71,271 research outputs found
On air temperature fluctuations immediately above a glacier surface
Developing remote sensing techniques for measuring meteorological parameters in surface layers of snow field
Edward Thompson's Ethics and Activism 1956–1963: Reflections on the Political Formation of The Making of the English Working Class
As well as a work of history, E. P. Thompson's The Making of the English Class (London: Gollancz, 1963) was written as a strategic intervention in wider political debates of the late 1950s about working class consciousness, identity, agency and organisation, and as a sustained expression and application of ‘socialist humanism’ to historical subjects. This essay situates the book within these debates, moving between The Making and Thompson's writings within the New Left, to show how the characteristic themes of his work—moral choice and agency, the complexities of working-class consciousness and culture, the role of intellectuals and of an ‘organised minority’—were developed through both. This provides us with a richer context for understanding both the moral sensibility that animates the book and key elements of its historiographical standpoint
Optical Spectroscopy of K-selected Extremely Red Galaxies
We have obtained spectroscopic redshifts for 24 red galaxies from a sample
with median Ks=18.7 and F814W - Ks > 4, using the Keck telescope. These
EROshave high resolution morphologies from HST (Yan & Thompson 2003). Among the
24 redshifts, the majority (92%) are at . We derived the
rest-frame J-band luminosity function at . Our result
suggests that the luminosity evolution between bright EROs at and the
present-day L massive galaxies is at most about 0.7 magnitude. Combining
the morphologies and deep spectroscopy revealed the following properties: (1)
86% of the spectra have absorption features from old stars, suggesting that the
dominant stellar populations seen in the rest-frame UV are old stars. 50% of
the sources have pure absorption lines, while the remaining 50% have emission
lines, indicating recent star formation. We conclude that the color criterion
for EROs is very effective in selecting old stellar populations at ,
and a large fraction of these systems with prominent old stellar populations
also have recent star formation. (2) The 12 emission line systems have the same
number of disk and bulge galaxies as in the remaining 12 pure absorption line
systems. We conclude that spectral classes do not have a simple, direct
correspondence with morphological types. (3) Three EROs could be isolated, pure
passively evolving early-type galaxies at . This implies that only a
small fraction (10%--15%) of early-type galaxies are formed in a rapid burst of
star formation at high redshifts and evolved passively since then. (Abridged).Comment: 27 pages, 8 figures. Accepted for publication in Astronomical
Journal, issue March 200
Kinetics and mechanism of the reaction between atomic chlorine and dimethyl selenide; comparison with the reaction between atomic chlorine and dimethyl sulfide
Dimethyl selenide is the most abundant gaseous selenium species in marine environments. In this work, the value of the rate coefficient for the gas-phase reaction between dimethyl selenide and Cl atoms has been determined for the first time. The value of the second-order rate coefficient obtained was (5.0±1.4)×10–10 cm3 molecule–1 s–1. The very fast nature of the reaction means that, when estimating the lifetime of dimethyl selenide in the atmosphere, loss due to reaction with Cl atoms should be considered along with loss due to reaction with O3 and with OH and NO3 radicals. Analysis of the available kinetic data suggests that at 760 Torr the dominant reaction pathway for the reaction of Cl atoms with dimethyl selenide will be the addition of Cl to the Se atom forming an adduct of the type CH3Se(Cl)CH3. Theoretical calculations, at the B3LYP/6-311++G(2df,p)//B3LYP/6-311++G(d,p) level of theory, show that at 298 K the value of rH for the formation of the adduct is –111.4 kJ mol–1. This value may be compared to –97.0 kJ mol–1, the value calculated for rH for the formation of the analogous sulfur adduct, CH3S(Cl)CH3, following the reaction between Cl atoms and dimethyl sulfide. Variational RRKM theory was used to predict the thermal decomposition rates of the two adducts back to starting materials. The estimated rate constant for the decomposition of the selenium adduct to the reactants is 5×10–5 s–1, compared to 0.02 s–1 in the case of the sulfur adduct. However, our calculations suggest that the CH3Se(Cl)CH3 adduct, which is initially formed highly excited, will not be stabilised under atmospheric conditions, but rather will decompose to yield CH3SeCl and CH3, a process that is calculated to be exothermic with respect to the initial reactants by 5.8 kJ mol–1. The formation of CH3SCl and CH3 from the sulfur adduct, on the other hand, is endothermic by 20.8 kJ mol–1 with respect to the initial reactants, and is thus not expected to occur
The Giant Flare of 1998 August 27 from SGR 1900+14: II. Radiative Mechanism and Physical Constraints on the Source
(ABBREVIATED) The extraordinary 1998 August 27 giant flare places strong
constraints on the physical properties of its source, SGR 1900+14. We make
detailed comparisons of the published data with the magnetar model. The giant
flare evolved through three stages, whose radiative mechanisms we address in
turn. A triggering mechanism is proposed, whereby a helical distortion of the
core magnetic field induces large-scale fracturing in the crust and a twisting
deformation of the crust and exterior magnetic field. The envelope of the
pulsating tail of the August 27 flare can be accurately fit, after ~40 s, by
