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41.
A model for simulating a long-term diffusion in concrete under submerged conditions has been developed. The model focuses on the interaction between cement hydrates and electrolyte solution adopting the physical properties of concrete as alternative parameters for estimating long-term diffusion. The model was verified by the large variety of long-term experimental data involving verification of cement hydrates, porosity properties, pH value, element distribution, and chloride penetration for sulphate-resistant Portland cement (SRPC) concretes. Evaluating impacts of hundreds of years’ exposure on concrete durability, a simulation was also performed for an exposure time of 500 years. The results confirmed the importance of ion–cement-hydrate interaction in the evaluation of a long-term diffusion of harmful substances such as chlorides into concrete. The simulation results show also that the solid phases of the SRPC concrete mix that was used are stable in the long-term. The threshold concentration of chlorides which may initiate reinforcement corrosion defined as Cl?/OH? ratio could be exceeded in concrete after moderate exposure period under the conditions investigated with typical protective concrete layers. Using of case-specific values for a threshold chloride content and evaluating the method used for estimating the initiation time of reinforcement corrosion are recommended in the structures with a long-design service life. 相似文献
42.
BACKGROUND: Stereo‐regulated polymerization of vinyl ethers (VEs) assumes significance because of its elegance and the resultant unique polymer properties. Although several Lewis acid catalysts polymerize VEs with good control of molecular weight, achieving stereo‐regularity is quite challenging. There are literature reports of a few catalyst systems capable of producing highly isotactic poly(vinyl ether) (PVE) only at lower temperatures with the polymer becoming atactic with an increase in reaction temperature. Hence innovating new catalyst systems which can produce highly stereo‐regular PVEs with high molecular weight at ambient temperature is quite challenging. RESULTS: We used two different titanium pre‐catalysts (1‐TiCl2 and 2‐TiCl2) for the polymerization of VEs. These pre‐catalysts in combination with methylaluminoxane (MAO)/borate polymerized VEs in higher conversions. Highly isotactic poly(n‐butylvinyl ether) (PBVE; 75% dyad isotactic ratio) was obtained with 1‐TiCl2/MAO at ambient temperature. CONCLUSION: We synthesized unimodal and highly isotactic PBVE with molecular weights of the order of 105 g mol?1 using the non‐metallocene‐type single‐site catalyst system 1‐TiCl2/MAO even at ambient temperature. The symmetry around the metal centre in the pre‐catalyst and the polymerization temperature played a major role in controlling the stereo‐regularization of the olefin inserted. Copyright © 2009 Society of Chemical Industry 相似文献
43.
Kari Lehtinen Markku Sipila Veikko Porra 《International Journal of Circuit Theory and Applications》1991,19(2):125-143
A higher-order diffusion model for a bipolar transistor has been developed. This model is based on the Padé approximation of the quasi-static expansions of the base and collector currents and gives improved accuracy for the simulation of fast transients and periodic operation at high frequencies. the effect of higher-order circuit elements on accuracy is demonstrated by calculating the transient response to a step excitation and by determining the scattering parameters of a transistor model with higher-order elements linearized about an operating point. the higher-order model is replaced by an equivalent circuit including only conventional elements, and the transient behaviour of these two models is compared. 相似文献
44.
Absorption in the phase-change layer of an optical disk located in the near field of a Fabry-Perot laser diode is studied with a combination of finite-difference time domain (FDTD) analysis and a phenomenological laser model that predicts the operational characteristics of a laser diode. Some numerical simulations are performed and results are presented. In addition, the combined FDTD/laser-simulation model is described briefly. 相似文献
45.
A polyphase filtering topology is proposed which uses parallel switchable RC-networks for accurate broadband 90∘ phasing. A 0.13μm CMOS prototype using the quadrature-generation network in a direct-conversion quadrature-modulator achieves
a measured image-rejection ratio of −39 dBc or better in 0.6–2.5 GHz while consuming only 66 mW from a 2.2 V single supply.
Esa Tiiliharjuwas born in Rovaniemi, Finland, in 1966. He received the M.Sc. degree in Information Technology in 1995, and the Lic.Tech
degree in electrical engineering in 1998, both from Helsinki University of Technology, Finland.
From 1996 to July 1997 he was employed as an assistant at Helsinki University of Technology. He has held a position as a research
assistant since 1997, and he is currently working towards his Ph.D. degree in the Electronic Circuit Design Laboratory at
Helsinki University of Technology.
His research interests include the design of integrated low-power circuits for portable telecommunication applications. He
has designed and measured several integrated circuits for this application area. He is the author or co-author of several
internationally-refereed conference and journal publications on analog integrated circuits.
Kari A.I. Halonenwas born in Helsinki, Finland, on May 23, 1958. He received the M.Sc. degree in electrical engineering from the Helsinki University
of Technology (HUT) in 1982 and the Ph.D. degree in electrical engineering from the Katholieke Universiteit Leuven, Heverlee,
Belgium, in 1987.
From 1982 to 1984, he was with HUT as an Assistant and with the Technical Research Center of Finland as a Research Assistant.
