Ahrer, E. M., Alderson, L., Batalha, N. M., Batalha, N. E., Bean, J. L., Beatty, T. G., et al. (2023). Identification of carbon dioxide in an exoplanet atmosphere. Nature, Early Access.
Abstract: Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (that is, elements heavier than helium, also called 'metallicity')(1-3), and thus the formation processes of the primary atmospheres of hot gas giants(4-6). It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets(7-9). Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2, but have not yielded definitive detections owing to the lack of unambiguous spectroscopic identification(10-12). Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science programme(13,14). The data used in this study span 3.0-5.5micrometres in wavelength and show a prominent CO2 absorption feature at 4.3micrometres (26-sigma significance). The overall spectrum is well matched by one-dimensional, ten-times solar metallicity models that assume radiative-convective-thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0micrometres that is not reproduced by these models.
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Aledo, J. A., Goles, E., Montalva-Medel, M., Montealegre, P., & Valverde, J. C. (2023). Symmetrizable Boolean networks. Inf. Sci., 626, 787–804.
Abstract: In this work, we provide a procedure that allows us to transform certain kinds of deterministic Boolean networks on minterm or maxterm functions into symmetric ones, so inferring that such symmetrizable networks can present only periodic points of periods 1 or 2. In particular, we deal with generalized parallel (or synchronous) dynamical systems (GPDS) over undirected graphs, i. e., discrete parallel dynamical systems over undirected graphs where some of the self-loops may not appear. We also study the class of anti-symmetric GPDS (which are non-symmetrizable), proving that their periodic orbits have period 4. In addition, we introduce a class of non-symmetrizable systems which admit periodic orbits with arbitrary large periods.
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Antico, F. C., Concha-Riedel, J., Valdivia, I., García Herrera, C., & Utrera, A. (2023). The fracture mechanical behavior of the interface between animal fibers, mortar, and earth matrices. A theoretical and experimental approach. Compos. B. Eng., 254, 110568.
Abstract: Theoretical-experimental research is presented to address the mechanics and failure mode of the interface between two matrices with brittle behavior, earth and mortar, and pig hair, an organic fiber that is a massive waste from the food industry worldwide. A comprehensive statistical analysis of the pull-out force is presented, accounting for the effect of fiber embedded length, diameter variability, and age of the matrices. Experimental results are contrasted with fracture-mechanics theories to describe its behavior in this matter. Results show that neither fiber length, variability of diameter, nor the age of the matrix influences the pull-out force of both matrices evaluated in this work. Our results show the brittle nature of these interfaces, which was also observed using a high-speed camera. The tensile load of the fibers was compared to the pull-out force, showing that these fibers always work within their elastic regime. This work contributes directly to the sustainable goals 9, 11, and 15 enacted by the United Nations in 2015, by contributing to the understanding of the fracture mechanics of a waste product used as reinforcement of construction matrices.
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Araya, H., Bahamonde, N., Fermín, L., Roa, T., & Torres, S. (2023). ON THE CONSISTENCY OF LEAST SQUARES ESTIMATOR IN MODELS SAMPLED AT RANDOM TIMES DRIVEN BY LONG MEMORY NOISE: THE JITTERED CASE. Stat. Sin., 33, 331–351.
Abstract: In numerous applications, data are observed at random times. Our main purpose is to study a model observed at random times that incorporates a long-memory noise process with a fractional Brownian Hurst exponent H. We propose a least squares estimator in a linear regression model with long-memory noise and a random sampling time called “jittered sampling”. Specifically, there is a fixed sampling rate 1/N, contaminated by an additive noise (the jitter) and governed by a probability density function supported in [0, 1/N]. The strong consistency of the estimator is established, with a convergence rate depending on N and the Hurst exponent. A Monte Carlo analysis supports the relevance of the theory and produces additional insights, with several levels of long-range dependence (varying the Hurst index) and two different jitter densities.
