Exterior Layer Research Articles

The effect of hybridization on the ballistic impact behavior of hybrid composite armors

In the present study, effect of hybridization on the hybrid composite armors under ballistic impact is investigated using hydrocode simulations. The hybrid composite armor is constructed using various combinations and stacking sequences of fiber reinforced composites having woven form of fibers specifically high specific-modulus/high specific-strength Kevlar fiber (KF), tough, high strain-to-failure fiber Glass fiber (GF) and high strength/high stiffness Carbon fiber (CF). Different combinations of composite armors studied are KF layer in GF laminate, GF layer in KF laminate, KF layer in CF laminate and CF layer in KF laminate at various positions of hybridized layers for a fixed thickness of the target. In this article the results obtained from the finite element model are validated for the case of KF layer in a GF laminate with experimental predictions reported in the literature in terms of energy absorption and residual velocity and good agreement is observed. Further, the effect of stacking sequence, projectile geometry and target thickness on the ballistic limit velocity, energy absorbed by the target and the residual velocity are presented for different combinations of hybrid composite armors. The simulations show that, at a fixed thickness of the hybrid composite armor, stacking sequence of hybridized layer shows significant effect on the ballistic performance. The results also indicate energy absorption and ballistic limit velocity are sensitive to projectile geometry. Specifically, it is found that arranging the KF layer at the rear side, GF layer in the exterior and CF layer on the front side offers good ballistic impact resistance. The hybrid composite armor consisting of a CF layer in KF laminate acquires maximum impact resistance and is the best choice for the design compared to that of other combinations studied.

Impact of polyelectrolyte coating in fluorescent response of Eu(III)-containing nanoparticles on small chelating anions including nucleotides

The present work introduces a novel route to sense the permeability of the polyelectrolyte layer deposited onto luminescent core. The use of ternary Eu(III) complexes as the luminescent core enables to detect the permeability of the polyelectrolyte layers through the change of the Eu(III)-centered luminescence. The chelating anions, such as adenosine phosphates, glutamic acid and ethylenediaminetetraacetic acid disodium salt were used as substrates. The origin of the fluorescent response is the complex formation of the substrates with the Eu(III) complexes, which is greatly affected by the equilibrium concentration of the substrates at the surface of the core. The latter in turn is influenced by the permeability of the polyelectrolyte layer. The obtained results highlight the impact of the nature of the exterior layer in the penetration of the substrates through the negatively and positively charged polyelectrolyte layers.

Transfer matrix method for the solution of multiple elliptic layers with different elastic properties. Part II: exterior finite elliptic matrix case

This paper provides the transfer matrix method for the solution of multiple elliptic layers with different elastic properties. In the study, the medium is composed of an elliptic inclusion and many confocal elliptic layers. In the present study, the exterior layer is a finite confocal elliptic layer. Some derivations in the present study are similar to those in Chen (Acta Mech 2014). However, some derivations in the present study are quite different from those in Chen (Acta Mech 2014). Equations for evaluating the coefficients in the Laurent series for complex potentials are suggested, which are derived from the transfer matrix and the boundary condition. A numerical example for the case of an elliptic inclusion and two confocal elliptic layers is provided in this paper.

Electrochemical performance of patterned LiFePO4 nano-electrode with a pristine amorphous layer

A patterned LiFePO4 nanorod with a pristine amorphous LiFePO4 surface layer was fabricated by controlling the temperature gradient from the interior to the exterior layer in high-temperature annealing process through designing hierarchical multilayer electrode structure. The three dimensional patterned LiFePO4 nanorods were prepared using tobacco mosaic virus nanoforest arrays. The results indicate that the nano-electrodes nearly reached the theoretical capacity at a very low C rate even without conductive coatings. The amorphous LiFePO4 can fast transport the Li-ion to inside crystal LiFePO4, thus enhancing the rate capability.

