A method for crack sizing using Laser Doppler Vibrometer measurements of Surface Acoustic Waves

The goal of non-destructive testing (NDT) is to determine the position and size of structural defects, in order to measure the quality and evaluate the safety of building materials. Most NDT techniques are rather complex, however, requiring specialized knowledge. In this article, we introduce an experimental method for crack detection that uses Surface Acoustic Waves (SAWs) and optical measurements. The method is tested on a steel beam engraved with slots of known depth. A simple model to determine the cracks size is also proposed. At the end of the article, we describe a possible application: fatigue crack sizing on a damaged slat track. This technique represents a first step toward a better understanding of the crack growth, especially in its early stages (preferably when the cracks can still be repaired) and when it is possible to assume a linear propagation of the crack front. The ultimate goal of this research program is to develop a useful method of monitoring aircraft components during fatigue testing.     

Clean seeding for flow visualization and velocimetry measurements

Flow visualization, particle image velocimetry (PIV), and laser Doppler velocimetry (LDV) are among the most useful tools available for experimental aerodynamics studies. Implementation of these techniques, however, requires that seed material be introduced into the flow. The undesirable qualities of the seeding material often prevent the use of flow visualization and velocimetry techniques in many test environments. This is particularly true for large-scale, closed-circuit tunnels where facility operators must weigh the risks of facility contamination, sensor damage, and safety concerns that might result from the introduction of seed particles. Identification of a practical clean seeding material that minimizes or eliminates these concerns would enable flow visualization and velocimetry techniques to be deployed in these facilities. Here, we demonstrate two seeding systems that have the potential to provide such a solution. The first system is a new concept which uses liquid carbon dioxide that can be made to form discrete particles as it expands from a high-pressure tank. PIV measurements are demonstrated in several flows, including supersonic and subsonic tunnels, using these residue-free seed particles. The second system utilizes a combination of steam and liquid nitrogen to produce an aerosol or fog that serves as flow seeding. Water- or steam-based seeding has been previously demonstrated for flow visualization in subsonic tunnels; here however, we utilize this seed material for PIV and LDV measurements as well as for flow visualization in a large supersonic tunnel.     

Pretreatment technique for siderite removal for organic carbon isotope and C:N ratio analysis in geological samples

A method for the removal of siderite from geological samples to determine organic carbon isotope compositions using elemental analysis isotope ratio mass spectrometry is presented which includes calculations for % organic carbon in samples that contain diagenetic carbonate. The proposed method employs in situ acidification of geological samples with 6 N HCl and silver capsule sample holders and was tested on modern peach leaf samples (NIST 1547) and ancient lacustrine samples from Valles Caldera, New Mexico. The in situ acidification technique eliminates potential errors associated with the removal of soluble organic material using standard acid decanting techniques and allows for removal of the less soluble siderite, which is not efficiently removed using vapor acidification techniques.     

Photo‐hardenable and patternable PDMS/SU‐8 hybrid functional material: A smart substrate for flexible systems

The fabrication of flexible electronics and systems, using rigid and brittle materials directly produced on stretchable substrate, leads to some issues and incompatibilities. These include rigidity for processing and modular flexibility for applications, macroscopic flexibility, and local rigidity to shield components from strain, compatibility with technological steps, and at the same time allowing patterning and machining. The development of smart substrate materials which meet such needs is therefore a promising route for flexible systems. Here, we demonstrate that by mixing polydimethylsiloxane (PDMS) and SU‐8 photoresist, we obtain both a photo‐hardenable and patternable stretchable hybrid material. A set of PDMS/SU‐8 and baking process combinations have been tested to determine an effective photo‐sensitive mixture. A standard photolithographic approach has been used on tensile test samples demonstrating a local hardening of millimeter‐sized ultraviolet exposed features and a local strain reduction reaching 35%. In addition, surface topography analysis and wet‐etching techniques have been used to demonstrate a light‐induced molding process and a selective etching of micrometer‐sized ultraviolet exposed patterns. The combined functional properties of the following material, its simplicity of implementation, and the well‐known assets of PDMS and SU‐8 make the PDMS/SU‐8 material very interesting and promising for various applications, especially stretchable systems. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1281–1291     

Steric and Electronic Factors Influence Regio‐isomeric Thiazole Formations Between Substituted Benzothioamides and Ethyl Bromopyruvate

We observed unexpected thiazole 1B formation when 2,6‐dichlorobenzothioamide 1 and ethyl bromopyruvate were reacted under basic conditions at elevated temperatures in ethanol. Thiazole 1B , regio‐isomeric to that expected under conventional Hantzsch conditions, was extensively characterized and later confirmed by single crystal X‐ray structure. We carried out this transformation with several substituted benzothioamides and found that the formation of the unexpected thiazole regio‐isomer was highly dependent on the steric as well as the electronic characteristics of the ortho‐substituents on the phenyl ring. A mechanism to account for this novel transformation was proposed.     

