Theoretical Study and Device Modeling of III-V Nanostructured Photovoltaics

A methodology for the modeling and theoretical analysis of novel nanostructured photovoltaic devices is presented in this work. The nanostructures in consideration are quantum wells and quantum dots composed of 111-V materials. Their incorporation into the space charge region of an otherwise conventional solar cell is presented as a means to increase photovoltaic energy conversion efficiency. The enhancement for both single- and multi-junction solar cells is also outlined. Limitations of the available models are briefly discussed. Analyzed results allow for the further optimization of these novel devices

Modeling solutions and simulations for advanced III-V photovoltaics based on nanostructures

It is the purpose of the work to develop methods for and present on the computational analyses of advanced III-V photovoltaic devices and their enhancement by the incorporation of semiconductor nanostructures. Such devices are currently being fabricated as part of the research efforts at the Nanopower Research Laboratories; therefore, this work aims to supplement and ground the experimental undertakings with a strong theoretical basis. This is accomplished by numerical calculations based on the detailed balance model and by physicsbased device simulation. The specific materials focus of this work is on the enhancement of the GaAs solar cell. The aforementioned methodologies are applied to this device and to distinct enhancement schemes. The detailed balance formalism is applied to the single-junction solar cell as an introduction leading up to the triple-junction device. A thorough analysis shows how the InGaP-GaAs-Ge triple-junction solar cell may be enhanced by the incorporation of nanostructures. The intermediate band solar cell is introduced as it may be realized by the coupling of a nanostructured array. The detailed balance analysis of this device is performed using the usual blackbody spectrum as well as the more realistic scenarios of illumination by the AM0 and AM1.5 solar spectra. Current research endeavors into placing an InAs quantum dot array in a GaAs solar cell are put into the context of these calculations. It is determined that, although the InAs/GaAs system is not ideal, it does exhibit a significant enhancement in performance over the standard single-junction device. The evaluation of a commercially available, physics-based, device simulation software package for use in advanced photovoltaics analysis is also performed. The application of this tool on the single-junction GaAs solar cell indicates that the current design used in experimental work is optimized. Recommendations are made, however, in the optimized design of the InGaP-GaAs dual-junction cell. The device simulator is shown to exhibit difficulties in evaluating the complete operation of advanced solar devices; however, the software is used to compute fundamental quantum mechanical variables in a nanostructured solar cell

Quantum Super-Resolution with Balanced Homodyne Detection in Low-Earth-Orbit

Quantum super-resolution involves resolving two sources below the Rayleigh limit using quantum optics. Such a technique would allow high-precision inter-satellite positioning and tracking on communication and navigation constellations. Due to the size, weight and power constraints typical of low-earth-orbit (LEO) satellites, a simple solution is often preferred. Here, we show that a balanced homodyne detection (BHD) setup using a shaped single-mode local oscillator can achieve super-resolution despite typical photonic losses. We further analyze the impact of a fluctuating and fixed centroid misalignment due to satellite pointing issues, and find that fixed misalignment is comparatively more detrimental to the performance of a BHD setup. Thus, our study provides a practical assessment of BHD to achieve super-resolution on a modern LEO satellite platform. Finally, we discuss how our analysis can be extended to stellar sources for astronomical applications.Comment: 9 pages, 5 figures, comments welcom

LEO Clock Synchronization with Entangled Light

Precision navigation and timing, very-long-baseline interferometry, next-generation communication, sensing, and tests of fundamental physics all require a highly synchronized network of clocks. With the advance of highly-accurate optical atomic clocks, the precision requirements for synchronization are reaching the limits of classical physics (i.e. the standard quantum limit, SQL). Efficiently overcoming the SQL to reach the fundamental Heisenberg limit can be achieved via the use of squeezed or entangled light. Although approaches to the Heisenberg limit are well understood in theory, a practical implementation, such as in space-based platforms, requires that the advantage outweighs the added costs and complexity. Here, we focus on the question: can entanglement yield a quantum advantage in clock synchronization over lossy satellite-to-satellite channels? We answer in the affirmative, showing that the redundancy afforded by the two-mode nature of entanglement allows recoverability even over asymmetrically lossy channels. We further show this recoverability is an improvement over single-mode squeezing sensing, thereby illustrating a new complexity-performance trade-off for space-based sensing applications.Comment: 6 pages, 4 figures, comments welcom

The Journal of Microelectronic Research 2008

https://scholarworks.rit.edu/meec_archive/1016/thumbnail.jp

Phylogenetic Relationships within the Opisthokonta Based on Phylogenomic Analyses of Conserved Single-Copy Protein Domains

