655 research outputs found
Spatio-temporal impact of salinated mine water on Lake Jormasjärvi, Finland
The salinization of freshwater environments is a global concern, and one of the largest sources of salinated water is the mining industry. An increasing number of modern mines are working with low grade sulfide ores, resulting in increased volumes of potentially harmful saline drainage. We used water monitoring data, together with data on sedimentary fossil remains (cladoceran, diatom and chironomid), to analyze the spatio-temporal (5 sampling locations and 3 sediment depths) impact of salinated mine water originating from the Talvivaara/Terrafame open cast mine on multiple components of the aquatic ecosystem of Lake Jormasjärvi, Finland. Lake Jormasjärvi is the fourth and largest lake in a chain of lakes along the path of the mine water. Despite the location and large water volume, the mine water has changed the chemistry of Lake Jormasjärvi, reflected in increased electrical conductivity values since 2010. The ecological impact is significant around the inflow region of the lake, as all biological indicator groups show a rapid and directional shift towards new species composition. There is a clear trend in improved water quality as one moves further from the point of inflow, and as one looks back in time. Our results show that salinated mine water may induce rapid and large scale changes, even far downstream along a chain of several sinking basins. This is of special importance in cases where large amounts of waste water are processed in the vicinity of protected habitats.Peer reviewe
Waste water discharge from a large Ni-Zn open cast mine degrades benthic integrity of Lake Nuasjärvi (Finland)
The Talvivaara/Terrafame multi-metal mining company is Europe’s largest nickel open cast mine, it is also known for the largest wastewater leakage in the Finnish mining history and a series of other accidents. In this paleolimnological study, influences of a recently constructed treated waste water discharge pipeline into Lake Nuasjärvi were investigated by analyzing past (pre-disturbance) and present community compositions of key aquatic organism groups, including diatoms, Cladocera and Chironomidae, along spatial (distance, water depth) gradients. In addition to defining ecological changes and impacts of saline mine waters in the lake, chironomids were used to quantitatively reconstruct bottom water oxygen conditions before and after the pipe installation (in 2015). The diatom and cladoceran communities, which reflect more the open-water habitat, showed only relatively minor changes throughout the lake, but a general decrease in diversity was observed within both groups. Chironomids, which live on substrates, showed more significant changes, including complete faunal turnovers and deteriorated benthic quality, especially at the sites close to the pipe outlet, where also chironomid diversity was almost completely lost. Furthermore, the reconstructed hypolimnetic oxygen values indicated a major oxygen decline and even anoxia at the sites near the pipe outlet. The limnoecological influence of the pipe decreased at sites located counter-flow or behind underwater barriers suggesting that the waste waters currently have location-specific impacts. Our study clearly demonstrates that whereas the upper water layers appear to have generally maintained their previous state, the deep-water layers close to the pipe outlet have lost their ecological integrity. Furthermore, the current hypolimnetic anoxia close to the pipe indicates enhanced lake stratification caused by the salinated mine waters. This study clearly exhibits the need to investigate different water bodies at several trophic levels in a spatiotemporal context to be able to reliably assess limnoecological impacts of mining.Peer reviewe
The Twin--Jet System in NGC 1052: VLBI-Scrutiny of the Obscuring Torus
NGC 1052 offers the possibility to study the obscuring torus around a
supermassive black hole, predicted by the standard model of active galactic
nuclei, over a wide range of wavelengths from the radio to the X-ray regime. We
present a detailed VLBI study of the parsec-scale structure of the ``twin-jet''
system in NGC 1052 in both total and polarized intensity and at multiple
frequencies. We report the detection of linearly polarized emission from the
base of the eastern jet at 5 GHz. While the radio spectrum in this region might
be still consistent with synchrotron self absorption, the highly inverted
spectrum of the western jet base represents a clear sign of pronounced
free-free absorption in a circumnuclear torus. We observe an abrupt change of
the brightness temperature gradient at a distance of pc to 0.3 pc
from the central engine. This might provide an observational signature of the
edge of the central torus, where the transition from an external
pressure-dominated jet regime to a more or less freely expanding jet takes
place. We determine the absorbing column density towards the western jet core
to be cm in good agreement with the values
derived from various X-ray observations. This suggests that the nuclear X-ray
emission and the jet emission imaged by VLBI originate on the same scales.Comment: 14 pages, 11 figures, needs aa.cls, accepted for publication in
Astronomy & Astrophysics, note that the resolution of figure 2 has been
decreased in comparison to the journal versio
The milliarcsecond-scale jet of PKS 0735+178 during quiescence
We present polarimetric 5 GHz to 43 GHz VLBI observations of the BL Lacertae
object PKS 0735+178, spanning March 1996 to May 2000. Comparison with previous
and later observations suggests that the overall kinematic and structural
properties of the jet are greatly influenced by its activity. Time intervals of
enhanced activity, as reported before 1993 and after 2000 by other studies, are
followed by highly superluminal motion along a rectilinear jet. In contrast the
less active state in which we performed our observations, shows subluminal or
slow superluminal jet features propagating through a twisted jet with two sharp
bends of about 90 deg. within the innermost three-milliarcsecond jet structure.
