Exciton polaritons in monoclinic zinc diphosphide

A classical theory based on excitons is insufficient to explain the reflectivity spectra of βZnP₂. Instead an exciton polariton picture is invoked and the polariton parameters are determined. Photoluminescence spectra are consistent with the polariton interpretation. Higher energy states of the exciton have been observed and from these the band gap and exciton binding energy in βZnP₂ have been deduced.     

Piecewise linear paths among convex obstacles

Let ℬ be a set ofn arbitrary (possibly intersecting) convex obstacles in ℝ ^d . It is shown that any two points which can be connected by a path avoiding the obstacles can also be connected by a path consisting ofO(n ^{(d−1)[d/2+1]}) segments. The bound cannot be improved below Ω(n ^d ); thus, in ℝ³, the answer is betweenn ³ andn ⁴. For open disjoint convex obstacles, a Θ(n) bound is proved. By a well-known reduction, the general case result also upper bounds the complexity for a translational motion of an arbitrary convex robot among convex obstacles. Asymptotically tight bounds and efficient algorithms are given in the planar case. This research was supported by The Netherlands' Organization for Scientific Research (NWO) and partially by the ESPRIT III Basic Research Action 6546 (PROMotion). J. M. acknowledges support by a Humboldt Research Fellowship. Part of this research was done while he visited Utrecht University.     

Insect pheromones and their analogues

A stereospecific synthesis has been achieved of tetradec-11E-enal and of tetradec-11E-en-l-ol and its acetate — components of the pheromones of many species of insects of the order Lepidoptera — from the readily available undecenoic acid, using the Knoevenagel reaction and catalytic hydroalumination.Institute of Chemistry, Bashkir Scientific Center, Urals Branch, Russian Academy of Sciences, Ufa. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 272–276, March–April, 1992.     

13C?13C coupling constants in derivatives of trans-stilbene and tetraphenylethylene. Determination of relative signs II

Magnitudes and signs of ¹³C? ¹³C coupling constants in compounds of the type Ph¹³CR¹R²? ¹³CR¹R²Ph have been determined and the results are discussed in a broader context. Two types of coupling constants, J(C-i, C-α) and J(C-i, C-β), between aromatic carbon atoms and the benzylic carbons, probably with different coupling mechanisms, are considered. Whereas ²J(C-2, C-α) are always found positive, ²J(C-1, C-β) in the present compounds are found to be negative or about zero. ³J(C-3, C-α) has the same sign as ²J(C-2, C-α). A ⁴J and a ⁵J were observed in trans-stilbene.     

Determination of relative signs of 13C?13C coupling constants in doubly labelled compounds

Analysis of the noise decoupled ¹³C spectra of doubly ¹³C labelled compounds where the two labelled carbons are identical, makes the determination of reltive signs of ¹³C? ¹³C coupling constants possible in a very simple way. The involved carbon form AA'X or AA'B spin systems.