Solid-State Excitation Laser for Laser-Ultrasonics

The inspection speed of laser-ultrasonics compared with conventional ultrasonic testing is limited by the pulse repetition rate of the excitation laser. The maximum pulse repetition rate reported up to now for CO2-lasers, which are presently used for nearly all systems, is in the range of 400 Hz. In this paper a new approach based on a diode-pumped solid-state laser is discussed, which is currently being developed. This new excitation laser is designed for a repetition rate of 1 kHz and will operate at a mid-IR wavelength of 3.3 m. The higher repeti-tion rate enables a higher inspection speed, whereas the mid-IR wavelength anticipates a better coupling efficiency. The total power for pumping the laser crystals is transported via flexible optical fibres to the compact laser head, thus allowing operation on a robot arm. The laser head consists of a master oscillator feeding several lines of power amplifiers and in-cludes nonlinear optical wavelength conversion by an optical parametric process. It is char-acterized by a modular construction which provides optimal conditions for operation at high average power as well as for easy maintenance. These features will enable building reliable, long-lived, rugged, smart laser ultrasonic systems in futur

Direct Numerical Simulation of a separated channel flow with a smooth profile

A direct numerical simulation (DNS) of a channel flow with one curved surface was performed at moderate Reynolds number (Re_tau = 395 at the inlet). The adverse pressure gradient was obtained by a wall curvature through a mathematical mapping from physical coordinates to Cartesian ones. The code, using spectral spanwise and normal discretization, combines the advantage of a good accuracy with a fast integration procedure compared to standard numerical procedures for complex geometries. The turbulent flow slightly separates on the profile at the lower curved wall and is at the onset of separation at the opposite flat wall. The thin separation bubble is characterized with a reversal flow fraction. Intense vortices are generated near the separation line on the lower wall but also at the upper wall. Turbulent normal stresses and kinetic energy budget are investigated along the channel.Comment: 23 pages, submitted to Journal of Turbulenc

Classification using a two-qubit quantum chip

Quantum computing has great potential for advancing machine learning algorithms beyond classical reach. Even though full-fledged universal quantum computers do not exist yet, its expected benefits for machine learning can already be shown using simulators and already available quantum hardware. In this work, we focus on distance-based classification using actual early stage quantum hardware. We extend earlier work and present a distance-based classification algorithm using only two qubits. We show that the results are similar to the theoretically expected results

Revisiting the Equivalence Problem for Finite Multitape Automata

The decidability of determining equivalence of deterministic multitape automata (or transducers) was a longstanding open problem until it was resolved by Harju and Karhum\"{a}ki in the early 1990s. Their proof of decidability yields a co_NP upper bound, but apparently not much more is known about the complexity of the problem. In this paper we give an alternative proof of decidability, which follows the basic strategy of Harju and Karhumaki but replaces their use of group theory with results on matrix algebras. From our proof we obtain a simple randomised algorithm for deciding language equivalence of deterministic multitape automata and, more generally, multiplicity equivalence of nondeterministic multitape automata. The algorithm involves only matrix exponentiation and runs in polynomial time for each fixed number of tapes. If the two input automata are inequivalent then the algorithm outputs a word on which they differ

Mass-Temperature Relation of Galaxy Clusters: A Theoretical Study

Combining conservation of energy throughout nearly-spherical collapse of galaxy clusters with the virial theorem, we derive the mass-temperature relation for X-ray clusters of galaxies $T=CM^{2/3}$. The normalization factor $C$ and the scatter of the relation are determined from first principles with the additional assumption of initial Gaussian random field. We are also able to reproduce the recently observed break in the M-T relation at T \sim 3 \keV, based on the scatter in the underlying density field for a low density $\Lambda$CDM cosmology. Finally, by combining observational data of high redshift clusters with our theoretical formalism, we find a semi-empirical temperature-mass relation which is expected to hold at redshifts up to unity with less than 20% error.Comment: 43 pages, 13 figures, One figure is added and minor changes are made. Accepted for Publication in Ap

Bound States in the Continuum Realized in the One-Dimensional Two-Particle Hubbard Model with an Impurity

