Photonic band-gap properties for two-component slow light

We consider two-component "spinor" slow light in an ensemble of atoms coherently driven by two pairs of counterpropagating control laser fields in a double tripod-type linkage scheme. We derive an equation of motion for the spinor slow light (SSL) representing an effective Dirac equation for a massive particle with the mass determined by the two-photon detuning. By changing the detuning the atomic medium acts as a photonic crystal with a controllable band gap. If the frequency of the incident probe light lies within the band gap, the light tunnels through the sample. For frequencies outside the band gap, the transmission probability oscillates with increasing length of the sample. In both cases the reflection takes place into the complementary mode of the probe field. We investigate the influence of the finite excited state lifetime on the transmission and reflection coefficients of the probe light. We discuss possible experimental implementations of the SSL using alkali atoms such as Rubidium or Sodium.Comment: 7 figure

Arcjet Testing of Woven Carbon Cloth for Use on Adaptive Deployable Entry Placement Technology

This paper describes arcjet testing and analysis that has successfully demonstrated the viability of three dimensional woven carbon cloth for dual use in the Adaptive Deployable Entry Placement Technology (ADEPT). ADEPT is an umbrella-like entry system that is folded for stowage in the launch vehicle s shroud and deployed in space prior to reaching the atmospheric interface. A key feature of the ADEPT concept is its lower ballistic coefficient for delivery of a given payload than those for conventional, rigid body entry systems. The benefits that accrue from the lower ballistic coefficient include factor of ten reductions of deceleration forces and entry heating. The former enables consideration of new classes of scientific instruments for solar system exploration while the latter enables the design of a more efficient thermal protection system. The carbon cloth now base lined for ADEPT has a dual use in that it serves as ADEPT s thermal protection system and as the "skin" that transfers aerodynamic deceleration loads to its umbrella-like substructure. The arcjet testing described in this paper was conducted for some of the higher heating conditions for a future Venus mission using the ADEPT concept, thereby showing that the carbon cloth can perform in a relevant entry environment. The ADEPT project considered the carbon cloth to be mission enabling and was carrying it as a major risk during Fiscal Year 2012. The testing and analysis reported here played a major role in retiring that risk and is highly significant to the success and possible adoption of ADEPT for future NASA missions. Finally, this paper also describes a preliminary engineering level code, based on the arcjet data, that can be used to estimate cloth thickness for future missions using ADEPT and to predict carbon cloth performance in future arcjet tests

Selection and Certification of TPS: Constraints and Considerations of Venus Missions

This presentation was part of the session : Probe Missions to the Giant Planets, Titan and VenusSixth International Planetary Probe WorkshopThe science community currently has interest in planetary entry probe missions to improve our understanding of the atmosphere of Saturn [1], missions to Venus and also sample return missions from comets and asteroids. In addition, the In-Space Propulsion Program has completed aerocapture mission design studies that have defined the requirements for the Thermal protection System (TPS) to Venus, Mars, Titan and Neptune. There have been investments in new TPS materials and to revive flight qualified materials such as PICA (used on Stardust and currently baselined for MSL and Orion) and Carbon-Phenolic, the TPS material of choice for Venus and Outer Planet missions. Mission studies have shown the heating rates for the "shallow" Saturn probes are in the range of (2 - 5) KW/cm2 in its H(2)/He atmosphere. Venus entry probes will experience heat fluxes in the similar range of (3 - 7) kW/cm(2) in CO2. High-speed Earth reentry missions from comets and asteroids will experience heating of the range of (1 - 5) kW/cm(2) and at pressures equal to or higher than Stardust. Aerocapture during Venus missions will experience heat fluxes in the range of (2 - 4) kW/cm(2) in CO2. Titan aero-capture missions will experience far smaller heating fluxes in the N2/methane atmosphere. Since the flight times are longer during aerocapture missions, TPS design requirements involve much larger heatloads at relatively lower heat-fluxes compared to those for direct entry probe missions. It is clear that qualification and certification of the heritage ablative materials or the development of new, ablative Thermal Protection System (TPS) materials for entry or aerocapture probe missions is needed [2] and the challenges are in testing, especially in the appropriate atmospheric gases. NASA Ames has nearly completed the construction of a small, low cost, 5 MW arc jet facility, called the Development Arcjet Facility (DAF) that will permit testing of small models at high heat fluxes and in different gases. This paper will review the entry conditions from a collection of mission studies to various solar system destinations, the testing needs of both newer as well as heritage TPS for each destination and provide the approach, we at NASA Ames plan to adopt, in testing and analysis by making use of both existing arc jet facilities as well as an affordable, small 5 MW arc jet that can be used for TPS development in test gases appropriate for the Neptune, Titan, Saturn, Venus or Earth applications. [1] Atreya, S. K., et. al. "Formation of Giant Planets and Their Atmospheres: Entry Probes for Saturn and Beyond; 5 th International Planetary Probe Workshop, June 25-29, Bordeaux, France. [2] Venkatapathy, E. and Laub, B. "Requirements for Development of Thermal Protection Systems for Multiple Missions: 5th International Planetary Probe Workshop, June 25-29, Bordeaux, France.NASA In-Space Propulsion Progra

TOM40 Mediates Mitochondrial Dysfunction Induced by α-Synuclein Accumulation in Parkinson's Disease.

