Влияние льдообразования в трещинах на поле температур в холодном слое ледника

The work focuses on modeling the warming of a glacier due to heat release during the refreezing of meltwater in glacier crevasses (cryo-hydrologic warming). The simulation is performed for a polythermal Arctic glacier with a regular network of crevasses filled with water at 0 °C, for the1-year period of freezing of water in crevasses in the cold layer of a glacier, below the active layer. The upper (active layer base) and lower (initial cold-temperate transition surface) boundaries of the cold layer are considered horizontal planes; the crevasses are assumed to be identical narrow straight parallel water-filled channels. These assumptions allow considering the corresponding mathematical problem in a 2D setting. The time-dependent temperature distribution in the modeled domain is calculated explicitly as the solution to a 2D initial boundary value problem for the heat equation with spatially distributed heat sources that model the network of crevasses. The initial temperature distribution and the spatial parameters of the model are set based on the field data from the polythermal glacier Austre Grønfjordbreen (Svalbard). For a fixed geometry of the crevasses (the distance between neighboring crevasses is 10 m, the depth is 10 m, the width is of order 0.1 m) we performed an analytical-solution-based simulation of the temperature field at the end of a year-long period of heating varying the active layer base temperature (-3, -2 °C) and the initial thickness of the cold layer (20, 40, 60 m). The results suggest that the temperature field is more influenced by the cold layer thickness than the upper boundary temperature. The maximum temperature increment is 1–2 °C depending on the simulated case. The cold-temperate transition surface shifts up under the crevasse area by a maximum of 3.4 m (only in the case of 20-m cold layer). The temperature field remains unperturbed at a distance of 20 m or more in any direction from the crevasse zone. Our results may be useful for quantitative comparison of cryo-hydrologic warming with other factors of the temperature state of glaciers.Для условий ледника Восточный Грёнфьорд (Западный Шпицберген) выполнено моделирование изменений температурного поля в холодном слое в конце годового периода отепления за счёт замерзания воды в трещинах. Показано, что температура в леднике повысится на 1–2 °C, граница холодного и тёплого льда сместится вверх максимум на 3,4 м, возмущения температурного поля распространятся не далее 20 м от области трещиноватости

Fuchs versus Painlev\'e

We briefly recall the Fuchs-Painlev\'e elliptic representation of Painlev\'e VI. We then show that the polynomiality of the expressions of the correlation functions (and form factors) in terms of the complete elliptic integral of the first and second kind, $K$ and $E$, is a straight consequence of the fact that the differential operators corresponding to the entries of Toeplitz-like determinants, are equivalent to the second order operator $L_E$ which has $E$ as solution (or, for off-diagonal correlations to the direct sum of $L_E$ and $d/dt$). We show that this can be generalized, mutatis mutandis, to the anisotropic Ising model. The singled-out second order linear differential operator $L_E$ being replaced by an isomonodromic system of two third-order linear partial differential operators associated with $\Pi_1$, the Jacobi's form of the complete elliptic integral of the third kind (or equivalently two second order linear partial differential operators associated with Appell functions, where one of these operators can be seen as a deformation of $L_E$). We finally explore the generalizations, to the anisotropic Ising models, of the links we made, in two previous papers, between Painlev\'e non-linear ODE's, Fuchsian linear ODE's and elliptic curves. In particular the elliptic representation of Painlev\'e VI has to be generalized to an ``Appellian'' representation of Garnier systems.Comment: Dedicated to the : Special issue on Symmetries and Integrability of Difference Equations, SIDE VII meeting held in Melbourne during July 200

The RNA acetyltransferase driven by ATP hydrolysis synthesizes N4-acetylcytidine of tRNA anticodon

The wobble base of Escherichia coli elongator tRNAMet is modified to N4-acetylcytidine (ac4C), which is thought to ensure the precise recognition of the AUG codon by preventing misreading of near-cognate AUA codon. By employing genome-wide screen of uncharacterized genes in Escherichia coli (‘ribonucleome analysis'), we found the ypfI gene, which we named tmcA (tRNAMet cytidine acetyltransferase), to be responsible for ac4C formation. TmcA is an enzyme that contains a Walker-type ATPase domain in its N-terminal region and an N-acetyltransferase domain in its C-terminal region. Recombinant TmcA specifically acetylated the wobble base of E. coli elongator tRNAMet by utilizing acetyl-coenzyme A (CoA) and ATP (or GTP). ATP/GTP hydrolysis by TmcA is stimulated in the presence of acetyl-CoA and tRNAMet. A mutation study revealed that E. coli TmcA strictly discriminates elongator tRNAMet from the structurally similar tRNAIle by mainly recognizing the C27–G43 pair in the anticodon stem. Our findings reveal an elaborate mechanism embedded in tRNAMet and tRNAIle for the accurate decoding of AUA/AUG codons on the basis of the recognition of wobble bases by the respective RNA-modifying enzymes