Long-term monitoring of wall paintings affected by soluble salts   总被引：1，自引：0，他引：1  

Konrad?ZehnderEmail author 《Environmental Geology》2007,52(2):353-367

Long-term monitoring of wall paintings in historical monuments aims at clarifying involved decay processes and at the same time controlling effects of interventions for conservation. Monitored decay processes relate to the crystallisation of various salts – particularly of nitronatrite and gypsum – from hygroscopic solutions accumulated in the zone of ground moisture. The salts crystallise in response to climatic variations and other environmental changes. Measures for conservation such as protection from water infiltration, reduction of heating temperature and reduction of surface salt accumulation cause a significant slow-down but not a stop of decay. The particular dynamics and causes of remaining slow decay processes are described on three sites in Switzerland: the convent church of Müstair, the crypt in the cathedral of Basel and the crypt in the Grossmünster church of Zürich.  相似文献   

The pattern speed of the bar in NGC 4596     

Joris Gerssen  Konrad Kuijken  Michael R. Merrifield 《Monthly notices of the Royal Astronomical Society》1999,306(4):926-930

The pattern speed is a defining parameter of any barred galaxy. A large number of model-dependent techniques have therefore been developed to derive the pattern speed. However, the only model-independent technique for measuring this quantity – the Tremaine–Weinberg method – has hitherto been applied to just one case, the SB0 galaxy NGC 936. In this paper, we apply the technique to a second system, the SBa galaxy NGC 4596. The resulting estimate for the pattern speed is Ω_p=52±13 km s⁻¹ kpc⁻¹. This result is corroborated by a spectrum obtained along the major axis of the bar in this system. The corotation radius associated with this pattern speed lies just beyond the end of the bar indicating a fast bar. Combining the bar major-axis spectra with data obtained from a Hubble Space Telescope WFPC2 image, we also find strong evidence for a nuclear disc.  相似文献   

Rapid decrease of soil erosion rates with soil formation and vegetation development in periglacial areas     

Alessandra Musso  Michael E. Ketterer  Konrad Greinwald  Clemens Geitner  Markus Egli 《地球表面变化过程与地形》2020,45(12):2824-2839

High mountainous areas are geomorphologically active environments which are strongly shaped by redistribution of sediments and soils. With the projected climate warming in the twenty-first century and the continued retreat of glaciers, the area of newly exposed, highly erodible sediments and soils will increase. This presents a need to better understand and quantify erosion processes in young mountainous soils, as an increase in erodibility could threaten human infrastructure (i.e. hydroelectric power, tourist installations and settlements). While soil development is increasingly well understood and quantified, a coupling to soil erosion rates is still missing. The aim of this study was, therefore, to assess how soil erosion rates change with surface age. We investigated two moraine chronosequences in the Swiss Alps: one in the siliceous periglacial area of Steingletscher (Sustenpass), with soils ranging from 30 a to 10 ka, and the other in the calcareous periglacial area of Griessgletscher (Klausenpass) with surfaces ranging from age of 110 a to 13.5 ka. We quantified the erosion rates using the ^239+240Pu fallout radionuclides and compared them to physical and chemical soil properties and the vegetation coverage. We found no significant differences between the two parent materials. At both chronosequences, the erosion rates were highest in the young soils (on average 5−10 t ha^-1 a^-1 soil loss). Erosion rates decreased markedly after 3−5 ka of soil development (on average 1−2.5 t ha^-1 a^-1 soil loss) to reach a more or less stable situation after 10−14 ka (on average 0.3–2 t ha^-1 a^-1). Climate change not only causes glacier retreat, but also increased sediment dynamics. Depending on the relief and vegetational development, it takes up to at least 10 ka to reach soil stability. The establishment of a closed vegetation cover with dense root networks seems to be the controlling factor in the reduction of soil erodibility. © 2020 John Wiley & Sons, Ltd.  相似文献   

The Deformational Response of a Viscoelastic Solid Earth Model Coupled to a Thermomechanical Ice Sheet Model     

Hannes Konrad  Malte Thoma  Ingo Sasgen  Volker Klemann  Klaus Grosfeld  Dirk Barbi  Zdeněk Martinec 《Surveys in Geophysics》2014,35(6):1441-1458

