1,821 research outputs found
The role of potassium as a promoter in iron catalysts for ammonia synthesis
Five ammonia synthesis catalysts, mainly differing in potassium content, were prepared from a commercial doubly promoted iron catalyst. The activities of these catalysts were measured at 350–450 °C and 5–200 atm. The experimental reaction rates were fitted to the modified Temkin rate equation. Increasing the potassium content from 0.1 to 3.8 wt% results in increasing the order in H2 from 0.7 to 1.5. The change from singly to doubly promoted behavior is gradual. The nature of catalysts with a relatively high K-content is changed, preventing the formation of NH (or NH2) groups so that N-atoms become the main species on the surface, which explains the higher order in H2
Nutzung von KI-Methoden für die Kupplungsentwicklung in automobilen Antriebssträngen = Use of AI methods for clutch development in automotive drivetrains
Im Spannungsfeld steigender Erwartungen an Fahrkomfort und Energieeffizienz stoßen aktuelle Entwicklungsmethoden der Modellbildung und Optimierung für Fahrzeugkupplungen an ihre Grenzen. In diesem Beitrag wird der Einsatz von KI-Methoden für die Kupplungsentwicklung untersucht und ein Überblick anhand verschiedener Anwendungsbeispiele in aktuellen Forschungsprojekten der Mercedes-Benz AG gegeben. Mittels überwachten Lernens und tiefen neuronalen Netzen werden ein Reibungszahlmodell sowie ein Temperaturmodell einer Kupplung mit hoher Abbildungsgüte entwickelt. Verstärkendes Lernen mit tiefen neuronalen Netzen wird zur Synthese von Regelungen für verschiedene Gangwechsel eingesetzt. Fahrzeugmessdaten werden mit Cluster-Algorithmen analysiert, um Handlungsempfehlungen für die Applikation des Motorwiederstarts eines hybriden Antriebsstrangs abzuleiten. Mit den gezeigten Methoden steigt das Automatisierungspotential in der Entwicklung und der Aufwand für die Übernahme komplexer Entwicklungsprozesse auf neue Getriebevarianten sinkt
The ENCOMPASS framework:a practical guide for the evaluation of public health programmes in complex adaptive systems
BackgroundSystems thinking embraces the complexity of public health problems, including childhood overweight and obesity. It aids in understanding how factors are interrelated, and it can be targeted to produce favourable changes in a system. There is a growing call for systems approaches in public health research, yet limited practical guidance is available on how to evaluate public health programmes within complex adaptive systems. The aim of this paper is to present an evaluation framework that supports researchers in designing systems evaluations in a comprehensive and practical way.MethodsWe searched the literature for existing public health systems evaluation studies. Key characteristics on how to conduct a systems evaluation were extracted and compared across studies. Next, we overlaid the identified characteristics to the context of the Lifestyle Innovations Based on Youth Knowledge and Experience (LIKE) programme evaluation and analyzed which characteristics were essential to carry out the LIKE evaluation. This resulted in the Evaluation of Programmes in Complex Adaptive Systems (ENCOMPASS) framework.ResultsThe ENCOMPASS framework includes five iterative stages: (1) adopting a system dynamics perspective on the overall evaluation design; (2) defining the system boundaries; (3) understanding the pre-existing system to inform system changes; (4) monitoring dynamic programme output at different system levels; and (5) measuring programme outcome and impact in terms of system changes.ConclusionsThe value of ENCOMPASS lies in the integration of key characteristics from existing systems evaluation studies, as well as in its practical, applied focus. It can be employed in evaluating public health programmes in complex adaptive systems. Furthermore, ENCOMPASS provides guidance for the entire evaluation process, all the way from understanding the system to developing actions to change it and to measuring system changes. By the nature of systems thinking, the ENCOMPASS framework will likely evolve further over time, as the field expands with more completed studies
Enriching the evidence base of co-creation research in public health with methodological principles of critical realism
With the popularity of co-creation research in public health and other fields, there is a need to strengthen its evidence-base by developing a framework based on meta-theoretical principles. The lack of applying meta-theoretical principles in co-creation research impedes the theory- and evidence building. Critical realism seems a promising candidate for providing meta-theoretical principles to enrich the evidence base of co-creation research in public health. To this purpose we searched for relevant papers on critical realism methodological principles, clarified and subsequently applied such principles to a co-creation public health case study. We provide explanatory steps to apply five principles; 1) focusing on understanding an event, like childhood over-weight, 2) exploring the broader structure and context surrounding the event, 3) constructing hypotheses about the underlying mechanism(s) of an event, 4) empirical testing to corroborate those hypotheses, and 5) using multiple methods and triangulation. Further, this study shows that critical realism can enrich co-creation research in public health by iteratively building theory and evidence following the five proposed principles
