Sharif Digital Repository

This paper presents an asymptotically-convergent nonlinear attitude estimator for rigid bodies using a rate gyro and GPS. Double-difference carrier phase measurement are provided by at least two GPS antennas. The unknown integer ambiguity factor related to GPS carrier phase measurement is estimated along with the attitude. An observability condition is derived to guarantee convergence of the estimator when a single baseline vector is available with more than four satellites in view. Finally, experimental test from a survey boat illustrates performance of the proposed observer. © 2018 IEEE  

We present an asymptotically convergent nonlinear attitude estimator using a rate gyro and GPS. Double-difference (DD) carrier phase measurements are provided by at least two GPS antennas. The unknown integer ambiguity factor related to GPS carrier phase measurement is estimated along with the attitude. An observability condition is derived to guarantee the convergence of the estimator when a single baseline vector is available with more than four satellites in view. A systematic procedure for tuning observer parameters is also presented. Finally, the experimental test from a light fixed-wing aircraft illustrates the performance of the proposed observer. © 1993-2012 IEEE  

In this paper, application of Endurance Time (ET) method in nonlinear seismic analysis of offshore pile supported systems has been studied. The ET method is a time-history analysis in which structures are subjected to intensifying artificial acceleration functions. The ET method reduces complexity and computational demand of conventional nonlinear seismic analysis, and it provides response at different seismic levels in a single ET analysis. The aforementioned methodology has been applied to a typical model of single pile and then to a functional jacket offshore platform in Persian Gulf region. Seismic response of aforesaid models by ET method has been compared with conventional time-history... 

Properties of FeCo nanocrystalline intermetallic powders prepared by salt-matrix hydrogen reduction of a milled Fe 2O 3-Co 3O 4 mixture were investigated. The product of 72 ks ball-milling at 350 rpm was CoFe 2O 4 nanopowder. Reduction of this powder for 3.6 ks by hydrogen at 750 °C resulted in the formation of Fe 0.67Co 0.33 stoichiometric compound. Scanning electron microscopy, electron dispersive spectrometry, X-ray diffraction and vibrating sample magnetometry were used to characterize the nanopowder. Using a salt-matrix (NaCl as a dispersion medium) resulted in the decrease of the reduction temperature and improvement of the morphology and magnetic properties of the nanopowder.... 

The dynamics of the Magellanic Stream (MS) as a series of clouds extending from the Magellanic Clouds (MCs) to the south Galactic pole is affected by the distribution and the amount of matter in the Milky Way. We calculate the gravitational effect of the Galactic disk on the MS in the framework of modified Newtonian dynamics (MOND) and compare with observations of the Stream's radial velocity. We consider the tidal force of the Galaxy, which strips material from the MCs to form the MS, and, using a no-halo model of the Galaxy, we ignore the effect of the drag of the Galactic halo on the MS. We also compare the MONDian dynamics with that in logarithmic and power-law dark halo models and show... 

Three different wire drawing schedules were attempted to examine the effects of reduction of area, die-angle and friction coefficient on the strain inhomogeneity of drawn copper wires. The microhardness distribution was studied over the transverse and longitudinal cross-sections. Inhomogeneity factor (I. F.) curves; I. F. = f(r), I. F. = g(2α) and I. F. = h(μ) were determined from the measurements. The results indicate that less strain inhomogeneity is achieved in drawing wires through dies with low angle, low friction coefficient and high reduction of area. Despite the variation in reduction of area and die-angle, the strain was distributed evenly at the center of the drawn wires. Contrary... 

Titanium carbonated hydroxyapatite (Ti/CHA) nanobiocomposites have extensive biological applications due to the excellent biocompatibility and similar characteristics to the human bone. Ti/CHA nanobiocomposite has good biological properties but it suffer from diverse characteristics especially in hardness, Young's modulus, apparent porosity and relative density. This investigation is an attempt to propose the predictive models using gene expression programming (GEP) to estimate these characteristics. In this regards, GEP is used to model and compare the effect of practical variables including pressure, Ti/CHA contents and sintering temperature on their monitored properties. To achieve this... 