We apply a coupled thermomechanical ice sheet—self-gravitating viscoelastic solid Earth model (SGVEM), allowing for the dynamic exchange of ice thickness and bedrock deformation, in order to investigate the effect of viscoelastic deformation on ice dynamics and vice versa. In a synthetic glaciation scenario, we investigate the interaction between the ice sheet and the solid Earth deformation, the glacial-isostatic adjustment (GIA), accounting for an atmospheric forcing depending on the ice sheet surface altitude. We compare the results from the coupled model to runs with the common elastic lithosphere/relaxing asthenosphere (ELRA) model, where the lithosphere is represented by a thin plate and the mantle relaxes with one characteristic relaxation time, as well as to a rigid Earth without any deformation. We find that the deformational behaviour of the SGVEM on ice dynamics (i.e. stored ice volume, ice thickness and velocity field) is comparable to the ELRA for an optimal choice of the parameters in steady state, but exhibits differences in the transient behaviour. Beyond the ice sheet, in the region of peripheral forebulge, the differences in the transient surface deformation between ELRA and SGVEM are substantial, demonstrating the inadequacy of the ELRA model for interpreting constraints on GIA in the periphery of the ice sheet, such as sea-level indicators and GPS uplift rates.  相似文献   

Comet 17P/Holmes: Possibility of a CO driven explosion     

Konrad J. Kossacki  Slawomira Szutowicz 《Icarus》2011,212(2):847-857

This work is a continuation of our previous paper about brightening of Comet 17P/Holmes (Kossacki, K.J., Szutowicz, S. [2010]. Icarus 207, 320–340). In that paper we presented results of simulations indicating that the nonuniform crystallization of amorphous water ice itself is probably not sufficient for an explosion. In the present work we investigate the possibility that the explosion is caused by a rapid sublimation of the CO ice leading to the rise of gas pressure above the tensile strength of the nucleus. We simulated evolution of a model nucleus in the orbit of Comet 17P/Holmes. The nucleus is composed of water ice, carbon monoxide ice and dust and has the shape of an elongated ellipsoid. The simulations include crystallization of amorphous ice in the nucleus, changes of the dust mantle thickness, and sublimation of the CO ice. In our model CO is mantling grains composed of dust and amorphous water ice. Orientation of the nuclear spin axis in space is the same as derived in Moreno et al. (Moreno, F., Ortiz, J.L., Santos-Sanz, P., Morales, N., Vidal-Nunez, M.J., Lara, L.M., Gutierrez, P.J. [2008]. Astrophys. J. 677, L63–L66) for Comet Holmes during recent brightening event. Hence, the angle between the orbital and the equatorial planes of the comet is I = 95°, and the cometocentric solar longitude at perihelion is Φ = 210°. The calculations are performed for the south pole being the sub-solar point close to time of the outburst. Our computations indicate, that the CO pressure within the comet nucleus can rise to high values. When the layer between the dust mantle and the crystallization front of the amorphous water ice is very fine grained, few microns in radius, the CO pressure within the nucleus can exceed 10 kPa. This value is the lowest estimate for the tensile strength of the nucleus of Comet Holmes (Reach, W.T., Vaubaillon, J., Lisse, C.M., Holloway, M., Rho, J. [2010]. Icarus 208, 276–292). Hence, when the gas pressure reaches this value the nucleus may explode.  相似文献   

The evolution of exposed ice in a fresh mid-latitude crater on Mars     

Konrad J. Kossacki  Ganna Portyankina 《Icarus》2011,211(1):195-206

Recent observations of the surface of Mars have shown several fresh mid-latitude craters. Some of these craters show exposed ice (Byrne, S. et al. [2009]. Science 325, 1674-1676.). In some craters, albedo of ice slowly decreases, while in others, it remains nearly constant. We attempt to determine influence of the regolith structure on the rate of sublimation of ice. For this purpose we performed numerical simulations describing evolution of the exposed ice in model craters located at middle latitudes.We consider a new model for the structure and evolution of the material at- and beneath the crater floors. In contrast to the previous study by Dundas and Byrne (Dundas, C.M., Byrne, S. [2010]. Icarus 206, 716-728.) we do not investigate sublimation of dirty ice, and the related formation of a sublimation lag. Instead, we consider sublimation of a pure ice layer on top of layered regolith. In our model the observed reflectivity decreases due to the sublimation-driven changes of the optical properties of thinning clean ice. This offers an alternative to the deposition of the dust embedded in ice (sublimation lag).We have shown that in our model among many parameters affecting ice sublimation rate, volumetric fraction of water ice in the subsurface beneath the crater has the strongest influence. Hence observed darkening of the ice patch on the crater floor might be sufficient to determine the content of water ice in the subsurface. Our calculations show that an albedo decrease of fresh ice patches in mid-latitude craters can be explained by either strong dust sedimentation or, if this is excluded, by sublimation of a thin layer of water ice from the regolith with large thermal inertia. This is consistent with a large volumetric fraction of water ice beneath the crater floor and contributes to evidence for an extended subsurface water reservoir on Mars.The overall conclusion of our work is that a thin post-impact surface ice coating over ice-rich ground beneath the crater floors is consistent with the observations.  相似文献   

Holocene climate change and its effect on lake ecosystem production on Northern Victoria Island, Canadian Arctic     

Marie-Claude Fortin  Konrad Gajewski 《Journal of Paleolimnology》2010,43(2):219-234

