Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
9
1
1996
02
01
Effects of D-Doping on Characteristics of AlAs/GaAs Barriers Grown by Mba at 400 ??C
1
8
EN
Mohammad
Moravvej Farshi
Electerical Engineering, Tarbiat Modarres University
farshi_k@modares.ac.ir
Effects 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.
AlAs,GaAs,Heterostructure,D,Doping
https://www.ije.ir/article_71138.html
https://www.ije.ir/article_71138_d41d8cd98f00b204e9800998ecf8427e.pdf
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
9
1
1996
02
01
Quadtree and Octree Grid Generation
9
18
EN
A. G. L.
Borthwick
Engineering, University of Oxford
hasnomail@ije.ir
Engineering 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.
Hierarchical Meshes,Quadtree,Octree,Integer Tree,Spatial Domain Decomposition,Grid Generation
https://www.ije.ir/article_71139.html
https://www.ije.ir/article_71139_d41d8cd98f00b204e9800998ecf8427e.pdf
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
9
1
1996
02
01
The Dc Electrical Potential Method for the Measumment of Fretting Cracks
19
28
EN
G. H.
Farrahi
https://orcid.org/00
School of Mechanical Engineering, Sharif University of Technology
farrahi@sharif.edu
As 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.
Fretting,Fretting Fatigue,Crack Measurement,Crack Growth
https://www.ije.ir/article_71140.html
https://www.ije.ir/article_71140_d41d8cd98f00b204e9800998ecf8427e.pdf
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
9
1
1996
02
01
Natural Convection from a Helical Heating Coil to the Surrounding Fluid.
29
36
EN
M. H.
Kharidar
Mechanical Engineering, Isfahan University of Technology
hasnomail@ije.ir
Majid
Molki
Mechanical Engineering, Southern Illinois University
mmolki@siue.edu
An 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.
Natural convection,Free Convection,heat transfer,Helical Coil
https://www.ije.ir/article_71141.html
https://www.ije.ir/article_71141_53fa78136e56982074d85e31e30602c1.pdf
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
9
1
1996
02
01
Contamination of the Konar Siah Karst Spring by Saltdom
37
44
EN
G.
Farhoodi
Geomatics Engineering, Shiraz University
hasnomail@ije.ir
E.
Raeisi
Geomatics Engineering, Shiraz University
raeisi@suno1.suse.ac.ir
There 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.
Karst Water,Spring,Water Contamination,Salt dome
https://www.ije.ir/article_71142.html
https://www.ije.ir/article_71142_608637e03c380fb625d53191013c31bb.pdf
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
9
1
1996
02
01
Relationship Between Ground Settlement Due to Tunnelling and Ground Physico-mechanical Peroperties (RESEARCH NOTES)
45
49
EN
M.
Vafaeian
Civil Engineering, Isfahan University of Technology
mahmood@cc.iut.ac.ir
Tunnel,soft ground,ground properties,ground deformation,relative settlment
https://www.ije.ir/article_71143.html
https://www.ije.ir/article_71143_d37bc89988d71fc27be5ad19cac6e70c.pdf
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
9
1
1996
02
01
On the Optimum Directivity of Uniformly Spaced Broadside Arrays of Parallel Half-Wave Dipoles (RESEARCH NOTES)
51
56
EN
Jalil
Rashed-Mohassel
0000-0002-3428-7893
School of Electrical & Computer Engineering, , College of Engineering, University of Tehran
jrashed@ut.ac.ir
The 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.
Antennas,Linear Arrays,Antenna Arrays,Arrays of Dipoles
https://www.ije.ir/article_71144.html
https://www.ije.ir/article_71144_65728e7f6fc25705d5a2e1b8eff1d780.pdf
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
9
1
1996
02
01
A Study of Dynamic Characteristics of a Multistory Building Using Ambient Vibration Tests (TECHNICAL NOTE)
57
60
EN
A.A.
Aaghaakouchak
Civil Engineering, Tarbiat Modarres University
a_agha@modares.ac.ir
Dynamic 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.
dynamic characteristics,Ambient Vibration,Dynamic Tests
https://www.ije.ir/article_71145.html
https://www.ije.ir/article_71145_9b7d669c03d7198e225fd0a524273428.pdf