Alex Skvortsov
Defence Science & Technology Organisation, Maritime Division, Faculty Member
- Artificial Intelligence, Biotechnology, Machine Learning, Wireless Sensor Networks, Applied Mathematics, Applied mathematics and Modelling, and 12 moreNetwork Theory, Turbulence modeling, Turbulence, Conservation Biology, Toxicology, Bayesian Inference, Data Fusion (Engineering), Multi Sensor Data Fusion, Diffusion, Particle Filter, Nonlinear dynamics, and Mathematical Biologyedit
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We study steady-state flux of particles diffusing on a flat surface and trapped by absorbing spikes of arbitrary length periodically protruding from a reflecting base. It is assumed that the particle concentration, far from this comblike... more
We study steady-state flux of particles diffusing on a flat surface and trapped by absorbing spikes of arbitrary length periodically protruding from a reflecting base. It is assumed that the particle concentration, far from this comblike boundary, is kept constant. To find the flux, we use a boundary regularization approach that replaces the initial highly rough and heterogeneous boundary by an effective boundary which is smooth and uniform. After such a replacement, the two-dimensional diffusion problem becomes essentially one-dimensional, and the steady-state flux can be readily found. Our main results are simple analytical expressions determining the position of the smooth effective boundary and its uniform trapping rate as functions of the spike length and interspike distance. It is shown that the steady-state flux to the effective boundary is identical to its counterpart to the initial boundary at large distances from this boundary. Our analytical results are corroborated by Br...
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<p>Material tracers at the ocean surface disperse under the influence of the quasi-random forces that act on the ocean surface. These forces may include ocean turbulence, wind, and surface waves. Currently, wind and... more
<p>Material tracers at the ocean surface disperse under the influence of the quasi-random forces that act on the ocean surface. These forces may include ocean turbulence, wind, and surface waves. Currently, wind and ocean turbulence are assumed to be the important drivers of dispersion of the floating tracer particles. Despite some theoretical results and laboratory experiments, the experimental proof of the significant contribution of wave induced dispersion in overall transport of large-scale geophysical systems remains elusive. This is mainly due to a lack of practical observations.</p><p>In this study we aim to estimate the contribution of wave-induced dispersion in comparison with conventional mechanisms of dispersion due to ocean turbulence. We do so through the analysis of in-situ observations of surface drifters deployed across the seas and oceans.  The experimental dataset include data from the Global Drifter Program and newly obtained data through cluster deployment of Spotter wave buoys. The results suggest that waves during marine storm conditions may be a critical driver of surface tracer dispersion during the first ten days after the storm and at horizontal length scales up to the order of 10 km. Our results imply that accurate information of wave conditions is required for accurate prediction of tracer dispersion at short to intermediate time and length scales.</p>
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Quantifying flow noise reduction caused by different surface coatings is a ubiquitous topic in aero- and hydroacoustics and is still an area of active research. Methods for doing so commonly involve huge costs in computational power... more
Quantifying flow noise reduction caused by different surface coatings is a ubiquitous topic in aero- and hydroacoustics and is still an area of active research. Methods for doing so commonly involve huge costs in computational power (coupled CFD and FE simulations) and infrastructure (experimental studies). These high costs often make assessment, prototyping or rigorous sensitivity analysis a challenging undertaking. A self-consistent analytical framework is proposed for rapid estimation of relative flow noise intensity for a significantly subsonic turbulent flow over an elastic boundary (such as a turbulent boundary layer). The method utilises the well-known analogy between motion of viscous flow and wave propagation in soft elastic media (materials with low shear moduli). Together with the turbulent flow represented by an ensemble of viscous (shear or vortex) waves, the problem is transformed into that of elastic wave propagation within a multi-layered medium. The resulting noise ...
