5,100 research outputs found
Interplanetary Coronal Mass Ejections observed by MESSENGER and Venus Express
Interplanetary coronal mass ejections (ICMEs) observed by the MESSENGER (MES)
and Venus Express (VEX) spacecraft have been catalogued and analysed. The ICMEs
were identified by a relatively smooth rotation of the magnetic field direction
consistent with a flux rope structure, coinciding with a relatively enhanced
magnetic field strength. A total of 35 ICMEs were found in the surveyed MES
data (primarily from March 2007 to April 2012), and 84 ICMEs in the surveyed
VEX data (from May 2006 to December 2013). The ICME flux rope configurations
have been determined. Ropes with northward leading edges were about four times
more common than ropes with southward leading edges, in agreement with a
previously established solar cycle dependence. Ropes with low inclinations to
the solar equatorial plane were about four times more common than ropes with
high inclinations, possibly an observational effect. Left and right-handed
ropes were observed in almost equal numbers. In addition, data from MES, VEX,
STEREO-A, STEREO-B and ACE were examined for multipoint signatures of the
catalogued ICMEs. For spacecraft separations below 15{\deg} in heliocentric
longitude, the second spacecraft observed the ICME flux rope in 82% of cases;
this percentage dropped to 49% for separations between 15 and 30{\deg}, to 18%
for separations between 30 and 45{\deg}, and to 12% for separations between 45
and 60{\deg}. As spacecraft separation increased, it became increasingly likely
that only the sheath and not the flux rope of the ICME was observed, in
agreement with the notion that ICME flux ropes are smaller in longitudinal
extent than the shocks or discontinuities that they often drive. Furthermore,
this study has identified 23 ICMEs observed by pairs of spacecraft close to
radial alignment. A detailed analysis of these events could lead to a better
understanding of how ICMEs evolve during propagation.Comment: 28 pages, 7 figure
Genetic algorithms: a pragmatic, non-parametric approach to exploratory analysis of questionnaires in educational research
Data from a survey to determine student attitudes to their courses are used as an example to show how genetic algorithms can be used in the analysis of questionnaire data. Genetic algorithms provide a means of generating logical rules which predict one variable in a data set by relating it to others. This paper explains the principle underlying genetic algorithms and gives a non-mathematical description of the means by which rules are generated. A commercially available computer program is used to apply genetic algorithms to the survey data. The results are discussed
An eighth-century inscribed cross-slab in Dull, Perthshire
The discovery of a cross-inscribed slab with an inscription is described. Because of its importance it was decided to invite specialist comment on this piece of sculpture and to publish it in advance of the full report on the excavations. The form of the monument, its inscription and archaeological context are considered. The text appears to consist of a Gaelic personal name. The script is a form of geometrical lettering which can be dated to the opening quarter of the eighth century. The form of the cross has Columban associations which sit well with place-name and other evidence which points to Dull having been a monastery founded from Iona by c. AD 700
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On the magnetospheric ULF wave counterpart of substorm onset
One nearâubiquitous signature of substorms observed on the ground is the azimuthal structuring of the onset auroral arc in the minutes prior to onset. Termed auroral beads, these optical signatures correspond to concurrent exponential increases in ground ultralow frequency (ULF) wave power and are likely the result of a plasma instability in the magnetosphere. Here, we present a case study showing the development of auroral beads from a Time History of Events and Macroscale Interactions during Substorms (THEMIS) allâsky camera with near simultaneous exponential increases in auroral brightness, ionospheric and conjugate magnetotail ULF wave power, evidencing their intrinsic link. We further present a survey of magnetic field fluctuations in the magnetotail around substorm onset. We find remarkably similar superposed epoch analyses of ULF power around substorm onset from space and conjugate ionospheric observations. Examining periods of exponential wave growth, we find the groundâ and spaceâbased observations to be consistent, with average growth rates of âŒ0.01 sâ1, lasting for âŒ4 min. Crossâcorrelation suggests that the spaceâbased observations lead those on the ground by approximately 1â1.5 min. Meanwhile, spacecraft located premidnight and âŒ10 RE downtail are more likely to observe enhanced wave power. These combined observations lead us to conclude that there is a magnetospheric counterpart of auroral beads and exponentially increasing ground ULF wave power. This is likely the result of the linear phase of a magnetospheric instability, active in the magnetotail for several minutes prior to auroral breakup
Photo- and solvatochromic properties of nitrobenzospiropyran in ionic liquids containing the [NTf2]- anion
The photo-, thermo- and solvatochromic properties of 2,3-dihydro-10,30,30-trimethyl-6-nitrospiro-
[1-benzopyran-2,20-1H-indole] (BSP-NO2) were studied in ILs containing the anion [NTf2]- by UV-Vis absorption spectroscopy, ab initio molecular orbital theory and density functional theory (DFT) calculations. It was found that the kinetics and thermodynamics of the BSP-NO2 MC (merocyanine) equilibrium was sensitive to the nature of the cation. It was also observed that the imidazolium cation can form a through-space orbital interaction with the MC isomer, rather than a simple electrostatic interaction, thus preventing the MC conversion back to the BSP-NO2 isomer. The BSP-NO2 MC equilibrium thus serves as a model system for studying modes of interaction of the cations in ionic liquids
Large Chiral Diffeomorphisms on Riemann Surfaces and W-algebras
The diffeomorphism action lifted on truncated (chiral) Taylor expansion of a
complex scalar field over a Riemann surface is presented in the paper under the
name of large diffeomorphisms. After an heuristic approach, we show how a
linear truncation in the Taylor expansion can generate an algebra of symmetry
characterized by some structure functions. Such a linear truncation is
explicitly realized by introducing the notion of Forsyth frame over the Riemann
surface with the help of a conformally covariant algebraic differential
equation. The large chiral diffeomorphism action is then implemented through a
B.R.S. formulation (for a given order of truncation) leading to a more
algebraic set up. In this context the ghost fields behave as holomorphically
covariant jets. Subsequently, the link with the so called W-algebras is made
explicit once the ghost parameters are turned from jets into tensorial ghost
ones. We give a general solution with the help of the structure functions
pertaining to all the possible truncations lower or equal to the given order.
This provides another contribution to the relationship between KdV flows and
W-diffeomorphimsComment: LaTeX file, 31 pages, no figure. Version to appear in J. Math. Phys.
Work partly supported by Region PACA and INF
N-methyl-N-alkylpyrrolidinium nonafluoro-1-butanesulfonate salts : Ionic liquid properties and plastic crystal behaviour
A series of N-methyl-N-alkylpyrrolidinium nonafluoro-1-butanesulfonate salts were synthesised and characterised. The thermophysical characteristics of this family of salts have been investigated with respect to potential use as ionic liquids and solid electrolytes. N-Methyl-N-butylpyrrolidinium nonafluoro-1-butanesulfonate (p1,4NfO) has the lowest melting point of the family, at 94 °C. Electrochemical analysis of p1,4 NfO in the liquid state shows an electrochemical window of ~6 V. All compounds exhibit one or more solid–solid transitions at sub-ambient temperatures, indicating the existence of plastic crystal phases.<br /
Isospin Splitting in the Baryon Octet and Decuplet
Baryon mass splittings are analyzed in terms of a simple model with general
pairwise interactions. At present, the masses are poorly known from
experiments. Improvement of these data would provide an opportunity to make a
significant test of our understanding of electromagnetic and quark-mass
contributions to hadronic masses. The problem of determining resonance masses
from scattering and production data is discussed.Comment: 9 pages, LATEX inc. 2 LATEX "pictures", CMU-HEP91-24-R9
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