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Araya, H., Bahamonde, N., Fermin, L., Roa, T., & Torres, S. (2023). ON THE CONSISTENCY OF THE LEAST SQUARES ESTIMATOR IN MODELS SAMPLED AT RANDOM TIMES DRIVEN BY LONG MEMORY NOISE: THE RENEWAL CASE. Stat. Sin., 33, 1–26.
Abstract: In this study, we prove the strong consistency of the least squares estimator in a random sampled linear regression model with long-memory noise and an independent set of random times given by renewal process sampling. Additionally, we illustrate how to work with a random number of observations up to time T = 1. A simulation study is provided to illustrate the behavior of the different terms, as well as the performance of the estimator under various values of the Hurst parameter H.
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Arias-Garzón, D., Tabares-Soto, R., Bernal-Salcedo. J., & Ruz, G. A. (2023). Biases associated with database structure for COVID-19 detection in X-ray images. Sci. Rep., 13, 3477.
Abstract: Several artificial intelligence algorithms have been developed for COVID-19-related topics. One that has been common is the COVID-19 diagnosis using chest X-rays, where the eagerness to obtain early results has triggered the construction of a series of datasets where bias management has not been thorough from the point of view of patient information, capture conditions, class imbalance, and careless mixtures of multiple datasets. This paper analyses 19 datasets of COVID-19 chest X-ray images, identifying potential biases. Moreover, computational experiments were conducted using one of the most popular datasets in this domain, which obtains a 96.19% of classification accuracy on the complete dataset. Nevertheless, when evaluated with the ethical tool Aequitas, it fails on all the metrics. Ethical tools enhanced with some distribution and image quality considerations are the keys to developing or choosing a dataset with fewer bias issues. We aim to provide broad research on dataset problems, tools, and suggestions for future dataset developments and COVID-19 applications using chest X-ray images.
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Arulraj, A., Murugesan, P. K., Rajkumar, C., Zamorano, A. T., & Mangalaraja, R. V. (2023). Nanoarchitectonics of Layered Metal Chalcogenides-Based Ternary Electrocatalyst for Water Splitting. Energies, 16(4), 1669.
Abstract: The research on renewable energy is actively looking into electrocatalysts based on transition metal chalcogenides because nanostructured electrocatalysts support the higher intrinsic activity for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). A major technique for facilitating the conversion of renewable and sustainable energy is electrochemical water splitting. The aim of the review is to discuss the revelations made when trying to alter the internal and external nanoarchitectures of chalcogenides-based electrocatalysts to enhance their performance. To begin, a general explanation of the water-splitting reaction is given to clarify the key factors in determining the catalytic performance of nanostructured chalcogenides-based electrocatalysts. To delve into the many ways being employed to improve the HER's electrocatalytic performance, the general fabrication processes utilized to generate the chalcogenides-based materials are described. Similarly, to enhance the OER performance of chalcogenides-based electrocatalysts, the applied complementary techniques and the strategies involved in designing the bifunctional water-splitting electrocatalysts (HER and OER) are explained. As a conclusive remark, the challenges and future perspectives of chalcogenide-based electrocatalysts in the context of water splitting are summarized.
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Aylwin, R., & Jerez-Hanckes, C. (2023). Finite-Element Domain Approximation for Maxwell Variational Problems on Curved Domains. SIAM J. Numer. Anal., Early Access.
Abstract: We consider the problem of domain approximation in finite element methods for Maxwell equations on curved domains, i.e., when affine or polynomial meshes fail to exactly cover the domain of interest. In such cases, one is forced to approximate the domain by a sequence of polyhedral domains arising from inexact meshes. We deduce conditions on the quality of these approximations that ensure rates of error convergence between discrete solutions -- in the approximate domains -- to the continuous one in the original domain.
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Aylwin, R., Henriquez, F., & Schwab, C. (2023). ReLU Neural Network Galerkin BEM. J. Sci. Comput., 95(2), 41.
