Fluorescence intermittency in blinking quantum dots: renewal or slow modulation?

We study time series produced by the blinking quantum dots, by means of an aging experiment, and we examine the results of this experiment in the light of two distinct approaches to complexity, renewal and slow modulation. We find that the renewal approach fits the result of the aging experiment, while the slow modulation perspective does not. We make also an attempt at establishing the existence of an intermediate condition.Comment: 27 pages, 8 figures. Accepted for pubblication on Journal of Chemical Physic

Velocity shear, turbulent saturation, and steep plasma gradients in the scrape-off layer of inner-wall limited tokamaks

The narrow power decay-length ($\lambda_q$), recently found in the scrape-off layer (SOL) of inner-wall limited (IWL) discharges in tokamaks, is studied using 3D, flux-driven, global two-fluid turbulence simulations. The formation of the steep plasma profiles measured is found to arise due to radially sheared $\vec{E}\times\vec{B}$ poloidal flows. A complex interaction between sheared flows and outflowing plasma currents regulates the turbulent saturation, determining the transport levels. We quantify the effects of sheared flows, obtaining theoretical estimates in agreement with our non-linear simulations. Analytical calculations suggest that the IWL $\lambda_q$ is roughly equal to the turbulent correlation length.Comment: 5 pages, 5 figure

Index Information Algorithm with Local Tuning for Solving Multidimensional Global Optimization Problems with Multiextremal Constraints

Multidimensional optimization problems where the objective function and the constraints are multiextremal non-differentiable Lipschitz functions (with unknown Lipschitz constants) and the feasible region is a finite collection of robust nonconvex subregions are considered. Both the objective function and the constraints may be partially defined. To solve such problems an algorithm is proposed, that uses Peano space-filling curves and the index scheme to reduce the original problem to a H\"{o}lder one-dimensional one. Local tuning on the behaviour of the objective function and constraints is used during the work of the global optimization procedure in order to accelerate the search. The method neither uses penalty coefficients nor additional variables. Convergence conditions are established. Numerical experiments confirm the good performance of the technique.Comment: 29 pages, 5 figure

A computational efficient modelling of laminar separation bubbles

In predicting the aerodynamic characteristics of airfoils operating at low Reynolds numbers, it is often important to account for the effects of laminar (transitional) separation bubbles. Previous approaches to the modelling of this viscous phenomenon range from fast but sometimes unreliable empirical correlations for the length of the bubble and the associated increase in momentum thickness, to more accurate but significantly slower displacement-thickness iteration methods employing inverse boundary-layer formulations in the separated regions. Since the penalty in computational time associated with the more general methods is unacceptable for airfoil design applications, use of an accurate yet computationally efficient model is highly desirable. To this end, a semi-empirical bubble model was developed and incorporated into the Eppler and Somers airfoil design and analysis program. The generality and the efficiency was achieved by successfully approximating the local viscous/inviscid interaction, the transition location, and the turbulent reattachment process within the framework of an integral boundary-layer method. Comparisons of the predicted aerodynamic characteristics with experimental measurements for several airfoils show excellent and consistent agreement for Reynolds numbers from 2,000,000 down to 100,000

Smart double panel with decentralised active dampers for control of sound transmission

This report presents the results of a theoretical study of active sound transmission control through a double panel. The double panel material and geometrical properties have been chosen so as to emulate section of an aircraft fuselage, or bodywork of a vehicle. It consists of two plates: an aluminium plate simply supported along all the edges and a honeycomb plate with all the edges free. The two plates, having the same length and width, are connected using elastic mounts, so that a double panel with a thin rectangular cavity between the plates is formed. Since the two plates are linked by the mounting system, and since the air is confined in the cavity between them, they form a structurally and acoustically coupled system. The sound transmission properties of the system are studied in such a way that the aluminium plate (“source panel”) is excited using a plane acoustic wave, while the honeycomb plate (“radiating panel”) radiates sound into free field.The aim of the active control is to reduce the sound transmitted in a broad frequency band, but with a particular focus on the reduction of the sound transmission at lower frequencies of the band. Decentralised velocity feedback control systems (applying active damping) are implemented, with purpose of reducing sound transmission at resonance frequencies. Control sensors and actuators are embedded into the double plate system as a regular array, so that a smart double panel is created. The theoretical study includes analysis of the passive sound transmission in terms of a parametric study, implementation of the active control using skyhook velocity sensors and skyhook force actuators, and the performance/stability analysis in case when reactive actuators and skyhook velocity sensors are used. In the latter case the actuating force is obtained using actuators located in the air cavity which can react off the two plate

Testing a quintessence model with CMBR peaks locations

We show that a model of quintessence with exponential potential, which allows to obtain general exact solutions, can generate location of CMBR peaks which are fully compatible with present observational data

Intrinsic and Extrinsic Galaxy Alignment

We show with analytic models that the assumption of uncorrelated intrinsic ellipticities of target sources that is usually made in searches for weak gravitational lensing due to large-scale mass inhomogeneities (``field lensing'') is unwarranted. If the orientation of the galaxy image is determined either by the angular momentum or the shape of the halo in which it forms, then the image should be aligned preferentially with the component of the tidal gravitational field perpendicular to the line of sight. Long-range correlations in the tidal field will thus lead to long-range ellipticity-ellipticity correlations that mimic the shear correlations due to weak gravitational lensing. We calculate the ellipticity-ellipticity correlation expected if halo shapes determine the observed galaxy shape, and we discuss uncertainties (which are still considerable) in the predicted amplitude of this correlation. The ellipticity-ellipticity correlation induced by angular momenta should be smaller. We consider several methods for discriminating between the weak-lensing (extrinsic) and intrinsic correlations, including the use of redshift information. An ellipticity--tidal-field correlation also implies the existence of an alignment of images of galaxies near clusters. Although the intrinsic alignment may complicate the interpretation of field-lensing results, it is inherently interesting as it may shed light on galaxy formation as well as on structure formation.Comment: 7 pages, submitted to MNRA

A computationally efficient modelling of laminar separation bubbles

The goal is to accurately predict the characteristics of the laminar separation bubble and its effects on airfoil performance. Toward this end, a computational model of the separation bubble was developed and incorporated into the Eppler and Somers airfoil design and analysis program. Thus far, the focus of the research was limited to the development of a model which can accurately predict situations in which the interaction between the bubble and the inviscid velocity distribution is weak, the so-called short bubble. A summary of the research performed in the past nine months is presented. The bubble model in its present form is then described. Lastly, the performance of this model in predicting bubble characteristics is shown for a few cases