Three-dimensional simulations of type Ia supernovae

We present the results of three-dimensional hydrodynamical simulations of the subsonic thermonuclear burning phase in type Ia supernovae. The burning front model contains no adjustable parameters so that variations of the explosion outcome can be linked directly to changes in the initial conditions. In particular, we investigate the influence of the initial flame geometry on the explosion energy and find that it appears to be weaker than in 2D. Most importantly, our models predict global properties such as the produced nickel masses and ejecta velocities within their observed ranges without any fine tuning.Comment: 7 pages, 5 figures, accepted by A&

Gramática castellana

Reproduction phototypique de l'edition princeps (1492)Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201

Zusammenhang zwischen Muskelfaseraktivierung, Sauerstoffkinetik und Levelling-Off der Sauerstoffaufnahme

Einleitung) Das Levelling-Off der Sauerstoffaufnahme (V̇O2) kennzeichnet eine Abflachung der V̇O2–Leistungsbeziehung im erschöpfenden Belastungsbereich. Es ist das einzig valide Kriterium für die Diagnostik der maximalen Sauerstoffauf-nahme (V̇O2max), welche wiederum die aerobe Leistungsfähigkeit repräsentiert und eine der wichtigsten leistungsphysiologischen Messgrößen darstellt. Trotz körperlicher Ausbelastung weisen jedoch in Abhängigkeit von dem Belastungsprotokoll und der Levelling-Off Definition nur 30-70% der Versuchspersonen ein Levelling-Off auf. Das Auftreten bzw. Ausbleiben eines Levelling-Off`s wird bisher auf die anaerobe Kapazität zurückgeführt. Die Befunde hinsichtlich des Zusammenhangs zwischen Kenngrößen der anaeroben Kapazität und der LO-Inzidenz sind jedoch inkonsistent. Eine mögliche Erklärung hierfür ist, dass die Belastungstoleranz im erschöpfenden Intensitätsbereich neben der anaeroben Kapazität durch die V̇O2-Kinetik bedingt wird. Die V̇O2-Kinetik wird wiederum mit der Muskelfaseraktivierung assoziiert. Des Weiteren deuten Studien darauf hin, dass die V̇O2-Kinetik und die Muskelfaseraktivierung durch eine intensive Erwärmung beschleunigt werden können. Das Ziel dieser Arbeit war es, den Einfluss der Muskelfaseraktivierung und der V̇O2-Kinetik auf die Levelling-Off-Inzidenz zu überprüfen. Hierfür wurden zwei Hypothesen aufgestellt: 1) Versuchspersonen mit Levelling-Off weisen eine schnellere V̇O2-Rampenkinetik auf, welche durch eine höhere Muskel-faseraktivierung bedingt ist. 2) Eine intensive Erwärmung führt zu einer Erhöhung der Muskelfaseraktivierung, einer schnelleren V̇O2-Rampenkinetik und dadurch zu einer Erhöhung der Levelling-Off-Inzidenz. Methodik) Die Überprüfung dieser Hypothesen erfolgte mittels Querschnitts- und experimentellen Forschungsdesigns. Hierbei wurden Probanden mit und ohne Levelling-Off verglichen (Hypothese 1), sowie die Muskelfaseraktivierung und die V̇O2-Kinetik mittels intensiver Erwärmung manipuliert (Hypothese 2). Zusätzlich wurde ein Simulationsmodell entwickelt, mit dem die empirischen Ergebnisse überprüft und erweitert wurden. Insgesamt wurden 5 Testserien mit jeweils 9 bis 20 