The effects of the silicon wafer resistivity on the performance of microelectrical discharge machining

In this study, the performance of Si wafer machining by employing the die-sinking microelectrical discharge machining technique is reported. Specifically, the machining performance was examined on both high- (1–10 Ω cm) and low-resistivity (0.001–0.005 Ω cm) Si wafers by means of using a range of discharge energies. In this regard, the machining time, material removal rate, surface quality, surface roughness, and material mapping, which are categorized among the important properties in micromachining, have been investigated. In order to analyze the surface properties and to perform the elemental analysis, the scanning electron microscope and energy-dispersive X-ray spectroscopy were used. In contrast, the 3D surface profiler was used to evaluate the roughness of machined surface. The results of this experimental study revealed that the electrical resistivity and discharge energy parameter of microelectrical discharge machining had a great influence on the Si wafer machining performances. The observations in this study indicated a decrease in machining time, high material removal rate, and high surface roughness with an increased discharge energy values. Overall, it was learnt that the minimum amount of energy required to machine Si wafer was 5 μJ for both low and high-resistivity Si. In addition, the highest material removal of 5.842 × 10^?5 mm³/s was observed for low-resistivity Si. On the contrary, the best surface roughness, R _a, of 0.6203 μm was achieved for high-resistivity Si and it also pointed to a higher carbon percentage after the machining process.     

Influence of PTFE as a solid lubricant on the mechanical,electrical, and tribological properties of CF-reinforced PC composites

The objective of this research was to study the effects of polytetrafluoroethylene (PTFE) as a solid lubricant on the mechanical, electrical, and tribological properties of carbon fiber (CF)-reinforced polycarbonate (PC) composites. Samples were prepared by means of single-screw extrusion and injection molding processes. The mechanical tests included tensile, flexural, and failing weight impact tests, while the electrical tests consisted of surface and volume resistivity tests. The tribological testing was conducted under dry sliding conditions using pin-on-disk configuration. The results showed that the addition of CF managed to significantly reduce the electrical resistivity as the CF loading approached 10–15 wt%. The addition of PTFE managed to reduce the resistivity of the composite, that is, from 4.51 to 0.53 × 10 (Ωcm). The incorporation of 15 wt%. CF resulted with an increase of 45% in tensile strength and 51.5% in flexural strength, while the addition of PTFE had a negative impact on both properties. It was shown that PTFE was able to reduce the friction coefficient, μ and wear rate, K up to 0.257 and 6.35 × 10⁶ (mm³/Nm), respectively, which can be attributed to the excellent abilities of PTFE to form transfer film. The composite consisting of 15 wt% CF and 10 wt%. PTFE showed highest improvement in term of electrical resistivity, and is deemed the most suitable composition for this study. Scanning electron microscopy was also carried out to further elucidate the fracture and wear mechanism of the PC/CF/PTFE composites.     

Synthesis of superhydrophobic nanocomposite coating films for self-cleaning glass using nanoemulsion technique

This work aims to fabricate new potent superhydrophobic-hybrid coated nanocomposites used as a self-cleaning coating on the glass surface. Three (styrene/vinyl acetate) copolymers with monomer molar ratios of 0.06:0.17, 0.12:0.11, and 0.17:0.06 denoted as Z1-, Z2-, and Z3-copolymers were synthesized using the emulsion phase inversion concentration (EPIC) method. Two functionalized SiO₂-NPs using dodecyl triethoxysilane and hexadecyl trimethoxysilane as coupling agents denoted as E-NPs and F-NPs, respectively were fabricated by a sol–gel process to promote the hydrophobicity properties of the synthesized SiO₂-NPs. New hybrid composites denoted as P_y and T_y(y = 1, 2, and 3) were fabricated by incorporating 1, 3, and 5 wt% of the functionalized SiO₂-NPs (E-NPs or F-NPs) into the Z3-copolymers matrix, respectively. The chemical structures of the synthesized copolymers, unfunctionalized SiO₂-NPs, and the hybrid composites were elucidated by FTIR and ¹HNMR spectroscopes. The surface wettability and topography of the glass-surface coated by synthesized (styrene/vinyl acetate) copolymers and the silica hybrid composites were analyzed using water contact angle, scanning electron, and atomic force microscopes. The results showed that a highly superhydrophobic coated hybrid composite with a contact angle of 161.48° was achieved by Z3-copolymer/F5-NPs denoted as T3-composite at F5-NPs concentration of 5 wt%.     

