Understanding surface discharge activity with epoxy silicon carbide nanocomposites

Surface discharge inception voltage (SDIV) with epoxy silicon carbide nanocomposite material in LN₂ medium is about three times higher than that in air. Under AC voltage that SDIV increases with increase in wt% of silicon carbide (SIC) material in epoxy nanocomposites. Dielectric measurements indicates an increase in temperature of the specimen and the weight percentage of SIC filler in epoxy resin increases the permittivity of the material. Also, irrespective of percentage of SiC in epoxy resin, the tan(δ) reduces with increase in frequency and the converse at room temperature. The UHF signal measured during surface discharge activity in air/LN₂ medium has frequency content in the range of 0.5–1.5 GHz. The charge decay characteristics of epoxy SiC nanocomposites indicate the deposited charge is less and the charge decay time reduces with increase in wt% of SiC in epoxy resin. The surface roughness caused due to surface discharge activity is high under negative DC voltage compared with positive DC/AC voltage. The phase resolved partial discharge (PRPD) analysis indicates discharges occur at the near peak of the AC voltage on inception of surface discharge and at higher stress it appears at the rising portion of AC voltage. POLYM. ENG. SCI., 57:1349–1355, 2017. © 2017 Society of Plastics Engineers     

Refractive index as an objective method for evaluation of rancidity in edible oils and fats

Common edible oils and fats (refined peanut oil, seasame oil, safflower oil, and butter oil, ghee) were exposed to direct sunlight, fluorescent light and Schaal Test. Data collected on refractive indices (N _D ²⁵ ) show an increase of the order of 0.001±0.0003 at the stage of development of perceptible rancid odor. The pattern of changes in refractive indices and peroxide values of these edible oils, autoxidized at 100±5 C, show that refractive indices indicate more precisely the termination of the induction periods than peroxide values.     

Parallel tempering simulation of the three-dimensional Edwards–Anderson model with compact asynchronous multispin coding on GPU

Monte Carlo simulations of the Ising model play an important role in the field of computational statistical physics, and they have revealed many properties of the model over the past few decades. However, the effect of frustration due to random disorder, in particular the possible spin glass phase, remains a crucial but poorly understood problem. One of the obstacles in the Monte Carlo simulation of random frustrated systems is their long relaxation time making an efficient parallel implementation on state-of-the-art computation platforms highly desirable. The Graphics Processing Unit (GPU) is such a platform that provides an opportunity to significantly enhance the computational performance and thus gain new insight into this problem. In this paper, we present optimization and tuning approaches for the CUDA implementation of the spin glass simulation on GPUs. We discuss the integration of various design alternatives, such as GPU kernel construction with minimal communication, memory tiling, and look-up tables. We present a binary data format, Compact Asynchronous Multispin Coding (CAMSC), which provides an additional 28.4% speedup compared with the traditionally used Asynchronous Multispin Coding (AMSC). Our overall design sustains a performance of 33.5 ps per spin flip attempt for simulating the three-dimensional Edwards–Anderson model with parallel tempering, which significantly improves the performance over existing GPU implementations.     

Fertilizer requirements for specified yield targets. I. Theoretical derivation of mathematical models for the computation of soil and fertilizer nutrient efficiencies

The conventional deduction procedure of computation of soil () and fertilizer () nutrient efficiencies for the amount of fertilizer required for specified yield targets does not make provision of the amount of soil nutrient derived by crops from the available pool of soil nutrients not accounted for in the amount extracted by a soil test procedure. The derivation of two mathematical models, viz., Tamil Nadu Agricultural University Model I [TNAU Model I] and Model II [TNAU Model II] is reported in this paper which aim at computing the soil () and fertilizer () nutrient efficiencies not accounted for by the conventional method.In the case of TNAU Model I, the relationship between the nutrient uptake (U) and the soil (S) and the fertilizer (F) nutrients was established by assuming a functional relationship of the type U =S +F such that 0 1 and 0 1. In TNAU Model II the same relationship was established as U =S +F + such that 0 1, 0 1 and > 0. The term in the latter model is a measure of the amount of soil nutrient the crop absorbs from a slowly available pool of nutrients not accounted for in the amounts extracted by the soil test procedure employed or applied through fertilizer.The field verification of these models is reported elsewhere.     

Axial mixing and scaleup of reciprocating plate columns

Axial mixing measurements in single phase (water) flow have been taken in open-type reciprocating plate columns of diameters 25.4 and 508 mm. In the case of the smaller column, two-phase axial mixing was measured, both in the dispersed phase (water dispersed in n-heptane) and the continuous phase (with n-heptane dispersed in water). Pulse injection of a tracer solution of ammonium chloride and methanol in water was used. Under single phase conditions, the axial dispersion coefficients were found to go through a minimum as the agitation level was increased from zero. The coefficients were nearly an order of magnitude higher in the 508 mm column than in the 25,4 mm column. In two phase flow in the 25,4 mm column, the continuous phase axial dispersion coefficients also went through a minimum as agitation was increased. The dispersed phase axial dispersion coefficients decreased monotonically as agitation was increased from zero. The results of this work and previous data are used in modelling the scale-up of reciprocating plate columns by means of Pratt's simplified technique. The existing empirical scale-up equation is consistent with an assumption that continuous phase mixing increased with column diameter but dispersed phase mixing remains unchanged.     

