Computer use in the elementary classroom: A survey of computer contact persons in four school districts

This article investigates the use of computers in the elementary classroom. The research involved a review of some literature and field research done at schools in four chosen school districts in Toronto and Vancouver. A questionnaire was distributed and interviews were conducted with elementary school teachers and district consultants. From this field research, information was collected on the availabilities of hardware, software, teacher implementation, as well as on teachers' perceptions on computer use in the classroom. The survey results illustrate the state of computer use in some elementary schools. The findings provide implications for integrating computer use into the curriculum, and lays the groundwork for further research on how best to use the technology for elementary education.     

钢结构稳定设计——理论与实践

本文提出了实际工程结构的非线性理论设计和分析方法(NIDA),并以澳门回归纪念馆的设计为例,展示了本方法的优越性.在设计过程中,设计者无需假设K系数和有效长度,在结构分析完成后便可迅速完成设计,因此本文提出的方法既经济又便利.尽管对于钢框架在往复荷载及动力荷载作用下的弹塑性大位移分析已经非常成熟,但本文的方法开创了结构的非线性分析及设计的新纪元,能够对现行的设计方法理论起到巨大的推动作用.     

On a relation between information inequalities and group theory

We establish a one-to-one correspondence between information inequalities and group inequalities. The major implication of our result is that we can prove information inequalities by proving the corresponding group inequalities, and vice versa. By giving a group-theoretic proof for all Shannon-type inequalities, we suggest that new inequalities could be discovered by making use of the rich set of tools in group theory. On the other hand, via a non-Shannon-type information inequality discovered by Zhang and Yeung (1997), we obtain a new inequality in group theory whose meaning is yet to be understood     

A hybrid PC/PLC architecture for manufacturing-system control—theory and implementation

This paper presents a novel and generic PC/PLC-based software/hardware architecture for the control of flexible manufacturing workcells. The proposed implementation methodology is based on the utilization of any one of the available formal discrete-event-system control theories in conjunction with state-of-the-art industrial programmable-logic controllers (PLCs). The methodology has been illustrated to be a viable technique through its actual implementation in our laboratory using a robotic-workcell testbed. The specific control theory used is a combination of Extended Moore Automata and Ramadge-Wonham Automata that has been developed by our research group. The modular control software architecture has been developed for MS-Windows environments (running on one PC interfaced to the PLCs) and allows the use of different formal control theories as well as different commercial PLC hardware. The effective graphical user interface provides a transparent programming environment, where users are not expected to have a full knowledge of the formal control theory used.     

99Tcm-MDP scintigraphy in high-voltage electrical burn patients

In high-voltage electrical burn injuries (> 1000 V), it is difficult to identify the site and extent of non-viable deep tissue damage for debridement to avoid further tissue injury from wound infection and the risk of sepsis. This prospective study was designed to evaluate the usefulness of 99Tcm-methylene di-phosphonate (99Tcm-MDP) scintigraphy in detecting the extent of tissue injury and determining the level of amputation required for electrical burn patients. Over a 5 year period, 33 high-voltage electrical burn patients were studied. Blood flow and blood pool studies revealed absent perfusion in 37 limbs, all of which eventually were amputated. In addition to a routine three-phase bone scan, images were obtained at 30-60 min (early images) to evaluate whether soft tissue injury could be detected better at that time. For comparison of the detection rate from the early images and bone (delayed) images, 164 corresponding spot views of both images were reviewed. Eighty-three and 125 tissue necrotic lesions were demonstrated by the early images and bone images respectively. All of the 83 lesions found by the early images were more clearly identified by the bone images. All but one of the 125 lesions underwent surgical debridement or amputation. We concluded that the blood flow and blood pool images correlated well with the level of amputation required. The site and extent of tissue necrotic lesions can be clearly identified on 99Tcm-MDP bone scans. Because the early images were less sensitive in detecting tissue necrosis, we suggest that early imaging is not necessary.     

