768 research outputs found
Jump Rope Vortex in Liquid Metal Convection
Understanding large scale circulations (LSCs) in turbulent convective systems
is important for the study of stars, planets and in many industrial
applications. The canonical model of the LSC is quasi-planar with additional
horizontal sloshing and torsional modes [Brown E, Ahlers G (2009) J. Fluid
Mech. 638:383--400; Funfschilling D, Ahlers G (2004) Phys. Rev. Lett.
92(19):194502; Xi HD et al. (2009) Phys. Rev. Lett. 102(4):044503; Zhou Q et
al. (2009) J. Fluid Mech. 630:367--390]. Using liquid gallium as the working
fluid, we show via coupled laboratory-numerical experiments that the LSC in a
tank with aspect ratios greater than unity takes instead the form of a "jump
rope vortex", a strongly three-dimensional mode that periodically orbits around
the tank following a motion much like a jump rope on a playground. Further
experiments show that this jump rope flow also exists in more viscous fluids
such as water, albeit with a far smaller signal. Thus, this new jump rope mode
is an essential component of the turbulent convection that underlies our
observations of natural systems
Instabile rationale Konjugationsklassen in reduktiven Gruppen
Sei eine zusammenhĂ€ngende quasizerfallende reduktive Gruppe ĂŒber einem perfekten Körper und sei die Charakteristik von gut. Steinberg und Kottwitz untersuchen die Frage, ob eine rationale Konjugationsklasse ein Element aus enthĂ€lt. Hierbei studieren sie die Konjugationsklasse in der einfach zusammenhĂ€ngenden Ăberlagerung von . Das Ziel dieser Arbeit ist es, einen weiteren Zugang fĂŒr quasizerfallende halbeinfache Gruppen anzugeben. Zu allererst beweisen wir, daĂ eine rationale Konjugationsklasse in einer zusammenhĂ€ngenden zerfallenden Gruppe ein Element aus besitzt. Dieses Resultat fĂŒhrt zu einer Klassifikation aller rationaler Konjugationsklassen in zusammenhĂ€ngenden, quasizerfallenden, einfachen Gruppen, die kein rationales Element enthalten. Das Cupprodukt beider ZugĂ€nge beschreibt dies
Performance diagnostics in ultramarathon - influencing factors, pacing-strategies and analysis of exercise protocols in the context of the Berlin Wall Race
Leistungsdiagnostische Untersuchungen sind wichtig fĂŒr die Laufzeitprognose im Langstreckenlauf. Allerdings hat sich gezeigt, dass bei Laufdisziplinen, die lĂ€nger als die Marathondistanz sind, sprich beim Ultramarathon, die Leistungsprognose ungenauer wird, da eine Vielzahl verschiedener Faktoren die Leistung mitbestimmen. Ein entscheidender Faktor ist unter anderem die Pacing-Strategie, also die Einteilung der Energiereserven im Wettkampfverlauf.
Ziel dieser Studie ist eine zusammenhĂ€ngende Beschreibung wesentlicher PrĂ€diktorvariablen fĂŒr die Laufleistung im Ultramarathon. Auch werden verschiedene Pacing-Muster im Hinblick auf die Ultramarathonleistung analysiert. Zudem wird der Einfluss von drei unterschiedlichen Belastungsprotokollen auf die Abbildung der Laktatschwellen bei der Laktatleistungsdiagnostik untersucht.
Insgesamt nahmen an der Studie zur Laktatleistungsdiagnostik 42 LangstreckenlĂ€ufer teil. Untersucht werden unterschiedliche Belastungsprotokolle, die sich in der StufenlĂ€nge und der Geschwindigkeitserhöhung unterscheiden. FĂŒr die Analyse der Pacing-Muster werden zudem Wettkampfzeiten und -zwischenzeiten der Probanden aus den Berliner MauerweglĂ€ufen 2016 und 2017 (100 Meilen) ausgewertet.
Die Analysen zeigen, dass die erreichte Maximalgeschwindigkeit im Laufbandtest, die Geschwindigkeit an der Lactate Threshold (LT) und die Geschwindigkeit an der Individuellen Anaeroben Schwelle (IAS) negativ mit der Wettkampfzeit korrelieren. Signifikante Korrelationen mit der Wettkampfzeit weisen ebenfalls leistungsrelevante Parameter, wie der Körperfettgehalt, die geplante Wettkampfzeit, das Jahreskilometerpensum der Vorjahre und Bestzeiten auf kĂŒrzeren Distanzen auf.
Zwischen zwei Belastungsprotokollen, die sich lediglich in der Steigerung der Laufbandgeschwindigkeit nach jeweils 3 Minuten unterscheiden, ergibt sich kein signifikanter Geschwindigkeitsunterschied an der LT und IAS. Im Gegensatz dazu sind die Geschwindigkeiten an den individuellen Laktatschwellen in diesen beiden Laufbandprotokollen signifikant höher als in einem weiteren Protokoll, in welchem die Geschwindigkeitserhöhung nach einer festgelegten Distanz von 1200 Metern erfolgt.
