37 results on '"McClintock, Peter Vaughan Elsmere"'
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2. Chapter 6 Capillary Turbulence on the Surfaces of Quantum Fluids
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Kolmakov, German Valentinovich, Brazhnikov, Maxim Yurievich, Levchenko, Alexander Alexeevich, Abdurakhimov, Leonid Victorovich, McClintock, Peter Vaughan Elsmere, and Mezhov-Deglin, Leonid Pavlovich
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- 2009
- Full Text
- View/download PDF
3. Capillary Turbulence on the Surfaces of Quantum Fluids
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Kolmakov, German Valentinovich, primary, Brazhnikov, Maxim Yurievich, additional, Levchenko, Alexander Alexeevich, additional, Abdurakhimov, Leonid Victorovich, additional, McClintock, Peter Vaughan Elsmere, additional, and Mezhov-Deglin, Leonid Pavlovich, additional
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- 2009
- Full Text
- View/download PDF
4. Unsolved Problems of Noise:Preface to the UPoN-2018 Special Issue of FNL
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Khovanov, Igor and McClintock, Peter Vaughan Elsmere
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Noise is universal and multi-faceted. In everyday life, the aspects we encounter tend to be annoying, for example, loud conversations when we wish to enjoy a quiet cup of tea, or students chatting during a lecture. But acoustic noise can sometimes be useful e.g. when it indicates that the kettle is boiling, as an essential prelude to the tea, or when it helps to awaken somnolent students at the end of the lecture thereby eliminating the mutual embarrassment of needing to awaken them.
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- 2019
5. From the potential of the mean force to a quasiparticle’s effective potential in narrow ion channels
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Barabash, Miraslau, Gibby, William Alexander Thomas, Guardiani, Carlo, Luchinsky, Dmitry, McClintock, Peter Vaughan Elsmere, Barabash, Miraslau, Gibby, William Alexander Thomas, Guardiani, Carlo, Luchinsky, Dmitry, and McClintock, Peter Vaughan Elsmere
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We consider the selective permeation of ions through narrow water-filled channels in the presence of strong interaction between the ions. These interactions lead to highly correlated ionic motion, which can conveniently be described via the concept of a quasiparticle. Here, we connect the quasiparticle’s effective potential and the multi-ion potential of the mean force, found through molecular dynamics simulations, and we validate the method on an analytical toy model of the KcsA channel. Possible future applications of the method to the connection between molecular dynamical calculations and the experimentally measured current-voltage and current-concentration characteristics of the channel are discussed.
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- 2019
6. Theory and experiments on multi-ion permeation and selectivity in the NaChBac ion channel
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Gibby, William Alexander Thomas, Barabash, Miraslau, Guardiani, Carlo, Luchinsky, Dmitry, Fedorenko, Olena, Roberts, Stephen Kenneth, McClintock, Peter Vaughan Elsmere, Gibby, William Alexander Thomas, Barabash, Miraslau, Guardiani, Carlo, Luchinsky, Dmitry, Fedorenko, Olena, Roberts, Stephen Kenneth, and McClintock, Peter Vaughan Elsmere
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The highly selective permeation of ions through biological ion channels is an unsolved problem of noise and fluctuations. In this paper, we motivate and introduce a non-equilibrium and self-consistent multi-species kinetic model, with the express aims of comparing with experimental recordings of current versus voltage and concentration and extracting important permeation parameters. For self-consistency, the behavior of the model at the two-state, i.e., selective limit in linear response, must agree with recent results derived from an equilibrium statistical theory. The kinetic model provides a good fit to data, including the key result of an anomalous mole fraction effect.
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- 2019
7. The Role of Noise in Determining Selective Ionic Conduction Through Nano-Pores
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Gibby, William Alexander Thomas, Barabash, Miraslau, Guardiani, Carlo, Luchinsky, Dmitry, McClintock, Peter Vaughan Elsmere, Gibby, William Alexander Thomas, Barabash, Miraslau, Guardiani, Carlo, Luchinsky, Dmitry, and McClintock, Peter Vaughan Elsmere
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The problem of predicting selective transport of ions through nano-pores from their structure in the biological and nano-technological systems is addressed. We use a molecular dynamics simulation to provide insight into the key physical parameters of nano-pores and develop a self-consistent analytic theory describing ionic conduction and selectivity through these devices. We analyse the ion's dehydration and excess chemical potential, derive an expression for the conductivity of the nano-pore, and emphasize the role of fluctuations in its performance. The theory is verified by comparison of the predicted current-voltage characteristics with the molecular dynamics results and experimental data obtained for a graphene nano-pore and the KcsA biological channel.
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- 2019
8. Methods in molecular biophysics: structure, dynamics, function for biology and medicine, 2nd edition:Book review
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McClintock, Peter Vaughan Elsmere
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Biological problems have been considered in the context of physics since at least the seventeenth century when e.g. Newton commented on information transmission along nerves. But it was the introduction of the double helix model of DNA, in the middle of the twentieth century, that demonstrating unequivocally that the processes of life are governed by basic physical principles. Since then, an immense number of specialised methods has been developed, applying physics to understand the structures and (to a lesser extent) functions of biomolecules. Zaccai et al. describe a wide variety of these methods in their comprehensive textbook.
