Time-varying Spatial Distribution Research Articles

Advanced Hydrodynamic Modelling of Flow at a River Bridge: Insights from 3D Computational Fluid Dynamics

Failure of river bridges is often due to hydraulic reasons, such as the development of severe scouring around piers and abutments. In many cases, the presence of bridge structures produces complex flow fields, which are difficult to predict using standard hydraulic models. This entails difficulties in estimating the hydrodynamic actions on the structure and the potential scour on the riverbed. A three-dimensional Computational Fluid Dynamics (3D CFD) model is used to analyze the flow field and the bed shear stresses at an existing bridge. The Volume of Fluid (VoF) method allows resolving the deformable free-surface, and the Detached Eddy Simulation (DES) approach allows resolving the dynamics of the energetically important turbulent eddies in the flow. The analysis deals with modeling the flow around a realistic, full-scale, multi-pier bridge in the Po River. Simulations considered different hydrodynamic regimes, i.e., the free-surface flow regime and the hypothetical pressure-flow regime which would occur when water levels are higher than the low chord of the bridge deck. The numerical application highlights the potential of the DES technique for analyzing the hydrodynamics of flow at bridges in natural river channels. Besides the turbulent flow fields and the description of the vortical structures, relevant results include the time-varying spatial distribution of the hydrodynamic forces acting on the different parts of the bridge and the time-varying distribution of the shear stress on the bed. This aspect is of particular interest because i) the estimation of drag forces on the structure components may be oversimplified using canonical, averaged formulas, and ii) the fluctuations in time of the bed shear stresses play a key role in determining the removal of sediments from the bed and the scour hole close to the bridge piers.

Kernel-based learning of birth process from evolving spatiotemporal RFS data stream in SMC[sbnd]CPHD filter for multi-target tracking

This paper presents a kernel-based framework to estimate the birth process in the sequential Monte Carlo cardinalized probability hypothesis density (SMCCPHD) filter from the evolving spatiotemporal birth random finite set data stream that can enhance the performance of the SMCCPHD based trackers when tracking targets with no a priori information on where and when targets can appear. The time-varying spatial distribution of birth events is modelled as a map with adaptive grid points and their corresponding density values. While the spatial distribution of birth density is estimated from the elements of the birth random finite sets (RFSs), the time-varying birth cardinality distribution is estimated from the cardinality of the birth RFSs. The corresponding estimations are eventually used by a SMCCPHD based tracker to adjust its filtering strength spatially and temporally for target tracking. Experimental results on both the synthetic and real video surveillance datasets show that the proposed algorithm can improve the tracking accuracy by more precisely eliminating clutters and more effectively capturing newborn targets.

Remote Sensing of Floral Resources for Pollinators – New Horizons From Satellites to Drones

Insect pollinators are affected by the spatio-temporal distribution of floral resources, which are dynamic across time and space, and also influenced heavily by anthropogenic activities. There is a need for spatial data describing the time-varying spatial distribution of flowers, which can be used within behavioral and ecological studies. However, this information is challenging to obtain. Traditional field techniques for mapping flowers are often laborious and limited to relatively small areas, making it difficult to assess how floral resources are perceived by pollinators to guide their behaviors. Conversely, remote sensing of plant traits is a relatively mature technique now, and such technologies have delivered valuable data for identifying and measuring non-floral dynamics in plant systems, particularly leaves, stems and woody biomass in a wide range of ecosystems from local to global scales. However, monitoring the spatial and temporal dynamics of plant floral resources has been notably scarce in remote sensing studies. Recently, lightweight drone technology has been adopted by the ecological community, offering a capability for flexible deployment in the field, and delivery of centimetric resolution data, providing a clear opportunity for capturing fine-grained information on floral resources at key times of the flowering season. In this review, we answer three key questions of relevance to pollination science – can remote sensing deliver information on (a) how isolated are floral resources? (b) What resources are available within a flower patch? And (c) how do floral patches change over time? We explain how such information has potential to deepen ecological understanding of the distribution of floral resources that feed pollinators and the parameters that determine their navigational and foraging choices based on the sensory information they extract at different spatial scales. We provide examples of how such data can be used to generate new insights into pollinator behaviors in distinct landscape types and their resilience to environmental change.

