利用神经网络控制连续浇铸过程中的热传导

In continuous casting, the cooling-solidification process must be based on the adaptation of heat transfer, which is directly connected to casting conditions such as casting speed, casting temperature, and cooling parameters. Most control schemes are based on the static relation between casting speed and water flow rate in each cooling zone; this constitutes an open loop that does not consider the dynamic surface temperature, which is an important parameter for the final slab quality. In steelmaking, the casting-speed changes affect the global heat transfer. An optimal operation requires an adjustment of the process control variables, i.e., global heat transfer. A learning neural network (NN) allows the identification and the control of a nonlinear heat transfer model in the continuous casting process. A heat transfer model was developed using the dynamic heat balance. A comparison between the experimental open loop results and those of the model simulation is considered. Following adaptation, the model is used for controlling the slab surface temperature in closed loop, using NN technology and PID controllers. The NN identification and control strategy gives a stable temperature closed loop control comparatively to the conventional PID.     

Protecting location privacy in mobile geoservices using fuzzy inference systems

Mobile geoservices, especially location-based services (LBSs), are becoming more popular each day. The most important goal of these services is to use a user’s location to provide location-aware services. Because the user’s spatial information can be abused by organizations or advertisers, and sometimes for criminal purposes, the protection of this information is a necessary part of such services. There has been substantial research on privacy protection in LBSs and mobile geoservices; most studies have attempted to anonymize the user and hide his/her identity or to engage the user in the protection process. The major defects of these previous approaches include an increased complexity of system architecture, a decrease in service capabilities, undesirable processing times, and a failure to satisfy users. Additionally, anonymization is not a suitable solution for context-aware services. Therefore, in this paper, a new approach is proposed to locate users with different levels of spatial precision, based on his/her spatio-temporal context and a user’s group, through fuzzy inference systems. The user’s location and the time of the request determine the spatio-temporal context of the user. A fuzzy rule base is formed separately for each group of users and services. An interview is a simple method to extract the rules. The spatial precision of a user’s location, which is obtained from a fuzzy system, goes to a spatial function called the conceptualization function, to determine the user’s location based on one of the following five levels of qualitative precision: geometrical coordinates, streets, parish, region, and qualitative location, such as the eastern part of the city. Thus, there is no need to anonymize users in mobile geoservices or to turn the service off. The applicability and efficiency of the proposed method are shown for a group of taxi drivers.     

Three new fuzzy neural networks learning algorithms based on clustering, training error and genetic algorithm

Three new learning algorithms for Takagi-Sugeno-Kang fuzzy system based on training error and genetic algorithm are proposed. The first two algorithms are consisted of two phases. In the first phase, the initial structure of neuro-fuzzy network is created by estimating the optimum points of training data in input-output space using KNN (for the first algorithm) and Mean-Shift methods (for the second algorithm) and keeps adding new neurons based on an error-based algorithm. Then in the second phase, redundant neurons are recognized and removed using a genetic algorithm. The third algorithm then builds the network in one phase using a modified version of error algorithm used in the first two methods. The KNN method is shown to be invariant to parameter K in KNN algorithm and in two simulated examples outperforms other neuro-fuzzy approaches in both performance and network compactness.     

Human reach envelope and zone differentiation for ergonomic design

In human‐centric design, the human reach envelope is one of the most important components to help layout design for workstations, vehicles, and aircrafts. It also can help people to study the range of motion of different body segments. Various methods have been developed to determine human reach envelopes. This article presents different methods and common challenges. Human reach envelopes only give feedback concerning whether a point is reachable. This is not enough for the designers. The more important information the designers need to know is the zones with different discomfort levels. This capability is a powerful tool for ergonomic designers. In addition, a methodology for workspace solid zone differentiation or surface zone differentiation in the three‐dimensional space is presented. © 2008 Wiley Periodicals, Inc.     

Review on Fischer–Tropsch synthesis in supercritical media

A detailed review of the recent works regarding applications of supercritical media in Fischer–Tropsch synthesis (FTS) is presented. Differences in activity, CH₄ and CO₂ selectivity, hydrocarbon and olefin distributions, catalyst stability and heat transfer between supercritical Fischer–Tropsch syntheses (SC-FTS) and conventional gas phase Fischer–Tropsch synthesis (GP-FTS) are compared. The effects of temperature, pressure, solvent type, supercritical media/syngas molar ratio on SC-FTS are discussed. Finally selective production of wax via SC-FTS is briefly presented. Experimental analyses reveal that unique properties of supercritical media can improve FTS catalyst activity and selectivity in SC-FTS due to higher heat and mass transfer rates in comparison to GP-FTS.     

The contribution of class-F fly ash to the strength of cementitious mixtures

The contribution of fly ash to the physical properties of cementitious mixtures has received considerable attention since its inclusion as an essential ingredient of High Performance Concrete (HPC). However, the chemical contribution to the overall structure development has not been fully understood because of the masking of its hydration products by those of cement. In a mixture of class-F fly ash and lime (Ca/Si=2), portlandite diminishes and C₄AH₁₃ forms due to addition of Al to solution. The latter converts to hydrogarnet and C₃ASH₄. CSH is detected at 3 days and continues to increase in intensity. The ²⁹Si magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) showed that the Al/Si ratio is 0.24 and the average chain length is 10 units. The presence of Al as approximately one-fifth of the Si in a chain length of 10 units suggests that Al tetrahedra may be present in bridging positions.     

Fast prototyping of high-aspect ratio, high-resolution X-ray masks by gas-assisted focused ion beam

The capacity of chemically-assisted focused ion beam (FIB) etching systems to undertake direct and highly anisotropic erosion of thin and thick gold (or other high atomic number {Z}) coatings on X-ray mask membranes/substrates provides new levels of precision, flexibility, simplification and rapidity in the manufacture of mask absorber patterns, allowing for fast prototyping of high-aspect ratio, high-resolution masks for deep X-ray lithography for the LIGA process. In preliminary demonstrations, an automated FIB system operating at 30 keV with a gallium liquid metal source and an iodine gas injection system was used for direct milling into a few micrometer thick gold of microstructures into the sub-hundred nanometer regime. Three-dimensional micromachining in bulk diamond is also reported to illustrate the capability of the technique.This work was made possible under funding for California Institute of Technology from NASA general contract (# NAS7-1407), the partial funding for CAMD from the DARPA grant HI-MEMS Development and Manufacturing (contract # N66001-98-1-8926). Patrick Deshaye (Norsam) microsculpting work is also gratefully acknowledged.This paper was presented at the Fourth International Workshop on High Aspect Ratio Microstructure Technology HARMST 2001 in June 2001.     

Hypernephroma in the solitary kidney: experience with 20 cases and review of the literature

Twenty patients with renal cell carcinoma in anatomically or functionally solitary kidneys were treated and followed for up to 18 years. Factors pertinent to management and survival of these patients and 66 other well documented similar patients reported in the literature are analyzed. Most of the patients were unusually young and a significant number had had nephrectomy for contralateral renal cell carcinoma. Survival was closely related to the earlier presence of malignant disease in the other kidney, the duration of the interval between detection of the 2 neoplasms and the stage of the lesion in the solitary kidney. Partial nephrectomy has been the most successful treatment. The mean survival in the Mayo Clinic series has been 6 years for patients still alive and 2.4 years for those dead at the time of this analysis. Results in this and other series emphasize the importance of thorough long-term followup after nephrectomy for hypernephroma and of aggressive therapy when the remaining kidney becomes involved. It is foolhardy to abandon hope merely because there is a malignant tumor in a solitary kidney.