4,734 research outputs found
Characterisation of HTSC ceramics from their resistive transition
The resistivity vs. temperature relation in bulk ceramic HTSC under
self-field conditions as well as in weak external magnetic fields is modelled
by local Lorentz force induced fluxon motion with temperature dependent
pinning. A pinning force density and two viscous drag coefficients in
intergrain and intragrain regions, respectively, can be used as characteristic
parameters describing the temperature, current, and external field dependences
of the sample resistance.Comment: 12 pages, LaTeX2e, 6 figures (epsfig), to be published in Supercond.
Sci. and Techno
A Comparison of Ultraviolet, Optical, and X-Ray Imagery of Selected Fields in the Cygnus Loop
During the Astro-1 and Astro-2 Space Shuttle missions in 1990 and 1995, far
ultraviolet (FUV) images of five 40' diameter fields around the rim of the
Cygnus Loop supernova remnant were observed with the Ultraviolet Imaging
Telescope (UIT). These fields sampled a broad range of conditions including
both radiative and nonradiative shocks in various geometries and physical
scales. In these shocks, the UIT B5 band samples predominantly CIV 1550 and the
hydrogen two-photon recombination continuum. Smaller contri- butions are made
by emission lines of HeII 1640 and OIII] 1665. We present these new FUV images
and compare them with optical Halpha and [OIII], and ROSAT HRI X-ray images.
Comparing the UIT images with those from the other bands provides new insights
into the spatial variations and locations of these different types of emission.
By comparing against shock model calculations and published FUV spectroscopy at
select locations, we surmise that resonance scattering in the strong FUV
permitted lines is widespread in the Cygnus Loop, especially in the bright
optical filaments typically selected for observation in most previous studies.Comment: 21 pages with 10 figures. See http://www.pha.jhu.edu/~danforth/uit/
for full-resolution figure
A scoping review of the uses of the care index in children
Objective: To conduct a scoping review of literature to describe how the care index (CI) and restorative index (RI) are used in child populations and to determine whether they are fit for purpose. Basic research design: Scoping review conducted using the Arksey and OâMalley (2005) framework. Method: Electronic and manual literature searches (1980â2015) were conducted. Titles and abstracts were screened, full-texts of potential studies were reviewed two reviewers extracted data independently, followed by data charting and summarising. Results: Out of 104 articles meeting all criteria, most were cross-sectional (92%), and 56% were conducted in UK and Brazil. Most commonly (63%) studies used CI and RI to obtain epidemiological data on dental care levels. Of the studies that defined CI and RI, most used and specified the standard definition. The CI and RI scores varied either due to patient related factors such as age, gender or dental care related factors including, cost of treatment and method of provider remuneration. Conclusion: Overall, it is recommended that future studies should clearly state the definitions and thresholds used to obtain CI and RI, which would enable comparison between communities and allow temporal trends to be studied. Additionally, deriving separate CI and RI scores for groups based on caries extent would help to highlight inequalities in the provision of care. Further research is needed to explore the applicability of CI and RI to changing approache
Explosive events - swirling transition region jets
In this paper, we extend our earlier work to provide additional evidence for
an alternative scenario to explain the nature of so-called `explosive events'.