Die Analysen der Pacing-Strategien wĂ€hrend des Berliner Mauerweglaufs zeigen ein invers J-förmiges Pacing-Muster. Dabei weisen LeistungsstĂ€rkere geringere Geschwindigkeits-verĂ€nderungen im Wettkampfverlauf auf als LeistungsschwĂ€chere. Ein gleichmĂ€Ăigeres Pacing scheint dementsprechend mit einer schnelleren Laufzeit im Ultramarathon verbunden zu sein. DarĂŒber hinaus können die Analysen erstmalig zeigen, dass die Geschwindigkeit an den individuellen Laktatschwellen signifikant mit der ânormiertenâ Laufgeschwindigkeit, sprich dem Pacing im Ultramarathon korreliert.
Zusammenfassend zeigt diese Studie, dass eine ganze Reihe von Parametern geeignet sind um die Ultramarathonleistung vorherzusagen. Dazu gehört die metabolische Ausdauerleistung, aber auch Faktoren wie die Lauferfahrung und das Pacing-Verhalten.Performance diagnostic tests are important for predicting race time in long-distance running. However, it has been shown that in running disciplines longer than the marathon distance, i.e. ultramarathon, prediction of performance becomes less accurate, since a variety of different factors influence the performance. A crucial factor is the pacing strategy, i.e. the distribution of energy reserves during the competition.
The aim of this study is to provide a comprehensive description of key predictors for the performance in ultramarathons. Different pacing patterns are also analyzed with respect to ultramarathon performance. In addition, three different protocols used in lactate performance diagnostics that differ in step-duration and -speed increase, were compared as to measurement of lactate thresholds.
A total of 42 long-distance runners were included. All participants were finishers of the 2016 and/or 2017 Berlin Wall Races (100 miles). For the analysis of the pacing patterns, race times and split times of the study participants from the two races were analyzed.
The results show that maximum speed achieved in the treadmill test, speed at the lactate threshold (LT), and speed at the individual anaerobic threshold (IAS) correlate negatively with the race time. Significant correlations with race time are also shown for performance-related parameters such as body fat, estimated race time, previous years' annual mileage, and best times over shorter distances.
When comparing different protocols used for performance diagnostic, there is no evidence of a significant difference in speed at the individual lactate thresholds (LT and IAS) between two exercise protocols that differ only in the increase in treadmill speed after 3 minutes. In contrast, speed at the individual lactate thresholds in these two protocols are significantly higher, respectively, than in another protocol in which the speed increase takes place after a fixed distance of 1200 meters.
During the Berlin Wall Race an inverse J-shaped pacing pattern was observed. Stronger performers show less variation in speed over the course than weaker performers, i.e. more even pacing associated with faster running time. Furthermore, the performance at individual lactate thresholds correlates significantly with ânormalizedâ running speeds. In summary, this study identifies a whole range of parameters that are suitable to predict ultramarathon performance. These include metabolic endurance capacity, but also factors like running experience and pacing behavior
Oscillatory thermal-inertial flows in liquid metal rotating convection
We present the first detailed thermal and velocity field characterization of
convection in a rotating cylindrical tank of liquid gallium, which has
thermophysical properties similar to those of planetary core fluids. Our
laboratory experiments, and a closely associated direct numerical simulation,
are all carried out in the regime prior to the onset of steady convective
modes. This allows us to study the oscillatory convective modes, sidewall modes
and broadband turbulent flow that develop in liquid metals before the advent of
steady columnar modes. Our thermo-velocimetric measurements show that strongly
inertial, thermal wind flows develop, with velocities reaching those of
comparable non-rotating cases. Oscillatory bulk convection and wall modes
coexist across a wide range of our experiments, along with strong zonal flows
that peak in the Stewartson layer, but that extend deep into the fluid bulk in
the higher supercriticality cases. The flows contain significant time-mean
helicity that is anti-symmetric across the midplane, demonstrating that
oscillatory liquid metal convection contains the kinematic components to
sustain system-scale dynamo generation.Comment: 29 pages, 12 figure
Improving the Cathodic Biofilm Growth Capabilities of Kyrpidia spormannii EA-1 by Undirected Mutagenesis
The biotechnological usage of carbon dioxide has become a relevant aim for future processes. Microbial electrosynthesis is a rather new technique to energize biological CO fixation with the advantage to establish a continuous process based on a cathodic biofilm that is supplied with renewable electrical energy as electron and energy source. In this study, the recently characterized cathodic biofilm forming microorganism Kyrpidia spormannii strain EA-1 was used in an adaptive laboratory evolution experiment to enhance its cathodic biofilm growth capabilities. At the end of the experiment, the adapted cathodic population exhibited an up to fourfold higher biofilm accumulation rate, as well as faster substratum coverage and a more uniform biofilm morphology compared to the progenitor strain. Genomic variant analysis revealed a genomically heterogeneous population with genetic variations occurring to various extends throughout the community. Via the conducted analysis we identified possible targets for future genetic engineering with the aim to further optimize cathodic growth. Moreover, the results assist in elucidating the underlying processes that enable cathodic biofilm formation
Ensemble averaged entanglement of two-particle states in Fock space
Recent results, extending the Schmidt decomposition theorem to wavefunctions
of identical particles, are reviewed. They are used to give a definition of
reduced density operators in the case of two identical particles. Next, a
method is discussed to calculate time averaged entanglement. It is applied to a
pair of identical electrons in an otherwise empty band of the Hubbard model,
and to a pair of bosons in the the Bose-Hubbard model with infinite range
hopping. The effect of degeneracy of the spectrum of the Hamiltonian on the
average entanglement is emphasised.Comment: 19 pages Latex, changed title, references added in the conclusion
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