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At least 631 records · Page 35

Study of magnetic notions in the solar photosphere and their implications for heating the solar atmosphere

This progress report covers the first year of NASA Grant NAGw-2545, a study of magnetic structure in the solar photosphere and chromosphere. We have made significant progress in three areas: (1) analysis of vorticity in photospheric convection, which probably affects solar atmospheric heating through the stresses it imposes on photospheric magnetic fields; (2) modelling of the horizontal motions of magnetic footpoints in the solar photosphere using an assumed relation between brightness and vertical motion as well as continuity of flow; and (3) observations and analysis of infrared CO lines formed near the solar temperature minimum, whose structure and dynamics also yield important clues to the nature of heating of the upper atmosphere. Each of these areas are summarized in this report, with copies of those papers prepared or published this year included.

Noyes, Robert W.↗

On the Dynamics of Small-Scale Solar Magnetic Elements

We report on the dynamics of the small-scale solar magnetic field, based on analysis of very high resolution images of the solar photosphere obtained at the Swedish Vacuum Solar Telescope. The data sets are movies from 1 to 4 hr in length, taken in several wavelength bands with a typical time between frames of 20 s. The primary method of tracking small-scale magnetic elements is with very high contrast images of photospheric bright points, taken through a 12 A bandpass filter centered at 4305 A in the Fraunhofer 'G band.' Previous studies have established that such bright points are unambiguously associated with sites of small-scale magnetic flux in the photosphere, although the details of the mechanism responsible for the brightening of the flux elements remain uncertain. The G band bright points move in the intergranular lanes at speeds from 0.5 to 5 km/s. The motions appear to be constrained to the intergranular lanes and are primarily driven by the evolution of the local granular convection flow field. Continual fragmentation and merging of flux is the fundamental evolutionary mode of small-scale magnetic structures in the solar photosphere. Rotation and folding of chains or groups of bright points are also observed. The timescale for magnetic flux evolution in active region plage is on the order of the correlation time of granulation (typically 6-8 minutes), but significant morphological changes can occur on timescales as short as 100 S. Smaller fragments are occasionally seen to fade beyond observable contrast. The concept of a stable, isolated subarcsecond magnetic 'flux tube' in the solar photosphere is inconsistent with the observations presented here.

Berger, T. E.↗

Laminar Dust Flames: A Program of Microgravity and Ground Based Studies at McGill

Fundamental knowledge of heterogeneous combustion mechanisms is required to improve utilization of solid fuels (e.g. coal), safe handling of combustible dusts in industry, and solid propulsion systems. The objective of the McGill University research program on dust combustion is to obtain a reliable set of data on basic combustion parameters for dust suspensions (i.e. laminar burning velocity, flame structure, quenching distance, flammability limits, etc.) over a range of particle sizes, dust concentrations, and types of fuel. This set of data then permits theoretical models to be validated and, when necessary, new models to be developed to describe the detailed reaction mechanisms and transport processes. Microgravity is essential to the generation of a uniform dust suspension of arbitrary particle size and concentration. When particles with a characteristic size on the order of tens of microns are suspended, they rapidly settle in a gravitational field. To maintain a particulate in suspension for time duration adequate to carry out combustion experiments invariably requires continuous convective flow in excess of the gravitational settling velocity (which is comparable with and can even exceed the dust laminar burning velocity). This makes the experiments turbulent in nature and thus renders it impossible to study laminar dust flames. Even for small particle sizes on the order of microns, a stable laminar dust flow can be maintained only for relatively low dust concentrations at normal gravity conditions. High dust loading leads to gravitational instability of the dust cloud and to the formation of recirculation cells in the dust suspension in a confined volume, or to the rapid sedimentation of the dense dust cloud, as a whole, in an unconfined volume. Many important solid fuels such as carbon and boron also have low laminar flame speeds (of the order of several centimeters per second). Convection that occurs in combustion products due to buoyancy disrupts the low speed dust flames and makes observation of such flames at normal gravity difficult.

