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A basic fact, having fundamental significance in quantum mechanics, is that hermitian (or self-adjoint) operators have only real eigenvalues. However, in certain applications in molecular physics, one deals with non-hermitian operators. We discuss a condition for non-hermitian operators to have real eigenvalues, proving that it is the case if and only if it can be decomposed as a product of two, generally non-commuting hermitian operators, one of which is positive definite. The theorem is illustrated on the example of non-hermitian effective Hamiltonians occurring in the non-perturbative form of the Bloch equation. [ABSTRACT FROM AUTHOR]

Despite the substantial literature and human factors guidance, evaluators report challenges in selecting cognitive workload measures for the evaluation of complex human–technology systems. A review of 32 articles found that self-report measures and secondary tasks were systematically sensitive to human–system interface conditions and correlated with physiological measures. Therefore, including a self-report measure of cognitive workload is recommended when evaluating human–system interfaces. Physiological measures were mainly used in method studies, and future research must demonstrate the utility of these measures for human–system evaluation in complex work settings. However, indexes of physiological measures showed promise for cognitive workload assessment. The review revealed a limited focus on the measurement of excessive cognitive workload, although this is a key topic in nuclear process control. To support human–system evaluation of adequate cognitive workload, future research on behavioural measures may be useful in the identification and analysis of underload and overload. This review provides background for the selection of cognitive workload measures for the evaluation of complex human–technology systems and identifies future research needs for applied cognitive workload assessment. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of assigning a number of operators, less than the number of machines, in a flow shop environment. We study two different problems. The first is the assignment of operators subject to a fixed job sequence; the second is on handling simultaneously the assignment of operators and the scheduling of jobs on the machines. We present complexity results and develop a new lower bound. Heuristic algorithms are designed for both problems. An experimental study is then conducted to evaluate the quality of our solving methods. The results show that the appropriate approach depends on the parameters of the problem, including the number of operators. The methods also provided results close to the theoretical lower bound in most of the cases. [ABSTRACT FROM AUTHOR]

Objectives. Previous research indicates that models for risk assessment of pressure equipment have not sufficiently or adequately integrated indicators of human factors and organizational factors. Methods. The goal of this article is to check the differences in attitudes of operators and managers engaged in the area of pressure equipment risk management. A questionnaire was designed and data were then collected from 253 operators and managers working with the same pressure equipment in Serbia. By applying a paired t test, differences in their attitudes were checked for issues described by the constructs of communication (COM), potentially hazardous materials and equipment (PHME), process safety (PS), safety and health at work (SHW), organizational change management (OCM), maintenance/inspection (MI) procedures, human error (HE), trainings and competences of employees for crisis situations (TCECS) and conducting research after accidents (CRAA). Results. It is statistically evident that the coincidence of attitudes accounted for less than 20% of questions. The highest coincidence is shown for PHME and TCECS, where one-half of the dimensions of the given constructs indicate that there are no statistically significant differences. Conclusions. The differences found could be used as an explanation for high-risk levels of pressure equipment exploitation and how they influence it. [ABSTRACT FROM AUTHOR]

A crucial issue in the debate about the correct treatment of natural language tense concerns covert variables: do we have reason to think there are any in the syntax, as the quantifier theorist maintains? If not, it seems we can quickly discount the quantifier theory from consideration, without even considering the data in its favour. And, indeed, there is a good reason to doubt that there are such variables: contemporary syntactic theory, notably, does not seem to posit them. I respond to this argument going from the premise that positing covert variables is illicit to the conclusion that quantifier theories of tense are false. I argue that the argument fails by suggesting a non-committal understanding of the process of positing covert variables. On this view, even if we are not doing fundamental syntax in so positing, nevertheless there is a reason to think we are doing something theoretically productive, because it seems like an important part of the practice of semantics and because it seems like semantics is a discipline which is making progress. The progress of semantics supports the methodology of positing variables at its heart; the quantifier theorist of tense, accordingly, need not worry about their syntactic commitments. [ABSTRACT FROM AUTHOR]

The diffusion risk model is considered in the presence of liquid reserves, credit and debit interest. For arbitrary boundary and any interval, the Laplace-Stieltjes transform (LST) of some exit times of the risk process are derived. The results are then used to find the probability and mathematical expectation of the exit times. Finally, several numerical examples be discussed in order to illustrate the applications of the LST of some exit times. [ABSTRACT FROM AUTHOR]

