Common pulse retrieval algorithm: a fast and universal method to retrieve ultrashort pulses

We present a common pulse retrieval algorithm (COPRA) that can be used for a broad category of ultrashort laser pulse measurement schemes including frequency-resolved optical gating (FROG), interferometric FROG, dispersion scan, time domain ptychography, and pulse shaper assisted techniques such as multiphoton intrapulse interference phase scan (MIIPS). We demonstrate its properties in comprehensive numerical tests and show that it is fast, reliable and accurate in the presence of Gaussian noise. For FROG it outperforms retrieval algorithms based on generalized projections and ptychography. Furthermore, we discuss the pulse retrieval problem as a nonlinear least-squares problem and demonstrate the importance of obtaining a least-squares solution for noisy data. These results improve and extend the possibilities of numerical pulse retrieval. COPRA is faster and provides more accurate results in comparison to existing retrieval algorithms. Furthermore, it enables full pulse retrieval from measurements for which no retrieval algorithm was known before, e.g., MIIPS measurements

Impacts of pollinator abundance on benefits from facultative pollination mutualism

Title from PDF of title page (University of Missouri--Columbia, viewed on December 7, 2010).The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Dissertation advisor: Dr. Candace Galen.Vita.Ph. D. University of Missouri--Columbia 2010.Partner abundance affects costs and benefits in obligate mutualisms, but its role in facultative partnerships is less clear. I investigated this topic in a small alpine pollination web in the Colorado Rocky Mountains consisting of two clovers, Trifolium dasyphyllum and T. parryi, that vary in specialization on a shared bumblebee pollinator, Bombus balteatus. I examined a) foraging choices of queen B. balteatus among the clovers and explanatory mechanisms behind observed foraging biases, b) how intraspecific and interspecific variation in pollination niche breadth impacts individual- to population-level plant responses to manipulated pollinator density, c) habitat-scale relationships between natural bumblebee colony abundance and clover reproductive rates, and d) the broader impacts of this research in the setting of an outreach program using pollinator gardens at a local high school. Results showed that architectural trait differences between the clovers leading to differences in foraging efficiency likely mediate preference of B. balteatus for T. parryi. Because of bees' preferences and a dearth of co-pollinators, T. parryi benefits more than T. dasyphyllum from increases in B. balteatus density at the individual plant level, at life stages linking individual success with population growth, at population levels, and across habitats; however benefits even for T. parryi are not unlimited. In addressing the broader impacts of this research in a K-12 setting, I found that components of the participant teachers' beliefs about using outdoor classrooms mediated the implementation and outcome of planned activities.Includes bibliographical reference

The Relevance of Maize Pollen for Assessing the Extent of Maize Production in Chaco Canyon

Opinion is hardly unanimous, but many authors endorse the idea that Chaco Canyon is and was a marginal place for growing corn (Zea mays), a chief source of food energy for Puebloan groups in the Southwest. Poor soils with “toxic” levels of salts, inadequate and unpredictable precipitation, and a short growing season have all been identified as contributing to the agricultural marginality of the place (Benson 2011a; Bryan 1954; Force et al. 2002; Judd 1954:59–61). Benson has been the most vocal proponent of this view of late, and his research has culminated in the conclusion that “the San Juan Basin, including Chaco Canyon, appears to be the least promising area for dryland farming; that is, it is too dry and its soils are Npoor, saline and too basic (high pH values) for the production of maize” (Benson 2011a:49–50; Benson 2011b). The Chaco Project’s experimental maize fields in the late 1970s seem to bear out this statement: “Chaco, under modern conditions, is indeed marginal as a corn growing environment” (Toll et al. 1985:124). If Chaco Canyon is as marginal for farming as many claim, then the cultural achievements of the Puebloans that lived there are all the more remarkable, and this marginality has figured prominently in many interpretations about how and why Chaco Canyon developed as it did (Judge 1979, 1989; Schelberg 1981, 1982; Sebastian 1983, 1991, 1992; Vivian 1984, 1990). Chacoans had to import not only beams for building, pottery for cooking and storage, and stone for flaked tools but also even the staff of life—corn. And when you add in such exotics as turquoise, parrots, copper bells, and cacao, the potential “trade” deficit looms large. If Chaco Canyon did not provide even enough food for basic sustenance, what was it that made the place so special in the first place? More importantly, what literally fueled the obvious cultural fluorescence of Chaco Canyon and ts massive labor-intensive construction projects? Wills and Dorshow (2012:138) observe that “the popular perspective that Chaco was mysterious or enigmatic is largely a response to this view of the canyon as agriculturally marginal.” Yet, how do we know what the agricultural potential of the canyon was during the Bonito phase (ca. A.D. 850–1140) or that Chacoans could not provide for themselves? Perhaps the pendulum has swung too far toward a pessimistic assessment of the maize farming in and around the canyon. Certainly, Navajo farmers with considerable traditional knowledge and a real stake in the outcome successfully grew corn within Chaco Canyon (Judd 1954:52–59), and in 1898, George Pepper photographed Navajo fields on the floodplain of Chaco Canyon proper that produced a bountiful corn harvest ( Figure 1a). Since photo documentation is not anecdotal, it seems a sufficient counter to assertions that farming of the Chaco floodplain was impossible because of high salinity. Judd’s records of Navajo maize harvests evidently come from a time of more favorable precipitation and growingseason length, but this, too, could have characterized much of the Bonito phase. Figure 1b shows another Navajo field on the main floodplain at harvest time. Navajo farmers clearly experienced agricultural risk (Huntington 1914:81), but evidently the canyon proved a sufficient attraction to entice early settlement by them (Brugge 1986), perhaps precisely because of its productive potential. Farming potential was likely the prime motivation for initial Basketmaker settlement, a time when supplemental extra-local sources of maize were improbable. Since everything is relative, Chaco Canyon may have seemed like a small Eden in the context of the vast “dreary wastes” (Huntington 1914:81) of the San Juan Basin at large

