2,308 research outputs found
Wall influence on dynamics of a microbubble
The nonlinear dynamic behaviour of microscopic bubbles near a wall is
investigated. The Keller-Miksis-Parlitz equation is adopted, but modified to
account for the presence of the wall. This base model describes the time
evolution of the bubble surface, which is assumed to remain spherical, and
accounts for the effect of acoustic radiation losses owing to liquid
compressibility in the momentum conservation. Two situations are considered:
the base case of an isolated bubble in an unbounded medium; and a bubble near a
solid wall. In the latter case, the wall influence is modeled by including a
symmetrically oscillating image bubble. The bubble dynamics is traced using a
numerical solution of the model equation. Subsequently, Floquet theory is used
to accurately detect the bifurcation point where bubble oscillations stop
following the driving ultrasound frequency and undergo period-changing
bifurcations. Of particular interest is the detection of the subcritical period
tripling and quadrupling transition. The parametric bifurcation maps are
obtained as functions of non-dimensional parameters representing the bubble
radius, the frequency and pressure amplitude of the driving ultrasound field
and the distance from the wall. It is shown that the presence of the wall
generally stabilises the bubble dynamics, so that much larger values of the
pressure amplitude are needed to generate nonlinear responses.Comment: 25 pages, 14 figure
A farm creaming experiment
A short time ago we were asked whether any injustice would result to either creamery-man or patron, if the latter should set his eveningās milk, skim it in the morning, mix the cream with the morningās milk and send the mixture to the creamery instead of sending the milk of both evening and morning, as is the usual custom. The most satisfactory way to answer all such queries is by practical demonstrations, and it was determined to conduct an experiment bearing on the point in question.
A short time ago we were asked whether any injustice would result to either creamery-man or patron, if the latter should set his eveningās milk, skim it in the morning, mix the cream with the morningās milk and send the mixture to the creamery instead of sending the milk of both evening and morning, as is the usual custom. The most satisfactory way to answer all such queries is by practical demonstrations, and it was determined to conduct an experiment bearing on the point in question
Sweet versus ripened cream butter
The experiments here described are similar to those described in Bulletin No. 18, but differ from them in that the cream is here ripened for a shorter time.
Ia each trial a quantity of thoroughly mixed cream, fresh from the separator, was divided into two parts, one of which was churned within a few hours, while still sweet; the other the next day after ripening (at about 60Ā° F.) for 17 to 21 hours. Salt and color were proportionately the same in all cases
Controlling the exchange interaction using the spin-flip transition of antiferromagnetic spins in NiFe / -FeO
We report studies of exchange bias and coercivity in ferromagnetic
NiFe layers coupled to antiferromagnetic (AF) (0001),
(110), and (112) -FeO layers. We show that AF
spin configurations which permit spin-flop coupling give rise to a strong
uniaxial anisotropy and hence a large coercivity, and that by annealing in
magnetic fields parallel to specific directions in the AF we can control either
coercivity or exchange bias. In particular, we show for the first time that a
reversible temperature-induced spin reorientation in the AF can be used to
control the exchange interaction.Comment: 15 pages, 5 figures, submitted to Phys. Rev. Let
Vertex Sparsifiers: New Results from Old Techniques
Given a capacitated graph and a set of terminals ,
how should we produce a graph only on the terminals so that every
(multicommodity) flow between the terminals in could be supported in
with low congestion, and vice versa? (Such a graph is called a
flow-sparsifier for .) What if we want to be a "simple" graph? What if
we allow to be a convex combination of simple graphs?
Improving on results of Moitra [FOCS 2009] and Leighton and Moitra [STOC
2010], we give efficient algorithms for constructing: (a) a flow-sparsifier
that maintains congestion up to a factor of , where , (b) a convex combination of trees over the terminals that maintains
congestion up to a factor of , and (c) for a planar graph , a
convex combination of planar graphs that maintains congestion up to a constant
factor. This requires us to give a new algorithm for the 0-extension problem,
the first one in which the preimages of each terminal are connected in .
Moreover, this result extends to minor-closed families of graphs.
Our improved bounds immediately imply improved approximation guarantees for
several terminal-based cut and ordering problems.Comment: An extended abstract appears in the 13th International Workshop on
Approximation Algorithms for Combinatorial Optimization Problems (APPROX),
2010. Final version to appear in SIAM J. Computin
Cloud Chamber Investigation of Anomalous Īø^0 Particles
Eighteen anomalous Īø^0, (Īø^0_(anom)), decay events observed in the California Institute of Technology magnet cloud chambers have been analyzed. Many of these decays are dynamically inconsistent with the Ļ^0āĻ^++Ļ^ā+Ļ^0 scheme, but most are consistent with the decay processes: Īø^0_(anom)āĻ^++Ļ^ā+Ī³, Ļ^Ā±+Ī¼^ā+Ī½, and Ļ^Ā±+e^ā+Ī½. However, at least one event is inconsistent with each decay scheme. From the locations of the decays in the cloud chamber, the lifetime is found to be significantly longer than that of the normal Īø^0 particle, called here the Īø^0_(Ļ2) particle. Other differences in the behavior of the Īø0anom and Īø^0_(Ļ2) particles were also observed in the (a) momentum distributions, (b) origin locations, (c) relative numbers of Īø^0_(anom) and Īø^0_(Ļ2) particles traveling upward, and (d) the types of V particles produced in association with the Īø^0_(anom) and Īø^0_(Ļ2). It is concluded that not all the Īø^0_(anom) decays can result from alternate decay modes of the Īø^0_(Ļ2). Moreover, many decays can be neither Ļ^0 decays nor alternate decays of the Īø^0_(Ļ2).