Pseudospectral solutions to some singular nonlinear BVPs

We solve by Laguerre collocation method two second order genuinely nonlinear singularly perturbed boundary value problems and a fourth order nonlinear one formulated on the half-line. First, we are concerned with solutions to a model equation for low Reynolds number flow, the so-called Cohen, Fokas, Lagerstrom model. Then we compute monotonously increasing solutions, the so-called "bubble type solutions", to density profile equation for the description of the formation of microscopical bubbles in a nonhomogeneous fluid. We compare the results obtained in the latter case with those carried out by shooting or polynomial collocation both coupled with domain truncation. A fourth order nonlinear boundary value problem supplied with mixed boundary conditions in origin as well as at infinity is also solved. The solution and its first three derivatives are obtained and compared with their counterparts obtained by Keller's box scheme. The collocation based on Laguerre functions avoids the domain truncation, exactly impose any kind of boundary conditions at infinity and resolve with reliable accuracy the sharp interior or exterior layer of the solutions. The method is fairly easy implementable and efficient in treating various types of nonlinearities. The accuracy of the method is also tested on the classical Blasius problem (a third order one). We solve with the same method the eigenvalue problem obtained by linearization around the constant solution, which corresponds to the case of a homogeneous fluid (without bubbles), and observe that this solution is stable.

Guarding the perimeter: protection of the mucosa by tissue-resident memory T cells.

Mucosal tissues are continually bombarded with infectious agents seeking to gain entry into the body. The absence of a tough physical exterior layer surrounding these tissues creates a unique challenge for the immune system, which manages to provide broad protection against a plethora of different organisms with the aid of special adaptations that augment immunity at these vulnerable sites. For example, specialized populations of memory T lymphocytes reside at initial sites of pathogen entry into the body, where they provide an important protective barrier. Similar anatomically-confined populations of pathogen-specific CD8 T cells can be found near the outer margins of the body following recovery from a variety of local infections, where they share very similar phenotypic characteristics. How these tissue-resident T cells are retained in a single anatomic location where they can promote immunity is beginning to be defined. Here, we will review current knowledge of the mechanisms that help establish and maintain these regional lymphocytes in the mucosal tissues and discuss relevant data that enhance our understanding of the contribution of these lymphocyte populations to protective immunity against infectious diseases.

Preparation and characterization of a novel poly(urea–formaldehyde) microcapsules with similar reflectance spectrum to leaves in the UV–Vis–NIR region of 300–2500 nm

A novel material with similar reflectance spectrum in the UV–Vis–NIR region of 300–2500 nm to leaves was developed by means of encapsulation. Hydrophilic poly(urea–formaldehyde) was employed as a wall-former, which tended to cure into solid on the exterior layer of the primary W/O emulsion containing chlorophyll in the oil phase as a core substance to generate microcapsules. In particular, the resultant poly(urea–formaldehyde) microcapsules were carefully characterized by UV-3600 UV–Vis–NIR spectrophotometer. The results indicated that the resultant green poly(urea–formaldehyde) microcapsules exhibited very similar spectral reflectance characteristics to leaves, and the similarity of the reflectance spectrum of green poly(urea–formaldehyde) microcapsules to that of plant leaves was up to 97.2% in the UV–Vis–NIR region of 300–2500 nm. In this regard, this new green poly(urea–formaldehyde) microcapsules is a promising candidate for materials with similar reflectance spectrum to leaves in the UV–Vis–NIR region of 300–2500 nm. The characterization of the microcapsules including FT-IR, SEM and FE-SEM were studied. Also, the factors influencing the reflectance spectrum in the UV–Vis–NIR region of 300–2500 nm of microcapsules were analyzed.

