National Aerospace Laboratories

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 (ANbO3), 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.

▪ Abstract This review pertains to the body of work dealing with internal recirculating flows generated by the motion of one or more of the containing walls. These flows are not only technologically important, they are of great scientific interest because they display almost all fluid mechanical phenomena in the simplest of geometrical settings. Thus corner eddies, longitudinal vortices, nonuniqueness, transition, and turbulence all occur naturally and can be studied in the same closed geometry. This facilitates the comparison of results from experiment, analysis, and computation over the whole range of Reynolds numbers. Considerable progress has been made in recent years in the understanding of three-dimensional flows and in the study of turbulence. The use of direct numerical simulation appears very promising.

Corrosion control of metals is of technical, economical, environmental, and aesthetical importance. The use of inhibitors is one of the best options of protecting metals and alloys against corrosion. The environmental toxicity of organic corrosion inhibitors has prompted the search for green corrosion inhibitors as they are biodegradable, do not contain heavy metals or other toxic compounds. As in addition to being environmentally friendly and ecologically acceptable, plant products are inexpensive, readily available and renewable. Investigations of corrosion inhibiting abilities of tannins, alkaloids, organic,amino acids, and organic dyes of plant origin are of interest. In recent years, sol-gel coatings doped with inhibitors show real promise. Although substantial research has been devoted to corrosion inhibition by plant extracts, reports on the detailed mechanisms of the adsorption process and identification of the active ingredient are still scarce. Development of computational modeling backed by wet experimental results would help to fill this void and help understand the mechanism of inhibitor action, their adsorption patterns, the inhibitor-metal surface interface and aid the development of designer inhibitors with an understanding of the time required for the release of self-healing inhibitors. The present paper consciously restricts itself mainly to plant materials as green corrosion inhibitors.

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
\nlarge 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
\nvery 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
\nperformance 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
\nthe recent developments on R&D of piezo materials in this review article.

Image registration and fusion are of great importance in defence and civilian sectors, e.g. , recognising a ground/air force vehicle and medical imaging. Pixel-level image fusion using wavelets and principal13; component analysis has been implemented and demonstrated in PC MATLAB. Different performance metrics with and without reference image are implemented to evaluate the performance of image fusion algorithms. As expected, the simple averaging fusion algorithm shows degraded13; performance. The ringing tone presented in the fused image can be avoided using wavelets with shift invariant property. It has been concluded that image fusion using wavelets with higher level of decomposition showed better performance in some metrics and in other metrics, principal components analysis showed better performance.13;

Smart materials, which exhibit piezoelectricity, find an eclectic range of applications in the industry. The direct piezoelectric effect has been widely used in sensor design, and the inverse piezoelectric effect has been applied in actuator design. Ever since 1954, PZT and BaTiO 3 were widely used for sensor and actuator applications despite their toxicity, brittleness, inflexibility, etc. With the discovery of PVDF in 1969, followed by development of copolymers, a flexible, easy to process, nontoxic, high density alternate with high piezoelectric voltage coefficient was available. In the past 20 years, heterostructural materials like polymer ceramic composites, have received lot of attention, since these materials combine the excellent pyroelectric and piezoelectric properties of ceramics with the flexibility, processing facility, and strength of the polymers resulting in relatively high dielectric permittivity and breakdown strength, which are not attainable in a single phase piezoelectric material. The current review article is an attempt to provide a compendium of all the work carried out with reference to PVDF‐PZT composites. The review article evaluates the effect of grain size, content and other factors under the purview of dielectric and piezoelectric properties while evaluating the sensitivity of the material for sensor application. POLYM. ENG. SCI., 55:1589–1616, 2015. © 2015 Society of Plastics Engineers

Chemistry of nanocrystalline oxide materials , Chemistry of nanocrystalline oxide materials , کتابخانه دیجیتال جندی شاپور اهواز

The equations for the lattice strains produced by nonhydrostatic compression are presented for all seven crystal systems in a form convenient for analyzing x-ray diffraction data obtained by newly developed methods. These equations have been used to analyze the data on cubic (bcc α-Fe) and hexagonal (hcp ε-Fe) systems. The analysis gives information on the strain produced by the hydrostatic stress component. A new method of estimating the uniaxial stress component from diffraction data is presented. Most importantly, the present analysis provides a general method of determining single crystal elastic constants to ultrahigh pressures.

A general expression has been derived using anisotropic elasticity theory for the lattice strain which corresponds to the x-ray diffraction measurement on the polycrystalline specimen (cubic system) compressed nonhydrostatically in an opposed anvil device. The expressions for the various diffraction geometries emerge as the special cases of this equation. The strain calculated using isotropic elasticity theory corresponds to the macroscopic strain in the specimen, and can be obtained from the present equation by letting the anisotropy factor 2(S11−S12)/S44=1. Further, it is shown that the ratio of the lattice strain to the macroscopic strain (in the direction of the lattice strain) produced by the deviatoric stress component depends on the Miller indices (hkl) of the lattice planes and the elastic anisotropy factor. This ratio is unity only if the crystallites constituting the specimen are elastically isotropic, and increases with increasing anisotropy of the crystallites.

