K. Sadrnezhaad and H. Ahmadian,
Volume 17, Issue 2 (4-1998)
Abstract
In this research a Cu-Zn-Al alloy is produced by melting the raw materials in an electric resistance furnace and then pouring it into a steel mould. The optimum way to achieve the final analysis in the hypo-eutectoid range is determined and the influence of the alloying element, Ti on the grain size and the shape memory properties of the samples are investigated. Solution treatment (done at 850˚C) followed by quenching in ice-water mixture results in the formation of the martensitic structure and the shape memory effect. Aging at temperatures bellow 200˚C results in the reduction of transformation temperatures, while aging at temperatures between 200˚C and 350˚C results in the enhancement of these temperatures and at temperatures above 350˚C results in the destruction of the shape memory properties. Effect of super-elasticity at 40˚C (between Md and Ms) is observed and tensile tests are run at 25˚C and -55˚C to verify the influence of the prevailing phase.
S. R. Bakhsi, M. Salehi, F. Ashrafizadeh,
Volume 17, Issue 2 (4-1998)
Abstract
A study for optimizing of siliconizing and borosiliconizing processes on carbon steels has been carried out. The process parameters, i.e, time and powder mixture, were considered for optimization of the case depth, surface quality and the hardness profile.
Time and temperature of the processes were 4 hr and 950˚C, respectively. Powder mixture in siliconizing process was 2.5% ferrosilicon, 2.5% NH4Cl and Al2O3, while the optimum simultaneous borosiliconizing process was obtained in a mixture of 90% boronizing powder and 10% siliconizing powder. These powders had already been optimized, individually. This is a depth of layer of about 150μm and maximum hardness value of 600HV0.1 in siliconized steels, and a depth of layer of about 100μm and a hardness value of greater than 3000 HV0.1 in borosiliconized steels. Microscopical tests by light microscopes, XRD and EDAX analyses indicated Fe3Si and Fe5Si3 phases within the surface layers of siliconized steel, and B(FeSi)3, Fe4.9Si2B, FeSi, FeB and Fe2B phases within the surface layers of borosiliconized steels.
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.
F. Vahabzadeh and A. Aiwazi,
Volume 17, Issue 2 (4-1998)
Abstract
Catalytic isomerization of glucose to fructose by immobilized glucose isomerase in an aqueous-ethanol medium was studied. Using Michaelis-Menten equation and Haldane relationship, the main kinetic parameters were determined: Kmf, Vmf, Kmr, Vmr. By comparing the aqueous-ethanol medium with an aqueous solution, the measured values of Kmr and Kmf were increased in the aqueous-ethanol solution, while the values for maximal velocities (Vmf and Vmr) were decreased in this medium. The results from these comparisons were discussed with reference to the rate constants in this isomerization reaction. The integrated form of the Michaelis-Menten equation was used with good approximation to predict the course of the isomerization reaction in the aqueous-ethanol solution.
H. Shakib and M. Sadrneshin,
Volume 18, Issue 1 (4-1999)
Abstract
In this study, the effective parameters on the inelastic response of asymmetric buildings is evaluated for an ensemble of real Iranian earthquake records by considering soil-structure interaction. Then, the design eccentricity obtained from the inelastic dynamic soil-structure analysis is compared with the design eccentricity of seisimic codes of Iran, ATC-3, New Zeland, Canada, Mexico, Australia and EC8. Finally, a formula for design eccentricity is proposed, regarding some important structural parameters.
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.
A. Sayadian,
Volume 18, Issue 1 (4-1999)
Abstract
Speaker verification from talking a few words of sentences has many applications. Many methods as DTW, HMM, VQ and MQ can be used for speaker verification. We applied MQ for its precise, reliable and robust performance with computational simplicity. We also used pitch frequency and log gain contour for further improvement of the system performance.
S. Feiz and S. Hemati,
Volume 18, Issue 1 (4-1999)
Abstract
One of the factors which limits the transmission capacity of the fiber optics communication channel is the material dispersion. Exact analytical study of the material dispersion is often complex and involves calculating the derivatives of the refractive index of the core. These calculations are too cumbersome to do, especially for high-order derivatives. So material dispersion has only been studied analytically in certain circumstances and with many simplifying assumptions. One of the best of such studies was done by Marcuse [10-12]. In this article, a new algorithm is presented which can be used to determine material dispersion more precisely. In this new approach, there is no need for simplifying assumptions and unlike the method in [10-13], it can be used for all kinds of optical sources.
