13 research outputs found

    Hierarchical finite element methods for compressible flow problems

    Get PDF
    The thesis is concerned with the introduction of the CG1-DG2 method and the design of an hp-adaptive algorithm in the context of convection-dominated problems in 2D. The CG1-DG2 method combines the continuous Galerkin (CG) method with the discontinuous Galerkin (DG) method by enriching the continuous linear finite element (CG1) space with discontinuous quadratic basis functions. The resulting finite element approximation is continuous at the vertices of the mesh but may be discontinuous across edges. Analysis of the CG1-DG2 discretization in the context of a scalar advection equation shows that the use of upwind-biased convective fluxes leads to an approximation which is stable and exhibits the same convergence rates as the quadratic discontinuous (DG2) method. However, the CG1-DG2 space has fewer degrees of freedom than the DG2 space. In the case of Poisson's equation different strategies known from the DG method can be adopted to approximate the numerical fluxes: the symmetric and non-symmetric interior penalty method as well as the Baumann-Oden method. A priori error estimates for the DG2 method can be shown to hold for the CG1-DG2 approximation as well. Numerical studies confirm that the proposed method is stable and converges at the same rate as the fully discontinuous piecewise-quadratic version. We also present an extension of the CG1-DG2 method to solve the Euler equations and show numerical results which indicate that the CG1-DG2 method gives results similar to those obtained by the DG method. The second part of this thesis presents an hp-adaptive framework for convection-dominated problems. The idea of this algorithm is to divide the mesh in smooth and non-smooth parts, where the smoothness refers to the regularity of the approximated solution. In smooth parts the polynomial degree is increased (p-adaptivity) whereas in non-smooth parts h-adaptivity for linear elements is used. Hereby, a parameter-free regularity estimator is used to determine the smoothness of a function and its gradient by comparing those with reconstructed approximations. In smooth elements the CG1-DG2 method is used. In non- smooth elements a flux-corrected transport scheme is applied and combined with h-adaptivity based on the so-called reference solution approach. Numerical experiments are performed for advection and advection-diffusion equations. Those show the advantage of the hp-adaptive algorithm over pure h-refinement in the context of FCT schemes

    Embedded discontinuous Galerkin transport schemes with localised limiters

    Get PDF
    Motivated by finite element spaces used for representation of temperature in the compatible finite element approach for numerical weather prediction, we introduce locally bounded transport schemes for (partially-)continuous finite element spaces. The underlying high-order transport scheme is constructed by injecting the partially-continuous field into an embedding discontinuous finite element space, applying a stable upwind discontinuous Galerkin (DG) scheme, and projecting back into the partially-continuous space; we call this an embedded DG scheme. We prove that this scheme is stable in L2 provided that the underlying upwind DG scheme is. We then provide a framework for applying limiters for embedded DG transport schemes. Standard DG limiters are applied during the underlying DG scheme. We introduce a new localised form of element-based flux-correction which we apply to limiting the projection back into the partially-continuous space, so that the whole transport scheme is bounded. We provide details in the specific case of tensor-product finite element spaces on wedge elements that are discontinuous P1/Q1 in the horizontal and continuous P2 in the vertical. The framework is illustrated with numerical tests

    Investigation of Hexavalent Chromium Flux to Groundwater at the 100-C-7:1 Excavation Site

    Full text link

    Traces of a trauma - pharmacological interventions of PTSD

    Get PDF
    Posttraumatic stress disorder (PTSD) is characterized by exaggerated trauma-related memories (contextual fear), increased avoidance of trauma-related cues, and hyperarousal. Pharmacotherapy of PTSD is still unsatisfactory, with SSRIs being the first choice drugs. However, as known for depressed patients, PTSD patients are prone for relapse of symptoms upon discontinuation of treatment. This urges for a refinement of therapeutic interventions and the identification of markers of treatment success. These issues were addressed in our mouse model of PTSD. In this model, mice are exposed to a brief, inescapable electric foot shock. Within 1 month after the trauma, they developed PTSD-like symptoms such as generalized contextual fear, generalized avoidance, and increased hyperarousal symptomatology. This time frame allows for pharmacological interventions during maturation of PTSD-like symptoms (i.e. preventive treatment) or at time points when the symptoms have fully developed (i.e. therapeutic treatment). The work presented in this thesis revealed the following key findings: (1) Fear incubation (i.e. simply the passage of time after trauma) was accompanied by highly selective changes in neuronal activity, as assessed by cytochrome c oxidase (CO) activity >1 month after trauma. (2) Chronic treatment with fluoxetine via drinking water starting either right after the trauma (preventive treatment) or 28 days later (therapeutic treatment) completely reversed the PTSD-like symptoms assessed during ongoing treatment 1 (preventive treatment) or 2 months (therapeutic treatment) after trauma. (3) Despite the similarities to PTSD-like symptoms, preventive treatment with fluoxetine abolished most of the trauma-related changes in CO activity, whereas those changes were maintained after therapeutic intervention. (4) If fluoxetine was washed out after 1 month of treatment, PTSD-like symptoms remained absent following preventive treatment, but re-occurred after therapeutic treatment. In conclusion, these data suggest preventive treatment with fluoxetine starting in the early aftermath of a trauma as a successful intervention strategy for preventing the development of PTSD-like symptoms. In contrast, therapeutic treatment abolishes the expression of symptoms, without curative effects. Chronic changes in CO activity reflect traces of a trauma. They might serve as an indicator of PTSD relapse

