Explicit Dynamic Model Research Articles

The Study on the Learning of Walking Gaits for Biped Robots

This paper presents a study on biped walking and balance control by reinforcement learning. The robot learns how to walk without prior knowledge of explicit dynamics model by a reinforcement learning approach. The Q-learning sharpens up the robot's walking gaits so as that improve the stability of each gait and reduce the number of the posture patterns in a gait cycle. In this paper, the learning agent employs an intuitive evaluation knowledge to help the biped robot with a basic walking skill learn to improve its behavior in terms of restricting ZMP to a certain region on each foot.

VULNERABILITY OF VEGETATION IN PARTS OF HIMALAYAS AND DYNAMIC GLOBAL VEGETATION MODELLING (DGVM) – STUDY USING VNIR AND THERMAL RESPONSES OF MODIS TIME SERIES DATA

Abstract. Vegetation responses to changing climate patterns need to be understood to devise adaptation strategy for a sustainable development, especially in the light of increasing climate related vulnerability. Dynamic Global Vegetation Models(DGVM) have the capacity and scope to develop understanding in this regard, due to their ability in simulating plant-vegetation-climate processes incorporating bioclimatic variables. However, prior to take up modelling using a spatially explicit DGVM, it may be imminent to prioritize the area for vulnerable contexts, so as to calibrate and validate the model optimally. Spatially explicit DGVMs require site level observations at canopy and leaf level/soil strata level for parametrization and implementation. Satellite data in VNIR and thermal regimes provide scope to understand the responses of various vegetation categories and enable to set up baseline addressing the foci of change as regions of vulnerability. Study carried out Western Himalayan transect using MODIS enhanced vegetation index and land surface temperature illustrates potential to differentiate areas that can be vulnerable due to warming trends disturbing cold to warm season energy level transition. Relations of these indices were studied in different vegetation categories and modelled spatially to derive potential vulnerable zones. Many sites showed high vulnerability while some sites showed distinct resilient behaviour by showing increase in EVI during warming periods. Potential zones were studied further using a spatially explicit Dynamic Global Vegetation Model for site level understanding. DGVM results in terms of biomass and carbon were studied to understand the trends in the vulnerable and resilient sites. Detailed characterisation of DGVM based modelling is underway to further diagnose the vulnerability contexts.

Drug delivery patterns for different stenting techniques in coronary bifurcations: a comparative computational study

The treatment of coronary bifurcation lesions represents a challenge for the interventional cardiologists due to the lower rate of procedural success and the higher risk of restenosis. The advent of drug-eluting stents (DES) has dramatically reduced restenosis and consequently the request for re-intervention. The aim of the present work is to provide further insight about the effectiveness of DES by means of a computational study that combines virtual stent implantation, fluid dynamics and drug release for different stenting protocols currently used in the treatment of a coronary artery bifurcation. An explicit dynamic finite element model is developed in order to obtain realistic configurations of the implanted devices used to perform fluid dynamics analysis by means of a previously developed finite element method coupling the blood flow and the intramural plasma filtration in rigid arteries. To efficiently model the drug release, a multiscale strategy is adopted, ranging from lumped parameter model accounting for drug release to fully 3-D models for drug transport to the artery. Differences in drug delivery to the artery are evaluated with respect to local drug dosage. This model allowed to compare alternative stenting configurations (namely the Provisional Side Branch, the Culotte and the Inverted Culotte techniques), thus suggesting guidelines in the treatment of coronary bifurcation lesions and addressing clinical issues such as the effectiveness of drug delivery to lesions in the side branch, as well as the influence of incomplete strut apposition and overlapping stents.

Large-eddy simulation of turbulent channel flow using explicit filtering and dynamic mixed models

