Search results for: optimized bias current density

Authors: H. Madi, L. Mouzai, M. Bouhadef

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The purpose of this article is to study the effects of plants cover on overland flow and, therefore, its influences on the amount of eroded and transported soil. In this investigation, all the experiments were conducted in the LEGHYD laboratory using a rainfall simulator and a soil tray. The experiments were conducted using an experimental plot (soil tray) which is 2m long, 0.5 m wide and 0.15 m deep. The soil used is an agricultural sandy soil (62,08% coarse sand, 19,14% fine sand, 11,57% silt and 7,21% clay). Plastic rods (4 mm in diameter) were used to simulate the plants at different densities: 0 stem/m2 (bared soil), 126 stems/m², 203 stems/m², 461 stems/m² and 2500 stems/m²). The used rainfall intensity is 73mm/h and the soil tray slope is fixed to 3°. The results have shown that the overland flow velocities decreased with increasing stems density, and the density cover has a great effect on sediment concentration. Darcy–Weisbach and Manning friction coefficients of overland flow increased when the stems density increased. Froude and Reynolds numbers decreased with increasing stems density and, consequently, the flow regime of all treatments was laminar and subcritical. From these findings, we conclude that increasing the plants cover can efficiently reduce soil loss and avoid denuding the roots plants.

Keywords: Soil erosion, vegetation, stems density, overland flow.

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Authors: Kimberly Jane S. Uy, Patricia Angela Reyes-Abu, Wen Yaw Chung

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A high precision temperature insensitive current and voltage reference generator is presented. It is specifically developed for temperature compensated oscillator. The circuit, designed using MXIC 0.5um CMOS technology, has an operating voltage that ranges from 2.6V to 5V and generates a voltage of 1.21V and a current of 6.38 ӴA. It exhibits a variation of ±0.3nA for the current reference and a stable output for voltage reference as the temperature is varied from 0°C to 70°C. The power supply rejection ratio obtained without any filtering capacitor at 100Hz and 10MHz is -30dB and -12dB respectively.

Keywords: Current reference, voltage reference, threshold voltage, temperature compensation, mobility.

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Authors: Waluyo, Ngapuli I. Sinisuka, Suwarno, Maman A. Djauhari

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This paper presents the experimental results of comparison between leakage currents and discharge currents. The leakage currents were obtained on polluted porcelain insulator. Whereas, the discharge currents were obtained on lightly artificial polluted porcelain specimen. The conducted measurements were leakage current or discharge current and applied voltage. The insulator or specimen was in a hermetically sealed chamber, and the current waveforms were analyzed using FFT. The result indicated that the leakage current (LC) on low RH condition the fifth harmonic would be visible, and followed by the seventh harmonic. The insulator had capacitive property. Otherwise, on 99% relative humidity, the fifth harmonic would also be visible, and the phase angle reached up to 12.2 degree. Whereas, on discharge current, the third harmonic would be visible, and followed by fifth harmonic. The third harmonic would increase as pressure reduced. On this condition, the specimen had a non-linear characteristics

Keywords: leakage current, discharge current, third harmonic, fifth harmonic, porcelain.

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Authors: Peter Odero Akuon

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A rain cell ratio model is proposed that computes attenuation of the smallest rain cell which represents the maximum rain rate value i.e. the cell size when rainfall rate is exceeded 0.01% of the time, R_0.01 and predicts attenuation for other cells as the ratio with this maximum. This model incorporates the dependence of the path factor r on the ellipsoidal path variation of the Fresnel zone at different frequencies. In addition, the inhomogeneity of rainfall is modeled by a rain drop packing density factor. In order to derive the model, two empirical methods that can be used to find rain cell size distribution D_c are presented. Subsequently, attenuation measurements from different climatic zones for terrestrial radio links with frequencies F in the range 7-38 GHz are used to test the proposed model. Prediction results show that the path factor computed from the rain cell ratio technique has improved reliability when compared with other path factor and effective rain rate models, including the current ITU-R 530-15 model of 2013.

Keywords: Packing density of rain drops, prediction model, rain attenuation, rain cell ratio technique.

