Natural-fiber polymer-matrix composites: Cheaper,tougher, and environmentally friendly

Natural fibers, especially lignocellulosic fibers extracted from plants, are gaining attention as polymer-matrix composite (PMC) reinforcements due to their comparative advantages over synthetic fibers. Natural fibers are relatively low cost, renewable, and biodegradable. Their production systems are associated with low equipment wear and are energy efficient. In addition, the incorporation of lignocellulosic fibers into PMCs may significantly improve some mechanical properties. This article presents an overview of the advantages and drawbacks of applying natural fibers, some of them relatively unknown, as reinforcements of PMCs. The mechanical behavior of composites incorporated with selected fibers is discussed in terms of the effect of surface micromorphology and the fiber/matrix interaction.     

Instruction set independent program encoding

Instruction encoding techniques have been designed for reducing the program memory footprint and improving processors performance. However, many techniques are instruction-set dependent thus minimizing the adoption in different application domains and target processors. This paper presents an instruction encoding technique and a software framework tool for the design of instruction encoders independent of the instruction set. Our approach is based on (1) a methodological extension of a pattern based instruction word (PBIW) algorithm for instruction encoding; (2) the design and implementation of a software framework for minimizing the design time frame of different instruction encoding algorithms; (3) a comprehensive set of experiments showing the impacts of those techniques on memory footprint, program performance, and processor design. Our proposed framework has been used to encode a wide range of programs compiled for the \(\rho \)-VEX and SPARCv8 instruction sets. The experiments show that the framework makes it able to match the PBIW encoding technique to different ISAs and target machines. The results with SPECint00, Media, MiBench, and simple benchmarks show a compression ratio up to 0.54 (46 % of size reduction) for PBIW-SPARC programs and up to 0.59 for PBIW-VEX programs. Encoded SPARC programs have a performance speedup up to 1.7 compared to non-encoded SPARC programs.     

Parameters Controlling Tensile and Compressive Strength of Artificially Cemented Sand

The enhancement of local soils with cement for the construction of stabilized pavement bases, canal lining, and support layer for shallow foundations shows great economical and environmental advantages, avoiding the use of borrow materials from elsewhere, as well as the need of a spoil area. The present research aims to quantify the influence of the amount of cement, the porosity, and the voids/cement ratio in the assessment of unconfined compressive strength (qu) and splitting tensile strength (qt) of an artificially cemented sand, as well as in the evaluation of qt/qu relationship. A program of splitting tensile tests and unconfined compression tests considering three distinct voids ratio and seven cement contents, varying from 1 to 12%, was carried out in the present study. The results show that a power function adapts well qt and qu values with increasing cement content and with reducing porosity of the compacted mixture. The voids/cement ratio is demonstrated to be an appropriate parameter to assess both qt and qu of the sand-cement mixture studied. Finally, the qt/qu relationship is unique for the sand-cement studied, being independent of the voids/cement ratio.     

Analytical approach to ground heat losses for high temperature thermal storage systems

A new approach to estimate the heat loss from thermal energy storage tank foundations is presented. Results are presented through analytical correlations based on numerical solutions for the steady‐state heat conduction problem for thermal energy slab‐on‐grade tanks with uniform insulation. Model results were verified with other well‐established benchmark problems with similar boundary conditions and validated with experimental data with excellent agreement. In addition to the TES foundation heat loss, new correlations for the maximum temperature and for the radial evolution of the temperature underneath the insulation layer are also provided, giving important information related to the tank foundation design. The correlated variables are of primordial importance in the tank foundation design because, due to the typical high operating storage temperatures, an inappropriate tank foundation insulation would lead not only to a not desired loss of energy but also to an inadmissible increase of the temperatures underneath the insulation layer, affecting the structural stability of the tank. The proposed correlations provide a quick method for the estimation of total tank foundation heat losses and soil maximum temperature reached underneath the insulation layer, saving time, and cost on the engineering tank foundation design process. Finally, a comprehensive parametric analysis of the variables of interest is made and a set of cases covering a wide range of tank sizes, insulation levels, depths to water table, and storage temperatures are solved.     