We report a bound state of the one-dimensional two-particle (bosonic or fermionic) Hubbard model with an impurity potential. This state has the Bethe-ansatz form, although the model is nonintegrable. Moreover, for a wide region in parameter space, its energy is located in the continuum band. A remarkable advantage of this state with respect to similar states in other systems is the simple analytical form of the wave function and eigenvalue. This state can be tuned in and out of the continuum continuously.Comment: A semi-exactly solvable model (half of the eigenstates are in the Bethe form

Un modèle d’estimation de l’état d’avancement de la période d’infection primaire par le Venturia inaequalis en verger de pommiers

La tavelure du pommier (Venturia inaequalis) demeure la principale maladie à laquelle ont à faire face les pomiculteurs. La connaissance de l'état de l'inoculum primaire est essentielle pour mener une lutte efficace et économique contre cette maladie. Les relations entre le probit de la proportion d'asques vidés et les variables degrés-jours (base 0°C) et précipitations rapportées pour Frelighsburg, Québec, de 1981 à 1983 ont été comparées aux émissions d'ascospores enregistrées dans six autres localités réparties sur un axe NE-SO de 320 km pour les années 1982, 1985 et 1987. La variabilité des coefficients de régression a indiqué que ces variables ne sont pas des prédicteurs satisfaisants de l'éjection des ascospores pour cette période de temps. De nouvelles variables fonctionnelles basées sur la température, la précipitation, la luminosité et le temps ont été utilisées pour la construction d'un modèle de prédiction; celui-ci utilise la transformation angulaire de la proportion d'asques vidés et fait appel à la technique des moindres carrés pondérés en régression multiple ainsi qu'à une correction de toutes les variables dépendantes et indépendantes par le coefficient d'autocorrélation. L'équation obtenue a été validée sur l'aire géographique et les années incluses dans l'étude. L'intérêt principal de cette équation réside dans la possibilité de prédire la progression de la proportion d'ascospores éjectées ainsi que la fin de la période des infections primaires.Apple scab (Venturia inaequalis) remains the main disease in apple production. The knowledge of the primary inoculum development is essential for an effective and economical control of this disease. The relationships between the probit of the proportion of empty asci and the variables degree-days (base 0°C) and precipitation reported for Frelighsburg, Quebec, from 1981 to 1983, were compared to ascospore ejections monitored in six other localities distributed on a 320 km NE-SW axis in 1982, 1985, and 1987. Variability of the regression coefficients indicated that these variables were unsatisfactory predictors of empty asci for this time period. New functional variables based on temperature, precipitation, luminosity and time are used to build a forecasting model. This model uses the angular transformation of the proportion of empty asci and was estimated by weighted least squares procedure in multiple regression with all dependent and independent variables corrected by the autocorrelation coefficient. The equation obtained was validated over the geographic area and years included in this study. An important application of this equation is forecasting the percentage of ejected ascospores and hence the end of the primary infection season

Évaluation au Québec d’un modèle de prédiction de la fin de la période annuelle d’éjection des ascospores du Venturia inaequalis.

Un modèle de prédiction de la fin de la période des éjections d'ascospores du Venturia inaequalis, développé à partir de données recueillies au New Hampshire, a été évalué dans sept localités de pomoculture québécoise, entre 1981 et 1987. Pour Frelighsburg 1983 et Saint-Joseph-du-Lac 1982, à la date à laquelle le modèle a estimé le niveau de 100% d'ascospores matures, les valeurs observées n'ont pas différé significativement des estimés; dans tous les autres cas, les valeurs observées ont été significativement inférieures aux estimés avec une différence variant entre 4,2 % et 35,4 %. Le modèle a aussi prédit trop tôt la fin de la période d'éjection des ascospores dans 12 cas sur 16, alors qu'il restait entre 14% et 70% des ascospores dans les pseudothèces.A model for forecasting the end of the Venturia inaequalis ascospore ejection period, developed from New Hampshire data, was evaluated in seven apple growing localities in the province of Quebec from 1981 to 1987. For Frelighsburg 1983 and Saint-Joseph-du-Lac 1982, at the date estimated by the model for the 100% mature ascospore level, the observed values were not significantly different from the estimates; in all other cases, the observed values were significantly lower than the estimates with a difference between 4.2 % and 35.4 %. The model has also underestimated the duration of the ascospore ejection period in 12 of 16 cases with 14% to 70% of the spores still remaining in the asci