A multi-proxy paleoenvironmental study from Lake WB02 (72.29°N, 109.87°W) on Northern Victoria Island, Nunavut, Canada provides an 8.4-ka record of chironomid and ecosystem production. Mean July air temperatures for this region during the Holocene were inferred from the fossil record. The chironomid assemblages contained 33 taxa and were dominated by Paracladius and Heterotrissocladius maeaeri-type. Primary production and chironomid food availability inferred from sediment biogenic silica and loss on ignition at 550°C, and chironomid concentrations, all exhibited synchronous patterns of change through time. Similar to other climate records from across the Arctic, the sediment and fossil data from Lake WB02 support the hypothesis of a warm and productive early to middle Holocene, a cool and generally unproductive middle to late Holocene and a return to a warmer, more productive environment in the past 100 years. Mean July air temperature reconstructions based on both the modern analogue technique (MAT) and weighted averaging partial least squares regression (WAPLS), however, failed to reflect these same changes. The difference between the qualitative and quantitative environmental reconstructions may be due to the restrictions associated with the use of these inference tools, the effects of which are more significant in unproductive ecosystems such as Arctic lakes.  相似文献   

A spatially explicit degree-day model of Rift Valley fever transmission risk in the continental United States     

Sarah K. Konrad  Scott N. Miller  Will K. Reeves 《GeoJournal》2011,76(3):257-266

A spatially explicit degree-day model was used to evaluate the risk of Rift Valley fever virus (RVFV) transmission by mosquitoes to humans and livestock within five target states in the continental United States: California, Minnesota, Nebraska, New York, and Texas. A geographic information system was used to model potential virus transmission based on a 12-day moving window assessment of the extrinsic incubation period theorized for RVFV in the United States. Risk of potential virus transmission in each state was spatially evaluated on a 10-km grid using average historical daily temperature data from 1994 to 2003. The highest levels of transmission risk occur in California and Texas, with parts of these states at risk of RVFV transmission for up to 8 months per year. Northern Minnesota, central New York, and most of coastal and high-elevation California are at low to null risk. Risk of impact to the livestock industry is greatest in California, Texas, and Nebraska. A standard global climate model was used to evaluate future risk in the year 2030 in Nebraska, and showed an increase of transmission risk days from approximately 3 to 4 months per year.  相似文献   

Impact of atmospheric parameters on the atmospheric Cherenkov technique     

Konrad Bernlhr 《Astroparticle Physics》2000,12(4):255-268

Atmospheric density profiles as well as several light absorption and scattering processes depend on geographic position and are generally time-variable. Their impact on the atmospheric Cherenkov technique in general (imaging or non-imaging) is investigated. Different density profiles lead to differences in Cherenkov light density of up to 60%. Seasonal variations at mid-latitude sites are of the order of 15–20%. The quest for improved energy calibration of Cherenkov experiments also shows the need for improved transmission calculations, taking all relevant processes into account and using realistic profiles of absorbers. Simulations including the scattering mechanisms also reveal the relevance of Rayleigh and Mie scattering for atmospheric Cherenkov experiments. Refraction and the differences between treating the atmosphere in plane-parallel or spherical geometry are also investigated.  相似文献   

Coupled Reactive Transport Modeling of Redox Processes in a Nitrate-Polluted Sandy Aquifer     

Konrad Miotliński 《Aquatic Geochemistry》2008,14(2):117-131

The reactive transport modeling of a complicated suite of reactions apparent in the aquifer during the application of N-containing fertilizers is reported. The unconfined sandy aquifer can be subdivided into an oxic zone which contains groundwater with oxygen and nitrate and an anoxic zone characterized by elevated iron and sulfate concentrations in groundwater. Oxygen and nitrate are being reduced by pyrite and organic matter that commonly apparent in the aquifer. The oxidation of pyrite is modeled using the local equilibrium approach, whereas decomposition of organic matter, with the adoption of kinetic approach. The system is buffered by dissolution of aluminum and iron oxides. The modeling process is a two-step procedure. First, the processes are modeled in the one-dimensional (1D) column using PHREEQC code. Subsequently, the calibrated and verified data were copied and used in two-dimensional (2D) PHAST model. Prior to the performance of reactive transport modeling operations with PHAST, a reliable flow model was executed. Finally, predictions are made for the distribution of water chemistry for the year 2008. Model predicts that sulfate derived from the ongoing pyrite oxidation is reduced by the dissolved organic carbon at the higher depth and forms pyrite by the reaction with iron. The results of this study highlight the importance of understanding the interplay between the transport and chemical reactions that occur during the input of nitrate to the aquifer. Reactive transport modeling incorporating the use of a newly developed code PHAST have proved to be a powerful tool for analyzing and quantifying such interactions.  相似文献