10,993 research outputs found
The correlation between soft and hard X-rays component in flares: from the Sun to the stars
In this work we study the correlation between the soft (1.6--12.4 keV, mostly
thermal) and the hard (20--40 and 60--80 keV, mostly non-thermal) X-ray
emission in solar flares up to the most energetic events, spanning about 4
orders of magnitude in peak flux, establishing a general scaling law and
extending it to the most intense stellar flaring events observed to date. We
used the data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager
(RHESSI) spacecraft, a NASA Small Explorer launched in February 2002. RHESSI
has good spectral resolution (~1 keV in the X-ray range) and broad energy
coverage (3 keV--20 MeV), which makes it well suited to distinguish the thermal
from non-thermal emission in solar flares. Our study is based on the detailed
analysis of 45 flares ranging from the GOES C-class, to the strongest X-class
events, using the peak photon fluxes in the GOES 1.6--12.4 keV and in two bands
selected from RHESSI data, i.e.20--40 keV and 60--80 keV. We find a significant
correlation between the soft and hard peak X-ray fluxes spanning the complete
sample studied. The resulting scaling law has been extrapolated to the case of
the most intense stellar flares observed, comparing it with the stellar
observations. Our results show that an extrapolation of the scaling law derived
for solar flares to the most active stellar events is compatible with the
available observations of intense stellar flares in hard X-rays.Comment: 9 pages, 10 figures. To be published in Astronomy and Astrophysic
Some investigations of refractory metal systems of thermionic interest
Investigating interdiffusion of W-Ta, W-Mo, and W-Nb systems in refractory temperature rang
Local Histories
This chapter looks at how local historical writing is prominent in medieval historiography, just as local affairs dominated most lives in the Middle Ages. However, the term and category local history is a modern concept, not a medieval one. Furthermore, even as a modern analytic category, local history can be problematic. One might ask whether the category should include powerful counties but not small kingdoms, or national histories with local sections or brief local elements. In England, the Anglo Saxon Chronicle was primarily concerned with national affairs, but also mentioned events in the particular monasteries where the various versions were written. This could provide curious juxtapositions, emphasizing the separate perception of the local and the national
Hard X-ray imaging facility for space shuttle: A scientific and conceptual engineering study
A shuttle-accommodated instrument for imaging hard X-rays in the study of nonthermal particles and high temperature particles in various solar and cosmic phenomena was defined and its feasibility demonstrated. The imaging system configuration is described as well as the electronics, aspect systems, mechanical and thermal properties and the ground support equipment
Microsecond resolution of quasiparticle tunneling in the single-Cooper-pair-transistor
We present radio-frequency measurements on a single-Cooper-pair-transistor in
which individual quasiparticle poisoning events were observed with microsecond
temporal resolution. Thermal activation of the quasiparticle dynamics is
investigated, and consequently, we are able to determine energetics of the
poisoning and un-poisoning processes. In particular, we are able to assign an
effective quasiparticle temperature to parameterize the poisoning rate.Comment: 4 pages, 4 fig
Modeling Solar Lyman Alpha Irradiance
Solar Lyman alpha irradiance is estimated from various solar indices using linear regression analyses. Models developed with multiple linear regression analysis, including daily values and 81-day running means of solar indices, predict reasonably well both the short- and long-term variations observed in Lyman alpha. It is shown that the full disk equivalent width of the He line at 1083 nm offers the best proxy for Lyman alpha, and that the total irradiance corrected for sunspot effect also has a high correlation with Lyman alpha
Moisture vaporization by Jersey and Holstein cows during diurnal temperature cycles as measured with a hygrometric tent.
Missouri Agricultural Experiment Station and the United States Department of Agriculture cooperating.Digitized 2007 AES.Includes bibliographical references (page [19])
Susan Reynolds
Susan Reynolds was elected to the British Academy after she had worked out a new framework for the medieval history of England, France, Germany and northern Italy. The breakthrough book was her Kingdoms and Communities in Western Europe 900–1300 (1984); it brought all levels of society together in a synthesis, and was a stunning achievement. Her subsequent Fiefs and Vassals (Oxford, 1994) left a generation reluctant even to use the word ‘feudalism’, and other important contributions continued until not long before she died. In 2001 she was honoured with a Festschrift entitled Law, Laity and Solidarities
The association of the Hale Sector Boundary with RHESSI solar flares and active longitudes
The heliospheric magnetic field (HMF) is structured into large sectors of
positive and negative polarity. The parts of the boundary between these sectors
where the change in polarity matches that of the leading-to-following sunspot
polarity in that solar hemisphere, are called Hale Sector Boundaries (HSB). We
investigate the flare occurrence rate near HSBs and the association between
HSBs and active longitudes. Previous work determined the times HSBs were at
solar central meridian, using the detection of the HMF sector boundary crossing
at the Earth. In addition to this, we use a new approach which finds the HSB
locations at all times by determining them from Potential Field Source Surface
(PFSS) extrapolations of photospheric magnetograms. We use the RHESSI X-ray
flare list for comparison to the HSB as it provides accurate flare locations
over 14 years, from February 2002 to February 2016, covering both Cycles 23 and
24. For the active longitude positions we use previously published work based
on sunspot observations. We find that the two methods of determining the HSB
generally agree and that 41% (Cycle 23) and 47% (Cycle 24) of RHESSI flares
occur within of the PFSS determined-HSB. The behaviour of the HSBs
varies over the two Cycles studied, and as expected they swap in hemisphere as
the Cycles change. The HSBs and active longitudes do overlap but not
consistently. They often move at different rates relative to each other (and
the Carrington solar rotation rate) and these vary over each Cycle. The HSBs
provide a useful additional activity indicator, particularly during periods
when active longitudes are difficult to determine
Report from solar physics
A discussion of the nature of solar physics is followed by a brief review of recent advances in the field. These advances include: the first direct experimental confirmation of the central role played by thermonuclear processes in stars; the discovery that the 5-minute oscillations of the Sun are a global seismic phenomenon that can be used as a probe of the structure and dynamical behavior of the solar interior; the discovery that the solar magnetic field is subdivided into individual flux tubes with field strength exceeding 1000 gauss. Also covered was a science strategy for pure solar physics. Brief discussions are given of solar-terrestrial physics, solar/stellar relationships, and suggested space missions
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