Numerical modelling of velocity profile parameters of the atmospheric boundary layer simulated in wind tunnels

Experimental and numerical modeling and simulations of the wind influence within the atmospheric boundary layer are essential tools in optimum building structural design. Each of these methods, however, has both advantages and disadvantages. In experimental investigations performed in wind tunnels, reliable results can be obtained, but detailed information of the wind profile parameters, such as the surface roughness length z 0 or the friction velocity u∗, are difficult to determine. Numerical simulations, on other hand, easily yield any information of the wind velocity profile. However, the reliability of numerical results strongly depends on the established and adopted computational model. This paper presents the computational fluid dynamics (CFD) analysis of the atmospheric boundary layer simulated in subsonic wind tunnels using appropriate types of obstacles, based on the SST k-ω turbulence model with optimized unstructured mesh and optimum selection of relevant physical model parameters, performed in Ansys Fluent software. Results have been compared with the measurements from the Assiut University wind tunnel with maximum velocity of 4 m/s, and from subsonic wind tunnel at Belgrade University, with maximum air velocity of 45 m/s. Detailed comparisons for velocity distributions with these experimental results have shown very good conformity. Also, the three-parameter fitting methods were successfully established to define surface roughness length z 0 and the friction velocity u∗. Obtained results have shown that the established numerical model is able to substitute a remarkable number of expensive wind tunnel tests hours within the operational investigations of wind influence on the building structures

Numerical modelling of velocity profile parameters of the atmospheric boundary layer simulated in wind tunnels

Experimental and numerical modeling and simulations of the wind influence within the atmospheric boundary layer are essential tools in optimum building structural design. Each of these methods, however, has both advantages and disadvantages. In experimental investigations performed in wind tunnels, reliable results can be obtained, but detailed information of the wind profile parameters, such as the surface roughness length z 0 or the friction velocity u∗, are difficult to determine. Numerical simulations, on other hand, easily yield any information of the wind velocity profile. However, the reliability of numerical results strongly depends on the established and adopted computational model. This paper presents the computational fluid dynamics (CFD) analysis of the atmospheric boundary layer simulated in subsonic wind tunnels using appropriate types of obstacles, based on the SST k-ω turbulence model with optimized unstructured mesh and optimum selection of relevant physical model parameters, performed in Ansys Fluent software. Results have been compared with the measurements from the Assiut University wind tunnel with maximum velocity of 4 m/s, and from subsonic wind tunnel at Belgrade University, with maximum air velocity of 45 m/s. Detailed comparisons for velocity distributions with these experimental results have shown very good conformity. Also, the three-parameter fitting methods were successfully established to define surface roughness length z 0 and the friction velocity u∗. Obtained results have shown that the established numerical model is able to substitute a remarkable number of expensive wind tunnel tests hours within the operational investigations of wind influence on the building structures

Modelling the light-curves of objects tidally disrupted by a black hole

Tidal disruption by massive black holes is a phenomenon, during which a large part of gravitational energy can be released on a very short time-scale. The time-scales and energies involved during X-ray and IR flares observed in Galactic centre suggest that they may be related to tidal disruption events. Furthermore, aftermath of a tidal disruption of a star by super-massive black hole has been observed in some galaxies, e.g. RX J1242.6-1119A. All these discoveries increased the demand for tools for tidal disruption study in curved space-time. Here we summarise our study of general relativistic effects on tidal deformation of stars and compact objects.Comment: 2 pages, to appear in the proceedings of the JENAM 2008, Symposium 7: "Grand Challenges in Computational Astrophysics

Taxing Artificial Intelligence and Robots: Critical assessment of Potential Policy Solutions and Recommendation for Alternative Approaches

