A continuous-time solver for quantum impurity models

We present a new continuous time solver for quantum impurity models such as those relevant to dynamical mean field theory. It is based on a stochastic sampling of a perturbation expansion in the impurity-bath hybridization parameter. Comparisons to quantum Monte Carlo and exact diagonalization calculations confirm the accuracy of the new approach, which allows very efficient simulations even at low temperatures and for strong interactions. As examples of the power of the method we present results for the temperature dependence of the kinetic energy and the free energy, enabling an accurate location of the temperature-driven metal-insulator transition.Comment: Published versio

Nitrogen fertiliser management with zone characterisation in grazed pasture systems

Spatial information is frequently used for managing arable crops. The idea of developing management zones is often to enable accurate fertiliser supply for local crop needs. This helps avoid excessive introduction of nutrients, such as nitrogen, into the environment, and also to reduce fertiliser costs. Despite the success of this concept in arable farming, it is a poorly adopted practice for the management of grazed pastures. Grazed pasture systems have an additional level of complexity compared to monoculture, annual crops. Pastures are typically perennial in nature with short intervals between harvests (by a grazing animal) and therefore require fertiliser applications to maintain biomass production. Additionally, pastures often consist of two or more desirable plant species and the distribution of waste from livestock results in many small patches of very high nutrient content. We propose a concept to create management zones of grazed dairy pastures, using the spatial attributes of pasture paddocks. The target will be to identify zones of most likely high nitrogen availability and use this information to estimate the required local fertiliser target. The spatial information required for this approach may include: soil variation, irrigation, animal density, slope, farm infrastructure (i.e troughs and shelter) and previous pasture growth. Using a geographical information system, the spatial information for an area can be utilised to create map layers. These layers can then be spatially related and zones for the application of varying amounts of fertiliser can be developed at the sub-paddock scale. We are in theprocess of deriving response curves for N-ramps on selected paddocks in NZ and Australia which have sufficient spatial variability of the mentioned site characteristics. We undertook a theoretical feasibility study to compare both uniform and variable nitrogen fertiliser application as an initial investigation of the potential benefit of zone management. The integrated result (value of feed –cost of fertiliser –cost of environmental impact) of applying nitrogen variably across a paddock of dynamic soil using a non-linear response function was slightly lower than for uniform application. It is expected however, that increased understanding of spatial variables in pastures will increase the benefits of zone management

Energy-filtered transmission electron microscopy of biological samples on highly transparent carbon nanomembranes

Ultrathin carbon nanomembranes (CNM) comprising crosslinked biphenyl precursors have been tested as support films for energy-filtered transmission electron microscopy (EFTEM) of biological specimens. Due to their high transparency CNM are ideal substrates for electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) of stained and unstained biological samples. Virtually background-free elemental maps of tobacco mosaic virus (TMV) and ferritin have been obtained from samples supported by ~ 1 nm thin CNM. Furthermore, we have tested conductive carbon nanomembranes (cCNM) comprising nanocrystalline graphene, obtained by thermal treatment of CNM, as supports for cryoEM of ice-embedded biological samples. We imaged ice-embedded TMV on cCNM and compared the results with images of ice-embedded TMV on conventional carbon film (CC), thus analyzing the gain in contrast for TMV on cCNM in a quantitative manner. In addition we have developed a method for the preparation of vitrified specimens, suspended over the holes of a conventional holey carbon film, while backed by ultrathin cCNM

Mimetischer Zauber: Die englischsprachige Rezeption deutscher Lieder in den USA, 1830-1880

