Towards a consolidated model for a collaborative courseware authoring system

Abstract In an effort to reduce the expensive resource requirements in courseware production and to allow effective management of, and communication and collaboration between authors, a model is needed to harmonize the diverse theoretical backgrounds such a process requires. To this end we look at five abstract models which where chosen for their apparent appropriateness within the general area of collaborative authoring and reuse of multimedia courseware. These models consist of a functional model of hypertext, an infrastructure model for an open collaborative authoring system, two object-oriented communication models, and a courseware production model. We attempt a consolidation of these models and ultimately make several conclusions, which are exposed during a conceptual harmonisation. The principal conclusion is that a hypermedia logical model is not by itself adequate to support collaboration and reuse. Our modeling conclusions have driven the design of a system which will be implemented and tested.     

旋转式伽玛刀的辐射剂量学

旋转式伽玛刀的辐射剂量学指标的物理测试在放射性医疗设备投放医院正式临床使用前是必不可少的，是对设备及其附件的设计、加工制造、安装以及电气控制系统等的全面综合性检定。用电离室作辐射剂量学的绝对测量，用胶片法进行相对测量，给出了测量结果并进行了讨论。     

Modeling and design of an AC to DC converter

A step-up/down single-phase AC-to-DC power converter without current sensor is proposed to achieve high performance and simple control logic. The power converter adopts a front-end diode rectifier so that only one active switch is required. The familiar state-space averaging technique for discontinuous mode DC-to-DC power converters is extended to model the proposed AC-to-DC converter. Unlike the existing model, which is valid only for a very low frequency range, namely below line frequency, the proposed model is applicable up to half switching frequency. The design of the controller is detailed. Selected experimental results are presented to verify the proposed theory     

Evaluation of Soybean Seedcoat Cracking During Drying:PART II. Using MRI

MRI techniques were developed and employed for non-destructive and noninvasive study of seedcoat cracking in low moisture soybean kernels during heated air drying. Proton density image and transient moisture distribution profile of a single soybean kernel can be obtained using MRI. These MRI techniques proved to be particularly useful for the continuous observation of initiation and propagation of seedcoat cracking during the entire period of drying process without interruption.

The proton density images of soybean kernels showed that seedcoat cracking was initiated perpendicular to the long axis of the kernel near the hilum. The transient moisture distribution profiles in soybean kernels during drying indicate that moisture gradient developed during drying was higher in the seedcoat than in the cotyledon. Drying temperature and initial average moisture content were positively correlated with the soyhean seedcoat crackig. The location of the     

制备2，4－二氯－5－氟苯甲酰乙酸甲酯的缩合剂及工艺研究

通过３种不同的碱来制备２，４－二氯－５－氟苯甲酰乙酸甲酯，优选得到了其最佳缩合剂甲醇钠；同时应用正交设计实验，研究了原料配比、反应时间、反应温度对收率的影响，在优选条件下收率为７８．５％。     

Surgical treatment of unilateral alveolar cleft

In this study, 16 cases of unilateral alveolar cleft with cleft lip and palate were repaired with autografts of cancellous bone (13 cases) or hydroxyapatite (3 cases). The grafts were covered by reflected mucoperiosteal flaps and a mucosal flap from the upper lip. Twelve of the thirteen cases were followed up for 1-5 years. Nine of whom using cancellous bone had bony continuity of the maxilla and 7 cases erupted permanent maxillary canines within the area of autografts. None of the 3 cases using hydroxyapatite erupted a canine tooth. The results showed that autograft was better than hydroxyapatite in terms of maxillary canine eruption.     

高频热处理技术的新进展

就高频感应加热设备、高频热处理的发展等若干问题进行较为详尽的评介,并提出几点看法.     

Pultruded fibre reinforced polyurethane composites II. Effect of processing parameters on mechanical and thermal properties

This paper presents a novel process for the fabrication of pultruded polyurethane (PU) composites. The effects of the processing parameters on the mechanical properties (flexural strength and flexural modulus, etc.) and thermal properties (HDT) of the fibre reinforced PU composites by pultrusion have been studied. The processing parameters investigated include pulling rate (in-line speed), die temperature, filler type and content, and post-cure time and temperature. Results show that the composites possessed various optimum pulling rates at different die temperatures. On the basis of the DSC diagram, the swelling ratio, the mechanical properties and the thermal properties of composites, the optimum die temperature can be determined. It is found that the mechanical and thermal properties increase with filler content for various types of filler. The mechanical and thermal properties increase at a suitable post-cure temperature and time. Furthermore, the properties which decreased due to the degradation of composite materials for a long post-cure time will be discussed.     

Mechanism of iodine vapor sorption in polyacetylene

Simultaneous measurements of weight uptake and conductivity variation during iodine vapor sorption of polyacetylenes (PA) at 20–25°C show that the sorption is a two-stages process. For the first stage, iodine diffusion to the fibrilar surface of the cis-rich and trans-rich PA is of Knudsen type pore diffusion as supported by the sorption measurements of hexane for the cis-rich PA, and has a diffusion coefficient in the order of 10⁷ cm²/sec. Conductivity of the PA rises rapidly and reaches a maximum at end of the stage. For the second stage, the diffusion is more restrictive and has a diffusion coefficient lower than the first stage by a factor of about 10 due to multilayer sorption of iodine, which leads to a decrease in the pore diameter and therefor the diffusion rate. In addition to the restricted diffusion in the second stage, diffusion of the iodine molecules adsorped on the fibrilar surface into the interior of the fibrils is appreciable for cis-rich PA (leading to a conductivity drop) and is negliglible for tran-rich PA (leading to insignificant variation in conductivity).