Investigation of the Shielding and Attenuation Effects of a Dynamical High-Density Chaff Cloud on the Signal Based on Voxel Splitting

Chaff jamming is a widely used passive interference method. A chaff cloud diffusion model for the widespread chaff cloud was presented. The high-density chaff cloud aerodynamic model can rapidly predict the chaff elements’ time-varying spatial orientation, location, and overall spatial distribution. Basing on these pieces of information, the radar cross section (RCS) for the single chaff fibre can be obtained based on the method of moments (MoM). For high-density chaff clouds, the attenuation and shielding effects on the signal must be considered. This paper proposed a voxel splitting method in rotated coordinates, dividing the chaff cloud into rectangular cells with one side perpendicular to the direction of radar entry. The varied polarized RCS features of the chaff cloud were simulated and analysed on this foundation. By dividing the chaff cloud into dynamic voxels and considering the uneven density distribution of the chaff cloud and the signal attenuation in each segment caused by the continuous fluctuating shape, fine-grained simulations of the chaff cloud radar echoes can be performed.

Studying the Perception of Sound in Space: Granular Sounds Spatialized in a High-Order Ambisonics System

Space is an important aspect of music composition that received little emphasis in certain periods of the history of Western music. However, in the twentieth century, electroacoustic music reintroduced this element by utilizing the different spatialization methods available. In this article, we discuss the methodology of analysis and the results of a study of the perception of sound in space involving sounds generated by granular synthesis that were spatialized in a high-order ambisonics system performed at CIRRMT’s Immersive Presence Laboratory at McGill University. We investigated two hypotheses of sound perception in space: 1) the variation of the granular synthesis parameters produces differences in the morphology of sounds perceived in their time-varying spatial distribution; and 2) the presence of more morphological sound variations when higher orders of ambisonics are employed, in addition to the generation of sound fields with more depth. In order to verify these hypotheses, we employed a method of analysis based on graphical representations of data derived from audio descriptors, such as graphical curves, a graphic representation of volume and phase space graphics. As a result, we observed that when higher orders of ambisonics are employed, the listener perceives more variations in frequency and intensity in sound spatialization, in addition to a preponderance of the decorrelation effect. Such effect is related to the presence of more diffuse sound fields.

Precise thickness profile measurement insensitive to spatial and temporal temperature gradients on a large glass substrate.

When manufacturing glass substrates for display devices, especially for large-sized ones, the time-varying spatial temperature gradient or distribution on the samples is remarkably observed. It causes serious degradation of thickness measurement accuracy due to the combination of thermally expanded thickness and temperature-dependent refractive index. To prevent or minimize the degradation in thickness measurement accuracy, the temperature distribution over an entire glass substrate has to be known in real time in synchronization with the thickness measurement to specify the refractive index of the sample based on an exact mathematical model of the temperature-dependent refractive index. In this paper, a measurement method for determining the thickness profile of a large glass substrate regardless of precise measurement of temperature distribution and the mathematical model of the refractive index was demonstrated. The widely used glass substrates with nominal thicknesses of 0.6 mm and 1.3 mm were measured at room and high temperatures. Through comparison of thickness profiles of hot glass substrates having large temperature gradients and those estimated through thermal expansion of thickness profiles measured at room temperature, it was confirmed that the proposed method can provide highly reliable thickness measurement results under such challenging conditions, unlike simple calculation from the optical thickness using the well-known refractive index.

Experimental Study on the Aperture of Geomagnetic Location Arrays

A method of locating a magnetic target based on geomagnetic total field is proposed. In the method, a conjugate gradient algorithm is introduced to eliminate the time-varying and uneven spatial distribution of geomagnetic total field. Then a structure of the measuring array of geomagnetic total field is designed. In the measuring array, the array aperture is a primary factor for the conjugate gradient algorithm. To determine an optimal aperture, we analyze the relationship between the array aperture and the localization accuracy. According to the localization theory based on geomagnetic total field, we simulate the process of determining an optimum array aperture. Based on the simulation, we propose the basis and principle of determining the optimum array aperture. To prove it, we use optically pumped magnetometers with different array apertures to carry out the experiments of locating a car in a suburb. Through the experiment, we get the experimental relationship between apertures and location accuracy. And the relationship agrees with the theory. The result shows that the method is feasible to determine the optimum aperture.

Performance Analysis of Reversible Binding Receptor Based Decode-and-Forward Relay in Molecular Communication Systems

Molecular communication (MC) allows nano-machines to communicate and cooperate with each other in a fluid environment. The diffusion-based MC is easily constrained by the transmit distance due to the severe attenuation of molecule concentrations. In this letter, we present a decode-and-forward relay strategy for the reversible binding receptor in the diffusion-based MC system. The time-varying spatial distribution of the information molecules based on the reversible association and dissociation between ligand and receptor at the surface of receiver is characterized. An analytical expression for the evaluation of expected error probability is derived, and the key factors impacting the performance are exploited. Results show that the proposal can improve the performance significantly with a constant molecular budget, in which the performance gain can be maximized through optimizing the position of the relay nodes and the number of molecules assigned to the source nodes.