The characteristics of the Īø^0_2 particle proposed by Gell-Mann and Pais are consistent with those of the Īø^0_(anom) particle, with the possible exception of the observed types of associations. An estimate was made of the relative number of Īø^0_(anom) to Īø^0_(Ļ2) particles observed to decay in the cloud chamber. If all Īø^0_(anom) decays are assumed to arise from decays of the Īø^0_2 particle, then a lower limit for the Īø^0_2 lifetime is found to be about 10^(ā9) sec
Pinholes May Mimic Tunneling
Interest in magnetic-tunnel junctions has prompted a re-examination of
tunneling measurements through thin insulating films. In any study of
metal-insulator-metal trilayers, one tries to eliminate the possibility of
pinholes (small areas over which the thickness of the insulator goes to zero so
that the upper and lower metals of the trilayer make direct contact). Recently,
we have presented experimental evidence that ferromagnet-insulator-normal
trilayers that appear from current-voltage plots to be pinhole-free may
nonetheless in some cases harbor pinholes. Here, we show how pinholes may arise
in a simple but realistic model of film deposition and that purely classical
conduction through pinholes may mimic one aspect of tunneling, the exponential
decay in current with insulating thickness.Comment: 9 pages, 3 figures, plain TeX; submitted to Journal of Applied
Physic
Detoxification in rehabilitation in England: effective continuity of care or unhappy bedfellows?
There is evidence that residential detoxification alone does not provide satisfactory treatment outcomes and that outcomes are significantly enhanced when clients completing residential detoxification attend rehabilitation services (Gossop, Marsden, Stewart, & Rolfe, 1999; Ghodse, Reynolds, Baldacchino, et al., 2002). One way of increasing the likelihood of this continuity of treatment is by providing detoxification and rehabilitation within the same treatment facility to prevent drop-out, while the client awaits a rehabilitation bed or in the transition process. However, there is little research evidence available on the facilities that offer both medical detoxification and residential rehabilitation. The current study compares self-reported treatment provision in 87 residential rehabilitation services in England, 34 of whom (39.1%) reported that they offered detoxification services within their treatment programmes. Although there were no differences in self-reported treatment philosophies, residential rehabilitation services that offered detoxification were typically of shorter duration overall, had significantly more beds and reported offering more group work than residential rehabilitation services that did not offer detoxification. Outcomes were also different, with twice as many clients discharged on disciplinary grounds from residential rehabilitation services without detoxification facilities. The paper questions the UK classification of residential drug treatment services as either detoxification or rehabilitation and suggests the need for greater research focus on the aims, processes and outcomes of this group of treatment providers
An inventory and condition survey of the Sandstone-Yalgoo-Paynes Find area, Western Australia
The inventory and condition survey of the Sandstone-Yalgoo-Paynes Find area, undertaken by the Department of Agriculture and Food, Western Australia (DAFWA) between 1992 and 1993, describes and maps the natural resources of the regionās pastoral leasehold land. This survey report provides a baseline record of the existence and condition of the areaās natural resources, to assist with the planning and implementation of land management practices. The report identified and described the condition of soils, landforms, vegetation, habitat, ecosystems, and declared plants and animals. It also assessed the impact of pastoralism and made land management recommendations. The area surveyed covers about 94 700kmĀ². Three small townships fall within the area, namely Sandstone in the east, Paynes Find in the south-centre and Yalgoo in the west. Apart from a very small portion of the Greenough River catchment in the far north-west, there are no major river catchments in the survey area. The survey area is drained internally into the salt lake systems of Lake Barlee, Lake Noondie, Lake Mason, Lake Moore and Mongers Lake. Pastoralism is the most extensive land use in the area. Fifty-four pastoral leases fall wholly, and twelve partly within the survey area and collectively occupy about 86 460kmĀ² (91% of the area). Twelve broad soil groups are identified in the survey area. The most outstanding characteristics of the soils are the predominant red colour and the widespread presence of a siliceous hardpan. Most soils are sandplains and granitic country, and variable depth red earths overlying hardpan on level to gently inclined plains. The flora of the area is diverse. 719 vascular species are recorded in the survey area, of which 706 are native. Cotton bush (Ptilotus obovatus), curara (Acacia tetragonophylla) and mulga (Acacia aneura) are the ubiquitous perennials in the survey area
Use of a passive acoustic sensor to predict success of ESWL treatment based on initial 500 shocks
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