2,538 research outputs found
Anisotropic focusing characteristics of micro-domain structures within crystalline Sr<sub>0.61</sub>Ba<sub>0.39</sub>Nb<sub>2</sub>O<sub>6</sub> : the crystal ball
We report the anisotropic focusing characteristics of a spherically configured region of micro-domains that have been induced within a cubic shaped crystal of Ce:doped Sr0.61Ba0.39Nb2O6. The internal spherical structure focuses extraordinary polarised light, but not ordinary polarised. The spherical region, which is easily observed via scattering, is formed as the crystal cools down, after a repoling cycle through the Curie temperature, with an applied field. Analytic modelling of the thermal gradients that exist within the crystal during cooling reveals a small (< 1°) temperature difference between the central and outside regions. The similarity in shape between these temperature profiles and the observed scattering region suggests a possible mechanism for the growth of this spherical micro-domained structure
Temperature sensitivity of repoling in strontium barium niobate near to the glassy transition
We report the observation of an enhanced temperature sensitivity for transient repoling near to the domain freezing temperature in ferroelectric strontium barium niobate. This work has important consequences for the use of optical fields to control domain patterns in such materials. We model the repoling characteristics of the material using a Vogel-Fulcher type response and present results showing the degree of repoling as a function of field and temperature, for short duration repoling times
Fibrinogen E fragment selectively disrupts the vasculature and inhibits the growth of tumours in a syngeneic murine model
We recently demonstrated that a fragment of human fibrinogen, fibrinogen E fragment, inhibits the migration and differentiation of human endothelial cells in vitro. Here we show that it exerts similar effects on murine endothelial cells in vitro, and selectively disrupts tumour endothelium in vivo, causing widespread intravascular thrombosis and retarding the growth of CT26 tumours in a syngeneic murine model
Playing with the future: social irrealism and the politics of aesthetics
In this paper we wish to explore the political possibilities of video games. Numerous scholars now take seriously the place of popular culture in the remaking of our geographies, but video games still lag behind. For us, this tendency reflects a general response to them as imaginary spaces that are separate from everyday life and 'real' politics. It is this disconnect between abstraction and lived experience that we complicate by defining play as an event of what Brian Massumi calls lived abstraction. We wish to short-circuit the barriers that prevent the aesthetic resonating with the political and argue that through their enactment, video games can animate fantastical futures that require the player to make, and reflect upon, profound ethical decisions that can be antagonistic to prevailing political imaginations. We refer to this as social irrealism to demonstrate that reality can be understood through the impossible and the imagined
Brane Universes with Gauss-Bonnet-Induced-Gravity
The DGP brane world model allows us to get the observed late time
acceleration via modified gravity, without the need for a ``dark energy''
field. This can then be generalised by the inclusion of high energy terms, in
the form of a Gauss-Bonnet bulk. This is the basis of the
Gauss-Bonnet-Induced-Gravity (GBIG) model explored here with both early and
late time modifications to the cosmological evolution. Recently the simplest
GBIG models (Minkowski bulk and no brane tension) have been analysed. Two of
the three possible branches in these models start with a finite density
``Big-Bang'' and with late time acceleration. Here we present a comprehensive
analysis of more general models where we include a bulk cosmological constant
and brane tension. We show that by including these factors it is possible to
have late time phantom behaviour.Comment: 12 pages, 19 figures. Minor modifications to text, comments on
phantom behaviour added. References added. As submitted to JCA
Discrete cilia modelling with singularity distributions
