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Book
1 online resource (Article No. e0146223 ) : digital, PDF file.
Huanglongbing (HLB) constitutes the most destructive disease of citrus worldwide, yet no established efficient management measures exist for it. Brassinosteroids, a family of plant steroidal compounds, are essential for plant growth, development and stress tolerance. As a possible control strategy for HLB, epibrassinolide was applied to as a foliar spray to citrus plants infected with the causal agent of HLB, ‘Candidatus Liberibacter asiaticus’. The bacterial titers were reduced after treatment with epibrassinolide under both greenhouse and field conditions but were stronger in the greenhouse. Known defense genes were induced in leaves by epibrassinolide. With the SuperSAGE technology combined with next generation sequencing, induction of genes known to be associated with defense response to bacteria and hormone transduction pathways were identified. Lastly, the results demonstrate that epibrassinolide may provide a useful tool for the management of HLB.
Book
1 online resource (8 p. ) : digital, PDF file.
This is the final Summary Report for the 2015 Aspen Winter Conference on "Progress and Applications on Modern Quantum Field Theory".
This document is the program for the 6th Annual Midwest Conference for Undergraduate Women in Physics, which was held at the University of Illinois at Urbana-Champaign on January 18-20, 2013. The goals of the conference were to foster a culture in which undergraduate women are encouraged and supported to pursue, and also to succeed in, higher education in physics; to provide career information to students in physics and related fields; to give women the resources, motivation, and confidence to apply to graduate school and successfully complete a Ph.D. program in Physics; to provide information and dispel misconceptions about the application process for graduate school and the diverse employment opportunities in physics and related fields, enabling women to make more informed decisions about their goals and attain them; and to connect female physics students with successful female physicists to whom they can relate and who can act as inspirational role models and mentors.
Book
1 online resource (28 p. ) : digital, PDF file.
We develop analytical models of the longitudinal and transverse wakes, on and off axis for realistic structures, and then compare them with numerical calculations, and generally find good agreement. These analytical "first order" formulas approximate the droop at the origin of the longitudinal wake and of the slope of the transverse wakes; they represent an improvement in accuracy over earlier, "zeroth order" formulas. In example calculations for the RadiaBeam/LCLS dechirper using typical parameters, we find a 16% droop in the energy chirp at the bunch tail compared to simpler calculations. With the beam moved to 200 m from one jaw in one dechiper section, one can achieve a 3 MV transverse kick differential over a 30 m length.
Book
Article No. 27294 : digital, PDF file.
We report that the change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs<sub>2</sub> possesses a very large negative magnetoresistance, with an unknown scattering mechanism. In conclusion, density functional calculations find that TaAs<sub>2</sub> is a new topological semimetal [Z<sub>2</sub> invariant (0; 111)] without Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions.
Book
Article No. 21660 : digital, PDF file.
Within the BaFe<sub>2</sub>As<sub>2</sub> crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba<sub>1-x</sub>Tl<sub>x</sub>Fe<sub>2</sub>As<sub>2</sub> crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Néel temperature rises with small x, and then falls with additional x. Specifically, we find that Néel and structural transitions in BaFe<sub>2</sub>As<sub>2</sub> (TN = T<sub>s</sub> = 133 K) increase for x = 0.05 (T<sub>N</sub> = 138 K, T<sub>s</sub> = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidence from single crystal X-ray diffraction and first principles calculations attributes the stronger magnetism in x = 0.05 to magneto-elastic coupling related to the shorter intraplanar Fe-Fe bond distance. With further thallium substitution, the transition temperatures decrease for x = 0.09 (T<sub>N </sub>= T<sub>s</sub> = 131 K), and this is due to charge doping. Finally, we illustrate that small changes related to 3d transition-metal state can have profound effects on magnetism.
Book
1 online resource (Article No. 023017 ) : digital, PDF file.
