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Bacterial cellulose (BC) samples were obtained in a static culture of K. xylinus under the effect of a low-intensity magnetic field, UV light, NaCl, and chloramphenicol. The effect of such stimuli on the amount of BC produced and its production rate, specific area, pore volume, and pore diameter were evaluated. The polysaccharide production was enhanced 2.28-fold by exposing K. xylinus culture to UV light (366 nm) and 1.7-fold by adding chloramphenicol (0.25 mM) to the medium in comparison to BC control. All the stimuli triggered a decrease in the rate of BC biosynthesis. BC membranes were found to be mesoporous materials with an average pore diameter from 21.37 to 25.73 nm. BC produced under a magnetic field showed the lowest values of specific area and pore volume (2.55 m2 g-1 and 0.024 cm3 g-1), while the BC synthesized in the presence of NaCl showed the highest (15.72 m2 g-1 and 0.11 cm3 g-1). FTIR spectra of the BC samples also demonstrated changes related to structural order. The rehydration property in these BC samples is not mainly mediated by the crystallinity level or porosity. In summary, these results support that BC production, surface, and structural properties could be modified by manipulating the physical and chemical stimuli investigated.
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In the present work, an analytical approximate solution of mixed electroosmotic/pressure driven flow of viscoelastic fluids between a parallel plates microchannel is reported. Inserting the Oldroyd, Jaumann, or both time derivatives into the Maxwell model, important differences in the velocity profiles were found. The presence of the shear and normal stresses is only close to the wall. This model can be used as a tool to understand the flow behavior of low viscosity fluids, as most of them experiment on translation, deformation and rotation of the flow. For practical applications, the volumetric flow rate can be controlled with two parameters, namely the gradient pressure and the electrokinetic parameter, once the fluid has been rheologically characterized.
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Antecedentes: Diversas investigaciones se realizan sobre el tiempo y naturaleza de uso del móvil en estudiantes universitarios pero escasas en el área de la medicina en el siglo de la tecnología. Objetivo: Establecer el tiempo y naturaleza de uso del teléfono móvil en estudiantes de cuarto año de medi-cina de cuarto año A en la Escuela Universi-taria de Ciencias de la Salud de la Universi-dad Nacional Autónoma de Honduras en el Valle de Sula (EUCS/UNAH-VS) en el primer semestre académico del 2017. Pacientes y Métodos: Estudio exploratorio-descriptivo. Población fue de 78, muestra no probabilísti-ca por conveniencia de 38 estudiantes, instrumento de recolección de datos se realizó a través del programa App Usage®que generó los resultados, se evaluaron los datos de frecuencias, porcentajes y medidas de tendencia central en Excel®. Resultados:Los datos reflejaron que el tiempo promedio de uso del móvil por los estudiantes fue de 5 horas 9 minutos (21.5%) del día. El uso se centró en aplicaciones móviles reactivas (distractor) con 4 horas 47 minutos (93%) y en aplicaciones móviles proactivas solo 22 minutos (7%). Conclusiones: Los datos de esta investigación indican que el patrón de uso del teléfono móvil es del 21.5% al día y la naturaleza del uso de los teléfonos celula-res por parte del estudiante de Medicina de cuarto año A de la UNAH-VS es de carácter reactivo o sea como distractor.Artículos OriginalesPALABRAS CLAVEAplicaciones Móviles, estudiantes de medi-cina, Teléfonos celulares...(AU)
Assuntos
Humanos , Estudantes de Medicina , Aplicações da Informática Médica , Webcast , Aplicativos Móveis/estatística & dados numéricos , Uso do Telefone CelularRESUMO
The production and crystallinity of 13C bacterial cellulose (BC) was examined in static culture of Komagataeibacter xylinus with different chemical and physical stimuli: the addition of NaCl or cloramphenicol as well as exposure to a magnetic field or to UV light. Crystalline BC biosynthesized under each stimulus was studied by XRD and solid state 13C NMR analyses. All treatments produced BC with enhanced crystallinity over 90% (XRD) and 80% (NMR) compared to the control (83 and 76%, respectively) or to Avicel (77 and 62%, respectively). The XRD data indicated that the crystallite size was 80-85â¯Å. Furthermore, changes on the allomorphs (Iα and Iß) ratio tendency of BC samples addressed to the stimuli were estimated using the C4 signal from 13C NMR data. These results showed a decrease of the allomorph Iα (3%) when BC was biosynthesized with UV light and chloramphenicol compared to control (58.79%). In contrast, the BC obtained with NaCl increased up to 60.31% of the Iα allomorph ratio.
Assuntos
Celulose/biossíntese , Gluconacetobacter xylinus/metabolismo , Espectroscopia de Ressonância Magnética/métodos , Difração de Raios X/métodos , Celulose/químicaRESUMO
The aim of this study was to evaluate the stability of color, betaxanthin, and betacyanin pigments in the presence of Cu(II)-dependent hydroxyl radicals (HOâ¢) from ultrasonicated purple cactus pear juice at amplitudes of 40%, 60%, and 80%, in comparison to untreated sample. L* parameter of juice treated at 40% and 80% amplitude for 25 and 15 min, respectively (11.3 and 9.3, respectively), were significantly higher compared to the control; b* and hue parameters of juice treated at 80%, 25 min showed values of 1.7 and 0.1, respectively. Color differences (ΔE) were lower (<3) for juices treated at high amplitude (80%) and short times (3-5 min). Juice treated at 40% 15 min, 60% 25 min, 80% 15 and 25 min presented high values of betacyanins (281.7 mg·L-1, 255.9 mg·L-1, 294.4 mg·L-1, and 276.7 mg·L-1, respectively). Betaxanthin values were higher in the juices treated at 40% 5 min and 80% 15 and 25 min (154.2 mg·L-1, 135.2 mg·L-1, and 128.5 mg·L-1, respectively). Purple cactus pear juice exhibited significant chelating activity of copper ions and great stability when exposed to HOâ¢.