Experimental parameters affecting hypercoulometric response in gas-phase coulometry

The response of an electron-capture detector designed for coulometric response was examined as a function of solute, pulse interval, carrier-gas type, solute amount, carrier-gas flow rate, and chromatographic-peak profile. For CCl3F, it was shown that the average numbers of electrons absorbed per molecule ranged from 1.0 to 4.1, varying primarily with pulse interval but also displaying a complex dependence on sample amount. Comparison of these results with theoretical expectations leads to the conclusion that a 1:1 "coulometric response" may not be observed under certain operating conditions. Because the specific conditions required depend on many variables, including, to some extent, sample amount, true coulometric operation of an electron-capture detector is difficult to establish and maintain. Effects which may contribute to the production of hypercoulometric response are critically discussed.     

Influence of loading rate on bond behaviour of reinforcing steel and prestressing strands

Pull-out tests with short embedment length were carried out within a wide range of loading rates. The highest loading rate which could be achieved on a Split-Hopkinson-bar equipment was about 500,000 times the loading rate in a static test. The test variables were the steel type, the concrete quality and the loading rates. It turned out that plain reinforcing bars and prestressing strands were insensitive to variations in the loading rate, whereas deformed bars showed a significantly higher bond resistance with increasing loading rate. This influence is more pronounced according as the concrete quality is lower and the bar displacements are smaller. An explanation of the phenomena is suggested.     

Experimental studies of the biological response to a new bone cement

As part of the assessment of the biological properties of a new bone cement (London Hospital cement) which contains poly(ethylmethacrylate) and n-butylmethacrylate, the monomer (n-butylmethacrylate) has been compared in toxicity studies with methylmethacrylate monomer, as used in conventional bone cement. N-butylmethacrylate monomer had an LD₅₀ of 1.0 to 1.2 ml kg^–1 and was therefore only slightly more toxic than methylmethacrylate monomer (LD₅₀ 1.2 ml kg^–1) when injected intraperitoneally into mice. It did not have any more significant cardiorespiratory depressive effect on intravenous infusion into rabbits, either in single or cumulative doses, when compared with methyl monomer (repeated infusions in 12 rabbits). Both monomers caused a transient bradycardia, tachypnoea, raised central venous pressure and arterial hypotension in low doses with rapid recovery, though the effects were sustained at higher cumulative doses of 60 mg kg^–1 and above. These results demonstrate that n-butylmethacrylate monomer does not differ significantly in toxicity from the monomer used in conventional cement and can therefore be used as a component in the new material.     

On the parameters influencing the deposition of polystyrene colloidal crystals

Colloidal crystals of polystyrene particles of 1.0, 1.4 and 2.8 μm diameter have been prepared by vertical deposition. The influence of parameters such as temperature, particle size and concentration as well as dispersion medium has been studied. The size of domain and the crystalline structure of the particle arrays have been analyzed by optical microscopy. The quality of the crystals has been improved (minimizing cracks) by controlling sedimentation (density matching), evaporation (volatility of the medium) and drying (co-solvents).     

Comparative study of the parameters influencing the machinability of leaded brasses

One of the main applications of brasses is the manufacture of fluid carrying systems. The shape of the final product is usually made by means of machining the rolled or extruded standard bars, so that effective and low cost machining operations are required. Leaded brasses are extensively used when a good machinability is required.Two leaded brasses bars (CuZn39Pb3 alloy) with the same geometry but with different behaviour in saw cutting operations have been characterized in this work. Chemical composition, mechanical and microstructural properties have been studied in order to clarify the observed differences during saw cutting machining.Significant differences have been found with respect to the size and distribution of lead globules and phase volume fractions (α + β′), that have been explained due to the existence of different solidification and cooling patterns in both products; being the lead distribution the most important characteristic relative to the leaded brass cutting performance.     

Experimental analysis on bond between PBO-FRCM strengthening materials and concrete

The effectiveness of externally bonded strengthening for reinforced concrete (RC) elements strongly depends on the bond between the strengthening material and the concrete and on the mechanical properties of the concrete cover. In this paper the bond between fiber reinforced cementitious matrix (FRCM) materials made out of a poliparafenilenbenzobisoxazole (PBO) net embedded in a cement based matrix and the concrete is experimentally analyzed. Experimental results of double shear tests involving different bond lengths and fibers cross sections are presented. The results allow to estimate the effective anchorage length and evidence that the debonding occurs at the fibers/matrix interface after a considerable fibers/matrix slip. They also confirms the effectiveness of the FRCM materials as external reinforcements for concrete. The obtained experimental results can be used to calibrate a local bond-slip relation to be used in the design of the external reinforcement.     

