scholarly journals Multi-Pulse Diode Rectifier for More-Electric Aircraft Applications: Parallel versus Series Topologies

2017 ◽  
Vol 13 (1) ◽  
pp. 138-144
Author(s):  
Ahmed Hafez ◽  
Ali Yousef
Keyword(s):  
Test Rig ◽  
Grid Systems ◽  
Aircraft Systems ◽  
Electric Aircraft ◽  
Analytical Formulas ◽  
Key Variables ◽  
Set Up ◽  
The Impact ◽  
More Electric Aircraft

This article analyzes thoroughly the performance of the Multi-Pulse Diode Rectifiers (MPDRs) regarding the quality of input/output voltage and currents. Two possible arrangements of MPDRs are investigated: series and parallel. The impact of the DC side connection on the performance of the MPDRs regarding the operation parameters and rectifier indices are comprehensively examined. Detailed analytical formulas are advised to identify clearly the key variables that control the operation of MPDRs. Moreover, comprehensive simulation results are presented to quantify the performance and validate the analytical analysis. Test-rig is set up to recognize the promising arrangement of MPDRs. Significant correlation is there between simulation and practical results. The analytical results are presented for aircraft systems (400Hz), and power grid systems (60Hz). This is to study the impact of voltage and frequency levels on the topology type of MPDRs. In general, each topology shows merits and have limitations.

scholarly journals The Impact of Nitrogen Fertilization and the Use of Biostimulants on the Yield of Two Maize Varieties (Zea mays L.) Cultivated for Grain

Agronomy ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1408
Author(s):  
Krzysztof Kapela ◽  
Anna Sikorska ◽  
Marek Niewęgłowski ◽  
Ewa Krasnodębska ◽  
Krystyna Zarzecka ◽  
...  
Keyword(s):  
Nitrogen Fertilization ◽  
Control Object ◽  
Maize Yield ◽  
Family Farm ◽  
Maize Varieties ◽  
Maize Grain ◽  
Set Up ◽  
Hybrid Cultivar ◽  
The Impact

The field experiment was carried out in 2015–2017 on a family farm in Toczyski Czortki, in the Mazovia voivodeship in Poland. The experiment was set up in a split–split–plot system in three replications. The area of one plot was 30 m−2. The studied factors were: I—two maize varieties: PR38N86 (medium late hybrid cultivar 280 FAO), P8400 (medium early hybrid cultivar 240 FAO); II—four doses of nitrogen fertilization: 1. control object—without the use of nitrogen (0 kg N·ha−1), 2. nitrogen dose—80 kg N·ha−1 (applied once before sowing), 3. nitrogen dose—120 kg N·ha−1 (applied once before sowing), 4. nitrogen dose—160 kg N·ha−1 (applied once before sowing); III—four types of biostimulants used: 1. control object—without using a biostimulant, 2. Asahi®SL biostimulant: I term—four-leaf phase (BBCH 14) at a dose of 0.60 dm3∙ha−1, II term—eight-leaf phase (BBCH 18) at a dose of 0.60 dm3∙ha−1, 3. Improver® biostimulant: I term—four-leaf phase (BBCH 14) at a dose of 1.00 dm3∙ha−1, II term—eight-leaf phase (BBCH 18) at a dose of 0.60 dm3∙ha−1, 4. Zeal® biostimulant: I term—six-leaf phase (BBCH 16) at a dose of 2.00 dm3∙ha−1. The aim of the study was to determine the effect of nitrogen fertilization and the use of biostimulants on the size and quality of yield of two varieties of maize grown for grain. Based on the conducted research, it was found that nitrogen doses influenced the amount of maize grain obtained. The highest yields were obtained using 120 kg N∙ha−1. Nitrogen doses significantly affected the studied maize yield components. The dose of 120 kg N∙ha−1 increased the number of grains in the cob, while the dose—160 kg N∙ha−1 exerted the best effect on obtaining the highest values of a thousand seeds. The biostimulants used in the experiment significantly affected the mass of one thousand seeds and the number of grains in the cob. In addition, Asahi®SL, Improver® and Zeal® biostimulants increased maize yield in each growing season studied.

scholarly journals Research on Blade-Casing Rub-Impact Mechanism by Experiment and Simulation in Aeroengines

