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Search Results: 1 - 10 of 355319 matches for " R. E. Mason "
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High spectral resolution time-resolved optical spectroscopy of V893 Sco
E. Mason,W. Skidmore,S. B. Howell,R. E. Mennickent
Physics , 2001, DOI: 10.1086/323431
Abstract: We present high resolution time-resolved optical spectra of the high inclination short orbital period dwarf nova V893 Sco. We performed spectral analysis through radial velocity measurements, Doppler mapping, and ratioed Doppler maps. Our results indicate that V893 Sco's accretion disk is dissimilar to WZ Sge's accretion disk, and does not fit any of the current accretion disk models. We derive the system parameters M1 and i, and present evidence for V893 Sco as a very young cataclysmic variable and an ER UMa star. We advance the hypothesis that all ER UMa stars may be newly formed cataclysmic variables.
Gemini Mid-IR Polarimetry of NGC 1068
R. E. Mason,C. Packham,S. Young,R. S. Fisher
Revista mexicana de astronomía y astrofísica , 2008,
Abstract:
Outflowing Diffuse Gas in the Active Galactic Nucleus of NGC 1068
T. R. Geballe,R. E. Mason,T. Oka
Physics , 2015, DOI: 10.1088/0004-637X/812/1/56
Abstract: Spectra of the archetypal Type II Seyfert galaxy NGC 1068 in a narrow wavelength interval near 3.7 microns have revealed a weak absorption feature due to two lines of the molecular ion H3+. The observed wavelength of the feature corresponds to velocity of -70 km/s relative to the systemic velocity of the galaxy, implying an outward flow from the nucleus along the line of sight. The absorption by H3+ along with the previously known broad hydrocarbon absorption at 3.4~microns probably are formed in diffuse gas that is in close proximity to the continuum source, i.e. within a few tens of parsecs of the central engine. Based on that conclusion and the measured H3+ absorption velocity and with the assumption of a spherically symmetric wind we estimate a rate of mass outflow from the AGN of ~1 Msun/yr.
Diagnostic Tests for Alzheimer's Disease: Rationale, Methodology, and Challenges
S. E. Mason,R. McShane,C. W. Ritchie
International Journal of Alzheimer's Disease , 2010, DOI: 10.4061/2010/972685
Abstract: There has been a large increase in the amount of research seeking to define or diagnose Alzheimer's disease before patients develop dementia. If successful, this would principally have clinical benefits both in terms of treatment as well as risk modification. Moreover, a better method for diagnosing predementia disease would assist research which seeks to develop such treatments and risk modification strategies. The evidence-based definition of a diagnostic test's accuracy is fundamental to achieve the above goals and to address this, the Cochrane Collaboration has established a Diagnostic Test Accuracy group dedicated to examining the utility and accuracy of proposed tests in dementia and cognitive impairment. We present here the assumptions and observations underpinning the chosen methodology as well as the initial methodological approach decided upon. 1. Introduction Acronyms were most useful when letters and reports were hand written or when one needed to save the ink on the typing ribbon. Nowadays, shorthand is unnecessary, especially when using it leads to confusion. Alzheimer’s disease and Alzheimer’s dementia are not synonymous, but when an author uses the acronym AD, it either suggests that the author believes (wrongly) that they are, or we (as the readers) are left in doubt as to which condition they were referring to. Alzheimer’s disease is a pathological diagnosis using a series of standardised criteria (e.g., Khachaturian, Consortium to Establish a Registry for Alzheimer’s Disease and Reagan [1–3]) whereas Alzheimer’s dementia is a clinical syndrome that is “possibly” or “probably” as a consequence of Alzheimer’s disease [4]. Alzheimer’s dementia is most commonly defined in a research setting using the NINCDS-ADRDA criteria which compared to results at autopsy, detects Alzheimer’s disease with a sensitivity of 91–98% [5]. However, there are a group of clinical conditions probably mediated by Alzheimer’s disease that do not satisfy the criteria for Alzheimer’s dementia and these have been described as a premanifest or incipient Alzheimer’s dementia. We prefer the term premanifest dementia and will use this term throughout. These conditions that will inevitably precede dementia are often indistinguishable from those caused by different pathologies and have therefore all been loosely referred to as Mild Cognitive Impairment; of which at least 16 prognostically weak definitions currently exist [6]. In Huntington’s Disease research, the availability of an accurate diagnostic test has allowed investigation of the clinical correlates of the
The Spatial Variation of the 3micron Dust Features in Circinus
M. D. Colling,P. F. Roche,R. E. Mason
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.14443.x
Abstract: We report spatially-resolved variations in the 3.4micron hydrocarbon absorption feature and the 3.3micron polycyclic aromatic hydrocarbon (PAH) emission band in the Circinus galaxy over the central few arcsec. The absorption is measured towards warm emitting dust associated with Coronal line regions to the east and west of the nucleus. There is an absorption optical depth tau(3.4um) ~0.1 in the core which decreases to the west and increases to the east. This is consistent with increased extinction out to ~40 pc east of the core, supported by the Coronal emission line intensities which are significantly lower to the east than the west. PAH emission is measured to be symmetrically distributed out to +/- 4 arcsec, outside the differential extinction region. The asymmetry in the 3.4micron absorption band reflects that seen in the 9.7micron silicate absorption band reported by Roche et al. (2006) and the ratio of the two absorption depths remains approximately constant across the central regions, with tau(3.4um) / tau(9.7um) ~ 0.06 +/-0.01. This indicates well-mixed hydrocarbon and silicate dust populations, with no evidence for significant changes near the nucleus.