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Acoustic coatings on maritime vehicles can significantly reduce the transmission of machinery noise in the ambient marine environment as well as absorb external acoustic waves. In this work, the performance of two types of phononic... more
Acoustic coatings on maritime vehicles can significantly reduce the transmission of machinery noise in the ambient marine environment as well as absorb external acoustic waves. In this work, the performance of two types of phononic crystals with steel backing is investigated for acoustic coating applications. The first type of phononic crystal comprises periodic voids embedded in a soft elastic medium. The second type of phononic crystal comprises hard scatterers arranged periodically in an elastic medium. The voids exhibit monopole resonance, leading to low sound transmission through the coating in a broad frequency range. In contrast, the hard scatterers exhibit dipole resonance which results in low sound reflection. The ratio of bulk to shear moduli of the elastic medium governs the monopole resonance, whereas the dipole resonance is governed by the ratio of the density of the scatterers to the density of the host medium. The effect of steel backing on the transmission side of th...
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Research Interests: Environmental Science, Geology, Physics, Mechanics, Computational Fluid Dynamics, and 14 moreMarine Engineering, Computation, Propeller, Boundary Element Method, Ships and Offshore Structures, Hull, Maritime Engineering, Offshore Geotechnical Engineering, Volume of Fluid Method, Wake, Time Domain Analysis, side impact, hydrodynamic loads, and propulsive efficiency
ABSTRACT Chemical sensor networks are used to detect the presence of hazardous chemicals released intentionally or accidentally into the atmosphere. Although many performance attributes of chemical sensor networks, such as energy... more
ABSTRACT Chemical sensor networks are used to detect the presence of hazardous chemicals released intentionally or accidentally into the atmosphere. Although many performance attributes of chemical sensor networks, such as energy utilization, detection delay, and false alarm characteristics, have been studied in the literature, the effect of spatial correlation of sensor readings on the network performance has not hitherto been studied. Because chemical tracers dispersing in the turbulent atmosphere are inherently spatially correlated, understanding how such correlations impact on the network performance is vital for chemical sensor network optimization. In this paper we investigate the impact of spatial correlation on the performance of chemical sensor networks.
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The aim of this study is to develop a simple phenomenological model for elastic wave propagation in a composite material formed by localized inclusions embedded in an elastic matrix. It is assumed that the material can be characterised by... more
The aim of this study is to develop a simple phenomenological model for elastic wave propagation in a composite material formed by localized inclusions embedded in an elastic matrix. It is assumed that the material can be characterised by only two aggregated parameters, viz., volume fraction of inclusions and their resonance frequency within the elastic matrix. The values of these two parameters are assumed to be given (i.e. from experimental measurements) or deduced from other models (also presented in the paper). The shear wave velocity in the elastic matrix is assumed to be much smaller than the velocity of longitudinal waves. A simple analytical expression for the effective longitudinal wave velocity that is uniformly valid for the entire frequency domain is derived (including proximity to the resonance frequency of inclusions) and validated with some paradigmatic results of the mean-field theories.
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Viruses of the family Rhabdoviridae infect a broad range of hosts from a variety of ecological and geographical niches, including vertebrates, arthropods, and plants. The arthropod-transmitted members of this family display considerable... more
Viruses of the family Rhabdoviridae infect a broad range of hosts from a variety of ecological and geographical niches, including vertebrates, arthropods, and plants. The arthropod-transmitted members of this family display considerable genetic diversity and remarkable genomic flexibility that enable coding for various accessory proteins in different locations of the genome. Here, we describe the genome of Holmes Jungle virus, isolated from Culex annulirostris mosquitoes collected in northern Australia, and make detailed comparisons with the closely related Ord River and Wongabel viruses, with a focus on identifying very small open reading frames (smORFs) in their genomes. This is the first systematic prediction of smORFs in rhabdoviruses, emphasising the intricacy of the rhabdovirus genome and the knowledge gaps. We speculate that these smORFs may be of importance to the life cycle of the virus in the arthropod vector.
