Symmetry Nonrestoration in a Resummed Renormalized Theory at High Temperature

We reinvestigate the interesting phenomenon of symmetry nonrestoration at high temperature in the multifield O(N_1) X O(N_2) model. We apply modified self-consistent resummation (MSCR) in order to obtain the scalar dressed masses and find in what circumstances a resummed multifield theory which has symmetry (non)restoration can be renormalized. It is shown that, aside from the consistency of the MSCR method, the basic ingredient that guarantees the renormalization of a multifield model within a resummation approach is the T^2 mass behavior of field theory at high temperature.Comment: 14 pages, 1 ps figure, revtex, Phys. Rev. D versio

Testing Luminescence Dating Methods for Small Samples from Very Young Fluvial Deposits

The impetus behind this study is to understand the sedimentological dynamics of very young fluvial systems in the Amazon River catchment and relate these to land use change and modern analogue studies of tidal rhythmites in the geologic record. Initial quartz optically stimulated luminescence (OSL) dating feasibility studies have concentrated on spit and bar deposits in the Rio Tapajós. Many of these features have an appearance of freshly deposited pristine sand, and these observations and information from anecdotal evidence and LandSat imagery suggest an apparent decadal stability. The characteristics of OSL from small (~5 cm) sub-samples from ~65 cm by ~2 cm diameter vertical cores are quite remarkable. Signals from medium-sized aliquots (5 mm diameter) exhibit very high specific luminescence sensitivity, have excellent dose recovery and recycling, essentially independent of preheat, and show minimal heat transfer even at the highest preheats. These characteristics enable measurement of very small signals with reasonable precision and, using modified single-aliquot regenerative-dose (SAR) approaches, equivalent doses as low as ~4 mGy can be obtained. Significant recuperation is observed for samples from two of the study sites and, in these instances, either the acceptance threshold was increased or growth curves were forced through the origin; recuperation is considered most likely to be a measurement artefact given the very small size of natural signals. Dose rates calculated from combined inductively coupled plasma mass spectrometry/inductively coupled plasma optical emission spectrometry (ICP-MS/ICP-OES) and high-resolution gamma spectrometry range from ~0.3 to 0.5 mGya−1 , and OSL ages for features so far investigated range from 13 to 34 years to several 100 years. Sampled sands are rich in quartz and yields of 212–250 µm or 250–310 µm grains indicate high-resolution sampling at 1–2 cm intervals is possible. Despite the use of medium-sized aliquots to ensure the recovery of very dim natural OSL signals, these results demonstrate the potential of OSL for studying very young active fluvial processes in these settings

Maximal acceleration or maximal accelerations?

We review the arguments supporting the existence of a maximal acceleration for a massive particle and show that different values of this upper limit can be predicted in different physical situations.Comment: 13 pages, Latex, to be published in Int. J. Mod. Phys.

Phase separation in asymmetrical fermion superfluids

Motivated by recent developments on cold atom traps and high density QCD we consider fermionic systems composed of two particle species with different densities. We argue that a mixed phase composed of normal and superfluid components is the energetically favored ground state. We suggest how this phase separation can be used as a probe of fermion superfluidity in atomic traps.Comment: 9 pages, LaTeX2e, version to appear in Phys.Rev.Let

La formacion de profesores de biologia a través del diseño, implementación y sistematización de unidades didácticas

En los procesos de formación de los futuros profesores, la planificación de su práctica y posterior reflexión se constituye en un aspecto fundamental que promoverá una educación en ciencias con calidad. Así, el desarrollo de una Unidad Didáctica (UD) se convierte en una experiencia de formación docente de los estudiantes del Proyecto Curricular Licenciatura en Biología de la Universidad Distrital Francisco José de Caldas (Bogotá). La (UD) recorre tres etapas: Planificación, implementación y sistematización. El resultado del trabajo permite al maestro en formación, reflexionar acerca de su práctica desde los presupuestos de la I-A, su papel como maestro y los retos que generan los procesos de enseñanza y aprendizaje de las ciencias en relación con los componentes epistemológico, disciplinar y didáctico, y sus implicaciones en la sociedad