Preparation and study of terephthalate copolyester of ethylene glycol and butane-1,4-diol

Summary Random terephthalate copolyesters of ethylene glycol and butane-1,4-diol of various compositions were prepared by trans-esterification of poly(ethylene terephthalate) (PET) with butane-1,4-diol (BD). Proton nuclear magnetic resonance spectroscopy (NMR) was used to elucidate the structure and compositions of copolyesters. The thermal behaviour of the copolyesters were investigated by differential thermal analysis (DTA). Intrinsic viscosities were measured in orthochlorophenol at 30°C.     

Survey of Deep Learning Paradigms for Speech Processing

Wireless Personal Communications - Spam detection in emails tends to be an endless research interest among many researchers and academicians. Even though email communication has become a major role...     

Interlaminar fatigue crack growth of cross-ply composites under thermal cycles

The fatigue growth of a fiber reinforced composite laminate was characterized under thermal cycling using a combined experimental and computational investigation. Twenty-four ply composite laminates ([0°₁₂/90°₁₂]) are fabricated with a pre-existing delamination, and subjected to thermal cycling in an environmental chamber. The large mismatch in the coefficients of thermal expansion is used to grow an interlaminar crack at the interface of the 0° and 90° laminae. This thermal fatigue crack growth behavior is investigated for different amplitudes of temperature change (ΔT = 30–140 °C). The inspection of fracture surfaces, after completion of the fatigue tests, reveals an angled or kinked crack front growth with greater propagation distances near the free-surfaces/edges. Due to the non-uniform crack growth across the specimen thickness, three-dimensional finite element analyses are performed to investigate the fatigue growth mechanisms under thermal load. From the analysis, the energy release rate as well as the mixed-mode stress intensity factors is calculated and the variations of these fracture parameters are found to be consistent with the observed crack front configuration. Using the computed results, the experimentally measured crack growth rates are also correlated with the amplitude of energy release rate, and a power law form of the fatigue law is established. The relevant coefficients as well as the threshold energy release rate are also determined. The present analysis is useful for not only understanding the fatigue delamination mechanisms under thermal cycling but also for estimating the threshold temperature variation that is needed to drive crack growth.     

Effect of Br gassing after Ar plasma treatment of polyolefins

For simulation and acceleration of artificial polymer ageing, polyolefin foils were exposed to low-pressure Ar plasma. Plasma particle bombardment and irradiation induce C–C and C–H bond scissions by σ?→?σ ^? excitations on the surface and in near-surface layers. Consequently, radicals are generated. They react by recombination, cross-linking, metastable trapping of the radical site or formation of olefinic double bonds. The long-living and metastable trapped C-radicals as well as double bonds in polyolefins were immediately exposed to bromine vapour without breaking the vacuum after switching-off the plasma. These reactive sites rapidly react with the molecular bromine under formation of C–Br bonds. For 5?min of argon plasma exposure, the elemental concentration of bromine was 13% for polyethylene and 22% Br/C for polypropylene as analysed by X-ray photoelectron spectroscopy. Nevertheless, not all C radical sites have reacted with bromine. Later on, when the polyolefins brought in contact with ambient air, an additional post-plasma reaction of the remaining trapped radicals with oxygen was observed. The oxygen concentrations were lower after bromine gassing, thus repressing partially the post-plasma oxidation in the analysed layer (ca. 6?nm) by radical quenching. Such bromination took place either at the surface or in near-surface layers because the Attenuated Total Reflectance (ATR)-FTIR spectra (sampling depth ca. 2500?nm) did not show significant changes for argon plasma-treated PE foils with and without bromine vapour exposure. Further addition of bromine may also occur on C=C double bonds.     

Improvement of Machinability using Laser-Aided Hybrid Machining for Inconel 718 Alloy

Hybrid machining is an emerging technique for difficult-to-cut materials to overcome the problems associated with conventional machining (CM). Inconel 718, a super alloy of nickel, is a high-temperature alloy commonly used in aircraft and thermal industries and categorized as one among the difficult-to-cut materials. In this study, the influence of cutting conditions of Inconel 718 alloy during laser-assisted hybrid machining (LAHM) is investigated and the results are compared with CM. During LAHM, the process parameters of cutting speed, feed rate, approach angle, and laser power are varied. The present work is carried out in two phases: (i) determination of effective heat-affected depth (HAD) during laser preheating (using central composite design (CCD) in response surface methodology); (ii) optimization of cutting conditions during machining (using Taguchi's method). Compared with CM, the LAHM shows the following reduction benefits: (i) 33% in feed force (Fx), 42% in thrust force (Fy), and 28% in cutting force; (ii) improved surface finish (surface roughness, Ra) of 28%; and (iii) reduction in tool wear by 50%. The chip morphology reveals the decrease in shear angle and increase in chip thickness during LAHM. No change in the hardness value of the machined surface after LAHM indicates the absence of subsurface damage.