The changes we need: Education post COVID-19

The COVID-19 pandemic has caused both unprecendented disruptions and massive changes to education. However, as schools return, these changes may disappear. Moreover, not all of the changes are necessarily the changes we want in education. In this paper, we argue that the pandemic has created a unique opportunity for educational changes that have been proposed before COVID-19 but were never fully realized. We identify three big changes that education should make post COVID: curriculum that is developmental, personalized, and evolving; pedagogy that is student-centered, inquiry-based, authentic, and purposeful; and delivery of instruction that capitalizes on the strengths of both synchronous and asynchronous learning

Is the “3 by 5” Initiative the Best Approach to Tackling the HIV Pandemic?

Background to the debate: The World Health Organization (WHO) and its partners aim to treat 3 million people infected with HIV in poor and middle income countries with antiretroviral treatment by the end of 2005. The ambitious “3 by 5” initiative has had its supporters and its critics since its announcement in 2002

A Spectral Lyapunov Function for Exponentially Stable LTV Systems

This paper presents the formulation of a Lyapunov function for an exponentially stable linear timevarying (LTV) system using a well-defined PD-spectrum and the associated PD-eigenvectors. It provides a bridge between the first and second methods of Lyapunov for stability assessment, and will find significant applications in the analysis and control law design for LTV systems and linearizable nonlinear time-varying systems

Tubular Organization of SnO2 Nanocrystallites for Improved Lithium Ion Battery Anode Performace

Porous tin oxide nanotubes were obtained by vacuum infiltration of tin oxide nanoparticles into porous aluminum oxide membranes, followed by calcination. The porous tin oxide nanotube arrays so prepared were characterized by FE-SEM, TEM, HRTEM, and XRD. The nanotubes are open-ended, highly ordered with uniform cross-sections, diameters and wall thickness. The tin oxide nanotubes were evaluated as a substitute anode material for the lithium ion batteries. The tin oxide nanotube anode could be charged and discharged repeatedly, retaining a specific capacity of 525 mAh/g after 80 cycles. This capacity is significantly higher than the theoretical capacity of commercial graphite anode (372 mAh/g) and the cyclability is outstanding for a tin based electrode. The cyclability and capacities of the tin oxide nanotubes were also higher than their building blocks of solid tin oxide nanoparticles. A few factors accounting for the good cycling performance and high capacity of tin oxide nanotubes are suggested.Singapore-MIT Alliance (SMA

Template Synthesis of Tubular Sn-Based Nanostructures for Lithium Ion Storage

We report herewith the preparation of SnO₂ nanotubes with very good shape and size control, and with and without a carbon nanotube overlayer, The SnO₂-core/carbon-shell nanotubes are excellent reversible Li ion storage compounds combining the best features of carbon (cyclability) and SnO₂ (capacity) to deliver a high specific capacity (~540-600 mAh/g) simultaneous with good cyclability (0.0375% capacity loss per cycle).Singapore-MIT Alliance (SMA

Prediction of Neighbor-Dependent Microbial Interactions From Limited Population Data

Modulation of interspecies interactions by the presence of neighbor species is a key ecological factor that governs dynamics and function of microbial communities, yet the development of theoretical frameworks explicit for understanding context-dependent interactions are still nascent. In a recent study, we proposed a novel rule-based inference method termed the Minimal Interspecies Interaction Adjustment (MIIA) that predicts the reorganization of interaction networks in response to the addition of new species such that the modulation in interaction coefficients caused by additional members is minimal. While the theoretical basis of MIIA was established through the previous work by assuming the full availability of species abundance data in axenic, binary, and complex communities, its extension to actual microbial ecology can be highly constrained in cases that species have not been cultured axenically (e.g., due to their inability to grow in the absence of specific partnerships) because binary interaction coefficients – basic parameters required for implementing the MIIA – are inestimable without axenic and binary population data. Thus, here we present an alternative formulation based on the following two central ideas. First, in the case where only data from axenic cultures are unavailable, we remove axenic populations from governing equations through appropriate scaling. This allows us to predict neighbor-dependent interactions in a relative sense (i.e., fractional change of interactions between with versus without neighbors). Second, in the case where both axenic and binary populations are missing, we parameterize binary interaction coefficients to determine their values through a sensitivity analysis. Through the case study of two microbial communities with distinct characteristics and complexity (i.e., a three-member community where all members can grow independently, and a four-member community that contains member species whose growth is dependent on other species), we demonstrated that despite data limitation, the proposed new formulation was able to successfully predict interspecies interactions that are consistent with experimentally derived results. Therefore, this technical advancement enhances our ability to predict context-dependent interspecies interactions in a broad range of microbial systems without being limited to specific growth conditions as a pre-requisite

