention over a motivational intervention when it comes to dietary changes in this sample of young adults. Moreover, changes in dietary self-efficacy may drive nutritional changes.info:eu-repo/semantics/publishedVersio