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Extending the Cutoff Wavelength of Thermophotovoltaic Devices via Band Structure Engineering
No full textAbstract: Thermophotovoltaics (TPVs) convert infrared radiation, or heat, into electricity via a photovoltaic diode. While TPVs can in principle convert radiation from any heat source, in practice they have been limited to high temperature applications due to the relatively large bandgap diodes employed. Development of narrow bandgap TPV diodes is required to optimally convert longer wavelength radiation from lower temperature sources. Overcoming the intrinsic limit of these reduced bandgap diodes, however, is no trivial matter. As the bandgap of a TPV diode decreases, the intrinsic carrier concentrations and parasitic recombination increase, leading to large dark currents. The increased dark current causes the open-circuit voltage and power of the diode to drop, rendering narrow bandgap TPV diodes inoperable. Our research aims to extend the operational cut-off wavelength of TPV devices to both a) more optimally convert the incident radiation from existing heat sources and b) enable lower temperature applications. With this goal in mind, we investigate a monovalent barrier structure, in which a wide bandgap barrier is inserted into the PN diode, for TPV devices. The barrier structure has proven successful at reducing dark currents in infrared photodetectors, which operate at low temperatures and reverse biases. TPV diodes must operate at higher temperatures, where the balance of dark current mechanisms differs. Here we explore the extent to which a monovalent barrier could be effective in reducing the dark current in narrow bandgap TPVs. The barrier diode design is facilitated by the use of superlattice structures, which consist of alternating nanometer-scale layers of materials. Unlike bulk materials, where the electronic bands are fixed, the electronic bands of these structures can be tuned by varying the thickness and periodicity of the superlattice layers. In this work we use the 8x8 k·p method to design the band offsets for a barrier structure consisting of III-V superlattice materials. Structures were grown using molecular beam epitaxy and fabricated into diodes using standard photolithography methods. Dark current measurements were taken to examine the effect of a barrier structure on TPV performance.Thesis (Ph.D.)--Tufts University, 2018.Submitted to the Dept. of Electrical Engineering.Advisor: Thomas Vandervelde.Committee: Rodolfo Salas, Matthew Panzer, and Kevin Grossklaus.Keyword: Energy
Timeline and Budget Development.
No full textThis presentation was given at First National Workshop in Nepal
Nutrition Proposal Writing in Nepal: Experiences from the past.
No full textThis presentation was given at First National Workshop in Nepal
Statistical Analysis-Methods to assess intervention.
No full textThis presentation was given at First National Workshop in Nepal.Keywords: Statistical analysis, interventions
Spatial decision dynamics during wayfinding: intersections prompt the decision-making process.
No full textAbstract: Intersections are critical decision points for wayfinders, but it is unknown how decision dynamics unfold during pedestrian wayfinding. Some research implies that pedestrians leverage available visual cues to actively compare options while in an intersection, whereas other research suggests that people strive to make decisions long before overt responses are required. Two experiments examined these possibilities while participants navigated virtual desktop environments, assessing information-seeking behavior (Experiment 1) and movement dynamics (Experiment 2) while approaching intersections. In Experiment 1, we found that participants requested navigation guidance while in path segments approaching an intersection and the guidance facilitated choice behavior. In Experiment 2, we found that participants tended to orient themselves toward an upcoming turn direction before entering an intersection, particularly as they became more familiar with the environment. Some of these patterns were modulated by individual differences in spatial ability, sense of direction, spatial strategies, and gender. Together, we provide novel evidence that deciding whether to continue straight or turn involves a dynamic, distributed decision-making process that is prompted by upcoming intersections and modulated by individual differences and environmental experience. We discuss implications of these results for spatial decision-making theory and the development of innovative adaptive, beacon-based navigation guidance systems.Keywords: Navigation, Decision-making, Wayfinding, Spatial cognition.Springer Open
Boko Haram Conflict Map.
No full textStudents in Tufts PJS150-5 Conflict Resolution (Spring 2018, Professor Amanda Donahoe) worked in small groups write a collaborative research paper, called a 'conflict map' in which they select and analyze a current world conflict and make an argument for a course of resolution. This conflict map analyzes the Boko Haram conflict in Nigeria
Design And Implementation of Prospective Intervention Studies In Human Nutrition.
No full textThis presentation was an opening presentation on First National Workshop in Nepal
Data Collection, Quality and Management.
No full textThis presentation was given at First National Workshop in Nepal
Research Question, Specific Aims and Hypothesis, and Outcomes.
No full textThis presentation was to give overview of the research specifics to the students at First National workshop