Recent Northern Hemisphere stratospheric HCl increase due to atmospheric circulation changes.

The abundance of chlorine in the Earth's atmosphere increased considerably during the 1970s to 1990s, following large emissions of anthropogenic long-lived chlorine-containing source gases, notably the chlorofluorocarbons. The chemical inertness of chlorofluorocarbons allows their transport and mixing throughout the troposphere on a global scale, before they reach the stratosphere where they release chlorine atoms that cause ozone depletion. The large ozone loss over Antarctica was the key observation that stimulated the definition and signing in 1987 of the Montreal Protocol, an international treaty establishing a schedule to reduce the production of the major chlorine- and bromine-containing halocarbons. Owing to its implementation, the near-surface total chlorine concentration showed a maximum in 1993, followed by a decrease of half a per cent to one per cent per year, in line with expectations. Remote-sensing data have revealed a peak in stratospheric chlorine after 1996, then a decrease of close to one per cent per year, in agreement with the surface observations of the chlorine source gases and model calculations. Here we present ground-based and satellite data that show a recent and significant increase, at the 2σ level, in hydrogen chloride (HCl), the main stratospheric chlorine reservoir, starting around 2007 in the lower stratosphere of the Northern Hemisphere, in contrast with the ongoing monotonic decrease of near-surface source gases. Using model simulations, we attribute this trend anomaly to a slowdown in the Northern Hemisphere atmospheric circulation, occurring over several consecutive years, transporting more aged air to the lower stratosphere, and characterized by a larger relative conversion of source gases to HCl. This short-term dynamical variability will also affect other stratospheric tracers and needs to be accounted for when studying the evolution of the stratospheric ozone layer.

Cryopreservation and plant regeneration from somatic embryos of Pinus patula.

Embryogenic tissue of Pinus patula Scheide et Deppe was cryopreserved for 8 weeks using sorbitol and dimethylsulfoxide (DMSO) as cryoprotectants. Results indicate that 0.3 M sorbitol and 5% DMSO had the best cryoprotecting effect. The recovered tissue initially underwent a lag phase but then continued to proliferate normally on MSG3 maintenance medium. Recovered tissue was placed onto MSG5 maturation medium, and embryos were isolated and germinated. Plantlet regeneration from the recovered tissue was achieved.

Vibration analysis in the detection of total hip prosthetic loosening.

This present paper reports on experiments which seek to obtain evidence of the usefulness of vibration in the diagnosis of implant loosening by utilizing extra information by considering the amplitude response at all frequencies (within a certain range) as well as spectral analysis of particular waveforms. This frequency response is essentially a study of the manner in which the amplitude of vibration of a system varies as the frequency of an input force of fixed amplitude is varied. The experimental technique involved the application of a sinusoidal force to the distal end of a femur containing an implanted prosthesis and collecting the output signal using an accelerometer placed at the proximal end. The output signal was stored on a computer with a digital signal processing board and subsequently analysed using the two signal processing techniques mentioned above. Data were collected when the implanted prosthesis was secure, and at various stages of loosening. Analysis of these data shows that prosthetic instability can be detected using both modalities of vibration analysis.

The design of an optical fiber pressure transducer for use in the upper airways.

The development of an optical fiber transducer for use in biomedical applications has been presented. The design was targeted for use in the upper airways of patients with sleep disorders stemming from partial or total occlusion of the airway. The transducer's preliminary specification was suited for that of upper airway manometry: a resolution of 10 Pa over the range +/- 5 kPa, a single transducer being less than 0.94 mm in diameter. Amplitude modulated optical fiber sensors are susceptible to loss due to bending of the fiber core and cladding. The design of the transducer uses a series of three optical fibers, one emitting and two receiving, the combination of the two receiving optical fibers is used to reduce effects of light loss: a bend radius of 50 mm is typical for the insertion into the naso-pharynx. The transducer transduction element is a silicone gel coated with reflective titanium dioxide, the meniscus deforms under pressure and modulates the intensity of light reflected back into the receiving optical fibers. The main disadvantage of optical fiber pressure transducers is their susceptibility to temperature drift. Temperature in the airway rarely changes more than 17 degrees C. The frequency of breathing and the high thermal mass of the catheter means that temperature drift in this application is not significant, and will cause an insignificant error of 12 Pa. The transducer is inexpensive to produce, and may be deemed disposable: approximately $20 in material costs (using current manufacturing techniques this can be halved). The system has the added advantage of being electrically, magnetically, and chemically passive. The potential for miniaturization is limited only by the mechanical strength of the optical fibers as mechanical problems associated with fragile elastic membranes do not apply.

