2,756 research outputs found
Mechanisms and Observations of Coronal Dimming for the 2010 August 7 Event
Coronal dimming of extreme ultraviolet (EUV) emission has the potential to be
a useful forecaster of coronal mass ejections (CMEs). As emitting material
leaves the corona, a temporary void is left behind which can be observed in
spectral images and irradiance measurements. The velocity and mass of the CMEs
should impact the character of those observations. However, other physical
processes can confuse the observations. We describe these processes and the
expected observational signature, with special emphasis placed on the
differences. We then apply this understanding to a coronal dimming event with
an associated CME that occurred on 2010 August 7. Data from the Solar Dynamics
Observatory's (SDO) Atmospheric Imaging Assembly (AIA) and EUV Variability
Experiment (EVE) are used for observations of the dimming, while the Solar and
Heliospheric Observatory's (SOHO) Large Angle and Spectrometric Coronagraph
(LASCO) and the Solar Terrestrial Relations Observatory's (STEREO) COR1 and
COR2 are used to obtain velocity and mass estimates for the associated CME. We
develop a technique for mitigating temperature effects in coronal dimming from
full-disk irradiance measurements taken by EVE. We find that for this event,
nearly 100% of the dimming is due to mass loss in the corona
Cryogenic-coolant He4-superconductor dynamic and static interactions
A composite superconducting material (NbTi-Cu) was evaluated with emphasis on post quench solid cooling interaction regimes. The quasi-steady runs confirm the existence of a thermodynamic limiting thickness for insulating coatings. Two distinctly different post quench regimes of coated composites are shown to relate to the limiting thickness. Only one regime,, from quench onset to the peak value, revealed favorable coolant states, in particular in He2. Transient recovery shows favorable recovery times from this post quench regime (not drastically different from bare conductors) for both single coated specimens and a coated conductor bundle
Modeling heat transfer from quench protection heaters to superconducting cables in Nb3Sn magnets
We use a recently developed quench protection heater modeling tool for an
analysis of heater delays in superconducting high-field Nb3Sn accelerator
magnets. The results suggest that the calculated delays are consistent with
experimental data, and show how the heater delay depends on the main heater
design parameters.Comment: 8 pages, Contribution to WAMSDO 2013: Workshop on Accelerator Magnet,
Superconductor, Design and Optimization; 15 - 16 Jan 2013, CERN, Geneva,
Switzerlan
Cryogenic-coolant He-4-superconductor interaction
The thermodynamic and thermal interaction between a type 2 composite alloy and cryo-coolant He4 was studied with emphasis on post quench phenomena of formvar coated conductors. The latter were investigated using a heater simulation technique. Overall heat transfer coefficients were evaluated for the quench onset point. Heat flux densities were determined for phenomena of thermal switching between a peak and a recovery value. The study covered near saturated liquid, pressurized He4, both above and below the lambda transition, and above and below the thermodynamic critical pressure. In addition, friction coefficients for relative motion between formvar insulated conductors were determined
The Thermal Properties of Solar Flares Over Three Solar Cycles Using GOES X-ray Observations
Solar flare X-ray emission results from rapidly increasing temperatures and
emission measures in flaring active region loops. To date, observations from
the X-Ray Sensor (XRS) onboard the Geostationary Operational Environmental
Satellite (GOES) have been used to derive these properties, but have been
limited by a number of factors, including the lack of a consistent background
subtraction method capable of being automatically applied to large numbers of
flares. In this paper, we describe an automated temperature and emission
measure-based background subtraction method (TEBBS), which builds on the
methods of Bornmann (1990). Our algorithm ensures that the derived temperature
is always greater than the instrumental limit and the pre-flare background
temperature, and that the temperature and emission measure are increasing
during the flare rise phase. Additionally, TEBBS utilizes the improved
estimates of GOES temperatures and emission measures from White et al. (2005).
TEBBS was successfully applied to over 50,000 solar flares occurring over
nearly three solar cycles (1980-2007), and used to create an extensive catalog
of the solar flare thermal properties. We confirm that the peak emission
measure and total radiative losses scale with background subtracted GOES X-ray
flux as power-laws, while the peak temperature scales logarithmically. As
expected, the peak emission measure shows an increasing trend with peak
temperature, although the total radiative losses do not. While these results
are comparable to previous studies, we find that flares of a given GOES class
have lower peak temperatures and higher peak emission measures than previously
reported. The resulting TEBBS database of thermal flare plasma properties is
publicly available on Solar Monitor (www.solarmonitor.org/TEBBS/) and will be
available on Heliophysics Integrated Observatory (www.helio-vo.eu)
Rewriting Logic Semantics of a Plan Execution Language
The Plan Execution Interchange Language (PLEXIL) is a synchronous language
developed by NASA to support autonomous spacecraft operations. In this paper,
we propose a rewriting logic semantics of PLEXIL in Maude, a high-performance
logical engine. The rewriting logic semantics is by itself a formal interpreter
of the language and can be used as a semantic benchmark for the implementation
of PLEXIL executives. The implementation in Maude has the additional benefit of
making available to PLEXIL designers and developers all the formal analysis and
verification tools provided by Maude. The formalization of the PLEXIL semantics
in rewriting logic poses an interesting challenge due to the synchronous nature
of the language and the prioritized rules defining its semantics. To overcome
this difficulty, we propose a general procedure for simulating synchronous set
relations in rewriting logic that is sound and, for deterministic relations,
complete. We also report on two issues at the design level of the original
PLEXIL semantics that were identified with the help of the executable
specification in Maude
Does contact with the justice system deter or promote future delinquency? Results from a longitudinal study of British adolescent twins
A critical evaluation of automatic atom mapping algorithms and tools
The identification of the atoms which change their position in chemical reactions is an important knowledge within the field of Metabolic Engineering. This can lead to new advances at different levels from the reconstruction of metabolic networks to the classification of chemical reactions, through the identification of the atomic changes inside a reaction. The Atom Mapping approach was initially developed in the 1960s, but recently suffered important advances, being used in diverse biological and biotechnological studies. The main methodologies used for atom mapping are the Maximum Common Substructure and the Linear Optimization methods, which both require computational know-how and powerful resources to run the underlying tools.
In this work, we assessed a number of previously implemented atom mapping frameworks, and built a framework able of managing the different data inputs and outputs, as well as the mapping process provided by each of these third-party tools. We evaluated the admissibility of the calculated atom maps from different algorithms, also assessing if with different approaches we were capable of returning equivalent atom maps for the same chemical reaction.ERDF -European Regional Development Fund(UID/BIO/04469/2013)info:eu-repo/semantics/publishedVersio
The Palladium-Catalyzed Aerobic Kinetic Resolution of Secondary Alcohols: Reaction Development, Scope, and Applications
The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23 °C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good-to-excellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones
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