Cation Hydration Energy and Surface Hydration Have Crucial Role On Thermodynamics of Clay Swelling

The swelling capacity and stability of clay play a crucial role in various areas ranging from cosmetics to oil extraction; hence change in their swelling behavior after cation exchange with the surrounding medium is important for their efficient utilization. Here we focus on understanding the role of different hydration properties of cation on the thermodynamics of clay swelling by water adsorption. We have used mica as the reference clay, Na+, Li+, and H+ ions as the interstitial cations, and performed grand canonical Monte Carlo simulations of water adsorption in mica pores (of widths d = 4−40 Å). We found that water adsorption in Na-, Li- and H-mica pores is qualitatively similar; however significant quantitative differences are observed, especially at smaller d. Higher water density in H-mica pores (ρH) was expected due to the smaller size of H+ ions having higher hydration energy. However, a counter-intuitive trend of ρLi > ρNa > ρb (bulk density) > ρH was observed due to adsorption energy where the contribution of mica framework atoms was also found to be significant. The disjoining pressure (Π), swelling free energy (∆Ωex), and several structural properties of confined water and ions were calculated to perform thermodynamic analysis of the system. Our detailed calculations have captured the structural evolution of ions and water, especially the transitions from mono- to bi- and multilayer as a function of d. Oscillatory behavior in the Π and ∆Ωex profiles with diminishing to zero for d ≥ 11 Å is observed in all three mica systems. A shift in the location of global minima of ∆Ωex towards the higher d values and ∆Ωex becoming more repulsive is observed in the increasing order of hydration energy of Na+, Li+, and H + ions. The ∆Ωex for Na-mica is characterized by global minima at d = 6 Å corresponding to crystalline swelling, a significant barrier for crystalline swelling from d = 6 to 9 Å and lower for crystalline (d = 9 Å) to osmotic swelling (d > 12 Å). For Li-mica, the energy barrier for crystalline to osmotic swelling is lesser compared to the Na-mica system, whereas for H-mica the ∆Ωex > 0 for all d thus favoring osmotic swelling. We found that the hydration of cations by surface atoms plays a key role in the thermodynamics of clay swelling. The Na+ ions hydrate more number of surface oxygens, act as anchors, and hold the mica pore at d = 6 Å by sharing hydrating water with ions of opposite sides forming an electrostatically connected bridge of mica Na-water-Na-mica. The Li+ ions do hydrate surface oxygen atoms, albeit lesser number and sharing of hydration shell with nearby Li+ ions is also minimum. Both, surface hydration and water sharing, is minimum in the H+ ion case, as they are mostly present in the center of the pore as diffusive ions; thus exerting a consistent osmotic pressure on the mica frameworks, favoring swelling.

Symmetry-protected solitons and bulk-boundary correspondence in generalized Jackiw–Rebbi models

We investigate the roles of symmetry and bulk-boundary correspondence in characterizing topological edge states in generalized Jackiw–Rebbi (JR) models. We show that time-reversal (T), charge-conjugation (C), parity (P), and discrete internal field rotation ($$Z_n$$ Z n ) symmetries protect and characterize the various types of edge states such as chiral and nonchiral solitons via bulk-boundary correspondence in the presence of the multiple vacua. As two representative models, we consider the JR model composed of a single fermion field having a complex mass and the generalized JR model with two massless but interacting fermion fields. The JR model shows nonchiral solitons with the $$Z_2$$ Z 2 rotation symmetry, whereas it shows chiral solitons with the broken $$Z_2$$ Z 2 rotation symmetry. In the generalized JR model, only nonchiral solitons can emerge with only $$Z_2$$ Z 2 rotation symmetry, whereas both chiral and nonchiral solitons can exist with enhanced $$Z_4$$ Z 4 rotation symmetry. Moreover, we find that the nonchiral solitons have C, P symmetries while the chiral solitons do not, which can be explained by the symmetry-invariant lines connecting degenerate vacua. Finally, we find the symmetry correspondence between multiply-degenerate global vacua and solitons such that T, C, P symmetries of a soliton inherit from global minima that are connected by the soliton, which provides a novel tool for the characterization of topological solitons.

