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1.
１　Ｉｎｔｒｏｄｕｃｔｉｏｎ　Ｓｉｎｇｕｌａｒｌｙｐｅｒｔｕｒｂｅｄｄｉｆｆｅｒｅｎｔｉａｌｅｑｕａｔｉｏｎｓｗｉｔｈｔｕｒｎｉｎｇｐｏｉｎｔｓａｒｅｖｅｒｙｉｍｐｏｒｔａｎｔｆｏｒｍａｔｈｅｍａｔｉｃｉａｎｓａｎｄｐｈｙｓｉｃｉｓｔｓｓｉｎｃｅｔｈｅｓｅｐｒｏｂｌｅｍｓｅｘｉｓｔｗｉｄｅｌｙｉｎｍａｎｙｐｒｏｂｌｅｍｓｏｆｐｈｙｓｉｃｓ．ＴｈｅｐｒｏｂｌｅｍｓｗｉｔｈｔｕｒｎｉｎｇｐｏｉｎｔｓｗｅｒｅｓｔｕｄｉｅｄｂｙＷｅｎｔｚａｌ,Ｋｒａｍｅｒｓ,Ｂｕｌｌｏｕｎｉｎ［１］,Ｌａｎｇｅｒ,Ａ…  相似文献   

2.
Exchange coupling and magnetization reversal mechanism in two series of Co_xNi_(1-x)/CoO(30 nm)(x=0.2 and 0.4)bilayers are studied by vector magnetometer.Two components of magnetization are measured parallel and perpendicular to the applied field.At low temperatures,coercivity H_c∝(t_(FM))~(-n),n=1.5 and 1.38 for x=0.2 and 0.4,respectively,in agreement with the random field model.At room temperature,the coercivity is nearly proportional to the inverse FM layer thickness.In addition to the exchange field and the coercivity,the characteristic of the magnetization reversal mechanism was found to change with temperature.At temperatures below 180 K,magnetization reversal process along the unidirectional axis is accompanied only by nucleation and pinning of domain wall while magnetization rotation is also involved at high temperatures.  相似文献   

3.
Solid oxide fuel cells(SOFCs) offer high energy conversion,low noise,low pollutant emission,and low processing cost.Despite many advantages,SOFCs face a major challenge in competing with other types of fuel cells because of their high operating temperature.The necessity to reduce the operational temperature of SOFCs has led to the development of research into the materials and fabrication technology of fuel cells.The use of composite cathodes significantly reduces the cathode polarization resistance and expands the triple phase boundary area available for oxygen reduction.Powder preparation and composite cathode fabrication also affect the overall performance of composite cathodes and fuel cells.Among many types of cathode materials,lanthanum-based materials such as lanthanum strontium cobalt ferrite(La1-xSrxCo1-yFeyO3- have recently been discovered to offer great compatibility with ceria-based electrolytes in performing as composite cathode materials for intermediate-to low-temperature SOFCs(IT-LTSOFCs).This paper reviews various ceria-based composite cathodes for IT-LTSOFCs and focuses on the aspects of progress and challenges in materials technology.  相似文献   

4.
Let K be a closed convex subset of a real reflexive Banach space E, T：K→K be a nonexpansive mapping, and f：K→K be a fixed weakly contractive （may not be contractive） mapping. Then for any t∈（0, 1）, let x1∈K be the unique fixed point of the weak contraction x1→tf（x）＋（1-t）Tx. If T has a fixed point and E admits a weakly sequentially continuous duality mapping from E to E^＊, then it is shown that {xt} converges to a fixed point of T as t→0. The results presented here improve and generalize the corresponding results in （Xu, 2004）.  相似文献   

5.
The interaction of two identical polar neutral molecules is modeled by two equal but oppositely charged point particles at a fixed distance of separation. The total Coulomb potential energy of this system is calculated as a function of this distance, x, and the distance, y, between their centers of mass. We find that when the y/x ratio is less than about 3.1619, the linear configuration has the lower energy, whereas when this ratio exceeds 3.1619, a stacked structure is more stable. Interestingly, when two real polar molecules, such as HF interact, neither of these structures are formed. It is ‘hydrogen bonded’. The NaF dimer on the other hand, has a global minimum as stacked structure at a y/x ratio of about 1, significantly smaller than 3.1619!  相似文献   

