Browsing by Subject "thermodynamics"

Sort by: Order: Results:

Now showing items 1-6 of 6
  • Hernández-Uribe, David; Spera, Frank J.; Bohrson, Wendy A.; Heinonen, Jussi S. (2022)
    Phase equilibria modeling is a powerful petrological tool to address both forward and inverse geological problems over a broad range of crustal and upper mantle conditions of pressure (P), temperature (T), composition (X), and redox (f(o2)). The development of thermodynamic databases, relatively realistic activity-composition (a-X) relations for solids, melts and fluids, pressure-volume-temperature (PVT) equations of state (EOS), and efficient numerical algorithms represent an inflection point in our ability to understand the nexus between tectonics and petrogenesis. While developed-and typically applied in isolation-by either metamorphic or igneous petrologists, some of the published thermodynamic models have overlapping P-T-X calibration ranges, which enables comparisons of model outcomes for similar conditions within the range of applicability. In this paper, we systematically compare the results of two such models that are routinely used for calculating phase equilibria in melt-bearing systems: rhyolite-MELTS (Gualda et al. 2012; Ghiorso and Gualda 2015) and the metabasite set of Green et al. (2016) using the thermodynamic database ds62 (Holland and Powell 2011) (hereafter denoted as "HPx-mb16"). We selected a N-MORB composition and modeled closed system equilibrium phase relations as a function of temperature at 0.25 and 1 GPa for N-MORB with 0.5 and 4 wt% H2O. Our results show that phase relations exhibit some key differences that, in some instances, impact geological inferences. For example, clinopyroxene and plagioclase stabilities are expanded to higher temperatures in HPx-mb16 compared to predictions from rhyolite-MELTS. Orthopyroxene and olivine are stable in greater proportions and at wider temperature ranges in rhyolite-MELTS compared to HPx-mb16. Importantly, HPx-mb16 predicts amphibole in all runs presented here, whereas amphibole is only predicted at high-P-high-H2O (1 GPa and 4 wt% H2O) in rhyolite-MELTS, and in lesser amounts. Garnet stability is systematically expanded at higher temperatures, and the proportion is greater in rhyolite-MELTS. In addition to phase assemblage differences, phase compositions may differ. For example, plagioclase anorthite content is systematically higher in HPx-mb16 (for the same set of conditions), whereas garnet Mg# is higher in rhyolite-MELTS. Calculated amphibole compositions are substantially different between the two models as well. Liquid compositions also show important differences. High-T liquids are generally similar in SiO2 contents but diverge at lower temperatures; in these cases, HIPx-mb16 liquids are SiO2-depleted compared to those produced by rhyolite-MELTS. Liquids are also systematically and substantially more mafic in HPx-mb16, and alumina and the alkali concentrations are relatively different and show different trends as a function of temperature at constant pressure. Overall, liquid compositions show the greatest differences near the solidus. Differences in modal abundances of phases and liquid compositions influence liquid trace-element signatures, and these differences can affect geological interpretations. Finally, a comparison between melting experiments of basaltic bulk composition and both thermodynamic models shows that rhyolite-MELTS better reproduces the higher temperature experiments, whereas HPx-mb16 better reproduces the lower temperature experiments. We discuss these and other similarities and differences to highlight the strengths and limitations of each model and to recognize that modeling results have important implications for interpretations of geologic processes. We recognize that our results are informed by a small subset of calculations over a limited range of conditions-but encourage further comparisons over a wider range of conditions and compositions.
