Showing 10 results for Density
A. Saatchi, H. Yan, and S. J. Harris,
Volume 20, Issue 1 (7-2001)
Abstract
Zinc was electrodeposited from an acidic sulphate solution on commercial steel sheet substrates galvanostatically at 10, 20, and 100 mA/cm2. The steel substrates had an average roughness number of 1.34 microns and a high percentage of its grains had their (111) planes parallel to the plate surface. During electrodeposition at 10 mA/cm2, on some specimens, there was an intense potential fluctuation around –870 mV vs Saturated Calomel Electrode (SCE). During this period zinc hydroxide precipitated on the surface. After a certain time, the potential dropped to –1020 for zinc deposition. Zinc nuclei were seen to precipitate from zinc hydroxide. Increasing current density changed nucleation mode from progressive to instantaneous, and also changed the size, morphology, and texture of zinc deposits.
Keywords: Zinc Electroplating, Current Density, Morphology, Orientation
A. Sayadiyan, K. Badi, M. Moin and N. Moghadam,
Volume 23, Issue 2 (1-2005)
Abstract
Hidden Markov Model is a popular statisical method that is used in continious and discrete speech recognition. The probability density function of observation vectors in each state is estimated with discrete density or continious density modeling. The performance (in correct word recognition rate) of continious density is higher than discrete density HMM, but its computation complexity is very high, especially in very large discrete utterance recognition problems. For real time implementation of very large discrete utterance recognition, we must use discrete density HMM (DDHMM). To increase the performance of DDHMM, one usual solution is fuzzy interpolation. In this study, we present a new method named Gaussian interpolation. We implemented and compared the performance of two types of interpolation methods for 1500 Persian speech command words. Results show that precision and flexibility of Gaussian interpolation is better thanthose of the fuzzy interpolation.
B. Saghafian, S. Rahimi Bandarabadi, H. Taheri Shahraeeni and J. Ghayoomian,
Volume 24, Issue 1 (7-2005)
Abstract
Rainfall is one of the most important climatic variables in the hydrology cycle. In flood estimation as well as environmental pollution studies in medium to large watersheds not only mus temporal pattern of rainfall t be known, but also the knowledge of its spatial distribution is required. Estimation of daily rainfall distribution without comparison and selection of
suitable methods may lead to errors in input parameters of rainfall – runoff models. Interpolation methods are among the techniques for estimating spatial distribution of rainfall. In this study, Thin Plate Smoothing Splines (TPSS), Weighted Moving Average (WMA) and Kriging are applied to estimate spatial daily rainfall in the southwest of Iran. Cross validation technique is used for comparison and evaluation of the methods. The results of analysis with two different station density showed that the TPSS method with power of 2 is the most accurate method in estimating daily rainfall. Zoning of the region also increased the interpolation accuracy. Generally speaking, division of the region based on cluster analysis improves accuracy compared with division by inter basin boundaries
Gh.r. Aghaei , M.r. Izadpanah, M. Eftekhari ,
Volume 32, Issue 2 (12-2013)
Abstract
Mechanical alloying technique is used for production of nanostructured soft magnetic alloys. In this work the back propagation (BP) artificial neural adopted to model the effect of various mechanical alloying parameters i.e. milling time and chemical composition, on the properties of Fe-Ni powders. Lattice parameter, grain size, lattice strain, coersivity and saturation intrinsic flux density are considered as the output of five BP neural networks. The results obtained show the efficiency of designed networks for the prediction of the properties of Fe-Ni powders.
M. Esmaeeli, A.mirhabibi ,
Volume 33, Issue 1 (7-2014)
Abstract
An important parameter in composite materials is mechanical behavior and matrix-reinforcement interface interaction under applied stresses. In this investigation, bending strength of carbon-carbon composites synthesized from wood was analyzed as a measure of the composite mechanical properties. Also, densification efficiency of the products was determined by measuring the bulk density and open porosity percentage. Using scanning electron microscopy, optical microscopy, X-Ray diffraction, and Raman spectroscopy, the final product was examined to evaluate and interpret the morphology and internal texture and results of mechanical test. The results showed that we are able to use an ordinary material such as wood for production of a unique product with great properties called two-dimensional carbon-carbon composites.
