Effects of mean piston speed,equivalence ratio and cylinder wall temperature on performance of an Atkinson engine

The performance of an air standard Atkinson cycle is analyzed using finite-time thermodynamics. In the model, the linear relation between the specific heat ratio of the working fluid and its temperature, the friction loss computed according to the mean velocity of the piston, the internal irreversibility described by using the compression and expansion efficiencies and the heat transfer loss are considered. The relations between the power output and the compression ratio and between the power output and the thermal efficiency are derived by detailed numerical examples. The results show that if the compression ratio is less than a certain value, the power output decreases with increasing mean piston speed, while if the compression ratio exceeds a certain value, the power output first increases and then starts to decrease with increasing mean piston speed. With further increase in the compression ratio, the increase of mean piston speed results in decreasing the power output. Throughout the compression ratio range, the power output increases with increasing cylinder wall temperature while it first increases and then starts to decrease with the increase of equivalence ratio. The conclusions of this investigation are of importance when considering the designs of actual Atkinson engines.     

Comparative Analysis of Cubic Spline and Kernel Estimation of a Probit Function

The least-squares cubic spline and the kernel estimators produce comparable mean squared errors, although the kernel produces smaller mean squared errors when the variable increases away from 0. Mean squared error increases with an increase in the number of knots (for the cubic spline) or reduced band width (for the kernel estimator). The cubic spline produces smaller mean squared errors when all observations are made at knots than when they are spaced out between knots. Irrespective of the exact form of the probit function g(x), the cubic spline estimator is asymptotically unbiased, while the kernel estimator only converges to g(x) under certain conditions. Moreover, the cubic spline is a smooth function, which is twice differentiable on the interval [0,1].     

Relatively spectral morphisms and applications to K-theory

Spectral morphisms between Banach algebras are useful for comparing their K-theory and their “noncommutative dimensions” as expressed by various notions of stable ranks. In practice, one often encounters situations where the spectral information is only known over a dense subalgebra. We investigate such relatively spectral morphisms. We prove a relative version of the Density Theorem regarding isomorphism in K-theory. We also solve Swan's problem for the connected stable rank, in fact for an entire hierarchy of higher connected stable ranks that we introduce.     

Uniqueness of Noncompact Spacelike Hypersurfaces of Constant Mean Curvature in Generalized Robertson–Walker Spacetimes

On any spacelike hypersurface of constant mean curvature of a Generalized Robertson–Walker spacetime, the hyperbolic angle between the future-pointing unit normal vector field and the universal time axis is considered. It is assumed that has a local maximum. A physical consequence of this fact is that relative speeds between normal and comoving observers do not approach the speed of light near the maximum point. By using a development inspired from Bochner's well-known technique, a uniqueness result for spacelike hypersurfaces of constant mean curvature under this assumption on , and also assuming certain matter energy conditions hold just at this point, is proved.     

A TWO‐STAGE INFORMATION‐THEORETIC APPROACH TO MODELING LANDSCAPE‐LEVEL ATTRIBUTES AND MAXIMUM RECRUITMENT OF CHINOOK SALMON IN THE COLUMBIA RIVER BASIN

ABSTRACT. Many anadromous salmonid stocks in the Pacific Northwest are at their lowest recorded levels, which has raised questions regarding their long‐term persistence under current conditions. There are a number of factors, such as freshwater spawning and rearing habitat, that could potentially influence their numbers. Therefore, we used the latest advances in information‐theoretic methods in a two‐stage modeling process to investigate relationships between landscape‐level habitat attributes and maximum recruitment of 25 index stocks of chinook salmon (Onocorhynchus tshawy‐tscha) in the Columbia River basin. Our first‐stage model selection results indicated that the Ricker‐type, stock recruitment model with a constant Ricker a, i.e., recruits‐per‐spawner at low numbers of fish) across stocks was the only plausible one given these data, which contrasted with previous unpublished findings. Our second‐stage results revealed that maximum recruitment of chinook salmon had a strongly negative relationship with percentage of surrounding subwatersheds categorized as predominantly containing U.S. Forest Service and private moderate‐high impact managed forest. That is, our model predicted that average maximum recruitment of chinook salmon would decrease by at least 247 fish for every increase of 33% in surrounding subwatersheds categorized as predominantly containing U.S. Forest Service and privately managed forest. Conversely, mean annual air temperature had a positive relationship with salmon maximum recruitment, with an average increase of at least 179 fish for every increase in 2°C mean annual air temperature.     

Advertising Response Functions and Media Planning

In the first part of this paper the definition and use of advertising response functions are examined critically. It is shown that advertising response functions cannot be regarded as models of the advertising process whose parameters are known, that only a small section of the complex functions often postulated is relevant to media planning, that measures of advertising impacts or exposures are relative rather than absolute, and consequently that the “response function” only shows a notional relationship between advertising response and exposure, which normally needs to be calibrated to the advertising appropriation.In the second part a media planning system which utilizes a “control parameter” rather than a “response function” is described. The main feature of the “control parameter” is that it adapts itself so that an appropriate relationship between response and exposure is used, whatever the appropriation. Other features of the system are described.     

