13,267 research outputs found
Evidence of a Plasmoid-Looptop Interaction and Magnetic Inflows During a Solar Flare/CME Eruptive Event
Observational evidence is presented for the merging of a downward-propagating
plasmoid with a looptop kernel during an occulted limb event on 2007 January
25. RHESSI lightcurves in the 9-18 keV energy range, as well as that of the 245
MHz channel of the Learmonth Solar Observatory, show enhanced nonthermal
emission in the corona at the time of the merging suggesting that additional
particle acceleration took place. This was attributed to a secondary episode of
reconnection in the current sheet that formed between the two merging sources.
RHESSI images were used to establish a mean downward velocity of the plasmoid
of 12 km/s. Complementary observations from the SECCHI suite of instruments
onboard STEREO-Behind showed that this process occurred during the acceleration
phase of the associated CME. From wavelet-enhanced EUVI, images evidence of
inflowing magnetic field lines prior to the CME eruption is also presented. The
derived inflow velocity was found to be 1.5 km/s. This combination of
observations supports a recent numerical simulation of plasmoid formation,
propagation and subsequent particle acceleration due to the tearing mode
instability during current sheet formation.Comment: 8 pages, 9 figures, ApJ (Accepted
Detection of 3-Minute Oscillations in Full-Disk Ly Emission During A Solar Flare
In this Letter we report the detection of chromospheric 3-minute oscillations
in disk-integrated EUV irradiance observations during a solar flare. A wavelet
analysis of detrended Lyman-alpha (from GOES/EUVS) and Lyman continuum (from
SDO/EVE) emission from the 2011 February 15 X-class flare (SOL2011-02-15T01:56)
revealed a 3-minute period present during the flare's main phase. The
formation temperature of this emission locates this radiation to the flare's
chromospheric footpoints, and similar behaviour is found in the SDO/AIA
1600\AA\ and 1700\AA\ channels, which are dominated by chromospheric continuum.
The implication is that the chromosphere responds dynamically at its acoustic
cutoff frequency to an impulsive injection of energy. Since the 3-minute period
was not found at hard X-ray energies (50-100 keV) in RHESSI data we can state
that this 3-minute oscillation does not depend on the rate of energization of
non-thermal electrons. However, a second period of 120 s found in both hard
X-ray and chromospheric emission is consistent with episodic electron
energization on 2-minute timescales. Our finding on the 3-minute oscillation
suggests that chromospheric mechanical energy should be included in the flare
energy budget, and the fluctuations in the Lyman-alpha line may influence the
composition and dynamics of planetary atmospheres during periods of high
activity.Comment: 6 pages, 5 figures. Accepted for publication in Astrophysics Journal
Letter
The Carboxyl-Terminal Segment of Apolipoprotein A-V Undergoes a Lipid-Induced Conformational Change
Apolipoprotein (apo) A-V is a 343-residue, multidomain protein that plays an important role in regulation of plasma triglyceride homeostasis. Primary sequence analysis revealed a unique tetraproline sequence (Pro293-Pro296) near the carboxyl terminus of the protein. A peptide corresponding to the 48-residue segment beyond the tetraproline motif was generated from a recombinant apoA-V precursor wherein Pro295 was replaced by Met. Cyanogen bromide cleavage of the precursor protein, followed by negative affinity chromatography, yielded a purified peptide. Nondenaturing polyacrylamide gel electrophoresis verified that apoA-V(296-343) solubilizes phospholipid vesicles, forming a relatively heterogeneous population of reconstituted high-density lipoprotein with Stokes’ diameters\u3e17 nm. At the same time, apoA-V(296-343) failed to bind a spherical lipoprotein substrate in vitro. Far-UV circular dichroism spectroscopy revealed the peptide is unstructured in buffer yet adopts significant R-helical secondary structure in the presence of the lipid mimetic solvent trifluoroethanol (TFE; 50% v/v). Heteronuclear multidemensional NMR spectroscopy experiments were conducted with uniformly 15N- and 15N/13C-labeled peptide in 50% TFE. Peptide backbone assignment and secondary structure prediction using TALOSþ reveal the peptide adopts R-helix secondary structure from residues 309 to 334. In TFE, apoA-V(296-343) adopts an extended amphipathic R-helix, consistent with a role in lipoprotein binding as a component of full-length apoA-V
SONTRAC: an imaging spectrometer for solar neutrons
An instrument capable of unambiguously determining the energy and direction of incident neutrons has important applications in solar physics-as well as environmental monitoring and medical/radiological sciences. The SONTRAC (SOlar Neutron TRACking) instrument is designed to operate in the neutron energy range of 20-250 MeV. The measurement principle is based on non-relativistic double scatter of neutrons off ambient protons (n-p scattering) within a block of densely packed scintillating fibers. Using this double-scatter mode it is possible to uniquely determine neutron energy and direction on an event-by-event basis. A fully operational science model of such an instrument has been built using 300 μm (250 μm active) scintillating fibers. The science model consists of a 5×5×5 cm cube of orthogonal plastic