Large-eddy simulations of turbulent channel flow at Reτ = 395 are performed using explicit filtering. Two different subfilter-scale models, the dynamic Smagorinsky mixed model and the dynamic global-coefficient mixed model, are formulated in accordance with the explicitly filtered governing equations. The use of explicit filtering separates the filtering operation from discretization, thereby producing a grid-independent solution. In explicit-filter large-eddy simulations, both the dynamic Smagorinsky mixed and the dynamic global-coefficient mixed subfilter-scale models are found to produce solutions close to the non-filtered direct numerical simulation data when explicit-filter widths in the streamwise and spanwise directions and at the center of the channel in the wall normal direction are about four times the grid spacings for direct numerical simulation. Solutions obtained using explicit-filter large-eddy simulation are compared with solutions obtained using implicit-filter large-eddy simulation in a range of filter and grid resolution. Explicit-filter large-eddy simulations performed on gradually refined grids with a fixed set of explicit-filter widths are found to produce grid-converged solutions for both models. Similarly in implicit-filter large-eddy simulation, predictive capabilities of subfilter-scale models in explicit-filter large-eddy simulation are found to be interfered with truncation errors when the ratio of the explicit-filter width to the grid spacing is small.

Advanced Gun System Gun and Projectile Dynamic Model Results and Correlation to Test Data

BAE Systems is currently developing and testing a 155 mm advanced gun system (AGS) and a long range land attack projectile (LRLAP) as a part of the DDG-1000 ship development program. For this development, it is important to understand the barrel and projectile dynamics, including the interaction of the barrel and the projectile in the bore as well as the projectile tip-off parameters at exit. An abaqus explicit dynamic finite element model has been developed to compare results with test data that were taken on June 18, 2003, at the BAE Systems site at the Alliant Techsystems Proving Ground (ATPG) during AGS propellant testing. The abaqus model includes the gun barrel, the projectile used for propellant testing (a steel slug), the M110 gun mount, and the recoil system. Features of the model incorporate settling of the barrel due to gravity, gun recoil, in-bore interaction of the projectile and the barrel using contact surfaces, and the initial flight of the projectile after bore exit. The abaqus model results have been compared with gun firing test data acquired during propellant testing at Elk River, MN. These comparisons include barrel and projectile displacements, angular velocities, and axial accelerations. The abaqus model results are also compared to similar models of the test conditions with the simulation of barrel dynamics (simbad) gun dynamics code and the ibhvg2 interior ballistics code.

Impact of climate change on water management in Dutch peat polders

A spatially explicit dynamic model was developed that combines water quantity and quality processes for an average Dutch peat polder. The model has been used to calculate the consequences of climate change for surface water level, groundwater level and nitrogen and phosphorus fluxes, based on time series (2036–2065) of the two most extreme climate change scenarios for the Netherlands (G and W+) developed by the Royal Dutch Meteorological Institute. It was calibrated using measured data from two existing polders. The results suggest that surface water levels will not change much in both scenarios. Hence, the current practice of letting extra water in during dry summer periods to maintain sufficient water levels will probably remain a viable solution to temporary summer droughts in the near future as the required water volumes are not likely to increase greatly. Late summer groundwater levels decrease substantially in the W+ scenario but not in the moderate G scenario. This drop in groundwater level would accelerate the on-going process of peat oxidation, resulting in increased soil subsidence, greenhouse gas emissions and nutrient release from mineralisation. The W+ scenario also led to higher nitrogen concentrations and lower phosphorus concentrations in the ditch network. Probably the reduced stream velocity in the W+ scenario results in an increased sedimentation of (adsorbed) phosphate. Sedimentation is a less important process in the nitrogen cycle, and the increased nitrogen concentrations anticipated in summer according to the W+ scenario are therefore probably the consequence of a reduced outlet of water due to increased evaporation. Additionally, an increased delivery of nitrogen through mineralisation could also contribute to the increased nitrogen concentrations in summer.

Potencial de uso do modelo century e sig para avaliar o impacto da agricultura sobre estoques regionais de carbono orgânico do solo

