Institute for Water and Environmental Problems

Barnaul, Russia

Institute for Water and Environmental Problems

Barnaul, Russia
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Grigori P.,Altai State University | Ivan P.,Altai State Technical University | Konstantin K.,Institute for Water and Environmental Problems | Darina M.,Altai State Technical University | Mikhail T.,Altai State Technical University
AIP Conference Proceedings | Year: 2016

In practice during polymer processing, we use branched polymeric materials with significant polydispersity quite often. This results in a necessity to take into account multiple relaxation processes for a description of the rheological equations of state. The aim of this contribution is to generalize the modified Pokrovskii and Vinogradov model for the case of multiple non-interacting modes. Each mode corresponds to a particular contribution of an individual polymer fraction to the stress tensor and is characterized by its corresponding relaxation time and viscosity. Simultaneously an internal friction notion is expressed by means of the parameters depending on the first invariant of the anisotropy tensor. Thus the generalized model can be applied to study polymeric materials at wider range of frequencies. Consequently, it implies a possibility to describe sufficiently slow flows of polydisperse polymers (both linear and branched) at a common theoretical approach. Theoretical modelling is compared with rheological characteristics measured for PE materials and there is a good agreement between the experiments and derived theoretical curves. © 2016 Author(s).

Herren P.-A.,Paul Scherrer Institute | Herren P.-A.,University of Bern | Eichler A.,Paul Scherrer Institute | Eichler A.,University of Bern | And 9 more authors.
Quaternary Science Reviews | Year: 2013

Glacier highstands since the Last Glacial Maximum are well documented for many regions, but little is known about glacier fluctuations and lowstands during the Holocene. This is because the traces of minimum extents are difficult to identify and at many places are still ice covered, limiting the access to sample material. Here we report a new approach to assess minimal glacier extent, using a 72-m long surface-to-bedrock ice core drilled on Khukh Nuru Uul, a glacier in the Tsambagarav mountain range of the Mongolian Altai (4130masl, 48°39.338'N, 90°50.826'E). The small ice cap has low ice temperatures and flat bedrock topography at the drill site. This indicates minimal lateral glacier flow and thereby preserved climate signals. The upper two-thirds of the ice core contain 200 years of climate information with annual resolution, whereas the lower third is subject to strong thinning of the annual layers with a basal ice age of approximately 6000 years before present (BP). We interpret the basal ice age as indicative of ice-free conditions in the Tsambagarav mountain range at 4100masl prior to 6000 years BP. This age marks the onset of the Neoglaciation and the end of the Holocene Climate Optimum. The ice-free conditions allow for adjusting the Equilibrium Line Altitude (ELA) and derive the glacier extent in the Mongolian Altai during the Holocene Climate Optimum. Based on the ELA-shift, we conclude that most of the glaciers are not remnants of the Last Glacial Maximum but were formed during the second part of the Holocene. The ice core derived accumulation reconstruction suggests important changes in the precipitation pattern over the last 6000 years. During formation of the glacier, more humid conditions than presently prevailed followed by a long dry period from 5000 years BP until 250 years ago. Present conditions are more humid than during the past millennia. This is consistent with precipitation evolution derived from lake sediment studies in the Altai. © 2013 Elsevier Ltd.

Eichler A.,Paul Scherrer Institute | Eichler A.,University of Bern | Tobler L.,Paul Scherrer Institute | Tobler L.,University of Bern | And 7 more authors.
Environmental Science and Technology | Year: 2012

Human activities have significantly altered atmospheric Pb concentrations and thus, its geochemical cycle, for thousands of years. Whereas historical Pb emissions from Western Europe, North America, and Asia are well documented, there is no equivalent data for Eastern Europe. Here, we present ice-core Pb concentrations for the period 1680-1995 from Belukha glacier in the Siberian Altai, assumed to be representative of emissions in Eastern Europe and the Altai. Pb concentrations and 207Pb/ 206Pb ratios were strongly enhanced during the period 1935-1995 due to the use of Pb additives in Russian gasoline mined in the Rudny Altai. Comparable to Western Europe and North America, Eastern European Pb emissions peaked in the 1970s. However, the subsequent downward trend in Eastern Europe was mainly caused by the economic crisis in the U.S.S.R. and not by a phase-out of leaded gasoline. Pb concentrations in the period 1680-1935, preceding the era of intensified industrialization in Russia, reflect the history of local emissions from Rudny Altai mining and related metallurgical processing primarily for the production of Russian coins. During this time, Altai ore Pb contributed about 40% of the regional atmospheric Pb. © 2012 American Chemical Society.

Eichler A.,Paul Scherrer Institute | Eichler A.,University of Bern | Tinner W.,University of Bern | Brutsch S.,Paul Scherrer Institute | And 5 more authors.
Quaternary Science Reviews | Year: 2011

Forest fires play a key role in the global carbon cycle and thus, can affect regional and global climate. Although fires in extended areas of Russian boreal forests have a considerable influence on atmospheric greenhouse gas and soot concentrations, estimates of their impact on climate are hampered by a lack of data on the history of forest fires. Especially regions with strong continental climate are of high importance due to an intensified development of wildfires. In this study we reconstruct the fire history of Southern Siberia during the past 750 years using ice-core based nitrate, potassium, and charcoal concentration records from Belukha glacier in the continental Siberian Altai. A period of exceptionally high forest-fire activity was observed between AD 1600 and 1680, following an extremely dry period AD 1540-1600. Ice-core pollen data suggest distinct forest diebacks and the expansion of steppe in response to dry climatic conditions. Coherence with a paleoenvironmental record from the 200 km distant Siberian lake Teletskoye shows that the vegetational shift AD 1540-1680, the increase in fire activity AD 1600-1680, and the subsequent recovery of forests AD 1700 were of regional significance. Dead biomass accumulation in response to drought and high temperatures around AD 1600 probably triggered maximum forest-fire activity AD 1600-1680. The extreme dry period in the 16th century was also observed at other sites in Central Asia and is possibly associated with a persistent positive mode of the Pacific Decadal Oscillation (PDO). No significant increase in biomass burning occurred in the Altai region during the last 300 years, despite strongly increasing temperatures and human activities. Our results imply that precipitation changes controlled fire-regime and vegetation shifts in the Altai region during the past 750 years. We conclude that high sensitivity of ecosystems to occasional decadal-scale drought events may trigger unprecedented environmental reorganizations under global-warming conditions. © 2011 Elsevier Ltd.

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