Goroshin, Sam↗

Solid Surface Wetting and the Deployment of Drops in Microgravity

The complete or partial deployment of liquid samples in low gravity is primarily influenced by the interfacial properties of the specific liquid and solid materials used because the overwhelming bias of the Earth gravitational acceleration is removed. This study addresses the engineering aspects of injecting and deploying drops of prescribed volume into an acoustic positioning chamber in microgravity. The specific problems of interest are the design, testing, and implementation of injector tips to be used in a simuttaneously retracting dual-injector system used in the Drop Physics Module microgravity experiment facility. Prior to release, the liquid to be deployed must be retained within a restricted area at the very end of the injectors even under dynamic stimuli due to continuous injection flow as well as to the stepped motion of the injectors, and the final released drop must have a well determined volume as well as negligible residual linear or angular momentum from the deployment process. The outcome of Earthbased short-duration low gravity experiments had been the selection of two types of injector tips which were flown as back-up parts and were successfully utilized during the USML-1 Spacelab mission. The combination of a larger contact surface, liquid pinning with a sharp edge, and selective coating of strategic tip surfaces with a non-wetting compound has allowed a significant increase in the success rate of deployment of simple and compound drops of aqueous solutions of glycerol and silicone oil. The diameter of the samples studied in the Drop Physics Module ranged between 0.3 and 2.7 cm. The tests conducted onsrbit with a manually operated small device have allowed the calibration of the volume deployed for a few drop sizes. The design for improved tips to be used during the next USML flight is based on these results.

Trinh, E. H.↗

Effect of whole-body and local heating on cutaneous vasoconstrictor responses in humans

Animal studies suggest that alpha-adrenergic-mediated vasoconstriction is compromised during whole-body heating. The purpose of this study was to identify whether whole-body heating and/or local surface heating reduce cutaneous alpha-adrenergic vasoconstrictor responsiveness in human skin. Protocol I: Six subjects were exposed to neutral skin temperature (i.e., 34 degrees C), whole-body heating, and local heating of forearm skin to increase skin blood flow to the same relative magnitude as that observed during whole-body heating. Protocol II: In eight subjects forearm skin was locally heated to 34, 37, 40, and 42 degrees C. During both protocols, alpha-adrenergic vasoconstrictor responsiveness was assessed by local delivery of norepinephrine (NE) via intradermal microdialysis. Skin blood flow was continuously monitored over each microdialysis membrane via laser-Doppler flowmetry. In protocol I, whole-body and local heating caused similar increases in cutaneous vascular conductance (CVC). The EC50 (log NE dose) of the dose-response curves for both whole body (-4.2 +/- 0.1 M) and local heating (-4.7 +/- 0.4 M) were significantly greater (i.e., high dose required to cause 50% reduction in CVC) relative to neutral skin temperature (- 5.6 +/- 0.0 M; P<0.05 for both). In both local and whole-body heated conditions CVC did not return to pre-heating values even at the highest dose of NE. In protocol II, calculated EC50 for 34, 37, 40, and 42 degrees C local heating was - 5.5 +/- 0.4, -4.6 +/- 0.3, -4.5 +/- 0.3, - 4.2 +/- 0.4 M, respectively. Statistical analyses revealed that the EC50 for 37,40 and 42 degrees C were significantly greater than the EC50 for 34 degrees C. These results indicate that even during administration of high concentrations of NE, alpha-adrenergic vasoconstriction does not fully compensate for local heating and whole-body heating induced vasodilatation in young, healthy subjects. Moreover, these data suggest that elevated local temperatures, above 37 degrees C, and whole-body heating similarly attenuate cutaneous alpha-adrenergic vasoconstriction responsiveness.

Non-NASA Center↗

Chromite-Plagioclase Assemblages as a New Shock Indicator; Implications for the Shock and Thermal Histories of Ordinary Chondrites

