735 research outputs found
Mechanical mode engineering with orthotropic metamaterial membranes
Metamaterials are structures engineered at a small scale with respect to the
wavelength of the excitations they interact with. These structures behave as
artificial materials whose properties can be chosen by design, mocking and even
outperforming natural materials and making them the quintessential tool for
manipulation of wave systems. In this Letter we show how the acoustic
properties of a silicon nitride membrane can be affected by nanopatterning. The
degree of asymmetry in the pattern geometry induces an artificial anisotropic
elasticity, resulting in the splitting of otherwise degenerate mechanical
modes. The artificial material we introduce has a maximum Ledbetter-Migliori
anisotropy of 1.568, favorably comparing to most bulk natural crystals. With an
additional freedom in defining arbitrary asymmetry axes by pattern rotation,
our approach can be useful for fundamental investigation of material properties
as well as for devising improved sensors of light, mass or acceleration based
on micromechanical resonators
Macro-micro relationship in nanostructured functional composites
This paper examines the results of the characterization of two functional composites: Poly(methyl methacrylate)
(PMMA)-Ce:YAG (yttrium aluminium garnet doped with cerium) and PMMA-cobalt hexacyanoferrate (CoHCF). The
composites were prepared as possible emitters in the fields of lighting thermal sensors. The prepared composites were characterized
using transmission electron microscopy (TEM), nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric
analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) analyses to study
the correlation between micro and macro characteristics. We found that the molecular interactions of the two different
fillers with the matrix were localized in different sites of the polymer chains. Moreover, the composites showed an
increased thermal strength and stiffness, in particular the PMMA-Ce:YAG composite
Interferometric control of absorption in thin plasmonic metamaterials: General two port theory and broadband operation
In order to extend the Coherent Perfect Absorption (CPA) phenomenology to broadband operation, the interferometric control of absorption is investigated in two-port systems without port permutation symmetry. Starting from the two-port theory of CPA treated within the Scattering Matrix formalism, we demonstrate that for all linear two-port systems with reciprocity the absorption is represented by an ellipse as function of the relative phase and intensity of the two input beams, and it is uniquely determined by the device single-beam reflectance and transmittance, and by the dephasing of the output beams. The basic properties of the phenomenon in systems without port permutation symmetry show that CPA conditions can still be found in such asymmetric devices, while the asymmetry can be beneficial for broadband operation. As experimental proof, we performed transmission measurements on a metal-semiconductor metamaterial, employing a Mach-Zehnder interferometer. The experimental results clearly evidence the elliptical feature of absorption and trace a route towards broadband operation
Metodologia para a determinação da intensidade de coloração em grãos de milho.
bitstream/CNPSA/15614/1/cot260.pd
Efeito da granulometria do milho sobre a digestibilidade das dietas para suínos em crescimento e terminação.
bitstream/item/58534/1/CUsersPiazzonDocuments223.pd
Optical properties of bulk high-entropy diborides for solar energy applications
So far, the studies regarding the innovative High-Entropy Borides (HEBs), which belong to the more general class of Ultra-high temperature ceramics (UHTCs), have been entirely confined to their fabrication or characterization from the microstructural, mechanical and oxidation resistance viewpoints. In this work, the optical properties of two members of HEBs, i.e. (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 and (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, are evaluated for the first time to assess their possible utilization in the thermal solar energy field. The bulk samples (96.5 % and 97.4 % dense, respectively) are obtained as single-phase products by Spark Plasma Sintering (1950 °C/20 min/20 MPa) starting from powders previously synthesized by Self-propagating High-temperature Synthesis (SHS). The optical characterization, whose results are discussed by comparing HEBs to the individual borides, shows that they are characterized by intrinsic spectral selectivity and low thermal emittance, resulting therefore interesting for high-temperature solar absorbers applications
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