Loosening of total hip arthroplasty. Diagnosis by vibration analysis.

The early diagnosis of aseptic loosening of a total hip replacement by plain radiography, scintigraphy and arthrography has been shown to be unreliable. It has been suggested that it may be possible to distinguish between a secure and a loose prosthesis using a vibration technique. We have assessed the use of this technique in vitro using models of early and late loosening. Late loosening with an unstable prosthesis can be reliably detected by vibration analysis, but this method was shown to have a very poor diagnostic sensitivity in early loosening when there is no obvious prosthetic instability.

New signal processing techniques for the decomposition of EMG signals.

This paper relates to the use of knowledge-based signal processing techniques in the decomposition of EMG signals. The aim of the research is to automatically decompose EMG signals recorded at force levels up to 20 per cent maximum voluntary contraction (MVC) into their constituent motor unit action potentials (MUAPS), and to display the MUAP shapes and firing times for the clinician. This requires the classification of nonoverlapping MUAPs and superimposed waveforms formed from overlapping MUAPs in the signal. Nonoverlapping MUAPs are classified using a statistical pattern-recognition method. The decomposition of superimposed waveforms uses a combination of procedural and knowledge-based methods. The decomposition method was tested on real and simulated EMG data recorded at force levels up to 20 per cent MVC. The different EMG signals contained up to six motor units (MUs). The new decomposition program classifies the total number of MUAP firings in an EMG signal with an accuracy always greater than 95 per cent. The decomposition program takes about 15s to classify all nonoverlapping MUAPs in EMG signal of length 1.0s and, on average, an extra 9s to classify each superimposed waveform.

Selective noninvasive electrode to study myoelectric signals.

The paper describes the design and construction of a selective surface electrode for use in a clinical environment. The main criterion of the design was to enable the recognition of individual motor unit action potential trains (MUAPTs) at moderate force levels. The main features of the electrode are, first, a small concentric bipolar arrangement to avoid electrode/muscle fibre alignment problems and to allow measurements within a small, well defined probed volume; secondly, the non-requirement for conducting paste or gel; and thirdly, the casing acting as an earth plate. All of these simplify its use. The results of tests undertaken with the electrode showed that it was able to pick up individual MUAPTs at up to 20 per cent of maximum voluntary contraction from the first dorsal interosseous muscle. Tests were carried out on the small hand muscles to further demonstrate the usefulness of the electrode. A computer program was written to calculate the shift in frequency of the power spectrum of the recorded myoelectric signal with muscle fatigue and hence indirectly to demonstrate the ability of the electrode to detect the reduction in muscle fibre conduction velocity.

Hydraulic input impedance measurements in physical models of the arterial wall.

A white noise method was used to measure the hydraulic input impedance and transmission characteristics in physical models of an arterial system made of single, unbranched latex tubes. The experimentally obtained impedance curves show a rise in modulus and a positive phase at high frequencies in the absence of wave reflections. Using the impedance moduli in the presence of wave reflections, wave velocity and attenuation were calculated. The influence of wall nonlinearity on hydraulic impedance was also examined. It is concluded that, in the model used neither wave reflections nor wall nonlinearity can account for the deviations of the experimental impedance curves from the theoretically predicted ones. Impedance moduli in the presence of reflections may be used to study transmission characteristics (wave velocity and attenuation) of the model.

