Parametric instabilities of rotor-support systems with application to industrial ventilators

Rotor support systems interaction with parametric excitation is considered for both unequal principal shaft stiffness (generators) and offset disc rotors (ventilators). Instability regions and types of instability are computed in the first case, and parametric resonances in the second case. Computed and experimental results are compared for laboratory machine models. A field case study of parametric vibrations in industrial ventilators is reported. Computed parametric resonances are confirmed in field measurements, and some industrial failures are explained. Also the dynamic influence and gyroscopic effect of supporting structures are shown and computed

Stabilization of the surface CDW order parameter by long-range Coulomb interaction

We study theoretically formation of two-dimensional (2D) charge density wave (CDW) in a system of conducting chains at the surface of an insulator due to interaction of quasi 1D surface electrons with phonons. We show that the unscreened long-range Coloumb interaction between the charges induced by fluctuations of the CDW phase stabilizes the finite order parameter value at finite temperatures, and thus the long-range order (LRO) exists. In the case of screened Coloumb interaction the phase fluctuations suppress the phase transition, but decay of the order parameter is rather slow, it obeys a power-law $\propto r^{-\gamma}$ with small exponent $\gamma

Lower Wenlock black shales in the northern Holy Cross Mountains, Poland: Sedimentary and geochemical controls on the Ireviken Event in a deep marine setting

The stratigraphic variability and geochemistry of Llandovery/Wenlock (L/W) Series boundary sediments in Poland reveals that hemipelagic sedimentation under an anoxic/euxinic water column was interrupted by low density bottom currents or detached diluted turbid layers that resulted in intermittent seafloor oxygenation. TOC values and inorganic proxies throughout the Wilków 1 borehole section suggest variable redox conditions. U/Mo ratios >1 throughout much of the Aeronian and Telychian Stages, together with an absence of pyrite framboids, suggests oxygenated conditions prevailed. However, elevated TOC near the Aeronian/Telychian boundary, together with increased U/Th and V/(V+Ni) ratios and populations of small pyrite framboids are consistent with the development of dysoxic/anoxic conditions at that time. U/Th, V/Cr and V/(V+Ni) ratios, as well as Uauthig and Mo concentrations suggest that during the Ireviken black shale (IBS) deposition, bottom-water conditions deteriorated from oxic during the Telychian to mostly suboxic/anoxic immediately prior to the L/W boundary, before a brief reoxygenation at the end of the IBS sedimentation in the Sheinwoodian Stage. Rapid fluctuations in U/Mo during the Ireviken Event (IE) are characteristic of fluctuating redox conditions that culminated in an anoxic/euxinic seafloor in the Sheinwoodian. Following IBS deposition, conditions once again became oxygen deficient with the development of a euxinic zone in the water column. The Aeronian to Sheinwoodian deep-water redox history was unstable, and rapid fluctuations of the chemocline across the L/W Series boundary probably contributed to the IE extinctions, which affected mainly pelagic and hemipelagic fauna

New constraints on the Middle Palaeozoic to enozoic burial and hermal history of the Holy ross Mts. (Central Poland) : results of numerical modelling

A 1-D burial-thermal modelling was performed using data from two borehole sections representative of the central part of the Holy Cross Mts. area. This area is located in the axial part of the Permian-Mesozoic Mid-Polish Trough that was inverted during the latest Cretaceous-Paleocene. The modelling involved different variants of restored stratigraphy of eroded Carboniferous to Cretaceous strata, whereas calibration was based on samples from cored Middle-Upper Devonian sediments. The modelling results are consistent with the assumption of a Variscan (Carboniferous-Early Permian) heat flow elevated up to 80 mWm-2, which is further confirmed by independent regional evidence. The zone of increased thermal maturity in the Devonian may be partly accounted for by a thicker Carboniferous section (by ca. 500 m) compared to previous estimates. Two variants of the post-Carboniferous geohistory were analysed. The variant of a thinner Permian-Mesozoic section, implying lower magnitude of the Late Cretaceous-Paleogene inversion, allows more realistic assumptions regarding heat flow distribution through time, including the possibility to incorporate an elevated Variscan heat flow. The alternative scenario, assuming deeper burial, generally lower heat flow and smaller Carboniferous thickness, is regarded as less probable. The accepted variant of the Permian-Mesozoic burial history implies that the total post-Carboniferous burial in the study area was on the order of 2000-2500 metres rather than 3000-3500 metres. The respective Upper Cretaceous thickness could have been 400 to 500 m instead of ca. 1000 m, whereas the Late Cretaceous Paleogene inversion more likely started in the Santonian than in the late Maastrichtian. Consequently, the preferred magnitude of total inversion was on the order of 2500 m

An ecosystem approach to public education and information at Eglin Air Force Base, Florida: 1992-1997: Final report

