AMIRKABIR
Year:2007 | Volume:18 | Issue:66-D|Papers Count:11

In this study, tensile and fatigue behavior of seven different structure (Tricot, Locknit, reverse Locknit, three needle Satin, four needle Satin, three needle Sharkskin and four needle Sharkskin) of warp knitted fabrics with three different course density (cpc) have been studied. The correlation between tensile and iv fatigue behavior of these fabrics with structural parameters have been investigated. The space of yarn movement and the length of underlaps are taken into consideration as basic parameters influencing the corresponding mechanical behavior. The obtained results show that with the increase in underlap length and/or cpc, the breaking extension percent is decreased while the breaking tenacity is increased. Cyclic extension causes stress relaxation and strain softening in the warp knitted fabrics. Application of Holloman's relation (s=K en) to the results of tensile and fatigue tests shows that strength coefficient (K) is decreased by fatigue process, while strain-hardening coefficient (n) is increased. By increasing underlap length, the cyclic stabilized load and strain-hardening coefficient is increased. Also, the cyclic stabilized load and the strain-hardening coefficient in fabrics with longer back guide bar underlap is higher than those with the same length in front guide bar.

This paper presents a robust algorithm for Voice Activity Detector (VAD) based on GARCH (Generalized Autoregressive Conditional Heteroscedasticity) Model, Variance Gamma Distribution (VGD) and binary Markov model.GARCH models are new statistical methods that are used especially in economic time series. There is a consensus that speech signals exhibit variances that change through time. GARCH models are a popular choice to model these changing variances.Speech signal is assumed to have VGD because the VGD has heavier tails than the Gaussian Distribution (GD) and the distribution of noise signal is assumed to be Gaussian.In the proposed method, heteroscedasticity will be modeled by GARCH and then the parameters of the distributions will be estimated recursively. Finally, using a binary Markov model and comparing it with an adaptive threshold, leads to the derivation of soft and hard detection. The simulation results show that the proposed VAD is able to operate down to -5 dB and in nonstationary environments.

Flotation de-inking is one of the most important processes worldwide for the removal of printed ink from recovered paper. It is also known that use of enzyme (cellulase) improves ink detachment from waste papers. The role of enzyme/substrate (waste paper) ratio and time of enzymatic treatment in the efficiency of flotation columns have been studied in this article. Standard experiments were carried out in a flotation column showed that optimization of the above mentioned parameters improves the overall efficiency of the process considerably. Using optimum enzyme/substrate ratio and enzymatic treatment time may also lower the operating costs of the process.

We introduce a Riemannin metric of diagonal type on the cotangent bundle of a Riemannian manifold and show that T*M with this metric is locally symmetric Einstein manifold. Also, we obtain a locally symmetric Kähler Einstein structure on the cotangent bundle of a Riemannian manifold of negative constant sectional curvature. Similar results are obtained on a tube around zero section in the cotangent bundle, in the case of a Riemannian manifold of positive constant sectional curvature.

In this investigation, a Look up Table method was used for reconstruction of the absorption spectra of dye solutions. In order to do so, bi-component dye solutions with different dye concentrations were prepared and the absorbance of each solution was measured in the visible region. The samples were divided into two groups; the first group was used for calibration and the second for evaluation. The system used for reconstruction had three inputs, concentration of first component and of second component and wavelength, with the absorbance value in certain wavelength as output. The root-mean-square errors, CIELAB colour differences, and concentration differences were determined as the difference between calculated and measured absorbance values for both calibration and test samples. The Look up Table method was compared with conventional regression method. The amount of RMS errors and colour and concentration differences for Look up Table method was significantly lower than that of regression method.

A series of novel monoazo disperse dyes based on N-ester-1,8-naphthalimide were synthesized. 4-Nitro- 1,8- naphthalic anhydride was reacted with ethyl glycinate and reduced to 4-Amino-N-ethyl glycinate-1,8- naphthalimide, then diazotized and coupled with a number of couplers. The absorption characteristics of the synthesized dyes were investigated and extinction coefficient, absorption maxima and solvatochromism effect were evaluated. The synthesized dyes applied on polyester fibers. Data showed that they were suitable for dyeing of polyester fibres, giving yellow to bluish red color. The dyes containing ester group revealed an alkali clearable properties.

In this paper the mechanism of solvent extraction of cerium (m) from sulfuric acid media by 0.1 molar Di(2- Ethylhexyl)-Phosphoric acid dissolved in kerosene at 25°C is investigated. The stoichiometry of the extracted species of cerium (m) is determined on the basis of the slope analysis method. The extraction reaction proceeds by Di-(2-Ethylhexyl)-Phosphoric acid via the cation exchange mechanism in the H2SO4 concentration range of 0.01-1M. The mechanism of extraction reaction is described and the experimental results for the parameters in the formula are obtained.Furthermore, the effect of Tri butyl phosphate on the extraction of cerium in an aqueous phase was discussed.

In this paper, three Beta zeolite samples have been first synthesized with different Si/AI ratio (11.65, 24.5 & 35.85). To synthesize these samples, hydrothermal method and tetra ethyl ammonium hydroxide template has been applied. To convert the zeolites to acidic form, an ion exchange process with ammonium chloride solution has been used. Finally, the reaction of methanol dehydration to olefins have been conducted in a fixed bed reactor with different space velocities (T= 400 °C, P=1bar & Methanol partial pressure = 0.2 bar). The results show that increasing the Si/Al ratio leads to an increase in catalyst stability against deactivation. The capacity of methanol conversion and selectivity of propane and butane have been also promoted by the above change.

Using the Moyal product, first we write down the noncommutative Hamiltonian of a two-dimensional harmonic oscillator in terms of ordinary commuting coordinates. In this new Hamiltonian a new term similar to the interaction with the magnetic field appears. This is then compared with the Hamiltonian of a charged harmonic oscillator moving on a two-dimensional plane under a magnetic field.

We construct new exact BPS solitons in various noncom mutative gauge theories by the "gauge" transformation of known BPS solitons. We show that the fluxon solution of the noncommutative gauge theory and its generalization are given by the solution generating technique of Harvey, Kraus and Larsen (HKG). Although this method generally produces non-BPS solution of equations of motion, the solution we obtain ate BPS.