Lead zirconate titanate (PZT) based piezoelectric materials are well known for their excellent piezoelectric properties. However, considering the toxicity of lead and its compounds, there is a ...general awareness for the development of environmental friendly lead-free materials as evidenced from the legislation passed by the European Union in this effect. Several classes of materials are now being considered as potentially attractive alternatives to PZTs for specific applications. In this paper, attempts have been made to review the recent developments on lead-free piezo materials emphasizing on their preparation, structure–property correlation, etc. In this context, perovskite systems such as bismuth sodium titanate, alkali niobates (ANbO
3
), etc. and non-perovskites such as bismuth layer-structured ferroelectrics are reviewed in detail. From the above study, it is concluded that some lead-free compositions show stable piezoelectric responses even though they do not match the overall performance of PZT. This has been the stimulant for growing research on this subject. This topic is of current interest to the researchers worldwide as evidenced from the large number of research publications. This has motivated us to come out with a review article with a view that it would give further impetus to the researchers already working in this area and also draw the attention of the others.
The growth of piezo science is phenomenal since the discovery of piezoelectricity in 1880. Among various piezoelectric materials, lead zirconate titanate (PZT) is a very popular and exhaustively ...studied piezo system which allows synthesis of large number of materials with wide range of properties due to formation of solid solutions over large range of Zr:Ti ratio. Also, this system accommodates wide range of dopants for modification of crystal structure. Due to this versatile nature, PZT has emerged as very popular among users and researchers worldwide. However, considering the toxicity of lead oxide, development of lead free piezo ceramics is encouraged in recent years. Some lead free piezo material systems such as BNT, BKT, KNN, BZT-BCT have been explored. However, development of lead free piezo devices and their performance in comparison with PZT devices are yet to be established. At this juncture, it was felt that an article reviewing the current status of development of piezo materials highlighting the change from PZT to various lead free systems would be of very much interest to the researchers. Therefore, efforts are made to bring out the recent developments on R&D of piezo materials in this review article.
To investigate the effects of copper (Cu), rice plant (Oryza sativa. L. var. MSE-9) was treated with different Cu concentrations (0, 10, 50 and 100μM) for 5 days in hydroponic condition. Gradual ...decrease in shoot and root growth was observed with the increase of Cu concentration and duration of treatment where maximum inhibition was recorded in root growth. Cu was readily absorbed by the plant though the maximum accumulation was found in root than shoot. Hydrogen peroxide (H2O2) production and lipid peroxidation were found increased with the elevated Cu concentration indicating excess Cu induced oxidative stress. Antioxidant enzymes superoxide dismutase (SOD), guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) and glutathione reductase (GR) were effectively generated at the elevated concentrations of Cu though catalase (CAT) did not show significant variation with respect to control. Ascorbate (ASH), glutathione (GSH) and proline contents were also increased in all the Cu treated plants compared with the control. SOD isoenzyme was greatly affected by higher concentration of Cu and it was consistent with the changes of the activity assayed in solution. The present study confirmed that excess Cu inhibits growth, induced oxidative stress by inducing ROS formation while the stimulated antioxidative system appears adaptive response of rice plant against Cu induced oxidative stress. Moreover proline accumulation in Cu stress plant seems to provide additional defense against the oxidative stress.
► Excess Cu negatively affects growth of the rice plant. ► Damage was more severe in root than shoot. ► Excess Cu led to oxidative stress in rice plant by inducing ROS generation. ► The plant tolerated the oxidative stress by increasing antioxidant defense system. ► Increased level of proline also reflects its association in tolerating the stress.
In this work, under-expanded cryogenic hydrogen jets were investigated experimentally for their ignition and flame characteristics. The test facility described herein, was designed and constructed to ...release hydrogen at a constant temperature and pressure, to study the dispersion and thermo-physical properties of cryogenic hydrogen releases and flames. In this study, a non-intrusive laser spark focused on the jet axis was used to measure the maximum ignition distance. The radiative power emitted by the corresponding jet flames was also measured for a range of release scenarios from 37 K to 295 K, 2–6 barabs through nozzles with diameters from 0.75 to 1.25 mm. The maximum ignition distance scales linearly with the effective jet diameter (which scales as the square root of the stagnant fluid density). A 1-dimensional (stream-wise) cryogenic hydrogen release model developed previously at Sandia National Laboratories (although this model is not yet validated for cryogenic hydrogen) was exercised to predict that the mean mole fraction at the maximum ignition distance is approximately 0.14, and is not dependent on the release conditions. The flame length and width were extracted from visible and infra-red flame images for several test cases. The flame length and width both scale as the square root of jet exit Reynolds number, as reported in the literature for flames from atmospheric temperature hydrogen. As shown in previous studies for ignited atmospheric temperature hydrogen, the radiative power from the jet flames of cold hydrogen scales as a logarithmic function of the global flame residence time. The radiative heat flux from jet flames of cold hydrogen is higher than the jet flames of atmospheric temperature hydrogen, for a given mass flow rate, due to the lower choked flow velocity of low-temperature hydrogen. This study provides critical information with regard to the development of models to inform the safety codes and standards of hydrogen infrastructure.
•Ignition distance and radiative heat flux are measured for cryogenic hydrogen jets.•The maximum ignition distance is greater for cryogenic hydrogen jet flames.•Normalized flame length is found to be proportional to the jet Reynolds number.•The flame length and radiative heat flux is higher for cryogenic jet flames.•A new correlation based on power-law is proposed to predict the radiation fraction.
