Narrow Results

In this study, natural crystalline material collected from the head of the Pomadasys maculatus fishes are characterized for their potential applications in various fields including laser optics. Interestingly, the natural otolith crystals exhibit two-photon absorption-induced optical limiting characteristics under Nd:YAG laser excitation. The optical limiting threshold for otolith crystals was found to be $6.22\times 10^{12}$W/m². The presence of Calcium (Ca), Copper (Cu), Potassium (K), and Sodium (Na) is confirmed by ICP-OES analysis. The presence of Ca is primarily from the functional group of otolith that was found on the surface of otolith. From the GCMS analysis, 25 compounds were found in the methanol extract of otolith. The magnetic property of Pomadasys maculatus fish sample was analyzed by vibrating sample magnetometer (VSM). The decomposition/mass loss over a temperature was analyzed by thermogravimetric analysis (TGA) and also the endo and exothermic event temperatures and phase transitions were observed from Differential Thermal Analysis (DTA).

Nanoferrites of CoGd${}_x$Fe${}_{2-x}$O₄ ($x=0.0,0.03,0.06,0.09,0.12$ and $0.15)$ were synthesized via sol–gel auto combustion. The fashioned samples were examined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer and UV spectroscopic analysis. A cubic spinel phase with no impurities was confirmed by XRD. Doping with Gd${}^{3+}$ ions raises the crystallite size from 20nm to 25nm and the lattice constant from 8.351Å to 8.413Å. Formations of two significant bands are supported by FTIR spectra between 590cm${}^{-1}$ and 601cm${}^{-1}$, 403cm${}^{-1}$ and 407cm${}^{-1}$, which approve the establishment of ferrite structure. FESEM certified the formation of the nanoparticles and the fact that most of the grains are spherical and agglomerated and the EDX spectrographs certified the existence of the elemental compositions. With an increase in Gd${}^{3+}$ ion, saturation magnetization (M${}_s$) and remanence magnetization (M${}_r$) dropped from 132emu/g to 69emu/g and 93emu/g to 41emu/g, respectively. The coercivity (H${}_c$) increased with gadolinium and at the $x=0.15$ recording the extreme value of $H_c=1715$Oe. UV-spectroscopy studies authorized the samples’ semiconducting nature because band gap values were found from 2.108eV to 1.992eV.

We evaluate the impact of the memory hierarchy of virtual shared memory computers on the design of algorithms for linear algebra. On classical shared memory multiprocessor computers, block algorithms are used for efficiency. We study here the potential and the limitations of such approaches on globally addressable distributed memory computers. The BBN TC2000 belongs to this class of computers and will be used to illustrate our discussion.

We describe the implementation of Level 3 BLAS and examine the performance of some of the LAPACK routines. The impact of the number of processors with respect to the choice of the variants of classical matrix factorizations (for example, KJI, JKI, JIK for the LU factorization) is discussed. We also study the factorization of sparse matrices based on a multifrontal approach. The ideas introduced for the parallelization of full linear algebra codes are applied to the sparse case. We discuss and illustrate the limitations of this approach in sparse multifrontal factorization.

We show that the speed-ups obtained on the BBN TC2000 for the class of methods presented here are comparable to those obtained on more classical shared memory computers, such as the Alliant FX/80, the CRAY-2 and the IBM 3090/VF.

Nickel zinc aluminum nanoferrites with general formula Ni_0.5Zn_0.5Fe_2-xAl_xO₄(x = 0.0, 0.05, 0.1, 0.15, 0.2 and 0.25) were prepared by citrate-gel autocombustion method and heat treated in air at 1100°C for 4 h. The crystallography, surface morphology and magnetic properties were studied by using X-ray diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM), respectively. XRD analysis confirms that the system exhibits polycrystalline single phase cubic spinel structure and absence of any secondary phases. The crystallite size estimated from Scherrer formula for the Gaussian peak (311) has been found to be around 30 nm. The results obtained show that with Al³⁺ doping, the lattice parameter decreases due to smaller ionic radii of Al³⁺ ions replaces larger Fe³⁺ ions. The distribution of Al³⁺ ions over tetrahedral (A) and octahedral (B) sites is estimated from X-ray intensity calculations. The arrangement of magnetic ions among the tetrahedral and octahedral sites due to the substitution of Al³⁺ ions modifies the saturation magnetization (M_s) and coercivity (H_c). The room temperature magnetization values increases up to x = 0.1 and then decreases for the increase in aluminum concentration above x > 0.1. Surface topography of the powder samples exhibits nearly spherical shape microstructure and the average grain size has been found to be 180 nm (x = 0.05). The observed variations in the structural and magnetic properties are discussed in the light of existing understanding.

