MATLAB应用于离散时间系统分析的教学探讨

在离散时间系统分析的课堂教学中，借助科学计算软件MATLAB能在阐述概念的同时。避免过多的手动运算，即时给出相关结果和函数图形，使得在有限的时间内展现整个系统分析的流程，节省了时间，改善了授课效果．     

The organs of prey capture and digestion in the miniature predatory bivalve Spheniopsis brasiliensis (Anomalodesmata: Cuspidarioidea: Spheniopsidae) expose a novel life-history trait

Spheniopsis brasiliensis, from depths of 17–148 m off the southern Atlantic coast of Brazil, is a predator of epipsammic micro-crustaceans which it sucks into the infra-septal chamber using a raptorial inhalant siphon and internally generated hydrostatic suction forces. Prey items, which include ostracods, are thought to be pushed into the funnel-shaped mouth using the foot. The stomach is capacious with a short style sac conjoined briefly with the mid gut and possessing a stubby crystalline style. Internal stomach architecture is simplified, with no identifiable sorting areas (unlike other cuspidarioids) and lined virtually completely by a gastric shield. The exoskeletal remains of digested prey are held in the posterior end of the stomach and not in a specialised waste storage pouch as in the con-familial Grippina coronata. The mid gut, hind gut and rectum are all extremely narrow and, thus, only the smallest of faeces can be accommodated and transmitted for anal discharge. Spheniopsis brasiliensis, like G. coronata is a self-fertilising simultaneous hermaphrodite with encapsulated lecithotrophic eggs brooded internally. Both taxa are thus ovovivaporous. It is also believed that both taxa are univoltine so that larvae and the exoskeletal prey remains are all released post mortem. Cuspidariids are generally regarded as dioecious but, recently, Cardiomya costellata has been shown to be a non-brooding simultaneous hermaphrodite. The distinguishing characters between cuspidariids and spheniopsids thus appear to be their differing reproductive strategies and life history traits.     

Forecasting using targeted diffusion indexes

The simplicity of the standard diffusion index model of Stock and Watson has certainly contributed to its success among practitioners, resulting in a growing body of literature on factor‐augmented forecasts. However, as pointed out by Bai and Ng, the ranked factors considered in the forecasting equation depend neither on the variable to be forecast nor on the forecasting horizon. We propose a refinement of the standard approach that retains the computational simplicity while coping with this limitation. Our approach consists of generating a weighted average of all the principal components, the weights depending both on the eigenvalues of the sample correlation matrix and on the covariance between the estimated factor and the targeted variable at the relevant horizon. This ‘targeted diffusion index’ approach is applied to US data and the results show that it outperforms considerably the standard approach in forecasting several major macroeconomic series. Moreover, the improvement is more significant in the final part of the forecasting evaluation period. Copyright © 2009 John Wiley & Sons, Ltd.     

Eulers “Harmony” Between the Principles of “Rest” and “Least Action”

In 1751, LEONHARD EULER established “harmony” between two principles that had been stated by PIERRE-LOUIS-MOREAU DE MAUPERTUIS a few years earlier. These principles are intended to be the foundations of Mechanics; they are the principle of rest and the principle of least action. My claim is that the way in which “harmony” is achieved sets the foundations of so called Analytical Mechanics: it discloses the physical bases of the general ideas, concepts, and motivations of the formalism. My paper intends to show what those physical bases are, and how a picture of the formalism issues from them. This picture is shown to be recast in JOSEPH-LOUIS LAGRANGES justification of the formalism, which strengthens my claim.     

The conceptual import of Carnot's theorem to the discovery of the entropy

Summary Among many other things, Carnot stated a principle and proved a theorem. In 1850, Clausius corrected Carnot's theory, modifying it according to Joule's principle. He might have considered a corollary of the theorem as the mathematical formulation of Carnot's principle. We challenge the corollary: it is based on hidden assumptions, nor is it true for all cycles. Clausius realized the corollary's lack of generality, but on different grounds. In 1854, he generalized the theorem, and gave an (other) expression to Carnot's principle. We analyze Clapeyron's account of Carnot's theory, Thomson's account of 1849 and some of Clausius belated comments on his 1850 paper, as well Clausius' paper of 1854. We hope that they shed light on the corollary's tacit hypotheses and on the meaning of Carnot's principle. It is our contention: Clausius took seriously a contemporary meaning of the principle, and looked for a condition of integrability that could express recovery of the initial conditions of the reservoirs. Furthermore, he seems to have had some prior knowledge of the form the expression of the principle should take. Actually, this was the theory's natural candidate.     

“Will someone say exactly what the H-theorem proves?” A study of Burbury's Condition A and Maxwell's Proposition II

Summary Many historians of science recognize that the outcome of the celebrated debate on Boltzmann's H-Theorem, which took place in the weekly scientific journal Nature, beginning at the end of 1894 and continuing throughout most of 1895, was the recognition of the statistical hypothesis in the proof of the theorem. This hypothesis is the Stosszahlansatz or hypothesis about the number of collisions. During the debate, the Stosszahlansatz was identified with another statistical hypothesis, which appeared in Proposition II of Maxwell's 1860 paper; Burbury called it Condition A. Later in the debate, Bryan gave a clear formulation of the Stosszahlansatz. However, the two hypotheses are prima facie different. Burbury interchanged them without justification or even warning his readers. This point deserves clarification, since it touches upon subtle questions related to the foundation of the theory of heat. A careful reading of the arguments presented by Burbury and Bryan in their various invocations of both hypotheses can clarify this technical point. The Stosszahlansatz can be understood in terms of geometrical invariances of the problem of a collision between two spheres. A byproduct of my analysis is a clarification of the debate itself, which is apparently obscure.     

The Concept of Sustainable Development Revisited

The concept of sustainable development is here revised in the light of a brief historical analysis, followed by a semantic analysis of the expressions development and sustainability. The authors criticize the common use of this concept in a loose way or in wide generalizations, to conclude, based on the principles of human ecology, that it is only possible to make it operational in limited spans of time and in limited spatial units.     

Adenosine-3,5-phosphate levels in brain structures of rats submitted to four different behavioral procedures

Summary Shuttle avoidance training decreased the cAMP content of rat brain (excluding hippocampus and caudate nucleus), amygdala and hypothalamus. Stimulation by tones alone had a similar effect, but only in the brain fraction. Pseudoconditioning or footshocks alone had no effect.With support from FAPERGS, CNPq, and PROPESP-UFRGS, Brasil. We are grateful to Miss Sonia Eisinger for her valuable technical assistance.