Models and Simulations in Material Science: Two Cases Without Error Bars

We discuss two research projects in material science in which the results cannot be stated with an estimation of the error: a spectro- scopic ellipsometry study aimed at determining the orientation of DNA molecules on diamond and a scanning tunneling microscopy study of platinum-induced nanowires on germanium. To investigate the reliability of the results, we apply ideas from the philosophy of models in science. Even if the studies had reported an error value, the trustworthiness of the result would not depend on that value alone.Comment: 20 pages, 2 figure

Civil-Military Relations in a Civilized State: Panama

This article traces and analyzes civil-military relations in Panama. After a brief overview of the role of the National Guard in the country politics, the article concentrates on political developments since the 1989 U.S. invasion to overthrow the Noriega regime and the subsequent elimination of the Panamanian military. The study seeks to shed light on political life in an armyless and politically and socially fractionalized country occupying a sensitive strategic location. The concluding part of the study speculates on the possibility that terrorism, domestic security concerns, and regional considerations may prompt Washington and Panamanian leaders to reverse the decision to abolish the country\u27s military institution

Interplay between optical, viscous and elastic forces on an optically trapped Brownian particle immersed in a viscoelastic fluid

We provide a detailed study of the interplay between the different interactions which appear in the Brownian motion of a micronsized sphere immersed in a viscoelastic fluid measured with optical trapping interferometry. To explore a wide range of viscous, elastic and optical forces, we analyze two different viscoelastic solutions at various concentrations, which provide a dynamic polymeric structure surrounding the Brownian sphere. Our experiments show that, depending of the fluid, optical forces, even if small, slightly modify the complex modulus at low frequencies. Based on our findings, we propose an alternative methodology to calibrate this kind of experimental set-up when non-Newtonian fluids are used. Understanding the influence of the optical potential is essential for a correct interpretation of the mechanical properties obtained by optically-trapped probe-based studies of biomaterials and living matter.Comment: Accepted for publication in Applied Physics Letter

Weak topologies for Carath\'eodory differential equations. Continuous dependence, exponential Dichotomy and attractors

We introduce new weak topologies and spaces of Carath\'eodory functions where the solutions of the ordinary differential equations depend continuously on the initial data and vector fields. The induced local skew-product flow is proved to be continuous, and a notion of linearized skew-product flow is provided. Two applications are shown. First, the propagation of the exponential dichotomy over the trajectories of the linearized skew-product flow and the structure of the dichotomy or Sacker-Sell spectrum. Second, how particular bounded absorbing sets for the process defined by a Carath\'eodory vector field $f$ provide bounded pullback attractors for the processes with vector fields in the alpha-limit set, the omega-limit set or the whole hull of $f$. Conditions for the existence of a pullback or a global attractor for the skew-product semiflow, as well as application examples are also given.Comment: 34 page

The influence of teachers\u27 beliefs on literacy instruction for at-risk first graders: A multiple case study

Through a multiple case study design the influence of teachers\u27 beliefs on literacy instruction for at-risk first graders was examined and described. A volunteer sample included five female teachers who taught in different high risk schools within the same school district. Five research questions guided the study: (1) What are teachers\u27 beliefs about instructing young at-risk children to read and write? (2) What do teachers say they do as they instruct young at-risk children to read and write? (3) What do teachers actually do as they instruct young at-risk children to read and write? (4) What influences teachers\u27 instructional decisions as they teach young at-risk children to read and write? (5) Are there congruencies between teachers\u27 stated beliefs and their practice?;Data were collected from interviews, observations, questionnaires and a reflective activity over an academic year. Through the constant comparative method twelve general findings emerged: (1) Teachers must possess an understanding of the individual needs of at-risk children and address those needs; (2) Teachers must recognize and build on children\u27s individual strengths; (3) Teachers should nurture children\u27s enthusiasm for learning to read and write; (4) The learning process should begin at the appropriate developmental level; (5) At-risk children should be continuously stimulated in order to build confidence necessary for learning. A structured environment is important to accomplishing this goal; (6) At-risk children break the bonds of at-riskness by becoming literate; (7) Literacy instructional theory does not influence teachers\u27 practice as much as their beliefs; (8) There is no single method of literacy instruction for at-risk children, a combination of pedagogical approaches best serves their literacy needs; (9) Teacher modeling is a positive motivational factor for at-risk children learning to read and write; (10) All at-risk children can learn; Other findings indicated: (1) Teachers\u27 literacy instructional decisions are influenced by multiple factors; (2) There are congruencies between teachers\u27 stated beliefs and practice; The five case studies validate the work of previous researchers who suggested that teachers\u27 beliefs are an integral part of classroom practice. The teachers provided documented instances of the congruency between beliefs and classroom practice

Gravimetric and Spectrophotometric Determinations of Curcuminoid Solubilities in Ethanol

Curcumin, a natural extract of turmeric, has many purported health benefits, but a part of its limited broader applicability is frequently attributed its poor solubility in water. This lack of solubility is one of the primary drives for the exploration and synthesis of new analogues, seeking more greater aqueous solubility. Bioactivity assays frequently make use of ethanol solutions of these curcuminoids, followed by subsequent dilution in water. We have explored the solubility of an array of curcuminoids in ethanol to ascertain substituent effects on this property. Additionally, a few curcuminoids containing a saturated ring in their backbone have tested to determine its impact on solubility. Both gravimetric and spectrophotometric means have been utilized to measure solubility. Beer\u27s Law plots of all local maxima in the UV-vis spectra of each curcuminoid have been produced to track linearity of the Absorbance-concentration relationship at each wavelength and correlation of each with gravimetrically determined solubilities

Insights on Reticulate Evolution in Ferns, with Special Emphasis on the Genus Ceratopteris

The history of life is often viewed as a evenly branching tree; however, in reality it is more like a tangled hedgerow. Many groups of organisms are known to have such a net-like or reticulate evolutionary history, but it is particularly common in ferns and lycophytes (also known as pteridophytes). This dissertation investigates how net-like evolution affects different groups of ferns, with a special emphasis on the model species C-fern (Ceratopteris richardii, also called the antler or water sprite fern). Genomic data are utilized to under-stand hybridization, cryptic species and reticulate evolution in two groups of ferns. The C-fern is shown to be a potential hybrid species, which has important implications for future research using this model organism