The Indus flood in 2010 was one of the greatest river disasters in recent history, which affected more than 14 million people in Pakistan. Although excessive rainfall between July and September 2010 ...has been cited as the major causative factor for this disaster, the human interventions in the river system over the years made this disaster a catastrophe. Geomorphic analysis suggests that the Indus River has had a very dynamic regime in the past. However, the river has now been constrained by embankments on both sides, and several barrages have been constructed along the river. As a result, the river has been aggrading rapidly during the last few decades due to its exceptionally high sediment load particularly in reaches upstream of the barrages. This in turn has caused significant increase in cross-valley gradient leading to breaches upstream of the barrages and inundation of large areas. Our flow accumulation analysis using SRTM data not only supports this interpretation but also points out that there are several reaches along the Indus River, which are still vulnerable to such breaches and flooding. Even though the Indus flood in 2010 was characterized by exceptionally high discharges, our experience in working on Himalayan rivers and similar recent events in rivers in Nepal and India suggest that such events can occur at relatively low discharges. It is therefore of utmost importance to identify such areas and plan mitigation measures as soon as possible. We emphasize the role of geomorphology in flood analysis and management and urge the river managers to take urgent steps to incorporate the geomorphic understanding of Himalayan rivers in river management plans.
The restoration of normal functioning of damaged body tissues is one of the major objectives of tissue engineering. Scaffolds are generally used as artificial supports and as substrates for ...regenerating new tissues and should closely mimic natural extracellular matrix (ECM). The materials used for fabricating scaffolds must be biocompatible, non-cytotoxic and bioabsorbable/biodegradable. For this application, specifically biopolymers such as PLA, PGA, PTMC, PCL etc. satisfying the above criteria are promising materials. Poly(ε-caprolactone) (PCL) is one such potential candidate which can be blended with other materials forming blends, copolymers and composites with the essential physiochemical and mechanical properties as per the requirement. Nanofibrous scaffolds are fabricated by various techniques such as template synthesis, fiber drawing, phase separation, self-assembly, electrospinning etc. Among which electrospinning is the most popular and versatile technique. It is a clean, simple, tunable and viable technique for fabrication of polymer-based nanofibrous scaffolds. The design and fabrication of electrospun nanofibrous scaffolds are of intense research interest over the recent years. These scaffolds offer a unique architecture at nano-scale with desired porosity for selective movement of small molecules and form a suitable three-dimensional matrix similar to ECM. This review focuses on PCL synthesis, modifications, properties and scaffold fabrication techniques aiming at the targeted tissue engineering applications.
Alumina is one of the most widely used ceramic material finds applications as structural component for high temperature applications, heat engine and aerospace applications, as electronic substrates ...etc. It is also used for adsorption / chemisorptions of heavy toxic metal ions such as arsenic or arsenate. The chemisorptions depends on exposed surface area, therefore, nanofibers with high surface area produced by electrospinning might be ideal for this application. In this study, attempts have been made to prepare alumina nanofibers by electrospinning technique by studying the effect of different chemical precursors and other processing parameters on morphology of nanofibers.
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•Synthesis of stable AgNPs using leaves of Desmodium gangeticum was demonstrated.•The synthesized nanoparticles solution was stable for more than four months.•The AgNPs were spherical ...in shape with moderate variation in particle sizes.•The synthesized AgNPs exhibited antimicrobial activity due to synergistic effects.
An aqueous leaf extract of Desmodium gangeticum was employed to synthesize silver nano particles. Rapid formation of stable silver nanoparticles were observed on exposure of the aqueous leaf extract with solution of silver nitrate. The silver nanoparticles were characterized by UV–visible spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis and transmission electron microscopy (TEM), and Fourier Transform Infra-Red spectroscopy (FTIR) UV–visible spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM), and Fourier Transform Infra-Red spectroscopy (FTIR). UV–visible spectrum of the aqueous medium peaked at 450nm corresponding to the plasmon absorbance of silver nanoparticles. SEM analysis revealed the spherical shape of the particles with sizes ranging from 18 to 39nm and the EDAX spectrum confirmed the presence of silver along with other elements in the plant metabolite. Further, these biologically synthesized nanoparticles were found to be highly toxic against pathogenic bacteria Escherichia coli, thus implying significance of the present study in production of biomedical products.
Developing an accurate and reliable model for the pressure strain correlation is a critical need for the success of the Reynolds Stress Modeling approach. This is challenging because replicating the ...non-local effects of pressure using a modeling basis composed of local tensors is limiting. In this paper we use physics based arguments and analysis of simulation data to select additional tensors to extend this modeling basis for pressure strain correlation modeling to formulate models with improved precision and robustness. We integrate these tensors in the modeling basis and develop separate models for the slow and rapid pressure strain correlation. This complete pressure strain correlation model is tested for different turbulent flows and its predictions are compared to prior pressure strain correlation models. We show that the new model with an extended tensor basis is able to show improvements in accuracy and reliability.
The severe acute respiratory syndrome coronavirus (SARS-CoV-2) pandemic of 2019 forced widespread use of face coverings as a mandatory step towards reducing infection by the virus. The face mask acts ...as a barrier for transmission of infected aerosols among its user and surrounding people. This has propelled pace of research and development of face masks around the world. This short review is an effort to present advances in materials and designs used for face masks. Details available in scientific literature and company brochures have been accessed and the use of nanomaterials and designs for the new generation of face masks have been discussed. Special attention was given to the face masks based on electrospun nanofiber-based membrane materials due to their nano-sized pores, light weight, and high filtration efficiency; therefore, they are commercially viable and popular among various products available in the market. Incorporation of metal organic framework (MOFs) and graphene have opened avenues to more advanced/multi-functional, reusable, and high capacity adsorption filtration membranes. Rapid prototyping/3-dimensional (3-D) printing techniques have been applied to shorten the time of manufacture of face masks. This review is expected to be very helpful for engineers, scientists, and entrepreneurs working on development of novel face masks required in plenty during this pandemic period.
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