Pore Stabilization in Cohesive Granular Systems

Cohesive powders tend to form porous aggregates which can be compacted by applying an external pressure. This process is modelled using the Contact Dynamics method supplemented with a cohesion law and rolling friction. Starting with ballistic deposits of varying density, we investigate how the porosity of the compacted sample depends on the cohesion strength and the friction coefficients. This allows to explain different pore stabilization mechanisms. The final porosity depends on the cohesion force scaled by the external pressure and on the lateral distance between branches of the ballistic deposit r_capt. Even if cohesion is switched off, pores can be stabilized by Coulomb friction alone. This effect is weak for round particles, as long as the friction coefficient is smaller than 1. However, for nonspherical particles the effect is much stronger.Comment: 10 pages, 15 figure

Kupferersatz im ökologischen Weinbau: Entwicklung und Anwendung neuer Formulierungs- und Produktionstechnologien für den praxisgerechten Einsatz bakterieller Antagonisten

Im vorliegenden Projekt wurde der Einsatz bakterieller Antagonisten als Kupferersatz zur Bekämpfung von Plasmopara viticola, dem Erreger des Falschen Mehltaus der Weinrebe, im ökologischen Weinbau optimiert. Mit Hilfe von Dual-Kultur-Tests wurden sechs bakterielle Antagonisten aus vorhandenen Antagonisten-Stammsammlungen selektiert (Testpilze: Pythium ultimum; Phytophthora infestans). Mittels Blattscheiben-Test im Labor konnte mit den ausgewählten Isolaten eine Befallsreduzierung auf unter 5 % Befallsstärke erzielt werden. Der Befall in der unbehandelten Kontrolle schwankte je nach Ansatz zwischen 19 % und 35 %. Unter Gewächshausbedingungen zeigte sich an Topfreben ebenfalls eine gute biologische Wirksamkeit gegen den Schadpilz. Die Kontrollpflanzen wiesen einen Befall zwischen 60 % und 77 % Befallsstärke auf, während die Blätter der Prüfglieder weniger als 5 % Befallsstärke zeigten. Zur Eliminierung des Kupferanteils wurden für die Freilandversuche drei hochwirksame Isolate ausgewählt und in die Bekämpfungsstrategie „Öko-Standard“ integriert. Die Isolate gehörten den Bakteriengattungen Pseudomonas spp. und Bacillus spp. an. Um die Wirksamkeit im Freiland zu steigern, wurden Formulierungshilfsstoffe ausgewählt, die den Bakterien kurz vor der Applikation zugesetzt wurden. Dabei fanden die Substanzen Xanthan gum, Trehalose und PHYTO-VITAL® Anwendung. Aufgrund des extremen Sommers im Jahr 2003 war der Peronospora-Befall im Weinberg so gering, dass keine aussagekräftigen Ergebnisse zum Einsatz unter Freilandbedingungen gemacht werden konnten. Studien zur Etablierung der Antagonisten auf dem Rebblatt haben gezeigt, dass die Blätter der bakterienbehandelten Versuchsglieder Bakteriendichten aufwiesen, die um etwa eine Zehnerpotenz höher lagen als die mit Kupfer behandelten Blätter. Um mögliche Gärbeeinflussungen zu erfassen, wurden die Moste im Kleinmaßstab (25-Liter Gärbehälter) vergoren. Bisher zeigten sich keine Abweichungen vom kupferhaltigen Versuchsglied „Öko-Standard“

Response of human engineered cartilage based on articular or nasal chondrocytes to interleukin-1? and low oxygen

Previous studies showed that human nasal chondrocytes (HNC) exhibit higher proliferation and chondrogenic capacity as compared to human articular chondrocytes (HAC). To consider HNC as a relevant alternative cell source for the repair of articular cartilage defects it is necessary to test how these cells react when exposed to environmental factors typical of an injured joint. We thus aimed this study at investigating the responses of HNC and HAC to exposure to interleukin (IL)-1? and low oxygen. For this purpose HAC and HNC harvested from the same donors (N=5) were expanded in vitro and then cultured in pellets or collagen-based scaffolds at standard (19%) or low oxygen (5%) conditions. Resulting tissues were analyzed after a short (3 days) exposure to IL-1?, mimicking the initially inflammatory implantation site, or following a recovery time (1 or 2 weeks for pellets and scaffolds, respectively). After IL-1? treatment, constructs generated by both HAC and HNC displayed a transient loss of GAG (up to 21.8% and 36.8%, respectively) and, consistently, an increased production of metalloproteases (MMP)-1 and -13. Collagen type II and the cryptic fragment of aggrecan (DIPEN), both evaluated immunohistochemically, displayed a trend consistent with GAG and MMPs production. HNC-based constructs exhibited a more efficient recovery upon IL-1? withdrawal, resulting in a higher accumulation of GAG (up to 2.6-fold) compared to the corresponding HAC-based tissues. On the other hand, HAC displayed a positive response to low oxygen culture, while HNC were only slightly affected by oxygen percentage. Collectively, under the conditions tested mimicking the postsurgery articular environment, HNC retained a tissue-forming capacity, similar or even better than HAC. These results represent a step forward in validating HNC as a cell source for cartilage tissue engineering strategies

