Temperature corrected sensor diagnostics for impedance-based SHM

Previously, a sensor diagnostics method has been developed for the impedance-based structural health monitoring technique. Impedance techniques utilize piezoelectric patches bonded to the structure of interest for inference of damage. Measuring the slope of piezoelectric susceptance allows unhealthy sensor to be identified. While this sensor diagnostics technique is very useful in detecting damaged sensors bonded to a structure, the method is also susceptible to temperature variations. The object of this study is to accurately provide sensor diagnostics at any temperature. The model developed should be accurate and easy to implement on health monitoring hardware. A frame structure is fabricated to simulate a real structure with complex boundary conditions for experimental testing in various thermal environments. A model predicting piezoelectric susceptance slope at any temperature is generated and validated on the frame structure in an extended temperature range.     

The electrochemistry of chromium in molten LiCl+KCl

Chronopotentiometric and steady-state voltammetric techniques have been employed to study the electroreduction processes:Cr(III)+eCr(II) andCr(II)+2eCr(0) separately, using the LiCl+KCl eutectic as solvent at 500°C.The adsorption of the ions on the electrode surfaces appears to play a role in the overall electrode processes; the degree of adsorption was correlated with the variation of exchange current density with concentration in the case of the Cr(II) ions. Fluoride ions had no effect on the electrode processes. The chronopotentiometric behaviour of Cr(III) ions was rather complex but adsorption appeared to play a part in this case also.     

Mediating stochastic switching of single molecules using chemical functionality

We have studied oligo(phenylene-ethynylene)s inserted into amide-containing alkanethiol self-assembled monolayers using scanning tunneling microscopy to demonstrate switching based on chemical functionality of the environment of the inserted molecules. The molecules show stability in two conductance states: an ON and an OFF state. We demonstrate bias-dependent switching due to hydrogen bonding between the inserted oligo(phenylene-ethynylene) and the matrix molecules. In addition, the inserted molecules exhibit fewer switching events than previously reported for alkanethiol matrixes, which we attribute to the rigidity of the hydrogen-bonded matrix.     

Multicomponent dye detection with californium-252 particle-desorption mass spectrometry

Particle-desorption mass spectrometry (PDMS) by using ²⁵²Cf was applied to multicomponent dye samples. A mixture of cesium iodide with three cationic dyes (rhodamine B, methyl violet and methylene blue), and a crude carotenoid sample extracted from a carrot were examined. In the positive-ion detection mode, the individual components of the dye mixture were identified by the detection of intactly desorbed preformed cations. In the carotenoid extract, two neutral components, carotene and lutein (xanthophyll), provided adduct ions, (M+H)⁺ In both examples, further fragmentation occurred, providing peaks useful for structural interpretation. These examples illustrate the ability of PDMS to acquire qualitative information from mixtures without a prior separation step.     

Molecular engineering of the polarity and interactions of molecular electronic switches

We have investigated and learned to control switching of oligo(phenylene ethynylene)s embedded in amide-containing alkanethiol self-assembled monolayers on Au{111}. We demonstrate bias-dependent switching of the oligo(phenylene ethynylene)s as a function of the interaction between the dipole moment of the oligo(phenylene ethynylene)s and the electric field applied between the scanning tunneling microscope tip and the substrate. We are able to invert the polarity of the switches by altering their design-inverting their dipole moments. For appropriately designed switches and matrix molecules, the conductance states are stabilized by intermolecular hydrogen bonding. These results further support the hypothesis that conductance switching in these molecules is due to hybridization changes at the molecule-substrate bonds due to tilting of the switch molecules.     

Extraction and determination of iron as the bathophenanthroline complex in high-purity niobium, tantalum, molybdenum and tungsten metals

A spectrophotometric method for determining iron in the range 0·001–0·125% in high-purity niobium, tantalum, molybdenum and tungsten metals is described. After sample dissolution and reduction of iron to the bivalent state with ascorbic acid and hydroxylamine hydrochloride, the red complex formed between iron^II and bathophenanthroline (4,7-diphenyl-1,10-phenanthroline) is extracted into n-arnyl alcohol and the absorbance of the resulting extract is determined at 536 mμ. Interference from copper is eliminated with thiourea. Cobalt, cadmium, nickel, manganese and zinc also interfere but the amounts of each of these impurities present in the four high-purity metals described are so low that their interference effects are negligible in the proposed method. Highly reproducible and precise results can be obtained with careful control of the pH during reduction and extraction.     

In situ deprotection and assembly of s-tritylalkanethiols on gold yields monolayers comparable to those prepared directly from alkanethiols

In this paper we describe a systematic study comparing the properties of self-assembled monolayers (SAMs) formed by in situ deprotection and assembly of S-triphenylmethyl (trityl)- and thiolacetate-protected alkanethiols to those of SAMs formed from the parent alkanethiols. The two in situ deprotections were carried out in trifluoroacetic acid and THF/ammonium hydroxide, respectively. Monolayers of octadecanethiol (ODT) and the peptide-containing alkanethiol 3-mercapto-N-n-pentadecylpropionamide (1ATC15) were assembled on gold using the two in situ methods and characterized by contact angle goniometry, X-ray photoelectron spectroscopy, polarization modulation infrared reflection absorption spectroscopy, and electrochemical characterization methods to assess how the monolayer properties compare to those of monolayers prepared by traditional methods. The results for the in situ deprotection of the trityl-protected molecules demonstrate that this method can afford high-quality monolayers that are nearly indistinguishable from those prepared directly from alkanethiols. The quality of the monolayers prepared using this method is shown to depend on the solubility of the trityl-protected compound in trifluoroacetic acid. The results for the in situ deprotection of acetyl-ODT indicate this method yields low-quality monolayers that contain mixtures of adsorbates bound as thiolates and thiolacetates. In situ trityl deprotection is a useful approach for monolayer formation that greatly simplifies the purification, handling, and assembly of thiol-containing monolayer precursors.     

General method validation guidelines for pharmaceutical samples

Method validation guidelines, which provide an organizational structure for the design and evaluation of a validation procedure, are presented for a wide range of pharmaceutical applications. The validation guidelines are based on the analyte concentration/sample matrix combination to which the method will be applied. These guidelines include the selection of appropriate validation parameters, design considerations for evaluation, and a discussion of acceptance guidelines for the determination of acceptable method performance. A set of tables is included which illustrates the selection and testing procedure and tailors the entire validation process to the specific characteristics of the determination to be made.