Large Eddy Simulation of the flow around an idealized high-speed train

For the optimization of modern high-speed trains it is essential to fully understand the instantaneous and time-averaged flow around the train body. Recent numerical studies are mostly based on solutions of the Reynolds Averaged Navier Stokes (RANS) equations to investigate the development of the flow. For the study presented here however Large Eddy Simulation (LES) has been performed to obtain more details regarding the time-dependent aerodynamic loads and more reliable results in general. Since the front of a train is subjected to the largest forces1, the focus of this study was laid on the flow around the train's nose. Therefore a simplified model of a high-speed train has been developed for the first Simulations. Also geometrically more complex train models will be considered. A further simplification of the set-up was to investigate a low Reynolds number flow in order to lower the already quite high computational costs that the application of the LES technique usually implies. Typical Reynolds numbers for investigations of the flow around a modern high-speed train are of the order of 10-15 Mio, based on the free stream velocity and the standard train width (d=3m). This study was conducted with a Reynolds number of 280000, also based on the free stream velocity and, since the model is a scaled version of the original train, the scaled train width (d=3/25m). Simulations have been performed without and with a side-wind leading an angle of attack of 30° to examine cross-wind effects. For subgrid-scale modeling the Smagorinsky model2 in combination with van Driest damping were used. The simulations have been carried out with a second order central differencing method on an unstructured grid with more than 9 Mio (no side-wind, 0°) and 15 Mio (angle of attack: 30°) cells. In Figure 1(a) and (b) the instantaneous velocity field in streamwise diirection is displayed. It shows the turbulent nature of the flow around this bluff body, especially in the wake of the train's head and below the undercarriage. The time-averaged flow behaviour around the train's head can be seen in Figure 2(a) and (b) where the streamlines projected onto the z-plane without and with sidewind component at a 30° angle of attack are presented. In Figure 2(a) two almost symmetrical vortices can be observed in the wake of the train's head. This is characteristic for a bluff body flow. For the 30° angle of attack there is a shift in the two vortices in the wake, since the flow around the body is no longer symmetrical

Optical Spectra in the Ferromagnetic States near the Charge Ordering

The optical conductivity is studied numerically for the ferromagnetic metallic state close to the charge ordering observed in perovskite manganites.Comment: 11 pages, Latex, 6 ps figure

"What's (the) Matter?", A Show on Elementary Particle Physics with 28 Demonstration Experiments

We present the screenplay of a physics show on particle physics, by the Physikshow of Bonn University. The show is addressed at non-physicists aged 14+ and communicates basic concepts of elementary particle physics including the discovery of the Higgs boson in an entertaining fashion. It is also demonstrates a successful outreach activity heavily relying on the university physics students. This paper is addressed at anybody interested in particle physics and/or show physics. This paper is also addressed at fellow physicists working in outreach, maybe the experiments and our choice of simple explanations will be helpful. Furthermore, we are very interested in related activities elsewhere, in particular also demonstration experiments relevant to particle physics, as often little of this work is published. Our show involves 28 live demonstration experiments. These are presented in an extensive appendix, including photos and technical details. The show is set up as a quest, where 2 students from Bonn with the aid of a caretaker travel back in time to understand the fundamental nature of matter. They visit Rutherford and Geiger in Manchester around 1911, who recount their famous experiment on the nucleus and show how particle detectors work. They travel forward in time to meet Lawrence at Berkeley around 1950, teaching them about the how and why of accelerators. Next, they visit Wu at DESY, Hamburg, around 1980, who explains the strong force. They end up in the LHC tunnel at CERN, Geneva, Switzerland in 2012. Two experimentalists tell them about colliders and our heroes watch live as the Higgs boson is produced and decays. The show was presented in English at Oxford University and University College London, as well as Padua University and ICTP Trieste. It was 1st performed in German at the Deutsche Museum, Bonn (5/'14). The show has eleven speaking parts and involves in total 20 people.Comment: 113 pages, 88 figures. An up to date version of the paper with high resolution pictures can be found at http://www.th.physik.uni-bonn.de/People/dreiner/Downloads/. In v2 the acknowledgements and a citation are correcte

Rotational motion and rheotaxis of human sperm do not require functional CatSper channels and transmembrane Ca2+ signaling.

