Search results for: non-uniform heat source/sink

Authors: N. Sozbir, M. Bulut, M.F.Oktem, A.Kahriman, A. Chaix

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TUSAT is a prospective Turkish Communication Satellite designed for providing mainly data communication and broadcasting services through Ku-Band and C-Band channels. Thermal control is a vital issue in satellite design process. Therefore, all satellite subsystems and equipments should be maintained in the desired temperature range from launch to end of maneuvering life. The main function of the thermal control is to keep the equipments and the satellite structures in a given temperature range for various phases and operating modes of spacecraft during its lifetime. This paper describes the thermal control design which uses passive and active thermal control concepts. The active thermal control is based on heaters regulated by software via thermistors. Alternatively passive thermal control composes of heat pipes, multilayer insulation (MLI) blankets, radiators, paints and surface finishes maintaining temperature level of the overall carrier components within an acceptable value. Thermal control design is supported by thermal analysis using thermal mathematical models (TMM).

Keywords: Spacecraft thermal control, design of thermal control.

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Authors: Antonis Constantinides, Christos Yiallouras, Christakis Damianou

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The application of today's semiconductor transistors in high power UHF DVB-T linear amplifiers has evolved significantly by utilizing LDMOS technology. This fact provides engineers with the option to design a single transistor signal amplifier which enables output power and linearity that was unobtainable previously using bipolar junction transistors or later type first generation MOSFETS. The quiescent current stability in terms of thermal variations of the LDMOS guarantees a robust operation in any topology of DVB-T signal amplifiers. Otherwise, progressively uncontrolled heat dissipation enhancement on the LDMOS case can degrade the amplifier’s crucial parameters in regards to the gain, linearity and RF stability, resulting in dysfunctional operation or a total destruction of the unit. This paper presents one more sophisticated approach from the traditional biasing circuits used so far in LDMOS DVB-T amplifiers. It utilizes a microprocessor control technology, providing stability in topologies where IDQ must be perfectly accurate.

Keywords: Amplifier, DVB-T, LDMOS, MOSFETS.

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Authors: A. Al-Sayyad, P. Lama, J. Bardon, P. Hirchenhahn, L. Houssiau, P. Plapper

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Composite metal–polymer materials, in particular titanium alloy (Ti-6Al-4V) to polyamide (PA6.6), fabricated by laser joining, have gained cogent interest among industries and researchers concerned with aerospace and biomedical applications. This work adopts infrared (IR) thermography technique to investigate effects of laser parameters used in the welding process on the three-dimensional temperature profile at the rear-side of titanium, at the region to be welded with polyamide. Cross sectional analysis of welded joints showed correlations between the morphology of titanium and polyamide at the weld zone with the corresponding temperature profile. In particular, spatial temperature profile was found to be correlated with the laser beam energy density, titanium molten pool width and depth, and polyamide heat affected zone depth.

Keywords: Laser welding, metals to polymers joining, process monitoring, temperature profile, thermography.

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Authors: Alfonso Bastías, Álvaro González

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The actual grow of the infrastructure in develop country require sophisticate ways manage the operation and control the quality served. This research wants to concentrate in the operation of this infrastructure beyond the construction. The infrastructure-s operation involves an uncertain environment, where unexpected variables are present every day and everywhere. Decision makers need to make right decisions with right information/data analyzed most in real time. To adequately support their decisions and decrease any negative impact and collateral effect, they need to use computational tools called decision support systems (DSS), but now the main source of information came from common users thought an extensive crowdsourcing

Keywords: Crowdsourcing, Learning Systems, Decision Support Systems, Infrastructure, Construction.

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Authors: Farid Vahedi

Abstract:

There is a great deal of interest in constructing Double Skin Facade (DSF) structures which are considered as modern movement in field of Energy Conservation, renewable energies, and Architecture design. This trend provides many conclusive alternatives which are frequently associated with sustainable building. In this paper a building with Double Skin Facade is considered in the semiarid climate of Tehran, Iran, in order to consider the DSF-s performance during hot seasons. Mathematical formulations calculate solar heat gain by the external skin. Moreover, Computational Fluid Dynamics (CFD) simulations were performed on the case study building to enhance effectiveness of the facade. The conclusion divulged difference of gained energy by the cavity and room with and without blind and louvers. Some solutions were introduced to surge the performance of natural ventilation by plunging the cooling loads in summer.