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Authors: S. Sobhanian, H. Naghshara, N. Sadeghi, S. Khorram

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The absolute Cu atoms density in Cu(2S1/2ÔåÉ2P1/2) ground state has been measured by Resonance Optical Absorption (ROA) technique in a DC magnetron sputtering deposition with argon. We measured these densities under variety of operation conditions: pressure from 0.6 μbar to 14 μbar, input power from 10W to 200W and N2 mixture from 0% to 100%. For measuring the gas temperature, we used the simulation of N2 rotational spectra with a special computer code. The absolute number density of Cu atoms decreases with increasing the N2 percentage of buffer gas at any conditions of this work. But the deposition rate, is not decreased with the same manner. The deposition rate variation is very small and in the limit of quartz balance measuring equipment accuracy. So we conclude that decrease in the absolute number density of Cu atoms in magnetron plasma has not a big effect on deposition rate, because the diffusion of Cu atoms to the chamber volume and deviation of Cu atoms from direct path (towards the substrate) decreases with increasing of N2 percentage of buffer gas. This is because of the lower mass of N2 atoms compared to the argon ones.

Keywords: Deposition rate, Resonance Optical Absorption, Sputtering.

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Authors: Shreyash Sinai Kunde, Siddhang Tendulkar, Shiv Prakash Gupta, Gaurav Kumar, Suresh Mikkili

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One of the major power quality concerns in modern times is the problem of current harmonics. The current harmonics is caused due to the increase in non-linear loads which is largely dominated by power electronics devices. The Shunt active filtering is one of the best solutions for mitigating current harmonics. This paper describes a fuzzy logic controller based (FLC) based three Phase Shunt active Filter to achieve low current harmonic distortion (THD) and Reactive power compensation. The performance of fuzzy logic controller is analysed under both balanced sinusoidal and unbalanced sinusoidal source condition. The above controller serves the purpose of maintaining DC Capacitor Voltage constant. The proposed shunt active filter uses hysteresis current controller for current control of IGBT based PWM inverter. The simulation results of model in Simulink MATLAB reveals satisfying results.

Keywords: Shunt active filter, Current harmonics, Fuzzy logic controller, Hysteresis current controller.

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Authors: M. Ahmadi Baseri, R. Mokhtari Malekabadi, A. Gandomkar

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Cities expansion, urban travels increase, the technology development, the automobile price cheapen, and the families' income ascending cause the considerable increase in automobile numbers of the city. This fact has led to the traffic creation and the automobile parking site shortage in the city. Also in Esfahan metropolis, the parking lots shortage has been the great problem of this town; in addition, in designing and constructing of the parking sites the traditional methods are utilized which do not have a reasonable and optimized usage of the valuable urban lands. In this article, by introducing the prefabricate mechanized parking system which is inexpensive, simple and quick, and occupies very small space, therefore provides the high content of parking site for the cities, we can eliminate the parking space shortage difficulty of the cities. The achieved results of this research represent that an optimized utilization of the existent urban spaces for parking site construction has not been accomplished. By employing the new parking site technologies such as mechanization categorized parking sites and the capacity prefabricate mechanized of each parking space have become 8 multiples; in this case, the valuable urban lands can be used in an optimized way.

Keywords: Public parking sites, New parking sites technologies, Prefabricate mechanized parking site, Isfahan City.

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Authors: Eggertson, E.C. Kapulla, R, Fokken, J, Prasser, H.M.

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The turbulent mixing of coolant streams of different temperature and density can cause severe temperature fluctuations in piping systems in nuclear reactors. In certain periodic contraction cycles these conditions lead to thermal fatigue. The resulting aging effect prompts investigation in how the mixing of flows over a sharp temperature/density interface evolves. To study the fundamental turbulent mixing phenomena in the presence of density gradients, isokinetic (shear-free) mixing experiments are performed in a square channel with Reynolds numbers ranging from 2-500 to 60-000. Sucrose is used to create the density difference. A Wire Mesh Sensor (WMS) is used to determine the concentration map of the flow in the cross section. The mean interface width as a function of velocity, density difference and distance from the mixing point are analyzed based on traditional methods chosen for the purposes of atmospheric/oceanic stratification analyses. A definition of the mixing layer thickness more appropriate to thermal fatigue and based on mixedness is devised. This definition shows that the thermal fatigue risk assessed using simple mixing layer growth can be misleading and why an approach that separates the effects of large scale (turbulent) and small scale (molecular) mixing is necessary.

