The book covers a wide range of security topics including Cryptographic Technologies, Network Security, Security Management, Information Assurance, Security Applications, Computer Security, Hardware ...Security, and Biometrics and Forensics.
Critical infrastructure networks, such as transport and power networks, are essential for the functioning of a society and economy. The rising transport demand increases the congestion in railway ...networks and thus they become more interdependent and more complex to operate. Also, an increasing number of disruptions due to system failures as well as climate changes can be expected in the future. As a consequence, many trains are cancelled and excessively delayed, and thus, many passengers are not reaching their destinations which compromises customers need for mobility. Currently, there is a rising need to quantify impacts of disruptions and the evolution of system performance. This review paper aims to set-up a field-specific definition of resilience in railway transport and gives a comprehensive, up-to-date review of railway resilience papers. The focus is on quantitative approaches. The review analyses peer-reviewed papers in Web of Science and Scopus from January 2008 to August 2019. The results show a steady increase of the number of published papers in recent years. The review classifies resilience metrics and approaches. It has been recognised that system-based metrics tend to better capture effects on transport services and transport demand. Also, mathematical optimization shows a great potential to assess and improve resilience of railway systems. Alternatively, data-driven approaches could be potentially used for detailed ex-post analysis of past disruptions. Finally, several rising future scientific topics are identified, spanning from learning from historical data, to considering interdependent critical systems and community resilience. Practitioners can also benefit from the review to understand a common terminology, recognise possible applications for assessing and designing resilient railway transport systems.
The hinged slab bridge is widely used in medium- and small-span bridges because of its simple structure and convenient construction. However, hinge joints damage is the main defect of this kind of ...bridge, and it is difficult to express the deterministic damage degree of hinge joints in the detection process. A system reliability evaluation method considering fuzzy detection information of hinge joints damage and member failure credibility is proposed in this paper. Firstly, the membership function is used to quantitatively express the fuzzy detection information of hinge joints, and the fuzzy variable is transformed to an equivalent random variable. Secondly, the functional relationship between the transverse distribution coefficient and hinge joints damage is constructed by the modified hinge-jointed plate method and response surface method, and the reliability of the member considering the fuzzy detection information of hinge joints damage is calculated by the first-order second-moment method (FOSM). Then, the failure credibility is introduced to represent the different possibilities of system failure caused by member failure, and a system reliability assessment method of different failure criteria considering member failure credibility is established based on copula theory. Finally, the applicability of the proposed method is verified by taking the reinforced concrete hinged slab bridge as a numerical example.
In this paper we consider the fault-tolerant stabilization problem for a class of nonlinear systems with uncertain parameters. Uncertainties caused by Markovian jumping actuator failures and ...stochastic noises are also taken into consideration. Different from most existing results, the number of actuator failures may be infinite and stochastic functions related to multi-Markovian variables have been introduced to denote the failure scaling factors for the actuators, which is practical, but challenging. Three main difficulties arise: first is how to establish fundamentals for systems involving multi-Markovian variables and stochastic noises, including the joint transition probability, the infinitesimal generator, the existence and uniqueness of the solution and so on; second is how to handle the extra transition rate related terms appearing in the infinitesimal generator of the Lyapunov function; last is how to cope with the involved higher order Hessian term in the Ito stochastic differentiation. By proposing a new adaptive fault tolerant control scheme, the boundedness in probability of all the closed-loop signals has been ensured. An example of altitude fault-tolerant control for a generic hypersonic air vehicle is presented to show the effectiveness of the proposed scheme.
•Uniaxial deformation tests of initially granular materials are presented.•Peak stress at failure is modelled using a statistical inter-particle length.•The more porous the material, the more ...accurate is failure prediction.•Error on failure prediction is explained by a statistical inter-pore length.•A correction for empirical failure forecasting laws is proposed.
