Minimal nets and minimal minimal surfaces

The 3-periodic nets of genus 3 ('minimal nets') are reviewed and their symmetries re-examined. Although they are all crystallographic, seven of the 15 only have maximum-symmetry embeddings if some links are allowed to have zero length. The connection bet

Recursos escolares y el desempeño en Lengua de la educación primaria. Resultados ONE 2010

Proporcionar información útil para acrecentar el conocimiento acerca de los factores que explican el nivel y las desigualdades en el desempeño de los alumnos

Polycontinuous geometries for inverse lipid phases with more than two aqueous network domains

Inverse bicontinuous cubic phases with two aqueous network domains separated by a smooth bilayer are firmly established as equilibrium phases in lipid/water systems. The purpose of this article is to highlight the generalisations of these bicontinuous geometries to polycontinuous geometries, which could be realised as lipid mesophases with three or more network-like aqueous domains separated by a branched bilayer. An analysis of structural homogeneity in terms of bilayer width variations reveals that ordered polycontinuous geometries are likely candidates for lipid mesophase structures, with similar chain packing characteristics to the inverse micellar phases (that once were believed not to exist due to high packing frustration). The average molecular shape required by global geometry to form these multi-network phases is quantified by the surfactant shape parameter, v/(al); we find that it adopts values close to those of the known lipid phases. We specifically analyse the 3etc(187 193) structure of hexagonal symmetry P63 /mcm with three aqueous domains, the 3dia(24 220) structure of cubic symmetry I 3d composed of three distorted diamond networks, the cubic chiral 4srs(24 208) with cubic symmetry P4232 and the achiral 4srs(5 133) structure of symmetry P42/nbc, each consisting of four intergrown undistorted copies of the srs net (the same net as in the QGII gyroid phase). Structural homogeneity is analysed by a medial surface approach assuming that the head-group interfaces are constant mean curvature surfaces. To facilitate future experimental identification, we provide simulated SAXS scattering patterns that, for the 4srs(24 208) and 3dia(24 220) structures, bear remarkable similarity to those of bicontinuous QGII-gyroid and QDII-diamond phases, with comparable lattice parameters and only a single peak that cannot be indexed to the well-established structures. While polycontinuous lipid phases have, to date, not been reported, the likelihood of their formation is further indicated by the reported observation of a solid tricontinuous mesoporous silicate structure, termed IBN-9, which formed in the presence of surfactants [Han et al., Nat. Chem., 2009, 1, 123]

Investigation of the micro- and nano-scale architecture of cellulose hydrogels with plant cell wall polysaccharides: a combined USANS/SANS study

The structure of protiated, deuterated and composite cellulose hydrogels with plant cell wall (PCW) polysaccharides has been investigated by combined USANS/SANS experiments, complemented with spectroscopy and microscopy. The broad size range covered by the USANS/SANS experiments enabled the identification of cellulose architectural features in the cross-sectional and longitudinal directions. In the cross-sectional direction, cellulose ribbons are modelled as core-shell structures. Xyloglucan and mixed linkage glucans interfere with the cellulose crystallisation process, reducing the crystallinity and establishing cross-bridges between ribbons. However, only xyloglucan is able to establish strong interactions with the cellulose microfibrils, affecting the properties of the ribbons' core. Longitudinally, the ribbons are hypothesised to present a ca. 1.4-1.5 μm periodic twist with a crystallite length of ca. 140-180 nm for the individual microfibrils. These results highlight the potential of USANS/SANS techniques to investigate the multi-scale architecture of cellulose hydrogels as well as the interaction mechanism between cellulose and PCW polysaccharides

Solução do Problema do sistema Mola-Massa com uso do método de Diferenças Finitas

O Método de Diferenças Finitas é um método consagradopor resolver equações lineares de segunda ordem com coeficientesconstantes, tais equações se fazem essenciais porque servem comomodelos matemáticos de alguns processos físicos. Este tabalho traz asoluções analítica e numérica de um Problema de Valor Inicial pararesolver o sistema mola-massa

Aplicação do Método de Diferenças Finitas para Calcular a Deformação de Placas

Neste trabalho obteve-se a solução numérica da Equação Diferencial Parcial de quarta ordem, que controla a deflexão de placas, via o Método de Diferenças Finitas. Após a discretização da placa gerou-se um sistema de equações lineares, cuja solução foi obtida por meio do método de Gauss-Seidel, com uso de um algoritmo implementado no software MatLab e comparada com o já consagrado software Robot Structural Analysis

Small angle neutron scattering study of a gehlenite-based ceramic fabricated from industrial waste