Keywords: Concentration measurements, Mixedness, Stablystratified turbulent isokinetic mixing layer, Wire mesh sensor

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Authors: Abdelgawad, Salah El-Tahawy

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This paper aimed to establish econometrical equation models for the Nile delta region in Egypt, which will represent a basement for future predictions of Lumpy skin disease outbreaks and its pathway in relation to climate change. Data of lumpy skin disease (LSD) outbreaks were collected from the cattle farms located in the provinces representing the Nile delta region during 1 January, 2015 to December, 2015. The obtained results indicated that there was a significant association between the degree of the LSD outbreaks and the investigated climate factors (temperature, wind speed, and humidity) and the outbreaks peaked during the months of June, July, and August and gradually decreased to the lowest rate in January, February, and December. The model obtained depicted that the increment of these climate factors were associated with evidently increment on LSD outbreaks on the Nile Delta of Egypt. The model validation process was done by the root mean square error (RMSE) and means bias (MB) which compared the number of LSD outbreaks expected with the number of observed outbreaks and estimated the confidence level of the model. The value of RMSE was 1.38% and MB was 99.50% confirming that this established model described the current association between the LSD outbreaks and the change on climate factors and also can be used as a base for predicting the of LSD outbreaks depending on the climatic change on the future.

Keywords: LSD, climate factors, econometric models, Nile Delta.

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Authors: Parchami A., Fatahian Dehkordi RF.

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The aim of the present investigation was to compare sex differences in thyroid gland structure of rabbits. Five adult male and five adult female (3.1-3.5 kg body weight) New Zealand white rabbits were used in the experiment. Results showed that at light microscopic level, there was no sex difference in microscopic appearance of the thyroid glands. At electron microscopic level, however, the mitochondria and the microvilli of the follicular cells are more numerous and the Golgi complex is also more extensive in male rabbits in comparison to females. Results obtained from micrometric measurements showed that the volume density of the follicles is higher in males than in females, but the differences are not statistically significant .The volume density of epithelium and the height of follicular cells are significantly greater in males than in females and reverse is true about the volume density of interstitium (p<0.05). The volume density of colloid is also greater in females (66±6) than in males (60±7) but the differences are not statistically significant .It was concluded that sex has limited effects on histomorphometric properties of thyroid gland in rabbits.

Keywords: Rabbit, Thyroid Gland, Sex difference, Electron microscope

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Authors: Han Run-Sheng, Li Wen-Yao, Wang Feng, Liu Fei, Qiu Wen-Long, Lei Li

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Accurately positioning detection of concealed deposits or ore-bodies is one of the difficult problems in mineral exploration field. Theory calculation and exploration practices for tunnel gravity indicate that 3D high-precision Tunnel Gravity Exploration Method (TGEM) can find concealed high-density three-dimensional ore-bodies in the depth. The ore-finding breakthroughs at the depth of the Zhaotong Maoping carbonate-hosted Zn–Pb–(Ag–Ge) deposit in Northeastern Yunnan have proved that the exploration method in combination with MEAHFZ method is effective to detect concealed high-density ore-bodies. TGEM may overcome anomalous ambiguity of other geophysical methods for 3D positioning of concealed ore-bodies.

Keywords: 3D tunnel gravity exploration method, concealed high-density ore-bodies, Zn–Pb–(Ag–Ge) deposit, Zaotong Maoping, Northeastern Yunnan.

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Authors: Tony Schönherr, Kimiya Komurasaki, Georg Herdrich

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The performance and the plasma created by a pulsed magnetoplasmadynamic thruster for small satellite application is studied to understand better the ablation and plasma propagation processes occurring during the short-time discharge. The results can be applied to improve the quality of the thruster in terms of efficiency, and to tune the propulsion system to the needs required by the satellite mission. Therefore, plasma measurements with a high-speed camera and induction probes, and performance measurements of mass bit and impulse bit were conducted. Values for current sheet propagation speed, mean exhaust velocity and thrust efficiency were derived from these experimental data. A maximum in current sheet propagation was found by the high-speed camera measurements for a medium energy input and confirmed by the induction probes. A quasilinear tendency between the mass bit and the energy input, the current action integral respectively, was found, as well as a linear tendency between the created impulse and the discharge energy. The highest mean exhaust velocity and thrust efficiency was found for the highest energy input.

Keywords: electric propulsion, low-density plasma, pulsed magnetoplasmadynamicthruster, space engineering.

