Varying constants, Gravitation and Cosmology

Fundamental constants are a cornerstone of our physical laws. Any constant varying in space and/or time would reflect the existence of an almost massless field that couples to matter. This will induce a violation of the universality of free fall. It is thus of utmost importance for our understanding of gravity and of the domain of validity of general relativity to test for their constancy. We thus detail the relations between the constants, the tests of the local position invariance and of the universality of free fall. We then review the main experimental and observational constraints that have been obtained from atomic clocks, the Oklo phenomenon, Solar system observations, meteorites dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic microwave background and big bang nucleosynthesis. At each step we describe the basics of each system, its dependence with respect to the constants, the known systematic effects and the most recent constraints that have been obtained. We then describe the main theoretical frameworks in which the low-energy constants may actually be varying and we focus on the unification mechanisms and the relations between the variation of different constants. To finish, we discuss the more speculative possibility of understanding their numerical values and the apparent fine-tuning that they confront us with.Comment: 145 pages, 10 figures, Review for Living Reviews in Relativit

Optimal foraging and community structure: implications for a guild of generalist grassland herbivores

A particular linear programming model is constructed to predict the diets of each of 14 species of generalist herbivores at the National Bison Range, Montana. The herbivores have body masses ranging over seven orders of magnitude and belonging to two major taxa: insects and mammals. The linear programming model has three feeding constraints: digestive capacity, feeding time and energy requirements. A foraging strategy that maximizes daily energy intake agrees very well with the observed diets. Body size appears to be an underlying determinant of the foraging parameters leading to diet selection. Species that possess digestive capacity and feeding time constraints which approach each other in magnitude have the most generalized diets. The degree that the linear programming models change their diet predictions with a given percent change in parameter values (sensitivity) may reflect the observed ability of the species to vary their diets. In particular, the species which show the most diet variability are those whose diets tend to be balanced between monocots and dicots. The community-ecological parameters of herbivore body-size ranges and species number can possibly be related to foraging behavior.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47765/1/442_2004_Article_BF00377109.pd

Current concepts in locking plate fixation of proximal humerus fractures

Despite numerous available treatment strategies, the management of complex proximal humeral fractures remains demanding. Impaired bone quality and considerable comorbidities pose special challenges in the growing aging population. Complications after operative treatment are frequent, in particular loss of reduction with varus malalignment and subsequent screw cutout. Locking plate fixation has become a standard in stabilizing these fractures, but surgical revision rates of up to 25% stagnate at high levels. Therefore, it seems of utmost importance to select the right treatment for the right patient. This article provides an overview of available classification systems, indications for operative treatment, important pathoanatomic principles, and latest surgical strategies in locking plate fixation. The importance of correct reduction of the medial cortices, the use of calcar screws, augmentation with bone cement, double-plate fixation, and auxiliary intramedullary bone graft stabilization are discussed in detail

La Comprensión de los Homicidios en América Latina: ¿Pobreza o Institucionalidad? Understanding homicides in Latin America: poverty or institutionalization?

Los homicidios ocurren en todo el mundo, pero no están homogéneamente distribuidos, cambian por zonas geográficas: continentes, países, regiones; en periodos de tiempo largos o cortos o por lo grupos sociales: edad, sexo, clase social o etnia. ¿Por qué en unos países hay más homicidios que en otros? ¿Por qué en unos países disminuyen los asesinatos y en otros se incrementan? Las explicaciones sociales de la violencia han tenido dos vertientes fundamentales: las teorías que la atribuyen a la pobreza y la desigualdad y las teorías de la institucionalidad o las normas sociales. Para discutir esas teorías el artículo analiza y compara los cambios ocurridos en Colombia, Venezuela y Brasil en la primera década del siglo XXI donde respectivamente disminuye, aumenta y se mantiene igual la tasa de homicidios. Utilizando la medición de seis variables (pobreza, desigualdad, desempleo, riqueza nacional, desarrollo humano y gobierno de la ley) y la técnica del análisis de trayectorias se encontró que la institucionalidad tiene una mayor fuerza explicativa en los cambios observados que la pobreza y la desigualdad. El texto concluye que la pobreza o la desigualdad influyen en la criminalidad y en los homicidios, aunque no de manera directa, sino mediadas por las instituciones.<br>Homicides occur the world over, but they are not homogeneously distributed by geographical areas (continents, countries, regions), either over long or short periods of time, or in social groups, namely age, gender, social class or ethnicity. Why are there more homicides in some countries than in others? Why do killings increase in some countries, while they decrease in others? There are two fundamental schools of thought for social explanations of crime and violence: those attributing its origins to poverty and inequality and those blaming institutionalization or social norms. To discuss these theories, this paper analyzes and compares the changes in Colombia, Venezuela and Brazil in the first decade of the twenty-first century, where the homicide rate has decreased, increased and remained the same, respectively. Using the measurement of six variables (poverty, inequality, unemployment, national wealth, human development and the rule of law) and the technique of trajectory analysis, the results revealed that institutionalization is more to blame for the change than poverty and inequality. The text concludes that poverty and inequality affect crime and homicides, although not directly, but mediated by the institutions instead