4,631 research outputs found
Methods of teaching equitation
Thesis (M.A.)--Boston University, 1949. This item was digitized by the Internet Archive
Solar Flare Impulsive Phase Emission Observed with SDO/EVE
Differential emission measures (DEMs) during the impulsive phase of solar
flares were constructed using observations from the EUV Variability Experiment
(EVE) and the Markov-Chain Monte Carlo method. Emission lines from ions formed
over the temperature range log T = 5.8 - 7.2 allow the evolution of the DEM to
be studied over a wide temperature range at 10s cadence. The technique was
applied to several M- and X-class flares, where impulsive phase EUV emission is
observable in the disk-integrated EVE spectra from emission lines formed up to
3 - 4 MK, and we use spatially-unresolved EVE observations to infer the thermal
structure of the emitting region. For the nine events studied the DEMs
exhibited a two component distribution during the impulsive phase, a low
temperature component with peak temperature of 1 - 2 MK, and a broad high
temperature one from 7 - 30 MK. A bimodal high temperature component is also
found for several events, with peaks at 8 and 25 MK during the impulsive phase.
The origin of the emission was verified using AIA images to be the flare
ribbons and footpoints, indicating that the constructed DEMs represent the
spatially-average thermal structure of the chromospheric flare emission during
the impulsive phase.Comment: 18 pages, 6 figures, accepted for publication in Ap
Apollo 9 multiband photography experiment 5065 Interim post-flight calibration report
Camera and filter postflight spectrum analysis for Apollo 9 multiband photography experimen
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The HERE project toolkit: a resource for programme teams interested in improving student engagement and retention
Fe XIII emission lines in active region spectra obtained with the Solar Extreme-Ultraviolet Research Telescope and Spectrograph
Recent fully relativistic calculations of radiative rates and electron impact
excitation cross sections for Fe {\sc xiii} are used to generate emission-line
ratios involving 3s3p--3s3p and
3s3p--3s3p3d transitions in the 170--225 \AA and 235--450 \AA
wavelength ranges covered by the Solar Extreme-Ultraviolet Research Telescope
and Spectrograph (SERTS). A comparison of these line ratios with SERTS active
region observations from rocket flights in 1989 and 1995 reveals generally very
good agreement between theory and experiment. Several new Fe {\sc xiii}
emission features are identified, at wavelengths of 203.79, 259.94, 288.56 and
290.81 \AA. However, major discrepancies between theory and observation remain
for several Fe {\sc xiii} transitions, as previously found by Landi (2002) and
others, which cannot be explained by blending. Errors in the adopted atomic
data appear to be the most likely explanation, in particular for transitions
which have 3s3p3d D as their upper level. The most useful Fe
{\sc xiii} electron density diagnostics in the SERTS spectral regions are
assessed, in terms of the line pairs involved being (i) apparently free of
atomic physics problems and blends, (ii) close in wavelength to reduce the
effects of possible errors in the instrumental intensity calibration, and (iii)
very sensitive to changes in N over the range 10--10
cm. It is concluded that the ratios which best satisfy these conditions
are 200.03/202.04 and 203.17/202.04 for the 170--225 \AA wavelength region, and
348.18/320.80, 348.18/368.16, 359.64/348.18 and 359.83/368.16 for 235--450 \AA.Comment: 11 pages, 8 figures, 10 tables, MNRAS, in pres
Radiative hydrodynamic modelling and observations of the X-class solar flare on 2011 March 9
We investigated the response of the solar atmosphere to non-thermal electron
beam heating using the radiative transfer and hydrodynamics modelling code
RADYN. The temporal evolution of the parameters that describe the non-thermal
electron energy distribution were derived from hard X-ray observations of a
particular flare, and we compared the modelled and observed parameters. The
evolution of the non-thermal electron beam parameters during the X1.5 solar
flare on 2011 March 9 were obtained from analysis of RHESSI X-ray spectra. The
RADYN flare model was allowed to evolve for 110 seconds, after which the
electron beam heating was ended, and was then allowed to continue evolving for
a further 300s. The modelled flare parameters were compared to the observed
parameters determined from extreme-ultraviolet spectroscopy. The model produced
a hotter and denser flare loop than that observed and also cooled more rapidly,
