Mulches and pheromones - plant protection tools for organic black currant production

Different mulches have been studied in organic currant production since 1997 at MTT Ecological Production in S:t Michel. Mulches, especially black plastic, suppressed weeds effectively. Since green mass mulch decomposes fast on the soil surface, it can be recommended mainly as an additional fertilizer. Lepidopterous pests Synanthedon tipuliformis, Euhyponomeutoides albithoracellus and Lampronia capitella are difficult to control even by chemicals. Therefore pheromone-based management was studied in 1999-2003

Image charge dynamics in time-dependent quantum transport

In this work we investigate the effects of the electron-electron interaction between a molecular junction and the metallic leads in time-dependent quantum transport. We employ the recently developed embedded Kadanoff-Baym method [Phys. Rev. B 80, 115107 (2009)] and show that the molecule-lead interaction changes substantially the transient and steady-state transport properties. We first show that the mean-field Hartree-Fock (HF) approximation does not capture the polarization effects responsible for the renormalization of the molecular levels neither in nor out of equilibrium. Furthermore, due to the time-local nature of the HF self-energy there exists a region in parameter space for which the system does not relax after the switch-on of a bias voltage. These and other artifacts of the HF approximation disappear when including correlations at the second-Born or GW levels. Both these approximations contain polarization diagrams which correctly account for the screening of the charged molecule. We find that by changing the molecule-lead interaction the ratio between the screening and relaxation time changes, an effect which must be properly taken into account in any realistic time-dependent simulation. Another important finding is that while in equilibrium the molecule-lead interaction is responsible for a reduction of the HOMO-LUMO gap and for a substantial redistribution of the spectral weight between the main spectral peaks and the induced satellite spectrum, in the biased system it can have the opposite effect, i.e., it sharpens the spectral peaks and opens the HOMO-LUMO gap.Comment: 18 pages, 26 figure

Time-dependent Landauer-Büttiker approach to charge pumping in ac-driven graphene nanoribbons

We apply the recently developed partition-free time-dependent Landauer-Büttiker (TD-LB) formalism to the study of periodically driven transport in graphene nanoribbons (GNRs). When an ac driving is applied, this formalism can be used to prove generic conditions for the existence of a nonzero dc component of the net current (pump current) through the molecular device. Time-reversal symmetry breaking in the driving field is investigated and found to be insufficient for a nonzero pump current. We then derive explicit formulas for the current response to a particular biharmonic bias. We calculate the pump current through different GNR configurations and find that the sign and existence of a nonzero pump current can be tuned by simple alterations to the static parameters of the TD bias. Furthermore, we investigate transient currents in different GNR configurations. We find a selection rule of even and odd harmonic response signals depending on a broken dynamical inversion symmetry in the bias

Transient charge and energy flow in the wide-band limit

The wide-band limit is a commonly used approximation to analyze transport through nanoscale devices. In this work we investigate its applicability to the study of charge and heat transport through molecular break junctions exposed to voltage biases and temperature gradients. We find that while this approximation faithfully describes the long-time charge and heat transport, it fails to characterize the short-time behavior of the junction. In particular, we find that the charge current flowing through the device shows a discontinuity when a temperature gradient is applied, while the energy flow is discontinuous when a voltage bias is switched on and even diverges when the junction is exposed to both a temperature gradient and a voltage bias. We provide an explanation for this pathological behavior and propose two possible solutions to this problem.Comment: 11 pages, 9 figure

Electron Traversal Times in Disordered Graphene Nanoribbons

Using the partition-free time-dependent Landauer–Büttiker formalism for transient current correlations, we study the traversal times taken for electrons to cross graphene nanoribbon (GNR) molecular junctions. We demonstrate electron traversal signatures that vary with disorder and orientation of the GNR. These findings can be related to operational frequencies of GNR-based devices and their consequent rational design

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Time-linear quantum transport simulations with correlated nonequilibrium Green's functions

We present a time-linear scaling method to simulate open and correlated quantum systems. The method inherits from many-body perturbation theory the possibility to choose selectively the most relevant scattering processes in the dynamics, thereby paving the way to the real-time characterization of correlated ultrafast phenomena in quantum transport. The open system dynamics is described in terms of an embedding correlator from which the time-dependent current can be calculated using the Meir-Wingreen formula. We show how to efficently implement the method through a simple grafting into recently proposed time-linear Green's function schemes for closed systems. Electron-electron and electron-phonon interactions can be treated on equal footing while preserving all fundametal conservation laws.Comment: 6 pages, 3 figure

Cheers: a linear-scaling KBE+GKBA code

The interaction of electrons with quantized phonons and photons underlies the ultrafast dynamics of systems ranging from molecules to solids, giving rise to a plethora of physical phenomena experimentally accessible using time-resolved techniques. Green's function methods offer an invaluable interpretation tool since scattering mechanisms of growing complexity can be selectively incorporated in the theory. cheers is a general-purpose nonequilibrium Green's function code that implements virtually all known many-body approximations and is designed for first principles studies of ultrafast processes in molecular and model solid state systems. The aims of generality, extensibility, efficiency, and user friendliness of the code are achieved through the underlying theory development and the use of modern software design practices. Here, we motivate the necessity for the creation of such a code and overview its design and capabilities.Comment: 15 pages, 4 figure

Selection for novel, acid-tolerant Desulfovibrio spp. from a closed Transbaikal mine site in a temporal pH- gradient bioreactor

Almost all the known isolates of acidophilic or acid-tolerant sulphate-reducing bacteria (SRB) belong to the spore-forming genus Desulfosporosinus in the Firmicutes. The objective of this study was to isolate acidophilic/acid-tolerant members of the genus Desulfovibrio belonging to deltaproteobacterial SRB. The sample material originated from microbial mat biomass submerged in mine water and was enriched for sulphate reducers by cultivation in anaerobic medium with lactate as an electron donor. A stirred tank bioreactor with the same medium composition was inoculated with the sulphidogenic enrichment. The bioreactor was operated with a temporal pH gradient, changing daily, from an initial pH of 7.3 to a final pH of 3.7. Among the bacteria in the bioreactor culture, Desulfovibrio was the only SRB group retrieved from the bioreactor consortium as observed by 16S rRNA-targeted denaturing gradient gel electrophoresis. Moderately acidophilic/acid-tolerant isolates belonged to Desulfovibrio aerotolerans - Desulfovibrio carbinophilus - Desulfovibrio magneticus and Desulfovibrio idahonensis - Desulfovibrio mexicanus clades within the genus Desulfovibrio. A moderately acidophilic strain, Desulfovibrio sp. VK (pH optimum 5.7) and acid-tolerant Desulfovibrio sp. ED (pH optimum 6.6) dominated in the bioreactor consortium at different time points and were isolated in pure cultur

Efficient computation of the second-Born self-energy using tensor-contraction operations

In the nonequilibrium Green’s function approach, the approximation of the correlation self-energy at the second-Born level is of particular interest, since it allows for a maximal speed-up in computational scaling when used together with the generalized Kadanoff-Baym ansatz for the Green’s function. The present day numerical time-propagation algorithms for the Green’s function are able to tackle first principles simulations of atoms and molecules, but they are limited to relatively small systems due to unfavorable scaling of self-energy diagrams with respect to the basis size. We propose an efficient computation of the self-energy diagrams by using tensor-contraction operations to transform the internal summations into functions of external low-level linear algebra libraries. We discuss the achieved computational speed-up in transient electron dynamics in selected molecular systems.ACKNO</h4