Design of a Catalysis In-Flight Experiment

in Proceedings of the 46 th AIAA Aerospace Sciences Meeting and Exhibit (2008)

Design of a model predictive controller for welding robot under impact loading

Poster (2012, February 23)

DESIGN OF A THREE-STAGE PROCESS, PHOTOLUMINESCENCE AND DEFECT SPECTROSCOPY OF CU(IN,GA)S2

Doctoral thesis (2022)

Cu(In,Ga)S2 is a chalcopyrite material suitable as the higher bandgap top cell in tandem applications in next generation multijunction solar cells. This owes primarily to the tunability of its bandgap ... [more ▼]

Cu(In,Ga)S2 is a chalcopyrite material suitable as the higher bandgap top cell in tandem applications in next generation multijunction solar cells. This owes primarily to the tunability of its bandgap from 1.5 eV in CuInS2 to 2.45 eV in CuGaS2, and its relative stability over time. Currently, a major hinderance to the potential use of Cu(In,Ga)S2 in tandem capacity remains a deficient single-junction device performance in the form of low open-circuit voltage (VOC) and low efficiency. Aside interfacial recombination which leads to losses in the completed Cu(In,Ga)S2 solar cell, deficiencies stems from a low optoelectronic quality of the Cu(In,Ga)S2 absorber quantified by the quasi-Fermi level splitting (QFLS) and which serves as the upper limit of VOC achievable by a solar cell device. In this thesis, the QFLS is compared with the theoretical VOC (SQ-VOC) in the radiative limit, and “SQ-VOC deficit” is defined to compare the difference between SQ-VOC and QFLS as a comparable measure of the optoelectronic deficiency in the absorber material. In contrast to the counterpart Cu(In,Ga)Se2 absorber which has produced highly efficient solar cell devices, the Cu(In,Ga)S2 absorber still suffers from a high SQ-VOC deficit. However, SQ-VOC deficit in Cu(In,Ga)S2 can be reduced by growing the absorbers under Cu-deficient conditions. For the effective use of Cu(In,Ga)S2 as the top cell in tandem with Si or Cu(In,Ga)Se2 as the bottom cell, an optimum bandgap of 1.6-1.7 eV is required, and this is realized in absorbers with Ga content up to [Ga]/([Ga]+[In]) ratio of 0.30-0.35. However, the increase of Ga in Cu-poor Cu(In,Ga)S2 poses a challenge to the structural and optoelectronic quality of the absorber, resulting from the formation of segregated Ga phases with steep Ga/bandgap gradient which constitutes a limitation to the quality of the Cu(In,Ga)S2 absorber layer with a highSQ-VOC deficit and low open circuit voltage and overall poor performance of the finalized solar cell. In this work, the phase segregation in Cu(In,Ga)S2 has been circumvented by employing higher substrate temperatures and adapting the Ga flux during the first-stage of deposition when growing the Cu(In,Ga)S2 absorbers. A more homogenous Cu(In,Ga)S2 phase and improved Ga/bandgap gradient is achieved by optimizing the Ga flux at higher substrate temperature to obtain a Cu(In,Ga)S2 absorber with high optoelectronic quality and low SQ-VOC deficit. Additionally, the variation of the Cu-rich phase when growing the Cu(In,Ga)S2 absorber layers was found to not only alter the notch profile and bandgap minimum of the absorbers, but also influence the optoelectronic quality of the absorber. Shorter Cu-rich phase in the absorbers led to narrower notch profile and higher bandgap. Ultimately, several steps in the three-stage deposition method used for processing the Cu(In,Ga)S2 absorbers were revised to enhanced the overall quality of the absorbers. Consequently, the SQ-VOC deficit in high bandgap Cu(In,Ga)S2 absorbers is significantly reduced, leading to excellent device performance. This thesis also examines the temperature- and compositional-related optoelectronic improvement in pure Cu-rich CuInS2 absorbers without Ga, where improvement in QFLS was initially linked to a reduction of nonradiative recombination channels with higher deposition temperatures and increase in Cu content. Findings through photoluminescence decay measurements show that the origin of the improved QFLS in CuInS2 is rather linked to changes in doping levels with variations of deposition temperature and Cu content. Finally, in order to understand and gain insight into the influence of Ga in Cu(In,Ga)S2, the electronic structure of CuGaS2 absorbers was investigated in dependence of excitation intensity and temperature by low temperature photoluminescence measurements. A shallow donor level and three acceptor levels were detected. It was found that similar acceptor levels in CuInSe2 and CuGaSe2 which are otherwise shallow become deeper in CuGaS2. These deep defects serve as nonradiative recombination channels and their appearance in the Ga-containing compound is be detrimental to the optoelectronic quality of Cu(In,Ga)S2 absorbers as Ga content is increased therefore limiting the optimum performance of Cu(In,Ga)S2 devices. [less ▲]

