196,331 research outputs found
Performance improvement of pulse width-amplitude modulation-based quasi-Z-source inverters: Analysis and implementation
No full textPulse width-amplitude modulation (PWAM) have been widely used in recent years to mitigate switching losses as well as reducing passive components' size. This paper precisely investigates this modulation approach in quasi-Z-source inverters (qZSI). It will be concluded that the existence of capacitive paths from load to source in such converters causes two undesired behaviors while utilizing PWAM, which increases total harmonic distortion and semiconductor stresses. Bypassing the capacitive paths is proposed in this paper to alleviate these issues. In order to implement this approach, a bidirectional quasi-Z-source inverter is studied. A design procedure is presented to achieve a fast dynamic response for tracking reference voltage. The operation of both conventional and bidirectional qZSI under different loads including resistive and resistive–inductive loads is investigated in the simulation and experiment. According to experimental results, by utilizing bidirectional qZSI, THD is improved from 12.34% to 3.51% for a lag load. Moreover, the voltage stress of the semiconductor no longer exists
Evaluation and selection of thin-layer models for drying kinetics of apricot (cv. NASIRY)
No full textE. Mirzaee, S. Rafiee, A. Keyhani(Agricultural Machinery Engineering Department, Faculty of Agricultural Engineering and Technology, University of Tehran, Karaj, Iran) Abstract: This paper presents the thin layer drying behavior of apricot (cv. NASIRY) at the air temperatures of 40ºC, 50ºC, 60ºC, 70ºC and air velocity of 1m/s and 2 m/s. In order to select a suitable form of the drying curve, 12 different thin layer drying models were fitted to experimental data. Fick’s second law was used as a major equation to calculate the moisture diffusivity with some simplification. The high values of coefficient of determination and the low values of reduced chi-square and root mean square error indicated that the Logarithmic model and the Midilli et al. model could satisfactorily describe the drying curve of apricot for drying air velocity of 1m/s and 2 m/s, respectively. According to the research results the calculated value of effective moisture diffusivity varied from 1.78×10-10–5.11×10-10 m2/s and the value of activation energy varied from a minimum of 24.01 kJ/mol to a maximum of 25.00 kJ/mol.Keywords: apricot, thin layer drying, effective moisture diffusivity, activation energy Citation: E. Mirzaee, S. Rafiee, A. Keyhani. Evaluation and selection of thin-layer models for drying kinetics of apricot (cv. NASIRY). Agric Eng Int: CIGR Journal, 2010, 12(2): 111-116.  
Smoothness-Increasing Accuracy-Conserving (SIAC) Filtering for Discontinuous Galerkin Solutions: Improved Errors Versus Higher-Order Accuracy
No full textSmoothness-increasing accuracy-conserving (SIAC) filtering has demonstrated its effectiveness in raising the convergence rate of discontinuous Galerkin solutions from order k + 12 to order 2k + 1 for specific types of translation invariant meshes (Cockburn et al. in Math. Comput. 72:577–606, 2003; Curtis et al. in SIAM J. Sci. Comput. 30(1):272–289, 2007; Mirzaee et al. in SIAM J. Numer. Anal. 49:1899–1920, 2011). Additionally, it improves the weak continuity in the discontinuous Galerkin method to k ? 1 continuity. Typically this improvement has a positive impact on the error quantity in the sense that it also reduces the absolute errors. However, not enough emphasis has been placed on the difference between superconvergent accuracy and improved errors. This distinction is particularly important when it comes to understanding the interplay introduced through meshing, between geometry and filtering. The underlying mesh over which the DG solution is built is important because the tool used in SIAC filtering—convolution—is scaled by the geometric mesh size. This heavily contributes to the effectiveness of the post-processor. In this paper, we present a study of this mesh scaling and how it factors into the theoretical errors. To accomplish the large volume of post-processing necessary for this study, commodity streaming multiprocessors were used; we demonstrate for structured meshes up to a 50× speed up in the computational time over traditional CPU implementations of the SIAC filter.Delft Institute of Applied MathematicsElectrical Engineering, Mathematics and Computer Scienc
On the use of boundary conditions and thermophysical properties of nanoparticles for application of nanofluids as coolant in nuclear power plants; a numerical study
No full textIn the first part of the present study, a thermal-hydraulic subchannel code hereafter called ‘SUBTHAC’ is developed to evaluate the enhancement effects of nanoparticles in core heat transfer. The first version of SUBTHAC (V1.0) can analyze the steady state flow of coolant with Al2O3, TiO2 or CuO as nanoparticles (other types of nanoparticles can be added by the user). Different output profiles can be selected such as fluid temperature, pressure and velocity for each subchannel, clad outside temperature for each fuel rod, axial and lateral mass flow, etc. SUBTHAC uses a dedicated algorithm to solve the subchannel equations and, unlike many other codes, allows for thermophysical parameters of nanoparticles to be a function of the temperature, leading to improvement the accuracy of results. Results computed by SUBTHAC for base fluid (pure water) are validated against those obtained by COBRA-EN code. In the next step, with the aim of validating the capability of nanofluid analysis of SUBTHAC code, its nanofluids results have been validated against reference CFD simulations. After the validation, comprehensive numerical comparisons are conducted to assess the enhancement of thermal-hydraulic parameters by using nanofluids. It is shown that, among Al2O3, TiO2 and CuO nanofluids with volumetric concentration in the range of 1–5%, TiO2-3% and CuO-3% are the best choices to increase fluid outlet temperature and decrease clad temperature, respectively. Using nanofluids with a concentration higher than 3% volumetric is not justifiable as the core pressure drop increases up to more than 20%. In the second part of the manuscript, some relevant remarks are put forward on the assignment of boundary conditions (BC, i.e. inlet velocity/inlet mass flux/inlet Reynolds number) and the adoption of reliable values for specific heat capacity of nanoparticles in operational temperature of NPPs. The effects of using the above boundary conditions and incorrect values of the specific heat (as adopted in the literature so far) are depicted by presenting some profiles of coolant and clad temperature. Selecting different BCs and incorrect values of specific heat for nanoparticles can jeopardize the results of calculations
