Additive Manufacturing (AM) is the significantly progressing field in terms of methods, materials, and performance of fabricated parts. Periodical evaluation on the understanding of AM processes and ...its evolution is needed since the field is growing rapidly. To address this requirement, this paper presents a detailed review of the Additive Manufacturing (AM) methods, materials used, and challenges associated with them. A critical review of the state of art materials in the categories such as metals and alloys, polymers, ceramics, and biomaterials are presented along with their applications, benefits, and the problems associated with the formation of microstructures, mechanical properties, and controlling process parameters. The perspectives and the status of different materials on the fabrication of thin-walled structures using AM techniques have also been discussed. Additionally, the main challenges with AM techniques such as inaccuracy, surface quality, reinforcement distribution, and other common problems identified from the literature are presented. On the whole, this paper provides a comprehensive outlook on AM techniques, challenges, and future research directions.
•A review on the basic and recent practices in additive manufacturing techniques is presented.•Use of metallic materials, ceramics, polymers, biomaterials and composites in additive manufacturing are reviewed.•Additive manufacturing in the fabrication of thin-walled structures and scaffolds are discussed.•The challenges in additive manufacturing found in literature and the scopes for future research works also detailed.
In this paper, we propose the application of a dual material gate (DMG) in a tunnel field-effect transistor (TFET) to simultaneously optimize the on-current, the off-current, and the threshold ...voltage and also improve the average subthreshold slope, the nature of the output characteristics, and immunity against the drain-induced barrier lowering effects. We demonstrate that, if appropriate work functions are chosen for the gate materials on the source side and the drain side, the TFET shows a significantly improved performance. We apply the technique of DMG in a strained double-gate TFET with a high- k gate dielectric to show an overall improvement in the characteristics of the device, along with achieving a good on-current and an excellent average subthreshold slope. The results show that the DMG technique can be applied to TFETs with different channel materials, channel lengths, gate-oxide materials, gate-oxide thicknesses, and power supply levels to achieve significant gains in the overall device characteristics.
Poly(lactic acid) (PLA) has become a “material of choice” in biomedical applications for its ability to fulfill complex needs that typically include properties such as biocompatibility, ...biodegradability, mechanical strength, and processability. Despite the advantages of pure PLA in a wider spectrum of applications, it is limited by its hydrophobicity, low impact toughness, and slow degradation rate. Blending PLA with other polymers offers a convenient option to enhance its properties or generate novel properties for target applications without the need to develop new materials. PLA blends with different natural and synthetic polymers have been developed by solvent and melt blending techniques and further processed based on end-use applications. A variety of PLA blends has been explored for biomedical applications such as drug delivery, implants, sutures, and tissue engineering. This review discusses the opportunities for PLA blends in the biomedical arena, including the overview of blending and postblend processing techniques and the applications of PLA blends currently in use and under development.
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Abstract
High quality silver (Ag) decorated CeO
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nanoparticles were prepared by a facile one-step chemical method. The samples were characterized by X-ray diffraction (XRD), scanning electron ...microscopy (SEM), High resolution transmission electron microscopy (HR-TEM), fourier transform infrared spectrometer (FT-IR), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), UV–Visible absorption (UV–Vis), photoluminescence (PL) and thermogravimetric analysis. The decoration of Ag on CeO
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surface was confirmed by XRD, EPR and HR-TEM analysis. Harmful textile pollutant Rose Bengal dye was degraded under sunlight using the novel Ag decorated CeO
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catalyst. It was found that great enhancement of the degradation efficiency for Ag/CeO
2
compared to pure CeO
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, it can be ascribed mainly due to decrease in its band gap and charge carrier recombination rate. The Ag/CeO
2
sample exhibited an efficient photocatalytic characteristic for degrading RB under visible light irradiation with a high degradation rate of 96% after 3 h. With the help of various characterizations, a possible degradation mechanism has been proposed which shows the effect of generation of oxygen vacancies owing to the decoration of Ag on the CeO
2
surface.