suggesting that additional energy input in the decay phase of the flare is
required. In the explosive evaporation phase a region of high-density cool
material propagated upward through the corona. This material underwent a rapid
increase in temperature as it was unable to radiate away all of the energy
deposited across it by the non-thermal electron beam and via thermal
conduction. A narrow and high-density ( cm) region at
the base of the flare transition region was the source of optical line emission
in the model atmosphere. The collision-stopping depth of electrons was
calculated throughout the evolution of the flare, and it was found that the
compression of the lower atmosphere may permit electrons to penetrate farther
into a flaring atmosphere compared to a quiet Sun atmosphere.Comment: 12 pages, 12 figure
Biomechanical testing of hip protectors following the Canadian Standards Association express document
Summary
A variety of hip protectors are available, but it is not clear which is the most effective and there is no standard test to evaluate their performance. This is the first study that uses a standard mechanical test on hip protectors. Some protectors perform well but others are almost ineffective, providing little to no protection to the wearer during a fall.
Introduction
Each year, over 70,000 patients are admitted to hospital in the UK with hip fractures. There are a variety of commercial hip protectors currently available. However, it is not explicitly clear which is the most effective with regard to maximum force attenuation, whilst still being both comfortable for the user and providing reasonable force reduction if misplaced from the intended position. The numerous test methods reported in the literature have given conflicting results, making objective comparison difficult for users, researchers, and manufacturers alike. The Canadian Standards Association (CSA) has therefore published an express document (EXP-08-17) with a draft standard test method. This paper presents initial results for a range of hip protectors.
Methods
Eighteen commercially available hip protectors were tested according to EXP-08-17. Each hip protector was impacted five times in correct anatomical alignment over the greater trochanter and once at 50 mm displacements in the anterior, posterior, and lateral directions.
Results
Considerable differences were identified between individual hip protectors in their ability to reduce impact forces on the femur (between 3% and 36% reduction in peak force). The performance was reduced when misplaced in many cases (maximum reduction only 20%).
Conclusions
This is the first study that uses a standard mechanical test on hip protectors. Previous studies have used a variety of methods, making it difficult to interpret results. We hope that these results using a standard test method will facilitate the effective comparison of results, as well as providing useful data for clinicians, users, and purchasers
Desperately seeking the IS in GIS
Geographical Information Systems (GIS) are now a widespread and important form of Information Technology (IT) use. In principle, Information Systems (IS) research is concerned with all forms of IT use. Yet despite this importance, GIS remains largely invisible in IS research. This paper illustrates this separation using bibliographic data drawn from both GIS and IS. It reviews discussion within IS as to the nature of the discipline and argues for a closer coupling between IS and GIS. It discusses Spatial Data Infrastructure (SDI), mobile computing and public participation GIS as examples of spatially related fields where further IS research would be beneficial
The Area Distribution of Solar Magnetic Bright Points
Magnetic Bright Points (MBPs) are among the smallest observable objects on
the solar photosphere. A combination of G-band observations and numerical
simulations is used to determine their area distribution. An automatic
detection algorithm, employing 1-dimensional intensity profiling, is utilized
to identify these structures in the observed and simulated datasets. Both
distributions peak at an area of 45000 km, with a sharp decrease
towards smaller areas. The distributions conform with log-normal statistics,
which suggests that flux fragmentation dominates over flux convergence.
Radiative magneto-convection simulations indicate an independence in the MBP
area distribution for differing magnetic flux densities. The most commonly
occurring bright point size corresponds to the typical width of intergranular
lanes.Comment: Astrophysical Journal, accepte
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