männlichen Versuchspersonen absolviert, in denen die Erwärmungsintensität, die Regenerationsdauer und die Belastungssteigerungsrate der Rampentests systematisch variiert wurden. Alle Belastungstests wurden auf einem Fahrradergometer absolviert. Die Messung der V̇O2 erfolgte mittels portablen Spirometriesystems. Die Muskelfaseraktivierung des Vastus lateralis, Vastus medialis und Gastrocnemius medialis wurde mit einem Oberflächen-Elektromyographiesystem (EMG) erfasst. Die Bestimmung der V̇O2- und EMG-Kinetik erfolgte mittels linearer und nicht-linearer Regressionsanalysen. Das Levelling-Off wurde anhand des Anstiegs der V̇O2 innerhalb der letzten 50 W quantifiziert. Für die Simulation des Einflusses der V̇O2-Kinetik auf die Levelling-Off-Inzidenz wurde das Rampenkinetiksimulati-onsmodell von Wilcox et al. (2016) um den V̇O2-Bedarf und die V̇O2-Defizit-Akkumulation erweitert. Ergebnisse) Hypothese 1: 10 der 24 Versuchspersonen aus den Testserien 2-4 wiesen ein Levelling-Off im Rampentest auf. Diese verfügten über eine schnellere V̇O2-Rampenkinetik, welche sich in einer kürzeren Verzögerung zu Rampenbeginn (MRT: 43,3 ± 8,6 vs. 52,8 ± 7,1 s; p = 0,007) und einem steileren Anstieg der V̇O2 im submaximalen Intensitätsbereich (∆V̇O2/∆P: 10,1 ± 0,2 vs. 9,2 ± 0,5 ml min-1 W-1; p < 0,001) äußerte. Die schnellere Rampenkinetik ging mit einer geringen V̇O2-Defizit-Akkumulation bis zwei Minuten vor Rampentestende (2,24 ± 0,40 vs. 2,78 ± 0,33 l; p = 0,001) einher. Bei Rampentestende unterschied sich das V̇O2-Defizit (4,34 ± 0,43 vs. 4,54 ± 0,60 l; p = 0,342) zwischen den Versuchspersonen mit und ohne Levelling-Off hingegen nicht. Die EMG-Kinetik (∆EMG/∆P: 0,56 ± 0,18 vs. 0,56 ± 0,26% W-1; p = 0,940) unterschied sich zwischen den Versuchspersonen mit und ohne Levelling-Off ebenfalls nicht. Hypothese 2: In keiner der 5 Testserien konnte eine systematische Beschleuni-gung der V̇O2- und EMG-Rampenkinetik oder eine Erhöhung der Levelling-Off-Inzidenz induziert werden. So kam es in den Testserien 1-4 zu keiner Änderung der ∆V̇O2/∆P (alle p > 0,05) und in der Testserie 5 sogar zu einer Reduktion (10,3 ± 0,7 vs. 9,4 ± 0,7 ml min-1 W-1; p 0,05). Simulationsansatz: Das Simulationsmodell bestätigte ebenfalls die Hypothese 1. Demnach steigt die Wahrscheinlichkeit für das Auftreten eines Levelling-Off`s bei einer gegebenen anaeroben Kapazität und V̇O2max mit schneller werdender V̇O2-Kinetik. Bezüglich der Hypothese 2 deuten die Befunde des Simulationsmodells darauf hin, dass die erwärmungsbedingte Beschleunigung der V̇O2-Kinetik für eine systematische Erhöhung der ∆V̇O2/∆P und der Levelling-Off-Inzidenz zu gering ist. Schlussfolgerung: Die V̇O2-Kinetik, jedoch nicht die Muskelfaseraktivierung, hat einen entscheidenden Einfluss auf das Auftreten eines Levelling-Off`s. Die Induktion eines Levelling-Off`s durch eine Beschleunigung der V̇O2-Kinetik und einer Erhöhung der Muskelfaseraktivierung mittels intensiver Erwärmung ist hingegen nicht möglich. Dies ist wahrscheinlich durch einen zu geringen Erwärmungseffekt auf die V̇O2-Rampenkinetik, bei gleichzeitiger Reduktion der anaeroben Kapazität, bedingt

