Sharif Digital Repository

Lattice Reduction (LR) has been proposed as a method to enhance the performance of MIMO detectors such as ZF, MMSE and V-BLAST. Until recently, the application of LR to the superior K-Best tree-search detection algorithm was not practical due to the significant increase in complexity of K-Best as a result of the distortion of tree symmetry caused by LR. However, in our recently published work we developed an innovative K-Best algorithm to accommodate tree-asymmetry with no additional complexity. In this work, we build on this result and perform a detailed analysis of the effect of various LR algorithms on the performance of LR-aided K-Best. We show that LLL and Seysen provide equivalent... 

We consider a combined time-hopping (TH) and spread-time (ST) multiple-access technique that uses an internal code. In this method, the duration of each bit is divided into Ns frames. The outputs of the encoder and a pseudorandom (PN) sequence specify the number of the frame in which the data bit is transmitted in ST code-division multiple-access (ST-CDMA) form using the second PN sequence. We consider the correlator receiver, followed by the channel decoder. We obtain the performance of the combined method in additive white Gaussian noise (AWGN) and fading channels in the presence of multiple-access interference (MAI) and narrowband interference (NBI). We also consider the conventional... 

Water shortage issues are growing through the globe at higher rate than population growth. On the bright side, various methods are devised to capture energy from renewable energy or waste heat from different sectors. Among all inspected approaches, waste heat capturing through cooling process of the wind turbines' generators for desalination at small scale is paid less attention. However, in large wind farms, the scale of this dissipated thermal heat becomes appreciable which can drive several desalination units. Due to the above-pointed facts, the waste heat of a wind turbine with nominal capacity of 7358 kW and height of 24 m for desalinating seawater is inspected here, using a... 

Dental composites of A2 color using Bis-GMA, urethane dimethacrylate and triethyleneglycol dimethycrylate resins (70/20/10), and silica filler (70 wt%, 75 wt%, and 80 wt%), a hybrid of nano- and microsilica particles, are made and subjected to the following tests: Fourier transform infrared spectroscopy (FTIR), particle size analyzer, scanning electron microscope (SEM), and also cytotoxicity. FTIR results show that an increase in filler amount yields to a decrease in degree of conversion. Therefore, there should be a compromise between degree of conversion and the filler amount. SEM images manifest the uniformity of silica particles. It is shown from the cytotoxicity tests that as the... 

The use of solar energy concentration systems for achieving performance enhancements in the Photovoltaic/thermal hybrid solar systems and reduction of initial costs is an idea that has been studied for years. In this article a new structure for parabolic trough photovoltaic/thermal collector is proposed and its thermal and electrical performances are experimentally investigated. The receiver of this concentrator contains a triangular channel with an outer surface covered with photovoltaic cells and thermoelectric modules with a specific arrangement so that in addition to absorbing heat, a larger portion of the solar radiation is directly converted to electricity. Hence, the performance of... 

A nanowire arrays system consisting of an ordered configuration of Pt, Ni and Co was constructed in single-bath solution through pulse electrodeposition. This structure was evaluated as a potential amperometric non-enzymatic sensor to detect glucose in alkaline solution. We observed a strong and fast amperometric response at low applied potential of 0.4 V vs. SCE over linear ranges of 0-0.2 mM and 0.2-8 mM glucose with sensitivities of 1125 and 333 μA mM-1 cm-2, respectively. We also observed a low detection limit for glucose of 1 μM. Correlation of the electronic and geometric modifications with the electrochemical performance characteristics enhanced catalytic activity of the electrode by... 

The different characteristics of UWSN and trade off between UWSN and WSN, have been discussed in many researches. Here, we aim to propose a new architecture for very large scale underwater sensor network. In deployment part of sensors, topology plays a crucial role in issues like communication performance, power consumption, network reliability and fault tolerance capabilities. Hence, it is so critical and should be analyzed how we deploy sensors in targets environment. For instance, to improve reliability of our networks in harsh conditions, it is so important to avoid deploying underwater sensors with single point of failure and bottleneck. For this purpose, we present enhanced clustering... 

Diffusive molecular communications (DiMC) have recently gained attention as a candidate for nano- to micro- and macro-scale communications due to its simplicity and energy efficiency. As signal propagation is solely enabled by Brownian motion mechanics, DiMC faces severe inter-symbol interference (ISI), which limits reliable and high data-rate communications. Herein, recent literature on DiMC performance enhancement strategies is surveyed; key research directions are identified. Signaling design and associated design constraints are presented. Studies on fundamental information theoretic limits of DiMC channel are reviewed. Classical and novel transceiver designs are discussed with an... 

Diffusive molecular communications (DiMC) have recently gained attention as a candidate for nano- to micro- and macro-scale communications due to its simplicity and energy efficiency. As signal propagation is solely enabled by Brownian motion mechanics, DiMC faces severe inter-symbol interference (ISI), which limits reliable and high data-rate communications. Herein, recent literature on DiMC performance enhancement strategies is surveyed; key research directions are identified. Signaling design and associated design constraints are presented. Studies on fundamental information theoretic limits of DiMC channel are reviewed. Classical and novel transceiver designs are discussed with an... 

