Search

The electromagnetic theory predicts that when a linearly polarized collimated field is focused by a high-angle focusing system, components perpendicular to the initial polarization are generated. The use of annular masks to reduce the area of the focal spot usually increases the magnitude of this phenomenon, known as depolarization. We present a class of masks, the three-ring masks, which are important because they narrow the central lobe of the focal intensity distribution without increasing the depolarization. This can be very useful in modern optical applications, such as confocal microscopy or multiphoton scanning microscopy. [ABSTRACT FROM AUTHOR]

New systems using solid particles for solar energy capturing, heat transfer and thermal energy storage have been proposed and analysed in direct particle solar receivers. In this work, black coloured silica sand was investigated as a possible solid particle for such combined systems. Two different methods based on a carbon coating approach were implemented to black colour the initial material to improve their solar absorption characteristics. The morphology of the raw and coloured sands was analysed by scanning electron microscopy (SEM), particle size characterisation and porosity measurements. The coating of the black-coloured silica sands was evaluated by thermogravimetry. Solar absorption was characterised in a double-beam UV-VIS spectrophotometer combined with an integrating sphere, and with enhancements of approximately 100%, found for both coloured sands. The thermal storage and heat transfer capabilities of the initial and coated sands were measured at different temperatures. Some improvements in the specific heat capacity and reductions in thermal conductivity due to porosity changes were observed. • Sand was black coloured through two different methods. • Coloured sands were evaluated as candidates for direct particle solar receivers. • SEM and TGA were used to study coating morphology and its stability with temperature. • The absorption is highly improved for the both black sands compared to the raw sand. • Improvements in Cp and reductions in thermal conductivity were observed. [ABSTRACT FROM AUTHOR]

In recent years, the interest in modelling activated sludge (AS) systems by means of Computational Fluid Dynamics (CFD) techniques has significantly increased. This work shows a successful case study combining CFD hydrodynamics and biokinetic modelling. The hydrodynamics is analysed by using the Reynolds-averaged Navier-Stokes equation for incompressible non-Newtonian fluids and SST turbulence model. Biokinetics has been included in the CFD as transport equations with source and sink terms defined by the Activated Sludge Model n°1 (ASM1). Furthermore, a strategy for reducing the computational cost while maintaining accuracy of the results of these calculations has been proposed. This strategy is based on a two-step solver configuration and the definition of a variable timestep scheme. The resulting CFD-ASM approach permits a proper evaluation of denitrification in the anoxic tanks as well as the reproduction of nitrate and readily biodegradable substrate distributions. To demonstrate the strength of the proposed CFD-ASM, it has been used to evaluate the operation of a full-scale AS system and optimize its performance through changes in the biological reactor anoxic zone. The original configuration has been retrofitted and modified after detecting intrinsic defects in the fluid behaviour within the tank. This study has been assessed by analysing hydrodynamics in detail and validating the simulation results with tracer tests and flow velocity measurements. Substantial variations on the Residence Time Distribution have been confirmed when modifying the internal elements of the tank configuration: the wall-bushing and the stirrer positioning. As a result of this work, an influential short circuiting was corrected improving hydrodynamics and increasing mean residence time, all favouring denitrification efficiency. Outcomes of this study show the benefit of CFD when applied to AS tanks. [ABSTRACT FROM AUTHOR]

The article discusses various papers published within the issue including one on estimating crop coefficients, another on the accuracy of eddy covariance, and a paper describing the bahiagrass crop coefficient.

Droplet volume and temperature affect contact angle significantly. Phase change heat transfer processes of nanofluids – suspensions containing nanometre-sized particles – can only be modelled properly by understanding these effects. The approach proposed here considers the limiting contact angle of a droplet asymptotically approaching zero-volume as a thermophysical property to characterise nanofluids positioned on a certain substrate under a certain atmosphere. Graphene oxide, alumina, and gold nanoparticles are suspended in deionised water. Within the framework of a round robin test carried out by nine independent European institutes the contact angle of these suspensions on a stainless steel solid substrate is measured with high accuracy. No dependence of nanofluids contact angle of sessile droplets on the measurement device is found. However, the measurements reveal clear differences of the contact angle of nanofluids compared to the pure base fluid. Physically founded correlations of the contact angle in dependency of droplet temperature and volume are obtained from the data. Extrapolating these functions to zero droplet volume delivers the searched limiting contact angle depending only on the temperature. It is for the first time, that this specific parameter, is understood as a characteristic material property of nanofluid droplets placed on a certain substrate under a certain atmosphere. Together with the surface tension it provides the foundation of proper modelling phase change heat transfer processes of nanofluids. [ABSTRACT FROM AUTHOR]

