Sharif Digital Repository

The yearly thermo-economic performance is dynamically investigated for three solar heating and cooling systems: solar heating and absorption cooling (SHAC), solar heating and ejector cooling (SHEC), and heating and solar vapor compression cooling (HSVC). First, the effects of important design parameters on the thermo-economic performance of the systems to supply the heating and cooling loads of the building are evaluated. The systems are parametrically analyzed with the weather conditions of Tehran, Iran. The results show that the life cycle costs (LCC) of the SHAC and HSVC systems are alike and much lower than those of the SHEC system. The HSVC system exhibits the best performance from... 

The yearly thermo-economic performance is dynamically investigated for three solar heating and cooling systems: solar heating and absorption cooling (SHAC), solar heating and ejector cooling (SHEC), and heating and solar vapor compression cooling (HSVC). First, the effects of important design parameters on the thermo-economic performance of the systems to supply the heating and cooling loads of the building are evaluated. The systems are parametrically analyzed with the weather conditions of Tehran, Iran. The results show that the life cycle costs (LCC) of the SHAC and HSVC systems are alike and much lower than those of the SHEC system. The HSVC system exhibits the best performance from... 

Spinal fusion surgery is usually followed by accelerated degenerative changes in the unfused segments above and below the treated segment(s), i.e., adjacent segment disease (ASD). While a number of risk factors for ASD have been suggested, its exact pathogenesis remains to be identified. Finite element (FE) models are indispensable tools to investigate mechanical effects of fusion surgeries on post-fusion changes in the adjacent segment kinematics and kinetics. Existing modeling studies validate only their intact FE model against in vitro data and subsequently simulate post-fusion in vivo conditions. The present study provides a novel approach for the comprehensive validation of a lumbar... 

In this paper we present an adaptive method for image compression that is based on complexity level of the image. The basic compressor/de-compressor structure of this method is a multilayer perceptron artificial neural network. In adaptive approach different Back-Propagation artificial neural networks are used as compressor and de-compressor and this is done by dividing the image into blocks, computing the complexity of each block and then selecting one network for each block according to its complexity value. Three complexity measure methods, called Entropy, Activity and Pattern-based are used to determine the level of complexity in image blocks and their ability in complexity estimation... 

With the declining energy resources and increase of pollutant emissions, a great deal of efforts has been focused on the development of alternatives for fossil fuels. One of the promising alternative fuels to gasoline in the internal combustion engine is natural gas [1-5]. The application of natural gas in current internal combustion engines is realistic due to its many benefits. The higher thermal efficiency due to the higher octane value and lower exhaust emissions including CO2 as a result of the lower carbon to hydrogen ratio of the fuel are the two important feature of using CNG as an alternative fuel. It is well known that computer simulation codes are valuable economically as a cost... 

This article presented an efficient deep learning technique to predict the compressive strength of high-performance concrete (HPC). This technique combined the convolutional neural network (CNN) and genetic algorithm (GA). Six CNN architectures were considered with different hyper-parameters. GA was employed to determine the optimum number of filters in each convolutional layer of the CNN architectures. The resulted CNN architectures were then compared to each other to find the best architecture in terms of accuracy and capability of generalization. It was shown that all of the proposed CNN models are capable of predicting the HPC compressive strength with high accuracy. Finally, the best of... 

Learning sparsifying dictionaries from a set of training signals has been shown to have much better performance than pre-designed dictionaries in many signal processing tasks, including image enhancement. To this aim, numerous practical dictionary learning (DL) algorithms have been proposed over the last decade. This paper introduces an accelerated DL algorithm based on iterative proximal methods. The new algorithm efficiently utilizes the iterative nature of DL process, and uses accelerated schemes for updating dictionary and coefficient matrix. Our numerical experiments on dictionary recovery show that, compared with some well-known DL algorithms, our proposed one has a better convergence... 

In this paper a novel technique using the Block Truncation Coding (BTC) to further improve the compression quality of a 4-tap integer wavelet filter is proposed. Experimental results reveal that noticeable improvements can be achieved using the proposed BTC-based technique. © 2003 IEEE  

Design techniques to enhance bandwidth and linearity of broadband multistage low-noise amplifiers (LNAs) are presented. A feedback amplifier circuit is proposed to compensate for transistor gain roll-off with frequency in other amplifier stages and extend overall bandwidth. Moreover, a transistor width tapering in a multistage LNA is applied to improve linearity. These techniques are adopted in a three-stage monolithic microwave integrated circuit (MMIC) LNA implemented in a 0.1-μm GaAs pHEMT process. The LNA features 18-43 GHz bandwidth, 21.6 dB average gain, and 1.8-2.7 noise figure (NF). It exhibits output 1-dB compression point of 11.5 dBm at 30 GHz and consumes 70 mA bias current from a... 

A 6-bit passive phase shifter for 2.5- to 3.2-GHz frequency band has been designed and implemented in a standard 0.18- μm CMOS technology. A new switched-network topology has been proposed for implementing the 5.625 ° phase shift step. The insertion loss of the circuit is compensated with an on-chip bidirectional amplifier. The measured return losses of the circuit are better than 8 dB with output 1-dB compression point of +9.5 dBm in the transmit mode and noise figure of 7.1 dB in the receive mode. The fabricated phase shifter demonstrates an average rms phase error of less than 2° over the entire operation bandwidth, which makes it suitable for high-precision applications  

Mechanized tunneling method using Tunnel Boring Machine (TBM) is being extensively employed in urban areas, especially when excavation takes place underneath the groundwater table. In this study, three-dimensional coupled Finite Element Analyses (FEA) have been performed to investigate the interaction mechanism between mechanized twin tunnels construction of Shiraz metro (line 2) and groundwater. Firstly, two soil constitutive models (Mohr-Coulomb and Modified Cam-Clay model) of Shiraz lean clay are validated against drained triaxial compression test data. Varying the permeability of the grout layer within the specified range, the base numerical model is then calibrated by the field data of... 

Cell survival during the early stages of transplantation and before new blood vessels formation is a major challenge in translational applications of 3D bioprinted tissues. Supplementing oxygen (O2) to transplanted cells via an O2 generating source such as calcium peroxide (CPO) is an attractive approach to ensure cell viability. Calcium peroxide also produces calcium hydroxide that reduces the viscosity of bioinks, which is a limiting factor for bioprinting. Therefore, adapting this solution into 3D bioprinting is of significant importance. In this study, a gelatin methacryloyl (GelMA) bioink that is optimized in terms of pH and viscosity is developed. The improved rheological properties... 

Compressed images such as JPEG when transmitted over communication channels are susceptible to channel noise and/or erasure, which causes losses of blocks of pixels or macroblocks. Recovery of a large block in an image is a difficult task. In this paper we propose a novel method that addresses this problem and can exactly recover a lost block. Moreover, the proposed algorithm is fast enough to be implemented in real time. Simulation results show that our method is faster than previous methods proposed in the literature with less distortion  

The goal of this paper is to reduce the antenna count in a millimeter (mm)-wave imaging system by proposing both hardware and software solutions. The concept of image sparsity in the transform domain is utilized to present the compressive sensing (CS) formulation for both mono-static and multistatic imaging at mm-wave frequencies. To reduce the complexity of the imaging system and reconstruction process, we introduce 1.5-D array structure, which is a random sparse array with orthogonal element locations. It is shown that the peak signal-to-noise ratio (PSNR) of the reconstructed image obtained by a 1.5-D array with 65% sparsity is very close to the PSNR of a uniform 2-D array for mono-static...