1. Numerical analysis of low-enthalpy deep geothermal energy extraction using a novel gravity heat pipe designUrban Gselman, Vid Peršak, Darko Goričanec, 2024, original scientific article Abstract: Geothermal energy, derived from the Earth’s internal heat, can be harnessed due to the
geothermal gradient between the Earth’s interior and its surface. This heat, sustained by radiogenic
decay, varies across regions, and is highest near volcanic areas. In 2020, 108 countries utilised
geothermal energy, with an installed capacity of 15,950 MWe for electricity and 107,727 MWt for
direct use in 2019. Low-enthalpy sources require binary systems for power production. Open-loop
systems face issues like scaling, difficult water treatment, and potential seismicity, while closed-loop
systems, using abandoned petroleum or gas wells, reduce costs and environmental impacts greatly.
The novel geothermal gravity heat pipe (GGHP) design eliminates parasitic power consumption by
using hydrostatic pressure for fluid circulation. Implemented in an abandoned well in north-east
(NE) Slovenia, the GGHP uses a numerical finite difference method to model heat flow. The system
vaporises the working fluid in the borehole, condenses it at the surface, and uses gravitational flow
for circulation, maintaining efficient heat extraction. The model predicts that continuous maximum
capacity extraction depletes usable heat rapidly. Future work will explore sustainable heat extraction
and potential discontinuous operation for improved efficiency.
Keywords: geothermal energy, geothermal gravity heat pipe, numerical modelling, single well closed-loop heat exchanger Published in DKUM: 03.09.2024; Views: 41; Downloads: 3 Full text (3,23 MB) |
2. Flavor symmetries and automatic enhancement in the 6D supergravity swamplandMirjam Cvetič, Ling Lin, Andrew P. Turner, 2022, original scientific article Abstract: We argue for the quantum-gravitational inconsistency of certain 6D N ¼ ð1; 0Þ supergravity theories, whose anomaly-free gauge algebra g and hypermultiplet spectrum M were observed by Raghuram et al. [J. High Energy Phys. 07 (2021) 048] to be realizable only as part of a larger gauge sector ðg0 ⊃ g; M0 ⊃ MÞ in F-theory. To detach any reference to a string theoretic method of construction, we utilize flavor symmetries to provide compelling reasons why the vast majority of such ðg; MÞ theories are not compatible with quantum gravity constraints, and how the “automatic enhancement” to ðg0 ; M0 Þ remedies this. In the first class of models, with g0 ¼ g ⊕ h, we show that there exists an unbroken flavor symmetry h acting on the matter M, which, if ungauged, would violate the no-global-symmetries hypothesis. This argument also applies to 1-form center symmetries, which govern the gauge group topology and massive states in representations different from those of massless states. In a second class, we find that g is incompatible with the flavor symmetry of certain supersymmetric strings that must exist by the completeness hypothesis. Keywords: supergravity theories, supersymmetric strings, quantum gravity constraints, Gauge theories, Higher-dimensional field theories, strings & branes, supergravity, symmetries Published in DKUM: 25.09.2023; Views: 258; Downloads: 8 Full text (317,88 KB) This document has many files! More... |
3. All eight- and nine-dimensional string vacua from junctionsMirjam Cvetič, Markus Dierigl, Ling Lin, Hao Y. Zhang, 2022, original scientific article Abstract: String and 5-brane junctions are shown to succinctly classify all known 8D N ¼ 1 string vacua. This requires an extension of the description for ordinary ½p; q-7-branes to consistently include O7þ planes, which then naturally encodes the dynamics of spn gauge algebras, including their p-form center symmetries. Central to this analysis are loop junctions, i.e., strings/5-branes which encircle stacks of 7-branes and O7þs. Loop junctions further signal the appearance of affine symmetries of emergent 9D descriptions at the 8D moduli space’s boundaries. Such limits reproduce all 9D string vacua, including the two disconnected rank (1,1) moduli components. Keywords: 9D string vacua, 8D string vacua, anomalies, M-theory, Non-Abelian gauge theories, quantum gravity, string dualities, strings & branes, supergravity, Gauge symmetries Published in DKUM: 22.09.2023; Views: 286; Downloads: 21 Full text (1,09 MB) This document has many files! More... |
4. Design optimization for symmetrical gravity retaining wallsErol Sadoğlu, 2014, original scientific article Abstract: The optimization for symmetrical gravity retaining walls of different heights is examined in this study. For this purpose, an optimization problem of continuous functions is developed. The continuous functions are the objective function defined as the cross-sectional area of the wall and the constraint functions derived from external stability and internal stability verifications. The verifications are listed as the overturning, the forward sliding, the bearing capacity, the shears in the stem and the bendings in the stem. The heights of the walls are selected as 2.0, 3.0, and 4.0 m in order to investigate the outline of the optimum cross-section and the effect of the wall height on the outline. Additionally, the