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- 2018
9. A review of Handbook of Ion Channels, by Jie Zheng and Matthew C. Trudeau
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McClintock, Peter Vaughan Elsmere, Kaufman, Igor Khaimovich, McClintock, Peter Vaughan Elsmere, and Kaufman, Igor Khaimovich
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Just lifting a finger involves the coordinated opening and closing of billions of ion channels. These natural nanotubes play an essential role in the physiology of all living creatures, from bacteria to humans [1, 2]. By providing for the exchange of ions across cellular membranes, they control a vast range of biological processes, and their dysfunction leads to numerous diseases.
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- 2018
10. Quantized Dehydration and the Determinants of Selectivity in the NaChBac Bacterial Sodium Channel
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Fedorenko, Olena, Kaufman, Igor Khaimovich, Gibby, William Alexander Thomas, Luchinsky, Dmitry, Roberts, Stephen Kenneth, McClintock, Peter Vaughan Elsmere, Fedorenko, Olena, Kaufman, Igor Khaimovich, Gibby, William Alexander Thomas, Luchinsky, Dmitry, Roberts, Stephen Kenneth, and McClintock, Peter Vaughan Elsmere
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A discrete electrostatic/diffusion model has been developed to describe the selective permeation of ion channels, based on ionic Coulomb blockade (ICB) and quantised dehydration (QD). It has been applied to describe selectivity phenomena measured in the bacterial NaChBac sodium channel and some of its mutants. Site-directed mutagenesis and the whole-cell patch-clamp technique were used to investigate how the value $Q_f$ of the fixed charge at the selectivity filter (SF) affected both valence and alike-charge selectivity. The new ICB/QD model predicts that increasing ${Q_f}$ should lead to a shift of selectivity sequences towards larger ion sizes and charges, a result that agrees with the present experiments and with earlier work. Comparison of the model with experimental data provides evidence for an {\it effective charge} $Q_f^*$ at the SF that is smaller in magnitude than the nominal $Q_f$ corresponding to the charge on the isolated protein residues. Furthermore, $Q_f^*$ was different for aspartate and glutamate charged rings and also depended on their position within the SF. It is suggested that protonation of the residues within the restricted space is an important factor in significantly reducing the effective charge of the EEEE ring. Values of $Q_f^*$ derived from experiments on the anomalous mole fraction effect (AMFE) agree well with expectations based on the ICB/QD model and have led to the first clear demonstration of the expected ICB oscillations in Ca$^{2+}$ conduction as a function of the fixed charge. Pilot studies of the dependence of Ca$^{2+}$ conduction on pH are consistent with the predictions of the model.
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- 2018
11. Experimental Realization of the Coupling Function Secure Communications Protocol and Analysis of its Noise Robustness
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Nadzinski, Gorjan, Dobrevski, Matej, Anderson, Christopher, McClintock, Peter Vaughan Elsmere, Stefanovska, Aneta, Stankovski, Mile, Stankovski, Tomislav, Nadzinski, Gorjan, Dobrevski, Matej, Anderson, Christopher, McClintock, Peter Vaughan Elsmere, Stefanovska, Aneta, Stankovski, Mile, and Stankovski, Tomislav
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There is an increasing need for everyday communications to be both secure and resistant to external perturbations. We have therefore created an experimental implementation of the coupling-function-based secure communication protocol, in order to assess its robustness to channel noise. The transmitter and receiver are implemented on single-board computers, thereby facilitating communication of the analog electronic signals. The information signals are encrypted at the transmitter as the timevariability of nonlinear coupling functions between dynamical systems. This results in a complicated nonlinear mixing and scrambling of the information. To replicate the channel noise, analog white noise is added to the encrypted signals. After digitization at the receiver, the decryption is performed with dynamical Bayesian inference to take account of time-varying dynamics in the presence of noise. The dynamical Bayesian approach effectively separates the deterministic information signals from the perturbations of dynamical channel noise. The experimental realization has demonstrated the feasibility, and established the performance, of the protocol for secure, reliable, communication even with high levels of channel noise.