O uso e as mudanças no uso e manejo dos solos figuram entre os principais fatores determinantes dos estoques de carbono orgânico do solo (COS). A modelagem dinâmica espacialmente explícita é uma técnica que vem sendo usada com sucesso em avaliações das alterações nos estoques regionais de COS. Assim, este trabalho objetivou utilizar o modelo Century associado a técnicas de geoprocessamento e sensoriamento remoto para avaliar os efeitos das alterações do uso agrícola e manejo do solo na dinâmica do carbono orgânico do solo (COS) em propriedades rurais do Distrito Santana, Ijuí - RS. Para isso, foi criada uma base de dados geoespaciais em ambiente ArcGis9.x com os planos temáticos: solos, elementos da paisagem e início do uso agrícola. Após reconstituídos os cenários históricos de manejo, o modelo Century 4.0 foi inicializado com dados edafoclimáticos locais, calibrado em duas etapas e validado, obedecendo-se à seguinte ordem: calibração principal - validação - calibração para generalizações. Na calibração principal, foram ajustados parâmetros internos do modelo, valendo-se da adição de carbono (C) pelo milho, trigo e soja e dos estoques de COS medidos em 2007 na camada de 0 a 20 cm da mata nativa e de uma lavoura adjacente, cuja conversão ocorreu entre 1901 e 1930 (lavoura mais antiga, localizada na área 1), sob Latossolo de topo. Em seguida, o Century, assim ajustado, foi estatisticamente validado com base em dados observados em 10 lavouras iniciadas em diferentes épocas, sob a mesma classe de solo e posição na paisagem, amostradas em 2007 na camada de 0 a 20 cm e distribuídas em quatro áreas homogêneas (áreas 1, 2, 3 e 4) dentro do Distrito Santana. Na calibração para generalizações, foram criadas quatro opções de "floresta subtropical" para representar a mata nativa de cada classe de solo em estudo (Latossolo, Chernossolo, Neossolo Regolítico e Neossolo Flúvico), a partir da opção de floresta tropical gerada na etapa de calibração principal, mantendo-se os ajustes já realizados naquela etapa e alterando apenas o parâmetro referente à máxima produção bruta mensal de biomassa pela floresta para que a variável de saída SOMTC (COS simulado) se estabilizasse, após o modelo ser executado por 3.000 anos (execução de equilíbrio), coincidindo com os estoques de COS medidos no solo sob vegetação nativa respectiva de cada classe de solo; em seguida, procedeu-se às simulações correspondentes a 54 unidades de simulação (US), por meio da interface i-Century, nas condições de solos cultivados com os cenários de manejo históricos (de 1901 até 2007). O Century, depois de calibrado, estimou adequadamente a dinâmica do C, reproduzindo a evolução dos estoques de COS ocorrida no Distrito Santana. Segundo essas estimativas, a adoção de práticas conservacionistas de manejo garante a redução das perdas de C causadas pelo processo erosivo e decomposição microbiana, havendo com isso aumento no estoque de COS.

Predicting the spread of feral populations of the American mink in Italy: is it too late for eradication?

Predicting the speed and direction of the spread of alien species is one of the ways in which models can contribute to managing invasions. In Italy, the American mink is an alien invasive living in feral populations whose distribution and impacts are little known. The aim of this study was to predict the likely distribution of the American mink across Italy and the rate of population spread. An extended spatially explicit population dynamics model (SEPM) was used to simulate mink expansion in Italy across a period of 20 years. We used the current and recent distribution of mink farms as the initial points of invasion and validated the model in two ways: (1) by comparing the predicted distribution with the distribution of known populations of mink in Italy; (2) by comparing the predicted rates of spread with those observed in real populations. The application of the model to the Italian landscape highlighted the possibility that mink are already widespread in the country even though only few reports of this species have ever been made. This is of serious conservation concern considering that mink has proven to be a damaging invasive elsewhere. However, the fact that this species should mostly be restricted to north-east Italy suggests that eradication may still be possible. This study highlights the risks posed by American mink and shows that modelling, which is generally less expensive than field studies, can be used to guide surveys and future management of alien invasives.

Modelling a single-bolt countersunk composite joint using implicit and explicit finite element analysis

In this paper the mechanical behaviour of a composite joint incorporating a single countersunk fastener is investigated both experimentally and numerically. Results from an explicit dynamics model are compared to those obtained from an implicit modelling approach and measurements from experimental tests. The explicit dynamics method is of interest due to its robust contact modelling, and the scalability of the procedure for application to large structures. The deformation of the joint models in the overlap region is verified experimentally using extensometers. Experimental measures of secondary bending, obtained using 3D digital image correlation (DIC), provide good agreement with the numerical results.

Validation of Finite Element Cutting Force Prediction for End Milling

Milling is a complicated metal machining process characterized by a rotating tool that produces continuously varying chip loads, simultaneous multi-flute contact, and interrupted cuts. The complex kinematic and dynamic nature of the process in conjunction with the highly nonlinear workpiece material behaviors poses unique challenges for analyses. In this paper, a three-dimensional explicit dynamic Lagrangian finite element-based model is presented. The key components of the model are highlighted and the force prediction capability of the model is validated against a substantial amount of engineering data. Good correlations between the prediction and the experiments were observed and some areas of further improvements for the model were identified.