Chromite in ordinary chondrites (OC) can be used as a shock indicator. A survey of 76 equilibrated H, L and LL chondrites shows that unshocked chromite grains occur in equant, subhedral and rounded morphologies surrounded by silicate or intergrown with metallic Fe-Ni and/or troilite. Some unmelted chromite grains are fractured or crushed during whole-rock brecciation. Others are transected by opaque veins; the veins form when impacts cause localized heating of metal-troilite intergrowths above the Fe-FeS eutectic (988 C), mobilization of metal-troilite melts, and penetration of the melt into fractures in chromite grains. Chromite-plagioclase assemblages occur in nearly every shock-stage S3-S6 OC; the assemblages range in size from 20-300 microns and consist of 0.2-20-micron-size euhedral, subhedral, anhedral and rounded chromite grains surrounded by plagioclase or glass of plagioclase composition. Plagioclase has a low impedance to shock compression. Heat from shock-melted plagioclase caused adjacent chromite grains to melt; chromite grains crystallized from this melt. Those chromite grains in the assemblages that are completely surrounded by plagioclase are generally richer in Al2O3, than unmelted, matrix chromite grains in the same meteorite. Chromite veinlets (typically 0.5-2 microns thick and 10-300 microns long) occur typically in the vicinity of chromite-plagioclase assemblages. The veinlets formed from chromite-plagioclase melts that were injected into fractures in neighboring silicate grains; chromite crystallized in the fractures and the residual plagioclase-rich melt continued to flow, eventually pooling to form plagioclase-rich melt pockets. Chromite-rich chondrules (consisting mainly of olivine, plagioclase-normative mesostasis, and 5-15 vol.% chromite) occur in many shocked OC and OC regolith breccias but they are absent from primitive type-3 OC. They may have formed by impact melting chromite, plagioclase and adjacent mafic silicates during higher-energy shock events. The melt was jetted from the impact site and formed droplets due to surface tension. Crystallization of these droplets may have commenced in flight, prior to landing on the parent-body surface. Chromite-plagioclase assemblages and chromite veinlets occur in 25 out of 25 shock-stage S1 OC of petrologic type 5 and 6 that I examined. Although these rocks contain unstrained olivine with sharp optical extinction, most possess other shock indicators such as extensive silicate darkening, numerous occurrences of metallic Cu, polycrystalline troilite, and opaque veins. It seems likely that these rocks were shocked to levels at least as high as shock-stage S3 and then annealed by heat generated during the shock event. During annealing, the olivine crystal lattices healed but other shock indicators survived. Published Ar-Ar age data for some SI OC indicate that many shock and annealing events occurred very early in the history of the parent asteroids. The common occurrence of shocked and annealed OC is consistent with collisions being a major mechanism responsible for metamorphosing OC.

Rubin, Alan E.↗

The Distant Magnetotail Under Long Duration, Very Northward IMF Conditions: October 22-24, 2003

A unique 32 hour interval of very northward Interplanetary Magnetic Field (IMF) on October 22-24, 2003 created a exceptionally thick cold dense magnetotail plasma sheet, a small polar cap and accompanying small tail lobe. These features were detected by the Cluster DMSP and FAST spacecraft and modeled by a global simulation as described in papers by Oieroset et al. (2005) and Li et al. (2005). During the same interval the Wind spacecraft was passing through the center of the magnetotail about 130 Re downstream of Earth. Wind results will be described that reveal a very unusual magnetotail characterized by (1) continual tailward flow of 200-400 km/s with densities in the range 0.2-3/cc, both of whch are clearly less than those expected in the magnetosheath, (2) a mostly northward Bz but with a predominant Bx field component with sign reversals indicating crossings between the two hemispheres of the tail, and (3) velocity waves superposed on the downstream flow with peak-to-peak amplitudes of 100 to 200 km/s, periods of 10 to 20 minutes and clockwise polarization. Low altitude DMSP and Fast measurements reveal an auroral oval with enhanced latitudinal thickness and a small polar cap filled with structured precipitzting electrons and few ions. A new global MHD simulation of the event exhibits a highly elliptical tail of diminished cross-section at 130 Re with major axis aligned with the northward IMF. The tail current sheet also tends to be aligned in a north-south direction with the two tail hemispheres to the east and west with their polarities depending on prior history of the IMF. The simulation appears to be consistent with many, but not all, of the observations. High latitude cusp reconnection and subsequent downtail flow of closed field lines may explain the tail structure, but the waves are more likely due to the Kelvin-Helmholtz instability often thought to occur during northward IMF conditions.