Li–Co nanoferrites (Li${}_{0.5-x/2}$Co${}_x$Fe${}_{2.5-x/2}$O₄) with x = 0.00, 0.03, 0.06, 0.09, and 0.12, were synthesized by chemical sol–gel method. Two different sintering techniques viz. conventional technique (CT) and microwave technique (MT) were employed to heat treat the synthesized samples with an aim to study the effect of sintering technique on the properties of the nanoferrites. Structural and microstructural properties of the samples were investigated using XRD and scanning electron microscopy (SEM) technique, respectively. The variation of room temperature dielectric constant and dielectric loss were measured as a function of frequency in the range 100 Hz–1 MHz and the normal dispersive behavior was observed. Magnetic properties were investigated using Vibrating Sample Magnetometer (VSM), while Soohoo’s method was used to measure Curie temperature. The results obtained have been discussed in the paper.

Iron-doped lead sulfide thin films were deposited on glass substrates using successive ionic layer adsorption and reaction method (SILAR) at room temperature. The X-ray diffraction pattern of the film shows a well formed crystalline thin film with face-centered cubic structure along the preferential orientation (1 1 1). The lattice constant is determined using Nelson Riley plots. Using X-ray broadening, the crystallite size is determined by Scherrer formula. Morphology of the thin film was studied using a scanning electron microscope. The optical properties of the film were investigated using a UV–vis spectrophotometer. We observed an increase in the optical band gap from 2.45 to 3.03eV after doping iron in the lead sulfide thin film. The cutoff wavelength lies in the visible region, and hence the grown thin films can be used for optoelectronic and sensor applications. The results from the photoluminescence study show the emission at 500–720nm. The vibrating sample magnetometer measurements confirmed that the lead sulfide thin film becomes weakly ferromagnetic material after doping with iron.

Nanocrystalline SnO₂ powder has been successfully synthesized by using tin(II) chloride dihydrate (SnCl${}_2\cdot 2$H₂O), distilled water and liquid ammonia by the simple chemical co-precipitation method at room temperature using different SnCl${}_2\cdot 2$H₂O molar concentration of 0.3M, 0.4M and 0.5M. The structural properties of the prepared SnO₂ and transition metal doped SnO₂ nanoparticles has been studied using X-ray diffraction method and scanning electron microscope. The composition of the powders has been analyzed using energy dispersive X-ray analysis. The XRD pattern of the SnO₂ nanoparticles indicates the formation of single-phase rutile tetragonal structure. The grain size is found to be in the range of 3–7nm and is found to increase with increasing SnCl₂ molar concentration. The absorption spectra revealed that the bandgap decreased from 3.74eV to 3.59eV with increasing SnCl₂ molar concentration. The photoluminescence spectra of SnO₂ nanoparticles showed a visible broad luminescence band in the region of 385–430nm. The magnetic studies have been carried out using the hysteresis loop obtained from a vibrating sample magnetometer. The SnO₂ samples using 0.3 and 0.4 SnCl₂ molar concentration exhibited ferromagnetic behavior whereas the SnO₂ sample prepared using 0.5M SnCl${}_2\cdot 2$H₂O exhibited paramagnetic nature.