An explicit numerical model for the study of snow's response to explosive air blast

Abstract In this paper, an analytic tool is used to examine the internal dynamic snow response during explosive events. An explicit nonlinear dynamic model (using ANSYS/AUTODYN) is presented where the explosion, shock propagation through air and snow response is simulated in a single analysis. This versatile approach handles the complex interactions from explosive events and solids, gases and liquids. Nonlinear interactions and responses are modeled during the detonation and subsequent propagation. The model predicts internal structural response during explosive events, including important parameters such as stress, strain, density changes, velocity and acceleration. Snow shock Hugoniots are used for volumetric constitutive relationships with the deviatoric relationships modeled as linear elastic. The analysis shows stress waves in the snow resulting from the explosive shock wave traveling over the surface. While the normal load transits the weak layer, a shear stress wave concentrated above the weak layer develops. The intensity at depth and lateral extent of the stress wave may be an important consideration for initiating avalanches with explosives. Examples with charges on and above the snow surface support the well known air burst advantage, but also show that the dynamic enhancement is not due to peak air pressure alone. Results for two explosive configurations support enhanced dynamic response with increased air pressure impulse, providing further insight into the suspended charge advantage. Charge size is briefly examined with larger explosives providing an advantage in stress wave intensity and range. Various snowpack configurations and explosive charges with variable locations can be examined with this approach. The analytic approach provides a tool for future detailed examination of critical avalanche control parameters.

Evaluation of Spatially Targeted Strategies to Control Non-Domiciliated Triatoma dimidiata Vector of Chagas Disease

BackgroundChagas disease is a major neglected tropical disease with deep socio-economical effects throughout Central and South America. Vector control programs have consistently reduced domestic populations of triatomine vectors, but non-domiciliated vectors still have to be controlled efficiently. Designing control strategies targeting these vectors is challenging, as it requires a quantitative description of the spatio-temporal dynamics of village infestation, which can only be gained from combinations of extensive field studies and spatial population dynamic modelling.Methodology/Principal FindingsA spatially explicit population dynamic model was combined with a two-year field study of T. dimidiata infestation dynamics in the village of Teya, Mexico. The parameterized model fitted and predicted accurately both intra-annual variation and the spatial gradient in vector abundance. Five different control strategies were then applied in concentric rings to mimic spatial design targeting the periphery of the village, where vectors were most abundant. Indoor insecticide spraying and insect screens reduced vector abundance by up to 80% (when applied to the whole village), and half of this effect was obtained when control was applied only to the 33% of households closest to the village periphery. Peri-domicile cleaning was able to eliminate up to 60% of the vectors, but at the periphery of the village it has a low effect, as it is ineffective against sylvatic insects. The use of lethal traps and the management of house attractiveness provided similar levels of control. However this required either house attractiveness to be null, or ≥5 lethal traps, at least as attractive as houses, to be installed in each household.Conclusion/SignificanceInsecticide and insect screens used in houses at the periphery of the village can contribute to reduce house infestation in more central untreated zones. However, this beneficial effect remains insufficient to allow for a unique spatially targeted strategy to offer protection to all households. Most efficiently, control should combine the use of insect screens in outer zones to reduce infestation by both sylvatic and peri-domiciliated vectors, and cleaning of peri-domicile in the centre of the village where sylvatic vectors are absent. The design of such spatially mixed strategies of control offers a promising avenue to reduce the economic cost associated with the control of non-domiciliated vectors.

A Journey from Science through Systems Science in Pursuit of Change

This article traces my attempts to come to grips with the problem of change. Systems science deals with general principles, but, as with science in general, is wedded to mechanistic models. Natural systems are not machines, are generative, and can change unpredictably. An example is given showing that explicit dynamical models are subverted by the present moment, which is non-existent in them. This moment can be modeled by a compositional hierarchy, but no change happens therein. Subsumptive hierarchies can serve as metaperspectives on change, modeling stages of development. The Second Law of thermodynamics provides the motivation for development, which can be modeled generally using thermodynamic and information theoretic (infodynamic) concepts. Development is progressive change, constitutive of different systems, and goes from vagueness toward increasingly more definite embodiment, ending up in senescence, which derives from information overload. While becoming increasingly burdened with information, the present moment, as such, still evades this developmental systematicity. Internalist thinking has emerged as an attempt to further come to grips with it.