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Authors: Karama M. AL-Tamimi, Munir A. Al-Absi

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A new OTA-based logarithmic-control variable gain current amplifier (LCCA) is presented. It consists of two Operational Transconductance Amplifier (OTA) and two PMOS transistors biased in weak inversion region. The circuit operates from 0.6V DC power supply and consumes 0.6 μW. The linear-dB controllable output range is 43 dB with maximum error less than 0.5dB. The functionality of the proposed design was confirmed using HSPICE in 0.35μm CMOS process technology.

Keywords: LCCA, OTA, Logarithmic, VGA, Weak inversion, Current-mode

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Authors: Ram Kumar Soni, Alok Jain, Rajiv Saxena

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The tree structured approach of non-uniform filterbank (NUFB) is normally used in perfect reconstruction (PR). The PR is not always feasible due to certain limitations, i.e, constraints in selecting design parameters, design complexity and some times output is severely affected by aliasing error if necessary and sufficient conditions of PR is not satisfied perfectly. Therefore, there has been generalized interest of researchers to go for near perfect reconstruction (NPR). In this proposed work, an optimized tree structure technique is used for the design of NPR non-uniform filterbank. Window functions of Blackman family are used to design the prototype FIR filter. A single variable linear optimization is used to minimize the amplitude distortion. The main feature of the proposed design is its simplicity with linear phase property.

Keywords: Tree structure, NUFB, QMF, NPR.

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Authors: Somayeh Gholami, Meysam Khakbaz

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The current-voltage characteristics of a PtSi/p-Si Schottky barrier diode was measured at the temperature of 85 K and from the forward bias region of the I-V curve, the electrical parameters of the diode were measured by three methods. The results obtained from the two methods which considered the series resistance were in close agreement with each other and from them barrier height (
), ideality factor (n) and series resistance () were found to be 0.2045 eV, 2.877 and 14.556 K
respectively. By measuring the I-V characteristics in the temperature range of 85-136 K the electrical parameters were observed to have strong dependency on temperature. The increase of barrier height and decrease of ideality factor with increasing temperature is attributed to the existence of barrier height inhomogeneities in the silicide-semiconductor structure.

Keywords: Schottky diode, barrier height, series resistance, I-V, barrier height inhomogeneities.

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Authors: Romisaa Ali

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The Policy Gradient approach is a subset of the Deep Reinforcement Learning (DRL) combines Deep Neural Networks (DNN) with Reinforcement Learning (RL). This approach finds the optimal policy of robot movement, based on the experience it gains from interaction with its environment. Unlike previous policy gradient algorithms, which were unable to handle the two types of error variance and bias introduced by the DNN model due to over- or underestimation, this algorithm is capable of handling both types of error variance and bias. This article will discuss the state-of-the-art SOTA policy gradient technique, trust region policy optimization (TRPO), by applying this method in various environments compared to another policy gradient method, the Proximal Policy Optimization (PPO), to explain their robust optimization, using this SOTA to gather experience data during various training phases after observing the impact of hyper-parameters on neural network performance.

Keywords: Deep neural networks, deep reinforcement learning, Proximal Policy Optimization, state-of-the-art, trust region policy optimization.

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Authors: Krzysztof Wawryn, Robert Suszyński, Bogdan Strzeszewski

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This paper presents two prototypes of low power low voltage current mode 9 bit pipelined a/d converters. The first and the second converters are configured of 1.5 bit and 2.5 bit stages, respectively. The a/d converter structures are composed of current mode building blocks and final comparator block which converts the analog current signal into digital voltage signal. All building blocks have been designed in CMOS AMS 0.35μm technology, then simulated to verify proposed concept. The performances of both converters are compared to performances of known current mode and voltage mode switched capacitance converter structures. Low power consumption and small chip area are advantages of the proposed converters.

Keywords: Pipelined converter, a/d converter, low power, lowvoltage, current mode.

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Authors: N. Tugrul, E. Sariburun, F. T. Senberber, A. S. Kipcak, E. Moroydor Derun, S. Piskin

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Boron-gypsum is a waste which occurs in the boric acid production process. In this study, the boron content of this waste is evaluated for the use in synthesis of magnesium borates and such evaluation of this kind of waste is useful more than storage or disposal. Magnesium borates, which are a sub-class of boron minerals, are useful additive materials for the industries due to their remarkable thermal and mechanical properties. Magnesium borates were obtained hydrothermally at different temperatures. Novelty of this study is the search of the solution density effects to magnesium borate synthesis process for the increasing the possibility of borongypsum usage as a raw material. After the synthesis process, products are subjected to XRD and FT-IR to identify and characterize their crystal structure, respectively.

