Stealth modification versus nuisance attacks in the LOCKSS peer-to-peer digital preservation system

The LOCKSS system is a world-wide peer-to-peer system for the preservation of academic journals and other archival information published on the Web. The system is deployed at over 200 libraries around the world and currently preserving titles of publishers representing more than 2000 academic titles. It consists of a large number of independent, low-cost, persistent Web caches that cooperate to detect and repair damage to their content by voting in “opinion polls.” Based on our experience working with the LOCKSS system, in this paper, we identify and characterize a fundamental tradeoff in the system’s ability to defend against adversaries with competing goals. In particular, the techniques used to defend against adversaries attempting stealth modification of content being preserved in the system are at odds with those used to identify nuisance adversaries simply trying to disrupt system procedures. We show that with a simple change to the design of the system’s preservation protocol we are able to create moderately strong defense against both of these competing adversaries simultaneously.     

Real-time behavior-based robot control

Behavior-based systems form the basis of autonomous control for many robots, but there is a need to ensure these systems respond in a timely manner. Unexpected latency can adversely affect the quality of an autonomous system’s operations, which in turn can affect lives and property in the real-world. A robots ability to detect and handle external events is paramount to providing safe and dependable operation. This paper presents a concurrent version of a behavior-based system called the Real-Time Unified Behavior Framework, which establishes a responsive basis of behavior-based control that does not bind the system developer to any single behavior hierarchy. The concurrent design of the framework is based on modern software engineering principles and only specifies a functional interface for components, leaving the implementation details to the developers. In addition, the individual behaviors are executed by a real-time scheduler, guaranteeing the responsiveness of routines that are critical to the autonomous system’s safe operation. Experimental results demonstrate the ability of this approach to provide predictable temporal operation, independent of fluctuations in high-level computational loads.     

Dynamics of a three-module vibration-driven system with non-symmetric Coulomb’s dry friction

In the present paper, a three-module vibration-driven system moving on a rough horizontal plane is modeled to investigate the relation among the system’s steady-state motion, external Coulomb’s dry friction force and internal excitations. Each module of the system represents a vibration-driven system composed of a rigid body and a movable internal mass. Major attention is focused on the primary resonance situation that the excitation frequency is close to the first-order natural frequency of the system. In the case that the external friction is low, the internal excitation is weak and the stick–slip motion is negligible, both methods of averaging and modal superposition are employed to study the steady-state motion of the system. Through a set of algebraic equations, an approximate value of the system’s average steady-state velocity is obtained. Several numerical examples are calculated to verify the validity of the analytical results both qualitatively and quantitatively. It is seen that big quantitative errors will appear if stick–slip motions occur. Then, two mechanisms for the possible stick–slip motions are put forward, which explain the errors on the average steady-state velocity. Numerical simulations verify our analysis on the stick–slip effects and their mechanisms. Finally, to maximize the average steady-state velocity of the system, optimal control problem is studied. It is shown that, in addition to modifying the friction coefficients, the improvement of the system’s efficiency can be provided by changing the initial phase shifts among the three internal excitations.     

Ubiquitous Memories: a memory externalization system using physical objects

In this paper we propose an object-triggered human memory augmentation system named “Ubiquitous Memories” that enables a user to directly associate his/her experience data with physical objects by using a “touching” operation. A user conceptually encloses his/her experiences gathered through sense organs into physical objects by simply touching an object. The user can also disclose and re-experience for himself/herself the experiences accumulated in an object by the same operation. We implemented a prototype system composed basically of a radio frequency identification (RFID) device. Physical objects are also attached to RFID tags. We conducted two experiments. The first experiment confirms a succession of the “encoding specificity principle,” which is well known in the research field of psychology, to the Ubiquitous Memories system. The second experiment aims at a clarification of the system’s characteristics by comparing the system with other memory externalization strategies. The results show the Ubiquitous Memories system is effective for supporting memorization and recollection of contextual events.     

