N. M. Spyrou

A critical study of the open-ended coaxial line sensor technique for RF and microwave complex permittivity measurements

An HP 8510 automatic network analyser and a six-port reflectometer have been used with a purpose-built calculable open-ended coaxial line sensor to measure the reflection coefficients of various materials, including dielectric reference liquids, in the frequency range 50 MHz-2.0 GHz. Factors crucial for calculable measurements have been identified including associated measurement uncertainties. The reference material measurements have been used in critical studies of: a commonly employed lumped equivalent circuit model of the fringing fields of the sensor; and a numerical point-matching theory of the propagating and evanescent modes, at the termination of the sensor. It is concluded that the inverse point-matching theory should enable a more widespread and accurate exploitation of the sensor technique for various applications including those in biomedicine and industrial quality control.

Correction for scatter in 3D brain PET using a dual energy window method

A method for scatter correction using dual energy window acquisition has been developed and implemented on data collected with a brain-PET tomograph operated in the septa retracted, 3D mode. Coincidence events are assigned to (i) an upper energy window where both photons deposit energy between 380 keV and 850 keV or (ii) a lower energy window where one or both photons deposit within 200 keV and 380 keV. Scaling parameters are derived from measurements of the ratios of counts from line sources due to scattered and unscattered events in the two energy windows in head-sized phantoms. A scaled subtraction of the two energy windows produces a distribution of scatter which is smoothed prior to subtraction from the upper energy window. In phantoms, the correction was found to restore the uniformity, contrast and linearity of activity concentration. Relative activity concentrations were restored to within 7% of their true values in a multicompartment phantom. The method was found to provide accurate correction for scattered events arising from activity outside the direct detector field of view. In a three-compartment phantom containing water, 18F and 11C scanned in dynamic, multiframe mode, the half-lives of the two isotopes were restored to within 2% of their true value.

No effect of glucagon-like peptide-1 on short-term satiety and energy intake in man

Centrally administered glucagon-like peptide-1 (GLP-1) inhibits feeding in fasted rats, but its role in human satiety has been largely unexplored. The present study investigated the effect of peripheral GLP-1 infusion on gastric emptying and satiety in man. Ten non-obese male subjects were infused in a randomized single-blind within-subject crossover study using saline infusion as control. They received either a GLP-1 infusion (1.2 pmol/kg per min) or a saline infusion for 1 h, at 18.00 hours. At 20 min after starting the infusion the gastric emptying of a 400 ml water load was measured. Subjects completed behavioural self-rating scales to assess hunger and satiety. After 40 min subjects were given a buffet meal ad libitum and their food intake was recorded. GLP-1 infusion raised circulating GLP-1 concentrations to approximately twice those seen following a meal. It did not affect circulating insulin levels but caused a small fall in glucose levels. Gastric emptying of the water load was significantly delayed by the GLP-1 infusion. Energy intake from the buffet was unaffected by GLP-1 infusion. Self-assessment of hunger and satiety was similarly unaffected by the infusion before the buffet meal, although subjects tended to be less hungry after the buffet meal following GLP-1 infusion (P < 0.09). GLP-1 infusion delayed gastric emptying but had a minimal effect on food intake and satiety. This study casts doubts on whether GLP-1 is a major satiety factor in man, although a raised circulating plasma glucose level, as would normally occur postprandially, might be necessary for GLP-1 to increase satiety.

In vivo dielectric properties of human skin from 50 MHz to 2.0 GHz

The authors report in vivo complex permittivity measurements of human skin using the open-ended coaxial line sensor technique. The results indicate that considerable differences exist between the skin complex permittivities obtained from different regions of the body. The in vivo dielectric properties of skin are found to depend for reproducibility upon the pressure and length of time of sensor application. Variations between individuals could also be significant. The potential biomedical uses of this technique are briefly discussed.

Trace elements in drinking and groundwater samples in southern Nigeria.

