Multidimensional Environments Research Articles

Recurrence of the Brownian Motion in Multidimensional Semi-selfsimilar Environments and Gaussian Environments

Asymptotic behavior of the one-dimensional Brownian motion in general random environments has been investigated by many researchers. However, many of the methods used in the argument are available only for the one-dimensional case. In this paper the multi-dimensional case of the problem is considered, and we obtain some sufficient conditions for recurrence of the multi-dimensional Brownian motion in random environments. By using the sufficient conditions we show that the recurrence of the Brownian motion in Gaussian environments under some conditions on the correlation functions.

Reinforcement Learning in Multidimensional Environments Relies on Attention Mechanisms

In recent years, ideas from the computational field of reinforcement learning have revolutionized the study of learning in the brain, famously providing new, precise theories of how dopamine affects learning in the basal ganglia. However, reinforcement learning algorithms are notorious for not scaling well to multidimensional environments, as is required for real-world learning. We hypothesized that the brain naturally reduces the dimensionality of real-world problems to only those dimensions that are relevant to predicting reward, and conducted an experiment to assess by what algorithms and with what neural mechanisms this "representation learning" process is realized in humans. Our results suggest that a bilateral attentional control network comprising the intraparietal sulcus, precuneus, and dorsolateral prefrontal cortex is involved in selecting what dimensions are relevant to the task at hand, effectively updating the task representation through trial and error. In this way, cortical attention mechanisms interact with learning in the basal ganglia to solve the "curse of dimensionality" in reinforcement learning.

Attention-Getting and/or Effort-Inducing? An Examination of How Incentive Compensation Motivates Quality and Quantity Performance in a Multidimensional Environment

We investigate the effectiveness of two proposed motivating properties of incentive compensation – the attention-getting property and the effort-inducing property – in a multidimensional task environment. Specifically, in a task environment with quantity and quality dimensions we empirically test the effects of the two properties on performance in an effort to gain a more thorough understanding of the workings of incentive compensation. Our experimental results indicate that the attention-getting property always has a positive performance effect on the task dimension to which attention is directed. We also find that the effort-inducing property has an incremental positive performance effect over and above the attention-getting property on the quality dimension, but not on the quantity dimension. Our analysis also highlights that the attention-getting and effort-inducing properties of incentive compensation have separate performance spillover effects onto non-incentivized task dimensions and we provide insight on how these spillover effects vary. Our study has direct implications for theoretical research on, and use in practice of, inventive compensation in multidimensional task environments.

Mobile Robot Path Planning by RRT* in Dynamic Environments

Robot navigation is challenging for mobile robots technology in environments with maps. Since finding an optimal path for the agent is complicated and time consuming, path planning in robot navigation is an axial issue. The objective of this paper is to find a reasonable relation between parameters used in the path planning algorithm in a platform which a robot will be able to move from the start point in a dynamic environment with map and plan an optimal path to specified goal without any collision with moving and static obstacles. For this purpose, an asymptotically optimal version of Rapidly-exploring Random Tree RRT algorithm, named RRT* is used. The algorithm is based on an incremental sampling which covers the whole space and acts fast. Moreover this algorithm is computationally efficient, therefore it can be used in multidimensional environments. The obtained results indicate that a feasible path for mobile holomonic robot may be found in a short time by using this algorithm. Also different standard distances measurements like (Chebyshev, Euclidean, and City Block) are examined, and coordinated with sampling node number in order to reach the suitable result based on environment circumstances.

