Analysis of polarization dynamics by singularity decomposition method

The driving point immittance (impedance or admittance) function is commonly used in electrical characterization of polarized materials and interfaces. The immittance function typically attenuates following a power function dependence on frequency. This fact has been recognized as a macroscopic dynamical property manifested by strongly interacting dielectric, viscoelastic and magnetic materials and interfaces between different conducting substances. Linear interfacial polarization processes which occur at metal electrode-electrolyte interfaces have been represented by the Fractional Power Pole [FPP] function in single or multiple stages. The FPP function is referred to as the Davidson-Cole function in the dielectrics literature. A related function widely used in mathematical modeling of dielectric and viscoelastic polarization dynamics is the Cole-Cole function. The fractional power factor which parametrizes the FPP or the Davidson-Cole function has been shown earlier to equal the logarithmic ratio of the locations of the pole-zero singularities. In this paper we first review a modified form of the singularity decomposition of the FPP function accomplished within a prescribed error range. The distribution spectrum and the corresponding simulation by a cascadeR-C network, as opposed to the synthesis by a ladderR-C network, are readily obtained as the next step in the simulation. The method is then applied to decompose the Cole-Cole function; the pole-zero placement of the singularity function is determined and the equivalent cascadeR-C network is synthesized.     

Ventricular beat classifier using fractal number clustering

A two-stage ventricular beat ‘associative’ classification procedure is described. The first stage separates typical beats from extrasystoles on the basis of area and polarity rules. At the second stage, the extrasystoles are classified in self-organised cluster formations of adjacent shape parameter values. This approach avoids the use of threshold values for discrimination between ectopic beats of different shapes, which could be critical in borderline cases. A pattern shape feature conventionally called a ‘fractal number’, in combination with a polarity attribute, was found to be a good criterion for waveform evaluation. An additional advantage of this pattern classification method is its good computational efficiency, which affords the opportunity to implement it in real-time systems.     

Non-linear function model of voice pitch dependency on physical and mental load

The present work describes that under increasing physical load the voice fundamental frequency (voice pitch) remains on a given level as long as the physical load is well tolerated by the subject, whereas heart rate and blood pressure continuously increase during increasing physical load. This voice pitch level was compared to voice pitch levels under mental load. Using a word recognition system, 11 well trained, young male subjects had to solve 2 moderate mental load tasks. Before, during and after each task, there were structured relaxation phases. The physical load protocol was a standard bicycle stress test. In each protocol phase the subjects had to count from 1 to 10 in order to provide a standardized speech sample. Heart rate and blood pressure were recorded in all phases. Voice frequency was at average 106 ± 5.2 Hz in the relaxation phases (‘rest level’) and was increased under mental load (115.9 ± 5.7 Hz, Pillais-P = 0.037). During physical stress testing, voice pitch remained unchanged (‘tolerated load level’) between 100 and 200 W (117.4 ± 4.8 Hz) and increased shortly before physical exhaustion (‘exhaustion level’, 275–350 W, 142.9 ± 5.6 Hz, Pillais-P = 0.007). In contrast, heart rate and blood pressure increased continuously with the physical load. Three voice pitch levels could be verified also individually for each subject. For the practical monitoring of emotional stress the individual anchor frequencies for these levels must be assessed. These data indicate that the relationship between both types of load and voice pitch is non-linear with multiple plateaus and transition functions between them.     

Modeling of the heart's ventricular conduction system using fractal geometry: Spectral analysis of the QRS complex

Many biological systems having one or more characteristics that remain constant over a wide range of scales may be considered self-similar or fractal. Geometrical and functional overview of the ventricular conduction system of the heart reveals that it shares structures common to a tree with repeatedly bifurcating “branches,” decreasing in length with each generation. This system may further simplify by assuming that the bifurcating and decreasing process is the same at any generation, that is, the shortening factor and the angle of bifurcation are the same for each generation. Under these assumptions, the conduction system can be described as a fractal tree. A model of the heart's ventricles which consists of muscle cells and a fractal conduction system is described. The model is activated and the dipole potential generated by adjacent activated and resting cells is calculated to obtain a QRS complex. Analysis of the frequency spectrum of the QRS complex reveals that the simulated waveforms show an enhancement in the high frequency components as generations are added to the conduction system. It was also found that the QRS complex shows a form of an inverse power law, which was predicted by the fractal depolarization hypothesis, with a highly correlated straight line for a log-power versus log frequency plot with a slope of approximately −4. Similar results were obtained using real QRS data from healthy subjects.     

