Flexural design curves of steel plate I-girders at elevated temperatures: I-girders with yield or local buckling failure mode

The present study was undertaken to characterize the structural behavior and ultimate flexural strength of steel plate I-girders under pure flexural moment at elevated temperatures. A novel design procedure along with flexural design curves was proposed to predict the flexural behavior of the I-girders and estimate corresponding ultimate flexural strengths. The main strategy of the procedure is to find an ambient-temperature equivalent of the I-girder by quantifying and formulating the effects of elevated temperatures. The proposed procedure comprises overall and partial phases. The former phase deals with the determination of equivalent laterally unbraced length, and the latter phase addresses the equivalent web and compression flange slenderness parameters. The calibration factor was defined to adapt the design curves to the effects of high compression flange slenderness parameters and residual stress at elevated temperatures. To generate comparative results, a numerical study was conducted by analyzing 216 finite element (FE) models. Fifty-four out of 216 FE models with different cross-sectional elements were dedicated to the I-girders fail by yield or local buckling failure mode, the results of which are reported in the present paper. Data fitting analysis was carried out to capture the variation of calibration factor with respect to compression flange slenderness parameters. By calibrating the proposed design procedure, the results were converged and, therefore, good conformity was reached between the numerical and parametric results.     

A Versatile,Digital Sequencer for Programmed Electrical Heating of Nonflame Atomizers

ABSTRACT

A simple, inexpensive, yet flexible digital sequencer is described for the programming of electrically heated nonflame atomizers. The system provides four distinct periods of operation and a three step analog output for controlling the atomizer heating during desolvation, ashing and atomization. The sequencer is sufficiently versatile to allow it to be used with any nonflame atomizer with only minor modifications. Performance tests of the sequencer with the graphite braid nonflame atomizer are presented and illustrate that results comparable to those obtained with a laboratory minicomputer can be readily achieved.     

Fibroblasts prevent apoptosis of IL-2-deprived T cells without inducing proliferation: a selective effect on Bcl-XL expression

Tumour hypoxia is well recognised as a major factor contributing to radioresistance. This article examines the role of hypoxia in influencing the treatment outcome following radiotherapy (RT), and reviews the rationale and results of clinical trials that utilise hypoxic sensitizers or cytotoxins in the treatment of head and neck carcinoma. Histologic evidence for tumour hypoxia in human neoplasms was first reported in 1955. Since then, direct measurement by microelectrodes has revealed heterogeneity in intratumoural oxygen concentrations, and low oxygen concentrations are associated with poor local-regional control by RT. These findings coupled with the result of nuclear imaging studies employing radiolabelled imidazoles, provide strong evidence for the existence of tumour hypoxia which influences RT treatment outcome. Hyperbaric oxygen (HBO) trials for head and neck cancer, conducted in the early 1970s, demonstrated that HBO improved local control and survival rates in patients with head and neck cancer receiving radiotherapy (RT). Since the mid-1970s, clinical research in overcoming tumour hypoxia was mainly centred on the use of nitro-imidazoles as hypoxic cell sensitizers. However, the results from several major clinical trials remain inconclusive. Specifically, the Radiation Therapy Oncology Group (RTOG) misonidazole head and neck trial (298 patients) showed no benefit. The Danish misonidazole trial (626 patients) showed no overall benefit, however positive results were observed in a subgroup (304 pharyngeal cancer patients). Although the European Organisation for Research and Teaching of Cancer (EORTC) misonidazole trial with hyperfractionated RT showed no benefit, the Danish nimorazole trial demonstrated an overall benefit in survival as well as local control. The European etanidazole (ETA) trial (374 patients) showed no advantage of adding the drug to RT. The RTOG ETA trial (504 patients) showed no global benefit. However, positive results were observed in a subset of patients with early nodal disease (197 patients). In addition, a recent meta-analysis by Overgaard, utilising pooled results in the literature demonstrated that modification of tumour hypoxia significantly improved local-regional control in head and neck cancers with an odds ratio of 1.23 (95% confidence limits 1.09 to 1.37). Hypoxic cytotoxins, such as tirapazamine, represent a novel approach in overcoming radioresistant hypoxic cells. Tirapazamine is a bioreductive agent which, by undergoing one electron reduction in hypoxic conditions, forms cytotoxic free radicals that produce DNA strand breaks causing cell death. In vitro and in vivo laboratory studies demonstrate that tirapazamine is 40 to 150 times more toxic to cells under hypoxic conditions as compared to oxygenated conditions and that tirapazamine is superior to ETA in enhancing fractionated irradiation in mouse SCCVII and other tumour types with an enhancement ratio of 1.5 to 3.0. Phase I studies demonstrated that therapeutic doses of tirapazamine can be given safely. A multi-institutional phase II trial using tirapazamine with concurrent RT for head and neck cancer is now in progress.     

