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.     

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.     

MS 1512–cB58: A case study of star formation, metal enrichment and superwinds in Lyman break galaxies

Recent advances in instrumentation and observing techniques have made it possible to begin to study in detail the stellar populations and the interstellar media of galaxies at redshift z = 3, when the universe was still in its ‘teen years’. I illustrate recent progress in this field with the latest observations of the gravitationally lensed galaxy MS 1512- cB58. This revised version was published online in September 2006 with corrections to the Cover Date.     

Fractional crystallization of high-K arc magmas: biotite- versus amphibole-dominated fractionation series in the Dariv Igneous Complex,Western Mongolia

Many studies have documented hydrous fractionation of calc-alkaline basalts producing tonalitic, granodioritic, and granitic melts, but the origin of more alkaline arc sequences dominated by high-K monzonitic suites has not been thoroughly investigated. This study presents results from a combined field, petrologic, and whole-rock geochemical study of a paleo-arc alkaline fractionation sequence from the Dariv Range of the Mongolian Altaids. The Dariv Igneous Complex of Western Mongolia is composed of a complete, moderately hydrous, alkaline fractionation sequence ranging from phlogopite-bearing ultramafic and mafic cumulates to quartz–monzonites to late-stage felsic (63–75 wt% SiO₂) dikes. A volumetrically subordinate more hydrous, amphibole-dominated fractionation sequence is also present and comprises amphibole (±phlogopite) clinopyroxenites, gabbros, and diorites. We present 168 whole-rock analyses for the biotite- and amphibole-dominated series. First, we constrain the liquid line of descent (LLD) of a primitive, alkaline arc melt characterized by biotite as the dominant hydrous phase through a fractionation model that incorporates the stepwise subtraction of cumulates of a fixed composition. The modeled LLD reproduces the geochemical trends observed in the “liquid-like” intrusives of the biotite series (quartz–monzonites and felsic dikes) and follows the water-undersaturated albite–orthoclase cotectic (at 0.2–0.5 GPa). Second, as distinct biotite- and amphibole-dominated fractionation series are observed, we investigate the controls on high-temperature biotite versus amphibole crystallization from hydrous arc melts. Analysis of a compilation of hydrous experimental starting materials and high-Mg basalts saturated in biotite and/or amphibole suggests that the degree of K enrichment controls whether biotite will crystallize as an early high-T phase, whereas the degree of water saturation is the dominant control of amphibole crystallization. Therefore, if a melt has the appropriate major-element composition for early biotite and amphibole crystallization, as is true of the high-Mg basalts from the Dariv Igneous Complex, the relative proximity of these two phases to the liquidus depends on the H₂O concentration in the melt. Third, we compare the modeled high-K LLD and whole-rock geochemistry of the Dariv Igneous Complex to the more common calc-alkaline trend. Biotite and K-feldspar fractionation in the alkaline arc series results in the moderation of K₂O/Na₂O values and LILE concentrations with increasing SiO₂ as compared to the more common calc-alkaline series characterized by amphibole and plagioclase crystallization and strong increases in K₂O/Na₂O values. Lastly, we suggest that common calc-alkaline parental melts involve addition of a moderate pressure, sodic, fluid-dominated slab component while more alkaline primitive melts characterized by early biotite saturation involve the addition of a high-pressure potassic sediment melt.     

Phlogopite- and clinopyroxene-dominated fractional crystallization of an alkaline primitive melt: petrology and mineral chemistry of the Dariv Igneous Complex,Western Mongolia

We present field relationships, petrography, and mineral major and trace element data for the Neoproterozoic Dariv Igneous Complex of the Altaids of Western Mongolia. This unique complex of high-K plutonic rocks is composed of well-exposed, km-scale igneous intrusions of wehrlites, phlogopite wehrlites, apatite-bearing phlogopite clinopyroxenites, monzogabbros, monzodiorites, and clinopyroxene-bearing monzonites, all of which are intruded by late stage lamprophyric and aplitic dikes. The biotite-dominated igneous complex intrudes depleted harzburgitic serpentinite. The observed lithological variability and petrographic observations suggest that the plutonic rocks can be ascribed to a fractionation sequence defined by olivine + clinopyroxene ± Fe–Ti oxides → phlogopite + apatite → K-feldspar + plagioclase → amphibole + quartz. Notably, phlogopite is the dominant hydrous mafic mineral. Petrogenesis of the observed lithologies through a common fractionation sequence is supported by a gradual decrease in the Mg# [molar Mg/(Fe_total + Mg) × 100] of mafic minerals. Crystallization conditions are derived from experimental phase petrology and mineral chemistry. The most primitive ultramafic cumulates crystallized at ≤0.5 GPa and 1,210–1,100 °C and oxygen fugacity (fO₂) of +2–3 ?FMQ (log units above the fayalite–quartz–magnetite buffer). Trace element modeling using clinopyroxene and apatite rare earth element compositions indicates that the dominant mechanism of differentiation was fractional crystallization. The trace element composition of a parental melt was calculated from primitive clinopyroxene compositions and compares favorably with the compositions of syn-magmatic lamprophyres that crosscut the fractionation sequence. The parental melt composition is highly enriched in Th, U, large ion lithophile elements, and light rare earth elements and has a pronounced negative Nb–Ta depletion, suggestive of an alkaline primitive melt originating from a subduction-imprinted mantle. Comparison with a global compilation of primitive arc melts demonstrates that Dariv primitive melts are similar in composition to high-K primitive melts found in some continental arcs. Thus, the high-K fractionation sequence exposed in the Dariv Igneous Complex may be a previously unrecognized important fractionation sequence resulting in alkali-rich upper crustal granitoids in continental arc settings.     

New insights into the stellar content and physical conditions of star-forming galaxies at z= 2–3 from spectral modelling

We have used extensive libraries of model and empirical galaxy spectra [assembled, respectively, from the population synthesis code of Bruzual and Charlot and the fourth data release of the Sloan Digital Sky Survey (SDSS)] to interpret some puzzling features seen in the spectra of high-redshift star-forming galaxies. We show that a stellar He  ii  λ1640 emission line, produced in the expanding atmospheres of Of and Wolf–Rayet stars, should be detectable with an equivalent width of 0.5–1.5 Å in the integrated spectra of star-forming galaxies, provided the metallicity is greater than about half solar. Our models reproduce the strength of the He  ii  λ1640 line measured in the spectra of Lyman-break galaxies for established values of their metallicities. With better empirical calibrations in local galaxies, this spectral feature has the potential of becoming a useful diagnostic of massive star winds at high, as well as low redshifts.
We also uncover a relationship in SDSS galaxies between their location in the [O  iii ]/Hβ versus [N  ii ]/Hα diagnostic diagram (the BPT diagram) and their excess specific star formation rate relative to galaxies of similar mass. We infer that an elevated ionization parameter U is at the root of this effect, and propose that this is also the cause of the offset of high-redshift star-forming galaxies in the BPT diagram compared to local ones. We further speculate that higher electron densities and escape fractions of hydrogen ionizing photons may be the factors responsible for the systematically higher values of U in the H  ii regions of high-redshift galaxies. The impact of such differences on abundance determinations from strong nebular lines are considered and found to be relatively minor.