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Solar drying is a sustainable process that may impact the quality of dried food. This is because, pigments contained in food are sensitive to sunlight, and exposure to ultraviolet radiation can affect them. We applied biopolymer-based coatings on strawberry, from hydro-colloidal solutions of Opuntia ficus indica-mucilage, fenugreek, xanthan gum, gum Arabic, and guar gum to evaluate their potential use as UV filters for solar drying of food. Thermal properties and the optical transmittance, absorbance and reflectance of the coatings were measured to assess their influence on food-sunlight interaction. During the drying experiments, the moisture content, total anthocyanins (TA), and total phenolic compounds (TPC) were measured. Optical and thermal properties are influenced by the biopolymer-based coatings. Also, the optical properties are influenced by the coating thickness. The differences in optical and thermal properties influence the drying process. Differences exist in the drying rate for strawberry slices with coating, compared with those without the coatings. In general, the TA and TPC content in the product are better preserved under solar drying than in control experiments done in a drying oven. A partial transmittance of solar UV radiation is recommended to obtain increased TA and TPC contents in the dried product.

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Photonic crystals (PCs) are built to control the propagation of light within their structure. These can be used for an assortment of applications where custom designed devices are of interest. Among them, one-dimensional PCs can be produced to achieve the reflection of specific and broad wavelength ranges. However, their design and fabrication are challenging due to the diversity of periodic arrangement and layer configuration that each different PC needs. In this study, we present a framework to design high reflecting PCs for any desired wavelength range. Our method combines three stochastic optimization algorithms (Random Search, Particle Swarm Optimization and Simulated Annealing) along with a reduced space-search methodology to obtain a custom and optimized PC configuration. The optimization procedure is evaluated through theoretical reflectance spectra calculated by using the Equispaced Thickness Method, which improves the simulations due to the consideration of incoherent light transmission. We prove the viability of our procedure by fabricating different reflecting PCs made of porous silicon and obtain good agreement between experiment and theory using a merit function. With this methodology, diverse reflecting PCs can be designed for any applications and fabricated with different materials.

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We consider a simple model to give a plausible mechanical explanation of what are the actual resting heart rates of mammals optimized for. We study what is the optimal frequency for a viscoelastic fluid circulating in a pulsatile way through a network of tubes and conclude that the heart rate is not optimized to transport blood through the whole net. Rather, actual resting heart rates of mammals happen at frequencies that optimize flow in vessels of radii that correspond to large arteries, which bring oxygenated blood rapidly far away from the heart, towards head and limbs. Our results for the optimal frequencies, obtained using observed radii of femoral arteries in mammals, agree best with the heart rates observed. We find a theoretical allometric relation between optimal flow frequency and radius: nu approximately R(-1). This one, agrees with the exponent obtained when plotting observed heart rates versus radii of both, femoral arteries and carotids in mammals of different sizes, from mice to horses.

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In this paper we study the propagation of light through an asymmetric array of dielectric multilayers built by joining two porous silicon substructures in a Fibonacci sequence. Each Fibonacci substructure follows the well-known recursive rule but in the second substructure dielectric layers A and B are exchanged. Even without mirror symmetry, this array gives rise to multiple transparent states, which follow the scaling properties and self-similar spectra of a single Fibonacci multilayer. We apply the transfer matrix formalism to calculate the transmittance. By setting the transfer matrix of the array equal to ± I, the identity matrix, frequencies of perfect light transmission are reproduced in our theoretical calculations. Although the light absorption of porous silicon in the optical range limits our experimental study to low Fibonacci generations, the positions of the transparent states are well predicted by the above-mentioned condition. We conclude that mirror symmetry in arrays of Fibonacci multilayers is sufficient but not necessary to generate multiple transparent states, opening broader applications of quasiperiodic systems as filters and microcavities of multiple frequencies.

