First Principles Calculations of Ionic Vibrational Frequencies in PbMg1/3Nb2/3O3

Lattice dynamics for several ordered supercells with composition PbMg1/3Nb2/3O (PMN) were calculated with first-principles frozen phonon methods. Nominal symmetries of the supercells studied are reduced by lattice instabilities. Lattice modes corresponding to these instabilities, equilibrium ionic positions, and infrared (IR) reflectivity spectra are reported.Comment: 6 pages; Fundamental physics of Ferroelectrics 200

Factors influencing adoption of conservation tillage in Australian cropping regions

The purpose of this research is to improve understanding of conservation tillage adoption decisions by identifying key biophysical and socio-economic factors influencing no-till adoption by grain growers across four Australian cropping regions. The study is based on interviews with 384 grain growers using a questionnaire aimed at eliciting perceptions relating to a range of possible long- and short-term agronomic interactions associated with the relative economic advantage of shifting to a no-tillage cropping system. Together with other farm and farmer-specific variables, a dichotomous logistic regression analysis was used to identify opportunities for research and extension to facilitate more rapid adoption decisions. The broader systems approach to considering conservation tillage adoption identified important determinants of adoption not associated with soil conservation and erosion prevention benefits. Most growers recognised the erosion-reducing benefits of no-till but it was not an important factor in explaining whether a grower was an adopter or non-adopter. Perceptions associated with shorter-term crop production benefits under no-till, such as the relative effectiveness of pre-emergent herbicides and the ability to sow crops earlier on less rainfall were influential. Employment of a consultant and increased attendance of cropping extension activities were strongly associated with no-till adoption, confirming the information and learning-intensive nature of adopting no-till cropping systems.adoption, conservation tillage, herbicide resistance, no-till, perceptions, weed management, Farm Management,

The molecular environment of massive star forming cores associated with Class II methanol maser emission

Methanol maser emission has proven to be an excellent signpost of regions undergoing massive star formation (MSF). To investigate their role as an evolutionary tracer, we have recently completed a large observing program with the ATCA to derive the dynamical and physical properties of molecular/ionised gas towards a sample of MSF regions traced by 6.7 GHz methanol maser emission. We find that the molecular gas in many of these regions breaks up into multiple sub-clumps which we separate into groups based on their association with/without methanol maser and cm continuum emission. The temperature and dynamic state of the molecular gas is markedly different between the groups. Based on these differences, we attempt to assess the evolutionary state of the cores in the groups and thus investigate the role of class II methanol masers as a tracer of MSF.Comment: 5 pages, 1 figure, IAU Symposium 242 Conference Proceeding

Quadrilateral-octagon coordinates for almost normal surfaces

Normal and almost normal surfaces are essential tools for algorithmic 3-manifold topology, but to use them requires exponentially slow enumeration algorithms in a high-dimensional vector space. The quadrilateral coordinates of Tollefson alleviate this problem considerably for normal surfaces, by reducing the dimension of this vector space from 7n to 3n (where n is the complexity of the underlying triangulation). Here we develop an analogous theory for octagonal almost normal surfaces, using quadrilateral and octagon coordinates to reduce this dimension from 10n to 6n. As an application, we show that quadrilateral-octagon coordinates can be used exclusively in the streamlined 3-sphere recognition algorithm of Jaco, Rubinstein and Thompson, reducing experimental running times by factors of thousands. We also introduce joint coordinates, a system with only 3n dimensions for octagonal almost normal surfaces that has appealing geometric properties.Comment: 34 pages, 20 figures; v2: Simplified the proof of Theorem 4.5 using cohomology, plus other minor changes; v3: Minor housekeepin

Giant Molecular Clouds are More Concentrated to Spiral Arms than Smaller Clouds

From our catalog of Milky Way molecular clouds, created using a temperature thresholding algorithm on the Bell Laboratories 13CO Survey, we have extracted two subsets:(1) Giant Molecular Clouds (GMCs), clouds that are definitely larger than 10^5 solar masses, even if they are at their `near distance', and (2) clouds that are definitely smaller than 10^5 solar masses, even if they are at their `far distance'. The positions and velocities of these clouds are compared to the loci of spiral arms in (l, v) space. The velocity separation of each cloud from the nearest spiral arm is introduced as a `concentration statistic'. Almost all of the GMCs are found near spiral arms. The density of smaller clouds is enhanced near spiral arms, but some clouds (~10%) are unassociated with any spiral arm. The median velocity separation between a GMC and the nearest spiral arm is 3.4+-0.6 km/s, whereas the median separation between smaller clouds and the nearest spiral arm is 5.5+-0.2 km/s.Comment: 11 pages, 3 figure

