Fabrication,characterization, and thermal property evaluation of silver nanofluids

Silver nanoparticles were successfully prepared in two different solvents using a microwave heating technique, with various irradiation times. The silver nanoparticles were dispersed in polar liquids (distilled water and ethylene glycol) without any other reducing agent, in the presence of the stabilizer polyvinylpyrrolidone (PVP). The optical properties, thermal properties, and morphology of the synthesized silver particles were characterized using ultraviolet-visible spectroscopy, photopyroelectric technique, and transmission electron microscopy. It was found that for the both solvents, the effect of microwave irradiation was mainly on the particles distribution, rather than the size, which enabled to make stable and homogeneous silver nanofluids. The individual spherical nanostructure of self-assembled nanoparticles has been formed during microwave irradiation. Ethylene glycol solution, due to its special properties, such as high dielectric loss, high molecular weight, and high boiling point, can serve as a good solvent for microwave heating and is found to be a more suitable medium than the distilled water. A photopyroelectric technique was carried out to measure thermal diffusivity of the samples. The precision and accuracy of this technique was established by comparing the measured thermal diffusivity of the distilled water and ethylene glycol with values reported in the literature. The thermal diffusivity ratio of the silver nanofluids increased up to 1.15 and 1.25 for distilled water and ethylene glycol, respectively.     

Synthesis,characterization and in-vitro behavior of natural chitosan-hydroxyapatite-diopside nanocomposite scaffold for bone tissue engineering

Composite materials based on a combination of biodegradable polymers and bioactive ceramics, including chitosan and hydroxyapatite are discussed as suitable materials for scaffold fabrication. Diopside is a member of bioactive silicates; it is a good choice for hard tissue engineering because of its biocompatibility with host tissue and high mechanical strength. Chitosan and hydroxyapatite were extracted from shrimp shell and bovine bone, respectively and diopside nanoparticles were prepared by the sol-gel method. The present study reports on a chitosan composite which was reinforced by hydroxyapatite and diopside; the scaffolds were fabricated by the freeze-drying method. The so-produced chitosan-hydroxyapatite-diopside (CS-HA-DP) scaffolds were further cross-linked using tripolyphosphate (TPP) to achieve enhanced mechanical strength. The ratios of the ceramic components in composites were 5-58-37, 10-55-35, and 15-52-33 (diopside-hydroxyapatite-chitosan, w/w %). The physicochemical properties of scaffolds were investigated using Fourier-transform infrared spectrometry (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) techniques. The effect of scaffolds composition on bioactivity and biodegradability were studied well. To investigate mechanical properties of samples, compression test was done. Results showed that the composite scaffold with 5% DP has the highest mechanical strength. The porosity of composites dropped from 92% to 76% by increasing the amount of DP. Cytocompatibility of the scaffolds was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, alkaline phosphatase (ALP) activity, and cell attachment studies using human osteoblast cells. Results demonstrated no sign of toxicity and cells were found to be attached to the pore walls within the scaffolds; moreover, results illustrated that the developed composite scaffolds could be a potential candidate for tissue engineering.     

Four Novel p.N385K,p.V36A,c.1033–1034insT and c.1417–1418delCT Mutations in the Sphingomyelin Phosphodiesterase 1 (SMPD1) Gene in Patients with Types A and B Niemann-Pick Disease (NPD)

Background: Types A and B Niemann-Pick disease (NPD) are autosomal-recessive lysosomal storage disorders caused by the deficient activity of acid sphingomyelinase due to mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene. Methods: In order to determine the prevalence and distribution of SMPD1 gene mutations, the genomic DNA of 15 unrelated Iranian patients with types A and B NPD was examined using PCR, DNA sequencing and bioinformatics analysis. Results: Of 8 patients with the p.G508R mutation, 5 patients were homozygous, while the other 3 were heterozygous. One patient was heterozygous for both the p.N385K and p.G508R mutations. Another patient was heterozygous for both the p.A487V and p.G508R mutations. Two patients (one homozygous and one heterozygous) showed the p.V36A mutation. One patient was homozygous for the c.1033–1034insT mutation. One patient was homozygous for the c.573delT mutation, and 1 patient was homozygous for the c.1417–1418delCT mutation. Additionally, bioinformatics analysis indicated that two new p.V36A and p.N385K mutations decreased the acid sphingomyelinase (ASM) protein stability, which might be evidence to suggest the pathogenicity of these mutations. Conclusion: with detection of these new mutations, the genotypic spectrum of types A and B NPD is extended, facilitating the definition of disease-related mutations. However, more research is essential to confirm the pathogenic effect of these mutations.     

