Paramecium: An Extensible Object-Based Kernel

In this paper we describe the design of an extensible kernel, called Paramecium. This kernel uses an object-based software architecture which together with instance naming, late binding and explicit overrides enables easy reconfiguration. Determining which components reside in the kernel protection domain is up to the user. An certification authority or one of its delegates certifies which components are trustworthy and therefore permitted to run in the kernel protection domain. These delegates may include validation programs, correctness provers, and system administrators. The main advantage of certifications is that it can handle trust and sharing in a non-cooperative environment

Presence and species identity of rumen flukes in cattle and sheep in the Netherlands

The purpose of the study was to gain knowledge about the prevalence and identity of rumen flukes (RF) in cattle and sheep in the Netherlands. Routine faecal examinations of diagnostic submissions between May 2009 and September 2014 showed a mean annual herd or flock RF prevalence of 15.8% for cattle and 8.0% for sheep. Prevalence in cattle was higher after 2012 than before, which may reflect a change in detection method as well as an increase in true prevalence. During November and December 2014, an abattoir survey was conducted to allow for scoring of rumen fluke burden and to obtain specimens for molecular species characterization. Over 8 visits to 5 abattoirs in areas deemed to pose a high risk for trematode infection, 116 cows and 41 sheep from 27 herds and 10 flocks were examined. Prevalence of RF was higher in beef cattle than in dairy cattle and higher in cattle than in sheep. Median fluke burden was >100 specimens per animal for most positive animals. Using a semi-quantitative RF density score as a gold standard, sensitivity and specificity of a modified quantitative Dorsman egg counting method were estimated at 82.6% and 83.3%, respectively. Of 14 collected adult rumen flukes, twelve (8 bovine and 4 ovine specimens) were identified as Calicophoron daubneyi. The other two, of bovine origin, were identified as Paramphistomum leydeni, which was unexpected as in other European countries all recently collected rumen flukes in both cattle and sheep were identified as C. daubneyi. The findings implicate that multiple rumen fluke species, intermediate host species and transmission cycles may play a role in rumen fluke infections in the Netherlands

An Object Model for Flexible Distributed Systems

this paper we describe a new model for constructing operating systems and applications in an integrated fashion. Compared to current approaches we provide high-level primitives for supporting distributed and parallel applications. We also provide the flexibility to configure both applications and kernels to only include the functionality that is actually used. The model we describe is based on objects. Objects are used to structure both applications programs and operating system kernels. They also provide the application interface to the operating system kernel, and access to hardware devices for both kernels and applications. By providing structuring mechanisms for large (distributed) objects, we believe that applications will be are easier to build. At the same time we provide flexibility by allowing extensions of operating system kernels and applications with new objects at run time[8], and by providing a way to bind to objects dynamically. An important aspect of a distributed system is the scalability of the system [6]. A scalable system should not depend on centralized resources or on algorithms that need global information. At the same time, a flexible system can use different algorithms depending on the situation. For example, the use of broadcasting and multicasting on a local Ethernet can be quite effective but should be avoided on a world wide scale. In this paper we discuss an object model that provides two kinds of objects: local objects and distributed objects. In Section 2 we describe the nondistributed (local) objects, followed by distributed objects in Section 3. We compare our work to that of others in Section 4. 2 Local object

Towards Object-based Wide Area Distributed Systems

In order to facilitate the construction of wide area distributed systems, it is necessary that we adopt a model that simplifies application development. In this position paper we advocate an object-based approach. Our approach allows for flexibility because many of the technical details of distribution, such as communication protocols, consistency rules, etc. can be hidden behind the objects' interfaces. In addition, we allow distributed objects to offer alternative implementations for an interface. A client may choose the most suitable implementation. We discuss the use of distributed objects as the means to this end, and compare our approach to existing ones. 1 Introduction Wide area distributed applications pose varying demands on the underlying operating systems, often making the development of the application itself a difficult task. For example, development of distributed applications often requires the following: ffl Support for expressing communication at a sufficiently high..

Bounds and asymptotics for the rate of convergence of birth-death processes

We survey a method initiated by one of us in the 1990's for finding bounds and representations for the rate of convergence of a birth-death process. We also present new results obtained by this method for some specific birth-death processes related to mean-field models and to the $M/M/N/N+R$ service system. The new findings pertain to the asymptotic behaviour of the rate of convergence as the number of states tends to infinity

Baanpolarisatie en flexibilisering op de Europese arbeidsmarkt: Beleidsimplicaties voor Nederland

Hervorming Sociale Regelgevin