Sharif Digital Repository

The primary source of surgical site infection is the deposition of flakes released from the exposed skin of surgical staff or the patient on the exposed surgical wound. In this study, a computational model for simulating air ow and thermal conditions in an operating room is developed, and transport and deposition of particulate contaminants near the wound are analyzed. The results show the formation of a thermal plume over the wound tissue, which is typically at a higher temperature than the surrounding. The thermal plume protects the wound from the deposition of contaminants. In addition, the computational model predicts an optimum value for the inlet air velocity that is mainly maintaining... 

In many countries, there are traditional houses made of stone, adobe and brick, which perform relatively weakly in earthquakes. To mitigate casualties in future earthquakes, it is necessary to evaluate the current status of these buildings and propose effective methods to retrofit them. One method of evaluating the performance of buildings in earthquakes is through the use of fragility curves. These diagrams show the probability of exceeding a specific state of damage versus seismic intensity parameters, such as PGA, MMI, la, CAV etc. Fragility curves will provide an important basis for analytical methods, based on probabilistic approaches. Much work has been done on bridges, concrete and... 

In hierarchical service networks, facilities at different levels provide different types of service. For example, in health care systems, general centers provide low-level services, such as primary health care, while specialized hospitals provide high-level services. Because of the demand congestion at service networks, the location of servers and their allocation of demand nodes can have a strong impact on the length of the queue at each server, as well as on the response time to service calls. This study attempts to develop hierarchical location-allocation models for congested systems by employing a queueing theory in a fuzzy framework. The parameters of each model are approximately... 

Welding is an important manufacturing process that can be automated and optimized. This paper focuses on the development of a robotic arc welding system, wherein a three-degree-of-freedom Selective Compliance Assembly Robot Arm (SCARA) is interfaced to a Gas Metal Arc Welding (GMAW) process. The entire system is composed of a robot linked to a GMAW system. Set points are derived using the desired mass and heat input, along with the weld speed. The stick-out and the current of the welding process are controlled using an Adaptive Neural Network Controller (ANNC). The trajectory of the robot or the weld profile is also controlled by implementing a Mixed Fuzzy-GA Controller (MFGAC) on a... 

The present study is concerned with the numerical simulation of free-surface waves and wave induced separation in the presence of an intrusion. The results of several simulations are reported. The first study was performed for a NACA0024 surface piercing hydrofoil over a range of several Froude numbers (0.19, 0.37, 0.55), along with wave breaking at Fr = 1.0 The NACA0024 foil was of particular interest, as it almost has no separation at large depths; thus the effect of the free-surface wave and the wave induced separation could be studied. Free- surface waves and wave induced separation results were evaluated and compared with both the available experimental data and the previous numerical... 

This paper introduces an analytical method for approximating the performance of a two-class priority M/M/1 system. The prioritized class-1 jobs are real-time, served either with the preemptive or non-preemptive Earliest- Deadline- First (EDF) policy and can preempt the non real-time class-2 jobs. The preempted service of the class-2 job is resumed from the time in instances where no class-1 job is in the system. The service discipline of class-2 jobs is FCFS. The required mean service times may depend on the class of the jobs. The real-time jobs have exponentially distributed relative deadlines until the end of service. The system is approximated by a Markovian model in the long run, which... 

The architecture of a hardwired simulator for implementation of a discrete event-driven simulation of digital systems at the logic level is presented. In the design of this system, attempts have been made to utilize techniques of high performance computing to have a system capable of simulating the digital circuits rapidly. The centralized event-driven simulation algorithm chosen here, has the advantages of being efficient and conceptually straightforward. The high reliability of the simulator has been taken care of through a collection of handshake signals between each two of the three main modules. © Sharif University of Technology, December 2007  

This paper presents a hybrid scheduling technique for generating the predictive schedules of passenger trains. The algorithm, which represents a combination of simulated annealing and a constraint-based heuristic, has been designed using an object-oriented methodology and is suitable for a primarily single-track railway with some double-track sections. The search process gets started from a good initial solution created by the scheduling heuristic and continues, according to the simulated annealing search control strategy. The heuristic is also used in the neighborhood exploration process. This hybrid approach solves the problem in a short span of time. Simulation experiments, with the real... 

In this paper, the application of regular Low-Density Parity-Check (LDPC) codes in Multi-Carrier Frequency-Hopping (MC-FH) CDMA systems is studied. To this end, different well-known constructions of regular LDPC codes are considered and the performance of LDPC coded MC-FH-CDMA systems, based on these constructions, are evaluated and compared in a frequency-selective slowly Rayleigh fading channel. These results are compared with those previously reported for super-orthogonal convolutionally coded MC-FH-CDMA systems. The simulation results indicate that the LDPC coded MC-FH-CDMA system significantly outperforms the uncoded and super-orthogonal convolutionally coded schemes. To alleviate the... 

The paper presents the application of a rule- based control scheme for an Advanced Static Var Compensator (ASVC) to improve power system transient stability. The proposed method uses a current reference, based on the Transient Energy Function (TEF) approach. The proposed scheme provides, also, a continuous control of the reactive power flow. The performance of the proposed approach is compared with that of a system using a conventional control method and of a system without ASVC. A single-machine system and an IEEE three machine system are used to verify the performance of the proposed method. © Sharif University of Technology  

The Per Tone equalization algorithm is a novel discrete multitone (DMT) equalization method with practical applications in subscriber digital loop systems. Unlike time domain DMT equalizers (TEQ), which equalize all DMT tones in a combined fashion, the Per Tone equalizer equalizes each tone separately. In this paper, the performance and complexity of this technique is investigated and compared with that of other TEQs. Furthermore, the behavior of this technique in different simulation conditions, such as over different standard CSA loops and in the presence of additive white Gaussian noise with variable power spectral density level and near end crosstalk (NEXT), is studied and compared with... 