From 1984 to 1987, he was a Research Assistant with the E.S.A.T. Laboratory, Katholieke Universiteit Leuven, with a temporary
grant from the Academy of Finland. Since 1988, he has been with the Electronic Circuit Design Laboratory, HUT, as a Senior
Assistant from 1988 to 1990, and as the Director of the Integrated Circuit Design Unit of the Microelectronics Center from
1990 to 1993. He was on leave of absence during the academic year 1992–1993, acting as Research and Development Manager with
Fincitec Inc., Finland. From 1993 to 1996, he was an Associate Professor, and since 1997, he has been a full Professor with
the Faculty of Electrical Engineering and Telecommunications, HUT. He became the Head of Electronic Circuit Design Laboratory
year 1998. He was the Technical Program Committee Chairman for the European Solid-State Circuits Conference in 2000. He is
the author or coauthor of over 150 international and national conference and journal publications on analog integrated circuits,
and holds several patents on analog integrated circuits. His research interests are in CMOS and BiCMOS analog integrated circuits,
particularly for telecommunication applications.
Dr. Halonen was an Associate Editor of the IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS–PART I: FUNDAMENTAL THEORY AND APPLICATIONS
from 1997 to 1999. He has been a Guest Editor for the IEEE JOURNAL OF SOLID-STATE CIRCUITS. He received the BeatriceWinner
Award from the IEEE International Solid-State Circuits Conference in 2002.[c-halonen.eps] 相似文献
46.
DSP software development has been tied down by extreme computational requirements. Furthermore, the DSP development tools available today are less advanced than in other embedded software design. This has lead to DSP software architectures that have not taken into account future expansion needs. Therefore, DSP software architectures have been inherently closed. Now, as system complexity increases, this design methodology becomes more of a burden, since it does not support component-based DSP software development that requires open interfaces.
In this paper, mobile-communications DSP software architectures are studied as cases, and key areas for improvements towards more open DSP software development are identified. Proposed solutions are judged against the limited resources of mobile communication terminals and the characteristics of communication DSPs. 相似文献
47.
The aim of this study has been to develop a mathematical model for water flow and binder migration in coated paper. The model can be used for simulation of the stages starting after the coating applicator including infrared and air drying sections. On the basis of the model the moisture, temperature and binder distribution can be determined across the paper thickness. Approximating equations concerning the paper properties are used in the model. We have measured the diffusion coefficient between the water and binder substances. Representative numerical examples are presented for separate and combined infrared and air drying processes. 相似文献
48.
Quantitative structure-activity relationships (QSARs) have proved increasingly useful for predicting the biological activities of molecules (e.g., their binding affinities to different receptors) and can be used in environmental chemistry as a preliminary tool for screening the activities of untested molecules, producing valuable information on which compounds should be tested more thoroughly with experimental affinity assays or in animals. The predictive ability of the consensus kNN QSAR method is corroborated here using a diverse set of 245 compounds, which have been assayed for their relative binding affinities to the estrogen receptor of four species: human (ER alpha and ER beta), calf, mouse, and rat. Leave-one-out cross-validation (LOO-CV) and gamma-randomization tests were applied to the QSAR models for internal validation, and separate training and test sets were used for external validation. The internal predictive abilities of the consensus models for all five data sets were convincing, with cross-validated correlation coefficients (LOO-CV q2 values) varying from 0.69 (human ER beta data) to 0.79 (human ER alpha data). The external predictive abilities were also encouraging, as the predictive r2 scores (pr-r2 values) varied from 0.62 (human ER beta data) to 0.77 (calf and mouse data). The results indicate that consensus kNN QSAR is a feasible method for rapid screening of the estrogenic activity of organic compounds. 相似文献
49.
Siitonen S Laakkonen P Vahimaa P Jefimovs K Kuittinen M Parikka M Mönkkönen K Orpana A 《Applied optics》2004,43(30):5631-5636
Ring-shaped and radial diffractive gratings are designed with rigorous diffraction theory to couple light of a nearly monochromatic LED into a thin planar light guide on the bottom side. The theoretical coupling efficiencies for ring-shaped and radial gratings are 41% and 66%, respectively. Optimized diffractive elements are manufactured with direct electron-beam lithography and reactive-ion-etching into SiO2 substrates. Good agreement between experimental and theoretical results for selected radial gratings is reached. Furthermore, the mass production tests using injection molding are carried out with good replicability. 相似文献
50.
Effect of sarsaponin on ruminal fermentation with particular reference to methane production in vitro 总被引:6,自引:0,他引:6
This experiment was designed to investigate the effects of different concentrations (0, 1.2, 1.8, 2.4, and 3.2 g/L) of sarsaponin on ruminal microbial methane production using the substrates soluble potato starch, cornstarch, or hay plus concentrate (1.5:1). Ruminal fluid was collected from a dairy cow, mixed with phosphate buffer (1:2) and incubated (30 ml) anaerobically at 38 degrees C for 6 and 24 h with or without sarsaponin. Excluding the lower level of sarsaponin, pH of the medium was slightly decreased. Ammonia-N concentration and numbers of protozoa were decreased in a dose-dependent manner. Total volatile fatty acids and total gas production were increased. Molar proportion of acetate was decreased and propionate was increased with a corresponding decrease in acetate:propionate ratio. Hydrogen production was decreased. As the concentration of sarsaponin increased from 1.2 to 3.2 g/L, fermentation of soluble potato starch, cornstarch, or hay plus concentrate decreased methane production from 20 to 60% (6 h) and 17 to 50% (24 h), 21 to 58% (6 h) and 18 to 52% (24 h), and 23 to 53% (6 h) and 15 to 44% (24 h), respectively. Excluding the lower dose concentration (1.2 g/L) of sarsaponin, in vitro disappearance of dry matter of hay plus concentrate was decreased after 24 h. In conclusion, these results show that sarsaponin stimulated the mixed ruminal microorganism fermentation as well as to inhibit methane production in vitro. 相似文献