Design of an Energy Efficiency Model and Architecture for Cloud Management using Prediction Models

Scientific Conference (2013, December 18)

In this paper, we present a new energy efficiency model and architecture for cloud management based on a prediction model with Gaussian Mixture Models. The methodology relies on a distributed agent model ... [more ▼]

In this paper, we present a new energy efficiency model and architecture for cloud management based on a prediction model with Gaussian Mixture Models. The methodology relies on a distributed agent model and the validation will be performed on OpenStack. This paper intends to be a position paper, the implementation and experimental run will be conducted in future work. The design concept leverages the prediction model by providing a full architecture binding the resource demands, the predictions and the actual cloud environment (Openstack). The prediction analysis feeds the power-aware agents that run on the compute nodes in order to turn the nodes into sleep mode when the load state is low to reduce the energy consumption of the data center. [less ▲]

Design of an Extractive Distillation Column for the Environmentally Benign Separation of Zirconium and Hafnium Tetrachloride for Nuclear Power Reactor Applications

in Energies (2015), 8(9),

Nuclear power with strengthened safety regulations continues to be used as an important resource in the world for managing atmospheric greenhouse gases and associated climate change. This study examined ... [more ▼]

Nuclear power with strengthened safety regulations continues to be used as an important resource in the world for managing atmospheric greenhouse gases and associated climate change. This study examined the environmentally benign separation of zirconium tetrachloride (ZrCl4) and hafnium tetrachloride (HfCl4) for nuclear power reactor applications through extractive distillation using a NaCl-KCl molten salt mixture. The vapor–liquid equilibrium behavior of ZrCl4 and HfCl4 over the molten salt system was correlated with Raoult’s law. The molten salt-based extractive distillation column was designed optimally using a rigorous commercial simulator for the feasible separation of ZrCl4 and HfCl4. The molten salt-based extractive distillation approach has many potential advantages for the commercial separation of ZrCl4 and HfCl4 compared to the conventional distillation because of its milder temperatures and pressure conditions, smaller number of required separation trays in the column, and lower energy requirement for separation, while still taking the advantage of environmentally benign feature by distillation. A heat-pump-assisted configuration was also explored to improve the energy efficiency of the extractive distillation process. The proposed enhanced configuration reduced the energy requirement drastically. Extractive distillation can be a promising option competing with the existing extraction-based separation process for zirconium purification for nuclear power reactor applications [less ▲]

DESIGN OF BIOMECHANICAL TESTING DEVICE FOR THE PELVIS INCLUDING GAIT MUSCLE FORCES

Scientific Conference (2022, June 27)

Design of continuously variable bicycle transmission

Report (2019)

As the people’s needs develop, so does the technology. Bicycles exist already for a long time, and ever since the appearance of electrically driven ones, the necessity to change their drivetrain and ... [more ▼]

