Using microstructures and composition to decipher the alterations of rodent teeth in modern regurgitation pellets—a good news-bad news story

Rodent accumulations are widely used for palaeoenvironmental reconstructions. But these accumulations are created through the activity of predators (carnivorous mammals, birds of prey), the predation and digestion of which modify the preservation of bones and teeth. The microstructures of dentine and enamel, as well as the mineralogy and composition of non-digested and digested Rodent teeth extracted from modern regurgitation pellets collected at Olduvai (Tanzania) from a bird of prey (Bubo sp.) are compared. Scanning electron microscopy (SEM), Electron Probe Micro Analysis (EPMA) and Raman spectrometry were used. The modifications induced by the digestion process are variable and depend on the tissue (enamel, dentine), tooth (incisor, molar) and the predator. For a given tissue of a tooth, the estimation of the intensity of the alteration varies according to the selected criteria. To classify the digested teeth in categories based on a single parameter to reconstruct environment is still subjective, even for modern accumulations. Moreover, to identify the interplay of diverse parameters to avoid biases in reconstructions is difficult

Big Neural Networks Waste Capacity

This article exposes the failure of some big neural networks to leverage added capacity to reduce underfitting. Past research suggest diminishing returns when increasing the size of neural networks. Our experiments on ImageNet LSVRC-2010 show that this may be due to the fact there are highly diminishing returns for capacity in terms of training error, leading to underfitting. This suggests that the optimization method - first order gradient descent - fails at this regime. Directly attacking this problem, either through the optimization method or the choices of parametrization, may allow to improve the generalization error on large datasets, for which a large capacity is required

A Test of Collective Rationality for Multi-Person Households

This paper provides a test of efficiency of consumption decisions in households with many decision-makers. It also presents a method of determining the number of these decision-makers. Information on some distribution factors in needed to implement this approach.Intra-household allocation, Collective model, Polygamy, Extended family, Pareto optimality

A new species of Cololejeunea (Lejeuneaceae: Cololejeuneoideae) from Panama

A new species of Cololejeunea section Protocolea, is described from Cerro Fábrega in Panama. The diagnostic characteristics of C. tixierii are lobes ovate-lanceolate, lobules never inflate but explanate or folded without forming a keel, reaching about half of the lobe length and perianth only faintly keeled at maturity

Hepaticae of Cerro Venamo, Venezuela, collected by J. Steyermark

A revision of herbarium material (NY) from Cerro Venamo, Venezuela (5°59’ N, 61°23’ W, 1890 m) yielded 77 hepatic species in 44 genera and 13 families. Most species have a neotropical distribution (75,32%), 6,49%, are pantropical and 9,09% are reported only from the tepuis

Low-Cost Experiments with Everyday Objects for Homework Assignments

We describe four classical undergraduate physics experiments that were done with everyday objects and low-cost sensors: mechanical oscillations, transmittance of light through a slab of matter, beam deformation under load, and thermal relaxation due to heat loss. We used these experiments to train students for experimental homework projects but they could be used and expanded in a variety of contexts: lecture demonstrations, low cost students' labs, science projects, distance learning courses...Comment: details on students where added : a section dedicated to the student difficulties and general feedback on this teaching unit. Minor typos were fixed. Published in Physics Educatio