In order to reduce the possibility of buckling problems related to the railway ballasted tracks, necessary measurements should be applied to improve the lateral resistance of tracks. There are different procedures for increasing the lateral force resistance of railway tracks that can be implemented using different materials to change the size, geometry, and dimensions of track components, especially sleepers. Although several studies have been conducted on winged sleepers, the present study investigates the application of mid-winged sleepers with a modified geometry and a dimension in the form of a novel approach. In this regard, several experimental tests and numerical modeling were... 

In the present research, proton exchange membranes based on partially sulfonated poly (ether sulfone) (S-PES) with various degrees of sulfonation were synthesized. It was found that the increasing of sulfonation degree up to 40% results in the enhancement of water uptake, ion exchange capacity and proton conductivity properties of the prepared membranes to 28.1%, 1.59 meq g -1, and 0.145 S cm -1, respectively. Afterwards, nanocomposite membranes based on S-PES (at the predetermined optimum sulfonation degree) containing various loading weights of organically treated montmorillonite (OMMT) were prepared via the solution intercalation technique. X-ray diffraction patterns revealed the... 

In this paper, the effects of different parameters on the hairiness of siro-jet spun yarns, such as the nozzle pressure, the distance between the front roller nip and inlet of the nozzle, and jet structure were investigated. Using the Taguchi method, it was concluded that the factor air pressure has the strongest effect and the factor distance between the front roller nip and inlet of the nozzle does not have a significant effect on the performance of the siro-jet spinning system in reducing yarn hairiness. A computational fluid dynamics model was developed to simulate the airflow pattern inside the jets. The effect of air pressure and the jet structure was simulated using Fluent 6.3... 

Different analysis methods have been used for voltage stability assessment. In comparison with static analysis methods, little work has been done on dynamic analysis of large interconnected power systems. Voltage instability can be studied effectively with a combination of static approaches and time simulations. This paper discusses voltage stability assessment using mixed static and dynamic techniques. Using static methods, a voltage stability based ranking is carried out to specify faint buses, generators and links in power system. The system is analyzed for most severe conditions. Then, time domain simulation is performed for the conditions determined by voltage instability ranking. The... 

A modified two-surface critical state plasticity model for saturated and unsaturated soil is presented in this study. The key modification in new model is inclusion of an alternative yield surface used to simulate the behavior of unsaturated soils in addition to corresponding saturated conditions. Moreover, a numerical technique is used to obtain an incremental stress–strain response from loading curves. Modification is applied continuously in each incremental step to return the final stress states and hardening parameters to the yield surface. Results revealed that the adopted modeling approach can predict two independent sets of laboratory unsaturated experiments under various conditions... 

This paper proposes a decentralized market-based model for long-term capacity investment decisions in a liberalized electricity market. Investment decisions are fundamentally based on total revenues gained by investors. In most electricity markets, the complementary mechanisms are designed to ensure a desired level of reliability while covering investment costs of the suppliers. In such an environment, investment decisions are highly sensitive to expectation of price signals in both of energy market and capacity mechanisms. In this work, the system dynamics concepts are used to model the structural characteristics of electricity market such as, long-term firms' behavior and relationships... 

The advent of agile methodologies, though contributing much to software development processes, had a more profound impact on project management processes. Through supporting adaptability in their process frameworks, agile methodologies deviated from conventional project management approaches. This novel attitude has resulted in the emergence of an agile framework for project management. The Agile Project Management Framework (APMF) consists of fine-grained project management practices applied in agile methodologies, and is fast emerging as an alternative to the conventional project management framework. However, there are deficiencies in both frameworks that prevent developers from enhancing... 

Catalysts as the dynamo of chemical reactions along with solvents play paramount roles in organic transformations in long-lasting modes. Thus, developing effective and biobased catalysts in nontoxic solvents is highly in demand. In this report, carbon quantum dots (CQDs) functionalized with-lysine (Lys-CQDs) were generated from entirely nature-derived materials; they were demonstrated to be a promising catalyst for C-N bond formation in choline chloride urea (ChCl/U), a natural deep eutectic solvent (NADES). Among a number of synthesized CQDs, Lys-CQD turned out to be a powerful catalyst in the model reaction with aniline to afford phenyl urea. This type of transformation is important...