The Parallelometer: a mechanical device to study curvature

A simple mechanical device is introduced, the parallelometer, that can be used to measure curvatures of surfaces. The device can be used as a practical illustration of parallel transport of a vector and to study Berry phase shift when it is carried along a loop on the surface. Its connection to the Foucault pendulum is discussed. The experimental results can be successfully compared with the theoretical expectations. The experiment is inexpensive and conceptually easy to perform and understand for a beginner

Localized anisotropic superconductors

We address the question of whether an anisotropic gap of symmetry is compatible with localized states in the normal phase. The issue is important for high- superconductors for which a superconductor-to-insulator transition is observed, together with a number of experiments that support d-wave pairing. We prove that d-wave superconductivity is compatible with a localized normal state. When the coherence length is of the order of the lattice constant, the effects of localization are important. We find a re-entrant behaviour of superconductivity in the strongly disordered phase.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48878/2/c83408.pd

Hamilton's principle: why is the integrated difference of kinetic and potential energy minimized?

I present an intuitive answer to an often asked question: why is the integrated difference K-U between the kinetic and potential energy the quantity to be minimized in Hamilton's principle? Using elementary arguments, I map the problem of finding the path of a moving particle connecting two points to that of finding the minimum potential energy of a static string. The mapping implies that the configuration of a non--stretchable string of variable tension corresponds to the spatial path dictated by the Principle of Least Action; that of a stretchable string in space-time is the one dictated by Hamilton's principle. This correspondence provides the answer to the question above: while a downward force curves the trajectory of a particle in the (x,t) plane downward, an upward force of the same magnitude stretches the string to the same configuration x(t).Comment: 7 pages, 4 figures. Submitted to the American Journal of Physic

Gyroscopically Stabilized Oscillators and Heat Baths

In this paper we analyze the stability of a gyroscopic oscillator interacting with a finite- and infinite-dimensional heat bath in both the classical and quantum cases. We consider a finite gyroscopic oscillator model of a particle on a rotating disc and a particle in a magnetic field and we examine stability before and after coupling to a heat bath. The heat bath is modelled in the finite-dimensional setting by a system of independent oscillators with mass. It is shown that if the oscillator is gyroscopically stable, coupling to a sufficiently massive heat bath induces instability even in the finite-dimensional setting. The key mechanism for instability in this paper is thus not induced by damping. The meaning of these ideas in the quantum context is discussed. The model extends the exact diagonalization analysis of an oscillator and field of Ford, Lewis, and O'Connell to the gyroscopic setting. We also discuss the interesting role that damping of Landau type plays in the infinite limit.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45132/1/10955_2004_Article_481221.pd

Fitting Parton Distribution Data with Multiplicative Normalization Uncertainties

We consider the generic problem of performing a global fit to many independent data sets each with a different overall multiplicative normalization uncertainty. We show that the methods in common use to treat multiplicative uncertainties lead to systematic biases. We develop a method which is unbiased, based on a self--consistent iterative procedure. We demonstrate the use of this method by applying it to the determination of parton distribution functions with the NNPDF methodology, which uses a Monte Carlo method for uncertainty estimation.Comment: 33 pages, 5 figures: published versio

Dinámica de uso y cobertura del suelo en un parque nacional mexicano

To understand the dynamics of land cover at the Parque Nacional Cofre de Perote, the rates of change in land use were compared at two different scales during the period 1995-2004. At the meso scale, these patterns were studied throughout the entire Parque Nacional Cofre de Perote, which is one of the 60 priority mountains of Mexico, and an important natural protected area of the country located in the state of Veracruz. At a micro scale, the work was focused in ejido El Conejo, located within the boundaries of this national park. Federal government digital orthophotos were used to determine changes in nine categories of land use. In both, the meso- and micro-scale, it was found that the predominant land cover categories are agriculture and forest. The probabilities of land cover change at both scales are low and essentially the same for most land use categories, reflecting both small gains in forest cover park-wide as well as the effectiveness of the ejido in managing natural resources within the park. The authors consider that the findings of the study may be applicable to the broader situation of national parks in Mexico and, finally, the importance of integrating local stakeholders in the management of natural protected areas is discussedPara entender la dinámica de la cobertura del suelo en el Parque Nacional Cofre de Perote, se hizo una comparación de las tasas de cambio de uso a dos escalas durante el periodo 1995-2004. A escala meso, se estudiaron estos patrones en toda la superficie del Parque Nacional Cofre de Perote, que es una de las 60 montañas prioritarias de México y también una importante área natural protegida del país ubicada en el estado de Veracruz. A escala micro el estudio se enfocó en el ejido El Conejo que se encuentra dentro de los límites de este parque nacional. Se utilizaron ortofotos digitales del gobierno federal para determinar el cambio en nueve categorías de uso del suelo. En ambas, meso y microescalas, se encontró que las categorías predominantes de cobertura son la agricultura y el bosque. Las probabilidades de cambio de cobertura del suelo en ambas escalas son bajas y tienen valores esencialmente iguales para la mayoría de las categorías de uso, reflejando tanto pequeñas ganancias en cobertura forestal en todo el parque como la efectividad del ejido en el manejo de recursos naturales dentro del parque. Se considera que los hallazgos de este estudio pueden ser aplicables a la situación prevaleciente en los restantes parques nacionales de México; al final se discute la importancia de integrar a los actores locales en el manejo de áreas naturales protegidasS

Effect of Organic Nutrition in the Nursery Growth and Nutrimental Content of Native Avocados of Ometepec, Guerrero, Mexico

In Mexico, there are several types of wild and criollo avocados that constitute a genetic heritage of this species; these avocados currently grow in an unordered manner on farmer's lands and in backyards, and they need to be studied as they are being lost because of agricultural activities and edaphoclimatic and phytosanitary factors. On the other hand, in orchards and avocado nurseries, high amounts of chemical fertilizers and pesticides are used affecting the physicochemical and microbiological properties of the soil, modifying the flora and fauna and polluting aquifers and springs that cause health problems among consumers. Therefore, it is very important to have a more friendly agriculture with the nature. The aim of this work was to evaluate under nursery conditions, the effect of organic fertilizers on 12 genotypes (rootstocks) of native avocados of Ometepec, Guerrero, Mexico, under an experimental design of random blocks, with four treatments: T1: sheep manure,T2: Bovine manure, T3: mycorrhizae and T4 (control: water) in four replicates. The variables were: plant height (PH), stem diameter (SD), number of leaves: young (NYL) and mature (NML) per plant; and the content of NO3-, K+, Ca2+ and Na+ ions obtained by petiole extraction, and the chlorophyll content measured with SPAD, in young (CYL) and mature (CML) leaves. Additionally, an analysis of variance and Tukey mean tests (P ≤ 0.01 and 0.05) and LSD (P ≤ 0.05) were done. It was found that sheep manure was superior to other treatments in PH (76.7 cm), SD (7.2 mm), NYL (6.5 leaves/plant), NML (18.4 leaves/plant), CML (40.2 SPAD) and Ca2+(1495ppm). In conclusion, the sheep manure was better than the bovine, mycorrhiza and control (water) as it affected positively the behavior of rootstocks in plant height, stem diameter and number of young and mature leaves. In addition, organic nutrition showed no significant response in the chlorophyll content of young and mature leaves. Young leaves only reached 50% of the chlorophyll content compared to mature leaves