the contracting surface of a relativistically hot, but inhomogeneous, trapped
fireball. We quantify the effects of direct neutrino-pair emission, thereby
deducing a lower bound ~ 10^{32} G-cm^3 to the magnetic moment of the confining
field. The radiative flux during the intermediate ~40 s of the burst appears to
exceed the trapped fireball fit. The spectrum and lightcurve of this smooth
tail are consistent with heating in an extended pair corona, possibly powered
by continuing seismic activity in the star. We consider in detail the critical
luminosity, below which a stable balance can be maintained between heating and
radiative cooling in a confined, magnetized pair plasma; but above which the
confined plasma runs away to local thermodynamic equilibrium. In the later
pulsating tail, the best fit temperature equilibrates at a value which agrees
well with the regulating effect of photon splitting. The remarkable four-peaked
substructure within each 5.16-s pulse provides strong evidence for the presence
of higher magnetic multipoles in SGR 1900+14. The corresponding collimation of
the X-ray flux is related to radiative transport in a super-QED magnetic field.Comment: 11 July 2001, accepted for publication in the Astrophysical Journa
In situ apparatus for the study of clathrate hydrates relevant to solar system bodies using synchrotron X-ray diffraction and Raman spectroscopy
Clathrate hydrates are believed to play a significant role in various solar
system environments, e.g. comets, and the surfaces and interiors of icy
satellites, however the structural factors governing their formation and
dissociation are poorly understood. We demonstrate the use of a high pressure
gas cell, combined with variable temperature cooling and time-resolved data
collection, to the in situ study of clathrate hydrates under conditions
relevant to solar system environments. Clathrates formed and processed within
the cell are monitored in situ using synchrotron X-ray powder diffraction and
Raman spectroscopy. X-ray diffraction allows the formation of clathrate
hydrates to be observed as CO2 gas is applied to ice formed within the cell.
Complete conversion is obtained by annealing at temperatures just below the ice
melting point. A subsequent rise in the quantity of clathrate is observed as
the cell is thermally cycled. Four regions between 100-5000cm-1 are present in
the Raman spectra that carry features characteristic of both ice and clathrate
formation. This novel experimental arrangement is well suited to studying
clathrate hydrates over a range of temperature (80-500K) and pressure
(1-100bar) conditions and can be used with a variety of different gases and
starting aqueous compositions. We propose the increase in clathrate formation
observed during thermal cycling may be due to the formation of a quasi
liquid-like phase that forms at temperatures below the ice melting point, but
which allows easier formation of new clathrate cages, or the retention and
delocalisation of previously formed clathrate structures, possibly as amorphous
clathrate. The structural similarities between hexagonal ice, the quasi
liquid-like phase, and crystalline CO2 hydrate mean that differences in the
Raman spectrum are subtle; however, all features out to 5000cm-1 are diagnostic
of clathrate structure.Comment: Astronomy & Astrophysics, in press. 6 page
Carbonate Formation in Non-Aqueous Environments by Solid-Gas Carbonation of Silicates
We have produced synthetic analogues of cosmic silicates using the Sol Gel
method, producing amorphous silicates of composition Mg(x)Ca(1-x)SiO3. Using
synchrotron X-ray powder diffraction on Beamline I11 at the Diamond Light
Source, together with a newly-commissioned gas cell, real-time powder
diffraction scans have been taken of a range of silicates exposed to CO2 under
non-ambient conditions. The SXPD is complemented by other techniques including
Raman and Infrared Spectroscopy and SEM imaging.Comment: 5 pages, 3 figures. Contribution to the Proceedings of the First
European Conference on Laboratory Astrophysics (ECLA
A tale of three kingdoms: Members of the Phylum Nematoda independently acquired the detoxifying enzyme cyanase through horizontal gene transfer from plants and bacteria
Horizontal gene transfer (HGT) has played an important role in the evolution of nematodes. Among candidate genes, cyanase, which is typically found only in plants, bacteria and fungi, is present in more than 35 members of the Phylum Nematoda, but absent from free-living and clade V organisms. Phylogenetic analyses showed that the cyanases of clade I organisms Trichinella spp., Trichuris spp. and Soboliphyme baturini (Subclass: Dorylaimia) represent a well-supported monophyletic clade with plant cyanases. In contrast, all cyanases found within the Subclass Chromadoria which encompasses filarioids, ascaridoids and strongyloids are homologous to those of bacteria. Western blots exhibited typical multimeric forms of the native molecule in protein extracts of Trichinella spiralis muscle larvae, where immunohisto- chemical staining localized the protein to the worm hypodermis and underlying muscle. Recombinant Trichinella cyanase was bioactive where gene transcription profiles support functional activity in vivo. Results suggest that: (1) independent HGT in parasitic nematodes originated from different Kingdoms; (2) cyanase acquired an active role in the biology of extant Trichinella; (3) acquisition occurred more than 400 million years ago (MYA), prior to the divergence of the Trichinellida and Dioctophymatida, and (4) early, free-living ances- tors of the genus Trichinella had an association with terrestrial plants
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