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- 2018
12. Coherence and coupling functions reveal microvascular impairment in treated hypertension
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Ticcinelli, Valentina, Stankovski, Tomislav, Iatsenko, Dmytro, Bernjak, Alan, Bradbury, Adam, Gallagher, Andrew, Clarkson, Peter B M, McClintock, Peter Vaughan Elsmere, and Stefanovska, Aneta
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The complex interactions that give rise to heart rate variability (HRV) involve coupled physiological oscillators operating over a wide range of different frequencies and length-scales. Based on the premise that interactions are key to the functioning of complex systems, the time-dependent deterministic coupling parameters underlying cardiac, respiratory and vascular regulation have been investigated at both the central and microvascular levels. Hypertension was considered as an example of a globally altered state of the complex dynamics of the cardiovascular system. Its effects were established through analysis of simultaneous recordings of the electrocardiogram, respiratory effort, and microvascular blood flow (by laser Doppler flowmetry). The signals were analysed by methods developed to capture time-dependent dynamics, including the wavelet transform, wavelet-based phase coherence, nonlinear mode decomposition and dynamical Bayesian inference, all of which can encompass the inherent frequency and coupling variability of living systems. Phases of oscillatory modes corresponding to the cardiac (around 1.0~Hz), respiratory (around 0.25~Hz) and vascular myogenic activities (around 0.1~Hz) were extracted and combined into two coupled networks describing the central and peripheral systems respectively. The corresponding spectral powers and coupling functions were computed. The same measurements and analyses were performed for three groups of subjects: healthy young (Y group, 24.4 +/- 3.4 y), healthy aged (A group, 71.1 +/- 6.6 y), and aged treated hypertensive patients (ATH group, 70.3 +/- 6.7 y). It was established that the degree of coherence between low-frequency oscillations near 0.1~Hz in blood flow and in HRV time series differs markedly between the groups, declining with age and nearly disappearing in treated hypertension. Comparing the two healthy groups it was found that the couplings to the cardiac rhythm from both respiration and vascular myogenic activity decrease significantly in aging. Comparing the data from A and ATH groups it was found that the coupling from the vascular myogenic activity is significantly weaker in treated hypertension subjects, implying that the mechanisms of microcirculation are not completely restored by current anti-hypertension medications.
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- 2017
13. Nonlinear Dynamics in Biological Systems
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McClintock, Peter Vaughan Elsmere
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- 2017
14. Fundamentals of fluorescence microscopy: exploring life with light, by Partha Pratim Mondal and Alberto Diaspro
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McClintock, Peter Vaughan Elsmere
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- 2017
15. Controlled thermonuclear fusion by Jean Louis Babin
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McClintock, Peter Vaughan Elsmere
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Thermonuclear fusion offers the possibility of virtually unlimited, low-carbon, electrical power generation without leaving an extensive legacy of radioactive waste. For almost as long as I can remember, its practical application has been predicted to be about 30 or 40 years in the future, so why does it never seem to come closer to reality?
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- 2017
16. The origin and nature of life on earth: the emergence of the fourth geosphere, by Eric Smith and Harold J. Morowitz
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McClintock, Peter Vaughan Elsmere and McClintock, Peter Vaughan Elsmere
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We now know a great deal about the nature of life on Earth. We understand how it functions and, in many cases, how it can be modified; but how it arose here in the first place remains an enduring mystery. It is well established that life in some form, probably akin to bacteria, was already flourishing about 3.8 billion years ago, i.e. almost as soon as the young Earth had cooled enough for it not to be cooked. Once life had appeared, it is not difficult to envisage how the combination of random mutation and Darwinian evolution (survival of the fittest) has brought us and the Earth to where we are today. There remain some notable residual problems, e.g. the seemingly improbable appearance of the complicated eukaryotic cell which forms the building blocks for the higher forms of life like plants and people but, in a rough-and-ready kind of way, the story seems clear and convincing. Unfortunately, however, no evidence remains about how the process got started.
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- 2017
17. Ionic Coulomb blockade and anomalous mole fraction effect in the NaChBac bacterial ion channel and its charge-varied mutants
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Kaufman, Igor Khaimovich, Fedorenko, Olena, Luchinsky, Dmitry, Gibby, William, Roberts, Stephen Kenneth, McClintock, Peter Vaughan Elsmere, Eisenberg, Robert S, Kaufman, Igor Khaimovich, Fedorenko, Olena, Luchinsky, Dmitry, Gibby, William, Roberts, Stephen Kenneth, McClintock, Peter Vaughan Elsmere, and Eisenberg, Robert S
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Background. The selectivity of biological cation channels is defined by a short, narrow selectivity filter, having a negative net fixed charge Qf. Voltage gated bacterial channels (NaChBac and some others) are frequently used in biophysics as simplified models of mammalian calcium and sodium channels. We report an experimental, analytic and numerical study of the effects of Qf and bulk ionic concentrations of Ca2+ and Na+ on conduction and selectivity of NaChBac channels, wild type and Qf-varied mutants. Methods. Site-directed mutagenesis and voltage clamp recordings were used to investigate the Na+/Ca2+ selectivity, divalent blockade and anomalous mole fraction effect (AMFE) for different NaChBac wild type/mutants channels and the properties dependence on Qf. Experimental results were compared with Brownian dynamics simulations and with analytic predictions of the ionic Coulomb blockade (ICB) model, which was extended to encompass bulk concentration effects. Results. It was shown that changing of Qf from –4e (for LESWAS wild type) to –8e (for LEDWAS mutant) leads to strong divalent blockade of the Na+ current by micromolar amounts of Ca2+ ions, similar to the effects seen in mammalian calcium channels. The BD simulations revealed a concentration-related logarithmic shift of the conduction bands. These results were shown to be consistent with ICB model predictions. Conclusions. The extended ICB model explains the experimental (divalent blockade and AMFE) and simulated (multi-ion bands and their concentration-related shifts) selectivity phenomena of NaChBac channel and its charge-varied mutants. These results extend the understanding of ion channel selectivity and may also be applicable to biomimetic nanopores with charged walls.