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Social contacts are an important channel for the propagation of disease through a population and should be considered in conjunction with traditional epidemic diffusion. Such channels should always be taken into account for a realistic... more
Social contacts are an important channel for the propagation of disease through a population and should be considered in conjunction with traditional epidemic diffusion. Such channels should always be taken into account for a realistic estimation of a long-term impact of a disease outbreak (natural or malicious) and for the best response options. This paper describes our recent experience in developing a simple agent-based model to simulate disease propagation through a social network and validating the results of the agent-based simulation by reconciling it with a well-known mathematical model.
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The automatic detection of passive tracers on a moving wavy surface has numerous applications in mathematics and engineering. In oceanography, among many examples, down-looking conventional optical cameras can be employed in wave tanks to... more
The automatic detection of passive tracers on a moving wavy surface has numerous applications in mathematics and engineering. In oceanography, among many examples, down-looking conventional optical cameras can be employed in wave tanks to investigate the mechanisms of particle dispersion induced by wave turbulence. In this context, we present a computational system to automatically track down the trajectories of several identical passive floaters under the influence of mechanically generated water waves with distinct spectral features.
Such functionality is not yet publicly available and a free/open source code within the Python programming environment is described and evaluated. The code is robust and fast, able to automatically identify drifters at 30 fps during approximately 40 seconds, while they remained in the camera’s field of view. The algorithm is an efficient tool with many operational and scientific applications
Such functionality is not yet publicly available and a free/open source code within the Python programming environment is described and evaluated. The code is robust and fast, able to automatically identify drifters at 30 fps during approximately 40 seconds, while they remained in the camera’s field of view. The algorithm is an efficient tool with many operational and scientific applications
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ABSTRACT The contaminant transport process governed by the advection–diffusion equation plays an important role in modelling industrial and environmental flows. In this article, our aim is to accurately reduce the 2-D advection–diffusion... more
ABSTRACT The contaminant transport process governed by the advection–diffusion equation plays an important role in modelling industrial and environmental flows. In this article, our aim is to accurately reduce the 2-D advection–diffusion equation governing the dispersion of a contaminant in a turbulent open channel flow to its 1-D approximation. The 1-D model helps to quickly estimate the horizontal size of contaminant clouds based on the values of the model coefficients. We derive these coefficients analytically and investigate numerically the model convergence. The derivation is based on the centre manifold theory to obtain successively more accurate approximations in a consistent manner. Two types of the average velocity profile are considered: the classical logarithmic profile and the power profile. We further develop the one-dimensional integrated radial basis function network method as a numerical approach to obtain the numerical solutions to both the original 2-D equation and the approximate 1-D equations. We compare the solutions of the original models with their centre-manifold approximations at very large Reynolds numbers. The numerical results obtained from the approximate 1-D models are in good agreement with those of the original 2-D model for both the logarithmic and power velocity profiles.
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Steady-state diffusion in long axisymmetric structures is considered. The goal is to assess one-dimensional approximations by comparing them with axisymmetric eigenfunction expansions. Two problems are considered in detail: a finite tube... more
Steady-state diffusion in long axisymmetric structures is considered. The goal is to assess one-dimensional approximations by comparing them with axisymmetric eigenfunction expansions. Two problems are considered in detail: a finite tube with one end that is partly absorbing and partly reflecting; and two finite coaxial tubes with different cross-sectional radii joined together abruptly. Both problems may be modelled using effective boundary conditions, containing a parameter known as the trapping rate. We show that trapping rates depend on the lengths of the finite tubes (and that they decay slowly as these lengths increase) and we show how trapping rates are related to blockage coefficients, which are well known in the context of potential flow along tubes of infinite length.
