Detection of hidden structures in nonstationary spike trains

We propose an algorithm for simultaneously estimating state transitions among neural states and nonstationary firing rates using a switching state-space model (SSSM). This algorithm enables us to detect state transitions on the basis of not only discontinuous changes in mean firing rates but also discontinuous changes in the temporal profiles of firing rates (e.g., temporal correlation). We construct estimation and learning algorithms for a nongaussian SSSM, whose nongaussian property is caused by binary spike events. Local variational methods can transform the binary observation process into a quadratic form. The transformed observation process enables us to construct a variational Bayes algorithm that can determine the number of neural states based on automatic relevance determination. Additionally, our algorithm can estimate model parameters from single-trial data using a priori knowledge about state transitions and firing rates. Synthetic data analysis reveals that our algorithm has higher performance for estimating nonstationary firing rates than previous methods. The analysis also confirms that our algorithm can detect state transitions on the basis of discontinuous changes in temporal correlation, which are transitions that previous hidden Markov models could not detect. We also analyze neural data recorded from the medial temporal area. The statistically detected neural states probably coincide with transient and sustained states that have been detected heuristically. Estimated parameters suggest that our algorithm detects the state transitions on the basis of discontinuous changes in the temporal correlation of firing rates. These results suggest that our algorithm is advantageous in real-data analysis.     

Low back strain in Danish semi-skilled construction work

Danish semi-skilled construction workers (SC-workers) perform a variety of tasks in building construction, civil engineering and rebuilding. A previous epidemiologic study indicated a high occurrence of low back pain (LBP) among these workers. The study was designed to quantify the major occupational risk factors associated with the development of LBP, i e, inclined postures, repetitive movements, heavy lifts, pushing/pulling motions, sudden unexpected strains and whole body vibrations in this group of construction workers. Firstly a study of occupational activity of 112 SC-workers on height construction sites during two separate five-days periods was carried out. This was followed by an observational study of the nine work tasks most common to SC-workers. Heavy lifts, pushing/pulling motions and sudden unexpected strain occurred most frequently in the work, while inclined postures, repetitive movements and whole body vibrations characterised different parts of the work. Assessments of the strain were made on the basis of techniques given in the literature.     

一种安全转移系统模型的构造及其运用

为提高安全性, 一般利用密码技术, 但系统运行过程的安全尚显不足, 为此基于行为时序逻辑TLA提出一种安全转移系统模型。通过设置安全属性, 构造安全行为, 使得系统在运行过程中的每次转移都满足安全属性, 从而提高过程的安全性。为此, 定义初始安全态、安全转移条件、安全状态、安全行为、安全运迹和安全转移系统, 并证明在安全转移系统中状态处处安全。安全转移系统中强调的是系统转移过程的安全性, 从而增强了系统运行的安全。通过实例的运用表明面向过程安全的建模为提高系统的安全性是有意义的。     

State-space support for path-based reward variables

Many sophisticated formalisms exist for specifying complex system behaviors, but methods for specifying performance and dependability variables have remained quite primitive. To cope with this problem, modelers often must augment system models with extra state information and event types to support particular variables. This often leads to models that are non-intuitive, and must be changed to support different variables. To address this problem, we extend the array of performance measures that may be derived from a given system model, by developing new performance measure specification and model construction techniques. Specifically, we introduce a class of path-based reward variables, and show how various performance measures may be specified using these variables. Path-based reward variables extend the previous work with reward structures to allow rewards to be accumulated based on sequences of states and transitions. To maintain the relevant history, we introduce the concept of a path automaton, whose state transitions are based on the system model state and transitions. Furthermore, we present a new procedure for constructing state spaces and the associated transition rate matrices that support path-based reward variables. Our new procedure takes advantage of the path automaton to allow a single system model to be used as the basis of multiple performance measures that would otherwise require separate models or a single more complicated model.     

Motor-unit recruitment in the trapezius muscle during arm movements and in VDU precision work

It has been hypothesized that shoulder myalgia, which is common in many occupations involving light-to-moderate manual work, is due to an overuse of low threshold muscle fibers, causing damage at the muscle cell level. The present study was undertaken to investigate in the trapezius muscle, (a) to what extent it is possible to track low threshold motor-units in non-isometric conditions, and (b) to study the effect of arm movements on recruitment and firing patterns. Intramuscular four lead fine wire electrodes were inserted in the trapezius muscle of four volunteers, who performed arm movements (shoulder abduction–adduction 0–90–0° in the scapula plane), as well as standardized work using computer mouse. Three channels of electromyography (EMG) were used for motor-unit action potential (MUAP) identification and signal decomposition. Results showed (a) that it was possible to perform signal tracking during slow movements, and (b) that there were motor-units that were active over a wide range of shoulder abduction movement, as well as in work with computer mouse. The findings indicate that stereotypic recruitment patterns exist in the trapezius muscle not only in static work, but also in work situations involving arm and shoulder movements.