The topological classification of one-dimensional symmetric quantum walks

We give a topological classification of quantum walks on an infinite 1D lattice, which obey one of the discrete symmetry groups of the tenfold way, have a gap around some eigenvalues at symmetry protected points, and satisfy a mild locality condition. No translation invariance is assumed. The classification is parameterized by three indices, taking values in a group, which is either trivial, the group of integers, or the group of integers modulo 2, depending on the type of symmetry. The classification is complete in the sense that two walks have the same indices if and only if they can be connected by a norm continuous path along which all the mentioned properties remain valid. Of the three indices, two are related to the asymptotic behaviour far to the right and far to the left, respectively. These are also stable under compact perturbations. The third index is sensitive to those compact perturbations which cannot be contracted to a trivial one. The results apply to the Hamiltonian case as well. In this case all compact perturbations can be contracted, so the third index is not defined. Our classification extends the one known in the translation invariant case, where the asymptotic right and left indices add up to zero, and the third one vanishes, leaving effectively only one independent index. When two translationally invariant bulks with distinct indices are joined, the left and right asymptotic indices of the joined walk are thereby fixed, and there must be eigenvalues at $1$ or $-1$ (bulk-boundary correspondence). Their location is governed by the third index. We also discuss how the theory applies to finite lattices, with suitable homogeneity assumptions.Comment: 36 pages, 7 figure

REPRESENTAÇÕES SOCIAIS DOS ADOLESCENTES ACERCA DA VIOLÊNCIA DOMÉSTICA

Com o objetivo de analisar as representações sociais dos adolescentes sobre a violência doméstica realizou-se esta pesquisa qualitativa junto a 18 alunos de escolas de ensino médio em Passo Fundo - RS, com técnicas projetivas e entrevistas semi-estruturadas, evidenciando-se a representação da violência como um fenômeno presente na sociedade, ancorada no consumo de drogas, na defesa pessoal com porte de armas e na conduta anti-social. A violência doméstica é representada como uma atitude de fuga e defesa, maléfica, intencional e impune e como uma banalização legitimada. Essas representações ancoram-se na sensação de abandono e rejeição, cuja superação deverá ser buscada de forma multidimensional para a internalização de novas práticas e condutas socialmente aceitas

Complete homotopy invariants for translation invariant symmetric quantum walks on a chain

We provide a classification of translation invariant one-dimensional quantum walks with respect to continuous deformations preserving unitarity, locality, translation invariance, a gap condition, and some symmetry of the tenfold way. The classification largely matches the one recently obtained (arXiv: 1611.04439) for a similar setting leaving out translation invariance. However, the translation invariant case has some finer distinctions, because some walks may be connected only by breaking translation invariance along the way, retaining only invariance by an even number of sites. Similarly, if walks are considered equivalent when they differ only by adding a trivial walk, i.e., one that allows no jumps between cells, then the classification collapses also to the general one. The indices of the general classification can be computed in practice only for walks closely related to some translation invariant ones. We prove a completed collection of simple formulas in terms of winding numbers of band structures covering all symmetry types. Furthermore, we determine the strength of the locality conditions, and show that the continuity of the band structure, which is a minimal requirement for topological classifications in terms of winding numbers to make sense, implies the compactness of the commutator of the walk with a half-space projection, a condition which was also the basis of the general theory. In order to apply the theory to the joining of large but finite bulk pieces, one needs to determine the asymptotic behaviour of a stationary Schrodinger equation. We show exponential behaviour, and give a practical method for computing the decay constants