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Jie Hong ◽  
Tianrang Li ◽  
Zhichao Liang ◽  
Dayi Zhang ◽  
Yanhong Ma
Keyword(s):  
High Speed ◽  
High Performance ◽  
Element Model ◽  
Physical Parameters ◽  
Test Rig ◽  
Calculation Results ◽  
Rotor Support ◽  
Blade Tip ◽  
Set Up ◽  
The Impact

Aeroengines pursue high performance, and compressing blade-casing clearance has become one of the main ways to improve turbomachinery efficiency. Rub-impact faults occur frequently with clearance decreasing. A high-speed rotor-support-casing test rig was set up, and the mechanism tests of light and heavy rub-impact were carried out. A finite element model of the test rig was established, and the calculation results were in good agreement with the experimental results under both kinds of rub-impact conditions. Based on the actual blade-casing structure model, the effects of the major physical parameters including imbalance and material characteristics were investigated. During the rub-impact, the highest stress occurs at the blade tip first and then it is transmitted to the blade root. Deformation on the impact blade tip generates easily with decreased yield strength, and stress concentration at the blade tip occurs obviously with weaker stiffness. The agreement of the computation results with the experimental data indicates the method could be used to estimate rub-impact characteristics and is effective in design and analyses process.

Housing Influence on Churning Losses in Geared Transmissions

2007 ◽  
Author(s):  
C. Changenet ◽  
P. Velex
Keyword(s):  
Fluid Flow ◽  
Qualitative Evaluation ◽  
Flow Regimes ◽  
Power Losses ◽  
Test Rig ◽  
Automotive Transmission ◽  
Transmission Geometry ◽  
Analytical Formulas ◽  
Set Up ◽  
Fluid Flow Regimes

In a previous paper, a series of analytical formulas were presented enabling accurate predictions of churning losses for one gear which is typical of automotive transmission geometry. However, this formulation does not take into account the influence of flanges and deflectors. In order to extend the proposed methodology, a test rig has been set up in which several moveable walls can be inserted thus making it possible to modify the radial and axial clearances, i.e., the distances between the tested gear and the walls. Based on a qualitative evaluation of the various fluid flow regimes possible in gearboxes, the influence of the global volume of the oil sump on churning losses is analyzed. By considering a number of flange and deflector arrangements, the following conclusions are drawn: a) radial clearances have a weaker influence than axial clearances and, b) power losses can be minimized by properly chosen axial clearances.

Impact of SSM/I Observations Related to Moisture, Clouds, and Precipitation on Global NWP Forecast Skill

2008 ◽  
Vol 136 (7) ◽  
pp. 2713-2726 ◽  
Author(s):  
G. A. Kelly ◽  
P. Bauer ◽  
A. J. Geer ◽  
P. Lopez ◽  
J-N. Thépaut
Keyword(s):  
Initial Conditions ◽  
Forecast Skill ◽  
Clear Sky ◽  
Microwave Imager ◽  
Set Up ◽  
The Tropics ◽  
The Impact ◽  
Northern And Southern Hemispheres ◽  
Experiment Duration

Abstract This paper presents the results from the Observing System Experiments (OSEs) with the current ECMWF data assimilation and modeling system for quantifying the impact on both analysis and forecast quality of Special Sensor Microwave Imager (SSM/I) observations sensitive to moisture and clouds as well as precipitation. SSM/I radiances have been assimilated operationally in clear-sky areas for 8 yr and in cloud- and rain-affected areas since June 2005. This paper examines experiments set up such that clear-sky and rain-affected observations were either added to a baseline with a restricted observing system configuration or withdrawn from the full system. The experiment duration was 10 weeks of which the first 14 days were excluded from the evaluation to allow the system to lose the memory of the initial conditions at day −1. It is shown that both clear-sky and rain-affected observations account for the bulk correction of moisture in the ECMWF analysis. SSM/I data adds 1 day of forecast skill over the first 48 h when evaluated in addition to a baseline-observing system. In the tropics, the rain-affected data contributes more skill to the moisture forecast than the clear-sky data at 700 hPa and above. In the Northern and Southern Hemispheres, the effect is generally weaker and slightly in favor of clear-sky observations. A similar performance can be seen with respect to the wind vector forecast skill, which reflects the connection between the analysis of moisture and dynamics.

