Showing papers by "University of Tabriz published in 1998"
TL;DR: A novel spectrophotometric method based on the development of a red colour with sodium bismuthate, as a sensitive chromogenic reagent, in aqueous medium at pH 3.0 nm has successfully been applied to determination of these catecholamines in pharmaceutical preparations.
97 citations
TL;DR: In this paper, it has been shown that all second-order associated differential equations obtained from the master function have the properties of parasupersymmetry and shape invariance, and all of the well-known one-dimensional shape invariant paras upersymmetric Hamiltonians have been obtained by an appropriate choice of master function and corresponding weight function.
90 citations
TL;DR: In this article, the electrocatalytic efficiency of the modified electrode towards hydrazine oxidation depends on solution pH, and the optimum range was found to be located between pH 5 and pH 7.
Abstract: The electrocatalytic oxidation of hydrazine has been studied on glassy carbon, Pt and Au electrodes modified by cobalt hexacyanoferrate (CoHCF) using cyclic voltammetry and rotating disc techniques. It has been shown that the oxidation of hydrazine to nitrogen occurs at the potential coinciding with that of Co(II) to Co(III) transformation in a CoHCF film, where no oxidation signal is observed at a bare glassy carbon electrode. A Tafel plot, derived from RDE voltammograms, exhibits a slope of 150 mV, indicating a one-electron charge transfer process to be the rate-limiting step. The electrocatalytic efficiency of the modified electrode towards hydrazine oxidation depends on solution pH, and the optimum range was found to be located between pH 5 and pH 7. The kinetic behaviour and location of the electrocatalytic process were examined using the W.J. Albery diagnosis table, and it was concluded that the reaction has either a “surface” or a “layer” reaction mechanism. Pt- and Au-CoHCF-modified electrodes show no significant electrocatalytic activity towards hydrazine oxidation.
88 citations
TL;DR: The suitability of metallic aluminum as an electrode material for the preparation of a chemically modified electrode by the simple electroless procedure is described in this paper, where the Ni and Ni-hexacyanoferrate (NiHCF)-coated aluminum electrodes were prepared and their electrochemical characteristics were studied.
86 citations
TL;DR: In this paper, a series of 5- ((4-heptyloxyphenyl)azo)-N - (4-alkoxymhenyl)-salicylaldimine and bis [5-((4-hexyloxyptonyl)-Salicyl-aldiminato]-copper (II) complex homologues (alkoxy=O n C m H 2 m +1 ; m = 3-7) have been synthesized and characterized by elemental analyses, IR and NMR spectroscopy.
77 citations
TL;DR: The proposed method for the separation and preconcentration of uranium (VI) by solid phase extraction (SPE) was successfully used for the determination of uranium in Caspian Sea and Persian Gulf water samples.
46 citations
TL;DR: In this article, the Redlich-Kister equation was used to measure the excess volumes and excess viscosities of the binary poly(propylene glycol) 425 + H2O, over the entire composition range.
Abstract: Viscosities, densities, and water activities for binary and ternary systems of poly(propylene glycol) 425 + H2O and poly(propylene glycol) 425 + MgSO4 + H2O have been measured at 25°C. From density and viscosity measurements, excess volumes and excess viscosities of the binary poly(propylene glycol) 425 + H2O, over the entire composition range, were obtained and correlated by means of a Redlich–Kister type equation. Viscosity, density. and water activity data for ternary system of poly(propylene glycol) 425 + MgSO4 + H2O were correlated by using a semiempirical equation.
44 citations
TL;DR: In this paper, the Fowler-Guggenheim equation was used to calculate the long-range electrostatic interactions of the ions in a PPG 425 aqueous two-phase system at 25°C.
37 citations
TL;DR: In this paper, the osmotic coefficients of methanol + LiCl, + LiBr, and + LiCH3COO were determined by the isopiestic method at 25 °C.
