Calculation of Optical Constants of As40S60-xSex Thick Films with High Accuracy using Wedge Shape Optical Model

This work has been focused primarily on the extraction of thicknesses, optical, and AC electrical parameters for as-prepared As40S60-xSex thin films, with (x=0, 20, 40, and 60 at. %). The thickness of such films has been calculated by the wedge method depending on the transmission spectra of their shrinkage in the range of 400 to 2500 nm. Swanepoels wedge relationships have been solved using the Mathcad 2000 program by minerr function to extract the film’s thickness. Depending on the obtained thickness of studied the thin films, the main optical parameters have been determined. The structural aspects of the studied thin films have also been studied using XRD and SEM techniques

Structural, Morphological and Optical Parameters of Zn(1-x) CuxS Thin Films for Optoelectronic Devices

In the present work, ZnS and Cu incorporated at (2%, 4%,6%, 8%, and 10%) thin films were growth onto hot glass substrates at substrates temperature 270 oC with thickness about 100 nm by chemical spray pyrolysis technique. The solutions of the spray consists of Zn(CH3COO)2.2H2O, SC(NH2)2 and CuCl2.2H2O with molar concentration 0.1M/L. The structure of the film was studied by XRD pattern, the results shows that the films were polycrystalline with cubic phase for pure ZnS and hexagonal phase for Zn1-xCuxS at x=10%. The optical constants, refractive index, n and extinction coefficient, k were determined The optical energy gap of the direct transition is also estimated, pure ZnS is 3.42 eV, and it increases as the Cu concentration increases from 3.49 to 3.67 eV. The room temperature photoluminescence (PL) of copper-doped zinc sulfide (ZnS:Cu) nanoparticles was studied. Through Gaussian fitting, the PL spectrum of undoped ZnS nanoparticles is deconvoluted into two blue luminescence peaks (centered at 411 nm and 455 nm, respectively), both of which can be attributed to the recombination of ZnS defect states. But for doped samples, a third peak at about 500 nm was also identified. Discussed the changes of all optical constants and PL spectra from the changes of optoelectronics microstructure parameter

Estimation of daily flow rate of photovoltaic water pumping systems using solar radiation data

This paper presents a simple model which allows us to contribute in the studies of photovoltaic (PV) water pumping systems sizing. The nonlinear relation between water flow rate and solar power has been obtained experimentally in a first step and then used for performance prediction. The model proposed enables us to simulate the water flow rate using solar radiation data for different heads (50 m, 60 m, 70 m and 80 m) and for 8S × 3P PV array configuration. The experimental data are obtained with our pumping test facility located at Madinah site (Saudi Arabia). The performances are calculated using the measured solar radiation data of different locations in Saudi Arabia. Knowing the solar radiation data, we have estimated with a good precision the water flow rate Q in five locations (Al-Jouf, Solar Village, AL-Ahsa, Madinah and Gizan) in Saudi Arabia. The flow rate Q increases with the increase of pump power for different heads following the nonlinear model proposed. Keywords: Photovoltaic water pumping system, Solar radiation data, Simulation, Flow rat

Evaluating the Impact of Transmission Range on the Performance of VANET

Recently, interest in the field of Vehicular Ad-hoc Networks (VANETs) has grown among research community to improve traffic safety and efficiency on the roads. Despite the many advantages, the transmission range in vehicular network remains one of the major challenges due to the unique characteristics of VANETs such as various communication environments, highly dynamic topology, high node mobility and traffic density. The network would suffer from a broadcast-storm in high vehicular density when a fixed transmission range in VANET is used, while in sparse vehicular density the network could be disconnected frequently. In this paper, we evaluated the impact of different transmission ranges and number of flows formed between vehicles in a highway scenario using AODV as routing protocol. In order to validate the simulation of VANET, traffic and network simulators (SUMO & NS-2) have been used. The performance was evaluated in terms of packet delivery ratio and end-to-end delay. The simulation results have shown that better performance was achieved in term of higher PDR and lower end-to-end delay for less than 500 meters transmission range. On the contrary, the PDR started to decrease and end-to-end delay increased when the transmission range exceeded 500 meters. The performance degraded as the number of flows increased

An Accurate Performance Analysis of Hybrid Efficient and Reliable MAC Protocol in VANET under Non-saturated Conditions

