Beyond network simulators: Fostering novel distributed applications and protocols through extendible design

Simulation has been of paramount importance to the development of novel Internet protocols. Such an approach typically focuses on one of three domains: wireless and other link-layer technologies, routing protocols, and transport-layer mechanisms and protocols. Existing techniques can tackle well simulation at layers 2, 3 and 4 of the TCP/IP architecture, but are not flexible enough to appropriately deal with application-layer protocols. These require simulators that support the modeling of networks and components with different levels of abstraction. Simmcast is an object-oriented framework that focuses on the necessary flexibility for application-layer protocol research. A simulation can be developed by the simple extension of building blocks that closely resemble components of a real network such as hosts, links and routers. The internal complexity of these components, however, is hidden from the user, so he/she can focus on the implementation of the desired protocol characteristics. This paper describes the flexible simulation architecture proposed and instantiated through Simmcast, and draws lessons from our experience in designing, implementing and deploying it. We also present framework instances used to evaluate application-layer protocols, exemplifying how different kinds of simulations can be developed with Simmcast.     

EWB软件在《高频电子技术》实验中的应用

本文介绍了EWB仿真软件的特点及其在《高频电子技术》课程教学中的具体应用,将传统的实验方法与EWB的相结合,还可以使学生对新知识产生浓厚的探索兴趣,能有效地提高实验教学质量。     

Transesterification of Canola Oil to Biodiesel Using CaO/Talc Nanopowder as a Mixed Oxide Catalyst

A series of heterogeneous catalysts including different molar ratios of CaO/talc was synthesized to study the transesterification reaction of canola oil and methanol under different reaction conditions. Characterization and kinetic results revealed that the activity of this catalyst was enhanced due to the increase of CaO/talc molar ratio value leading to an improvement in the biodiesel production. Moreover, the effect of various parameters on the activity of the undertaken catalysts was studied in order to determine the optimum process conditions. Leaching measurements and the durability of the CaO/talc catalyst under several reaction cycles were evaluated and proved it to be a stable catalyst.     

Ethanolysis of waste cottonseed oil over lithium impregnated calcium oxide: Kinetics and reusability studies

A series of Li/CaO catalysts has been prepared by impregnating 0.5–5.0 wt% Li in CaO by wet chemical method. Prepared Li/CaO catalysts have been characterized by powder X-ray diffraction, scanning electron and transmission electron microscopy and Brunauer–Emmett–Teller (BET) surface area studies, in order to establish the structure and surface morphology of the catalyst. Hammett indicator test study was performed to determine the basic strength of the Li/CaO catalysts. The prepared Li/CaO catalysts have been employed as a heterogeneous catalyst for the transesterification of waste cottonseed oil (having 2.8 wt% free fatty acid contents) with ethanol. Under optimal reaction conditions viz., ethanol/oil molar ratio of 12:1, catalyst to oil weight fraction of 5% and 65 °C reaction temperature, 98% fatty acid ethyl ester yield was obtained in 2.5 h of reaction duration. Under the optimized reaction conditions, the pseudo first order constant and Arrhenius activation energy were found to be 0.03 min⁻¹ and 70.0 kJ mol⁻¹, respectively. Further Li/CaO catalyst was also found to be effective for the ethanolysis and methanolysis of vegetable oils having up to 3.4 wt% free fatty acids. The use of 3-Li/CaO catalyst is advantageous considering that it not only utilizes waste cottonseed oil as a feedstock, but also renewable and nontoxic alcohol, ethanol, for the biodiesel production.     

Taming distributed system complexity through formal patterns

Many distributed systems are real-time, safety-critical systems with strong qualitative and quantitative formal requirements. They often need to be reflective and adaptive, and may be probabilistic in their algorithms and/or their operating environments. All this makes these systems quite complex and therefore hard to design, build and verify. To tame such system complexity, this paper proposes formal patterns, that is, formally specified solutions to frequently occurring distributed system problems that are generic, executable, and come with strong formal guarantees. The semantics of such patterns as theory transformations in rewriting logic is explained; and a representative collection of useful patterns is presented to ground all the key concepts and show their effectiveness.     

Not all digital venture ideas are created equal: Implications for venture creation processes

Digital ventures are formed around ideas that have digital artifacts at their core. We develop theory that explains how the composition of digital artifacts influences venture creation processes. First, we develop propositions that link differences in the embodiment and coupling of digital artifact components to tensions in venture creation process inputs, behaviors, and outputs. Second, we link compositional differences in digital artifacts to differences in venture creation process initiation, duration, and outcome. Our theorizing establishes a foundation for future research on digital artifacts within and beyond entrepreneurship contexts, and for future research on entrepreneurship within and beyond digital artifact contexts.     

Specifying safety-critical systems with a decidable duration logic

Punctual timing constraints are important in formal modelling of safety-critical real-time systems. But they are very expensive to express in dense time. In most cases, punctuality and dense-time lead to undecidability. Efforts have been successful to obtain decidability; but the results are either non-primitive recursive or nonelementary. In this paper we propose a duration logic which can express quantitative temporal constraints and punctuality timing constraints over continuous intervals and has a reasonable complexity. Our logic allows most specifications that are interesting in practice, and retains punctuality. It can capture the semantics of both events and states, and incorporates the notions duration and accumulation. We call this logic ESDL (the acronym stands for Event- and State-based Duration Logic). We show that the satisfiability problem is decidable, and the complexity of the satisfiability problem is NEXPTIME. ESDL is one of a few decidable interval temporal logics with metric operators. Through some case studies, we also show that ESDL can specify many safety-critical real-time system properties which were previously specified by undecidable interval logics or their decidable reductions based on some abstractions.     

Energy Savings through Microwave Selective Heating of Pd/AC Catalyst Particulates in a Fixed‐Bed Reactor

Microwave radiation is a novel energy source to drive chemical reactions. In conventional reactors, however, the heat created either escapes through uninsulated reactor walls, or the microwave radiation is attenuated by insulated walls. Here, microwave selective heating of Pd catalyst particles supported on activated carbon particulates was examined in a fixed‐bed reactor using a novel vacuum‐filled Dewar‐like double‐walled continuous‐flow reactor. This reactor was developed toward energy savings in performing such organic reactions as the transformation of the hydride methyl cyclohexane to toluene.