Keywords: Double Skin Façade Buildings, Energy Conservation, Renewable Energy, Natural Ventilation, Semi-arid Climate.

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Authors: Jia Xu

Abstract:

There is a lot of bottom space in the teaching area of Zijingang Campus of Zhejiang University, which benefits to the ventilation, heat dissipation, circulation, partition of quiet and noisy areas and diversification of spaces. Hangzhou is hot in summer but cold in winter, so teachers and students spend much less time in the bottom space of buildings in winter than in summer. Recently, depending on the teachers and students’ proposals, the school transformed the bottom space in the teaching area to provide space for relaxing, chatting and staying in winter. Surveying and analyzing the existing ways to transform, the paper researches deeply on the transformation projects of bottom space in the teaching buildings. It is believed that this paper can be a salutary lesson to make the bottom space in the teaching areas of universities richer and bring more diverse activities for teachers and students.

Keywords: Bottom space, teaching area, transformation, Zijingang Campus of Zhejiang University.

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Authors: Olufunke O. Ezekiel, Abiodun A. Oriku

Abstract:

The seeds of cotton (Gossypium hirsutum) fall among the lesser known oil seeds. Cottonseeds are not normally consumed in their natural state due to their gossypol content, an antinutrient. The effect of processing on the sensory characteristics and chemical composition of cottonseed and its extract was studied by subjecting the cottonseed extract to heat treatment (boiling) and the cottonseed to fermentation. The cottonseed extract was boiled using the open pot and the pressure pot for 30 minutes respectively. The fermentation of the cottonseed was carried out for 6 days with samples withdrawn at intervals of 2 days. The extract and fermented samples were subjected to chemical analysis and sensory evaluated for colour, aroma, taste, mouth feel, appearance and overallacceptability. The open pot sample was more preferred. Fermentation for 6 days resulted into a significant reduction in gossypol level of the cottonseed; however, sample fermented for 2 days was most preferred.

Keywords: Cottonseed, boiling, extract, fermentation, True protein.

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Authors: F. Hadjaj, A. Belghachi, A. Halmaoui, M. Belhadj, H. Mazouz

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A laser is essentially an optical oscillator consisting of a resonant cavity, an amplifying medium and a pumping source. In semiconductor diode lasers, the cavity is created by the boundary between the cleaved face of the semiconductor crystal and air, and has reflective properties as a result of the differing refractive indices of the two media. For a GaAs-air interface a reflectance of 0.3 is typical and therefore the length of the semiconductor junction forms the resonant cavity. To prevent light being emitted in unwanted directions from the junction, sides perpendicular to the required direction are roughened. The objective of this work is to simulate the optical resonator Fabry-Perot and explore its main characteristics, such as FSR, finesse, linewidth, transmission and so on, that describe the performance of resonator.

Keywords: Fabry-Perot Resonator, laser diode.

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Authors: S. Jain, Y. Deshpande

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The fluid mechanics principle is used extensively in designing axial flow fans and their associated equipment. This paper presents a computational fluid dynamics (CFD) modeling of air flow distribution from a radiator axial flow fan used in an acid pump truck Tier4 (APT T4) Repower. This axial flow fan augments the transfer of heat from the engine mounted on the APT T4. CFD analysis was performed for an area weighted average static pressure difference at the inlet and outlet of the fan. Pressure contours, velocity vectors, and path lines were plotted for detailing the flow characteristics for different orientations of the fan blade. The results were then compared and verified against known theoretical observations and actual experimental data. This study shows that a CFD simulation can be very useful for predicting and understanding the flow distribution from a radiator fan for further research work.

Keywords: Computational fluid dynamics (CFD), acid pump truck (APT) Tier4 Repower, axial flow fan, area weighted average static pressure difference, and contour plots.

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Authors: Zdenek Kolka, Otakar Wilfert, Viera Biolkova

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The paper deals with an analysis of visibility records collected from 210 European airports to obtain a realistic estimation of the availability of Free Space Optical (FSO) data links. Commercially available optical links usually operate in the 850nm waveband. Thus the influence of the atmosphere on the optical beam and on the visible light is similar. Long-term visibility records represent an invaluable source of data for the estimation of the quality of service of FSO links. The model used characterizes both the statistical properties of fade depths and the statistical properties of individual fade durations. Results are presented for Italy, France, and Germany.