Alpha-synuclein (α-Syn) accumulation/aggregation and mitochondrial dysfunction play prominent roles in the pathology of Parkinson's disease. We have previously shown that postmortem human dopaminergic neurons from PD brains accumulate high levels of mitochondrial DNA (mtDNA) deletions. We now addressed the question, whether alterations in a component of the mitochondrial import machinery -TOM40- might contribute to the mitochondrial dysfunction and damage in PD. For this purpose, we studied levels of TOM40, mtDNA deletions, oxidative damage, energy production, and complexes of the respiratory chain in brain homogenates as well as in single neurons, using laser-capture-microdissection in transgenic mice overexpressing human wildtype α-Syn. Additionally, we used lentivirus-mediated stereotactic delivery of a component of this import machinery into mouse brain as a novel therapeutic strategy. We report here that TOM40 is significantly reduced in the brain of PD patients and in α-Syn transgenic mice. TOM40 deficits were associated with increased mtDNA deletions and oxidative DNA damage, and with decreased energy production and altered levels of complex I proteins in α-Syn transgenic mice. Lentiviral-mediated overexpression of Tom40 in α-Syn-transgenic mice brains ameliorated energy deficits as well as oxidative burden. Our results suggest that alterations in the mitochondrial protein transport machinery might contribute to mitochondrial impairment in α-Synucleinopathies

Landscape, Memory, and the Shifting Regional Geographies of Northwest Bosnia-Herzegovina

Writing and arguing with older discourses that have informed the subdiscipline of regional geography and setting them against new ways of conceiving of the region, this article considers the northwest of Bosnia-Herzegovina as a site that calls for a newly animated form of regional study. Of particular concern here is the role that memory and commemorative practices play in such a spatial schema. The monumental landscapes of the Tito regime and its collective commemoration of World War II sit alongside and are troubled by the more recent traumas and spaces of unmarked death associated with the ethnic war in Bosnia during the early 1990s. Read together, northwest Bosnia-Herzegovina functions as a vivid exemplar for understanding traumatic historical mourning as a phenomenological process that is inseparable from the wider geopolitical landscape

Adaptable Functionality of Transcriptional Feedback in Bacterial Two-Component Systems

A widespread mechanism of bacterial signaling occurs through two-component systems, comprised of a sensor histidine kinase (SHK) and a transcriptional response regulator (RR). The SHK activates RR by phosphorylation. The most common two-component system structure involves expression from a single operon, the transcription of which is activated by its own phosphorylated RR. The role of this feedback is poorly understood, but it has been associated with an overshooting kinetic response and with fast recovery of previous interrupted signaling events in different systems. Mathematical models show that overshoot is only attainable with negative feedback that also improves response time. Our models also predict that fast recovery of previous interrupted signaling depends on high accumulation of SHK and RR, which is more likely in a positive feedback regime. We use Monte Carlo sampling of the parameter space to explore the range of attainable model behaviors. The model predicts that the effective feedback sign can change from negative to positive depending on the signal level. Variations in two-component system architectures and parameters may therefore have evolved to optimize responses in different bacterial lifestyles. We propose a conceptual model where low signal conditions result in a responsive system with effectively negative feedback while high signal conditions with positive feedback favor persistence of system output

Functional Assessment of EnvZ/OmpR Two-Component System in Shewanella oneidensis

EnvZ and OmpR constitute the bacterial two-component signal transduction system known to mediate osmotic stress response in a number of Gram-negative bacteria. In an effort to understand the mechanism through which Shewanella oneidensis senses and responds to environmental osmolarity changes, structure of the ompR-envZ operon was determined with Northern blotting assay and roles of the EnvZ/OmpR two-component system in response to various stresses were investigated with mutational analysis, quantitative reverse transcriptase PCR (qRT-PCR), and phenotype microarrays. Results from the mutational analysis and qRT-PCR suggested that the EnvZ/OmpR system contributed to osmotic stress response of S. oneidensis and very likely engaged a similar strategy employed by E. coli, which involved reciprocal regulation of two major porin coding genes. Additionally, the ompR-envZ system was also found related to cell motility. We further showed that the ompR-envZ dependent regulation of porin genes and motility resided almost completely on ompR and only partially on envZ, indicating additional mechanisms for OmpR phosphorylation. In contrast to E. coli lacking ompR-envZ, however, growth of S. oneidensis did not show a significant dependence on ompR-envZ even under osmotic stress. Further analysis with phenotype microarrays revealed that the S. oneidensis strains lacking a complete ompR-envZ system displayed hypersensitivities to a number of agents, especially in alkaline environment. Taken together, our results suggest that the function of the ompR-envZ system in S. oneidensis, although still connected with osmoregulation, has diverged considerably from that of E. coli. Additional mechanism must exist to support growth of S. oneidensis under osmotic stress

A Bacterial Ras-Like Small GTP-Binding Protein and Its Cognate GAP Establish a Dynamic Spatial Polarity Axis to Control Directed Motility

Directional control of bacterial motility is regulated by dynamic polarity inversions driven by pole-to-pole oscillation of a Ras family small G-protein and its associated GTPase-activating protein