    Spin Projection and Correlation Experiments in Nanoelectronic Devices

    Get PDF
    A key element in quantum computing applications is the ability to measure non-local correlations, known as entanglement, as well as reliably generate them. A naturally occurring source of entangled spin pairs is the superconducting condensate, from which spin singlet Cooper pairs can be split into two QDs on each side of a s-wave superconductor. Such Cooper pair splitter (CPS) devices have already been demonstrated in various systems, such as InAs nanowires (NWs), carbon nanotubes (CNTS) and graphene. A strong charge current correlation between the two output terminals has been demonstrated already, but a spin correlation, as expected for split singlet states, is missing and is even conceptually problematic so far. Such spin correlation measurements, i.e. the expectation value of the product of spin projection operators \left of the two QDs in a CPS device, requires efficient spin readout of the split electrons without destroying the superconducting state of the emitter. The idea is to use the two QDs for spin filtering, achievable by applying locally different magnetic fields. A lower CPS current is then expected for the parallel spin projection axes with respect to the antiparallel ones. In general, the most essential requirements for such an complex experiment can be summarized as: (1) highly polarized QDs with large electrical tunability of the QD spin polarization for efficient spin detection in close proximity to a superconductor; (2) coexistence of superconductivity and locally varying magnetic fields in close proximity to each other, such that the critical field of the superconductor is much higher than the local magnetic field strength; and (3) the CPS current in both QDs should exhibit non-local spin correlations in a specific pattern, i.e. higher for antiparallel spin projection axes.\ In this thesis, we investigate all the above criteria using electron spin transport through engineered QDs in InAs NWs, chosen predominantly due to their large g-factors in QDs. We first show a new approach to control electron spin currents in QDs using stray magnetic fields locally generated from individual nanomagnets. Using this approach, we demonstrate electrically tunable highly efficient spin injection and detection in a double quantum dot spin valve (DQD-SV). We then use this efficient spin detection technique in a Cooper pair splitter device to perform spin readout and filtering of the CPS conductance signal. In addition, electron spin state engineering at very large magnetic fields through the Pauli spin blockade (PSB) effect is also presented

    Improving water asset management when data are sparse

    Get PDF
    Ensuring the high of assets in water utilities is critically important and requires continuous improvement. This is due to the need to minimise risk of harm to human health and the environment from contaminated drinking water. Continuous improvement and innovation in water asset management are therefore, necessary and are driven by (i) increased regulatory requirements on serviceability; (ii) high maintenance costs, (iii) higher customer expectations, and (iv) enhanced environmental and health/safety requirements. High quality data on asset failures, maintenance, and operations are key requirements for developing reliability models. However, a literature search revealed that, in practice, there is sometimes limited data in water utilities - particularly for over-ground assets. Perhaps surprisingly, there is often a mismatch between the ambitions of sophisticated reliability tools and the availability of asset data water utilities are able to draw upon to implement them in practice. This research provides models to support decision-making in water utility asset management when there is limited data. Three approaches for assessing asset condition, maintenance effectiveness and selecting maintenance regimes for specific asset groups were developed. Expert elicitation was used to test and apply the developed decision-support tools. A major regional water utility in England was used as a case study to investigate and test the developed approaches. The new approach achieved improved precision in asset condition assessment (Figure 3–3a) - supporting the requirements of the UK Capital Maintenance Planning Common Framework. Critically, the thesis demonstrated that, on occasion, assets were sometimes misallocated by more than 50% between condition grades when using current approaches. Expert opinions were also sought for assessing maintenance effectiveness, and a new approach was tested with over-ground assets. The new approach’s value was demonstrated by the capability to account for finer measurements (as low as 10%) of maintenance effectiveness (Table 4-4). An asset maintenance regime selection approach was developed to support decision-making when data are sparse. The value of the approach is its versatility in selecting different regimes for different asset groups, and specifically accounting for the assets unique performance variables