A Qualidade da colonoscopia de um serviço Brasileiro de alto fluxo medida através da taxa de detecção de adenomas

INTRODUÇÃO. Evidências mostram que a maioria dos Cânceres Colorretais pós-colonoscopia de rastreio são atribuíveis a lesões não detectadas e/ou por polipectomia incompleta. A Taxa de Detecção de Adenomas (TDA) é definida pela prevalência em que pelo menos um adenoma é encontrado em colonoscopias de rastreio de pacientes assintomáticos e de risco habitual para o Câncer Colorretal (CCR), sendo um importante indicador de qualidade de colonoscopias de um colonoscopista ou de um serviço de colonoscopias. Devido a isso, a Sociedade Americana de Endoscopia Gastrointestinal (ASGE) e o Colégio Americano de Gastroenterologia (ACG) criou metas mínimas de TDA como referência de qualidade mínima de colonoscopias, sendo estabelecido uma TDA global mínima de 25%, de 30% para amostras de pacientes masculinos e 20% para amostras de pacientes femininos. Ainda, é estabelecido que TDAs mais elevadas se associam com um risco reduzido de CCR. OBJETIVOS. Este trabalho objetiva medir a TDA de um serviço de endoscopia brasileiro de alta demanda e comparar com os valores de referência propostos pela ASGE. MÉTODOS. Estudo transversal, descritivo e documental a partir de prontuários de pacientes da clínica Gastrocenter e do laboratório de Anatomia Patológica Virchow submetidos à colonoscopia no período de novembro de 2017 a novembro de 2018. Após avaliação de critérios de inclusão e exclusão, foram avaliadas 757 colonoscopias de rastreio de CCR de pacientes entre 45 e 85 anos de risco habitual. Os exames foram realizados por 12 colonoscopistas. Após avaliação dos dados encontrados eles foram confrontados com a literatura. RESULTADOS. Das 757 colonoscopias avaliadas, 390 era de pacientes do sexo feminino e 367 eram de pacientes do sexo masculino. No total foram encontrados e avaliados 307 adenomas, sendo 162 em pacientes do sexo feminino e 145 em pacientes do sexo masculino. A TDA global foi calculada em 40,5%, sendo de 39,5% entre pacientes masculinos e de 41,5% entre pacientes femininos. Todos os valores foram superiores de forma estatisticamente significativa. DISCUSSÃO. Alguns aspectos em relação a elevada TDA do serviço podem ser ressaltadas como a elevada experiência em número de exames realizados pelo corpo médico do serviço, o baixo índice de preparos inadequados de cólon e a sedação realizada exclusivamente por médico anestesiologista. CONCLUSÃO. A TDA encontrada no serviço estudado neste trabalho foi consideravelmente maior que o piso da TDA estabelecido pela ASGE. Os resultados contaram com significância estatística tanto na comparação entre o TDA geral do trabalho e o TDA recomendado pela literatura, quanto na mesma comparação entre os TDAs de cada sexo individualmente.

Combinatorial optimization by weight annealing in memristive hopfield networks

The increasing utility of specialized circuits and growing applications of optimization call for the development of efficient hardware accelerator for solving optimization problems. Hopfield neural network is a promising approach for solving combinatorial optimization problems due to the recent demonstrations of efficient mixed-signal implementation based on emerging non-volatile memory devices. Such mixed-signal accelerators also enable very efficient implementation of various annealing techniques, which are essential for finding optimal solutions. Here we propose a “weight annealing” approach, whose main idea is to ease convergence to the global minima by keeping the network close to its ground state. This is achieved by initially setting all synaptic weights to zero, thus ensuring a quick transition of the Hopfield network to its trivial global minima state and then gradually introducing weights during the annealing process. The extensive numerical simulations show that our approach leads to a better, on average, solutions for several representative combinatorial problems compared to prior Hopfield neural network solvers with chaotic or stochastic annealing. As a proof of concept, a 13-node graph partitioning problem and a 7-node maximum-weight independent set problem are solved experimentally using mixed-signal circuits based on, correspondingly, a 20 × 20 analog-grade TiO2 memristive crossbar and a 12 × 10 eFlash memory array.

