417 research outputs found
Nachbauprobleme bei Apfelkulturen
Bei wiederholtem Anbau von Obstbäumen am gleichen Standort wird häufig verminderter Wuchs und reduzierter Ertrag beobachtet. Dieses Phänomen wird als Nachbauproblem oder Bodenmüdigkeit bezeichnet. Auch Schweizer Apfelproduzenten sind davon betroffen. Die ACW untersucht mögliche Ursachen
STM microscopy of the CDW in 1T-TiSe2 in the presence of single atom defects
We present a detailed low temperature scanning tunneling microscopy study of
the commensurate charge density wave (CDW) in 1-TiSe in the presence of
single atom defects. We find no significant modification of the CDW lattice in
single crystals with native defects concentrations where some bulk probes
already measure substantial reductions in the CDW phase transition signature.
Systematic analysis of STM micrographs combined with density functional theory
modelling of atomic defect patterns indicate that the observed CDW modulation
lies in the Se surface layer. The defect patterns clearly show there are no
2-polytype inclusions in the CDW phase, as previously found at room
temperature [Titov A.N. et al, Phys. Sol. State 53, 1073 (2011). They further
provide an alternative explanation for the chiral Friedel oscillations recently
reported in this compound [J. Ishioka et al., Phys. Rev. B 84, 245125, (2011)].Comment: 5 pages, 4 figure
Doping nature of native defects in 1T-TiSe2
The transition metal dichalcogenide 1T-TiSe2 is a quasi two-dimensional
layered material with a charge density wave (CDW) transition temperature of
TCDW 200 K. Self-doping effects for crystals grown at different temperatures
introduce structural defects, modify the temperature dependent resistivity and
strongly perturbate the CDW phase. Here we study the structural and doping
nature of such native defects combining scanning tunneling
microscopy/spectroscopy and ab initio calculations. The dominant native single
atom dopants we identify in our single crystals are intercalated Ti atoms, Se
vacancies and Se substitutions by residual iodine and oxygen.Comment: 5 pages, 3 figure
Exciton condensation driving the periodic lattice distortion of 1T-TiSe2
We address the lattice instability of 1T-TiSe2 in the framework of the
exciton condensate phase. We show that, at low temperature, condensed excitons
influence the lattice through electron-phonon interaction. It is found that at
zero temperature, in the exciton condensate phase of 1T-TiSe2, this exciton
condensate exerts a force on the lattice generating ionic displacements
comparable in amplitude to what is measured in experiment. This is thus the
first quantitative estimation of the amplitude of the periodic lattice
distortion observed in 1T-TiSe2 as a consequence of the exciton condensate
phase.Comment: 5 pages, 3 figures and 1 tabl
Synthesis of structurally diverse 3,4-dihydropyrimidin-2(1H)-ones via sequential Biginelli and Passerini reactions
The Biginelli reaction was combined with the Passerini reaction for the first time in a sequential multicomponent tandem reaction approach. After evaluation of all possible linker components and a suitable solvent system, highly functionalized dihydropyrimidone–α-acyloxycarboxamide compounds were obtained in good to excellent yields. In a first reaction step, different 3,4-dihydropyrimidin-2(1H)-one acids were synthesized, isolated and fully characterized. These products were subsequently used in a Passerini reaction utilizing a dichloromethane/dimethyl sulfoxide solvent mixture. By variation of the components in both multicomponent reactions, a large number of structurally diverse compounds could be synthesized. In addition, a one-pot Biginelli–Passerini tandem reaction was demonstrated. All products were carefully characterized via 1D and 2D NMR as well as IR and HRMS
Manual of VIKAASA: An application capable of computing and graphing viability kernels for simple viability problems
This manual introduces and provides usage details for an application we have developed called VIKAASA, as well as the library of functions underlying it. VIKAASA runs in GNU Octave or MATLAB®, using the numerical computing and graphing capabilities of those packages to approximate, visualise and test viability kernels for viability problems involving a differential inclusion of two or more dynamic variables, a rectangular constraint set and a single scalar control
