水力压裂优化设计研究及应用

压裂优化设计的主要参数是无因次采液指数、无因次支撑剂数、无因次裂缝导流能力,弄清它们之间的关系是水力压裂优化设计的关键。经对裂缝优化设计的基本理论进行分析,结合自主研发的OptiStim系统,对水力压裂过程展开了研究分析得知,高渗地层采用压裂增产效果优于低渗地层,使用优质支撑剂、增加支撑剂量能提高压后产量。但为优选出最佳的水力压裂设计方案,需要根据油井具体情况,综合考虑各方面因素。     

Influence of zinc oxide and eugenol sealer on concentration of zinc, calcium and copper in rat tissues

A zinc oxide and eugenol root canal sealer (Roth 811) and sterile saline solution were injected into the dorsal thoracic midline of 70 male Wistar-Furth rats. Every day for the next 7 days, 10 animals were sacrificed by either inhalation. The liver, heart, kidneys and brain were removed from the animals and analysed for zinc, calcium and copper concentrations by flame atomic absorption spectrophotometry. The tissue around the injection site was also surgically removed and prepared for histological evaluation under a microscope. The injection of Roth 811 significantly affected the concentrations of zinc, calcium and copper in some of the examined organs, especially on the 4th and 5th day. The inflammatory reaction adjacent to the material was severe during the first 3 days while on the 7th day the presence of connective tissue with collagen formation was observed.     

Dynamic routing and admission control for virtual circuit networks

The dynamic joint routing and admission control problem in multiple class multiple source-destination virtual circuit networks is considered. A nonlinear dynamic queueing model for virtual circuit networks that considers the dynamic interaction among the virtual circuit and packet processes is introduced. Then a multi-objective cost function of rejecting and maintaining virtual circuits, as well as of delaying and servicing packets is defined. The combined problem is formulated as an optimal control problem. Necessary optimality conditions are provided by Pontryagin's maximum principle. Sufficient optimality conditions based on the convexity of the Hamiltonian function are also given. For the finite horizon, the optimal controls can be found after numerically solving a Two-Point Boundary-Value Problem. For the longrun stationary equilibrium, the state-dependent routing and admission controls are derived.This work was supported by the National Science Foundation under Grant DMC-8452002 together with matching funds from AT&T Information Systems.     

Experimental study of the biocompatibility of four root canal sealers and their influence on the zinc and calcium content of several tissues

Four root canal sealers (AH-26, Roth 811, CRCS, and Sealapex) were tested for tissue biocompatibility in rat connective tissue. Each sealer was placed in Teflon tubes and implanted subcutaneously in Wistar-Furth rats. The implants were removed after 7, 14, and 21 days, fixed, and histologically prepared for microscopical evaluation. Brain, liver, kidneys, and uterus were removed from the animals killed at the first experimental period (7 days) and analyzed for zinc and calcium concentration by flame atomic absorption spectrophotometry. In total, 100 specimens were examined. At the seventh day, the most irritant material was seen to be AH-26, but this inflammatory reaction decreased with time. Roth 811 and Sealapex caused moderate-to-severe inflammatory reaction, whereas CRCS caused mild to moderate. CRCS and Roth 811 induced redistribution of zinc, whereas AH-26 induced changes in calcium content in some organs.     

Image quality evaluation and patient dose assessment of medical fluoroscopic X-ray systems: a national study

This study presents the results from a survey conducted by the Greek Atomic Energy Commission (GAEC), during the period 1998-2003, in 530 public and private owned fluoroscopic X-ray systems in Greece. Certain operational parameters for conventional and remote control systems were assessed, according to a quality control protocol developed by GAEC on the basis of the current literature. Public (91.5%) and private (81.5%) owned fluoroscopic units exhibit high-contrast resolution values over 1 lp mm(-1). Moreover, 88.5 and 87.1% of the fluoroscopic units installed in the public and private sector, respectively, present Maximum Patient Entrance Kerma Rate values lower than 100 mGy min(-1). Additionally, 68.3% of the units assessed were found to perform within the acceptance limits. Finally, the third quartile of the Entrance Surface Dose Rate distribution was estimated according to the Dose Reference Level definition and found equal to 35 mGy min(-1).     

