Chiral Porphyrin Assemblies Investigated by a Modified Reflectance Anisotropy Spectroscopy Spectrometer.

Reflectance anisotropy spectroscopy (RAS) has been largely used to investigate organic compounds: Langmuir-Blodgett and Langmuir-Schaeffer layers, the organic molecular beam epitaxy growth in situ and in real time, thin and ultrathin organic films exposed to volatiles, in ultra-high vacuum (UHV), in controlled atmosphere and even in liquid. In all these cases, porphyrins and porphyrin-related compounds have often been used, taking advantage of the peculiar characteristics of RAS with respect to other techniques. The technical modification of a RAS spectrometer (CD-RAS: circular dichroism RAS) allows us to investigate the circular dichroism of samples instead of the normally studied linear dichroism: CD-RAS measures (in transmission mode) the anisotropy of the optical properties of a sample under right and left circularly polarized light. Although commercial spectrometers exist to measure the circular dichroism of substances, the "open structure" of this new spectrometer and its higher flexibility in design makes it possible to couple it with UHV systems or other experimental configurations. The importance of chirality in the development of organic materials (from solutions to the solid state, as thin layers deposited-in liquid or in vacuum-on transparent substrates) could open interesting possibilities to a development in the investigation of the chirality of organic and biological layers. In this manuscript, after the detailed explanation of the CD-RAS technique, some calibration tests with chiral porphyrin assemblies in solution or deposited in solid film are reported to demonstrate the quality of the results, comparing curves obtained with CD-RAS and a commercial spectrometer.

Advances in Optical Sensors for Persistent Organic Pollutant Environmental Monitoring.

Optical chemical sensors are widely applied in many fields of modern analytical practice, due to their simplicity in preparation and signal acquisition, low costs, and fast response time. Moreover, the construction of most modern optical sensors requires neither wire connections with the detector nor sophisticated and energy-consuming hardware, enabling wireless sensor development for a fast, in-field and online analysis. In this review, the last five years of progress (from 2017 to 2021) in the field of optical chemical sensors development for persistent organic pollutants (POPs) is provided. The operating mechanisms, the transduction principles and the types of sensing materials employed in single selective optical sensors and in multisensory systems are reviewed. The selected examples of optical sensors applications are reported to demonstrate the benefits and drawbacks of optical chemical sensor use for POPs assessment.

A comparative study of bio-inspired protective scales using 3D printing and mechanical testing.

Flexible natural armors from fish, alligators or armadillo are attracting an increasing amount of attention for their unique combinations of hardness, flexibility and light weight. The extreme contrast of stiffness between hard scales and surrounding soft tissues gives rise to unusual and attractive mechanisms, which now serve as models for the design of bio-inspired armors. Despite this growing interest, there is little guideline for the choice of materials, optimum thickness, size, shape and arrangement for the protective scales. In this work, we explore how the geometry and arrangement of hard scales can be tailored to promote scale-scale interactions. We use 3D printing to fabricate arrays of scales with increasingly complex geometries and arrangements, from simple squares with no overlap to complex ganoid-scales with overlaps and interlocking features. We performed puncture tests and flexural tests on each of the 3D printed materials, and we report the puncture resistance - compliance characteristics of each design on an Ashby chart. The interactions between the scales can significantly increase the resistance to puncture, and these interactions can be maximized by tuning the geometry and arrangement of the scales. Interestingly, the designs that offer the best combinations of puncture resistance and flexural compliance are similar to the geometry and arrangement of natural teleost and ganoid scales, which suggests that natural evolution has shaped these systems to maximize flexible protection. This study yields new insights into the mechanisms of natural dermal armor, and also suggests new designs for personal protective systems. STATEMENT OF SIGNIFICANCE: Flexible natural armors from fishes, alligators or armadillos are attracting an increasing amount of attention for their unique and attractive combinations of hardness, flexibility and low weight. Despite a growing interest in bio-inspired flexible protection, there is still little guideline for the choice of materials, optimum thickness, size, shape and arrangement of the protective scales. In this work, we explore how the geometry and arrangement of hard scales affect puncture resistance and flexural compliance, using 3D printing and mechanical testing. Our main finding is that the performance of the scaled skin in terms of puncture resistance can be significantly improved by slight changes in their geometry and arrangement. Our results also suggest that natural evolution has shaped scaled skins to maximize flexible protection. This study yields new insights into the mechanics of natural dermal armors, and also suggests new designs for personal protective systems.