As the people’s needs develop, so does the technology. Bicycles exist already for a long time, and ever since the appearance of electrically driven ones, the necessity to change their drivetrain and transmission started getting more important. What makes the development of bicycles even more impressive is the fact that their efficiency ranks first among travelling animals and machines, if we consider the energy consumed by moving a certain distance as a function of body weight. Different bicycle drivetrains are researched and explained in this report, especially CVT hubs. A continuously variable transmission based on a patent of Hiroyuki Urabe has been designed with the CAD method, and their main parts were analysed using the FEA method. The final construction has a theoretical total ratio of 400% and a mass of about 2.7kg (without lubricant). This transmission is using the principles of frictional traction to transfer torque. In general, this work shows how the designing process proceeded and gives an idea, how this type of gearbox could be constructed. [less ▲]

Design of Mechanically Actuated Aerodynamic Braking System on a Formula Student Race Car

in Journal of the Institution of Engineers (India): Mechanical Engineering Division (2017), 99

Every second in a racing competition counts the performance of a team against the other. Many innovative and sophisticated techniques are being employed to overcome loses in time and add to the ... [more ▼]

Every second in a racing competition counts the performance of a team against the other. Many innovative and sophisticated techniques are being employed to overcome loses in time and add to the performance of the vehicle. Especially in a car racing challenge there is more freedom to install these innovative systems to empower the car to maximum efficiency due to availability of more space. At the global spectrum there are few events which encourage such innovations. Formula Student Racing competitions are one of the global events organized by the Society of Automotive Engineers of different countries which gives opportunity to university students to build and race formula style cars. Like any other racing competitions in this high octane event having an inch over their opponents is always an advantage. Not just better acceleration and high velocities but also good deceleration is required to excel in the competition. Aerodynamic braking system is utilizing the aerodynamic drag force to create high deceleration. This mechanism can be installed on any car with spoilers with minimum modification. Being a student event great amount of care needs to be given to the safety concerns of the driver [less ▲]

Design of nonlinear predictors for adaptive predictive coding of speech signals

in Proceedings of the 21st Telecommunications Forum Telfor (TELFOR) (2013, November)

Linear predictive coding is probably the most frequently used technique in speech signal processing. Its main advantage comes from the analogy of the simplified vocal tract model with speech production ... [more ▼]

Linear predictive coding is probably the most frequently used technique in speech signal processing. Its main advantage comes from the analogy of the simplified vocal tract model with speech production system. However, this neglects nonlinearities in the speech production process. The paper deals with nonlinear prediction of speech based on truncated Volterra series. Long-term one-tap Volterra predictor is designed in order to decrease computational complexity. Further improvements are obtained using frame/subframe structure and fractional delay. [less ▲]

Design of Proactive Scenarios and Rules for Enhanced e-Learning

in Proceedings of the 4th International Conference on Computer Supported Education, Porto, Portugal 16-18 April, 2012 (2012)

We show in this position paper how we designed Proactive Scenarios for an automatic and enhanced management of the online assignments on MoodleTM for both student and teacher users, through their ... [more ▼]

We show in this position paper how we designed Proactive Scenarios for an automatic and enhanced management of the online assignments on MoodleTM for both student and teacher users, through their implementation with Proactive Rules to be run on top of our prototype Proactive Engine developed for this LMS. According to the diversity of issues that arise from the users activity on LMS, Proactive Scenarios are of two main types, which differ in their main goals, features and complexity. Meta Scenarios are devoted to capture major events of interest and to trigger off the dedicated Target Scenarios, which will undertake the appropriate actions. These Proactive Scenarios will thus take care of specifically predefined situations such as notifications, reminders, problem prevention, user guiding etc. In our opinion, LMS supplemented by such capabilities could provide a boosted effect on the students’ learning process as it takes an individual approach for each user and therefore could be characterized as a type of intelligent tutoring system. However, in order to sustain or modify the direction of our research activity, we now consider to undertake empirical studies on real-life online courses using the Enhanced E-learning Platform, which runs our Proactive Scenarios. [less ▲]