  • Annila, Arto; Salthe, Stanley (2010)
  • Multia, Evgen (Helsingfors universitet, 2017)
    The literature part of this thesis reviewed the process of obtaining affinity information with quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) biosensors. Basic principles of these biosensors were also evaluated, along with the principles of data acquisition and finally the data processing. The raw data produced by QCM or SPR can be used to study biomolecular interactions qualitatively and quantitatively. These techniques are also powerful in obtaining kinetic and thermodynamic information of the biomolecular interactions. SPR and QCM can produce data easily, but data interpretation can be sometimes problematic. This is partly due to misconceptions on how the sensograms should be interpreted. Many of the interpretational problems can and should be avoided long before the modeling of the data takes place to obtain reliable affinity data. The literature part of this thesis also presents tools for developing good experimental design. Well-designed experimental set-up is the most important element for producing good biosensor data. One should also estimate from the sensogram shapes what kind of analysis is needed. This was explained in detail in the literature part, pointing out the key elements how sensograms with certain shape should be interpreted and further analyzed to obtain affinity constants. Data analysis part of the literature review provides also information how to use appropriate models (e.g. fitting equilibrium, kinetic or complex data) with extensive examples. Surface site distribution model will be also covered as the tool to analyze complex biomolecular interactions by QCM and SPR. In the experimental part, affinity of anti-human apoB-100 monoclonal antibody (anti-apoB-100 Mab) towards different lipoproteins was studied with partially filling affinity capillary (PF-ACE) electrophoresis and QCM. PF-ACE with adsorption energy distribution (AED) calculations provided information on the heterogeneity of the interactions. For the first time, a modified surface site distribution model called Interaction map was utilized to model QCM data of lipoprotein interactions with anti-apoB-100 Mab. With the Interaction maps, it was possible to distinguish different kinetics of low-density lipoprotein (LDL) and anti-apoB-100 Mab interactions. Affinity constants obtained were used to evaluate thermodynamics of these interactions. Both methods were also used to evaluate interactions with other apoB-100 containing lipoproteins: intermediate-density lipoprotein (IDL) and very lowdensity lipoprotein (VLDL). It was found that the Interaction maps could distinguish two different kinetics from the mixture of IDL-VLDL with distinct affinity constants. Both methods agreed well with the affinity constants. It was found that the anti-apoB-100 Mab used in this study, had a high affinity towards apoB-100 containing lipoproteins. In the second part of the experimental, a convective interaction media (CIM) based LDL isolation platform was developed. In these studies, anti-apoB-100 Mab was immobilized on the CIM-disk and was used to isolate LDL from human plasma and serum samples. It was found that apolipoprotein based separation of LDL from plasma was possible, although not without difficulties, since apoB-100 is not only present in LDL, but also in VLDL and IDL. To circumvent this problem different antibodies (anti-apoE and anti-apoAI) were utilized to capture VLDL and IDL from the plasma before the interaction of LDL with the anti-apoB-100 CIM-disk. LDL was successfully isolated with this approach in a significantly reduced time compared to conventional ultracentrifugation method used for LDL isolation.
  • Yang, Yu; Zhijun, Li; Leppäranta, Matti; Cheng, Bin; Shi, Liqiong; Lei, Ruibo (2016)
    Landfast sea ice forms and remains fixed along the coast for most of its life time. In Prydz Bay, landfast ice is seasonal due to melting, mechanical breakage and drift of ice in summer. Its annual cycle of thickness and temperature was examined using a one-dimensional thermodynamic model. Model calibration was made for March 2006 to March 2007 with forcing based on the Chinese National Antarctic Research Expedition data, which consisted of in situ ice and snow observations and meteorological records at the Zhongshan Station. The observed maximum annual ice thickness was 1.74 m. The ice broke and drifted out in summer when its thickness was 0.5-1.0 m. Oceanic heat flux was estimated by tuning the model with observed ice thickness. In the growth season, it decreased from 25 Wm(-2) to 5W m(-2), and in summer it recovered back to 25 W m(-2). Albedo was important in summer; by model tuning the estimated value was 0.6, consistent with the ice surface being bare all summer. Snow cover was thin, having a minor role. The results can be used to further our understanding of the importance of landfast ice in Antarctica for climate research and high-resolution ice-ocean modelling.
  • Kohout, Tomas; Bucko, Michal; Rasmus, Kai; Leppäranta, Matti; Matero, Ilkka (2014)
    Non-invasive geophysical prospecting and a thermodynamic model were used to examine the structure, depth and lateral extent of the frozen core of a palsa near Lake Peerajärvi, in northwest Finland. A simple thermodynamic model verified that the current climatic conditions in the study area allow sustainable palsa development. A ground penetrating radar (GPR) survey of the palsa under both winter and summer conditions revealed its internal structure and the size of its frozen core. GPR imaging in summer detected the upper peat/core boundary, and imaging in winter detected a deep reflector that probably represents the lower core boundary. This indicates that only a combined summer and winter GPR survey completely reveals the lateral and vertical extent of the frozen core of the palsa. The core underlies the active layer at a depth of ~0.6 m and extends to about 4 m depth. Its lateral extent is ~15 m x ~30 m. The presence of the frozen core could also be traced as minima in surface temperature and ground conductivity measurements. These field methods and thermodynamic models can be utilized in studies of climate impact on Arctic wetlands.
  • Annila, Arto (2022)
    Decision-making is described as a natural process, one among others, consuming free energy in the least time. The thermodynamic tenet explains why data associated with decisions display the same patterns as any other data: skewed distributions, sigmoidal cumulative curves, oscillations, and even chaos. Moreover, it is shown that decision-making is intrinsically an intractable process because everything depends on everything else. However, no decision is arbitrary but bounded by free energy, such as resources and propellants, and restricted by mechanisms like molecular, neural, and social networks. The least-time maximation of entropy, equivalent to the minimization of free energy, parallels the optimization of subjective expected utility. As the system attains a state of balance, all driving forces vanish. Then there is no need or use to make further decisions. In general, the thermodynamic theory regards those decisions well-motivated that take into account forces, i.e., causes comprehensively in projecting motions, i.e., consequences.