Fairfield, Donald H.↗

Making Superconducting Welds between Superconducting Wires

A technique for making superconducting joints between wires made of dissimilar superconducting metals has been devised. The technique is especially suitable for fabrication of superconducting circuits needed to support persistent electric currents in electromagnets in diverse cryogenic applications. Examples of such electromagnets include those in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) systems and in superconducting quantum interference devices (SQUIDs). Sometimes, it is desirable to fabricate different parts of a persistent-current-supporting superconducting loop from different metals. For example, a sensory coil in a SQUID might be made of Pb, a Pb/Sn alloy, or a Cu wire plated with Pb/Sn, while the connections to the sensory coil might be made via Nb or Nb/Ti wires. Conventional wire-bonding techniques, including resistance spot welding and pressed contact, are not workable because of large differences between the hardnesses and melting temperatures of the different metals. The present technique is not subject to this limitation. The present technique involves the use (1) of a cheap, miniature, easy-to-operate, capacitor-discharging welding apparatus that has an Nb or Nb/Ti tip and operates with a continuous local flow of gaseous helium and (2) preparation of a joint in a special spark-discharge welding geometry. In a typical application, a piece of Nb foil about 25 m thick is rolled to form a tube, into which is inserted a wire that one seeks to weld to the tube (see figure). The tube can be slightly crimped for mechanical stability. Then a spark weld is made by use of the aforementioned apparatus with energy and time settings chosen to melt a small section of the niobium foil. The energy setting corresponds to the setting of a voltage to which the capacitor is charged. In an experiment, the technique was used to weld an Nb foil to a copper wire coated with a Pb/Sn soft solder, which is superconducting. The joint was evaluated as part of a persistent-current circuit having an inductance of 1 mH. A current was induced in a loop, and no attenuation of the current after a time interval 1,000 s was discernible in a measurement having a fractional accuracy of 10(exp -4): This observation supports the conclusion that the weld had an electrical resistance <10(exp -10) omega.

Penanen, Konstantin I.↗

The Solar Dynamics Observatory: Your Eye on the Sun

The Solar Dynamics Observatory (SDO) was launched on February 11,2010 into partly cloudy skies over Cape Canaveral, Florida. SDO moved into a 28 degree inclined geosynchronous orbit over the longitude of the ground station in New Mexico. SDO is the first Space Weather Mission in NASA's Living With a Star Program. SDO's main goal is to understand and predict those solar variations that influence life on Earth and our technological systems. The SDO science investigations will determine how the Sun's magnetic field is generated and structured, how this stored magnetic energy is released into the heliosphere as the solar wind, energetic particles, and variations in the solar irradiance. The SDO mission consists of three scientific investigations (AIA, EVE, and HMI), a spacecraft bus, and a dedicated Ka-band ground station to handle the 150 Mbps data flow. SDO continues a long tradition of NASA missions providing calibrated solar spectral irradiance data, in this case using multiple measurements of the irradiance and rocket underflights of the spacecraft. The other instruments on SDO will be used to explain and develop predictive models of the solar spectral irradiance in the extreme ultraviolet. Science teams at LMSAL, LASP, and Stanford are responsible for processing, analyzing, distributing, and archiving the science data. We will talk about the building of SDO, its launch, and the data and science it will provide to NASA.

Pesnell, William Dean↗

The Solar Dynamics Observatory: Your On-Orbit Eye on the Sun

The Solar Dynamics Observatory (SDO) was launched on February 11, 2010 into the partly cloudy skies above Cape Canaveral, Florida. Over the next month SDO moved into a 28 degree inclined geosynchronous orbit at the longitude of the ground station in New Mexico. SDO is the first Space Weather Mission in NASA's Living With a Star Program. SDO's main goal is to understand and predict those solar variations that influence life on Earth and our technological systems. The SDO science investigations will determine how the Sun's magnetic field is generated and structured, how this stored magnetic energy is released into the heliosphere as the solar wind, energetic particles, and variations in the solar irradiance. The SDO mission consists of three scientific investigations (AIA, EVE, and HMI), a spacecraft bus, and a dedicated Ka-band ground station to handle the 150 Mbps data flow. SDO continues a long tradition of NASA missions providing calibrated solar spectral irradiance data, in this case using multiple measurements of the irradiance and rocket underflights of the spacecraft. The other instruments on SDO will be used to explain and develop predictive models of the solar spectral irradiance in the extreme ultraviolet. Science teams at LMSAL, LASP, and Stanford are responsible for processing, analyzing, distributing, and archiving the science data. We will talk about the launch of SDO and describe the data and science it is providing to NASA.