Engineers and scientist have a long tradition in trying to improve the thermophysical properties of convective heat carriers such as water and transformer oil. Technological developments of the last decades allow the dispersion of particle of sizes ranging between 10 and 100 nm in these liquids. In a large number of recent studies the resulting nanofluids have been reported to display anomalously high increase of convective heat transfer. The present study compiles experiments from five independent research teams investigating convective heat transfer in nanofluid flow in pipes, pipe with inserted twisted tape, annular counter flow heat exchanger, and coil and plate heat exchangers. The results of all these experiments unequivocally confirm that Newtonian nanofluid flow can be consistently characterized by employing Nusselt number correlations obtained for single-phase heat transfer liquids such as water when the correct thermophysical properties of the nanofluid are utilized. It is also shown that the heat transfer enhancement provided by nanofluids equals the increase in the thermal conductivity of the nanofluid as compared to the base fluid independent of the nanoparticle concentration or material. These results demonstrate that no anomalous phenomena are involved in thermal conduction and forced convection based heat transfer of nanofluids. The experiments are theoretically supported by a fundamental similarity analysis of nanoparticle motion in nanofluid flow. [ABSTRACT FROM AUTHOR]

In the computational modeling of two-phase flow, many uncertainties are usually faced in simulations and validations with experiments. This has traditionally made it difficult to provide a general method to predict the two-phase flow characteristics for any geometry and condition, even for bubbly flow regimes. Thus, we focus our research on studying in depth the bubbly flow modeling and validation from a critical point of view. The conditions are intentionally limited to scenarios where coalescence and breakup can be neglected, to concentrate on the study of bubble dynamics and its interaction with the main fluid. This study required the development of a solver for bubbly flow with higher resolution level than TFM and a new methodology to obtain the data from the simulation. In Part II, taking profit of the detailed data provided by the CFD-DEM solver presented in Part I, we propose a novel methodology based on virtual sensor probes, to perform a rigorous validation and to investigate the experimental data. The same approximation used for processing the experimental datasets applies to simulation data, then the same assumptions are considered. In this way we can study an extended number of disperse phase variables as bubble velocity, void fraction, interfacial area concentration, mean chord length and distribution, Sauter mean diameter, bubble frequency and missing ratio, in addition to other variables as bubble size distribution or carrier phase velocity and turbulence. Several upward bubbly flow scenarios from datasets of different authors are used to validate the solver using this methodology. Finally, an axial evolution validation is performed including a discussion motivated by the comparison between experiments and the data from the virtual probes. [ABSTRACT FROM AUTHOR]

In the computational modeling of two-phase flow, many uncertainties are usually faced in simulations and validations with experiments. This has traditionally made it difficult to provide a general method to predict the two-phase flow characteristics for any geometry and condition, even for bubbly flow regimes. Thus, we focus our research on studying in depth the bubbly flow modeling and validation from a critical point of view. The conditions are intentionally limited to scenarios where coalescence and breakup can be neglected, to concentrate on the study of bubble dynamics and its interaction with the main fluid. This study required the development of a solver for bubbly flow with higher resolution level than TFM and a new methodology to obtain the data from the simulation. Part I shows the development of a solver based on the CFD-DEM formulation. The motion of each bubble is computed individually with this solver and aspects as inhomogeneity, nonlinearity of the interfacial forces, bubble-wall interactions and turbulence effects in interfacial forces are taken into account. To develop the solver, several features that are not usually required for traditional CFD-DEM simulations but are relevant for bubbly flow in pipes, have been included. Models for the assignment of void fraction into the grid, seeding of bubbles at the inlet, pressure change influence on the bubble size and turbulence effects on both phases have been assessed and compared with experiments for an upward vertical pipe scenario. Finally, the bubble path for bubbles of different size have been investigated and the interfacial forces analyzed. [ABSTRACT FROM AUTHOR]

Background: Hepatitis C is an important public health problem about which there is currently scarce epidemiological information. The objective of this study is to describe and analyse the demographic and epidemiological characteristics of hospitalized cases of hepatitis C in the Spanish population between 2004 and 2013.Methods: The study uses the Hospital Discharge Records Database of the Spanish National Health System. It is a retrospective descriptive epidemiological study. The variables analysed were year of infection, age, sex, diagnostic category, days admitted and co-morbidity.Results: There have been a total of 351,996 hospitalizations; 225,138 men (64%) and 126,858 women (36%). They are divided between acute hepatitis 8161 (2.3%); chronic hepatitis 325,185 (92.4%) and unspecified hepatitis 18,650 (5.3%). The mean age for men is 53.7 (+/-15.2) and for women 62.3 (+/-17.3). 22.8% also present with an Human immunodeficiency virus (HIV) disease coinfection, and 14.7% with opioid dependencies. The trend is for a gradual increase in cases without statistical significance.Conclusions: The Hepatitis C cases hospitalized had high levels of chronicity, which entails two distinct patterns of illness in men and women - who are affected in different age ranges. [ABSTRACT FROM AUTHOR]

