Interfacial instability of liquid films coating the walls of a parallel-plate channel and sheared by a gas flow

The stability and coupling of liquid films coating the walls of a parallel-plate channel and sheared by a pressure-driven gas flow along the channel center plane is studied. The films are susceptible to a long-wavelength instability. For sufficiently low Reynolds numbers and thick gas layers, the dynamic behavior is found to be described by two coupled nonlinear partial differential equations. A linear stability analysis is conducted under the condition that the material properties and the initial undisturbed liquid-film thicknesses are equal. The linear analysis is utilized to determine whether the interfaces are predominantly destabilized by the variations of the shear stress or by the pressure gradient acting upon them. The analysis of the weakly nonlinear equations performed for this case shows that instabilities corresponding to a vanishing Reynolds number are absent from the system. Moreover, for this configuration, the patterns emerging along the two interfaces are found to be identical in the long-time limit, implying that the films are fully synchronized. A different setup, where the liquid films have identical material properties but their undisturbed thicknesses differ, is studied numerically. The results show that, even for this configuration, the interfacial waves remain phase-synchronized and closely correlated for an extended period of time. These findings are particularly relevant for gaseous flow through narrow ducts with liquid-coated walls.     

Detecting and preventing replay attacks in industrial automation networks operated with profinet IO

Modern industrial facilities consist of controllers, actuators and sensors that are connected via traditional IT equipment. The ongoing integration of these systems into the communication network yields to new threats and attack possibilities. In industrial networks, often distinct communication protocols like Profinet IO (PNIO) are used. These protocols are often not supported by typical network security tools. In this work, we present two attack techniques that allow to take over the control of a PNIO device, enabling an attacker to replay previously recorded traffic. We model attack detection rules and propose an intrusion detection system (IDS) for industrial networks which is capable of detecting those replay attacks by correlating alerts from traditional IT IDS with specific PNIO alarms. As an additional effort, we introduce defense in depth mechanisms in order to prevent those attacks from taking effect in the physical world. Thereafter, we evaluate our IDS in a physical demonstrator and compare it with another IDS dedicated to securing PNIO networks. In a conceptual design, we show how network segmentation with flow control allows for preventing some, but not all of the attacks.     

Data Parallel Algorithmic Skeletons with Accelerator Support

Hardware accelerators such as GPUs or Intel Xeon Phi comprise hundreds or thousands of cores on a single chip and promise to deliver high performance. They are widely used to boost the performance of highly parallel applications. However, because of their diverging architectures programmers are facing diverging programming paradigms. Programmers also have to deal with low-level concepts of parallel programming that make it a cumbersome task. In order to assist programmers in developing parallel applications Algorithmic Skeletons have been proposed. They encapsulate well-defined, frequently recurring parallel programming patterns, thereby shielding programmers from low-level aspects of parallel programming. The main contribution of this paper is a comparison of two skeleton library implementations, one in C++ and one in Java, in terms of library design and programmability. Besides, on the basis of four benchmark applications we evaluate the performance of the presented implementations on two test systems, a GPU cluster and a Xeon Phi system. The two implementations achieve comparable performance with a slight advantage for the C++ implementation. Xeon Phi performance ranges between CPU and GPU performance.     

SkaSim – Skalierbare HPC‐Software für molekulare Simulationen in der chemischen Industrie

This article outlines advances in molecular modeling and simulation using massively parallel high‐performance computers (HPC). In the SkaSim project, partners from the HPC community collaborated with users from science and industry. The aim was to optimize the prediction of thermodynamic property data in terms of efficiency, quality and reliability using HPC methods. In this context, various topics were dealt with: atomistic simulation of homogeneous gas bubble formation, surface tension of classical fluids and ionic liquids, multicriteria optimization of molecular models, the development of the molecular simulation codes ls1 mardyn and ms2, atomistic simulation of gas separation processes, molecular membrane structure generators, transport resistors and the evaluation of predictive property data models based on specific mixture types.     

Abwasserreinigung mit Schilf in einer mobilen Wurzelraumkläranlage

A mobile root‐zone wastewater treatment system with a reaction zone consisting solely of reed roots as the growth surface for microorganisms was tested for temporary applications in the treatment of municipal wastewater. Pretreated municipal wastewater from a large‐scale wastewater treatment plant was fed to this system during the 2016 vegetation period. The outlet limit values for chemical oxygen demand and biochemical oxygen demand were adhered to reliably at an inlet volumetric flow rate of 1200 L d^?1. Short‐term loading peaks of up to 1800 L d^?1 did not lead to overloading of the system.     

