Measurement of plane wave acoustic fields in flow ducts

The response of a fluid loaded plate is derived as function of the incident pressure in the fluid. The results are compared with full scale measurements made in the aft peak tank on a ship. Propeller induced pressure and hull plate velocity were measured with flush-mounted hydrophones and accelerometers. It is found that for a typical aft body construction the boundaries of the plate elements can be assumed to be simply supported. The plate model agrees well with full scale measurements down to 40 Hz. Below this frequency global vibrations determine the response of the hull. Both theoretical and experimental results indicate that the field induced by the vibrating plate elements can be considerable. The response of a plate can be decreased if the width of the plate is decreased or the plate thickness increased.     

Untersuchungen über Molekulargewichtsverteilungen von Hochpolymeren, 5. Mitt.: Thermische Styrolpolymerisate bei Verzögerung durch Thymochinon

Zusammenfassung Die Molekulargewichtsverteilung eines in Gegenwart von Thymochinon durch thermische Polymerisation erhaltenen Polystyrols wird untersucht.Es handelt sich um eine wahrscheinlichste VerteilungSchulz-Verteilung mit dem Kopplungsgrad 1). Die Verteilung stimmt mit der schon früher aus kinetischen Messungen postulierten zusätzlichen Übertragungswirkung des Thymochinons überein.Mit 1 Abbildung     

Zur Kenntnis der elektrochemischen Polymerisationsanregung

Ohne Zusammenfassung     

Erratum

Ohne Zusammenfassung     

Flavour violation in supersymmetric theories

We investigate in detail the question of lepton-flavour violation in a SU(2) × U(1) supersymmetric model, where the breaking of supersymmetry (SUSY) is achieved through the coupling to N = 1 supergravity. It is shown that in the limit of degenerate neutrino masses, lepton flavour is exactly conserved. Allowing for neutrino masses compatible with present experimental limits, we analyse SUSY contributions to several lepton-flavour violating processes, comparing the size of these contributions with those already present in the standard Glashow-Salam-Weinberg model. In the case of μ → eγ, SUSY leads to a branching ratio two or three orders of magnitude larger than the corresponding branching ratio in the standard model, for gravitino and photino masses compatible with the experimental limits on the muon anomalous magnetic moment. In contrast, SUSY contributions to are always small, of the order of 10⁻² of the corresponding amplitudes in the standard model, if the gravitino and photino masses are constrained by the K_L − K_S mass difference.     

Chromotropic acid-functionalized polyurethane foam: A new sorbent for on-line preconcentration and determination of cobalt and nickel in lettuce samples

A chromotropic acid-functionalized polyurethane foam has been developed for use in an on-line preconcentration system for cobalt and nickel determination. The packing material was prepared by covalent coupling of chromotropic acid with the polyurethane foam through an azo group. Co and Ni ions were sorbed in the mini-column, from which they could be eluted directly to the nebulizer-burner system of a flame atomic absorption spectrometer. Elution of cobalt and nickel from the mini-column can be accomplished with 0.50 and 0.75 M HCl solutions, respectively. The enrichment factors obtained were 22 (Co) and 27 (Ni), for 60 s preconcentration time, and 57 (Co) and 59 (Ni), if a preconcentration time of 180 s was used. Under the optimum conditions, the proposed procedure allowed the determination of metals with detection limits of 0.43 (cobalt) and 0.52 microg/L (nickel), respectively, on using preconcentration periods of 180 s. The accuracy of the developed procedure was evaluated by analysis of the certified reference materials NIST 1515 Apple Leaves and NIST 1570a Spinach Leaves. The method was applied to the analysis of lettuce samples. The contents of cobalt in the samples analyzed varied from 0.75 to 0.98 microg/g. Nickel was not detected in the lettuce samples.     

Straightforward three-component palladium-catalysed synthesis of pyridazin-3(2H)-one libraries

A simple and straightforward three-component methodology for the solution phase high-throughput synthesis of 2,5-disubstituted pyridazin-3(2H)-one libraries has been developed. The diversity at position 5 of the heterocycle is determined by the use of Suzuki, Sonogashira, Heck or Stille coupling.     

Asymptotic limit law for the close approach of two trajectories in expanding maps of the circle

Summary Given two pointsx, yS ¹ randomly chosen independently by a mixing absolutely continuous invariant measure of a piecewise expanding and smooth mapf of the circle, we consider for each >0 the point process obtained by recording the timesn>0 such that |f ⁿ (x)–f ⁿ (y)|. With the further assumption that the density of is bounded away from zero, we show that when tends to zero the above point process scaled by –1 converges in law to a marked Poisson point process with constant parameter measure. This parameter measure is given explicity by an average on the rate of expansion off.Partially supported by FAPESP grant number 90/3918-5     

On the Optimal Control of a Random Walk with Jumps and Barriers

The modeling and optimal control of a class of random walks (RWs) is investigated in the framework of the Chapman-Kolmogorov (CK) and Fokker-Planck (FP) equations. This class of RWs includes jumps driven by a compound Poisson process and are subject to different barriers. A control mechanism is investigated that is included in the CK stochastic transition matrix and the purpose of the control is to track a desired discrete probability density function and attain a desired terminal density configuration. Existence and characterization of optimal controls are discussed. The proposed approach allows the derivation of a new FP model that accommodates the presence of the jumps and guarantees conservation of total probability in the case of reflecting barriers, which are modelled by appropriate operators. Results of numerical experiments are presented that successfully validate the proposed control framework.