Keywords: Computer networks, free-space optical links, meteorology, quality of service.

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Authors: Brigita Altenbaher

Abstract:

The friction between two metal surfaces results in a high frequency noise (squealing) which also occurs during the braking of wagons with rail brakes in the process of shunting at a marshalling yard with a hump. At that point the noise level may exceed 130dB, which is extremely unpleasant for workers and inhabitants. In our research we developed a new composite material which does not change braking properties, is capable of taking extremely high pressure loads, reduces noise and is environmentally friendly. The noise reduction results had been very good and had shown a decrease of the high frequency noise almost completely (by 99%) at its source. With our technology we had also reduced general noise by more than 30dBA.

Keywords: Composite heavily fluid compound, hump yard, noise reduction, rail brakes.

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Authors: Brajesh Kumar Jha, Neeru Adlakha, M. N. Mehta

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Calcium [Ca2+] is an important second messenger which plays an important role in signal transduction. There are several parameters that affect its concentration profile like buffer source etc. The effect of stationary immobile buffer on Ca2+ concentration has been incorporated which is a very important parameter needed to be taken into account in order to make the model more realistic. Interdependence of all the important parameters like diffusion coefficient and influx over [Ca2+] profile has been studied. Model is developed in the form of advection diffusion equation together with buffer concentration. A program has been developed using finite volume method for the entire problem and simulated on an AMD-Turion 32-bit machine to compute the numerical results.

Keywords: Ca2+ profile, buffer, Astrocytes, Advection diffusion, FVM

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Authors: Wei-hua Ai, Wei Yan, Xiang Li

Abstract:

Data compression is used operationally to reduce bandwidth and storage requirements. An efficient method for achieving lossless weather radar data compression is presented. The characteristics of the data are taken into account and the optical linear prediction is used for the PPI images in the weather radar data in the proposed method. The next PPI image is identical to the current one and a dramatic reduction in source entropy is achieved by using the prediction algorithm. Some lossless compression methods are used to compress the predicted data. Experimental results show that for the weather radar data, the method proposed in this paper outperforms the other methods.

Keywords: Lossless compression, weather radar data, optical linear prediction, PPI image

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Authors: Tatyana R. Radeva, Ivan S. Yatchev, Dimitar N. Karastoyanov, Nikolay I. Stoimenov, Stanislav D. Gyoshev

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The paper presents coupled electromagnetic and thermal field analysis of busbar system (of rectangular cross-section geometry) submitted to short circuit conditions. The laboratory model was validated against both analytical solution and experimental observations. The considered problem required the computation of the detailed distribution of the power losses and the heat transfer modes. In this electromagnetic and thermal analysis, different definitions of electric busbar heating were considered and compared. The busbar system is a three phase one and consists of aluminum, painted aluminum and copper busbar. The solution to the coupled field problem is obtained using the finite element method and the QuickField™ program. Experiments have been carried out using two different approaches and compared with computed results.

Keywords: Busbar system, coupled problems, finite element method, short-circuit currents.

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Authors: N. Stevulova, I. Schwarzova

Abstract:

The possibility of using industrial hemp as a source of natural fibers for purpose of construction, mainly for the preparation of lightweight composites based on hemp hurds is described. In this article, an overview of measurement results of important technical parameters (compressive strength, density, thermal conductivity) of composites based on organic filler - chemically modified hemp hurds in three solutions (EDTA, NaOH and Ca(OH)₂) and inorganic binder MgO-cement after 7, 28, 60, 90 and 180 days of hardening is given. The results of long-term water storage of 28 days hardened composites at room temperature were investigated. Changes in the properties of composites caused by chemical treatment of hemp material are discussed.

Keywords: Hemp hurds, chemical modification, lightweight composites, testing material properties.

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Authors: Pedro Luis Ferrer Penalver, Edmundo da Silva Braga

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In this paper, the performance of a simple surge protection for a direct current circuit was simulated. The protection circuit was developed from modified electric macro models of a gas discharge tube and a transient voltage suppressor diode. Moreover, a combination wave generator circuit was used as source of energy surges. The simulations showed that the circuit presented ensures immunity corresponding with test level IV of the IEC 61000-4-5:2014 international standard. The developed circuit can be modified to meet the requirements of any other equipment to be protected. Similarly, the parameters of the combination wave generator can be changed to provide different surge amplitudes.

