Sharif Digital Repository

Optical fiber doped with lead salts quantum dots (QDs) of different radii, has previously been proposed as a wide-band amplifier in the optical communication range. The emission and absorption spectra of QDs are size-dependent. Optical fiber amplifier doped with QDs of different sizes is an inhomogeneous gain medium. This inhomogeneity is the principle of operation of wide-band quantum-dot-doped fiber amplifiers (QDFAs). To study the effects of inhomogeneity such as spectral hole burning on the amplifier behavior, a fiber amplifier with an arbitrary size distribution of QDs is taken into consideration. The light propagation equations and rate equations for the inhomogeneous medium are... 

A bacterial strain was isolated and cultured from the oil excavation areas in tropical zone in southern Iran. It was affiliated with Pseudomonas. The biochemical characteristics and partial sequenced 16S rRNA gene of isolate, MR01, was identical to those of cultured representatives of the species Pseudomonas aeruginosa. This bacterium was able to produce a type of biosurfactant with excessive foam-forming properties. Compositional analysis revealed that the extracted biosurfactant was composed of high percentages lipid (∼65%, w/w) and carbohydrate (∼30%, w/w) in addition to a minor fraction of protein (∼4%, w/w). The best production of 2.1 g/l was obtained when the cells were grown on... 

The present work deals with a novel approach for grafting a sol-gel based sorbent, using diazonium salts for preparation of an unbreakable capillary microextraction (CME) device in on-line combination with high performance liquid chromatography (HPLC). The use of diazonium salts modifier allowed all types of metallic and non-metallic substrates to be used without any limitation. Substrates including copper, brass, stainless steel and polytetrafluoroethylene (PTFE) were chosen to be functionalized by chemical or electrochemical reduction of 4-amino phenyl acetic acid. Then, 3-(trimethoxysilyl)propylamine (3TMSPA) was selected as the precursor and the only reagent for preparation of the... 

A method based on direct immersion solid-phase microextraction (DI-SPME) coupled with high performance liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection (HPLC-PIF-FD) was developed to extract three pyrethroid insecticides, i.e. cyfluthrin, cypermethrin, and flumethrin from water samples. A sol-gel based coating fiber using 3-(trimethoxysilyl propyl) amine as precursor was prepared and used for the extraction of the pyrethroids from groundwater samples. A post-column photochemical reactor was designed and constructed for the derivatization of these environmentally important pollutants to increase their fluorescence... 

A head-space solid-phase microextraction (HS-SPME) method coupled to GC-MS was developed to extract fentanyl from human plasma. The protein binding was reduced by acidification and, eventually, the sample was deproteinized with trichloroacetic acid. The parameters influencing adsorption (extraction time, temperature, pH and salt addition) and desorption (desorption time and temperature) of the analyte on the fibre were investigated and validated for method development. The developed method proved to be rapid, simple, easy and inexpensive and offers high sensitivity and reproducibility. Linear range was obtained from 0.1 ng/ml to 2 μg/ml. The limit of detection was 0.03 ng/ml while an... 

In situ prepared iminium salts are very effective electrophiles in Baylis-Hillman reactions and react with methyl acrylate in the presence of a catalytic amount of a tertiary amine at ambient temperatures to afford the corresponding Baylis-Hillman adducts. The product undergoes conjugated addition with (trimethylsilyl)dialkylamines to give the diamine 5 in good yields. © 2002 Elsevier Science Ltd. All rights reserved  

Self-propagating exothermic reactions during mechanical milling of FeCl 3/CoCl 2 mixture together with sodium seeds resulted in formation of Fe 50Co 50 nanoparticles. Highly exothermic reactions resulted in temperature raise and formation of Fe 50Co 50 phase within the first 5min; however Fe 50Co 50 single-phase was obtained after 30min of milling. The products were characterized by XRD, SEM, EDS, TEM and VSM. Obtained results showed that both milling time and NaCl salt matrix affected the size, morphology, microstructure and magnetic properties of the produced particles  

Properties of FeCo nanocrystalline intermetallic powders prepared by salt-matrix hydrogen reduction of a milled Fe 2O 3-Co 3O 4 mixture were investigated. The product of 72 ks ball-milling at 350 rpm was CoFe 2O 4 nanopowder. Reduction of this powder for 3.6 ks by hydrogen at 750 °C resulted in the formation of Fe 0.67Co 0.33 stoichiometric compound. Scanning electron microscopy, electron dispersive spectrometry, X-ray diffraction and vibrating sample magnetometry were used to characterize the nanopowder. Using a salt-matrix (NaCl as a dispersion medium) resulted in the decrease of the reduction temperature and improvement of the morphology and magnetic properties of the nanopowder.... 