Rapid urban development has led to a critical negative impact on water bodies flowing in and around urban areas. In the present study, 25 physiochemical and biological parameters have been studied on ...water samples collected from the entire section of a small river originating and ending within an urban area. This study envisaged to assess the water quality status of river body and explore probable sources of pollution in the river. Weighted arithmetic water quality index (WQI) was employed to evaluate the water quality status of the river. Multivariate statistical techniques namely cluster analysis (CA) and principal component analysis (PCA) were applied to differentiate the sources of variation in water quality and to determine the cause of pollution in the river. WQI values indicated high pollution levels in the studied water body, rendering it unsuitable for any practical purpose. Cluster analysis results showed that the river samples can be divided into four groups. Use of PCA identified four important factors describing the types of pollution in the river, namely (1) mineral and nutrient pollution, (2) heavy metal pollution, (3) organic pollution, and (4) fecal contamination. The deteriorating water quality of the river was demonstrated to originate from wide sources of anthropogenic activities, especially municipal sewage discharge from unplanned housing areas, wastewater discharge from small industrial units, livestock activities, and indiscriminate dumping of solid wastes in the river. Thus, the present study effectively demonstrates the use of WQI and multivariate statistical techniques for gaining simpler and meaningful information about the water quality of a lotic water body as well as to identify of the pollution sources.
•Imposition of restriction on people movement plays a vital role in global air quality concentration levels.•The concentration of major air pollutants was measured during lockdown period and compared ...with previous years.•There is a significant reduction in Annual monthly average of air pollutants concentration due to impact of COVID-19.•The outbreak of COVID-19 around the globe was assessed.
It is well known that pandemics not only change people's social habits but have also changed most activities related to energy consumption, especially industry and transport. Over the past year, a plethora of case studies have been published mapping the environmental impacts in specific locations in terms of changes in wastewater composition, noise, solar radiation and more. However, policymakers are demanding a global perspective and are looking for a synthesis of all these reports that will indicate whether, or to what extent, these changes interact with global climate change. The most urgent question is whether artificially inducing such a pandemic could be justified, given the loss of human life and economic losses. Robust analysis on air pollutants such as PM2.5, PM10, NOx, SO2, CO, O3 and NH3 confirmed significant improvement in air quality indicators especially in India and China. The study indicates that key hypotheses can be confirmed or refuted, but further measurements are needed.
Using calibrated simulations, we report a detailed study of the doping-less tunnel field effect transistor (TFET) on a thin intrinsic silicon film using charge plasma concept. Without the need for ...any doping, the source and drain regions are formed using the charge plasma concept by choosing appropriate work functions for the source and drain metal electrodes. Our results show that the performance of the doping-less TFET is similar to that of a corresponding doped TFET. The doping-less TFET is expected to be free from problems associated with random dopant fluctuations. Furthermore, fabrication of doping-less TFET does not require a high-temperature doping/annealing processes and therefore cuts down the thermal budget, opening up possibilities for fabricating TFETs on single crystal silicon-on-glass substrates formed by wafer scale epitaxial transfer.
Surface cooling induced by tropical cyclones (TCs) is about three times larger during premonsoon than during postmonsoon season in the Bay of Bengal. We investigate processes responsible for this ...seasonal contrast using an ocean general circulation model. The model is forced by TC winds prescribed from an analytic vortex using observed TC tracks and intensities during 1978–2007. The simulation accurately captures the seasonal cycle of salinity, temperature, and barrier layer in this region, with fresher waters, deeper upper‐ocean stratification, and thicker barrier layers during postmonsoon season. It also reproduces the three times larger TC‐induced cooling during premonsoon than during postmonsoon season. This difference is essentially related to seasonal changes in oceanic stratification rather than to differences in TC wind energy input. During the postmonsoon season, a deeper thermal stratification combined with a considerable upper‐ocean freshening strongly inhibits surface cooling induced by vertical mixing underneath TCs. On average, thermal stratification accounts for ∼60% of this cooling reduction during postmonsoon season, while haline stratification accounts for the remaining 40%. Their respective contributions however strongly vary within the Bay: haline stratification explains a large part of the TC‐induced cooling inhibition offshore of northern rim of the Bay (Bangladesh‐Myanmar‐east coast of India), where salinity seasonal changes are the strongest, while thermal stratification explains all the cooling inhibition in the southwestern Bay. This study hence advocates for an improved representation of upper‐ocean salinity and temperature effects in statistical and dynamical TCs forecasts that could lead to significant improvements of TC intensity prediction skill.
Key Points
TC‐induced cooling in Bay of Bengal is far weaker during post than pre‐monsoon
Thermal stratification changes account for ~70% of this cooling inhibition
Haline stratification explains most of cooling inhibition along Bay northern rim
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