Relevance to industry

Occupationally related chronic shoulder pain is an increasing problem in industry, in manual work as well as in computer work. This paper presents results of studies on muscular activity patterns during movements which support the notion that chronic pain may be evoked by overuse syndromes at the muscular fiber level. Practical precautions to reduce such risks are discussed.     

Robotics software systems

A robotics software “system” is defined here as one which allows robot users to program robot tasks in terms of key states of the task, instead of manipulator motions. It consists of two subsystems: a language system and a planning system. The language system involves the design of syntax and semantics of a robot programming language whereas the planning system determines specific manipulator movements for a given task defined in a task-level language. This paper describes the major components of a robotics software system and reviews principal research findings in the related aspects including programming languages, manipulator and world modelings, motion planning, and graphic simulation. Underlying research issues are addressed at the end.     

H2 control strategy for Na ion channels on the neural cellular membrane

The channel gating process of neural cells is the first step of neural information transmission. We have proposed a kinetic model for state transitions for a sodium (Na) ion gating channel under H2 control. The channel state consisted of an open state, three closed but activated states, and four inactivated but not closed states. This modeling was based strictly on molecular biological observations. Three charged amino acid helixes of the specific subunits of the Na channel hole act as activating gates. Another helix of the subunit having membrane voltagesensing properties behaves as an inactivating particle that invades the Na channel hole after membrane depolarization. This particle blocks the free movements of the three activating gates and inactivates the Na channel gating function. In total there are eight channel states, which consist of four inactivated states, three closed states, and one open state. We expressed the transitions among these states by eight linear differential equations using the law of conservation. For the control principle, the channel system is always exposed to a biological mimetic that is a false transmitter and competes for the channel sites with Na ions. Hence, we regarded such biological agencies as noises in the system that disturb the effective transmission of information, i.e., rapid transitions through the channel gating systems. The physiological Na gating is understood to minimize influences from the disturbing noises on the transition of the channels states, and we have proposed the H2 control principle. The computed results of temporal changes in the amount of channel species per unit membrane area showed rapid changes and then termination. This behavior was strongly dependent on the membrane potential. Our modeling could describe the rapid excitation and resetting of the Na ion channel gating function of the neural system. These results strongly reflect the digital nature of the neural system. The present investigation could be used to evaluate the function of neural systems that minimizes the influences of noises on the information transmission process by the transitions of the Na ion channel gating state.     

进程创建的语义及等价性

针对一个基于共享变量的带有进程创建的命令式语言,用变迁系统描述了它的结构操作语义,并用扩展的状态变迁迹模型定义了它的指称语义,在该模型下,状态变迁被区分为两种不同形式,分别表示发生在原进程和被创建进程中的状态变迁,这样便可以定义适当的语义复合运算,在对命令的指称进行复合时根据变迁类型的不同对变迁迹进行串行或交错连接,恰当地反映了进程的并发运行受创建命令在程序中的相对位置的限制,最后证明了这两个语义     

Head movements during two computer work tasks assessed by accelerometry

We investigated whether potential differences in head inclinations and accelerations for two highly similar computer work tasks could be detected using (1) a triaxial accelerometer and (2) a simulated uniaxial accelerometer.Ten subjects’ head movements were registered with a triaxial accelerometer system for two similar document-management tasks at their work place: a fully electronic document-management task and one also involving paper documents.In situations where head movements were small, a triaxial accelerometer was able to discriminate between the different degrees of static work of the neck in terms of range of head inclinations and accelerations. A difference in head acceleration was also found by using a simulated uniaxial accelerometer. Thus, in terms of head movement and for work similar to this office work, potential dynamic differences in observationally similar work tasks can be investigated by using a triaxial accelerometer. For acceleration alone, a uniaxial accelerometer can also be used.     

Multi-aspect target discrimination using hidden Markov models and neural networks

This paper presents a new multi-aspect pattern classification method using hidden Markov models (HMMs). Models are defined for each class, with the probability found by each model determining class membership. Each HMM model is enhanced by the use of a multilayer perception (MLP) network to generate emission probabilities. This hybrid system uses the MLP to find the probability of a state for an unknown pattern and the HMM to model the process underlying the state transitions. A new batch gradient descent-based method is introduced for optimal estimation of the transition and emission probabilities. A prediction method in conjunction with HMM model is also presented that attempts to improve the computation of transition probabilities by using the previous states to predict the next state. This method exploits the correlation information between consecutive aspects. These algorithms are then implemented and benchmarked on a multi-aspect underwater target classification problem using a realistic sonar data set collected in different bottom conditions.     