The English-language reception of German songs in the United States was a textual practice that extended across many social contexts in the 19th century. Translation, adaptation and circulation of these songs were a form of rhetorical and quasi mimetic representation that helped various American discourses constitute their worlds and identities (Transcendentalism, reform movements, revivalism, education, popular culture, political parties and the Civil War). Homi Bhabha's concept of the "Third Space" is a valid approach to the reception as these discourses made German songs part of their negotiations of American national identity, class, moral values, gender, and ethnicity, thus creating their own usable as well as ambivalent German point of reference. German and American cultures did not simply coexist in symbiotic relations. Rather, as the reception shows, they constructed their identities and differences through multiple intertextual relations within a shared discursive sphere of song. Cultural transfer was thus as much an inside as an outside phenomenon. The dissertation builds on extensive archival research and a collection of several hundred German songs, each with melody and English text, ranging from the Classics, Romanticism, the Napoleonic Wars, to German, Austrian and Swiss folk songs. The main objective is to move the American reception of German songs from its hidden archival existence into the light of scholarly investigation by applying an interdisciplinary Cultural Studies approach. The dissertation uses Michel Foucault's discourse analysis to refine this approach methodologically, demonstrating with an in-depth archeology the discursive function of the songs within their contexts. Two results of this analysis are crucial. First, it goes significantly beyond the existing scholarship on German-American relations in the 19th century (New England Transcendentalists, immigrant history) as it explores the German within the wider contexts of American popular culture. Second, by doing so it reads these relations against their scholarly and collective narratives, sharing Walter Benjamin's emancipatory vision of history as a site of potentially many readings. In addition, the dissertation contributes to a broader understanding of German literature within the historical, cultural and interdisciplinary contexts of German Studies

Integrated quantized electronics: a semiconductor quantized voltage source

The Josephson effect in superconductors links a quantized output voltage Vout = f \cdot(h/2e) to the natural constants of the electron's charge e, Planck's constant h, and to an excitation frequency f with important applications in electrical quantum metrology. Also semiconductors are routinely applied in electrical quantum metrology making use of the quantum Hall effect. However, despite their broad range of further applications e.g. in integrated circuits, quantized voltage generation by a semiconductor device has never been obtained. Here we report a semiconductor quantized voltage source generating quantized voltages Vout = f\cdot(h/e). It is based on an integrated quantized circuit of a single electron pump operated at pumping frequency f and a quantum Hall device monolithically integrated in series. The output voltages of several \muV are expected to be scalable by orders of magnitude using present technology. The device might open a new route towards the closure of the quantum metrological triangle. Furthermore it represents a universal electrical quantum reference allowing to generate quantized values of the three most relevant electrical units of voltage, current, and resistance based on fundamental constants using a single device.Comment: 15 pages, 3 figure

Single-walled carbon nanotubes and nanocrystalline graphene reduce beam-induced movements in high-resolution electron cryo-microscopy of ice-embedded biological samples

For single particle electron cryo-microscopy (cryoEM), contrast loss due to beam-induced charging and specimen movement is a serious problem, as the thin films of vitreous ice spanning the holes of a holey carbon film are particularly susceptible to beam-induced movement. We demonstrate that the problem is at least partially solved by carbon nanotechnology. Doping ice-embedded samples with single-walled carbon nanotubes (SWNT) in aqueous suspension or adding nanocrystalline graphene supports, obtained by thermal conversion of cross-linked self-assembled biphenyl precursors, significantly reduces contrast loss in high-resolution cryoEM due to the excellent electrical and mechanical properties of SWNTs and graphene

Vitamin D receptor genotype BB is associated with higher serum osteocalcin in first pregnancy

Aim: Serum osteocalcin was shown in a previous study on first trimester pregnant women to correlate with bone density and to distinguish between fast and slow bone losers. The objective of the present study is to examine whether serum osteocalcin is related to vitamin D receptor (VDR) BsmI polymorphism in pregnant women. Study design: We determined osteocalcin serum levels and VDR BsmI genotype in 97 healthy first trimester pregnant women consecutively recruited during six months. Results: BB (21%), Bb (38%) and bb (41%) genotypes showed similar osteocalcin serum levels. However, in primigravidas (n=38) the BB genotype was significantly associated with higher mean osteocalcin level (9.67 ng/mL) than the Bb (8.07ng/mL) and the bb genotype (8.14ng/mL), respectively (P<0.05). The VDR genotype was the only independent parameter to correlate with serum osteocalcin (P<0.05). Conclusion: Only primigravidas show in the first trimester a relation between the bone formation parameter serum osteocalcin and the VDR genotype BB which indicates a higher risk of fractures. For further clinical applications serum osteocalcin and VDR genotype should be tested on a cohort of primigravidas including measurements of bone densit