In this work, PEG 1500, MgSO4 and water were used to create an aqueous two-phase system and the effect of temperature was surveyed by obtaining binodal data and equilibrium data at 35, 40 and 45 C; compositions of mixture were obtained by atomic absorption spectrometer and refractometery method. Results showed that with increasing temperature, the solution tends to attain a two-phase region and the slope and length of tie lines increases. Modified Wilson equation was used to correlate this system, adjustable parameters were evaluated directly from experimental data and good agreement with experimental data was obtained. The overall average relative deviation was found to be less than 6%  

A number of challenges including instability, nonconvergence, nonuniqueness, nonoptimality, and lack of a general guideline for inverse modelling have limited the application of automatic calibration by generic inversion codes in solving the saltwater intrusion problem in real-world cases. A systematic parameter selection procedure for the selection of a small number of independent parameters is applied to a real case of saltwater intrusion in a small island aquifer system in the semiarid region of the Persian Gulf. The methodology aims at reducing parameter nonuniqueness and uncertainty and the time spent on inverse modelling computations. Subsequent to the automatic calibration of the... 

This paper presents an evolutionary based approach to achieve optimal management of a coastal aquifer to control saltwater intrusion. An improved Elitist Continuous Ant Colony Optimization (ECACO) algorithm is employed for optimal control variables setting of coastal aquifer management problem. The objectives of the optimal management are; maximizing the total water-pumping rate, while controlling the drawdown limits and protecting the wells from saltwater intrusion. Since present work is one of the first efforts towards the application of an ECACO algorithm, sharp interface solution for steady state problem is first exploited. The performance of the developed optimization model is evaluated... 

The system, Pd(OAc)2/imidazolium salts (L2), was found as an efficient catalyst in the Heck coupling reaction of olefins with aryl halides and Suzuki reactions of various aryl halides with aryl boronic acids under aerobic condition. This catalytic system demonstrates great tolerance to a wide range of groups on all substrates of aryl halides, alkenes and aryl boronic acids  

Hydro-mechanical behavior of unsaturated collapsible soils can be drastically affected by saline infiltrations. Saline infiltrations into the underlain soil layers of the urban transportation and lifelines due to deicing or existence of traffic pollutants has been a common issue of concern for years in many countries. Additionally, many reports have been published so far, indicating the construction of roads and railways on unsaturated collapsible soils. In this research, hydro-mechanical characteristics of an unsaturated collapsible loessial soil diluted with saturated solutions of three different salts that are frequently involved in transportation infrastructure (namely NaCl, CaCl2 and... 

Although numerous molecular methods for spinal muscular atrophy (SMA) detection have been exploited, most of hem are laborious, time consuming and costly. Recently, gold nanoparticles (AuNPs) have attracted attention in the field of colourimetric bioanalysis, because AuNP aggregation can be tracked with the naked eye as well as ultraviolet-visible (UV-vis) peak analysis. Here, based on a non-cross linking platform, a colourimetric-based method was used to evaluate the capability of thiolated oligo-AuNPs (Au nanoprobes) to distinguish between normal individuals, carriers and those with SMA. In this platform, removal of the repulsive force of the Au nanoprobes using high salt concentration... 

Density Current is formed when a fluid with heavier density than the surrounding fluid flows down an inclined bed. These types of flows are common in nature and can be produced by; salinity, temperature inhomogeneities, or suspended particles of silt and clay. Driven by the density difference between inflow and clear water in reservoirs, density current plunges clear water and moves towards a dam, while density current flows on a sloping bed. The vertical spreading due to water entrainment has an important role in determining the propagation rate in the longitudinal direction. In this work, two-dimensional steady-state salt solutions' density currents were investigated by means of... 

This paper presents for the first time a mathematical model for a mechanism of controlled drug release involving both ion exchange and transient counter diffusion of a drug and counterions. Numerical analysis was conducted to study the effect of different factors on drug release kinetics including environmental condition, material properties, and design parameters. The concentration profiles of counterions and drug species, the moving front of ion exchange, and three distinct regions inside a microsphere, namely unextracted region, ion-exchange region and drug diffusion region, were revealed by model prediction. The numerical results indicated that the rate of drug release increased with an...