Applying fractal analysis to short sets of heart rate variability data

The aim of this study was to explore the interchangeability of fractal scaling exponents derived from short- and long-term recordings of real and synthetic data. We compared the α₁ exponents as obtained by detrended fluctuation analysis from RR-interval series (9 am to 6 pm) of 54 adults in normal sinus rhythm, and the α₁ estimated from shorted segments of these series involving only 50, 100, 200 and 300 RR intervals. Three series of synthetic data were also analysed. The principal finding of this study is the lack of individual agreement between α₁ derived from long and short segments of HRV data as indicated by the existence of bias and low intraclass correlation coefficient (r _i  = 0.158). The extent of variation in the estimation of α₁ from real data does not only appear related to segments’ length, but also to different dynamics among subjects or lack of uniform scaling behaviour. However, we did find statistical agreement between the means of α₁ exponents from long and short segments, even for segments involving just 50 RR intervals. According to results of synthetic series, the 95% confidence interval found for the variation of α₁ using segments with 300 samples is [−0.1783 + 0.1828]. Caution should be taken concerning the use of short segments to obtain representative exponents of fractal RR dynamics; a circumstance not fully considered in several studies.     

Gait control system for functional electrical stimulation using neural networks

In functional electrical stimulation (FES) systems for restoring walking in spinal cord injured (SCI) individuals, hand switches are the preferred method for controlling stimulation timing. Through practice the user becomes an ‘expert’ in determining when stimulation should be applied. Neural networks have been used to ‘clone’ this expertise but these applications have used small numbers of sensors, and their structure has used a binary output, giving rise to possible controller oscillations. It was proposed that a threelayer structure neural network with continuous function, using a larger number of sensors, including ‘virtual’ sensors, can be used to ‘clone’ this expertise to produce good controllers. Using a sensor set of ten force sensors and another of 13 ‘virtual’ kinematic sensors, a good FES control system was constructed using a three-layer neural network with five hidden nodes. The sensor set comprising three sensors showed the best performance. The accuracy of the optimum three-sensor set for the force sensors and the virtual kinematic sensors was 90% and 93%, respectively, compared with 81% and 77% for a heel switch. With 32 synchronised sensors, binary neural networks and continuous neural networks were constructed and compared. The networks using continuous function had significantly fewer oscillations. Continuous neural networks offer the ability to generate good FES controllers.     

Evaluating rescaled range analysis for time series

Rescaled range analysis is a means of characterizing a time series or a one-dimensional (1-D) spatial signal that provides simultaneously a measure of variance and of the long-term correlation or “memory,” The trend-corrected method is based on the statistical self-similarity in the signal: in the standard approach one measures the ratioR/S on the rangeR of the sum of the deviations from the local mean divided by the standard deviationS from the mean. For fractal signalsR/S is a power law function of the length τ of each segment of the set of segments into which the data set has been divided. Over a wide range of τ's the relationship is:R/S=aτ ^M, wherek is a scalar and theH is the Hurst exponent. (For a 1-D signalf(t), the exponentH=2-D, withD being the fractal dimension.) The method has been tested extensively on fractional Brownian signals of knownH to determine its accuracy, bias, and limitations.R/S tends to give biased estimates ofH, too low forH>0.72, and too high forH<0.72. Hurst analysis without trend correction differs by finding the rangeR of accumulation of differences from the global mean over the total period of data accumulation, rather than from the mean over each τ. The trend-corrected method gives better estimates ofH on Brownian fractal signals of knownH whenH≥0.5, that is, for signals with positive correlations between neighboring elements. Rescaled range analysis has poor convergence properties, requiring about 2,000 points for 5% accuracy and 200 for 10% accuracy. Empirical corrections to the estimates ofH can be made by graphical interpolation to remove bias in the estimates. Hurst's 1951 conclusion that many natural phenomena exhibit not random but correlated time series is strongly affirmed.     

Computerised method for acquisition and display of gastrointestinal motility data

A computerised system is developed for the acquisition and display of gastrointestinal motility data which utilises a purpose developed software program called ‘PC-motil’, running on an IBM compatible microcomputer. ‘PC-motil’ displays data during collection, writes data to disk file and compresses all data at the end of a study on to a single monitor screen for convenient overview. Any area of interest, in single or multiple channels, may be selected and expanded for detailed examination. This system is tested by the recording of gastric and jejunal motility patterns of 11 healthy volunteers in fasting and fed states. All antral and jejunal migrating motor complexes (MMCs) in fasting studies, as well as all fed motility patterns were recognisable in both ‘compressed’ and ‘expanded’ form. The reproduction of motility patterns by the computer based system was indistinguishable from that of a conventional analogue chart recorder. This computerised system provides a convenient and cost-effective means of acquisition, storage and display of motility data in digital form.     

