Post-bifurcation behavior in the plastic range

In the first part of the paper a simple model is used to introduce some of the analytical and physical features of post-bifurcation phenomena in continuous elastic-plastic systems. An analysis is presented for the initial post-bifurcation behavior of a class of elastic-plastic solids subject to loads characterized by a single load parameter. Bifurcations which occur at the lowest possible load are singled out for attention. The theory makes connection with Hill's general theory of bifurcation and uniqueness in elastic-plastic solids and Koiter's general approach to the initial post-buckling behavior of conservative elastic systems. Buckling of an axially compressed column in the plastic range is used to illustrate the theory.     

Electrochemiluminescence enzyme immunoassay for TNT

Details of an electrochemiluminescence (ECL) enzyme immunoassay for TNT (2,4,6-trinitrotoluene) are reported. The design and construction of a computer controlled flow injection electrochemiluminometer in which the immunoassays are carried out is described. This system is used to select and pump solutions through a flow cell, which contains a gold working electrode as part of a three-electrode arrangement. The deposition of a re-usable immunosorbent dextran surface anchored to a gold surface in the flow cell by chemiadsorbed thiol groups is described. Antibodies are labeled with the enzyme glucose oxidase and used in competitive immunoassays in which the separation step is carried out by concentrating unbound antibodies on the immunosorbent surface. Hydrogen peroxide generated by the enzyme label when glucose is pumped through the flow cell is detected using luminol ECL. Light intensity was inversely proportional to the concentration of TNT in the sample in the range 0-100 ppb. The results are compared with colorimetric ELISA's carried out using the same reagents, and potential for developing a portable instrument for use in the field is discussed.     

Developmental toxicity of benzotriazole in the protochordate Ciona intestinalis (Chordata, Ascidiae)

Benzotriazoles (BT) are applied as anticorrosive and de-icing agents and have been detected in a variety of aquatic ecosystems and municipal wastewater effluents. We have assessed the developmental effects of benzotriazole (CAS number 95-14-7) to the marine invertebrate Ciona intestinalis (Chordata, Ascidiae). At 15 ± 1 °C, the 24 h No-Observed Effect Concentration (NOEC) and Lowest Observed Effect Concentration (LOEC) values based on embryo morphological development were 100 and >100 mg L⁻¹, respectively (nominal concentration under static conditions). After 48 h, the NOEC and LOEC values were 10 and 32 mg L⁻¹, respectively. Light and electron microscopy studies on benzotriazole-exposed larva indicated that the primary target cells were the extra-embryonic test cells, which are known to play a significant apoptotic role during ascidian metamorphosis. The visible decline of test cells in benzotriazole-exposed larvae raises the possibility that the compound interferes with the regulation of embryo development in protochordates such as C. intestinalis. Further research is warranted to assess the potential longer term sublethal impacts of benzotriazole in aquatic organisms.     

Synthetic strategies to a telomere-targeted pentacyclic heteroaromatic salt

Three routes have been explored to synthesise the telomere-targeted agent 3,11-difluoro-6,8,13-trimethyl-8H-quino[4,3,2-kl]acridinium methosulfate . Application of a 6-(2-azidophenyl)phenanthridine precursor gave an entry to the indazolo[2,3-f]phenanthridine ring system not the required quino[4,3,2-kl]acridine. A six step synthesis starting from 2,6-dibromo-4-methylbenzonitrile via a 1-arylacridin-9(10H)-one intermediate, or , gave the required in low overall yield (<10%). The most efficient route entailed the one-pot (five step) conversion of 1,2-dimethyl-6-fluoroquinolinium methosulfate to in 33% yield employing triethylamine as base and nitrobenzene as solvent.     

Isobaric thermal behavior of glasses during uniform cooling and heating. III. Predictions from the multiparameter KAHR model

The behavior of the multiparameter KAHR model (put forward by Kovacs, Aklonis, Hutchinson, and Ramos) has been investigated using a single-box retardation spectrum to describe the kinetics of volume and enthalpy recovery of glasses in three-step thermal cycles involving colling, isothermal annealing, and subsequent reheating. It has been shown that during the heating stage, the system may display up to three peaks in the expansion coefficient and the specific heat. The shifts of the peak temperatures T_p with respect to each of the four experimental variables Y_i defining the thermal history are analyzed systematically in terms of a set of reduced variables, scaled by two of the material constants of the system. These shifts, from which the various partial derivatives (?T_p/?Y_i)_j≠i are estimated, are determined for five values of another material parameter x, which characterizes the relative contributions (O ≤ x ≤ 1) of temperature and structure to the retardation times. the results show that the upper peak is always small and is insensitive to the characteristics of the spectrum and to the value of x, while the relevant peak temperature depens only slightly on the cooling and heating rates. On the Other hand, the magnitude and the shifts of the main peak depend on all the experimental variables and the material constants in a rather complex manner. It is shown, however, that in limiting situations, involving fast heating of well-stabilized glasses, the shifts of the relevant peak temperature T?all reduce to a linear function of x^?1. since this relationship is rather insensitive to the shape of the spectrum, the experimental determination of any one of the nonzero partial derivatives of T? provides a simple means for an independent estimate of the value of the important material constant x. Finally, the shifts of the upper and main peaks relative to each other will be analyzed in terms of the pertinent experimental variables and compared with actual data reported in the literature for polymer glasses.     

Finite element approximation of a model for phase separation of a multi-component alloy with a concentration-dependent mobility matrix

We consider a model for phase separation of a multi-componentalloy with a concentration-dependent mobility matrix and logarithmicfree energy. In particular we prove that there exists a uniquesolution for sufficiently smooth initial data. Further, we provean error bound for a fully practical piecewise linear finiteelement approximation in one and two space dimensions. Finallynumerical experiments with three components in one space dimensionare presented.     

Sum frequency generation at 309 nm using a violet and a near-IR DFB diode laser for detection of OH

We have used a violet diode laser at 404 nm and a distributed feedback diode laser at 1320 nm to produce 0.8 nW of radiation at 309 nm by sum frequency generation in beta-barium borate. The UV radiation was tuned mode-hop-free over 30 GHz and used to detect OH radicals produced in a microwave discharge. By chopping the UV light at 500 Hz, we observed a concentration of 2×10¹² cm^-3 with a signal to noise ratio of 30:1. Received: 16 November 2001 / Revised version: 23 January 2002 / Published online: 14 March 2002