Improved in situ gamma-ray transmission densitometer for marine sediments

The first-generation University of Illinois gamma-ray transmission densitometer, designed for the in situ measurement of sediment bulk density, was modified by incorporating in the detector probe (1) an Americium-241 alpha particle pulser and an anti-walk gain stabilization control to maintain better temperature stability and (2) a small power supply and a IC preamplifier to eliminate the need for a high-voltage coaxial cable between the detector and external signal conditioning electronics package. This second-generation Lehigh University system has been successfully deployed since 1971 in routine use from ships and submersibles in the Atlantic and Pacific Oceans and the Gulf of Mexico. Results are presented of system operations to (1) measure bulk density over the range of 1.2–1.8 Mg/m³ in the Hudson Canyon, (2) penetrate 1.9 m into the seafloor in the San Diego trough and, (3) be lowered to a water depth of 3.6 km in the Gulf of Mexico.     

Geochemistry of suspended matter from the Baltic Sea 2. Results of bulk trace metal analysis by AAS

In 1984, on a transect covering the whole Baltic Sea and parts of the adjacent North Sea, 160 water samples were taken and analysed for their concentrations of particulate and dissolved metals. In addition, the suspended materials were investigated for their elemental bulk composition.The particulate fractions represented from about 5% (Cd, Cu and Ni) to 50% (Fe and Pb) of the total (particulate plus dissolved) concentrations. For some elements (Ba, Cd, Cu, Pb and Zn), the particulate matter from the surface microlayer was enriched with respect to those suspended materials taken from 0.2 m depth. This could reflect the atmospheric input of metal-rich aerosols. In anoxic deep waters, maximum contents of Zn (6400 μg g⁻¹), Cu (1330 μg g⁻¹) and Cd (12 μg g⁻¹) were observed in the particulate matter, indicating sulphidic forms. On the other hand, under oxic conditions the distribution coefficients (K_d) decreased with the water depth (Cd, Fe and Pb).Relative to global background levels, the particulate matter contained metal “excesses” amounting to more than 90% of the total contents (Cd, Mn, Pb and Zn). Automated electron probe X-ray microanalysis (EPXMA) revealed that the elemental composition of sediments is mainly governed by post-depositional processes of early diagenesis and is only weakly related to the composition of suspended matter in the overlying water body. For instance, in relation to surface mud sediments of the central Baltic net-sedimentation basins, Zn, Cd, Cu and Mn had 30–100% higher levels in the suspended materials. The general pattern of metal contents of particulate matter taken from 10 m depth on a transect between the Bothnian Bay and the North Sea were—possibly as a result of anthropogenic inputs—rather similar for Pb, Zn and Cu. For Fe and Mn, the distribution patterns along the transect were probably governed by the natural loading characteristics and by the biogeochemistry of those elements.     

Measurement of the signal to noise ratio in seismic profiling

The measurement of the signal to noise ratio in continuous seismic profiling systems is carried out by means of a small general purpose digital computer equipped with an analog to digital converter. The computer is programmed to compute and compare the power spectrum of a sample of noise to the power spectrum of a sample of noise plus an echo. Power spectra of some twenty to fifty shots are averaged to yield reliable estimates of the signal to noise ratio as a function of frequency. The observed spectra agree well with spectra calculated from signals measured near to an air-gun. This measurement of signal to noise ratio as a function of frequency provides unambiguous information for the adjustment of the necessary band-pass filter thus improving the operation of a continuous seismic profiler.     

Molecular identification of ascaridoid nematodes from the deep-sea onion-eye grenadier (Macrourus berglax) from the East Greenland Sea

Macrourus berglax from the East Greenland Sea was studied for the presence of ascaridoid nematodes in 2001, 2002 and 2003. The fishes were collected between 278 and 413 m water depth using a benthopelagic net. Based on the amplification of the internal transcribed spacer ITS-1, 5.8S, ITS-2 and flanking sequences (=ITS+), three ascaridoid nematode species were identified. The prevalence of infestation during the 3 years ranged from 42.9% to 62.9% and 22.9% to 40.0% for the anisakids Anisakis simplex (s.s.) and Pseudoterranova decipiens (s.s.), respectively, and from 28.6% to 60.0% for the raphidascarid Hysterothylacium aduncum. A total of 18 specimens, two of each species and examination year, revealed no sibling species, suggesting a limited distribution of other ascaridoid siblings into the deep sea. The ITS-1, 5.8S and ITS-2 sequences of A. simplex (s.s.) from the East Greenland Sea did not differ from previously published sequence data (GenBank) from other regions in the Atlantic and Pacific oceans. The sequences of P. decipiens (s.s.) corresponded most closely to those of specimens from Richardson Bay, western Pacific, and differed in four positions (0.5%). They corresponded least to those of specimens from Japan (1.5%). The sequence data for H. aduncum differed in two positions in the ITS-1 (0.2%) and three positions in the ITS-2 (0.3%) from sequences from Japan. A high genetic similarity between the regions can be explained by (a) extensive final host migration in the case of A. simplex (s.s.), (b) an overlapping distribution of final host populations along the continental shelves for P. decipiens (s.s.) and (c) a low host specificity and large population size in the intermediate and final hosts for H. aduncum. The occurrence of the identified species in the macrourid fish underlines the potential of cosmopolitan ascaridoid nematodes to distribute not only horizontally but also vertically in the deep sea.     