Classifications of lymphoma; reflections of time and technology

‘Nowhere in pathology has a chaos of names so clouded clear concepts as in the subject lymphoid tumors’. R.A. Willis.     

Scaling Characteristics of Heart Rate Time Series Before the Onset of Ventricular Tachycardia

Ventricular tachycardia (VT) provokes sudden cardiac death (SCD), which is a major cause of mortality in developed countries. Implantable cardioverter-defibrillators (ICDs) are an efficient therapy for SCD prevention. In this study we analyze heart rate variability (HRV) in data stored by ICDs. In 29 patients exhibiting VT episodes, the last 1000 normal beat-to-beat intervals are analyzed and compared to an individually acquired control time series (CON). HRV analysis is performed with standard parameters of time and frequency domain as suggested by the HRV Task Force. For scaling analyses of heart rate time series, the fractal dimension is analysed, applying Higuchi’s algorithm (HFD). Furthermore, detrended fluctuation analysis (DFA) is performed. None of the standard HRV parameters shows significant differences between CON and VT. Before the onset of VT, the scaling characteristics by means of HFD and DFA are significantly changed. In conclusion, scaling analysis reveals changes in autonomic heart rate modulation preceding VT.     

Reasons women give for abortion: a review of the literature

The aim was to identify from empirical research that used quantitative or qualitative methods the reasons women give for having an abortion. A search was conducted of peer-reviewed, English language publications indexed in eight computerized databases with publication date 1996–2008, using keywords ‘abortion’ and ‘reason’ (Medline: ‘induced abortion’ OR ‘termination of pregnancy’ OR ‘elective abortion’ and ‘reason’). Inclusion criteria were empirical research on humans that identified women’s reasons for undergoing an abortion, conducted in ‘high-income’ countries. 19 eligible papers were found. Despite variation in methods of generating, collecting, and analysing reasons, and the inadequacy of methodological detail in some papers, all contributed to a consistent picture of the reasons women give for having an abortion, with three main categories (‘Woman-focused’, ‘Other-focused’, and ‘Material’) identified. Ambivalence was often evident in women’s awareness of reasons for continuing the pregnancy, but abortion was chosen because continuing with the pregnancy was assessed as having adverse effects on the life of the woman and significant others. Women’s reasons were complex and contingent, taking into account their own needs, a sense of responsibility to existing children and the potential child, and the contribution of significant others, including the genetic father.     

Experimental and theoretical modelling of intra-aortic balloon pump operation

The performance of intra-aortic balloon pumping is assessed on the basis of a mock circulation and a theoretical model of arterial pulse propagation. The parameters investigated include timing of onset and speed of inflation and deflation as well as pumped air volume. The models used do not contain any active peripheral elements with regulatory capabilities and so the simulated heart adjusts its stroke volume mechanically according to the operating conditions. The observed and calculated changes of typical quantities in terms of ‘stroke’ volume, ‘LV’, ‘aortic’ and ‘peripheral’ pressures are to be attributed, therefore, to the influence of the mechanical pump operation without physiological reactions of the circulatory system as a whole. It is found that timing details of the counterpulsation have a minor influence on the overall mechanical pump performance. Accordingly, the influence of physiological reactions of the cardiovascular system to changes in pump operation seems to be far more important than the one caused by the purely mechanical changes themselves. However, rapid inflation and deflation of the balloon may be accompanied by severe opening or closing shocks, respectively.     

The use of a ‘phantom scalp’ to assess the possible direct pickup of mobile phone handset emissions by electroencephalogram electrode leads

A ‘Phantom Scalp’ was constructed from a conducting foam mat to form a layer under a 62-electrode electroencephalogram cap closely approximating the electrical properties of a human scalp. The mat was placed over a polystyrene manikin head to preserve a correct anatomical arrangement. Electrical signals were recorded with a Global System for Mobile (GSM) communications mobile phone handset in place against the side of the ‘head’. Amplitude spectra were compared for three phone conditions: ‘off’, ‘standby’ and ‘transmit’. At 217 Hz, significant differences were obtained between ‘transmit’ and the other two conditions, but no significant differences were noted for the physiologically important range 0.5–30 Hz. An anomalous difference was noted for one electrode in the range 30–45 Hz.     