The levels of Al, Sn, Cs, Rb, Sr, Br, Cr, Mo, Co, Ba, Cu, Zn, Cd, Pb, Mn, Se, As, V and Ni were determined in drinking water supplies (public taps, domestic taps and treated water from public water sources) and groundwater supplies (boreholes and shallow wells) in some parts of Southern Nigeria. The water samples were analysed using inductively coupled plasma mass-spectrometry (ICP-MS). The mean levels (microgram/l) of all the elements ranged between 0.35 microgram/l for Cs and 87.3 micrograms/l for Zn in the drinking waters and between 0.54 microgram/l for Co and 420.3 micrograms/l for Ba in the groundwaters. A comparison of the elemental concentrations with WHO guidelines showed that with the exception of violations of Cd, Cr and Se limits in some of the drinking water samples, the levels of all the other elements investigated were below the WHO maximum allowable concentrations.

Traffic pollution: preliminary elemental characterisation of roadside dust in Lagos, Nigeria

Roadside dust collected from different parts of Lagos metropolis were analysed for heavy metals and other trace elements using a combination of instrumental neutron activation analysis (INAA), inductively coupled plasma-optical emission spectrometry (ICP-OES), and flame atomic absorption spectrometry (FAAS). The results show a positive correlation of the concentration of Pb and some other vehicular emission-related elements with the traffic density. Automotive emission was also found to be the main contributor to Pb concentration in the roadside dust but some elements which hitherto have been linked with automotive emission, such as cadmium and nickel, did not show any strong correlation with traffic density.

The atmospheric deposition of major, minor and trace elements within and around three cement factories

Total atmospheric deposits of particulate matter within the premises of three Nigerian cement factories were collected and characterised for about 25 elements using a combination of Energy Dispersive X-ray Fluorescence Spectrometry (EDXRF) and Instrumental Neutron Activation Analysis (NAA). Some toxic heavy metals like As, Pb, Ni, Co, Zn, Cu, Cr, as well as S, Ca, P were found to be highly enriched in the neighbourhood compared to the control sites. Deposition rates of the cement marker element, Ca, decreased exponentially with increasing distance from the factories.

Cyclic activation analysis—A review

The setting of cyclic activation and its development in a historical context is attempted and a case is made for the usefulness of the method in the analysis of materials via short-lived isotopes. The theory of cyclic activation analysis is presented and the resulting detection limits shown to be superior to the conventional one-shot irradiation-counting sequence. The possibility of determining the half-life of an isotope from the data accumulated in the same experiment is also highlighted. Problems and applications are illustrated by experimental results obtained from a variety of sample matrices, mainly biological and environmental, with the use of a reactor irradiation facility, since the use of both isotopic neutron sources and neutron generators are discussed elsewhere. It should therefore be viewed as a personal and selective review of the field. Epithermal cyclic neutron activation analysis is suggested as an area demanding consideration and a new cyclic activation system is introduced.

Microstructural simulation and imaging of granular flows in two- and three-dimensional hoppers

Abstract Distinct element simulations of granular flows in two- and three-dimensional hoppers are compared with imaging data from conventional photography and gamma-ray tomography where information of the order of the particle size can be extracted. A novel feature of these comparisons is that both particle and vessel dimensions are matched exactly between the experiments and the computer simulations, thereby leaving little scope for speculation regarding śscale effects’ which are often used to justify scepticism over the validity of simulation predictions. Another novel feature of the work is that quantitative comparisons are provided during the entire period of filling and discharge events rather than selecting an arbitrary ‘snapshot’ in time, as is often the case in such simulation studies. Microstructural inspection of two-dimensional photographs of systems with large disc particles provides quantitative information which shows good agreement with simulation in terms of packing height, static and flowing voidage, stagnant/flow boundaries in funnel flow and heap/repose angles. Three-dimensional solids fraction data from packed beds of 7 mm diameter maple peas obtained by transmission gamma-ray tomography show encouraging agreement with simulation. An important result of these investigations is the degree of correlation between the flowing voidage and flow velocity of particles which are individually both affected by variations in particle size and shape but are mutually compensating in their effects on the simulated and measured discharge rates. In general, the simulations produce a less dilated assembly moving at smaller velocities.

Neutron activation studies of trace elements in tree rings

The levels of twelve elements most of which are either considered essential to plant growth or have been detected in air filter samples in an air pollution survey, have been monitored in three transverse sections of trees, two elms (ring porous trees) and one cedar (a conifer). Two dimensional distributions of these elements around the tree rings of the section and radially from ring to ring, have been obtained to see if tree rings can be analysed for use as a record of historical pollution.