Pesnell, W. Dean↗

Feasibility of Ultraviolet Light Emitting Diodes as an Alternative Light Source for Photocatalysis

The objective of this study was to determine whether ultraviolet light emitting diodes (UV-LEDs) could serve as an alternative photon source efficiently for heterogeneous photocatalytic oxidation (PCO). An LED module consisting of 12 high-power UV-A LEDs was designed to be interchangeable with a UV-A fluorescent black light blue (BLB) lamp in a Silica-Titania Composite (STC) packed bed annular reactor. Lighting and thermal properties were characterized to assess the uniformity and total irradiant output. A forward current of (I(sub F)) 100 mA delivered an average irradiance of 4.0 m W cm(exp -2), which is equivalent to the maximum output of the BLB, but the irradiance of the LED module was less uniform than that of the BLB. The LED- and BLB-reactors were tested for the oxidization of 50 ppmv ethanol in a continuous flow-through mode with 0.94 sec space time. At the same irradiance, the UV-A LED reactor resulted in a lower PCO rate constant than the UV-A BLB reactor (19.8 vs. 28.6 nM CO2 sec-I), and consequently lower ethanol removal (80% vs. 91%) and mineralization efficiency (28% vs. 44%). Ethanol mineralization increased in direct proportion to the irradiance at the catalyst surface. This result suggests that reduced ethanol mineralization in the LED- reactor could be traced to uneven irradiance over the photocatalyst, leaving a portion of the catalyst was under-irradiated. The potential of UV-A LEDs may be fully realized by optimizing the light distribution over the catalyst and utilizing their instantaneous "on" and "off' feature for periodic irradiation. Nevertheless, the current UV-A LED module had the same wall plug efficiency (WPE) of 13% as that of the UV-A BLB. These results demonstrated that UV-A LEDs are a viable photon source both in terms of WPE and PCO efficiency.

Levine, Langanf H.↗

Using Supra-Arcade Downflows as Probes of Electron Acceleration During Solar Flares

Extracting information from coronal features above flares has become more reliable with the availability of increasingly higher spatial and temporal-resolution data in recent decades. We are now able to sufficiently probe the region high above long-duration flaring active regions where reconnection is expected to be continually occurring. Flows in the supra-arcade region, first observed with Yohkoh/SXT, have been theorized to be associated with newly-reconnected outflowing loops. High resolution data appears to confirm these assertions. Assuming that these flows are indeed reconnection outflows, then the detection of those directed toward the solar surface (i.e. downflowing) should be associated with particle acceleration between the current sheet and the loop footpoints rooted in the chromosphere. RHESSI observations of highly energetic particles with respect to downflow detections could potentially constrain electron acceleration models. I will discuss measurements of these supra-arcade downflows (SADs) in relation to reconnection model parameters and present preliminary findings comparing the downflow timings with high-energy RHESSI lightcurves.

Savage, Sabrina L.↗

Using Supra-Arcade Downflows as Probes of Particle Acceleration in Solar Flares

Extracting information from coronal features above flares has become more reliable with the availability of increasingly higher spatial- and temporal-resolution data in recent decades. We are now able to sufficiently probe the region high above long-duration flaring active regions where reconnection is expected to be continually occurring. Flows in the supra-arcade region, first observed with Yohkoh/SXT, have been theorized to be associated with newly-reconnected outflowing loops. High resolution data appears to confirm these assertions. Assuming that these flows are indeed reconnection outflows, then the detection of those directed toward the solar surface (i.e. downflowing) should be associated with particle acceleration between the current sheet and the loop footpoints rooted in the chromosphere. RHESSI observations of highly energetic particles with respect to downflow detections could potentially constrain electron acceleration models. We provide measurements of these supra-arcade downflows (SADs) in relation to reconnection model parameters and present preliminary findings comparing the downflow timings with high-energy RHESSI lightcurves.