Monomolecular and Bimolecular Recombination of Electron–Hole Pairs at the Interface of a Bilayer Organic Solar Cell

While it has been argued that field‐dependent geminate pair recombination (GR) is important, this process is often disregarded when analyzing the recombination kinetics in bulk heterojunction organic solar cells (OSCs). To differentiate between the contributions of GR and nongeminate recombination (NGR) the authors study bilayer OSCs using either a PCDTBT‐type polymer layer with a thickness from 14 to 66 nm or a 60 nm thick p‐DTS(FBTTh₂)₂ layer as donor material and C₆₀ as acceptor. The authors measure JV‐characteristics as a function of intensity and charge‐extraction‐by‐linearly‐increasing‐voltage‐type hole mobilities. The experiments have been complemented by Monte Carlo simulations. The authors find that fill factor (FF) decreases with increasing donor layer thickness (L_p) even at the lowest light intensities where geminate recombination dominates. The authors interpret this in terms of thickness dependent back diffusion of holes toward their siblings at the donor–acceptor interface that are already beyond the Langevin capture sphere rather than to charge accumulation at the donor–acceptor interface. This effect is absent in the p‐DTS(FBTTh₂)₂ diode in which the hole mobility is by two orders of magnitude higher. At higher light intensities, NGR occurs as evidenced by the evolution of s‐shape of the JV‐curves and the concomitant additional decrease of the FF with increasing layer thickness.     

Delay discrimination and reversal eyeblink classical conditioning in abstinent chronic alcoholics.

[Correction Notice: An erratum for this article was reported in Vol 23(2) of Neuropsychology (see record 2009-02621-003). The lifetime drinking data listed in Table 1 on p. 198 was not correctly calculated and underestimated lifetime exposure to alcohol. The corrected lifetime variables from that table are included.] Evidence has shown that alcoholism leads to volume reductions in brain regions critical for associative learning using the eyeblink classical conditioning paradigm (EBCC). Evidence indicates that cerebellar shrinkage causes impairment in simple forms of EBCC, whereas changes in forebrain structures result in impairment in more complex tasks. In this study, the ability of abstinent alcoholics and matched control participants to acquire learned responses during delay discrimination and discrimination reversal was examined and related to severity of drinking history and neuropsychological performance. During discrimination learning, one tone (CS+) predicted the occurrence of an airpuff (unconditioned stimulus), and another tone (CS-) served as a neutral stimulus; then the significance of the tones was reversed. Alcoholics who learned the initial discrimination were impaired in acquiring the new CS+ after the tones reversed; this is a function that has previously been linked to forebrain structures. It is suggested that a factor important to alcoholic addiction may be the presence of alcoholic-related associative responses that interfere with the ability to learn new more adaptive associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reduced-order preconditioning for bidomain simulations

Simulations of the bidomain equations involve solving large, sparse, linear systems of the form Ax = b. Being an initial value problems, it is solved at every time step. Therefore, efficient solvers are essential to keep simulations tractable. Iterative solvers, especially the preconditioned conjugate gradient (PCG) method, are attractive since memory demands are minimized compared to direct methods, albeit at the cost of solution speed. However, a proper preconditioner can drastically speed up the solution process by reducing the number of iterations. In this paper, a novel preconditioner for the PCG method based on system order reduction using the Arnoldi method (A-PCG) is proposed. Large order systems, generated during cardiac bidomain simulations employing a finite element method formulation, are solved with the A-PCG method. Its performance is compared with incomplete LU (ILU) preconditioning. Results indicate that the A-PCG estimates an approximate solution considerably faster than the ILU, often within a single iteration. To reduce the computational demands in terms of memory and run time, the use of a cascaded preconditioner was suggested. The A-PCG was applied to quickly obtain an approximate solution, and subsequently a cheap iterative method such as successive overrelaxation (SOR) is applied to further refine the solution to arrive at a desired accuracy. The memory requirements are less than those of direct LU but more than ILU method. The proposed scheme is shown to yield significant speedups when solving time evolving systems.     

Pulse-to-pulse polarization-switching method for high-repetition-rate lasers

We report a method that enables dynamic switching of the pulse-to-pulse linear polarization orientation of a high-pulse-rate laser. The implications for laser micromachining, where polarization direction can be important, are also discussed.