Minimal Interspecies Interaction Adjustment (MIIA): Inference of Neighbor-Dependent Interactions in Microbial Communities

An intriguing aspect in microbial communities is that pairwise interactions can be influenced by neighboring species. This creates context dependencies for microbial interactions that are based on the functional composition of the community. Context dependent interactions are ecologically important and clearly present in nature, yet firmly established theoretical methods are lacking from many modern computational investigations. Here, we propose a novel network inference method that enables predictions for interspecies interactions affected by shifts in community composition and species populations. Our approach first identifies interspecies interactions in binary communities, which is subsequently used as a basis to infer modulation in more complex multi-species communities based on the assumption that microbes minimize adjustments of pairwise interactions in response to neighbor species. We termed this rule-based inference minimal interspecies interaction adjustment (MIIA). Our critical assessment of MIIA has produced reliable predictions of shifting interspecies interactions that are dependent on the functional role of neighbor organisms. We also show how MIIA has been applied to a microbial community composed of competing soil bacteria to elucidate a new finding that – in many cases – adding fewer competitors could impose more significant impact on binary interactions. The ability to predict membership-dependent community behavior is expected to help deepen our understanding of how microbiomes are organized in nature and how they may be designed and/or controlled in the future

Diseño de elementos estructurales de acero sometidos a flexo-compresión : desarrollo teórico y estudio comparativo

Esta memoria presenta, en primer lugar, la teoría y los principios de la estabilidad estructural de los elementos flexo-comprimidos. Incluye tanto los nuevos métodos utilizados para el análisis y diseño de los "beam-columns" como su proceso de desarrollo e incorporación al Eurocódigo 3 (ec3 2005) y a la norma americana (AISC LRFD 1994). En segundo lugar, se realiza un estudio exhaustivo del factor de momento uniforme equivalente de pandeo lateral (FMUE). Este factor se emplea para determinar el momento critico elástico, y éste a su vez se emplea para verificar el estado limite último de un elemento sometido a flexión pura y a flexo-compresión. De la revisión bibliográfica se desprende que las normas pueden proporcionar valores de FMUE muy conservadores en vigas simplemente apoyadas, y no conservadores en vigas con apoyos diseñados para prevenir la flexión lateral y el alabeo. Con el propósito de aclarar las situaciones en donde los FMUE de las normas aparecen contradictorios con los resultados computacionales recientes, se brinda en esta memoria un conjunto de valores de FMUE, que fueron obtenidos usando el Método de Elementos Finitos y la técnica de Diferencias Finitas, una atención muy especial se ha puesto en los casos donde la flexión lateral y el alabeo son impedidos en los apoyos del elemento puesto que son pocos los resultados que existen para estos casos. Una de las grandes ventajas de la norma americana (AISC LRFD 1994) y de la norma británica CBS 5950-1 2000) es que proporcionan expresiones sencillas para determinar el FMUE para cualquier distribución de momentos; sin embargo, estas expresiones no toman en cuentan las restricciones de los apoyos extremos del elemento. En esta memoria, se plantea una nueva expresión general para calcular el FMUE, que es aplicable a cualquier distribución de momentos y condiciones de enlaces, y que proporciona mejores resultados que las expresiones dadas por el AISC LRFD (1994) y BS 5950-1 (2000). Por último, con el propósito de identificar similitudes y diferencias en las filosofías de diseño del AISC LRFD (1994) y ec3 (2005), se realiza en este trabajo un estudio comparativo de los estados límites últimos de los elementos sometidos a compresión pura, flexión pura y flexo-compresión. Para cuantificar la diferencia en resistencia, se trabajó con perfiles laminados de secciones H e I, los cuales fueron analizados con diferentes valores de esbeltez y con los casos más frecuentes de distribuciones lineales y parabólicas de momentos. Los resultados son presentados gráficamente en diagramas de interacción para facilitar su interpretación. Este estudio comparativo muestra que las capacidades resistentes dadas por el AISC LRFD (1994) y los dos métodos el EC3 (2005) pueden diferir apreciablemente cuando el valor de la esbeltez es alto y el elemento flexo-comprimido está sometido a una distribución lineal de momento bi-triangular.Trabajo de investigació