1,271 research outputs found
Abundances of Baade's Window Giants from Keck/HIRES Spectra: II. The Alpha- and Light Odd Elements
We report detailed chemical abundance analysis of 27 RGB stars towards the
Galactic bulge in Baade's Window for elements produced by massive stars: O, Na,
Mg, Al, Si, Ca and Ti. All of these elements are overabundant in the bulge
relative to the disk, especially Mg, indicating that the bulge is enhanced in
Type~II supernova ejecta and most likely formed more rapidly than the disk. We
attribute a rapid decline of [O/Fe] to metallicity-dependent yields of oxygen
in massive stars, perhaps connected to the Wolf-Reyet phenomenon. he explosive
nucleosynthesis alphas, Si, Ca and Ti, possess identical trends with [Fe/H],
consistent with their putative common origin. We note that different behaviors
of hydrostatic and explosive alpha elements can be seen in the stellar
abundances of stars in Local Group dwarf galaxies. We also attribute the
decline of Si,Ca and Ti relative to Mg, to metallicity- dependent yields for
the explosive alpha elements from Type~II supernovae. The starkly smaller
scatter of [/Fe] with [Fe/H] in the bulge, as compared to the halo, is
consistent with expected efficient mixing for the bulge. The metal-poor bulge
[/Fe] ratios are higher than ~80% of the halo. If the bulge formed from
halo gas, the event occured before ~80% of the present-day halo was formed. The
lack of overlap between the thick and thin disk composition with the bulge does
not support the idea that the bulge was built by a thickening of the disk
driven by the bar. The trend of [Al/Fe] is very sensitive to the chemical
evolution environment. A comparison of the bulge, disk and Sgr dSph galaxy
shows a range of ~0.7 dex in [Al/Fe] at a given [Fe/H], presumably due to a
range of Type~II/Type~Ia supernova ratios in these systems.Comment: 51 pages, 6 tables, 27 figures, submitte
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DNAzymes as Catalysts for l-Tyrosine and Amyloid β Oxidation
Single-stranded deoxyribonucleic acids have an enormous potential for catalysis by applying tailored sequences of nucleotides for individual reaction conditions and substrates. If such a sequence is guanine-rich, it may arrange into a three-dimensional structure called G-quadruplex and give rise to a catalytically active DNA molecule, a DNAzyme, upon addition of hemin. Here, we present a DNAzyme-mediated reaction, which is the oxidation of l-tyrosine toward dityrosine by hydrogen peroxide. With an optimal stoichiometry between DNA and hemin of 1:10, we report an activity of 101.2 ¹ 3.5 ΟUnits (ΟU) of the artificial DNAzyme Dz-00 compared to 33.0 ¹ 1.8 ΟU of free hemin. Exemplarily, DNAzymes may take part in neurodegeneration caused by amyloid beta (Aβ) aggregation due to l-tyrosine oxidation. We show that the natural, human genome-derived DNAzyme In1-sp is able to oxidize Aβ peptides with a 4.6% higher yield and a 33.3% higher velocity of the reaction compared to free hemin. As the artificial DNAzyme Dz-00 is even able to catalyze Aβ peptide oxidation with a 64.2% higher yield and 337.1% higher velocity, an in-depth screening of human genome-derived DNAzymes may identify further candidates with similarly high catalytic activity in Aβ peptide oxidation
Mapping Tumor Spheroid Mechanics in Dependence of 3D Microenvironment Stiffness and Degradability by Brillouin Microscopy
Altered biophysical properties of cancer cells and of their microenvironment contribute to cancer progression. While the relationship between microenvironmental stiffness and cancer cell mechanical properties and responses has been previously studied using two-dimensional (2D) systems, much less is known about it in a physiologically more relevant 3D context and in particular for multicellular systems. To investigate the influence of microenvironment stiffness on tumor spheroid mechanics, we first generated MCF-7 tumor spheroids within matrix metalloproteinase (MMP)-degradable 3D polyethylene glycol (PEG)-heparin hydrogels, where spheroids showed reduced growth in stiffer hydrogels. We then quantitatively mapped the mechanical properties of tumor spheroids in situ using Brillouin microscopy. Maps acquired for tumor spheroids grown within stiff hydrogels showed elevated Brillouin frequency shifts (hence increased longitudinal elastic moduli) with increasing hydrogel stiffness. Maps furthermore revealed spatial variations of the mechanical properties across the spheroidsâ cross-sections. When hydrogel degradability was blocked, comparable Brillouin frequency shifts of the MCF-7 spheroids were found in both compliant and stiff hydrogels, along with similar levels of growth-induced compressive stress. Under low compressive stress, single cells or free multicellular aggregates showed consistently lower Brillouin frequency shifts compared to spheroids growing within hydrogels. Thus, the spheroidsâ mechanical properties were modulated by matrix stiffness and degradability as well as multicellularity, and also to the associated level of compressive stress felt by tumor spheroids. Spheroids generated from a panel of invasive breast, prostate and pancreatic cancer cell lines within degradable stiff hydrogels, showed higher Brillouin frequency shifts and less cell invasion compared to those in compliant hydrogels. Taken together, our findings contribute to a better understanding of the interplay between cancer cells and microenvironment mechanics and degradability, which is relevant to better understand cancer progression
Influence of Contaminants in Steel Mill Exhaust Gases on Cu/ZnO/Al<sub>2</sub>O<sub>3</sub> Catalysts Applied in Methanol Synthesis