The strong power law behavior of the specific heat jump ${\rm{\Delta }}C\; $ versus T c $({\rm{\Delta }}C/{T}_{{\rm{c}}}\sim {T}_{{\rm{c}}}^{\alpha }, \alpha \approx 2)$, first observed by Bud'ko et al (2009 Phys. Rev. B 79 220516), has been confirmed with several families of the Fe-based superconducting compounds with various dopings. We tested a minimal two band BCS model to understand this anomalous behavior and showed that this non-BCS relation between ${\rm{\Delta }}C\; $ versus T c is a generic property of the multiband superconducting state paired by a dominant interband interaction (${V}_{\mathrm{inter}}\gt {V}_{\mathrm{intra}}$) reflecting the relation $\frac{{{\rm{\Delta }}}_{{\rm{h}}}}{{{\rm{\Delta }}}_{{\rm{e}}}}\sim \sqrt{\frac{{N}_{{\rm{e}}}}{{N}_{{\rm{h}}}}}$ near T c, as in the ${S}_{\pm }$-wave pairing state. We also found that this ${\rm{\Delta }}C\; $ versus T c power law can continuously change from the ideal BNC scaling to a considerable deviation by a moderate variation of the impurity scattering rate ${{\rm{\Gamma }}}_{0}$ (non-pair-breaking). Finally, as a result, our model provides a consistent explanation why the electron-doped Fe-based superconductors follow the ideal BNC scaling very well while the hole-doped systems often show varying degree of deviations.
Book
1 online resource (Article No. 24223 ) : digital, PDF file.
In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. In conclusion, our findings open up the exciting possibility of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale.
Book
1 online resource (Article No. 013024 ) : digital, PDF file.
The superionic phase transition of ${\mathrm{Cu}}_{2-x}\mathrm{Se}$ accompanies drastic changes in transport properties. The Seebeck coefficient increases sharply while the electrical conductivity and thermal diffusivity drops. Such behavior has previously been attributed to critical phenomena under the assumption of a continuous phase transition. However, applying Landau's criteria suggests that the transition should be first order. Using the phase diagram that is consistent with a first order transition, we show that the observed transport properties and heat capacity curves can be accounted for and modeled with good agreement. The apparent critical phenomena is shown to be a result of compositional degree-of-freedom. In conclusion, understanding of the phase transition allows to explain the enhancement in the thermoelectric figure-of-merit that is accompanied with the transition.
Book
220 p. : digital, PDF file.
This is a 220 page book with research and engineering highlights from the Advanced Photon Source at Argonne National Laboratory for the year 2015.
Book
Article No. 221 : digital, PDF file.
Species and phylogenetic lineages have evolved to differ in the way that they acquire and deploy resources, with consequences for their physiological, chemical and structural attributes, many of which can be detected using spectral reflectance form leaves. Recent technological advances for assessing optical properties of plants offer opportunities to detect functional traits of organisms and differentiate levels of biological organization across the tree of life. We connect leaf-level full range spectral data (400–2400 nm) of leaves to the hierarchical organization of plant diversity within the oak genus (Quercus) using field and greenhouse experiments in which environmental factors and plant age are controlled. We show that spectral data significantly differentiate populations within a species and that spectral similarity is significantly associated with phylogenetic similarity among species. Furthermore, we show that hyperspectral information allows more accurate classification of taxa than spectrally-derived traits, which by definition are of lower dimensionality. Finally, model accuracy increases at higher levels in the hierarchical organization of plant diversity, such that we are able to better distinguish clades than species or populations. This pattern supports an evolutionary explanation for the degree of optical differentiation among plants and demonstrates potential for remote detection of genetic and phylogenetic diversity.
Book
Article No. 11717 : digital, PDF file.
The promise of ultrafast light-field-driven electronic nanocircuits has stimulated the development of the new research field of attosecond nanophysics. An essential prerequisite for advancing this new area is the ability to characterize optical near fields from light interaction with nanostructures, with sub-cycle resolution. Here we experimentally demonstrate attosecond near-field retrieval for a tapered gold nanowire. Furthermore, by comparison of the results to those obtained from noble gas experiments and trajectory simulations, the spectral response of the nanotaper near field arising from laser excitation can be extracted.
Book
1 online resource (p. 4521-4531 ) : digital, PDF file.