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Additive Manufacturing (AM) technologies have been emerged as a fabrication method to obtain engineering components within a short span of time. Desktop 3D printing, also referred as additive layer manufacturing technology is one of the powerful method of rapid prototyping (RP) technique that fabricates three dimensional engineering components. In this method, 3D digital CAD data is converted directly to a product. In the present investigation, ABS + hydrous magnesium silicate composite was considered as the starting material. Mechanical properties of ABS + hydrous magnesium silicate composite material were evaluated. ASTM D638 and ASTM D760 standards were followed for carrying out tensile and flexural tests, respectively. Samples with different layer thickness and printing speed were prepared. Based on the experimental results, it is suggested that low printing speed, and low layer thickness has resulted maximum tensile and flexural strength, as compared to all the other process parameters samples.

This paper reviews the potential of polymer and ceramic matrix composites for aerospace/space vehicle applications. Special, unique and multifunctional properties arising due to the dispersion of nanoparticles in ceramic and metal matrix are briefly discussed followed by a classification of resulting aerospace applications. The paper presents polymer matrix composites comprising majority of aerospace applications in structures, coating, tribology, structural health monitoring, electromagnetic shielding and shape memory applications. The capabilities of the ceramic matrix nanocomposites to providing the electromagnetic shielding for aircrafts and better tribological properties to suit space environments are discussed. Structural health monitoring capability of ceramic matrix nanocomposite is also discussed. The properties of resulting nanocomposite material with its disadvantages like cost and processing difficulties are discussed. The paper concludes after the discussion of the possible future perspectives and challenges in implementation and further development of polymer and ceramic nanocomposite materials.

X-ray diffraction data obtained under nonhydrostatic compression of a polycrystalline sample yield an estimate of the single-crystal elasticity tensor of the material when analyzed using appropriate equations. The analysis requires as input the aggregate shear modulus from independent measurements. The high-pressure elastic moduli of face-centered-cubic FeO, body-centered-cubic iron ( $\ensuremath{\alpha}$-Fe), and the pressure-induced hexagonal close-packed iron ( $\ensuremath{\epsilon}$-Fe) are obtained. This analysis currently provides the only method of determining single-crystal elasticity tensors in the megabar pressure range and of studying elasticity of very high-pressure phases.

Surgical sutures are used to facilitate closure and healing of surgical- or trauma-induced wounds by upholding tissues together to facilitate healing process. There is a wide range of suture materials for medical purpose and the main types include absorbable and nonabsorbable. Recently, there is a growth in the development of classes of suture materials based on their properties and capabilities to improve tissue approximation and wound closure. This review outlines and discusses the current and emerging trends in suture technology including knotless barbed sutures, antimicrobial sutures, bio-active sutures such as drug-eluting and stem cells seeded sutures, and smart sutures including elastic, and electronic sutures. These newer strategies expand the versatility of sutures from being used as just a physical entity approximating opposing tissues to a more biologically active component enabling delivery of drugs and cells to the desired site with immense application potential in both therapeutics and diagnostics. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1544-1559, 2016.

Using energy-dispersive x-ray diffraction techniques together with the theory describing lattice strains under nonhydrostatic compression, the behavior of a layered sample of gold and rhenium has been studied at pressures of 14--37 GPa. For gold, the uniaxial stress component t is consistent with earlier studies and can be described by $t=0.06+0.015P$ where P is the pressure in GPa. The estimated single-crystal elastic moduli are in reasonable agreement with trends based on extrapolated low-pressure data. The degree of elastic anisotropy increases as $\ensuremath{\alpha},$ the parameter which characterizes stress-strain continuity across grain boundaries, is reduced from 1.0 to 0.5. For rhenium, the apparent equation of state has been shown to be strongly influenced by nonhydrostatic compression, as evidenced by its dependence on the angle $\ensuremath{\psi}$ between the diffracting plane normal and the stress axis. The bulk modulus obtained by inversion of nonhydrostatic compression data can differ by nearly a factor of 2 at angles of $0\ifmmode^\circ\else\textdegree\fi{}$ and $90\ifmmode^\circ\else\textdegree\fi{}.$ On the other hand, by a proper choice of $\ensuremath{\psi},$ d spacings corresponding to quasihydrostatic compression can be obtained from data obtained under highly nonhydrostatic conditions. The uniaxial stress in rhenium over the pressure range from 14--37 GPa can be described by $t=2.5+0.09P.$ The large discrepancy between x-ray elastic moduli and ultrasonic data and theoretical calculations indicates that additional factors such as texturing or orientation dependence of t need to be incorporated to more fully describe the strain distribution in hexagonal-close-packed metals.

