A finite element computational framework for enhanced photostrictive performance in 0–3 composites

Photostriction is a multiphysics phenomenon comprising of both photovoltaic effect and converse piezoelectric effect. The extensively researched photostrictive material is lead lanthanum zirconate titanate, i.e., Pb_0.92La_0.08(Zr_0.65Ti_0.35)_0.98O₃ (PLZT) ceramic. In contrast to the traditional approaches of improving deflection response, the current study proposes a 0–3 composite model to substantially enhance the effective material properties, which in turn significantly improves the deflection response. A computational framework based on finite element analysis is employed to 0–3 photostrictive composite of PLZT as matrix and Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ (PMN-35PT) as the inclusions. The representative volume element (RVE) or unit cell technique is used to incorporate the local variation of constituent properties and to calculate photostrictive properties such as effective elastic, dielectric, piezoelectric, and pyroelectric properties. An opto-electro-thermo-mechanical finite element formulation was engaged to get the actuation response of photostrictive material bonded to cantilever and simply supported beam. The maximum deflection for cantilever beam attached to photostrictive composite patch having 25% inclusions volume fraction in 0–3 composite is found to be 38% more in comparison to pure PLZT material. It is established that the opto-electro-mechanical 0–3 composite actuators possess high potential in lightweight, compact and wireless actuation applications.

     

Dissolution of laves phase by re-austenitization and tempering of creep strength enhanced ferritic steel

ABSTRACT

Formation of Laves phase in creep strength enhanced ferritic steel is investigated using re-austenitization and tempering treatment. The as-received material is exposed to 620°C for 4560?h aging, and then re-austenitizated at 1050°C for 1?h, and followed by tempering at 760°C for different times (2 and 4?h). After re-austenitization and tempering, the dissolution of Laves phase is observed while grain size and microhardness have not changed significantly. A model is suggested to quantify the dissolution of W-containing Laves phase. Thermo-Calc is used to predict driving forces for precipitation of Laves and M23C6 phases.     

Synergistic effect of Mill scale and MoS2 in geopolymer composites for EMI shielding application

Journal of Materials Science: Materials in Electronics - This study reports the development of a synergistic composition of geopolymer for EMI shielding building material using micron-sized...     

The Influence of Nanoparticle Shape on Protein Corona Formation

Nanoparticles have become an important utility in many areas of medical treatment such as targeted drug and treatment delivery as well as imaging and diagnostics. These advances require a complete understanding of nanoparticles' fate once placed in the body. Upon exposure to blood, proteins adsorb onto the nanoparticles surface and form a protein corona, which determines the particles' biological fate. This study reports on the protein corona formation from blood serum and plasma on spherical and rod‐shaped nanoparticles. These two types of mesoporous silica nanoparticles have identical chemistry, porosity, surface potential, and size in the y‐dimension, one being a sphere and the other a rod shape. The results show a significantly larger amount of protein attaching from both plasma and serum on the rod‐like particles compared to the spheres. Interrogation of the protein corona by liquid chromatography–mass spectrometry reveals shape‐dependent differences in the adsorption of immunoglobulins and albumin proteins from both plasma and serum. This study points to the need for taking nanoparticle shape into consideration because it can have a significant impact on the fate and therapeutic potential of nanoparticles when placed in the body.     

Friction Study of a Ni Nanodot-patterned Surface

Nanoscale frictional behavior of a Ni nanodot-patterned surface (NDPS) was studied using a TriboIndenter by employing a diamond tip with a 1 μm nominal radius of curvature. The Ni NDPS was fabricated by thermal evaporation of Ni through a porous anodized aluminum oxide (AAO) template onto a Si substrate. Surface morphology and the deformation of the NDPS were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), before and after friction/scratch testing. SEM images after scratching clearly showed that, similar to what was assumed at the macroscale, the frictional force is proportional to the real area of contact at the nanoscale. It was found that adhesion played a major role in the frictional performance, when the normal load was less than 20 μN and plastic deformation was the dominant contributor to the frictional force, when the normal load was between 60 μN and 125 μN. Surprisingly, a continuum contact mechanics model was found to be applicable to the nanoscale contact between the tip and the inhomogeneous Ni NDPS at low loads. The coefficient of friction (COF) was also found to depend on the size of the tip and was four times the COF between a 100 μm tip and the Ni NDPS. Finally, the critical shear strength of the Ni nanodots/Si substrate interface was estimated to be about 1.24 GPa.     

