Systematic errors in PIV by realizing velocity offsets with the rotating mirror method

The observation of a flowfield in PIV via a mirror causes aberrations in the image plane which can reach several percent of the displacement to be measured. These imaging errors are investigated theoretically and the results are confirmed by comparison with experimental data. Several experimental parameters are discussed in respect to their influence on the displacement errors.     

The discretized flow on domains of attraction: a structural stability result

It is well known that, for stepsize sufficiently small, compactattractors of ordinary differential equations persist underdiscretization. The present paper describes the structure ofthe discrete-time dynamical system obtained via discretizationon A(M_h)\M_h where M_h is the approximate attractor and A(M_h)is its domain of attraction. The existence of a smooth embeddinginto a continuous-time parallelizable flow is proved. The constructioncan be used to define sections for discretizations and can beinterpreted as a justification of the method of modified equations.     

Chemically-enabled synthesis of 1,2,3,4-tetrahydroisoquinolin-1-ones

We have developed a number of efficient protocols for the facile synthesis of 1,2,3,4-tetrahydroisoquinolin-1-ones. This synthetic methodology allowed concise and efficient exploration of the SAR in all areas of the molecule. A number of these methods proved to be versatile, efficient and amenable to parallel synthesis.     

Synthesis of ortho-substituted nitroaromatics via improved Negishi coupling conditions

We describe modified Negishi coupling conditions that allow improved access to ortho-nitrophenylalanine derivatives. These useful amino acid intermediates can be further elaborated into biologically active lactams and cyclic hydroxamic acid targets.     

Localization in NiTi tubes under bending

Nearly equiatomic NiTi can exhibit pseudoelastic behavior due to reversible solid-to-solid stress induced phase transformation at room level temperatures. In tension, the transformation leads to localized deformation of several percent that tends to spread at nearly constant stress. The deformation is recovered upon unloading while again localized deformation is exhibited. Under compression, while still pseudoelastic, the transformation strains are smaller, the stress is higher, the response is monotonic, and the deformation is essentially homogeneous. This study examines how this texture-driven, complex material asymmetry affects a simple structure: the bending of a tube. To this end, NiTi tubes are bent in a custom four-point bending facility under rotation control and isothermal conditions. The phase transformations lead to a closed moment-rotation hysteresis comprised of loading and unloading moment plateaus. During loading, localized nucleation of martensite results in a high curvature for the transformed sections of the tube and low curvature for the untransformed. Martensite, which corresponds to the higher curvature regime, spreads gradually while the moment remains nearly constant. The nucleation of martensite is in the form of bands inclined to the axis of the tube that organize themselves into diamond shaped deformation patterns on the tensioned side of the structure. The patterns are similar to those observed in bending of steel tubes with Lüders bands, however, for NiTi they develop only on the tensioned side due to the material asymmetry. A lower moment plateau is traced upon unloading with similar localized bending and the erasure of the diamond deformation patterns. This complex behavior was found to repeat for a number of temperatures in the pseudoelastic regime of NiTi with the moment-rotation hysteresis moving to higher or lower moment levels depending on the temperature.     

Development of a scalable synthetic route towards a 2,2,6-trisubstituted chiral morpholine via stereoselective hydroalkoxylation

A scalable synthetic route towards a chiral 2,2,6-trisubstituted chiral morpholine, which is a known opioid antagonist, was developed. The synthetic route involves incorporating an aryl group via Suzuki-Miyaura coupling and stereoselective hydroalkoxylation catalyzed by trifluoromethanesulfonic acid. Late stage incorporation of both the aryl and N-alkyl groups make this route suitable for further SAR studies on this molecule.     

A general strategy for the synthesis of cyclic N-aryl hydroxamic acids via partial nitro group reduction

We describe a generalized approach to stereocontrolled synthesis of substituted cyclic hydroxamic acids (3-amino-1-hydroxy-3,4-dihydroquinolinones) by selective reduction of substituted 2-nitrophenylalanine substrates. Compounds in this series have antibacterial properties and have also recently been reported as KAT II inhibitors. The key nitrophenyl alanine intermediates are prepared enantioselectively in excellent yield by phase transfer catalyzed alkylation of the corresponding nitrobenzyl bromides. The scope and limitations of the reductive cyclization transformation have been explored with attention to the effects of substitution pattern and electronics on reaction efficiency and byproduct formation. In addition, a novel activated trifluoroethyl ester cyclization strategy has been developed as an alternate approach to the most sterically demanding systems in this series.