Many of the eukaryotic phylogenomic analyses published to date were based on alignments of hundreds to thousands of genes. Frequently, in such analyses, the most realistic evolutionary models currently available are often used to minimize the impact of systematic error. However, controversy remains over whether or not idiosyncratic gene family dynamics (i.e., gene duplications and losses) and incorrect orthology assignments are always appropriately taken into account. In this paper, we present an innovative strategy for overcoming orthology assignment problems. Rather than identifying and eliminating genes with paralogy problems, we have constructed a data set comprised exclusively of conserved single-copy protein domains that, unlike most of the commonly used phylogenomic data sets, should be less confounded by orthology miss-assignments. To evaluate the power of this approach, we performed maximum likelihood and Bayesian analyses to infer the evolutionary relationships within the opisthokonts (which includes Metazoa, Fungi, and related unicellular lineages). We used this approach to test 1) whether Filasterea and Ichthyosporea form a clade, 2) the interrelationships of early-branching metazoans, and 3) the relationships among early-branching fungi. We also assessed the impact of some methods that are known to minimize systematic error, including reducing the distance between the outgroup and ingroup taxa or using the CAT evolutionary model. Overall, our analyses support the Filozoa hypothesis in which Ichthyosporea are the first holozoan lineage to emerge followed by Filasterea, Choanoflagellata, and Metazoa. Blastocladiomycota appears as a lineage separate from Chytridiomycota, although this result is not strongly supported. These results represent independent tests of previous phylogenetic hypotheses, highlighting the importance of sophisticated approaches for orthology assignment in phylogenomic analyses. © The Author 2011. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved

A developmental perspective on the evolution of the nervous system.

The evolution of nervous systems in animals has always fascinated biologists, and thus multiple evolutionary scenarios have been proposed to explain the appearance of neurons and complex neuronal centers. However, the absence of a robust phylogenetic framework for animal interrelationships, the lack of a mechanistic understanding of development, and a recapitulative view of animal ontogeny have traditionally limited these scenarios. Only recently, the integration of advanced molecular and morphological studies in a broad range of animals has allowed to trace the evolution of developmental and neuronal characters on a better-resolved animal phylogeny. This has falsified most traditional scenarios for nervous system evolution, paving the way for the emergence of new testable hypotheses. Here we summarize recent progress in studies of nervous system development in major animal lineages and formulate some of the arising questions. In particular, we focus on how lineage analyses of nervous system development and a comparative study of the expression of neural-related genes has influenced our understanding of the evolution of an elaborated central nervous system in Bilateria. We argue that a phylogeny-guided study of neural development combining thorough descriptive and functional analyses is key to establish more robust scenarios for the origin and evolution of animal nervous systems

Acoelomorpha: earliest branching bilaterians or deuterostomes?

The Acoelomorpha is an animal group comprised by nearly 400 species of misleadingly inconspicuous flatworms. Despite this, acoelomorphs have been at the centre of a heated debate about the origin of bilaterian animals for 150 years. The animal tree of life has undergone major changes during the last decades, thanks largely to the advent of molecular data together with the development of more rigorous phylogenetic methods. There is now a relatively robust backbone of the animal tree of life. However, some crucial nodes remain contentious, especially the node defining the root of Bilateria. Some studies situate Acoelomorpha (and Xenoturbellida) as the sister group of all other bilaterians, while other analyses group them within the deuterostomes which instead suggests that the last common bilaterian ancestor directly gave rise to deuterostomes and protostomes. The resolution of this node will have a profound impact on our understanding of animal/bilaterian evolution. In particular, if acoelomorphs are the sister group to Bilateria, it will point to a simple nature for the first bilaterian. Alternatively, if acoelomorphs are deuterostomes, this will imply that they are the result of secondary simplification. Here, we review the state of this question and provide potential ways to solve this long-standing issue. Specifically, we argue for the benefits of (1) obtaining additional genomic data from acoelomorphs, in particular from taxa with slower evolutionary rates; (2) the development of new tools to analyse the data; and (3) the use of metagenomics or metatranscriptomics data. We believe the combination of these three approaches will provide a definitive answer as to the position of the acoelomorphs in the animal tree of life

What makes an animal? The molecular quest for the origin of the Animal Kingdom

What makes an animal? To find the answer we need to integrate data from disciplines such as phylogenetics, palaeontology, ecology, development, anatomy and physiology, as well as molecular biology and genomics. Knowledge of which groups branched before and after the origin of animals is essential. Recent advances in molecular phylogenetics, together with the discovery of new eukaryotic lineages, have drawn a new picture of the ancestry of animals. The nature of the early diverging animal lineages and the timing of the transition are in a state of flux. Various factors have been linked to this striking transition to multicellularity, including changes in environmental conditions and the ecological interactions between unicellular eukaryotes. The current wealth of genomic data has also shed new light on this question. The analysis of the genome of various close relatives of animals has revealed the importance that recycling of ancient genes into metazoan biological functions played into animal origins. A recent study reconstructing the genome of the last common ancestor of extant animals has unveiled an unprecedented emergence of new genes, highlighting the role of genomic novelty in the origin of metazoans