Polymer-derived silicon nitride aerogels as shape stabilizers for low and high-temperature thermal energy storage

This work presents a new skeleton material for thermal energy storage (TES), a silicon nitride aerogel obtained through the pyrolysis of a pre-ceramic polymer. Silicon nitride offers a good combination of thermal conductivity, high-temperature resistance, and chemical inertness. The aerogel porosity can be spontaneously infiltrated with molten NaNO₃, which is a typical phase change material (PCM) in high-temperature TES. The Si₃N₄/NaNO₃ composite exhibits excellent thermal properties with a thermal energy storage efficiency of 82 %, a limited molten salt leakage, and good stability to thermal cycling. The aerogel withstands oxidation up to high temperature and is chemically inert even in contact with salts. This novel aerogel shows also a notable paraffin absorption ability (used in room temperature TES) with negligible leakage even when in contact with absorbent paper. The so-obtained composite reached ≈ 82.4 vol % of organic PCM and a thermal energy storage efficiency of ≈ 62 % compared to neat paraffin.     

Computing optical flow across multiple scales: An adaptive coarse-to-fine strategy

Single-scale approaches to the determination of the optical flow field from the time-varying brightness pattern assume that spatio-temporal discretization is adequate for representing the patterns and motions in a scene. However, the choice of an appropriate spatial resolution is subject to conflicting, scene-dependent, constraints. In intensity-base methods for recovering optical flow, derivative estimation is more accurate for long wavelengths and slow velocities (with respect to the spatial and temporal discretization steps). On the contrary, short wavelengths and fast motions are required in order to reduce the errors caused by noise in the image acquisition and quantization process.Estimating motion across different spatial scales should ameliorate this problem. However, homogeneous multiscale approaches, such as the standard multigrid algorithm, do not improve this situation, because an optimal velocity estimate at a given spatial scale is likely to be corrupted at a finer scale. We propose an adaptive multiscale method, where the discretization scale is chosen locally according to an estimate of the relative error in the velocity estimation, based on image properties.Results for synthetic and video-acquired images show that our coarse-to-fine method, fully parallel at each scale, provides substantially better estimates of optical flow than do conventional algorithms, while adding little computational cost.     

Zeolite filled siloxane composite foams: Compression property

In this article, mechanical behavior under compression loads of an innovative adsorbent material, based on silicone composite foams filled with SAPO 34 zeolite, is presented. The innovative composite foams were obtained profiting by the dehydrogenative coupling of siloxane constituents. These new adsorbent systems have been proposed to overcome to the low mechanical stability of conventional SAPO‐34 coating for adsorption chiller. In this concern, static and cyclic compressive tests at room temperature have been carried out. Samples at increasing content of SAPO 34 zeolite were tested to evaluate the influence of the filler content on the mechanical behavior of the composite foam. The results showed that the presence of zeolite reduces the elastic limit of the foam and increases the strength. The foams evidenced also acceptable mechanical stability to cyclic compressive loads. The encouraging results confirm the possible use of these new composite foams as adsorbent materials for cyclic adsorption heat pumps. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46145.     

Novel Synthetic Approach to Tune the Surface Properties of Polymeric Films: Ionic Exchange Reaction between Sulfonated Polyarylethersulfones and Ionic Liquids

Currently, no studies dealing with the role played by ionic liquids on tailoring surface features of polymer films are available. In this work, ionic liquids influence on the surface of sulfonated polyarylethersulfones was investigated. Sulfonated polyarylethersulfones with different degrees of sulfonation were synthesized; their surface properties were modulated through an ionic exchange reaction between the K⁺ cation of sulfonated polyarylethersulfones and ionic liquids, synthesized changing the length of cation of apolar groups. Hydrophobic properties of sulfonated polyarylethersulfones–ionic liquids films improve with both an increase in degrees of sulfonation and the length of ionic liquids alkyl chains due to higher surface roughness, as shown by scanning electron microscopy and atomic force microscopy.     

