The 550-au Mission: a critical discussion     

S. G. Turyshev  B-G. Andersson 《Monthly notices of the Royal Astronomical Society》2003,341(2):577-582

We have studied the science rationale, goals and requirements for a mission aimed at using the gravitational lensing from the Sun as a way of achieving high angular resolution and high signal amplification. We find that such a mission concept is compromised by several practical problems. Most severe are the effects due to the plasma in the solar atmosphere which cause refraction and scattering of the propagating rays. These effects either limit the frequencies that can be observed to those above ∼1 THz, or they move the optical point outwards beyond the vacuum value of ≥550 au. (Thus for observing frequency of 300 GHz the optical point is moved outwards to ∼ 680 au.) Density fluctuations in the inner solar atmosphere will further cause random pathlength differences for different rays. The corrections for the radiation from the Sun itself will also be a major challenge at any wavelength used, but could be mitigated with coronographic techniques. Given reasonable constraints on the spacecraft (particularly in terms of size and propulsion), source selection as well as severe navigational constraints further add to the difficulties for a potential mission. Nevertheless, unbiased surveys of small-scale structure on the sky at short wavelengths might be the most promising application of such a mission.  相似文献   

Modelling the effect of low soil temperatures on transpiration by Scots pine     

Per‐Erik Mellander  Manfred Sthli  David Gustafsson  Kevin Bishop 《水文研究》2006,20(9):1929-1944

For ecosystem modelling of the Boreal forest it is important to include processes associated with low soil temperature during spring‐early summer, as these affect the tree water uptake. The COUP model, a physically based SVAT model, was tested with 2 years of soil and snow physical measurements and sap flow measurements in a 70‐year‐old Scots pine stand in the boreal zone of northern Sweden. During the first year the extent and duration of soil frost was manipulated in the field. The model was successful in reproducing the timing of the soil warming after the snowmelt and frost thaw. A delayed soil warming, into the growing season, severely reduced the transpiration. We demonstrated the potential for considerable overestimation of transpiration by the model if the reduction of the trees' capacity to transpire due to low soil temperatures is not taken into account. We also demonstrated that the accumulated effect of aboveground conditions could be included when simulating the relationship between soil temperature and tree water uptake. This improved the estimated transpiration for the control plot and when soil warming was delayed into the growing season. The study illustrates the need of including antecedent conditions on root growth in the model in order to catch these effects on transpiration. The COUP model is a promising tool for predicting transpiration in high‐latitude stands. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Site descriptive modelling during characterization for a geological repository for nuclear waste in Sweden     

A. Ström  J. Andersson  K. Skagius  A. Winberg 《Applied Geochemistry》2008

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EPR investigation of the methyl radical,the hydrogen atom and carbon oxide radicals in Maxixe-type beryl     

Lars Olov Andersson 《Physics and Chemistry of Minerals》2008,35(9):505-520

The EPR spectra of Maxixe-type beryl contain a large number of overlapping signals. The angular dependence of the 1:3:3:1 signal typical for the CH₃ radical shows that this radical is located at the center of the channel cavity with its symmetry axis parallel to the crystal c-axis and is rotating around this axis. Its EPR spectrum is axially symmetric with g _// = 2.00263, g _⊥ = 2.00249 and A_// = 2.288 mT, A_⊥ = 2.256 mT. These anisotropies have the opposite signs of those found for surface-adsorbed methyl radicals. Hydrogen atoms are located at position 2a at the center of the beryl cavity and the EPR parameters of the narrow doublet signal are A ₀ = 1,407 MHz and g = 2.00230. Another doublet signal, which is broader and has axial symmetry with g _// = 2.00265, g _⊥ = 2.00625 and A_// = 0.895 mT, A_⊥ = 0.885 mT, could come from a HCO₃ radical. One narrow and easily saturated signal with g _// = 2.00227 and g _⊥ = 2.00386 is interpreted to arise from a carbon monoxide radical in the beryl channel, oriented with its axis parallel to the crystal c-axis. Additional weak doublet lines, which have similar g values as the carbon monoxide radical, are created by nearby hydrogens. A powder spectrum with g _// = 2.0017 and g _⊥ = 2.0004 appears upon UV irradiation of the single crystal and is easily saturated. This spectrum is interpreted to arise from a carbon dioxide radical, which rotates around its symmetry axis.  相似文献   