Savage, Sabrina↗

Single and Multi-Pulse Low-Energy Conical Theta Pinch Inductive Pulsed Plasma Thruster Performance

Fabricated and tested CTP IPPTs at cone angles of 20deg, 38deg, and 60deg, and performed direct single-pulse impulse bit measurements with continuous gas flow. Single pulse performance highest for 38deg angle with impulse bit of approx.1 mN-s for both argon and xenon. Estimated efficiencies low, but not unexpectedly so based on historical data trends and the direction of the force vector in the CTP. Capacitor charging system assembled to provide rapid recharging of capacitor bank, permitting repetition-rate operation. IPPT operated at repetition-rate of 5 Hz, at maximum average power of 2.5 kW, representing to our knowledge the highest average power for a repetitively-pulsed thruster. Average thrust in repetition-rate mode (at 5 kV, 75 sccm argon) was greater than simply multiplying the single-pulse impulse bit and the repetition rate.

Hallock, Ashley K.↗

NextGen Flight Deck Surface Trajectory-Based Operations (STBO): Contingency Holds

The purpose of this pilot-in-the-loop taxi simulation was to investigate a NextGen Surface Trajectory-Based Operations (STBO) concept called "contingency holds." The contingency-hold concept parses a taxi route into segments, allowing an air traffic control (ATC) surface traffic management (STM) system to hold an aircraft when necessary for safety. Under nominal conditions, if the intersection or active runway crossing is clear, the hold is removed, allowing the aircraft to continue taxiing without slowing, thus improving taxi efficiency, while minimizing the excessive brake use, fuel burn, and emissions associated with stop-and-go taxi. However, when a potential traffic conflict exists, the hold remains in place as a fail-safe mechanism. In this departure operations simulation, the taxi clearance included a required time of arrival (RTA) to a specified intersection. The flight deck was equipped with speed-guidance avionics to aid the pilot in safely meeting the RTA. On two trials, the contingency hold was not released, and pilots were required to stop. On two trials the contingency hold was released 15 sec prior to the RTA, and on two trials the contingency hold was released 30 sec prior to the RTA. When the hold remained in place, all pilots complied with the hold. Results also showed that when the hold was released at 15-sec or 30-sec prior to the RTA, the 30-sec release allowed pilots to maintain nominal taxi speed, thus supporting continuous traffic flow; whereas, the 15-sec release did not. The contingency-hold concept, with at least a 30-sec release, allows pilots to improve taxiing efficiency by reducing braking, slowing, and stopping, but still maintains safety in that no pilots "busted" the clearance holds. Overall, the evidence suggests that the contingency-hold concept is a viable concept for optimizing efficiency while maintaining safety.

NextGen↗

Repetitive Interrogation of 2-Level Quantum Systems

Trapped ion clocks derive information from a reference atomic transition by repetitive interrogations of the same quantum system, either a single ion or ionized gas of many millions of ions. Atomic beam frequency standards, by contrast, measure reference atomic transitions in a continuously replenished "flow through" configuration where initial ensemble atomic coherence is zero. We will describe some issues and problems that can arise when atomic state selection and preparation of the quantum atomic system is not completed, that is, optical pumping has not fully relaxed the coherence and also not fully transferred atoms to the initial state. We present a simple two-level density matrix analysis showing how frequency shifts during the state-selection process can cause frequency shifts of the measured clock transition. Such considerations are very important when a low intensity lamp light source is used for state selection, where there is relatively weak relaxation and re-pumping of ions to an initial state and much weaker 'environmental' relaxation of the atomic coherence set-up in the atomic sample.

Rabi interrogation↗

Turbo-Brayton Power Converter

Future NASA space missions will require advanced thermal-to-electric power converters that are reliable, efficient, and lightweight. Creare, LLC, is developing a turbo-Brayton power converter that offers high efficiency and specific power. The converter employs gas bearings to provide maintenance free, long-life operation. Discrete components can be packaged to fit optimally with other subsystems, and the converter's continuous gas flow can communicate directly with remote heat sources and heat rejection surfaces without the need for ancillary heat-transfer components and intermediate flow loops. Creare has completed detailed analyses, trade studies, fabrication trials, and preliminary designs for the components and converter assembly. The company is fabricating and testing a breadboard converter.

Breedlove, Jeffrey↗