scholarly journals Barriers and Challenges Going from Conventional to Cryogenic Superconducting Propulsion for Hybrid and All-Electric Aircrafts

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6861
Author(s):  
Francisco Ferreira da Silva ◽  
João F. P. Fernandes ◽  
Paulo Jose da Costa Branco
Keyword(s):  
Electric Machines ◽  
Specific Power ◽  
Propulsion Systems ◽  
Aircraft Systems ◽  
Electric Aircraft ◽  
Alternative Materials ◽  
High Specific Power ◽  
Barriers And Challenges ◽  
The Impact ◽  
Fuel Source

The development of electric aircraft is becoming an important technology for achieving the goals set by the European Commission for the reduction of gases emissions by 2050 in the aeronautical transportation system. However, there is a technology gap between the current values of specific power in commercial electric machines and those required for aeronautical applications. Therefore, the search for alternative materials and non-conventional designs is mandatory. One emergent solution is using superconducting machines and systems to overcome the current limits of conventional electrical machines. This work reviews the new hybrid and all-electric aircraft tendencies, complementing it with recent research on the design and development of high specific power superconducting machines. This includes the main topologies for hybrid and all-electric aircraft, with an overview of the ongoing worldwide projects of these aircraft types, systematizing the main characteristics of their propulsion systems. It also includes the research on superconducting machines to achieve high specific power and consider the impact on the redesign of aircraft systems, the electrical, cooling, and fuel source systems.

scholarly journals CARACTERIZACIÓN AMBIENTAL DE LA ENSENADA DE PLAYA GRANDE, ESTADO SUCRE, VENEZUELA

2016 ◽  
Author(s):  
J. Castañeda ◽  
William James Senior ◽  
Arístide Márquez ◽  
Ángel González
Keyword(s):  
Single Point ◽  
Coastal Region ◽  
Fecal Coliforms ◽  
Trade Winds ◽  
Human Contact ◽  
Hydrographic Conditions ◽  
Chemical Conditions ◽  
Set Up ◽  
The Impact

The hydrographic conditions and sanitary quality of the waters of the coastal region of Playa Grande Baywere studied during May 2003. We set up 21 stations to collect surface and bottom samples and three current meters – anupward-mounted hydroacoustic profiler and two single-point Doppler current sensors that operated for 14 days. Samples werecollected in 5-L Niskin bottles equipped with a lid-closing device operated through a cable. The samples were studied accordingto established methods for seawater analysis. The pH ranged between 7.93 and 8.31; the temperature, between 22.0 and 24.0ºC; the salinity, between 36.56 and 37.17 units; the color, between 15 and 30 Pt-Co units. The biochemical oxygen demandranged between 4.05 and 68.96 mg/L; and total nitrogen, between 0.53 and 1.27 mg/L. Total phosphate fluctuated between0.02 and 0.16 mg/L; lipids, between 0.08 and 0.39 mg/L; aliphatic hydrocarbons, between 0.01 and 0.12 mg/L. Detergents didnot exceed the value of 0.02 mg/L. In some cases, total and fecal coliforms reached values beyond the limit of 1000 NMP/100ml for total coliforms set by the Ministry of the Environment for type 4 waters (partial and total human contact). Thequality of these waters shows the impact of effluents, running mostly from east to west, in the sector of Campo Ajuro. Thephysical and chemical conditions of the waters of this bay may vary throughout the year as a consequence of the dynamicconditions prevailing in the region. It is recommended that these studies be carried out at least twice a year: during the dryseason (December to May), when the trade winds increase, and during the rainy season (June to November).

Educating Students for E-Entrepreneurship in the UK, the USA and China

2009 ◽  
Vol 23 (3) ◽  
pp. 243-252 ◽  
Author(s):  
Cindy Millman ◽  
Wang-Chan Wong ◽  
Zhengwei Li ◽  
Harry Matlay
Keyword(s):  
Entrepreneurship Education ◽  
Policy Makers ◽  
Rigorous Research ◽  
Growing Body ◽  
The Usa ◽  
Political Conditions ◽  
Set Up ◽  
The Uk ◽  
The Impact