Preventive maintenance scheduling for repairable system with deterioration

Maintenance as an important part in manufacturing system can keep equipment in good condition. Many maintenance policies help to decrease the unexpected failures and reduce high operational cost such as conventional preventive maintenance. But these conventional preventive maintenance policies have the same time interval T that may easily neglect system’s reliability, because the system deteriorates with increased usage and age. Hence, this study has developed a reliability-centred sequential preventive maintenance model for monitored repairable deteriorating system. It is supposed that system’s reliability could be monitored continuously and perfectly, whenever it reaches the threshold R, the imperfect repair must be performed to restore the system. In this model, system’s failure rate function and operational cost are both considered by the effect of system’s corresponding condition, which helps to decide the optimal reliability threshold R and preventive maintenance cycle number. Finally, through case study, the simulation results show that the improved sequential preventive maintenance policy is more practical and efficient.     

Goal-driven risk assessment in requirements engineering

Risk analysis is traditionally considered a critical activity for the whole software system’s lifecycle. Risks are identified by considering technical aspects (e.g., failures of the system, unavailability of services, etc.) and handled by suitable countermeasures through a refined design. This, however, introduces the problem of reconsidering system requirements. In this paper, we propose a goal-oriented approach for analyzing risks during the requirements analysis phase. Risks are analyzed along with stakeholder interests, and then countermeasures are identified and introduced as part of the system’s requirements. This work extends the Tropos goal modeling formal framework proposing new concepts, qualitative reasoning techniques, and methodological procedures. The approach is based on a conceptual framework composed of three main layers: assets, events, and treatments. We use “loan origination process” case study to illustrate the proposal, and we present and discuss experimental results obtained from the case study.     

Developing comprehensive acceptance tests from use cases and robustness diagrams

In agile development processes, the rewards from acceptance testing are maximized by using the practice to drive the development process. Traditionally, User Stories are used in agile projects to describe a system’s usage scenarios and are utilized as a basis for developing acceptance tests. This paper introduces a technique that aims to achieve the benefits of acceptance testing within large-scale development projects that deploy a V-model development process, specifically those that utilize use case models. The approach is based on utilizing a number of artifacts: use case models supported by robustness diagrams and domain models. The feasibility of the proposed approach is demonstrated by applying it to a real-world system—the RestoMapper system. The results show that a comprehensive set of acceptance tests can be developed based upon use case models.     

An architecture-driven software mobility framework

Software architecture has been shown to provide an appropriate level of granularity for assessing a software system’s quality attributes (e.g., performance and dependability). Similarly, previous research has adopted an architecture-centric approach to reasoning about and managing the run-time adaptation of software systems. For mobile and pervasive software systems, which are known to be innately dynamic and unpredictable, the ability to assess a system’s quality attributes and manage its dynamic run-time behavior is especially important. In the past, researchers have argued that a software architecture-based approach can be instrumental in facilitating mobile computing. In this paper, we present an integrated architecture-driven framework for modeling, analysis, implementation, deployment, and run-time migration of software systems executing on distributed, mobile, heterogeneous computing platforms. In particular, we describe the framework’s support for dealing with the challenges posed by both logical and physical mobility. We also provide an overview of our experience with applying the framework to a family of distributed mobile robotics systems. This experience has verified our envisioned benefits of the approach, and has helped us to identify several avenues of future work.     

The UK Cleanfeed system — Lessons for the German debate?

As readers of this journal will of course know, the Zugangserschwerungsgesetz has caused considerable and often very profound debate in Germany about the limits of legal and technological interference with the freedom of access to information, culminating in the temporary refusal of the President to sign the law into action. In the UK by contrast, a core aspect of this law, the technical prevention of access to sites hosting illegal content by ISPs, was introduced through the so called “Cleanfeed system” as early as 1996, with little or no public debate, and bypassing by and large all parliamentary procedure and scrutiny. This article has a threefold aim: First, it gives a brief account of the history and implementation of the UK Cleanfeed system1; second, it explains some of its more unusual aspects by putting them into the historical and constitutional context of policing in the UK, and third, it highlights those experiences made with the system that are of direct relevance for the German discussion.     

