123 research outputs found
A Numerical Acoustic Fluid-structure Model of a Therapeutic Ultrasound Angioplasty Device
Ultrasonic angioplasty involves the use of ultrasonic vibrations delivered to the distal-tip of small diameter wire waveguides and is an emerging technology the may have potential use in the treatment of complicated atherosclerotic plaques during cardiovascular surgery. Complicated plaques, including chronic total occlusions and calcified lesions, seriously reduce success rates during standard intervention involving guidewire access, followed by balloon dilation or stent delivery. The large amplitude (0-150 μm) wire waveguide distal-tip displacements in the low-frequency ultrasonic (18-45 kHz) range have been shown to disrupt plaque material by direct contact ablation and cavitation, acoustic streaming and pressure wave components in adjacent fluid 1. The effects on this surrounding fluid are complex and are related to the distal-tip geometry, frequency of operation, vibration amplitude, as well as the operating environment, including, fluid properties and boundary conditions. While the majority of work to date on ultrasound angioplasty has focused on experimental and clinical studies 2, 3, further understanding of distal-tip effects is necessary. This work describes a numerical fluid-structure model of the wire waveguide distal-tip and is used to predict the pressures developed in the fluid region near the tip wall, the acoustic pressure field and, with the inclusion of appropriate threshold intensity, when cavitation will occur. The model has been validated against experimental acoustic pressure field results reported in the literature. The model can be further used to predict the effects of parameters such as distal-tip geometry, displacement amplitude and frequency of operation and will prove a valuable design aid in the choice of optimum powers to disrupt various biological materials
Superextendons with a modified measure
For superstrings, the consequences of replacing the measure of integration
in the Polyakov's action by where is
a density built out of degrees of freedom independent of the metric
defined in the string are studied. As in Siegel reformulation of
the Green Schwarz formalism the Wess-Zumino term is the square of
supersymmetric currents. As opposed to the Siegel case, the compensating fields
needed for this do not enter into the action just as in a total derivative.
They instead play a crucial role to make up a consistent dynamics. The string
tension appears as an integration constant of the equations of motion. The
generalization to higher dimensional extended objects is also studied using in
this case the Bergshoeff and Sezgin formalism with the associated additional
fields, which again are dynamically relevant unlike the standard formulation.
Also unlike the standard formulation, there is no need of a cosmological term
on the world brane.Comment: typos corrected, references adde
Fractional helicity, Lorentz symmetry breaking, compactification and anyons
We construct the covariant, spinor sets of relativistic wave equations for a
massless field on the basis of the two copies of the R-deformed Heisenberg
algebra. For the finite-dimensional representations of the algebra they give a
universal description of the states with integer and half-integer helicity. The
infinite-dimensional representations correspond formally to the massless states
with fractional (real) helicity. The solutions of the latter type, however,
break down the (3+1) Poincar\'e invariance to the (2+1) Poincar\'e
invariance, and via a compactification on a circle a consistent theory for
massive anyons in =2+1 is produced. A general analysis of the ``helicity
equation'' shows that the (3+1) Poincar\'e group has no massless irreducible
representations with the trivial non-compact part of the little group
constructed on the basis of the infinite-dimensional representations of
sl(2,\CC). This result is in contrast with the massive case where integer and
half-integer spin states can be described on the basis of such representations,
and means, in particular, that the (3+1) Dirac positive energy covariant
equations have no massless limit.Comment: 19 pages; minor changes, references added. To appear in Nucl. Phys.