Abstract: The osmotic coefficients of methanol + LiCl, + LiBr, and + LiCH3COO were determined by the isopiestic method at 25 °C. NaI in methanol solutions up to 4.33 mol·kg -1 were used as the isopiestic reference with osmotic coefficients calculated from vapor pressure data reported by Barthel and Tomasula. Experimental osmotic coefficient data are reliably represented by the Pitzer model with and without the β(2) term. The parameters for these equations, along with the corresponding standard deviations, are presented for these systems. The set of Pitzer parameters b = 3.2, α1 = 2.0 may be used. Including the β(2) term with α2 = 1.4 improves the fit for all of the investigated solutes, so that the standard deviations reduce from 0.015 to 0.006 for LiCl, from 0.009 to 0.005 for LiBr, and from 0.005 to 0.004 for LiCH3COO in methanol solutions at 25 °C.
34 citations
TL;DR: A Multi-Layer Perceptron Artificial Neural Network is employed to enable the mass that is applied to a weighing platform to be rapidly and accurately estimated before the platform has settled to the steady state.
32 citations
TL;DR: In this article, a lumped-parameter approach is adapted for the prediction of the steadystate and transient thermal behaviour of a prototype multiple teeth per stator pole switched reluctance motor (SRM), of TEFC (Totally Enclosed fan-cooled) design as an illustrative example.
Abstract: A lumped-parameter approach is adapted for the prediction of the steady-state and transient thermal behaviour of a prototype multiple teeth per stator pole switched reluctance motor (SRM), of TEFC (Totally Enclosed fan-cooled) design as an illustrative example. The merit of the method has been demonstrated by its application to the induction motor and experimental verification. The SRM is subdivided into simple geometries and the equivalent circuits and the proper connection of these equivalent circuits are presented. The combination of these circuits forms the full model which is used for prediction of the temperature rise of different parts of the motor.
TL;DR: In this article, it was shown that the GL (2, c ) group together with its contracted form is responsible for solvability of solvable potentials and also for their nice properties such as shape invariance, parasupersymmetry and degeneracy.
TL;DR: The proposed method was applied to the determination of nitrite in rain and river water and is mostly free from interference, especially from large amounts of nitrate and ammonium ions.
TL;DR: In this paper, the structure of subgroups which are the union of three conjugate classes was determined and the subgroups were analyzed in the context of the Group Conference on Groups Conference, St Andrews, Bath, 1997.
TL;DR: The information-based reduced-dimensionality formulation of the recently introduced geometric approach to fault identification in stochastic structural systems presents a formal and systematic procedure for the proper selection of a minimal dimensionality feature vector and leads to substantial simplification and potentially improved fault identification.
Abstract: An information-based reduced-dimensionality formulation of the recently introduced geometric approach to fault identification in stochastic structural systems is presented. The feature vector, which conveys the system information used in fault identification and is a key element of the general geometric approach, is transformed into a suitable coordinate system, within which information compression may be best achieved. Dimensionality selection is subsequently based on bounding of the information loss, expressed in terms of logarithmic entropy, below a certain threshold. The information-based reduced-dimensionality formulation thus presents a formal and systematic procedure for the proper selection of a minimal dimensionality feature vector and leads to substantial simplification and potentially improved fault identification. Its application to fault identification in a laboratory-scale beam and a planar truss structure demonstrates high effectiveness and performance characteristics essentially equivalent to those of the full-dimensionality formulation.
TL;DR: The suitability of the proposed method for the determination of lead in free-lead gasoline and gas oil was demonstrated as a typical example of application.
TL;DR: In this article, a simple and rapid spectrofluorimetric method is described for the determination of aliphatic and aromatic amines on the basis of ammonia and aniline, respectively.
Abstract: A simple and rapid spectrofluorimetric method is described for the determination of aliphatic and aromatic amines on the basis of ammonia and aniline, respectively. Aromatic amines in samples were reacted at pH 5.5 with fluram immoblised on an Octadecylsilane Solid Phase Extraction (ODS-SPE) cartridge. The produced pyrrolinones were adsorbed on SPE and separated from the aliphatic amines. Analysis of these compounds was carried out by elution of SPE with 1 ml Tetrahydrofuran (THF) and determination of fluorescence intensity at excitation wavelength 400 nm and emission wavelength 475 nm. Aliphatic amines after passing from SPE were collected and reacted with fluram at pH 9.2, and extracted into dichloromethane at pH 3 and quantitated fluorimetrically. Linear dynamic ranges and detection limits (LOD) were 1–20, 0.43 mg 1−1 and 1-200, 0.39 μg 1−1 for ammonia and aniline, respectively. The proposed method was successfuly applied for the evaluation of these compounds in local well waters and municipal...
