Dilaton Stabilization in Brane Gas Cosmology

Brane Gas Cosmology is an M-theory motivated attempt to reconcile aspects of the standard cosmology based on Einstein's theory of general relativity. Dilaton gravity, when incorporating winding p-brane states, has verified the Brandenberger--Vafa mechanism --a string-motivated conjecture which explains why only three of the nine spatial dimensions predicted by string theory grow large. Further investigation of this mechanism has argued for a hierarchy of subspaces, and has shown the internal directions to be stable to initial perturbations. These results, however, are dependent on a rolling dilaton, or varying strength of Newton's gravitational constant. In these proceedings we show that it is not possible to stabilize the dilaton and maintain the stability of the internal directions within the standard Brane Gas Cosmology setup.Comment: 6 pages, no figures. To appear in the Proceedings of MRST 2004, held at Concordia University, Montreal, QC, 12-14 May 200

Thermochronological evolution of calcite formation at the potential Yucca Mountain repository site, Nevada: Part 2 fluid inclusion analyses and UPb dating

The presence of two-phase fluid inclusions in thin secondary mineral crusts at the potential Yucca Mountain nuclear waste repository has raised questions regarding the origin, timing, and temperature of past fluid flow through the repository horizon. The geologically recent passage of fluids with high temperatures would call into question the suitability of the site for the storage of high level nuclear waste. This study determined the thermal history of fluid flow through the site using fluid inclusion analyses and constrained the timing of thermal fluids by dating silica minerals spatially associated with the fluid inclusions using U-Pb techniques. Results provide a detailed time-temperature history of fluid migration through primary and secondary pore spaces during the past 8 to 9 million years. One hundred and fifty-five samples were collected in the unsaturated zone from the C-shaped Exploratory Studies Facility (ESF), the ECRB cross drift which crosses the potential repository horizon, and exploratory alcoves. Detailed petrographic and paragenetic studies indicated that the oldest secondary minerals consisted of heterogeneously distributed calcite with lesser chalcedony, quartz, opal, and fluorite. The oldest secondary minerals were overgrown by intermediate bladed calcite. The youngest secondary minerals include chemically distinct Mgenriched, growth-zoned sparry calcite (MGSC) and intergrown U-enriched opal. Fluid inclusion petrography indicated that 50 % of the samples (n = 78) contained fluid inclusion assemblages with two-phase fluid inclusions, and that assemblages of liquid-only fluid inclusions represent \u3e 96% of all fluid inclusions within the secondary minerals. Assemblages of two-phase inclusions also contain liquid-only inclusions that did not nucleate a vapor-bubble owing to formation at relatively low temperatures. Virtually all two-phase fluid inclusions occur in paragenetically old calcite; rare two-phase inclusion assemblages were observed in old fluorite (n = 3) and quartz (n = 2). Rare two-phase fluid inclusions were observed in early-intermediate calcite; sparse, irregularly shaped liquid-only inclusions form the only fluid inclusion assemblages observed in late-intermediate minerals and young MGSC. Homogenization temperatures for calcite across the site are generally 45 - 60 °C, but higher temperatures reaching 83 °C were recorded in the north portal and ramp of the ESF and cooler temperatures of ~ 35 - 45 °C were recorded in the intensely fracture zone. Samples from lithophysal cavities in the ESF and ECRB contain multiple populations of two-phase inclusions. Inclusion temperatures are highest in early calcite (\u3e 45 °C) and cooler in paragenetically younger early calcite, indicating cooling with time. The cooler temperatures coincide with temperatures recorded in the intensely fractured zone and indicate that secondary minerals in the intensely fractured zone began to precipitate later than secondary minerals in other locations. Freezing point depressions determined for inclusions range from -0.2 to -1.6 °C indicating trapping of a low salinity fluid. A small number of fluid inclusions in fluorite and quartz were identified and evaluated. Four inclusions in these minerals homogenized at temperatures higher than those recorded for calcite (91 ° - 95 °C) . Two approaches were used to constrain the timing of thermal fluids at Yucca Mountain. First, the age of MGSC was determined, and it provides a minimum age for fluids with elevated temperatures owing to the presence of only liquid-only inclusions in MGSC. Results indicate that MGSC began to precipitate across the site between 2.90 ± 0.06 Ma and about 1.95 ± 0.06 Ma, and MGSC has continued to precipitate to within the last half million years. These ages constrain fluids with elevated temperatures to have accessed the site more than about 2.90 Ma. Second, more precise temporal constraints were determined for samples in which datable opal or chalcedony occur in the intermediate or older parts of the mineral crusts, or are spatially related to 2-phase fluid inclusions. Such ages indicate that two-phase fluid inclusions are older than 5.32 ± 0.02 Ma, and that fluids with elevated temperatures were present at Yucca Mountain before this time. Results from this study are consistent with a model of descending meteoric water that infiltrated the cooling tuff sequence, became heated, and precipitated secondary minerals within the vadose zone. Fluid inclusions indicate that fluids with elevated temperatures were present during the early history of Yucca Mountain. Sparse, liquid-only fluid inclusions in late intermediate to young calcite indicate that secondary minerals were precipitated from low temperature fluids during the past 5 million years. This study demonstrates that the hypothesis of geologically recent upwelling hydrothermal fluids is untenable and should not disqualify Yucca Mountain as a potential nuclear waste storage site