scintillating fiber layers. Two orthogonal imaging chains, employing image intensifiers and CCD cameras, allow full 3-dimensional reconstruction of scattered proton particle tracks. We report the results of the science model instrument calibration using 35-65 MeV protons. The proton calibration is the first step toward understanding the instrument response to n-p scatter events. Preliminary results give proton energy resolution of 2% (6%) at 67.5 (35) MeV, and angular resolution of 2° (4.5°) at 67.5 (35) MeV. These measurements are being used to validate detailed instrument simulations that will be used to optimize the instrument design and develop quantitative estimates of science return. Based on the proton calibration, neutron energy and angular resolution for a 10×10×10 cm version of SONTRAC is expected to be ~5% an
Charge Transfer-oxy Radical Mechanism for Anti-cancer Agents
The proposal is advanced that anti-cancer drugs generally function by charge transfer resulting in formation of toxic oxy radicals which destroy the neoplasm. Electrochemical studies were performed with some of the main types of agents: iminium ions (adenine iminium from alkylating species, iminium metabolite of 6-mercaptopurine, nitidine, other polynuclear iminiums) and metal complexes (Pt(II)diaquodiammine-guanosine, copper salicylaldoximes). Reduction potentials ranged from -0.4 to -1.2 V. Literature data for quinones are presented and radiation is discussed. Based on the theoretical framework, a rationale is offered for the carcinogen-anti-cancer paradox and the role of antioxidants
Three path interference using nuclear magnetic resonance: a test of the consistency of Born's rule
The Born rule is at the foundation of quantum mechanics and transforms our
classical way of understanding probabilities by predicting that interference
occurs between pairs of independent paths of a single object. One consequence
of the Born rule is that three way (or three paths) quantum interference does
not exist. In order to test the consistency of the Born rule, we examine
detection probabilities in three path intereference using an ensemble of
spin-1/2 quantum registers in liquid state nuclear magnetic resonance (LSNMR).
As a measure of the consistency, we evaluate the ratio of three way
interference to two way interference. Our experiment bounded the ratio to the
order of , and hence it is consistent with Born's rule.Comment: 11 pages, 4 figures; Improved presentation of figures 1 and 4,
changes made in section 2 to better describe the experiment, minor changes
throughout, and added several reference
Velocity Characteristics of Evaporated Plasma Using Hinode/EIS
This paper presents a detailed study of chromospheric evaporation using the
EUV Imaging Spectrometer (EIS) onboard Hinode in conjunction with HXR
observations from RHESSI. The advanced capabilities of EIS were used to measure
Doppler shifts in 15 emission lines covering the temperature range T=0.05-16 MK
during the impulsive phase of a C-class flare on 2007 December 14. Blueshifts
indicative of the evaporated material were observed in six emission lines from
Fe XIV-XXIV (2-16 MK). Upflow velocity (v_up) was found to scale with
temperature as v_up (km s^-1)~8-18 T (MK). Although the hottest emission lines,
Fe XXIII and Fe XXIV, exhibited upflows of >200 km s^-1, their line profiles
were found to be dominated by a stationary component in contrast to the
predictions of the standard flare model. Emission from O VI-Fe XIII lines
(0.5-1.5 MK) was found to be redshifted by v_down (km s^-1)~60-17 T (MK) and
was interpreted as the downward-moving `plug' characteristic of explosive
evaporation. These downflows occur at temperatures significantly higher than
previously expected. Both upflows and downflows were spatially and temporally
correlated with HXR emission observed by RHESSI that provided the properties of
the electron beam deemed to be the driver of the evaporation. The energy flux
of the electron beam was found to be >5x10^10 ergs cm^-2 s^-1 consistent with
the value required to drive explosive chromospheric evaporation from
hydrodynamic simulations.Comment: 9 pages, 7 figures, 1 table, ApJ (Accepted
Development and performance of the Fast Neutron Imaging Telescope for SNM detection
FNIT (the Fast Neutron Imaging Telescope), a detector with both imaging and energy measurement capabilities, sensitive to neutrons in the range 0.8-20 MeV, was initially conceived to study solar neutrons as a candidate design for the Inner Heliosphere Sentinel (IHS) spacecraft of NASA\u27s Solar Sentinels program and successively reconfigured to locate fission neutron sources. By accurately identifying the position of the source with imaging techniques and reconstructing the Watt spectrum of fission neutrons, FNIT can detect samples of special nuclear material (SNM), including heavily shielded and masked ones. The detection principle is based on multiple elastic neutron-proton scatterings in organic scintillators. By reconstructing n-p event locations and sequence and measuring the recoil proton energies, the direction and energy spectrum of the primary neutron flux can be determined and neutron sources identified. We describe the design of the FNIT prototype and present its energy reconstruction and imaging performance, assessed by exposing FNIT to a neutron beam and to a Pu fission neutron source
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