The sleeping brain as a complex system

'Complexity science' is a rapidly developing research direction with applications in a multitude of fields that study complex systems consisting of a number of nonlinear elements with interesting dynamics and mutual interactions. This Theme Issue 'The complexity of sleep' aims at fostering the application of complexity science to sleep research, because the brain in its different sleep stages adopts different global states that express distinct activity patterns in large and complex networks of neural circuits. This introduction discusses the contributions collected in the present Theme Issue. We highlight the potential and challenges of a complex systems approach to develop an understanding of the brain in general and the sleeping brain in particular. Basically, we focus on two topics: the complex networks approach to understand the changes in the functional connectivity of the brain during sleep, and the complex dynamics of sleep, including sleep regulation. We hope that this Theme Issue will stimulate and intensify the interdisciplinary communication to advance our understanding of the complex dynamics of the brain that underlies sleep and consciousness.     

Why Catalonia cannot be considered as a regional innovation system

We present a model to assess the systemness of an innovation system. Patent and citation datawith an institutional address in Catalonia (1986-1996) were analyzed in terms of relationallinkages and the development in these distributions over time was evaluated using methods fromsystems dynamics. Relational linkages are extremely scarce. A transition at the system's levelcould be indicated around 1990 when using institutional addresses, but not when using cognitivecategories. The institutional restructuring has led to changes in the pattern of linkages(coauthorship, etc.), but the reproduction of the system's knowledge base has remaineddifferentiated. We conclude that although a system in several other respects, Catalonia cannot(yet) be considered as a (knowledge-based) innovation system. The existence of a mechanism forthe integration could not be indicated at the regional level.     

The cerium-nitrogen-oxygen system. Oxygen as a component in the “binary” Ce-N system at 950°C

Cerium nitride prepared by reacting the metal with nitrogen at 795°C is inhomogeneous with an outer nitride layer surrounding a core of cerium oxynitride. Long annealing at 950°C produces a homogeneous product. The variation of the lattice parameter of the cerium nitride in two phase cerium nitride-metal mixtures indicates the system must be considered as ternary with oxygen as the third component. The literature value of 5.023₅Å for the lattice parameter of CeN is believed to refer to a low oxygen content substoichiometric nitride and extrapolation predicts 5.020Å as the lattice parameter of oxygen free, stoichiometric CeN.     

Case studies considered as retroactive experiments

A methodology for combining automobile crash investigation case studies into an overall statistical analysis is presented. The method considers each case study as an experiment identified by a set of independent variables. For each experiment a dependent variable—such as occupant injury—is measured. Analysis of the relationship between the independent variables and the dependent variable can then he performed. A specific example which uses multiple regression analysis to fit an injury prediction model is presented. Residuals from this model are used to show the effect on injury reduction of restraint systems.     

Application of thermal battery in the ice storage air-conditioning system as a subcooler

This article experimentally investigates the thermal performance of a thermal battery used in the ice storage air-conditioning system as a subcooler. The thermal battery utilizes the superior heat transfer characteristics of two-phase closed thermosyphon and eliminates the drawbacks found in convectional energy storage systems. Experimental investigations are first conducted to study the thermal behavior of thermal battery under different charge temperatures (−5 °C to −9 °C) in which water is used as the energy storage material. This study also examines the thermal performance of the subcooled ice storage air conditioner under different cooling loads. Experimental data of temperature variation of water, ice fraction, refrigerant mass flow rate and coefficient of performance (COP) are obtained. The results show that supercooling phenomenon appears in the water and it can be ended when the charge temperature is lower than −6 °C. The system gives 28% more cooling capacity and 8% higher COP by the contribution of the thermal battery used as a subcooler.     

