Estudio de la propagación de ondas guiadas sobre un riel ferroviario

La propagación de ondas elásticas en estructuras donde por lo menos una de las dimensiones es mucho mayor que las otras dos, las llamadas ondas guiadas, es un tema actualmente vinculado atécnicas de Ensayos No Destructivos. Varios sistemas basados en este tipo de ondas permiten definir regiones con daño en forma rápida solo con una entrada que será emisora receptora, esto tiene gran ventaja en el estudio de estructuras de difícil acceso. Otra de las características de los métodos de detección de daño basados en la propagación de este tipo de ondas es que permite también escanear con rapidez grandes regiones de inspección. Existen muchas estructuras de gran interés en ingeniería, en las cuales se puede aplicar técnicas de inspección basadas en ondas guiadas, tubos, cables, rieles, recipientes a presión, entre otros. El estudio de este tipo de ondas fue iniciado por Lamba comienzos del siglo XX, el mismo propuso una solución analítica para representar la propagación espacial-temporal de este tipode ondas para el caso de una placa. La propagación de ondas guiadas en estas estructuras tienen la característica de ser muy sensible a la forma de la dimensión finita de la estructura en análisis. El estudio de estas ondas es fundamental en el cálculo de las llamadas curvas de dispersión que serán específicaspara cada geometría estudiada. Estas curvas de dispersión permiten describir, dada una excitaciónaplicada sobre la estructura en análisis, en qué ondas modales dicha excitación se va a descomponer.Publicado en: Mecánica Computacional vol. XXXV no.33Facultad de Ingenierí

Silicon startup schools:technocracy, algorithmic imaginaries and venture philanthropy in corporate education reform

Technology companies are investing billions of dollars in educational technology, but also creating their own alternative schools. This article traces the emergence of four prototypical ‘silicon startup schools’ as exemplars of a technocratic mode of corporatized education reform: IBM’s P-TECH, part of its Smarter Cities program; AltSchool, a chain of schools based on ‘makerspaces’ established by a former Google executive; Kahn Lab School, a new ‘experimental’ school launched by the founder of the online Kahn Academy; and XQ Super School Project, a ‘crowdsourcing’ project to redesign American high schools funded philanthropically by the wife of Steve Jobs of Apple. Startup schools are analysed as prototype educational institutions that originate in the culture, discourse and ideals of Silicon Valley venture capital and startup culture, and that are intended to relocate its practices to the whole social, technical, political and economic infrastructure of schooling. These new schools are being designed as scalable technical platforms; funded by commercial ‘venture philanthropy’ sources; and staffed and managed by executives and engineers from some of Silicon Valley’s most successful startups and web companies. Together, they constitute a powerful shared ‘algorithmic imaginary’ that seeks to ‘disrupt’ public schooling through the technocratic expertise of Silicon Valley venture philanthropists

Spectrum and Inoculum Size Effect of a Rapid Antigen Detection Test for Group A Streptococcus in Children with Pharyngitis

BACKGROUND: The stability of the accuracy of a diagnostic test is critical to whether clinicians can rely on its result. We aimed to assess whether the performance of a rapid antigen detection test (RADT) for group A streptococcus (GAS) is affected by the clinical spectrum and/or bacterial inoculum size. METHODS: Throat swabs were collected from 785 children with pharyngitis in an office-based, prospective, multicenter study (2009-2010). We analysed the effect of clinical spectrum (i.e., the McIsaac score and its components) and inoculum size (light or heavy GAS growth) on the accuracy (sensitivity, specificity, likelihood ratios and predictive values) of a RADT, with laboratory throat culture as the reference test. We also evaluated the accuracy of a McIsaac-score-based decision rule. RESULTS: GAS prevalence was 36% (95CI: 33%-40%). The inoculum was heavy for 85% of cases (81%-89%). We found a significant spectrum effect on sensitivity, specificity, likelihood ratios and positive predictive value (p<0.05) but not negative predictive value, which was stable at about 92%. RADT sensitivity was greater for children with heavy than light inoculum (95% vs. 40%, p<0.001). After stratification by inoculum size, the spectrum effect on RADT sensitivity was significant only in patients with light inoculum, on univariate and multivariate analysis. The McIsaac-score-based decision rule had 99% (97%-100%) sensitivity and 52% (48%-57%) specificity. CONCLUSIONS: Variations in RADT sensitivity only occur in patients with light inocula. Because the spectrum effect does not affect the negative predictive value of the test, clinicians who want to rule out GAS can rely on negative RADT results regardless of clinical features if they accept that about 10% of children with negative RADT results will have a positive throat culture. However, such a policy is more acceptable in populations with very low incidence of complications of GAS infection

The Flaveria bidentis β-Carbonic Anhydrase Gene Family Encodes Cytosolic and Chloroplastic Isoforms Demonstrating Distinct Organ-Specific Expression Patterns1[OA]

Carbonic anhydrase (CA) catalyzes the interconversion of CO2 and bicarbonate, the forms of inorganic carbon used by the primary carboxylating enzymes of C3 and C4 plants, respectively. Multiple forms of CA are found in both photosynthetic subtypes; however, the number of isoforms and the location and function of each have not been elucidated for any single plant species. Genomic Southern analyses showed that the C4 dicotyledon Flaveria bidentis ‘Kuntze’ contains a small gene family encoding β-CA and cDNAs encoding three distinct β-CAs, named CA1, CA2, and CA3, were isolated. Quantitative reverse transcription-polymerase chain reactions showed that each member of this β-CA family has a specific expression pattern in F. bidentis leaves, roots, and flowers. CA3 transcripts were at least 50 times more abundant than CA2 or CA1 transcripts in leaves. CA2 transcripts were detected in all organs examined and were the most abundant CA transcripts in roots. CA1 mRNA levels were similar to those of CA2 in leaves, but were considerably lower in roots and flowers. In vitro import assays showed CA1 was imported into isolated pea (Pisum sativum) chloroplasts, whereas CA2 and CA3 were not. These results support the following roles for F. bidentis CAs: CA3 is responsible for catalyzing the first step in the C4 pathway in the mesophyll cell cytosol; CA2 provides bicarbonate for anapleurotic reactions involving nonphotosynthetic forms of phosphoenolpyruvate carboxylase in the cytosol of cells in both photosynthetic and nongreen tissues; and CA1 carries out nonphotosynthetic functions demonstrated by C3 chloroplastic β-CAs, including lipid biosynthesis and antioxidant activity