Task acquisition with a description logic reasoner

In many knowledge based systems the application domain is modeled in an object-centered formalism. Research in knowledge acquisition has given evidence that this approach allows one to adequately model the conceptual structures of human experts. However, when a novice user wants to describe a particular task to be solved by such a system he has to be well acquainted with the underlying domain model, and therefore is charged with the burden of making himself familiar with it. We aim at giving automated support to a user in this process, which we call task acquisition. This paper describes the TACOS system, which guides a user through an object-centered domain model and gives support to him in specifying his task. A characteristic of TACOS is that the user can enter only information that is meaningful and consistent with the domain model. In order to identify such information, TACOS exploits the ability of a description logic based knowledge representation system to reason about such models

Stabilizing a metalloid Zn12_{12} unit within a polymetallide environment in [K2_{2}Zn20_{20}Bi16_{16}]6−^{6-}

The access to molecules comprising direct Zn–Zn bonds has become very topical in recent years for various reasons. Low-valent organozinc compounds show remarkable reactivities, and larger Zn–Zn-bonded gas-phase species exhibit a very unusual coexistence of insulating and metallic properties. However, as Zn atoms do not show a high tendency to form clusters in condensed phases, synthetic approaches for generating purely inorganic metalloid Zn$_{x}$ units under ambient conditions have been lacking so far. Here we show that the reaction of a highly reductive solid with the nominal composition K$_{5}$Ga$_{2}$Bi$_{4}$ with ZnPh2 at room temperature yields the heterometallic cluster anion [K$_{2}$Zn$_{20}$Bi$_{16}$]$^{6-}$. A 24-atom polymetallide ring embeds a metalloid {Zn$_{12}$} unit. Density functional theory calculations reveal multicenter bonding, an essentially zero-valent situation in the cluster center, and weak aromaticity. The heterometallic character, the notable electron-delocalization, and the uncommon nano-architecture points at a high potential for nano-heterocatalysis

Milk fatty acids estimated by mid-infrared spectroscopy and milk yield can predict methane emissions in dairy cows

Ruminant enteric methane emission contributes to global warming. Although breeding low methane-emitting cows appears to be possible through genetic selection, doing so requires methane emission quantification by using elaborate instrumentation (respiration chambers, SF6 technique, GreenFeed) not feasible on a large scale. It has been suggested that milk fatty acids are promising markers of methane production. We hypothesized that methane emission can be predicted from the milk fatty acid concentrations determined by mid-infrared spectroscopy, and the integration of energy-corrected milk yield would improve the prediction. Therefore, we examined relationships between methane emission of cows measured in respiration chambers and milk fatty acids, predicted by mid-infrared spectroscopy, to derive diet-specific and general prediction equations based on milk fatty acid concentrations alone and with the additional consideration of energy-corrected milk yield. Cows were fed diets differing in forage type and linseed supplementation to generate a large variation in both CH4 emission and milk fatty acids. Depending on the diet, equations derived from regression analysis explained 61 to 96% of variation of methane emission, implying the potential of milk fatty acid data predicted by mid-infrared spectroscopy as novel proxy for direct methane emission measurements. When data from all diets were analyzed collectively, the equation with energy-corrected milk yield (CH4 (L/day) = − 1364 + 9.58 × energy-corrected milk yield + 18.5 × saturated fatty acids + 32.4 × C18:0) showed an improved coefficient of determination of cross-validation R2 CV = 0.72 compared to an equation without energy-corrected milk yield (R2 CV = 0.61). Equations developed for diets supplemented by linseed showed a lower R2 CV as compared to diets without linseed (0.39 to 0.58 vs. 0.50 to 0.91). We demonstrate for the first time that milk fatty acid concentrations predicted by mid-infrared spectroscopy together with energy-corrected milk yield can be used to estimate enteric methane emission in dairy cows. © 2018, The Author(s)