A Validated Multiscale In-Silico Model for Mechano-sensitive Tumour Angiogenesis and Growth

Vascularisation is a key feature of cancer growth, invasion and metastasis. To better understand the governing biophysical processes and their relative importance, it is instructive to develop physiologically representative mathematical models with which to compare to experimental data. Previous studies have successfully applied this approach to test the effect of various biochemical factors on tumour growth and angiogenesis. However, these models do not account for the experimentally observed dependency of angiogenic network evolution on growth-induced solid stresses. This work introduces two novel features: the effects of hapto- and mechanotaxis on vessel sprouting, and mechano-sensitive dynamic vascular remodelling. The proposed three-dimensional, multiscale, in-silico model of dynamically coupled angiogenic tumour growth is specified to in-vivo and in-vitro data, chosen, where possible, to provide a physiologically consistent description. The model is then validated against in-vivo data from murine mammary carcinomas, with particular focus placed on identifying the influence of mechanical factors. Crucially, we find that it is necessary to include hapto- and mechanotaxis to recapitulate observed time-varying spatial distributions of angiogenic vasculature.

Modeling and Simulation of Molecular Communication Systems with a Reversible Adsorption Receiver

In this paper, we present an analytical model for the diffusive molecular communication (MC) system with a reversible adsorption receiver in a fluid environment. The widely used concentration shift keying (CSK) is considered for modulation. The time-varying spatial distribution of the information molecules under the reversible adsorption and desorption reaction at the surface of a receiver is analytically characterized. Based on the spatial distribution, we derive the net number of newly-adsorbed information molecules expected in any time duration. We further derive the number of newly-adsorbed molecules expected at the steady state to demonstrate the equilibrium concentration. Given the number of newly-adsorbed information molecules, the bit error probability of the proposed MC system is analytically approximated. Importantly, we present a simulation framework for the proposed model that accounts for the diffusion and reversible reaction. Simulation results show the accuracy of our derived expressions, and demonstrate the positive effect of the adsorption rate and the negative effect of the desorption rate on the error probability of reversible adsorption receiver with last transmit bit-1. Moreover, our analytical results simplify to the special cases of a full adsorption receiver and a partial adsorption receiver, both of which do not include desorption.

Reconstruction of the deep temperature by the acoustothermometric method and with consideration for the heat conduction equation

An acoustothermometric algorithm for reconstruction of the time-varying spatial temperature distribution is proposed and studied. The algorithm is based on the following a priory information: temperature variations is described by the heat conduction equation. Two distribution parameters are determined: the source and the temperature conductivity coefficient. Reconstruction is carried out on the basis of experimental data obtained when the model object (beef liver) is heated up. Obtaining these data requires 10 seconds (for a measurement error of about 0.1 K). In the reconstruction process, an error of about 0.5 K, which completely meets the medical requirements, is attained.

Thermomechanical finite-element analysis and dynamics characterization of three-plug oscillating heat pipes

Presented here are a nonlinear thermomechanical finite-element model of U-shaped three-plug oscillating heat pipes (OHPs) and numerical methods that can accurately predict the model’s oscillation frequency and calculate the time-varying spatial distribution of temperature and the global heat transfer efficiency. The model accounts for the influences of nonlinear spring effect of vapor bubbles, mass transferring effect, fluid filling ratio, operating temperature, gravity, pressure loss due to pipe bend, and temperature difference between the evaporator and condenser. Dynamics of OHPs is characterized using a newly developed time–frequency analysis algorithm, and an Euler predictor–corrector method with convergence check is used to solve for the temperature distribution within the fluid plug. Results show that an OHP is a parametrically excited nonlinear thermomechanical system. An explicit formula for accurate prediction of the model’s oscillation frequency is derived, and it reveals that the oscillation frequency is mainly determined by the fluid plug mass, initial vapor pressure, and the vapor-plug-length/pipe-cross-sectional-area ratio. Parameters that determine the oscillation amplitude include the temperature difference between the evaporator and condenser, heat transfer coefficients, fluid filling ratio, and initial temperature. Moreover, the existence of gravity directing from the evaporator to the condenser increases the oscillation frequency. These results provide better understanding of heat transfer mechanisms of OHPs and can be used to optimize designs of OHPs.