Navigation of sperm in fluid flow, called rheotaxis, provides long-range guidance in the mammalian oviduct. The rotation of sperm around their longitudinal axis (rolling) promotes rheotaxis. Whether sperm rolling and rheotaxis require calcium (Ca2+ ) influx via the sperm-specific Ca2+ channel CatSper, or rather represent passive biomechanical and hydrodynamic processes, has remained controversial. Here, we study the swimming behavior of sperm from healthy donors and from infertile patients that lack functional CatSper channels, using dark-field microscopy, optical tweezers, and microfluidics. We demonstrate that rolling and rheotaxis persist in CatSper-deficient human sperm. Furthermore, human sperm undergo rolling and rheotaxis even when Ca2+ influx is prevented. Finally, we show that rolling and rheotaxis also persist in mouse sperm deficient in both CatSper and flagellar Ca2+ -signaling domains. Our results strongly support the concept that passive biomechanical and hydrodynamic processes enable sperm rolling and rheotaxis, rather than calcium signaling mediated by CatSper or other mechanisms controlling transmembrane Ca2+ flux

Evidence for charge localization in the ferromagnetic phase of La_(1-x)Ca_(x)MnO_3 from High real-space-resolution x-ray diffraction

High real-space-resolution atomic pair distribution functions of La_(1-x)Ca_(x)MnO_3 (x=0.12, 0.25 and 0.33) have been measured using high-energy x-ray powder diffraction to study the size and shape of the MnO_6 octahedron as a function of temperature and doping. In the paramagnetic insulating phase we find evidence for three distinct bond-lengths (~ 1.88, 1.95 and 2.15A) which we ascribe to Mn^{4+}-O, Mn^{3+}-O short and Mn^{3+}-O long bonds respectively. In the ferromagnetic metallic (FM) phase, for x=0.33 and T=20K, we find a single Mn-O bond-length; however, as the metal-insulator transition is approached either by increasing T or decreasing x, intensity progressively appears around r=2.15 and in the region 1.8 - 1.9A suggesting the appearance of Mn^{3+}-O long bonds and short Mn^{4+}-O bonds. This is strong evidence that charge localized and delocalized phases coexist close to the metal-insulator transition in the FM phase.Comment: 8 pages, 8 postscript figures, submitted to Phys. Rev.

Suppression of charge-ordering and appearance of magnetoresistance in a spin-cluster glass manganite La0.3Ca0.7Mn0.8Cr0.2O3

The magnetic properties of electron-doped manganite La0.3Ca0.7MnO3 and La0.3Ca0.7Mn0.8Cr0.2O3 polycrystalline samples prepared by sol-gel technique have been investigated between 5 and 300 K in magnetic fields ranging from 0 to 5 T. The transition at 260 K, attributed to charge ordering in La0.3Ca0.7MnO3, is completely suppressed in the Cr-substituted sample while the onset of a magnetic remanence followed by the appearance of a magnetic irreversibility at lower temperatures is observed in both samples. These features indicate that ferromagnetic clusters coexist with either an antiferromagnetic phase for La0.3Ca0.7MnO3 or a spin-cluster glass phase for La0.3Ca0.7Mn0.8Cr0.2O3 at the lowest temperatures. The exponential temperature dependence of the resistivity for the Cr-substituted sample is consistent with the small polaron hopping model for 120 K < T < 300 K, while the data are better described by Mott's hopping mechanism for T < 120 K. Whereas the parent compound La0.3Ca0.7MnO3 is known to show no magnetoresistance, a large negative magnetoresistance is observed in the La0.3Ca0.7Mn0.8Cr0.2O3 sample below 120 K. The appearance of the CMR is attributed to spin dependent hopping between spin clusters and/or between ferromagnetic domains

