Characterization of ultrashort optical pulses with third-harmonic-generation based triple autocorrelation

We present a method to obtain complete information of femtosecond pulses. By measuring triple-optical autocorrelation directly with third-harmonic generation, without spectral information, a temporal pulse shape can be obtained by analytical calculation without direction-of-time ambiguity. Combining the resulting optical pulse shape with its corresponding optical spectrum, the exact phase and color variations in time can all be recovered with a Gerchberg-Saxton algorithm through an iterative calculation with an O(n) complexity.     

Desorption of surfactant and sintering of surface-modified PdxNi1 − x nanoparticles

A series of Pd_xNi_1 − x nanoparticles in a diameter of 6-7 nm were prepared by wet chemical reduction. They were then modified with two surfactants, stearic acid (SA) and polyethylene glycol (PEG). Desorption of the surfactant was studied using a temperature programmed desorption technique, and the sintering behavior of surface-modified Pd_xNi_1 − x nanoparticles was examined. Since surface energy of the nanoparticles depends on the alloy composition, it can be correlated with the desorption temperature of surfactant from the nanoparticle surface. Because Ni has a higher surface energy, the surfactant desorption temperature increases as the Ni content increases. With the same stoichiometry, the desorption temperature of SA is always higher than that of PEG. The SA-modified nanoparticles have higher thermal stability and are less sintered than PEG-modified nanoparticles. The sintering and growth behavior of the nanoparticles can be correlated with variation of surface energy due to different surface modification.     

Solution and applications of the Lyapunov equation for controlsystems

Recent advances in control systems analysis and design have implied new uses for the Lyapunov equation of the form AX+XA^T+Q=0. Implementation requirements for the incorporation of the use of Lyapunov equations in practical design, however, point out the need for a set of specialized numerical procedures. This special set of numerical procedures must efficiently solve large, sparse Lyapunov equations, solve sets of Lyapunov equations that differ only in the coefficient matrix Q, and provide good low rank estimates of the Lyapunov equation solution X in the case where low rank approximations are applicable. Discussions of the motivations for the solution of these problems and of candidate solution approaches are provided     

Trefftz,collocation, and other boundary methods—A comparison

In this article we survey the Trefftz method (TM), the collocation method (CM), and the collocation Trefftz method (CTM). We also review the coupling techniques for the interzonal conditions, which include the indirect Trefftz method, the original Trefftz method, the penalty plus hybrid Trefftz method, and the direct Trefftz method. Other boundary methods are also briefly described. Key issues in these algorithms, including the error analysis, are addressed. New numerical results are reported. Comparisons among TMs and other numerical methods are made. It is concluded that the CTM is the simplest algorithm and provides the most accurate solution with the best numerical stability. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007     

Precision winding of fiber optic filament. II. Winding control

For pt.I see ibid., vol.39, no.3, p.258-67 (1992). The winding of fiber optic filament in the hoop, or precision, pattern is considered. Various automatic control options that have been designed and tested are described. The controllers are designed to regulate the fiber lag angle, which is the angle at which the feed filament approaches the take-up spool. Successful, flawless winding is directly related to accurate lag regulation. The contributions are distinguished by the fact that the automatic winding rate is 10 to 30 times greater than that achieved before by operator-assisted winding     

Sulfur adsorption on Fe(1 1 0): a DFT study

The adsorption of atomic S on the Fe(1 1 0) surface is examined using density functional theory (DFT). Three different adsorption sites are considered, including the atop, hollow and bridge sites and the S is adsorbed at a quarter monolayer coverage in a p(2 × 2) arrangement. The hollow site is found to be the most stable, followed by the bridge and atop sites. At all three sites, S adsorption results in relatively minor surface reconstruction, with the most significant being that for the hollow site, with lateral displacements of 0.09 Å. Comparisons between S-adsorbed and pure Fe surfaces revealed reductions in the magnetic moments of surface-layer Fe atoms in the vicinity of the S. At the hollow site, the presence of S causes an increase in the surface Fe d-orbital density of states between 4 and 5 eV. However, S adsorption has no significant effect on the structure and magnetic properties of the lower substrate layers.     

On the Smoothness of a Generalized Solution of the First Initial Boundary-Value Problem for Strongly Parabolic Systems in a Cylinder with Nonsmooth Base with Respect to Time Variable

We consider the first initial boundary-value problem for strongly parabolic systems in an infinite cylinder with nonsmooth boundary. We establish conditions for the existence of generalized solutions, an estimate for this solutions, and an estimate for the derivative of the solution.