Nonlinear stabilitty for steady vortex pairs

In this article, we prove nonlinear orbital stability for steadily translating vortex pairs, a family of nonlinear waves that are exact solutions of the incompressible, two-dimensional Euler equations. We use an adaptation of Kelvin's variational principle, maximizing kinetic energy penalised by a multiple of momentum among mirror-symmetric isovortical rearrangements. This formulation has the advantage that the functional to be maximized and the constraint set are both invariant under the flow of the time-dependent Euler equations, and this observation is used strongly in the analysis. Previous work on existence yields a wide class of examples to which our result applies.Comment: 25 page

New approaches to investigating the function of mycelial networks

Fungi play a key role in ecosystem nutrient cycles by scavenging, concentrating, translocating and redistributing nitrogen. To quantify and predict fungal nitrogen redistribution, and assess the importance of the integrity of fungal networks in soil for ecosystem function, we need better understanding of the structures and processes involved. Until recently nitrogen translocation has been experimentally intractable owing to the lack of a suitable radioisotope tracer for nitrogen, and the impossibility of observing nitrogen translocation in real time under realistic conditions. We have developed an imaging method for recording the magnitude and direction of amino acid flow through the whole mycelial network as it captures, assimilates and channels its carbon and nitrogen resources, while growing in realistically heterogeneous soil microcosms. Computer analysis and modeling, based on these digitized video records, can reveal patterns in transport that suggest experimentally testable hypotheses. Experimental approaches that we are developing include genomics and stable isotope NMR to investigate where in the system nitrogen compounds are being acquired and stored, and where they are mobilized for transport or broken down. The results are elucidating the interplay between environment, metabolism, and the development and function of transport networks as mycelium forages in soil. The highly adapted and selected foraging networks of fungi may illuminate fundamental principles applicable to other supply networks

The Effects of Thermal Metamorphism on the Amino Acid Content of the CI-Like Chondrite Y-86029

Carbonaceous chondrites con-tain a diverse suite of amino acids that varies in abundance and structural diversity depending on the degree of aqueous alteration and thermal histo-ry that the parent body experienced [1 - 3]. We recently determined the amino acid contents of several fragments of the Sutter's Mill CM2 chon-drite [4]. In contrast with most other CM2 chon-drites, the Sutter's Mill meteorites showed minimal evidence for the presence of indigenous amino acids. A notable difference between the Sutter's Mill meteorites and other CM2 chondrites are that the Sutter's Mill stones were heated to tempera-tures of 150 - 400 C [4], whereas most other CM2 chondrites do not show evidence for thermal met-amorphism [5]. Because empirical studies have shown that amino acids rapidly degrade in aqueous solutions above 150 C and the presence of miner-als accelerates this degradation [6], a plausible explanation for the lack of amino acids observed in the Sutter's Mill meteorites is that they were destroyed during metamorphic alteration. Fewer CI chondrites have been analyzed for amino acids because only a small number of these meteorites have been recovered. Nevertheless, indigenous amino acids have been reported in the CI chondrites Ivuna and Orgueil [7]. Here we report on the amino acid analysis of the CI-like chondrite, Yamato 86029 (Y-86029; sample size of 110 mg). Just as the Sutter's Mill meteorites were thermally metamporphosed CM2 chondrites, Y-86029 has experienced thermal metamorphism at higher temperatures than Orgueil and Ivuna (normal CI chondrites) experienced, possibly up to 600 C [8]

Suppression of Octahedral Tilts and Associated Changes of Electronic Properties at Epitaxial Oxide Heterostructure Interfaces

Epitaxial oxide interfaces with broken translational symmetry have emerged as a central paradigm behind the novel behaviors of oxide superlattices. Here, we use scanning transmission electron microscopy to demonstrate a direct, quantitative unit-cell-by-unit-cell mapping of lattice parameters and oxygen octahedral rotations across the BiFeO3-La0.7Sr0.3MnO3 interface to elucidate how the change of crystal symmetry is accommodated. Combined with low-loss electron energy loss spectroscopy imaging, we demonstrate a mesoscopic antiferrodistortive phase transition and elucidate associated changes in electronic properties in a thin layer directly adjacent to the interface