The electron storage ring as a source of infrared radiation

The characteristics of synchrotron radiation in the infrared region have been investigated at the Berlin electron storage ring BESSY using Fourier spectroscopy. In accordance with calculation, it was found that BESSY at 100 mA beam current delivers higher fluxes than a conventional source only in the spectral region below 30 cm^?1, provided the interferometer is the throughput-limiting element. If, however, the throughput is limited by small sample size or, if the experiment requires a large f-number, the high brightness of synchrotron radiation could already yield flux advantages at several hundred wavenumbers. The possible application in one particular experiment - infrared reflection-absorption spectroscopy of adsorbed molecules on metal single crystal surfaces - is discussed. In the course of the investigations described here, it was also established that the short light pulses of the synchrotron radiation (～ 100 ps) do not adversely affect the resolution in Fourier transform spectroscopy.     

Adsorption on straight and bent optical fibers considered as a perturbation problem

The effect of a thin adsorbed layer of a foreign material on the modal propagation constant in an optical fiber is calculated by the use of a time-independent perturbation theory. The effect is measured on a straight fiber but is enhanced on a bent fiber because of tunneling, which is analogous to the Zener effect in quantum mechanics. Experimental results obtained with a fiber interferometer are presented.     

Numerical life estimation after fatigue failure of a complex component

Failure of a large ethylene‐reciprocating compressor was found to be due to fatigue growth of cracks in the crosshead of one of the cylinders, initiated at material defects near stress raisers. Total fatigue crack growth time was required in order to identify the cause of the failure. The applied stress field near the initiation sites and along fatigue path was estimated using FEM. The stresses were found to vary steeply and become partly compressive along a large part of the fatigue crack path. A weight function based on numerical method was developed, which was able to predict exactly the shape of the crack front during propagation. Fatigue crack initiation was traced to a disassembly 6 months before final failure. This failure was found to be jointly the result of non‐conformities in manufacture and maintenance.     

Crack growth predictions in a complex helicopter component under spectrum loading

Fatigue crack growth predictions have been made on a helicopter round‐robin crack configuration. The crack configuration was a small corner defect at the edge of a large central hole in a flanged plate made of 7010 aluminium alloy and the component was subjected to a simulated helicopter spectrum loading. The crack growth rate data and the stress‐intensity factor (K) solution for the crack configuration were provided in the round‐robin. The FASTRAN life‐prediction code was used to predict fatigue crack growth under various load histories on the aluminium alloy, such as Rotorix and Asterix, on both compact tension C(T) specimens and the complex crack configuration. A BEASY three‐dimensional stress‐intensity factor solution for the round‐robin problem was also provided for this paper and is compared with the original K solution. Comparisons are made between measured and predicted fatigue crack growth lives for both crack configurations. The predicted lives for the C(T) specimens were 15–30% longer than the measured lives; and crack growth in the round‐robin configuration agreed very well in the early stages of crack growth, but the life was 30% short of the test results at the final crack length.     

A storage assignment policy in a man-on-board automated storage/retrieval system

This paper deals with a man-on-board automated storage/retrieval system where each customer order consists of a number of different items and is picked one at a time. For the system the problem examined is to allocate storage locations dedicatedly to items so that the total travel time required to pick all the given orders per period is minimized. The problem is shown to be formulated as a variant of the generalized assignment model. A heuristic for the storage layout problem is developed based on the group technology concept considering both order structure and frequency. Through the heuristic, close relationships between items are identified from the order structure, and then based on the relationships the items are compelled to be stored closely in the storage rack following a space-filling curve. Experimental results are provided to describe the performance of the heuristic     

Resiliency as a component importance measure in network reliability

This paper seeks to define the concept of resiliency as a component importance measure related to network reliability. Resiliency can be defined as a composite of: (1) the ability of a network to provide service despite external failures and (2) the time to restore service when in the presence of such failures. Although, Resiliency has been extensively studied in different research areas, this paper will study the specific aspects of quantifiable network resiliency when the network is experiencing potential catastrophic failures from external events and/or influences, and when it is not known a priori which specific components within the network will fail. A formal definition for Category I resiliency is proposed and a step-by-step approach based on Monte-Carlo simulation to calculate it is defined. To illustrate the approach, two-terminal networks with varying degrees of redundancy, have been considered. The results obtained for test networks show that this new quantifiable concept of resiliency provides insight into the performance and topology of the network. Future use for this work could include methods for safeguarding critical network components and optimizing the use of redundancy as a technique to improve network resiliency.     