Compositional SOS and beyond: a coalgebraic view of open systems

In this paper we address the issue of providing a structured coalgebra presentation of transition systems with algebraic structure on states determined by an equational specification Γ. More precisely, we aim at representing such systems as coalgebras for an endofunctor on the category of Γ-algebras. The systems we consider are specified by using arbitrary SOS rules, which in general do not guarantee that bisimilarity is a congruence. We first show that the structured coalgebra representation works only for systems where transitions out of complex states can˜be derived from transitions out of corresponding component states. This decomposition property of transitions indeed ensures that bisimilarity is a congruence. For a system not satisfying this requirement, next we propose a closure construction which adds context transitions, i.e., transitions that spontaneously embed a state into a bigger context or vice versa. The notion of bisimulation for the enriched system coincides with the notion of dynamic bisimilarity for the original one, i.e., with the coarsest bisimulation which is a congruence. This is sufficient to ensure that the structured coalgebra representation works for the systems obtained as result of the closure construction.     

Automatic generation of test specifications for coverage of system state transitions

Adequate system testing of present day application programs requires satisfactory coverage of system states and transitions. This can be achieved by using a system state model. However, the system state models are rarely constructed by system developers, as these are large and complex. The only state models that are constructed by the developers are those of individual objects. However test case generation for state-based system testing based on traversal of statecharts of individual objects appears to be infeasible, since system test cases would have to be specified in the form of scenario sequences rather than transitions on individual object statecharts. In this paper, we propose a novel approach to coverage of elementary transition paths of an automatically synthesized system state model. Our technique for coverage of elementary transition paths would also ensure coverage of all states and transitions of the system model.     

‘Light’ and ‘heavy’ work in the housekeeping service of a hospital

Work is organized based in part on the perceptions, by managers and workers, of workers, their abilities and the characteristics of the work to be done. Physical tasks in factories and services have often been divided into ‘light’ and ‘heavy’, a division that often corresponds formally or informally to gender. We have observed the work of cleaners on wards and in offices in an acute-care hospital, using several indicators of workload to identify and characterize typical work situations. ‘Heavy’ work was characterized by neutral postures, walking, repetitive movements involving the articulations of the upper limb pushing a 1-6 kg (wet or dry) mop, with occasional more intense effort. ‘Light’ work was characterized by flexed postures, walking, rapid repetitive movements involving the articulations of the upper limb and light weights (dusting) or 1-3 kg weights (emptying wastebaskets), with more occasional intense effort. We did not discover any compelling reason to divide cleaning into ‘light’ and ‘heavy’ work. Task assignment by sex may appear to be a solution to excessive job demands which would be better addressed by job re-design.     

From SOS Specifications to Structured Coalgebras: How to Make Bisimulation a Congruence

In this paper we address the issue of providing a structured coalgebra presentation of transition systems with algebraic structure on states determined by an equational specification Γ. More precisely, we aim at representing such systems as coalgebras for an endofunctor on the category of Γ-algebras. The systems we consider are specified by using a quite general format of SOS rules, the algebraic format, which in general does not guarantee that bisimilarity is a congruence.We first show that the structured coalgebra representation works only for systems where transitions out of complex states can be derived from transitions out of corresponding component states. This decomposition property of transitions indeed ensures that bisimilarity is a congruence. For a system not satisfying this requirement, next we propose a closure construction which adds context transitions, i.e., transitions that spontaneously embed a state into a bigger context or vice-versa. The notion of bisimulation for the enriched system coincides with the notion of dynamic bisimilarity for the original one, that is, with the coarsest bisimulation which is a congruence. This is sufficient to ensure that the structured coalgebra representation works for the systems obtained as result of the closure construction.     