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- 2017
18. Vibrational resonance in an inhomogeneous medium with periodic dissipation
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Roy-Layinde, T. O., Laoye, J. A., Popoola, O. O., Vincent, Uchechukwu Enyim, McClintock, Peter Vaughan Elsmere, Roy-Layinde, T. O., Laoye, J. A., Popoola, O. O., Vincent, Uchechukwu Enyim, and McClintock, Peter Vaughan Elsmere
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The role of nonlinear dissipation in vibrational resonance (VR) is investigated in an inhomogeneous system characterized by a symmetric and spatially-periodic potential, and subjected to non-uniform, state-dependent, damping and a bi-harmonic driving force. The contributions of the parameters of the high frequency signal to the system’s effective dissipation are examined theoretically in comparison to linearly-damped systems, for which the parameter of interest is the effective stiffness in the equation of slow vibration. We show that the VR effect can be enhanced by varying the nonlinear dissipation parameters; and that it can be induced by a parameter that is shared by the damping inhomogeneity and the system potential. Furthermore, we have apparently identified the origin of the nonlinear-dissipation-enhanced response: we provide evidence of its connection to an Hopf bifurcation, accompanied by monotonic attractor enlargement in the VR regime.
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- 2017
19. Coupling functions:universal insights into dynamical interaction mechanisms
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Stankovski, Tomislav, Pereira, Tiago, McClintock, Peter Vaughan Elsmere, Stefanovska, Aneta, Stankovski, Tomislav, Pereira, Tiago, McClintock, Peter Vaughan Elsmere, and Stefanovska, Aneta
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The dynamical systems found in Nature are rarely isolated. Instead they interact and influence each other. The coupling functions that connect them contain detailed information about the functional mechanisms underlying the interactions and prescribe the physical rule specifying how an interaction occurs. Here, we aim to present a coherent and comprehensive review encompassing the rapid progress made recently in the analysis, understanding and applications of coupling functions. The basic concepts and characteristics of coupling functions are presented through demonstrative examples of different domains, revealing the mechanisms and emphasizing their multivariate nature. The theory of coupling functions is discussed through gradually increasing complexity from strong and weak interactions to globally-coupled systems and networks. A variety of methods that have been developed for the detection and reconstruction of coupling functions from measured data is described. These methods are based on different statistical techniques for dynamical inference. Stemming from physics, such methods are being applied in diverse areas of science and technology, including chemistry, biology, physiology, neuroscience, social sciences, mechanics and secure communications. This breadth of application illustrates the universality of coupling functions for studying the interaction mechanisms of coupled dynamical systems.
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- 2017
20. Calorimetric observation of single He2* excimers in a 100 mK He bath
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Carter, Faustin W., Hertel, Scott A., McClintock, Peter Vaughan Elsmere, McKinsey, Daniel N., Prober, Daniel E., Carter, Faustin W., Hertel, Scott A., McClintock, Peter Vaughan Elsmere, McKinsey, Daniel N., and Prober, Daniel E.
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We report the first calorimetric detection of individual He2* excimers within a bath of superfluid 4He. The detector used in this work is a single superconducting titanium transition edge sensor (TES) with an energy resolution of 1 eV, immersed directly in the helium bath. He2* excimers are produced in the surrounding bath using an external gamma-ray source. These excimers exist either as short-lived singlet or long-lived triplet states. We demonstrate detection (and discrimination) of both states: in the singlet case the calorimeter records the absorption of a prompt 15 eV photon, and in the triplet case the calorimeter records a direct interaction of the molecule with the TES surface, which deposits a distinct fraction of the 15 eV, released upon decay, into the surface. We also briefly discuss the detector fabrication and characterization.
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- 2017
21. Coupling functions : universal insights into dynamical interaction mechanisms
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Stankovski, Tomislav, Pereira, Tiago, McClintock, Peter Vaughan Elsmere, Stefanovska, Aneta, Stankovski, Tomislav, Pereira, Tiago, McClintock, Peter Vaughan Elsmere, and Stefanovska, Aneta
- Abstract
The dynamical systems found in Nature are rarely isolated. Instead they interact and influence each other. The coupling functions that connect them contain detailed information about the functional mechanisms underlying the interactions and prescribe the physical rule specifying how an interaction occurs. Here, we aim to present a coherent and comprehensive review encompassing the rapid progress made recently in the analysis, understanding and applications of coupling functions. The basic concepts and characteristics of coupling functions are presented through demonstrative examples of different domains, revealing the mechanisms and emphasizing their multivariate nature. The theory of coupling functions is discussed through gradually increasing complexity from strong and weak interactions to globally-coupled systems and networks. A variety of methods that have been developed for the detection and reconstruction of coupling functions from measured data is described. These methods are based on different statistical techniques for dynamical inference. Stemming from physics, such methods are being applied in diverse areas of science and technology, including chemistry, biology, physiology, neuroscience, social sciences, mechanics and secure communications. This breadth of application illustrates the universality of coupling functions for studying the interaction mechanisms of coupled dynamical systems.