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This work explores the heavy metal retention capacity of materials developed from minerals that are abundant in nature, with low cost and minimum environmental impact. To accomplish this objective we have: (a) characterized commercial samples of calcite (CA) and hydroxyapatite (HAP)--including their surface properties (BET area, electrophoretic mobility, SEM, and X-ray energy dispersive spectroscopy); and, (b) qualified and quantified the interaction of Cd, Zn and Co with calcite (CaCO3) and hydroxyapatite [Ca5(PO4)3OH] through batch experiments, in a range of metal concentrations (4Zn>Co and Cd>Zn approximately Co, respectively. Retention increased with pCa and pH and could be modeled by: (a) a non-ideal ion exchange mechanism (Me/Ca) for the adsorption of Cd, Zn and Co onto CA; and, (b) a mechanism of non-ideal ion exchange and specific adsorption (Me/Ca and identical with PO4O-Me) in the case of HAP. The pH dependence is indirect in CA and is related to its solubility changes (pCa increases with pH, and so does sorption of Cd, Zn and Co). Both materials, HAP and CA, can be used for heavy metal retention. The former has better performance for water treatment due to its greater efficiency for the retention of Cd, Zn and Co (over two orders of magnitude per gram of material) and its lower solubility in a wide range of pH (6

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We report the first observation of oscillations of the electromagnetic field in an optical superlattice based on porous silicon. These oscillations are an optical equivalent of well-known electronic Bloch oscillations in crystals. Elementary cells of our structure are composed by microcavities whose coupling gives rise to the extended collective modes forming optical minigaps and minibands. By varying thicknesses of the cavities along the structure axis, we have created an effective electric field for photons. A very high quality factor of the confined optical state of the Wannier-Stark ladder may allow lasing in porous silicon-based superlattices.

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An experimental study of the dynamic response of a Newtonian fluid and a Maxwellian fluid under an oscillating pressure gradient is presented. Laser Doppler anemometry is used in order to determine the velocity of the fluid inside a cylindrical tube. In the case of the Newtonian fluid, the dissipative nature is observed. In the dynamic response of the Maxwellian fluid an enhancement at the frequencies predicted by theory is observed.

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The dynamic response of an electrically conducting fluid (either Newtonian or Maxwellian) flowing between straight concentric circular cylinders under a constant radial magnetic field, is analyzed. The isothermal flow is studied using the time Fourier transform, so that the dynamic generalization of Darcy's law in the frequency domain is obtained and analytical expressions for the dynamic permeability are derived. For the Newtonian case, the range of frequencies where the dynamic permeability approaches the static value is enlarged the smaller the gap between the cylinders and the higher the magnetic-field strength. For the Maxwell fluid, the presence of the inner cylinder shifts the frequencies that lead to the enhancement of the real part of the dynamic permeability to larger values and increases its maximum values relative to the case where the inner cylinder is absent. In addition, the Ohmic dissipation causes the damping of the amplitude of the response.

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Noventa y cinco pacientes con trauma colonico fueron recibidos en el Hospital de Caldas de Manizales, en el periodo comprendido entre febrero de 1997 y marzo de 1999; de estos, 74 (77.9 por ciento) presentaban criterios aceptados en la literatura mundial como condicionantes para la realizacion de colostomia, de los cuales fueron tratados con reparo primario 49 (66.2 por ciento), reseccion y anastomosis, 5 (6.7 por ciento), y con colostomia, 20 (27 por ciento). Treinta y un pacientes (41.8 por ciento) tenían un ATI mayor que 25; 72 (97.2 por ciento) presentaban un CIS CISFLINT de II y III; se presentaron episodios de shock en el 21 por ciento de los casos al ingreso, en 14.8 por ciento durante el acto quirurgico, y en el 8.1 por ciento de manera persistente; 17 (22.9 por ciento) pacientes tuvieron contaminacion fecal de manera moderada o severa, 54 por ciento de los traumas fueron tratados en un tiempo mayor a 6 horas; el 82.4 por ciento de los lesionados presentaba heridas asociadas al momenta de establecerse el tratamiento. Existieron complicaciones en el 35.1 por ciento de los pacientes tratados con reparo primario o reseccion y anastomosis, y en el 70 por ciento de los tratados con colostomia. En el grupo analizado se presentaron 2 dehiscencias, sin desenlace fatal. Con el apoyo de una regresion logistica se concluyo que, independientemente de los factores de riesgo asociados, el reparo primario o la reseccion y anastomosis deben ser las tecnicas de eleccion en los pacientes con trauma colonico, pues la evolucion es más favorable y con menos complicaciones asociadas y evita la necesidad de un segundo tiempo quirurgico, como ocurre en el caso de la colostomia.

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