Transient numerical study of the effect of ambient temperature on 2-D cereal grain storage in cylindrical silos

A numerical study was performed on the transient heat and mass convection of grain storage in a cylindrical silo. Temperature gradients were induced by the heat of respiration, and thermal gradients were generated by variations of the temperature surrounding the cavity. The model was developed using the equations of heat, mass, and momentum transport for multiphasic media. The equation that represents the environmental temperature along the day-night cycle was obtained via a least squares regression using statistical data. In this study, the effects of different geometric ratios (A) and Rayleigh (Ra) numbers on the isotherms, flow patterns, and concentration isolines were analyzed. The governing equations were solved using discretization of the spatial coordinates by orthogonal collocation with Legendre polynomials and an implicit-trapezoidal formulation for time. The resulting algebraic system was solved by employing the Newton-Raphson with LU factorization method. A computer code called NEWIMPC2 in the FORTRAN 90 language was developed; this code was used to calculate the dynamics and hot regions in the bulk mass grain in the cavity. The thermodynamic properties for sorghum were used in the simulation, although the model is applicable to any cereal grains. For simulation data, typical prevailing conditions in the Bajio, an agricultural region located in Guanajuato State, were used. When the geometric ratio (A) increases, the hot nucleus is displaced toward the top of the cavity. In the case of Rayleigh numbers (Ra), a small increase significantly increases the stiffness of the parabolic equations. The ambient temperature has a significant effect on the formation of hot regions inside the cavity. When Ra increases, an increase can be observed in the temperature of the hot nucleus, with this temperature reaching 31 °C near the top wall of the enclosure. There was no evidence of the formation of multicellular flows.     

Multiple Quantum Nuclear Coherences in Pulsed ENDOR Spectroscopy

Experimental and theoretical aspects of multiple quantum (MQ) NMR coherence phenomena for paramagnetically coupled nuclei are presented. The spin interactions responsible for MQ NMR coherences observed in pulsed EPR and pulsed ENDOR (Electron Nuclear Double Resonance) are contrasted with those responsible for MQ coherences in pulsed NMR spectroscopy. MQ NMR coherences in pulsed ENDOR spectroscopy are demonstrated experimentally and described using an operator formalism approach. Detailed discussions of the phase incrementation technique for detecting MQ NMR coherences in ENDOR spectroscopy, different microwave excitation schemes for the preparation of nuclear spin order, off-resonance excitation, and the evolution of MQ coherences under free precession are presented. Experimental results on a single crystal of irradiated malonic acid and on the conjugated polyene polymer poly acetylene are presented.     

Preparation and characterization of safe microparticles based on xylan

This work describes the preparation and evaluation of safe xylan-based microparticles prepared by cross-linking polymerization using sodium trimetaphosphate. The resulting microparticles were evaluated for morphology, particle size, polymer-cross-link agent interaction, and in vitro toxicity. The microparticles showed narrow monodisperse size distributions with their mean sizes being between 3.5 and 12.5?µm in dried state. FT-IR analyzes confirmed the interaction between sodium trimetaphosphate and xylan during the cross-linking process with formation of phosphate ester bonds. Additionally, the X-ray diffraction patterns and FT-IR analyzes suggested that little or no cross-linking agent remained inside the microparticles. Furthermore, the in-vitro studies using Artemia salina and human erythrocytes revealed that the microparticles are not toxic. Therefore, the overall results suggest that these xylan microparticles can be used as a platform for new drug delivery system.     

Ozone oxidation of β-lactam antibiotic molecules and toxicity decrease in aqueous solution and industrial wastewaters heavily contaminated

In this work, ozone oxidation of the antibiotics amoxicillin (AMX), cephalexin, and ceftriaxone was investigated in different samples: (i) aqueous solutions (100 mg L^?1), (ii) an industrial wastewater containing AMX at 125 mg L^?1 (chemical oxygen demand 6000 mg O₂ L^?1), and (iii) a heavily contaminated industrial wastewater containing the antibiotics at a total concentration of 320 mg L^?1. High performance liquid chromatography, molecular absorption spectrophotometry in the ultraviolet/visible region, and total organic carbon measurements showed that ozonation of antibiotics solutions led to removal higher than 95% with 10–20% mineralization. Industrial wastewater also showed very good efficiency for antibiotic removal (80–98%) after ozonation. Moreover, Microtox® test showed 86% toxicity reduction for the industrial wastewater.     