This paper presents a small angle neutron scattering (SANS) study of a novel porous gehlenite-based ceramic, synthesised from a homogeneous powder mixture of soda-lime-silicate (SLS) glass, α-alumina, calcite and calcium fluoride via solid-state sintering at 1200 °C. The products of sintering at single temperatures from 600 to 1200 °C are examined by X-ray diffraction (XRD). Sintering of the mixture below 1200 °C forms two intermediate phases (Na₂ CaSi₃ O₈ and Ca₄ Si₂ O₇ F₂ ). Nepheline and α-alumina are minor phases in the gehlenite-based ceramic fabricated through sintering at 1200 °C. The microstructure of the gehlenite-based ceramic is investigated using field-emission scanning electron microscopy (FESEM) and SANS at the Australian Centre for Neutron Scattering. This study also evaluated the specific surface area of the gehlenite-based ceramic (~3.0 m² cm⁻ ³) from quantitative analysis of SANS data

Disk diffusion method for fluconazole susceptibility testing of Candida spp. isolates

Fil: Rodero, L. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Micología; Argentina.Fil: Córdoba, Susana. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Micología; Argentina.Fil: Vivot, W. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Micología; Argentina.Fil: Campo, M. Universidad Católica Argentina. Cátedra de Microbiología; Argentina.Fil: Corfield, P. Universidad Católica Argentina. Cátedra de Microbiología; Argentina.Fil: Olguín, C. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Micología; Argentina.Fil: Cuirolo, A. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Micología; Argentina.Fil: Soria, M. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Micología; Argentina.Fil: Guelfand, L. Universidad Católica Argentina. Cátedra de Microbiología; Argentina.Fil: Canteros, C. E. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Micología; Argentina.Fil: Davel, Graciela Odelsia. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Micología; Argentina.Fil: Red de Vigilancia de la Resistencia a los Antimicrobianos WHONET; Argentina.Se estudiaron 1193 aislamientos clínicos para estandarizar y evaluar un método de difusión con discos de fluconazol de lectura visual, que permita detectar levaduras sensibles al antifúngico. Las especies analizadas fueron: Candida albicans (n=584), Candida parapsilosis (n=196), Candida tropicalis (n=200), Candida glabrata (n=113), Candida krusei (n=50), Candida spp. y otras levaduras oportunistas (n=50). Los discos fueron manufacturados en el INEIANLIS “Dr. Carlos G. Malbrán”. Se midieron los halos de inhibición del crecimiento producidos por fluconazol y la concentración inhibitoria mínima (CIM) por el método de referencia M27-A2 modificado por EUCAST. Se establecieron los valores de corte del método de difusión en: ³ 16 mm para levaduras sensibles a fluconazol (CIM £ 8 μg/ml), entre 9 y 15 mm para sensibles dependientes de la dosis (CIM = 16-32 mg/ml) y £ 8 mm para resistentes (CIM ³ 64 μg/ml). El método de difusión tuvo 94,7% de concordancia con el de referencia, con 0,2% de errores very major y 0,3% de errores major. La reproducibilidad inter e intralaboratorio fue muy buena. Para detectar aislamientos sensibles a fluconazol, este método resulta confiable y de bajo costo; sin embargo, es conveniente que los aislamientos con halos £ 15 mm sean reevaluados por el método de referencia. (EN) In order to standardize and evaluate a disk diffusion method with visual reading to detect in vitro fluconazole susceptibility of yeast, 1193 clinical isolates were tested. These included 584 Candida albicans, 196 Candida parapsilosis, 200 Candida tropicalis, 113 Candida glabrata, 50 Candida krusei and 50 Candida spp. and other opportunistic yeasts. The disks were manufactured in the INEI-ANLIS “Dr. Carlos G. Malbrán”. The disk diffusion method results were compared to MIC results obtained by the reference CLSI M27-A2 broth microdilution method modified by EUCAST. The interpretative breakpoints for in vitro susceptibility testing of fluconazole were established at: zone diameter ³ 16 mm for MIC £ 8 μg/ml (susceptible isolates), between 9 and 15 mm for MIC = 16-32 mg/ml (susceptible dose-dependent isolates), and £ 8 mm for MIC ³ 64 μg/ml (resistant isolates). Overall agreement between the two methods was 94.7%, with 0.2% very major errors, and 0.3% major errors. Inter - and intralaboratory agreement was good. The disk diffusion method for drug susceptibility testing of Candida spp. isolates is inexpensive, reliable and reproducible. However, when the inhibition zone diameter is £ 15 mm, it is advisable to test the isolate by the reference microdilution method