3D-printing and mechanics of bio-inspired articulated and multi-material structures.

3D-printing technologies allow researchers to build simplified physical models of complex biological systems to more easily investigate their mechanics. In recent years, a number of 3D-printed structures inspired by the dermal armors of various fishes have been developed to study their multiple mechanical functionalities, including flexible protection, improved hydrodynamics, body support, or tail prehensility. Natural fish armors are generally classified according to their shape, material and structural properties as elasmoid scales, ganoid scales, placoid scales, carapace scutes, or bony plates. Each type of dermal armor forms distinct articulation patterns that facilitate different functional advantages. In this paper, we highlight recent studies that developed 3D-printed structures not only to inform the design and application of some articulated and multi-material structures, but also to explain the mechanics of the natural biological systems they mimic.

Stretch-and-release fabrication, testing and optimization of a flexible ceramic armor inspired from fish scales.

Protective systems that are simultaneously hard to puncture and compliant in flexion are desirable, but difficult to achieve because hard materials are usually stiff. However, we can overcome this conflicting design requirement by combining plates of a hard material with a softer substrate, and a strategy which is widely found in natural armors such as fish scales or osteoderms. Man-made segmented armors have a long history, but their systematic implementation in a modern and a protective system is still hampered by a limited understanding of the mechanics and the design of optimization guidelines, and by challenges in cost-efficient manufacturing. This study addresses these limitations with a flexible bioinspired armor based on overlapping ceramic scales. The fabrication combines laser engraving and a stretch-and-release method which allows for fine tuning of the size and overlap of the scales, and which is suitable for large scale fabrication. Compared to a continuous layer of uniform ceramic, our fish-scale like armor is not only more flexible, but it is also more resistant to puncture and more damage tolerant. The proposed armor is also about ten times more puncture resistant than soft elastomers, making it a very attractive alternative to traditional protective equipment.

Tuning of strain and surface roughness of porous silicon layers for higher-quality seeds for epitaxial growth.

Sintered porous silicon is a well-known seed for homo-epitaxy that enables fabricating transferrable monocrystalline foils. The crystalline quality of these foils depends on the surface roughness and the strain of this porous seed, which should both be minimized. In order to provide guidelines for an optimum foil growth, we present a systematic investigation of the impact of the thickness of this seed and of its sintering time prior to epitaxial growth on strain and surface roughness. Strain and surface roughness were monitored in monolayers and double layers with different porosities as a function of seed thickness and of sintering time by high-resolution X-ray diffraction and profilometry, respectively. Unexpectedly, we found that strain in double and monolayers evolves in opposite ways with respect to layer thickness. This suggests that an interaction between layers in multiple stacks is to be considered. We also found that if higher seed thickness and longer annealing time are to be preferred to minimize the strain in double layers, the opposite is required to achieve smoother layers. The impact of these two parameters may be explained by considering the morphological evolution of the pores upon sintering and, in particular, the disappearance of interconnections between the porous seed and the bulk as well as the enlargement of pores near the surface. An optimum epitaxial growth hence calls for a trade-off in seed thickness and annealing time, between minimum-strained layers and rougher surfaces. PACS CODES: 81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties; 81.05.Rm Porous materials; granular materials; 82.80.Ej X-ray, Mössbauer and other γ-ray spectroscopic analysis methods.

Palatability and stability of shortbread made with low saturated fat content.

High consumption of saturated fatty acids (SFA) is associated with increased risk of cardiovascular disease and the European Food Safety Agency has called for lower SFA intake. This study assessed the formulation of low SFA shortbreads by replacing 60% and 70% of the butter content with high oleic sunflower oil and water. The quality of the low SFA shortbreads was evaluated through acidity, peroxide value, moisture, ash content, water activity, pH, protein, fat content, and fatty acid profiles. A sensory evaluation was performed to ascertain the effect on flavor. Stability of the new formulations was assessed by conducting accelerated shelf-life studies. The high oleic sunflower oil replacement of butter at levels of 60% and 70% decreased the final SFA content by 52% and 61%, respectively. On the other hand, monounsaturated fat content increased 55% on average while polyunsaturated fat content increased by 40%. Furthermore the new formulations possess quality parameters similar to those of traditional shortbreads (TSs). The study of the shelf life of the products showed that there are no significant variations in peroxide values, malondialdehyde content, or fatty acid profiles in biscuits over time, confirming their high stability. The quantitative descriptive analysis showed that the TS and low SFA shortbreads have similar sensory profiles, and the consumer tests indicated that the low SFA shortbreads were well liked.