S.a. Shojaosadati, M.r. Rezaei and B. Rasouli,
Volume 18, Issue 1 (4-1999)
Abstract
In this research the microorganism was initially isolated and selected after evaluation based on COD reduction of cheese whey and biomass production. The selected microorganism was identified as Trichosporon sp. The cultivation conditions of the microorganism were optimized under batch: temperature 30˚C initial pH = 6 aeration speed = 2 ν.ν.m and agitation rate: 800 rpm. Under these conditions, the specific growth rate and biomass doubling time were measured as 0.59 h-1 and 1.16 h, respectively. The COD reduction and biomass production under optimized batch conditions after 24 hours were obtained as 52% and 8.73 g L-1, respectively. The optimized conditions under continuous cultivation were: temperature, 30˚C agitation rate, 800 rpm aeration speed, 2 ν.ν.m dilution rate, 0.42 h-1 pH in fermentor, 4-5. Under these conditions the biomass production, COD reduction and productivity were obtained as: 8.17 g L-1, 53.21%, and 3.4 g L-1 h-1 respectively.
The nutritional value of biomass was evaluated for crude protein, nucleic acid, fat, ass and moisture content. According to the results, the single cell protein obtained in this research is suitable and valuable for animal and poultry feed.
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.
M. T. Kazemi,
Volume 18, Issue 1 (4-1999)
Abstract
Realistic prediction of concrete shrinkage and creep requires the calculation of the distributions of relative humidity at various times. Although the distributions of the relative humidity can be computed by numerical methods from the differential equation for diffusion, simple prediction formulas can facilitate structural analysis. The purpose of this paper is to present a simple formula for slabs and walls, which agrees with the shrinkage prediction formula and with the measurements of pore relative humidity. The drying process may be considered as one-dimensional in space for walls and slabs. A simple explicit formula with three parameters is formulated. In a more simplified version, a single parameter formula is developed. The parameter can be estimated from the existing empirical relations for shrinkage time parameter.
A. Fattah and B. Tahmasebi,
Volume 18, Issue 1 (4-1999)
Abstract
The kinematics and dynamics of two industrial cooperating robots are presented in this paper. The NOC (natural orthogonal complement) method is used to derive the dynamical equations for the motion of two cooperating robots. The joint torques of the two robots are determined based on the optimization techniques in order to obtain unique solution for joint torques. To this end, minimizing the crushing force and moment on the moving object as well as minimizing the joint torques of the two robots are the two methods which are used to determine the joint torques. As an example, the joint angles and their time derivatives as well as the time history of joint torques of two cooperating Puma 560 robots are determined.
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.
M. Farzin and M. Tajdari,
Volume 18, Issue 1 (4-1999)
Abstract
In this article, stress analysis and energy estimation during cold-roll forming of symmetrical channel sections have been discussed. Geometry of sheet strip is pre-estimated by a shape function. Then longitudinal, transversal and shear strains have been calculated. Using both the Levy-Mises and the Prandtl Reuss equations, and also considering the Bauschinger effect, stress distributions have been obtained. Preestimated geometry can be modified by minimization of deformation energy. Strains and stresses at different points have been represented and predicted strains have been satisfactorily compared with experimental data. Application of the Levy-Mises equations for reducing computational time, presentation of stress distributions including shear stresses, and consideration of the Bauschinger effect are the new concepts of this paper.
M Sobhani, M. Rafeeyan,
Volume 18, Issue 1 (4-1999)
Abstract
This paper presents a robust controller design methodology for a class of linear uncertain multivariable systems with hard time-domain constraints on their outputs and control signals in response to step disturbance inputs. In this approach, the m×m MIMO system is replaced by m2 SISO systems and then, using the QFT technique, desirable controllers are synthesized. The final controller will be diagonal and since its entries are designed separately with suitable bandwidths, an economic design can be achieved. The application of this new method will be demonstrated through an example.
A. Said and M.a. Golozar,
Volume 18, Issue 1 (4-1999)
Abstract
Combustion synthesis has been used to produce Fe-(Ti,W)C composites. A simple reactor was designed which made it possible to ignite the samples under controlled atmosphere. Samples with different W/Ti ratio were ingnited under argon atmosphere by an electric arc and a self-propagating reaction was initiated in each sample. Different composites such as WC in Fe-Ti matrix, WC+(Ti,W)C in Fe matrix, and (Ti, W)C in iron matrix were produced by changing W/Ti ratio in the starting materials. Examination of the microstructure revealed that WC had an angular morphology while (Ti, W)C particles were spherical.
M. Salehi,
Volume 18, Issue 1 (4-1999)
Abstract
In this research, tribological behavior of Ti-Ni-P intermetallic coatings on titanium substrates have been investigated under dry reciprocating conditions. Hardness profile testing results exhibit that high surface hardness has been attained and static indentation result shows that the intermetallic coating has better adhesion strength than the conventional ceramic coatings. In this respect, these coatings have been able to protect the substrate under different loading and tribological conditions. The results show that Ti-Ni-P intermetallic coatings produced by diffusion processes have good adhesion to titanium substrate, offer a low coefficient of friction and prevent the galling of titanium to the steel counterface. The effect of increasing thickness was to increase the load-bearing capacity of the coating. Experimental findings also suggest that Ti-Ni-P intermetallic coatings would contribute to the expansion of industrial applications of titanium alloys.
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.
