Construction of fiber-optic bundle light-collection systems and calculations of collection efficiency

This paper describes the position-sensitive light-collection system that we use in our fast-beam laser experiments. The collection system consists of fiber-optic bundles whose facets are arranged to accept light emitted from a beam of fluorescent atoms. The flexibility of the fiber bundles allows their use in scanning collection systems with precise position sensitivity. We describe calculations of geometrical collection efficiency using a numerical integration scheme and compare the results with measurements. We also compare the collection efficiencies of the different fiber bundle arrangements that we used as our apparatus evolved with the implementation of various improvements.     

Lacton-Bildung durch ringerweiternde Fragmentierung von Epoxycyclodecanon-Derivaten

Lactones from Epoxycyclodecanone Derivatives by Ring Enlargement Involving Fragmentation Reactions A stereospecific ring-enlargement reaction of alkyl esters of 2,3-epoxy-1-(3-hydroxypropyl)-10-oxocyclo-decanecarboxylic-acid derivatives is described, involving Grob fragmentation of in situ formed hemiacetals. The assignment of the relative configuration of the starting materials was accomplished on the basis of ¹H-NMR data. The rearrangement of the epoxides 9 and 10 (with cis-orientation of the ester group and the epoxide ring, Scheme 1) gives the lactone 15 as the single and as the major product, respectively, with (Z)-configuration of the newly formed C?C bond. A concerted reaction mechanism is assumed. The formation of a small amount of 12 from 10 is probably due to a competitive two-step carbanion pathway. The reaction of the diastereoisomers 7 and 8 leads to the lactones 11 and 12 , respectively, as the only ring-enlargement products (Scheme 1), with (E)-configuration of the newly formed C?C bond. On the basis of our results, we cannot distinguish in this case between a concerted and a two-step carbanion mechanism. This type of reaction takes place only in the presence of an ester group; no ring enlargement was detected in case of compound 20 (Scheme 3), which is the de(alkoxycarbonyl) derivative of 9 . The eliminative opening of the epoxide ring in the epoxylactone 17 affords 11 as the single product (Scheme 2). A carbanion mechanism was assumed for this reaction.     

Stagnation point flow of a micropolar fluid towards a stretching sheet

The steady two-dimensional stagnation point flow of an incompressible micropolar fluid over a stretching sheet when the sheet is stretched in its own plane with a velocity proportional to the distance from the stagnation point, has been studied in this paper. The resulting equations of non-linear ordinary coupled differential equations are solved numerically using the Keller-box method. The results obtained for velocity, microrotation and skin friction are shown in tables and graphs. Comparison with the recent results of Mahapatra and Gupta {Heat Mass Transfer 38 (2002) 517} for the corresponding problem of a viscous fluid (K=0) has been done and it has been shown that the results are in excellent agreement.     

Stochastic transition in a classical nonlinear dynamical system: A Lennard-Jones chain

Theoretical and Mathematical Physics -     

R-matrix method for a surface with one groove of arbitrary profile

The R-matrix propagation algorithm is applied to solve the problem of electromagnetic scattering from a perfectly conducting plane surface with one groove of arbitrary profile. Using the multilayer approximation, the fields inside each layer are written as modal expansions. The reflected intensity is obtained in both the fundamental cases of polarization, which are treated separately. Numerical examples are shown for several profiles of the groove, and comparisons with results known from physical optics are presented for the validation of the method.     

Imidazolriazole and oxazolotriazole analogs of midafltir |4-amino-2,2,5,5, -tetrakis(trifluoromethyl)-3-imidazolin|

Imidazotriazole (5) and oxazolotriazole (10) analogs of CNS depressant 4-amitio-2,2,5,5-tetrakis(trifluoromethyl)-3-imidazoline (miduflur) were prepared and found to he much less active.     

On the relation between the divergence of trajectories and the Kolmogorov-Sinai entropy

Automorphisms of the torus are considered and the Kolmogorov-Sinai entropy explicitly computed via rate of growth of volumes. The usual rate of growth of exponentiating trajectories is shown to give only a lower bound to K-S entropy.