Amino-acid based coordination polymers

Five new transition metal–amino acid coordination polymers, including two copper compounds 1D-{Cu(d-α-PhGly)2} (1), 1D-{Cu(l-Trp)2} (2) and three cadmium compounds 2D-{Cd(d-Leu)2} (3) 2D-{Cd(d-Phe)2} (4) and 2D-{[Cd(d-Phe)(4,4′-bipy)H2O][NO3]} (5) are structurally characterized (PhGly=phenylglycinato, Trp=tryptophanato, Leu=leucinato, Phe=phenylalaninato in enantiopure form, 4,4′-bipy=4,4′-bipyridine). Single crystals were obtained by slow diffusion of the metal salt and the ligand in a water–methanol mixture. The enantiopure amino acetate ligands led to homochiral crystallization of 1–5 in the non-centrosymmetric space group P21. Characterization by single-crystal X-ray diffraction, infrared and Raman spectroscopy showed that the copper compounds 1 and 2 form twofold helices around the 21 screw axis and the cadmium compounds 3–5 yield two-dimensional coordinative layers also with twofold helices around the 21 axes for 3 and 4. The Cu-amino-acetate/carboxlyate helices are connected by N–H···O hydrogen bonds and very long Cu⋯O–carboxylate contacts to supramolecular 2D layers. Crystal packings of 2D layer structures in 1–4 show a separation of the hydrophobic alkyl groups from the hydrophilic M-amino-carboxylate region. Charge-assisted Cu(+)⋯(−)O interactions and N–H···(−)O hydrogen-bonding interactions in the hydrophilic region are the driving force of “hydrophobic exterior layer” formation with a hydrophilic interior exposing the hydrophobic alkyl groups to the exterior. Stacking of the layers occurs through weak van der Waals interactions between the alkyl groups. This correlates with the crystal morphology, with formation of thin crystal plates along the stacking direction.In 5 the Cd-μ-amino carboxylate-κN,O:O′ units with a pentagonal–bipyramidal Cd atom form strands, and these strands are then joined through the rigid 4,4′-bipy linkers to a coordinative 2D layer. The nitrate anions connect these layers with charge-assisted (aqua)O–H···(−)O(nitrate) and (amino)N–H···(−)O(nitrate) hydrogen bonds to a supramolecular 3D network.

Carbon Nanofiber Synthesis within 3-Dimensional Sintered Nickel Microfibrous Matrices: Optimization of Synthesis Conditions

This study focuses on the process of optimization for carbon nanofiber synthesis at the exterior and the interior of 3-dimensional sintered nickel microfibrous networks. Synthesis of carbon nanofibers (CNF) by catalytic decomposition of acetylene (ethyne) was conducted at atmospheric pressure and short reaction times (10 min). Two factors evaluated during the study were (a) CNF quality (observed by SEM and Raman spectroscopy) and (b) rate of reaction (gravimetrically measured carbon yield). Independent optimization variables included redox faceting pretreatment of nickel, synthesis temperature, and gas composition. Faceting resulted in an 8-fold increase in the carbon yield compared to an untreated substrate. Synthesis with varying levels of hydrogen maximized the carbon yield (9.31 mg C/cm2catalyst). The quality of CNF was enhanced via a reduction in amorphous carbon that resulted from the addition of 20% ammonia. Optimized growth conditions that led to high rates of CNF deposition preferentially deposited this carbon at the exterior layer of the nickel microfibrous networks (570°C, 78% H2, 20% NH3, 2% C2H2, faceted Ni.). CNF growth within the 3-dimensional nickel networks was accomplished at the conditions selected to lower the gravimetric reaction rate (470°C, 10% H2, 88% N2, 2% C2H2, nonfaceted Ni).

Hydrophobic-exterior layer structures and magnetic properties of trinuclear copper complexes with chiral amino alcoholate ligands

The trinuclear secondary building unit (SBU) {Cu3(μ-L)4X2} constructed from chelating and alcoholate-O-bridging chiral amino alcoholate (amino alkoxido, μ-L) and terminal halide ligands (X) gives rise to two-dimensional (2D) homochiral supramolecular polymers through the bridging action of the halide ligand. Compounds 2D-[Cu3(μ-L)4(μ3-X)2] {X = Br (1 to 4), X = Cl (5, 6); L = amino-ethanolate (1, 5), (R)-2-amino-propan-1-olate (2), (R)-2-amino-butan-1-olate (ab) (3, 6), (R)-2-amino-2-phenyl-ethanolate (4)} were synthesized from 2-amino alcohol, LH with CuBr2 or CuCl2, respectively, in the presence of triethylamine (TEA). The crystal packing of isomorphous 2D-[Cu3(μ-L)4(μ3-X)2] shows a separation of the hydrophobic alkyl from the hydrophilic amino-/alcoholate-/Cu–Br-region. Charge-assisted Cu(2+)⋯(−)Br- and hydrogen-bonding interactions in the hydrophilic region are the driving force of “hydrophobic exterior layer” formation with a hydrophilic interior exposing the hydrophobic alkyl groups to the exterior. Stacking of the layers through weak van-der-Waals interactions between the alkyl groups correlates with formation of thin crystal plates along the stacking direction. A lower ligand concentration yields both dinuclear and mononuclear SBUs in one-dimensional (1D-) homochiral coordination polymers 1D-[{Cu2(μ-ab)2Br2}2{(μ3-Br)Cu(abH)2Br}{(μ3-Br)Cu(abH)(CH3OH)Br}] (7) and 1D-[{Cu2(μ-ab)2Cl2}2{(μ3-Cl)Cu(abH)(CH3CH2OH)Cl}2] (8). In {[Cu(rac-abH)(rac-ab)H2O]ClO4}2 (9) two SBUs combine through charge assisted H-bonds to a dimeric unit. Temperature dependent magnetic susceptibility measurements of 1 and 3 show ferromagnetic coupling but no magnetic ordering. However, at temperatures lower than 3 K an onset of long-range magnetic ordering can be observed. AC magnetic measurements in the range of 1.9 K to 5 K at different frequencies show that the long range magnetic ordering is achieved at lower temperatures than that. Correlation of magnetic coupling with the Cu–O–Cu angle is in agreement with the structural parameters of 1 and 3. Very good agreement between experimental and DFT calculated J,j coupling constants shows that the interaction between the terminal copper(II) ions in these linear trinuclear SBUs is operative and it cannot be neglected.