An evaluation of some additional factors influencing the effectiveness of warning letters

The primary objectives of the study were to determine the effectiveness of two types of warning letters and an informational pamphlet in reducing the subsequent collision and conviction records of pre-negligent drivers. An additional study objective was to determine the effectiveness of a follow-up reinforcement letter sent to collision and conviction free drivers. The results six months subsequent to treatment showed no significant treatment effects on convictions, but a positive pamphlet effect on collisions. The follow-up reinforcement analysis for collision and conviction free drivers showed no significant treatment effects on collisions. On convictions, however, there was a main effect attributable to type of warning letter as well as an interaction between type of warning letter, pamphlet condition, and follow-up reinforcement. No treatment conditions were significantly influenced by subject characteristics.     

Experimental studies of the fibre pull-out problem

The fibre pull-out problem was studied experimentally using a method which enabled direct measurement of the energy release rate of de-bond and also observation of the fracture process involved. Preliminary test results indicated that the process was a twostage one, with de-bond initiating at the fibre tip, followed later by de-bond initiating at the free surface end. If a flaw of sufficient size was present then a stage-two de-bond would occur. Results showed reasonable agreement between experimental results and computer measurements.     

On the in-plane shear response of the high bond strength concrete masonry walls

Conventional unreinforced masonry walls subject to in-plane shear loading fail due to exceedance of shear and tensile bond strengths. This paper examines whether or not the in-plane shear capacity of masonry walls would increase with the increase in the bond strengths through experimental and numerical investigations. For these investigations, shear walls were built with high bond strength polymer cement mortar; they were applied in thin layers of 2 mm thickness each. Material tests were carried out to characterise the bond and the compressive strengths of the high bond strength thin layer mortared masonry; the bond strengths were found approximately double that of the conventional 10 mm thick cement mortars. The shear walls, however, exhibited significantly lower capacity (contrasting the expectation) and displayed base course sliding mode of failure. To ascertain the validity of the experimental results, a combined surface contact—interface element micro finite element (FE) modelling technique was formulated; the results adequately reproduced the experimental datasets. The validated FE model was then applied to examine the effect of the aspect ratios and pre-compression levels to the failure modes, deformation and strength of the high bond strength shear walls and is shown that once the pre-compression exceeds 15% of the masonry compressive strength, the base sliding failure mode changes to the diagonal cracking mode with corresponding increase in in-plane shear capacity. Therefore, it is concluded that the increase the bond strength without regard to pre-compression could adversely affect the safety of the high bond strength unreinforced masonry shear walls.     

Identification of design parameters influencing manufacture and properties of cold-bonded pond ash aggregate

This paper explores the feasibility and the process of converting of pond ashes – a waste material into artificial aggregates – a value added product. As a first step, identification of the parameters influencing manufacture and properties of artificial aggregate with pond ash has been carried out. Pond ash of both bituminous and lignite type have been chosen to make aggregate through pelletization and cold-bonding. The parameters identified are moisture content, binder dosage, pelletization enhancer and strength enhancer dosage. The range of parameters are varied and the designed experimental runs are carried out by adopting statistical technique known as central composite design of Response Surface Methodology. The physical properties of aggregate like bulk density, water absorption and open porosity and the strength property of aggregate represented through 10% fines value have been determined for the influence of parameters thus identified. Microstructure and phase composition of aggregate are represented by SEM and XRD respectively. Ordinary Portland cement, locally available hydrated lime, and hardening admixture are used as binders at varying amounts from 10% to 20% by weight. Calcium hydroxide and sodium sulphate are used as pelletization and strength enhancing admixture respectively. It is observed that the dosage of binder, strength and pelletization enhancing admixture improved the properties of aggregate. The results indicated, potentially exposes a new avenue to convert pond ash – a waste material into a value added product.     

