Rate of shear of an ultrasonic oscillating rod viscosity probe.

Ultrasonic oscillating rod probes have recently been used by researchers to measure viscosity and/or density in fluids. However, in order to use such probes to characterise the rheological properties of fluids, it is necessary to define the shear rate produced by the probe. This paper proposes an analytical solution to estimate the shear rate of ultrasonic oscillating rod viscosity probes and a method to measure their maximum operational shear rate. A relationship is developed which relates the torsional surface velocity of an oscillating cylindrical rigid body to the rate of shear in its vicinity. The surface displacement and torsional surface velocity of a torsional probe of length 1000 mm and diameter 1mm were measured over the frequency range from 525 to 700 kHz using a laser interferometer and the maximum shear rate estimated. The reported work provides the basis for characterising shear rate for such probes, enabling their application for rheological investigations.

Evolution of spider silks: conservation and diversification of the C-terminus.

Analysis of DNA sequences coding for the C-terminus of spider silk proteins from a range of spiders suggests that many silk C-termini share a common origin, and that their physical properties have been highly conserved over several hundred million years. These physical properties are compatible with roles in protein synthesis, silk function and in recruiting accessory proteins. Phylogenetic relationships among different silk genes suggest that any recombination has been insufficient to homogenize the different types of silk gene, which appear to have evolved independently of one another. The types of nucleotide substitutions that have occurred suggest that selection may have operated differently in the various silk lineages. Amino acid sequences of flagelliform silk C-termini differ substantially from the other types of spider silk studied, but they are expected to have very similar physical properties and may perform a similar function.

Safe introduction of warfarin for thrombotic prophylaxis in atrial fibrillation requiring only a weekly INR.

A new protocol for initiating warfarin therapy was introduced to reduce the workload in the Anticoagulant Clinic. A total of 200 outpatients, with a median age of 74 years, requiring anticoagulation for atrial fibrillation, commenced warfarin 3 mg daily for 1 week. Patients were initially seen weekly, and subsequent warfarin doses were dictated by the International Normalized Ratio (INR) on days 8 and 15; 84% of patients followed the protocol correctly: of these 86% had an INR > or =2 by day 15 and >98% had INR >2 by day 22. By day 22, 58% of patients achieved a stable dose, 85% by day 29 and >95% by day 36. Day 8 INR was predictive of the final maintenance dose required. No patient suffered any thrombotic or haemorrhagic complications in the first month: only three patients had an INR >3 on day 8, and 11 patients had an INR >4 on day 15. Patient age and sex were not sufficiently related to warfarin requirement to provide useful predictive information. This protocol, requiring only weekly INRs, has proved safe and effective for outpatient warfarinization, and has reduced clinic attendances in this population.

Convergence criteria for scattering models of ultrasonic wave propagation in suspensions of particles.

Scattering models used to simulate the attenuation and phase velocity of an ultrasonic wave propagating through a suspension of particles involve the summation of an infinite series of partial waves. The accuracy of computation is influenced by the number of terms included in the harmonic series, and the number of terms required depends upon the scatterer size compared with wavelength. It is shown that the errors in modelled attenuation and phase velocity resulting from premature truncation can be significant when modelling higher values of particle diameter-frequency product. A useful and simple heuristic is presented, in which the number of terms in the summation of the infinite series needed for satisfactory convergence to a final value is a function of the particle diameter-frequency product and of the compressive wave velocity in the continuous phase.

Quantitative classification of adhesive bondline dimensions using Lamb waves and artificial neural networks.

Adhesive bonding of metal assemblies is gaining acceptance for use with safety critical structures, and there is a need for effective inspection for both quality assurance (QA) and the assessment of condition in service. One aspect of QA is the need for the dimensions of adhesive bondlines to be within tolerance and measurable. This paper describes the application of ultrasonic Lamb waves in the determination of the principal dimensions of two forms of adhered joints (Lap and T-form) between metal plates. Low order Lamb wave modes (s0 and a1) are propagated across adhered bond-lines, and the received signals are transformed to the modulus frequency domain (FD). The FD data are used as input to artificial neural networks (ANNs), which are trained to associate features in the input data with principal bondline dimensions. The performance of different network structures and simplified forms of these is examined, and the technique gives reliable estimates of the required dimensions in bondlines not included in network training. The interconnected weights of simplified networks provide evidence of the features in Lamb wave signals that underlie the successful operation of the method.