A two-phase queuing system with access control and correlated arrival processes

A two-phase queuing system with access control is studied whose first phase consists of an infinite number of servers, while the second one consists of a finite number of servers. To the first phase, a Markovian input flow of queries arrives. On completion of the first-phase service, the customer either leaves the system or is passed to the second phase. In addition, a Markovian input flow of queries that do not require any first-phase service arrives to the second phase. An algorithm for finding a steady-state distribution of the system’s state probabilities is given, and some problems of the system’s paramaters optimization are considered.     

Dependable domestic systems design: A socio-technical approach

This paper describes a model that defines the attributes of domestic systems that lead to system dependability and a user-oriented specification method for support systems based on this model. We start by discussing technical dependability models and discuss how these have to be extended for use in a domestic context. We present an extended dependability model based on a socio-technical perspective. This extends the technical notion of dependability to take into account fitness for purpose, acceptability and adaptability. We then go on to discuss MDDS – a questionnaire-based method that reflects the socio-technical dependability model. It is intended for use by social care professionals who are specifying and designing support systems for older or disabled people. MDDS provides a basis for examining a design from a dependability perspective. We illustrate the use of the method and conclude with a discussion of its qualitative evaluation.     

基于Oracle8i的大容量HLR系统的可靠性设计与实现

文章介绍了HLR系统对可靠性的要求,和该HLR系统的结构。深入分析了影响HLR系统可靠性的各种因素,并研究和对比了各种可靠性技术与Oracle8i数据库的各种备份方式。提出了一个包括用户数据层、操作系统层和物理层的系统可靠性方案。     

Microprocessor-based data acquisition system for respiratory signals

Microprocessors are having an increasing role in online measurements in the medical field instead of large computers because of their compactness, low cost and ease of operation. This paper describes a microprocessor-based data acquisition system representing the primary stage in designing a larger online acquisition and processing system for measurement and correlation of respiratory signals. The system designed has the features of easy communication, flexibility of operation and system's software and hardware. The system uses a mass storage unit for permanent data storage. A detailed discussion of the hardware and software is presented.     

PeerCare: Supporting Awareness of Rhythms and Routines for Better Aging in Place

Caring for the elderly is becoming a key challenge for society, given the shortage of trained personnel and the increased age of the population. Innovative approaches are needed to help the elderly remain at home longer and more safely, that is, to age in place. One popular strategy is to monitor the activity of the elderly: this focuses on obtaining information for caregivers rather than supporting the elderly directly. We propose an alternative, i.e. to enhance their inter-personal communication. We report the results of a user study with 14 independent elderly women and discuss the existing role that communication plays in maintaining their independence and well-being. We highlight the importance of peer support relationships, which we call PeerCare, and how awareness of each other’s rhythms and routines helps them to stay in touch. We then describe the deployment of a technology probe, called markerClock, which a pair of elderly friends used to improve their awareness of each other’s rhythms and routines. We conclude with a discussion of how such communication appliances enhance the awareness of rhythms and routines among elderly peers and can improve their quality of life and provide safer and more satisfying aging in place.     

Real-time reliability prediction for dynamic systems with both deteriorating and unreliable components

As an important technology for predictive maintenance, failure prognosis has attracted more and more attentions in recent years. Real-time reliability prediction is one effective solution to failure prognosis. Considering a dynamic system that is composed of normal, deteriorating and unreliable components, this paper proposes an integrated approach to perform real-time reliability prediction for such a class of systems. For a deteriorating component, the degradation is modeled by a time-varying fault process which is a linear or approximately linear function of time. The behavior of an unreliable component is described by a random variable which has two possible values corresponding to the operating and malfunction conditions of this component. The whole proposed approach contains three algorithms. A modified interacting multiple model particle filter is adopted to estimate the dynamic system’s state variables and the unmeasurable time-varying fault. An exponential smoothing algorithm named the Holt’s method is used to predict the fault process. In the end, the system’s reliability is predicted in real time by use of the Monte Carlo strategy. The proposed approach can effectively predict the impending failure of a dynamic system, which is verified by computer simulations based on a three-vessel water tank system.     

