58 research outputs found
Ein Beitrag zur Erforschung der Steinkegelaltäre vom Typ Rungger Egg. Vorbericht über die Ausgrabungen am Wallnereck in der Gemeinde Ritten (Südtirol)
No full textA Contribution to the Study of Conical Stone Altars of the Rungger Egg Type.
Preliminary Report on the Excavations at Wallnereck in the Municipalty of Ritten(South Tyrol)The site at Wallnereck in the municipality of Ritten (Bozen province, Italy) is one of themany conical stone pyramids of the Rungger Egg or Bozen type that have often been mentioned in the literature. The excavation provides the first detailed insight into the use and characteristics of such a site. It is indeed a burnt-offering place, as has been assumed by most authors, but in the case of Wallnereck it was not the conical stone pyramid that was used as a cremation site, but instead the area below it. Additionally, a dating framework for the construction of the complex could be worked out in the stage Ha D / Lt A
Riduzione e controllo di NOx nelle emissioni da impianti di termodistruzione di RSU attraverso l'utilizzo di urea
No full textNon-equilibrium Green’s Function Methods for Spin Transport and Dynamics
No full textThe modeling of spintronic devices is a theoretical challenge, since one has to describe accurately both the electronic structure of the constituent materials and their charge- and spin-transport properties. In this chapter we present the state-of-the-art quantum transport theory appropriate for this task. The theory is based on the so-called non-equilibrium Green’s function formalism, which is combined with density functional theory in order to provide a first principles description of materials properties. This allows for the evaluation of the steady-state charge and spin current through a quantum system at a finite applied bias voltage between the electrodes. It also describes the spin-transfer torque that flowing spins exert on localized magnetic moments, which is able to switch the magnetization of a magnetic system. In this chapter the detailed discussion about the principal methodological aspects is accompanied by the review of a number of technologically relevant applications
DFT+Σ2 method for electron correlation effects at transition metal surfaces
No full textWe present a computational approach for electronically correlated metallic surfaces and interfaces, which combines density functional and dynamical mean-field theory using a multiorbital perturbative solver for the many-body problem. Our implementation is designed to describe ferromagnetic metallic thin films on a substrate. The performances are assessed in detail for a Fe monolayer on a W(110) substrate, a prototypical nanoscale magnetic system. Comparing our results to photoemission data, we find qualitative and quantitative improvements in the calculated spectral function with respect to the results of density functional theory within the local spin density approximation. In particular, the spin splitting of the d states is drastically reduced and, at the same time, their spectral width becomes narrower. The method is, therefore, able to account for the main correlation effects in the system
Robust organic radical molecular junctions using acetylene terminated groups for c-au bond formation
No full textOrganic paramagnetic and electroactive molecules are attracting interest as core components of molecular electronic and spintronic devices. Currently, further progress is hindered by the modest stability and reproducibility of the molecule/electrode contact. We report the synthesis of a persistent organic radical bearing one and two terminal alkyne groups to form Au-C σ bonds. The formation and stability of self-assembled monolayers and the electron transport through single-molecule junctions at room temperature have been studied. The combined analysis of both systems demonstrates that this linker forms a robust covalent bond with gold and a better-defined contact when compared to traditional sulfur-based linkers. Density functional theory and quantum transport calculations support the experimental observation highlighting a reduced variability of conductance values for the C-Au based junction. Our findings advance the quest for robustness and reproducibility of devices based on electroactive molecules.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.QN/van der Zant LabQN/Afdelingsburea