Ultrasonic Monitoring of Oil-in-Water Emulsions Undergoing Depletion Flocculation

The paper describes a three-part experiment on flocculating emulsions in order to determine whether ultrasonic spectroscopy could be used to detect and characterize the flocculation process. Three emulsions which represented unflocculated, partially flocculated, and fully flocculated systems were prepared. They were characterized independently using direct microscopic examination and their creaming behavior. Ultrasonic spectroscopic measurements of the flocculating emulsions showed large changes during the flocculation process, which were not readily modeled using single particle scattering theory. The ultrasonic properties of the unflocculated emulsion did not change during the measurement period. The results demonstrate that ultrasonic techniques are capable of detecting the flocculation process. There is clear potential to use ultrasonic techniques to characterize flocculated structures, but more work is needed on the theoretical analysis of the interaction of ultrasound with particle aggregates. Copyright 1997Academic Press

Acoustic absorption due to proton transfer in solutions of proteins, peptides and amino acids at neutral pH.

Measurements of ultrasonic absorption in the frequency range 2 to 60 MHz have been made on solutions of the amino acid histidine, dipeptides glycyl tyrosine and histidyl tyrosine, and proteins lysozyme and bovine serum albumin. Measurements were carried out at 37 degrees C and covered the pH range 6.8 to 7.7. Mechanisms for the observed excess acoustic absorption involving bimolecular and intramolecular proton transfer are considered.

Modulation of muscarinic cholinoceptor-stimulated inositol 1,4,5-trisphosphate accumulation by N-methyl-D-aspartate in neonatal rat cerebral cortex.

The mechanisms by which N-methyl-D-aspartate (NMDA) receptor activation can modulate muscarinic receptor-stimulated phosphoinositide turnover have been studied in neonatal rat cerebral cortex slices. A maximally effective concentration of carbachol (1 mM) caused a large stimulation of both total [3H]inositol phosphate ([3H]InsPx) accumulation (30-40-fold over basal levels after 15 min in the presence of 5 mM LiCl) and inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] mass accumulation (consisting of a rapid peak increase of about 8-10-fold within 15 sec followed by a sustained plateau rise of 4-5-fold which persisted for > 10 min). Low concentrations of NMDA enhanced carbachol-stimulated [3H]InsPx and Ins(1,4,5)P3 accumulations with a maximal effect being observed at 10 microM NMDA. However, at higher concentrations of NMDA (30-300 microM) a dramatic inhibition of these indices of phosphoinositide turnover was observed. Time-course studies demonstrated that NMDA (100 microM) caused a significant enhancement of the initial increases in [3H]InsPx and Ins(1,4,5)P3 accumulations stimulated by carbachol, with the profound inhibitory effects becoming evident at longer incubation times. The modulatory effects of NMDA were antagonized by D-2-amino-5-phosphonopentanoate and MK-801. Reducing extracellular calcium concentration ([Ca2+]e) to the low micromolar range decreased basal Ins(1,4,5)P3 accumulation and attenuated the response to carbachol. Under these conditions NMDA (10-100 microM) caused only a potentiation of agonist-stimulated Ins(1,4,5)P3 accumulation. Under control conditions ([Ca2+]e = 1.3 mM), addition of MK-801 (1 microM) 10 min after carbachol + 100 microM NMDA challenge failed to reverse the inhibitory effect of NMDA on carbachol-stimulated [3H]InsPx accumulation. Furthermore, pre-incubation of cerebral cortex slices with 100 microM NMDA for 15 min (followed by extensive washing of slices to remove NMDA) dramatically decreased [3H]inositol incorporation into the cellular inositol phospholipid fraction and decreased basal and carbachol-stimulated Ins(1,4,5)P3 mass accumulations. We conclude that the enhancement of agonist-stimulated phosphoinositide turnover seen at concentrations of NMDA up to 10 microM may be due to Ca2+ entry and Ca2+ facilitation of phosphoinositide-specific phospholipase C activity. In contrast, the inhibitory effect of high concentrations of NMDA on agonist-stimulated phosphoinositide turnover may be due to progressive, irreversible and, at least in part, Ca(2+)-dependent damage to the cell populations in the slice preparation responding to muscarinic-receptor stimulation.