The use of pesticides in horticultural sector in Niger has become an integral part of modern agriculture. Nevertheless, their inappropriate use can generate negative health effects to operators. A study was carried out among Kongou farmers in order to assess their potential dermal exposure (PDE). The UK-POEM model was used to quantify the PDE during mixing/loading and application according to the local practices. In order to determine which parts of the operator body are subject to most contamination during spraying and to validate the theoretical model used, a patch method was used with a tartrazine dye. The deposits of the tartrazine on patches were measured by colorimetry thanks to the absorbance value determined after their extraction in water and a calibration curve. A total of ten spraying trials (five trials with the hand-held sprayer and five others with the backpack sprayer) were performed by different producers at 0.5 and 1 m height for each trial. The survey shows that 92% of the farmers are illiterate and the most common active substances identified are organophosphate or pyrethroids insecticides. Seventy percent of operators do not use any personal protective equipment (PPE) during mixing/loading or spraying. The predictive systemic exposure levels vary from 0.0027 mg kg−1 bw per day to 0.7692 mg kg−1 bw per day for backpack sprayer and from 0.0261 mg kg−1 bw per day to 0.9788 mg kg−1 bw per day for hand-held sprayer, several times higher the Acceptable Operator Exposure Level (AOEL) for some actives substances. Theoretical modeling indicates more exposure of operator by a hand-held sprayer than a backpack sprayer. The patch method results show that the deposits of dye increase when the position of sprayer nozzle increases from 0.5 to 1 m for the two sprayers. All parts of the operator body are contaminated but lower body parts and chest are the most exposed. The patch method results also show that hand spraying contaminates operator more than backpack spraying, confirming the results of the theoretical model. [ABSTRACT FROM AUTHOR]

By the Many Categories problem, I mean the prima facie violation of Ockham's Razor by realists about universals: there is, it might seem, just too much variety. Thus, David Armstrong posits both properties and relations. He also theorises about determinates of determinables. Another influential realist, E. J. Lowe distinguishes non-substantial from substantial universals. Yet again, both Armstrong and Lowe include in their ontology abstract particulars in addition to universals. My aim in this paper is to offer a unification of these categories using an operator-theory. First, I show how operators provide a theory of abstract particulars of relations and of impure relational properties. Then, using impure relational properties I derive the Fregean Abstraction Principle. After some metaphysics of mathematics, I provide a theory of determinables. Finally, I consider kinds and substances. [ABSTRACT FROM AUTHOR]

Surfing tourism has the potential to provide significant economic income and employment opportunities. However, the development of surfing tourism in the Mentawai Islands, Indonesia, has raised important questions regarding its impacts and sustainability. Economic leakages, increased pressure on the environment and resources, and adverse effects on local communities have been shown as the major barriers to sustainable development. This article provides insights into how surfing tourism operators perceive the development and impacts of the Mentawai Islands surfing tourism industry. This research project uses an interpretive qualitative approach and follows a case study methodology utilising semi-structured interviews with resort and charter boat surfing tourism operators. The study also investigated possible future directions for creating a more sustainable surfing tourism industry in the Mentawai Islands. Findings from the research showed that charter boat operators and resort operators had differing views as to how surfing tourism had developed: resort operators believed it to be sustainable, while charter boat operators felt it was unsustainable. A key finding of this study was that operators felt that surfing tourism had dramatically altered the traditional Mentawai village of Katiet and was producing adverse socio-cultural impacts on the local community. It is recommended that future research explore the issue of the impacts of surfing tourism development on other remote locations in Indonesia and other surfing tourism destinations around the globe. [ABSTRACT FROM AUTHOR]

Decision-making in complex systems such as nuclear power plants (NPPs) is a difficult task at best. The safety and integrity of many such high-capital cost-intensive installations depend on the operator's capability to correctly diagnose and take appropriate measures to avoid any abnormal operations of an NPP. Therefore, the role of the expert systems in the offline training programs for the operators is ever increasing. In this paper, we describe the development of an expert system, "QNP_SHELL," to assist, offline QNPP operators and plant personnel in a better familiarization to infer the anticipated and foreseen malfunctions from the observed symptoms. QNP_SHELL's inferencing mechanism is of the "Rule-based" type and to search the knowledge base it adopts the "Depth First" technique. The diagnostic performance of the trainee operators using QNP_SHELL on various accidents at QNPP has been found, through both the qualitative and quantitative evaluations, satisfactory. [ABSTRACT FROM AUTHOR]