Data-driven modeling of phase interactions between spontaneous MEG oscillations.

Synchronization between distributed rhythms in the brain is commonly assessed by estimating the synchronization strength from simultaneous measurements. This approach, however, does not elucidate the phase dynamics that underlies synchronization. For this, an explicit dynamical model is required. Based on the assumption that the recorded rhythms can be described as weakly coupled oscillators, we propose a method for characterizing their phase-interaction dynamics. We propose to model ongoing magnetoencephalographic (MEG) oscillations as weakly coupled oscillators. Based on this model, the phase interactions between simultaneously recorded signals are characterized by estimating the modulation in instantaneous frequency as a function of their phase difference. Furthermore, we mathematically derive the effect of volume conduction on the model and show how indices for strength and direction of coupling can be derived. The methodology is tested using simulations and is applied to ongoing occipital-frontal MEG oscillations of healthy subjects in the alpha and beta bands during rest. The simulations show that the model is robust against the presence of noise, short observation times, and model violations. The application to MEG data shows that the model can reconstruct the observed occipital-frontal phase difference distributions. Furthermore, it suggests that phase locking in the alpha and beta band is established by qualitatively different mechanisms. When the recorded rhythms are assumed to be weakly coupled oscillators, a dynamical model for the phase interactions can be fitted to data. The model is able to reconstruct the observed phase difference distribution, and hence, provides a dynamical explanation for observed phase locking.

Dynamic modeling of forest conversion: Simulation of past and future scenarios of rural activities expansion in the fringes of the Xingu National Park, Brazilian Amazon

The present work is committed to simulate the expansion of agricultural and cattle raising activities within a watershed located in the fringes of the Xingu National Park, Brazilian Amazon. A spatially explicit dynamic model of land cover and land use change was used to provide both past and future scenarios of forest conversion into such rural activities, aiming to identify the role of driving forces of change in the study area. The employed modeling platform – Dinamica EGO – consists in a cellular automata environment that embodies neighborhood-based transition algorithms and spatial feedback approaches in a stochastic multi-step simulation framework. Biophysical variables and legal restrictions drove this simulation model, and statistical validation tests were then conducted for the generated past simulations (from 2000 to 2005), by means of multiple resolution fitting methods. Based on optimal calibration of past simulations, future scenarios were conceived, so as to figure out trends and spatial patterns of forest conversion in the study area for the year 2015. In all simulated scenarios, pasturelands remained nearly stable throughout the analyzed period, while a large expansion in croplands took place. The most optimistic scenario indicates that more than 50% of the natural forest will be replaced by either cropland or pastureland by 2015. This modeling experiment revealed the suitability of the adopted model to simulate processes of forest conversion. It also indicates its possible further applicability in generating simulations of deforestation for areas with expanding rural activities in the Amazon and in tropical forests worldwide.

Environmental Fluctuations and Level of Density-Compensation Strongly Affects the Probability of Fixation and Fixation Times

The probability of, and time to, fixation of a mutation in a population has traditionally been studied by the classic Wright-Fisher model where population size is constant. Recent theoretical expansions have covered fluctuating populations in various ways but have not incorporated models of how the environment fluctuates in combination with different levels of density-compensation affecting fecundity. We tested the hypothesis that the probability of, and time to, fixation of neutral, advantageous and deleterious mutations is dependent on how the environment fluctuates over time, and on the level of density-compensation. We found that fixation probabilities and times were dependent on the pattern of autocorrelation of carrying capacity over time and interacted with density-compensation. The pattern found was most pronounced at small population sizes. The patterns differed greatly depending on whether the mutation was neutral, advantageous, or disadvantageous. The results indicate that the degree of mismatch between carrying capacity and population size is a key factor, rather than population size per se, and that effective population sizes can be very low also when the census population size is far above the carrying capacity. This study highlights the need for explicit population dynamic models and models for environmental fluctuations for the understanding of the dynamics of genes in populations.