Evaluation of the evolution of relationships between topics over time

Topics that attract public attention can originate from current events or developments, might be influenced by situations in the past, and often continue to be of interest in the future. When respective information is made available textually, one possibility of detecting such topics of public importance consists in scrutinizing, e.g., appropriate press articles using—given the continual growth of information—text processing techniques enriched by computer routines which examine present-day textual material, check historical publications, find newly emerging topics, and are able to track topic trends over time. Information clustering based on content-(dis)similarity of the underlying textual material and graph-theoretical considerations to deal with the network of relationships between content-similar topics are described and combined in a new approach. Explanatory examples of topic detection and tracking in online news articles illustrate the usefulness of the approach in different situations.     

The Relationship of Teacher‐Facilitated,Inquiry‐Based Instruction to Student Higher‐Order Thinking

Commissions, studies, and reports continue to call for inquiry‐based learning approaches in science and math that challenge students to think critically and deeply. While working with a group of middle school science and math teachers, we conducted more than 100 classroom observations, assessing several attributes of inquiry‐based instruction. We sorted the observations into two groups based on whether students both explored underlying concepts before receiving explanations and contributed to the explanations. We found that in both math and science classrooms, when teachers had students both explore concepts before explanations and contribute to the explanations, a higher percent of time was spent on exploration and students were more frequently involved at a higher cognitive level. Further, we found a high positive correlation between the percent of time spent exploring concepts and the cognitive level of the students, and a negative correlation between the percent of time spent explaining concepts and the cognitive level. When we better understand how teachers who are successful in challenging students in higher‐order thinking spend their time relative to various components of inquiry‐based instruction, then we are better able to develop professional development experiences that help teachers transition to more desired instructional patterns.     

Low-dimensional topology and ordering groups

This expository paper explores the interaction of group ordering with topological questions, especially in dimensions 2 and 3. Among the topics considered are surfaces, braid groups, 3-manifolds and their structures such as foliations and mappings between them. A final section explores currently ongoing research regarding spaces of homeomorphisms and their orderability properties. This is not meant to be a comprehensive survey, but rather just a taste of the rich relationship between topology and the theory of ordered groups.     

NA样本概率密度函数核估计的相合性

设{X     

信息披露制度、公司风险投资(CVC)信息披露与公司价值

信息披露制度对信息披露水平的影响及其经济效果一直是学术研究的热点。在交易所信息披露制度文件基础上,本文构建了可靠的CVC信息披露水平指数。研究发现信息披露制度的出台有效地提高了CVC信息披露水平。利用信息披露制度出台这一准自然实验,采用双重差分法发现CVC信息披露水平的提高增加了上市公司价值,进一步研究发现不确定性和市场竞争程度会对二者关系产生调节作用。该研究结果说明信息披露制度具有积极的政策效用,也为CVC信息披露制度的出台提供了经验证据。     

绩效度量的一致性、敏感性及准确性关系研究

将环境的波动性和度量噪音看作是影响绩效度量的两类不同的随机误差,在Linear-exponential-normal框架下,建立了以价值绩效度量和补偿绩效度量的线性组合为基础的收益激励模型,并分析了激励强度与绩效度量的一致性、敏感性和准确性之间的关系,以及环境波动性对上述关系的影响.研究发现,在确定性环境条件下,激励强度与绩效度量的"信号噪音比"成正比关系,但绩效度量的一致性的提高并不必然增加该度量指标在激励契约中的权重,而要视敏感性或噪音相对于一致性的变化幅度来定.特别地,在绩效度量的敏感性与一致性之间并不存在权衡取舍关系.研究还发现,波动性与激励强度之间存在负向关系,且波动性的存在降低了绩效度量的一致性和敏感性,但波动性对绩效度量的准确性的影响则呈非单调性变化.     

Improving Penalized Least Squares through Adaptive Selection of Penalty and Shrinkage

Estimation of the mean function in nonparametric regression is usefully separated into estimating the means at the observed factor levels—a one-way layout problem—and interpolation between the estimated means at adjacent factor levels. Candidate penalized least squares (PLS) estimators for the mean vector of a one-way layout are expressed as shrinkage estimators relative to an orthogonal regression basis determined by the penalty matrix. The shrinkage representation of PLS suggests a larger class of candidate monotone shrinkage (MS) estimators. Adaptive PLS and MS estimators choose the shrinkage vector and penalty matrix to minimize estimated risk. The actual risks of shrinkage-adaptive estimators depend strongly upon the economy of the penalty basis in representing the unknown mean vector. Local annihilators of polynomials, among them difference operators, generate penalty bases that are economical in a range of examples. Diagnostic techniques for adaptive PLS or MS estimators include basis-economy plots and estimates of loss or risk.     

