The effects of stress on a ferromagnet on a minor hysteresis loop

Reversible and irreversible changes in magnetization due to stress on a minor hysteresis loop were studied at various magnetic field strengths. It was found that the irreversible changes were not always directed toward the principal anhysteretic, contrary to Jiles and Atherton's hypothesis (1986). Also, two different demagnetization methods were used within the minor loop to test the existence of postulated offset anhysteretic curves. The results of asymmetric demagnetizations seemed to support this suggestion     

20-mW widely tunable laser module using DFB array and MEMS selection

The authors describe a novel configuration for a wavelength selectable laser that provides wide tuning and distributed-feedback (DFB) performance and reliability at a fundamentally low cost structure. The configuration consists of a DFB laser array and a micromechanical mirror that selects one element of the array. The MEMS tilt mirror also loosens the tolerances, since the fine optical alignment is done electronically. Only one laser is operated at a time, with coarse tuning realized by selecting the correct laser and fine tuning by adjusting the chip temperature. The 33-nm total tuning at 20-mW fiber coupled power is obtained in a fully functional module.     

Comparing the effects of representational tools in collaborative and individual inquiry learning

Constructing a representation in which students express their domain understanding can help them improve their knowledge. Many different representational formats can be used to express one’s domain understanding (e.g., concept maps, textual summaries, mathematical equations). The format can direct students’ attention to specific aspects of the subject matter. For example, creating a concept map can emphasize domain concepts and forming equations can stress arithmetical aspects. The focus of the current study was to examine the role of tools for constructing domain representations in collaborative inquiry learning. The study was driven by three questions. First, what are the effects of collaborative inquiry learning with representational tools on learning outcomes? Second, does format have differential effects on domain understanding? And third, does format have differential effects on students’ inclination to construct a representation? A pre-test post-test design was applied with 61 dyads in a (face-to-face) collaborative learning setting and 95 students in an individual setting. The participants worked on a learning task in a simulation-based learning environment equipped with a representational tool. The format of the tool was either conceptual or arithmetical or textual. Our results show that collaborative learners outperform individuals, in particular with regard to intuitive knowledge and situational knowledge. In the case of individuals a positive relation was observed between constructing a representation and learning outcomes, in particular situational knowledge. In general, the effects of format could not be linked directly to learning outcomes, but marked differences were found regarding students’ inclination to use or not use specific formats.     

A robot to detect and control broad‐leaved dock (Rumex obtusifolius L.) in grassland

Broad‐leaved dock is a common and troublesome grassland weed with a wide geographic distribution. In conventional farming the weed is normally controlled by using a selective herbicide, but in organic farming manual removal is the best option to control this weed. The objective of our work was to develop a robot that can navigate a pasture, detect broad‐leaved dock, and remove any weeds found. A prototype robot was constructed that navigates by following a predefined path using centimeter‐precision global positioning system (GPS). Broad‐leaved dock is detected using a camera and image processing. Once detected, weeds are destroyed by a cutting device. Tests of aspects of the system showed that path following accuracy is adequate but could be improved through tuning of the controller or adoption of a dynamic vehicle model, that the success rate of weed detection is highest when the grass is short and when the broad‐leaved dock plants are in rosette form, and that 75% of weeds removed did not grow back. An on‐farm field test of the complete system resulted in detection of 124 weeds of 134 encountered (93%), while a weed removal action was performed eight times without a weed being present. Effective weed control is considered to be achieved when the center of the weeder is positioned within 0.1 m of the taproot of the weed—this occurred in 73% of the cases. We conclude that the robot is an effective instrument to detect and control broad‐leaved dock under the conditions encountered on a commercial farm. © 2010 Wiley Periodicals, Inc.     

Using Co-Lab to build System Dynamics models: Students’ actions and on-line tutorial advice

Modeling offers a promising form of constructivist learning for students. By making and executing models of dynamic systems in a computer environment, students are stimulated to learn about the specific domain that is modeled as well as about the process of modeling in general. However, learning by modeling also leads to characteristic student mistakes, based on a combination of faulty domain knowledge and insufficient modeling skills. In this article, we describe a method of generating advice to students during their modeling process. The on-line advice system was informed by our observations of a teacher who gave advice via a textual communication tool to students building models with a System Dynamics model editor. The first version of the on-line advice system was evaluated in two ways: first, three teachers evaluated the advice the system generated for students’ final solutions; second, we analyzed the advice the system provided as it was used by a sample of students who were building a physics model. These evaluations showed that the overall approach, including matching a student solution to a family of reference solutions together with the other mechanisms of the advice system, is valid. However, they also highlighted the difficulty of building ‘intelligent’ support to help students to improve their models and gain modeling expertise. The article concludes with a discussion of our current efforts to improve the advice system based on the lessons learnt, which suggest extension of the range of solution representations and of the operations of the advice method.     

Toward objective software process information: experiences from a case study

A critical problem in software development is the monitoring, control and improvement in the processes of software developers. Software processes are often not explicitly modeled, and manuals to support the development work contain abstract guidelines and procedures. Consequently, there are huge differences between ‘actual’ and ‘official’ processes: “the actual process is what you do, with all its omissions, mistakes, and oversights. The official process is what the book, i.e., a quality manual, says you are supposed to do” (Humphrey in A discipline for software engineering. Addison-Wesley, New York, 1995). Software developers lack support to identify, analyze and better understand their processes. Consequently, process improvements are often not based on an in-depth understanding of the ‘actual’ processes, but on organization-wide improvement programs or ad hoc initiatives of individual developers. In this paper, we show that, based on particular data from software development projects, the underlying software development processes can be extracted and that automatically more realistic process models can be constructed. This is called software process mining (Rubin et al. in Process mining framework for software processes. Software process dynamics and agility. Springer Berlin, Heidelberg, 2007). The goal of process mining is to better understand the development processes, to compare constructed process models with the ‘official’ guidelines and procedures in quality manuals and, subsequently, to improve development processes. This paper reports on process mining case studies in a large industrial company in The Netherlands. The subject of the process mining is a particular process: the change control board (CCB) process. The results of process mining are fed back to practice in order to subsequently improve the CCB process.     

仲丁醇-正丁烷加压汽液相平衡

实验测定了仲丁醇-正丁烷体系在0.5MPa和0.7MPa压力下的恒压汽液相平衡数据。温度和压力的测量精度分别为±0.05K和±6.4KPa。汽、液相组成分析的相对误差为±0.5％。用热力学方法对实测相平衡数据进行了关联,结果表明:非电解质溶液NRTL模型能较好描速仲丁醇-正丁烷体系的非理想行为。ASOG基团贡献模型对研究体系汽液相平衡组成的予测值与实测结果吻合较好。