TL;DR: A simple method was developed to induce sporulation in Drechslera graminea using straw extract from the barley cultivars Arta, Bowman, Bracken, Clark, Gallatin, and Salmas, with significant differences in sporulation among isolates from dif- ferent areas as well as among isolate originating from the same barley field.
Abstract: A simple method was developed to induce sporulation in Drechslera graminea. Thirty-six isolates of D. graminea, gathered from Canada, Germany, Montana, and Syria, were cultured, developed vigor- ous colonies and produced abundant conidia. Spor- ulation of the fungus was induced using straw extract from the barley cultivars Arta, Bowman, Bracken, Clark, Gallatin, and Salmas. There were significant differences in sporulation among isolates from dif- ferent areas as well as among isolates originating from the same barley field. Incubating the culture plates at 16 C under fluorescent light (12 h light/12 h dark) for 5 d following incubation under near ul- traviolet (NUV) light for 7 d resulted in 40% higher conidia production. Extract of seed, green straw or green leaves of barley as well as extract of mature wheat straw did not induce sporulation in D. grami- nea in culture. Twenty-one of the 36 isolates pro- duced pycnidia following the 7-day incubation under NUV light. Five of 25 isolates grown on V8-juice agar failed to sporulate. Germination of conidia of 12 iso- lates ranged from 72 to 99%.
TL;DR: Using the symmetry of (d + 1)-simplex fractals with decimation number b = 2, the current distribution has been determined using the renormalization group technique, based on the independent Schur's invariant polynomials of current distributions.
Abstract: Using the symmetry of (
d
+1)-simplex fractals with decimation number b
=2, the current distribution has been determined. Then using the renormalization group technique, based on the independent Schur's invariant polynomials of current distributions, the multifractal spectrum of even moments of current distributions has been evaluated analytically up to order six for an arbitrary value of d. Also the scaling exponents of order 8 and order 10 have been calculated numerically up to d
=30.
TL;DR: In this paper, the Duru-Kleinert fixed energy amplitude leads to the path integral for the propagation amplitude in the closed FRW quantum cosmology with scale factor as one degree of freedom.
TL;DR: In this article, the influence of α-iron on the amount of residue in the H-decrepitated and roller milled powder in some Nd(Pr)-Fe-B based alloys has been investigated.
01 Feb 1998-Compel-the International Journal for Computation and Mathematics in Electrical and Electronic Engineering
TL;DR: In this article, different shapes of the boundary surfaces within the power transformers are reviewed and the surface charge distribution function on the two surface elements, which have the majority of usage, are recognized and the resultant potential and electric field intensity equations are derived.
Abstract: In this paper, different shapes of the boundary surfaces within the power transformers are reviewed. The surface charge distribution function on the two surface elements, which have the majority of usage, are recognized and the resultant potential and electric field intensity equations are derived. A numerical interpolation idea is presented and extended to evaluate the values of the existing integrals within the equations. Fulfilment of this idea removes the problems due to the singularity of the integrands and it leads to a shorter computation time for the boundary element method. This idea is applied to a typical problem and results are compared with the corresponding values obtained using the numerical integration. Finally, the electric field within the interior space of a power transformer is estimated using the developed computer program based on the boundary element method.
TL;DR: A method to determine flux distribution in a sample transformer using Auto-CAD, where the mesh preparing boundary source and material data and extraction of flux from the solution are almost all done automatically.
Abstract: Design of electrical devices requires calculation of magnetic flux distribution within the object. This paper describes a method to determine flux distribution in a sample transformer using Auto-CAD. The mesh preparing boundary source and material data and extraction of flux from the solution are almost all done automatically. The user is thus removed from the numerical analysis chores that, formerly, greatly reduced effectiveness. The method can also be applied to other heavily saturated electrical devices.
