سال:1391 | دوره: | شماره: |تعداد مقالات:7

Surface mechanical attrition treatment (SMAT) was applied to the samples of a type AISI 304 stainless steel in order to induce grain refinement as well as formation of twins. Transmission electron microscopy and X-ray diffraction analysis results showed that the average grain size at the surface of the SMATed sample was about 10 nm. The untreated and SMATed samples were then welded using a one-pass gas tungsten arc procedure. The heat-affected zone (HAZ) of the samples was examined by optical microscopy and corrosion tests. Results of the double loop electrochemical potentiokinetic reactivation tests showed that the degree of sensitization in the HAZ for the SMATed sample was very low as compared to that of the untreated one. The pre-SMATed sample was resistant to intergranular corrosion. This is mainly due to the formation of high density of twins which are not prone to carbide precipitation because of their regular and coherent atomic structure and extreme low grain boundary energy as compared with those of other grain boundaries.

Rifampin (RIF) is one of the front-line drugs in therapy of tuberculosis (TB). The emergence of multidrug-resistant strains of mycobacteria has greatly contributed to the increased incidence of TB. Nano-based formulation of several antimicrobials has been shown to improve either antibacterial efficacy or pharmacokinetic behavior. In this study, RIF-loaded solid lipid nanoparticles (SLNs) were prepared by a modified microemulsion-based method and their particle size, zeta potential, encapsulation efficiency, morphology, and antibacterial activity against Mycobacterium fortuitum were evaluated. The resulting SLNs were spherical with diameter of about 100 nm, with low negative zeta potential, and an encapsulation efficiency of 82%. The formulation also sustained the drug release for 72 h. The antimycobacterial efficacy was greatly improved against M. fortuitum, and the minimum inhibitory concentration of drug-loaded SLNs was eight times less than free RIF. Drug-free SLNs and the ingredients showed no antibacterial effect. It can be concluded that as expected, solid lipid nanoparticles are promising vehicles for enhanced antimycobacterial effect of rifampin.

Silver nanoparticles are nanoparticles of silver which are in the range of 1 and 100 nm in size. Silver nanoparticles have unique properties which help in molecular diagnostics, in therapies, as well as in devices that are used in several medical procedures. The major methods used for silver nanoparticle synthesis are the physical and chemical methods. The problem with the chemical and physical methods is that the synthesis is expensive and can also have toxic substances absorbed onto them. To overcome this, the biological method provides a feasible alternative.The major biological systems involved in this are bacteria, fungi, and plant extracts. The major applications of silver nanoparticles in the medical field include diagnostic applications and therapeutic applications. In most of the therapeutic applications, it is the antimicrobial property that is being majorly explored, though the anti-inflammatory property has its fair share of applications. Though silver nanoparticles are rampantly used in many medical procedures and devices as well as in various biological fields, they have their drawbacks due to nanotoxicity. This review provides a comprehensive view on the mechanism of action, production, applications in the medical field, and the health and environmental concerns that are allegedly caused due to these nanoparticles.The focus is on effective and efficient synthesis of silver nanoparticles while exploring their various prospective applications besides trying to understand the current scenario in the debates on the toxicity concerns these nanoparticles pose.

In this paper, a novel 12-bit current-steering binary-weighted digital-to-analog converter (DAC) based on nanoampere bits is designed and modified for high-definition television (HDTV) applications. As a part of a widely used consumer appliance, it is aimed to be such designed to consume power as low as possible.Hence, as a distinguished idea, prime concentration is focused on the reduction of the currents providing the bits of the proposed DAC. To do this, current mirrors operating in the weak inversion region are arranged to establish the least significant bit (LSB) current as low as 10 nA while the power supply is also reduced to 1 V, resulting to an ultralow power of 52.9mW. Many other powerful ideas are then deliberately combined to maintain both high speed and very low glitches required for HDTV application despite those ultralow currents and power. The result is a speed of 100 MS/s, an ultralow glitch of ≃10.91 fAs, |INL| ≤ 0.988 LSB, |DNL| ≤0.99 LSB, and a spurious-free dynamic range of ≃73 dB. These results caused the proposed DAC to execute a distinguished overall performance (defined as figure of merit) greatly better than some other advanced ones by outstanding ratios of 77 to 277, 185. Hspice simulations with the SMIC 0.18-mm complementary metal-oxide semiconductor technology have been used to validate the proposed circuit. Performance evaluation of the proposed DAC versus Monte Carlo simulations and also a wide range of temperature variations proved both its well mismatch insensitivity and thermal stability.

TiO2 particulate films with optically confined anatase phase were deposited on glass substrates using an aqueous precursor by dip-coating method. The precursor solution was prepared by mixing appropriate amounts of titanium tetraisopropoxide, isopropyl alcohol, and Triton X-100 in an airtight vessel. Without further treatment, the solution was used for the coating process. After deposition, the films were baked at 300oC, 450oC, and 600oC for 15 min in air atmosphere using a box furnace. Physical properties of such films were investigated by X-ray diffraction, scanning electron microscopy, and UV-visible spectrophotometry. Effective mass approximation theory was applied to explain the optical confinement effect which is realized in those films because of its crystallite size.The energy bandgap values for the confined anatase phase of TiO2 particulates were predicted by the effective mass approximation model and are in good agreement with our experimental results. These observed results were discussed in detail.

Two-dimensional semiconductor quantum-dot systems are typical nanoscale structures in which a few number of electrons is confined in a small region of space by applying external electric gate potentials. While the detailed form of the confining potential depends on the specific experimental setup, the parabolic confinement model has commonly been used because of its simplicity. Clearly, on those instances in which the experimental setup involves placement of gate potentials with sharp geometric features, the area depleted of electrons; thus, the quantum-dot region cannot be considered circular. If, for simplicity, we consider the confinement region of the electrons as square in shape, then an accurate calculation of the properties of such square-patterned quantum dot should be made using a realistic confinement potential originating from that particular configuration. We calculated exactly such a confinement potential for a square quantum dot. The particular analytic form of this realistic potential is complicated given its dependence on the two-dimensional position coordinates, rather than simply the distance from the center of the quantum dot. In this work, we choose to substitute the realistic confinement potential for a square-patterned quantum dot with an approximated circular symmetric potential. We assess the quality of this approximation and discuss instances in which one can reliably use the approximated simplified potential instead of the computationally unyielding exact one.

Controlled conduction of magnetic spins is desired for data processing in modern spintronic devices. Transition metal-doped ZnO is a potential candidate for this purpose. We studied the effects of cobalt doping on structural, absorbance, and magnetic properties of ZnO nano-particles. Different compositions (Zn0.99Co0.1O, Zn0.97Co0.3O, and Zn0.95Co0.5O) of cobalt-doped ZnO were fabricated using metallic chlorides by co-precipitation method. XRD revealed standard ZnO wurtzite crystal structure without lattice distortion due to impurities but showed presence of additional phases at higher doping ratios. Fourier transformed infrared spectroscopy also confirmed the standard ZnO profiles at lower doping ratios but additional phases at higher doping. Vibrating sample magnetometer showed soft ferromagnetic behavior for low impurity samples and harder ferromagnetic behavior for higher doping at room temperature. A simultaneous differential scanning calorimetry/thermo gravimetric analysis was performed to study the phase variations during crystallization.