The influence of impurities in steel mill exhaust gases on ternary Cu/ZnO/Al2O3 catalysts was studied for conventional methanol synthesis, which is one of the central reactions within the crossâindustrial approach of Carbon2ChemÂŽ. A series of hydrocarbons was identified as inert spectators for methanol synthesis. Several catalyst poisons like Nâcontaining compounds or O2 show reversible characteristics at low pressure. However, by increasing the partial pressure of O2, poisoning becomes irreversible, indicating different poisoning mechanisms concerning the reversibility of deactivation
Stellar Iron Abundances at the Galactic Center
We present measurements of [Fe/H] for six M supergiant stars and three giant
stars within 0.5 pc of the Galactic Center (GC) and one M supergiant star
within 30 pc of the GC. The results are based on high-resolution (lambda /
Delta lambda =40,000) K-band spectra, taken with CSHELL at the NASA Infrared
Telescope Facility.We determine the iron abundance by detailed abundance
analysis,performed with the spectral synthesis program MOOG.The mean [Fe/H] of
the GC stars is determined to be near solar,[Fe/H] = +0.12 0.22. Our
analysis is a differential analysis, as we have observed and applied the same
analysis technique to eleven cool, luminous stars in the solar neighborhood
with similar temperatures and luminosities as the GC stars. The mean [Fe/H] of
the solar neighborhood comparison stars, [Fe/H] = +0.03 0.16, is similar
to that of the GC stars. The width of the GC [Fe/H] distribution is found to be
narrower than the width of the [Fe/H] distribution of Baade's Window in the
bulge but consistent with the width of the [Fe/H] distribution of giant and
supergiant stars in the solar neighborhood.Comment: 41 pages, 9 figures, ApJ, in pres
Cancer patientsâ experiences of using an Interactive Health Communication Application (IHCA)
Interactive Health Communication Applications (IHCAs) are increasingly used in health care. Studies document that IHCAs provide patients with knowledge and social support, enhance self- efficacy and can improve behavioural and clinical outcomes. However, research exploring patientsâ experiences of using IHCAs has been scarce. The aim of this study was to explore cancer patientsâ perspectives and experiences related to the use of an IHCA called WebChoice in their homes. Qualitative interviews were conducted with infrequent, medium and frequent IHCA usersâsix women and four men with breast and prostate cancer. The interviews were transcribed and analyzed inspired by interactionistic perspectives. We found that some patientsâ perceived WebChoice as a âfriend,â others as a âstranger.â Access to WebChoice stimulated particularly high frequency users to position themselves as âinformation seeking agents,â assuming an active patient role. However, to position oneself as an âactive patientâ was ambiguous and emotional. Feelings of âcalmnessâ, ânormalization of symptomsâ, feelings of âbeing part of a communityâ, feeling âupsetâ and âvulnerableâ, as well as âfeeling supportedâ were identified. Interaction with WebChoice implied for some users an increased focus on illness. Our findings indicate that the interaction between patients and an IHCA such as WebChoice occurs in a variety of ways, some of which are ambivalent or conflicting. Particularly for frequent and medium frequency users, it offers support, but may at the same time reinforce an element of uncertainty in their life. Such insights should be taken into consideration in the future development of IHCAs in healthcare in general and in particular for implementation into patientsâ private sphere
Effects of Potassium and Manganese Promoters on Nitrogen-Doped Carbon Nanotube-Supported Iron Catalysts for COâ Hydrogenation
Nitrogen-doped carbon nanotubes (NCNTs) were used as a support for iron (Fe) nanoparticles applied in carbon dioxide (CO2) hydrogenation at 633 K and 25 bar (1 bar = 105 Pa). The Fe/NCNT catalyst promoted with both potassium (K) and manganese (Mn) showed high performance in CO2 hydrogenation, reaching 34.9% conversion with a gas hourly space velocity (GHSV) of 3.1 L¡(g¡h)â1. Product selectivities were high for olefin products and low for short-chain alkanes for the K-promoted catalysts. When Fe/NCNT catalyst was promoted with both K and Mn, the catalytic activity was stable for 60 h of reaction time. The structural effect of the Mn promoter was demonstrated by X-ray diffraction (XRD), temperature-programmed reduction (TPR) with molecular hydrogen (H2), and in situ X-ray absorption near-edge structure (XANES) analysis. The Mn promoter stabilized wĂźstite (FeO) as an intermediate and lowered the TPR onset temperature. Catalytic ammonia (NH3) decomposition was used as an additional probe reaction for characterizing the promoter effects. The Fe/NCNT catalyst promoted with both K and Mn had the highest catalytic activity, and the Mn-promoted Fe/NCNT catalysts had the highest thermal stability under reducing conditions
Fast-, Light-Cured Scintillating Plastic for 3D-Printing Applications
Additive manufacturing techniques enable a wide range of possibilities for novel radiation detectors spanning simple to highly complex geometries, multi-material composites, and metamaterials that are either impossible or cost prohibitive to produce using conventional methods. The present work identifies a set of promising formulations of photocurable scintillator resins capable of neutron-gamma pulse shape discrimination (PSD) to support the additive manufacturing of fast neutron detectors. The development of these resins utilizes a step-by-step, trial-and-error approach to identify different monomer and cross-linker combinations that meet the requirements for 3D printing followed by a 2-level factorial parameter study to optimize the radiation detection performance, including light yield, PSD, optical clarity, and hardness. The formulations resulted in hard, clear, PSD-capable plastic scintillators that were cured solid within 10 s using 405 nm light. The best-performing scintillator produced a light yield 83% of EJ-276 and a PSD figure of merit equaling 1.28 at 450â550 keVee
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