Dimensionality of Local Minimizers of the Interaction Energy

In this work we consider local minimizers (in the topology of transport distances) of the interaction energy associated to a repulsive-attractive potential. We show how the imensionality of the support of local minimizers is related to the repulsive strength of the potential at the origin.Comment: 27 page

Nonlocal interactions by repulsive-attractive potentials: radial ins/stability

In this paper, we investigate nonlocal interaction equations with repulsive-attractive radial potentials. Such equations describe the evolution of a continuum density of particles in which they repulse each other in the short range and attract each other in the long range. We prove that under some conditions on the potential, radially symmetric solutions converge exponentially fast in some transport distance toward a spherical shell stationary state. Otherwise we prove that it is not possible for a radially symmetric solution to converge weakly toward the spherical shell stationary state. We also investigate under which condition it is possible for a non-radially symmetric solution to converge toward a singular stationary state supported on a general hypersurface. Finally we provide a detailed analysis of the specific case of the repulsive-attractive power law potential as well as numerical results. We point out the the conditions of radial ins/stability are sharp.Comment: 42 pages, 7 figure

3d Quantum Gravity and Effective Non-Commutative Quantum Field Theory

We show that the effective dynamics of matter fields coupled to 3d quantum gravity is described after integration over the gravitational degrees of freedom by a braided non-commutative quantum field theory symmetric under a kappa-deformation of the Poincare group.Comment: 4 pages, to appear in Phys. Rev. Letters, Proceedings of the conference "Quantum Theory and Symmetries 4" 2005 (Varna, Bulgaria), v2: some clarifications on the Feynman propagator and slight change in titl

Space charge induced luminescence in epoxy resin

Dielectric breakdown of epoxies is preceded by a light emission from the solid state material, so-called electroluminescence. Very little is known however on the luminescence properties of epoxy. The aim of this paper is to derive information that can be used as a basis to understand the nature of the excited states and their involvement in electrical degradation processes

Electroluminescence excitation mechanisms in an epoxy resin under divergent and uniform field

Electroluminescence excitation mechanisms have been investigated in epoxy resin under divergent and uniform field situations. Metallic wires embedded in the resin were used to produce field divergence whereas film samples were metallised to obtain a uniform field. Electroluminescence under divergent field was stimulated by an impulse voltage. Light was emitted on the positive and negative fronts of the square pulses when the field exceeded 20 kV/mm at the wire surface, with equal intensity and without polarity dependence. There was evidence of space charge accumulation around the wires in multiple-pulse experiments. Charge injection and extraction occurring at both fronts of the pulse provide the condition for EL excitation. Further excitation of the EL during the plateau of the voltage pulse is prevented by the opposite field of the trapped charge. Field computation with and without space charge supports the proposed interpretation. A DC voltage was used for the uniform field experiments. A continuous level of electroluminescence is found at 175 kV/mm. Charging/discharging current measurements and space charge profile analyses using the pulsed electro-acoustic (PEA) technique were performed at different fields up to the EL level. Dipolar orientation generates a long lasting transient current that prevents the conduction level being reached within the experimental protocol (one hour poling time). The continuous EL emission is nevertheless associated with a regime where the conduction becomes dominant over the orientational polarization. Polarization and space charge contribute to the PEA charge profiles. Homo-charge injection at anode and cathode is seen at 20 kV/mm and a penetration of positive space charge in the bulk is detected above 100 kV/mm, suggesting an excitation of the continuous EL by bipolar charge recombination

The relationship between charge distribution, charge packet formation and electroluminescence in XLPE under DC

Different reports describing the internal distribution of space charge in cross-linked polyethylene (XLPE) under DC field have been published recently. The most striking fact observed is the organization of the space charge into charge packets that cross the insulation. All models for charge packet formation imply that carrier recombination will occur. As the recombination region is potentially a luminescence one it is of interest to record the electroluminescence in this regime. This topic is addressed in this paper

X-ray microanalysis in STEM of short-term physico-chemical reactions at bioactive glass particles / biological fluids interface. Determination of O/Si atomic ratios

Short-term physico-chemical reactions at the interface between bioactive glass particles and biological fluids are studied and we focus our attention on the measurements of O/Si atomic ratio. The studied bioactive glass is in the SiO2-Na2O-CaO-P2O5-K2O-Al2O3-MgO system. The elemental analysis is performed at the submicrometer scale by STEM associated with EDXS and EELS. We previously developed an EDXS quantification method based on the ratio method and taking into account local absorption corrections. In this way, we use EELS data to determine, by an iterative process, the local mass thickness which is an essential parameter to correct absorption in EDXS spectra. After different delays of immersion of bioactive glass particles in a simulated biological solution, results show the formation of different surface layers at the bioactive glass periphery. Before one day of immersion, we observe the presence of an already shown (Si,O,Al) rich layer at the periphery. In this paper, we demonstrate that a thin electron dense (Si,O) layer is formed on top of the (Si,O,Al) layer. In this (Si,O) layer, depleted in aluminium, we point out an increase of oxygen weight concentration which can be interpreted by the presence of Si(OH)4 groups, that permit the formation of a (Ca,P) layer. Aluminium plays a role in the glass solubility and may inhibit apatite nucleation. After the beginning of the (Ca,P) layer formation, the size of the electron dense (Si,O) layer decreases and tends to disappear. After two days of immersion, the (Ca,P) layer grows in thickness and leads to apatite precipitatio

Observation of Droplet Size Oscillations in a Two-Phase Fluid under Shear Flow

Experimental observations of droplet size sustained oscillations are reported in a two-phase flow between a lamellar and a sponge phase. Under shear flow, this system presents two different steady states made of monodisperse multilamellar droplets, separated by a shear-thinning transition. At low and high shear rates, the droplet size results from a balance between surface tension and viscous stress whereas for intermediate shear rates, it becomes a periodic function of time. A possible mechanism for such kind of oscillations is discussed

A short response-time atomic source for trapped ion experiments

Ion traps are often loaded from atomic beams produced by resistively heated ovens. We demonstrate an atomic oven which has been designed for fast control of the atomic flux density and reproducible construction. We study the limiting time constants of the system and, in tests with $^{40}\textrm{Ca}$, show we can reach the desired level of flux in 12s, with no overshoot. Our results indicate that it may be possible to achieve an even faster response by applying an appropriate one-off heat treatment to the oven before it is used.Comment: 5 pages, 7 figure