Keywords: Boron-gypsum, hydrothermal synthesis, magnesium borate, solution density.

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Authors: N. Shanmugapriya, R. Nallusamy

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Content-based image retrieval (CBIR) uses the contents of images to characterize and contact the images. This paper focus on retrieving the image by separating images into its three color mechanism R, G and B and for that Discrete Wavelet Transformation is applied. Then Wavelet based Generalized Gaussian Density (GGD) is practical which is used for modeling the coefficients from the wavelet transforms. After that it is agreed to Histogram of Oriented Gradient (HOG) for extracting its characteristic vectors with Relevant Feedback technique is used. The performance of this approach is calculated by exactness and it confirms that this method is wellorganized for image retrieval.

Keywords: Content-Based Image Retrieval (CBIR), Relevant Feedback, Histogram of Oriented Gradient (HOG), Generalized Gaussian Density (GGD).

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Authors: E. Selçuk, Z. Karaçor, P. Yardımcı

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Trade liberalization and its effects on the economies of developing countries have been investigated by many different studies, and some of them have focused on its impact on the current account balance. Turkey, as being one of the countries, which has liberalized its foreign trade in the 1980s, also needs to be studied in terms of the impact of liberalization on current account deficits. Therefore, the aim of this study is to find out whether trade liberalization has affected Turkey’s trade and current account balances. In order to determine this, yearly data of Turkey from 1980 to 2013 is used. As liberalization dummy, the year 1989, which was set for Turkey, is selected. Structural break test and model estimation results show that trade liberalization has a negative impact on trade balance but do not have a significant impact on the current account balance.

Keywords: Budget deficit, current account, liberalization, Turkish economy.

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Authors: K. G. Firouzjah, A. Sheikholeslami

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The perfect operation of common Active Filters is depended on accuracy of identification system distortion. Also, using a suitable method in current injection and reactive power compensation, leads to increased filter performance. Due to this fact, this paper presents a method based on predictive current control theory in shunt active filter applications. The harmonics of the load current is identified by using o–d–q reference frame on load current and eliminating the DC part of d–q components. Then, the rest of these components deliver to predictive current controller as a Threephase reference current by using Park inverse transformation. System is modeled in discreet time domain. The proposed method has been tested using MATLAB model for a nonlinear load (with Total Harmonic Distortion=20%). The simulation results indicate that the proposed filter leads to flowing a sinusoidal current (THD=0.15%) through the source. In addition, the results show that the filter tracks the reference current accurately.

Keywords: Active filter, predictive current control, low pass filter, harmonic omitting, o–d–q reference frame.

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Authors: Tsietsi J. Pilusa, Robert Huberts, Edison Muzenda

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In this study, the theoretical relationship between pressure and density was investigated on cylindrical hollow fuel briquettes produced of a mixture of fibrous biomass material using a screw press without any chemical binder. The fuel briquettes were made of biomass and other waste material such as spent coffee beans, mielie husks, saw dust and coal fines under pressures of 0.878-2.2 Mega Pascals (MPa). The material was densified into briquettes of outer diameter of 100mm, inner diameter of 35mm and 50mm long. It was observed that manual screw compression action produces briquettes of relatively low density as compared to the ones made using hydraulic compression action. The pressure and density relationship was obtained in the form of power law and compare well with other cylindrical solid briquettes made using hydraulic compression action. The produced briquettes have a dry density of 989 kg/m3 and contain 26.30% fixed carbon, 39.34% volatile matter, 10.9% moisture and 10.46% ash as per dry proximate analysis. The bomb calorimeter tests have shown the briquettes yielding a gross calorific value of 18.9MJ/kg.