Hydrogel-based microreactors as a functional component of microfluidic systems

A simple two-step method for fabricating poly(ethylene glycol) (PEG) hydrogel-based microreactors and microsensors within microfluidic channels is described. The intrachannel micropatches contain either a dye, which can report the pH of a solution within a fluidic channel, or enzymes that are able to selectively catalyze specific reactions. Analytes present within the microfluidic channel are able to diffuse into the micropatches, encounter the enzymes, and undergo conversion to products, and then the products interact with the coencapsulated dye to signal the presence of the original substrate. The micropatches are prepared by photopolymerizing the PEG precursor within the channel of a microfluidic system consisting of a poly(dimethylsiloxane) mold and a glass plate. Exposure takes place through a slit mask oriented perpendicular to the channel, so the size of the resulting micropatch is defined by the channel dimensions and the width of the slit mask. Following polymerization, the mold is removed, leaving behind the micropatch(es) atop the glass substrate. The final microfluidic device is assembled by irreversibly binding the hydrogel-patterned glass slide to a second PDMS mold that contains a larger channel. Multiple micropatches containing the same or different enzymes can be fabricated within a single channel. The viability of this approach is demonstrated by sensing glucose using micropatches copolymerized with glucose oxidase, horseradish peroxidase, and a pH-sensitive dye.     

Design of class-based storage racks for minimizing travel time in a three-dimensional storage system

This paper deals with a new storage structure layout method called ‘cubic-in-time’, for minimizing the travel time of selected handling equipment in a three-dimensional palletized storage system. Storage-system design algorithms for minimizing travel times are described, the results are analysed, and some general conclusions are drawn.     

Dynamic component testing of a series system with redundant subsystems

We consider the component testing problem of a series system with redundant subsystems where all components fail exponentially. The main feature of our model is that the component failure rates are not constant parameters, but in fact change in a dynamic fashion with respect to time. The optimal component testing problem is formulated as a semi-infinite linear program. We present an algorithmic procedure to compute optimal test times based on the column generation technique, and illustrate it with numerical results.     

Design and storage cycle time analysis for the automated storage system with a conveyor and a rotary rack

In this paper, we analyse the performance of an automated Work-In-Process (WIP) storage system consisting of a conveyor and a rotary rack. The stability condition and the expected storage cycle time are derived to analyse the performance of the WIP storage system. As part of the storage cycle time analysis, the derived expected waiting times at the conveyor and the rotary rack are important performance measures that can be used for buffer-sizing purpose in such systems. Given the fixed storage space of the rotary rack, we also develop a heuristic approach to determine the near optimum ‘shape’ of the rotary rack so that the expected storage cycle time is minimized. Numerical results are presented to examine the storage cycle time model and the proposed shape design. The analytical model introduces a simple approach over simulation with acceptable accuracy; it is useful when designing such WIP storage systems. Moreover, it can be expanded to model more complex systems. The derived model also provides insightful information on the design parameters that a typical simulation tool can hardly provide.     

配位氢化物储氢合金的研究现状

配位氢化物储氢合金是最近几年发展起来的新型储氢合金，和稀土系AB5型、AB2、镁基和Fe-Ti系储氢材料相比，配位氢化物储氢合金的储氢量要明显高于前者。针对目前研究较多的NaAlH4、LiAlH4、LiBH4和Li2NH储氢合金的研究现状进行了概述。     

Optimal maintenance scheduling in a two identical component parallel redundant system

This paper presents equations which can be used to evaluate the failure frequency and the failure rate of a two identical component parallel redundant system in which each component can operate in its wearout period and the failure rate of each component is not constant. The optimum maintenance interval for a two identical component parallel redundant system can be obtained using these equations. The proposed approach is presented and illustrated using several numerical examples. The optimum maintenance interval for each component in a two identical parallel redundant system will depend on factors such as failure rate, repair and maintenance times of each component in the system. The proposed method should prove useful in reliability centered maintenance applications.