The compressibilities of the monotellurides of Pr, Sm, Eu, Tm, and Yb and the monoselenide and sulfide of Sm have been investigated to \ensuremath{\sim} 300 kbar using high-pressure $x$-ray-diffraction techniques. SmTe, SmSe, TmTe, and YbTe show abnormal volume changes in the 20-50-, 15-40-, 15-30-, and 150-200-kbar regions of pressure, respectively. SmS shows an abrupt decrease in volume at 6.5 kbar. Since there is no change in structure, the anomalously large volume changes have been explained on the basis of a pressure-induced $4f\ensuremath{-}5d$ electronic collapse which involves a change in the valence state of the rare-earth ion from ${2}^{+}$ towards the ${3}^{+}$ state. The results of high-pressure x-ray studies on Sm chalcogenides are consistent with the conclusions drawn in the earlier work from high-pressure resistivity measurements. PrTe, SmTe, and EuTe exhibit a phase transition from NaCl-type to CsCl-type structure at pressures of about 90 \ifmmode\pm\else\textpm\fi{} 10, 110 \ifmmode\pm\else\textpm\fi{} 10, and 110 \ifmmode\pm\else\textpm\fi{} 10 kbar, respectively. It appears that a pressure-induced NaCl-to-CsCl transition may be commonly encountered in rare-earth monochalcogenides.

In the Unmanned Air Vehicle (UAV) navigation the main challenge is estimating and maintaining the accurate values of UAVs position and orientation. The onboard Inertial Measurement Unit (IMU) provide the measurements but it is mainly affected from the accumulated error due to drift in measurements. Traditionally the Global Position System (GPS) measurements of vehicles position data can be fused with IMU measurements to compensate the accumulated error, But the GPS signals is not available everywhere and it will be degraded or fully not available in hostile areas, building structures and water bodies. Researchers already evolved methods to handle the UAV navigation in GPS denied environment by using Vision based navigation like Visual Odometry (VO) and Simultaneous Localisation and Mapping (SLAM). In this survey paper we attempted to understand the existing research towards vision based navigation and finally proposed a Modular Multi-Sensor Data Fusion technique for UAV navigation in the GPS denied environment.

Red light emitting cubic Y1.95Eu0.05O3 nanophosphors have been synthesized by a low temperature solution combustion method using ethylene diamine tetra acetic acid (EDTA) as fuel. The systematic studies on the effect of calcination temperature on its structural, photoluminescence (PL), and thermoluminescence (TL) properties were reported. The crystallinity of the samples increases, and the strain is reduced with increasing calcination temperature. SEM micrographs reveal that samples lose their porous nature with an increase in calcination temperature. PL spectra show that the intensity of the red emission (611 nm) is highly dependent on the calcination temperature and is found to be 10 times higher when compared to as-formed samples. The optical band gap (Eg) was found to reduce with an increase of calcination temperature due to reduction of surface defects. The thermoluminescence (TL) intensity was found to be much enhanced in the 1000 °C calcined sample. The increase of PL and TL intensity with calcination temperature is attributed to the decrease of the nonradiative recombination probability, which occurs through the elimination of quenching defects. The trap parameters (E, b, s) were estimated from Chen’s glow peak shape method and are discussed in detail for their possible usage in dosimetry.

The mutual coupling between antenna elements affects the antenna parameters like terminal impedances, reflection coefficients and hence the antenna array performance in terms of radiation characteristics, output signal-to-interference noise ratio (SINR), and radar cross section (RCS). This coupling effect is also known to directly or indirectly influence the steady state and transient response, the resolution capability, interference rejection, and direction-of-arrival (DOA) estimation competence of the array. Researchers have proposed several techniques and designs for optimal performance of phased array in a given signal environment, counteracting the coupling effect. This paper presents a comprehensive review of the methods that model and mitigate the mutual coupling effect for different types of arrays. The parameters that get affected due to the presence of coupling thereby degrading the array performance are discussed. The techniques for optimization of the antenna characteristics in the presence of coupling are also included.

An inexpensive and facile one-step method to develop a superhydrophobic coating on the copper surface is reported. Superhydrophobic CuO/Cu(OH)2 surfaces were prepared by a simple solution-immersion process at room temperature, without using a low surface energy material. The structure and composition of as-prepared CuO/Cu(OH)2 hierarchical structure were confirmed by X-ray diffraction, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The growth stage was carefully examined by field emission scanning electron microscopy (FESEM), and it was observed that initially Cu(OH)2 nanoneedle arrays were formed on the copper surface and subsequently the CuO microflowers formed on the nanoneedle arrays. The contact angle as a function of immersion time was studied using a contact angle goniometer. The correlation between the microstructure of the immersed copper surface and the contact angle was examined carefully using FESEM and atomic force microscopy (AFM). Our results based on FESEM and AFM studies show that the CuO/Cu(OH)2 coatings demonstrate superhydrophobicity only for an optimal combination of the solid region (i.e., microflowers and nanoneedles) and air pockets (i.e., voids). The maximum static water contact angle on the prepared surface was 159°. The wettability transition of the CuO/Cu(OH)2 surface from superhydrophobicity to superhydrophilicity was studied by the alteration of oxygen plasma treatment and dark storage. The FESEM, AFM, and XPS studies showed that this transformation was mainly due to the morphological changes that occur in addition to the chemical changes taking place on the CuO/Cu(OH)2 surface under the influence of oxygen plasma. XPS analysis demonstrated that the incorporation of oxygen species by oxygen plasma activation accounted for the highly hydrophilic character of the surface.