Interaction of an optical soliton with a dispersive wave

Scattering of a dispersive wave by optical solitons is studied experimentally in photonic crystal fibers in cases when the soliton and the dispersive wave have either identical or orthogonal polarization states. Observations of new resonant frequencies are reported. The experimental results are compared to numerical simulations and predictions from the recently derived wave vector matching conditions.     

Copper-catalyzed intermolecular hydroamination of alkenes

[reaction: see text] Regioselective additions of arylsulfonamides to vinylarenes, norbornene, and cyclohexadiene were achieved using a copper-diphosphine catayst under mild reaction conditions. These processes appear to be ligand-accelerated.     

Enantioselective alkylation of aldehydes with chiral organomagnesium amides (COMAs)

[reaction: see text] Dialkylmagnesiums react with chiral secondary amines to form chiral organomagnesium amides (COMAs). These reagents alkylate aldehydes to form secondary alcohols with enantioselectivities up to 91:9 er.     

Using combined forecasts with changing weights for electricity demand profiling

Day-ahead half-hourly demand forecasts are required for scheduling and for calculating the daily electricity pool price. One approach predicts turning points on the demand curve and then produces half-hourly forecasts by a heuristic procedure, called profiling, which is based on a past demand curve. This paper investigates possible profiling improvements. Using a cubic smoothing spline in the heuristic leads to a slight improvement. Often, several past curves could reasonably be used in the profiling method. Consequently, there are often several demand curve forecasts available. Switching and smooth transition forecast combination models are considered. These models enable the combining weights to vary across the 48 half-hours, which is appealing as different forecasts may be more suitable for different periods. Several criteria are used to control the changing weights, including weather, and the methodology is extended to the case of more than two forecasts. Empirical analysis gives encouraging results.     

Optimization of spot-welded structures

This paper addresses the optimization problem of a spot-welded structure under fatigue life consideration. The so-called umbrella model of spot welds and the radial stresses around a spot weld were introduced into the optimization process. The idea was to study the optimization problem using the type of analysis which is now considered to be valid for fatigue life prediction. Two formations were considered: one maximizes the stiffness of a structure under fatigue life constraints and the other seeks the maximum fatigue life of the structure. The optimization results show that the optimization process has successfully found the global minimum values of the corresponding objective functions for both the formations.     

Opening crystallography

Structural Chemistry - This essay surveys results of the past 4 years, starting with a week-long workshop on “Soft Packings, Nested Clusters, and Condensed Matter” held in...     

The optimal exchange algorithm and comparisons with the generalized remes algorithm † ‡

This paper is concerned with the general problem of the determination of the best uniform approximation of a given function. A special case is the calculation of the minimax solution of an overdetermined linear system. Single point exchange algorithms produce successive approximate solutions for such problems. An example is furnished by the generalized Remes algorithm, which includes both the original Remes algorithm and the Stiefel algorithm as special cases. The optimal exchange algorithm is similar, but it has the important feature that every exchange is optimal in a certain desirable sense. It is proved that eventually the optimal exchange and generalized Remes algorithms coincide. However, early exchanges in the latter algorithm can be far from optimal and quite inefficient. A combination of the optimal exchange and generalized Remes algorithms is suggested as a reasonable strategy.