An Experimental Assessment of the Energy Performance of Novel Concrete Walls Embedded with Mini Solar Collectors

Experimental measurements from a twelve-month trial are used to assess the energy performance of a solar-heated stratified concrete wall panel. The panel comprises an interior layer of high thermal mass concrete and an exterior layer of insulating concrete that is embedded with a solar thermal collector covering 10% of the panel's face. Results indicate that the collector improves the energy performance of stratified concrete panels by more than 15%.

C/SiC/Si-Mo-B/glass multilayer oxidation protective coating for carbon/carbon composites

To prevent carbon/carbon (C/C) composites from oxidation, a self-sealing multilayer oxidation resistant coating including a C/SiC gradient inner layer, a Si-Mo-B middle layer and a glass exterior layer was prepared by pack cementation and slurry method. Scanning electron microscopy and X-ray diffraction were used to analyze the microstructure and phase composition of the as-prepared coating. The isothermal and thermal shock oxidation resistance of the coating was also investigated. The results showed that the multilayer coating exhibited excellent oxidation resistance from room temperature to 1873K. It could effectively protect C/C composites for 100h at 1173K and 150h at 1873K, and endure 40 thermal cycles between 1873K and room temperature. The excellent oxidation and thermal shock resistance could be attributed to the gradient structure and the self-sealing property of the multilayer coating.

Synergistic Effect of POSS on Mechanical Properties, Flammability, and Thermal Degradation of Intumescent Flame Retardant Polylactide Composites

The intumescent flame retardant polylactide/polyhedral oligomeric silsesquioxane (IFR-PLA/POSS) composites were prepared via a melt blending method. The morphology of the PLA nanocomposites was assessed by transmission electron microscopy (TEM). Dynamic mechanical analysis (DMA) and tensile tests showed that the incorporation of POSS enhanced the mechanical properties of the PLA matrix. The limiting oxygen index (LOI) values increased from 20.0% for neat PLA to 40.0% for PLA based on 22.5 wt% IFR and 7.5 wt% POSS, and the latter could pass UL-94 V0 rating. Thermal gravimetric analysis (TGA) showed that the thermal stability of the residual char at the later stages of the thermal degradation was significantly improved. The dynamic Fourier transform infrared (FTIR) spectra suggested that the thermally stable poly(phosphoricacid) and polysiloxane derivatives were formed during the thermal degradation process of PLA/POSS composite. The scanning electron microscope (SEM) and X-ray photoelectron spectrography (XPS) indicated that the residual char of flame retardant PLA/POSS composite had a exterior layer with a compact and continual surface, while the interior had a porous structure, which was composed of cross-linked phosphorous oxynitride and carbonized aromatic networks.

A New Heat Transfer Model for Floor Configuration Layer of the Low-Temperature Water Floor Radiant Heating System

The floor configuration layer and the floor radiant heat transferred by heat transferred configuration layer exterior with other walls are taken into account in this paper, then physical and mathematics models are developed. Simulation results as well as testing results are compared and analyzed to prove that the models and the calculation methods are right.

