Real time plasma equilibrium reconstruction in a Tokamak

The problem of equilibrium of a plasma in a Tokamak is a free boundary problemdescribed by the Grad-Shafranov equation in axisymmetric configurations. The right hand side of this equation is a non linear source, which represents the toroidal component of the plasma current density. This paper deals with the real time identification of this non linear source from experimental measurements. The proposed method is based on a fixed point algorithm, a finite element resolution, a reduced basis method and a least-square optimization formulation

One loop calculation in lattice QCD with domain-wall quarks

One loop corrections to the domain-wall quark propagator are calculated in massless QCD. It is shown that no additative counter term to the current quark mass is generated in this theory, and the wave function renormalization factor of the massless quark is explicitly evaluated. We also show that an analysis with a simple mean-field approximation can explain properties of the massless quark in numerical simulations of QCD with domain-wall quarks.Comment: 24 pages, REVTeX, with 3 epsf figure

Field Theoretical Approach to Electrochemical Deposition

In this work we present an application of the lambda-phi^4 field theoretical model to the adsorption of atoms and molecules on metallic surfaces - the electrochemical deposition. The usual approach to this system consists in the computational simulation using Monte Carlo techniques of an effective lattice-gas Hamiltonian. We construct an effective model towards a comparison between the lattice-gas Hamiltonian and the discrete version of the lambda-phi^4 Hamiltonian, obtaining the relationships between the model parameters and electrochemical quantities. The lambda-phi^4 model is studied in the mean field approximation, and the results are fitted and compared to numerical simulated and experimental data.Comment: 9 pages, 5 figure

Self-synchronized duty-cycling for sensor networks with energy harvesting capabilities: Implementation in Wiselib

In this work we present a protocol for a self- synchronized duty-cycling mechanism in wireless sensor net- works with energy harvesting capabilities. The protocol is im- plemented in Wiselib, a library of generic algorithms for sensor networks. Simulations are conducted with the sensor network simulator Shawn. They are based on the specifications of real hardware known as iSense sensor nodes. The experimental results show that the proposed mechanism is able to adapt to changing energy availabilities. Moreover, it is shown that the system is very robust against packet loss.Postprint (published version

Structure and optical properties of high light output halide scintillators

Structural and optical properties of several high light output halide scintillators and closely related materials are presented based on first principles calculations. The optical properties are based on the Engel-Vosko generalized gradient approximation and the recently developed density functional of Tran and Blaha. The materials investigated are BaBr$_2$, BaIBr, BaCl$_2$, BaF$_2$, BaI$_2$, BiI$_3$, CaI$_2$, Cs$_2LiYCl$_6$, CsBa$_2$Br$_5$, CsBa$_2$I$_5$, K$_2$LaBr$_5$, K$_2$LaCl$_5$,K$_2$LaI$_5$, LaBr$_3$, LaCl$_3$, SrBr$_2$, and YI$_3$. For comparison results are presented for the oxide CdWO$_4$. We find that the Tran Blaha functional gives greatly improved band gaps and optical properties in this class of materials. Furthermore, we find that unlike CdWO$_4$, most of these halides are highly isotropic from an optical point of view even though in many cases the crystal structures and other properties are not. This general result is rationalized in terms of halide chemistry. Implications for the development of ceramic halide scintillators are discussed

Dynamical nuclear spin polarization induced by electronic current through double quantum dots

We analyze electron spin relaxation in electronic transport through coherently coupled double quantum dots in the spin blockade regime. In particular, we focus on hyperfine interaction as the spin relaxation mechanism. We pay special attention to the effect of the dynamical nuclear spin polarization induced by the electronic current on the nuclear environment. We discuss the behaviour of the electronic current and the induced nuclear spin polarization versus an external magnetic field for different hyperfine coupling intensities and interdot tunnelling strengths. We take into account, for each magnetic field, all hyperfine mediated spin relaxation processes coming from the different opposite spin levels approaches. We find that the current as a function of the external magnetic field shows a peak or a dip, and that the transition from a current dip to a current peak behaviour is obtained by decreasing the hyperfine coupling or by increasing the interdot tunnelling strength. We give a physical picture in terms of the interplay between the electrons tunnelling out of the double quantum dot and the spin flip processes due to the nuclear environment.Comment: 25 pages and 8 figures. To be published in New Journal of Physic

Summer sudden Na number density enhancements measured with the ALOMAR Weber Na Lidar

We present summer Na-densities and atmospheric temperatures measured 80 to 110 km above the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR). The Weber Na Lidar is part of ALOMAR, located at 69° N in Norway, 150 km north of the Arctic Circle. The sun does not set here during the summer months, and measurements require a narrowband Faraday Anomalous Dispersion Optical Filter (FADOF). <br><br> We discuss an observed sudden enhancement in the Na number density around 22:00 UT on 1 to 2 June 2006. We compare this observation with previous summer measurements and find a frequent appearance of Na number density enhancements near local midnight. We describe the time of appearance, the altitude distribution, the duration and the strength of these enhancements and compare them to winter observations. We investigate possible formation mechanisms and, as others before, we find a strong link between these Na number density enhancements and sporadic E layers

Positional Encoding by Robots with Non-Rigid Movements

Consider a set of autonomous computational entities, called \emph{robots}, operating inside a polygonal enclosure (possibly with holes), that have to perform some collaborative tasks. The boundary of the polygon obstructs both visibility and mobility of a robot. Since the polygon is initially unknown to the robots, the natural approach is to first explore and construct a map of the polygon. For this, the robots need an unlimited amount of persistent memory to store the snapshots taken from different points inside the polygon. However, it has been shown by Di Luna et al. [DISC 2017] that map construction can be done even by oblivious robots by employing a positional encoding strategy where a robot carefully positions itself inside the polygon to encode information in the binary representation of its distance from the closest polygon vertex. Of course, to execute this strategy, it is crucial for the robots to make accurate movements. In this paper, we address the question whether this technique can be implemented even when the movements of the robots are unpredictable in the sense that the robot can be stopped by the adversary during its movement before reaching its destination. However, there exists a constant $\delta > 0$, unknown to the robot, such that the robot can always reach its destination if it has to move by no more than $\delta$ amount. This model is known in literature as \emph{non-rigid} movement. We give a partial answer to the question in the affirmative by presenting a map construction algorithm for robots with non-rigid movement, but having $O(1)$ bits of persistent memory and ability to make circular moves

Polarization dependent photoionization cross-sections and radiative lifetimes of atomic states in Ba

The photoionization cross-sections of two even-parity excited states, $5d6d ^3D_1$ and $6s7d ^3D_{2}$, of atomic Ba at the ionization-laser wavelength of 556.6 nm were measured. We found that the total cross-section depends on the relative polarization of the atoms and the ionization-laser light. With density-matrix algebra, we show that, in general, there are at most three parameters in the photoionization cross-section. Some of these parameters are determined in this work. We also present the measurement of the radiative lifetime of five even-parity excited states of barium.Comment: 11 pages, 7 figure

Synthesis of N-Heterocylic Carbene-Containing Metal Complexes from 2-(Pentafluorophenyl)imidazolidines

N-Heterocyclic carbene (NHC)-containing metal complexes are prepared through a simple, base-free method involving the decomposition of 2-(pentafluorophenyl)imidazolidines under mild thermolytic conditions. Ruthenium, iridium, and rhodium complexes containing NHC ligands with different electronic and steric parameters are reported