Sequestering carbon dioxide in a closed underground volume

The capture and subsequent geologic sequestration of CO₂ has been central to plans for managing CO₂ produced by the combustion of fossil fuels. The magnitude of the task is overwhelming in both physical needs and cost, and it entails several components including capture, gathering and injection. The rate of injection per well and the cumulative volume of injection in a particular geologic formation are critical elements of the process.Published reports on the potential for sequestration fail to address the necessity of storing CO₂ in a closed system. Our calculations suggest that the volume of liquid or supercritical CO₂ to be disposed cannot exceed more than about 1% of pore space. This will require from 5 to 20 times more underground reservoir volume than has been envisioned by many, and it renders geologic sequestration of CO₂ a profoundly non-feasible option for the management of CO₂ emissions.Material balance modeling shows that CO₂ injection in the liquid stage (larger mass) obeys an analog of the single phase, liquid material balance, long-established in the petroleum industry for forecasting undersaturated oil recovery. The total volume that can be stored is a function of the initial reservoir pressure, the fracturing pressure of the formation or an adjoining layer, and CO₂ and water compressibility and mobility values.Further, published injection rates, based on displacement mechanisms assuming open aquifer conditions are totally erroneous because they fail to reconcile the fundamental difference between steady state, where the injection rate is constant, and pseudo-steady state where the injection rate will undergo exponential decline if the injection pressure exceeds an allowable value. A limited aquifer indicates a far larger number of required injection wells for a given mass of CO₂ to be sequestered and/or a far larger reservoir volume than the former.     

Exploiting Selfishness,Altruism and Common Welfare to Enhance Performance of Routing Protocols for Mobile Ad hoc Networks

Mobile Ad hoc Networks are sensitive to selfish behavior that may occur due to restricted power or other resources. Several approaches have been investigated so far to address this problem. In many of them, upon detection, a selfish node is punished with isolation from network services access and in most cases with no possibility for redemption. In this paper, we show that selfish behavior can be exploited to improve network performance. We modify an existing routing protocol by introducing an altruism coefficient to model the overall satisfaction of every node from the network services. When the altruism coefficient is increased, the selfish behavior is decreased. We extend our approach by introducing a common welfare factor, which actually enforces the nodes to cooperate when the network connectivity is critical. A network simulator is utilized to show the impact of our schemes on the performance of the routing protocol when selfish nodes are present in the network.

     

Measuring instant emotions based on facial expressions during computer-based assessment

Emotions are very important during learning and assessment procedures. However, measuring emotions is a very demanding task. Several tools have been developed and used for this purpose. In this paper, the efficiency of the FaceReader during a computer-based assessment (CBA) was evaluated. Instant measurements of the FaceReader were compared with the researchers’ estimations regarding students’ emotions. The observations took place in a properly designed room in real time. Statistical analysis showed that there are some differences between FaceReader’s and researchers’ estimations regarding Disgusted and Angry emotions. Results showed that FaceReader is capable of measuring emotions with an efficacy of over 87% during a CBA and that it could be successfully integrated into a computer-aided learning system for the purpose of emotion recognition. Moreover, this study provides useful results for the emotional states of students during CBA and learning procedures. This is actually the first time that student’s instant emotions were measured during a CBA, based on their facial expressions. Results showed that most of the time students were experiencing Neutral, Angry, and Sad emotions. Furthermore, gender analysis highlights differences between genders’ instant emotions.     

The design and evaluation of a computerized adaptive test on mobile devices

The use of computerized adaptive testing (CAT) has expanded rapidly over recent years mainly due to the advances in communication and information technology. Availability of advanced mobile technologies provides several benefits to e-learning by creating an additional channel of access with mobile devices such as PDAs and mobile phones. This paper describes the design issues that were considered for the development and the implementation of a CAT on mobile devices, the computerized adaptive test on mobile devices (CAT-MD). Throughout the development of the system, formative evaluation was an integral part of the design methodology. The recommendations, suggestions and the results of the formative evaluation were used to improve the system in order to make the assessment procedure more effective and efficient. These results of the formative evaluation are also presented here.     

The effects of adsorption phenomena in the evaluation of vapour-dominated geothermal reservoirs

Previous reservoir engineering studies of vapour-dominated geothermal reservoirs have generally been analogous to conventional-model studies for natural gas reservoirs. In this work, the concept that considerable adsorbed water may exist in a vapour-dominated zone is examined in detail. Experimental and theoretical evidence of adsorption phenomena is described. The implications of adsorption on material balance calculations and on well test analysis are then determined by incorporating adsorption effects into existing models. The resulting new methods of analysis provide a more realistic estimate of the nature and extent of the vapour-dominated zone. In particular, the new methods result in a considerable reduction in the estimated formation thickness and suggest that fracture porosity has been underestimated using conventional models for a naturally fractured reservoir. The importance of the adsorption phenomenon in reserve estimation is of considerable magnitude. This work shows that a reserve estimate based on geologic evidence and the thermodynamic properties of steam could be as much as one order of magnitude lower than the actual mass of water present.