In recent years, investments in technology have resulted in an exponential growth of AI/robots. It is argued that some of these innovations are able to outperform and replace humans in various types of jobs. Accordingly, concerns regarding government revenues have been raised, as AI/robots could trigger widespread unemployment with the result that less tax revenue will accrue to the government. This contribution, as a start, analyses whether or not this is truly a concern. In order to do so, the authors map the Industrial Revolution(s) that humankind has witnessed and then conduct a literature review of economic and demographic studies relevant to the debate. The economic studies indicate two different directions, that is, some argue that AI/robots (Industry 4.0) will increase human jobs whereas others argue that jobs could disappear. At the same time, the demographic perspective indicates that a purely economic employment-focused view of AI/robots is bound to lead to inconclusive results. Assuming that this is a probable concern, the authors summarize selected measures taken by governments as well as the various options that have been considered in academic literature to introduce taxes on AI/robots. Subsequently, the authors analyse the various “taxing” options from the perspective of commonly accepted tax policy principles applicable to electronic commerce (Ottawa Taxation Framework conditions). This analysis indicates that several proposals (e.g. proposals that treat AI/robots as independently taxable subjects or proposals that attribute income to owners of AI/robots) breach the principles of (i) neutrality; (ii) simplicity and certainty; (iii) efficiency; (iv) effectiveness and fairness; and (v) flexibility. Thus, such measures should not be pursued. The authors also conclude that, at this stage, targeted taxes on AI/robots should not be introduced, as this would also be contrary to the measures taken by governments globally to promote research and development (R&D) (input or output incentives). The present contribution therefore suggests that governments need to be proactive rather than reactive in this area. This could be achieved by monitoring the impact of AI/robots on a regular basis, and if the trend indicates that jobs are disappearing or revenues are declining, then the article suggests that states raise funds from an earmarked education tax. The funds raised from this tax, among other objectives, should be used to finance and foster professional educational programmes to reskill workers, besides assisting and guiding them to transition into new roles. However, a national measure may not be sufficient to tackle the issue (issues) at stake, especially in light of the demographic perspective discussed in the contribution. Thus, considering some jurisdictions may not be in a position to implement or fully benefit from an education tax, the authors also discuss the possibility of implementing a global fiscal redistribution mechanism (multilateral solution) from developed (surrender jurisdictions) to developing countries (recipient jurisdictions). The latter, depending on its scope, could be in the form of a global education tax or more broadly a planetary tax