Keywords: Bio briquettes, biomass fuel, coffee grounds, fuelbriquettes

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Authors: Farag Ahwide, Souhel Bousheha

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A technical assessment has been made of electricity generation, considering wind turbines ranging between Vestas (V80-2.0 MW and V112-3.0 MW) and the air density is equal to 1.225 Kg/m3, at different towns in Libya. Wind speed might have been measured each 3 hours during 10 m stature at a time for 10 quite sometime between 2000 Furthermore 2009, these towns which are spotted on the bank from claiming Mediterranean ocean also how in the desert, which need aid Derna 1, Derna 2, Shahat, Benghazi, Ajdabya, Sirte, Misurata, Tripoli-Airport, Al-Zawya, Al-Kofra, Sabha, Nalut. The work presented long term "wind data analysis in terms of annual, seasonal, monthly and diurnal variations at these sites. Wind power density with different heights has been studied. Excel sheet program was used to calculate the values of wind power density and the values of wind speed frequency for the stations; their seasonally values have been estimated. Limit variable with rated wind pace to 10 different wind turbines need to be been estimated, which is used to focus those required yearly vitality yield of a wind vitality change framework (WECS), acknowledging wind turbines extending between 600 kW and 3000 kW).

Keywords: Energy yield, wind turbines, wind speed, wind power density.

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Authors: P Bumb, U Desideri, F Quattrocchi, L Arcioni

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This paper presents the feasibility study of CO2 sequestration from the sources to the sinks in the prospective of Italian Industries. CO2 produced at these sources captured, compressed to supercritical pressures, transported via pipelines and stored in underground geologic formations such as depleted oil and natural gas reservoirs, un-minable coal seams and deep saline aquifers. In this work, we present the optimized pipeline infrastructure for the CO2 with appropriate constraints to find lower cost system by the use of nonlinear optimization software LINGO 11.0. This study was conducted on CO2 transportation complex network of Italian Industries, to find minimum cost network for transporting the CO2 from sources to the sinks.

Keywords: CCS, CO2, ECBM, EU, NAP, LINGO, UNMIG.

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Authors: Petru Manescu, Joseph Azencot, Michael Beuve, Hamid Ladjal, Jacques Saade, Jean-Michel Morreau, Philippe Giraud, Behzad Shariat

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Organ motion, especially respiratory motion, is a technical challenge to radiation therapy planning and dosimetry. This motion induces displacements and deformation of the organ tissues within the irradiated region which need to be taken into account when simulating dose distribution during treatment. Finite element modeling (FEM) can provide a great insight into the mechanical behavior of the organs, since they are based on the biomechanical material properties, complex geometry of organs, and anatomical boundary conditions. In this paper we present an original approach that offers the possibility to combine image-based biomechanical models with particle transport simulations. We propose a new method to map material density information issued from CT images to deformable tetrahedral meshes. Based on the principle of mass conservation our method can correlate density variation of organ tissues with geometrical deformations during the different phases of the respiratory cycle. The first results are particularly encouraging, as local error quantification of density mapping on organ geometry and density variation with organ motion are performed to evaluate and validate our approach.

Keywords: Biomechanical simulation, dose distribution, image guided radiation therapy, organ motion, tetrahedral mesh, 4D-CT.

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Authors: Zhiping Wu, Meiqin Chen, Haikuan Yang, Yunchu Hu

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Fire disaster is the major factor to endanger the public and environmental safety. People lost their life during fire disaster mainly be attributed to the dense smoke and toxic gas under combustion, which hinder the escape of people and the rescue of firefighters under fire disaster. The smoke suppression effect of several transitional metals oxide on the epoxy resin treated with intumescent flame retardant and titanate couple agent (EP/IFR/Titanate) system have been investigated. The results showed manganese dioxide has great effect on reducing the smoke density rate (SDR) of EP/IFR/Titanate system; however it has little effect to reduce the maximum smoke density (MSD) of EP/IFR/Titanate system. Copper oxide can decrease the maximum smoke density (MSD) and smoke density rate of EP/IFR/Titanate system substantially. The MSD and SDR of EP/IFR/Titanate system can reduce 20.3% and 39.1% respectively when 2% of copper oxide is introduced.

Keywords: copper oxide, epoxy resin, intumescent flameretardant, smoke suppression.

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Authors: Bao Thach Nguyen, Abbas Mohajerani

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A typical flexible pavement structure consists of the surface, base, sub-base and subgrade soil. The loading traffic is transferred from the top layer with higher stiffness to the layer below with less stiffness. Under normal traffic loading, the behaviour of flexible pavement is very complex and can be predicted by using the repeated load triaxial test equipment in the laboratory. However, the nature of the repeated load triaxial testing procedure is considered time-consuming, complicated and expensive, and it is a challenge to carry out as a routine test in the laboratory. Therefore, the current paper proposes a numerical approach to simulate the repeated load triaxial test by employing the discrete element method. A sample with particle size ranging from 2.36mm to 19.0mm was constructed. Material properties, which included normal stiffness, shear stiffness, coefficient of friction, maximum dry density and particle density, were used as the input for the simulation. The sample was then subjected to a combination of deviator and confining stress and it was found that the discrete element method is able to simulate the repeated load triaxial test in the laboratory.