TL;DR: The resin was found to be a clean and sensitive chromogenic reagent for the spectrophotometric determination of some catecholamine drugs and the calibration graphs of absorption versus concentration in the range studied were linear.
TL;DR: In this article, the tunneling rate with exact prefactor was calculated to first order in ℏ for a closed FRW universe filled with perfect fluid violating the strong energy condition, by applying the dilute-instanton approximation on the corresponding Duru-Kleinert path integral.
Abstract: The tunneling rate, with exact prefactor, is calculated to first order in ℏ for a closed FRW universe filled with perfect fluid violating the strong energy condition. The calculations are performed by applying the dilute-instanton approximation on the corresponding Duru–Kleinert path integral.
TL;DR: In this paper, the electrochemical behavior of nifedipine (I), nitrendipine(II) and their photodegradation products has been studied by employing electrochemical techniques in chloroform and in 1:4 mixture of chloropropanol using piperidinium perchlorate (PPC) as supporting electrolyte.
Abstract: The electrochemical behavior of nifedipine (I), nitrendipine(II) and their photodegradation products has been studied by employing electrochemical techniques in chloroform and in 1:4 mixture of chloroform-isopropanol using piperidinium perchlorate (PPC) as supporting electrolyte. It has been shown that I and II undergo in a 4e, 4H+ irreversible reduction reaction, while the reduction product, phenylhydroxylamine, is oxidized in a 2e, 2H+ reversible process to an unstable nitrosophenyl compound. Photodegradation of I and II by sunlight produces a nitrosophenyl derivative which is reversibly reduced to the corresponding unstable phenylhydroxylamine. No significant change is observed in electrochemical properties of drugs by passing from chloroform to chloroform-isopropanol mixture. The possibility of analysis of I and II by dp polarography is also verified.
TL;DR: In this article, exact results of isotropic turbulence in three dimensions when the pressure gradient is negligible were investigated. And they showed that the density-density correlator behaves as | x 1 − x 2 | −α 3, where α 3 = 2+ 1 6 √33.
24 May 1998
TL;DR: In this paper, a modified algorithm of the deadbeat control (DBC) strategy is applied to control an active filter that eliminates undesirable harmonics and provides unity power-factor for a thyristor controlled rectifier load.
Abstract: In this paper, a modified algorithm of the deadbeat control (DBC) strategy is applied to control an active filter that eliminates undesirable harmonics and provides unity power-factor for a thyristor controlled rectifier load. The DBC strategy gives three control voltages, that are synthesized by applying space vector PWM (SVPWM) and equal area vector PWM (EAVPWM) methods. Simulation results show that the filtering goals are achieved and in the second synthesizing procedure, limitation on switching frequency is decreased.
24 May 1998
TL;DR: This paper presents a new power circuit for a parallel loaded resonant DC/DC converter (PLR) with only one controlled switching device and use of a new switching pattern makes it possible to control the output voltage in a very simple manner.
Abstract: Resonant converters are widely used in various branches of industry. These converters with a rectifier circuit at output stage can be used as a DC to DC converter. In this case, the control of DC voltage magnitude at the output is the most important factor in converter operation. On the other hand, as the switching frequency in these converters may be up to the range of megahertz, the subtraction of switching devices not only simplifies the control circuit, but also reduces the losses and cost. This paper presents a new power circuit for a parallel loaded resonant DC/DC converter (PLR) with only one controlled switching device. In this circuit the rectifier bridge is not necessary and use of a new switching pattern makes it possible to control the output voltage in a very simple manner.
TL;DR: In this paper, it was shown that a closed FRW universe with a perfect fluid with small violation of strong energy condition is more probable to tunnel than the same universe with large violation of the strong energy conditions.
Abstract: The tunneling rate, with exact prefactor, is calculated to first order in \hbar for a closed FRW universe filled with perfect fluid violating the strong energy condition. The calculations are performed by applying the dilute-instanton approximation on the corresponding Duru-Kleinert path integral. It is shown that a closed FRW universe filled with a perfect fluid with small violation of strong energy condition is more probable to tunnel than the same universe with large violation of strong energy condition.