Grand challenges in evolutionary developmental biology

EVO-DEVO'S IDENTITY There is a widespread consensus on the view that evolutionary developmental biology (evo-devo) is the discipline eventually borne to fill the gap between evolutionary biology and developmental biology, following a divorce between these two fields that extended over more than half a century (Amundson, 2005). On closer inspection, however, this broadly acceptable perspective discloses a wealth of questions, if looked at retrospectively, and of potentially divergent possibilities, if looked at prospectively. The slow pace of integration between the different threads that were converging into evo-devo was well expressed by Raff (2000) in a survey of the main issues in this field. Some 15 years ago Raff, one of the discipline's founding fathers, remarked that "What constitutes the fundamental problems for a science of evolutionary developmental biology (evo-devo) depends on whether the scientist is a developmental biologist, a paleontologist or an evolutionary biologist" and drafted a list of at the time hot issues. Evo-devo has answered these questions only in part. However, this discipline is now mature for addressing a number of more precise, and more challenging questions, as I will argue in this article. To date, two sets of problems have been primarily floated in discussions about the identity and research targets of evo-devo. On the one hand are those centered around the (controversial) notions of evolvability, robustness and constraint in connection with the increasing appreciation of the intricacies of the genotype→phenotype map (Alberch, 1991; Altenberg, 1995; West-Eberhard, 2003; Pigliucci, 2010; Wagner and Zhang, 2011). On the other hand are those centered around the notions of origination, innovation, and novelty, the so-called "innovation triad." To Hendrikse et al. (2007), for example, evolvability is the key issue that justifies recognizing evo-devo as an autonomous discipline. Others, e.g., Muller and Newman (2005), focus instead on the innovation triad. Unfortunately, for all these candidates to core concept of evo-devo, too many alternative definitions have been proposed (or, more dangerously, implicitly assumed), thus adding new items to the dramatically increasing series of biological terms on whose definition there seem to be more and more disagreement. Eventually, we should probably learn to accept that multiple notions associated with each of these terms deserve to be retained and perhaps recognized by adjectival specifications. Similar terminological refinement is applied to other biological terms such as species (e.g., Claridge et al., 1997), homology (e.g., Minelli and Fusco, 2013a), and gene (e.g., Beurton et al., 2000). In discussing the concept of gene in historical perspective, Muller-Wille and Rheinberger (2009) have sensibly recalled Friedrich Nietzsche's (1887; second essay, para. 13) dictum, that "all concepts in which an entire process is semiotically concentrated elude definition; only that which has no history is definable." In addition to terminological ambiguity, there is an another problem with the "innovation triad"—the problem that these terms are all framed in terms of "origins." Framing definitions in terms of origin requires splitting the evolutionary sequence in two contiguous segments, "before" and "after" the origination of a new feature. This splitting is a natural consequence if origination indeed "refers to the specific causality of the generative conditions that underlie both the first origins and the later innovations of phenotypes" and especially "the very first beginnings of phenotypes, e.g., the origin of multicellular assemblies, of complex tissues, and of the generic forms that result from the self-organizational and physical principles of cell interaction (Newman, 1992, 1994). In contrast, innovation [evolutionary modes and mechanisms] and novelty [their phenotypic outcome] designate the processes and results of introducing new characters into already existing phenotypic themes of a certain architecture (bodyplans)" (Muller and Newman, 2005, p. 490). This separation, however, is artificial. The better we know a process, the less we are able to identify its exact origins, these instead being determined by arbitrary choice. In science, and especially in biological disciplines with a strong historical dimension such as evolutionary biology and developmental biology, we should frame questions in terms of transitions rather than origins

Molecular genetic analysis of podocyte genes in focal segmental glomerulosclerosis—a review

This review deals with podocyte proteins that play a significant role in the structure and function of the glomerular filter. Genetic linkage studies has identified several genes involved in the development of nephrotic syndrome and contributed to the understanding of the pathophysiology of glomerular proteinuria and/or focal segmental glomerulosclerosis. Here, we describe already well-characterized genetic diseases due to mutations in nephrin, podocin, CD2AP, alpha-actinin-4, WT1, and laminin β2 chain, as well as more recently identified genetic abnormalities in TRPC6, phospholipase C epsilon, and the proteins encoded by the mitochondrial genome. In addition, the role of the proteins which have shown to be important for the structure and functions by gene knockout studies in mice, are also discussed. Furthermore, some rare syndromes with glomerular involvement, in which molecular defects have been recently identified, are briefly described. In summary, this review updates the current knowledge of genetic causes of congenital and childhood nephrotic syndrome and provides new insights into mechanisms of glomerular dysfunction