Inertia-based spectrum slicing for symmetric quadratic eigenvalue problems

[EN] In the quadratic eigenvalue problem (QEP) with all coefficient matrices symmetric, there can be complex eigenvalues. However, some applications need to compute real eigenvalues only. We propose a Lanczos-based method for computing all real eigenvalues contained in a given interval of large-scale symmetric QEPs. The method uses matrix inertias of the quadratic polynomial evaluated at different shift values. In this way, for hyperbolic problems, it is possible to make sure that all eigenvalues in the interval have been computed. We also discuss the general nonhyperbolic case. Our implementation is memory-efficient by representing the computed pseudo-Lanczos basis in a compact tensor product representation. We show results of computational experiments with a parallel implementation in the SLEPc library.Agencia Estatal de Investigacion, Grant/Award Number: TIN2016-75985-PCampos, C.; Román Moltó, JE. (2020). Inertia-based spectrum slicing for symmetric quadratic eigenvalue problems. Numerical Linear Algebra with Applications. 27(4):1-17. https://doi.org/10.1002/nla.2293S117274Tisseur, F., & Meerbergen, K. (2001). The Quadratic Eigenvalue Problem. SIAM Review, 43(2), 235-286. doi:10.1137/s0036144500381988Veselić, K. (2011). Damped Oscillations of Linear Systems. Lecture Notes in Mathematics. doi:10.1007/978-3-642-21335-9Grimes, R. G., Lewis, J. G., & Simon, H. D. (1994). A Shifted Block Lanczos Algorithm for Solving Sparse Symmetric Generalized Eigenproblems. SIAM Journal on Matrix Analysis and Applications, 15(1), 228-272. doi:10.1137/s0895479888151111Campos, C., & Roman, J. E. (2012). Strategies for spectrum slicing based on restarted Lanczos methods. Numerical Algorithms, 60(2), 279-295. doi:10.1007/s11075-012-9564-zLi, R., Xi, Y., Vecharynski, E., Yang, C., & Saad, Y. (2016). A Thick-Restart Lanczos Algorithm with Polynomial Filtering for Hermitian Eigenvalue Problems. SIAM Journal on Scientific Computing, 38(4), A2512-A2534. doi:10.1137/15m1054493Guo, C.-H., Higham, N. J., & Tisseur, F. (2010). An Improved Arc Algorithm for Detecting Definite Hermitian Pairs. SIAM Journal on Matrix Analysis and Applications, 31(3), 1131-1151. doi:10.1137/08074218xNiendorf, V., & Voss, H. (2010). Detecting hyperbolic and definite matrix polynomials. Linear Algebra and its Applications, 432(4), 1017-1035. doi:10.1016/j.laa.2009.10.014NakatsukasaY NoferiniV. Inertia laws and localization of real eigenvalues for generalized indefinite eigenvalue problems;2017. Preprint arXiv:1711.00495.Parlett, B. N., & Chen, H. C. (1990). Use of indefinite pencils for computing damped natural modes. Linear Algebra and its Applications, 140, 53-88. doi:10.1016/0024-3795(90)90222-xCampos, C., & Roman, J. E. (2016). Restarted Q-Arnoldi-type methods exploiting symmetry in quadratic eigenvalue problems. BIT Numerical Mathematics, 56(4), 1213-1236. doi:10.1007/s10543-016-0601-5Guo, C.-H., & Lancaster, P. (2005). Algorithms for hyperbolic quadratic eigenvalue problems. Mathematics of Computation, 74(252), 1777-1792. doi:10.1090/s0025-5718-05-01748-5Li, H., & Cai, Y. (2015). Solving the real eigenvalues of hermitian quadratic eigenvalue problems via bisection. The Electronic Journal of Linear Algebra, 30, 721-743. doi:10.13001/1081-3810.1979RomanJE CamposC RomeroE andTomasA. SLEPc users manual. DSIC‐II/24/02–Revision 3.9. D. Sistemes Informàtics i Computació Universitat Politècnica de València;2018.Hernandez, V., Roman, J. E., & Vidal, V. (2005). SLEPc. ACM Transactions on Mathematical Software, 31(3), 351-362. doi:10.1145/1089014.1089019Guo, J.-S., Lin, W.-W., & Wang, C.-S. (1995). Numerical solutions for large sparse quadratic eigenvalue problems. Linear Algebra and its Applications, 225, 57-89. doi:10.1016/0024-3795(93)00318-tSleijpen, G. L. G., Booten, A. G. L., Fokkema, D. R., & van der Vorst, H. A. (1996). Jacobi-davidson type methods for generalized eigenproblems and polynomial eigenproblems. BIT Numerical Mathematics, 36(3), 595-633. doi:10.1007/bf01731936Bai, Z., & Su, Y. (2005). SOAR: A Second-order Arnoldi Method for the Solution of the Quadratic Eigenvalue Problem. SIAM Journal on Matrix Analysis and Applications, 26(3), 640-659. doi:10.1137/s0895479803438523Güttel, S., & Tisseur, F. (2017). The nonlinear eigenvalue problem. Acta Numerica, 26, 1-94. doi:10.1017/s0962492917000034Yang, L., Sun, Y., & Gong, F. (2018). The inexact residual iteration method for quadratic eigenvalue problem and the analysis of convergence. Journal of Computational and Applied Mathematics, 332, 45-55. doi:10.1016/j.cam.2017.10.003Keçeli, M., Corsetti, F., Campos, C., Roman, J. E., Zhang, H., Vázquez-Mayagoitia, Á., … Wagner, A. F. (2018). SIESTA-SIPs: Massively parallel spectrum-slicing eigensolver for an ab initio molecular dynamics package. Journal of Computational Chemistry, 39(22), 1806-1814. doi:10.1002/jcc.25350Voss, H., Werner, B., & Hadeler, K. P. (1982). A minimax principle for nonlinear eigenvalue problems with applications to nonoverdamped systems. Mathematical Methods in the Applied Sciences, 4(1), 415-424. doi:10.1002/mma.1670040126Higham, N. J., Mackey, D. S., & Tisseur, F. (2009). Definite Matrix Polynomials and their Linearization by Definite Pencils. SIAM Journal on Matrix Analysis and Applications, 31(2), 478-502. doi:10.1137/080721406Al-Ammari, M., & Tisseur, F. (2012). Hermitian matrix polynomials with real eigenvalues of definite type. Part I: Classification. Linear Algebra and its Applications, 436(10), 3954-3973. doi:10.1016/j.laa.2010.08.035Gohberg, I., Lancaster, P., & Rodman, L. (1980). Spectral Analysis of Selfadjoint Matrix Polynomials. The Annals of Mathematics, 112(1), 33. doi:10.2307/1971320RozložnÍk, M., Okulicka-DŁużewska, F., & Smoktunowicz, A. (2015). Cholesky-Like Factorization of Symmetric Indefinite Matrices and Orthogonalization with Respect to Bilinear Forms. SIAM Journal on Matrix Analysis and Applications, 36(2), 727-751. doi:10.1137/130947003Lu, D., Su, Y., & Bai, Z. (2016). Stability Analysis of the Two-level Orthogonal Arnoldi Procedure. SIAM Journal on Matrix Analysis and Applications, 37(1), 195-214. doi:10.1137/151005142Campos, C., & Roman, J. E. (2016). Parallel Krylov Solvers for the Polynomial Eigenvalue Problem in SLEPc. SIAM Journal on Scientific Computing, 38(5), S385-S411. doi:10.1137/15m1022458Higham, N. J., Mackey, D. S., Mackey, N., & Tisseur, F. (2007). Symmetric Linearizations for Matrix Polynomials. SIAM Journal on Matrix Analysis and Applications, 29(1), 143-159. doi:10.1137/050646202BalayS AbhyankarS AdamsM et al. PETSc users manual. ANL‐95/11 ‐ Revision 3.10. Argonne National Laboratory;2018.Betcke, T., Higham, N. J., Mehrmann, V., Schröder, C., & Tisseur, F. (2013). NLEVP. ACM Transactions on Mathematical Software, 39(2), 1-28. doi:10.1145/2427023.2427024Assink, J., Waxler, R., & Velea, D. (2017). A wide-angle high Mach number modal expansion for infrasound propagation. The Journal of the Acoustical Society of America, 141(3), 1781-1792. doi:10.1121/1.497757