Modification of orthopedic implant surfaces through advanced nanoscale coating methods has made a major breakthrough in maximizing implantation success. Adjustable drug release and biocompatibility are among the most momentous features since they can significantly prevent the implantation failure. In this study, the potential of silk fibroin (SF) nanofibers fabricated via electrospinning, along with titanium oxide nanotube arrays (TNTs) formed through anodization, were exploited to produce a cyto-biocompatible, well-controlled drug delivery system. Highly-ordered TNTs were formed in an organic electrolyte solution within 2 h at the voltage of 60 V under temperature controlling (16 °C).... 

Network-on-Chip (NoC) paradigm has emerged as a revolutionary methodology to integrate numerous IP blocks on a single chip. The achievable performance of adopting NoCs is constrained by the performance limitation mainly imposed by the metal wires that are the physical realization of communication channels. According to the International Technology Roadmap for Semiconductors (ITRS) report, new interconnect paradigms providing huge bandwidth is in need for future products. The current wired channels have limited bandwidth, and consequently, they limit the performance enhancements that NoC architectures can provide. Optical interconnects are capable of achieving better performance via... 

In ad hoc wireless networks, there are scenarios where the desired destination is located in the range of other transmitters, so that the efforts on setting up communication with this terminal will fail due to collisions that may occur between transmitted control frames and undesired received control and data frames. This phenomenon becomes a bottleneck when most of data transmissions experience packet fragmentation. In such scenarios, the desired destination becomes unreachable during the data transfer of neighboring nodes. Using the same PHY of IEEE 802.11 and making slight modifications in its MAC, a new medium access control scheme equipped by a novel transmission scheduling algorithm is... 

The search for higher ship speeds and better propulsive performance has resulted in many performance enhancement techniques. One technique is to introduce an air film along the bottom of the hull to reduce skin friction drag. The air film system opens many possibilities for using designs with larger payloads such as barges and tankers, as well as catamarans with larger deck space which otherwise are not attractive because of their higher propulsion power. Although reducing hull drag by air injection was proposed in the beginning of this century, it still remains to be fully exploited. In this thesis, two models are used to do the experiments. The first one was a simple catamaran model and... 

The boiling phenomena in a quiescent fluid is the nucleate pool boiling which has attracted much interest in the thermal management studies. This paper investigates the effect of the installed Twisted Tape Fins (TTFs) on the heat transfer from a surface with a temperature above the water saturation point to a coil condenser. Four different arrangements of TTFs (1, 3, 5, and 9 TTFs) are fabricated and their boiling performance in distilled water at atmospheric pressure is experimentally tested. It was observed that the increase in the boiling heat transfer coefficient of the plate with nine TTFs compared to that of the plain one is 15.5%. Furthermore, the effect of TTFs heights on the heat... 

Extensive low-speed wind-tunnel tests are performed to study the flow field structure over a dual-surface canard, known as split canard, in comparison to the conventional configurations. Surface pressure for both steady deflections and unsteady oscillations of the canard are measured and compared for both canard-alone and split-canard cases. The split canard shows a superior advantage at high angles of attack, where a delay in the vortex breakdown phenomena on the canard surface is observed. For the split-canard configuration, the downwash of the front canard reduces the effective angle of attack at the inboard section of the rear element which postpones formation of the leading-edge vortex.... 

A considerable amount of energy is lost in the parabolic trough solar collectors due to the poor capability of working fluid in full absorption of the concentrated solar irradiation across the receiver tube. A new hybrid method is recommended here to cover up such deficiency by simultaneously using a rotary absorber tube and magnetic field inducer with nanofluid. Results showed that the combination effects of the receiver rotation and the magnetic field improve the convection mechanism in the absorber and increase both energetic and exergetic performance of the collector. The study reveals that there is an optimal rotational speed in the each magnetic field intensity for different... 

A considerable amount of energy is lost in the parabolic trough solar collectors due to the poor capability of working fluid in full absorption of the concentrated solar irradiation across the receiver tube. A new hybrid method is recommended here to cover up such deficiency by simultaneously using a rotary absorber tube and magnetic field inducer with nanofluid. Results showed that the combination effects of the receiver rotation and the magnetic field improve the convection mechanism in the absorber and increase both energetic and exergetic performance of the collector. The study reveals that there is an optimal rotational speed in the each magnetic field intensity for different... 

The casing treatment and flow injection upstream of the rotor tip are two effective approaches in suppressing instabilities or recovering from a fully developed stall. This paper presents numerical simulations for a high-speed transonic compressor rotor, NASA Rotor 37, applying a state-of-the-art design for the blade tip injection. This is characterized by introducing a jet flow directly into the casing treatment machined into the shroud. The casing treatment is positioned over the blade tip region and exceeds the impeller axially by ∼30 per cent of the tip chord both in the upstream and in the downstream directions. To numerically solve the governing equations, the three-dimensional finite...