Covariance density estimation for autoregressive spectral modelling of point processes.

The use of autoregressive modelling has acquired great importance in time series analysis and in principle it may also be applicable in the spectral analysis of point processes with similar advantages over the nonparametric approach. Most of the methods used for autoregressive spectral analysis require positive semidefinite estimates for the covariance function, while current methods for the estimation of the covariance density function of a point process given a realization over the interval [0, T] do not guarantee a positive semidefinite estimate. This paper discusses methods for the estimation of the covariance density and conditional intensity function of point processes and present alternative computational efficient estimation algorithms leading always to positive semidefinite estimates, therefore adequate for autoregressive spectral analysis. Autoregressive spectral modelling of point processes from Yule-Walker type equations and Levinson recursion combined with the minimum AIC or CAT principle is illustrated with neurobiological data.

Frequency response of the arterial wall.

The high frequency response of human common iliac arterial segments in vitro was investigated. It was found that at those high frequencies the response resembles that of a second order underdamped system. However, to stimulate the arterial response throughout the frequency range, a higher order model is required. A fifth order system appears to describe the observed behaviour in a satisfactory way between 0.02 and 200 Hz.

Circumferential and longitudinal viscoelasticity of human iliac arterial segments in vitro.

A random noise technique was used to measure the circumferential and longitudinal dynamic elasticity of human common iliac arteries in vitro. For circumferential measurements the frequency ranged from 0.016 to 20 Hz; the phase lag of diameter behind pressure was found to be almost constant (about 5 degrees) and the Young's modulus of elasticity to increase rapidly at first and then more gradually beyond 1-2 Hz. Somewhat similar results were obtained for longitudinal elasticity. Arterial segments were found to be anisotropic when kept at in vivo length and under normal distending pressure.

Arterial system configuration and wave reflection.

On the assumption that the arterial segments between branching points are cylindrical, the relationship between total arterial cross-sectional area and the distance from the heart for the entire length of the arterial system is derived. Based on this relationship, a model of the whole arterial system is proposed; it is composed of three tubes of common origin and of unequal lengths and cross-sectional areas. This model may be useful for simulation purposes, with particular reference to pulse wave reflections.

Physical modelling of the arterial wall. Part 2: Simulation of the non-linear elasticity of the arterial wall.

In part 1 it was established that the elasticity of tubes made from natural rubber is, at low pressures, close to that of the arterial wall; in this part a method is described for reinforcing the walls of rubber tubes so that they may be used for simulating arterial elasticity at higher pressures. The technique is versatile in that, within reasonable limits, wall non-linearity can be modified; tubes with non-linear wall elasticity were produced and tested. A modification of the method enabled us to produce geometrically non-uniform rubber tubes which may be useful in the construction of physical models of the arterial system.

Physical modelling of the arterial wall. Part 1: Testing of tubes of various materials.

Tubes of various elastic materials were tested using a purpose-built apparatus to select those most appropriate for physical simulation of the arterial wall. The influences of temperature and longitudinal stress were measured in selected tubes. It was found that the static elasticity of latex tubes is close to that of the arterial wall for intraluminal pressures corresponding to the lower range of intra-arterial pressures.

Photoelectric transducer for measuring the length and diameter of elastic vessels.

This photoelectric transducer was developed to measure diameter and length variations in arterial segments in vitro and in elastic tubes. Its construction is simple, its nonlinearity small and its sensitivity adequate. The cut-off frequency is 300 Hz and its small phase lag changes linearly with frequency.

A low-cost colorimeter.

A need for a colorimeter with low capital and maintenance costs has been suggested for countries with foreign exchange problems and no local medical instrumentation industry. This paper puts forward a design for such a device based on a domestic light-bulb, photographic filters and photovoltaic cells. The principle of the design is the use of a balancing technique involving twin light paths for test solution and reference solution and an electronic bridge circuit. It is shown that proper selection of the components will allow the cost objectives to be met and also provide acceptable linearity, precision, accuracy and repeatability.