physical and mechanical properties of the soil are kept constant in order to compare only the effect of the height on the geometry. The upper and lower bounds of the solution space are specified to be as wide as possible and the minimum dimensions suggested for the gravity retaining walls are not taken into account. A common feature of the optimum cross-sections of walls with different heights is to have a very wide lower part like a wall foundation and a slender stem. However, other than the forward sliding constraint, the bending constraints are active at the optimum values of the variables. Keywords: gravity retaining wall, nonlinear optimization, continuous variables, interior point method Published in DKUM: 14.06.2018; Views: 1575; Downloads: 198 Full text (168,77 KB) This document has many files! More... |
5. Load transfer and stress in a piled gravity retaining wallQun Chen, Li Wan, Changrong He, Zihui Lai, 2010, original scientific article Abstract: The piled retaining wall is a new type of railway retaining structure in China. In the current design, the retaining wall, the beam and the piles are assumed to be independent components. Both the mutual action of the retaining wall, the piles and beam, and the influence of the soil or rock foundation on the structure are not fully considered, so that there are some limitations in the current design method. In this paper, using field observations and a three-dimensional finite-element analysis, the lateral earth pressure on the wall back, the stress distributions and the forces of the reinforcements in the beam and the pile were studied. The simulation results were in good agreement with the field observation data. These results revealed that the tensile stresses were very small and that these stresses were positive in most zones in the beam and the pile. It can also be observed that the tensile stresses or forces in the beam and pile obtained in this study were much smaller than those obtained using the current design method. This clarified the fact that the current design method used for the beam and the pile was very conservative and that it should be optimized to consider the effect of the foundation on the whole structure and the interactions among the different components. Keywords: piled gravity retaining wall, field observation, finite-element analysis, stress, load transfer mechanism Published in DKUM: 11.06.2018; Views: 1156; Downloads: 88 Full text (558,92 KB) This document has many files! More... |
6. Methods for control of seepage in RCC dams with wathertight and drainage measuresYueming Zhu, Stephan Semprich, Erich Bauer, Cuiping Yuan, Dongmei Sun, 2006, original scientific article Abstract: The technologies for construction of roller-compacted concrete (RCC) dams have been considerably developed during recent years in China. At the time being, they have been successfully applied to the constructions of even extreme-high gravity dams and medium to high arch dams. There are a few of hundreds of RCC dams (RCCD) under design and/or construction in China. One of the main concerned technical problems according to the construction is about the understanding of the property of seepage in RCCDs and the relevant theory and methods for the control of the seepage. In order to overcome the problem, the senior author has been engaged in a wide study on the property and methods for control of seepage in RCCDs for more than 10 years. The property of seepage, measures for watertightness and drainage, optimal design and construction schemes for control of seepage in the dams have been essentially understood either in theory and practice. The results have been applied for the construction and the backanalysis of several dams. The paper describes the research findings in detail with respect to the theoretical fundament and their application for a high RCC gravity dam. Keywords: gravity dam, Roller-compacted concrete, RCC, seepage, anisotropic permeability, drainage Published in DKUM: 17.05.2018; Views: 1308; Downloads: 56 Full text (209,12 KB) This document has many files! More... |
7. Compactifications of deformed conifolds, branes and the geometry of qubitsMirjam Cvetič, G. W. Gibbons, Christopher N. Pope, 2016, original scientific article Abstract: We present three families of exact, cohomogeneity-one Einstein metrics in (2n + 2) dimensions, which are generalizations of the Stenzel construction of Ricci-flat metrics to those with a positive cosmological constant. The first family of solutions are Fubini-Study metrics on the complex projective spaces CPn+1, written in a Stenzel form, whose principal orbits are the Stiefel manifolds V-2(Rn+2) = SO(n+2)/SO(n) divided by Z(2). The second family are also Einstein-Kahler metrics, now on the Grassmannian manifolds G(2)(Rn+3) = SO(n+3)/((SO(n+1)xSO(2)), whose principal orbits are the Stiefel manifolds V-2(Rn+2) (with no Z(2) factoring in this case). The third family are Einstein metrics on the product manifolds Sn+1 x Sn+1, and are Kahler only for n = 1. Some of these metrics are believed to play a role in studies of consistent string theory compactifications and in the context of the AdS/CFT correspondence. We also elaborate on the geometric approach to quantum mechanics based on the Kahler geometry of Fubini-Study metrics on CPn+1, and we apply the formalism to study the quantum entanglement of qubits. Keywords: conformal field models, string theory, models of quantum gravity, differential geometry, algebraic geometry Published in DKUM: 27.06.2017; Views: 1480; Downloads: 397 Full text (586,14 KB) This document has many files! More... |
