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1.
Phys Rev E ; 109(4-1): 044135, 2024 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-38755901

RESUMEN

We investigate steady-state current fluctuations in two models of hardcore run-and-tumble particles (RTPs) on a periodic one-dimensional lattice of L sites, for arbitrary tumbling rate γ=τ_{p}^{-1} and density ρ; model I consists of standard hardcore RTPs, while model II is an analytically tractable variant of model I, called a long-ranged lattice gas (LLG). We show that, in the limit of L large, the fluctuation of cumulative current Q_{i}(T,L) across the ith bond in a time interval T≫1/D grows first subdiffusively and then diffusively (linearly) with T: 〈Q_{i}^{2}〉∼T^{α} with α=1/2 for 1/D≪T≪L^{2}/D and α=1 for T≫L^{2}/D, where D(ρ,γ) is the collective- or bulk-diffusion coefficient; at small times T≪1/D, exponent α depends on the details. Remarkably, regardless of the model details, the scaled bond-current fluctuations D〈Q_{i}^{2}(T,L)〉/2χL≡W(y) as a function of scaled variable y=DT/L^{2} collapse onto a universal scaling curve W(y), where χ(ρ,γ) is the collective particle mobility. In the limit of small density and tumbling rate, ρ,γ→0, with ψ=ρ/γ fixed, there exists a scaling law: The scaled mobility γ^{a}χ(ρ,γ)/χ^{(0)}≡H(ψ) as a function of ψ collapses onto a scaling curve H(ψ), where a=1 and 2 in models I and II, respectively, and χ^{(0)} is the mobility in the limiting case of a symmetric simple exclusion process; notably, the scaling function H(ψ) is model dependent. For model II (LLG), we calculate exactly, within a truncation scheme, both the scaling functions, W(y) and H(ψ). We also calculate spatial correlation functions for the current and compare our theory with simulation results of model I; for both models, the correlation functions decay exponentially, with correlation length ξ∼τ_{p}^{1/2} diverging with persistence time τ_{p}≫1. Overall, our theory is in excellent agreement with simulations and complements the prior findings [T. Chakraborty and P. Pradhan, Phys. Rev. E 109, 024124 (2024)1539-375510.1103/PhysRevE.109.024124].

2.
Bioinformatics ; 40(4)2024 Mar 29.
Artículo en Inglés | MEDLINE | ID: mdl-38608194

RESUMEN

MOTIVATION: Dysregulation of a gene's function, either due to mutations or impairments in regulatory networks, often triggers pathological states in the affected tissue. Comprehensive mapping of these apparent gene-pathology relationships is an ever-daunting task, primarily due to genetic pleiotropy and lack of suitable computational approaches. With the advent of high throughput genomics platforms and community scale initiatives such as the Human Cell Landscape project, researchers have been able to create gene expression portraits of healthy tissues resolved at the level of single cells. However, a similar wealth of knowledge is currently not at our finger-tip when it comes to diseases. This is because the genetic manifestation of a disease is often quite diverse and is confounded by several clinical and demographic covariates. RESULTS: To circumvent this, we mined ∼18 million PubMed abstracts published till May 2019 and automatically selected ∼4.5 million of them that describe roles of particular genes in disease pathogenesis. Further, we fine-tuned the pretrained bidirectional encoder representations from transformers (BERT) for language modeling from the domain of natural language processing to learn vector representation of entities such as genes, diseases, tissues, cell-types, etc., in a way such that their relationship is preserved in a vector space. The repurposed BERT predicted disease-gene associations that are not cited in the training data, thereby highlighting the feasibility of in silico synthesis of hypotheses linking different biological entities such as genes and conditions. AVAILABILITY AND IMPLEMENTATION: PathoBERT pretrained model: https://github.com/Priyadarshini-Rai/Pathomap-Model. BioSentVec-based abstract classification model: https://github.com/Priyadarshini-Rai/Pathomap-Model. Pathomap R package: https://github.com/Priyadarshini-Rai/Pathomap.