Velocity measurements for a solar active region fan loop from Hinode/EIS observations
P. R. Young,B. O'Dwyer,H. E. Mason
Physics , 2011, DOI: 10.1088/0004-637X/744/1/14
Abstract: The velocity pattern of a fan loop structure within a solar active region over the temperature range 0.15-1.5 MK is derived using data from the EUV Imaging Spectrometer (EIS) on board the Hinode satellite. The loop is aligned towards the observer's line-of-sight and shows downflows (redshifts) of around 15 km/s up to a temperature of 0.8 MK, but for temperatures of 1.0 MK and above the measured velocity shifts are consistent with no net flow. This velocity result applies over a projected spatial distance of 9 Mm and demonstrates that the cooler, redshifted plasma is physically disconnected from the hotter, stationary plasma. A scenario in which the fan loops consist of at least two groups of "strands" - one cooler and downflowing, the other hotter and stationary -- is suggested. The cooler strands may represent a later evolutionary stage of the hotter strands. A density diagnostic of Mg VII was used to show that the electron density at around 0.8 MK falls from 3.2 x 10^9 cm^-3 at the loop base, to 5.0 x 10^8 cm^-3 at a projected height of 15 Mm. A filling factor of 0.2 is found at temperatures close to the formation temperature of Mg VII (0.8 MK), confirming that the cooler, downflowing plasma occupies only a fraction of the apparent loop volume. The fan loop is rooted within a so-called "outflow region" that displays low intensity and blueshifts of up to 25 km/s in Fe XII 195.12 A (formed at 1.5 MK), in contrast to the loop's redshifts of 15 km/s at 0.8 MK. A new technique for obtaining an absolute wavelength calibration for the EIS instrument is presented and an instrumental effect, possibly related to a distorted point spread function, that affects velocity measurements is identified.
Spectroscopic Observations of a Coronal Loop: Basic Physical Plasma Parameters Along the Full Loop Length
G. R. Gupta,Durgesh Tripathi,Helen E. Mason
Physics , 2014, DOI: 10.1088/0004-637X/800/2/140
Abstract: Coronal loops are the basic structures of the solar transition region and corona. The understanding of physical mechanism behind the loop heating, plasma flows, and filling are still considered a major challenge in the solar physics. The mechanism(s) should be able to supply mass to the corona from the chromosphere and able to heat the plasma over 1 MK within the small distance of few hundred km from the chromosphere to the corona. This problem makes coronal loops an interesting target for detailed study. In this study, we focus on spectroscopic observations of a coronal loop, observed in its full length, in various spectral lines as recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) on-board Hinode. We derive physical plasma parameters such as electron density, temperature, pressure, column depth, and filling factors along the loop length from one foot-point to the another. The obtained parameters are used to infer whether the observed coronal loop is over-dense or under-dense with respect to gravitational stratification of the solar atmosphere. These new measurements of physical plasma parameters, from one foot-point to another, provide important constraints on the modeling of the mass and energy balance in the coronal loops.
Discovery of Two New Faint Cataclysmic Variables
S. B. Howell,E. Mason,M. Huber,R. Clowes
Physics , 2002, DOI: 10.1051/0004-6361:20021532
Abstract: We report on the discovery of two new faint cataclysmic variables. The objects were selected as candidates from two different imaging surveys aimed at the discovery of such faint systems. One survey used color and variability while the other used color and H$_\alpha$ emission as selection criteria. We present our spectra of the two new variables and discuss their properties. A discussion of the implication of these discoveries on the space density of faint cataclysmic variables is presented.
The short orbital period CV h_0242-28
E. Mason
Revista mexicana de astronomía y astrofísica , 2004,
Abstract: Presento resultados preliminares de espectroscop a VLT+FORS2 con resoluci on temporal de la variable cat- acl smica recientemente descubierta (CV) H 0242-28.
Partially-erupting prominences: a comparison between observations and model-predicted observables
D. Tripathi,S. E. Gibson,J. Qiu,L. Fletcher,R. Liu,H. Gilbert,H. E. Mason
Physics , 2009, DOI: 10.1051/0004-6361/200809801
Abstract: AIM: To investigate several partially-erupting prominences to study their relationship with other CME-associated phenomena and to compare these observations with observables predicted by a model of partially-expelled flux ropes (Gibson & Fan, 2006a, b). METHODS: We have studied 6 selected events with partially-erupting prominences using multi wavelength observations recorded by the Extreme-ultraviolet Imaging Telescope (EIT), Transition Region and Coronal Explorer (TRACE), Mauna Loa Solar Observatory (MLSO), Big Bear Solar Observatory (BBSO) and soft X-ray telescope (SXT). The observational features associated with partially-erupting prominences were then compared with the predicted observables from the model. RESULTS: The partially-expelled-flux-rope (PEFR) model of Gibson & Fan (2006a, b) can explain the partial eruption of these prominences, and in addition predicts a variety of other CME-related observables that provide evidence for internal reconnection during eruption. We find that all of the partially-erupting prominences studied in this paper exhibit indirect evidence for internal reconnection. Moreover, all cases showed evidence of at least one observable unique to the PEFR model, e.g., dimmings external to the source region, and/or a soft X-ray cusp overlying a reformed sigmoid. CONCLUSIONS: The PEFR model provides a plausible mechanism to explain the observed evolution of partially-erupting-prominence-associated CMEs in our study.
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