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- 2017
22. Extraction of instantaneous frequencies from ridges in time-frequency representations of signals
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Iatsenko, D., McClintock, Peter Vaughan Elsmere, and Stefanovska, Aneta
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In signal processing applications, it is often necessary to extract oscillatory components and their properties from time-frequency representations, e.g. the windowed Fourier transform or wavelet transform. The first step in this procedure is to find an appropriate ridge curve: a sequence of amplitude peak positions (ridge points), corresponding to the component of interest and providing a measure of its instantaneous frequency. This is not a trivial issue, and the optimal method for extraction is still not settled or agreed. We discuss and develop procedures that can be used for this task and compare their performance on both simulated and real data. In particular, we propose a method which, in contrast to many other approaches, is highly adaptive so that it does not need any parameter adjustment for the signal to be analysed. Being based on dynamic path optimization and fixed point iteration, the method is very fast, and its superior accuracy is also demonstrated. In addition, we investigate the advantages and drawbacks that synchrosqueezing offers in relation to curve extraction. The codes used in this work are freely available for download.
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- 2016
23. Essentials of in vivo Biomedical Imaging
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McClintock, Peter Vaughan Elsmere
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Review of Essentials of in vivo Biomedical Imaging edited by Simon R. Cherry, Ramsey D. Badawi and Jinyi Qi, CRC Press, London, 2015, pp. xvi + 272. Scope: edited book, £63.99, ISBN 978-1-4398-9874-1 (Hardcover). Level: postgraduates, research scientists.
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- 2016
24. Mid-Ocean Ridges
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McClintock, Peter Vaughan Elsmere
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The Earth’s mid-ocean ridges form a single, connected, topological feature which, as Roger Searle points out, is the longest mountain range in the world. They have developed as a result of the sea floor spreading associated with tectonic movements. Although this idea is now very soundly based and almost universally accepted, it is actually of surprisingly recent origin.
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- 2016
25. Superfluid States of Matter
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McClintock, Peter Vaughan Elsmere
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Review of Superfluid States of Matter by Boris Svistunov, Egor Babaev, and Nikolay Prokof ’ev, CRC Press, London, 2015, pp. xix + 561. Scope: monograph, £63.99, ISBN 978-1-4398-0275-5 (Hardcover). Level: postgraduates, research scientists.
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- 2015
26. Ionic Coulomb blockade and anomalous mole fraction effect in NaChBac bacterial ion channels
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Kaufman, I. Kh, Fedorenko, O. A., Luchinsky, D. G., Gibby, W. A. T., Roberts, Stephen, McClintock, Peter Vaughan Elsmere, Eisenberg, R. S., Kaufman, I. Kh, Fedorenko, O. A., Luchinsky, D. G., Gibby, W. A. T., Roberts, Stephen, McClintock, Peter Vaughan Elsmere, and Eisenberg, R. S.
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We report an experimental study of the influences of the fixed charge and bulk ionic concentrations on the conduction of biological ion channels, and we consider the results within the framework of the ionic Coulomb blockade model of permeation and selectivity. Voltage clamp recordings were used to investigate the Na$^+$/Ca$^{2+}$ anomalous mole fraction effect (AMFE) exhibited by the bacterial sodium channel NaChBac and its mutants. Site-directed mutagenesis was used to study the effect of either increasing or decreasing the fixed charge in their selectivity filters for comparison with the predictions of the Coulomb blockade model. The model was found to describe well some aspects of the experimental (divalent blockade and AMFE) and simulated (discrete multi-ion conduction and occupancy band) phenomena, including a concentration-dependent shift of the Coulomb staircase. These results substantially extend the understanding of ion channel selectivity and may also be applicable to biomimetic nanopores with charged walls.
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- 2016
27. Physics and biology:from molecules to life
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McClintock, Peter Vaughan Elsmere and McClintock, Peter Vaughan Elsmere
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It has long been appreciated that Physics is essential to the understanding of many aspects of biology. As Jacques Prost points out in his Preface to Physics and Biology, the explosion of research activity at the interface between the two subjects over the last twenty years has led to investment on an unprecedented scale.
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- 2016
28. Ionic Coulomb blockade
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Kaufman, Igor Kh., McClintock, Peter Vaughan Elsmere, Kaufman, Igor Kh., and McClintock, Peter Vaughan Elsmere
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Classical ionic conduction through an inorganic monolayer nanopore is analogous to the quantum-mechanical phenomenon of electronic Coulomb blockade in quantum dots.