The effectiveness of resources created by students as partners in explaining the relevance of mathematics in engineering education

First-year engineering students often struggle to see the relevance of theoretical mathematical concepts for their future studies and professional careers. This is an issue, as students who do not see relevance in fundamental parts of their studies may disengage from these parts and focus their efforts on other subjects they think will be more useful to them. In this study, we surveyed engineering students enrolled in a first-year mathematics subject on their perceptions of the relevance of the individual mathematical topics taught. Surveys were administered at the start of semester when some of these topics were unknown to them, and again at the end of semester when students had not only studied all these topics but also watched a set of animated videos. These videos had been produced by higher-year students to explain where they had seen applications of the mathematical concepts presented in the first year. We notice differences between the perceived relevance of topics for future study and for professional careers, with relevance to study rated higher than relevance to careers. We also find that the animations are seen as helpful in understanding the relevance of first-year mathematics. The majority of students indicated that lecturers with students as partners should work collaboratively to produce future videos.     

It's about time: the relationships between coverage and instructional practices in college calculus

This paper is based on a large-scale empirical study designed to investigate Calculus I programmes across the United States to better understand the relationship between instructors' concerns about coverage, instructional practices, and the nature of the material covered. We found that there was no association between instructors feeling pressured to go through material quickly to cover all the required topics and intended pacing. Furthermore, our results suggest that both intended pacing and feelings of pressure are poor indicators of instructional practices.     

The welfare effects of public opinion polls

This paper presents an experimental study of the effects of polls on voters’ welfare. The analysis shows that polls have a different effect on closely divided and lopsided divided electorates. The data show that in closely divided electorates (and only for these electorates) the provision of information on the voters’ distribution of preferences significantly raises the participation of subjects supporting the slightly larger team relative to the smaller team. This causes a substantial increase on the frequency of electoral victories of the larger team. As a consequence, we observe a steep decrease in the welfare of the members of the smaller team because they vote more often and yet they loose the elections more frequently. Polls are detrimental to aggregate welfare in closely divided electorates because the decrease in the payoffs of the minority is stronger than the increase in the payoffs of the majority. In lopsided divided electorates polls don’t have a significant different effect on the voters’ turnout conditional on their team size. We do observe an increase on the frequency of electoral victories of the larger team after the provision of information, but this is in part due to smaller teams’ members voting less frequently and saving the participation costs. As a consequence, while polls have a negative effect on the relative payoffs of the minority for these electorates as well, they have a positive effect on total welfare.     

区间删失下恒定应力部分加速寿命试验的统计分析（英文）

In this paper, a statistical analysis method is proposed to research life characteristics of products based on the partially accelerated life test. We discuss the statistical analysis for constant-stress partially accelerated life tests with Lomax distribution based on interval censored samples. The EM algorithm is used to obtain the maximum likelihood estimations(MLEs) and interval estimations for the shape parameter and acceleration factor.The average relative errors(AREs), mean square errors(MSEs), the confidence intervals for the parameters, and the influence of the sample size are discussed. The results show that the AREs and MSEs of the MLEs decrease with the increase of sample size. Finally, a simulation sample is used to estimate the reliability under different stress levels.     

An effective computer modelling approach to the study of aeroelastic characteristics of an aircraft composite wing with high aspect ratio

Static aeroelastic and flutter characteristics of an aircraft composite wing with high aspect ratio were analysed by an effective Computational Fluid Dynamics and Computational Structure Dynamics coupled method. Effects of stiffness distribution on aeroelastic characteristics were considered. Honeycomb core sandwich composite was considered to be equivalent to an orthotropic material by stiffness and inertance equivalent method to allow highly efficient numerical simulation, which was used for analysis of bending and torsional stiffness distribution. The results showed that the redistributed aerodynamic load leads to a decrease of pressure difference between the upper and lower airfoils. The flutter speed of the composite wing is near 0.64 Ma. Both bending and torsional stiffness increases with a small increase of beam size. Stiffness of the wing root has a major influence generally on the static aeroelastic characteristics. Both the lift coefficient and the loss percent decrease with a small increase of beam size. Effects of stiffness distribution on frequency are not obvious. Flutter speed remains close to the initial value when the beam size is changed.     

Monotonicity properties of the superposition operator and their applications

We establish some properties of the superposition operator which are associated with monotonicity. Those properties are expressed in terms of the notion of degree of decrease or degree of increase. An application of the obtained results to the study of solvability of a quadratic Volterra integral equation is also derived.     

二次曲面和平面位置关系的判式

在解析几何中有二次曲线与直线位置关系的讨论、二次曲面与直线位置关系的讨论,而二次曲面与平面相关位置关系的探讨较少.本文给出二次曲面a11x2+a22y2+a33z2+2a12xy+2a13xz+2a23yz+2a14x+2a24y+2a34z+a44=0(1)和平面Ax+By+Cz+D=0(2)的相对位置的判别式Δ=a11a12a13a14Aa21a22a23a24Ba31a32a33a34Ca41a42a43a44DA B C D0(aij=aji).(3)并证明了:若Δ>0,则二次曲面(1)与平面(2)相交;若Δ=0,则(1)和(2)相切;若Δ<0,则(1)和(2)相离.