Abstract: We introduce Neural Network (NN for short) approximation architectures for the numerical solution of Boundary Integral Equations (BIEs for short). We exemplify the proposed NN approach for the boundary reduction of the potential problem in two spatial dimensions. We adopt a Galerkin formulation-based method, in polygonal domains with a finite number of straight sides. Trial spaces used in the Galerkin discretization of the BIEs are built by using NNs that, in turn, employ the so-called Rectified Linear Units (ReLU) as the underlying activation function. The ReLU-NNs used to approximate the solutions to the BIEs depend nonlinearly on the parameters characterizing the NNs themselves. Consequently, the computation of a numerical solution to a BIE by means of ReLU-NNs boils down to a fine tuning of these parameters, in network training. We argue that ReLU-NNs of fixed depth and with a variable width allow us to recover well-known approximation rate results for the standard Galerkin Boundary Element Method (BEM). This observation hinges on existing well-known properties concerning the regularity of the solution of the BIEs on Lipschitz, polygonal boundaries, i.e. accounting for the effect of corner singularities, and the expressive power of ReLU-NNs over different classes of functions. We prove that shallow ReLU-NNs, i.e. networks having a fixed, moderate depth but with increasing width, can achieve optimal order algebraic convergence rates. We propose novel loss functions for NN training which are obtained using computable, local residual a posteriori error estimators with ReLU-NNs for the numerical approximation of BIEs. We find that weighted residual estimators, which are reliable without further assumptions on the quasi-uniformity of the underlying mesh, can be employed for the construction of computationally efficient loss functions for ReLU-NN training. The proposed framework allows us to leverage on state-of-the-art computational deep learning technologies such as TENSORFLOW and TPUs for the numerical solution of BIEs using ReLU-NNs. Exploratory numerical experiments validate our theoretical findings and indicate the viability of the proposed ReLU-NN Galerkin BEM approach.
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Aylwin, R., Jerez-Hanckes, C., Schwab, C., & Zech, J. (2023). Multilevel Domain Uncertainty Quantification in Computational Electromagnetics. Math. Models Methods Appl. Sci., 33(04), 877–921.
Abstract: We continue our study [Domain Uncertainty Quantification in Computational Electromagnetics, JUQ (2020), 8:301--341] of the numerical approximation of time-harmonic electromagnetic fields for the Maxwell lossy cavity problem for uncertain geometries. We adopt the same affine-parametric shape parametrization framework, mapping the physical domains to a nominal polygonal domain with piecewise smooth maps. The regularity of the pullback solutions on the nominal domain is characterized in piecewise Sobolev spaces. We prove error convergence rates and optimize the algorithmic steering of parameters for edge-element discretizations in the nominal domain combined with: (a) multilevel Monte Carlo sampling, and (b) multilevel, sparse-grid quadrature for computing the expectation of the solutions with respect to uncertain domain ensembles. In addition, we analyze sparse-grid interpolation to compute surrogates of the domain-to-solution mappings. All calculations are performed on the polyhedral nominal domain, which enables the use of standard simplicial finite element meshes. We provide a rigorous fully discrete error analysis and show, in all cases, that dimension-independent algebraic convergence is achieved. For the multilevel sparse-grid quadrature methods, we prove higher order convergence rates which are free from the so-called curse of dimensionality, i.e. independent of the number of parameters used to parametrize the admissible shapes. Numerical experiments confirm our theoretical results and verify the superiority of the sparse-grid methods.
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Balocchi, F., Galleguillos, M., Rivera, D., Stehr, A., Arumi, J. L., Pizarro, R., et al. (2023). Forest hydrology in Chile: Past, present, and future. J. Hydrol., 616, 128681.
