Experimental study of gamma radiation induced degradation of a piezoresistive pressure sensor

Microsystem Technologies - This paper reports the experimental investigation of gamma radiation induced degradation of a piezoresistive pressure sensor with total dose exposure up...     

Visualizing Thermally Activated Memristive Switching in Percolating Networks of Solution-Processed 2D Semiconductors

Memristive systems present a low-power alternative to silicon-based electronics for neuromorphic and in-memory computation. 2D materials have been increasingly explored for memristive applications due to their novel biomimetic functions, ultrathin geometry for ultimate scaling limits, and potential for fabricating large-area, flexible, and printed neuromorphic devices. While the switching mechanism in memristors based on single 2D nanosheets is similar to conventional oxide memristors, the switching mechanism in nanosheet composite films is complicated by the interplay of multiple physical processes and the inaccessibility of the active area in a two-terminal vertical geometry. Here, the authors report thermally activated memristors fabricated from percolating networks of diverse solution-processed 2D semiconductors including MoS₂, ReS₂, WS₂, and InSe. The mechanisms underlying threshold switching and negative differential resistance are elucidated by designing large-area lateral memristors that allow the direct observation of filament and dendrite formation using in situ spatially resolved optical, chemical, and thermal analyses. The high switching ratios (up to 10³) that are achieved at low fields (≈4 kV cm⁻¹) are explained by thermally assisted electrical discharge that preferentially occurs at the sharp edges of 2D nanosheets. Overall, this work establishes percolating networks of solution-processed 2D semiconductors as a platform for neuromorphic architectures.     

Kinetics and mechanism of the alkali-catalyzed p-cresol–formaldehyde reaction

The kinetics of the reaction of p-cresol with formaldehyde in relation to the functionality of p-cresol using NaOH as catalyst has been studied at temperatures of (65 ± 0.05)°C, (70 ± 0.05)°C, (75 ± 0.05)°C, and (80 ± 0.05)°C. The pH maintained was 7.0, 8.0, 9.0, 9.4, and 10.0. The reaction follows a second-order rate law. The rate was found to increase with increase in pH. The stepwise rate constants (k₁ and k₂) for the formation of monomethylol-p-cresol and dimethylol-p-cresol, respectively, were calculated from the overall rate constant k. The values of Arrhenius parameters and the entropy of activation for the overall as well as the stepwise reactions were calculated. The experimental and calculated values of k at pH 10.0 and temperatures 65, 70, 75, and 80°C were found to agree well within experimental errors. A mechanism conforming to the energies and entropies of activation of the reaction is suggested.     

Studies on epoxidized rubber seed oil as plasticizer for acrylonitrile butadiene rubber

The application of rubber seed oil (RSO) and epoxidized RSO (ERSO) as a plasticizer in acrylonitrile butadiene rubber (NBR) was studied using RSO and ERSO with different levels of epoxidation. The results indicated that ERSO could be used as a less leachable and low volatility plasticizer for NBR. The use of ERSO in NBR gave better abrasion resistance whereas the tensile strength and tear strength were comparable to those vulcanizates that contained dioctyl phthalate as a plasticizer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 668–673, 2003     

A tetracene-based single-electron transistor as a chlorine sensor

An organic molecular single-electron transistor (SET) based on a tetracene quantum dot has been modeled and employed for sensing of chlorine gas, within the framework of density functional theory. The sensing behavior of the SET is estimated through a charge-stability diagram and total energy as a function of gate potential (TE vs. V_g) for varying distances of chlorine from the SET quantum dot, which could be used as an electronic fingerprint for detection. The better sensing ability, high power efficiency and large operational temperature range of tetracene SET, in comparison to conventional sensors, makes it a very powerful candidate for a chlorine gas sensor.     

Saponin-loaded SBA-15: release properties and cytotoxicity to Panc-I cancer cells

In this study, first time a nanoformulation, saponin-loaded SBA-15 has been developed for an improved and continuous release. The SBA-15 nanopowder was synthesized by a hydrothermal process. Saponin was introduced into the mesoporous channels of SBA-15 and its concentration in SBA-15 was measured by UV–visible spectrophotometry. The pristine SBA-15 and saponin-loaded SBA-15 were characterized by small-angle XRD, FESEM, HRTEM, TGA, FTIR. N₂ adsorption–desorption isotherms were used to measure the specific surface area and pore channel structure parameters of pristine and loaded SBA-15. Saponin release was studied in phosphate buffered saline (pH 7.4), which revealed that the release rate could be effectively controlled. The controlled drug release is highly desired for cancer treatment. The cytotoxicity of pristine and loaded SBA-15 was analyzed on Panc-I cancer cells. Both the pristine SBA-15 and saponin-loaded SBA-15 nanoparticles showed specific toxicity on the cancer cells. The preliminary results showed that saponin-loaded SBA-15 could be an effective therapeutic agent for Panc-I cancer cells.     

