No Arabic abstract
Our paper offers an analysis of how Dante describes the tre giri (three rings) of the Holy Trinity in Paradiso 33 of the Divine Comedy. We point to the myriad possibilities Dante may have been envisioning when he describes his vision of God at this final stage in his journey. Saiber focuses on the features of shape, motion, size, color, and orientation that Dante details in describing the Trinity. Mbirika uses mathematical tools from topology (specifically, knot theory) and combinatorics to analyze all the possible configurations that have a specific layout of three intertwining circles which we find particularly compelling given Dantes description of the Trinity: the round figures arranged in a triangular format with rotational and reflective symmetry. Of the many possible link patterns, we isolate two particularly suggestive arrangements for the giri: the Brunnian link and the (3,3)-torus link. These two patterns lend themselves readily to a Trinitarian model.
We suggest a method of solving the problem of existence of a triangle with prescribed two bisectors and one third element which can be taken as one of the angles, the sides, the heights or the medians, or the third bisector.
Using the standard Coxeter presentation for the symmetric group $S_n$, two reduced expressions for the same group element are said to be commutation equivalent if we can obtain one expression from the other by applying a finite sequence of commutations. The resulting equivalence classes of reduced expressions are called commutation classes. How many commutation classes are there for the longest element in $S_n$?
In this paper JK_s data from the VISTA Magellanic Cloud (VMC) survey are used to investigate the tip of the red giant branch (TRGB) as a distance indicator. A linear fit to recent theoretical models is used which reads M_{K_s} = -4.196 -2.013 (J-K_s), valid in the colour range 0.75 < (J-K_s) < 1.3 mag and in the 2MASS system. The observed TRGB is found based on a classical first-order and a second-order derivative filter applied to the binned luminosity function using the sharpened magnitude that takes the colour term into account. Extensive simulations are carried out to investigate any biases and errors in the derived distance modulus (DM). Based on these simulations criteria are established related to the number of stars per bin in the 0.5 magnitude range below the TRGB and related to the significance with which the peak in the filter response curve is determined such that the derived distances are unbiased. The DMs based on the second-order derivative filter are found to be more stable and are therefore adopted, although this requires twice as many stars per bin. The TRGB method is applied to specific lines-of-sight where independent distance estimates exist, based on detached eclipsing binaries in the LMC and SMC, classical Cepheids in the LMC, RR Lyrae stars in the SMC, and fields in the SMC where the star formation history (together with reddening and distance) has been derived from deep VMC data. The analysis shows that the theoretical calibration is consistent with the data, that the systematic error on the DM is approximately 0.045 mag, and that random errors of 0.015 mag are achievable. Reddening is an important element in deriving the distance: we find mean DMs ranging from 18.92 (for a typical E(B-V) of 0.15 mag) to 19.07 mag (E(B-V) about 0.04) for the SMC, and ranging from 18.48 (E(B-V) about 0.12 mag) to 18.57 mag (E(B-V) about 0.05) for the LMC.
Appearing in 1921 as an equation for small-amplitude waves on the surface of an infinitely deep liquid, the Nekrasov equation quickly became a source of new results. This manifested itself both in the field of mathematics (theory of nonlinear integral equations of A.I. Nekrasov; 1922, later - of N.N. Nazarov; 1941), and in the field of mechanics (transition to a fluid of finite depth - A.I. Nekrasov; 1927 and refusal on the smallness of the wave amplitude - Yu.P. Krasovskii; 1960).The main task of the author is to find out the prehistory of the Nekrasov equation and to trace the change in approaches to its solution in the context of the nonlinear functional analysis development in the 1940s - 1960s. Close attention will be paid to the contribution of European and Russian mathematicians and mechanics: A.M. Lyapunov, E. Schmidt, T. Levi-Civita, A. Villat, L. Lichtenstein, M.A. Krasnoselskii, N.N. Moiseev, V.V. Pokornyi, etc. In the context of the development of qualitative methods for the Nekrasov equation investigating, the question of the interaction between Voronezh school of nonlinear functional analysis under the guidance of Professor M.A. Krasnoselskii and Rostov school of nonlinear mechanics under the guidance of Professor I.I. Vorovich.
We survey recent results on the mathematical stability of Bitcoin protocol. Profitability and probability of a double spend are estimated in closed form with classical special functions. The stability of Bitcoin mining rules is analyzed and several theorems are proved using martingale and combinatorics techniques. In particular, the empirical observation of the stability of the Bitcoin protocol is proved. This survey article on the mathematics of Bitcoin is published by the Newsletter of the European Mathematical Society, vol.115, 2020, p.31-37. Continuation of arXiv:1601.05254 (EMS Newsletter, 100, 2016 p.32).