Abstract: This paper reviews the current knowledge of hydrological processes in Chilean temperate forests which extend along western South America from latitude 29 degrees S to 56 degrees S. This geographic region includes a diverse range of natural and planted forests and a broad sweep of vegetation, edaphic, topographic, geologic, and climatic set-tings which create a unique natural laboratory. Many local communities, endangered freshwater ecosystems, and downstream economic activities in Chile rely on water flows from forested catchments. This review aims to (i) provide a comprehensive overview of Chilean forest hydrology, to (ii) review prior research in forest hydrology in Chile, and to (iii) identify knowledge gaps and provide a vision for future research on forest hydrology in Chile. We reviewed the relation between native forests, commercial plantations, and other land uses on water yield and water quality from the plot to the catchment scale. Much of the global understanding of forests and their relationship with the water cycle is in line with the findings of the studies reviewed here. Streamflow from forested catchments increases after timber harvesting, native forests appear to use less water than plantations, and streams draining native forest yield less sediment than streams draining plantations or grassland/shrublands. We identified 20 key knowledge gaps such as forest groundwater systems, soil-plant-atmosphere interactions, native forest hydrology, and the effect of forest management and restoration on hydrology. Also, we found a paucity of research in the northern geographic areas and forest types (35-36 degrees S); most forest hydrology studies in Chile (56%) have been conducted in the southern area (Los Rios Region around 39-40 degrees S). There is limited knowledge of the geology and soils in many forested areas and how surface and groundwater are affected by changes in land cover. There is an opportunity to advance our understanding using process-based investigations linking field studies and modeling. Through the establishment of a forest hydrology science “society” to coor-dinate efforts, regional and national-scale land use planning might be supported. Our review ends with a vision to advance a cross-scale collaborative effort to use new nation-wide catchment-scale networks Long-term Ecosystem Research (LTER) sites, to promote common and
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Balocchi, F., Galleguillos, M., Rivera, D., Stehr, A., Arumi, J. L., Pizarro, R., et al. (2023). Forest Hydrology in Chile; paste, present, and future" (vol 616, 128681, 2023). J. Hydrol., 617(B), 129025.
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Benedikt, M., Kikot, S., Ostropolski-Nalewaja, P., & Romero, M. (2023). On Monotonic Determinacy and Rewritability for Recursive Queries and Views. ACM Trans. Comput. Log., 24(2), 16.
Abstract: A query Q is monotonically determined over a set of views V if Q can be expressed as a monotonic function of the view image. In the case of relational algebra views and queries, monotonic determinacy coincides with rewritability as a union of conjunctive queries, and it is decidable in important special cases, such as for conjunctive query views and queries. We investigate the situation for views and queries in the recursive query language Datalog. We give both positive and negative results about the ability to decide monotonic determinacy, and also about the co-incidence of monotonic determinacy with Datalog rewritability.
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Bhat, S. M., Ahmed, S., Bahar, A. N., Wahid, K. A., Otsuki, A., & Singh, P. (2023). Design of Cost-Efficient SRAM Cell in Quantum Dot Cellular Automata Technology. Electronics, 12(2), 367.
Abstract: SRAM or Static Random-Access Memory is the most vital memory technology. SRAM is fast and robust but faces design challenges in nanoscale CMOS such as high leakage, power consumption, and reliability. Quantum-dot Cellular Automata (QCA) is the alternative technology that can be used to address the challenges of conventional SRAM. In this paper, a cost-efficient single layer SRAM cell has been proposed in QCA. The design has 39 cells with a latency of 1.5 clock cycles and achieves an overall improvement in cell count, area, latency, and QCA cost compared to the reported designs. It can therefore be used to design nanoscale memory structures of higher order.
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Bravo, V., Hernandez, R., & Venegas, O. (2023). Two-Point Distortion Theorems for Harmonic Mappings. Bull. Malaysian Math. Sci., 46(3), 100.