The utility and limitations of size and spacing guidelines for designing marine protected area (MPA) networks

Marine protected areas (MPAs) implemented to conserve biodiversity must protect many species with a broad range of movement characteristics. To meet that goal, size and spacing guidelines have been used in MPA network design as a proxy for explicitly representing connectivity and species movement. However, there has been no assessment of the biological effects of these simple rules. We evaluated these guidelines by estimating population persistence with a spatially explicit population model over: (1) an idealized coastline and (2) an example from California, USA. Persistence of a species within an MPA network depends strongly on its movement characteristics; therefore we used the number of combinations of larval dispersal distances and adult home range diameters as an index representing the number of species that could be protected by a MPA network. The index of species protected usually increased steadily with increasing MPA size. By contrast, decreasing MPA spacing only produced large increases in the index when spacing became close enough to allow species persistence via network connectivity rather than self replenishment. Species persistence also depended on the exploitation rate outside MPAs. Size and spacing guidelines are a simple and useful way to begin the MPA network design process, but meeting these guidelines does not guarantee persistence for all populations one may wish to protect. The use of spatially explicit population dynamics models that evaluate population persistence directly provides a more comprehensive basis for comparing proposed MPA network designs.

Characterization of the Dispersal of Non-Domiciliated Triatoma dimidiata through the Selection of Spatially Explicit Models

BackgroundChagas disease is a major parasitic disease in Latin America, prevented in part by vector control programs that reduce domestic populations of triatomines. However, the design of control strategies adapted to non-domiciliated vectors, such as Triatoma dimidiata, remains a challenge because it requires an accurate description of their spatio-temporal distributions, and a proper understanding of the underlying dispersal processes.Methodology/Principal FindingsWe combined extensive spatio-temporal data sets describing house infestation dynamics by T. dimidiata within a village, and spatially explicit population dynamics models in a selection model approach. Several models were implemented to provide theoretical predictions under different hypotheses on the origin of the dispersers and their dispersal characteristics, which we compared with the spatio-temporal pattern of infestation observed in the field. The best models fitted the dynamic of infestation described by a one year time-series, and also predicted with a very good accuracy the infestation process observed during a second replicate one year time-series. The parameterized models gave key insights into the dispersal of these vectors. i) About 55% of the triatomines infesting houses came from the peridomestic habitat, the rest corresponding to immigration from the sylvatic habitat, ii) dispersing triatomines were 5–15 times more attracted by houses than by peridomestic area, and iii) the moving individuals spread on average over rather small distances, typically 40–60 m/15 days.Conclusion/SignificanceSince these dispersal characteristics are associated with much higher abundance of insects in the periphery of the village, we discuss the possibility that spatially targeted interventions allow for optimizing the efficacy of vector control activities within villages. Such optimization could prove very useful in the context of limited resources devoted to vector control.

The wildlife picture index, monitoring and conservation

The wildlife picture index, monitoring and conservation

Parameterizing the formation rate of new particles: The effect of nuclei self-coagulation

The study is based on the work of Lehtinen et al. (2007) [Lehtinen, K. E. J., Dal Maso, M., Kulmala, M., & Kerminen, V.-M. (2007). Estimating nucleation rates from apparent particle formation rates and vice versa: Revised formulation of the Kerminen–Kulmala equation. Journal of Aerosol Science, 38, 988–994] who derived formulae connecting “real” and “apparent” nucleation rates. The parameterization neglected self-coagulation of newly formed particles and clusters, however, and here we have extended the previous work to include the effects of the self-coagulation. Our main focus was on calculating the “apparent” nucleation rate, i.e. the rate at which particles appear at sizes larger than the critical cluster size, as a function of the “real” nucleation rate. The revised parameterization was comprehensively tested against an explicit aerosol dynamic model at diverse atmospheric conditions. It was found out that nuclei self-coagulation has importance to new particle formation when J nuc / Q>10 −2 where J nuc is the nucleation rate and Q is the production rate of condensable vapours. This corresponds to the nucleation rates ranging from >10 cm −3 s −1 (free troposphere) to >10 4 cm −3 s −1 (polluted boundary layer) depending on the atmospheric conditions. In terms of the particle number concentration, the calculations performed with the explicit model and the predictions of revised parameterization were generally within an order of magnitude. Several issues related to applications in large-scale models were also discussed.