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We derive an approximate formula for the mean first-passage time (MFPT) to a small absorbing target of arbitrary shape inside an elongated domain of a slowly varying axisymmetric profile. For this purpose, the original Poisson equation in... more
We derive an approximate formula for the mean first-passage time (MFPT) to a small absorbing target of arbitrary shape inside an elongated domain of a slowly varying axisymmetric profile. For this purpose, the original Poisson equation in three dimensions is reduced an effective one-dimensional problem on an interval with a semi-permeable semi-absorbing membrane. The approximate formula captures correctly the dependence of the MFPT on the distance to the target, the radial profile of the domain, and the size and the shape of the target. This approximation is validated by Monte Carlo simulations.
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New scaling laws for the evolution of strong convective buoyant thermals are presented. These strong thermals can be formed by rapid energy release in the environment (e.g., explosion, volcano eruption). The new scaling laws are the... more
New scaling laws for the evolution of strong convective buoyant thermals are presented. These strong thermals can be formed by rapid energy release in the environment (e.g., explosion, volcano eruption). The new scaling laws are the power-law relations between the elevation and radius of the thermal and the time since its release. It is shown that the exponents of these power-laws are determined by the density contrast (or total energy) associated with the thermal. At the limit of a weak thermal our model is in agreement with the celebrated work of Batchelor, Morton and Turner. Experimental data from literature are presented to support our findings. Variety of new scaling laws for buoyant thermals valid outside the Boussinesq approximation Validation of the new scaling laws with experimental data Energy based criterion for observation of different scaling laws. Variety of new scaling laws for buoyant thermals valid outside the Boussinesq approximation Validation of the new scaling laws with experimental data Energy based criterion for observation of different scaling laws.
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Experimental results for passive tracer dispersion in the turbulent surface layer under convective conditions are presented. In this case, the dispersion of tracer particles is determined by the interplay of two mechanisms: buoyancy and... more
Experimental results for passive tracer dispersion in the turbulent surface layer under convective conditions are presented. In this case, the dispersion of tracer particles is determined by the interplay of two mechanisms: buoyancy and advection. In the atmospheric surface layer under stable stratification the buoyancy mechanism dominates when the distance from the ground is greater than the Monin-Obukhov length, resulting in a different exponent in the scaling law of relative separation of lagrangian particles (deviation from the celebrated Richardson's law). This conclusion is supported by our extensive atmospheric observations. Exit-time statistics are derived from our experimental dataset, which demonstrates a significant difference between tracer dispersion in the convective and neutrally stratified surface layers.
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The toxins associated with infectious diseases are potential targets for inhibitors which have the potential for prophylactic or therapeutic use. Many antibodies have been generated for this purpose, and the objective of this study was to... more
The toxins associated with infectious diseases are potential targets for inhibitors which have the potential for prophylactic or therapeutic use. Many antibodies have been generated for this purpose, and the objective of this study was to develop a simple mathematical model that may be used to evaluate the potential protective effect of antibodies. This model was used to evaluate the contributions of antibody affinity and concentration to reducing antibody-receptor complex formation and internalization. The model also enables prediction of the antibody kinetic constants and concentration required to provide a specified degree of protection. We hope that this model, once validated experimentally, will be a useful tool for in vitro selection of potentially protective antibodies for progression to in vivo evaluation.
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The paper presents an algorithm for syndromic surveillance of an epidemic outbreak formulated in the context of stochastic nonlinear filtering. The dynamics of the epidemic is modeled using a generalized compartmental epidemiological... more
The paper presents an algorithm for syndromic surveillance of an epidemic outbreak formulated in the context of stochastic nonlinear filtering. The dynamics of the epidemic is modeled using a generalized compartmental epidemiological model with inhomogeneous mixing. The syndromic (typically non-medical) observations of the number of infected people (e.g. visits to pharmacies, sale of certain products, absenteeism from work/study etc.) are used for estimation. The state of the epidemic, including the number of infected people and the unknown parameters of the model, are estimated via a particle filter. The numerical results indicate that the proposed framework can provide useful early prediction of the epidemic peak if the uncertainty in prior knowledge of model parameters is not excessive.