Abstract: We establish two-point distortion theorems for sense-preserving planar harmonic map -pings f = h + g in the unit disk D which satisfy harmonic versions of the univalence criteria due to Becker and Nehari. In addition, we also find two-point distortion theo-rems for the cases when h is a normalized convex function and, more generally, when h(D) is a c-linearly connected domain.
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Bugedo, G., Tobar, E., Alegria, L., Oviedo, V., Arellano, D., Basoalto, R., et al. (2023). Development of mechanical ventilators in Chile. Chronicle of the initiative "Un Respiro para Chile. Rev. Med. Chile, 150(7), 958–965.
Abstract: At the beginning of the COVID-19 pandemic in Chile, in March 2020, a projection indicated that a significant group of patients with pneumonia would require admission to an Intensive Care Unit and connection to a mechanical ventilator. Therefore, a paucity of these devices and other supplies was predicted. The initiative “Un respiro para Chile” brought together many people and institutions, public and private. In the course of three months, it allowed the design and building of several ventilatory assistance devices, which could be used in critically ill patients.
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Caceres-Vasquez, J., Jara, D. H., Costamagna, J., Martinez-Gomez, F., Silva, C. P., Lemus, L., et al. (2023). Effect of non-covalent self-dimerization on the spectroscopic and electrochemical properties of mixed Cu(i) complexes. RSC Advances, 13(2), 825–838.
Abstract: A series of six new Cu(i) complexes with ([Cu(N-{4-R}pyridine-2-yl-methanimine)(PPh3)Br]) formulation, where R corresponds to a donor or acceptor p-substituent, have been synthesized and were used to study self-association effects on their structural and electrochemical properties. X-ray diffraction results showed that in all complexes the packing is organized from a dimer generated by supramolecular pi stacking and hydrogen bonding. H-1-NMR experiments at several concentrations showed that all complexes undergo a fast-self-association monomer-dimer equilibrium in solution, while changes in resonance frequency towards the high or low field in specific protons of the imine ligand allow establishing that dimers have similar structures to those found in the crystal. The thermodynamic parameters for this self-association process were calculated from dimerization constants determined by VT-H-1-NMR experiments for several concentrations at different temperatures. The values for K-D (4.0 to 70.0 M-1 range), Delta H (-1.4 to -2.6 kcal mol(-1) range), Delta S (-0.2 to 2.1 cal mol(-1) K-1 range), and Delta G(298) (-0.8 to -2.0 kcal mol(-1) range) are of the same order and indicate that the self-dimerization process is enthalpically driven for all complexes. The electrochemical profile of the complexes shows two redox Cu(ii)/Cu(i) processes whose relative intensities are sensitive to concentration changes, indicating that both species are in chemical equilibrium, with the monomer and the dimer having different electrochemical characteristics. We associate this behaviour with the structural lability of the Cu(i) centre that allows the monomeric molecules to reorder conformationally to achieve a more adequate assembly in the non-covalent dimer. As expected, structural properties in the solid and in solution, as well as their electrochemical properties, are not correlated with the electronic parameters usually used to evaluate R substituent effects. This confirms that the properties of the Cu(i) complexes are usually more influenced by steric effects than by the inductive effects of substituents of the ligands. In fact, the results obtained showed the importance of non-covalent inte
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Canessa, E., Chaigneau, S. E., Moreno, S., & Lagos, R. (2023). CPNCoverageAnalysis: An R package for parameter estimation in conceptual properties norming studies. Behav. Res. Methods, 55, 554–569.
