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 $\sqrt{-\gamma}d^2 x$ in the Polyakov's action by $\Phi d^2 x$ where $\Phi$ is a density built out of degrees of freedom independent of the metric $\gamma_{ab}$ 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)$D$ Poincar\'e invariance to the (2+1)$D$ Poincar\'e invariance, and via a compactification on a circle a consistent theory for massive anyons in $D$=2+1 is produced. A general analysis of the ``helicity equation'' shows that the (3+1)$D$ 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)$D$ 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