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- 2016
29. Insights into ion channel selectivity with ionic Coulomb Blockade
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Gibby, William, Luchinsky, Dmitry, Kaufman, Igor Khaimovich, McClintock, Peter Vaughan Elsmere, Stefanovska, Aneta, Eisenberg, R. S., Gibby, William, Luchinsky, Dmitry, Kaufman, Igor Khaimovich, McClintock, Peter Vaughan Elsmere, Stefanovska, Aneta, and Eisenberg, R. S.
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The flow of ions through a biological ion channel can be considered as transitions between occupied energy levels in the channel and either of the connecting bulk reservoirs [2]. Discreteness of ions and an electrostatic exclusion principle ensure that the number of channel energy levels equals the number of occupying ions. Using these fundamental physical principles we have recently introduced [1] an ionic Coulomb blockade (ICB) theory developed by analogy with the similar phenomenon of electron tunnelling in quantum dots [2,3]. In this picture channel selectivity is governed by energy level changes [1]. We present details of the ICB theory for ion transitions through the channel. It incorporates physiological solutions and channel properties: physical dimension, voltage drop and fixed charge, and hence allows for comparison with physiological data. The set of kinetic equations obtained using ICB is analysed. The channel probability of occupancy as a function of transition rates (and hence fixed charge and number of ions) is obtained in the steady-state approximation. It is shown that this probability displays the staircase structure familiar from analysis of occupancy in quantum dots. It is also shown that current through the channel displays sharp peaks as a function of fixed charge, hence relating channel selectivity to the structure and position of energy levels. The contribution of hydration energy is also discussed. We anticipate that inclusion of this energy into ICB theory will provide an important insight into the selectivity and conductivity of ion channels.
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- 2016
30. Influence of the liquid helium meniscus on neutron reflectometry data
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Kinane, C. J., Kirichek, O., Charlton, T. R., McClintock, Peter Vaughan Elsmere, Kinane, C. J., Kirichek, O., Charlton, T. R., and McClintock, Peter Vaughan Elsmere
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Neutron reflectometry offers a unique opportunity for the direct observation of nano-stratification in 3He-4He mixtures in the ultra-low temperature limit. Unfortunately the results of recent experiments could not be well-modelled on account of a seemingly anomalous variation of reflectivity with momentum transfer. We now hypothesize that this effect is attributable to an optical distortion caused by the liquid’s meniscus near the container wall. The validity of this idea is tested and confirmed through a subsidiary experiment on a D2O sample, showing that the meniscus can significantly distort results if the beam size in the horizontal plane is comparable with, or bigger than, the diameter of the container. The meniscus problem can be eliminated if the beam size is substantially smaller than the diameter of the container, such that reflection takes place only from the flat region of the liquid surface thus excluding the meniscus tails. Practical measures for minimising the meniscus distortion effect are discussed.
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- 2016
31. Alterations in the coupling functions between cortical and cardio-respiratory oscillations due to anæsthesia with propofol and sevoflurane
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Stankovski, Tomislav, Petkoski, Spase, Raeder, Johan, Smith, Andrew, McClintock, Peter Vaughan Elsmere, Stefanovska, Aneta, Stankovski, Tomislav, Petkoski, Spase, Raeder, Johan, Smith, Andrew, McClintock, Peter Vaughan Elsmere, and Stefanovska, Aneta
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The precise mechanisms underlying general anæsthesia pose important and still open questions. To address them, we have studied anæsthesia induced by the widely-used (intravenous) propofol and (inhalational) sevoflurane anæsthetics, computing cross-frequency coupling functions between neuronal, cardiac, and respiratory oscillations in order to determine their mutual interactions. The phase domain coupling function reveals the form of the function defining the mechanism of an interaction, as well as its coupling strength. Using a method based on dynamical Bayesian inference, we have thus identified and analyzed the coupling functions for six relationships. By quantitative assessment of the forms and strengths of the couplings, we have revealed how these relationships are altered by anæsthesia, also showing that some of them are differently affected by propofol and sevoflurane. These findings, together with the novel coupling function analysis, offer a new direction in the assessment of general anæsthesia and neurophysiological interactions in general.
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- 2016
32. Putative resolution of the EEEE selectivity paradox in L-type Ca2+ and bacterial Na+ biological ion channels
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Kaufman, Igor Kh, Luchinsky, Dmitrii Georgievich, Gibby, William A. T., McClintock, Peter Vaughan Elsmere, Eisenberg, R. S., Kaufman, Igor Kh, Luchinsky, Dmitrii Georgievich, Gibby, William A. T., McClintock, Peter Vaughan Elsmere, and Eisenberg, R. S.