A Context-aware Decision Support Tool for Assessing and Mitigating Drivers of Civil Instability

Military planners and decision-makers face a number of challenges with the shift towards operating within diverse, multi-dimensional, and unconventional environments. Leaders require a deeper understanding of the broader social and civil context in which operations occur, including the underlying factors that contribute to instability and the drivers of conflict. This understanding is often derived through the analysis of textual data. Both traditional and non-traditional sources – such as news articles, blog entries, and tweets – represent a vast amount of data that can be brought to bear on problems ranging from measuring the progress of missions to forecasting important changes in the environment. The volume and velocity of this data requires processing tools that can help users understand the concepts and events being discussed. Additionally, these data are inherently ambiguous, and the automated processing techniques necessary for aggregating and analyzing data may introduce further uncertainty. The validity and veracity of data, sources, assumptions, and conclusions must be carefully considered prior to action. Planners and decision-makers require new, data-driven tools that aid in selecting the best course of action through interactive exploration and assessment processes. In this paper, we describe an ongoing research and development effort to create a context-driven, web-based tool that aids planning and decision-making by providing a more comprehensive understanding of the civil component of operational environments. This tool allows users to rapidly find, organize, and assess complex data across multiple phases of civil information management. This includes: (1) researching and assessing civil vulnerabilities; (2) developing plans to address identified vulnerabilities; and (3) tracking ongoing trends and progress towards goals and objectives. Our tool assists the user in each phase by collecting, processing, and recommending data and analyses that are contextually relevant to their task. By offloading data collection, supporting data organization, and providing personalized recommendations, our tool allows users to focus their efforts on verifying, interpreting, and assessing the information needed to recommend the best course of action.

Analysis on Historic Landscape Space Configurations and Evolutions of Qijiang Ancient Town

The landscape spaces of Qijiang ancient town take on special combined characteristics of contrary space sequence. The space configurations are unique and diversiform, particular about the whole harmony between inner and outer environments, human and space. The space-time configurations reflect ordered, blending and continuous in inner and outer landscape spaces. The contrary space configurations experienced more than 2000-year historic evolutions. The landscape spaces have extended continuously and reasonably complying with the combined characteristics of contrary space sequences. But in the late of last century, a lot of the landscape spaces were destroyed. Analysis on the contrary space configurations and evolutions will help us to look for the relationships and rules of the original spaces, and supply references to recovering multidimensional and sustainable ancient environments spaces.

Two-Sided Investment and Matching with Multidimensional Cost Types and Attributes

Heterogeneous buyers and sellers must make investments before entering a continuum assignment market. I show that efficient ex post contracting equilibria (Cole, Mailath, and Postlewaite 2001b) exist in a general assignment game framework. I then shed light on what enables and what precludes coordination failures. A simple condition—absence of technological multiplicity—guarantees efficient investments for each pair, but a mismatch of agents may still occur. However, using optimal transport theory, I also show that mismatch is heavily constrained in certain multidimensional environments with differentiated agents and no technological multiplicity. Under technological multiplicity, even extreme ex ante heterogeneity need not preclude inefficiencies. (JEL C78, D41, D86)

A Wicked Problem: Early Childhood Safety in the Dynamic, Interactive Environment of Home

Young children being injured at home is a perennial problem. When parents of young children and family workers discussed what influenced parents’ perceptions and responses to child injury risk at home, both “upstream” and “downstream” causal factors were identified. Among the former, complex and interactive facets of society and contemporary living emerged as potentially critical features. The “wicked problems” model arose from the need to find resolutions for complex problems in multidimensional environments and it proved a useful analogy for child injury. Designing dynamic strategies to provide resolutions to childhood injury, may address our over-dependence on ‘tame solutions’ that only deal with physical cause-and-effect relationships and which cannot address the complex interactive contexts in which young children are often injured.