Approximations of stochastic hybrid systems: A compositional approach
No full textIn this paper we propose a compositional framework for the construction of approximations of the interconnection of a class of stochastic hybrid systems.As special cases, this class of systems includes both jump linear stochastic systems and linear stochastic hybrid automata. In the proposed framework, an approximation is itself a stochastic hybrid system, which can be used as areplacement of the original stochastic hybrid system in a controller design process. We employ a notion of so-called stochastic simulation function to quantify the error between the approximation and the original system. In the first part of the paper, we derive sufficient conditions which facilitate the compositional quantification of the error between the interconnection of stochastic hybrid subsystems and that of their approximations using the quantified error between the stochastic hybrid subsystems and their corresponding approximations. In particular, we show how to constructstochastic simulation functions for approximations of interconnectedstochastic hybrid systems using the stochastic simulation function for the approximation of each component.In the second part of the paper, we focus on a specific class of stochastic hybrid systems, namely, jump linear stochastic systems, and propose a constructive scheme to determine approximations together with their stochasticsimulation functions for this class of systems. Finally, we illustrate the effectiveness of the proposed results by constructing an approximation of the interconnection of four jump linear stochastic subsystems in a compositionalway.Accepted Author ManuscriptTeam Tamas Keviczk
Predicting the conductance of strongly correlated molecules: the Kondo effect in perchlorotriphenylmethyl/Au junctions
No full textStable organic radicals integrated into molecular junctions represent a practical realization of the single-orbital Anderson impurity model. Motivated by recent experiments for perchlorotriphenylmethyl (PTM) molecules contacted to gold electrodes, we develop a method that combines density functional theory (DFT), quantum transport theory, numerical renormalization group (NRG) calculations and renormalized super-perturbation theory (rSPT) to compute both equilibrium and non-equilibrium properties of strongly correlated nanoscale systems at low temperatures effectively from first principles. We determine the possible atomic structures of the interfaces between the molecule and the electrodes, which allow us to estimate the Kondo temperature and the characteristic transport properties, which compare well with experiments. By using the non-equilibrium rSPT results we assess the range of validity of equilibrium DFT + NRG-based transmission calculations for the evaluation of the finite voltage conductance. The results demonstrate that our method can provide qualitative insights into the properties of molecular junctions when the molecule-metal contacts are amorphous or generally ill-defined, and that it can further give a fully quantitative description when the experimental contact structures are well characterized.A. D. and I. R. acknowledge the financial support from the EU project ACMOL (FET Young Explorers, No. 618082). A. D. received additional support from EU Marie Sklodowska-Curie project SPINMAN (No. SEP-210189940) and from the Ministerio de Economía y Competitividad de España
(No. FPDI-2013-16641). I. R. acknowledges additional financial support from the EU H2020 programme PETMEM project (Grant No. 688282). I. R. thanks the Cambridge CSD3 HPC centre for providing part of the computing resources. W. H. A., L. C. and D. V. acknowledge the financial support from the Deutsche Forschungsgemeinschaft through TRR80/F6, TRR80/G7 and the FOR1346/P3. E. Muñoz acknowledges financial support by Fondecyt (Chile) No. 1141146. M. M. Radonjić acknowledges the support from Ministry of Education, Science, and Technological Development of the Republic of Serbia under project ON171017. S. Kirchner acknowledges support by the National Key R&D Program of the MOST of China, grant No. 2016YFA0300202, the National Science Foundation of China, grant No. 11774307 and No. 11474250, and the U.S.