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The highly selective permeation of ions through biological ion channels can be described and explained in terms of fluctuational dynamics under the influence of powerful electrostatic forces. Hence valence selectivity, e.g. between Ca2+ and Na+ in calcium and sodium channels, can be described in terms of ionic Coulomb blockade, which gives rise to distinct conduction bands and stop-bands as the fixed negative charge Qf at the selectivity filter of the channel is varied. This picture accounts successfully for a wide range of conduction phenomena in a diversity of ion channels. A disturbing anomaly, however, is that what appears to be the same electrostatic charge and structure (the so-called EEEE motif) seems to select Na+ conduction in bacterial channels but Ca2+ conduction in mammalian channels. As a possible resolution of this paradox it is hypothesised that an additional charged protein residue on the permeation path of the mammalian channel increases |Qf | by e, thereby altering the selectivity from Na+ to Ca2+. Experiments are proposed that will enable the hypothesis to be tested.
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- 2016
33. Physics and biology : from molecules to life
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McClintock, Peter Vaughan Elsmere and McClintock, Peter Vaughan Elsmere
- Abstract
It has long been appreciated that Physics is essential to the understanding of many aspects of biology. As Jacques Prost points out in his Preface to Physics and Biology, the explosion of research activity at the interface between the two subjects over the last twenty years has led to investment on an unprecedented scale.
- Published
- 2016
34. Ageing of the couplings between cardiac, respiratory and myogenic activity in humans
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Ticcinelli, Valentina, Stankovski, Tomislav, McClintock, Peter Vaughan Elsmere, Stefanovska, Aneta, Ticcinelli, Valentina, Stankovski, Tomislav, McClintock, Peter Vaughan Elsmere, and Stefanovska, Aneta
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The balance and functionality of the cardiovascular system are maintained by a network of couplings between the different oscillations involved. We study the effect of ageing on these interactions through the application of wavelet analysis, and by the use of dynamical Bayesian inference to compute coupling functions. The method, applied to phases extracted from microvascular flow recorded by laser Doppler flowmetry (LDF), reveals the coupling functions between oscillations propagated to the smallest vessels. Consistent with earlier work based on analysis of cardiac and respiratory phases obtained from direct measurements, our analysis demonstrates an impairment of the propagated cardio-respiratory coupling with ageing. The coupling weakens despite the increased cardiac component in the LDF with ageing. Our results bring new insight to the effect of ageing on cardiovascular regulation that might help improve the diagnostic potential of LDF monitors.
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- 2015
35. Coulomb blockade oscillations in biological ion channels
- Author
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Kaufman, Igor Khaimovich, Gibby, William, Luchinsky, Dmitry, McClintock, Peter Vaughan Elsmere, Eisenberg, Robert S., Kaufman, Igor Khaimovich, Gibby, William, Luchinsky, Dmitry, McClintock, Peter Vaughan Elsmere, and Eisenberg, Robert S.
- Abstract
The conduction and selectivity of calcium/sodium ion channels are described in terms of ionic Coulomb blockade, a phenomenon based on charge discreteness, an electrostatic exclusion principle, and stochastic ion motion through the channel. This novel approach provides a unified explanation of numerous observed and modelled conductance and selectivity phenomena, including the anomalous mole fraction effect and discrete conduction bands. Ionic Coulomb blockade and resonant conduction are similar to electronic Coulomb blockade and resonant tunnelling in quantum dots. The model is equally applicable to other nanopores.
- Published
- 2015
36. The discriminatory value of cardiorespiratory interactions in distinguishing awake from anaesthetised states: a randomised observational study
- Author
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Kenwright, David Alasdair, Bernjak, Alan, Draegni, Tomas, Dzeroski, Saso, Entwistle, Michael, Horvat, Martin, Kvandal, Per, Landsverk, Svein Aslak, McClintock, Peter Vaughan Elsmere, Musizza, Bojan, Petrovcic, J., Raeder, Johan, Sheppard, Lawrence, Smith, Andrew F, Stankovski, Tomislav, Stefanovska, Aneta, Kenwright, David Alasdair, Bernjak, Alan, Draegni, Tomas, Dzeroski, Saso, Entwistle, Michael, Horvat, Martin, Kvandal, Per, Landsverk, Svein Aslak, McClintock, Peter Vaughan Elsmere, Musizza, Bojan, Petrovcic, J., Raeder, Johan, Sheppard, Lawrence, Smith, Andrew F, Stankovski, Tomislav, and Stefanovska, Aneta
- Abstract
Depth of anaesthesia monitors usually analyse cerebral function with or without other physiological signals; noninvasive monitoring of the measured cardiorespiratory signals alone would offer a simple, practical alternative. We aimed to investigate whether such signals, analysed with novel, non-linear dynamic methods, would distinguish between the awake and anaesthetised states. We recorded ECG, respiration, skin temperature, pulse and skin conductivity before and during general anaesthesia in 27 subjects in good cardiovascular health, randomly allocated to receive propofol or sevoflurane. Mean values, variability and dynamic interactions were determined. Respiratory rate (p = 0.0002), skin conductivity (p = 0.03) and skin temperature (p = 0.00006) changed with sevoflurane, and skin temperature (p = 0.0005) with propofol. Pulse transit time increased by 17% with sevoflurane (p = 0.02) and 11% with propofol (p = 0.007). Sevoflurane reduced the wavelet energy of heart (p = 0.0004) and respiratory (p = 0.02) rate variability at all frequencies, whereas propofol decreased only the heart rate variability below 0.021 Hz (p < 0.05). The phase coherence was reduced by both agents at frequencies below 0.145 Hz (p < 0.05), whereas the cardiorespiratory synchronisation time was increased (p < 0.05). A classification analysis based on an optimal set of discriminatory parameters distinguished with 95% success between the awake and anaesthetised states. We suggest that these results can contribute to the design of new monitors of anaesthetic depth based on cardiovascular signals alone.