GPS signal acquisition using the repeatability of successive code phase measurements

This paper introduces a new method for GPS signal acquisition, which is based on the repeatability of successive code phase measurements and the M-of-N search algorithm. The performance of the proposed method in terms of probability of signal detection is similar to that of traditional methods, except that the calculation of the probability of detection does not rely on the noise distribution or the Carrier-to-Noise ratio (C/N₀). The code phase repeatability-based method is presented along with equations for probability of detection and probability of false detection. If the distribution of the noise is known, it also provides an estimate of the C/N₀. The proposed method is illustrated for coherent and non-coherent acquisition and C/N₀ estimation.     

Comparison of dissolved and particulate arsenic distributions in shallow aquifers of Chakdaha, India, and Araihazar, Bangladesh

Background  

The origin of the spatial variability of dissolved As concentrations in shallow aquifers of the Bengal Basin remains poorly understood. To address this, we compare here transects of simultaneously-collected groundwater and aquifer solids perpendicular to the banks of the Hooghly River in Chakdaha, India, and the Old Brahmaputra River in Araihazar, Bangladesh.     

Cu 2p absorption spectroscopy as a probe for the site occupancy of (ZnxCu1−x)WO4 solid solution

The solid solution sanmartinite (ZnWO₄)—cuproscheelite (CuWO₄) has been studied using Cu 2p X-ray absorption spectroscopy. While a single L₃ absorption peak is observed for CuWO₄, two distinct L₃ absorption peaks with a separation of ～0.8 eV are observed for the intermediate samples in the solid solution. The two peaks represent distinct Cu sites: one with all CuO₆ next nearest neighbours in the (Cu,Zn)O₆ chains, another having at least one ZnO₆ next nearest neighbour. Both sites show a linear increase in covalency as a function of increasing Cu-content. The relative intensities of the two absorption peaks is dependent upon the Cu-content and has been used to model the site occupancies. The results reveal that the local structural effects can be associated with a composition-dependent structural phase transition from P2/c (ZnWO₄) to P $\bar 1$ (CuWO₄). Deviations from a single-site model are explained in terms of the local environments, and evidence for site preferences and local clustering are explored.     

A plan for a new generation 2M-class telescope in Indonesia

One of the prime astrophysical interests of the Observatorium Bosscha is, and has always been, double star research: visual double star research with the double-60 cm Zeiss telescope (dedicated in 1928), and theoretical research of evolved massive spectroscopic binaries (since 1972). For one thing, this is the very reason that this IAU Colloquium No. 80, celebrating the 60th anniversary of the Observatorium Bosscha in Lembang, is devoted to binary astrophysics.Up to now, visual, photographic, and photometric tools have been used for binary research at the Observatorium Bosscha. An important, essential additional tool for binary research is spectrographic equipment, in order to measure radial velocities of binary components.Therefore, we suggest to make a plan for a new modern telescope, a reflector with a primary mirror of about 2 m in diameter and with a modern spectrograph/detector combination for radial velocity measurements.At a number of major astronomical observatories scientists have been considerating to erect new telescopes devoted primarily to radial velocity measurements. The reason for this is that at the end of this decade the parallax and proper motion measurements to be made by the ESA astrometric satellite Hipparcos will become available of more than 100 000 single stars and double stars. At that time there will be a compelling need for radial velocity measurements of all these stars to complement the parallax and proper motion measurements. With the combination of this data enormous progress will be made in double star research, and in the study of galactic dynamics, another topic of interest of the Observatorium Bosscha. If it could be realized to build such a dedicated radial velocity telescope in Indonesia, Indonesian astronomers could take a leading role in this field of research.Without going into technical details, we would like to emphasize here that such a new instrument should be a trueNew Generation Telescope, and that the Institut Teknologi Bandung should participate from the very beginning in its design, construction and assembling, and the subsequent servicing; ITB could participate in the field of optics, mechanics, and electronics. Modern astronomy offers tremendous challenges to technology, which are of great interest to technological institutes. The new telescope should be computer controlled, and the spectrograph should have a modern digital read-out (Reticon, IPCS, or CCD). The telescope should have one of those recently becoming availablethin mirrors, allowing more mechanical freedom. It could be a telescope with a siderostat which feeds the light into a fixed telescope, thus improving both the stability of the telescope and that of the spectrograph. In this way the staff and students of ITB, as well as the technical staff of the Observatorium Bosscha will be drawn into modern techniques of many varieties. And for ITB such an enterprise may even have a spin-off into other fields than astronomy.One aspect which is of great importance for the new telescope is the selection of its site. The present site of the Observatorium Bosscha in Lembang is a good one, but for a new modern telescope one wants to make sure that it is going to be located at the most ideal site.Therefore an Indonesian site-survey should be initiated promptly. Site survey equipment is available at many big observatories and could be borrowed. The site survey should extend over at least 4–5 years to monitor the meteorological and environmental situation at many sites.In the meantime the design and fund rainsing can be considered. Modern day astronomy depends on financial support from governments and inter-governmental organizations. Therefore it is urged that a proposal for a new telescope as indicated above clearly describes the advantages of such a new telescope both for astrophysical research in Indonesia, and for the introduction of new technologies in Indonesian technological institutes.The recently formed Steering Committee for Indonesian-Netherlands Astrophysics (INA) is willing to explore the possibilities for this plan. We hope that after investigating the interest of ITB in this matter, a proposal could be made before the end of this year.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia 3–7 June, 1983.