Determination of Rare Earth Elements and Yttrium in Nine Geochemical Reference Samples Using a Novel Group Separation Procedure Involving Mixed-Acid Elution Ion-Exchange Chromatography

Rare earth data for nine well-known geochemical reference samples were obtained using a rapid and efficient cation exchange chromatographic separation procedure. It involves the use of a mixed-acid eluent (HCI and HNO3) on a 15 x 1 cm column of Bio-Rad AG50–X8 (200–400 mesh) to remove matrix and many trace elements from rock solutions. The rare earth elements are removed from the column using 60 ml 7M HNO3. The pre-concentration procedure described is routinely used in this laboratory for the determination of the rare earth elements by mass spectrometry-isotope dilution, and has been satisfactorily used for their determination using inductively-coupled plasma-source atomic emission spectrometry.     

Direct measurement of the Si–O bond length and orientational disorder in the high-temperature phase of cristobalite

Neutron total scattering measurements from powdered samples of cristobalite have been used to determine the local structure in both the tetragonal and cubic phases. The results for the cubic phase show directly that the Si–O bonds are tilted at an angle of around 17° to the unit cell [111] direction. It is striking that the structure of β-cristobalite over the range 5–10 Å is closer to that of silica glass than α-cristobalite, which suggests that the local structure of β-cristobalite is not likely to consist of domains with the structure of α-cristobalite. The measurements show a small thermal expansion of the Si–O bonds over the temperature range 570–950 K.     

Flow resistance in the Great Belt,the biggest strait between the North Sea and the Baltic Sea

The Danish Straits are part of the transition area between the North Sea and the central Baltic Sea. More precisely, the Danish Straits connect Kattegat to the Arkona Basin and includes the relatively narrow and shallow sub-areas: Great Belt, Little Belt, Fehmarn Belt and Sound. The flow resistances in the straits are hydraulically determined by among other factors, the contractions, sills and stratification found in the straits. Close to the entrance to the Arkona Basin the Darss and Drogden Sills are located that trap inflowing dense water partially before it enters the central Baltic Sea. Hence, the resistances in the Danish Straits are of crucial importance for the stratification and ecosystems in the central Baltic Sea. The present work comprises calculations of flow resistance in the Great Belt based on measurements collected as part of the Great Belt Fixed Link investigations. The specific resistance in the Great Belt is determined to be an average of 41.2 × 10⁻¹² s² m⁻⁵, but it depends heavily on the interface position. When calculating long-term discharge time-series on the basis of the momentum equation it is advised to apply a seasonal varying resistance.     

The hydrodynamics and salinity regime of a coastal lagoon – The Coorong,Australia – Seasonal to multi-decadal timescales

The Coorong is a choked coastal lagoon in South Australia that forms part of the terminal lake system at the end of the River Murray, Australia’s major river. It is an inverse estuary with a constricted channel connection to the sea at one end and extends parallel to the coast for more than 100 km away from this inlet. The present paper considers the physical dynamics of the Coorong, particularly its ecologically important salinity and water level regimes, and how these respond to connectedness with the ocean, barrage flows and meteorological conditions. The approach combines hydrodynamic modelling with measurements and considers temporal variation in the system ranging from seasonal to multi-decadal timescales.     

南极Amanda湾帝企鹅卵的生态生物学及与其它南极海鸟卵的比较

对南极Amanda湾帝企鹅的卵进行了生态生物学观测与相应的统计分析。结果显示,帝企鹅卵为典型的卵形卵,平均长、短径分别为121.3mm和83.8mm;平均卵容量409.3ml(322.6-506.4ml),卵的平均壳厚为1.11mm(0.94-1.23mm)。帝企鹅和南方巨鹱、白眉企鹅以及灰贼鸥等南极海鸟的卵相比较,卵的形态大小与容量成正比,同时,容量较大的卵具有较厚的卵壳,以增强对卵的保护。这些海鸟卵的生态生物学特征,包括保护色的有无、卵容量的大小,以及卵壳厚度等特征参数,是这些海鸟种的明显特征,并与亲鸟在繁殖期的窝卵数以及孵化习性相协调,以达到对南极环境的适应与生存。     

Binary formation in stellar clusters

We consider how the tidal potential of a stellar cluster or a dense molecular cloud affects the fragmentation of gravitationally unstable molecular cloud cores. We find that molecular cloud cores which would collapse to form a single star in the absence of tidal shear, can be forced to fragment if they are subjected to tides. This may enhance the frequency of binaries in star-forming regions such as Ophiuchus and the frequency of binaries with separations ≲100 au in the Orion Trapezium Cluster. We also find that clouds which collapse to form binary systems in the absence of a tidal potential will form bound binary systems if exposed to weak tidal shear. However, if the tidal shear is sufficiently strong, even though the cloud still collapses to form two fragments, the fragments are pulled apart while they are forming by the tidal shear and two single stars are formed. This sets an upper limit for the separation of binaries that form near dense molecular clouds or in stellar clusters.