Fire management policy and environmental NGO movement: critical contemporary perspectives, indicators and prospects in savannas, Ghana     

Sylvanus Sefenu Per Doe 《GeoJournal》2008,71(2-3):159-170

Fire management policy is an intrinsic tool that cannot be neglected in the management of the processes of sustainable natural resource utilisation and human-induced burning in savannas but that has rather been a predominating case in most savanna regions in sub-Saharan Africa. Where an official fire policy exists, it is principally not efficiently implemented or consistently practised. New fire policy trends have recently emerged out of institutionally vibrant relations amongst environmental non-governmental organizations (NGOs), local civil societies and government institutions in Ghana. The real outcomes from the relations have been the formulation of a new fire policy and unprecedented (re)production of robust institutional capital suitable for the management of savanna fire and the environment. This article draws on these outcomes to review fire occurrences and contemporary fire policy issues, the essence of building environmental NGO alliances and the prospects of engaging major grassroots stakeholders in fire management processes. It then explores new convertible indicators from and within the subspaces of the policy to generate important information to further new theoretical thinking of fire policies rather than conventionally uncritical rethinking of fire management in the savannas.  相似文献   

Application of the Single-Bubble Airgun Technique for OBS-Data Acquisition Across the Jan Mayen Ridge,North Atlantic     

Mjelde  Rolf  Fjellanger  Jan Petter  Digranes  Per  Kodaira  Shuichi  Shimamura  Hideki  Shiobara  Hajime 《Marine Geophysical Researches》1997,19(1):81-96

A 140 km long wide-angle seismic profile has been acquired by use of 6 Ocean Bottom Seismographs across the Jan Mayen Ridge, North Atlantic. The profile was acquired twice; once with a traditionally tuned standard source and secondly with a somewhat smaller source tuned on the first bubble pulse. Analysis of the frequency content of the data reveals that the single-bubble source within the 10-15 Hz frequency range generates a signal with a level about 5 db above that of the standard source. These differences can partly be related to differences in airgun depth. The higher output level for these frequencies enables the single-bubble source to resolve intra-crustal structures with a higher degree of certainty, when compared to the data acquired by use of the standard source array. The standard source seems to generate slightly more energy for frequencies around 6 Hz, probably due to the use of a large 1200 in/sup3 gun in this array. These low frequencies a re of importance for mapping of lower crustal and upper mantle structures, and it is recommended that this is taken into account when seismic sources for mapping of deep crustal and upper mantle structures are designed.  相似文献   

On the sulphur chemistry of a super-anoxic fjord, Framvaren, South Norway     

Leif G. Anderson  David Dyrssen  Per O.J. Hall 《Marine Chemistry》1988,23(3-4)

The concentrations of total carbonate (C_t), sulphate, sulphide, thiols and oxygen, the ratio between the stable sulphur isotopes ³⁴S and ³²S in sulphate and sulphide, and the density (used to calculate salinity) were determined on samples from the water column of Framvaren, a superanoxic fjord in southern Norway. From a depth of 18m (the oxic-anoxic boundary) the initial sulphate concentration, ([SO₄]_init), as calculated from salinity, is significantly higher than the sum of the measured sulphur species. This is attributed to a loss of sulphur from the water column. The amount of total carbonate produced, corrected for the initial concentration (C_t - 2.4 Sal/35) is found to be proportional to the amount of sulphate consumed, ([SO₄]_init - [SO₄]), according to the following relation C_t- 2.4 Sal/35 = 1.84 ([SO₄]_init - [SO₄]). Isotopic fractionation caused by bacterial sulphate reduction in the anoxic part of the water column produces sulphide with a δ³⁴S 40‰ lower than the δ³⁴S for sulphate at corresponding depths. The isotopic fractionation also results in δ³⁴S value for the remaining sulphate at depths below 80 m being considerably higher than the mean value for ocean water, which is close to + 20‰. The δ³⁴S values for sulphate at depths between 10 and 50 m were lower than + 20‰ which indicates oxidation of sulphide, which follows upon diffusion of sulphide from deeper parts of the water column and inflow of oxygenated seawater over the sill into the anoxic water of the fjord. A conclusive scenario of the Framvaren sulphur chemistry is presented.  相似文献   