Mechanical properties of sintered meso-porous silicon: a numerical model.

: Because of its optical and electrical properties, large surfaces, and compatibility with standard silicon processes, porous silicon is a very interesting material in photovoltaic and microelectromechanical systems technology. In some applications, porous silicon is annealed at high temperature and, consequently, the cylindrical pores that are generated by anodization or stain etching reorganize into randomly distributed closed sphere-like pores. Although the design of devices which involve this material needs an accurate evaluation of its mechanical properties, only few researchers have studied the mechanical properties of porous silicon, and no data are nowadays available on the mechanical properties of sintered porous silicon. In this work we propose a finite element model to estimate the mechanical properties of sintered meso-porous silicon. The model has been employed to study the dependence of the Young's modulus and the shear modulus (upper and lower bounds) on the porosity for porosities between 0% to 40%. Interpolation functions for the Young's modulus and shear modulus have been obtained, and the results show good agreement with the data reported for other porous media. A Monte Carlo simulation has also been employed to study the effect of the actual microstructure on the mechanical properties.

Two-scale simulation of drop-induced failure of polysilicon MEMS sensors.

In this paper, an industrially-oriented two-scale approach is provided to model the drop-induced brittle failure of polysilicon MEMS sensors. The two length-scales here investigated are the package (macroscopic) and the sensor (mesoscopic) ones. Issues related to the polysilicon morphology at the micro-scale are disregarded; an upscaled homogenized constitutive law, able to describe the brittle cracking of silicon, is instead adopted at the meso-scale. The two-scale approach is validated against full three-scale Monte-Carlo simulations, which allow for stochastic effects linked to the microstructural properties of polysilicon. Focusing on inertial MEMS sensors exposed to drops, it is shown that the offered approach matches well the experimentally observed failure mechanisms.

Jogos cooperativos na escola: A concepção de professores de educação física / Cooperative games in school: the idea that physical education teacher

Como contribuir para uma prática na Educação Física Escolar que tenha maior coerência com os desafios vividos pela Educação hoje, como inclusão, participação, cooperação, solidariedade e exercício de cidadania? Essa questão norteou a definição do nosso problema de pesquisa: Qual a concepção dos professores de Educação Física Escolar sobre os Jogos Cooperativos? O objetivo da pesquisa foi levantar dados que possam contribuir para o aprofundamento da discussão sobre os Jogos Cooperativos na Educação Física Escolar. Na busca de atingir nosso objetivo, dividimos o trabalho em duas etapas: Na primeira, partindo da revisão bibliográfica, procuramos explorar aspectos da Educação, da Educação Física e dos Jogos Cooperativos pertinentes ao contexto dessa pesquisa. Na segunda etapa, buscamos levantar os dados referentes às concepções dos professores de Educação Física sobre os Jogos Cooperativos. Com esse objetivo, realizamos entrevistas com oito sujeitos. Após tal levantamento, categorizamos as respostas, analisamos e interpretamos os dados. Os dados levantados revelaram as seguintes concepções dos sujeitos: não haveria possibilidade de equilíbrio e co-existência entre os Jogos Cooperativos e Competitivos nas aulas, ou seja, a opção por uma estrutura implicaria na exclusão da outra; os Jogos Cooperativos podem contribuir positivamente para a Educação Física, no entanto, não foram explicitados conceitos e características que demonstrassem o conhecimento de tais jogos; quando os Jogos Cooperativos foram apontados como parte integrante da prática dos sujeitos, eles ficaram restritos à ação individual do professor, não demonstrando articulação com outros docentes ou equipe técnica da escola; e, ainda, a prática dos Jogos Cooperativos tem pouca repercussão em um mundo competitivo. Os resultados apontam que os Jogos Cooperativos são um conhecimento ainda novo e pouco explorado, necessitando por isso de um número maior de pesquisas que conduzam a desdobramentos na prática docente, e para a necessidade de uma articulação coletiva na escola, que possa subsidiar e potencializar a prática dos Jogos Cooperativos, ampliando sua ação para além do espaço das aulas de Educação Física (AU)