Research Interests: Computer Science, Algorithms, Biology, Communicable Diseases, Medicine, and 13 moreStochastic processes, Biological Sciences, Disease Outbreaks, Humans, Mathematical Sciences, Data Collection, Prior Knowledge, Particle Filter, Nonlinear Filter, Statistical models, Quantitative Method, Mathematical Biosciences, and Syndromic surveillance
The dynamics of particle transport under the influence of localised high energy anomalies (explosions) is a complicated phenomena dependent on many physical parameters of both the particle and the medium it resides in. Here we present a... more
The dynamics of particle transport under the influence of localised high energy anomalies (explosions) is a complicated phenomena dependent on many physical parameters of both the particle and the medium it resides in. Here we present a conceptual model that establishes simple scaling laws for particle dispersion in relation to the energy released in a blast, properties of the medium, physical properties of particles and their initial position away from a blast epicenter. These dependencies are validated against numerical simulations and we discuss predictions of the model which can be validated experimentally. Other applications and extensions to the framework are also considered.
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A reaction-diffusion model of receptor-toxin-antibody (RTA) interaction is studied numerically. The protective properties of an antibody against a given toxin are evaluated for a spherical cell placed into a toxin-antibody solution. The... more
A reaction-diffusion model of receptor-toxin-antibody (RTA) interaction is studied numerically. The protective properties of an antibody against a given toxin are evaluated for a spherical cell placed into a toxin-antibody solution. The selection of parameters for numerical simulation approximately corresponds to the practically relevant values reported in the literature (ricin and monoclonal antibody 2B11) with the significant ranges in variation to allow demonstration of different regimes of intracellular transport. The proposed refinement of the RTA model may become important for the consistent evaluation of protective potential of an antibody and for the estimation of the time period during which the application of this antibody becomes the most effective. It can be a useful tool for in vitro selection of potential protective antibodies for progression to in vivo evaluation.
The problem of environmental monitoring using a wireless network of chemical sensors with a limited energy supply is considered. Since the conventional chemical sensors in active mode consume vast amounts of energy, an optimisation... more
The problem of environmental monitoring using a wireless network of chemical sensors with a limited energy supply is considered. Since the conventional chemical sensors in active mode consume vast amounts of energy, an optimisation problem arises in the context of a balance between the energy consumption and the detection capabilities of such a network. A protocol based on "dynamic sensor collaboration" is employed: in the absence of any pollutant, majority of sensors are in the sleep (passive) mode; a sensor is invoked (activated) by wake-up messages from its neighbors only when more information is required. The paper proposes a mathematical model of a network of chemical sensors using this protocol. The model provides valuable insights into the network behavior and near optimal capacity design (energy consumption against detection). An analytical model of the environment, using turbulent mixing to capture chaotic fluctuations, intermittency and non-homogeneity of the pol...
Research Interests: Cognitive Science, Computer Science, Distributed Computing, Physics, Energy Consumption, and 11 moreEnvironmental Monitoring, Performance Analysis, Wireless Network, Sensor Network, Multi Sensor Data Fusion, Mathematical Model, Information and Network Security, Analytical Model, Turbulent Mixing, Chemical Sensor, and Information network
This paper presents a succinct review of attempts in the literature to use game theory to model decision-making scenarios relevant to defence applications. Game theory has been proven as a very effective tool in modelling the... more
This paper presents a succinct review of attempts in the literature to use game theory to model decision-making scenarios relevant to defence applications. Game theory has been proven as a very effective tool in modelling the decision-making processes of intelligent agents, entities, and players. It has been used to model scenarios from diverse fields such as economics, evolutionary biology, and computer science. In defence applications, there is often a need to model and predict the actions of hostile actors, and players who try to evade or out-smart each other. Modelling how the actions of competitive players shape the decision making of each other is the forte of game theory. In past decades, there have been several studies that applied different branches of game theory to model a range of defence-related scenarios. This paper provides a structured review of such attempts, and classifies existing literature in terms of the kind of warfare modelled, the types of games used, and th...