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Go to Editorial ManagerIn this paper, the experimental thermal performance for a parabolic trough solar concentrator (PTSC) combined with helical tube receiver and directed by two axes solar tracking system at different amount of water flow rates has been analyzed. The experimental test results of thermal performance with regard to temperature rise of water, useful heat gain and collector thermal efficiency for the PTSC prototype at controlled water flow rates (2.3, 22.5 and 29.4 L/h) are collected. The results show that the increase of water mass flow rates causes decrease in the average water output temperature as (120.8, 63.82 and 46.08oC), respectively, the maximum outlet temperature becomes (160.5, 76, 47) oC, respectively, and thus, the average useful heat gain will be (1249.4, 732, 732.5W), respectively and the average thermal efficiency decreases as (73.021, 49.51 and 44.31 %), respectively. The experimental results show that decrease the water mass flow rate by 74.4%, causes an increase in the thermal efficiency of the PTSC by 64.7%.
Free Space Optics (FSO) plays a vital role in modern wireless communications due to its advantages over fiber optics and RF techniques where a transmission of huge bandwidth and access to remote places become possible._x000D_ The specific aim of this research is to analyze the Bit-Error Rate (BER) for FSO communication system when the signal is sent the over medium of turbulence channel, where the fading channel is described by the Gamma-Gamma model. The signal quality is improved by using Optical Space-Time Block- Code (OSTBC) and then the BER will be reduced. Optical 2×2 Alamouti scheme required 14 dB bit energy to noise ratio (Eb/N0) at 10-5 bit error rate (BER) which gives 3.5 dB gain as compared to no diversity scheme._x000D_ The results show that using Multiple-Input-Multiple-Output (MIMO) technique represented by Alamouti scheme gives the improved BER performance as compared with no diversity (Single-Input-Single-Output (SISO)) technique.
An orthogonal chaotic vectors based differential chaos shift keying (OCV-DCSK) digital communication system is presented. In this system the data transmission rates are increased by sending M bits in the same frame without needing for synchronization and channel state information since it use the benefit of non-coherent modulation of the DCSK and the orthogonality of chaotic vectors in the same scenario as QCSK system but instead of using Hilbert transform to create two orthogonal signals in QCSK, Gram Schmidt process is used to create M orthogonal chaotic signals from the M non-orthogonal chaotic signal. In the proposed system the analytical expression for OCV-DCSK are derived in AWGN and multipath fading channels. The simulation results show that the derived analytical expression have matched the Monte-Carlo simulation of the proposed system. Furthermore, comparison between orthogonal chaotic vectors and non-orthogonal, that are generated either as different initial conditions with the same chaotic generator or as different types of chaotic maps, reveals its superior BER performance in multipath fading channel.
Recently, major part of convection heat transfer researches focus on increasing fins efficiency by increasing thermal performance for the same fin volume. Metal foam is a promising way to achieve this aim. Performance analysis has been carried out to investigate the heat transfer characteristics of copper fin foam samples. The samples have been compared with the solid metal fin heat transfer. A forced convection heat transfer had been applied to a four specimens. An electrical heater heats up the fins, which are subjected to a stream of the ambient air driven by a blower fan as heat dissipated. The heat flux had been fixed along the tests with three different air velocity used; the forced heat convection had been simulated. The pores density of copper fin foam is varied in the range of 10, 20 & 40 pores per inches (PPI). Thermal performance of copper fin foam has been evaluated in terms of average Nusselt number and thermal resistance of heat sinks. The increasing in the heat transfer rate and average Nusselt number when used metal foam has been found in the range of 36-133 % compare to solid copper. Furthermore, it has been proven that this increment reaches the maximum value for a given PPI even when raise the air velocity.
In an original article, an addition was made to the well-known Taguchi’s methodical design literature by proposing how Poisson distribution may be incorporated into the Taguchi method for enhanced performance analysis in optimization. While the article is recent, it was found compelling enough to apply this novel concept of Poisson distribution to a growing area of maintenance research known as maintenance downtime analysis. Consequently, this paper contributes to the expanding research neighborhood through a Taguchi optimization method based on Poisson distribution related to the maintenance process optimization. A valuable method to optimize maintenance downtime was developed wherein the Poisson distribution was used to achieve the probability of maintenance downtime. An important foundation of the method is the Taguchi scheme. These elements were transformed into the factor-level design of the Poisson enhanced Taguchi scheme while the framework was tested using data from a process industry for validation. Interesting, the Taguchi's signal-to-noise quotient led to an enhanced set of limiting factors for better reliability of the system as G1H1I1J1K3. By interpretation, the following was found: downtime (204.61 mins), probability density function (0.00187), and cumulative density function (0.00776). The combination of these factors and levels will enhance maintenance downtime in the process industry as a result of their contributions. The outcome revealed the competence of the model to optimization schemes.
This paper proposes a design for a network connected over public networks using Virtual Private Network (VPN) technique. The network consists of five sites; center server and four customer service sites, each site consists of a number of LANs depending on the user services requirements. This work aims to measure the effect of VPN on the performance of a network. Four approaches are implements: Network design without using VPN, network design using VPN with centralized servers, network design using VPN with distributed servers, and network design using server load balance.The OPNET and BOSON simulation results show higher response time for packet transmission due to effect of VPN tunneling. The concurrent activation of application execution is used as a solution to the delay problem of the initial timing period while the application proceeds. The results dealing with QoS are E-mail, FTP, voice services traffic and IP traffic dropped. The VPN Tunnels is in the range of (0.01 to 0.02) sec.; along with this simulator there are four VPN tunnels in the network. Also, a special server’s load balance is used to manage distribution of the server processing load across all other network servers to achieve the best response