مجله علوم و فنون هوایی
سال سیزدهم شماره 1 (تابستان 1390)

This study has shown that if a photo detector which was made by Be+ implantation in InSb p+-n is protected by a SiO2 layer، better Electro- optical results will be gained in contrast with the case where it has direct implantation and does not have SiO2 layer. The dose and the energy of the of Gained photodiode by Be+ ion were 4×1014 cm2 and 100 KeV. I-V while a layer with the thickness of 0. 25 μm was covered over InSb p+-n in the thermal condition of 350 ˚C within 30 min and with the Leakage current of 200 nA/cm2 in the 50mV Reverse bias. The detectivity in the peak value was 9×1010 cmHz1/2W-1.

The effects of the generator excitation current limit، the on-load tap changer (OLTC) and load dynamics on voltage stability in C-130 aircraft power system are analyzed in state space. The variation of the number and coordinates of the equilibrium points with parameters of the system arc discussed. I n addition، a small-disturbance voltage stability region of a simple system is constructed. When the dynamic of voltage collapse is considered، it is more convenient to analyze it in the state space rather than in the input/output parameter space. The voltage stability of a system is determined by the dynamic characteristics of both the OLTC and the load. The generator excitation current limit affects the voltage stability by changing the small-disturbance voltage stability region and the equilibrium points of the system. After a small disturbance، the mode of voltage instability، fast instability or longer-term instability depends on the composition of the- load as well as the value of the system reactance.

In this paper we describe small signal models for Flyback converter as power Factor Preregulators in Discontinuous Conduction Mode (voltage follower approach) and constant frequency، using CIECA approach. In fact، a low power factor reduced the power available from the utility grid، while a high harmonic distortion of the line current causes EMI problems and cross_ interferences، through the line impedance، between different systems connected to the same grid. Implementations with and without input voltage feed forward، using resistive load، constant power and constant current loads are analyzed، and their respective transfer function are obtained. The applicability of an integrated circuit (usually used in continuous conduction mode) in the control loop is also presented. Simulation results are presented، validating the models to be used in control loop design.

A zinc phosphate coating was formed on AZ31 magnesium alloy. The effect of temperature on phosphate coating was investigated. All measurements showed that the phosphate coating was uniform and well adhered. Polarization curves and salt spray tests were used to assess the corrosion protection of coating. All measurements showed that the phosphate coating afforded considerable protection against corrosion. From results obtained، it was deduced that the optimum phosphating temperature was 45°C. Morphology of phosphate film on magnesium alloy was investigated by scanning electron microscopy (SEM).

As we know in real condition، most components are subjected to variable amplitude loading and their amplitude، average value and loading frequency varies with time But fatigue relations are obtained from constant amplitude loading. For this reason for fatigue calculation، it is necessary we convert variable amplitude loading to constant amplitude loading for a component which is subjected to variable amplitude loading. In this paper first we discuss about the property of variable amplitude loading and then the simplest form of this loading which contains a complex blocks of constant amplitude loading and Miner and Madiag’s methods are introduced. After this stage، we demonstrate how a arbitrary variable amplitude loading is conerted to constant amplitude loading. the method used here is Rainflow and its algorithm and flowchart are discussed here. Because in this method، hand calculation specially in complex loading is difficult to do، a MATLAB program is written and with using this program، the calculation will be don simply. At the end of this article، application of converting variable amplitude loading to constant amplitude loading in aerospace technology will be demonstrated.

In this paper، practical fatigue analysis methodology and Commercially available software، ANSYS and Fe-safe، were utilized as to estamate the fatigue life of SH’s Main gear drag beam. SH’s Main gear drag beam is the most important part of this helicopter and with respect to its application، this component is subjected to random loading and then its fatigue life is important. In this paper first with using of ANSYS، the component is modeled and boundary condition and loading is applied to the model and then with life prediction Fe-safe software، fatigue life of this component for given loading is gained. The loading spectrum chosen for this work was that of a generalized helicopter loading sequence which is Felix28. with utilizing of this research، fatigue life of SH’s Main gear drag beam was calculated and we can use this calculated fatigue life in maintenance manual and prevent instantinuse and unexpected fracture and determine if this reworked part is suitable for continued service.

The aim of present study was to investigate the concept of organizational citizenship behavior، and it s features، dimensions، antecedents، and consequences. Therefore، four questions around subject has been designed and considered. The research method was document analysis and for gathering required information، sake answering research questions، existing، relevant and available documents and proofs has been gathered and analyzed with qualitative method. Research findings are: 1- the most important features of organizational citizenship behaviors including: this behaviors are an internal tendency، a discretionary and spontaneous in nature، aren''t explicitly or directly recognized by formal system، and aren''t formally rewarded or sanctioned by the organization. 2- the most important dimensions of organizational citizenship behavior are: sportsmanship، altruism، civic virtue، conscientiousness، organizational loyalty، self development، and courtesy. 3- many studies has been done about organizational citizenship behavior، findings show that the most important variables that predict such behaviors are: job satisfaction، organizational justice، personality، leadership behaviors، role perception، organizational commitment، and employees age. 4- generally، the most important consequences of organizational citizenship behavior are: enhancing organizational effectiveness، performance and productivity، promotion of positive relationships among employees، more efficiency in resource allocation، providing the flexibility needed for innovation، guiding the efficient use of scarce resources، improving costumer service.