Influence of Ball Burnishing Process on Equal Channel Angular Pressed Mg-Zn-Si Alloy on the Evolution of Microstructure and Corrosion Properties

Silicon - In the present study, Mg-4Zn-1Si alloy was subjected to equal channel angular pressing (ECAP) up to 4 passes at 300 °C, followed by ball burnishing using 0.3 mm...     

A (2, 2) Visual Cryptography Technique with Improved Contrast

ABSTRACT

Visual cryptography is a technique used to share a secret among many participants. The problem with visual cryptography technique is that the secret is not perfectly recovered, i.e. a black secret pixel is perfectly recovered but a white secret pixel is recovered with less contrast. Because of this, the overall quality of recovered secret is poor. So to improve the quality of recovered secret image, we need to improve the contrast. In this paper, we have proposed a (2, 2) visual cryptography technique with improved contrast as compared to the traditional (2, 2) visual cryptography scheme (VCS). In the proposed technique, we have used additional basis matrices for encrypting the secret pixels. The quality of the recovered secret image is compared with traditional (2, 2) VCS using various image quality metrics.     

Carbon Fibers from Polyethylene-Based Precursors

Polyethylene fibers are attractive as carbon fiber precursors due to their high carbon content and ease of manufacture. Also, highly ordered and oriented fibers with extraordinary physical and mechanical properties are available today. However, being thermoplastic fibers, they soften or melt at a fairly low temperature, losing their fiber form. These precursors have to be stabilized by introducing cross links in them so that they can withstand the higher temperatures of carbonization. Heating in a sulfuric acid bath was investigated as a possible means of stabilizing these fibers. The process of stabilization was studied using several characterization techniques, such as thermal analyses (DSC and TGA), color change, tensile properties, X-ray diffraction and electron microscopy. The fibers had a tendency to shrink to a great extent and the tension had a major role during the process of sulfonation. Some of the stabilized fibers were carbonized and their properties were evaluated     

Fabrication of citric acid crosslinked β‐cyclodextrin/hydroxyethylcellulose hydrogel films for controlled delivery of poorly soluble drugs

β‐cyclodextrin grafted hydroxyethylcellulose (βCD‐g‐HEC) hydrogel films were prepared for the controlled release of poorly soluble model drug (ketoconazole) using citric acid as crosslinking agent. The active βCD and carboxyl content of the hydrogel films were determined by phenolphthalein assay and acid–base titration. The films were characterized by solid state ¹³C NMR, ATR–FTIR, thermogravimetric analysis, and differential scanning calorimetric, and analyzed for tensile strength, swelling ratio, drug loading, release, hemocompatibility, in vitro cytotoxicity, and implantation test. An increase in the concentration of βCD in feed increased the active βCD content of the hydrogel films but reduced their extent of interpolymer crosslinking. The βCD‐g‐HEC hydrogel films with high active βCD content showed maximum drug loading whereas those with high crosslinking density were capable of controlling the drug release for long duration. Hemolysis assay and in vitro cytotoxicity study revealed the biocompatible nature of the hydrogel films whereas implantation test indicated their minimal inflammatory effect. From the overall results, βCD‐g‐HEC hydrogel films were found to be better alternative to the previously reported βCD‐HPMC and βCD‐CMC hydrogel films for enhanced loading and long‐term release, respectively, of the poorly soluble drugs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46452.     

Optical spectroscopy of rare earth-doped oxyfluoro-tellurite glasses to probe local environment

\(\hbox {TeO}_{2}\)-based glasses with a general formula \(65\hbox {TeO}_{2}{-}5\hbox {BaF}_{2}{-}30\hbox {ZnF}_{2}\) (TBZ) (in mol%) were prepared by usual melt quenching technique. Three mol% of europium (Eu) or erbium (Er) were added to the prepared glass at the expense of \(\hbox {TeO}_{2}\). Raman, photoluminescence (PL), UV–visible absorption studies were carried out on the glass samples. Raman spectra of the undoped and doped glasses were analysed using the peak shift and the intensity variation along with full width at half-maximum (FWHM). It was found that Eu-doped TBZ glass has a greater tendency towards depolymerizing the glass matrix by influencing the conversion of \(\hbox {TeO}_{4}\) to \(\hbox {TeO}_{3}\) units compared to Er-doped and undoped glasses. PL spectra of the glass samples show emission due to different possible transitions. Position of the peak of the de-convoluted spectra shows the position of the particular Stark component and the FWHM is a measure of the inhomogeneous broadening. The UV–visible absorption spectra are used to calculate the optical density and to determine the band edge of the glass samples by fitting to the Mott equation. It is seen that Eu-doped TBZ glass has a lesser bandgap than that of Er-doped glass.     