6.
Objective: To investigate the relationship between post-operative cognitive dysfunction (POCD) and regional cerebral oxygen saturation (rSO2) and β-amyloid protein (Aβ) in patients undergoing laparoscopic pancreaticoduodenectomy. Methods: Fifty patients undergoing elective laparoscopic pancreaticoduodenectomy received five groups of neuropsychological tests 1 d pre-operatively and 7 d post-operatively, with continuous monitoring of rSO2 intra-operatively. Before anesthesia induction (t 0), at the beginning of laparoscopy (t 1), and at the time of pneumoperitoneum 120 min (t 2), pneumoperitoneum 240 min (t 3), pneumoperitoneum 480 min (t 4), the end of pneumoperitoneum (t 5), and 24 h after surgery, jugular venous blood was drawn respectively for the measurement of Aβ by enzyme-linked immunosorbent assay (ELISA). Results: Twenty-one cases of the fifty patients suffered from POCD after operation. We found that the maximum percentage drop in rSO2 (rSO2, %max) was significantly higher in the POCD group than in the non-POCD group. The rSO2, %max value of over 10.2% might be a potential predictor of neurocognitive injury for those patients. In the POCD group, the plasma Aβ levels after 24 h were significantly higher than those of pre-operative values (P<0.01). After 24 h, levels of plasma Aβ in the POCD group were significantly higher than those in the non-POCD group (P<0.01). Conclusions: The development of POCD in patients undergoing laparoscopic pancreaticoduodenectomy is associated with alterations of rSO2 and Aβ. Monitoring of rSO2 might be useful in the prediction of POCD, and Aβ might be used as a sensitive biochemical marker to predict the occurrence of POCD.  相似文献   

7.
This paper considers the synchronization of solutions for lattices of the coupled non-autonomous Chen system. By using the Lyapunov function, we show that when the second coupled operator is negative definite self-adjoint and its coefficient is suitable large, the Chen coupled lattice system is bounded dissipative (In particular, the solutions for lattices of the coupled autonomous Chen system converge to zero as t → ∞). The synchronization between any two solutions of the coupled Chen system can be slaved only by coefficients in the x- or y-component for the suitably large second coupled coefficient. Finally, some numerical simulations are given. Project supported by the National Natural Science Foundation of China (Grant No.10771139)  相似文献   

8.
１ＩｎｔｒｏｄｕｃｔｉｏｎＤｉｆｅｒｅｎｔｉａｌｅｑｕａｔｉｏｎｓｗｉｔｈｔｕｒｎｉｎｇｐｏｉｎｔｓｅｘｉｓｔｗｉｄｅｌｙｉｎｍａｎｙｐｒｏｂｌｅｍｓｏｆｍａｔｈｅｍａｔｉｃｓｐｈｙｓｉｃｓ,ｓｏｔｈｅｓｅｐｒｏｂｌｅｍｓａｒｅｖｅｒｙｉｍｐｏｒｔａ...  相似文献   

9.
Numerical simulation and experimental tests were carried out to examine the hydrodynamic behaviors of a double-column floating system of gravity cage under wave conditions. A floating system of gravity cage can be treated as a small-sized floating structure when compared with the wavelengths. The main problem in calculating the wave loads on the small-sized floating structure is to obtain the reasonable force coefficients, which may differ from a submerged structure. In this paper, the floating system of gravity cage is simplified to a 2D problem, where the floating system is set symmetrically under wave conditions. The motion equations were deduced under wave conditions and a specific method was proposed to resolve the problem of wave forces acting on a small-sized floating system of gravity cage at water surface. Results of the numerical method were compared with those from model tests and the hydrodynamic coefficients Cn and Cr were studied. It is found that Cn ranges from 0.6 to 1.0 while Cr is between 0.4 and 0.6 in this study. The results are useful for research on the hydrodynamic behavior of the deep-water gravity sea cages.  相似文献   

10.
Conventional treatments of functions start by building a rule of correspondence betweenx-values andy-values, typically by creating an equation of the formy=f(x). We call this acorrespondence approach to functions. However, in our work with students we have found that acovariational appraoch is often more powerful, where students working in a problem situation first fill down a table column withx-values, typically by adding 1, then fill down ay-column through an operation they construct within the problem context. Such an approach has the benefit of emphasizing rate-of-change. It also raises the question of what it is that we want to cal rate across different functional situations. We make two initial conjectures, first that a rate can be initially understood as aunit per unit comparison and second that a unit is theinvariant relationship between a successor and its predecessor. Based on these conjectures we describe a variety of multiplicative units, then propose three ways of understanding rate of change in relation to exponential functions. Finally we argue that rate is different than ratio and that an integrated understanding of rate is built from multiple concepts.  相似文献   