Biomedical signal processing (in four parts). Part 3. The power spectrum and coherence function.

This is the third in a series of four tutorial papers on biomedical signal processing and concerns the estimation of the power spectrum (PS) and coherence function (CF) od biomedical data. The PS is introduced and its estimation by means of the discrete Fourier transform is considered in terms of the problem of resolution in the frequency domain. The periodogram is introduced and its variance, bias and the effects of windowing and smoothing are considered. The use of the autocovariance function as a stage in power spectral estimation is described and the effects of windows in the autocorrelation domain are compared with the related effects of windows in the original time domain. The concept of coherence is introduced and the many ways in which coherence functions might be estimated are considered.

Changes in inositol 1,4,5-trisphosphate and inositol 1,3,4,5- tetrakisphosphate mass accumulations in cultured adrenal chromaffin cells in response to bradykinin and histamine.

In previous studies it has been shown that both bradykinin and histamine increase the formation of 3H-labeled inositol phosphates in adrenal chromaffin cells prelabelled with [3H]inositol and that both these agonists stimulate release of catecholamines by a mechanism dependent on extracellular calcium. Here, we have used mass assays of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] to investigate changes in levels of these two candidates as second messengers in response to stimulation with bradykinin and histamine. Bradykinin increased the mass of Ins(1,3,4,5)P4 despite the failure in earlier studies with [3H]inositol-labelled cells to observe a bradykinin-mediated increase in content of [3H]InsP4. Bradykinin elicited a very rapid increase in level of Ins(1,4,5)P3, which was maximal at 5-10 s and then rapidly decreased to a small but sustained elevation at 2 min. The bradykinin-elicited Ins(1,3,4,5)P4 response increased to a maximum at 30-60 s and at 2 min was still elevated severalfold above basal levels. Histamine, which produced a larger overall total inositol phosphate response in [3H]inositol-loaded cells, produced significantly smaller Ins(1,4,5)P3 and Ins(1,3,4,5)P4 responses compared with bradykinin. The bradykinin stimulation of Ins(1,4,5)P3 accumulation was partially dependent on a high (1.8 mM) extracellular Ca2+ concentration, whereas the Ins(1,3,4,5)P4 response was almost completely lost when the extracellular Ca2+ concentration was reduced to 100 nM. Changes in the inositol polyphosphate second messengers are compared with the time course of bradykinin-stimulated increases in free intracellular Ca2+ concentrations and noradrenaline release.

Biomedical signal processing (in four parts). Part 2. The frequency transforms and their inter-relationships.

This is the second in a series of four tutorial papers on biomedical signal processing, and it concerns the relationships between commonly used frequency transforms. It begins with the Fourier series and Fourier transform for continuous time signals and extends these concepts for aperiodic discrete time data and then periodic discrete time data. The Laplace transform is discussed as an extension of the Fourier transform. The z-transform is introduced and the ideas behind the chirp-z transform are described. The equivalence between the time and frequency domains is described in terms of Parseval's theorem and the theory of convolution. The use of the FFT for fast convolution and fast correlation is described for both short recordings and long recordings that must be processed in sections.

Biomedical signal processing (in four parts). Part 1. Time-domain methods.

This is the first of a series of four tutorial papers on biomedical signal processing. It provides an introduction to terminology and basic ideas for testing for randomness and trend, and for the determination of basic signal properties in the time domain, given the uncertainties associated with the estimation process. Techniques outlined in the paper are: the coherent average, cross-correlation and covariance, autocorrelation and phase-shift averaging.

Signal preprocessing system for the small intestinal electromyogram.