On the dependence between UV luminosity and Lyman-alpha equivalent width in high redshift galaxies
We show that with the simple assumption of no correlation between the
Ly-alpha equivalent width and the UV luminosity of a galaxy, the observed
distribution of high redshift galaxies in an equivalent width - absolute UV
magnitude plane can be reproduced. We further show that there is no dependence
between Ly-alpha equivalent width and Ly-alpha luminosity in a sample of
Ly-alpha emitters. The test was expanded to Lyman-break galaxies and again no
dependence was found. Simultaneously, we show that a recently proposed lack of
large equivalent width, UV bright galaxies (Ando et al. 2006) can be explained
by a simple observational effect, based on too small survey volumes.Comment: 7 pages, 3 figures, 2 tables, accepted in MNRA
Doubling Expression of the Low Density Lipoprotein Receptor by Truncation of the 3′-Untranslated Region Sequence Ameliorates Type III Hyperlipoproteinemia in Mice Expressing the Human ApoE2 Isoform
The primary receptor mediating clearance of apolipoprotein (apo)E- and apoB100-containing lipoproteins from the circulation is the low density lipoprotein (LDL) receptor. Reduced expression of the LDLR is believed to be a precipitating factor in the pathogenesis of type III hyperlipoproteinemia (HLP) in some humans homozygous for the apoE2 allele (APOE*2). To test the effect of genetic changes in LDL receptor expression on the pathogenesis of type III HLP, we have generated a variant allele at the endogenous mouse Ldlr locus that expresses the human LDL receptor transcript. Transcription of the human LDLR minigene is regulated by the endogenous mouse promoter sequence, but a truncation of 3'-untranslated region results in increased mRNA stability. Consequently, in liver of heterozygotes, steady state levels of mouse and human LDLR transcripts are 50 and 180% the levels of total transcript in wild type mice, respectively. Overall, the 2.3-fold normal level of LDLR message in heterozygotes completely ameliorates type III HLP caused by the homozygosity for the human APOE*2 allele, normalizing their plasma lipoprotein profile. We conclude that a modest increase in expression of the LDLR through message stabilization is sufficient to prevent precipitation of type III HLP in mice
Are There Age Spreads in Star Forming Regions?
A luminosity spread at a given effective temperature is ubiquitously seen in
the Hertzsprung-Russell (HR) diagrams of young star forming regions and often
interpreted in terms of a prolonged period (>=10 Myr) of star formation. I
review the evidence that the observed luminosity spreads are genuine and not
caused by astrophysical sources of scatter. I then address whether the
luminosity spreads necessarily imply large age spreads, by comparing HR diagram
ages with ages from independent clocks such as stellar rotation rate, the
presence of circumstellar material and lithium depletion. I argue that whilst
there probably is a true luminosity dispersion, there is little evidence to
support age spreads larger than a few Myr. This paradox could be resolved by
brief periods of rapid accretion during the class I pre main-sequence phase.Comment: To appear in the proceedings of JENAM10: Star Clusters in the Era of
Large Surveys, 8 page
The Extreme Hosts of Extreme Supernovae
We use GALEX ultraviolet (UV) and optical integrated photometry of the hosts
of seventeen luminous supernovae (LSNe, having peak M_V < -21) and compare them
to a sample of 26,000 galaxies from a cross-match between the SDSS DR4 spectral
catalog and GALEX interim release 1.1. We place the LSNe hosts on the galaxy
NUV-r versus M_r color magnitude diagram (CMD) with the larger sample to
illustrate how extreme they are. The LSN hosts appear to favor low-density
regions of the galaxy CMD falling on the blue edge of the blue cloud toward the
low luminosity end. From the UV-optical photometry, we estimate the star
formation history of the LSN hosts. The hosts have moderately low star
formation rates (SFRs) and low stellar masses (M_*) resulting in high specific
star formation rates (sSFR). Compared with the larger sample, the LSN hosts
occupy low-density regions of a diagram plotting sSFR versus M_* in the area
having higher sSFR and lower M_*. This preference for low M_*, high sSFR hosts
implies the LSNe are produced by an effect having to do with their local
environment. The correlation of mass with metallicity suggests that perhaps
wind-driven mass loss is the factor that prevents LSNe from arising in
higher-mass, higher-metallicity hosts. The massive progenitors of the LSNe
(>100 M_sun), by appearing in low-SFR hosts, are potential tests for theories
of the initial mass function that limit the maximum mass of a star based on the
SFR.Comment: 8 pages, 3 figures, 2 tables, accepted to ApJ, amended references and
updated SN designation
Differential modulation of diet-induced obesity and adipocyte functionality by human apolipoprotein E3 and E4 in mice
Apolipoprotein E (apoE), a key protein in lipid metabolism, is highly expressed in adipose tissues. Studies have shown that human APOE*4 is associated with a lower body mass index but with a greater risk of coronary heart disease compared with other APOE alleles. To define the isoform-specific role of apoE in regulating the expandability and functionality of adipose tissues, we investigated the effects of diet-induced obesity in mice whose endogenous Apoe gene has been replaced by either the human APOE*3 or APOE*4 allele
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