Revisiting Christfried Jakob’s concept of the dual onto-phylogenetic origin and ubiquitous function of the cerebral cortex: a century of progress

This paper revisits a concept combining the evolution, ontogeny and histophysiology of the cerebral cortex, presented, in a quest to explain cognition and behavior, by the neurobiologist Christfried Jakob (1866–1956) at the Second Annual Meeting of the International Society for Medical Psychology and Psychotherapy, organized by Oskar Vogt (1870–1959) in Munich in 1911. Jakob suggested a dual onto-phylogenetic origin and a ubiquitous cortical function, claiming that most receptive pathways end up in an ‘outer fundamental layer’, which derives from the rhinencephalic apparatus, whereas the ‘inner fundamental layer’ contains effector elements and derives from the striatum. With advancing evolution, the two fundamental layers become intermingled. By attributing a functional homogeneity to the cortex, Jakob contradicted the theories of Flechsig and Cajal on ‘association’ and ‘mnemonic’ areas. The merit of Jakob’s concept rests, a century later, with the current resurgence of biological research at the evolutionary–developmental interface and the broadening anticipated from the re-integration of these two fields, especially by adding a functional dimension to the morphological traits.     

Migration of the true pacemaker within the sinoatrial cell aggregate in man

The functional anatomy of the sinoatrial node (SAN) in man is first reviewed, together with its possible anatomical substructure. The true group pacemaker (PM) shift under autonomic drive is then related to a continuous competition between the intrinsic auto-firing period hierarchy and the autonomic topological susceptibility hierarchy. Accordingly, the PM ‘skip’ to both lower and higher periods following an abrupt and consistent acetylcholine (ACh) release at the SAN periphery, and the PM ‘slip’ towards a relocation of the next period, as a possible response to a slower and smaller ACh release, are considered. The PM ‘skip’ and ‘slip’ as boundaries of the true PM excursion within the SAN during the respiratory cycle, and their statistical properties, are then examined. Under current heart rate control menus in normals, the PM skip appears to follow central influence, whereas the conservative or slipping PMs suggest peripheral control. Finally, interpretation of the PM skip as a salutary sign of functional reserve is proposed, and a method of alleviating the PM skip which confounds electrophysiological testing of the SAN function in patients is devised.     

Non-constraining sleep/wake monitoring system using bed actigraphy

This paper introduces a new method, bed actigraphy (BACT) for user-friendly sleep-wake monitoring. BACT provides a non-intrusive acquisition of activity data, and in particular does not require that sensors be attached to the subject’s body. The system consists of four load-sensing cells supporting the bed, an A/D converter, and a microcontroller with appropriate software. The performance of BACT was compared to that of standard polysomnography (PSG) recordings and wrist-worn actigraphy (ACT). Ten normal volunteers underwent overnight PSG recordings and were examined simultaneously with BACT and ACT. An automatic scoring algorithm scored each 30-s epoch of the BACT recordings for either ‘Wake’ or ‘Sleep.’ A sleep specialist manually scored the PSG recordings, and the results were divided into ‘Wake’ and ‘Sleep’ categories. The three methods showed a significant correlation when compared with in the contingency test. The mean epoch-by-epoch agreements between the BACT and PSG, ACT and PSG, and BACT and ACT recordings were 95.2, 92.9, and 94.3%, respectively. The mean absolute differences in sleep percentage (SP) between them were 1.8 ± 0.82, 3.4 ± 1.45, and 1.9 ± 1.16 %, respectively. BACT differentiation of the ‘Wake’ and ‘Sleep’ stages proved to be sufficiently robust, and its results were comparable to PSG analysis. This finding supports the experimental and clinical value of bed-activity monitoring during sleep.     

