Cosmological Parameters from Cosmic Microwave Background Anisotropies: Status and Prospects     

Alessandro Melchiorri  Carolina J. Ödman 《Astrophysics and Space Science》2003,283(4):457-468

A survey is made of the present constraints on cosmological parameters from Cosmic Microwave Background Anisotropies. This revised version was published online in July 2006 with corrections to the Cover Date.  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   

Karst hydrogeology of Kusluk-Dilmetas karst springs, Van-Eastern Turkey     

Murat H. Özler 《Environmental Geology》2001,41(3-4):257-268

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Main sequence for rotating stars of intermediate mass     

D. Eryurt-Ezer  H. Kirbiyik  N. Özkara 《Astrophysics and Space Science》1986,126(1):29-50

We have investigated the evolutionary behaviour of intermediate mass (2, 3, 4, 5, and 7M ) Population I stars, assuming two different rates of rotation at the threshold of stability.In the first part of the study, stars are assumed to start with a critical rotation (fast rotation model) and to progress to the point of rotational instability. The stars evolve by losing mass and become rotationally unstable before they reach the zero-age Main Sequence. It is argued that multiple star systems might be formed through the evolution of rapidly rotating stars. An expression for the rotational mass loss rate is derived as a function of the physical parameters of stars.In the second part of the study, stars are assumed to rotate at a rate below the critical value (slow rotation model). The evolution of slowly rotating stars is followed as far as zero-age Main Sequence on the theoretical Hertzsprung-Russell diagram and compared with that of normal stars. The evolutionary paths are found to be more or less similar to those of normal stars; but their positions on the Main Sequence are characterized by effective temperatures and luminosities lower than those of normal stars. The zero-age Main-Sequence times of these stars are longer than those of normal stars. The rotational rates obtained for the zero-age Main Sequence are in good agreement with observed values.  相似文献   

A geological and geotechnical investigation of the settlement area of Zümrüt Building (Konya, Turkey) which caused 92 fatalities due to its collapse     

Adnan Özdemir 《Environmental Geology》2008,53(8):1695-1710

This study examines the local geological conditions and soil structure as possible causes of the collapse of the Zümrüt Building 2 February 2004. This catastrophe resulted in 92 fatalities and 35 injuries. This study also examines other views which claim weak soil structure, elastic and consolidation settlement of soil and excessive groundwater extraction as well as subsidence resulting from the underground silt erosion as possible factors. Zümrüt Building was constructed on normally consolidated, low plasticity clay. The underground water table was 30 m in depth. The internal friction angle of soil was 8°–30°, its cohesion was between 34 and 127 kN/m² and standard penetration test numbers varied between 11 and 50. The underground water level beneath Zümrüt Building had risen 4.5 m since its construction. Therefore the claim that subsidence resulting from the decrease of underground water level contributed to the collapse is incorrect. Secondly the settlement, resulting from the filling up of the pores created by the silt receding with the underground water, was 4.4 mm in total, and attributing this as the primary cause of the collapse is also incorrect. Soil properties, in situ and laboratory test results showed that the existing and/or expected settlement and the differential ground settlement in the Zümrüt building vicinity had the potential to cause structural damage. The tensile stresses caused by differential settlements recorded here are thought to be an indicator, but not the main cause contributing to the collapse of the building. The Zümrüt Building collapse was due to several compounding mistakes during the construction phase. These were geotechnical and other project faults and the use of low quality construction materials. The resulting catastrophe caused 92 fatalities, 35 injuries and a material loss of approximately US$7 million.  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   

Elucidating the dynamics and mixing agents of a shallow fjord through age tracer modelling     

Karin E. Gustafsson  Jrgen Bendtsen 《Estuarine, Coastal and Shelf Science》2007,74(4):641