The nature of multiple magnetostructural transformations in HoCo<sub>2</sub> has been studied by employing magnetic and specific heat measurements, temperature and magnetic field dependent X-ray powder diffraction, and first-principles calculations. Unexpected increase of magnetization observed below the spin-reorientation temperature (T<sub>SR</sub>) suggests that the low-temperature transition involves a reduction of Co moment. First principles calculations confirm that the paramagnetic cubic to ferrimagnetic tetragonal transformation at T<sub>C</sub> is assisted by itinerant electron metamagnetism, and that the reduction of Co moment in HoCo<sub>2</sub> occurs in parallel with the ferrimagnetic tetragonal to the nearly ferromagnetic orthorhombic transformation at T<sub>SR</sub>via the rearrangement of both 3d states of Co and 5d states of Ho. The ac magnetic susceptibility measurements show significant magnetic frustration below T<sub>C</sub>. Furthermore, in contrast to earlier reports neither ac nor dc magnetic susceptibilities show anomalies in the paramagnetic region obeying the Curie–Weiss law.
Book
Article No. 26348 : digital, PDF file.
Electron microscopy is undergoing a transition; from the model of producing only a few micrographs, through the current state where many images and spectra can be digitally recorded, to a new mode where very large volumes of data (movies, ptychographic and multi-dimensional series) can be rapidly obtained. In this paper, we discuss the application of so-called “big-data” methods to high dimensional microscopy data, using unsupervised multivariate statistical techniques, in order to explore salient image features in a specific example of BiFeO<sub>3</sub> domains. Remarkably, k-means clustering reveals domain differentiation despite the fact that the algorithm is purely statistical in nature and does not require any prior information regarding the material, any coexisting phases, or any differentiating structures. While this is a somewhat trivial case, this example signifies the extraction of useful physical and structural information without any prior bias regarding the sample or the instrumental modality. Further interpretation of these types of results may still require human intervention. Finally, however, the open nature of this algorithm and its wide availability, enable broad collaborations and exploratory work necessary to enable efficient data analysis in electron microscopy.
Book
1 online resource (3 p. ) : digital, PDF file.
In the last grant period we explored the Na+ binding site of the recently discovered light-driven sodium ion pump. The rationale was that comparison of this novel system to the similar proton pumps and chloride ion pumps would reveal the amazingly (and unexpectedly) wide variety of structural features that govern conversion of light-energy into biologically useful transmembrane gradients and thus production of biomass. A thorough description of this system would establish the basis for continuing our funded research on these proteins.
Book
1 online resource (8 p. ) : digital, PDF file.
Stereoselective oxidation of C–H and C=C bonds are catalyzed by nonheme iron enzymes. Inspired by these bioinorganic systems, our group has been exploring the use of nonheme iron complexes as catalysts for the oxidation of hydrocarbons using H2O2 as an environmentally friendly and atom-efficient oxidant in order to gain mechanistic insights into these novel transformations. In particular, we have focused on clarifying the nature of the high-valent iron oxidants likely to be involved in these transformations.
Book
Article No. 19017 : digital, PDF file.
Here, the interactions between electric field and the mechanical properties of materials are important for the applications of microelectromechanical and nanoelectromechanical systems, but relatively unexplored for nanoscale materials. Here, we observe an apparent correlation between the change of the fractured topography of Nb-doped SrTiO<sub>3</sub> (Nb:STO) within the presence of a built-in electric field resulting from the Schottky contact at the interface of a metallic LaNiO<sub>3</sub> thin film utilizing cross-sectional scanning tunneling microscopy and spectroscopy. The change of the inter-atomic bond length mechanism is argued to be the most plausible origin. This picture is supported by the strong-electric-field-dependent permittivity in STO and the existence of the dielectric dead layer at the interfaces of STO with metallic films. These results provided direct evidence and a possible mechanism for the interplay between the electric field and the mechanical properties on the nanoscale for perovskite materials.
Book
1 online resource (9 p. ) : digital, PDF file.