High pressure compressor component performance report

A compressor optimization study defined a 10 stage configuration with a 22.6:1 pressure ratio, an adiabatic efficiency goal of 86.1%, and a polytropic efficiency of 90.6%; the corrected airflow is 53.5 kg/s. Subsequent component testing included three full scale tests: a six stage rig test, a 10 stage rig test, and another 10 stage rig test completed in the second quarter of 1982. Information from these tests is used to select the configuration for a core engine test and an integrated core/low spool test. The test results will also provide data base for the flight propulsion system. The results of the test series with both aerodynamic and mechanical performance of each compressor build are presented. The second 10 stage compressor adiabatic efficiency was 0.848 at a cruise operating point versus a test goal of 0.846

Leptogenesis with Left-Right domain walls

The presence of domain walls separating regions of unbroken $SU(2)_L$ and $SU(2)_R$ is shown to provide necessary conditions for leptogenesis which converts later to the observed Baryon aymmetry. The strength of lepton number violation is related to the majorana neutrino mass and hence related to current bounds on light neutrino masses. Thus the observed neutrino masses and the Baryon asymmetry can be used to constrain the scale of Left-Right symmetry breaking.Comment: References added, To appear in Praman

Energy efficient engine. Fan and quarter-stage component performance report

The fan configuration for the general Electric/NASA Energy Efficient Engine was selected following an extensive preliminary design study. The fan has an inlet radius ratio of 0.342 and a specific flowrate of 208.9 Kg/sec/sq. m (42.8 1bm/sec/sq. ft). The design corrected tip speed is 411.5 m/sec (1350 ft/sec) producing a bypass flow total-pressure ratio of 1.65 and a core flow total-pressure ratio of 1.6. The design bypass ratio is 6.8. The aerodynamic design point corresponds to the maximum climb power setting at Mach 0.8 and 10.67 Km (35,000 ft) altitude. The fully-instrumented fan component was tested in the Lynn Large Fan Test Facility in 1981. The overall performance results, reported herein, showed excellent fan performance with the fan meeting all of its component test goals of flow, efficiency and stall margin

The protein import apparatus of chloroplasts

Routing of cytosolically synthesized precursor proteins into chloroplasts is a specific process which involves a multitude of soluble and membrane components. In this review we wil1 focus on early events of the translocation pathway of nuclear coded plastidic precursor proteins and compare import routes for polypeptide of the outer chloroplast envelope to that of internal chloroplast compartments. A number of proteins housed in the chloroplast envelopes have been implied to be involved in the translocation process, but so far a certain function has not been assigned to any of these proteins. The only exception could be an envelope localized hsc 70 homologue which could retain the import competence of a precursor protein in transit into the organelle

Status of Electroweak Phase Transition and Baryogenesis

I review recent progress on the electroweak phase transition and baryogenesis, focusing on the minimal supersymmetric standard model as the source of new physics.Comment: 10 pp, 6 figures; plenary talk given at 6th Workshop on High Energy Physics Phenomenology, 4 Jan. 2000, Chennai, India. v.2: added reference

Transient domain walls and lepton asymmetry in the Left-Right symmetric model

It is shown that the dynamics of domain walls in Left-Right symmetric models, separating respective regions of unbroken SU(2)_L and SU(2)_R in the early universe, can give rise to baryogenesis via leptogenesis. Neutrinos have a spatially varying complex mass matrix due to CP-violating scalar condensates in the domain wall. The motion of the wall through the plasma generates a flux of lepton number across the wall which is converted to a lepton asymmetry by helicity-flipping scatterings. Subsequent processing of the lepton excess by sphalerons results in the observed baryon asymmetry, for a range of parameters in Left-Right symmetric models.Comment: v2 version accepted for publication in Phys. Rev. D. Discussion in Introduction and Conclusion sharpened. Equation (12) corrected. 16 pages, 3 figure files, RevTeX4 styl

Black Holes and Black String-like Solutions in Codimension-2 Braneworlds

We discuss black hole solutions with a Gauss-Bonnet term in the bulk and an induced gravity term on a thin brane of codimension-2. We show that these black holes can be localized on the brane, and they can be extended further into the bulk by a warp function. These solutions have regular horizons and no other curvature singularities appear apart from the string-like ones. The projection of the Gauss-Bonnet term on the brane imposes a constraint relation which dictates the form of matter on the brane and in the bulk.Comment: 9 pages, no figures, plenary talk given at the 7th Friedmann International Seminar on Gravitation and Cosmology, 29 June-5 July 2008, Joao Pessoa, Brazil, to appear in the proceeding