Keywords: Combination wave generator, IEC 61000-4-5, Pspice simulation, surge protection.

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Authors: S. Saadi, S. Benissaad, S. Poncet, Y. Kabar

Abstract:

In photovoltaic (PV) cells, most of the absorbed solar radiation cannot be converted into electricity. A large amount of solar radiation is converted to heat, which should be dissipated by any cooling techniques. In the present study, the cooling is achieved by inserting triangular ribs in the duct. A comprehensive two-dimensional thermo-fluid model for the effective cooling of PV cells has been developed. It has been first carefully validated against experimental and numerical results available in the literature. A parametric analysis was then carried out about the influence of the number and size of the ribs, wind speed, solar irradiance and inlet fluid velocity on the average solar cell and outlet air temperatures as well as the thermal and electrical efficiencies of the module. Results indicated that the use of triangular ribbed channels is a very effective cooling technique, which significantly reduces the average temperature of the PV cell, especially when increasing the number of ribs.

Keywords: Effective cooling, numerical modeling, photovoltaic cell, triangular ribs.

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Authors: Asep Bayu Dani Nandiyanto, Asep Suhendi, Yutaka Kisakibaru, Takashi Ogi, Kikuo Okuyama

Abstract:

An ordered porous antimony-doped tin oxide (ATO) film was successfully prepared using a simple coating process with colloidal templates. The facile production was effective when a combination of 16-nm ATO (as a model of an inorganic nanoparticle) and polystyrene (PS) spheres (as a model of the template) weresimply coated to produce a composite ATO/PS film. Heat treatment was then used to remove the PS and produce the porous film. The porous film with a spherical pore shape and a highly ordered porous structure could be obtained. A potential way for the control of pore size could be also achieved by changing initial template size. The theoretical explanation and mechanism of porous formation were also added, which would be important for the scaling-up prediction and estimation.

Keywords: Porous structure film; ATO particle; Ultra-low refractive index; vertical drop method; Low-density material;

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Authors: Shaharin A. Sulaiman, Mizuan Minhat

Abstract:

This paper presents development of an ignition system using spark electrodes for application in a research explosion vessel. A single spark is aimed to be discharged with quantifiable ignition energy. The spark electrode system would enable study of flame propagation, ignitability of fuel-air mixtures and other fundamental characteristics of flames. The principle of the capacitive spark circuit of ASTM is studied to charge an appropriate capacitance connected across the spark gap through a large resistor by a high voltage from the source of power supply until the initiation of spark. Different spark energies could be obtained mainly by varying the value of the capacitance and the supply current. The spark sizes produced are found to be affected by the spark gap, electrode size, input voltage and capacitance value.

Keywords: Ignition, Spark Electrode, Flame

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Authors: Amir A. N, Fadzilan A. M, Baskaran G.

Abstract:

In this paper, we proposed an invention of an accessory into a communication device that will help humans to be connected universally. Generally, this device will be made up of crystal and will combine many technologies that will enable the user to run various applications and software anywhere and everywhere. Bringing up the concept of from being user friendly, we had used the crystal as the main material of the device that will trap the surrounding lights to produce projection of its screen. This leads to a lesser energy consumption and allows smaller sized battery to be used, making the device less bulky. Additionally, we proposed the usage of micro batteries as our energy source. Thus, researches regarding crystal were made along with explanations in details of specification and function of the technology used in the device. Finally, we had also drawn several views of the invention from different sides to be visualized.

Keywords: Crystal, Communication Technology, Future concept device, Micro batteries.

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Authors: H. M. Farghally, N. M. Ahmed, H. T. El-Madany, D. M. Atia, F. H. Fahmy

Abstract:

Energy is required in almost every aspect of human activities and development of any nation in the world. Increasing fossil fuel price, energy security and climate change have important bearings on sustainable development of any nation. The renewable energy technology is considered one of the drastic approaches which taken over the world to reduce the energy problem. The preservation of vegetables by freezing is one of the most important methods of retaining quality in agricultural products over long-term storage periods. Freezing factories show high demand of energy for both heat and electricity; the hybrid Photovoltaic/Thermal (PV/T) systems could be used in order to meet this requirement. This paper presents PV/T system design for freezing factory. Also, the complete mathematical modeling and MATLAB SIMULINK of PV/T collector is introduced. The sensitivity analysis for the manufacturing parameters of PV/T collector is carried out to study their effect on both thermal and electrical efficiency.

