Capacity of nano-reactors of AOT micro-emulsions to form and sustain ultra small semiconductor quantum dots

Microemulsions (MEs) are increasingly being used as nano-reactors for the formation and synthesis of nanoparticles or quantum dots (QDs). In this paper, we study the capacity of aqueous nanoreactors of AOT microemulsions for the formation of ultrasmall semiconductor QDs by fixing w = ([H2O]/[AOT]) and varying the concentration of CdS up to 100 mM. The CdS QDs in the MEs are evaluated using UV-vis spectroscopy, XRD, TEM, and light scattering. Particles are found to be controlled in 8.7 A-11.8 A. The UV-vis spectra are analysed using an accurate tight-binding (TB) approach and effective mass approximation (EMA). The TB method, being much more accurate than the EMA, gives results in good agreement with X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD reveals that the particles are mostly zinc-blend at low concentrations (> or =20 mM) but a mixture of zinc-blend and wurtzite at higher concentrations (100 mM). High concentrations of CdS are useful to improve the yield while best-utilizing nanoreactors and to give a tight control over size and polydispersity. MEs containing CdS are found to be stable over a month when kept in the dark.     

RA-OABC: An Optimal Framework for Resource Assignment in WCDMA Networks Using Oppositional Artificial Bee Colony Algorithm with Repair Strategies

Wireless Personal Communications - In this paper, we propose a new optimal framework with repair strategy to resolve major issues in the assignment of resources to mobile terminals (plainly to...     

On the design of inscribed triangle circular fractal antenna for UWB applications

In this article, an ultrawide band inscribed triangle circular fractal antenna is presented. The antenna has been designed on FR4 substrate dielectric constant ?_r = 4.3 and thickness of substrate 1.53 mm with initial dimension of 30 mm diameter. The experimental result of fractal antenna exhibits the excellent ultra bandwidth from 2.25 GHz to 15 GHz corresponds to 147.83% impedance bandwidth at VSWR 2:1. This ultrawide band characteristcs of antenna has been achieved by using the CPW-fed and fractal concept. The measured radiation pattern of fractal antenna is nealy omnidirectional in azimuth plane and bidirectional in elevation plane. The measured group delay of proposed antenna is almost constant throughout the band. Such type of antenna is very useful for UWB communication system.     

Development and evaluation of nanostructured lipid carriers of cytarabine for treatment of meningeal leukemia

Lipid matrix based carriers are able to provide sustained release, increase the drug transport into cancer cells and overcome the drug resistance. Therefore, nanostructured lipid carriers (NLC) were prepared and coated with polysorbate 80 to overcome the blood brain barrier for achieving effective treatment of meningeal leukemia. NLC were prepared by melt emulsification followed by ultrasonication, producing particles of 90.7 +/- 4.28 nm size with appreciable amount of drug entrapment (49.5 +/- 2.24%), considering the hydrophilic nature of the drug. The polysorbate 80 coated cytarabine loaded NLC (Cyt-NLC) thus produced were non-aggregated and had almost spherical, smooth and uniform shape. Results of DSC and XRD studies indicated that Cyt was entrapped inside the lipid as molecular dispersion. In-vitro release pattern showed initial fast release (15.87 +/- 1.524% in 1 h) followed by sustained release upto 72 h (89.90 +/- 1.11%). In-vitro cell line studies demonstrated that blank NLC showed no significant cytotoxic effects on leukemic EL-4 cells whereas Cyt-NLC exhibited concentration dependent cytotoxicity. At 48 and 72 h, cytotoxicity of Cyt-NLC was found to be significantly more than that of Cyt solution and the percentage cell viability decreased with increasing concentration of Cyt-NLC. The lyophilized Cyt-NLC formulation was found to be stable with respect to size and total drug content at refrigerated condition (2-8 degrees C) for 3 months. These results suggest that polysorbate 80 coated Cyt-NLC can be explored for treatment of meningeal leukemia owing to their ability of sustained drug release and improved cytotoxic effect in leukemic EL-4 cell line.     

Simultaneous Determination of Pyridoxine Hydrochloride and Doxylamine Succinate from Tablets by Ion Pair Reversed-Phase High-Performance Liquid Chromatography (RP-HPLC)

A new, simple, precise, and rapid ion pair reversed-phase high-performance liquid chromatography (RP-HPLC) method has been developed for the simultaneous determination of pyridoxine hydrochloride (PYR) and doxylamine succinate (DOX) in tablets. The stationary phase was a Microbondapak C18 column (10 μ, 300 mm × 3.9 mm i.d.). The mobile phase was water:methanol (60:40) containing 10 mM heptanesulfonic acid and 0.25% triethylamine and adjusted to pH 2.2 with orthophosphoric acid. Detection was carried out at 263 nm using an ultraviolet (UV) detector. The flow rate was 1.0 ml/min, and retention times were 3.65 min and 7.32 min for PYR and DOX, respectively. The linearity was obtained in the concentration range 0.5-500 μg/ml for PYR and DOX. Mean percentage recoveries were 100.20% and 101.20% for PYR and DOX, respectively.     

Kinetics of fluid–solid reaction with an insoluble product: zinc borate by the reaction of boric acid and zinc oxide

Mixing parameters influencing the final particle size and conversion of zinc oxide were studied for the formation of zinc borate. Formation of zinc borate was via a fluid–solid reaction. The process was kinetically controlled above the minimum speed for particle suspension, N_s. The reaction kinetics was developed and the rate constant was estimated. Copyright © 2004 Society of Chemical Industry     

Micro hardness measurements on lead silicate glass

The synthesis of lead silicate glass suitable for fabrication of compression type glass to metal seals has been studied with varying amounts of modifier ions (Na, K and Ba). A three-stage heating schedule was evolved for the preparation of glass. While, some of the constituents were taken in the form of oxides, the others were either in the form of carbonates or nitrates. Dependence of micro hardness of these glasses on the relative content of Na₂O, K₂O and BaO was investigated. The concentration of these oxides was varied in the range 0–16 wt%. The modifier ions were seen to affect the micro hardness in a combplex manner. While the micro hardness of glass without Na₂O and 13 wt% K₂O was found to be 504 kg/mm², it turned out to be 547 kg/mm² for a glass with 13 wt% of Na₂O in the absence of K₂O. However, the micro hardness of the glass synthesized having optimum composition with oxides of Na, K and Ba in the proportion of 5, 8 and 4 wt%, respectively was 455 kg/mm². The glass powder was found to be suitable for making single- and multi-pin seals which could withstand pressures up to 1·2×10⁴ psi and vacuum of 10⁻⁸ Torr.     

Complex permeability studies of Li1+ substituted Cu-Zn ferrites

Compositions having the general formula Zn_0.5Cu_0.5−tLi_2tFe₂O₄, where t=0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1, have been synthesized by using coprecipitation techniques using oxalate precursors. The initial permeability was calculated from the inductance measurements with a torroidal core of 100 turns, using the formula L=0.0046 μ_i N² h log d₂/d₁. There is a decrease in initial permeability (μ_i) with the substitution of Li¹⁺ ions which is explained on the Globus model. The values of rotational permeability (μ_rk) and μ_w have been calculated. In all the compositions, the main contribution to the initial permeability is due to domain wall motion. With addition of Li¹⁺ ions the wall permeability μ_w decreases, which suggest that these ions cause impedance to the domain wall motion. The frequency variation of μ′ and μ″ clearly indicate the low-frequency dispersion which may be attributed to the domain wall movements. From the L.F. studies it is concluded that the losses are minimum in the frequency region of 10 KHz to 1 MHz as expected for lithium ferrites.