A correlation for the pressure drop in monolithic silica columns

To gain insight into how the pressure drop in monolithic silica columns is determined by the microscopic details of the pore structure, a series of well-validated computational fluid dynamics simulations has been performed on a simplified model structure, the so-called tetrahedral skeleton column. From these simulations, a direct correlation between the pressure drop and two main structural properties (skeleton thickness and column porosity) of the monolithic skeleton could be established. The correlation shows good agreement with the experimental pressure-drop data available from the literature on silica monoliths, especially when a correction for the flow-through pore size heterogeneity is made. The established correlation also yields a much more accurate representation of the relation between the flow resistance and the bed porosity than does the Kozeny-Carman model, making it much better suited for porosity optimization calculations.     

Designing assembly lines with humans and collaborative robots: A genetic approach

Human-robot collaboration represents a significant evolutionary step in manufacturing. A crucial point is to establish a proper task assignment to combine robot productivity with human flexibility. In this regard, this paper proposes a genetic algorithm to approach the Assembly Line Balancing Problem (ALBP) in the case of human-robot collaborative work. The aim is the minimization of: i) the assembly line cost, evaluated according to the number of workers and equipment on the line, including collaborative robots, ii) the number of skilled workers on the line, iii) the energy load variance among workers, based on their energy expenditures and thus on their physical capabilities and on the level of collaboration with robots.     

Ultra‐low‐noise large‐bandwidth transimpedance amplifier

Equivalent input current noise and bandwidth are the most relevant parameters qualifying a low‐noise transimpedance amplifier. In the conventional topology consisting of an operational amplifier in a shunt‐shunt configuration, the equivalent input noise decreases as the feedback resistor (R_F), which also sets the gain, increases. Unfortunately, as R_F increases above a few MΩ, as it is required for obtaining high sensitivity, the bandwidth of the system is set by the parasitic capacitance of R_F and reduces as R_F increases. In this paper, we propose a new topology that allows overcoming this limitation by employing a large‐bandwidth voltage amplifier together with a proper modified feedback network for compensating the effect of the parasitic capacitance of the feedback resistance. We experimentally demonstrate, on a prototype circuit, that the proposed approach allows to obtain a bandwidth in excess of 100 kHz and an equivalent input noise of about 4 fA/ , corresponding to the current noise of the 1 GΩ resistor that is part of the feedback network. The new approach allows obtaining larger bandwidth with respect to those obtained in previously proposed configurations with comparable background noise. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermoplastic composites based on poly(ethylene 2,6‐naphthalate) and basalt woven fabrics: Static and dynamic mechanical properties

Composites based on poly(ethylene 2,6‐naphthalate) and basalt woven fabrics have been investigated with the aim to develop composites with a minimum service temperature of 100°C. Laminates have been manufactured by using the film‐stacking technique. A very low void content and a good fabric impregnation has been obtained as confirmed by the morphological analysis performed with scanning electron microscopy. Static flexural modulus and strength have been measured at 20, 60, and 100°C and compared with the dynamic mechanical behavior, evaluated from −100 to 220°C. A very good agreement has been detected between static and dynamic tests, proving that the dynamic mechanical analysis can be used to estimate the flexural modulus in a wide temperature range. Poly(ethylene 2,6‐naphthalate)/basalt composites have exhibited (at 20°C) a flexural modulus and strength as high as 20 GPa and 320 MPa, respectively. The flexural modulus and the flexural strength at 100°C have been found to be equal to 18 GPa and 230 MPa, confirming that this system can retain very good mechanical properties at a service temperature of 100°C. POLYM. COMPOS., 37:2549–2556, 2016. © 2015 Society of Plastics Engineers     

Effect of processing conditions on dimensions of sisal fibers in thermoplastic biodegradable composites

Biodegradable composites based on treated and untreated sisal fiber and mater Bi‐Z were processed using an internal batch mixer. The effect of processing conditions (temperature, speed of rotation, and time of mixing) and alkaline treatment on the dimensions of sisal fiber was studied. The length and diameter of the initial fibers were reduced during mixing and this effect was correlated to the magnitude of the shear stress developed in the mixer. An increase of the speed of rotation and/or a reduction of temperature produced fibers of smaller dimensions but with a higher aspect ratio l/d. Alkaline treatment increased the kinetics associated to the reduction of the fiber's dimensions. A semiempirical model was employed to predict the size of the fibers versus the time of mixing. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1084–1091, 2001     

Biocomposites based on sea algae fibers and biodegradable thermoplastic matrices

Composites were prepared by mixing thermoplastic biodegradable polymers with sea algae fibers. Tensile mechanical properties were analyzed as a function of fiber concentration. The effect of processing, such as compression molding and calendering, on the mechanical properties of the materials was investigated. Composites showed higher elastic modulus and lower strength than the matrix components. Fiber damaging, characterized by a reduction of both length and diameter, was observed in the composites. Films, prepared by calendering operations, showed anisotropic properties due to fiber alignment. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 583–592, 1999     

Some criteria to help the experimental setup of assembly cells with cooperating robots

A pragmatic approach for aid in the designing of assembly cells with cooperating robots is presented in this paper. The conditions justifying the use of multiple cooperation have been previously defined. Effort was then focused on the appropriate characterization of the assembly tasks with the aim of helping find solutions for solving both collision and coordination problems. The capability of the laboratory used for experimental studies on cooperating robots is also illustrated. The presented criteria have been applied to the cell setup of a mechanical assembly process.     

Visible luminescence of lanthanide ions in Ca3Sc2Si3O12 and Ca3Y2Si3O12

The crystalline materials Ca₃Sc₂Si₃O₁₂ and Ca₃Y₂Si₃O₁₂ were characterized by different crystal structures, as the former is a cubic garnet, while the latter is an orthorhombic compound. We investigated the optical spectroscopy of these materials doped with several trivalent lanthanide ions and compared the results for the two hosts. Polycrystalline samples were prepared by solid state reaction, both undoped and doped with the trivalent lanthanide ions Eu³⁺, Tb³⁺ and Sm³⁺. Emission, excitation and Raman spectra of these materials were measured at temperatures ranging from 300 to 10 K. The optical spectra were assigned and discussed, and the effects of the crystal structure of the host on the spectroscopic behaviour were addressed. The technological potential of these compounds in the field of optical materials and devices was discussed.     

Structural Characterization and High-Temperature Behavior of Silicon Oxycarbide Glasses Prepared from Sol-Gel Precursors Containing Si-H Bonds

Silicon oxycarbide glasses have been synthesized by inert atmosphere pyrolysis at 1000°C of gel precursors obtained by cohydrolysis of triethoxysilane, HSi(OEt)₃, and methyl-diethoxysilane, HMeSi(OEt)₂. The oxycarbide structures have been carefully characterized by means of different techniques such as ²⁹Si magic angle spinning nuclear magnetic resonance (MAS-NMR) and Raman spectroscopies, X-ray diffraction (XRD), and chemical analysis. Experimental results clearly indicate that, depending on the composition of the starting gels, the resulting oxycarbide glass either is formed by a pure oxycarbide phase or contains an extra carbon or silicon phase. By increasing the temperature up to 1500°C, the oxycarbide glasses display compositional and weight stability; however, the amorphous network undergoes structural rearrangements that lead to the precipitation of nano-sized β-SiC crystallites into amorphous silica. Crystallization of metallic silicon is also clearly observed at 1500°C for the samples in which the presence of Si-Si bonds was postulated at 1000°C.