8. Black hole thermodynamics from a variational principle: asymptotically conical backgroundsSong-ok An, Mirjam Cvetič, Ioannis Papadimitriou, 2016, original scientific article Abstract: The variational problem of gravity theories is directly related to black hole thermodynamics. For asymptotically locally AdS backgrounds it is known that holographic renormalization results in a variational principle in terms of equivalence classes of boundary data under the local asymptotic symmetries of the theory, which automatically leads to finite conserved charges satisfying the first law of thermodynamics. We show that this connection holds well beyond asymptotically AdS black holes. In particular, we formulate the variational problem for N = 2 STU supergravity in four dimensions with boundary conditions corresponding to those obeyed by the so called 'subtracted geometries'. We show that such boundary conditions can be imposed covariantly in terms of a set of asymptotic second class constraints, and we derive the appropriate boundary terms that render the variational problem well posed in two different duality frames of the STU model. This allows us to define finite conserved charges associated with any asymptotic Killing vector and to demonstrate that these charges satisfy the Smarr formula and the first law of thermodynamics. Moreover, by uplifting the theory to five dimensions and then reducing on a 2-sphere, we provide a precise map between the thermodynamic observables of the subtracted geometries and those of the BTZ black hole. Surface terms play a crucial role in this identification. Keywords: M-Theory, Black Holes, String Theory, Gauge-gravity correspondence Published in DKUM: 27.06.2017; Views: 2851; Downloads: 388 Full text (834,82 KB) This document has many files! More... |
9. AdS(2) holographic dictionaryMirjam Cvetič, Ioannis Papadimitriou, 2016, original scientific article Abstract: We construct the holographic dictionary for both running and constant dilaton solutions of the two dimensional Einstein-Maxwell-Dilaton theory that is obtained by a circle reduction from Einstein-Hilbert gravity with negative cosmological constant in three dimensions. This specific model ensures that the dual theory has a well de fined ultraviolet completion in terms of a two dimensional conformal field theory, but our results apply qualitatively to a wider class of two dimensional dilaton gravity theories. For each type of solutions we perform holographic renormalization, compute the exact renormalized one-point functions in the presence of arbitrary sources, and derive the asymptotic symmetries and the corresponding conserved charges. In both cases we find that the scalar operator dual to the dilaton plays a crucial role in the description of the dynamics. Its source gives rise to a matter conformal anomaly for the running dilaton solutions, while its expectation value is the only non trivial observable for constant dilaton solutions. The role of this operator has been largely overlooked in the literature. We further show that the only non trivial conserved charges for running dilaton solutions are the mass and the electric charge, while for constant dilaton solutions only the electric charge is non zero. However, by uplifting the solutions to three dimensions we show that constant dilaton solutions can support non trivial extended symmetry algebras, including the one found by Comp ere, Song and Strominger [1], in agreement with the results of Castro and Song [2]. Finally, we demonstrate that any solution of this specific dilaton gravity model can be uplifted to a family of asymptotically AdS(2) x S-2 or conformally AdS(2) x S-2 solutions of the STU model in four dimensions, including non extremal black holes. The four dimensional solutions obtained by uplifting the running dilaton solutions coincide with the so called 'subtracted geometries', while those obtained from the uplift of the constant dilaton ones are new. Keywords: 2D gravity, AdS-CFT correspondence, black holes, space-time symmetries Published in DKUM: 27.06.2017; Views: 2986; Downloads: 387 Full text (1,01 MB) This document has many files! More... |
10. Geomehanska analiza opornega zidu OZ - 02 pri hitri cesti Jagodje - LucijaNuša Vodušek, 2017, diploma project paper Abstract: V projektni nalogi je predstavljena analiza mejnega stanja nosilnosti v programu GEO5 2016/Gravity Wall za oporni zid OZ - 02, ki se nahaja na odseku hitre ceste Jagodje – Lucija. Za analizo mejnega stanja nosilnosti, so bile potrebne tudi terenske in laboratorijske raziskave hribine, ki so del projektne naloge. Glede na pridobljene rezultate raziskav je bila opravljena klasifikacija hribine. Zaključek naloge vključuje analizo krožnih porušnic po Bishopovi metodi. Keywords: Gradbeništvo, oporni zid, geomehanika, analiza mejnega stanja, GEO5 2016/Gravity Wall. Published in DKUM: 21.12.2016; Views: 1841; Downloads: 279 Full text (1,32 MB) |