Nondestructive detection of damage in aluminum: Electromagenetic discharge imaging

Electromagnetic Discharge Imaging (EDI) is applied for the nondestructive detection of imperfections and inhomogeneities in solids. These imperfections were introduced mechanically by drilling holes of different sizes and chemically by applying corrosive agents to aluminum specimens. The results are influenced by a host of variables associated with the waveform generator, the dielectric air gap and the specimen type. Correlation is thus established between the electromagnetic discharge image and the degree of material damage. Detection of material damage was also made possible even when the specimen surface was a layer of opaque insulation material.     

Characterization of strain-induced damage in composites based on the dissipated energy density Part III. General material constitutive relation

An approach to characterizing failure behavior and degree of load induced internal damage in composite materials and structures is formulated in Part I of this work. It is based on a systematic experimental procedure to observe the response of composite materials subjected to multiaxial load environment. The energy dissipated by internal failure mechanisms is employed as a measure of internal damage and is characterized by an energy dissipation function, which is identified by means of a deconvolution procedure using data provided by NRL's automated in-plane loader testing machine.Part II of this work will display the dissipated energy density distributions in composite specimens that are used for the in-plane loader machine and naval structures, while Part III presents a general theory that includes the derivation for the constitutive behavior of the damaged composites.     

Natural time analysis of critical phenomena: The case of acoustic emissions in triaxially deformed Etna basalt

Acoustic emissions exhibit complex correlations between space, time, and magnitude. As such, they present a unique example for a complex time series. We apply the recently introduced method of natural time analysis, which enables the detection of long-range temporal correlations even in the presence of heavy tails and find that the acoustic emissions exhibits features similar to that of other equilibrium or non-equilibrium critical systems such as worldwide seismicity as presented in the Centennial earthquake catalogue which includes global seismicity events with magnitude _Mw>7.0$M_w>7.0$. These results support the universal behaviour of the fracturing processes from the laboratory to the global scale.     

On the non-extensive nature of the isothermal depolarization relaxation currents in cement mortars

The study of isothermal depolarization current relaxation during the cement hardening process follows a generalized exponential function, which explicitly introduces hierarchically constrained dynamics and macroscopic interactions. The interactions are associated to the non-extensive entropy parameter q, which varies during hardening evolution. Combining ideas of Levy and Tsallis statistics we argue that a Levy walk type mechanism can organize the geometry of the cement mortar heterogeneous system. The estimation of non-extensive q parameter safe concludes that cement's hardening is a subextensive process.     

Ultrasensitive Determination of Vitamin B12 Using Disposable Graphite Screen‐Printed Electrodes and Anodic Adsorptive Voltammetry

A facile, rapid and ultra‐sensitive method for the determination of vitamin B₁₂ (cyanocobalamin) at the sub‐nanomolar concentration range by using low‐cost, disposable graphite screen‐printed electrodes is described. The method is based on the cathodic preconcentration of square planar vitamin B_12s, as occurred due to the electro reduction of Co(III) center in vitamin B_12a to Co(I), at ?1.3 V versus Ag/AgCl/3 M KCl for 40 s. Then, an anodic square wave scan was applied and the height of the peak appeared at ca. ?0.73 V versus Ag/AgCl/3 M KCl, due to the oxidation of Co(I) to Co(II) in the adsorbed molecule, was related to the concentration of the vitamin B₁₂ in the sample. EDTA was found to serve as a key‐component of the electrolyte by eliminating the background signal caused by metal cations impurities contained in the electrolyte (0.1 M phosphate buffer in 0.1 M KCl, pH 3). It also blocks trace metals contained in real samples, thus eliminating their interference effect. The method was optimized to various working parameters and under the selected conditions the calibration curve was linear over the range 1×10^?10–8×10^?9 mol L^?1 vitamin B₁₂ (R²=0.994), while the limit of detection for a signal‐to‐noise ratio of 3 (7×10^?11 mol L^?1 vitamin B₁₂) is the lowest value of any reported in the literature for the electrochemical determination of vitamin B₁₂. The sensors were successfully applied to the determination of vitamin B₁₂ in pharmaceutical products.     

Identification and quantification of glutathione adducts of clozapine using ultra-high-performance liquid chromatography with orthogonal acceleration time-of-flight mass spectrometry and inductively coupled plasma mass spectrometry

The application of sulphur-specific detection via ultra-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (UPLC/ICPMS) to detect and quantify the glutathione (GSH)-adducts produced via the in vitro formation of reactive metabolites is demonstrated. The adducts were formed in human liver microsomes supplemented with unlabelled GSH for clozapine. The calculation of adduct concentration was performed via comparison of the peak areas to calibration curves constructed from omeprazole, a sulphur-containing compound over the range of 0.156 to 15.62 μM of sulphur with a detection limit of 1.02 ng of sulphur on-column. Identification of the adducts was performed using conventional UPLC/time-of-flight (TOF)-MS with the calculation of clozapine intrinsic clearance carried out by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). The use of ICPMS in this way appears to offer a novel, rapid and sensitive means of determining the quantity of GSH conjugates with the combined adducts producing 0.9 μM of reactive metabolite out of a total of 3.5 μM of metabolites. The GSH adduct therefore represents 26% of this total produced as a result of the metabolism of drug to reactive species.     

Combination of molecular rods and half-discs: transition from lamellar to columnar order in multichain mononuclear ortho-palladated metallomesogens

Novel ortho-palladated phenylpyrimidine-1,3-diketonato organyls with successively increasing numbers of alkyl chains were synthesized and investigated by polarizing optical microscopy and X-ray diffraction. A discontinuous transition from a lamellar to a columnar organization is observed, dependent on the number of chains: molecules with four or five chains from smectic phases (SmA, SmC), the related compound with six chains in the molecule is nonmesomorphic, whereas molecules with seven or eight chains form hexagonal columnar mesophases.     

A [24-MC-6] zinc metallacoronate with a nonsteroidal antiinflammatory drug as the constructing ligand

The interaction of ZnCl(2) with 2-dipyridylketonoxime (=Hpko) and flufenamic acid (=Hfluf) in a basic methanolic solution leads to the formation of a hexanuclear 24-membered metallacoronate, [Zn(6)(OH)(2)(pko)(4)(fluf)(6)] (1), with a [Zn-O-C-O] repeat unit and a nonsteroidal antiinflammatory drug as the constructing ligand. Compound 1 retains its structure in a dimethyl sulfoxide solution, as shown by (1)H NMR spectroscopy and molar conductance.