Sharif Digital Repository

Most part of Iran is dominated by arid and semi-arid areas due to low annual rainfall. The need for production of fresh water from brackish water is considerably high, especially in dry regions. In this study 1 month daily-based experimental data from a solar still site has been reported. The technical and operational problems of this site which finally contributed to the total cease of the site are described. Then a detailed analysis is investigated on progress of a prototype which constructed in order to solve the site's problems. The results of 1 month of experimental data of the final design showed that the last prototype could be used to solve the current problems of the site. The... 

Improper interparticle connection between carbon-based materials, poor interface bonding between the carbon counter electrodes (CEs) and substrate, and low surface area are the main limitations of carbon-based CEs in dye-sensitized solar cells. In this study, we utilized foamed cement and binder for adherence and surface area improvement in carbon-based CEs, such as graphite, multi-walled carbon nanotubes, and carbon black (CB). The results revealed that incorporating foamed cement into carbon materials improved the resistance, short-circuit current density, fill factor, and power conversion efficiency of the device. The porous cement/CB nanocomposite CE with a photoconversion efficiency of... 

This paper addresses the estimation of the integer part of the carrier frequency offset (CFO) in orthogonal frequency division multiplexing (OFDM) systems. A novel method is presented based on the maximum likelihood (ML) approach that jointly estimates the channel impulse response (CIR) and the integer CFO. The new scheme estimates the CIR by using pilots and obtains the estimate of the integer CFO by taking advantage of the effect of the CFO on the CIR and data symbols. The performance of the new method is evaluated in Rayleigh fading channels. The results demonstrate that the proposed scheme significantly outperforms the previous methods  

This paper deals with timing and frequency synchronization in orthogonal frequency-division multiplexing (OFDM) systems. A robust multistage scheme that works in the time domain, independent of the preamble structure, is proposed. After coarse-timing estimation, joint timing and integer frequency synchronization is performed. Then, fractional frequency correction is carried out, and finally, fine-timing estimation completes the synchronization process. The new timing estimation method is flexible and can be adjusted according to the degree of channel distortion. Furthermore, frequency synchronization is efficiently accomplished with an estimation range that is as large as the bandwidth of... 

This paper addresses the problem of frame detection in orthogonal frequency-division multiplexing (OFDM) systems. Using fourth-order statistics, a novel approach is presented for detection of a preamble composed of two identical parts in the time domain. First, it is demonstrated that sufficient statistics for detection of a periodic preamble do not exist, and conventional methods are not optimal. Next, looking at the detection of a preamble from the viewpoints of hypothesis testing and classification, a new method is presented based on the idea that fourth-order statistics can increase class separability (between-class distance) and consequently improve detection performance. It is proven... 

This study presents a novel method for frame timing estimation in OFDM systems. The new method is based on the generation and utilization of a new sequence from the two available preambles in the practical OFDM systems (such as WiMAX and WLAN) for correlation, and is capable of having an extended correlation length. The superior performance of the new method is demonstrated in terms of mean square error (MSE) in comparison with the previous methods  

In this paper, we propose a novel timing synchronization method for Orthogonal Frequency Division Multiplexing (OFDM) systems. The new method takes advantage of symmetrical correlation between some parts of the transmitted training symbol and produces an impulse-like timing metric. While reducing the complexity, our method provides an easy and efficient way for timing estimation. The proposed method does not need any differential cross-correlation or frequency correction to produce an impulse-like timing metric. It is shown that the new timing metric outperforms the previously presented methods in fading channels  

In this study, an industrial acetylene hydrogenation unit is simulated utilizing three available kinetic models. The results are compared against six-day experimental data and the best model is selected. Effects of feed temperature and the amount of injected hydrogen on ethylene selectivity are also studied. According to the simulation results, the unit is not working under its optimum conditions. Furthermore, by reduction of the hydrogen flow rate to 52 kg/h, process selectivity is increased. In addition, a new approach is proposed to modify the hydrogenation process and reduce undesired by-products. In the simulation of the modified process, hydrogenation reactors temperature, hydrogen... 

In this paper, the problem of coarse timing synchronization in orthogonal frequency-division multiplexing (OFDM) systems is investigated, and two new timing metrics with better performance are presented. The new metrics take advantage of two novel differential normalization functions that are based on the fourth-order statistics and are designed depending on the value of carrier frequency offset (CFO). The proposed timing metrics are theoretically evaluated using two different class separability criteria. It is shown that the new schemes considerably increase the difference between the correct and wrong timing points in comparison with previous methods. The computational complexity of the... 

In this paper, we propose an improved timing estimation method for orthogonal frequency division multiplexing (OFDM) systems. The proposed preamble-aided method is independent of the preamble structure and is based on taking advantage of the whole products available from a given preamble for its correlation. Capable of having an extended correlation length far beyond those used by the previous methods, the proposed scheme presents an estimator with a remarkable performance in severe noise conditions. Further, we introduce a reduced complexity estimator along with the complexity assessments. We finally evaluate the performance of the proposed method in terms of mean square error (MSE). The... 

This paper introduces a well-balanced second-order finite volume scheme, based on the Q-scheme of Roe, for simulating granular type flows. The proposed method is applied to solve the incompressible Euler equations under Savage-Hutter assumptions. The model is derived in a local coordinate system along a non-erodible bed to take its curvature into account. Moreover, simultaneous appearance of flowing/static regions is simulated by considering a basal friction resistance which keeps the granular flow from moving when the angle of granular flow is less than the angle of repose. The proposed scheme preserves stationary solutions up to second order and deals with different situations of wet/dry... 