Conversion of Electrical and Synaptic Actions into Impulse Discharge Patterns in Purkinje Neurons with Active Dendrites: A Simulation Study

We studied relations between the cell output spiking patterns (neuronal codes) and the intensity of input signals on a model of cerebellar Purkinje neuron with reconstructed dendritic arborization and nonlinear membrane properties. The input influences were either a depolarizing current, I s, applied at the soma or tonic synaptic excitation resulting in a synaptic conductivity, G s homogeneously distributed over the dendrites. The spiking patterns were distinguished based on periodical or nonperiodical (stochastic) sequences of spikes and/or their groups (bursts). The role of dendrites in pattern forming was revealed from time-varying spatial distributions of the dendritic membrane potential and the corresponding voltages in the soma and distal axon. As integrative indicators, interspike intervals, ISIs, and mean firing rates, f, characterized the output spiking, while mean voltage differences, ΔĒ, between the remotest equidistant sites in all pairs of the sister dendrite branches characterized the electrical heterogeneity of the arborization. To explore a wide range of conditions, I st and G s were varied, respectively, from 0.55 to 1.4 nA and from 50 μS/cm2 to 7 mS/cm2 On average, the output firing rate f increased with increased intensities of either input signal. The f-I st and f-G s relations, however, differed from each other. The former was an approximately logarithmic function with small deviations at mid-range currents, while the latter was a nonmonotonically increasing function with remarkable slope breaks within an intermediate Gs range. Within the intensity ranges, the electrical heterogeneity of the arborization ΔĒ increased with greater I st, but it first increased and then decreased with increasing G s. The leading pattern-forming factor of dendritic origin consists of transitions of the dendritic domains between states of spatially homogeneous near-resting depolarization (down-state) and spatially heterogeneous high depolarization (up-state) manifested as the appearance of slow plateau-like depolarization potentials. The latter were generated with phase shifts between dendritic subtrees in response to the applied current I st > 1.5 nA (about threefold greater than the threshold current) or in response to synaptic activation of low (G s ≤ 66 μS/cm2) and high (G s > 75 μS/cm2), but not intermediate intensities. Under these conditions, the output patterns were either continuous firing with nearly constant ISIs or simple periodical sequences of identical bursts accompanied by moderate elevations of ΔĒ. At intermediate synaptic intensities, the synchronous transitions were periodically perturbed by nonsynchronous ones, leading to generation of several dissimilar bursts or “single spike-burst” complexes. These events were associated with the largest ΔĒ elevations indicating the greatest electrical heterogeneity of the arborization. Such desynchronized transitions are explained by the existence of an asymmetry-induced difference in the transfer properties of the dendrite subtrees, leading to increased differences in the electrical states. We conclude that the dendritic arborization of Purkinje neurons behaves like a complex of high-threshold low-frequency spatial electrical oscillators, while the axo-somatic trigger zone has a low threshold and is capable of providing a high firing frequency. These properties determine the conversion of the input signal intensity into output firing patterns depending on which of these coupled oscillators is at present the predominant receiver of the input signal and also on the input intensity.

Charge transfer during intracloud lightning from a time-dependent multidipole model

[1] A time-dependent, multidipole (TDMD) model has been developed to show the charge transfer during intracloud (IC) flashes with high time and space resolution. This model combines high-speed electric field measurements from a balloon-borne instrument (Esonde) and three-dimensional lightning maps from the New Mexico Tech Lightning Mapping Array (LMA). The result is a time-varying spatial distribution of charge along lightning channels, which reveals several details about charge transfer during IC flashes. For example, a flash in 2004 initially deposited negative charge in one region and later transferred part of it to another region at a lower altitude where the negative leader was more highly branched. A flash in 2007 shows charge distributions along a main channel and two short branches; each of the three channels had different charges per unit length of channel.

Nonlinear Reduced-Order Analysis with Time-Varying Spatial Loading Distributions

Oscillating shocks acting in combination with high-intensity acoustic loadings present a challenge to the design of resilient hypersonic-flight vehicle structures. This paper addresses some features of this loading condition and certain aspects of a nonlinear reduced-order analysis with emphasis on system identification, leading to the formation of a robust modal basis. The nonlinear dynamic response of a composite structure subject to the simultaneous action of locally strong oscillating pressure gradients and high-intensity acoustic loadings is considered. The reduced-order analysis used in this work has been previously demonstrated to be both computationally efficient and accurate for time-invariant spatial loading distributions, provided that an appropriate modal basis is used. The challenge of the present study is to identify a suitable basis for loadings with time-varying spatial distributions. Using a proper orthogonal decomposition and modal expansion, it is shown that such a basis can be developed. The basis is made more robust by incrementally expanding it to account for changes in the location, frequency, and span of the oscillating pressure gradient.