Multi-scale failure of porous materials is an important phenomenon in nature and in material physics – from controlled laboratory tests to rockbursts, landslides, volcanic eruptions and earthquakes. A key unsolved research question is how to accurately forecast the time of system-sized catastrophic failure, based on observations of precursory events such as acoustic emissions (AE) in laboratory samples, or, on a larger scale, small earthquakes. Until now, the length scale associated with precursory events has not been well quantified, resulting in forecasting tools that are often unreliable. Here we test the hypothesis that the accuracy of the forecast failure time depends on the inter-flaw distance in the starting material. We use new experimental datasets for the deformation of porous materials to infer the critical crack length at failure from a static damage mechanics model. The style of acceleration of AE rate prior to failure, and the accuracy of forecast failure time, both depend on whether the cracks can span the inter-flaw length or not. A smooth inverse power-law acceleration of AE rate to failure, and an accurate forecast, occurs when the cracks are sufficiently long to bridge pore spaces. When this is not the case, the predicted failure time is much less accurate and failure is preceded by an exponential AE rate trend. Finally, we provide a quantitative and pragmatic correction for the systematic error in the forecast failure time, valid for structurally isotropic porous materials, which could be tested against larger-scale natural failure events, with suitable scaling for the relevant inter-flaw distances.
One of the most serious technology roadblocks for SiC DMOSFETs is the significant occurrence of early failures in time-dependent-dielectric-breakdown testing. Conventional screening methods have ...proved ineffective, because the remaining population is still plagued with poor reliability. The traditional local thinning model for extrinsic (early) failures, which guides the screening through burn-in measures, simply does not work. The fact that improved cleanliness control in the fabrication process does little to reduce early failures also suggests that local thinning due to contamination is not the root cause. In this paper, we propose a new lucky defect model where bulk defects in the gate oxide, introduced during growth, are responsible for the early failures. We argue that a local increase in leakage current via trap-assisted tunneling leads to early oxide breakdown. This argument is supported with oxide breakdown observations in SiC/SiO 2 DMOSFETs, as well as simulations that examine various defect distributions and their impact on the resultant early failure distributions.
Abstract Objectives The aim of this study was to assess the clinical performance of CAD/CAM partial coverage posterior restorations made by CEREC AC Bluecam system after 5 years. Methods 159 ceramic ...partial coverage posterior restorations were placed in 109 patients in a private practice. The restorations were made using CEREC AC Bluecam with CEREC Blocs or Empress CAD blocks. The clinical performance of the restorations was evaluated with modified California Dental Association (CDA) guidelines, gingival and plaque indices, probing pocket depth, and bleeding on probing in a period of 5 years. Patients’ satisfaction was assessed using visual analogue scale. The Kaplan–Meier method was used to analyze survival probability of the restorations ( α = 0.05). Results The restorations included 102CEREC Blocs and 57 Empress CAD. The survival rates of CEREC Blocs and Empress CAD blocks were 96.0% and 94.6%, respectively ( P = 0.67). A total of 7 (4.5%) failures were found. The failures were not significantly influenced by restoration size, type and position of teeth. The ceramic fracture was significantly more in nonvital teeth ( P = 0.04). The periodontal parameters were not significantly different between the restored and control teeth except plaque index. The mean score of patients’ satisfaction was 94.4 ± 8.1. Conclusions Chair-side CEREC AC ceramic partial coverage posterior restorations were clinically successful restorations with mean survival rate of 95.5% after 5 years. Clinical significance Conservative chair-side CAD/CAM ceramic restorations with less reduction of tooth structure can be a successful restorative method with acceptable survival rate and patient’s satisfaction.
There are typically three types of models involved in a geotechnical analysis, i.e., the geologic model, the ground model, and the geotechnical model, each of which may be associated with uncertainty ...to a different extent. However, in a typical geotechnical analysis the geological uncertainty is seldom characterized and considered explicitly. In this paper, we discuss the probabilistic tools developed in the geotechnical profession for tasks such as uncertainty characterization, assessment of impact of uncertainties, uncertainty reduction, and evaluation of the value of uncertainty reduction. We postulate that the same tools may be used for a unified treatment of various types of uncertainties in a geotechnical analysis, which would necessitate the collaboration of the engineering geologists and the geotechnical engineers to comprehensively characterize these uncertainties consistently. To this end, the probabilistic tools or methods that are widely used in geotechnical engineering are examined to determine their applicability in the evaluation of geological uncertainties. Examples are provided to illustrate various concepts introduced in this paper.