Abstract: In conceptual properties norming studies (CPNs), participants list properties that describe a set of concepts. From CPNs, many different parameters are calculated, such as semantic richness. A generally overlooked issue is that those values are
only point estimates of the true unknown population parameters. In the present work, we present an R package that allows us to treat those values as population parameter estimates. Relatedly, a general practice in CPNs is using an equal number of participants who list properties for each concept (i.e., standardizing sample size). As we illustrate through examples, this procedure has negative effects on data�s statistical analyses. Here, we argue that a better method is to standardize coverage (i.e., the proportion of sampled properties to the total number of properties that describe a concept), such that a similar coverage is achieved across concepts. When standardizing coverage rather than sample size, it is more likely that the set of concepts in a CPN all exhibit a similar representativeness. Moreover, by computing coverage the researcher can decide whether the
CPN reached a sufficiently high coverage, so that its results might be generalizable to other studies. The R package we make available in the current work allows one to compute coverage and to estimate the necessary number of participants to reach a target coverage. We show this sampling procedure by using the R package on real and simulated CPN data.
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Carrasco, P., & Hernandez, R. (2023). Schwarzian derivative for convex mappings of order a. Anal. Math. Phys., 13(2), 22.
Abstract: The main purpose of this paper is to obtain sharp bounds of the norm of Schwarzian derivative for convex mappings of order alpha in terms of the value of f '' (0), in particular, when this quantity is equal to zero. In addition, we obtain sharp bounds for distortion and growth for this mappings and we generalize the results obtained by Suita (J Hokkaido Univ Ed Sect II A 46(2):113-117, 1996) and Yamashita (Hokkaido Math J 28:217-230, 1999) for this particular case.
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Chen, Y., Bo Liu, B., Luo, Y., Martinez-Villalobos, C., Guoyu Ren, G., Huang, Y., et al. (2023). Relative Contribution of Moisture Transport during TC-Active and TC-Inactive Periods to the Precipitation in Henan Province of North China: Mean State and an Extreme Event. J. Clim., 36(11), 3611–3623.
Abstract: A Lagrangian model—the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT)—is used to quantify changes in moisture sources and paths for precipitation over North China’s Henan Province associated with tropical cyclone (TC) over the western North Pacific (WNP) during July–August of 1979–2021. During TC-active periods, an anomalous cyclone over the WNP enhances southeasterly and reduces southwesterly moisture transport to Henan. Accordingly, compared to TC-inactive periods, moisture contributions from the Pacific Ocean (PO), eastern China (EC), and the local area (Local) are significantly enhanced by 48.32% (16.73% versus 11.28%), 20.42% (9.44% versus 7.84%), and 2.89% (4.91% versus 4.77%), respectively, while moisture contributions from the Indian Ocean (IO), Southwestern China (SWC), Eurasia (EA), and the South China Sea (SCS) are significantly reduced by −31.90% (8.61% versus 12.64%), −16.27% (4.60% versus 5.50%), −8.81% (19.10% versus 20.95%), and −6.92% (12.18% versus 13.09%). Furthermore, the moisture transport for a catastrophic extreme rainfall event during 17–22 July (“21⋅7” event) influenced by Typhoon Infa is investigated. Compared to the mean state during TC-active periods, the moisture contribution from the PO was substantially increased by 126.32% (37.87% versus 16.73%), while that from IO significantly decreased by −98.26% (0.15% versus 8.61%) during the “21⋅7” event. Analyses with a bootstrap resampling method show that moisture contributions from the PO fall outside the +6σ range, for both the TC-active and TC-inactive probability distributions. Thus, the “21⋅7” event is rare and extreme in terms of the moisture contribution from the PO, with the occurrence probability being less than 1 in 1 million times.
Significance Statement
Henan, one of the most populated provinces in China, experienced a catastrophic extreme precipitation event in July 2021 (the “21⋅7” event), coinciding with the activity of a tropical cyclone (TC) over the western North Pacific, which helps establish the moisture channel. Using a Lagrangian model, we provide a better understanding of how moisture transport changes associated with TC for the mean state of 1979–2021, and reveal how extreme is the moisture transport for the “21⋅7” event with the bootstrap technique. It is found that during active TC periods, the moisture contribution from the Pacific Ocean (the Indian Ocean) is significantly enhanced (reduced). For every 1 000 000 six-day events, less than one instance like the “21⋅7” event should be expected.
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