Thermal stability analysis of high temperature superconducting magnet coils under overcurrent pulses

This paper presents some numerical simulation results of thermal behavior on the high temperature superconducting (HTS) magnet coils wounded by Bi2223/Ag multifilamentary tapes subjected to an overcurrent pulse using the finite element method (FEM). The analytical results show that the time-varying spatial temperature distribution of the HTS magnet coils under the condition of different overcurrent pulses has an important influence on its stability estimation, and the temperature dependence of minimum propagation current plays a key role in the stability analysis of the HTS magnet. Through the FEM analysis, the permitted duration time of 5-multiple overcurrent pulse has been obtained for the HTS magnet under the various operating conditions and cooling conditions. In this paper, an analytical method for determining the stability of the HTS magnet coils subjected to an overcurrent pulse has been proposed and a stability criterion has been presented. The critical current and minimum propagation current can be chosen as the restrictive condition of operating current in the HTS magnet coils subjected to an overcurrent pulse.

Control of Unsteady Solidification Via Optimized Magnetic Fields

ABSTRACT This article presents a numerical procedure for automatically controlling desired features of a melt undergoing solidification by applying an external magnetic field whose time-varying intensity and spatial distribution are obtained by the use of a hybrid optimization algorithm. The intensities of the magnets along the boundaries of the container were discretized by using B-splines. The inverse problem is then formulated to find the magnetic boundary conditions (the coefficients of the B-splines) in such a way that the gradients of temperature along the gravity direction are minimized at each instant as the solidification front advances through a moving melt. For this task, a hybrid optimization code was used that automatically switches among the following six optimization modules; the Davidon-Fletcher-Powell (DFP) gradient method, a genetic algorithm (GA), the Nelder-Mead (NM) simplex method, quasi-Newton algorithm of Pshenichny-Danilin (LM), differential evolution (DE), and sequential quadratic programming (SQP). Transient Navier-Stokes and Maxwell's equations were discretized by using a finite volume method in a generalized curvilinear nonorthogonal coordinate system. For the phase change problems, an enthalpy formulation was used. The computer code was validated against analytical and numerical benchmark results with very good agreements in both cases.

Weighted waypoint mobility model and its impact on ad hoc networks

To realistically evaluate performance of ad hoc networks we propose a generic framework called the Weighted Way Point (WWP) mobility model. WWP model captures preferences in choosing destinations of pedestrian mobility patterns in a campus environment. We estimate the parameters of this model using mobility survey data for the USC campus. We further compare WWP model with widely used Random Waypoint (RWP) model and demonstrate that in the WWP model mobile nodes display uneven (clustering), time-varying spatial distribution. WWP model is also less mobile than RWP model with typical parameter settings. The clustering effect can cause lower success rate of route discovery in ad hoc networks.

Fast collision detection among multiple moving spheres

This paper presents an event-driven approach that efficiently detects collisions among multiple ballistic spheres moving in the 3D space. Adopting a hierarchical uniform space subdivision scheme, we are able to trace the trajectories of spheres and their time-varying spatial distribution. We identify three types of events to detect the sequence of all collisions during our simulation: collision, entering, and leaving. The first type of event is due to actual collisions, and the other two types occur when spheres move from subspace to subspace in the space. Tracing all such events in the order of their occurring times, we are able to avoid fixed time step simulation. When the size of the largest sphere is bounded by a constant multiple of that of the smallest, it takes O(n~/sub c/ log n+n~/sub e/ log n) time with O(n) space after O(n log n) time preprocessing to simulate n moving spheres, where n~/sub c/ and n~/sub e/ are the number of actual collisions and that of entering and leaving events during the simulation, respectively. Since n~/sub e/, depends on the size of subspaces, we modify the collision model from kinetic theory for molecular gas to determine the subspace sizes for the space subdivision scheme, that minimize simulation time. Experimental results show that collision detection can be done in linear time in n over a large range.

The ORL active floor [sensor system

A novel type of sensor system called the active floor is presented that allows the time-varying spatial weight distribution of the active office environment to be captured. The properties of the active floor are described, showing that it differs substantially from other commonly encountered sensor systems. Furthermore, classification of the footstep signature of a number of individuals is attempted by application of the hidden Markov model technique.