Flow over periodic hills - Numerical and experimental study in a wide range of Reynolds numbers

The paper presents a detailed analysis of the flow over smoothly contoured constrictions in a plane channel. This configuration represents a generic case of a flow separating from a curved surface with well-defined flow conditions which makes it especially suited as benchmark case for computing separated flows. The hills constrict the channel by about one third of its height and are spaced at a distance of 9 hill heights. This setup follows the investigation of Fröhlich et al. [Fröhlich J, Mellen CP, Rodi W, Temmerman L, Leschziner MA. Highly resolved large-eddy simulation of separated flow in a channel with streamwise periodic constrictions. J Fluid Mech 2005;526:19-66] and complements it by numerical and experimental data over a wide range of Reynolds numbers. We present results predicted by direct numerical simulations (DNS) and highly resolved large-eddy simulations (LES) achieved by two completely independent codes. Furthermore, these numerical results are supported by new experimental data from PIV measurements. The configuration in the numerical study uses periodic boundary conditions in streamwise and spanwise direction. In the experimental setup periodicity is achieved by an array of 10 hills in streamwise direction and a large spanwise extent of the channel. The assumption of periodicity in the experiment is checked by the pressure drop between consecutive hill tops and PIV measurements. The focus of this study is twofold: (i) Numerical and experimental data are presented which can be referred to as reference data for this widely used standard test case. Physical peculiarities and new findings of the case under consideration are described and confirmed independently by different codes and experimental data. Mean velocity and pressure distributions, Reynolds stresses, anisotropy-invariant maps, and instantaneous quantities are shown. (ii) Extending previous studies the flow over periodic hills is investigated in the wide range of Reynolds numbers covering 100?Re?10,595. Starting at very low Re the evolution and existence of physical phenomena such as a tiny recirculation region at the hill crest are documented. The limit to steady laminar flow as well as the transition to a fully turbulent flow stage are presented. For 700?Re?10,595 turbulent statistics are analyzed in detail. Carefully, undertaken DNS and LES predictions as well as cross-checking between different numerical and experimental results build the framework for physical investigations on the flow behavior. New interesting features of the flow were found.     

Raiding the Noosphere: the open development of networked RAID support for the Linux kernel

The Noosphere is a term borrowed by open‐source advocate Eric Raymond to denote the virtual world of the Internet. Fitting a new driver into the Linux kernel requires a ‘noospheric’ strategy as well as an engineering strategy, because the code is part of the open‐source development process, not its end. This article recounts the technology and the development process followed for a ‘fast and intelligent’ driver extension to the existing Linux software RAID subsystem. The development adapts the kernel RAID subsystem for use in the context of network‐attached storage. Copyright © 2005 John Wiley & Sons, Ltd.     

How good are patients with panic disorder at perceiving their heartbeats?

Palpitations are among the most common symptoms of panic attacks. The present review addresses the question of whether systematic differences in heartbeat perception exist between patients with panic disorder and control subjects. Paradigms involving the comparison of heartbeat sensations with external signals such as discrimination task have failed to find group differences. Recent improvements in methodology may give clearer results in future studies. The majority of studies using the mental tracking paradigm have shown that panic disorder patients show a better heartbeat perception than controls. Discrepant results are probably related to different instructions and differences in sample characteristics such as the inclusion of patients on medication affecting the cardiovascular system. More accurate heartbeat perception, may, however, be restricted to those patients who show agoraphobic avoidance behavior. It is also conceivable that group differences in the mental tracking paradigm are due to attentional biases or a tendency to interpret weak sensations as heartbeats rather than differences in perceptual sensitivity. More ambulatory studies are needed to test whether the results can be generalized to the patients' natural environment. So far ambulatory studies have established superior heartbeat perception only in the subgroup of panic disorder patients with cardiac neurosis. A 1-year prospective study showed that heartbeat perception as assessed with the mental tracking paradigm predicted maintenance of panic attacks. This supports the clinical significance of the findings. Increased cardiac awareness may increase the probability of anxiety-inducing bodily sensations triggering the vicious cycle of panic. Laboratory and ambulatory monitoring studies showed that panic disorder patients respond with anxiety when they think that their heart rate has accelerated. Increased cardiac awareness may also contribute to the maintenance of the disorder by motivating the patients to avoid situations in which these sensations occur.     

A wafer-bonded floating-element shear stress microsensor withoptical position sensing by photodiodes

This paper discusses a noninvasive sensing technique for the direct measurement of low-magnitude shear stresses in laminar and turbulent air flows. The sensing scheme detects the flow-induced in-plane displacement of a microfabricated floating-element structure (500 μm×500 μm×7 μm), using integrated photodiodes. The wall-mounted floating-element sensors were fabricated using a wafer-bonding technology. The sensors were calibrated in a custom-designed laminar flow cell and subsequently shown to be able to transduce shear stresses of 0.01 Pa during tests in a low-speed wind tunnel     

Multiple signal representation simulation of photonic devices,systems, and networks

Photonic systems design requires simulation over a wide range of scales; from wavelength-sized resonances in lasers and filters, to interactions in global networks. To design these global systems, while considering the effects of the smallest component, requires sophisticated simulation technology. We have developed the Photonic Transmission Design Suite, which includes five different signal representations, so that the details of device performance can be efficiently considered within a large network simulation. Alternatively, a design can be studied using a coarse signal representation before switching to a detailed representation for further refinement. We give examples of the application of these representations, and show how the representation of a signal is adapted as it propagates through a system to optimize simulation efficiency     

Enthalpy of formation of B2-Fe1−x Al x and B2-(Ni,Fe)1−x Al x

The enthalpy of formation of the ordered B2 phases in the Fe-Al and Fe-Ni-Al systems was measured with very good accuracy using a special, laboratory-built differential-solution calorimeter. The measurements were performed at 1073 K as a function of composition, with an accuracy of about 1 pct. The enthalpy of formation of B2-FeAl is most negative for the composition Fe_0.50Al_0.50 (−36.29 kJ/mol). Compounds with Al contents less than about 40 at. pct show a deviation from the linear dependence of the enthalpy of formation with composition which prevails for Al contents larger than 40 at. pct. Upon replacing Fe by Ni while maintaining a constant Al content, the enthalpy of formation of B2-(Fe,Ni)Al compounds becomes more negative. With decreasing Al content and for a constant Fe/Ni ratio, the enthalpy of formation of the ternary phase becomes less negative.     

The Bonn Open Synthesis System 3

The Bonn Open Synthesis System (BOSS) is an open-source software distribution for unit selection speech synthesis that aims to be easily extensible to new target languages and different applications. To achieve this flexibility, many aspects of the software have been changed in recent years, including the addition of a refined interface to synthesis modules and a more strict separation of language-specific and language-independent code. This article wants to give an overview of the architecture from a technical perspective and explain how it can be adapted for a particular purpose and voice. This is preceded by a short introduction to the unit selection paradigm in general and a section on the specifics of the approach taken by BOSS. A particular focus will be placed on the extensions made for the integration of Polish during which some of the flexibilisation measures were conducted. Further information on the application to Polish but with an emphasis on the linguistic, phonetic and acoustic aspects as well as the speech corpus used can be found in the second part of this two-part article, “Polish unit selection speech synthesis with BOSS”, also published in this issue of the Journal.