20,010 research outputs found
Measurement of pressure and assessment of cavitation for a 22.5-kHz intra-arterial angioplasty device
This study was performed to understand better the mechanisms of action of an (22.5 kHz) ultrasonic wire catheter device used to remove atheromatous plaque in diseased blood vessels (ultrasonic angioplasty). During a clinical procedure, the wire acts as an acoustic waveguide to transfer acoustic energy from a generator outside the body to the ball tip of the wire, which is inserted in the blood vessel. The acoustic field radiated by the vibrating ball tip (1.5- to 3.0-mm diameter), was mapped in a relatively large (600 L) water tank and compared to the field from a well-characterized simple source. A dipolelike radiation pattern due to the translating ball tip was observed. At low power settings, standing wave effects in a smaller cylindrical volume (200-mm diameter, 350-mm height), which was used to simulate anthropometric dimensions, increase relative to the larger tank measurements. The standing wave ratio is dependent upon the pc characteristics of the medium and the dimensions of the volume, rather than on the absorption at this frequency. At high power-settings of the device, cavitation at the tip of the wire was measured using a 20-MHz passive cavitation detection scheme
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Shopping for food: lessons from a London borough
Purpose – This paper aims to measure access to food in an inner London borough. Design/methodology/approach – There were six phases, which included designing food baskets, consultation with local residents and a shop survey. Recognising the cultural make-up of the borough food baskets and menus were developed for four key communities, namely: White British, Black Caribbean, Turkish, and Black African. Three areas were identified for the study and shopping hubs identified with a 500-metre radius from a central parade of shops. Findings – The findings paint an intricate web of interactions ranging from availability in shops to accessibility and affordability being key issues for some groups. It was found that in the areas studied there was availability of some key healthy items, namely fresh fruit and vegetables, but other items such as: fresh meat and poultry, fish, lower fat dairy foods, high fibre pasta and brown rice were not available. Access was found to be defined, by local people, as more extensive than just physical distance to/from shops – for many shopping was made more difficult by having to use taxis and inconvenient buses. Small shops were important in delivering healthy food options to communities in areas of deprivation and were judged to offer a better range and more appropriate food than the branches of the major supermarket chains. Research limitations/implications – The importance of monitoring the impact of shops and shop closures on healthy food availability is emphasised. From a policy perspective the findings suggest that approaches based on individual agency need to be balanced with upstream public health nutrition approaches in order to influence the options available. Originality/value – The paper is arguably the first to examine and dissect the issue of food availability and accessibility in the inner London borough in question, especially in the light of its proposed redevelopment for the London Olympics in 2012
Evolution of a Primordial Black Hole Population
We reconsider in this work the effects of an energy absorption term in the
evolution of primordial black holes (hereafter PBHs) in the several epochs of
the Universe. A critical mass is introduced as a boundary between the accreting
and evaporating regimes of the PBHs. We show that the growth of PBHs is
negligible in the Radiation-dominated Era due to scarcity of energy density
supply from the expanding background, in agreement with a previous analysis by
Carr and Hawking, but that nevertheless the absorption term is large enough for
black holes above the critical mass to preclude their evaporation until the
universe has cooled sufficiently. The effects of PBH motion are also discussed:
the Doppler effect may give rise to energy accretion in black-holes with large
peculiar motions relative to background. We discuss how cosmological
constraints are modified by the introduction of the critical mass since that
PBHs above it do not disturb the CMBR. We show that there is a large range of
admissible masses for PBHs above the critical mass but well below the
cosmological horizon. Finally we outline a minimal kinetic formalism, solved in
some limiting cases, to deal with more complicated cases of PBH populationsComment: RevTex file, 8 pp., 3 .ps figures available upon request from
[email protected]
High-Resolution Near Infrared Spectroscopy of HD 100546: II. Analysis of variable rovibrational CO emission lines
We present observations of rovibrational CO in HD 100546 from four epochs
spanning January 2003 through December 2010. We show that the equivalent widths
of the CO lines vary during this time period with the v=1-0 CO lines
brightening more than the UV fluoresced lines from the higher vibrational
states. While the spectroastrometric signal of the hot band lines remains
constant during this period, the spectroastrometric signal of the v=1--0 lines
varies substantially. At all epochs, the spectroastrometric signals of the UV
fluoresced lines are consistent with the signal one would expect from gas in an
axisymmetric disk. In 2003, the spectroastrometric signal of the v=1-0 P26 line
was symmetric and consistent with emission from an axisymmetric disk. However,
in 2006, there was no spatial offset of the signal detected on the red side of
the profile, and in 2010, the spectroastrometric offset was yet more strongly
reduced toward zero velocity. A model is presented that can explain the
evolution of the equivalent width of the v=1-0 P26 line and its
spectroastrometric signal by adding to the system a compact source of CO
emission that orbits the star near the inner edge of the disk. We hypothesize
that such emission may arise from a circumplanetary disk orbiting a gas giant
planet near the inner edge of the circumstellar disk. We discuss how this idea
can be tested observationally and be distinguished from an alternative
interpretation of random fluctuations in the disk emission.Comment: 18 pages, 10 figure
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