Structural and constitutional studies of some cerium-praseodymium alloys

Room temperature X-ray diffraction studies on some powdered Ce-Pr alloys indicate that the face-centred-cubic (f c c) structure extends from 0 to 65% Pr and the double hexagonal (d h c p) structure from 66 to 100% Pr, after a heat treatment of 600° C for 2 h and quickly cooling to room temperature. Variations of atomic volume with composition in both ranges indicate that the volume difference between the f c c form of praseodymium and the d h c p form is similar to that observed for (d h c p) and (f c c) lanthanum, whereas extrapolation to 100% Ce from the d h c p range gave an atomic volume for the d h c p Ce appreciably in excess of the atomic volume of f c c -Ce. This volume expansion is consistent with a slight change of the effective valency of the cerium atoms in the d h c p solid solutions when compared with the -Ce but there is uncertainty as to the precise atomic volume of d h c p -Ce. The DTA studies indicate a narrow liquidus/solidus separation and the electrical resistivity and DTA measurements indicate a regular change with composition in the transition temperature of the high temperature b c c phase. For the d h c pf c c transition there is a marked variation in the width of the hysteresis loop across the Ce-Pr system which can be correlated with the degree of plastic deformation involved in the transformation. There is a marked increase in the slope of the transition temperature with composition for the Pr-rich alloys and no such transition is observed for the praseodymium samples after one heating cycle. A possible d h c pfc c transition, however, is indicated by the DTA traces of the commercially pure praseodymium sample on cycling with temperature and this has been attributed to the influence of interstitial impurities.This praseodymium was kindly loaned by Dr D. Fort of the Centre of Materials Science, University of Birmingham, and the metal had been purified by solid state electrolysis to give a resistance ratio of 200.     

Structural and dielectric studies of some niobate-titanate systems

Ferroelectric ceramics of the general formulax (Li_1/2 La_1/2 TiO₃) (1−x) (LiNbO₃) have been found to have tungsten bronze (TTB) and ilmenite type structure in the ranges 0·8≤x≤1·0 and 0≤x≤0·2 respectively. The system is biphasic in the other ranges. All single phase materials exhibit dielectric anomalies in the temperature range 300–600 K. The high dielectric constant of the TTB phase is explained as due to the existence of localised rotational excitons arising from a large number of defect structural units and their coupling with one of the low frequency lattice modes. Information about the lattice modes to which the rotational excitons are coupled has been obtained from Raman spectra. Deceased     

Experimental and theoretical studies of palygorskite clays

We have studied the structure and properties of palygorskite clays. A structure analysis was performed using two different models to reproduce the monoclinic and orthorhombic lattices, using the atomic positions and cell parameters of palygorskite structure suggested by several authors, we simulated structures using Molecular Dynamics and Quantum Mechanics. Modifications on the structure and elemental atom changes were made to obtain more stable configurations. X-ray diffraction patterns and high resolution electron microscopy images from simulated structures were compared with experimental results. It could be observed that orthorhombic model shows a better fitting than monoclinic models. These results might help to understand many of the properties of archaeological pigments, such as, Maya Blue, in which palygorskite clay was the main component.     

Experimental estimation of the measurement unit of electromagnetic field parameters

Translated from Izmeritel'naya Tekhnika, No. 7, pp. 38–39, July, 1990.     

Experimental and analytical studies in crack initiation under fatigue: Part I — Experimental studies

Mechanistic investigations of damage evolution before crack initiation in an amorphous polymer show that damage consists of a core of highly dense crazing and a peripheral less dense zone of crazing. Damage characterization is carried out at consecutive configurations of the damage zone. Analysis of the kinematics of damage at different times involves comparisons of the inertia moments of damage distributions. The results indicate that damage evolution between consecutive configurations can be approximated by a linear transformation of the space variables. Thus, the process of damage growth can be described by translation and deformation of the damage zone. The growth rates of the damage zone movements decrease until crack initiation. In all cases, the average densities exhibit a damping type behavior with the number of cycles. The crack initiates within a core zone immediately ahead of the stress concentrator. The experimental results suggest that damage density within the core zone is independent of the loading conditions considered herein. This value is approximately equal to the damage density around the crack tip during slow crack propagation. The crack length at initiation is found to increase exponentially with the stress level. A simple decaying exponential relationship relates the crack initiation times and the applied stress level. This result is consistent with the fracture models based on absolute reaction theories.