Sharif Digital Repository

With over 8 million inhabitants and 4 million motor vehicles on the streets, Tehran is one of the most crowded and polluted cities in the Middle East. Frequent exceedances of national daily PM2.5 limit have been reported in this city during the last decade, yet, the chemical composition and sources of fine particles are poorly determined. In the present study, 24-hour PM2.5 samples were collected at two urban sites during two separate campaigns, a one-year period from 2014 to 2015 and another three-month period at the beginning of 2017. Concentrations of organic carbon (OC), elemental carbon (EC), inorganic ions, trace metals and specific organic molecular markers were measured by chemical... 

In this paper application of Ionic Polymer Metal Composite (IPMC) as actuator in a deformable ring capable of locomotion is studied. Such a deformable ring moves as a result of gravitational force acting on its body when its shape changes. It can be used in exploration, search and rescue missions in future, where using conventional robots with rigid bodies and actuators is impossible. Large deformation induced by small stimulating voltage, low stiffness the sensing characteristics that in future work can be used in feedback control make IPMC a good choice for such an application. In this work first a model for IPMC is introduce that can be used in simulating deformation of IPMC in different... 

This paper describes a vector quantization of a 600 bps speech coding parameters based on the Mixed Excitation Linear Prediction (MELP) model, which was accepted as a standard in communication on narrow-band HF channels. The MELP speech coders are robust in difficult background noise environments and intended mostly for military communications. To reduce the bit rate, a joint vector quantization of multi-frame is developed that takes advantage of inherent inter-frame redundancy of the MELP parameters. By grouping parameters of 4 frames into a multi-frame and using vector quantization, bit rate is decreased 4 times and output speech is still intelligible  

Computed tomography (CT) simulators are versatile tools for scanning protocol evaluation, optimization of geometrical design parameters, assessment of image reconstruction algorithms, and evaluation of the impact of future innovations attempting to improve the performance of CT scanners. Computational human phantoms (CHPs) play a key role in simulators for the radiation dosimetry and assessment of image quality tasks in the medical x-ray systems. Since the construction of patient-specific CHPs can be both difficult and time-consuming, nominal standard/reference CHPs have been established, yielding significant discrepancies in the special design and optimization demands of patient dose and... 

For all exoplanet candidates, the reliability of a claimed detection needs to be assessed through a careful study of systematic errors in the data to minimize the false positives rate. We present a method to investigate such systematics in microlensing data sets using the microlensing event OGLE-2013-BLG-0446 as a case study. The event was observed from multiple sites around the world and its high magnification (Amax ∼ 3000) allowed us to investigate the effects of terrestrial and annual parallax. Real-time modeling of the event while it was still ongoing suggested the presence of an extremely low-mass companion (∼3M) to the lensing star, leading to substantial follow-up coverage of the... 

This paper presents a simulation-based optimization approach for railway timetabling, which is made interesting by the need for trains to stop periodically to allow passengers to pray. The developed framework is based on integration of a simulation model and an evolutionary path re-linking algorithm with the capability of scheduling trains, subject to the capacity constraints in order to minimize the total waiting times. A customized deadlock avoidance method has been developed which is based on a conditional capacity allocation. The proposed look-ahead deadlock avoidance approach is effective and easy to implement in the simulation model. A case study of the Iranian Railway (RAI) is... 

Several investigators worked on various aspects of tensile behavior of concrete because of its wide usage in structural design. One of the observable phenomena during tensile failure of concrete is strain softening, i.e. a negative slope in the stress-deformation diagrams. There are many kinds of experiment-based softening curves for concrete. In current research, use of newly introduced concept of fractal geometry and a failure model yields to a new softening curve for concrete. This new curve is denominated "Quasi-fractal" softening curve, which is a theorybased softening model. Comparison of Quasi-fractal softening curve with a set of proposed experimental softening curves has been... 

To achieve an exact three-dimensional command to line of sight (CLOS) guidance law, a novel control scheme comprising feed-forward terms (to exactly compensate known kinematics) accompanied by an adaptive nested saturated feedback strategy is presented. A square-root cubature Kalman filter is designed as the CLOS non-linear guidance filter. Performance of the proposed guidance law is compared with the augmented proportional navigation (APN), at the absence and presence of target maneuvers, autopilot dynamics and non-ideal tracking filter. Simulation results demonstrate the satisfactory performance of proposed strategy. © 2018 Concern CSRI Elektropribor, JSC  

A finite element analysis of a double layered shell with a circular hole is carried out with the computer aided engineering software Abaqus (Dassault Systèmes, FR). The model proposed has been used to perform a stress analysis on three pipes with different sized hole. Moreover, thermal expansion has been implemented in the testing. For the purpose of the research, the elastic properties of the materials have been considered and the results compared with the ones previously published in literature. The outcome of the investigation will benefit towards the design of optimal and sustainable pipes with circular cut outs  

Background: As global rates of mortality decrease, rates of non-fatal injury have increased, particularly in low Socio-demographic Index (SDI) nations. We hypothesised this global pattern of non-fatal injury would be demonstrated in regard to bony hand and wrist trauma over the 27-year study period. Methods: The Global Burden of Diseases, Injuries, and Risk Factors Study 2017 was used to estimate prevalence, age-standardised incidence and years lived with disability for hand trauma in 195 countries from 1990 to 2017. Individual injuries included hand and wrist fractures, thumb amputations and non-thumb digit amputations. Results: The global incidence of hand trauma has only modestly... 

Context. Trans-Neptunian objects (TNOs) and Centaurs are remnants of our planetary system formation, and their physical properties have invaluable information for evolutionary theories. Stellar occultation is a ground-based method for studying these distant small bodies and has presented exciting results. These observations can provide precise profiles of the involved body, allowing an accurate determination of its size and shape. Aims. The goal is to show that even single-chord detections of TNOs allow us to measure their milliarcsecond astrometric positions in the reference frame of the Gaia second data release (DR2). Accurate ephemerides can then be generated, allowing predictions of...