Keywords: Discrete element method, repeated load triaxial, pavement materials.

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Authors: Siming Wang, Qing Ni, Yu Wu, Ruihai Xu, Hong Ye

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Porous electric heaters, compared to conventional electric heaters, exhibit excellent heating performance due to their large specific surface area. Porous electric heaters employ porous metallic materials or conductive porous ceramics as the heating element. The former attains a low heating power with a fixed current due to the low electrical resistivity of metal. Although the latter can bypass the inherent challenges of porous metallic materials, the fabrication process of the conductive porous ceramics is complicated and high cost. This work proposed a porous ceramic electric heater with dielectric honeycomb ceramic as a substrate and surface conductive coating as a heating element. The conductive coating was prepared by the sol-gel method using silica sol and methyl trimethoxysilane as raw materials and graphite powder as conductive fillers. The conductive mechanism and degradation reason of the conductive coating was studied by electrical resistivity and thermal stability analysis. The heating performance of the proposed heater was experimentally investigated by heating air and deionized water. The results indicate that the electron transfer is achieved by forming the conductive network through the contact of the graphite flakes. With 30 wt% of graphite, the electrical resistivity of the conductive coating can be as low as 0.88 Ω∙cm. The conductive coating exhibits good electrical stability up to 500 °C but degrades beyond 600 °C due to the formation of many cracks in the coating caused by the weight loss and thermal expansion. The results also show that the working medium has a great influence on the volume power density of the heater. With air under natural convection as the working medium, the volume power density attains 640.85 kW/m3, which can be increased by 5 times when using deionized water as the working medium. The proposed honeycomb ceramic electric heater has the advantages of the simple fabrication method, low cost, and high-volume power density, demonstrating great potential in the fluid heating field.

Keywords: Conductive coating, honeycomb ceramic electric heater, high specific surface area, high volume power density.

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Authors: Wullapa Wongsinlatam

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Back propagation algorithm (BP) is a widely used technique in artificial neural network and has been used as a tool for solving the time series problems, such as decreasing training time, maximizing the ability to fall into local minima, and optimizing sensitivity of the initial weights and bias. This paper proposes an improvement of a BP technique which is called IM-COH algorithm (IM-COH). By combining IM-COH algorithm with cuckoo search algorithm (CS), the result is cuckoo search improved control output hidden layer algorithm (CS-IM-COH). This new algorithm has a better ability in optimizing sensitivity of the initial weights and bias than the original BP algorithm. In this research, the algorithm of CS-IM-COH is compared with the original BP, the IM-COH, and the original BP with CS (CS-BP). Furthermore, the selected benchmarks, four time series samples, are shown in this research for illustration. The research shows that the CS-IM-COH algorithm give the best forecasting results compared with the selected samples.

Keywords: Artificial neural networks, back propagation algorithm, time series, local minima problem, metaheuristic optimization.

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Authors: R. Rama Kishore, Sunesh

Abstract:

This paper presents an optimized, robust, and secured watermarking technique. The methodology used in this work is the combination of entropy and chaotic grid map. The proposed methodology incorporates Discrete Cosine Transform (DCT) on the host image. To improve the imperceptibility of the method, the host image DCT blocks, where the watermark is to be embedded, are further optimized by considering the entropy of the blocks. Chaotic grid is used as a key to reorder the DCT blocks so that it will further increase security while selecting the watermark embedding locations and its sequence. Without a key, one cannot reveal the exact watermark from the watermarked image. The proposed method is implemented on four different images. It is concluded that the proposed method is giving better results in terms of imperceptibility measured through PSNR and found to be above 50. In order to prove the effectiveness of the method, the performance analysis is done after implementing different attacks on the watermarked images. It is found that the methodology is very strong against JPEG compression attack even with the quality parameter up to 15. The experimental results are confirming that the combination of entropy and chaotic grid map method is strong and secured to different image processing attacks.

Keywords: Digital watermarking, discrete cosine transform, chaotic grid map, entropy.

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