Silica-supported boron trifluoride (BF3·SiO2) is an efficient, readily available and reusable catalyst for the synthesis of 1,2,4,5-tetrasubstituted imidazoles using benzil, an aromatic aldehyde and an amine in the presence of ammonium acetate. This one-pot procedure is very simple, affording good to excellent yields. © 2008 Elsevier Ltd. All rights reserved  

A four-step synthetic strategy was applied to achieve novel methacrylic monomers. 5-Norbornene-2,2-dimethanol was prepared from a Diels-Alder reaction of cyclopentadiene and acrolein, followed by the treatment of the adduct with an HCHO/ KOH/MeOH solution. The resulting 1,3-diol (1) was then acetalized with different aromatic aldehydes having OH groups on the ring to produce four spiroacetal derivatives. The reaction of methacryloyl chloride with the phenolic derivatives led to four new methacrylic monomers that were identified spectrochemically (mass, FTIR, 1H-NMR, and 13C-NMR spectroscopy). Free radical solution polymerization was used to prepare novel spiroacetal-norbornene containing... 

Compound 3-benzyl-2H-pyrano[3,2-c]chromene-2,5(6H)-dione(3), was prepared and fully characterized. The vibrational modes (FT-IR) and NMR data ( 1H and 13C chemical shifts) were compared with the results of Density Functional Theory (DFT) method at the B3LYP/cc-PVTZ level. The calculated vibrational frequencies and NMR chemical shifts are in good agreement with the experimental results. The electronic (UV-Vis) spectrum was calculated using the TD-DFT method in CH2Cl2 with the Polarizable Continuum Model using the integral equation formalism variant (IEFPCM) and was correlated to the experimental spectra. The assignment and analysis of the frontier HOMO and LUMO orbitals indicate that... 

Frame aggregation (FA) mechanisms improve the throughput of WLANs. In this paper, the effect of the FA mechanism on the throughput of wireless local area networks (WLANs) has been investigated. To this end, we propose an analytical model in order to analyze an IEEE 802.11n network comprised of an access point (AP) and several conventional nodes (CNs), all in the coverage area of each other. With respect to the heavier download traffic compared to the upload one, in our scenario, only the AP uses an FA mechanism and the other nodes use the basic IEEE 802.11 standard. In our proposed analytical model, the maximum downlink (DL) throughput is derived. Regarding the asymmetry among nodes, our... 

In this investigation a new type of superabsorbent hydrogel based on agar was prepared, and the effect of the feed ratio of some components (acrylic acid, MBA, APS and agar) on the swelling capacity of the hydrogel was systematically studied. Maximum water absorbency of the optimized final product was found to be 1,100∈g/g in distilled water. The structure of the hydrogel was characterized by FT-IR method and morphology of the samples was examined by scanning electron microscopy (SEM). Swelling properties of optimized hydrogel sample in different swelling mediums were investigated. The optimum hydrogel were also loaded with potassium nitrate and its potential for controlled release of... 

Stress is a body's natural way of responding to any kind of demand or challenge that everyone experiences from time to time. Although short-Term stress typically does not impose a health burden, exposure to prolonged stress can lead to significant adverse physiological and behavioral changes. Coping with the impact of stress is a challenging task and in this context, stress assessment is essential in preventing detrimental long-Term effects. The public embracement of connected wearable Internet of Things (IoT) devices, as well as the proliferation of Artificial Intelligence (AI) and Machine Learning (ML) technologies, have generated new opportunities for personalized stress tracking and... 

In the present study, the fluid characteristics of triangular turbulent jet flow are considered experimentally and numericafly. The results of spatially developed three- dimensional jet, issued from an equilateral triangular nozzle are presented. The jet is discharged to both bounded and unbounded domains. Because of the wind tunnel set up restrictions, the experimental study has done just for the bounded domain. The hot-wire anemometry is used for experimental study. A numerical method employing control volume approach with collocated grid arrangement which couples the velocity and pressure fields with SIMPLEC algorithm is introduced to discrete the governing equations of fluid flow. The... 

In this research, the effect of alternative fuels and the inlet charged air temperature is numerically investigated on the performance of a turbocharged spark-ignition engine. For this purpose, a one-dimensional engine and turbocharger model is created in an engine simulation and performance analysis software and validated with former experimental results. Then, the model is run with four fuel types, including two gasoline types with different octane numbers and two ethanol–gasoline blend fuels—E25 and E85. In each case, the inlet charged air temperature is changed from cold to hot condition and performance characteristics such as the spark advance timing, brake torque, brake-specific fuel... 

Monitoring and controlling the depth of anesthesia is really important, since over dosing and under dosing can be dangerous for the patients. Pharmacokinetic-Pharmacodynamic models vastly used for describing the relationship between input anesthetic agents and output patient endpoint variables. As there is a large variety between the patients so for controlling the depth of anesthesia we need a controller which should be robust enough and also because the anesthesia process is nonlinear and contains time delay, among them all the proposed methods for controlling the depth of anesthesia, model predictive controllers (MPCs) are good choices. Extended dynamic matrix control (EDMC) can be...