Showing 238 results for Gh
S.dilmaghani and F. Zainalli,
Volume 17, Issue 2 (4-1998)
Abstract
In this research, 210 concrete cube specimens (15cm) were made replacing 0, 5, 10, 15, 20, 25, 30, 35, 40, 50, and 60 percent of slag powder from Isfahan Steel Mill for cement. The control specimens were made with 350 kg/m3 cement content and the water cement ratio in all specimens was 0.51. The Slump value and compressive strength of concrete specimens in 7, 28 and 90 days were obtained and the results were compared. The test results show that replacement of 25 to 35 percent or slag powder for cement gives satisfactory results in obtaining concrete with suitable compressive strength and slump value. Also the results indicate that by increasing the percentage of slag powder replaced for cement, the shrinkage of the concrete and its resistance against sulphates will increase.
B. Ghahreman,
Volume 17, Issue 2 (4-1998)
Abstract
A knowledge of rainfall distribution over a finite area is needed for small bydraulic structures design. Hydrologists have always been concerned about Depth- Area- Duration (DAD) for a specific storm in a watershed. An intense storm occurred on June 6, 1992 which claimed some lives in parts of Mashhad, Khorasan Province, Iran. Data of rainfall depth at 29 raingauge stations around the city and its suburbs were gathered. There also exist three automatic raingauges at Mashhad airport, the College of Agriculture, and Khorasan Water Authority and one at Toroq Dam in Mashhad suburb. A survey of hyetographs for June 6, 1992 of these stations revealed that the airport raingauge did not work well while dimensionless mass curves for other raingauges were quite similar. Two rain centers at the College of Agriculture (with 50 mm rainfall) and Wheat Silage (with 53 mm rainfall) were detected. The DAD relationships for this storm were derived. Intensity- Duration- Frequency (IDF) curves for the airport station were derived and were compared with those of the College of Agriculture and Khorasan Water Authority. In the absence of an abnormal topography, the Theissen method was utilized for deriving a regional IDF for Mashhad City. Intensity- Duration- Frequency- Area (IDFA) curves, a new concept in hydrometeorology, has been initiated for the first time for Mashhad. Combination of regional IDF with DAD of the most intense storm in Mashhad was a key to represent such a new concept.
M. A. Massoumnia, Gh, Alizadeh and H. R. Momeni,
Volume 17, Issue 2 (4-1998)
Abstract
In this paper, a new guidance method for surface to surface ballistic missiles without mandatory engine cut-off will be presented. The complexity of solid fuel engine cut-off demands a comprehensive method for guiding these missiles. In the method presented in this paper, a certain guidance law is applied such that by transmitting appropriate commands to the control system, by changing the missile's path and also through wasting additional fuel energy, the missile velocity will be equal to the desired one at the end of the burning time. The results of the simulation indicate that the aforementioned guidance method is quite effective and practical with long-range missiles having thrust vector control.
M. H. Ghassemian Yazdi,
Volume 18, Issue 1 (4-1999)
Abstract
Manual fingerprint classification algorithms are very time consuming, and usually not accurate. Fast and accurate fingerprint classification is essential to each AFIS (Automatic Fingerprint Identification System). This paper investigates a fingerprint classification algorithm that reduces the complexity and costs associated with the fingerprint identification procedure. A new structural algorithm for classification of fingerprints is described. This algorithm is based on structural features: "core" and "delta", and their orientation. The accuracy and speed of the proposed method is tested for a large number of fingerprint images with different initial qualities. The results are independent of image orientation and, show a significant classification performance.
S. M. T. Fatemi Ghomi, M. Rabbani,
Volume 18, Issue 1 (4-1999)
Abstract
Considering the network structure is one of the new approaches in studying stochastic PERT networks (SPN). In this paper, planar networks are studied as a special class of networks. Two structural reducible mechanisms titled arc contraction and deletion are developed to convert any planar network to a series-parallel network structure.