The mixing agents and their role in the dynamics of a shallow fjord are elucidated through an Eulerian implementation of artificial tracers in a three-dimensional hydrodynamic model. The time scales of vertical mixing in this shallow estuary are short, and the artificial tracers are utilized in order to reveal information not detectable in the temperature or salinity fields. The fjord's response to external forcing is investigated through a series of model experiments in which we quantify vertical mixing, transport time scales of fresh water runoff and estuarine circulation in relation to external forcing.Using age tracers released at surface and bottom, we quantify the time scales of downward mixing of surface water and upward mixing of bottom water. Wind is shown to be the major agent for vertical mixing at nearly all depth levels in the fjord, whereas the tide or external sea level forcing is a minor agent and only occasionally more important just close to the bottom. The time scale of vertical mixing of surface water to the bottom or ventilation time scale of bottom water is estimated to be in the range 0.7 h to 9.0 days, with an average age of 2.7 days for the year 2004.The fjord receives fresh water from two streams entering the innermost part of the fjord, and the distribution and age of this water are studied using both ageing and conservative tracers. The salinity variations outside this fjord are large, and in contrast to the salinity, the artificial tracers provide a straight forward analysis of river water content. The ageing tracer is used to estimate transport time scales of river water (i.e. the time elapsed since the water left the river mouth). In May 2004, the typical age of river water leaving the fjord mouth is 5 days. As the major vertical mixing agent is wind, it controls the estuarine circulation and export of river water. When the wind stress is set to zero, the vertical mixing is reduced and the vertical salinity stratification is increased, and the river water can be effectively exported out of the fjord.We also analyse the river tracer fields and salinity field in relation to along estuary winds in order to detect signs of wind-induced straining of the along estuary density gradient. We find that events of down estuary winds are primarily associated with a reduced along estuary salinity gradient due to increased surface salinity in the innermost part of the fjord, and with an overall decrease in vertical stratification and river water content at the surface. Thus, our results show no apparent signs of wind-induced straining in this shallow fjord but instead they indicate increased levels of vertical mixing or upwelling during down estuary wind events.  相似文献   

The POC / Th ratio of settling particles isolated using split flow-thin cell fractionation (SPLITT)     

rjan Gustafsson  Jenny Larsson  Per Andersson  Johan Ingri 《Marine Chemistry》2006,100(3-4):314

The common assumption that the ratio between particulate organic carbon (POC) and particulate ²³⁴Th obtained from shallow sediment traps and filterable particles are representative of the ratio in the total particle settling flux should be treated with caution in view of well-known biases associated with tethered shallow sediment traps and the decoupling between size and settling velocity of many natural particle regimes. To make progress toward reliably constraining the POC / ²³⁴Th ratio on truly settling particles, we have tested here a settling collection technique designed to remove any hydrodynamic bias; split flow-thin cell fractionation (SPLITT). These first results from a North Sea fjord and an open Baltic Sea time-series station indicates that the POC / ²³⁴Th ratio on the more complete particle-settling spectrum, isolated with SPLITT, was higher than the POC / ²³⁴Th ratio obtained simultaneously from tethered shallow sediment traps in seven out of seven parallel deployments with an average factor of 210%. The POC / ²³⁴Th ratio from the SPLITT was either in the same range or higher than that obtained on filtered “bulk” particles. To explain this novel data we hypothesize that the slowest settling fraction is organic-matter rich and does not strongly complex ²³⁴Th (i.e., high POC / ²³⁴Th). We suggest that this ultra-slow sinking fraction is better collected by SPLITT than with tethered sediment traps because of minimized hydrodynamic bias.This was tested using the ratio of POC / Al as a tracer of detrital mineral-ballast influenced settling velocity. The higher POC / Al ratios in SPLITT samples relative to in traps is consistent with the hypothesis that SPLITT is better suited for collecting also the slow-settling component of sinking particles. This important slow-settling component appears to here consist primarily of non-APS/TEP components of plankton exudates or other less-strongly ²³⁴Th-complexing organic matter. Further applications of the SPLITT technique are likely to return increasingly new insights on the composition (including “truly settling” POC / ²³⁴Th) of the total spectrum of particles settling out of the upper ocean.  相似文献   

On the longitudinal distribution of the solar surges     

Atίla Özgüç 《Solar physics》1989,123(2):381-383

After re-examination of data presented by Verma (1984), some misuse of solar parameteres published in Solar Geophysical Data is presented. Consequently some conclusions made by Verma (1984, 1986) on about the longitudinal distribution of cool solar surges based on these misuses are discussed.  相似文献   

Interferometric observations of HCN and CN towards carbon stars     

M. Lindqvist  R. Lucas  H. Olofsson  A. Omont  K. Eriksson  B. Gustafsson 《Astrophysics and Space Science》1995,224(1-2):501-502

Using the IRAM interferometer we have observed four carbon stars (U Cam, CIT6, Y CVn, IRC+40540) in the HCN(J=1 0) and CN(N=1 0) lines. Here we present some results for CIT6 and U Cam.  相似文献