The intestinal EMG obtained from chronically implanted electrodes in canine preparations provides for the evaluation of intestinal motor activity and its control. The basic electrical rhythm (BER) and spike components on the EMG signal provide evidence of control activity and a measure of contraction intensity, respectively. A hardware system is presented in which these two components are separated by filters and the contraction spikes counted in fixed epochs to yield a contraction spike per unit time record against time. The signal is also available in parallel binary form at the end of each epoch, together with a data-ready signal for direct acquisition by computer. Tests of system performance and operating protocols are given. The preprocessor is used as a fast front end to a digital signal processing system specifically built for intestinal EMG analyses.

The rate of substrate cycling between fructose 6-phosphate and fructose 1,6-bisphosphate in skeletal muscle from cold-exposed, hyperthyroid or acutely exercised rats.

The effects of cold-exposure, the hyperthyroid state and a single exercise bout in vivo on the maximal enzyme activities of 6-phosphofructokinase and fructose-1,6-bisphosphatase in vastus lateralis muscle and the rates of fructose 6-phosphate/fructose 1,6-bisphosphate cycling measured in epitrochlearis muscle in vitro were investigated. In all cases significant changes in substrate cycling rates were observed, whether in the absence of added hormones in vitro (acute exercise), or when stimulated by insulin plus adrenaline (cold-exposure), or with respect to the catecholamine-sensitivity of the cycling rate (the hyperthyroid state).

A controllable artificial afterload for isolated heart studies.

This paper presents an artificial afterload, based on the Westerhof model, for use in isolated heart preparations. The system has adjustable elements representing peripheral resistance and total arterial compliance, together with a fixed element representing aortic impedance. It is controlled by a computer in a manner which incorporates feed forward and feedback techniques. The system maintains constant 'arterial' pressure in the face of large excursions of the flow through it. It can be programmed to change this pressure in a dynamic fashion. The time taken to recover from large changes in flow and to reset the pressure is at most 3 S. Absolute values of peripheral resistance are easily obtained without any knowledge of the actual flow being required. Tests of the system demonstrate its stability and rapid transient characteristics.

Effects of an adenosine-receptor antagonist on insulin-resistance in soleus muscle from obese Zucker rats.

The decreased sensitivity of glycolysis to insulin seen in isolated soleus muscles from genetically obese Zucker rats was abolished by addition of the adenosine-receptor antagonist 8-phenyltheophylline to the incubation medium; 8-phenyltheophylline had no effect on the sensitivity of glycogen synthesis to insulin. These findings suggest that changes in the sensitivity of glucose utilization by muscles of genetically obese rats may be explained, in part, by a modification in either the concentration of adenosine or the affinity of adenosine receptors in skeletal muscle.

The design of digital filters for biomedical signal processing. Part 3: The design of Butterworth and Chebychev filters.

The first two papers in this series reviewed the basic concepts which apply to digital filter theory and presented design techniques based on the z plane pole-zero plot. In this paper these methods are used to develop digital versions of Butterworth and Chebychev filters. The basic theory of both filter types is reviewed and the bilinear transformation is used to derive the z-transforms of the filters from their s-plane continuous time descriptions. Recurrence relationships which may be used to implement filters of various orders are developed. The impulse and frequency responses of the elements are illustrated and examples are given of their application to ECG data.

The design of digital filters for biomedical signal processing. Part 2: Design techniques using the z-plane.

Design methods for digital filters using z-plane techniques are developed out of the basic concepts described in part 1. The relationship between impulse response shape and side lobe generation in the frequency response is investigated by means of rectangular, triangular and cosine window filters. The limited choice of cut-off frequencies available for simple linear phase digital filters is explained. Design direct from the frequency domain is summarized. z-plane techniques for the design of high- and band-pass digital filters and the digital equivalents of analogue filters are described. s-plane to z-plane mapping by means of the Bilinear transformation is compared to the direct z-transform method of filter design.

Effects of starvation on the maximal activities of some glycolytic and citric acid-cycle enzymes and glutaminase in mucosa of the small intestine of the rat.

Starvation decreases activities of some glycolytic and citric acid-cycle enzymes, and increases those of glucose 6-phosphatase and fructose bisphosphatase, whereas that of glutaminase is unchanged. These findings may be of significance for the control of glucose metabolism in the absorptive cells of the intestine.