We discuss in detail techniques for modelling flows due to finite and infinite arrays of beating cilia. An efficient technique, based on concepts from previous âsingularity modelsâ is described, that is accurate in both near and far-fields. Cilia are modelled as curved slender ellipsoidal bodies by distributing Stokeslet and potential source dipole singularities along their centrelines, leading to an integral equation that can be solved using a simple and efficient discretisation. The computed velocity on the cilium surface is found to compare favourably with the boundary condition. We then present results for two topics of current interest in biology. 1) We present the first theoretical results showing the mechanism by which rotating embryonic nodal cilia produce a leftward flow by a âposterior tilt,â and track particle motion in an array of three simulated nodal cilia. We find that, contrary to recent suggestions, there is no continuous layer of negative fluid transport close to the ciliated boundary. The mean leftward particle transport is found to be just over 1 ÎŒm/s, within experimentally measured ranges. We also discuss the accuracy of models that represent the action of cilia by steady rotlet arrays, in particular, confirming the importance of image systems in the boundary in establishing the far-field fluid transport. Future modelling may lead to understanding of the mechanisms by which morphogen gradients or mechanosensing cilia convert a directional flow to asymmetric gene expression. 2) We develop a more complex and detailed model of flow patterns in the periciliary layer of the airway surface liquid. Our results confirm that shear flow of the mucous layer drives a significant volume of periciliary liquid in the direction of mucus transport even during the recovery stroke of the cilia. Finally, we discuss the advantages and disadvantages of the singularity technique and outline future theoretical and experimental developments required to apply this technique to various other biological problems, particularly in the reproductive system
Effect of continuum couplings in fusion of halo Be on Pb around the Coulomb barrier
The effect of continuum couplings in the fusion of the halo nucleus Be
on Pb around the Coulomb barrier is studied using a three-body model
within a coupled discretised continuum channels (CDCC) formalism. We
investigate in particular the role of continuum-continuum couplings. These are
found to hinder total, complete and incomplete fusion processes. Couplings to
the projectile bound excited state redistribute the complete and
incomplete fusion cross sections, but the total fusion cross section remains
nearly constant. Results show that continuum-continuum couplings enhance the
irreversibility of breakup and reduce the flux that penetrates the Coulomb
barrier. Converged total fusion cross sections agree with the experimental ones
for energies around the Coulomb barrier, but underestimate those for energies
well above the Coulomb barrier.Comment: 15 pages, 7 figures, accepted in Phys. Rev.
Bounded and unitary elements in pro-C^*-algebras
A pro-C^*-algebra is a (projective) limit of C^*-algebras in the category of
topological *-algebras. From the perspective of non-commutative geometry,
pro-C^*-algebras can be seen as non-commutative k-spaces. An element of a
pro-C^*-algebra is bounded if there is a uniform bound for the norm of its
images under any continuous *-homomorphism into a C^*-algebra. The *-subalgebra
consisting of the bounded elements turns out to be a C^*-algebra. In this
paper, we investigate pro-C^*-algebras from a categorical point of view. We
study the functor (-)_b that assigns to a pro-C^*-algebra the C^*-algebra of
its bounded elements, which is the dual of the Stone-\v{C}ech-compactification.
We show that (-)_b is a coreflector, and it preserves exact sequences. A
generalization of the Gelfand-duality for commutative unital pro-C^*-algebras
is also presented.Comment: v2 (accepted
Possibility of cyclic Turnarounds In Brane-world Scenario: Phantom Energy Accretion onto Black Holes and its consequences
A universe described by braneworlds is studied in a cyclic scenario. As
expected such an oscillating universe will undergo turnarounds, whenever the
phantom energy density reaches a critical value from either side. It is found
that a universe described by RSII brane model will readily undergo oscillations
if, either the brane tension, \lambda, or the bulk cosmological constant,
\Lambda_{4}, is negative. The DGP brane model does not readily undergo cyclic
turnarounds. Hence for this model a modified equation is proposed to
incorporate the cyclic nature. It is found that there is always a remanent mass
of a black hole at the verge of a turnaround. Hence contrary to known results
in literature, it is found that the destruction of black holes at the
turnaround is completely out of question. Finally to alleviate, if not solve,
the problem posed by the black holes, it is argued that the remanent masses of
the black holes do not act as a serious defect of the model because of Hawking
evaporation.Comment: 10 pages, 2 figures; International Journal of Theoretical Physics
(2012
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