Dynamic hardness measurements using a dropped ball: with application to 1018 steel

A practical method for measuring the hardness of metals at high strain rates (>10³ s⁻¹), using a dropped ball, is developed and demonstrated on cold-rolled plain carbon (1018) steel. The metal is assumed to be one-dimensional and rigid plastic. By formulating the problem in terms of the lateral, rather than the depth, dimensions of the indentation, the dynamic hardness can be obtained at load, obviating the need for rebound energy corrections. In addition, the Tabor strain equation relating to equivalent unidirectional compression is derived, and methods are also derived to include “piling-up” around indentations for plastic flow at constant volume. A previously unrecognized phenomenon that can occur in projectile indentation of metals, “ballistic strain softening”, is described. It is related to the fact that the dynamic hardness obtained by this test is a function of the ball radius times the strain rate divided by the strain. As a result, comparison of the dropped ball test flow stress data with those of constant strain rate tests requires a transform of the Tabor strain and strain rate data to constant strain rate conditions. When this is done, the dynamic yield stress data that are determined as a function of the effective strain rates agree with comparable published data for mild steel obtained using more conventional tests. The results also show that there is greatly enhanced strain hardening in irons and steels above a critical strain rate, which increases with purity. A dislocation model is used to explain this increase in terms of an additional dislocation generation mechanism coming into play.     

Evaluating the use of tricationic reagents for the detection of doubly charged anions in the positive mode by ESI-MS

The analysis of anions remains an important task for many areas of science, and new sensitive analytical methods continue to be of great interest. In this study, we present the use of 17 tricationic reagents for use as gas-phase ion pairing agents for divalent anions. When the anion pairs with the tricationic reagent, an overall positive charge is retained and enables detection by ESI-MS in the positive mode. The 17 tricationic reagents were made from 1 of 4 core structures and 7 terminal charged groups. The effect of these structural elements on the detection sensitivity of the complex is examined empirically. A comparison of signal-to-noise ratios achieved in positive and negative modes also is presented.     

Measuring and modelling air mass flow rate in the injection stretch blow moulding process

The injection stretch blow moulding process involves the inflation and stretching of a hot preform into a mould to form bottles. A critical process variable and an essential input for process simulations is the rate of pressure increase within the preform during forming, which is regulated by an air flow restrictor valve. The paper describes a set of experiments for measuring the air flow rate within an industrial ISBM machine and the subsequent modelling of it with the FEA package ABAQUS. Two rigid containers were inserted into a Sidel SBO1 blow moulding machine and subjected to different supply pressures and air flow restrictor settings. The pressure and air temperature were recorded for each experiment enabling the mass flow rate of air to be determined along with an important machine characteristic known as the ‘dead volume’. The experimental setup was simulated within the commercial FEA package ABAQUS/Explicit using a combination of structural, fluid and fluid link elements that idealize the air flowing through an orifice behaving as an ideal gas under isothermal conditions. Results between experiment and simulation are compared and show a good correlation.     

Sensitive gas chromatographic-high resolution mass spectrometric method for the determination of methylmalonic acid in bovine plasma

A sensitive and highly specific method for the determination of methylmalonic acid (MMA) in bovine plasma is described. Following solvent extraction and butylation, samples are analysed by gas chromatography and detected using high-resolution mass spectrometry. The limit of detection for the assay was 0.025 mumol l-1 MMA and the recovery of added MMA ranged from 98 to 103%. The application of the method is demonstrated for the analysis of MMA in plasma taken from cattle that had been maintained on a cobalt-deficient diet for 64 weeks.     

Simultaneous determination of mycophenolic acid and its glucuronide in human plasma using a simple high-performance liquid chromatography procedure

We describe a reversed-phase HPLC method for determination of total mycophenolic acid (MPA), its free concentration (MPAf), and the glucuronide metabolite (MPAG), based on simple sample preparation and gradient elution chromatography. The compounds were quantified in parallel by absorbance at 254 nm and 215 nm in the internal standard mode. Linearity was verified up to 50 mg/L for MPA and up to 500 mg/L for MPAG (r >0.999). Detection limits at 215 and 254 nm were, respectively, 0.01 and 0.03 mg/L for MPA, and 0.03 and 0.1 mg/L for MPAG. The recovery of MPA was 95-106%; recovery of MPAG was 96-106%. The imprecision (CV) for MPA (0.2-25 mg/L) was <8.4% (254 nm) and <4.4% (215 nm) within day (n = 12) and <9.2% (254 nm) and <6.2% (215 nm) between days (n = 12). The imprecision for MPAG (10-250 mg/L) was <4.9% (254 nm) and <3.4% (215 nm) within day, and <6.1% (254 nm) and <5.9% (215 nm) between days. For quantification of MPAf, 100 microL of ultrafiltrate was applied directly to the column. The detection limit was 0.005 mg/L at 215 nm and 0.015 mg/L at 254 nm. In the range between 18-210 microg/L, the within-day CVs were <11.8% (n = 12) and the between-day CVs were <15.8% (n = 12).     

Chromosomal localization of angiotensin II type 1 receptor isoforms in the rat

The cDNA sequences of two different isoforms of the rat angiotensin II type 1 receptors, AT1A and AT1B, have been reported. A single set of polymerase chain reaction primers was used to amplify sequence from both AT1A and AT1B from rat genomic DNA. Genomic DNA from a panel of rat x mouse somatic hybrid cell lines which had been characterized as to the rat chromosomal content was then amplified with these primers. The amplified products from rat AT1A and AT1B were distinguished from each other and those of the mouse by the use of differential restriction patterns. Using this method, AT1A was localized to rat chromosome 17 and AT1B to rat chromosome 2.     

Balloon catheter systems for PTCA: the importance of the catheter length

This complex study was designed to measure the transport and excretion characteristics of gadolinium ethoxybenzyl diethylenetriaminepentacetic acid (Gd-EOB-DTPA) in dog's livers following bolus and infusion. Simultaneous T1 magnetic resonance imaging was performed to measure maximum signal enhancement. Anaesthetized dogs had cannulation of the common bile duct and urinary bladder for collections and cannulation of the femoral artery and vein for monitoring, blood sampling and infusion. Gd-EOB-DTPA was administered by bolus (range 12.5-200 mumol/kg) and infusion (range 0.4-6.4 mumol/min per kg). An hepatic transport maximum 0.09-0.15 mumol/min/kg was achieved with a blood concentration of 0.03-0.06 mumol/mL. Marked hepatic affinity for Gd-EOB-DTPA was demonstrated with measurements of liver concentration. Maximum T1 signal enhancement was achieved with blood Gd-EOB-DTPA concentration of 0.02-0.03 mumol/mL and a liver concentration of 1-2 mumol/g. The transport maximum for Gd-EOB-DTPA in the dog was similar to that for ipodate and iodipamide and effective imaging was achieved with sub-maximal doses. The maximum signal enhancement at blood concentrations less than required for maximum transport suggest a wide latitude for effective clinical imaging.