Proper motion estimates from the data presented here allow us to constrain the
jet viewing angle to values < 9 deg., and the bulk Lorentz factor to be between
2 and 4.Comment: 11 pages, 12 figures. Accepted for publication in A&
The analysis of freshwater pearl mussel shells using mu-XRF (micro-x-ray fluorescence) and the applicability for environmental reconstruction
Freshwater pearl mussel is a highly threatened species, and many populations are currently on the brink of local extinction. For example, in south Finland, only two populations are currently viable. Even though the reasons for the mussels' demise are relatively well known, the long-term impacts of water quality are not completely resolved. Here, mu-XRF analysis and historical records were used to evaluate whether the differences in water chemistry or past environmental changes in three rivers in southern Finland are visible in mussel shell chemistry. The results show that the cracks inside mussel shells, invisible to the naked eye, may greatly affect the elemental composition results. Further, anomalies which could be related to inclusion of detrital matter inside the shells were detected. Manganese (Mn) seems to be related to mussel growth dynamics, especially in the nacreous layer, while high values of iron (Fe) and Mn are also present at the top sections of the prismatic layer. Line scan analysis revealed high variation between replicates. The mu-XRF method could be used as prescreening method in mussel sclerochemistry studies, but more studies are needed to clarify the ability of FPM shells to reliably record the environmental conditions
VLBA Observations of Sub-Parsec Structure in Mrk 231: Interaction between a Relativistic Jet and a BAL Wind
We report on the first high frequency VLBI observations of the nearby broad
absorption line quasar (BALQSO), Mrk 231. Three epochs of observations were
achieved at 15 GHz and 22 GHz, two of these included 43 GHz observations as
well. The nuclear radio source is resolved as a compact double. The core
component experienced a strong flare in which the flux density at 22 GHz
increased by (45 mJy) in three months. Theoretical models of the flare
imply that the emission is likely enhanced by very strong Doppler boosting of a
highly relativistic ejecta with a kinetic energy flux, . Combining our data with two previous epochs of 15 GHz data,
shows marginal evidence for the slow advance of the secondary component
(located pc from the core) over a 9.4 year span. We estimate
that the long term time averaged kinetic energy flux of the secondary at
. Low frequency VLBA observations
indicate that the secondary is seen through a shroud of free-free absorbing gas
with an emission measure of . The
steep spectrum secondary component appears to be a compact radio lobe that is
associated with a working surface between the ram-pressure confined jet, and a
dense medium that is likely to be the source of the free-free absorption. The
properties of the dense gas are consistent with the temperatures, displacement
from the nucleus and the column density of total hydrogen commonly associated
with the BAL wind.Comment: To appear in Ap
Task-oriented reading efficiency: interplay of general cognitive ability, task demands, strategies and reading fluency
The associations among readers’ cognitive skills (general cognitive ability, reading skills, and attentional functioning), task demands (easy versus difficult questions), and process measures (total fixation time on relevant and irrelevant paragraphs) was investigated to explain task-oriented reading accuracy and efficiency (number of scores in a given time unit). Structural equation modeling was applied to a large dataset collected with sixth-grade students, which included samples of dysfluent readers and those with attention difficulties. The results are in line with previous findings regarding the dominant role of general cognitive ability in the accuracy of task-oriented reading. However, efficiency in task-oriented reading was mostly explained by the shorter viewing times of both paragraph types (i.e., relevant and irrelevant), which were modestly explained by general cognitive ability and reading fluency. These findings suggest that high efficiency in task orientation is obtained by relying on a selective reading strategy when reading both irrelevant and relevant paragraphs. The selective reading strategy seems to be specifically learned, and this potentially applies to most students, even those with low cognitive abilities
Performance of HPGe Detectors in High Magnetic Fields
A new generation of high-resolution hypernuclear gamma$-spectroscopy
experiments with high-purity germanium detectors (HPGe) are presently designed
at the FINUDA spectrometer at DAPhiNE, the Frascati phi-factory, and at PANDA,
the antiproton proton hadron spectrometer at the future FAIR facility. Both,
the FINUDA and PANDA spectrometers are built around the target region covering
a large solid angle. To maximise the detection efficiency the HPGe detectors
have to be located near the target, and therefore they have to be operated in
strong magnetic fields B ~ 1 T. The performance of HPGe detectors in such an
environment has not been well investigated so far. In the present work VEGA and
EUROBALL Cluster HPGe detectors were tested in the field provided by the ALADiN
magnet at GSI. No significant degradation of the energy resolution was found,
and a change in the rise time distribution of the pulses from preamplifiers was
observed. A correlation between rise time and pulse height was observed and is
used to correct the measured energy, recovering the energy resolution almost
completely. Moreover, no problems in the electronics due to the magnetic field
were observed.Comment: submitted to Nucl. Instrum. Meth. Phys. Res. A, LaTeX, 19 pages, 9
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