LF-SegNet: A Fully Convolutional Encoder–Decoder Network for Segmenting Lung Fields from Chest Radiographs

Wireless Personal Communications - Segmentation of lung fields is an important pre-requisite step in chest radiographic computer-aided diagnosis systems as it precisely defines the...     

Effect of Si3N4 Addition on Compressive Creep Behavior of Hot‐Pressed ZrB2–SiC Composites

Compressive creep studies have been carried out on hot‐pressed ZrB₂–SiC (ZS) and ZrB₂–SiC–Si₃N₄ (ZSS) composites in air under stress and temperature ranges of 93–140 MPa and 1300°C–1425°C, respectively for time durations of ≈20–40 h. The results of these studies have shown the creep resistance of ZS composite to be greater than that of ZSS. As the temperature is increased from 1300°C to 1425°C, the stress exponent of ZS decreases from 1.7 to 1.1, whereas that of ZSS drops from 1.6 to 0.6. The activation energies for these composites have been found as ≈95 ± 32 kJ/mol at temperatures ≤1350°C, and as ≈470 ± 20 kJ/mol in the range of 1350°C–1425°C. Studies of the postcreep microstructures using scanning and transmission electron microscopy have shown the presence of glassy film with cracks at both ZrB₂ grain boundaries and ZrB₂–SiC interfaces. These results along with calculated values of activation volumes suggest grain‐boundary sliding as the major damage mechanism, which is controlled by O^2? diffusion through SiO₂ at ≤1350°C, and by viscoplastic flow of the glassy interfacial film at temperatures ≥1350°C. Studies by transmission electron microscopy have shown formation of crystalline precipitates of Si₂N₂O near ZrB₂–SiC interfaces in ZSS tested at ≥1400°C, which along with stress exponent values <1 suggests that grain‐boundary sliding involving solution‐precipitation‐type mechanism is operative at these temperatures.     

Covalent assembly-disassembly of poly(ether imine) dendritic macromolecular monomers and megamers

Abstract

Poly(ether imine) dendritic macromolecules were undertaken to study the reversible dendrimer monomer-megamer assembly-disassembly in aqueous solutions. Synthesis of thiol functionalized poly(ether imine) (PETIM) dendrimers and their covalent aggregation behavior in the aqueous solution of ethanol/water (2:1) is demonstrated. The dendritic megamers were characterized using microscopic techniques. Kinetics of the aggregation behavior was followed using turbidity measurements, light-scattering and atomic force microscopic techniques. Inherent luminescence behavior of PETIM dendrimer monomers was retained in the dendrimer megamers also, which allowed visualization of the megamers through confocal microscopy. Extent of thiol functionalities that remained after the megamer assembly was estimated through Ellman's assay. Subsequent to megamer assembly, disassembly of megamers to dendrimer monomers was conducted, using dithiothreitol reagent. Water-insoluble sudan I dye was encapsulated in dendrimer megamer and subsequent release profile was assessed during the disassembly in aqueous solutions. The studies were conducted using first, second and third generations, representing 4, 8 and 16 sulfhydryl groups at their peripheries of dendrimers, respectively.     

A low-power asynchronous interleaved sampling algorithm for cochlear implants that encodes envelope and phase information

Cochlear implants currently fail to convey phase information, which is important for perceiving music, tonal languages, and for hearing in noisy environments. We propose a bio-inspired asynchronous interleaved sampling (AIS) algorithm that encodes both envelope and phase information, in a manner that may be suitable for delivery to cochlear implant users. Like standard continuous interleaved sampling (CIS) strategies, AIS naturally meets the interleaved-firing requirement, which is to stimulate only one electrode at a time, minimizing electrode interactions. The majority of interspike intervals are distributed over 1-4 ms, thus staying within the absolute refractory limit of neurons, and form a more natural, pseudostochastic pattern of firing due to complex channel interactions. Stronger channels are selected to fire more often but the strategy ensures that weaker channels are selected to fire in proportion to their signal strength as well. The resulting stimulation rates are considerably lower than those of most modern implants, saving power yet delivering higher potential performance. Correlations with original sounds were found to be significantly higher in AIS reconstructions than in signal reconstructions using only envelope information. Two perceptual tests on normal-hearing listeners verified that the reconstructed signals enabled better melody and speech recognition in noise than those processed using tone-excited envelope-vocoder simulations of cochlear implant processing. Thus, our strategy could potentially save power and improve hearing performance in cochlear implant users.