Higher Spins from Tensorial Charges and OSp(N|2n) Symmetry
It is shown that the quantization of a superparticle propagating in an N=1,
D=4 superspace extended with tensorial coordinates results in an infinite tower
of massless spin states satisfying the Vasiliev unfolded equations for free
higher spin fields in flat and AdS_4 N=1 superspace. The tensorial extension of
the AdS_4 superspace is proved to be a supergroup manifold OSp(1|4). The model
is manifestly invariant under an OSp(N|8) (N=1,2) superconformal symmetry. As a
byproduct, we find that the Cartan forms of arbitrary Sp(2n) and OSp(1|2n)
groups are GL(2n) flat, i.e. they are equivalent to flat Cartan forms up to a
GL(2n) rotation. This property is crucial for carrying out the quantization of
the particle model on OSp(1|4) and getting the higher spin field dynamics in
super AdS_4, which can be performed in a way analogous to the flat case.Comment: LaTeX, 21 page (JHEP style), misprints corrected, added comments on
the relation of results of hep-th/0106149 with hep-th/9904109 and
hep-th/9907113, references adde
The Fuzzy Disc
We introduce a finite dimensional matrix model approximation to the algebra
of functions on a disc based on noncommutative geometry. The algebra is a
subalgebra of the one characterizing the noncommutative plane with a * product
and depends on two parameters N and theta. It is composed of functions which
decay exponentially outside a disc. In the limit in which the size of the
matrices goes to infinity and the noncommutativity parameter goes to zero the
disc becomes sharper. We introduce a Laplacian defined on the whole algebra and
calculate its eigenvalues. We also calculate the two--points correlation
function for a free massless theory (Green's function). In both cases the
agreement with the exact result on the disc is very good already for relatively
small matrices. This opens up the possibility for the study of field theories
on the disc with nonperturbative methods. The model contains edge states, a
fact studied in a similar matrix model independently introduced by
Balachandran, Gupta and Kurkcuoglu.Comment: 17 pages, 8 figures, references added and correcte
Partial Deconfinement in Color Superconductivity
We analyze the fate of the unbroken SU(2) color gauge interactions for 2
light flavors color superconductivity at non zero temperature. Using a simple
model we compute the deconfining/confining critical temperature and show that
is smaller than the critical temperature for the onset of the superconductive
state itself. The breaking of Lorentz invariance, induced already at zero
temperature by the quark chemical potential, is shown to heavily affect the
value of the critical temperature and all of the relevant features related to
the deconfining transition. Modifying the Polyakov loop model to describe the
SU(2) immersed in the diquark medium we argue that the deconfinement transition
is second order. Having constructed part of the equation of state for the 2
color superconducting phase at low temperatures our results are relevant for
the physics of compact objects featuring a two flavor color superconductive
state.Comment: 9 pp, 4 eps-figs, version to appear in PR
A Conformally Invariant Holographic Two-Point Function on the Berger Sphere
We apply our previous work on Green's functions for the four-dimensional
quaternionic Taub-NUT manifold to obtain a scalar two-point function on the
homogeneously squashed three-sphere (otherwise known as the Berger sphere),
which lies at its conformal infinity. Using basic notions from conformal
geometry and the theory of boundary value problems, in particular the
Dirichlet-to-Robin operator, we establish that our two-point correlation
function is conformally invariant and corresponds to a boundary operator of
conformal dimension one. It is plausible that the methods we use could have
more general applications in an AdS/CFT context.Comment: 1+49 pages, no figures. v2: Several typos correcte
Emotional intelligence and British expatriates’ cross-cultural adjustment in international construction projects
© 2016 Informa UK Limited, trading as Taylor & Francis Group. Today’s internationalized business demands global mindset, intercultural sensitivity and the ability to skilfully negotiate through cross-cultural interactions. Therefore, the overall aim was to investigate the influence of emotional intelligence (EI) on cross-cultural adjustment (CCA) of British expatriates working on International Architectural, Engineering and Construction assignments in Sub-Saharan Africa, China, Middle East and Indian Sub-Continent. Specifically, the causal relationship between EI and three facets of CCA i.e. work, general and interaction adjustment was explored. A sequential exploratory mixed methods design was adopted. These include extensive review of existing literature, eighteen unstructured interviews, and questionnaire survey of 191 British expatriates operating in 29 different countries from the four regions under investigation. Structural equation modelling was used to assess the causal relationship between EI and CCA. Results show that EI accounted for 91, 64 and 24% of the variance in work, interaction and general adjustment respectively. Overall, the model was able to explain 60% variance in CCA, suggesting that EI competencies play a huge role in facilitating an expatriate understand and adapt to host country culture. The findings would help decision-makers (HR managers) during expatriate selection process, in understanding that along with technical skills, it is the emotional competencies that are crucial in assisting expatriates adjust to foreign way of life
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