Smooth Graphs for Visual Exploration of Higher-Order State Transitions

In this paper, we present a new visual way of exploring state sequences in large observational time-series. A key advantage of our method is that it can directly visualize higher-order state transitions. A standard first order state transition is a sequence of two states that are linked by a transition. A higher-order state transition is a sequence of three or more states where the sequence of participating states are linked together by consecutive first order state transitions. Our method extends the current state-graph exploration methods by employing a two dimensional graph, in which higher-order state transitions are visualized as curved lines. All transitions are bundled into thick splines, so that the thickness of an edge represents the frequency of instances. The bundling between two states takes into account the state transitions before and after the transition. This is done in such a way that it forms a continuous representation in which any subsequence of the timeseries is represented by a continuous smooth line. The edge bundles in these graphs can be explored interactively through our incremental selection algorithm. We demonstrate our method with an application in exploring labeled time-series data from a biological survey, where a clustering has assigned a single label to the data at each time-point. In these sequences, a large number of cyclic patterns occur, which in turn are linked to specific activities. We demonstrate how our method helps to find these cycles, and how the interactive selection process helps to find and investigate activities.     

ST-Audit: guideline-based automatic auditing of electronic patient records

This work presents the ST-Audit system that audits a patient record for conformance to a particular clinical guideline. The system uses ST-Guide which models a guideline as a set of states and transitions. The audit system tries to find a path in the state/transition diagram that corresponds to the actions taken by the physician, taking into consideration issues such as the unavailability of all the data needed to evaluate the transitions. The system was used to audit an outpatient clinic regarding their procedure for hypertension treatment (using the VI JNC guideline for hypertension), and the results of the number of non-compliant actions were presented and discussed. A follow up auditing showed a small but statistically significant reduction on the number of non-compliant actions for patients treated after the first audit.     

Functional work breaks in a high-demanding work environment: an experimental field study

Work breaks are known to have positive effects on employees’ health, performance and safety. Using a sample of twelve employees working in a stressful and cognitively demanding working environment, this experimental field study examined how different types of work breaks (boxing, deep relaxation and usual breaks) affect participants’ mood, cognitive performance and neurophysiological state compared to a control condition without any break. In a repeated measures experimental design, cognitive performance was assessed using an auditory oddball test and a Movement Detection Test. Brain cortical activity was recorded using electroencephalography. Individual’s mood was analysed using a profile of mood state. Although neurophysiological data showed improved relaxation of cortical state after boxing (vs. ‘no break’ and ‘deep relaxation’), neither performance nor mood assessment showed similar results. It remains questionable whether there is a universal work break type that has beneficial effects for all individuals.

Practitioner Summary: Research on work breaks and their positive effects on employees’ health and performance often disregards break activities. This experimental field study in a stressful working environment investigated the effect of different work break activities. A universal work break type that is beneficial for this workplace could not be identified.     

Acquisition of state transitions and concept formation in neural networks

Searching of state transitions is an important subject of problem solving in artificial intelligence, computer science, engineering and operations research. In artificial intelligence, a breadth-first search is optimal, with uniform cost, but it takes considerable time to obtain a solution. Neural networks process state transitions in parallel with learning ability. The authors have developed a search procedure for state transitions, that resembles a breadth-first search, using neural networks. First, the input pattern states are self-organized in the neural network, which consists of a Kohonen layer followed by a state-planning layer. The state-planning layer makes lateral connections between the cells of transitions. Then, the initial and the target states are given as a problem. The network shows an optimal transition pathway of states in the neuron firings. Next, the state-transition procedure is developed for the formation of a concept for action planning. Here, as the action planning, an integration between the symbols and the action pattern is carried out in the extended neural network.     

Articulation of work process models for organizational alignment and informed information system design

Articulating and representing procedural aspects of work in conceptual models is a prerequisite for informed information system (IS) design. Instruments supporting articulation need to establish common ground about the interaction of the collaborating actors. This article proposes a methodology for the articulation of work processes by inexperienced modelers. It consists of phases of articulation and consolidation of case-based models and interactive elaboration toward comprehensive representation of the process via virtual enactment. The resulting models can be directly interpreted by IS. A case study confirms that the methodology meets the identified requirements and identifies areas of improvement.     

EXPERIMENTAL IMPLEMENTATION OF AN ARTIFICIAL IMMUNE SYSTEM ON A ROBOTIC MANIPULATOR

An artificial immune system (AIS) has been used to realize robust control of a robotic manipulator. The AIS recognizes “self” and “non-self” operation of a closed-loop system, where self is defined as a condition where controller gains are appropriate for a given manipulator configuration. As configuration changes occur, the changing performance of the system indicates a transition to non-self. When non-self operation is first detected, the corresponding dynamic response is defined as a receptor and a genetic algorithm (GA) is called to optimize the controller for the new configuration. A library of receptors is built as additional configuration changes are experienced. For subsequent self to non-self transitions, new and recorded receptors are compared. In the event of a high correlation between the receptors, previously determined controller gains are implemented without calling the GA. The system is agile and robust and can recognize and respond to recognized receptors within a single reference step.