The role of inflation in creating the key policy rate – validation of Taylor's Rule in case of Serbia

Debido a las altas expectativas de inflación, el Banco Nacional de Serbia ha elegido la estabilidad de precios como el objetivo principal de la política monetaria y la tasa de política clave como el principal instrumento de regulación monetaria. Sin embargo, a pesar de la regla de Taylor claramente definida, la tasa de política clave no siempre sigue el movimiento de la tasa de inflación. En consecuencia, el objetivo de este estudio es evaluar los efectos de la tasa de inflación en la tasa clave de política y la posibilidad de utilizar la regla de Taylor en las condiciones originales de baja inflación. Con base en el objeto definido de la investigación, probamos la siguiente hipótesis: la tasa de inflación tuvo un impacto estadísticamente significativo en la tasa de política clave en todo el período analizado, entre 2007 y 2015. La misma observación se probó para dos subperíodos entre 2007 y 2011 y entre 2012 y 2015. Por lo tanto, se puede concluir que existe un impacto medio estadísticamente significativo de la tasa de inflación en la tasa de política clave, pero la representatividad del modelo podría ser mayor. La falta de reacción de la tasa clave de política monetaria a la inflación enfatiza la necesidad de redefinir los instrumentos de política monetaria y modificar la estrategia de metas de inflación.Due to high inflation expectations, the National Bank of Serbia has chosen price stability as the primary objective of monetary policy and the key policy rate as the main instrument of monetary regulation. However, despite a clearly defined Taylor rule, the key policy rate does not always follow the movement of the rate of inflation. Accordingly, the aim of this study is to test the effects of inflation rate on the key policy rate and the possibility of using Taylor rule in the original conditions of low inflation. Based on the defined object of the research, we tested the following hypothesis: inflation rate had statistically significant impact on the key policy rate in the whole analyzed period, between 2007 and 2015. The same observation was tested for two sub-periods between 2007 and 2011 and between 2012 and 2015. Therefore, it can be concluded that there is statistically significant moderate impact of inflation rate on the key policy rate, but representativeness of the model could be higher. The lack of reaction of the key policy rate to inflation stresses the need for redefining monetary policy instruments and modifying the strategy of inflation targeting

Pregled predavanja održanih na VI internacionalnom kongresu geometara 1938 godine

Pregled predavanja održanih na VI internacionalnom kongresu geometara 1938 godine

Uloga katastarskog plana u narodnoj privredi

Uloga katastarskog plana u narodnoj privredi

Uloga katastarskog plana u narodnoj privredi

Uloga katastarskog plana u narodnoj privredi

[Odontodysplasia]

Odontodsplasia predstavlja vrlo retku razvojnu anomaliju zuba. Nije karakteristična za spol i rasu. Napada lokalne površine obe vilice i obe denticije. Rendgenogram pokazuje karakteristične deficite gledjia naročito dentina. Etiologija nepoznata.Odontođysplasia presents rare development anoma\u27y of teeht. It is not characteristić for race and sex. It affects local surfaces of both jaws and bcth primary and succedaneous teeth. Roentgenographic examinations reveal characteristic deficient of enamel and especialiy dentin. Etiology is unknown.Odontodysplasia is eine seltene Er.twickiungsanomalie der Zahne, die keine Rasssn cder Geshlecht-karakteristick darstellt. Sie betrifft beide Kiefer, die Milchzahne wie bleibendes Gebiss. Rentgenographische Untresuuchnugen ziegen gewisse Veranderungen in Zahn supstanzen, besonders im Dentin. Die Aetioiogie ist unbekannt