•The uncertainties associated with geologic, ground and geotechnical models are discussed•Probabilistic methods can be used to characterize these uncertainties•Reliability methods can be used to consider the effect of these uncertainties•The Bayesian method can be used for uncertainty reduction•The value of uncertainty reduction can be assessed through decision analysis
Volcanic calderas are enclosed topographic depressions that are commonly delimited by steep annular cliffs (caldera walls). The walls represent degraded scarps of ring faults that accommodated ...caldera collapse. Here, we assess the mechanical controls on caldera wall morphology and failure by: (i) analysing slope properties of recently formed calderas; (ii) examining analytical solutions for slope failure; and (iii) simulating progressive slope failure via Distinct Element Method (DEM) numerical modelling. Average slope angles of the caldera walls in nature range from 20° to 65° and slope heights range from 99 m to 1080 m. Smaller slope heights are weakly tied to greater slope inclinations. Almost 60% of sampled caldera wall profiles show a steeper upper section and a gentler lower section, which in numerical models are reproduced as an upper slope comprising intact wall rock and a lower slope comprising failed material inclined at the angle of repose. Moreover, modelled material with a low angle of internal friction and low cohesion exhibits shear failure, whereas material with high friction and high cohesion shows tension cracking, buckling and toppling. The slope height and inclination data from the numerical models agree well with those in nature. The numerical model data correspond more closely to analytically-predicted failure planes than critical (i.e. limit equilibrium) slopes because they are short-lived and therefore unlikely to be sampled in either model or nature. If rock mass cohesions or friction angles constrained analytically from natural slopes are determined by assuming the slope is critical, they are likely to be underestimates. The homogeneous numerical models here give an estimated natural rock mass cohesion of 0.5 MPa or less. This is much lower than typical laboratory-scale cohesion values, and it highlights the importance of strength reduction when upscaling mechanical parameters from laboratory experiments for modelling slope stability and volcano deformation.
•We compare natural observations, numerical models, and analytical solutions.•Caldera slopes are bilinear with intact steep upper slopes controlled by cohesion.•Mechanical properties determine slope failure mechanism and caldera geometry.•Caldera slopes are typically sub-critical because critical slopes are short-lived.•Cohesion at the rock mass scale is ≤0.5 MPa for volcanic edifices.
A shaking table test was conducted to study the dynamic response of a tunnel across a main-sliding surface under seismic action for the first time, and acceleration and dynamic strain data were ...obtained. A strain-time domain analysis method was implemented to reveal the distribution of the strain field strength factors in the tunnel lining. The plastic effect coefficient (PEC) was proposed to describe the extent of plastic deformation of the tunnel lining, and the applicability of the seismic cumulative failure effect (SCFE) in the stress strength analysis was assessed. The acceleration field of the tunnel lining was also analyzed in the time–frequency domain. The magnification of the Arias intensity (MIa) was applied to characterize the whole-local deformation damage of the tunnel lining, which was considered from the aspects of deformation characteristics, frequency domain, and energy. The results suggest that the residual strain (RS) and PEC are more sufficient to describe the plastic deformation characteristics of the tunnel lining than the increment of the peak dynamic strain (ΔPDS). In addition, PEC has a more definite physical meaning than RS; thus, it is capable of defining the SCFE of the tunnel lining, which describes the stages of deformation effects, including the elastic deformation effect stage (<0.15 g), elastic–plastic deformation effect stage (0.15–0.3 g), and plastic deformation effect stage (0.3–0.6 g). In addition, according to MIa energy and different frequency-domain incremental displacement analyses, the low-frequency component of seismic waves results in global deformation of the lining section, whereas the high-frequency component causes vault and arch waist-H local deformation. The results of MIa and PEC values can provide a scientific basis for identifying the seismic failure state of the tunnel lining and appropriate seismic reinforcement.
•Shaking table test of tunnel crossing main-sliding surface is carried out for the first time.•The PEC is proposed to characterize the plastic deformation degree of tunnel lining.•The MIa method for characterizing the whole-local deformation damage of tunnel lining is presented.•The calculated values of MIa and PEC damage indexes can be used as an effective early warning and forecasting model.
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