Qualitative Simulations Research Articles

Modeling of wave propagation and absorption in electron cyclotron resonance ion source plasmas

The performance of electron cyclotron resonance ion sources (ECRIS) is critically dependent on the resonant absorption of microwave power. However, currently there is little understanding of the propagation and absorption of electromagnetic waves in these ion sources. Measurement of the electromagnetic fields in a source is difficult without perturbing the plasma, and theory is hindered by the complex interaction between the waves, the plasma, the walls of the device, and the magnetic field. In this paper we present the results of quantitative 1D and qualitative 3D simulations of wave propagation and absorption in an electron cyclotron resonance ion source. The 1D simulations use the hot plasma dielectric tensor, which has not previously been applied to ECRIS modeling. The 3D simulations are the first attempt to include absorption by the plasma in calculating the structure of the electromagnetic fields in an ECRIS. These simulations demonstrate that the wave propagation and absorption is strongly dependent on the plasma. The results of the simulations are compared to experimental measurements of the mode structure, energy absorption, and frequency scaling.

Tumour–host dynamics under radiotherapy

Tumour–host interaction is modelled by the Lotka–Volterra equations. Qualitative analysis and simulations show that this model reproduces all known states of development for tumours. Radiotherapy effect is introduced into the model by means of the linear-quadratic model and the periodic Dirac delta function. The evolution of the system under the action of radiotherapy is simulated and parameter space is obtained, from which certain threshold of effectiveness values for the frequency and applied doses are derived. A two-dimensional logistic map is derived from the modified Lotka–Volterra model and used to simulate the effectiveness of radiotherapy in different regimens of tumour development. The results show the possibility of achieving a successful treatment in each individual case by employing the correct therapeutic strategy.

A heuristic simulation model of Lake Ontario circulation and mass balance transport

The redistribution of suspended organisms and materials by large-scale currents is part of natural ecological processes in large aquatic systems but can contribute to ecosystem disruption when exotic elements are introduced into the system. Toxic compounds and planktonic organisms spend various lengths of time in suspension before settling to the bottom or otherwise being removed. We constructed a simple physical simulation model, including the influence of major tributaries, to qualitatively examine circulation patterns in Lake Ontario. We used a simple mass balance approach to estimate the relative water input to and export from each of 10 depth regime-specific compartments (nearshore vs. offshore) comprising Lake Ontario. Despite its simplicity, our model produced circulation patterns similar to those reported by more complex studies in the literature. A three-gyre pattern, with the classic large counterclockwise central lake circulation, and a simpler two-gyre system were both observed. These qualitative simulations indicate little offshore transport along the south shore, except near the mouths of the Niagara River and Oswego River. Complex flow structure was evident, particularly near the Niagara River mouth and in offshore waters of the eastern basin. Average Lake Ontario residence time is 8 years, but the fastest model pathway indicated potential transport of plankton through the lake in as little as 60 days. This simulation illustrates potential invasion pathways and provides rough estimates of planktonic larval dispersal or chemical transport among nearshore and offshore areas of Lake Ontario.

Qualitative analysis and simulations of a free boundary problem for multispecies biofilm models

The work presents an analysis of solutions to a free boundary value problem for a multispecies biofilm growth model in one space dimension. The mathematical model consists of a system of nonlinear partial differential equations and a free boundary. It is quite general and can include a large variety of special situations. An existence and uniqueness theorem is discussed and properties of solutions are given. As a numerical application, simulations for a heterotrophic–autotrophic competition are developed by the method of characteristics.

Tendências na Análise de Impactos da Implementação de Barragens: Lições do Estudo de Caso das Barragens de Uso Múltiplo da Bacia do Rio Santa Maria

This article discusses trends in the analysis of possible impacts of dams, considering different aspects that should be included in the analysis, such as multiple uses, water balance of concessions, fragmentation of rivers, changes in riparian vegetation, in wetlands, altered sediment regimes and water quality in the reservoir and their implications locally and downstream from the dam. The methodological approach used combines qualitative analysis and simulations, structured by a compartmentalization of the river basin reaches resulting from the introduction of the dam; the upstream basin, the reservoir proper and the river downstream. It also included a discussion on the effects of changing land use and cover, and about groundwater. The analyses take into account the existing studies on the region. The balance of impacts was performed for the case study of the dams of Taquarembo and Jaguari in the Santa Maria River basin, in Rio Grande do Sul. As a result, several recommendations are presented for studies required during the environmental licensing period, which will provide information for a works management plan and impact mitigation. The study concludes that it is necessary to integrate environmental and water resources management through a scale study of a watershed based on studies of environm

Impacts of air interface admission control and user mobility on UTRAN transport simulations