Keywords: Renewable energy, Hybrid PV/T system, Sensitivity analysis.

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Authors: Arnab Majumdar, Sanjoy Sadhukhan

Abstract:

Although gun barrel steels are an important variety from defense view point, available literatures are very limited. In the present work, an IF grade Ni-Cr-Mo-V high strength low alloy steel is produced in Electric Earth Furnace-ESR Route. Ingot was hot forged to desired dimension with a reduction ratio of 70-75% followed by homogenization, hardening and tempering treatment. Sample chemistry, NMIR, macro and micro structural analyses were done. Mechanical properties which include tensile, impact, and fracture toughness were studied. Ultrasonic testing was done to identify internal flaws. The existing high strength low alloy Ni-Cr-Mo-V steel shows improved properties in modified processing route and heat treatment schedule in comparison to properties noted earlier for manufacturing of gun barrels. The improvement in properties seems to withstand higher explosive loads with the same amount of steel in gun barrel application.

Keywords: Gun barrel steels, IF grade, physical properties, thermal and mechanical processing, mechanical properties, ultrasonic testing.

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Authors: Hachmia Faqihi, Maarouf Saad, Khalid Benjelloun, Mohammed Benbrahim, M. Nabil Kabbaj

Abstract:

This paper investigates and presents a cable-driven robot to lower limb rehabilitation use in sagittal plane. The presented rehabilitation robot is used for a trajectory tracking in joint space. The paper covers kinematic and dynamic analysis, which reveals the tensionability of the used cables as being the actuating source to provide a rehabilitation exercises of the human leg. The desired trajectory is generated to be used in the control system design in joint space. The obtained simulation results is showed to be efficient in this kind of application.

Keywords: Cable-driven multibody system, computed-torque controller, lower limb rehabilitation, tracking trajectory.

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Authors: S. Gao, S. Srirattayawong

Abstract:

In this study, a computational fluid dynamics (CFD) model has been developed for studying the effect of surface roughness profile on the EHL problem. The cylinders contact geometry, meshing and calculation of the conservation of mass and momentum equations are carried out using the commercial software packages ICEMCFD and ANSYS Fluent. The user defined functions (UDFs) for density, viscosity and elastic deformation of the cylinders as the functions of pressure and temperature are defined for the CFD model. Three different surface roughness profiles are created and incorporated into the CFD model. It is found that the developed CFD model can predict the characteristics of fluid flow and heat transfer in the EHL problem, including the main parameters such as pressure distribution, minimal film thickness, viscosity, and density changes. The results obtained show that the pressure profile at the center of the contact area directly relates to the roughness amplitude. A rough surface with kurtosis value of more than 3 has greater influence over the fluctuated shape of pressure distribution than in other cases.

Keywords: CFD, EHL, Kurtosis, Surface roughness.

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Authors: D.Toghraie, A.R.Azimian

Abstract:

Molecular dynamics simulation of annular flow boiling in a nanochannel with 70000 particles is numerically investigated. In this research, an annular flow model is developed to predict the superheated flow boiling heat transfer characteristics in a nanochannel. To characterize the forced annular boiling flow in a nanochannel, an external driving force F ext ranging from 1to12PN (PN= Pico Newton) is applied along the flow direction to inlet fluid particles during the simulation. Based on an annular flow model analysis, it is found that saturation condition and superheat degree have great influences on the liquid-vapor interface. Also, the results show that due to the relatively strong influence of surface tension in small channel, the interface between the liquid film and vapor core is fairly smooth, and the mean velocity along the stream-wise direction does not change anymore.