Vehicular Ad Hoc Networks (VANETs) is a technology supporting two types of applications, safety and service applications with higher and lower priorities respectively. Thereby, Medium Access Control (MAC) protocol is designed to provide reliable and efficient data broadcasting based on prioritization. Different from the IEEE 1609.4 (legacy), HER-MAC protocol is a new multi-channel MAC proposed for VANETs, offering remarkable performance with regards to safety applications transmission. This paper focuses on the analysis of packet delivery ratio of the HER-MAC protocol under non-saturated conditions. 1-D and 2-D Markov chains have been developed for safety and non-safety applications respectively, to evaluate mathematically the performance of HER-MAC protocol. The presented work has taken into account the freezing of the backoff timer for both applications and the backoff stages along with short retry limit for non-safety applications in order to meet the IEEE 802.11p specifications. It highlights that taking these elements into consideration are important in modeling the system, to provide an accurate estimation of the channel access, and guarantees that no packet is served indefinitely. More precise results of the system packet delivery ratio have been yield. The probability of successful transmission and collisions were derived and used to compute the packet delivery ratio. The simulation results validate the analytical results of our models and indicate that the performance of our models outperformed the existing models in terms of the packet delivery ratio under different number of vehicles and contention window

Modeling and analysis of IEEE 1609.4 MAC in the presence of error-prone channels

Vehicular Ad Hoc Networks (VANETs) have been developed to improve the safety, comfort and efficiency of driving on the road. The IEEE 1609.4 is a standard intended to support multi-channel in VANETs. These channels include one control channel for safety applications and six service channels for service applications. However, there is still no comprehensive analysis for the average delay and system throughput of IEEE 1609.4 MAC in VANETs considering error-prone channel under non-saturated conditions. In this paper, we propose an analytical models based on 1-D and 2-D Markov chain to evaluate the performance analysis of IEEE 1609.4 MAC in the presence of error-prone channels. Besides, freezing of the back-off timer is taken into consideration to provide an accurate estimation of access to the channel. The simulation results have been carried out to validate the analytical results of our model. The results show that the performance of our model outperforms the existing model in terms of packet delivery ratio and average delay of safety packets over CCH, and system throughput of service packets over SCHs

A Comprehensive Performance Analysis of IEEE 802.11p based MAC for Vehicular Communications Under Non-saturated Conditions

Reliable and efficient data broadcasting is essential in vehicular networks to provide safety-critical and commercial service messages on the road. There is still no comprehensive analysis of IEEE 802.11p based MAC that portrays the presence of buffer memory in vehicular networks. Besides, most of the analytical works do not fulfill some of the IEEE 802.11p specifications, such as short retry limit and back-off timer freezing. This paper proposes a 1-D and 2-D Markov model to analyze mathematically IEEE 802.11p based MAC for safety and non-safety messages respectively. The work presented in this paper takes into account the traffic arrival along with the first-order buffer memory and freezing of the back-off timer as well, to utilize the channel efficiently and provide higher accuracy in estimation of channel access, yielding more precise results of the system throughput for non-safety messages and lower delay for safety messages. Furthermore, back-off stages with a short retry limit were applied for non-safety messages in order to meet the IEEE 802.11p specifications, guaranteeing that no packet is served indefinitely, avoiding the overestimation of system throughput. A simulation was carried out to validate the analytical results of our model

Maximising system throughput in wireless powered sub-6 GHz and millimetre-wave 5G heterogeneous networks

Millimetre wave (mm-Wave) bands and sub-6 GHz are key technologies in solving the spectrum critical situation in the fifth generation (5G) wireless networks in achieving high throughput with low transmission power. This paper studies the performance of dense small cells that involve a millimetre wave (mm-Wave) band and sub-6 GHz that operate in high frequency to support massive multiple-input-multiple-output systems (MIMO). In this paper, we analyse the propagation path loss and wireless powered transfer for a 5G wireless cellular system from both macro cells and femtocells in the sub-6 GHz (µWave) and mm-Wave tiers. This paper also analyses the tier heterogeneous in downlink for both mm-Wave and sub-6 GHz. It further proposes a novel distributed power to mitigate the inter-beam interference directors and achieve high throughput under game theory-based power constraints across the sub-6 GHz and mm-Wave interfaces. From the simulation results, the proposed distributed powers in femtocell suppresses inter-beam interference by minimising path loss to active users (UEs) and provides substantial power saving by controlling the distributed power algorithm to achieve high throughput

Structural, optical and electrical characteristics of sulfur incorporated ZnSe thin films

In the present study, polycrystalline materials of ZnSe1-xSx (x = 0, 0.25, 0.5, 0.75 and 1) were prepared by a conventional solid-state reaction method. Thin films of ZnSe1-xSx of about 1 μm have been produced using evaporation method. The importance of ZnSe1-xSx compound is the tunability of band gap when incorporating S into the ZnSe. Adding S at the expense of Se in ZnSe to form Zn-Se-S, which has a wider energy gap window layer to permit more light to reach the junction of solar cell. Both of optical constants (n, k) and film thickness have been determined precisely in terms of envelop method. Optical absorption spectra showed that band gap values increase with increasing S content. The electrical conductivity of ZnSe1-xSx was studied and exhibit two type of variation versus temperature. The activation energy of linear portion of the low temperature range is lower than the activation energy of linear portion of high temperature range and it increases with increasing the sulfur content in all films in both temperature ranges