In series-parallel SPN, the completion time distribution function can be calculated only by means of multiplication and convolution operations. For the first time, series-parallel networks are studied on the basis of the structural viewpoint. These networks belong to planar networks class. A key theorem provides capability of application of these mechanisms for non series-parallel planar networks
A.r. Khaloo, and P. Bagheri,
Volume 18, Issue 1 (4-1999)
Abstract
In this paper, moment-curvature behavior and ductility of prestressed concrete members based on nonlinear analysis is investigated. Influence of various design parameters on ductility of flexural members is determined according to appropriate materials models for stress-strain curves of concrete, prestressing steel and conventional reinforcements. Parameters studied include reinforcing index (ω ̅), compressive steel ratio, type of prestressing steel and cross-sectional shape of members. The reinforcing index is the most influential parameter on ductility of prestressed members. This variable contains the influence of several other parameters, such as compressive strength of concrete and reinforcing ratio, and links prestressed, ordinary reinforced and partially prestressed concrete sections. For maximum permissible reinforcing index of 0.36β1 based on ACI design code, curvature ductility is between 1.5 to 3.0 and for ω ̅=0.2, which is the maximum value allowed for moment redistribution, ductility is greater than 4.0, and for ω ̅ less than 0.1, a ductility of greater than 10.0 is achievable. Influence of magnitude of ultimate strength of prestressing steel and cross-sectional shape on ductility is insignificant. Confinement has considerable effect on ductility.
Seid H. Pourtakdoust, S.a. Fazelzadeh Haghighi,
Volume 18, Issue 1 (4-1999)
Abstract
Guidance and control of aircraft in the landing phase imposes extra pilot work loads, hence application of automatic landing control systems is of great importance. In this study automatic landing control systems are introduced and an optimal landing control system is designed. The control system performance criteria are based on minimum control effort. The designed system is simulated for a transport category aircraft in accordance with FAR requirements. The results show that the designed system is completely capable of controlling the aircraft in its landing corridor.
M. Nematbakhsh, S. Jani, M.s. Sadeghipoor and S. Noori-Khorasani,
Volume 18, Issue 1 (4-1999)
Abstract
The excess accumulation of water in lung interstitial or alveolar is called pulmonary edema which is caused by factors that upset the normal Starling balance in micro-circulation. Pulmonary edema disturbs the alveolar gas exchanges which are normally regulated by the respiratory system. Mathematical modelling of pulmonary edema may help to predict the lung conditions and the mechanisms involved in the formation of edema. With the help of lung anatomy and physiology, the properties of alveolar sheet were determined and the Starling forces were considered during pulmonary filtration. A nonlinear partial differential equation was solved for the blood pressure in alveolar sheet. The mathematical simulation of lymphatic pumps was obtained and the process of fluid accumulation under normal and abnormal conditions was investigated. The results indicate that the rate of edema formation is strongly related to lung blood pressured, serum protein concentration, and reflection coefficient physiological data also confirm the results from this study.
H. Khaloozadeh, A. Khaki Sedigh and C. Lucas,
Volume 18, Issue 1 (4-1999)
Abstract
This paper employs a general non-linear analysis tool to analyse the nature of time series associated with the price (returns) of a particular company in Tehran Stock Exchange. It is shown that the behavior of the process associated with the price (returns) time-series of this company is weakly chaotic, and due to the non-random behavior of the process, short term prediction of stock price is possible. It is also shown, using the correlation dimension estimation analysis, that a modeling of the price fluctuations based solely on the price data is insufficient to establish a model for future price prediction and that other variables involved in the process must be accounted for.
H. Farzanehfard, Z. Ghassemi and H. Moghbeli,
Volume 18, Issue 2 (7-1999)
Abstract
H. Ghoudjehbaklou and S. Salamatian,
Volume 18, Issue 2 (7-1999)
Abstract
Gh. A. Montazer, H.r. Momeni and A.kh. Sedigh,
Volume 18, Issue 2 (7-1999)
Abstract
S. Gh. Etemad and F. Bakhtiari,
Volume 18, Issue 2 (7-1999)
Abstract
M. A. Golozar and R. Bagheri,
Volume 19, Issue 1 (7-2000)
Abstract
In this paper
, the effect of curing time and temperature as well as various primers on durability of high density polyethylene on plain carbon steel have been investigated. The aim is to increase adhesion, improve durability and also to produce a defect-free in order to improve the corrosion resistance of steel substrate. For this purpose, after surface preparation and applying a primer (zinc phosphate, polyvinylalcohol, resol, stearic acid, and polyurethane) polymer coating was applied using electrostatic powder coating system. Coatings having 300 µ thickness were produced and then subjected to primary and secondary curing treatments. In addition to adhesion, ductility, and corrosion tests, quality of coatings were studied using scanning electron microscopy. The results obtained revealed that, surface porosity and uniformity of metal/coating interface is a function of curing time and temperature, as well as of the primers used. The best results obtained after curing for 45 min at 230˚C. The effects of primers were as following: no primers
M. Naghipour and M. Raoufi,
Volume 19, Issue 1 (7-2000)
Abstract
Most Codes such as API and BSI recommend Morison’s equation to estimate hydrodynamic forces on offshore structures. Significant differences exist among these Codes due to using different methods of analysis and estimation of force coefficients. In this paper, data from full scale tests have been used to evaluate random waves and uniform current actions on the smooth piles.