Fundamental Solutions in the Theory of Thermoelasticity for Solids with Double Porosity

In this article, the linear theory of thermoelasticity for solids with double porosity is considered. The fundamental solutions for the systems of steady vibrations (including quasi-static case) and equilibrium equations are constructed by means of elementary functions; the basic properties of such solutions are also established.     

Lipid oxidation promotes acrylamide formation in fat-rich model systems

Lipid oxidation is one of the major chemical reactions occurring during food processing or storage and may have a strong impact on the final quality of foods. A significant role of carbonyl compounds derived from lipid oxidation in acrylamide formation has been recently proposed. In this work, the effect of lipid oxidation level on acrylamide formation was investigated by thermal treatment of differently formulated fat-rich model systems. Results showed that lipid oxidation positively influenced the formation of acrylamide. The effect was more evident in sugar-free system where lipid become the main sources of carbonyls. Catechins reduced acrylamide formation presumably by trapping carbohydrates and/or preventing lipid oxidation. More acrylamide was formed in model systems composed with sunflower oil than in those containing palm oil which is less susceptible to oxidation.In systems containing higher amount of water, acrylamide formation was delayed due to evaporative cooling. In these systems, the effect of catechin was more pronounced and the effect of lipid oxidation became detectable only after a prolonged reaction time.These findings suggested that lipid oxidation could become a relevant factor for acrylamide formation, particularly for dry foods with low carbohydrate content.     

Optically Inspired Nanomagnonics with Nonreciprocal Spin Waves in Synthetic Antiferromagnets

Integrated optically inspired wave-based processing is envisioned to outperform digital architectures in specific tasks, such as image processing and speech recognition. In this view, spin waves represent a promising route due to their nanoscale wavelength in the gigahertz frequency range and rich phenomenology. Here, a versatile, optically inspired platform using spin waves is realized, demonstrating the wavefront engineering, focusing, and robust interference of spin waves with nanoscale wavelength. In particular, magnonic nanoantennas based on tailored spin textures are used for launching spatially shaped coherent wavefronts, diffraction-limited spin-wave beams, and generating robust multi-beam interference patterns, which spatially extend for several times the spin-wave wavelength. Furthermore, it is shown that intriguing features, such as resilience to back reflection, naturally arise from the spin-wave nonreciprocity in synthetic antiferromagnets, preserving the high quality of the interference patterns from spurious counterpropagating modes. This work represents a fundamental step toward the realization of nanoscale optically inspired devices based on spin waves.     

High-resolution multi-bit second-order incremental converter with 1.5-μV residual offset and 94-dB SFDR

This paper describes an incremental converter based on a second order ???? modulator. The scheme uses a 3-bit DAC with inherent linearity, an optimal reset of integrators, and gives rise to an effective offset cancellation with a novel technique based on single or double chopping. The circuit, fabricated in a mixed 0.18-0.6???m CMOS technology, obtains 1.5-??V residual offset with 2V_PP fully differential range. The measured resolution is 19 bit obtained with 512 clock periods.     

Numerical optimization of heat recovery steam cycles: Mathematical model, two-stage algorithm and applications

Most of the advanced integrated energy systems need a heat recovery steam cycle (HRSC), either fired or unfired, that recovers the waste heat from gas turbines and process units in order to generate electric power and supply mechanical power to compressors, heat to endothermic processes, and steam to external users. The key feature of such HRSCs is the integration between the heat recovery steam generator (HRSG) and the external heat exchangers. This paper presents a rigorous mathematical programming model, a linear approximation, and a two-stage algorithm for optimizing the design of integrated HRSGs and HRSCs, simultaneously considering the HRSG together with the heat recovery steam network and the intensive steam cycle variables. A detailed application of the methodology is described for an integrated gasification combined cycle plant with CO₂ capture and results for other interesting plants are reported. A significant efficiency gain is obtained with respect to usual practice designs.