Chiral Floquet systems and quantum walks at half period

We classify periodically driven quantum systems on a one-dimensional lattice, where the driving process is local and subject to a chiral symmetry condition. The analysis is in terms of the unitary operator at a half-period and also covers systems in which this operator is implemented directly, and does not necessarily arise from a continuous time evolution. The full-period evolution operator is called a quantum walk, and starting the period at half time, which is called choosing another timeframe, leads to a second quantum walk. We assume that these walks have gaps at the spectral points $\pm1$, up to at most finite dimensional eigenspaces. Walks with these gap properties have been completely classified by triples of integer indices (arXiv:1611.04439). These indices, taken for both timeframes, thus become classifying for half-step operators. In addition a further index quantity is required to classify the half step operators, which decides whether a continuous local driving process exists. In total, this amounts to a classification by five independent indices. We show how to compute these as Fredholm indices of certain chiral block operators, show the completeness of the classification, and clarify the relations to the two sets of walk indices. Within this theory we prove bulk-edge correspondence, where second timeframe allows to distinguish between symmetry protected edge states at $+1$ and $-1$ which is not possible with only one timeframe. We thus resolve an apparent discrepancy between our above mentioned index classification for walks, and indices defined (arXiv:1208.2143). The discrepancy turns out to be one of different definitions of the term `quantum walk'.Comment: 25 pages, 2 figure

Quantum Walks: Schur Functions Meet Symmetry Protected Topological Phases

This paper uncovers and exploits a link between a central object in harmonic analysis, the so-called Schur functions, and the very hot topic of symmetry protected topological phases of quantum matter. This connection is found in the setting of quantum walks, i.e. quantum analogs of classical random walks. We prove that topological indices classifying symmetry protected topological phases of quantum walks are encoded by matrix Schur functions built out of the walk. This main result of the paper reduces the calculation of these topological indices to a linear algebra problem: calculating symmetry indices of finite-dimensional unitaries obtained by evaluating such matrix Schur functions at the symmetry protected points ± 1. The Schur representation fully covers the complete set of symmetry indices for 1D quantum walks with a group of symmetries realizing any of the symmetry types of the tenfold way. The main advantage of the Schur approach is its validity in the absence of translation invariance, which allows us to go beyond standard Fourier methods, leading to the complete classification of non-translation invariant phases for typical examples. © 2021, The Author(s)

The impacts of floral fragrances and ant contamination on pollinator behavioral responses

Abstract only availableWorld economy, including agriculture and food production, is heavily dependant on animal pollination. For this reason, it is important to understand factors that mediate plant-pollinator interactions. We investigated behavioral responses of the bumblebee Bombus kirbyellus, an important pollinator in alpine ecosystems, to floral scent compounds found in the alpine wildflower Polemonium viscosum. We also examined how contamination by the nectar-thieving ant, Formica neorufibarbus gelida, impacts bumblebee preferences among these floral scents. We conducted field "interviews" of queen B. kirbyellus foragers, providing a choice between cut inflorescences of P. viscosum spiked with sucrose or sucrose + 2-phenol ethanol (2-PE), a common floral scent component of P. viscosum and many other plant species. We also documented insect visitors to naturally occurring P. viscosum inflorescences spiked with sucrose solutions with or without 2-PE. To understand whether nectar thieves affect cues mediating pollinator foraging, we measured queen B. kirbyellus consumption rates of sucrose and sucrose + 2-PE solutions with or without ant contamination. Additionally, we tested the impact of 2-PE on ants by sealing them in Petri dishes containing filter paper doused with sucrose or varying strengths of 2-PE. Bumblebees preferred plain sucrose solutions over sucrose + 2-PE, showing increased consumption and visitation rates on the former. However, ant contamination had no effect on consumption or visitation. No variation in natural insect visitation was observed among spiked P. viscosum inflorescences. Interestingly, high concentrations of 2-PE resulted in significantly increased ant mortality rates compared to sucrose or lower 2-PE concentrations. While floral scents have generally been considered as attractants to animal pollinators or seed dispersers, our results show that under some circumstances floral scent compounds may function as deterrents. Future investigation of additional scent compounds and natural variance of 2-PE concentration could clarify the roles of floral fragrances in plant animal interactions.NSF Undergraduate Mentoring in Environmental Biolog