A finite element model to predict the ablation depth in pulsed laser ablation

This work presents development of a two-dimensional finite element model to predict temperature distribution and ablation depth in a laser ablation process. The model considers a number of aspects of the process, which hitherto have been considered independently in the literature. The aspects considered include: temperature dependent material properties of the target material, effect of plasma shielding on the incident laser flux, and temperature dependent absorptivity and absorption coefficient of the target. It was evident that these considerations have resulted in a significant improvement in the ability of the model to predict the ablation depth. Finally, the predicted ablation depth was found to match extremely well with experimental results at lower laser fluences, though at higher fluences there is a marginal overestimation.     

Compressive and ultrasonic properties of polyester/fly ash composites

The addition of hollow fillers having appropriate mechanical properties can decrease the density of the resulting composite, called syntactic foams, while concurrently improving its mechanical properties. In this study, hollow fly ash particles, called cenospheres, are used as fillers in polyester matrix material. Cenospheres are a waste by-product of coal combustion and, as such, are available at very low cost. In this study, the composites were synthesized by settling cenospheres in a glass tube filled with liquid polyester resin and subsequently curing the resin. This process resulted in a functionally graded structure containing a gradient in the cenosphere volume fraction along the sample height. Uniform radial sections were cut from each composite and were characterized to observe the relationship between cenosphere volume fraction and compressive properties of the composite. The composite was also tested using ultrasonic non-destructive evaluation method. Results show that the modulus of the composites increases with increasing cenosphere volume fraction. The modulus of composites containing more than 4.9 vol% cenosphere was found to be higher than the matrix resin. In general, the modulus of composites increased from 1.33 to 2.1 GPa for composites containing from 4.9–29.5 vol% cenospheres. The specific strength of the composite was found to be as high as 2.03 MPa/(kg/m³) compared to 0.96 MPa/(kg/m³) for the neat resin. Numerous defects present in fly ash particles caused a reduction in the strength of the composite. However, the reduction in the strength was found to be only up to 22%. Increase of over 110% in the specific modulus and only a slight decrease in the strength indicates the possibility of significant saving of weight in the structures using polyester/fly ash syntactic foams.     

Theoretical and Experimental Insight into the Mechanism for Spontaneous Vertical Growth of ReS2 Nanosheets

Rhenium disulfide (ReS₂) differs fundamentally from other group‐VI transition metal dichalcogenides (TMDs) due to its low structural symmetry, which results in its optical and electrical anisotropy. Although vertical growth is observed in some TMDs under special growth conditions, vertical growth in ReS₂ is very different in that it is highly spontaneous and substrate‐independent. In this study, the mechanism that underpins the thermodynamically favorable vertical growth mode of ReS₂ is uncovered. It is found that the governing mechanism for ReS₂ growth involves two distinct stages. In the first stage, ReS₂ grows parallel to the growth substrate, consistent with conventional TMD growth. However, subsequent vertical growth is nucleated at points on the lattice where Re atoms are “pinched” together. At such sites, an additional Re atom binds with the cluster of pinched Re atoms, leaving an under‐coordinated S atom protruding out of the ReS₂ plane. This under‐coordinated S is “reactive” and binds to free Re and S atoms, initiating growth in a direction perpendicular to the ReS₂ surface. The utility of such vertical ReS₂ arrays in applications where high surface‐to‐volume ratio and electric‐field enhancement are essential, such as surface enhanced Raman spectroscopy, field emission, and solar‐based disinfection of bacteria, is demonstrated.     

PPSTS: Privacy Preservation in Geographical Data by Spatio-Temporal Shifting Using Elliptic Curve Cryptography

Wireless Personal Communications - The massive growth in modern wireless technologies and devices has resulted in increase in spectrum demands and energy consumption of wireless sensor network...     

A Thermoplastic Polyurethane /Nanosilica Composite via Melt Mixing Process and its Properties

Silicon - This investigation reports the preparation and properties of thermoplastic polyurethane/silica nanocomposite prepared via melt mixing process. In this case, nanosilica at different...     

Effects of Ionic Liquid Additive Concentration on Scuffing and Wear in Oil-Starved EHL Contacts

Abstract

We show how various concentrations ranging from 0 to 5.0?wt% of the ionic liquid (IL) trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate added to a fully formulated aviation DOD-PRF-85734 gearbox lubricant affects the properties of the lubricant, including scuffing resistance under starved lubrication conditions, coefficient of friction (COF), wear rate, and lubricant chemical stability. Specimen surfaces were then characterized using scanning electron microscopy, energy-dispersive spectroscopy, and auger electron spectroscopy. Scuffing and wear properties were found to generally improve with IL concentration, which we hypothesize is due to the presence of a phosphorous-rich film observed on specimens exposed to IL.     

An Adaptive Weighted Min-Mid-Max Value Based Filter for Eliminating High Density Impulsive Noise

In this study, non-orthogonal multiple access (NOMA) together with cognitive radio (CR) benefit to the vehicle-to-everything (V2X) as promising application with high spectrum efficiency. We have higher priority to evaluate system performance of the secondary network in such CR-NOMA system operating in the context of V2X. We first arrange vehicles belonging to serving group in this CR-NOMA assisted V2X, and it is beneficial to serve massive connections for vehicles. There are two scenarios studied in this paper, with and without the support of CR scheme. In our proposed system, two system metrics need be investigated to evaluate performance of vehicles that need higher quality of service (QoS). Our results indicate that the outage performance gap among two vehicles exists since different transmit power allocation factors were assigned to them. In particular, the outage probability is first derived in exact forms and then the bit error rate (BER) can be further achieved. In specific situations, the optimal outage probability can be obtained by numerical simulations. Simulation results are also provided to verify the correctness of the derived expressions and it exhibits advantages of the proposed CR-NOMA assisted V2X system in terms of two main metrics such as outage probability and BER.