- Published
- 2015
37. Scaling laws associated with a symmetry-break in the energy distribution in a set of dynamical systems: application to discrete mappings
- Author
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Silva, Matheus Palmero [UNESP], Universidade Estadual Paulista (Unesp), Leonel, Edson Denis [UNESP], and McClintock, Peter Vaughan Elsmere
- Subjects
Diffusion ,Mapeamentos discretos ,Discrete mappings ,Chaos ,Difusão ,Caos - Abstract
Submitted by MATHEUS PALMERO SILVA null (matheuspalmero@gmail.com) on 2017-10-23T17:38:42Z No. of bitstreams: 1 Palmero-Dissertação-Final+Ficha.pdf: 7872041 bytes, checksum: 4aced1a4e65b4822d5cad50fbfb47973 (MD5) Rejected by Luiz Galeffi (luizgaleffi@gmail.com), reason: Solicitamos que realize uma nova submissão seguindo as orientações abaixo: Inserir o número do processo de financiamento FAPESP nos agradecimentos da tese/dissertação. Corrija estas informações e realize uma nova submissão contendo o arquivo correto. Agradecemos a compreensão. on 2017-10-26T16:22:04Z (GMT) Submitted by MATHEUS PALMERO SILVA null (matheuspalmero@gmail.com) on 2017-10-26T16:38:06Z No. of bitstreams: 1 Palmero-Dissertação-Final+Ficha.pdf: 7872232 bytes, checksum: 5757e6926325d1f74438fff3cd26d5e0 (MD5) Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-10-26T16:55:48Z (GMT) No. of bitstreams: 1 silva_mp_me_rcla.pdf: 7872232 bytes, checksum: 5757e6926325d1f74438fff3cd26d5e0 (MD5) Made available in DSpace on 2017-10-26T16:55:48Z (GMT). No. of bitstreams: 1 silva_mp_me_rcla.pdf: 7872232 bytes, checksum: 5757e6926325d1f74438fff3cd26d5e0 (MD5) Previous issue date: 2017-09-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Nesta dissertação, investigamos propriedades estatísticas de alguns sistemas dinâmicos descritos por mapeamentos discretos nas proximidades de duas transições: (i) integrabilidade para não integrabilidade e; (ii) crescimento limitado de energia para crescimento ilimitado de energia (aceleração de Fermi). O foco principal está na descrição do comportamento da distribuição de probabilidade da velocidade/energia das partículas em dinâmica caótica. A quebra de simetria da distribuição de probabilidade leva a uma escala adicional àquelas já conhecidas na literatura e, com este estudo, acreditamos que a quebra de simetria também possa explicar um fenômeno que já vem sendo observado em mapeamentos discretos. Fenômeno este, até então descrito apenas fenomenologicamente, teve sua primeira observação na publicação seminal de investigação de leis de escala em mapeamentos discretos no periódico Phys. Rev. Let. 93, 014101 (2004), de Edson D. Leonel, Peter V. E. McClintock e Jafferson K. L. Silva. Nossa contribuição para o problema está no desenvolvimento de descrições analíticas e verificações numéricas, baseadas em um estudo sistemático do comportamento difusivo das trajetórias caóticas no espaço de fases dos sistemas dinâmicos de interesse. In this dissertation, we investigate statistical properties of some dynamical systems described by discrete mappings near two types of transitions: (i) integrability to non-integrability; (ii) limited to unlimited diffusion in energy (Fermi acceleration). The main goal is to describe the behaviour of the probability density of the velocity/energy for a set of particles moving in a chaotic dynamics. The break of symmetry in the probability distribution leads to an additional scaling to those are already known in the literature and, with this study, we believe that the symmetry break might also explain a well-known phenomenon observed for discrete mappings. This phenomenon, it has been reported so far phenomenologically. A first observation in an area-preserving mapping was in a letter published in Phys. Rev. Let. 93, 014101 (2004), authored by Edson D. Leonel, Peter V. E. McClintock and Jafferson K. L. Silva. Our contribution to the problem is on the development of an analytical approach and numerical verifications, based essentially on a systematic study of the diffusive behaviour of chaotic trajectories on the phase space of dynamical systems of interest. FAPESP: 2014/27260-5
- Published
- 2017
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