Molecular Weight Distribution of Low Molecular Weight Polyols Derived from Fatty Acid Methyl Esters

A series of commercial polyether polyols with well-defined molecular weights (MW) was used along with propylene glycol and dipropylene glycol as gel permeation chromatography (GPC) calibration standards to determine the MW and oligomeric composition of the synthesized low MW fatty acid methyl ester (FAME) polyols, having an MW of lower than 600 Da. This GPC analysis was compared to the one calibrated against the commercially-available polystyrene (PS) standards and to the number-average molecular weight (M _n) obtained via vapor pressure osmometry (VPO) technique. The MW of FAME polyols obtained with GPC calibrated against polyether polyols were closer to the M _n values obtained via VPO than the MW obtained via GPC calibrated against PS standards. Using the reliable GPC calibration, the MW distribution and the hydroxyl functionality of FAME polyols were determined with greater confidence.     

Dielectric and AC conductivity studies of novel porous armalcolite nanocomposite‐based humidity sensor

Armalcolite, a current motivated rare earth ceramic usually available in the moon, had been used for the first time, as dielectric‐type humidity sensors. The armalcolite nanocomposite was prepared using multistep solid‐state sintering under high pressure and a high‐sensitive dielectric sensor was developed for humidity controlling applications. Different concerning phases developed by the proper sintering were analyzed precisely by X‐ray diffraction (XRD) as well as scanning electron microscopy (SEM). At 100 Hz frequency, the obtained dielectric constant was 24 times greater at 95% relative humidity (RH) as compared to 33% RH. The armalcolite‐based sensor showed lower hysteresis (<3.5%), good stability, and faster response (~18 seconds) and recovery (~35 seconds) times compared to conventional humidity sensors. The sensing mechanism of the nanocomposite was categorically determined by the analyzed characteristics parameters such as dielectric constants, normalized loss tangent, and alternating current conductivity properties. This study also confirmed that the whole conduction mechanism was accomplished by electrons or ions and dipoles in the entire RH range. Therefore, the present armalcolite‐based porous nanocomposite would be a potential sensing material for novel humidity sensors.     

A Review on Food Values of Selected Tropical Fruits’ Seeds

Fruit seeds are usually thrown out as waste during processing or after human consumption. Over the years, researchers have dedicated their effort to assess the food and nutritional values of many different fruit seeds. In this review, the research findings releated to the food values of ten different fruit seeds namely, guava, pumpkin, papaya, honeydew, mangosteen, rambutan, watermelon, mango, and durian were discussed. For several fruit seeds, the macro nutrient components such as oil, protein, and carbohydrate of are found to vary due to either varietal defferences or geographical variations. Among the seeds discussed, the range of oil content was from 1.8 to 49.0% while the range of protein content was from 6 to 40.0%. While the high oil bearing fruit seeds are potential new sources of oil, those with high protein content can be used for recovery of protein. As some of fruit seeds are edible and found to possess a host of phytonutrients, they can be harnessed for medicinal purposes. This review concludes that utilization of fruit seeds could not only bring health and wealth but also help to minimize the waste disposal problem of agro-based industries.     