11.
In a series of simultaneous two-choice preference tests, water snakes (Natrix r. rhombifera) displayed a significant preference for a clean area of a test chamber vs an area soiled by a conspecific. No differential responsiveness was found for a clean area as compared to an area soiled by either a sympatric species of garter snake (Thamnophis sirtalis) or by the individual water snake Ss. A similar series of tests with individual garter snakes (Thamnophis radix) revealed significant preferences for areas soiled either by the Ss themselves or by conspecifics as compared to clean areas. No preferences were found for a clean area of the test chamber vs an area soiled by a sympatric water snake (Natrix r. r.). The possible role of chemical cues in the mediation of dispersion and social responsiveness was discussed.  相似文献   

12.
This study was conducted in an attempt to investigate the effectiveness of an educational card game we developed for learning human immunology. Two semesters of evaluation were included to examine the impact of the game on students’ understanding and perceptions of the game-based instruction. Ninety-nine senior high school students (11th graders) were recruited for the first evaluation, and the second-semester group consisted of 72 students (also 11th graders). The results obtained indicate that students did learn from the educational card game. Moreover, students who learned from playing the game significantly outperformed their counterparts in terms of their understanding of the processes and connections among different lines of immunological defense (first semester: t = 2.92, p < 0.01; second semester: t = 3.45, p < 0.01) according to the qualitative analysis of an open-ended question. They generally had positive perceptions toward the game-based instruction and its learning efficiency, and they felt the game-based instruction was much more interesting than traditional didactic lectures (first semester: t = 2.79, p < 0.01; second semester: t = 2.41, p < 0.05). This finding is evidence that the educational card game has potential to facilitate students’ learning of how the immune system works. The implications and suggestions for future work are further discussed.
Play is necessary for the development of higher intelligence; for if we were provided with perfected instincts, as insects are, life would be automatic and there would be no such thing as education and no increase of ability or intelligence, either in the individual or the species.— Mitchell and Mason, 1935 , 56–57
  相似文献   

13.
This contribution looks at the competency development during teacher training and entry into work. The multi-perspective research design makes it possible to collate data at five stages within this transition process: at the start (t1), in the middle (t2) and on completion (t3) of teacher training for primary school level (year 1–6) student teachers in two education colleges in Switzerland, as well as novice teachers at the start (t4) and on competition (t5) of their first year of work. The data covers eleven topic areas. This paper will present findings of data analysis for two of these topic areas for all five stages of measurement: (a) knowledge of lesson planning was captured using case vignettes and (b) teaching practice during the study program and in the first year of work was recorded on video. The same data was collated from the teaching staff involved in the practical training of the student teachers. The statements on the case vignettes were studied using content-analysis. The lesson videos were analyzed using low-inference coding for the visible occurrences during teaching and with a high-inference rating on the quality of the lessons. The results, including those for a comparison of student teachers and novice teachers with practical teacher training staff, give insights into the effectiveness of teacher training and the impact of practical experience in the first year of work on knowledge of how to plan lessons and on the form and quality of teaching. Overall, the new training at both education colleges can be given a pleasingly positive appraisal in terms of professionalization. It is, however, also possible to recognize where and to what extent a need for further developing the standard of professionalization of teaching still exists.  相似文献   

14.
In this paper, a multi-objective particle swarm optimization （MOPSO） algorithm and a nondominated sorting genetic algorithm II （NSGA-II） are used to optimize the operating parameters of a 1.6 L, spark ignition （SI） gasoline engine. The aim of this optimization is to reduce engine emissions in terms of carbon monoxide （CO）, hydrocarbons （HC）, and nitrogen oxides （NOx）, which are the causes of diverse environmental problems such as air pollution and global warming. Stationary engine tests were performed for data generation, covering 60 operating conditions. Artificial neural networks （ANNs） were used to predict exhaust emissions, whose inputs were from six engine operating parameters, and the outputs were three resulting exhaust emissions. The outputs of ANNs were used to evaluate objective functions within the optimization algorithms： NSGA-II and MOPSO. Then a decision-making process was conducted, using a fuzzy method to select a Pareto solution with which the best emission reductions can be achieved. The NSGA-II algorithm achieved reductions of at least 9.84%, 82.44%, and 13.78% for CO, HC, and NOx, respectively. With a MOPSO algorithm the reached reductions were at least 13.68%, 83.80%, and 7.67% for CO, HC, and NOx, respectively.  相似文献   