Investigation of the wear mechanism of carbon-fiberreinforced acetal

The friction and wear characteristics of acetal reinforced with 25 wt.% of randomly dispersed carbon fibers were investigated and compared with those of the base resin. The addition of carbon fibers to the polymer decreased the coefficient of friction and wear rate for the composite material sliding against a hardened and ground steel disk for extended periods of time. A number of surface topography parameters pertinent to the wear process, i.e. arithmetic average roughness, autocorrelation function, asperity density, tip radius of curvature, distribution of the radii of curvature and heights of asperity peaks, and ordinale heights, were calculated and evaluated for the sliding surface of the disk. The worn surfaces of filled and unfilled polymer pins were examined by scanning electron microscopy to investigate the probable wear mechanism for these materials. It was found that the wear of reinforced polymers proceeds by the pulling-out of the broken and worn fibers.     

Removal of alpha case on titanium alloy surfaces using chemical milling

Elevated temperature deformation processing of titanium such as during forging causes the formation of alpha case, a brittle layer on the processed components. Alpha case removal has been attempted by several methods, however, in-depth understanding of chemical milling to this end is not evident from the prevailing literature. This work therefore undertakes experimental analysis of chemical milling to remove alpha case generated on titanium alloys after deformation after forging. Several compositions of chemicals and heat treatment conditions for titanium work-material were evolved. Effectiveness of these methods and their applications in removing alpha case on forged titanium alloy were investigated by performing a series of experiments. After the alpha case removal, the titanium work surfaces were examined using optical and scanning electron microscopy as well as electron back scattered diffraction and X-ray diffraction. The optimum results achieved show that 8% HF and 10% HNO₃ solution with 13 min and 30-s etching time is more effective in completely removing alpha case layer by chemical etching of Ti-6Al-4V alloy work specimens heated in air at 930°C.     

Material removal characteristics of full aperture optical polishing process

Precision surfaces of optical grade have been in great demand for various applications such as high-power laser systems, astronomical reflecting telescopes glass mirrors, folding mirrors of avionics displays, reflectors, guides for transmission of hot and cold neutron beams for neutron exploration setups, electronic substrate, display covers and substrates for biomedical imaging and sensing, etc. Generation of such surfaces has been a challenge; particularly the polishing operation of optical fabrication process is quite critical which determines the final surface quality. To achieve the required optical surface parameters, a good control and systematic understanding of polishing process and its parameters are required. However, the conventional or full aperture optical polishing process still depends on operator's skills to achieve the target surface quality. To exploit the process to the extent, it is must to have a scientific understanding of material removal behavior of the polishing process, which will lead to the process becoming deterministic. This article has attempted to address this issue. Authors have summarized different material removal theories and discussed various mathematical models as proposed by researchers so far. Attempt has been made to come up with knowledge gaps which are required to be bridged in future.     

Correlated In Situ Low‐Frequency Noise and Impedance Spectroscopy Reveal Recombination Dynamics in Organic Solar Cells Using Fullerene and Non‐Fullerene Acceptors

Non‐fullerene acceptors based on perylenediimides (PDIs) have garnered significant interest as an alternative to fullerene acceptors in organic photovoltaics (OPVs), but their charge transport phenomena are not well understood, especially in bulk heterojunctions (BHJs). Here, charge transport and current fluctuations are investigated by performing correlated low‐frequency noise and impedance spectroscopy measurements on two BHJ OPV systems, one employing a fullerene acceptor and the other employing a dimeric PDI acceptor. In the dark, these measurements reveal that PDI‐based OPVs have a greater degree of recombination in comparison to fullerene‐based OPVs. Furthermore, for the first time in organic solar cells, 1/f noise data are fit to the Kleinpenning model to reveal underlying current fluctuations in different transport regimes. Under illumination, 1/f noise increases by approximately four orders of magnitude for the fullerene‐based OPVs and three orders of magnitude for the PDI‐based OPVs. An inverse correlation is also observed between noise spectral density and power conversion efficiency. Overall, these results show that low‐frequency noise spectroscopy is an effective in situ diagnostic tool to assess charge transport in emerging photovoltaic materials, thereby providing quantitative guidance for the design of next‐generation solar cell materials and technologies.