Dynamics of Primordial Black Hole Formation

We present a numerical investigation of the gravitational collapse of horizon-size density fluctuations to primordial black holes (PBHs) during the radiation-dominated phase of the Early Universe. The collapse dynamics of three different families of initial perturbation shapes, imposed at the time of horizon crossing, is computed. The perturbation threshold for black hole formation, needed for estimations of the cosmological PBH mass function, is found to be $\delta_{\rm c} \approx 0.7$ rather than the generally employed $\delta_{\rm c} \approx 1/3$, if $\delta$ is defined as \Delta M/\mh, the relative excess mass within the initial horizon volume. In order to study the accretion onto the newly formed black holes, we use a numerical scheme that allows us to follow the evolution for long times after formation of the event horizon. In general, small black holes (compared to the horizon mass at the onset of the collapse) give rise to a fluid bounce that effectively shuts off accretion onto the black hole, while large ones do not. In both cases, the growth of the black hole mass owing to accretion is insignificant. Furthermore, the scaling of black hole mass with distance from the formation threshold, known to occur in near-critical gravitational collapse, is demonstrated to apply to primordial black hole formation.Comment: 10 pages, 8 figures, revtex style, submitted to PR

Composition-Controlled Laser-Induced Alloying of Colloidal Au–Cu Hetero Nanoparticles

Due to their optical properties (localized surface plasmon resonance, LSPR), colloidally dispersed metal nanoparticles are well suited for selective heating by high-energy laser radiation above their melting point without being limited by the boiling point of the solvent, which represents an excellent complement to wet-chemical nanoparticle synthesis. By combining wet-chemical synthesis and postsynthesis laser treatment, the advantages of both methods can be used to specifically control the properties of nanoparticles. Especially in the colloidal synthesis of nanoalloys consisting of two or more metals with different redox potentials, wet-chemical synthesis quickly reaches its limits in terms of composition control and homogeneity. For this reason, the direct synthesis path is divided into two parts to take the strengths of both methods. After preparing Au–Cu hetero nanoparticles by wet-chemical synthesis, nanoalloys with previous adjusted composition can be formed by postsynthesis laser treatment. The formation of these nanoalloys can be followed by different characterization methods, such as transmission electron microscopy (TEM), where the fusion of both metal domains and the formation of spherical and homogeneous Au–Cu nanoparticles can be observed. Moreover, the alloy formation can be followed by different shifts of X-ray diffraction (XRD) reflections and LSPR maxima depending on the composition

Nanosecond Pulsed Laser-Heated Nanocrystals Inside a Metal-Organic Framework Matrix

Investigations on gold and gold-zinc oxide nanocrystals encapsulated in a matrix of a metal-organic framework (ZIF-8) upon plasmonic heating with nanosecond laser pulses are presented. Irradiation of Au@ZIF-8 composite particles leads to heating of the gold core and decomposition of surrounding matrix acting as temperature probe. Cavities inside the ZIF-8 matrix are found on TEM images after irradiation. Their size is determined dependent on laser energy density and the generated heat at the gold core after absorption of a laser pulse approximated. The surrounding of the gold cores can be heated up to ZIF-8 decomposition over a distance up to 60 nm. This represents a method to visualize heat transfer from the gold cores to the ZIF-8 matrix in three dimensions. Studies on ZIF-8 encapsulated Au@ZnO dot-rod particles give insight in heat transfer between the particle components and show the applicability of the method to different, more complex systems. © 2022 The Authors. ChemNanoMat published by Wiley-VCH GmbH

Systematic evaluation of agarose- and agar-based bioinks for extrusion-based bioprinting of enzymatically active hydrogels