The bi-directed, fast Doppler motion of explosive events observed
spectroscopically in the transition region emission is classically interpreted
as a pair of bidirectional jets moving upward and downward from a reconnection
site. We discuss the problems of such a model. In our previous work, we focused
basically on the discrepancy of fast Doppler motion without detectable motion
in the image plane. We now suggest an alternative scenario for the explosive
events, based on our observations of spectral line tilts and bifurcated
structure in some events. Both features are indicative of rotational motion in
narrow structures. We explain the bifurcation as the result of rotation of
hollow cylindrical structures and demonstrate that such a sheath model can also
be applied to explain the nature of the puzzling `explosive events'. We find
that the spectral tilt, the lack of apparent motion, the bifurcation, and a
rapidly growing number of direct observations support an alternative scenario
of linear, spicular-sized jets with a strong spinning motion.Comment: 9 pages, 3 figures, accepted for publication in Solar Physic
Modulation transfer spectroscopy of the D1 transition of potassium: theory and experiment
We report on a study of modulation transfer spectroscopy of the 4S1/2 â 4P1/2 (D1) transition of naturally abundant potassium in a room-temperature vapour cell. This transition is critical for laser cooling and optical pumping of potassium and our study is therefore motivated by the need for robust laser frequency stabilisation. Despite the absence of a closed transition, the small ground-state hyperfine splitting in potassium results in strong crossover features in the D1 modulation transfer spectrum. To emphasise this we compare the D1 and D2 spectra of potassium with those of rubidium. Further, we compare our experimental results with a detailed theoretical simulation, examining different pumpâprobe polarisation configurations to identify the optimal signals for laser frequency stabilisation. We find good agreement between the experiment and the theory, especially for the lin â„ lin polarisation configuration
Development of a sensitive method to extract and detect low numbers of Cryptosporidium oocysts from adult cattle faecal samples:results from the MRC ALL97 clinical trial
AbstractCryptosporidium transmission studies to date have concluded that adult cattle are not a significant source of oocysts contributing to clinical cryptosporidiosis in calves on farm. However current methods of sample processing have been optimised for calf faecal samples and may be less sensitive when used on adult samples due to lower numbers of oocysts and larger size of samples. A modified and novel method of oocyst extraction and concentration was developed and applied in an experiment involving spiking adult cattle faecal samples with known concentrations of Cryptosporidium oocysts. The results showed an increased sensitivity of detection from 100oocysts/g of faecal sample using conventional protocols to 5oocysts/g using the newly developed method. As it is important to be able to accurately assess the contribution of adult ruminants to the transmission of Cryptosporidium, both on farm and in the environment, the development of the techniques described here is likely to make an important contribution to Cryptosporidium transmission studies in future and in subsequent control strategies aimed at the reduction of Cryptosporidium infection in calves on farm
Impact of previous hepatitis B infection on the clinical outcomes from chronic hepatitis C? A population-level analysis
Chronic coinfection with hepatitis C virus (HCV) and hepatitis B virus (HBV) is associated with adverse liver outcomes. The clinical impact of previous HBV infection on liver disease in HCV infection is unknown. We aimed at determining any association of previous HBV infection with liver outcomes using antibodies to the hepatitis B core antigen (HBcAb) positivity as a marker of exposure. The Scottish Hepatitis C Clinical Database containing data for all patients attending HCV clinics in participating health boards was linked to the HBV diagnostic registry and mortality data from Information Services Division, Scotland. Survival analyses with competing risks were constructed for time from the first appointment to decompensated cirrhosis, hepatocellular carcinoma (HCC) and liverârelated mortality. Records of 8513 chronic HCV patients were included in the analyses (87 HBcAb positive and HBV surface antigen [HBsAg] positive, 1577 HBcAb positive and HBsAg negative, and 6849 HBcAb negative). Multivariate causeâspecific proportional hazards models showed previous HBV infection (HBcAb positive and HBsAg negative) significantly increased the risks of decompensated cirrhosis (hazard ratio [HR]: 1.29, 95% CI: 1.01â1.65) and HCC (HR: 1.64, 95% CI: 1.09â2.49), but not liverârelated death (HR: 1.02, 95% CI: 0.80â1.30). This is the largest study to date showing an association between previous HBV infection and certain adverse liver outcomes in HCV infection. Our analyses add significantly to evidence which suggests that HBV infection adversely affects liver health despite apparent clearance. This has important implications for HBV vaccination policy and indications for prioritization of HCV therapy
Chokka squid on the Agulhas Bank: life history and ecology
Available knowledge is reviewed and new data incorporated in a synthesis of the life history and ecology of the chokka squid Loligo vulgaris reynaudii. We attempt to show that these aspects are essential to rational management of the resource. The life cycle is descriptionbed in detail from the egg to adult stage, mainly in biological terms, including a comprehensive descriptionption of maturation, migration and reproduction. Possible ecological interactions, particularly those of paralarvae and copepods, are discussed. Predator-prey relationships and the current state of knowledge on the effect of the physical environment on squid availability and abundance are summarized
Patchy Reconnection in a Y-Type Current Sheet
We study the evolution of the magnetic field in a Y-type current sheet
subject to a brief, localized magnetic reconnection event. The reconnection
produces up- and down-flowing reconnected flux tubes which rapidly decelerate
when they hit the Y-lines and underlying magnetic arcade loops at the ends of
the current sheet. This localized reconnection outflow followed by a rapid
deceleration reproduces the observed behavior of post-CME downflowing coronal
voids. These simulations support the hypothesis that these observed coronal
downflows are the retraction of magnetic fields reconnected in localized
patches in the high corona.Comment: 4 pages, 3 figure
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