UMTS Terrestrial Radio Access Network (UTRAN) Transport Network Layer dimensioning has been of great interest among network researchers and planners due to the limit of Iub bandwidth. This paper investigates the potential impacts caused by Connection Admission Control (CAC) mechanism of the air interface and User Mobility (UM) on simulations carried out for the UTRAN transport network domain. Independent from the TNL CAC mechanism of the transport network which is in charge of Iub link bandwidth, the Radio CAC function deals with the highly non-linear resources needed for an attempted connection depending on its specific propagation and interference situation. The consideration of the air interface acting as bottleneck results into a less challenging amount of traffic for the transport domain. In addition, mobile user behaviors, e.g. UM, may dynamically change traffic load at the air interface, and in consequence affect Iub load, which has a very close correlation with cell load. In this work, a simulation model with Radio CAC mechanism and Handover strategies is implemented to study this correlation, and evaluate the UTRAN transport network performance given a limited radio capacity. The analysis on the impacts of the Radio CAC and UM are derived from qualitative simulations.

Path Dependence in Decision-Making Processes: Exploring the Impact of Complexity under Increasing Returns

AbstractThe development of path-dependent processes basically refers to positive feedback in terms of increasing returns as the main driving forces of such processes. Furthermore, path dependence can be affected by context factors, such as different degrees of complexity. Up to now, it has been unclear whether and how different settings of complexity impact path-dependent processes and the probability of lock-in. In this paper we investigate the relationship between environmental complexity and path dependence by means of an experimental study. By focusing on the mode of information load and decision quality in chronological sequences, the study explores the impact of complexity on decision-making processes. The results contribute to both the development of path-dependence theory and a better understanding of decision-making behavior under conditions of positive feedback. Since previous path research has mostly applied qualitative case-study research and (to a minor part) simulations, this paper makes a further contribution by establishing an experimental approach for research on path dependence.

Phase-field modeling of dry snow metamorphism

Snow on the ground is a complex three-dimensional porous medium consisting of an ice matrix formed by sintered snow crystals and a pore space filled with air and water vapor. If a temperature gradient is imposed on the snow, a water vapor gradient in the pore space is induced and the snow microstructure changes due to diffusion, sublimation, and resublimation: the snow metamorphoses. The snow microstructure, in turn, determines macroscopic snow properties such as the thermal conductivity of a snowpack. We develop a phase-field model for snow metamorphism that operates on natural snow microstructures as observed by computed x-ray microtomography. The model takes into account heat and mass diffusion within the ice matrix and pore space, as well as phase changes at the ice-air interfaces. Its construction is inspired by phase-field models for alloy solidification, which allows us to relate the phase-field to a sharp-interface formulation of the problem without performing formal matched asymptotics. To overcome the computational difficulties created by the large difference between diffusional and interface-migration time scales, we introduce a method for accelerating the numerical simulations that formally amounts to reducing the heat- and mass-diffusion coefficients while maintaining the correct interface velocities. The model is validated by simulations for simple one- and two-dimensional test cases. Furthermore, we perform qualitative metamorphism simulations on natural snow structures to demonstrate the potential of the approach.

Action Research, Simulation, Team Communication, and Bringing the Tacit Into Voice Society for Simulation in Healthcare

In healthcare, professionals usually function in a time-constrained paradigm because of the nature of care delivery functions and the acute patient populations usually in need of emergent and urgent care. This leaves little, if no time for team reflection, or team processing as a collaborative action. Simulation can be used to create a safe space as a structure for recognition and innovation to continue to develop a culture of safety for healthcare delivery and patient care. To create and develop a safe space, three qualitative modified action research institutional review board-approved studies were developed using simulation to explore team communication as an unfolding in the acute care environment of the operating room. An action heuristic was used for data collection by capturing the participants' narratives in the form of collaborative recall and reflection to standardize task, process, and language. During the qualitative simulations, the team participants identified and changed multiple tasks, process, and language items. The simulations contributed to positive changes for task and efficiencies, team interactions, and overall functionality of the team. The studies demonstrated that simulation can be used in healthcare to define safe spaces to practice, reflect, and develop collaborative relationships, which contribute to the realization of a culture of safety.

Supersonic plasma jet interaction with gases and plasmas

The interaction of supersonic plasma jets with dense gases and plasmas has been studied experimentally and theoretically. Collimated plasma jets were generated from the laser pulse interaction with solid targets. The jet propagates with the velocity exceeding 400 km/s and transports the energy of a few kJ/cm2. The interaction of such a jet with an Ar and He gases at various pressures has been studied by using optical and X-ray diagnostics. Qualitative estimates and numerical simulations with a radiative hydrodynamic code explain a sequence of physical processes during the interaction. Experimental and numerical results show that, by changing ambient material, the working surface structure changes from an adiabatic outflow to a radiative cooling jet. The applications of this phenomenon to astrophysical conditions and the inertial confinement fusion are discussed.