M. Haerifar, M. Zandrahimi,
Volume 34, Issue 1 (5-2015)
Abstract
In the present study, 304 stainless steel (SS) was electrochemically plated with nanocrystalline Mn-Cu alloy coatings from a bath containing ammonium sulfate. The effects of current density on the microstructure, crystallographic structure, and chemical composition of the deposits were studied. The results showed that at low current densities, discontinuous coatings with a large amount of Cu can be obtained. Further increase in current density resulted in amorphous, compact and heterogeneous coatings with a small amount of Cu. The presence of Cu at low contents in precipitated coatings delayed the phase transformation of as-deposited ductile g-Mn to the brittle and hard a-Mn. However, the results did not show any specific changes in the grain size of the coatings with variation of current densities.
V. Rajaei, K. Raeissi, M. Shamanian, H. Rashtchi,
Volume 35, Issue 1 (6-2016)
Abstract
In this study, Ni-Mo nanocrystalline alloys were prepared on steel substrates by electrodeposition method from citrate-ammonia bath by applying current densities 30, 60 and 100 mA/cm2. Results indicated that the obtained coatings were uniform and compact. Moreover, molybdenum content in the alloy and current efficiency decreased with increasing electrodeposition current density. X-ray diffraction analyses indicated that all coatings were composed of face-centered cubic solid solution of molybdenum in nickel with grain size of 9-5 nanometer. Moreover, the most intensive plane in X-ray diffragtogram was (111). On the othe hand, roughness measurements indicated that surface roughness escalated with increasing current density. Corrosion behavior study showed decrease in corrosion current density of substrate with applying Ni-Mo alloy coatings. In addition, corrosion current density reduced with increasing molybdenum content of the coating and the minimum amount was related to the coating with 13 atomic percent molybdenum.
H. Salehi, P. Amiri, Y. Loveimi Motlagh,
Volume 37, Issue 1 (6-2018)
Abstract
In this article, the electronic and optical properties of bulk TiC and its narrow nanowires were investigated using Quantum-Espresso/PWSCF computational package in the framework of density functional theory. According to the results, this compound showed a metallic behavior in the bulk structure, but the small diameters of the nanowires against the bulk structure showed a semiconducting behavior. This deviation became negligible at the higher diameters. In both structures, the electronic results were compatible with the optical calculations of the structure under consideration. Considering the optical results, the structure of bulk TiC had the maximum amount of refractive index value and this amount could be decreased by a reduction in the nanowire diameters. Also, the optical results indicated that by increasing the size of nanowires, the ELLOS value was raised toward the corresponding bulk value
S. Faraji, Gh. Dini, M. Zahraei,
Volume 37, Issue 1 (6-2018)
Abstract
Manganese ferrite nanoparticles (NPs) have different applications, especially in medical diagnosis and treatment as well as the biomolecule separation,. In this research, the effects of various parameters such as the pH of reaction solution and the hydrothermal process duration on the synthesis of spinel phase in NPs were evaluated. Crystal structure, chemical composition, morphology and size of synthesized particles were investigated by the X-ray diffraction (XRD) analysis and field-emission scanning electron microscopy (FE-SEM) equipped with energy dispersive spectroscopy (EDS). The XRD results showed that the process duration of 12 h and pH=11 were suitable for the formation of monophase manganese ferrite NPs. The FE-SEM investigations showed that the average size of the synthesized NPs was about 50 nm. Moreover, the EDS analysis showed the presence of about 20% of manganese in the NPs structure. Hydrothermally synthesized manganese ferrite NPs in this researchcould be, therefore, a good candidate for the biomedical application due to their small size and narrow size distribution.
H. Salehi, N. Zhulayi Bakhoda, P. Amiri,
Volume 38, Issue 4 (1-2020)
Abstract
In this research, the optical properties of tungsten disulfide including dielectric function, the static refractive index, the imaginary part of the dielectric function, optical band gap, energy loss spectrum and its magnetic properties have been studied. Calculations have been done by using Quantum Espresso package which is based on density functional theory and pseudo-potential technique. The static refractive indices of this compound at diffrent x and z directions were calculated 3.66 and 2.55, respectively. The amount of optical band gap, obtained from the imaginary part of dielectric function, was estimated to be 1.45 eV. In addition, bulk plasmon energy, obtained from energy loss spectrum at x and z directions, were obtained to be 17.95 eV and 17.25 eV, respectively.
