Sharif Digital Repository

Due to the necessity for methods that are able to handle complexities of systems, use of Method Engineering (ME) to construct more adaptable and flexible methods has become of importance. Assemblybased approach is the most well-known approach of ME that performs method construction by reusing and assembling different method fragments. This approach, like other approaches of ME, suffers from the lack of suitable guidelines. In this way, architecture-centric method engineering (ArCME) is a new approach which aims at performing ME processes in a more disciplined and cohesive way. In this paper, process of assemblybased ME is enhanced by ArCME. Furthermore, benefits of implementing the process... 

Single Nucleotide Polymorphisms (SNPs), a single DNA base varying from one individual to another, are believed to be the most frequent form responsible for genetic differences. Genotype is the conflated information of a pair of haplotypes on homologous chromosomes. Although haplotypes have more information for disease associating than individual SNPs and genotype, it is substantially more difficult to determine haplotypes through experiments. Hence, computational methods which can reduce the cost of determining haplotypes become attractive alternatives. MEC, as a standard model for haplotype reconstruction, is fed by fragments as input to infer the best pair of haplotypes with minimum error... 

In this study, the effects of milling time, chemical composition and heat treatment on microstructure and magnetic properties of nanocrystalline Fe-Si (6.5-25 at.% Si) alloys prepared by mechanical alloying have been investigated. The results show that increasing the milling time or the Si content, decreases the lattice parameter and increases the internal microstrain. The prepared powders mainly consist of micron-sized particles with an average grain size of less than 20 nm. The specific saturation magnetization values are slightly less than those of single crystal or conventional Fe-Si alloys and decrease as Si content increases. The coercive force values of the nanocrystalline as-milled... 

In the present paper, a practical thermal treatment process has been introduced to stress relieve the iron powders in a soft magnetic composite. The composites were pressed and treated at different pressures and temperatures. Also, some of the samples were treated for various periods of time at 200°C. Density, electrical resistivity and transverse rupture strength of the samples were measured and fracture surfaces were studied by SEM. A series of tests were performed to determine the DC magnetic properties of the samples. It has been shown that there are optimum amounts of resin content and compaction pressure and temperature, rather than time is the dominant factor in stress relief of the... 

We have studied the electrical and magnetic properties of RuGd 2-xCexSr2Cu2O10-δ (Ru-1222) with content of Ce = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, prepared by the standard solid-state reaction technique. To determine how the magnetic and superconducting properties of this layered cuprate system can be affected by Ce substitution, the resistivity and magnetoresistivity have been measured at various temperatures. Resistivity curves reveal the presence of four regions for various contents of x. In high temperatures, system is paramagnetic. Magnetic transition from paramagnetic state to antiferromagnetic state occurs at 140 K for x = 0, which varies very slowly with increasing Ce substitution for Gd.... 

In this study, internal microstrain of an iron-resin composite produced by powder metallurgy has been calculated using the Williamson-Hall method. The effects of microstrain evolution during different processing conditions on magnetic properties such as coercive force and hysteresis loss have been investigated. The results show that there are regular and similar changes of coercivity and hysteresis loss. Both of these properties are directly dependant on the pinning effect of the internal microstrain against the movement of magnetic domain walls during magnetization process. © 2006 Elsevier B.V. All rights reserved  

This paper presents the densification and microstructure of bilayer structures made from 316L and 17-4PH stainless steels powders during sintering. The requirements for such objects could be magnetic properties at one area of the part and non-magnetic properties at another area of the object. A pressureless solid state sintering method in conjunction with a powder layering technique was used. The sintering was carried out at temperatures ranging from 1100 to 1340 °C for 120 min in hydrogen and vacuum atmospheres. Non-isothermal sintering behavior was also examined by dilatometric analysis. It was found that the strain rate of 17-4PH stainless steel powder is higher than that of 316L during... 

The single-domain particles, especially FeCo fine particles have many applications in magnetic information technology. We have prepared Fe 1-xCox fine particles for different x by borohydride method and measured the magnetic and structural properties of the samples. We have then determined the variations of coercivity and anisotropy energy versus x in Fe1-xCox fine particles. The obtained results have been analyzed on the basis of various magnetic anisotropies. Magnetic anisotropies affect the coercivity of the medium for each x as follows: shape and crystal anisotropies for x=0, surface and crystal anisotropies for x=1, shape, induced and crystal anisotropies for x=0.3 and 0.5, and shape... 

In this study, structural and magnetic properties of nanocrystalline Fe-Si-Ni powders produced by mechanical alloying (MA) have been investigated. The samples with different chemical compositions and milling times were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The alloy powders with average grain size 8-19 nm were synthesized by milling for 35-100 h. Coercivity (Hc) and crystallite size exhibited a similar decrease by increasing the mechanical alloying time. Maximum saturation magnetization (Ms) and minimum Hc were obtained at the composition of Fe87Si10Ni5 after 70 h milling. © 2005 Elsevier B.V. All rights reserved  

Analytical studies on the effect of charge and magnetic impurities in a spin-polarized electron gas (SPEG) are carried out using a Thomas-Fermi semiclassical approximation (TFSA). The susceptibility matrix of an SPEG is calculated within the TFSA framework. Charge, spin and mixed charge-spin screening lengths are defined and calculated for the bulk metals (Fe, Co and Ni). It is found that these screening lengths do not strongly depend on temperature in metallic samples. Based on the Ruderman-Kittel-Kasuya-Yoshida (RKKY) model, the magnetic response function is then used to calculate the dependence of the exchange coupling between two ferromagnetic layers. It is seen that the exchange... 

Tetragonal Gd1-xPrxBaSrCu3O 7-δ (0 ≤ x ≤ 1) polycrystalline samples have been prepared by the standard solid-state reaction, and characterized by XRD and SEM. Resistance measurements and XRD patterns show site mixing between rare earth R and Sr is less than R and Ca. Contrary to Gd1-xPrxBa 2Cu3O7-δ, a hump on the ρ(T) curve is observed at about 80 K. Based on the resistivity measurements, the effect of Pr substitution in the 1113 structure, in comparison with the 123 structure, on the increase of pseudogap temperature is investigated. The normal state resistivity has been analyzed by the two and three dimensional variable range hopping (2D-VRH and 3D-VRH) and Coulomb gap. For the low... 

Anodic aluminum oxide (AAO) was used as a template to prepare highly ordered Ni-Fe-Co alloy nanowire arrays. This membrane was fabricated with two-step anodizing method. It is found that there is an optimum barrier thickness to obtain a successful electrodeposition in pores of AAO. The thickness of barrier layer can be modified by additional electrochemical process after completing the anodizing step. Barrier layer thinning can create a rooted structure at the bottom side of the AAO pores and the electrodeposited nanowire arrays. The triple Ni-Fe-Co alloy was deposited in AAO membrane by ac voltage in a simple sulfate bath. The composition of nanowires shows anomalous deposition features... 

In this work, milled Nd12.8Fe79.8B7.4-type powders with three different oxygen contents were processed into sintered anisotropic magnets via a standard powder metallurgy technique. Minimizing the oxygen content within the powder material, resulted in an almost full densification in the sintered magnets even at the lower end of the sintering temperature limit. Under this condition, the amount of hard magnetic Φ phase (Nd2Fe14B) was maximized in the structure of sintered bodies, which resulted in the highest energy density [BHmax] values. In the sintered magnets made from the powder with a higher oxygen content, full densification could only be obtained at the upper end of the sintering...