Four time and frequency domain analysis methods were used to estimate Cd & Cm. Force Time Series Fitting Method (LS-TS) has given better results than the others. Furthermore, the errors from estimating hydrodynamic forces on smooth piles are more than those on rough piles.
S. M. Borghei and D. Rajabi Siahboomi,
Volume 19, Issue 1 (7-2000)
Abstract
This paper is about experimental results for partial reduction of vortex at vertical pipe intakes. One of the easiest and practical ways of reducing vortex effect is to use anti-vortex plates or baffles. These plates can be used to avoid the vortex completely or partially. This paper will concentrate on the latter case. Rectangular plates with different dimensions have been placed at different positions to the intake pipe. Three different pipe diameters (D), 50, 75 and 100 mm, have been used. Vortex reduction percentages have been measured for each case at a constant discharge in such a way that at a given discharge, three water heads on intake pipe, namely, the water head without plate (Hn.p.), water head with plate (H), and water head with complete vortex voidance (Hn.v.), have been measured and analyzed. Plate dimensions and positions have been chosen as a multiple of pipe diameter in order to analyze and introduce the results in nondimensional form. The results of more than 6000 data points show that a plate as small as DX1.5D at the right position can reduce the vortex effect and, hence, increase, the discharge for the same head by 80%. Finally the results are presented in graph and tables format for each plate, showing the effect at best plate positions.
M. T. Ahmadian and S.sadeghi,
Volume 19, Issue 1 (7-2000)
Abstract
A nonlinear model consisting “yaw, roll, longitudinal, lateral and pitch” has been developed in which, tire and suspension characteristics have been considered. Tire model is based on the elliptic concept and tire Calspan data. According to this tire model, cornering force and aligning moment are computed as a function of slip and camber (inclination) angles, normal load, tire adhesion characteristics and skid number. The effects of suspension systems and the component of lateral and longitudinal weight transfers, are considered. Finally the equations of motion are droven, vehicle handling behavior and effect of anti roll stiffness on handling characteristics are shown.
A. Mireshghi and J. Jamshidi,
Volume 19, Issue 1 (7-2000)
Abstract
The basic structure of a reactor physics laboratory environment simulation software, developed using object modeling technique (OMT), and based on the reactor point kinetic equation, is presented. Also, various capabilities of the simulator in teaching the fundamental concepts of reactor physics are discussed.
In this virtual laboratory, student can perform seven different experiments, namely, reactor start up and control, critical mass measurement, critical thermal power measurement, control rod reactivity worth measurement, fuel poisons effects, reactor core void effects, and fine control rod drop. The user-friendly software and the technical instructions embedded provide a convenient environment for performing the experiments. The result presentation, in text and graphical format, both during and after the experiments, is another facility making the software powerful and an easy-to-use educational software.
M.ghavami and S. Gazor,
Volume 19, Issue 2 (1-2001)
Abstract
In this paper we introduce a simple, computationally inxepentsive, adaptive recursive structure for enhancing bandpass signals highly corrupted by broad-band noise. This adaptive algorithm, enhancing input signals, enables us to estimate the center frequency and the bandwidth of the input signal. In addition, an important feature of the proposed structure is that the conventional bias existing in the estimated frequency and bandwidth of the previously proposed structure will be canceled using an appropriate postfilter. Besides, the enhancement of multiple adjacent sinusoids can be obtained by adaptive adjustment of the bandwidth of the simple bandpass filter. The effects of the proposed postfilter in canceling the bias of the center frequency and bandwidth will be demonstrated through computer simulation.
M. Setayesh Nazar, M. Parsa Moghaddam, H. Javidi, and M. R. Haghifam,
Volume 19, Issue 2 (1-2001)
Abstract
This paper describes a new method for the evaluation of non-utility generation impacts on preventive-corrective control of power systems. The proposed method relies on a mixed integer nonlinear optimization and is capable of recognizing the effectiveness of demand side preventive-corrective actions. A number of cases are presented to illustrate the consequences of introducing demand side actions. In particular, it is shown that using the proposed method can significantly reduce total security cost. This algorithm provides a basis for negotiations between the power system operators and potential providers of demand side preventive-corrective actions.
