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

Temporal expression of alternatively spliced forms of tissue factor pathway inhibitor in mice.

BACKGROUND: Mouse tissue factor pathway inhibitor (TFPI) is produced in three alternatively spliced isoforms that differ in domain structure and mechanism for cell surface binding. Tissue expression of TFPI isoforms in mice was characterized as an initial step for identification of their physiological functions. METHODS AND RESULTS: Sequence homology demonstrates that TFPIalpha existed over 430 Ma while TFPIbeta and TFPIgamma evolved more recently. In situ hybridization studies of heart and lung did not reveal any cells exclusively expressing a single isoform. Although our previous studies have demonstrated that TFPIalpha mRNA is more prevalent than TFPIbeta or TFPIgamma mRNA in mouse tissues, western blot studies demonstrated that TFPIbeta is the primary protein isoform produced in adult tissues, while TFPIalpha is expressed during embryonic development and in placenta. Consistent with TFPIbeta as the primary isoform produced within adult vascular beds, the TFPI isoform in mouse plasma migrates like TFPIbeta in SDS-PAGE and mice have a much smaller heparin-releasable pool of plasma TFPIalpha than humans. CONCLUSIONS: The data demonstrate that alternatively spliced isoforms of TFPI are temporally expressed in mouse tissues at the level of protein production. TFPIalpha and TFPIbeta are produced in embryonic tissues and in placenta while adult tissues produce almost exclusively TFPIbeta

Temporal expression of alternatively spliced forms of tissue factor pathway inhibitor in mice.

BACKGROUND: Mouse tissue factor pathway inhibitor (TFPI) is produced in three alternatively spliced isoforms that differ in domain structure and mechanism for cell surface binding. Tissue expression of TFPI isoforms in mice was characterized as an initial step for identification of their physiological functions. METHODS AND RESULTS: Sequence homology demonstrates that TFPIalpha existed over 430 Ma while TFPIbeta and TFPIgamma evolved more recently. In situ hybridization studies of heart and lung did not reveal any cells exclusively expressing a single isoform. Although our previous studies have demonstrated that TFPIalpha mRNA is more prevalent than TFPIbeta or TFPIgamma mRNA in mouse tissues, western blot studies demonstrated that TFPIbeta is the primary protein isoform produced in adult tissues, while TFPIalpha is expressed during embryonic development and in placenta. Consistent with TFPIbeta as the primary isoform produced within adult vascular beds, the TFPI isoform in mouse plasma migrates like TFPIbeta in SDS-PAGE and mice have a much smaller heparin-releasable pool of plasma TFPIalpha than humans. CONCLUSIONS: The data demonstrate that alternatively spliced isoforms of TFPI are temporally expressed in mouse tissues at the level of protein production. TFPIalpha and TFPIbeta are produced in embryonic tissues and in placenta while adult tissues produce almost exclusively TFPIbeta

Development of reaching during mid-childhood from a Developmental Systems perspective

Inspired by the Developmental Systems perspective, we studied the development of reaching during mid-childhood (5-10 years of age) not just at the performance level (i.e., endpoint movements), as commonly done in earlier studies, but also at the joint angle level. Because the endpoint position (i.e., the tip of the index finger) at the reaching target can be achieved with multiple joint angle combinations, we partitioned variability in joint angles over trials into variability that does not (goal-equivalent variability, GEV) and that does (non-goal-equivalent variability, NGEV) influence the endpoint position, using the Uncontrolled Manifold method. Quantifying this structure in joint angle variability allowed us to examine whether and how spatial variability of the endpoint at the reaching target is related to variability in joint angles and how this changes over development. 6-, 8- and 10-year-old children and young adults performed reaching movements to a target with the index finger. Polynomial trend analysis revealed a linear and a quadratic decreasing trend for the variable error. Linear decreasing and cubic trends were found for joint angle standard deviations at movement end. GEV and NGEV decreased gradually with age, but interestingly, the decrease of GEV was steeper than the decrease of NGEV, showing that the different parts of the joint angle variability changed differently over age. We interpreted these changes in the structure of variability as indicating changes over age in exploration for synergies (a family of task solutions), a concept that links the performance level with the joint angle level. Our results suggest changes in the search for synergies during mid-childhood development

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