Heavy Metal Contamination of Soil by Quarry Dust at Asonomaso in the Ashanti Region of Ghana
Environmental pollution caused by quarry dust and heavy metals is a problem for many years in Asonomaso. The main aim of this paper was to determine the amount and types of heavy metal pollutants associated with the quarrying and also identify the probable adverse effects they have on human health and the environment. About 30 quarry dust samples were collected from two sampling sites between August and November, 2011 for analysis using AAS. Evaluation using SPSS 17.0 statistical programme revealed appreciable amounts of As, Hg, Mn, Cu Zn and Pb and Fe which differ from one site to another. AAS analysis revealed relatively higher concentrations of As, Ag, Cu and Zn in both primary and secondary quarry dust than dust away from the site. However, concentrations of Mn, Fe and Pb were higher in secondary quarry dust and dust away from the primary site. Heavy metal pollution of the Asonomaso environ attributable to the quarry is thus significant and its repercussions on the health of the residents must be seriously looked at. Keywords: Quarry Dust, Heavy-metal, Impact, Asonomaso
Chiral charge order in 1-TiSe: importance of lattice degrees of freedom
We address the question of the origin of the recently discovered chiral
property of the charge-density-wave phase in 1-TiSe which so far lacks a
microscopic understanding. We argue that the lattice degrees of freedom seems
to be crucial for this novel phenomenon. We motivate a theoretical model that
takes into account one valence and three conduction bands, a strongly screened
Coulomb interaction between the electrons, as well as the coupling of the
electrons to a transverse optical phonon mode. The Falicov-Kimball model
extended in this way possesses a charge-density-wave state at low temperatures,
which is accompanied by a periodic lattice distortion. The charge ordering is
driven by a lattice deformation and electron-hole pairing (excitonic)
instability in combination. We show that both electron-phonon interaction and
phonon-phonon interaction must be taken into account at least up to quartic
order in the lattice displacement to achieve a stable chiral charge order. The
chiral property is exhibited in the ionic displacements. Furthermore, we
provide the ground-state phase diagram of the model and give an estimate of the
electron-electron and electron-phonon interaction constants for 1-TiSe.Comment: 13 pages, 11 figures, revised and extended versio
Revealing the role of electrons and phonons in the ultrafast recovery of charge density wave correlations in 1-TiSe
Using time- and angle-resolved photoemission spectroscopy with selective
near- and mid-infrared photon excitations, we investigate the femtosecond
dynamics of the charge density wave (CDW) phase in 1-TiSe, as well as
the dynamics of CDW fluctuations at 240 K. In the CDW phase, we observe the
coherent oscillation of the CDW amplitude mode. At 240 K, we single out an
ultrafast component in the recovery of the CDW correlations, which we explain
as the manifestation of electron-hole correlations. Our momentum-resolved study
of femtosecond electron dynamics supports a mechanism for the CDW phase
resulting from the cooperation between the interband Coulomb interaction, the
mechanism of excitonic insulator phase formation, and electron-phonon coupling.Comment: 9 pages, 6 figure
Orbital breathing effects in the computation of x-ray d-ion spectra in solids by ab initio wave-function-based methods
In existing theoretical approaches to core-level excitations of
transition-metal ions in solids relaxation and polarization effects due to the
inner core hole are often ignored or described phenomenologically. Here we set
up an ab initio computational scheme that explicitly accounts for such physics
in the calculation of x-ray absorption and resonant inelastic x-ray scattering
spectra. Good agreement is found with experimental transition-metal -edge
data for the strongly correlated cuprate LiCuO, for which we
determine the absolute scattering intensities. The newly developed methodology
opens the way for the investigation of even more complex electronic
structures of group VI B to VIII B correlated oxide compounds
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