This project addressed a need for ecosystem management education of appropriate content and medium for audiences of Eglin Air Force Base, in northwestern Florida. The goal of this project was to better understand the various constituencies of Eglin Air Force Base and to develop effective methods of communication about Eglin's natural resources for those audiences. In a broader sense, this research sought to fulfill the need for a model of appropriate education in support of ecosystem management on public lands in the United States. The project was funded by a grant from the Legacy Natural Resources Program of the U.S. Department of Defense. (181 page document

Influence of palaeoweathering on trace metal concentrations and environmental proxies in black shales

The mineralogical and chemical compositions of Lower Carboniferous (Tournaisian) marine black shale from the Kowala quarry, the Holy Cross Mountains, Poland, were investigated. This study focuses on disturbances in palaeoenvironmental proxies caused by palaeoweathering, which progressively changed the major and trace element abundances. Palaeomagnetic investigations reveal that the Devonian – Carboniferous succession was weathered during the Permian-Triassic by the infiltration of oxidizing fluids related to karstification following post-Variscan exhumation. The weathering process led to vermiculitization of chlorite, partial dissolution of calcite and replacement of pyrite by hematite and goethite. Moreover, the concentrations of some trace metals, including Co, Cu, Pb, Mo, Ni, As and U, significantly decreased. Consequently, some elemental abundance ratios that are used as environmental proxies, including U/Th, Ni/Co and V/Cr, were altered. Elements that are bound to iron sulphides (e.g., Mo) appear to be especially prone to mobilization by even a lightly weathered black shale. The documented weathering, including changes in elemental concentrations, can potentially create misinterpretations of the original palaeoenvironmental conditions. In addition, the palaeoweathering of the studied samples appears to have substantially changed the carbon, oxygen, nitrogen and molybdenum stable isotope values. The nitrogen and molybdenum stable isotope ratios, in particular, appear to be most sensitive to the effects of weathering and therefore are good indicators of (palaeo)weathering processes. The major cause of these changes is the decay of organic matter and pyrite. For the organic carbon stable isotopes ratios, the main factor that controlls this process appears to be the preferential degradation of labile organic matter. A combination of the total organic carbon (TOC), total sulphur (TS) content, Mo concentration and stable isotope compositions seems to be the most useful for identify (palaeo)weathering. Our results suggest that reductions in TS and Mo in tandem with diminished Mo stable isotope values in the absence of obvious changes to the TOC content provide the most compelling evidence of (palaeo)weathering

New constraints on the Middle Palaeozoic to Cenozoic burial and thermal history of the Holy Cross Mts. (Central Poland): results from numerical modelling

A 1-D burial-thermal modelling was performed using data from two borehole sections representative of the central part of the Holy Cross Mts. area. This area is located in the axial part of the Permian-Mesozoic Mid-Polish Trough that was inverted during the latest Cretaceous-Paleocene. The modelling involved different variants of restored stratigraphy of eroded Carboniferous to Cretaceous strata, whereas calibration was based on samples from cored Middle-Upper Devonian sediments. The modelling results are consistent with the assumption of a Variscan (Carboniferous-Early Permian) heat flow elevated up to 80 mWm-2, which is further confirmed by independent regional evidence. The zone of increased thermal maturity in the Devonian may be partly accounted for by a thicker Carboniferous section (by ca. 500 m) compared to previous estimates. Two variants of the post-Carboniferous geohistory were analysed. The variant of a thinner Permian-Mesozoic section, implying lower magnitude of the Late Cretaceous-Paleogene inversion, allows more realistic assumptions regarding heat flow distribution through time, including the possibility to incorporate an elevated Variscan heat flow. The alternative scenario, assuming deeper burial, generally lower heat flow and smaller Carboniferous thickness, is regarded as less probable. The accepted variant of the Permian-Mesozoic burial history implies that the total post-Carboniferous burial in the study area was on the order of 2000-2500 metres rather than 3000-3500 metres. The respective Upper Cretaceous thickness could have been 400 to 500 m instead of ca. 1000 m, whereas the Late Cretaceous-Paleogene inversion more likely started in the Santonian than in the late Maastrichtian. Consequently, the preferred magnitude of total inversion was on the order of 2500 m

Temperature dependence of surface magnetization in local-moment systems

We present a theory to study the temperature-dependent behavior of surface states in a ferromagnetic semi-infinite crystal. Our approach is based on the single-site approximation for the \emph{s-f} model. The effect of the semi-infinite nature of the crystal is taken into account by a localized perturbation method. Using the mean-field theory for the layer-dependent magnetization, the local density of states and the electron-spin polarization are investigated at different temperatures for ordinary and surface transition cases. The results show that the surface magnetic properties may differ strongly from those in the bulk and the coupling constant of atoms plays a decisive role in the degree of spin polarization. In particular, for the case in which the exchange coupling constant on the surface and between atoms in the first and second layer is higher than the corresponding in the bulk, an enhancement of surface Curie temperature and hence the spin polarization can be obtained.Comment: 9 pages,8 figure