Noise-assisted Multibit Storage Device

In this paper we extend our investigations on noise-assisted storage devices through the experimental study of a loop composed of a single Schmitt trigger and an element that introduces a finite delay. We show that such a system allows the storage of several bits and does so more efficiently for an intermediate range of noise intensities. Finally, we study the probability of erroneous information retrieval as a function of elapsed time and show a way for predicting device performance independently of the number of stored bits.Comment: 5 figure

Absence of singular superconducting fluctuation corrections to thermal conductivity

We evaluate the superconducting fluctuation corrections to thermal conductivity in the normal state which diverge as T approaches T_c. We find zero total contribution for one, two and three-dimensional superconductors for arbitrary impurity concentration. The method used is diagrammatic many-body theory, and all contributions -- Aslamazov-Larkin (AL), Maki-Thompson (MT), and density-of-states (DOS) -- are considered. The AL contribution is convergent, whilst the divergences of the DOS and MT diagrams exactly cancel.Comment: 4 pages text; 2 figure

Connecting geodesics and security of configurations in compact locally symmetric spaces

A pair of points in a riemannian manifold makes a secure configuration if the totality of geodesics connecting them can be blocked by a finite set. The manifold is secure if every configuration is secure. We investigate the security of compact, locally symmetric spaces.Comment: 27 pages, 2 figure

Surface Half-Metallicity of CrAs in the Zinc-Blende Structure

The development of new techniques such as the molecular beam epitaxy have enabled the growth of thin films of materials presenting novel properties. Recently it was made possible to grow a CrAs thin-film in the zinc-blende structure. In this contribution, the full-potential screened KKR method is used to study the electronic and magnetic properties of bulk CrAs in this novel phase as well as the Cr and As terminated (001) surfaces. Bulk CrAs is found to be half-ferromagnetic for all three GaAs, AlAs and InAs experimental lattice constants with a total spin magnetic moment of 3 $\mu_B$. The Cr-terminated surface retains the half-ferromagnetic character of the bulk, while in the case of the As-termination the surface states destroy the gap in the minority-spin band.Comment: 4 pages, 2 figures, new text, new titl

Modelling of Optical Detection of Spin-Polarized Carrier Injection into Light-Emitting Devices

We investigate the emission of multimodal polarized light from Light Emitting Devices due to spin-aligned carriers injection. The results are derived through operator Langevin equations, which include thermal and carrier-injection fluctuations, as well as non-radiative recombination and electronic g-factor temperature dependence. We study the dynamics of the optoelectronic processes and show how the temperature-dependent g-factor and magnetic field affect the polarization degree of the emitted light. In addition, at high temperatures, thermal fluctuation reduces the efficiency of the optoelectronic detection method for measuring spin-polarization degree of carrier injection into non-magnetic semicondutors.Comment: 15 pages, 7 figures, replaced by revised version. To appear in Phys. Rev.

The Grover algorithm with large nuclear spins in semiconductors

We show a possible way to implement the Grover algorithm in large nuclear spins 1/2<I<9/2 in semiconductors. The Grover sequence is performed by means of multiphoton transitions that distribute the spin amplitude between the nuclear spin states. They are distinguishable due to the quadrupolar splitting, which makes the nuclear spin levels non-equidistant. We introduce a generalized rotating frame for an effective Hamiltonian that governs the non-perturbative time evolution of the nuclear spin states for arbitrary spin lengths I. The larger the quadrupolar splitting, the better the agreement between our approximative method using the generalized rotating frame and exact numerical calculations.Comment: 11 pages, 18 EPS figures, REVTe