As the world's fossil fuel resources are being depleted and their costs increase, there is an urgent need to discover and develop new processes for the conversion of renewable, biomass resources into fuels and chemical feedstocks. Research and development in this area have been given high priority by both governmental agencies and industry. To increase the energy content and decrease the boiling points of biomass-derived carbohydrates and polyols to the useful liquid range it is necessary to chemically remove water (dehydrate) and, preferably, oxygen (deoxygenate/reduce). The poly-hydroxylic nature of carbohydrates is attractive for their use as functionalized chemical building blocks, but it presents a daunting challenge for their selective conversion to single product chemicals or fuels. The long term, practical objective of this project is to develop catalytic processes for the deoxydehydration (DODH) of biomass-derived carbohydrates and polyols to produce unsaturated alcohols and hydrocarbons of value as chemical feedstocks and fuels; DODH: polyol + reductant --(LMOx catalyst)--> unsaturate + oxidized reductant + H2O. Limited prior studies have established the viability of the DODH process with expensive phosphine reductants and rhenium-catalysts. Initial studies in the PI's laboratory have now demonstrated: 1) the moderately efficient conversion of glycols to olefins by the economical sulfite salts is catalyzed by MeReO3 and Z+ReO4-; 2) effective phosphine-based catalytic DODH of representative glycols to olefins by cheap LMoO2 complexes; and 3) computational studies (with K. Houk, UCLA) have identified several Mo-, W-, and V-oxo complexes that are likely to catalyze glycol DODH. Seeking practically useful DODH reactions of complex polyols and new understanding of the reactivity of polyoxo-metal species with biomass-oxygenates we will employ a two-pronged approach: 1) investigate experimentally the reactivity, both stoichiometric and catalytic, of polyoxo-complexes and practical reductants with representative polyols to establish structure/reactivity relationships and reaction mechanisms; and b) carry out parallel computational studies of these reactions and their mechanisms- both analytical and predictive. Our prioritized action plan is: (1) to optimize the catalytic efficiency, assess the substrate scope/selectivity, and address key mechanistic aspects of Re-catalyzed, sulfite-driven DODH reactions; (2) use the findings from (1), together with computational predictions, to discover new, effective non-precious metal catalysts for sulfite-driven DODH reactions; and 3) to initiate exploratory studies of CO- and H2-driven DODH. Successful execution of this research project will: 1) provide practical chemical processes for the conversion of biomass into useful chemicals and fuels: 2) bring fundamental new understanding of chemical reactions involving metal-oxo catalysts; and 3) provide educational and technical training of future energy scientists.
Book
16 p. : digital, PDF file.
<i>Brachypodium distachyon</i> (<i>Brachypodium</i>) has emerged as a useful model system for studying traits unique to graminaceous species including bioenergy crop grasses owing to its amenability to laboratory experimentation and the availability of extensive genetic and germplasm resources. Considerable natural variation has been uncovered for a variety of traits including flowering time, vernalization responsiveness, and above-ground growth characteristics. However, cell wall composition differences remain underexplored. Therefore, we assessed cell wall-related traits relevant to biomass conversion to biofuels in seven <i>Brachypodium</i> inbred lines that were chosen based on their high level of genotypic diversity as well as available genome sequences and recombinant inbred line (RIL) populations. Senesced stems plus leaf sheaths from these lines exhibited significant differences in acetyl bromide soluble lignin (ABSL), cell wall polysaccharide-derived sugars, hydroxycinnamates content, and syringyl:guaiacyl:p-hydroxyphenyl (S:G:H) lignin ratios. Free glucose, sucrose, and starch content also differed significantly in senesced stems, as did the amounts of sugars released from cell wall polysaccharides (digestibility) upon exposure to a panel of thermochemical pretreatments followed by hydrolytic enzymatic digestion. Correlations were identified between inbred line lignin compositions and plant growth characteristics such as biomass accumulation and heading date (HD), and between amounts of cell wall polysaccharides and biomass digestibility. Finally, stem cell wall p-coumarate and ferulate contents and free-sugars content changed significantly with increased duration of vernalization for some inbred lines. Taken together, these results show that <i>Brachypodium</i> displays substantial phenotypic variation with respect to cell wall composition and biomass digestibility, with some compositional differences correlating with growth characteristics. Moreover, besides influencing HD and biomass accumulation, vernalization was found to affect cell wall composition and free sugars accumulation in some <i>Brachypodium</i> inbred lines, suggesting genetic differences in how vernalization affects carbon flux to polysaccharides. Lastly, the availability of related RIL populations will allow for the genetic and molecular dissection of this natural variation, the knowledge of which may inform ways to genetically improve bioenergy crop grasses.