Understanding boundary condition effects on the corrosion kinetics of class H well cement

Abstract Storing carbon dioxide in depleted petroleum reservoirs is a viable strategy for carbon mitigation, but ensuring that the sequestered CO 2 remains in the formation is vital to the success of such projects. There is great concern for the development of leakage pathways through annuli between the well cement and the formation or the casing. Predicting the behavior of such potential leakage pathways is critical. Numerical simulations conducted using a reactive transport module match well with experimental studies, but also show the necessity of quantifying the transport and mechanical properties of the leached solid cementitious solids–predominantly silica gel–produced by carbonic acid corrosion of well cement. Bench-top experiments have been performed with the following goals in mind: (1) to investigate the parameter space of relevant corrosion boundary conditions, e.g. pH, CO 2 concentration, and calcium ion concentration, (2) to produce samples that can be used to quantify the transport and mechanical properties of acid corroded Class H well cement, and (3) to validate and improve the accuracy of numerical simulations of the reaction of well cement with carbonic acid. Class H cement samples were uniaxially corroded via exposure to a brine of constant composition. Constant composition is ensured by constant renewal of the brine at a rate larger than cement reaction rate. H + , Ca 2+ and CO 2 total aqueous concentration in the NaCl brine are controlled independently by adding known amounts of NaCl, HCl, CaCl 2 and NaHCO 3 and by controlling CO 2 partial pressure. Microscopic (30X) time-lapse videos were taken of each sample so that corrosion front movements could be accurately measured. These experiments have yielded corrosion front measurements that clearly show that corrosion front advancement is diffusion controlled (i.e., linear as a function of the square root of time). The uniaxial corrosion of these samples has not only allowed for detailed measurements of the corrosion front, but also affords the opportunity to measure the mechanical properties of the corroded samples as a function of depth. The one-dimensional corrosion also allows for measuring the diffusion coefficient of the outer layer of silica gel by low field Nuclear Magnetic Resonance (NMR). Measuring the kinetics under various boundary conditions has validated the modeling results reported by Huet et al.. The measurements of mechanical and transport properties can now be used to improve the predictive power of these simulations by providing much needed information on the exterior layer of corroded Class H well cement. Additionally, these experiments offer experimental validation that the corrosion kinetics are enhanced by the presence of CO 2 and open the door to better understanding of the mechanism of, and boundary conditions that might lead to, “pore-plugging” by the corrosion products, which in turn leads to a drastic retardation of the corrosion reaction.

On a new crush trigger for energy absorption of composite tubes

A new crush trigger, called crown trigger, is introduced at one end of carbon-fibre-reinforced polymer circular tubes. Quasi-static compression tests are performed on the tubes to investigate their energy absorption characteristics. It is observed that all tubes are crushed in a brittle fracturing mode. Both crown trigger and bevel trigger can effectively control the position of crushing initiation, reduce the peak load and increase the crushing stability. It is also found that the tube wall of each specimen is delaminated mainly into three layers. The relatively intact exterior layer may constrain the axial splits of the middle layer, make the lamina bundles break off near the base, slow down the central wall crack propagation and thus eliminate a low-performance failure mode. As compared with the bevel trigger, the crown trigger provides nearly the same specific energy absorption but 18.4% lower specific triggering stress and 21.2% higher crushing load efficiency.

Facile route for preparation of silver nanoparticle-coated precipitated silica

In this research, a facile route was used to prepare silver nanoparticle-coated precipitated silica using sodium silicate, a cheap precursor. Precipitated silica (PS) was synthesized by dropping 8% H2SO4 into a mixed solution of sodium silicate 24% (Na2O·3.4SiO2) and NaCl 4%; under constant stirring. The precipitated silica was then modified by simultaneous addition of 3-aminopropyltriethoxysilane (3-APTES) and 8% H2SO4. The resulting material was aged at 80°C for 1h to produce amino-functionalized precipitated silica (AFPS). Silver nanoparticle-coated precipitated silica (Ag–NPS) was synthesized by adding silver nitrate (AgNO3). The synthesis procedure also involved mixing for 2h and dropping 0.05M sodium borohydride (NaBH4). The final products, namely, PS, AFPS, and Ag–NPS were characterized using BET analyzer, FE-SEM, TEM and XRD. Silver nanoparticles with an average size ranging from 18 to 25nm were found mostly coated on the exterior layer of the precipitated silica. The synthesis method reported in this work is facile and might be used for large-scale industrial production of inexpensive Ag–NPS.