Flow injection determination of aluminium by spectrofluorimetric detection after complexation with N-o-vanillidine-2-amino-p-cresol: the application to natural waters

An on-line flow injection spectrofluorimetric method for the direct determination of aluminium in water samples is described. The method is based on the reaction of aluminium with N-o-vanillidine-2-amino-p-cresol (OVAC) in acidic medium at pH 4.0 to form a water-soluble complex. The excitation and emission wavelengths were 423.0 and 553.0 nm, respectively, at which the OVAC-Al complex gave the maximum fluorescence intensity at pH 4.0 in a 50% methanol-50% water medium at 50 °C. An interference from fluoride ions was minimised by the addition of Be²⁺. Other ions were found not to interfere at the concentrations likely to be found in natural waters. The proposed methods were validated in terms of linearity, repeatability, detection limit, accuracy and selectivity. Under these conditions, the calibration was linear up to 1000 μg L⁻¹ (r = 0.999). The limit of detection (3σ) for the determination of Al(III) was 0.057 μg L⁻¹ and the precision for multiple determinations of 3 ng mL⁻¹ Al(III) prepared in ultra-pure water was found to be 0.62% (n = 10).The Schiff base ligand could be used to determine ultra-trace aluminium from natural waters. Analysis of environmental certified reference materials showed good agreement with the certified values. The procedure was found to be equally applicable to both freshwater and saline solutions, including seawater.     

Nanoparticle-assisted surface immobilization of phospholipid liposomes

Phospholipid liposomes (100-200 nm diameter) are deposited onto solid substrates after stabilizing them against fusion with the solid by allowing charged nanoparticles to adsorb at approximately 25% surface coverage. The immobilized vesicles remain stable over a period of days. Epifluorescence imaging shows that they diffuse freely over surfaces with the same charge but adsorb tightly onto surfaces with opposite charge. Nanoparticle adsorption to surface patterns of opposite charge provides a facile method to create large-scale surface-supported arrays of intact liposomes. This surface attachment method is simple chemically and applies generally for solid surfaces that can be hydrophobic or hydrophilic. Offering routes to localize proteins and other vesicle-contained objects at surfaces in tailored spatial patterns, these immobilized liposome arrays may find diverse applications in the emerging field of nanobiotechnology.     

PDMS melts on mica studied by confocal Raman scattering

We report surprising surface-induced torsional alignment of polydimethylsiloxane (PDMS) chains in contact with the muscovite (001) mica surface with and without confinement. The alignment was measured by polarized confocal Raman spectroscopy over diffraction-limit circular spots with approximately 0.3 microm diameter. Our discussion here focuses on the intense symmetric methyl-group vibration centered at 2907 cm(-1), whose Raman scattering intensity is found to depend on whether incident light is polarized in the x or y direction of the surface, the x direction being parallel to one of the mica optical axes. Furthermore, the Raman peak broadens significantly relative to that of bulk PDMS while remaining Lorentzian in shape, implying slower but homogeneous vibrational dephasing. However, the preferred orientation differs, apparently stochastically, from spot to spot on the surface. Possible origins of this heterogeneous surface-induced structure are discussed.     

Induction of persistent double strand breaks following multiphoton irradiation of cycling and G1-arrested mammalian cells-replication-induced double strand breaks

DNA double strand breaks (DSBs) are amongst the most deleterious lesions induced within the cell following exposure to ionizing radiation. Mammalian cells repair these breaks predominantly via the nonhomologous end joining pathway which is active throughout the cell cycle and is error prone. The alternative pathway for repair of DSBs is homologous recombination (HR) which is error free and active during S- and G2/M-phases of the cell cycle. We have utilized near-infrared laser radiation to induce DNA damage in individual mammalian cells through multiphoton excitation processes to investigate the dynamics of single cell DNA damage processing. We have used immunofluorescent imaging of gamma-H2AX (a marker for DSBs) in mammalian cells and investigated the colocalization of this protein with ATM, p53 binding protein 1 and RAD51, an integral protein of the HR DNA repair pathway. We have observed persistent DSBs at later times postlaser irradiation which are indicative of DSBs arising at replication, presumably from UV photoproducts or clustered damage containing single strand breaks. Cell cycle studies have shown that in G1 cells, a significant fraction of multiphoton laser-induced prompt DSBs persists for > 4 h in addition to those induced at replication.     

In Situ Synthesis of an Aptamer‐Based Polyvalent Antibody Mimic on the Cell Surface for Enhanced Interactions between Immune and Cancer Cells

An ability to promote therapeutic immune cells to recognize cancer cells is important for the success of cell‐based cancer immunotherapy. We present a synthetic method for functionalizing the surface of natural killer (NK) cells with a supramolecular aptamer‐based polyvalent antibody mimic (PAM). The PAM is synthesized on the cell surface through nucleic acid assembly and hybridization. The data show that PAM has superiority over its monovalent counterpart in powering NKs to bind to cancer cells, and that PAM‐engineered NK cells exhibit the capability of killing cancer cells more effectively. Notably, aptamers can, in principle, be discovered against any cell receptors; moreover, the aptamers can be replaced by any other ligands when developing a PAM. Thus, this work has successfully demonstrated a technology platform for promoting interactions between immune and cancer cells.