On the quantitative evaluation of metamorphic fluid composition: Verification of the results of physicochemical simulations for water-mineral-rock reactions

This paper reports the results of a comparison of the qualitative physicochemical simulations (by the Winsel program complex) of the composition of the reacting fluid with experimental data on the water-electrolyte (NaCl, HCl, NaOH, and KOH)-mineral (quartz, corundum, microcline, and plagioclase) system and the water-electrolyte-rock (granite and pelite) system at 400–800°C and 1–10 kbar. Constraints are proposed for the temperature, pressure, and the composition of the electrolyte at which the simulation results are consistent with the experimental data.

Towards a structured approach to building qualitative reasoning models and simulations

Successful transfer and uptake of qualitative reasoning technology for modelling and simulation in a variety of domains has been hampered by the lack of a structured methodology to support formalisation of ideas. We present a framework that structures and supports the capture of conceptual knowledge about system behaviour using a qualitative reasoning approach. This framework defines a protocol for representing content that supports the development of a conceptual understanding of systems and how they behave. The framework supports modellers in two ways. First, it structures and explicates the work involved in building models. Second, it facilitates easier comparison and evaluation of intermediate and final results of modelling efforts. We show how this framework has been used in developing qualitative reasoning models about three case studies of sustainable development in different river systems.

Alternative community structures in a kelp-urchin community: A qualitative modeling approach

Shifts in interaction patterns within a community may result from periodic disturbances and climate. The question arises as to the extent and significance of these shifting patterns. Using a novel approach to link qualitative mathematical models and field data, namely using the inverse matrix to identify the community matrix, we reconstructed community networks from kelp forests off the Oregon Coast. We simulated all ecologically plausible interactions among community members, selected the models whose outcomes match field observations, and identified highly frequent links to characterize the community network from a particular site. We tested all possible biologically reasonable community networks through qualitative simulations, selected those that matched patterns observed in the field, and further reduced the set of possibilities by retaining those that were stable. We found that a community can be represented by a set of alternative structures, or scenarios. From 11,943,936 simulated models, 0.23% matched the field observations; moreover, only 0.006%, or 748 models, were highly reliable in their predictions and met conditions for stability. Predator–prey interactions as well as non-predatory relationships were consistently found in most of the 748 models. These highly frequent connections were useful to characterize the community network in the study site. We suggest that alternative networks provide the community with a buffer to disturbance, allowing it to continuously reorganize to adapt to a variable environment. This is possible due to the fluctuating capacities of foraging species to consume alternate resources. This suggestion is sustained by our results, which indicate that none of the models that matched field observations were fully connected. This plasticity may contribute to the persistence of these communities. We propose that qualitative simulations represent a powerful technique to raise new hypotheses concerning community dynamics and to reconstruct guidelines that may govern community patterns.

ON TAXIS FOR CONTROL AND ITS QUALITATIVE SOLUTION ON MOBILE ROBOTS

Animals show a great ability to move on real world. Taxis is a motion control technique used by simple animals. In this paper mathematical equations are derived from a taxis model for non-holonomous vehicles. A qualitative technique is applied to analyse the solutions of the nonlinear derived motion equations. To validate the model and qualitative analysis several simulations are performed.

Features of the femtosecond pulse propagation in air

The features of propagation of femtosecond laser pulses in the atmosphere are studied by numerical methods. The type of propagation is determined by the relation between processes of multiphoton ionisation and multiple small-scale self-focusing (filamentation). It is found that the process develops step by step and filamentation occurs without the pulse energy loss until the intensity threshold is achieved. After the achievement of the threshold, ionisation losses appear which are accompanied by the defocusing action of the electron plasma resulting in the intensity decrease. When the intensity becomes lower than the ionisation threshold, self-focusing can again appear. The characteristic features of the final stage of filamentation can be explained by the Bespalov—Talanov theory. By using the time-averaged equations and parallel methods, a program complex is developed for qualitative simulations of the propagation of high-power laser pulses over long distances.

Q-SEE: Qualitative Simulation Support System in Economic Education

In this paper, we present a support method of economic learning system based on qualitative simulation. We employ qualitative simulations because this lets the learners can understand the conceptual principles in economic dynamics. In existing learning system with qualitative simulation, users are not supported effectively in building qualitative simulation model. To solve the problem, we propose a support process and methods based on users condition. In our system, users conditions are classified into 4 phases. Based on the phases, our system helps users make qualitative simulation model step by step. Furthermore, our system supports users through making partial-adjacent relationships/graph model and supports users displaying errors about inconsistency and incorrect rule when there are inconsistency and mistaken relationship in the graph model made by users. The work focuses on interactively helping a learner to develop a qualitative model of an economic system as a teaching tool. The system has three key advantages. (1) Our system supports users’ learning based on condition and process in which users make simulation models. (2) Users can make qualitative simulation model without their confusion because it is easy for users to make the model with consistency, propriety and adequacy using our system. (3) Users can make qualitative simulation model effectively because users can understand the detail and all over the model using our support system. The contributions of this paper are mainly showing the support process and support method in building qualitative simulation model.

