30,122 research outputs found
Theory of the cold collision frequency shift in 1S--2S spectroscopy of Bose-Einstein-condensed and non-condensed hydrogen
We show that a correct formulation of the cold collision frequency shift for
two photon spectroscopy of Bose-condensed and cold non-Bose-condensed hydrogen
is consistent with experimental data. Our treatment includes transport and
inhomogeneity into the theory of a non-condensed gas, which causes substantial
changes in the cold collision frequency shift for the ordinary thermal gas, as
a result of the very high frequency (3.9kHz) of transverse trap mode. For the
condensed gas, we find substantial corrections arise from the inclusion of
quasiparticles, whose number is very large because of the very low frequency
(10.2Hz) of the longitudinal trap mode. These two effects together account for
the apparent absence of a "factor of two" between the two possibilities.
Our treatment considers only the Doppler-free measurements, but could be
extended to Doppler-sensitive measurements. For Bose-condensed hydrogen, we
predict a characteristic "foot" extending into higher detunings than can arise
from the condensate alone, as a result of a correct treatment of the statistics
of thermal quasiparticles.Comment: 16 page J Phys B format plus 6 postscript figure
Survival of thermophilic spore-forming bacteria in a 90+ year old milk powder from Ernest Shackelton's Cape Royds Hut in Antarctica
Milk powder taken to Antarctica on Shackelton's British Antarctic Expedition in 1907 was produced in New Zealand by a roller drying process in the first factory in the world dedicated to this process. Thermophilic bacilli are the dominant contaminants of modern spray-dried milk powders and the 1907 milk powder allows a comparison to be made of contaminating strains in roller-dried and spray-dried powders. Samples of milk powder obtained from Shackelton's Hut at Cape Royds had low levels of thermophilic contamination (<500 cfu ml−1) but the two dominant strains (Bacillus licheniformis strain F and Bacillus subtilis) were typical of those found in spray-dried powders. Soil samples from the floor of the hut also contained these strains, whereas soils distant from the hut did not. Differences in the RAPD profiles of isolates from the milk powder and the soils suggest that contamination of the milk from the soil was unlikely. It is significant that the most commonly encountered contaminant strain in modern spray-dried milk (Anoxybacillus flavithermus strain C) was not detected in the 1907 sample
Novel Dynamical Resonances in Finite-Temperature Bose-Einstein Condensates
We describe a variety of intriguing mode-coupling effects which can occur in
a confined Bose-Einstein condensed system at finite temperature. These arise
from strong interactions between a condensate fluctuation and resonances of the
thermal cloud yielding strongly non-linear behaviour. We show how these
processes can be affected by altering the aspect ratio of the trap, thereby
changing the relevant mode-matching conditions. We illustrate how direct
driving of the thermal cloud can lead to significant shifts in the excitation
spectrum for a number of modes and provide further experimental scenarios in
which the dramatic behaviour observed for the mode at JILA (Jin {\it et
al.} 1997) can be repeated. Our theoretical description is based on a
successful second-order finite-temperature quantum field theory which includes
the full coupled dynamics of the condensate and thermal cloud and all relevant
finite-size effects
Inhibition of lipolysis: A novel explanation for the hypothermic actions of acetaminophen in non-febrile rodents
Acetaminophen is both widely used to treat children with fever and is also responsible for thousands being hospitalised annually. Historically the antipyretic actions of acetaminophen were attributed to the inhibition of cyclooxygenase (COX-1/2) enzymes and more recently a novel COX-1 variant (COX-3) located in the brain. However, the evidence for acetaminophen-mediated COX inhibition remains contentious. This study assesses the impact of acetaminophen and other putative COX-3 inhibitors on the release of fatty acids during lipolysis as an alternative mechanism by which antipyretics can reduce body temperature during fever. 3T3-L1 adipocytes, primary brown adipocytes and isolated mitochondria were exposed to COX-3 inhibitors and lipolysis and mitochondrial electron transport chain function assessed. Acetaminophen, aminopyrine and antipyrine at 1–10 mM caused a significant decrease (up to 70%; P < 0.01, from control) in lipolysis within 1, 3 and 24 h without affecting cell viability. The inhibition was observed regardless of where along its signalling pathway lipolysis was stimulated. All three compounds were found to significantly attenuate mitochondrial function by up to 30% for complex I and 40% for complex II (P < 0.01, from control). These novel observations combined with the known limited inhibition of the COX enzymes by acetaminophen suggest both the antipyretic and hypothermia induced by acetaminophen and related compounds could be attributed to the direct inhibition of lipolysis and mitochondrial function, rather than cyclooxygenase inhibition centrally. Further these observations could provide new drug targets for reducing fever with the added bonus of fewer individuals being hospitalized by accidental acetaminophen overdose
Substituted phenylarsonic acids; structures and spectroscopy
Full NMR and ESI-MS spectra, and differential scanning calorimeter data are presented for 15 substituted phenylarsonic acids, including two new fluoro-substituted examples. X-ray crystal structure determinations of five examples (phenylarsonic acid and the 4-fluoro-, 4-fluoro-3-nitro-, 3-amino-4-hydroxy- and 3-amino-4-methoxy-substituted derivatives) were determined and the H-bonding crystal-packing patterns analysed
The Place of the Imperial Smelting Process in Non-ferrous Metallurgy
The Imperial Smelting process is a blast furnace process for the simultaneous recovery of zinc and lead. It was developed at Avonmouth, England, by the imperial smelting corporation. Although the first commercial furnace was built only in 1959, there are now eight others operating under licence in various countries. Two more come into operation during 1968 and two more are under construction. It is estimated that in 1968 the furnaces in operation will produce together some 430000 tons of zinc and 220,000 tons of lead. It can therefore be claimed that the proces has already made a considerable impact in non-ferrous metallurgy
The Impact of the Imperial Smelting Furnace on Non-ferrous Metallurgy
IN 1936 at the Avonmouth Works of the National Smelting Company in England, zinc was produced by both the Hori-zontal Process and by the Vertical Retort Process, then recently installed under licence from the New Jersey
Zinc Company.
In the Research Department we were not satisfied
with either process. The Horizontal Process was inter-mittent in operation, and was a heavy consumer of
fuel. In addition, the vast number of small retorts
which were used, required a considerable amount of
labour, and the work was hot and arduous. The Vertical
Retort Process represented a considerable improvement,
in that it was continuous in operation, and the consi-derably fewer retorts required much less labour and
the thermal efficiency was higher. It was still essen-tially a small unit operation however, maintenance
costs were high, and to make good briquettes, a coal
of special quality was required, which was in limited supply
Spatial entanglement of paired photons generated in cold atomic ensembles
Cold atomic ensembles can mediate the generation of entanglement between
pairs of photons. Photons with specific directions of propagation are detected,
and the entanglement can reside in any of the degrees of freedom that describe
the whole quantum state of the photons: polarization, spatial shape or
frequency. We show that the direction of propagation of the generated photons
determines the spatial quantum state of the photons and therefore, the amount
of entanglement generated. When photons generated in different directions are
combined, this spatial distinguishing information can degrade the quantum
purity of the polarization or frequency entanglement.Comment: 5 pages, 4 figures. Submitted to Phys. Rev. A.; one figure (Fig. 3)
was added, typos and labels in figure 2 were correcte
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