Seasonal dynamics of CO2 profiles across a soil chronosequence,Santa Cruz,California

Concentrations of CO₂ in soil atmosphere and CO₂ efflux were measured across a marine terrace soil chronosequence near Santa Cruz, California. Soil development, specifically the formation of an argillic horizon, has created a two-tier soil gas profile in the older terrace soils. The soil above the argillic horizon has seasonal variations in soil CO₂ associated with plant respiration. The older soils with dense argillic horizons maintain a year round ～1%CO₂ below the argillic horizon. The CO₂efflux during the growing season is higher on the older terraces.     

Das südliche Rheintal an der Zeitwende von Rhät und Lias

Ohne Zusammenfassung     

Deriving Star Formation Histories: Evolutionary or Population Synthesis Codes versus Color-Magnitude Diagrams

The goal of this project is to analyze the integrated-light spectrum of a region in the LMC bar, for which HST images are already available yielding color-magnitude diagrams reaching the oldest main-sequence turnoff. Then, we can derive the star formation history in this field through evolutionary/population synthesis of the integrated light from 330 to 990 nm by a variety of independent methods and compare the results with the - in principle - more reliable results derived from the analysis of the color-magnitude diagram (CMD). This confrontation is the key ‘truth-test’ needed for the understanding of the abilities and the limitations of the evolutionary/population synthesis methods that must be applied of necessity to unresolved nearby and far-away galaxies. We report here on the observational part of the project. This revised version was published online in September 2006 with corrections to the Cover Date.     

The large-scale polarization of the microwave foreground

Most of the useful information about inflationary gravitational waves and reionization is on large angular scales where Galactic foreground contamination is the worst, so a key challenge is to model, quantify and remove polarized foregrounds. We use the Leiden radio surveys to quantify the polarized synchrotron radiation at large angular scales, which is likely to be the most challenging polarized contaminant for the WMAP satellite. We find that the synchrotron E- and B-contributions are equal to within 10% from 408–820 MHz with a hint of E-domination at higher frequencies. We quantify Faraday rotation and depolarization effects and show that they cause the synchrotron polarization percentage to drop both towards lower frequencies and towards lower multipoles.     

Chemostatanlage zur kontinuierlichen Kultur von Algen

The apparatus described was assembled using relatively inexpensive parts and makes the cultivation of various forms of algae under steady-state conditions and different flowrates (variation under 0.5%) possible. There was no difference in the biodensity in the reactor compared to that in the outflow.     

W-shaped occultation signatures: Inference of entwined particle orbits in charged planetary ringlets

Observed W-shaped occultation signatures of certain narrow ringlets in the ring systems of Saturn and Uranus imply a concentration of material near their inner and outer radial edges. A model is proposed where edge bunching is a natural consequence of particles in entwined elliptical orbits, with the same particles alternately defining both edges. While such orbits cross over in radius, collisions would not occur if they have small inclinations, the same fixed argument of periapse ω, and other parameters whereby the particles would “fly in formation” along compressed helical paths relative to the core of the ringlet, which is taken to be a circle in the equatorial plane. For this model to match the observed ring thickness and ringlet widths, orbit inclinations i must be much smaller than their eccentricities e, which themselves would be very small compared to unity. Thus, the meridional cross section of the resultant torus would be a very thin ellipse of thickness proportional to i∣cos ω∣, tilted slightly from the equatorial plane by (i/e)∣sin ω∣ radians. However, gravitational perturbations due to the oblateness of the planet would cause a secular change in ω so that this cross section would collapse periodically to a tilted line, and collisions would then occur. If this collapse could be prevented, the torus could remain in a continuous state of nearly zero viscosity. Stabilization against collapse appears possible due to several remarkable characteristics that are added to the model when the particles are electrically charged. First, because of inherent features of the torus structure, a weak electric force could counter the key effect of the vastly larger oblateness force. Second, because the electric perturbation also affects i, there is a large region in ω,i space where stability against cross-sectional collapse is automatic. For this region, the thickness of the elliptical cross section would expand and contract in concert with the way that the major axis of the ellipse rocks back and forth relative to the equatorial plane. The period of these “rocking and breathing” changes would be from 1 to 3 weeks for a torus in the C ring of Saturn, for example. The electric effects could change considerably without driving the parameters of the torus from the stable domain where cross-sectional collapse does not occur. While specialized and in several important ways still incomplete, the proposed model could account for the W-shaped patterns and explain how very dense ringlets might endure without energy loss due to collisions. It also appears to be capable of explaining the observed sorting of particles by size within a ringlet. Several characteristics of the model suggest definitive tests of its applicability, including its prediction that a nonsymmetrical W-shaped occultation signature could be reversed a half orbit away, and that grazing solar illumination of tilted ringlets might cast shadows that change with time in a prescribed way.     

Spatially coherent oscillations in microwave bursts

Solar microwave burst observations (made with the WSRT) with high time and high spatial resolution show large-scale (> 8000 km) short-period (1.5 s) modulations of the source. It is argued that an interpretation in terms of Alfvén oscillations in the microwave source is ruled out by this observation. Instead it must be the source of the fast electrons, that produce the microwaves, that is oscillating. The fluctuating acceleration region is identified with a volume where a sheared field is compressed against a flux tube by an unstable current. MHD oscillations in the overlying fluxtube are caused by the pushing force. The rapidly expanding current plays a major role in the flare theory of van Tend and Kuperus (1978).     

Near-infrared spectra of laboratory H2O-CH4 ice mixtures

We present 1.25-19 μm infrared spectra of pure solid CH₄ and H₂O/CH₄=87, 20, and 3 solid mixtures at temperatures from 15 to 150 K. We compare and contrast the absorptions of CH₄ in solid H₂O with those of pure CH₄. Changes in selected peak positions, profiles, and relative strength with temperature are presented, and absolute strengths for absorptions of CH₄ in solid H₂O are estimated. Using the two largest (ν₃+ν₄) and (ν₁+ν₄) near-IR absorptions of CH₄ at 2.324 and 2.377 μm (4303 and 4207 cm⁻¹), respectively, as examples, we show that peaks of CH₄ in solid H₂O are at slightly shorter wavelength (higher frequency) and broader than those of pure solid CH₄. With increasing temperature, these peaks shift to higher frequency and become increasingly broad, but this trend is reversible on re-cooling, even though the phase transitions of H₂O are irreversible. It is to be hoped that these observations of changes in the positions, profiles, and relative intensities of CH₄ absorptions with concentration and temperature will be of use in understanding spectra of icy outer Solar System bodies.