This paper analyzes the effects of additives on the properties of Iron oxide. The Iron oxide was synthesized using the co-precipitation method. The X-ray diffraction (XRD) peaks of resultant Iron oxide perfectly matched with JCPDS #860550 ($\alpha$ phase of Iron oxide / Hematite). The additives like Cobalt oxide, Nickel metal, Indium oxide and Tin metal with diverse properties procured in readymade forms were mechanically mixed with Iron oxide in 1:99, 3:97, 5:95 and 7:93 weight ratios, respectively. The XRD peaks for additives were prominent for 7:93 (Additive: Base Material) weight % ratio samples. Therefore, for further studies, only these samples were used. In this study, variations in XRD intensity, lattice parameters, unit cell volume, grain size, micro-strains (W-H analysis), dislocation density and stacking fault probability were analyzed. The specific surface area of particles was calculated by scanning electron microscope analysis. The presence of additives was also confirmed by energy dispersive spectra (EDS). The M-H loops (Vibrating Sample Magnetometer analysis) for samples under investigation showed rare vertical shifts. The weak magnetic behavior of bare Hematite (1.0 emu/gm) sample improved to antiferromagnetic behavior due to the addition of Cobalt oxide (7.89 emu/gm) and Nickel metal (2.76 emu/gm). The addition of Indium oxide (0.65 emu/gm) and Tin metal (0.73 emu/gm) samples showed a decreased magnetic saturation.

In our study, a simple strategy to fabricate an efficient cobalt-based nanocatalyst is reported. The as-fabricated cobalt nanoparticles (Co NPs) that supported on reduced amine-functionalized graphene oxide (Co@RGO-NH${}_2)$ have been fabricated through reduction of Co${}^{2+}$ and GO-NH₂ by sodium borohydride under mild conditions. The morphology, elemental analysis, chemical composition, surface area and magnetic property of the as-fabricated Co@RGO-NH₂ nanocatalyst have been investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) and vibrating sample magnetometer (VSM), respectively. Characterization showed that Co@RGO-NH₂ nanocatalyst possesses a high surface area (232.05 m²/g) and good magnetic property. Obviously, the as-fabricated Co@RGO-NH₂ nanocatalyst exhibited a fascinating catalytic activity towards the catalytic reduction of different substituted nitro anilines pollutants ($o$-nitroaniline, $m$-nitroaniline and $p$-nitroaniline), as well as, the degradation of cationic methylene blue and anionic Congo red dyes. Furthermore, the reused Co@RGO-NH₂ nanocatalyst has shown high catalytic activity for all the catalytic reactions even after the fifth cycle, asserting the high stability of the as-fabricated heterogeneous catalyst.

The study of magnetic nanostructures is interesting because of its applications. Some of them are the development of magnetic refrigerators, ferrofluids, drug delivery systems, fabrication of devices with giant magnetoresistance effects, and high-frequency transformers. The physical and chemical properties of metal changes due to silica coating. The interaction potential can be manipulated using surface coatings and also the particle shape can be controlled. Nanoparticles with a proper surface coating are of interest for several other applications in optoelectronic devices and in the biomedical field. Thus, developing a new synthetic route for these particles and investigating the stability of magnetic materials are of great importance. Silica coating improves the chemical stability and electrical resistivity of the material. In this study, Ni₃Fe (core) nanoparticles were prepared and the silica shell for this core was synthesized. The as-prepared X-ray diffraction (XRD) patterns and 300°C annealed sample of Ni₃Fe/SiO₂ shows a characteristic hump in the low angle range confirming the presence of amorphous cristobalite phase of SiO₂. The size of the Ni₃Fe cluster in the Ni₃Fe/SiO₂ composite was estimated to be 8nm and 9nm, respectively, for the as-prepared and annealed samples. Vibrating sample magnetometer (VSM) measurements show the Ni₃Fe to silica ratio to be 59:41. A small decrease in the coercivity value, is probably due to morphological changes associated with the coating. Scanning electron microscope (SEM) studies of the as-prepared and annealed Ni₃Fe/SiO₂ powder particles are of flowerlike morphology and in agglomeration. The impedance spectra were found at room temperature for the as-prepared samples.