Dependence of pulser driving responses on electrical and motional characteristics of NDE ultrasonic probes

Acoustic performance in ultrasonic transmitters can be improved by means of a suitable electrical driving response and matching/tuning networks. It is important to predict this electrical response, but doing so is not easy because it departs notably from the nominal pattern with the loading probes. In practice, the analysis of HV pulser spikes in NDE applications requires fairly complex models in the transient regime and, in addition, non-linear problems could arise, especially in the case of tuned transmitters. In this paper, the most relevant influences of loading characteristics of NDT ultrasonic probes on the pulser electrical driving responses are evaluated in time and frequency domains. Conventional pulse generators and typical NDE pulsers are considered. Driving responses are analysed across commercial ultrasonic probes and, alternatively, across similar purely electrical loads. Distinct influences on pulser responses from electrical and motional sections of the probes are identified. All these aspects are studied on the basis of experimental and computer results.     

Spin-singlet clusters in the ladder compound NaV2O5

The space group of alpha(')-NaV2O5 turns below T(c) = 34 K from Pmmn with all V sites equivalent, into Fmm2 with three independent vanadium sites per layer. This is incompatible with models of charge ordering into V4+ and V5+. Our structure determination indicates that the phase transition consists of a charge ordering with three distinct valence states, formally V4+, V4.5+, and V5+. The singlet formation is not associated with dimerization on the spin ladder, but with the formation of spin clusters. Finally, we ascribe the quadrupling of the c axis to the large polarizability of the V2O5 skeleton.     

The hydrocyanation of free and polymer-bound benzoquinone

The polymer-bound quinone2 has been prepared and used in column form with organic solvents for the convenient preparation of other quinones. In contrast to the solution reaction hydrocyanation of this quinone by the Thiele-Meisenheimer reaction did not yield a useful proportion of polymer-bound dicyanohydroquinone but instead gave a mixture of products including much monocyanohydroquinone. Helferich and Bodenbender's 2,3-dicyanocyclohexan-1, 4-dione is in fact wholly the di-enol and is a likely intermediate in the hydrocyanation of benzoquinone, being oxidised by the latter to 2,3-dicyanocyclohex-2-ene-1, 4-dione which tautomerises to the observed product, 2,3-dicyanohydroquinone. A lower accessibility to polymer-bound reactants as compared with those in solution is implied by these results.     

Eine Untersuchung der Konformations-Gleichgewichte von Pyridinal dehyden in Dekahydronaphthalin-L?sung

Ohne Zusammenfassung     

p-AMINOBENZOIC ACID-SUNLAMP SENSITIZATION OF PYRIMIDINE DIMER FORMATION AND TRANSFORMATION IN HUMAN CELLS

Abstract In the presence of sunlamp radiation, p -aminobenzoic acid sensitizes pyrimidine dimer formation in the DNA of human skin fibroblasts. It also sensitizes the sunlamp-induced transformation of such cells to anchorage-independent growth.