Where to Settle—Settlement Preferences of Mytilus galloprovincialis and Choice of Habitat at a Micro Spatial Scale

The global mussel aquaculture industry uses specialised spat catching and nursery culture ropes made of multi-filament synthetic and natural fibres to optimise settlement and retention of mussels for on-growing. However, the settlement ecology and preferences of mussels are poorly understood and only sparse information exists in a commercial context. This study quantified the settlement preferences of pediveligers and plantigrades of Mytilus galloprovincialis on increasingly complex surfaces and settlement locations at a micro spatial scale on and within ropes under commercial hatchery operating conditions using optical microscopy and X-ray micro-computed tomography (µCT). M. galloprovincialis has clear settlement preferences for more complex materials and high selectivity for settlement sites from the pediveliger through to the plantigrade stage. Pediveligers of M. galloprovincialis initially settle inside specialised culture ropes. Larger pediveligers were located close to the exterior of ropes as they increased in size over time. In contrast, smaller individuals were located deeper inside of the ropes over time. This study demonstrates that X-ray µCT is an excellent non-destructive technique for mapping settlement and attachment sites of individuals as early as one day post settlement, and quantifies the number and location of settled individuals on and within ropes as a tool to understand and optimise settlement in complex multi-dimensional materials and environments.

Promoting Mindfulness Through Contemplative Education

For years, higher education institutions in the United States have developed courses in the field of liberal education that focus on social, political, economic and environmental issues with a global outlook. As such, students are taught critical thinking, critical reasoning, and critical writing skills. While students learn to engage in debates, decisive speaking, and critical analysis, they are rarely taught to feel compassionate toward these issues. Hence, in the current global community in which many countries are at war, or are facing poverty and financial crises, it is essential that higher education institutions prepare knowledgeable citizens that not only ascertain critical assessment and judgment skills, but also ascertain the art of contemplation. This article reviews literature from various disciplines and suggests that higher education institutions must work toward integrating contemplative education and mindfulness in their curriculum in order to enhance students’ learning and understanding through contemplation and personal insight. Furthermore, it is essential that higher education institutions implement multidimensional educational strategies that encourage a vigorous and universal understanding of cross-cultural communication. Additionally, this paper examines the role of elements, such as experience, contemplations, and transformation, in teaching and preparing future graduates for the current global community. Furthermore, it evaluates strategies that can be used by higher education leaders in creating multidimensional and effective learning environments.

Linking Dispersal and Immigration in Multidimensional Environments

Many problems in ecology require the estimation of rates of dispersal of individuals or propagules across physical boundaries. Such problems arise in invasion ecology, forest dynamics, and the neutral theory of biodiversity. In a forest plot, for example, one might ask what proportion of the seed rain originates from outside the plot. A recent study presented analytical approximations that relate the rate of immigration across a boundary to plot geometry and to the parameters of a dispersal kernel in one- and two-dimensional environments. In this study, we provide a more rigorous derivation of these expressions and we derive a more general expression that applies in environments of arbitrary dimension. We discuss potential applications of the one-, two-, and three-dimensional results to ecological problems.

Model fusion using fuzzy aggregation: Special applications to metal properties

To improve the modelling performance, one should either propose a new modelling methodology or make the best of existing models. In this paper, the study is concentrated on the latter solution, where a structure-free modelling paradigm is proposed. It does not rely on a fixed structure and can combine various modelling techniques in ‘symbiosis’ using a ‘master fuzzy system’. This approach is shown to be able to include the advantages of different modelling techniques altogether by requiring less training and by minimising the efforts relating optimisation of the final structure. The proposed approach is then successfully applied to the industrial problems of predicting machining induced residual stresses for aerospace alloy components as well as modelling the mechanical properties of heat-treated alloy steels, both representing complex, non-linear and multi-dimensional environments.

Regulation of nutrient intake in nectar-feeding birds: insights from the geometric framework

