A Fully Depleted pn-Junction CCD for Infrared-, UV- and X- ray detection

This paper describes the performance of the Fully Depleted pn-junction CCD (pn-CCD) system, developed for ESA's XMM-satellite mission for soft x-ray imaging and spectroscopy in the single photon counting mode in the 100 eV to 10 keV photon range. The 58 mm x 60 mm large pn-CCD array, designed and fabricated at the Semiconductor Lab (Halbleiterlabor) of the Max-Planck-Institut, uses pn-junctions for registers and as backside structure. This concept naturally enables full depletion of the detector volume independent of the silicon wafer's resistivity and thickness, and as such make it an efficient detector for the x-ray region and the infrared. For high detection efficiency in the soft x-ray region and UV, an ultrathin pn-CCD backside deadlayer has been realized. Each pn-CCD-channel is equipped with its own on-chip JFET amplifier which, in combination with the CAMEX-amplifier and multiplexing chip, facilitates parallel readout and fast data rate: the cooled pn-CCD system can be read out at a data rate up to 3 MHz with an electronic noise floor of ENC < 5 e-.     

A versatile birefringent filter

The theory of the olc birefringent filter is complicated and the general formulae describing its optical properties do not invite to any simple physical picture. Due to these formal difficulties, many of its inherent possibilities have not been fully appreciated. In this paper we point out some new possibilities for filters based on this general design.The detailed shape of the transmission profile is a function of the angles of the crystal plate optic axes. It is shown how unwanted transmission sidelobes can be suppressed to any desired level by altering the distribution of plate angles. By the same means, the transmission band can be split into two symmetrically placed replicas, and the distance between the two bands can be varied. In this way the filter can easily be tuned over half the free spectral range.Some of the error sources that are important to filter performance are discussed. An expression is given for the amount of parasitic light introduced by errors in the orientation of the plate optic axes and it is found that errors as large as 0°.5 can be tolerated. A laboratory experiment with 16 birefringent plates has shown that accuracies an order of magnitude better than this figure can easily be achieved. Manufacturing errors in the thickness of the plates can be compensated for by assembling the pile of plates in a particular way. The very strict tolerances usually quoted can therefore be considerably relaxed.     

Evaluating environmental drivers of Holocene changes in water chemistry and aquatic biota composition at Lake Loitsana,NE Finland

This study presents a detailed analysis of geochemical and biotic proxies in a lake sediment profile to assess the effects of local and regional environmental drivers on the Holocene development of Lake Loitsana, situated in the northern boreal forest of NE Finland. Multi-proxy studies, in particular those that include a detailed plant macrofossil record, from the part of the northern boreal zone of Fennoscandia which has not been affected by treeline fluctuations, are scarce and few of these records date back to the earliest part of the Holocene. A 9-m sediment sequence of gyttja overlying silts representing the last c. 10,700 cal year, allowed for a high-resolution study with emphasis on the early to mid-Holocene lake history. The lacustrine sediments were studied using lithology, loss-on-ignition and C/N ratios, micro- and macro-fossils of aquatic and wetland taxa, diatoms, chironomids and accelerator mass spectrometry ¹⁴C dating on terrestrial plant macrofossils. Our study shows that the local development at Loitsana was complex and included a distinct glacial lake phase and subsequent drainage, a history of fluvial input affected by nearby wetland expansion, and lake infilling in an eventual esker-fed shallow lake. Enhanced trophic conditions, due to morphometric eutrophication, are recorded as Glacial Lake Sokli drained and open water conditions became restricted to a relatively small Lake Loitsana depression. pH appears to have been stable throughout the Holocene with a well-buffered lake due to the local carbonatite bedrock (Sokli Carbonatite Massif). The fossil assemblage changes are best explained by a complex mixture of drivers, including water-body conditions (i.e. depth, turbidity and turbulence), rate of sediment input, and the general infilling of the lake, highlighting the need to carefully evaluate the possible influence of such local factors as palaeoenvironmental conditions are reconstructed based on aquatic proxies.     

Holocene paleoenvironmental change inferred from two sediment cores collected in the Tibetan lake Taro Co

Journal of Paleolimnology - The Tibetan Plateau, also known as the “Water Tower of Asia” because of its function as a water storage and supply region, responds dramatically to modern...     

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Isotopic composition of Sr,Nd, and Pb in pirssonite,shortite and calcite carbonatites from Oldoinyo Lengai volcano,Tanzania

Doklady Earth Sciences -     

Magmatic evolution of the Easter microplate-Crough Seamount region (South East Pacific)

The Easter microplate-Crough Seamount region located between 25° S–116° W and 25° S–122° W consists of a chain of seamounts forming isolated volcanoes and elongated (100–200 km in length) en echelon volcanic ridges oriented obliquely NE (N 065°), to the present day general spreading direction (N 100°) of the Pacific-Nazca plates. The extension of this seamount chain into the southwestern edge of the Easter microplate near 26°30 S–115° W was surveyed and sampled. The southern boundary including the Orongo fracture zone and other shallow ridges (< 2000 m high) bounding the Southwest Rift of the microplate consists of fault scarps where pillow lava, dolerite, and metabasalts are exposed. The degree of rock alternation inferred from palagonitization of glassy margins suggests that the volcanic ridges are as old as the shallow ridges bounding the Southwest Rift of the microplate. The volcanics found on the various structures west of the microplate consist of depleted (K/Ti < 0.1), transitional (K/Ti = 0.11–0.25) and enriched (K/Ti > 0.25) MORBs which are similar in composition to other more recent basalts from the Southwest and East Rifts spreading axes of the Easter microplate. Incompatible element ratios normalized to chondrite values [(Ce/Yb)_N = 1–2.5}, {(La/Sm)_N = 0.4–1.2} and {(Zr/Y)_N = 0.7–2.5} of the basalts are also similar to present day volcanism found in the Easter microplate. The volcanics from the Easter microplate-Crough region are unrelated to other known South Pacific intraplate magmatism (i.e. Society, Pitcairn, and Salas y Gomez Islands). Instead their range in incompatible element ratios is comparable to the submarine basalts from the recently investigated Ahu and Umu volcanic field (Easter hotspot) (Scientific Party SO80, 1993) and centered at about 80 km west of Easter Island. The oblique ridges and their associated seamounts are likely to represent ancient leaky transform faults created during the initial stage of the Easter microplate formation ( 5 Ma). It appears that volcanic activity on seamounts overlying the oblique volcanic ridges has continued during their westward drift from the microplate as shown by the presence of relatively fresh lava observed on one of these structures, namely the first Oblique Volcanic Ridge near 25° S–118° W at about 160 km west of the Easter microplate West Rift. Based on a reconstruction of the Easter microplate, it is suggested that the Crough seamount (< 800 m depth) was formed by earlier (7–10 Ma) hotspot magmatic activity which also created Easter Island.     

Neutral composition changes during a period of increasing magnetic activity

Neutral composition data obtained by the gas analyzer aboard the satellite ESRO 4 are investigated for a period of increasing magnetic activity. The prominent feature observed is the development of localized disturbance zones in the high-and mid-latitude regions which show a significant enhancement in argon and nitrogen densities and a simultaneous decrease in helium densities. The behavior of oxygen within these zones is complex, and both increases and decreases are observed. Both the latitudinal extent and the magnitude of the disturbed regions increase with growing magnetic activity. In contrast the low-latitude region exhibits moderate enhancements of all constituents. Using the AE index as an indicator of magnetic activity, we find that at higher latitudes the atmospheric response time is of the order of one orbital revolution or less. Comparisons with other observations and with a theoretical model by Mayr and Volland (1974) show good agreement.