Impact of Human Intervention and Climate Change on Natural Flow Regime

According to the ‘natural flow paradigm’, any departure from the natural flow condition will alter the river ecosystem. River flow regimes have been modified by anthropogenic interventions and climate change is further expected to affect the biotic interactions and the distribution of stream biota by altering streamflow. This study aims to evaluate the hydrologic alteration caused by dam construction and climatic changes in a mesoscale river basin, which is prone to both droughts and monsoonal floods. To analyse the natural flow regime, 15 years of observed streamflow (1950–1965) prior to dam construction is used. Future flow regime is simulated by a calibrated hydrological model Soil and Water Assessment Tool (SWAT), using ensemble of four high resolution (~25 km) Regional Climate Model (RCM) simulations for the near future (2021–2050) based on the SRES A1B scenario. Finally, to quantify the hydrological alterations of different flow characteristics, the Indicators of Hydrological Alteration (IHA) program based on the Range of Variability Approach (RVA) is used. This approach enables the assessment of ecologically sensitive streamflow parameters for the pre- and post-impact periods in the regions where availability of long-term ecological data is a limiting factor. Results indicate that flow variability has been significantly reduced due to dam construction with high flows being absorbed and pre-monsoon low flows being enhanced by the reservoir. Climate change alone may reduce high peak flows while a combination of dam and climate change may significantly reduce variability by affecting both high and low flows, thereby further disrupting the functioning of riverine ecosystems. We find that, in the Kangsabati River basin, influence of dam is greater than that of the climate change, thereby emphasizing the significance of direct human intervention.     

Thermal bonding of polypropylene nonwovens: Effect of bonding variables on the structure and properties of the fabrics

Properties of the point‐bonded nonwoven fabrics are dependent on the bonding conditions, in addition to those of the polymer/fiber. Thermally bonded carded webs were produced and characterized to investigate the role of bond area, bond size, and bonding temperature on the structure and properties of point‐bonded nonwoven fabrics. It was observed that the bond strength increases with bond area and bond size. The effects of bond area and bond size on fiber morphology were negligible. Significant morphological differences were observed in the bonded and the unbonded regions of the thermally bonded webs. To see how the staple fiber studies relate to the behavior of continuous filaments, similar sets of samples were produced and characterized by using the spunbond system. The observed trends for properties with respect to bonding conditions were similar for spunbond samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3593–3600, 2004     

Cold roll bonding of multi-layered bi-metal laminate composites

Multi-layered laminate composites of dissimilar metals have assumed importance industrially. Cold roll bonding can produce multi-layered sheet composites. Study of the effect of rolling and material variables on the bonding characteristics needs to be studied in order to predict the optimum bonding conditions and the final composition of the laminate sheets. In this work, cold roll bonding of multi-layered bimetals has been modeled using the slab method. The effect of anisotropy has been included. Effects of different process and material variables are analyzed. Novel experiments were performed on multilayered Ti–Al system and the numerical results from the model were compared with the experimental results. A good agreement was observed between the model and experimental results.     

Mathematical Modeling of Withering Characteristics of Tea Leaves

The withering characteristics of tea leaves were examined for different temperatures. Tea leaves were withered at a temperature range of 20-45°C with a constant air velocity of 1.1 m/s. The experimental results illustrated the absence of constant-rate drying period and withering took place only in the falling-rate period. During the falling-rate period, at constant drying air flow rate, the drying rate increased and drying time decreased with the increase in drying air temperature. Drying models of Henderson and Pabis and Page were evaluated based on mean bias error (E_MB), root mean square error (E_RMS), correlation coefficient (R²), and the chi square (χ²). The Henderson and Pabis model was found to be a better model for describing the withering characteristics of tea leaves for each of the temperatures of 20, 25, 30, and 35°C. The values obtained from Page model were found to be more reasonable for temperatures of 40 and 45°C than the other model. Both the models closely fitted the withering data within a certain range of temperature. The Henderson and Pabis model gave better prediction and satisfactorily described the withering characteristics of tea leaves at temperatures lower than 40°C whereas the Page model fitted well at temperatures greater than 40°C.