4,628 research outputs found
Partial-Transfer Absorption Imaging: A versatile technique for optimal imaging of ultracold gases
Partial-transfer absorption imaging is a tool that enables optimal imaging of
atomic clouds for a wide range of optical depths. In contrast to standard
absorption imaging, the technique can be minimally-destructive and can be used
to obtain multiple successive images of the same sample. The technique involves
transferring a small fraction of the sample from an initial internal atomic
state to an auxiliary state and subsequently imaging that fraction absorptively
on a cycling transition. The atoms remaining in the initial state are
essentially unaffected. We demonstrate the technique, discuss its
applicability, and compare its performance as a minimally-destructive technique
to that of phase-contrast imaging.Comment: 10 pages, 5 figures, submitted to Review of Scientific Instrument
A Search for Environmental Effects on Type Ia Supernovae
We use integrated colors and B and V absolute magnitudes of Type Ia supernova
(SN) host galaxies in order to search for environmental effects on the SN
optical properties. With the new sample of 44 SNe we confirm the conclusion by
Hamuy et al. (1996a) that bright events occur preferentially in young stellar
environments. We find also that the brightest SNe occur in the least luminous
galaxies, a possible indication that metal-poorer neighbourhoods produce the
more luminous events. The interpretation of these results is made difficult,
however, due to the fact that galaxies with younger stellar populations are
also lower in luminosity. In an attempt to remove this ambiguity we use models
for the line strengths in the absorption spectrum of five early-type galaxies,
in order to estimate metallicities and ages of the SN host galaxies. With the
addition of abundance estimates from nebular analysis of the emission spectra
of three spiral galaxies, we find possible further evidence that luminous SNe
are produced in metal-poor neighborhoods. Further spectroscopic observations of
the SN host galaxies will be necessary to test these results and assist in
disentangling the age/metallicity effects on Type Ia SNe.Comment: 14 pages, 5 figures, to appear in the September 2000 issue of The
Astronomical Journa
Is environmental radon gas associated with the incidence of neurodegenerative conditions? A retrospective study of multiple sclerosis in radon affected areas in England and Wales
To test whether an association exists between radon gas concentration in the home and increased multiple sclerosis (MS) incidence, a retrospective study was undertaken of MS incidence in known areas of raised domestic radon concentration in England and Wales, using The Health Improvement Network (THIN) clinical research database.The study population comprised 20,140,498 person-years of clinical monitoring (males: 10,056,628: 49.93%; females: 10,083,870: 50.07%), representing a mean annual population of 2.5 million individuals. To allow for the possible latency of MS initiation following exposure, data extraction was limited to patients with at least five years registration history with the same GP practice before first diagnosis. Patient records were allocated to one of nine radon concentration bands depending on the average radon level in their postcode sector.MS incidence was analysed by searching for patients with first MS diagnosis over the eight calendar years 2005-2012 inclusive. 1512 new MS cases were diagnosed, 1070 females, 442 males, equivalent to raw incidence rates of 7.51, 10.61 and 4.40 per 105person-years respectively, comparable to previously reported results. Of these new cases, 115 could be allocated to one of the radon bands representing high radon areas.Standardising to the UK 2010 population, excess relative risk (ERR) figures for MS were calculated for each radon band. Linear regression of ERR against mean band radon concentration shows a positive gradient of 0.22 per 100 Bq·m-3(R2= 0.25, p = 0.0961) when forced through the origin to represent a linear-no-threshold response. The null hypothesis falls inside the 95% confidence interval for the linear fit and therefore this fit is not statistically significant. We conclude that, despite THIN sampling around 5% of the population, insufficient data was available to confirm or refute the hypothesised association between MS incidence and radon concentration
Prescribing practices for intravenous aminoglycosides in UK cystic fibrosis clinics: a questionnaire survey
Background: Intravenous aminoglycoside antibiotics are widely used to treat pulmonary infection with Pseudomonas aeruginosa in individuals with cystic fibrosis (CF). Over the last decade evidence has accumulated showing that the choice of aminoglycoside and the dosing regimen may help reduce adverse effects such as nephrotoxicity.
Methods: We undertook an online survey to determine current practice in UK CF Centres.
Results: We received a response from 35/48 (73%) centres. A once daily regimen was used in 30/35 (86%) centres. Around one third had stopped using gentamicin in the last 10 years. In most cases respondents reported changing practice in response to new evidence or evidence based guidelines. Obstacles to introducing evidence based practice were identified both at the level of the CF Centre and the hospital trust.
Conclusions: A once daily aminoglycoside regimen is now used in the majority of UK CF Centres. Tobramycin is first line and many centres have stopped using gentamicin. Obstacles to evidence based practice remain in a minority of centres
Transient response of sap flow to wind speed
Transient responses of sap flow to step changes in wind speed were experimentally investigated in a wind tunnel. A Granier-type sap flow sensor was calibrated and tested in a cylindrical tube for analysis of its transient time response. Then the sensor was used to measure the transient response of a well-watered Pachira macrocarpa plant to wind speed variations. The transient response of sap flow was described using the resistance–capacitance model. The steady sap flow rate increased as the wind speed increased at low wind speeds. Once the wind speed exceeded 8.0 m s−1, the steady sap flow rate did not increase further. The transpiration rate, measured gravimetrically, showed a similar trend. The response of nocturnal sap flow to wind speed variation was also measured and compared with the results in the daytime. Under the same wind speed, the steady sap flow rate was smaller than that in the daytime, indicating differences between diurnal and nocturnal hydraulic function, and incomplete stomatal closure at night. In addition, it was found that the temporal response of the Granier sensor is fast enough to resolve the transient behaviour of water flux in plant tissue
Relationship between dynamical heterogeneities and stretched exponential relaxation
We identify the dynamical heterogeneities as an essential prerequisite for
stretched exponential relaxation in dynamically frustrated systems. This
heterogeneity takes the form of ordered domains of finite but diverging
lifetime for particles in atomic or molecular systems, or spin states in
magnetic materials. At the onset of the dynamical heterogeneity, the
distribution of time intervals spent in such domains or traps becomes stretched
exponential at long time. We rigorously show that once this is the case, the
autocorrelation function of the renewal process formed by these time intervals
is also stretched exponential at long time.Comment: 8 pages, 4 figures, submitted to PR
Implementation and first-year impacts of the UK Employment Retention and Advancement (ERA) demonstration
Universal Intermediate Phases of Dilute Electronic and Molecular Glasses
Generic intermediate phases with anomalous properties exist over narrow
composition ranges adjacent to connectivity transitions. Analysis of both
simple classical and complex quantum percolation shows how topological concepts
can be used to understand many mysterious properties of high temperature
superconductors, including the remarkably similar phase diagrams of
La(2-x)SrxCuO4 and C(60+y).Comment: 13 pages, 2 figs., 21 ref
Excitation spectrum of a two-component Bose-Einstein condensate in a ring potential
A mixture of two distinguishable Bose-Einstein condensates confined in a ring
potential has numerous interesting properties under rotational and
solitary-wave excitation. The lowest-energy states for a fixed angular momentum
coincide with a family of solitary-wave solutions. In the limit of weak
interactions, exact diagonalization of the many-body Hamiltonian is possible
and permits evaluation of the complete excitation spectrum of the system.Comment: 4 pages, 1 figur
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