A mechanism for mitigation of blade–vortex interaction using leading edge blowing flow control

The interaction of a vortical unsteady flow with structures is often encountered in engineering applications. Such flow structure interactions (FSI) can be responsible for generating significant loads and can have many detrimental structural and acoustic side effects, such as structural fatigue, radiated noise and even catastrophic results. Amongst the different types of FSI, the parallel blade–vortex interaction (BVI) is the most common, often encountered in helicopters and propulsors. In this work, we report on the implementation of leading edge blowing (LEB) active flow control for successfully minimizing the parallel BVI. Our results show reduction of the airfoil vibrations up to 38% based on the root-mean-square of the vibration velocity amplitude. This technique is based on displacing an incident vortex using a jet issued from the leading edge of a sharp airfoil effectively increasing the stand-off distance of the vortex from the body. The effectiveness of the method was experimentally analyzed using time-resolved digital particle image velocimetry (TRDPIV) recorded at an 800 Hz rate, which is sufficient to resolve the spatio-temporal dynamics of the flow field and it was combined with simultaneous accelerometer measurements of the airfoil, which was free to oscillate in a direction perpendicular to the freestream. Analysis of the flow field spectra and a Proper Orthogonal Decomposition (POD) of the TRDPIV data of the temporally resolved planar flow fields indicate that the LEB effectively modified the flow field surrounding the airfoil and increased the convecting vortices stand-off distance for over half of the airfoil chord length. It is shown that LEB also causes a redistribution of the flow field spectral energy over a larger range of frequencies.     

Synthesis of 4-acetylcolchicine

The synthesis of 4-acetylcolchicine ( 1 ) by Swern dehydrogenation of the corresponding mixture of 4-[(R)-1-hydroxyethyl]- and 4-[(S)-1-hydroxyethyl]colchicine ( 3a and 3b , respectively) is described (cf. Scheme). The X-ray analysis of 1 (cf. Fig.), crystallized from MeOH, showed the presence of MeOH in the crystals.     

Generalized sine equations,III

Summary We solve the equationf(x + y)f(x – y) = P(f(x), f(y)) under various conditions on the unknown functionsf, P.     

Generalized sine equations,II

In this paper we solve the equations

Low Level Lead Determination After Membrane Complexation and TXRF Analysis

New membranes containing a few micrograms of various complexing reagents in a Nafion^® matrix were produced on the surface of quartz glasses (reflectors). The reflectors were immersed in standard water solutions containing various, very low concentrations of lead salts (1–50ngmL^–1). The reflectors were left in 5–500mL solutions for many hours; when the equilibration stage was complete, they were cleaned with ultrapure water and left to dry. The stability (adhesion) of the membranes was tested. Analysis of the samples was performed by Total Reflection X-Ray Fluorescence and cross-evaluated by Atomic Absorption Spectrometry. A few ngmL^–1 of the lead were determined. The effect of various experimental parameters (complexing agent, membrane composition, equilibrium time, sample volume etc.) was examined.     

On non-multiaffine consistent-around-the-cube lattice equations

We show that integrable involutive maps, due to the fact they admit three integrals in separated form, can give rise to equations, which are consistent around the cube and which are not in the multiaffine form assumed in Adler et al. (2003) [1]. Lattice models, which are discussed here, are related to the lattice potential KdV equation by nonlocal transformations (discrete quadratures).     

8-Bromo-7-hydroxyquinoline as a photoremovable protecting group for physiological use: mechanism and scope

Two-photon excitation (2PE) of "caged" biomolecules represents a powerful method to investigate the temporal and spatial relevance of physiological function in real time and on living tissue, because the excitation volume can be restricted to 1 fL. Additionally, low-energy IR light is used, which minimizes tissue destruction and enables deeper penetration into tissue preparations. Exploitation of this technology for studying cell physiology requires the further development of photoremovable protecting groups with sufficient sensitivity to 2PE for use in "caged" compounds. 8-Bromo-7-hydroxyquinoline (BHQ) is efficiently photolyzed by classic 1PE (365 nm) and 2PE (740 nm) under simulated physiological conditions (aqueous buffer of high ionic strength, pH 7.2) to release carboxylates, phosphates, and diols-functional groups commonly found on bioactive molecules such as neurotransmitters, nucleic acids, and drugs. It is stable in the dark, soluble in water, and exhibits low levels of fluorescence, which will enable use in conjunction with fluorescent indicators of biological function. BHQ-protected effectors are synthetically accessible. Stern-Volmer quenching, time-resolved infrared (TRIR), and (18)O-labeling experiments suggest that the photolysis occurs through a solvent-assisted photoheterolysis (S(N)1) reaction mechanism on the sub-microsecond time scale. BHQ has the requisite photochemical and photophysical properties as a photoremovable protecting group to regulate the action of biological effectors in cell and tissue culture with light, especially 2PE.     

Low-degree points on Hurwitz-Klein curves

We investigate low-degree points on the Fermat curve of degree 13, the Snyder quintic curve and the Klein quartic curve. We compute all quadratic points on these curves and use Coleman's effective Chabauty method to obtain bounds for the number of cubic points on each of the former two curves.