A nectar diet is simple in nutritional composition and easily digested, but may vary greatly in its proportions of sugar and water. Here, we apply the geometric framework, a modelling approach for investigating how animals balance nutrient needs in multidimensional and dynamic nutritional environments, to captive whitebellied sunbirds (Cinnyris talatala). We address the question of how these small birds (~8g) prioritise sugar and water intake, and how dietary salt content interacts with sugar and water intake. Sunbirds kept at 20°C and provided with moderate to high sucrose concentrations (≥1M), together with supplementary water, converge on an intake target of 2.79gday(-1) of sucrose and 7.72gday(-1) of water: equivalent to 0.85M sucrose. When the birds are given more dilute sucrose concentrations, they defend their sugar intake by over-ingesting water, up to a ceiling of 47gday(-1). Sugar intake thus gets priority over water intake, but the birds have a finite capacity to over-ingest water to gain the target level of sugar. Regulation appears to be less precise when birds are given a choice between two sucrose solutions than when they choose between a sugar solution and supplementary water. Intake targets vary in response to internal and external factors, and sunbirds increase their sugar intake in response to increased activity and cold, irrespective of nectar concentration. They also compensate for interruptions in foraging activity, whether overnight or during the day. Interactive effects become evident when sodium is included as a third nutrient: on very dilute nectar (≤0.1M), where sunbirds lose body mass, the addition of sodium to the diet helps to achieve the carbohydrate intake target, while raising the ceiling on water intake. This analysis provides a new perspective on nectarivory, while adding to the comparative database on nutrient regulation and emphasising water as a nutrient.

Collision-free path planning in multi-dimensional environments

Reliable path-planning and generation of collision-free trajectories has become an area of active research over the past decade where the field robotics has probably been the most active area. This paper' s main objective is to analyse the advantages and disadvantages of two of the most popular techniques used in collision-free trajectory generation in n-dimensional spaces. The importance of analysing such techniques within a generalised framework is evident as path-planning is used in a variety of fields such as designing medical drugs, computer animation and artificial intelligence and, of course, robotics. The review provided in this paper starts by drawing a historical map of path-planning and the techniques used in its early stages. The main concepts involved in artificial potential fields and probabilistic roadmaps will be addressed as these are the most influential methods and have been widely used in specialised literature.

Multi-dimensional particle swarm optimization in dynamic environments

Particle swarm optimization (PSO) was proposed as an optimization technique for static environments; however, many real problems are dynamic, meaning that the environment and the characteristics of the global optimum can change in time. In this paper, we adapt recent techniques, which successfully address several major problems of PSO and exhibit a significant performance over multi-modal and non-stationary environments. In order to address the pre-mature convergence problem and improve the rate of PSO’s convergence to the global optimum, Fractional Global Best Formation (FGBF) technique is used. FGBF basically collects all the best dimensional components and fractionally creates an artificial Global Best particle ( aGB) that has the potential to be a better “guide” than the PSO’s native gbest particle. To establish follow-up of local optima, we then introduce a novel multi-swarm algorithm, which enables each swarm to converge to a different optimum and use FGBF technique distinctively. Finally for the multi-dimensional dynamic environments where the optimum dimension also changes in time, we utilize a recent PSO technique, the multi-dimensional (MD) PSO, which re-forms the native structure of the swarm particles in such a way that they can make inter-dimensional passes with a dedicated dimensional PSO process. Therefore, in a multi-dimensional search space where the optimum dimension is unknown, swarm particles can seek for both positional and dimensional optima. This eventually pushes the frontier of the optimization problems in dynamic environments towards a global search in a multi-dimensional space, where there exists a multi-modal problem possibly in each dimension. We investigated both standalone and mutual applications of the proposed methods over the moving peaks benchmark (MPB), which originally simulates a dynamic environment in a unique (fixed) dimension. MPB is appropriately extended to accomplish the simulation of a multi-dimensional dynamic system, which contains dynamic environments active in several dimensions. An extensive set of experiments show that in traditional MPB application domain, FGBF technique applied with multi-swarms exhibits an impressive speed gain and tracks the global peak with the minimum error so far achieved with respect to the other competitive PSO-based methods. When applied over the extended MPB, MD PSO with FGBF can find optimum dimension and provide the (near-) optimal solution in this dimension.

