Considerations on the planned use of a scientific balance on Mars

The balance is the most widely used complex measuring instrument in science and techniques. To install a balance on Mars is a challenge for numerous aspects of in situ measurements in the next decade. By means of a balance useful parameters could be determined and a variety of investigations could be carried out there. Possible applications of a balance on Mars are reviewed. Choice of type and demands on the balance with regard to the conditions on Mars are discussed. The first step is to test a load cell with strain gauge deflection sensor.     

Insights into the Intraspecific Variability of the above and Belowground Emissions of Volatile Organic Compounds in Tomato

The in-vivo monitoring of volatile organic compound (VOC) emissions is a potential non-invasive tool in plant protection, especially in greenhouse cultivation. We studied VOC production from above and belowground organs of the eight parents of the Multi-Parent Advanced Generation Intercross population (MAGIC) tomato population, which exhibits a high genetic variability, in order to obtain more insight into the variability of constitutive VOC emissions from tomato plants under stress-free conditions. Foliage emissions were composed of terpenes, the majority of which were also stored in the leaves. Foliage emissions were very low, partly light-dependent, and differed significantly among genotypes, both in quantity and quality. Soil with roots emitted VOCs at similar, though more variable, rates than foliage. Soil emissions were characterized by terpenes, oxygenated alkanes, and alkenes and phenolic compounds, only a few of which were found in root extracts at low concentrations. Correlation analyses revealed that several VOCs emitted from foliage or soil are jointly regulated and that above and belowground sources are partially interconnected. With respect to VOC monitoring in tomato crops, our results underline that genetic variability, light-dependent de-novo synthesis, and belowground sources are factors to be considered for successful use in crop monitoring.     

Colloidal Analysis of Particles Extracted from Microalloyed Steels

Different colloidal particle characterization methods are examined for their suitability to determine the particle size distribution of particles extracted from steels. Microalloyed steels are dissolved to extract niobium and titanium carbonitride particles that are important for the mechanical properties of these steels. Such particles have sizes ranging from several nanometers to hundreds of nanometers depending on the precipitation stage during the thermomechanically controlled rolling process. The size distribution of the particles is analyzed by dynamic light scattering (DLS), analytical ultracentrifugation (AUC), and hollow fiber flow field-flow fractionation (HF5) and compared to data obtained for reference particles as well as data from electron microscopy, the standard sizing technique used in metallurgy today. AUC and HF5 provide high-quality size distributions, average over large particle numbers that enables statistical analysis, and yield useful insights for alloy design; however, DLS fails due to a lack of resolution. Important aspects in the conversion and comparison of size distributions obtained for broadly distributed particle systems with different measurement principles and the role of surfactants used in sample preparation are discussed.     

Microscopic calculations of beta decay far from stability

Beta decay properties of nuclei far from stability are of decisive importance for the understanding of the element synthesis in the universe and the determination of the age of the universe by means of cosmochronometers. A new large scale microscopic calculation ofβ ^?-decay half-lives up to the neutron drip line is presented. This new approach uses the proton-neutron quasiparticle random phase approximation with a Gamow-Teller residual interaction.     

CO<Subscript>2</Subscript> activation on single crystal based ceria and magnesia/ceria model catalysts

Novel multifunctional ceria based materials may show an improved performance in catalytic processes involving CO₂ activation and reforming of hydrocarbons. Towards a more detailed understanding of the underlying surface chemistry, we have investigated CO₂ activation on single crystal based ceria and magnesia/ceria model catalysts. All model systems are prepared starting from well-ordered and fully stoichiometric CeO₂(111) films on a Cu(111) substrate. Samples with different structure, oxidation state and compositions are generated, including CeO_2-x/Cu(111) (reduced), MgO/CeO_2-x/Cu(111) (reduced), mixed MgO-CeO₂/Cu(111) (stoichiometric), and mixed MgO-CeO_2-x/Cu(111) (reduced). The morphology of the model surfaces is characterized by means of scanning tunneling microscopy (STM), whereas the electronic structure and reactivity is probed by X-ray photoelectron spectroscopy (XPS). The experimental approach allows us to compare the reactivity of samples containing different types of Ce³⁺, Ce⁴⁺, and Mg²⁺ ions towards CO₂ at a sample temperature of 300 K. Briefly, we detect the formation of two CO₂-derived species, namely carbonate (CO₃ ^2-) and carboxylate (CO₂ ^-) groups, on the surfaces of all investigated samples after exposure to CO₂ at 300 K. In parallel to formation of the carbonate species, slow partial reoxidation of reduced CeO_2-x/Cu(111) occurs at large doses of CO₂. The reoxidation of the reduced ceria is largely suppressed on MgO-containing samples. The tendency for reoxidation of Ce³⁺ to Ce⁴⁺ by CO₂ decreases with increasing degree of intermixing between MgO and CeO_2-x. Additionally, we have studied the stability of the formed carbonate species as a function of annealing temperature.     

Sources of Error in Sorption and Density Measurements

In sorption measurements, volumetric or gravimetric procedures are commonly used to determine the amount adsorbed. At low pressures, thermomolecular flow and pressure differences according to Knudsen's law disturb measurements. In volumetry, calibration of the dead space is required; in gravimetry, the influence of buoyancy has to be taken into account. In both cases, adsorption of the calibrating gas, usually helium, may disturb the measurements [1]. From the calibration measurements, the density of the sample can in principle be calculated. However, it has been observed in many experiments that its value depends on the calibrating gas. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nuclear signatures in high-order harmonic generation from laser-driven muonic atoms

High-order harmonic generation from muonic atoms exposed to intense laser fields is considered. Our particular interest lies in effects arising from the finite nuclear mass and size. We numerically perform a fully quantum mechanical treatment of the muon-nucleus dynamics by employing modified soft-core and hard-core potentials. It is shown that the position of the high-energy cutoff of the harmonic spectrum depends on the nuclear mass, while the height of the spectral plateau is sensitive to the nuclear radius. We also demonstrate that gamma-ray harmonics can be generated from muonic atoms in ultrastrong VUV fields, which have potential to induce photonuclear reactions.