Growth of InAs/InP core-shell nanowires with various pure crystal structures

We have studied the epitaxial growth of an InP shell on various pure InAs core nanowire crystal structures by metal-organic vapor phase epitaxy. The InP shell is grown on wurtzite (WZ), zinc-blende (ZB), and {111}- and {110}-type faceted ZB twin-plane superlattice (TSL) structures by tuning the InP shell growth parameters and controlling the shell thickness. The growth results, particularly on the WZ nanowires, show that homogeneous InP shell growth is promoted at relatively high temperatures (～500?°C), but that the InAs nanowires decompose under the applied conditions. In order to protect the InAs core nanowires from decomposition, a short protective InP segment is first grown axially at lower temperatures (420-460?°C), before commencing the radial growth at a higher temperature. Further studies revealed that the InP radial growth rate is significantly higher on the ZB and TSL nanowires compared to WZ counterparts, and shows a strong anisotropy in polar directions. As a result, thin shells were obtained during low temperature InP growth on ZB structures, while a higher temperature was used to obtain uniform thick shells. In addition, a schematic growth model is suggested to explain the basic processes occurring during the shell growth on the TSL crystal structures.     

Temperature distribution reconstruction in Czochralski crystal growth process

A mechanical geometric crystal growth model is developed to describe the crystal length and radius evolution. The crystal radius regulation is achieved by feedback linearization and accounts for parametric uncertainty in the crystal growth rate. The associated parabolic partial differential equation (PDE) model of heat conduction is considered over the time‐varying crystal domain and coupled with crystal growth dynamics. An appropriately defined infinite‐dimensional representation of the thermal evolution is derived considering slow time‐varying process effects. The computational framework of the Galerkin's method is used for parabolic PDE order reduction and observer synthesis for temperature distribution reconstruction over the entire crystal domain. It is shown that the proposed observer can be utilized to reconstruct temperature distribution from boundary temperature measurements. The developed observer is implemented on the finite‐element model of the process and demonstrates that despite parametric and geometric uncertainties present in the model, the temperature distribution is reconstructed with the high accuracy. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2839–2852, 2014     

Investigations on landmine detection by BF3 detector

Experiments were carried out to investigate the possible use of neutron backscattering for the detection of polyethylene (PE) sample buried in the soil. In detection of landmine by neutrons, the neutron detector and its shield play an important role. In this paper, the effects of graphite, heavy water, polyethylene and boric acid moderators on the flux of back scattered neutrons were investigated. We have also experimentally verified the effect of BF3 detector shield and obtained good agreement with theory.     

Prevascularized Micro?/Nano?Sized Spheroid/Bead Aggregates for Vascular Tissue Engineering

Efficient strategies to promote microvascularization in vascular tissue engineering, a central priority in regenerative medicine, are still scarce; nano- and mi...     

Thermal diffusivity measurement of Au nanofluids of very low concentration by using photoflash technique

In this paper, the application of photoflash technique to measuring the thermal diffusivity of gold nanofluids of very low concentration at room temperature was presented. The nanofluid samples were prepared from the pulse laser ablation procedure. The thermal diffusivity was obtained by fitting the theoretical temperature signal to the experimental data, and it was found to increase linearly from 1.47 × 10⁻³ cm² s⁻¹ to 1.68 × 10⁻³ cm² s⁻¹ as the concentration increased from 1.11 mg/L to 3.18 mg/L. The increase in thermal diffusivity in these multidispersed nanofluids was attributed to the higher nanoparticle concentration as well as to the increasing presence of the smaller size nanoparticles.     

Effect of Y2O3 and Er2O3 co-dopants on phase stabilization of bismuth oxide

Bi₂O₃ compositions were prepared to investigate the effect of rare earth metal oxides as co-dopants on phase stability of bismuth oxide. Compositions containing 9-14 mol% of Y₂O₃ and Er₂O₃ were synthesized by solid state reaction. The structural characterization was carried out using X-ray powder diffraction. The XRD results show that the samples containing 12 and 14 mol% total dopants had cubic structure, whereas the samples with lower dopant concentrations were tetragonal. Comparing the lattice parameters of the cubic phases of (Bi₂O₃)_0.88(Y₂O₃)_0.06(Er₂O₃)_0.06 and (Bi₂O₃)_0.86(Y₂O₃)_0.07(Er₂O₃)_0.07 revealed that lattice parameter decreases by increasing the dopant concentration. The XRD pattern and the powder density results indicated the formation of solid solution in the studied systems. After annealing samples with cubic phase at 600 °C for various periods of time, phase transformation to tetragonal and rhombohedral occurs.