A new Multi Sine-Cosine algorithm for unconstrained optimization problems

The Sine-Cosine algorithm (SCA) is a population-based metaheuristic algorithm utilizing sine and cosine functions to perform search. To enable the search process, SCA incorporates several search parameters. But sometimes, these parameters make the search in SCA vulnerable to local minima/maxima. To overcome this problem, a new Multi Sine-Cosine algorithm (MSCA) is proposed in this paper. MSCA utilizes multiple swarm clusters to diversify & intensify the search in-order to avoid the local minima/maxima problem. Secondly, during update MSCA also checks for better search clusters that offer convergence to global minima effectively. To assess its performance, we tested the MSCA on unimodal, multimodal and composite benchmark functions taken from the literature. Experimental results reveal that the MSCA is statistically superior with regards to convergence as compared to recent state-of-the-art metaheuristic algorithms, including the original SCA.

An existence level for the residual sum of squares of the power-law regression with an unknown location parameter

In a recent paper [JUKIĆ, D.: A necessary and sufficient criterion for the existence of the global minima of a continuous lower bounded function on a noncompact set, J. Comput. Appl. Math. 375 (2020)], a new existence level was introduced and then was used to obtain a necessary and sufficient criterion for the existence of the global minima of a continuous lower bounded function on a noncompact set. In this paper, we determined that existence level for the residual sum of squares of the power-law regression with an unknown location parameter, and so we obtained a necessary and sufficient condition which guarantee the existence of the least squares estimate.

Predicting the Conformational Variability of Oncogenic GTP-bound G12D Mutated KRas-4B Proteins at Cell Membranes

KRas proteins are the largest family of mutated Ras isoforms, participating in a wide variety of cancers. Due to their importance, large effort is being carried out on drug development by small-molecule inhibitors. However, understanding protein conformational variability remains a challenge in drug discovery. In the case of the Ras family, their multiple conformational states can affect the binding of potential drug inhibitors. To overcome this challenge, we propose a computational framework based on combined all-atom Molecular Dynamics and Metadynamics simulations able to accurately access conformational variants of the target protein. We tested the methodology using a G12D mutated GTP bound oncogenic KRas-4B protein located at the interface of a DOPC/DOPS/cholesterol model anionic cell membrane. Two main orientations of KRas-4B at the anionic membrane have been obtained and explored. The corresponding angles have been taken as reliable reaction coordinates so that free-energy landscapes have been obtained by well-tempered metadynamics simulations, revealing the local and global minima of KRas-4B binding to the cell membrane, unvealing reactive paths of the system between the two preferential orientations and highlighting opportunities for targeting the unique metastable states through the identification of druggable pockets.

Dimension-Wise Particle Swarm Optimization: Evaluation and Comparative Analysis

This article evaluates a recently introduced algorithm that adjusts each dimension in particle swarm optimization semi-independently and compares it with the traditional particle swarm optimization. In addition, the comparison is extended to differential evolution and genetic algorithm. This presented comparative study provides a clear exposition of the effects introduced by the proposed algorithm. Performance of all evaluated optimizers is evaluated based on how well they perform in finding the global minima of 24 multi-dimensional benchmark functions, each having 7, 14, or 21 dimensions. Each algorithm is put through a session of self-tuning with 100 iterations to ensure convergence of their respective optimization parameters. The results confirm that the new variant is a significant improvement over the traditional algorithm. It also obtained notably better results than differential evolution when applied to problems with high-dimensional spaces relative to the number of available particles.

Logistic Regression for Gastric Cancer Classification using epidemiological risk factors in Cases and Controls

The main purpose of this study is to design a machine learning classifier that can accurately classify between gastric cancer (cases) patient and healthy individuals (controls) from epidemiological and environmental factors. The dataset contains missing values which are replaced by median using imputation technique. The basic idea of this work is to reduce the cost function by applying gradient descent to detect the optimal global minima. The proposed logistic regression has utilized 29 features as the input and produces an accuracy of 98.51%. This accuracy is achieved with learning rate 0.000915 and number of iterations 150000, which are devised for training the logistic regression model.