Rapid Tempering of Martensitic Stainless Steel AISI420: Microstructure,Mechanical and Corrosion Properties

In this research, the effect of rapid tempering on the microstructure, mechanical properties and corrosion resistance of AISI 420 martensitic stainless steel has been investigated. At first, all test specimens were austenitized at 1050 °C for 1 h and tempered at 200 °C for 1 h. Then, the samples were rapidly reheated by a salt bath furnace in a temperature range from 300 to 1050 °C for 2 min and cooled in air. The tensile tests, impact, hardness and electrochemical corrosion were carried out on the reheated samples. Scanning electron microscopy was used to study the microstructure and fracture surface. To investigate carbides, transmission electron microscopy and also scanning electron microscopy were used. X-ray diffraction was used for determination of the retained austenite. The results showed that the minimum properties such as the tensile strength, impact energy, hardness and corrosion resistance were obtained at reheating temperature of 700 °C. Semi-continuous carbides in the grain boundaries were seen in this temperature. Secondary hardening phenomenon was occurred at reheating temperature of 500 °C.     

Measuring Grain Boundary Character Distributions in Ni-Base Alloy 725 Using High-Energy Diffraction Microscopy

We use high-energy X-ray diffraction microscopy (HEDM) to characterize the microstructure of Ni-base alloy 725. HEDM is a non-destructive technique capable of providing three-dimensional reconstructions of grain shapes and orientations in polycrystals. The present analysis yields the grain size distribution in alloy 725 as well as the grain boundary character distribution (GBCD) as a function of lattice misorientation and boundary plane normal orientation. We find that the GBCD of Ni-base alloy 725 is similar to that previously determined in pure Ni and other fcc-base metals. We find an elevated density of Σ9 and Σ3 grain boundaries. We also observe a preponderance of grain boundaries along low-index planes, with those along (1 1 1) planes being the most common, even after Σ3 twins have been excluded from the analysis.

     

The Effect of Nanoparticles on the Mass Transfer in Liquid–Liquid Extraction

This article investigates the effect of nanoparticles on mass transfer in the liquid–liquid extraction for the chemical system of n-butanol–succinic acid–water. For this purpose, nanofluids containing various concentrations of ZnO, carbon nanotubes (CNT), and TiO₂ nanoparticles in water, as base fluid, were prepared. To examine the flow mode effect on mass transfer rate, different fluid modes including dropping and jetting were employed in the process. Results show that mass transfer rate enhancement depends on the kinds and the concentration of nanoparticles and the modes of flow. It was observed that after adding nanoparticles, the mass transfer rate significantly increases up to two-fold for ZnO nanoparticles. Furthermore, the results indicate that under the circumstances in which the mass flow rate is high enough, the effect of nanoparticles on the mass transfer phenomenon is too slight.     

Review of titania nanotubes: Fabrication and cellular response

Titania (TiO₂) nanotube is gaining prominence as an implantation material due to its unique properties such as high specific surface area and the ability to exhibit positive cellular response. In this paper, we briefly review the current state of fabrication methods to synthesize nanotubular TiO₂ surface topography, and discuss its effect on cellular response of different cells in terms of cell adhesion, proliferation and differentiation. In vitro and in vivo studies by using TiO₂ nanotubes are also presented establishing the potential of nanotubes in biomedical applications. Finally, an outlook of future growth of research in TiO₂ nanostructures beyond the nanotubes is provided     

Removal of Diazinon from aqueous solution by electrocoagulation process using aluminum electrodes

Electrocoagulation (EC) is an electrochemical method to treat polluted wastewaters and aqueous solutions. In this paper, the removal of Diazinon was studied by EC on aluminum electrode. The effect of several parameters such as initial concentration of Diazinon, current density, solution conductivity, effect of pH, and electrolysis time were investigated on EC performance. The obtained results showed that the removal efficiency of EC depends on the current density, initial concentration of Diazinon and electrolysis time. The optimum pH is 3 and also the solution conductivity has no significant effect on removal efficiency.