Knowledge management in a multicultural environment: a South African perspective

PurposeNumerous authors contend that there are dissimilarities in the way people, especially those from different cultural backgrounds, interpret or accept knowledge sharing. Ribiere and Sitar argue that, as a result of their educational systems, western cultures do not encourage a social exemplar of knowledge sharing. Yeh and Ma concur, arguing that western cultures are more likely to embrace values of self‐determination, independence and the attainment of personal interest. In contrast, Yang argues that Asian cultures nurture a sharing and teamwork environment or approach to activities. Very little is mentioned in literature about knowledge sharing in African cultures and/or African organisations. Specifically, not much is known regarding knowledge sharing in settings where the roles of dominance of one culture over another are reversed or neutralised, either by force or law, or by natural progression. The purpose of this paper is to address this issue.Design/methodology/approachBeing in the fortunate position of working for a culturally diversified multinational organisation based in South Africa, one of the authors was able to determine, on a first‐hand basis, how different cultural backgrounds impact upon knowledge sharing. In the organisation under review, research subjects' opinions on knowledge sharing, culture and other knowledge management (KM) issues were surveyed by means of a structured questionnaire consisting of 21 descriptive questions. Phenomenological research was chosen since it is a qualitative research method that attempts to understand participants' perspectives, perceptions and views of a phenomenon. The analysis that follows consists of descriptive statistics used for each question, as well as the testing of hypotheses regarding the relationships between explanatory and response variables.FindingsAs in other studies, cultural issues such as language proficiency, education and schooling, gender biases, age and work experience, were all found to influence the knowledge‐sharing inclination of individuals either directly or indirectly. However, when individuals have been exposed to past political turmoil leading to present empowerment policies such as affirmative action, knowledge distribution takes on a different dimension – one in which knowledge sharing becomes a power play. African individuals, irrespective of whether they are black or white, display much more of a sense of power in knowledge sharing than do their European counterparts.Originality/valueThe paper is of relevance to knowledge management practitioners, scholars and professionals interested in the sharing and management of knowledge in extremely diversified and multidimensional environments.

Improved Rate Laws and Population Balance Simulation Methods; CRE Applications, Including the Combustion Synthesis of Valuable Nano-Particles

Using ‘flame-synthesized’ nanoparticles (nps) as one prototypical application, we illustrate our recent progress in two broad areas of current CRE-interest, viz., the development of: 1. Improved rate laws/transport coefficients for next-generation Eulerian, multi-(state) variable population-balance formulations, and 2. Quadrature-based multi-variate moment methods (hereafter QMOM) suitable for articulation with evolving Eulerian CFD simulation methods Admittedly, in previous work much insight was obtained by introducing deliberately (over-) simplified rate laws (for nucleation, Brownian coagulation, vapor growth/evaporation, sintering, thermophoresis, ) into the generally nonlinear integro-partial differential equation called the ‘population balance’ equation (PBE). However, despite the complexity of this equation, and the need to satisfy it along with many other local PDE-balance principles in multi-dimensional CRE environments, in our view current requirements for reactor design, as well as the frequent need to infer meaningful physico-chemical parameters based on laboratory measurements on populations rather than individual ‘particles’, make the introduction of more accurate rate/transport laws essential for next-generation particle synthesis reactor models. Our present examples are motivated both by measurements/calculations of the structure of laminar counterflow flames synthesizing Al2O3 nps and/or the predicted performance of well-mixed steady-flow devices in which sintering or sublimation occurs. Corresponding illustrative results, which focus on the rate laws for sphere dissolution or aggregate Brownian coagulation support our contentions that: i) systematic introduction of more accurate rate laws (including nucleation, sintering, growth, )/transport coefficients will be essential to meet the quantitative demands of next-generation PBE-based CRE-simulation models for high-value particulate synthesis equipment, and, ii) QMOM is able to incorporate realistic rate laws and faithfully generate their effects on important ‘moments’ characterizing the product joint distribution functions.