    The Protein Tyrosine Phosphatase SHP2 as a Mediator of Differential Cellular Sensitivity to EGFR Kinase Inhibitors

    Get PDF
    SRC homology 2 domain-containing phosphatase 2 (SHP2) is a ubiquitously expressed cytosolic protein tyrosine phosphatase. Downstream of epidermal growth factor receptor (EGFR) and other receptors, SHP2 is activated by binding to phosphotyrosine-containing receptors and adapter proteins, is required for complete extracellular regulated kinase 1/2 (ERK) pathway activity, which promotes cellular proliferation and survival, and regulates other signaling processes. In this thesis, we explored the signaling functions of SHP2 in lung and brain cancer cell systems with or without clinically relevant mutations that render EGFR constitutively active and developed computational models of EGFR-mediated SHP2 activation. In non-small cell lung cancer cells, SHP2 promoted ERK-dependent resistance to EGFR inhibition, but in cells with EGFR kinase-activating mutations this SHP2 functional role was impaired through sequestration of biochemically active SHP2 with internalization-impaired EGFR mutants. In glioblastoma multiforme cells, SHP2 simultaneously promoted ERK activity and antagonized STAT3 phosphorylation such that SHP2 drove proliferation while also promoting sensitivity to EGFR and c-MET co-inhibition. These SHP2 functions were perturbed by sufficiently high expression of the EGFR variant III mutant. Furthermore, SHP2 was found to regulate EGFRvIII and c-MET phosphorylation and control hypoxia-inducible factor expression in a way that may regulate tumorigenesis. We next developed computational models and associated quantitative experimental data sets to gain quantitative understanding of the regulation of protein complexes containing SHP2 and GRB2-associated binder 1 (GAB1), the primary phosphorylated adapter with which SHP2 associates following EGFR activation. Our analysis revealed that in some cell settings EGFR activity is amplified by intermediary SRC family kinases (SFKs) which drive GAB1 phosphorylation and enable GAB1-SHP2 complexes to persist in the cytosol distal from EGFR. A reaction-diffusion model further predicted that EGFR-initiated GAB1-SHP2 complexes persist over the entire cell length scale, which could permit membrane-localized EGFR to regulate signaling events through SHP2 at subcellular locations where EGFR itself is not present. Overall, these results motivate the continued search for specific SHP2 inhibitors, while providing a contextual basis for predicting when such interventions may be particularly effective, and establish a quantitative framework for understanding EGFR\u27s ability to activate SHP2 and how this might be perturbed in different pathological contexts

    1989 summer study program in Geophysical Fluid Dynamics : general circulation of the oceans

    Get PDF
    The success of this summer's Geophysical Fluid Dynamics Program owes much to Myrl Hendershott's excellent and engaging survey of the Oceans General Circulation, including recent developments In the Theory of Recirculation Gyres and Thermocline Ventilation.Funding was provided by the National Science Foundation through Grant Number OCE-89-0101

    Wind Power Integration into Power Systems: Stability and Control Aspects

    Get PDF
    Power network operators are rapidly incorporating wind power generation into their power grids to meet the widely accepted carbon neutrality targets and facilitate the transition from conventional fossil-fuel energy sources to clean and low-carbon renewable energy sources. Complex stability issues, such as frequency, voltage, and oscillatory instability, are frequently reported in the power grids of many countries and regions (e.g., Germany, Denmark, Ireland, and South Australia) due to the substantially increased wind power generation. Control techniques, such as virtual/emulated inertia and damping controls, could be developed to address these stability issues, and additional devices, such as energy storage systems, can also be deployed to mitigate the adverse impact of high wind power generation on various system stability problems. Moreover, other wind power integration aspects, such as capacity planning and the short- and long-term forecasting of wind power generation, also require careful attention to ensure grid security and reliability. This book includes fourteen novel research articles published in this Energies Special Issue on Wind Power Integration into Power Systems: Stability and Control Aspects, with topics ranging from stability and control to system capacity planning and forecasting
    corecore