Interior and exterior boundaries to the workspace of mechanical manipulators

Analytical methods for identifying the boundary to the workspace of serial mechanical manipulators and the boundary to voids in the workspace are presented. The determination of parametric equations of surface patches that envelop the workspace of serial manipulators was presented elsewhere and is extended in this paper to an analytical method for void identification. Because of the ability to identify closed-form surface patches that exist internal and external to the workspace, a mathematical formulation based on the concept of a normal acceleration function is introduced. Admissible motion in the normal direction to a point on a singular surface is delineated and characterized by definiteness properties of a quadratic form. An enclosure bound by surface patches that do not admit normal motion is identified as a void. Several examples are treated using this formulation to illustrate the method.     

Latency Low Handover Mechanism Considering Data Traffic Lost Preventing for Proxy Mobile IPv6 Over WLAN

Typical PMIPv6 supports mobility management for the Mobile Host (MH) in localized domains over variant Wireless Local Area Network technologies. The typical PMIPv6 adopted in reactive mode in which break-before-make technique may concern, which results in long disruption latency and inevitable data traffic loss that negatively affects MH’s communication performance. This article proposes a proactive latency low handover mechanism, which corresponds to make-before-break technique in order to support MH’s seamless and fast roaming in PMIPv6 network. The proposed mechanism proactively performs a pre-registration and pre-access authentication processes tightly together intended for the MH in advance of a handover situation involved in typical PMIPv6, thereby enabling the MH to re-configure its interface more quickly after a handover. Consequently, the associated mobility-related signallings along with their latencies are reduced significantly and the continuity of the MH communication session is granted. Furthermore, an efficient buffering technique with optimized functions is introduced at the MH’s anchor mobility entity to prevent data traffic loss and save their transmission cost. Through various simulation evaluations via ns-2, we study and analyse different mobility aspects, such as handover latency, data traffic loss, throughput, end-to-end traffic delay, traffic transmission cost and signalling cost, with respect to different traffic sources like CBR-UDP and FTP-TCP. Several experiments were conducted, revealing numerous results that verify the proposed mechanisms’ superior performance over existing scheme.     

Shear strength of wood to wood adhesive based on palm kernel oil

A polyurethane adhesive system was prepared by reacting a resin consisting of palm kernel oil‐based polyester and dimethyl cyclohexanediamine with an aliphatic adduct based on 2,4‐diphenylmethane diisocyanate (MDI). Brushing technique was used for applying the adhesive (of thickness 0.05–0.10 mm) onto the wood substrate. Shear strength test for substrates that have been exposed to moisture and various degrees of heat was carried out. Collected data indicated that the adhesive exposed to heat at 70°C has the highest shear strength. At this point, the shear force was at the maximum of 2562 N with strength of 2.65 MPa. However, at higher testing temperature, there is a decrease in the shear force and strength of the adhesive. The presence of moisture, however, does not affect much on the shear strength. The morphological observations via optical microscope were made to explain the relationship of heat and moisture with the shear strength of the adhesive. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1759–1764, 2006     

Mutation and evolution of microsatellites in Drosophila melanogaster

Levels of nucleotide polymorphism in the Drosophila melanogaster genome are correlated with rates of recombination. This relationship may be due to hitchhiking of advantageous mutations (selective sweeps) or to continual removal of deleterious mutations from the genome (background selection). One test of the relative contributions of selective sweeps and background selection to the observed levels of variation in the genome of D. melanogaster is to compare levels of nucleotide variability (with a mutation rate on the order of 10(-9) per nucleotide per generation) with more rapidly evolving DNA loci such as microsatellites. This test depends critically on details of the mutational process of microsatellites. In this paper, we summarize our studies of microsatellite characteristics and mutation rates in D. melanogaster. We find that D. melanogaster microsatellites are short and have a mutation rate (6.5 x 10(-6) per locus per generation) several orders of magnitude lower than mammals studied to date. We further show that genetic variation at 18 dinucleotide repeat microsatellites in a population of D. melanogaster from Maryland is correlated with regional rates of recombination. These and other microsatellite data suggest that both background selection and selective sweeps may contribute to the correlation between DNA sequence variation and recombination in Drosophila.