Total curvatures of geodesic spheres associated to quadratic curvature invariants

Total scalar curvatures of geodesic spheres obtained by integrating the second-order scalar invariants of the curvature tensor are investigated. The first terms in their power-series expansions are derived and these results are used to characterize the two-point homogeneous spaces among Riemannian manifolds with adapted holonomy. Dedicated to Professor L. VanheckeMathematics Subject Classification (2000) 53C25, 53C30     

Thermo gravimetric analysis of supramolecular complexes of p-tert-butylcalix[6]arene and ammonium cations: crystal structure of diethylammonium complex

Thermo gravimetric analysis of ammonium-p-tert-butylcalix[6]arene salts were carried out to determine the stoichiometry of the inclusion compounds and the temperature of leaving of the ammonium cation, as amine, from the solid phase by a reverse proton transfer reaction to calixarene. The chain length of the amine molecules and their relative basicity order are the main factors which determine the decomplexation temperatures for the ammonium salts of piperidinium, diethylammonium, ethylenediammonium, morpholinium, s-butylammonium, butylammonium, hexylammonium and triethylammonium salts of p-tert-butylcalix[6]arene anion. The solid state structure of bis-diethylammonium-p-tert-butylcalix[6]arene dianion is reported. The calix moiety adopts a 1,2,3 alternate conformation, with one ammonium as exo-calix and other as endo-calix, with an intricate array of hydrogen bonds between phenol, phenolate and ammonium cations.     

Refractive and geometric lens characterization through multi-wavelength digital speckle pattern interferometry

Physical parameters of different types of lenses were measured through digital speckle pattern interferometry (DSPI) using a multimode diode laser as light source. When such lasers emit two or more longitudinal modes simultaneously the speckle image of an object appears covered of contour fringes. By performing the quantitative fringe evaluation the radii of curvature as well as the refractive indexes of the lenses were determined. The fringe quantitative evaluation was carried out through the four- and the eight-stepping techniques and the branch-cut method was employed for phase unwrapping. With all these parameters the focal length was calculated. This whole-field multi-wavelength method does enable the characterization of spherical and aspherical lenses and of positive and negative ones as well.     

Timing error estimation for baseband multicarrier modulation

In this paper, the topic of timing error estimation for baseband discrete multitone modulation is addressed in the context of high‐speed digital subscriber line applications. To the authors' best knowledge, this problem is sparsely and not in depth treated in the literature. In this study the modified Cramer–Rao lower bound is derived, two conventional estimators are considered and a new one is proposed. Behavior of these estimators is evaluated in terms of bias, variance and computational complexity in a wide variety of scenarios, concluding that the proposed estimator appears to be superior in all instances. Copyright © 2008 John Wiley & Sons, Ltd.     

Strong convergence rates for the estimation of a covariance operator for associated samples

Let X _n , n ≥ 1, be a strictly stationary associated sequence of random variables, with common continuous distribution function F. Using histogram type estimators we consider the estimation of the two-dimensional distribution function of (X ₁,X _k+1) as well as the estimation of the covariance function of the limit empirical process induced by the sequence X _n , n ≥ 1. Assuming a convenient decrease rate of the covariances Cov(X ₁,X _n+1), n ≥ 1, we derive uniform strong convergence rates for these estimators. The condition on the covariance structure of the variables is satisfied either if Cov(X ₁,X _n+1) decreases polynomially or if it decreases geometrically, but as we could expect, under the latter condition we are able to establish faster convergence rates. For the two-dimensional distribution function the rate of convergence derived under a geometrical decrease of the covariances is close to the optimal rate for independent samples.      

Squeezing transfer from vibrations to a cavity field in an ion-trap laser

We present a novel way to produce squeezed light in an optical cavity. The main idea is to transfer vibrational squeezing from the motion of a trapped ion to the photons in a cavity. We use the dipolar coupling of the motion of a three-level ion with one cavity mode and two different kind of pumps. The first pump is an oscillating electric field that drives the ion into a vibrational squeezed state. The second pump consists of two lasers resonant with the ionic levels that makes the transfer possible.     

Using a risk-based approach to project scheduling: A case illustration from semiconductor manufacturing

This paper introduces a risk-based optimization method to schedule projects. The method uses risk mitigation and optimal control techniques to minimize variables such as the project duration or the cost estimate at completion. Mitigation actions reduce the risk impacts that may affect the system. A model predictive control approach is used to determine the set of mitigation actions to be executed and the time in which they are taken. A real-life project in the field of semiconductor manufacturing has been taken as an example to show the benefits of the method in a deterministic case and a Monte Carlo simulation has also been carried out.     

Quenching of I (2P1/2) by halogen cyanides

Relaxation rate constants for the collisional deactivation of I (²P_1/2) by halogen cyanides were measured by time resolved atomic absorption. The values obtained were (1.2 ± 0.1) × 10^?15, (5.2 ± 0.7) × 10^?15, and (2.6 ± 0.4) × 10^?14 cm³ molecule^?1 s^?1 for ClCN, BrCN, and ICN, respectively. Quenching efficiencies are discussed in view of the stability of linear molecules to form the transient complex as well as the similarities assumed between halogen cyanides and interhalogen diatomic molecules.