A novel immersed boundary/Fourier pseudospectral method for flows with thermal effects

ABSTRACT

A novel immersed boundary method (IBM) for flows with thermal effects is proposed, combining high accuracy and low computational cost, provided by the Fourier pseudospectral method (FPSM), for the possibility of handling complex and nonperiodical geometries using the IBM. With focus on incompressible flow problems modeled by Navier-Stokes, mass, and energy equations, the method of manufactured solutions is used for the numerical verification of Dirichlet boundary conditions imposed via the IBM. Then, the proposed method is applied on two different 2-D cases: (1) energy transfer due to natural convection in a square cavity, and (2) an annulus between horizontal concentric cylinders nonuniformly heated. Good agreement with available data in the literature has been achieved.     

Effect of inoculum pretreatment on the microbial community structure and its performance during dark fermentation using anaerobic fluidized-bed reactors

The effect of two different inoculum pretreatments, thermal and cell wash-out (A1 and A2, respectively) on the performance of anaerobic fluidized bed reactors for hydrogen production was determined. The reactors were operated for 112 days under the same operational conditions using glucose as substrate at increasing organic loading rates and decreasing hydraulic retention times. Both treatments were effective avoiding methanogenesis. Reactor A2 showed better performance and stability than reactor A1 in each one of the different operational conditions. Cell wash-out treatment produced higher hydrogen volumetric production rates and yields than thermal treatment (7 L H₂/L-d, 3.5 mol H₂/mol hexose, respectively). DGGE analysis revealed that the microbial communities developed were affected by the inoculum treatment. Organisms from the genera Clostridium and Lactobacillus predominated in both reactors, with their relative abundances linked to hydrogen production. Resilience was observed in both reactors after a period of starvation.     

Validation of a three dimensional PEM fuel cell CFD model using local liquid water distributions measured with neutron imaging

This work presents the validation carried out for a three dimensional CFD 50 cm² PEM fuel cell model, particularly focus on the prediction of liquid water distributions within the cell. The CFD model was previously validated against a set of experimental polarization curves, where model results adequately matched the experimental curves. An extension of the validation is presented in this work, by performing a comparison of the local liquid water distributions predicted by the model with the liquid water distributions of the real cell. The experimental measurements were obtained by means of Neutron Imaging, where a set of different cell operating conditions was tested. Although the exact quantitative results are not directly comparable due to differences in the cell setup, qualitative results show a very good agreement between the model results and the water distributions observed in the neutron radiographs. A model validation approach using local variable distributions (such as liquid water in this case) in addition to the integral quantities (i.e. polarization curves) is necessary to ensure the validity of models.     

Selective Determination of Lysine in Dry-Cured Meats Using a Sensor Based on Lysine-α-Oxidase Immobilised on a Nylon Membrane

An enzymatic sensor employing lysine oxidase (LOx) with the immobilised enzyme system by crosslinking with glutaraldehyde using an immunodyne ABC nylon membrane, in combination with an oxygen electrode, has been optimised to determine the lysine content in dry-cured ham and dry-fermented sausage at different cured times. The amperometric signal obtained due to the oxygen depletion (consumed oxygen) during the lysine oxidation was recorded at 5 s in the immobilised enzyme sensor, and the reaction rates (slope) were related to the lysine content. A linear relationship between the consumed oxygen as a function of time (mg O₂/l/s) and the lysine concentration in the range 10–250 μM (R ²?=?0.9946) for the immobilised enzyme system was found. The immobilised enzyme sensor showed a high specificity and sensibility. Nevertheless, the stability of the immobilised enzyme at the assay temperature was very poor, and thus, a new membrane was required for each analysis. The analysis of lysine with the immobilised enzyme system in cured meat samples revealed very good agreement with the determination performed through standard HPLC methodology, which validated the use of this sensor as an alternative technique to evaluate cured meat quality.