Summary: The relation between age and mortality after hip fracture was analyzed in elderly patients. 5.5% of the 31,884 patients died. Compared to those 65-74 years old, the multivariate OR for mortality for those 75-84 and ≥85 were 2.11 (95% CI: 1.61-2.77) and 4.10 (95% CI: 3.14-5.35). Purpose: To analyze the impact of Elixhauser comorbidities on the relation between age and mortality after hip fracture in elderly patients. Methods: Cross-sectional study of the population ≥65 years old hospitalized in Spain in 2013 with a diagnosis of fall-related hip fracture in the Basic Minimum Set Data (BMSD). The impact of Elixhauser comorbidities on the association between mortality and age groups (65-74, 75-84, ≥85) was analyzed by logistic regression models with progressive adjustment for demographic variables and comorbidities introduced individually. Results: We identified 31,884 patients, 5.5% of which died during hospitalization. Compared with those 65-74 years old, the multivariate OR of mortality for those 75-84 and ≥85 years old decreased from 2.23 (95% CI: 1.71-2.90) and 4.57 (95% CI: 3.54-5.90) to 2.11 (95% CI: 1.61-2.77) and 4.10 (95% CI: 3.14-5.35), respectively after adjustment for comorbidities. The OR of mortality for men was 1.77 (95% CI: 1.58-1.98) compared to women. The comorbidities with higher OR for mortality were congestive heart failure (OR: 3.88; 95% CI: 3.42-4.41), metastasis (OR: 3.44; 95% CI: 2.27-5.20), fluid and electrolyte disorders (OR: 2.95; 95% CI: 2.47-3.52), coagulation deficiencies (OR: 2.87; 95% CI: 2.08-3.96), and liver disease (OR: 2.40; 95% CI: 1.82-3.17). Conclusions: The association between age and mortality after hip fracture remains after adjusting for numerous comorbidities. However, some potentially controllable disorders are associated with an increased risk for mortality, thus, improving their management could benefit survival. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the use of whole-body plethysmography as a non- invasive method to determine the respiratory parameters and profiles in two tortoise species belonging to the genus Testudo. Pulmonary functions and volumetric parameters were determined in 10 adults of Testudo hermanni and in seven Testudo marginata animals, using whole-body plethysmography. A profile pattern was regularly observed: an inspiratory flow peak, an expiratory peak, an apnoea phase and a second expiratory peak, previous to the beginning of the next respiratory cycle. Positive and significant correlation was observed between the inspiratory time, weight and length of the tortoises. Larger tortoises showed a higher time of inhalation. The peak of inspiratory flow was correlated with the sex, being longer in the females. T. marginata had an inspiratory time longer than that of T. hermanii. In T. hermanii, differences related to the sex were observed in the tidal volume, peak inspiratory flow, peak expiratory flow, expiratory flow of 50 per cent and enhanced pause, which could be related to the smaller size of males. The results suggest that additional information on new technologies currently used in pet medicine or even in human medicine should be developed and adjusted as alternative ways to support the rehabilitation of turtles and tortoises. [ABSTRACT FROM AUTHOR]

Abstract: Hydraulic redistribution is the process of passive water movement from deeper moist soil to shallower dry soil layers using plant roots as conduits. Results from this study indicate that this phenomenon exists among two shrub species (Guiera senegalensis and Piliostigma reticulatum) that co-exist with annual food crops in Sahelian agro-ecosystems. Real-time measurements were conducted for soil water content, soil water potential and microclimate variables notably; air temperature, relative humidity, wind speed, precipitation and solar irradiance. Additionally, sap flow measurements were conducted in shrub roots using the thermal dissipation technique on intact and coppiced shrubs. Monthly predawn leaf water potential was measured using a portable pressure chamber. Soil water potential (Ψ s) at the 20 cm depth declined significantly during the dry season with diel changes in Ψ s of −0.6 to −1.1 MPa. These variations were attributed to passive water release from shrub roots resulting in overnight rewetting of drier upper soil layers. Sap flow measurements on tap and lateral shrub roots indicated daily reversals in the direction of flow. During the peak of the dry season, both positive (toward shrub) and negative (toward soil) flows were observed in lateral shrub roots with sap flow in the lateral roots frequently negative at night and rapidly becoming positive soon after sunrise. The negative sap flow at night in superficial lateral roots and the periodic positive flow in the descending tap roots were indicative of hydraulic redistribution. Hydraulic redistribution may be an important mechanism for drought stress avoidance while maintaining plant physiological functions in both shrubs and neighboring annuals in water-limited environments. [Copyright &y& Elsevier]