Karyotype diversity and the origin of grapefruit

Grapefruit is a group of citrus of recent origin, probably resulting from a cross between pummelo and sweet-orange. Aiming to investigate this putative origin and the genetic variability among grapefruit cultivars, the karyotype of six grapefruits, two pummelos, and one tangelo cultivar (grapefruit × tangerine) were analyzed using sequential CMA/DAPI double staining and FISH with rDNA probes. The karyotypes of grapefruit ‘Duncan’ and ‘Foster’ differ from those of ‘Flame’, ‘Henderson’, ‘Marsh’ and ‘Rio Red’. The former have two chromosomes with a single CMA⁺ band in both terminal regions (C type chromosome) and six chromosomes with only one CMA⁺ terminal band (D type), whereas the latter have three C and five D type chromosomes. All accessions investigated exhibited two chromosomes with 5S rDNA but a variable number of 45S rDNA. The two former grapefruits displayed four 45S rDNA sites, whereas the remaining grapefruit cultivars had five. The two pummelos showed identical karyotypes, homozygous for CMA⁺ bands and their four rDNA sites. From each pummelo chromosome pair one chromosome seems to be present in grapefruit karyotypes. The different grapefruit karyotypes might result from independent crosses between pummelos of different karyotypic constitution and sweet-oranges. The chromosome markers found in the tangelo ‘Orlando’ and the position of their two 45S rDNA confirm the grapefruit ‘Duncan’ and the tangerine ‘Dancy’ as their parents.     

Mindful pregnancy and childbirth: effects of a mindfulness-based intervention on women’s psychological distress and well-being in the perinatal period

This pilot study explored the effects of an 8-week mindfulness-based cognitive therapy group on pregnant women. Participants reported a decline in measures of depression, stress and anxiety; with these improvements continuing into the postnatal period. Increases in mindfulness and self-compassion scores were also observed over time. Themes identified from interviews describing the experience of participants were: ‘stop and think’, ‘prior experience or expectations’, ‘embracing the present’, ‘acceptance’ and ‘shared experience’. Childbirth preparation classes might benefit from incorporating training in mindfulness.     

Finger interaction during maximal radial and ulnar deviation efforts: experimental data and linear neural network modeling

The purpose of this study was to characterize finger interactions during radial/ulnar deviation, including interactions with flexion movements. Subjects performed single-finger and multi-finger maximal voluntary contraction (MVC), and maximal forces and various indices of interaction among the fingers were quantified. MVCs in radial/ulnar deviation were 50–80% as strong as in flexion. Along with the ‘master’ fingers (i.e., those explicitly instructed to produce force), substantial force production was also observed in ‘slave’ fingers (i.e., those not explicitly instructed to produce force), a phenomenon termed: force ‘enslaving’. In addition, a drop in MVC during multi-finger tasks as compared to single finger tasks (force ‘deficit’) was also observed. A previously unreported phenomenon that we term: ‘preferred direction enslaving’ was also apparent; both master and slave fingers produced force in the instructed direction with a non-zero perpendicular component. Due to the architectural separation of the involved muscles, preferred direction enslaving provides strong evidence that enslaving results from neural rather than biomechanical factors. A final new phenomenon: ‘negative deficit’, or force ‘facilitation’ was observed in 46.4% of the trials in 21 out of 23 subjects during multi-finger lateral efforts and was further demonstrative of extensive interconnection among neurons serving hand muscles. The data were modeled with high accuracy (∼4% mean square error) using a linear neural network with motor ‘commands’ as inputs and finger forces as outputs. The proposed network, equivalent to linear regression, can be used to determine the extent to which finger forces are influenced by peripheral constraints during functional prehensile activities.     

Age Differences in Genetic and Environmental Variations in Stress-Coping During Adulthood: A Study of Female Twins

The way people cope with stressors of day to day living has an important influence on health. The aim of the present study was to explore whether genetic and environmental variations in stress-coping differ over time during adulthood. The brief COPE was mailed to a large sample of the UK female twins (N = 4,736) having a wide range of age (20–87 years). Factor analyses of the items of the brief COPE yielded three coping scales: ‘Problem-Solving’, ‘Support Seeking’, and ‘Avoidance’. Monozygotic and dizygotic twin correlations tended to become lower with age for all three scales, suggesting that unique environmental factors may become more important with age during adulthood. Model-fitting results showed that relative influences of unique environmental factors increased from 60 % at age 20 years to 74% at age 87 years for ‘Problem-Solving’ and 56 % at age 20 years to 76% at age 87 years for ‘Avoidance’. During the same age period, genetic factors decreased from 40 to 26 % for ‘Problem-Solving’ and from 44 to 24 % for ‘Avoidance’. For ‘Seeking Support’, the magnitude of genetic and unique environmental factors was not significantly different across the adulthood. For all three scales, shared environmental effects were negligible. Overall, our findings implicate that the effects of environment that stem from idiosyncratic experience of stressful life events accumulate and become increasingly important in adulthood.