15.
研究目的：建立2000-2020年中国氮氧化物排放清单,了解中国主要行业和省份氮氧化物的排放情况,为评估氮氧化物的环境影响和制定相关减排政策提供依据。创新要点：分析了中国主要省份产业结构对氮氧化物排放量的影响;根据不同情景分析,预测2020年中国氮氧化物的排放量。研究方法：1．基于自底向上法,根据不同类型化石燃料的氮氧化物排放因子,结合化石燃料消耗量,建立中国2000-2010年氮氧化物排放清单;2．基于IPAT方程,并以中国2000--2010年的国内生产总值增长数据和氮氧化物排放量为依据,分三种情景,分析2011-2020年中国能源消耗和氮氧化物排放趋势。重要结论：2010年中国氮氧化物的排放量约是2000年的两倍：自2009年起,中国氮氧化物总排放量超过,二氧化硫总排放量;主要由于产业结构和地区生产总值的不同,中国东部和西部氮氧化物排放量有明显差异;制造业、电力行业和交通运输业是中国氮氧化物的主要排放源,其中交通运输业氮氧化物排放量呈现逐年增长趋势;预计2020年中国氮氧化物排放量为19．7Mt。  相似文献   

16.
Koundinya Vajjha 《Resonance》2010,15(9):843-849
A Pythagorean triple is a triad of positive integers (x, y, z) which satisfy the Pythagoras’ equation x 2 + y 2 = z 2. In this article, we shall consider triples of the form (i, i + 1, k), and the recurrence relations governing them. In the process, we also solve completely the equation i 2+ (i + 1)2 = k 2.  相似文献   

17.
A k-ε-kp multi-fluid model was used to simulate confined swirling gas-solid two phase jet comprised of particle-laden flow from a center tube and a swirling air stream entering the test section from the coaxial annular. After considering the drag force between the two phases and gravity, a series of numerical simulations of the two-phase flow of 30μm, 45μm, 60μm diameter particles were performed on a x×r＝50×50 mesh grid respectively. The results showed that the k-ε-kp multi-fluid model can be applied to predict moderate swirling multi-phase flow. When the particle diameter is large, the collision of the particles with the wall will influence the prediction accuracy. The bigger the diameter of the particles, the stronger the collision with the wall, and the more obvious the difference between measured and calculated results.  相似文献   

18.
To determine the progress women have made in the last 20 years in terms of contributions to the knowledge base (i.e., authorship) and reputations as leading contributors (i.e., appointments as editors and editorial board members) in educational psychology, we analyzed data from six journals: theAmerican Educational Research Journal, Contemporary Educational Psychology,theEducational Psychologist, Educational Psychology Review,theJournal of Experimental Education,and theJournal of Educational Psychology.Results indicated that (a) women's progress in terms of authorships could be predicted by their increasing representation as educational psychologists, (b) opportunities for females to become editorial board members seem to be getting better, and (c) opportunities for females to become editors seem to be getting worse.  相似文献   

19.
A completion rate of an institution I of year x is defined as the proportion of starting students during year x that succeed in graduating at I at some point in the future. In this paper, a new method is proposed to estimate such completion rate. This indicator is entirely based on the population of drop-out students during one academic year x at the institution I. The proposed method is not based on a cohort of students so it allows an estimation of the current school effectiveness without substantial delay. Furthermore a statistical framework is presented in which completion rates can be studied. The proposed methodology results in a statistical estimator with a bias that stays small under appropriate assumptions.  相似文献   

20.
Optimizing the operation of coal-fired power plants to reduce nitrogen oxide (NO x ) emissions requires accurate modeling of the NO x emission process. The careful selection of input parameters not only forms the basis of accurate modeling, but can also be used to reduce the complexity of the model. The present study employs the least squares support vector machine-supervised learning method to model NO x emissions based on historical real time data obtained from a 1000-MW once-through boiler. The initial input parameters are determined by expert knowledge and operational experience, while the final input parameters are obtained by sensitivity analysis, where the variation in model accuracy for a given set of data is analyzed as one or several input parameters are successively omitted from the calculations, while retaining all other parameters. Here, model accuracy is evaluated according to the mean relative error (MRE). This process reduces the parameters required for NO x emission modeling from an initial number of 33 to 7, while the corresponding MRE is reduced from 3.09% to 2.23%. Moreover, a correlation of 0.9566 between predicted and measured values was obtained by applying the model with just these seven input parameters to a validation dataset. As such, the proposed method for selecting input parameters serves as a reference for related studies.  相似文献   

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