In this era of rapid multi-scale economic, environmental, and social change the continuation of any given tourism phenomenon into the long-term future should not be taken for granted. The field of tourism studies is largely accounting for the influences of complex change on tourism. However, dive tourism research is lagging behind in this regard. A resilience framework for the study of dive tourism systems is proposed that addresses the need to better account for the threats posed by complex change and the ways dive tourism is responding. The effectiveness of the framework is demonstrated through a case study in the US Virgin Islands. In-depth, semi-structured interviews were carried out with dive operators and government officials. Findings show that perturbations to dive tourism include a lack of support from the larger social–political system, the recent US economic downturn, and an invasive fish species. On the other hand, sources of resilience include dive operators’ formation of self-advocating organizations, recognition of an inexperienced and increasingly frugal client base, and their own contributions to environmental protection. Gaps in the existing theoretical and applied knowledge about dive tourism can be filled through research on (1) social and economic perturbations to dive tourism and (2) ways dive operators respond to perturbations to maintain their resilience. [ABSTRACT FROM AUTHOR]

The literature on the risk perceptions, knowledge levels, and attitudes of operators, workers, and residents in relation to non-dietary exposure to agricultural pesticides is reviewed. No literature was identified in relation to bystander exposure. Research has primarily been conducted on participants in developing countries and migrant workers in the United States. For operators and workers, illiteracy, poverty, and a perception that exposure to pesticides is an inevitable part of their work results in limited adoption of safety precautions while using and storing pesticides. As a result, risk communication activities aimed at operator and workers need to take account of the wider socioeconomic and cultural conditions in which workers and operators are working and living. There is less research focused on residents’ and bystanders’ perceptions, attitudes, and behaviors. The lack of European data in general, and residents’ and bystanders’ data in particular, represents a knowledge gap that is pertinent to emerging EU legislation requiring residents’ and bystanders’ inclusion in pesticide risk assessment. This review provides a comprehensive overview that can assist policy-makers, and risk communicators in the development of targeted training and awareness-raising material for operators, workers, bystanders, and residents. Areas for future research are suggested. [ABSTRACT FROM AUTHOR]

In this paper, we define and study a generalized multiparameter function of Mittag-Leffler type. Some special cases and basic properties including its Mellin–Barnes-type integral representation, recurrence relation, and expansion are given. The Laplace transform and the first Sonine integral of the generalized function are evaluated. Differential and integral equations with the Erdelyi–Kober operator are established. The Cauchy problem for the multiparameter differential equation is formulated and its solution is obtained. [ABSTRACT FROM PUBLISHER]

A cartographic interaction primitive is a basic unit of interactivity that is combined with other primitives in sequence when using interactive maps. The construction of a taxonomy of these basic interaction primitives is considered the 'grand challenge of interaction', as such taxonomies provide a consistent lexicon for describing map-based interaction strategies and interface designs, inform the design of scientific experiments to investigate the nature of cartographic interaction, and ultimately lead to design and use guidelines for interactive maps. The purpose of this research is not to offer a new framework of interaction primitives-as there are many in existence-but to organize and synthesize extant strategies for parsing interaction within Cartography and the related fields of Human-Computer Interaction, Information Visualisation, and Visual Analytics into a logical framework. Norman's stages of action model provides a useful foundation for conceptualizing interaction primitives, with organisation of extant taxonomies by the model resulting in three dominant approaches for parsing interaction: (1) an objective-based approach, compartmentalizing cartographic interaction according to the kinds of tasks the user may wish to complete with a cartographic interface; (2) an operator-based approach, compartmentalizing cartographic interaction according to the unique cartographic interfaces that make manipulation of a cartographic representation possible; and (3) an operand-based approach, compartmentalizing cartographic interaction according to characteristics of the digital/virtual object with which the user is interacting. Extant interaction primitive taxonomies representative of each of these three approaches are treated in turn, synthesizing key themes within each approach and identifying important concordances and discordances across the associated taxonomies. [ABSTRACT FROM AUTHOR]

This article contains results of Watson convolution and translation. For this, a space of multipliers on the space T(λ, μ) is developed. A continuity result for Watson translation is obtained. Also, a structure theorem is developed to study the continuity result for convolution of two distributions. [ABSTRACT FROM AUTHOR]

Wireless sensor network layout, also known as sensor node deployment, is a complex NP-complete optimization task that determines most of the functioning features of a wireless sensor network. Coverage, connectivity and lifetime (handled through its opposing parameter, power consumption), are three of the most important characteristics of the service, and are taken into consideration in this article within a multi-objective approach of the problem. Leveraging on the specific properties of the wireless sensor nodes and networks, the Proximity Avoidance Coverage-preserving Operator (PACO) for local improvement is presented, described and tested. The testbed consists of a set of state-of-the-art multi-objective optimization algorithms with different configurations, and problem instances of varying size. In all the scenarios, and more specially in the algorithmic settings that already produce high performance solutions, PACO has proven to be a robust enhancement to the raw optimization technique, without requiring additional computation, that easily scales through problem complexity. [ABSTRACT FROM AUTHOR]