Forecasting credit portfolio components with a Markov chain model

We consider the forecasting problem for components of a bank’s credit portfolio, in particular, for the share of non-performing loans. We assume that changes in the portfolio are described by a Markov random process with discrete time and finite number of states. By the state of a loan we mean that it belongs to a certain group of loans with respect to the existence and duration of arrears. We assume that the matrix of transitional probabilities is not known exactly, and information about it is collected during the system’s operation.     

A survey on self-healing systems: approaches and systems

Present large-scale information technology environments are complex, heterogeneous compositions often affected by unpredictable behavior and poor manageability. This fostered substantial research on designs and techniques that enhance these systems with an autonomous behavior. In this survey, we focus on the self-healing branch of the research and give an overview of the current existing approaches. The survey is introduced by an outline of the origins of self-healing. Based on the principles of autonomic computing and self-adapting system research, we identify self-healing systems’ fundamental principles. The extracted principles support our analysis of the collected approaches. In a final discussion, we summarize the approaches’ common and individual characteristics. A comprehensive tabular overview of the researched material concludes the survey.     

A harmonised model for safety assessment and certification of safety-critical systems in the transportation industries

This paper describes a model for the assessment and certification of safety-critical programmable electronic systems in the transportation industries. The proposed model is founded on the significant commonalities between emerging international safety-related standards in the automotive, railway and aerospace industries. It contains a system development and a safety assessment process which rationalise and unify the common requirements among the standards in these areas. In addition, it defines an evolutionary process for the development of the system’s safety case. The safety case process shows how the evidence produced in the progression of safety assessment can be structured in order to form an overall argument about the safety of the system. We conclude that it is possible to use this model as the basis of a generic approach to the certification of systems across the transportation sector.     

Mechanical-Hydraulic Co-Simulation of Full Hydraulic Articulated Steering System

With the development and improvement of the hydraulic steering system, the articulated steering system became the research focus of numerous domestic and foreign scholars. The full hydraulic steering system with a compact structure and ease of operation, is widely used in articulated steering mode. Furthermore, its performance can directly impact the steering sensitivity and stability. This paper studies the working principle and actual structure of the priority valve and the steering control valve, which are very important. By setting up a mathematic model, the system’s load-sensing characteristics and the impact of steering control valve bypass throttle damping on steering stability can be analyzed. The Hydraulic Components Design (HCD) model was established for the hydraulic part of this system. It is proved that the model can reflect the system’s actual properties by comparing simulation and experimental results. The dynamic model is based on its actual prototype parameters by taking the tire and ground forces into account. The steering process’s dynamic characteristics are co-simulated in the 1D+3D system model by combining AMESim and Virtual.Lab Motion. The simulation results show that the system’s load-sensing characteristics ensure the sensitivity of the steering operation, and the bypass throttle damping has significantly improved the operation stability and lowered down the cylinder pressure fluctuations. This can improve the system performance by appropriate optimization.

     

Dependability analysis of DES based on MARTE and UML state machines models

UML (Unified Modeling Language) is a standard design notation which offers the state machines diagram to specify reactive software systems. The “Modeling and Analysis of Real-Time and Embedded systems” profile (MARTE) enables UML with capabilities for performance analysis. MARTE has been specialized in a “Dependability Analysis and Modeling” profile (DAM), then providing UML with dependability assets. In this work, we propose an approach for the automatic transformation of UML-DAM models into Deterministic and Stochastic Petri nets and the subsequent dependability analysis.