Osteosclerosis in the extinct Cayaoa Bruneti (Aves, anseriformes) : insights on behavior and fligftlessness

Fil: Mendoza, Ricardo de. División Paleontología Vertebrados. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La PlataFil: Tambussi, Claudia Patricia. Centro de Investigaciones en Ciencias de la Tierra (CICTERRA). Universidad Nacional de Córdoba; Argentin

Are biological systems poised at criticality?

Many of life's most fascinating phenomena emerge from interactions among many elements--many amino acids determine the structure of a single protein, many genes determine the fate of a cell, many neurons are involved in shaping our thoughts and memories. Physicists have long hoped that these collective behaviors could be described using the ideas and methods of statistical mechanics. In the past few years, new, larger scale experiments have made it possible to construct statistical mechanics models of biological systems directly from real data. We review the surprising successes of this "inverse" approach, using examples form families of proteins, networks of neurons, and flocks of birds. Remarkably, in all these cases the models that emerge from the data are poised at a very special point in their parameter space--a critical point. This suggests there may be some deeper theoretical principle behind the behavior of these diverse systems.Comment: 21 page

Updated Nucleosynthesis Constraints on Unstable Relic Particles

We revisit the upper limits on the abundance of unstable massive relic particles provided by the success of Big-Bang Nucleosynthesis calculations. We use the cosmic microwave background data to constrain the baryon-to-photon ratio, and incorporate an extensively updated compilation of cross sections into a new calculation of the network of reactions induced by electromagnetic showers that create and destroy the light elements deuterium, he3, he4, li6 and li7. We derive analytic approximations that complement and check the full numerical calculations. Considerations of the abundances of he4 and li6 exclude exceptional regions of parameter space that would otherwise have been permitted by deuterium alone. We illustrate our results by applying them to massive gravitinos. If they weigh ~100 GeV, their primordial abundance should have been below about 10^{-13} of the total entropy. This would imply an upper limit on the reheating temperature of a few times 10^7 GeV, which could be a potential difficulty for some models of inflation. We discuss possible ways of evading this problem.Comment: 40 pages LaTeX, 18 eps figure

First Results from KamLAND: Evidence for Reactor Antineutrino Disappearance

KamLAND has been used to measure the flux of $\bar{\nu}_e$'s from distant nuclear reactors. In an exposure of 162 ton$\cdot$yr (145.1 days) the ratio of the number of observed inverse $\beta$-decay events to the expected number of events without disappearance is $0.611\pm 0.085 {\rm (stat)} \pm 0.041 {\rm (syst)}$ for $\bar{\nu}_e$ energies $>$ 3.4 MeV. The deficit of events is inconsistent with the expected rate for standard $\bar{\nu}_e$ propagation at the 99.95% confidence level. In the context of two-flavor neutrino oscillations with CPT invariance, these results exclude all oscillation solutions but the `Large Mixing Angle' solution to the solar neutrino problem using reactor $\bar{\nu}_e$ sources

Darwin’s progress and the problem of slavery

Legendary as a ‘genius’ out of time, Charles Darwin is said to have revolutionized our understanding of life on earth by explaining nature-history as the purposeless product of directionless variation naturally selected through a chancy struggle for existence. Yet, whatever may be deduced from his theory of natural selection as understood today, Darwin himself was not bound by any such conclusions. His vision of nature-history, for all its haphazardness, was directional, meliorative and hopeful. In the 1830s he went out of his way to develop privately a subversive theory of human evolution, and he pursued the subject with tenacity for three decades before publishing The descent of man in 1871. Underpinning his research was a belief in racial brotherhood rooted in the greatest moral movement of the age, for the abolition of slavery. Darwin extended the abolitionists’ common-descent image to the rest of life, making not just the races, but all races, kin. Human slavery, however, did not evolve into or out of existence. To Darwin it was a ‘sin’ to ‘expiate’ by moral action, and the Origin of species was written with a view towards undermining slavery’s creationist ideologues, most notably the Harvard professor Louis Agassiz. Intractable slavery collided with Darwin’s post-Christian progressivism in the US Civil War, clouding his hopes for humanity, but the Northern victory in 1865 enabled him to carry ‘the grand idea of God hating sin and loving righteousness’ into The descent of man, where the driving of formerly enslaved races out of existence is naturalized as a byproduct of historical progress in which ‘virtue will be triumphant’ at last