Operator impact on productivity and cost using similar processor machines was addressed in this case study. The study had two objectives: (1) determine the extent of operator productivity variation between six processor operators in a harvesting operation; and (2) determine potential cost implications associated with operator productivity variation. The study was carried out on the Zululand coastal plains near Kwambonambi. A multistem mechanised harvesting system, working in Eucalyptus grandis × camaldulensis pulpwood stands (with an average rotation length of seven years) was observed. The operators had all been operating their respective processors for 18 months; i.e. since the inception of the harvesting operation and had received similar in-house training. Time studies were carried out on the processors’ cycle times, and note taken of the respective operators working the machines during the time studies. Cycle time for each machine was measured as the time between a delimbed and debarked tree length leaving the processor head and the following tree length leaving the head. The required number of observations per processor was determined by cycle time and work element time variation. It was found that operators varied by up to 58% in terms of productivity, 24% in terms of utilisation and 70% in terms of cost. The potential difference in cost between using the cheapest operator and the most expensive operator was R9.34 m−3, R4 438 d−1 and R1 384 752 y−1. [ABSTRACT FROM AUTHOR]

The classical central simple theory of associative algebras generalizes, in this article, to a central simple theory of nonassociative algebras with operators and a related central irreducible theory of modules. These theories are motivated by, and apply to, problems of constructing and classifying simple Jordan Lie algebras, irreducible modules, and birings. [ABSTRACT FROM AUTHOR]

This article describes how a presentation from the point of view of differential operators can be used to (partially) unify the myriad techniques in an introductory course in ordinary differential equations by providing students with a powerful, flexible paradigm that extends into (or from) linear algebra. [ABSTRACT FROM AUTHOR]

Previous research has identified that six factors (each of which comprises numerous variables) impact upon plant operator productivity. These factors are: daily workload, motivation, management, maintenance, education and training, and stress and fatigue. In order lo explore and better understand the complex interrelationships that exist between these factors, an iterative empirical examination of each (in turn) was undertaken. This article reports on analysis of the first of these factors (daily workload), which comprises 51 variables identified from earlier pilot studies. A field study practical experiment and follow-on questionnaire were used as the data capture mechanisms. The experiment produced productivity time data, while the questionnaire yielded a mixture of interval (Likert scale) and Boolean data. The standard deviation technique was utilized to define and delineate the boundaries of the dependent variable (excavation time) into good, average and poor categories of plant operator production performance. A generalized feed-forward artificial neural network model was then created to simulate plant operators' productivity, Cumulatively, outputs derived from mean squared error, confusion matrix and correlation coefficients highlighted that the developed model is reasonably accurate, although further improvement to classification performance could be made. Finally, sensitivity analysis revealed the impact that each independent variable bad upon predicting the dependent variable while also identifying which were non-significant in terms of being predictors. The latter exercise confirmed that 19 of the original 51 variables could satisfactorily categorize operator production performance. [ABSTRACT FROM AUTHOR]

A Wavelet-Galerkin procedure was introduced in a previous paper to exhibit the transient response of parametrically excited systems involving both irregular time-varying coefficients and a relatively large number of degrees of freedom. The main scope of the present study is to introduce a wavelet technique allowing to seek periodic orbits of such dynamical systems and the associated periodic initial conditions. A few academic instances including a 1 dof Mathieu oscillator and a 3-dof system illustrate the relevance of the method by comparison with well established numerical techniques such as Runge-Kutta for example. Prospective researches are finally set to extend the wavelet method to the nonlinear case. [ABSTRACT FROM AUTHOR]

A two-sided assembly line balancing problem is typically found in plants producing large-sized high-volume products, e.g. buses and trucks. The features specific to the assembly line are described in this paper, which are associated with those of: (i) two-sided assembly lines; (ii) positional constraints; and (iii) balancing at the operational time. There exists a large amount of literature in the area of line balancing, whereby it has mostly dealt with one-sided assembly lines. A new genetic algorithm is developed to solve the problem, and its applicability and extensibility are discussed. A genetic encoding and decoding scheme, and genetic operators suitable for the problem are devised. This is particularly emphasized using problem-specific information to enhance the performance of the genetic algorithm (GA). The proposed GA has a strength that it is flexible in solving various types of assembly line balancing problems. An experiment is carried out to verify the performance of the GA, and the results are reported. [ABSTRACT FROM AUTHOR]