A growing body of research evaluates various aspects of entrepreneurship education (such as curriculum, delivery and assessment) and links it to outcomes in terms of both the number and quality of entrepreneurs entering an economy. There is, however, a marked paucity of empirically rigorous research appraising the impact of entrepreneurship education on graduates' intentions and perceived ability to set up Internet-based e-enterprises that can operate across temporal and geographical boundaries. This paper provides a comparative overview of entrepreneurship education in the UK, the USA and China with a focus on IT and non-IT students' e-entrepreneurship intentions, perceptions and outcomes. The research on which the paper is based was carried out in two distinct phases: first, focus groups were used to design, pilot and develop a comprehensive research questionnaire for use in a wider, multi-country survey; second, questionnaires were then distributed to students in IT and non-IT related disciplines in the UK, the USA and China. The preliminary results show that most respondents were slow to conceptualize and contextualize e-entrepreneurship in the prevailing socio-economic and political conditions of their countries of origin. There were no significant differences between students of IT and non-IT disciplines in their perceptions of the viability and practicality of engaging in e-entrepreneurship. Generic support initiatives appear to neglect the vast portfolio of skills needs for graduates engaging in Internet trading. The authors recommend that entrepreneurship education providers should engage with emergent models of e-entrepreneurship and that policy makers should provide innovative initiatives to cater for the specific needs of e-entrepreneurs.

ToeHold Artisans Collaborative: Building Entrepreneurial Capabilities to Tackle Poverty

2008 ◽  
Vol 12 (02) ◽  
pp. 187-213 ◽  
Author(s):  
Sindhu Shanmugam ◽  
S. Ramakrishna Velamuri
Keyword(s):  
Social Enterprises ◽  
Non Profit ◽  
Self Help ◽  
Economic Stagnation ◽  
Effective Organization ◽  
Set Up ◽  
Self Help Groups ◽  
The Impact ◽  
Group Enterprise

Toehold Artisans Collaborative (TAC) is a project launched by the Asian Center for Entrepreneurship Initiatives (ASCENT), a non-profit organization based in Bangalore, to build entrepreneurial capacity in a community of footwear artisans of the small southern Indian town of Athani. Prior to ASCENT's involvement, which began in 1998, the artisans of Athani were making a subsistence wage, which did not even guarantee them two square meals a day. They could not send their children to school and were thus suffering from economic stagnation. TAC is an established Group Enterprise of 14 women Self Help Groups (SHG). Even though women's SHGs are the direct stakeholders, the men are not left out — they are treated as co-preneurs for all inputs, exposure to international fairs and production purposes. The front end of TAC is a customer-centric business enterprise that has taken the exquisite footwear brand 'ToeHold™' to challenging international mainstream markets. The backend is an artisan-centric social enterprise striving for improvement in the quality of life of about 400 artisans' families. The case documents how TAC was set up and evolved during the 1998–2006 period, the challenges it faced and continues to face, and the impact it has had on the artisan community. It is useful for examining the effective organization and running of social enterprises.

The Impact of Beam Broadening on the Quality of Radar Polarimetric Data

2007 ◽  
Vol 24 (5) ◽  
pp. 729-744 ◽  
Author(s):  
Alexander V. Ryzhkov
Keyword(s):  
Correlation Coefficient ◽  
Cross Correlation ◽  
Horizontal Gradients ◽  
Analytical Formulas ◽  
Radar Resolution ◽  
Differential Reflectivity ◽  
The Impact ◽  
Nonuniform Beam ◽  
Beam Broadening

Abstract The impact of beam broadening on the quality of radar polarimetric data in the presence of nonuniform beam filling (NBF) is examined both theoretically and experimentally. Cross-beam gradients of radar reflectivity Z, differential reflectivity ZDR, and differential phase ΦDP within the radar resolution volume may produce significant biases of ZDR, ΦDP, and the cross-correlation coefficient ρhv. These biases increase with range as a result of progressive broadening of the radar beam. They are also larger at shorter radar wavelengths and wider antenna beams. Simple analytical formulas are suggested for estimating the NBF-induced biases from the measured vertical and horizontal gradients of Z, ZDR, and ΦDP. Analysis of polarimetric data collected by the KOUN Weather Surveillance Radar-1988 Doppler (WSR-88D) demonstrates that frequently observed perturbations of the radial ΦDP profiles and radially oriented “valleys” of ρhv depression can be qualitatively and quantitatively explained using the suggested NBF model.

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