Effects of pulp bleach plant effluents on hepatic xenobiotic biotransformation enzymes in fish: Laboratory and field studies     

L. Frlin  T. Andersson  B.-E. Bengtsson  J. Hrdig  . Larsson 《Marine environmental research》1985,17(2-4)

The present preliminary report on studies of the influence of pulp bleach plant effluents on hepatic biotransformation enzymes in fish is a part of a major characterisation of biochemical and physiological effects of effluents from pulp industries in Sweden. Our studies on the xenobiotic biotransformation enzymes demonstrate, so far, that the pulp effluents have the potential to strongly induce 7-ethoxyresorufin-O-deethylase activity (EROD) in fish liver and that fish living in the receiving water of an effluent from a pulp bleach plant have induced hepatic EROD activities as well as higher hepatic UDP glucuronyltransferase activities than those living in an unpolluted area. It is thus apparent that measures of induction of biotransformation enzymes in fish liver may be a useful approach in monitoring the presence of potential hazardous compounds released from pulp industries.  相似文献   

Size distribution of colloidal trace metals and organic carbon during a coastal bloom in the Baltic Sea   总被引：1，自引：0，他引：1  

Johan Ingri  Susanna Nordling  Jenny Larsson  Jenny Rnnegrd  Nina Nilsson  Ilia Rodushkin  Ralf Dahlqvist  Per Andersson   rjan Gustafsson 《Marine Chemistry》2004,91(1-4):117-130

The physico-chemical speciation of organic carbon and selected metals was measured during a coastal bloom in Ekhagen Bay, Baltic Sea, using ultrafiltration.One important objective with the study was to see if any depletion of trace metals could be measured in the directly bioavailable fraction (<1000 Da, the soluble low molecular weight fraction, LMW) during a plankton bloom. Filters with five different cut-offs were used (1 kD (1000 Da), 5 kD, 10 kD, 100 kD and 0.22 μm) in order to delineate the size distribution of colloidal organic carbon (COC) and trace metals.During the bloom in May, LMW Al, Co, Cu, Mn and Ni concentrations decreased although the colloidal and particulate concentrations were relatively high. Data show that desorption of colloidal and particulate bound trace metals to the LMW fraction was slower than the process depleting the LMW fraction.Estimates of the maximum active uptake of Cu, Ni and Mn by the phytoplankton, and the loss of non-bioactive Al from the LMW fraction, indicate that processes other than active uptake by phytoplankton must contribute to the observed depletion of trace metals in the LMW fraction. Hence, in order to estimate the bioavailable pool of trace metals for plankton during bloom conditions, these other processes must be understood and quantified.Transparent Exopolymeric Particles (TEP, reflecting sugar-rich phytoplankton exudates) increased around eight times during the plankton bloom. We hypothesize that the formation of TEP is a process that might be important for the transfer of trace metals from the LMW to the particulate fraction during the phytoplankton bloom, but the significance of TEP for this depletion in Baltic Sea surface water remains to be shown.  相似文献   

The Lake Rossfjord herring (Clupea harengus L.) and its environment     

Hognestad  Per T. 《ICES Journal of Marine Science》1994,51(3):281-292

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