Expert system for predicting unstable angina based on Bayesian networks

The use of computer-based clinical decision support (CDS) tools is growing significantly in recent years. These tools help reduce waiting lists, minimise patient risks and, at the same time, optimise the cost health resources. In this paper, we present a CDS application that predicts the probability of having unstable angina based on clinical data. Due to the characteristics of the variables (mostly binary) a Bayesian network model was chosen to support the system. Bayesian-network model was constructed using a population of 1164 patients, and subsequently was validated with a population of 103 patients. The validation results, with a negative predictive value (NPV) of 91%, demonstrate its applicability to help clinicians. The final model was implemented as a web application that is currently been validated by clinician specialists.     

Signal Integrity Enhancement in Digital Circuits

This article proposes a new methodology for enhancing SoC signal integrity without degrading performance in the presence of power-ground voltage transients. The underlying principle is the dynamic adaptation of the clock duty cycle to propagation delay variation along disturbed logic paths. This methodology makes digital circuits more robust to power line fluctuations while maintaining the at-speed clock rate.     

Probabilistic modeling of a parabolic trough collector power plant – An uncertainty and sensitivity analysis

In this work, an uncertainty and sensitivity analysis for the annual performance of a parabolic trough collector plant based on a probabilistic modeling approach of the solar-to-thermal energy conversion process has been accomplished. Realistic probability functions have been assigned to the most relevant solar field performance parameters. The Latin Hypercube sampling method has been used to create equal probable parameter combinations. The so obtained sample matrix has been used to run multiple annual electricity yield simulations in SimulCET, a validated parabolic trough collector plant simulation software, developed by the National Renewable Energy Center (CENER) in Spain García-Barberena et al., 2012. This procedure has led to a representative distribution for the annual plant performance, given the uncertainty in the input data. For this study the parabolic trough power plant model has been run in solar driven operation mode, without the use of thermal storage or fossil fuel back up. While being aware of the great influence of the solar irradiation on the power plant performance, only one single reference meteorological year has been used as solar input data. This has been done in order to emphasize the influence of technical design- as well as solar field maintenance parameters, factors that can be controlled or affected by mankind. In order to assess and rank the impact of each varied model parameter a multiple linear regression has been performed. The standardized regression coefficients, the Pearson correlation coefficients as well as the coefficient of multiple determination R² are discussed. Varied parameters are the collector mirror reflectance, the collector mirror cleanliness factor, the collector glass tube transmittance, the collector receiver tube absorptance, and the collector receiver tube heat loss characteristic. Based on existing and published bibliography, a set of parameter distributions and ranges have been chosen for this work and the simulation results show that the cleanliness factor has the strongest influence on the model output. The cleanliness is followed (in this sequence) by the mirror reflectance, the glass tube transmittance, the receiver tube absorptance and, finally, by the receiver tube heat loss characteristic.     

Hydrodynamics and particle collection in turbulent bed contactor

Perforated spheres with 10% and 25% free area, oblate spheroids and the conventional plain spheres were tested as packing medium in a Turbulent Bed Contactor (TBC). Hydrodynamics and particle collection experiments were carried out in a column having 0.264 m diameter, at 3 static bed heights and several gas and liquid flow rates. Alumina (1.5 to 5.5 μm) was used as test powder for particle collection experiments. The higher efficiency of particle collection, the lower bed expansions and the higher fluidization velocities of perforated spheres, indicates that this packing type is suitable as contacting medium for particle collection in TBCs.     

Dynamic peroxide method for kLaO2 estimation

BACKGROUND: A reliable k_La_O2 estimation methodology in bioreactors is a recurrent topic in the literature owing to the significance of this value, particularly in respirometric measurements. The most common methodologies for k_La_O2 estimation consist of modeling the profile of dissolved oxygen (DO) obtained after a perturbation of the system aeration. Among them, the dynamic peroxide method (DPM), which consists of a small addition of peroxide hydrogen for a sudden increase in the DO level, is a promising methodology. RESULTS: This work studies the reliability of k_La_O2 estimates using DPM. Different experiments were performed with sludge cultures enriched with heterotrophs, nitrifiers and polyphosphate accumulating organisms (PAO). The influence of several operational conditions (i.e. air flow, sludge concentration, H₂O₂ volume addition) on k_La_O2 estimates was studied and the reliability of DPM was compared with the widely used reaeration methodology. An application of DPM in the assessment of oxygen surface transfer in a mechanically stirred bioreactor is described. CONCLUSION: DPM is a reliable methodology for k_La_O2 estimation that can be successfully applied to heterotrophs, nitrifiers and PAO without observing any inhibitory effect ([H₂O₂] ≤ 6 mg L^?1). Copyright © 2009 Society of Chemical Industry