The dynamical equation of the spinning electron

We obtain by invariance arguments the relativistic and non-relativistic invariant dynamical equations of a classical model of a spinning electron. We apply the formalism to a particular classical model which satisfies Dirac's equation when quantised. It is shown that the dynamics can be described in terms of the evolution of the point charge which satisfies a fourth order differential equation or, alternatively, as a system of second order differential equations by describing the evolution of both the center of mass and center of charge of the particle. As an application of the found dynamical equations, the Coulomb interaction between two spinning electrons is considered. We find from the classical viewpoint that these spinning electrons can form bound states under suitable initial conditions. Since the classical Coulomb interaction of two spinless point electrons does not allow for the existence of bound states, it is the spin structure that gives rise to new physical phenomena not described in the spinless case. Perhaps the paper may be interesting from the mathematical point of view but not from the point of view of physics.Comment: Latex2e, 14 pages, 5 figure

Documentation of the Fourth Order Band Model

A general circulation model is presented which uses quadratically conservative, fourth order horizontal space differences on an unstaggered grid and second order vertical space differences with a forward-backward or a smooth leap frog time scheme to solve the primitive equations of motion. The dynamic equations for motion, finite difference equations, a discussion of the structure and flow chart of the program code, a program listing, and three relevent papers are given

A Meta-Analysis of Technical Efficiency in Farming: A Multi-Country Perspective

The objective of this study is to undertake a meta-analysis seeking to explain the variation in average technical efficiency focusing on the agricultural sector. For this purpose, a meta-analysis of 126 technical efficiency studies on the agricultural sector of developing and developed countries was undertaken. In addition, the study contributes to cross-country productivity literature because the existing body of work in this area typically uses aggregate (i.e., national) level data to estimate total factor productivity and has ignored the technical efficiency component of productivity. The econometric results suggest that stochastic frontier models generate higher mean technical efficiency estimates than deterministic models, while parametric frontier models yield lower estimates than nonparametric. The difference between parametric and non-parametric frontiers is reduced when the translog specification is used. Also, frontier models using cross-sectional data produce lower estimates than those based on panel data. The econometric results also suggest that low-income countries (LICs) present a lower mean technical efficiency than high-income countries (HICs). A more detailed analysis reveals that Western European countries and Australia present, on average, the highest levels of mean technical efficiency among all regions after accounting for some methodological features of the studies. Eastern European countries exhibit the lowest estimate followed by Asian and African countries, while studies from Latin America and Caribbean countries, and from North American countries are in an intermediate position.Farm Management,

A stochastic-dynamic model for global atmospheric mass field statistics

A model that yields the spatial correlation structure of atmospheric mass field forecast errors was developed. The model is governed by the potential vorticity equation forced by random noise. Expansion in spherical harmonics and correlation function was computed analytically using the expansion coefficients. The finite difference equivalent was solved using a fast Poisson solver and the correlation function was computed using stratified sampling of the individual realization of F(omega) and hence of phi(omega). A higher order equation for gamma was derived and solved directly in finite differences by two successive applications of the fast Poisson solver. The methods were compared for accuracy and efficiency and the third method was chosen as clearly superior. The results agree well with the latitude dependence of observed atmospheric correlation data. The value of the parameter c sub o which gives the best fit to the data is close to the value expected from dynamical considerations

Classical to quantum correspondence in dissipative directed transport

We compare the quantum and classical properties of the (Quantum) Isoperiodic Stable Structures -- (Q)ISSs -- which organize the parameter space of a paradigmatic dissipative ratchet model, i.e. the dissipative modified kicked rotator. We study the spectral behavior of the corresponding classical Perron-Frobenius operators with thermal noise and the quantum superoperators without it for small $\hbar_{\rm eff}$ values. We find a remarkable similarity between the classical and quantum spectra. This finding significantly extends previous results -- obtained for the mean currents and asymptotic distributions only -- and on the other hand unveils a classical to quantum correspondence mechanism where the classical noise is qualitatively different from the quantum one. This is crucial not only for simple attractors but also for chaotic ones, where just analyzing the asymptotic distribution reveals insufficient. Moreover, we provide with a detailed characterization of relevant eigenvectors by means of the corresponding Weyl-Wigner distributions, in order to better identify similarities and differences. Finally, this model being generic, it allows us to conjecture that this classical to quantum correspondence mechanism is a universal feature of dissipative systems.Comment: 7 pages, 6 figure

WHAT IS THE LENGTH OF A SNAKE?

The way that herpetologists have traditionally measuredlive snakes is by stretching them on a ruler andrecording the total length (TL). However, due to the thinconstitution of the snake, the large number of intervertebraljoints, and slim muscular mass of most snakes,it is easier to stretch a snake than it is to stretch anyother vertebrate. The result of this is that the length ofa snake recorded is infl uenced by how much the animalis stretched. Stretching it as much as possible is perhapsa precise way to measure the length of the specimenbut it might not correspond to the actual length ofa live animal. Furthermore, it may seriously injure a livesnake. Another method involves placing the snake in aclear plexiglass box and pressing it with a soft materialsuch as rubber foam against a clear surface. Measuringthe length of the snake may be done by outlining itsbody with a string (Fitch 1987; Frye 1991). However, thismethod is restricted to small animals that can be placedin a box, and in addition, no indications of accuracy of thetechnique are given. Measuring the snakes with a fl exibletape has also been reported (Blouin-Demers 2003)but when dealing with a large animals the way the tapeis positioned can produce great variance on the fi nal outcome.In this contribution we revise alternative ways tomeasuring a snake and propose a method that offers repeatableresults. We further analyze the precision of thismethod by using a sample of measurements taken fromwild populations of green anacondas (Eunectes murinus)with a large range of sizes

La gobernabilidad controamericana en los noventa. Consideraciones sobre las posibilidades democráticas en la postguerra

El ensayo discute las posibilidades de construir la vida democrática en sociedades que salen de la guerra y la violencia, con rencores, pobreza e intolerancia. Con las causas que la provocaron, agravadas ahora. Tal es la situación de Guatemala, El Salvador y Nicaragua, afectadas por una guerra civil en la década de los ochenta. Señala las condiciones para alcanzar la única gobernabilidad deseada, la democrática, basada en la legitimidad y la eficiencia de las cohortes gobernantes; se apoya en un concepto de sociedad civil que destaca el valor de la participación de los intereses privados, animados por un sentido social en sus múltiples formas, dispuestos a la vida pública y política. El ensayo termina con dos ejemplos de ingobernabilidad en Nicaragua y Guatemala.The article discusses the situation of Nicaragua, Guatemala and El Salvador once the internal or external wars in these countries are almost finished. Generalized political violence may be about to disappear but the social, economic and political conditions produce that stable democracy is still more a goal than a reality. According to the argument, transitions to democracy are not finished since governability will be hard to achieve. Efficiency and legitimacy are two basic challenges that Central American polities must achieve to talk about consolidated democracy

A New Hybrid Type of Deployable Structure: Origami-scissor Hinged

Deployable structures can transform, expand and contract due to their geometric, material and mechanical properties; applications spread across multiple fields including aerospace technology and temporary, mobile and transformable architecture. There are many different types of deployable structures. For instance, the art of origami has developed concepts for paper folds that can expand and contract. Another type is that of scissorhinged structures, made by bars joined by pivots. These two different types, origami and scissors, have so far remained separate types within the field. This geometry research unifies both types and makes an origamiscissor structure, which has a double deployment. This new technology has potential applications in architecture and engineering, such as transportable pavilions, aerospace or robotic applications