Coulomb explosion induced by intense ultrashort laser pulses in two-dimensional clusters

The phenomenon of Coulomb explosion is studied through qualitative numerical simulations of clusters irradiated with intense ultrashort laser pulses. We introduce a semiquantum approach which allows us to model two different types of materials---akin to rare gases and dielectrics---and which is appropriate for both low- and high-energy domains, i.e., the thermodynamic regime and the Coulomb explosion regime. Through a detailed study of clusters submitted to laser pulses of various intensities, we demonstrate that Coulomb explosion is the process responsible for cluster explosion under femtosecond laser pulses. We examine the differences in the dynamics of explosion of rare-gas clusters as a function of the wavelength of the incident laser radiation. For dielectric clusters, our simulations reveal a fragmented explosion mechanism; the influence of the size of the cluster is also studied.

Tertiary Scale Behaviour during Finishing Hot Rolling of Steel Flat Products

Steel strip surface oxidation during hot mill processing represents an industrial and environmental problem: secondary oxide is removed after roughing, but tertiary oxide scales already start to form before entering the finishing stands. Their properties affect the final steel surface quality and its response to further processing. Controlling the oxide layer growth kinetics and mechanical properties can make pickling easier and improve downstream behaviour. A thin wustite-dominated scale layer (<20 μm) is created under controlled conditions in an original laboratory device adequately positioned in a compression test machine to investigate plane strain compression. A first series of oxidation tests were performed on a ULC steel grade to measure the kinetics of oxide scale growth. The samples were first heated up under a protective atmosphere (nitrogen), before being oxidised in air at different temperatures for various oxidation times. These experiments can be considered fair quantitative and qualitative simulations of scale growth as it occurs in a hot strip mill, insofar as the results thus obtained are in good agreement with the literature. After the oxide growth, plane strain compression (PSC) was performed immediately to simulate the hot rolling process. The oxide layers were characterised before and after compression tests by optical and secondary electron microscopy. As expected, the oxide is seen to deform during compression. The obtained oxide layers exhibit good adhesion to the substrate and homogeneity over the thickness, even after compression.

Modelling population and community dynamics with qualitative reasoning

Ecological knowledge has been characterised as incomplete, fuzzy, uncertain, sparse, empirical, and non-formalised. It is often expressed in qualitative terms, verbally or diagrammatically. There is a need for new and efficient computer-based tools for making this knowledge explicit, well organised, processable, and integrated with quantitative knowledge. Qualitative reasoning is an area of artificial intelligence that creates representations for continuous aspects of the world to support reasoning with little information. Particularly relevant for our work are qualitative representations of differential equations, (in-)equality reasoning and the explicit representation of causal relationships between quantities. We present qualitative models and simulations of population and community dynamics in the Brazilian Cerrado vegetation. The models are organised in clusters of predictive simulation models. The first cluster implements a general theory of population dynamics, with the explicit representation of processes such as natality, mortality, immigration, emigration, colonisation, and population growth. These models are the basis for more complex community models. The second cluster represents interactions between two populations, such as symbiosis, competition, and predation. The third cluster represents the Cerrado succession hypothesis, a commonsense theory of succession in the Cerrado vegetation. It is assumed that fire frequency influences a number of environmental factors. When fire frequency increases succession leads to open grasslands and when fire frequency decreases the vegetation becomes woody and denser. This article shows the potential of qualitative reasoning for ecological modelling, particularly for answering questions of interest and making scientifically valid predictions using only qualitative terms.

Qualitative models about stream ecosystem recovery: Exploratory studies

Most of water ecosystems are endangered by human actions, in spite of their importance for all living systems. Qualitative models and simulations may be useful for stream ecosystem recovery in many ways: for understanding such systems, to predict values of variables and to combine such understanding with restoration and proactive management. However, building qualitative models puts new challenges both for qualitative reasoning and ecological modelling research. This study describes the development of qualitative models and simulations about the effects of pollution by organic matter and its consequences on the amount of dissolved oxygen and mortality of fish. We present simulations of effective and ineffective management practices, which may result in increasing and reducing fish stocks. Problems we found and solutions we implemented during the modelling effort are discussed, including the explicit representation of assumptions and the role of ambiguities in the outcomes of the models. Developing qualitative theories for water ecology will require a better understanding of the basic processes, such as photosynthesis and respiration. These complex processes are related to both energy flow and nutrient cycling, and have impact on different parts of the whole ecosystem. We argue that new ontologies and qualitative domain theories will be required in order to tackle these complex interactions between physical, chemical and biological phenomena observed in water systems.