Sources of drug information and drug use behavior among adolescent students in Region VI, Texas
No full textTypescript (photocopy).Purpose. The purpose of this study was to determine sources of drug information as well as the scope of the drug use problem among adolescent students in Texas Education Agency (TEA) Region VI. Furthermore, the intent was to compare 8th and 10th grade students with regard to their sources of drug information, and with regard to their prevalence and frequency of drug use behavior. Procedure. This study was a descriptive-comparative research project. The subjects were 1023 eighth and tenth grade students who were asked to complete a two-part self-administered questionnaire. Analysis of Variance (ANOVA) and Z-Score Test of proportions were used to analyze the data. Results. 1) Television, parents, magazines, friends, and teachers were the most frequently cited sources of providing much or a great amount of drug information. Church, doctors, and police were frequently cited as providing little or no information. 2) Eighth graders reported receiving more information than 10th graders from doctors, teachers, parents, police, and TV. Tenth graders, on the other hand, reported receiving more information from their friends than did 8th graders. 3) With the exception of alcoholic beverages, 8th graders reported receiving more information than 10th graders about all other categories of drugs. 4) Inhalants and marijuana were reported as the most widely used illicit drugs among students. Conclusions. Based on the data analyses and within the limitations of this study, the following conclusions were made: First, TV is a major source of drag information in all categories of drags for adolescent students. Younger students rely on conventional sources such as parents and teachers for drag information. Older students, on the other hand, rely on their friends for their drag information. In general, 8th grade students report receiving more information about drags than do 10th graders. Second, drag use is a problem among adolescent students in this region with alcohol, inhalants and marijuana being reported as the most widely used drags. Prevalence of drug use is higher among older students than among younger students. Tenth graders are using drugs such as alcohol and marijuana more frequently than 8th graders
UV accelerated aging of RTV/SiO2 nanocomposites: Study on surface microstructure, hydrophobicity, and electrical properties
No full textRTV-SiR coatings are widely used to preserve ceramic insulators in high voltage power lines. These coatings enhance insulators’ resistance to environmental factors, such as contamination and moisture, as well as UV irradiation. The functional lifespan of RTV-SiR could be improved via addition of different nanoparticles such as SiO2. In this research, the effect of nano silica content on surface microstructure, hydrophobicity, and electrical properties of RTV-SiR before and after UV irradiation was studied by FESEM, AFM, surface roughness, contact angle, hydrophobicity transfer ability, dielectric parameters, and electric resistance. Results demonstrated that the optimal percentage of filler in the composite could make an appropriate surface roughness and increases hydrophobicity. Also, the excessive destruction of the RTV-SiR caused by UV irradiation is prevented by nano silica. Moreover, the contact angle of the coating reached the first level in a shorter period of time after applying pollution thanks to the presence of nano silica. Eventually, composite samples illustrated better performance than pure RTV-SiR, and the best properties were observed in samples containing 3 wt% silica
Amino-silane co-functionalized h-BN nanofibers with anti-corrosive function for epoxy coating
No full textIn this research, hexagonal boron nitride nanofibers co-functionalized with polydopamine and (3-aminopropyl) triethoxysilane (Fh-BNNFs) are used for developing anti-corrosion solvent-based nanocomposite epoxy coatings. The h-BNNFs are successfully synthesized by utilizing inexpensive precursors of melamine and boric acid. The prepared nanomaterials are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, thermal gravimetric analysis, field emission scanning electron microscopy, and N2 adsorption/desorption isotherms. The corrosion resistance of the pure and nanocomposite epoxy coatings is investigated by electrochemical impedance spectroscopy, Potentiodynamic polarization tests, salt spray, and pull-off adhesion measurements. The results indicate that the epoxy nanocomposite coatings containing optimum amount of the Fh-BNNFs show superior corrosion resistance. Moreover, density functional theory (DFT) method is applied to investigate the energetics and interaction mechanisms at each interface within the epoxy matrix
Dry Sliding Wear and Corrosion Performance of Mg-Sn-Ti Alloys Produced by Casting and Extrusion
No full textThe aim of the present study is to investigate the role of Ti on corrosion and the wear properties of Mg-5Sn-xTi (x = 0, 0.15, 0.75, 1.5 wt.%) alloys. The samples were fabricated by conventional casting followed by hot extrusion, and the studies were examined by means of a pin-on-disc tribometer at various loads of 6, 10, and 20 N with constant sliding velocities of 0.04 m/s at ambient temperature. The corrosion performance, using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), was studied in a basic solution containing 3.5 wt.% NaCl. The observation indicated a drop in the wear rate with an increase in Ti, while the average coefficient of friction was raised in higher Ti contents compared to the base material. The sample with 0.15 wt.% Ti exhibited superior wear properties at 6 and 10 N of normal force, while the sample with 0.75 wt.% Ti presented better wear resistance for 20 N. Electrochemical test observations demonstrated that the Ti deteriorated the corrosion features of the Mg-5Sn alloy, owing to the galvanic effects of Ti. The Mg-5Sn alloy exhibited excellent corrosion behavior (corrosion potential (Ecorr) = −1.45V and current density (Icorr) = 43.92 A/cm2). The results indicated the significant role of Ti content in modulating wear and corrosion resistance of the Mg-5Sn alloy
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
- …