Extrusion-based 3D bioprinting enables the production of customized hydrogel structures that can be employed in flow reactors when printing with enzyme-containing inks. The present study compares inks based on either low-melt agarose or agar at different concentrations (3–6%) and loaded with the thermostable enzyme esterase 2 from the thermophilic organism Alicyclobacillus acidocaldarius (AaEst2) with regard to their suitability for the fabrication of such enzymatically active hydrogels. A customized printer setup including a heatable nozzle and a cooled substrate was established to allow for clean and reproducible prints. The inks and printed hydrogel samples were characterized using rheological measurements and compression tests. All inks were found to be sufficiently printable to create lattices without overhangs, but printing quality was strongly enhanced at 4.5% polymer or more. The produced hydrogels were characterized regarding mechanical strength and diffusibility. For both properties, a strong correlation with polymer concentration was observed with highly concentrated hydrogels being more stable and less diffusible. Agar hydrogels were found to be more stable and show higher diffusion rates than comparable agarose hydrogels. Enzyme leaching was identified as a major drawback of agar hydrogels, while hardly any leaching from agarose hydrogels was detected. The poor ability of agar hydrogels to permanently immobilize enzymes indicates their limited suitability for their employment in perfused biocatalytic reactors. Batch-based activity assays showed that the enzymatic activity of agar hydrogels was roughly twice as high as the activity of agarose hydrogels which was mostly attributed to the increased amount of enzyme leaching. Agarose bioinks with at least 4.5% polymer were identified as the most suitable of the investigated inks for the printing of biocatalytic reactors with AaEst2. Drawbacks of these inks are limited mechanical and thermal stability, not allowing the operation of a reactor at the optimum temperature of AaEst2 which is above the melting point of the employed low-melt agarose

In Athletes, the Diurnal Variations in Maximum Oxygen Uptake Are More Than Twice as Large as the Day-to-Day Variations

In competitive sports any substantial individual differences in diurnal variations in maximal performance are highly relevant. Previous studies have exclusively focused on how the time of day affects performance and disregarded the maximal individual diurnal variation of performance. Thus, the aims of this study were (1) to investigate the maximum diurnal variation in maximum oxygen uptake (VO2max), (2) to compare the diurnal variation of VO2max during the day to the day-to-day variation in VO2max, and (3) to investigate if there is a time-of-day effect on VO2max. Ten male and seven female athletes (mean VO2max: 58.2 ± 6.9 ml/kg/min) performed six maximal cardiopulmonary exercise tests including a verification-phase at six different times of the day (i.e., diurnal variation) and a seventh test at the same time the sixth test took place (i.e., day-to-day variation). The test times were 7:00, 10:00, 13:00, 16:00, 19:00, and 21:00. The order of exercise tests was the same for all participants to ensure sufficient recovery but the time of day of the first exercise test was randomized. We used paired t-tests to compare the nadir and peak of diurnal variations, day-to-day variations and the difference between diurnal and day-to-day variations. The mean difference in VO2max was 5.0 ± 1.9 ml/kg/min (95% CI: 4.1, 6.0) for the diurnal variation and 2.0 ± 1.0 ml/kg/min (95% CI: 1.5, 2.5) for the day-to-day variation. The diurnal variation was significantly higher than the day-to-day variation with a mean difference of 3.0 ± 2.1 ml/kg/min (95% CI: 1.9, 4.1). The linear mixed effects model revealed no significant differences in VO2max for any pairwise comparison between the different times of the day (all p &gt; 0.11). This absence of a time-of-day effect is explained by the fact that peak VO2max was achieved at different times of the day by different athletes. The diurnal variations have meaningful implications for competitive sports and need to be considered by athletes. However, the results are also relevant to research. To increase signal-to-noise-ratio in intervention studies it is necessary to conduct cardiopulmonary exercise testing at the same time of the day for pre- and post-intervention exercise tests

The CMS Phase-1 pixel detector upgrade

The CMS detector at the CERN LHC features a silicon pixel detector as its innermost subdetector. The original CMS pixel detector has been replaced with an upgraded pixel system (CMS Phase-1 pixel detector) in the extended year-end technical stop of the LHC in 2016/2017. The upgraded CMS pixel detector is designed to cope with the higher instantaneous luminosities that have been achieved by the LHC after the upgrades to the accelerator during the first long shutdown in 2013–2014. Compared to the original pixel detector, the upgraded detector has a better tracking performance and lower mass with four barrel layers and three endcap disks on each side to provide hit coverage up to an absolute value of pseudorapidity of 2.5. This paper describes the design and construction of the CMS Phase-1 pixel detector as well as its performance from commissioning to early operation in collision data-taking.Peer reviewe