Systems of random linear equations and the phase transition in MacArthur's resource-competition model

Complex ecosystems generally consist of a large number of different species utilizing a large number of different resources. Several of their features cannot be captured by models comprising just a few species and resources. Recently, Tikhonov and Monasson have shown that a high-dimensional version of MacArthur's resource competition model exhibits a phase transition from a 'vulnerable' to a 'shielded' phase in which the species collectively protect themselves against an inhomogeneous resource influx from the outside. Here we point out that this transition is more general and may be traced back to the existence of non-negative solutions to large systems of random linear equations. Employing Farkas' Lemma we map this problem to the properties of a fractional volume in high dimensions which we determine using methods from the statistical mechanics of disordered systems.Comment: Updated version accepted for publication in Europhysics Letters. New titel, additional References and expanded supplementary material. 5 pages, 3 figure

An Evaluation of Selected Retouching Media for Acrylic Emulsion Paint

In this study, polar and non-polar retouching media were analyzed to assess their applicability and reversibility on acrylic emulsion paint films (Golden and Schmincke acrylic paints). Acrylic emulsion paints are very sensitive to a variety of solvents. Only water, short-chain alcohols and aliphatic hydrocarbons are considered suitable for their treatment. Therefore, the retouching media used in this study were chosen for their solubility in each of these solvents. Distilled water and ethanol were used in order to test the reversibility of the polar retouching. Noctane, nhexane and diethyl ether, which offer weak dispersive interactions but different vapor pressures, were employed for swab removal of the non-polar retouching. Extraction tests with different polar and non-polar solvents, showed which components were leached out of the acrylic paint film sample during swab removal of retouching media. Gloss measurements and photomicrographs taken of the paint film samples before and after the application of the retouching displayed variations when compared to untreated reference samples. Both measurements were taken again after reversibility tests in order to demonstrate any changes in morphology and gloss of the paint film samples

CXS: Coherent X-ray scattering at the UE49-SGM at BESSY II

The coherent soft-x-ray scattering experiment CXS has been developed to study nano-structured magnetic and nonmagnetic thin film samples in transmission or reflection geometry. A nanometer precision movable sample stage in a 1 Tesla magnet vector field together with a movable CCD detector, variable in sample – CCD distance, allows both XMCD and XMLD experiments in transmission and reflection as well as imaging techniques such as Fourier transform holography and ptychography

German catalysis meeting - 50 years and as young as ever

50 Years Young: The 50th annual meeting of the German Catalysis Society (GeCatS), hosted by DECHEMA, was recently held in Weimar. The long-standing history of this conference reflects a good tradition for chemists and chemical engineers from Germany and other countries to come together and discuss about the current progress in catalysis in academia and industry

Why Privacy-Preserving Protocols Are Sometimes Not Enough: A Case Study of the Brisbane Toll Collection Infrastructure

The use of Electronic Toll Collection (ETC) systems is on the rise, as these systems have a significant impact on reducing operational costs. Toll service providers (TSPs) access various information, including drivers’ IDs and monthly toll fees, to bill drivers. While this is legitimate, such information could be misused for other purposes violating drivers’ privacy, most prominent, to infer drivers’ movement patterns. To this end, privacy-preserving ETC (PPETC) schemes have been designed to minimize the amount of information leaked while still allowing drivers to be charged. We demonstrate that merely applying such PPETC schemes to current ETC infrastructures may not ensure privacy. This is due to the (inevitable) minimal information leakage, such as monthly toll fees, which can potentially result in a privacy breach when combined with additional background information, such as road maps and statistical data. To show this, we provide a counterexample using the case study of Brisbane’s ETC system. We present two attacks: the first, being a variant of the presence disclosure attack, tries to disclose the toll stations visited by a driver during a billing period as well as the frequency of visits. The second, being a stronger attack, aims to discover cycles of toll stations (e.g., the ones passed during a commute from home to work and back) and their frequencies. We evaluate the success rates of our attacks using real parameters and statistics from Brisbane’s ETC system. In one scenario, the success rate of our toll station disclosure attack can be as high as 94%. This scenario affects about 61% of drivers. In the same scenario, our cycle disclosure attack can achieve a success rate of 51%. It is remarkable that these high success rates can be achieved by only using minimal information as input, which is, e.g., available to a driver’s payment service provider or bank, and by following very simple attack strategies without exploiting optimizations. As a further contribution, we nalyze how the choice of various parameters, such as the set of toll rates, the number of toll stations, and the billing period length, impact a driver’s privacy level regarding our attacks

Optical inter-site spin transfer probed by energy and spin-resolved transient absorption spectroscopy

Optically driven spin transport is the fastest and most efficient process to manipulate macroscopic magnetization as it does not rely on secondary mechanisms to dissipate angular momentum. In the present work, we show that such an optical inter-site spin transfer (OISTR) from Pt to Co emerges as a dominant mechanism governing the ultrafast magnetization dynamics of a CoPt alloy. To demonstrate this, we perform a joint theoretical and experimental investigation to determine the transient changes of the helicity dependent absorption in the extreme ultraviolet spectral range. We show that the helicity dependent absorption is directly related to changes of the transient spin-split density of states, allowing us to link the origin of OISTR to the available minority states above the Fermi level. This makes OISTR a general phenomenon in optical manipulation of multi-component magnetic systems. Optically driven spin transfer is the fastest process to manipulate magnetism. Here, the authors show that this process emerges as the dominant mechanism in femtosecond spin dynamics enabling to the engineering of functional magnetic systems for future all optical technologies

Microstructuring of Steel and Hard Metal using Femtosecond Laser Pulses

AbstractNew results on three-dimensional micro-structuring of tungsten carbide hard metal and steel using femtosecond laser pulses will be presented. For the investigations, a largely automated high-precision fs-laser micromachining station was used. The fs-laser beam is focused onto the sample surface using different objectives. The investigations of the ablation behaviour of the various materials in dependence of the laser processing parameters will be presented. In the second part, complex 3D microstructures with a variety of geometries and resolutions down to a few micrometers will be presented. On of the Goal of these investigations was to create defined microstructures in tooling equipments such as cutting inserts

Raman and NMR spectroscopic and theoretical investigations of the cubic laves-phases REAl2 (RE = Sc, Y, La, Yb, Lu)

The cubic Laves-phase aluminides REAl2 with RE = Sc, Y, La, Yb and Lu were prepared from the elements by arc-melting or using refractory metal ampoules and induction heating. They all crystallize in the cubic crystal system with space group Fd3̄m and adopt the MgCu2 type structure. The title compounds were characterized by powder X-ray diffraction and spectroscopically investigated using Raman and 27Al and in the case of ScAl2 by 45Sc solid-state MAS NMR. In both, the Raman and NMR spectra, the aluminides exhibit only one signal due to the crystal structure. DFT calculations were used to calculate Bader charges illustrating the charge transfer in these compounds along with NMR parameters and densities of states. Finally, the bonding situation was assessed by means of ELF calculations rendering these compounds aluminides with positively charged REδ+ cations embedded in an [Al2]δ− polyanion