Two-dimensional hydrodynamic core-collapse supernova simulations with spectral neutrino transport

Supernova models with a full spectral treatment of the neutrino transport are presented, employing the PROMETHEUS/VERTEX neutrinohydrodynamics code with a variable Eddington factor closure of the O(v/c) moments equations of neutrino number, energy, and momentum. Our ray-by-ray plus approximation developed for two- (or three-) dimensional problems assumes that the local neutrino distribution function is azimuthally symmetric around the radial direction, which implies that the nonradial flux components disappear. Other terms containing the angular velocity components are retained in the moments equations and establish a coupling of the transport at different latitudes by lateral derivatives. Also lateral components of the neutrino pressure gradients are included in the hydrodynamics equations. This approximative approach for neutrino transport in multi-dimensional environments is motivated and critically assessed with respect to its capabilities, limitations, and inaccuracies in the context of supernova simulations. In this first paper of a series, one- (1D) and two-dimensional (2D) core-collapse calculations for a (nonrotating) 15 M ○. star are discussed, uncertainties in the treatment of the equation of state - numerical and physical - are tested, Newtonian results are compared with simulations using a general relativistic potential, bremsstrahlung and interactions of neutrinos of different flavors are investigated, and the standard approximation in neutrino-nucleon interactions with zero energy transfer is replaced by rates that include corrections due to nucleon recoil, thermal motions, weak magnetism, and nucleon correlations. Models with the full implementation of the ray-by-ray plus spectral transport were found not to explode, neither in spherical symmetry nor in 2D when the computational grid is constrained to a lateral wedge (<±45°) around the equator. The success of previous two-dimensional simulations with grey, flux-limited neutrino diffusion can therefore not be confirmed. An explosion is obtained in 2D for the considered 15 M ○. progenitor, when the radial velocity terms in the neutrino momentum equation are omitted. This manipulation increases the neutrino energy density in the convective gain layer by about 20-30% and thus the integral neutrino energy deposition in this region by about a factor of two compared to the non-exploding 2D model with the full transport. The spectral treatment of the transport and detailed description of charged-current processes leads to proton-rich neutrino-heated ejecta, removing the problem that previous explosion models with approximate neutrino treatment overproduced N = 50 closed neutron shell nuclei by large factors.

High-fidelity passive force-reflecting virtual environments

Passivity theory is applied to the creation of synthetic, complex multidimensional haptic environments. It can be shown that under appropriate conditions, sufficiently high rendering rates can guarantee the passivity of a simulation produced by a haptic device coupled to a discrete-time realization of a nominally passive environment. The creation of a passive, globally defined, virtual environment is either analytically complex or computationally costly. A method is described whereby a passive environment is created from transitions between locally defined force models that encode static conservative force fields. This is applied to the haptic rendering of tool contact with deformable bodies, in which sparse force-deflection responses are used to define local models. Passivity, continuity, and fidelity are provided by response-function interpolation rather than by interpolation of forces, as in previous methods. The work also includes an illustrative example.

Motor rehabilitation using virtual reality

Virtual Reality (VR) provides a unique medium suited to the achievement of several requirements for effective rehabilitation intervention. Specifically, therapy can be provided within a functional, purposeful and motivating context. Many VR applications present opportunities for individuals to participate in experiences, which are engaging and rewarding. In addition to the value of the rehabilitation experience for the user, both therapists and users benefit from the ability to readily grade and document the therapeutic intervention using various systems. In VR, advanced technologies are used to produce simulated, interactive and multi-dimensional environments. Visual interfaces including desktop monitors and head-mounted displays (HMDs), haptic interfaces, and real-time motion tracking devices are used to create environments allowing users to interact with images and virtual objects in real-time through multiple sensory modalities. Opportunities for object manipulation and body movement through virtual space provide frameworks that, in varying degrees, are perceived as comparable to similar opportunities in the real world. This paper reviews current work on motor rehabilitation using virtual environments and virtual reality and where possible, compares outcomes with those achieved in real-world applications.