Keywords: Lennard-Jones Potential, Molecular DynamicsSimulation, Periodic Boundary Conditions (PBC), Non-EquilibriumMolecular Dynamics (NEMD), Annular Flow Boiling

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Authors: Tahereh Talebi, Reza Ghomashchi, Pejman Talemi, Sima Aminorroaya

Abstract:

A high quality crack-free film of Bi₂Te₃ material has been deposited for the first time using electrophoretic deposition (EPD) and microstructures of various films have been investigated. One of the most important thermoelectric (TE) applications is Bi₂Te₃ to manufacture TE generators (TEG) which can convert waste heat into electricity targeting the global warming issue. However, the high cost of the manufacturing process of TEGs keeps them expensive and out of reach for commercialization. Therefore, utilizing EPD as a simple and cost-effective method will open new opportunities for TEG’s commercialization. This method has been recently used for advanced materials such as microelectronics and has attracted a lot of attention from both scientists and industry. In this study, the effect of media of suspensions has been investigated on the quality of the deposited films as well as their microstructure. In summary, finding an appropriate suspension is a critical step for a successful EPD process and has an important effect on both the film’s quality and its future properties.

Keywords: Bi2Te3, electrical conductivity, electrophoretic deposition, thermoelectric materials, thick films.

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Authors: Behrouzinia P., Irani R. A., Saidi M.H.

Abstract:

In this paper, a one-dimensional numerical approach is used to study the effect of applying electrohydrodynamics on the temperature and species mass fraction profiles along the microcombustor. Premixed mixture is H2-Air with a multi-step chemistry (9 species and 19 reactions). In the micro-scale combustion because of the increasing ratio of area-to-volume, thermal and radical quenching mechanisms are important. Also, there is a significant heat loss from the combustor walls. By inserting a number of electrodes into micro-combustor and applying high voltage to them corona discharge occurs. This leads in moving of induced ions toward natural molecules and colliding with them. So this phenomenon causes the movement of the molecules and reattaches the flow to the walls. It increases the velocity near the walls that reduces the wall boundary layer. Consequently, applying electrohydrodynamics mechanism can enhance the temperature profile in the microcombustor. Ultimately, it prevents the flame quenching in microcombustor.

Keywords: micro-combustor, electrohydrodynamics, temperature profile, wall quenching

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Authors: Ioannis Neokosmidis, Nikos Gkekas, Thomas Kamalakis, Thomas Sphicopoulos

Abstract:

In high powered dense wavelength division multiplexed (WDM) systems with low chromatic dispersion, four-wave mixing (FWM) can prove to be a major source of noise. The MultiCanonical Monte Carlo Method (MCMC) and the Split Step Fourier Method (SSFM) are combined to accurately evaluate the probability density function of the decision variable of a receiver, limited by FWM. The combination of the two methods leads to more accurate results, and offers the possibility of adding other optical noises such as the Amplified Spontaneous Emission (ASE) noise.

Keywords: Monte Carlo, Nonlinear optics, optical crosstalk, Wavelength-division Multiplexing (WDM).

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Authors: Mahmoud M. Tash, S. Alkahtani

Abstract:

The present study was undertaken to investigate the effect of pre-aging and aging parameters (time and temperature) on the mechanical properties of Al-Mg-Zn (7075) alloys. Ultimate tensile strength, 0.5% offset yield strength and % elongation measurements were carried out on specimens prepared from cast and heat treated 7075 alloys. Aging treatments were carried out for the as solution treated (SHT) specimens (after quenching in warm water). The specimens were aged at different conditions; Natural aging was carried out at room temperature for different periods of time. Double aging was performed for SHT conditions (pre-aged at different time and temperature followed by high temperature aging). Ultimate tensile strength, yield strength and % elongation as a function of different pre-aging and aging parameters are analyzed to acquire an understanding of the effects of these variables and their interactions on the mechanical properties of Be-treated 7075 alloys.

Keywords: Duplex Aging Treatment, Mechanical Properties, Al-Mg-Zn (7075) alloys.

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Authors: Bit-Na Kwon, Dong-Hyun Ha, Hyoung-Kyu Song

Abstract:

In wireless communication, space-time block code (STBC), cyclic delay diversity (CDD) and space-time cyclic delay diversity (STCDD)are used as the spatial diversity schemes and have been widely studied for the reliablecommunication. If these schemes are used, the communication system can obtain the improved performance. However,the quality of the system is degraded when the distance between a source and a destination is distant in wireless communication system. In this paper, the cooperative transmission scheme using two sources is proposed and improves the performance of the wireless communication system.

Keywords: OFDM, Cooperative communication, CDD, STBC, STCDD.

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