In this paper, the performances of both uncoded and coded multiple access TH-UWB systems, introduced in [1-3] in multipath Rayleigh fading channels, are evaluated. The receiver is a selective diversity combining receiver, known as SRake. Based on a Gaussian distribution assumption for the multiple access interference at the output of the SRake receiver and by using a virtual branch technique, as introduced in [4,5], the bit error rates for uncoded and coded schemes are derived. The performance analysis shows that the effective order of diversity achieved by the coded scheme is the product of the number of branches of the SRake receiver and the Hamming distance of the code applied.... 

A unified multiple-access performance analysis and comparison of three multicarrier spread-spectrum multiple-access schemes, namely, MC-CDMA (Multicarrier Code-Division Multiple-Access), MC-FH (Multicarrier Frequency Hopping) and a hybrid of the above systems, called DS-MC-FH (Direct-Sequence MC-FH), in a multirate environment, where each user can have several multirate services, is provided. In MC-CDMA and MC-FH systems, users and their diverse services are differentiated by means of only one kind of signature code. However, in a DS-MCFH scheme, different users and different services of the same user are distinguished through the first and second signature codes, respectively. The... 

To ensure an optimized borehole in terms of heat capacity and cost-effectiveness, it is necessary to predict the heating performance of underground U-tube heat exchangers (boreholes) so that proper parameters such as length, diameter, material, etc. can be designed and selected. To this end, employing reliable equations is essential to predicting the heating performance of a borehole and also, to resolving the design issues. In this study, a single vertical U-tube borehole with a constant wall temperature is considered and analytical equations for temperature distribution in the surrounding ground around the borehole are evaluated based on one- and two-dimensional heat conduction,... 

Numerous studies have investigated driving equations used to predict the slip factor in centrifugal compressors so far. Inevitably, through these studies, the ow field characteristics have been simplified and the effects of the related parameters have been neglected. The present study, experimentally and numerically, investigates the slip phenomenon in a specific centrifugal compressor with complex blade curves and splitter blades, considering the main effective parameters such as the number of blades, exit angle, etc. To this end, a three-dimensional simulation of the viscous flow field of the compressor via an appropriate turbulence method was performed. In addition, an experimental study... 

The present study aims to reliably quantify the seismic response parameters of steel diagrid structural systems. To this end, in addition to the conventional Static Pushover Analysis (SPA), Dynamic Pushover Analysis (DPA) based on Incremental Dynamic Analysis (IDA) technique was taken into account. FEMA P-695 recommends a methodology for establishing Seismic Performance Factors (SPFs). The objective of the present study was to propose a simpler framework for estimating and validating SPFs while applying the concepts of FEMA P-695 guideline. The results showed that the R factors obtained through SPA procedure for steel diagrid systems were conservative and the IDAbased probabilistic method... 

Transitional boundary layer over a pitching airfoil at low Reynolds number (Re = 2:7 × 105) is experimentally investigated using space-frequency and time-frequency analyses of hot- film signals. Boundary layer events are visualized based on the space-frequency and time-frequency plots. The precursor phenomenon for turbulent and fully separated flows is presented based on the time-frequency analysis. A new technique based on time-frequency analysis of hot- film signals is introduced to measure the transition onset and relaminarization locations. This technique functions based on the analysis of high-frequency disturbances of the measured data. Significant attention has been drawn to the... 

Transitional boundary layer over a pitching airfoil at low Reynolds number (Re = 2:7 × 105) is experimentally investigated using space-frequency and time-frequency analyses of hot- film signals. Boundary layer events are visualized based on the space-frequency and time-frequency plots. The precursor phenomenon for turbulent and fully separated flows is presented based on the time-frequency analysis. A new technique based on time-frequency analysis of hot- film signals is introduced to measure the transition onset and relaminarization locations. This technique functions based on the analysis of high-frequency disturbances of the measured data. Significant attention has been drawn to the... 

Workers' absence considerably a ects the performance of labor-intensive construction projects. Identifying such absence patterns assists construction project managers in preparing proper project organization, reducing the absence rate, and improving the project performance. Despite its critical role, no study has investigated the absence pattern in the construction industry in Iran. This study addresses this gap by identifying the worker's absence pattern and providing recommendations to reduce the absence rate. First, a comprehensive literature review is conducted on the impacts of in uential factors in the worker's absence. Then, a questionnaire-based survey is designed and distributed... 

Various control charts have been proposed to monitor generalized linear pro les in Phase II. However, the robustness of the proposed methods in detecting di erent types and especially di erent directions of changes is not well-studied in the literature. In real-world applications, di erent kinds of change such as drift and multiple changes are likely to occur, which can be isotonic (increasing) or antitonic (decreasing). This paper studies the robustness of the Rao Score Test (RST) method, T2, and Multivariate Exponential Weighted Moving Average (MEWMA) in di erent types, drift and multiple, and directions of changes. The RST method also bene ts from a change-point detection approach whose...