Procedural embodiment and magic in linear equations

How do students think about algebra? Here we consider a theoretical framework which builds from natural human functioning in terms of embodiment – perceiving the world, acting on it and reflecting on the effect of the actions – to shift to the use of symbolism to solve linear equations. In the main, the students involved in this study do not encapsulate algebraic expressions from process to object, they do not solve ‘evaluation equations’ such as by ‘undoing’ the operations on the left, they do not find such equations easier to solve than , and they do not use general principles of ‘do the same thing to both sides.’ Instead they build their own ways of working based on the embodied actions they perform on the symbols, mentally picking them up and moving them around, with the added ‘magic’ of rules such as ‘change sides, change signs.’ We consider the need for a theoretical framework that includes both embodiment and process-object encapsulation of symbolism and the need for communication of theoretical insights to address the practical problems of teachers and students

A new species of Anastrepha from Amazonia : with redescriptions of A. caudata Stone and A. hendeliana Lima (Diptera: Tephritidae)

Three species of Anastrepha from upper Amazonia are described or redescribed and illustrated. They are considered closely related and are placed in the A. caudata species group. Anastrepha caudata Stone 1942 is redescribed based on the holotype, the only known specimen. Its type locality is probably São Paulo de Olivença in Amazonas, Brazil, not the state or city of São Paulo as previously assumed. Anastrepha hendeliana Lima 1934, new status, is removed from synonymy with A. longicauda Lima 1934 based on specimens from Brazil (Amazonas and Rondonia) and Colombia (Caquetá). The female is described for the first time. Anastrepha brunnealata, n. sp., is described from specimens from Venezuela (Amazonas) and probably Peru (Loreto). Anastrepha longicauda Lima is placed in the dentata species group.Se describen o redescriben e ilustran tres especies de Anastrepha del Amazonia. Ellas están consideradas cercanamente relacionadas y las ubican en el grupo de especies caudata. Se redescribe Anastrepha caudata Stone 1942 basado en el holotipo, el único especimen conocido. La localidad tipo probablemente es São Paulo de Olivença en el Amazonas, Brasil, no el estado o la ciudad de São Paulo como se asumió anteriormente. Se remueve Anastrepha hendeliana Lima 1934, stat. n., de la sinonómia de A. longicauda Lima 1934 basado en especimenes de Brasil (Amazonas y Rondonia) y Colombia (Caquetá). La hembra es descrita por primera vez. Se describe Anastrepha brunnealata, sp. n., de especimenes de Venezuela (Amazonas) y probablemente Peru (Loreto). Se ubica Anastrepha longicauda Lima en el grupo de especies dentata

Varying c and Particle Horizons

We explore what restrictions may impose the second law of thermodynamics on varying speed of light theories. We find that the attractor scenario solving the flatness problem is consistent with the generalized second law at late time.Comment: Latex file, 8 pages, to be published in Physics Letters

Lensing Magnification: Implications for Counts of Submillimeter Galaxies and SZ Clusters

We study lensing magnification of source galaxies by intervening galaxy groups and clusters using a halo model. Halos are modeled with truncated NFW profiles with ellipticity added to their lensing potential and propagated to observable lensing statistics. We present the formalism to calculate observable effects due to a distribution of halos of different masses at different redshifts along the l ine of sight. We calculate the effects of magnification on the number counts of high-redshift galaxies. Using BLAST survey data for submillimeter galaxies (SMGs), we find that magnification affects the steep, high flux par t of the counts by about 60%. The effect becomes much stronger if the intrinsic distribution is signi ficantly steeper than observed. We also consider the effect of this high-redshift galaxy population on contaminating the Sunyaev-Zel'dovich (SZ) signal of massive clusters using the halo model approach. We find that for the majority of clusters expected to be detected with ongoing SZ surveys, there is significant contamination from the Poisson noise due to background SMGs. This contr ibution can be comparable to the SZ increment for typical clusters and can also contaminate the SZ decrement of low mass clusters. Thus SZ observations, especially for the increment part of the SZ spectrum, need to include careful modeling of this irreducible contamination for mass estimation. Lensing further enhances the contamination, especially close to the cores of massive clusters and for very disturbed clusters with large magnification cross-section.Comment: 21 pages, 14 figures, Submitted to MNRA

The fate of (phantom) dark energy universe with string curvature corrections

We study the evolution of (phantom) dark energy universe by taking into account the higher-order string corrections to Einstein-Hilbert action with a fixed dilaton. While the presence of a cosmological constant gives stable de-Sitter fixed points in the cases of heterotic and bosonic strings, no stable de-Sitter solutions exist when a phantom fluid is present. We find that the universe can exhibit a Big Crunch singularity with a finite time for type II string, whereas it reaches a Big Rip singularity for heterotic and bosonic strings. Thus the fate of dark energy universe crucially depends upon the type of string theory under consideration.Comment: 6 pages and 3 figures, discussion on dynamically evolving dilaton and modulus included, references added, version to appear in Physics Letters

On the coefficients of the liquid drop model mass formulae and nuclear radii

The coefficients of different mass formulae derived from the liquid drop model and including or not the curvature energy, the diffuseness correction to the Coulomb energy, the charge exchange correction term, different forms of the Wigner term and different powers of the relative neutron excess $I=(N-Z)/A$ have been determined by a least square fitting procedure to 2027 experimental atomic masses. The Coulomb diffuseness correction $Z^2/A$ term or the charge exchange correction $Z^{4/3}/A^{1/3}$ term plays the main role to improve the accuracy of the mass formula. The Wigner term and the curvature energy can also be used separately for the same purpose. The introduction of an $|I|$ dependence in the surface and volume energies improves slightly the efficiency of the expansion and is more effective than an $I^4$ dependence. Different expressions reproducing the experimental nuclear charge radius are provided. The different fits lead to a surface energy coefficient of around 17-18 MeV and a relative equivalent rms charge radius r$_0$ of 1.22-1.23 fm.Comment: 19 pages, 1 figure, accepted for publication in Nuclear Physics

Senescence in vitro and ionising radiations—the human diploid fibroblast model

The influence of ionising radiations on ageing is still controversial. Since Hayflick established the concept that diploid cells have finite lifespan in vitro, human diploid fibroblast (HDF) cultures have been recognised as a potent experimental model for cytogerontological investigations. In this study HDF cultures in phase II were exposed to acute irradiation with either X-rays on fast neutrons. The replicative potentials and labelling indices with [3H]thymidine were measured post irradiation until the cultures ceased growth in phase III. Cell mortality was measured by cloning. The apparent loss in replicative potential of irradiated mass cultures was wholly attributable to the loss of viable clonogenic cells. The current concept of precocious clonal senescence in vitro as a late effect of irradiation in clonogenic survivors is not supported by the present experiments. Instead, our results suggest that exposure to a single dose of ionising radiations either causes total replicative incapacitation (killing) of HDF cells and their progeny early after irradiation or leaves their replicative potentials unperturbed