Army RDECOM – Atlantic Grant No. W911NF-17-1-0108.Peer reviewe
Dramatic Changes in the Ratio of Homologous Recombination to Nonhomologous DNA-End Joining in Oocytes and Early Embryos of<i>Xenopus laevis</i>
No full textWe have developed a versatile plasmid vector (pReco-sigma) for recombination studies. When linearized and introduced into the cells of interest, pReco-sigma allows the simultaneous determination of the relative frequencies of homologous recombination versus nonhomologous DNA-end joining (also termed end-to-end joining), the latter an example of illegitimate recombination processes. As a system we made use of stage VI oocytes and fertilized eggs of the African clawed frog Xenopus laevis, which were previously described to support homologous recombination and DNA-end joining, respectively. Extending these earlier findings, we show that oocytes yield > 80% of the homologously recombined product, whereas in eggs a highly efficient DNA-end joining activity predominates (> 95%). Both reactions, homologous recombination and DNA-end joining, are shown to occur quickly, with the majority of the respective products being formed within the first 20 minutes of incubation under optimal conditions. In fertilized eggs, up to 50% of all injected linear DNA molecules are recircularized by DNA-end joining. With high amounts of injected DNA per fertilized egg, DNA-end joining is reduced, presumably due to competition for essential factors, and homologous recombination becomes readily detectable. As there is a sequence of rapid cleavage divisions after fertilization of the egg, the fast and highly efficient DNA-end joining, even though it is error-prone at the junction site, seems to be best suited to cope with DNA double-strand breaks that might occur in the genome during early embryogenesis. On the other hand, the long-lived oocytes seem to repair DNA double-strand breaks via homologous recombination. This latter property may be exploited both in Xenopus and in other organisms to achieve homologous integration of exogenous DNA into germ cells for gene targeting
Interface and transport properties of Fe/V/MgO/Fe and Fe/V/Fe/MgO/Fe magnetic tunneling junctions
No full textThe interface and transport properties of Fe/V/MgO/Fe and Fe/V/Fe/MgO/Fe magnetic tunneling junctions
are investigated by using density-functional theory and nonequilibrium Green?s-function methods. Bader
analysis reveals that the Fe layer at the interface with MgO loses a small amount of charge with respect to its
bulk value, in contrast to a previous study
W. H. Butler, X.-G. Zhang, T. C. Schulthess, and J. M. MacLaren
Phys, Rev. B
63
, 054416
2001
. At the same time at the Fe/V interface a magnetic moment is induced on the
V layer by proximity. Importantly, the direction of the magnetization of the first V monolayer immediately
close to the MgO barrier oscillates with the total V-layer thickness and the relative stability of a particular
magnetic configuration weakens as such a thickness is increased. These two aspects pose a challenge to the
Fe/V/MgO/Fe device signal stability. A more intriguing situation is found for Fe/V/Fe/MgO/Fe junctions. Their
transport properties depend sensitively on the thickness of the Fe layer intercalated between V and the MgO
barrier. This is the result of resonances through quantum-well states of
1
symmetry localized in the interca-
lated Fe layer. In particular, for some geometries we find a massive magnetoresistance obtained by simply
switching the direction of the magnetization of the Fe interlayer, while keeping the direction of the electrodes
fixed. This effect may be employed in the design of new spin valves with extremely high spin polarization but
still relatively large current densitie
Homologous recombination and DNA-end joining reactions in zygotes and early embryos of zebrafish (Danio rerio) and Drosophila melanogaster.
No full textA linear DNA with partial sequence redundancy can be recircularized in cells by either nonhomologous end joining (NEJ) or by homologous recombination (HR). We have studied the relative contributions of these processes in zygotes or early embryos of species that serve as model organisms for developmental genetics. Thus, we have microinjected a linearized plasmid substrate into zygotes of zebrafish (Danio rerio) or into the posterior end of Drosophila melanogaster early embryos before pole cell formation. Similar to the situation observed previously in Xenopus zygotes/early embryos, we detected a large preponderance of DNA-end joining over homologous recombination. A comparison of end-joined junctions revealed that from the three species tested, zebrafish introduced the least number of sequence distortions upon DNA-end joining, while Drosophila produced the largest deletions (average 14 bp) with occasional nucleotide patch insertions, reminiscent of the N nucleotides at V(D)J junctions in mammalian immune receptor genes. Double-strand gap repair by homologous sequences ('homologous recombination') involving a bimolecular reaction was readily detectable in both zebrafish and Drosophila. This involved specifically designed recombination substrates consisting of a mutagenized linear plasmid and DNA fragments carrying the wild-type sequence. Our results show that the basic machinery for homologous recombination is present at early developmental stages of these two genetic model organisms. However, it seems that for any experimental exploitation, such as targeted gene disruption, one would have to inhibit or bypass the overwhelming DNA-end joining activity
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