Materials and Energy Research CenterInternational Journal of Engineering1025-24959119960201Effects of D-Doping on Characteristics of AlAs/GaAs Barriers Grown by Mba at 400 ??C1871138ENMohammad Moravvej FarshiElecterical Engineering, Tarbiat Modarres UniversityJournal Article19700101Effects of d-doping on barriers effective heights and series resistance of highly doped n-type GaAs/AIAs/GaAs/AlAs/GaAs heterostructures, grown by molecular beam epitaxy (MBE) at 400?°C, have been studied. As it was expected, inclusion of an n+ d-doped layer at each hetero-interface has reduced the barriers heights and series resistance of the structure significantly, while p+ d-doped layers have enhanced the barriers heights and the sructure series resistance. Using the Arrhenius plots, values of the effective heights for normal, n+ d-doped and p+ d-doped barriers were estimated to be 50,20 and 170 meV, respectively. The approximated values of the specific resistances, Rc, at room temperature and around zero volt bias, for the respected devices are 8x10-3 W-cm2, 4x10-4 W-cm2 and 6x10-2 W-cm2, respectively.Materials and Energy Research CenterInternational Journal of Engineering1025-24959119960201Quadtree and Octree Grid Generation91871139ENA. G. L. BorthwickEngineering, University of OxfordJournal Article19700101Engineering analysis often involves the accurate numerical solution of boundary value problems in discrete form. Hierarchical quadtree (or octree) grid generation offers an efficient method for the spatial discretisation of arbitrary-shaped two- (or three-) dimensional domains. It consists of recursive algebraic splitting of sub-domains into quadrants (or cubes), leading to an ordered hierarchical data structure with regard to the storage of mesh information. This paper describes quadtree Cartesian grid generation in detail and gives examples of its application to a circular geometry. The method is simple, rapid and does not experience difficulties with convergence (unlike curvilinear boundary-fitted mapping). Furthermore, the mesh may easily be adapted while preserving a well-ordered integer data structure. Extension to three-dimensions using octrees is straightforward.Materials and Energy Research CenterInternational Journal of Engineering1025-24959119960201The Dc Electrical Potential Method for the Measumment of Fretting Cracks192871140ENG. H. FarrahiSchool of Mechanical Engineering, Sharif University of Technologyhttps://orcid.org/00Journal Article19700101As fretting fatigue cracks are initiated at an early stage of life, the fretting fracture process is dominated by the stable growth of cracks. Hence the measurement of crack length is very important. This paper demonstrates the suitability of the DC potential drop technique for the measurement of fretting cracks. A calibration has been established for monitoring crack growth in BS L65 copper aluminium alloy and an example of fretting crack measurements is presented in the form of crack length versus number of cycles and also crack growth rate versus crack length. The former shows that 80% of the specimen life is spent in crack growth.Materials and Energy Research CenterInternational Journal of Engineering1025-24959119960201Natural Convection from a Helical Heating Coil to the Surrounding Fluid.293671141ENM. H. KharidarMechanical Engineering, Isfahan University of TechnologyMajid MolkiMechanical Engineering, Southern Illinois UniversityJournal Article19700101An experimental study is reported on natural convection heat transfer from a helical heating coil to the surrounding fluid. The coil is heated electrically and the surrounding fluid is selected to be water. The range of parameters are: Rayleigh number, 879 ?£ Ra ?£ 780168, Prandtl number, 4.22 ?£ Pr ?£ 10.02, dimensionless coil diameter,7.69 ?£ Dave /d ?£ 10.77, number of coil rings, 2 ?£ N ?£ 8, and the dimensionless coil pitch 1/d= 1. The results are correlated by means of a modified Nusselt number. The proposed correlation is a convenient tool for estimating heat transfer from helical coils.https://www.ije.ir/article_71141_53fa78136e56982074d85e31e30602c1.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-24959119960201Contamination of the Konar Siah Karst Spring by Saltdom374471142ENG. FarhoodiGeomatics Engineering, Shiraz UniversityE. RaeisiGeomatics Engineering, Shiraz UniversityJournal Article19700101There are about 200 salt plugs in the southern part of the Zagros Mountain Ranges and the Persian Gulf in Iran (Kent, 1970). The salt comes from the Hormuz salt Formation at the base of the Phanerozoic zone. It moves upward due to the buoyancy, the latteral pressure resulting from the opening of the Red Sea to the southwest, and the weight of several thousand meters of overlying sediments. It merges like a mushroom and its movement faciliated where the area is more fractured. Outcrops of geological formations subject to karst are found in about 23% of the surface area in the middle of southern Iran. They form aquifers of good water quality, especially in Ears province. In general, the electrical conductivity is less than 500 micosiemens per centimeter. In some parts of Ears province, the salt piercements are adjacent to the carbonatic rocks; hence, the karstic waters are of poor quality. The Konar Siah spring, located in the vicinity of Firoozabad, flows out from the Sarvak Limestone Formation. This spring is adjacent to the saltdome; thus, its water is very contaminated. A geologic map on a scale of 1: 50000 is prepared. In addition, the concentration of the following ions: Ca, Na, Mg, K, SO4, HCO3, and Cl; PH, EC and the temperature, and also the discharge of the Konar Siah spring have been determined tri-weekly for a duration of 9 months. The discharge of a few seasonal springs issuing from the saltdome has been measured as well. Based on the observations, the study concludes that the saltdome is the source of water contamination.https://www.ije.ir/article_71142_608637e03c380fb625d53191013c31bb.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-24959119960201Relationship Between Ground Settlement Due to Tunnelling and Ground Physico-mechanical Peroperties (RESEARCH NOTES)454971143ENM. VafaeianCivil Engineering, Isfahan University of TechnologyJournal Article19700101https://www.ije.ir/article_71143_d37bc89988d71fc27be5ad19cac6e70c.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-24959119960201On the Optimum Directivity of Uniformly Spaced Broadside Arrays of Parallel Half-Wave Dipoles (RESEARCH NOTES)515671144ENJalil Rashed-MohasselSchool of Electrical & Computer Engineering, , College of Engineering, University of Tehran0000-0002-3428-7893Journal Article19700101The nominal directivity for uniformly spaced broadside parallel half-wave dipoles associated with a uniform excitation is evaluated. The amplitude distribution for an optimized directivity is then obtained for different numbers of elements with the separations between the dipoles as a variable. The optimum and nominal directivities are compared for different spacings of the elements. While these directivities are different for small separations, they are practically the same for increased spacings of the array elements.https://www.ije.ir/article_71144_65728e7f6fc25705d5a2e1b8eff1d780.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-24959119960201A Study of Dynamic Characteristics of a Multistory Building Using Ambient Vibration Tests (TECHNICAL NOTE)576071145ENA.A. AaghaakouchakCivil Engineering, Tarbiat Modarres UniversityJournal Article19700101Dynamic characteristics of a typical multistory building in Iran have been studied in two different stages of building construction, using ambient vibration tests. Finite element models have also been used to determine these characteristics and to verify test results. The results indicated the agreements and also differences between conventional theoretical models and the behaviour of real structures.https://www.ije.ir/article_71145_9b7d669c03d7198e225fd0a524273428.pdf