Evolution of micro-arc oxidation behaviors of the hot-dipping aluminum coatings on Q235 steel substrate

Micro-arc oxidation (MAO) is not applicable to prepare ceramic coatings on the surface of steel directly. In this work, hybrid method of MAO and hot-dipping aluminum (HDA) were employed to fabricate composite ceramic coatings on the surface of Q235 steel. The evolution of MAO coatings, such as growth rate, thickness of the total coatings, ingrown and outgrown coatings, cross section and surface morphologies and phase composition of the ceramic coatings were studied. The results indicate that both the current density and the processing time can affect the total thickness, the growth rate and the ratio of ingrown and outgrown thickness of the ceramic coatings. The total thickness, outgrown thickness and growth rate have maximum values with the processing time prolonged. The time when the maximum value appears decreases and the ingrown dominant turns to outgrown dominant little by little with the current density increasing. The composite coatings obtained by this hybrid method consists of three layers from inside to outside, i.e. Fe–Al alloy layer next to the substrate, aluminum layer between the Fe–Al layer and the ceramic coatings which is as the top exterior layer. Metallurgical bonding was observed between every of the two layers. There are many micro-pores and micro-cracks, which act as discharge channels and result of quick and non-uniform cooling of melted sections in the MAO coatings. The phase composition of the ceramic coatings is mainly composed of amorphous phase and crystal Al2O3 oxides. The crystal Al2O3 phase includes κ-Al2O3, θ-Al2O3 and β-Al2O3. Compared with the others, the β-Al2O3 content is the least. The MAO process can be divided into three periods, namely the common anodic oxidation stage, the stable MAO stage and the ceramic coatings destroyed stage. The exterior loose part of the ceramic coatings was destroyed badly in the last period which should be avoided during the MAO process.

Synthetic Hydrophilic Materials with Tunable Strength and a Range of Hydrophobic Interactions

AbstractThe ability to vary, adjust, and control hydrophobic interactions is crucial in manipulating interactions between biological objects and the surface of synthetic materials in aqueous environment. To this end a grafted polymer layer (multi‐component mixed polymer brush) is synthesized that is capable of reversibly exposing nanometer‐sized hydrophobic fragments at its hydrophilic surface and of tuning, turning on, and turning off the hydrophobic interactions. The reversible switching occurs in response to changes in the environment and alters the strength and range of attractive interactions between the layer and hydrophobic or amphiphilic probes in water. The grafted layer retains its overall hydrophilicity, while local hydrophobic forces enable the grafted layer to sense and attract the hydrophobic domains of protein molecules dissolved in the aqueous environment. The hydrophobic interactions between the material and a hydrophobic probe are investigated using atomic force microscopy measurements and a long‐range attractive and contact‐adhesive interaction between the material and the probe is observed, which is controlled by environmental conditions. Switching of the layer exterior is also confirmed via protein adsorption measurements.

A New Method in the Design of a Dynamic Pedorthosis for Children With Residual Clubfoot

Clubfoot is a common pediatric orthopaedic deformity. Despite the popularity of Ponseti’s method and night splints such as the Denis–Browne method, there is still an 11–47% rate of deformity relapse reported in the literature. The technique to make traditional orthotics is dependent on a nonweight-bearing casting or foot imprint. These splints outdate clinical treatment trends and only apply to patients who are of nonwalking age. This study shows that a new procedure utilizing computer aided design and the finite element method can be employed to develop a customized weight-bearing dynamic orthotic. In addition, the plantar pressure distribution and the trajectory of the center of this pressure distribution are used to design the orthotic. It is shown that the trajectory of the center of pressure, traditionally used in gait analysis, can be used not only to quantify the severity of the foot deformity but to design a custom orthotic as well. Also, the new procedure allows the custom orthotic to be designed and analyzed within a day. The new orthotic design is composed of soft foam interior layers and a polymer supportive exterior layer. It is proved that rapid prototyping technologies employing selective laser sintering can be used to construct these layers to produce a custom orthotic within a 24 h time frame.