Fast detection of venous air embolism in Doppler heart sound usingthe wavelet transform

The introduction of air bubbles into the systemic circulation can result in significant morbidity. Real-time monitoring of continuous heart sound in patients detected by precordial Doppler ultrasound is, thus, vital for early detection of venous air embolism (VAE) during surgery. In this study, the multiscale feature of wavelet transforms (WT's) is exploited to examine the embolic Doppler heart sound (DHS) during intravenous air injections in dogs. As both humans and dogs share similar physiological conditions, the authors' methods and results for dogs are expected to be applicable to humans. The WT of DHS at scale 2 ^j(j=1,2) selectively magnified the power of embolic, but not the normal, heart sound. Statistically, the enhanced embolic power was found to be sensitive (P<0.01 at 0.01 ml of injected air) and correlated significantly (P<0.0005, τ=0.83) with the volume of injected air from 0.01 to 0.10 ml. A fast detection algorithm of O(N) complexity with unit complexity constant for VAE was developed (processing speed=8 ms per heartbeat), which confirmed the feasibility of real-time processing for both humans and dogs     

浅谈碾压混凝土的施工技术

介绍碾压混凝土坝发展的历程，简述了碾压混凝土筑坝技术以及施工工艺、特点、程序、质量控制等相关方面的施工经验。     

Effect of grain boundary phase on the thermal conductivity of aluminium nitride ceramics

AIN with high thermal conductivity was fabricated by pressureless sintering with Y₂O₃ as the sintering aid. The thermal conductivity was observed to increase with sintering time (up to 8 h) at 1810 °C. The distribution of the sintering aid was identified as one of the major factors influencing the thermal conductivity in AIN. Non-uniform distribution of the grain boundary phase was found to be associated with a significant amount of porosity, resulting in the enhancement of phonon scattering and thereby lowering the thermal conductivity.     

Modification of hypoxia-induced injury in cultured rat astrocytes by high levels of glucose

BACKGROUND AND PURPOSE: Preexisting hyperglycemia exacerbates central nervous system injury after transient global and focal cerebral ischemia. Increased anaerobic metabolism with resultant lactic acidosis has been shown to cause the hyperglycemic, neuronal injury. The contribution of astrocytes in producing lactic acidosis under hyperglycemic/ischemic conditions is unclear, whereas the protective role of astrocytes in ischemic-induced neuronal injury has been documented. The ability of astrocytes to maintain energy status and ion homeostasis under hyperglycemic conditions could ultimately reduce neuronal injury. Therefore, we determined the effects of increased glucose concentrations on glucose utilization, lactate production, extracellular pH, and adenosine triphosphate concentrations in hypoxia-treated astrocyte cultures. METHODS: Primary astrocytes were prepared from neonatal rat cerebral cortices. After 35 days in vitro, cultures were incubated with 0-60 mmol/L glucose and subjected to hypoxic conditions at 95% N2/5% CO2 for 24 hours. In addition, under high-glucose conditions (30 mmol/L), astrocytes were exposed to up to 72 hours of hypoxia. Determination of lactate dehydrogenase efflux, adenosine triphosphate concentrations, and extracellular lactate concentrations defined astrocyte status. Equiosmolar levels of mannitol were added in place of high glucose concentrations to distinguish hyperosmotic effect. RESULTS: When physiological concentrations of glucose (7.5 mmol/L) or lower concentrations were used, significant cell damage occurred with 24 hours of hypoxia, as determined by increased efflux of lactate dehydrogenase and loss of cell protein. When higher glucose concentrations (15-60 mmol/L) were used, efflux of lactate dehydrogenase was similar to that observed in normoxic cultures, despite an increased utilization of glucose. Lactate concentrations in the media at low or normal glucose concentrations exceeded normoxic levels, but higher glucose concentrations (15-30 mmol/L) failed to increase lactate levels further. Values of adenosine triphosphate for hypoxic astrocytes treated with high glucose concentrations were significantly higher than those of astrocytes with zero or low glucose levels. In cultures exposed to hypoxia and high glucose levels (30 mmol/L), no cellular injury was observed before 48 hours of hypoxia. Lactate concentrations in the media increased during the first 24 hours of hypoxia and reached steady state. The pH of the media decreased to 6.4 after 24 hours and 5.5 at 48 hours. The latter pH was concomitant with a marked increase in extracellular lactate dehydrogenase activity. Hyperosmotic mannitol failed to protect cultured astrocytes against hypoxia. CONCLUSIONS: Hypoxic injury to mature astrocytes was reduced by the presence of 15-60 mmol/L glucose in the medium during 24-30 hours of hypoxia. Injury occurred when the pH of the medium was < 5.5. This protection was not afforded by the hyperosmotic effect of high glucose concentrations, nor was the hypoxic injury at later time periods with 30 mmol/L glucose mediated solely by lactate accumulation.