Asunto(s)
Minería de Datos , Humanos , Minería de Datos/métodos , Biología Computacional/métodos , Procesamiento de Lenguaje Natural
3.
Phys Rev E ; 109(2-1): 024124, 2024 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-38491605

RESUMEN

We characterize collective diffusion of hardcore run-and-tumble particles (RTPs) by explicitly calculating the bulk-diffusion coefficient D(ρ,γ) for arbitrary density ρ and tumbling rate γ, in systems on a d-dimensional periodic lattice. We study two minimal models of RTPs: Model I is the standard version of hardcore RTPs introduced in [Phys. Rev. E 89, 012706 (2014)10.1103/PhysRevE.89.012706], whereas model II is a long-ranged lattice gas (LLG) with hardcore exclusion, an analytically tractable variant of model I. We calculate the bulk-diffusion coefficient analytically for model II and numerically for model I through an efficient Monte Carlo algorithm; notably, both models have qualitatively similar features. In the strong-persistence limit γ→0 (i.e., dimensionless ratio r_{0}γ/v→0), with v and r_{0} being the self-propulsion speed and particle diameter, respectively, the fascinating interplay between persistence and interaction is quantified in terms of two length scales: (i) persistence length l_{p}=v/γ and (ii) a "mean free path," being a measure of the average empty stretch or gap size in the hopping direction. We find that the bulk-diffusion coefficient varies as a power law in a wide range of density: D∝ρ^{-α}, with exponent α gradually crossing over from α=2 at high densities to α=0 at low densities. As a result, the density relaxation is governed by a nonlinear diffusion equation with anomalous spatiotemporal scaling. In the thermodynamic limit, we show that the bulk-diffusion coefficient-for ρ,γ→0 with ρ/γ fixed-has a scaling form D(ρ,γ)=D^{(0)}F(ρav/γ), where a∼r_{0}^{d-1} is particle cross section and D^{(0)} is proportional to the diffusion coefficient of noninteracting particles; the scaling function F(ψ) is calculated analytically for model II (LLG) and numerically for model I. Our arguments are independent of dimensions and microscopic details.

4.
BMC Infect Dis ; 24(1): 220, 2024 Feb 19.
Artículo en Inglés | MEDLINE | ID: mdl-38373908

RESUMEN

BACKGROUND: Invasive Aspergillosis (IA) is a life-threatening fungal disease with significant mortality rates. Timely diagnosis and treatment greatly enhance patient outcomes. This study aimed to explore the association between patient age and the development of IA, as well as the potential implications for risk stratification strategies. METHODS: We searched National Center for Biotechnology Information (NCBI) databases for publications until October 2023 containing age characteristics of patients with and without IA. A random-effects model with the application of inverse-variance weighting was used to pool reported estimates from each study, and meta-regression and subgroup analyses were utilized to assess sources of heterogeneity. RESULTS: A systematic review was conducted, resulting in the inclusion of 55 retrospective observational studies with a total of 13,983 patients. Meta-analysis revealed that, on average, patients with IA were approximately two and a half years older (95% Confidence Interval [CI] 1.84-3.31 years; I2 = 26.1%) than those without the disease (p < 0.0001). No significant moderators could explain the observed heterogeneity in age difference. However, subgroup analysis revealed that age differences were more pronounced within particular patient groups compared to others. For example, patients with and without IA who had primary severe lung infections exhibited a greater difference in mean age than other patient cohorts. CONCLUSIONS: Further research, such as individual patient data meta-analysis, is necessary to better understand the potential relationship between increasing age and the likelihood of IA. Improved risk stratification strategies based on patient age could potentially enhance the early detection and treatment of IA, ultimately improving patient outcomes.


Asunto(s)
Aspergilosis , Infecciones Fúngicas Invasoras , Humanos , Estudios Retrospectivos , Aspergilosis/diagnóstico , Aspergilosis/tratamiento farmacológico , Infecciones Fúngicas Invasoras/diagnóstico , Bases de Datos Factuales , Probabilidad
5.
Sci Rep ; 14(1): 1495, 2024 Jan 17.
Artículo en Inglés | MEDLINE | ID: mdl-38233406

RESUMEN

Inaccuracy in the All Indian Summer Monsoon Rainfall (AISMR) forecast has major repercussions for India's economy and people's daily lives. Improving the accuracy of AISMR forecasts remains a challenge. An attempt is made here to address this problem by taking advantage of recent advances in machine learning techniques. The data-driven models trained with historical AISMR data, the Niño3.4 index, and categorical Indian Ocean Dipole values outperform the traditional physical models, and the best-performing model predicts that the 2023 AISMR will be roughly 790 mm, which is typical of a normal monsoon year.

6.
Heliyon ; 9(9): e19991, 2023 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-37809886

RESUMEN

The frequency and intensity of climate change and resulting impacts are more prevalent in South Asian countries, particularly in Bangladesh. Relative humidity (RH) is a crucial aspect of climate, and higher RH variability has far-reaching impacts on human health, agriculture, environment, and infrastructure. While temperature and rainfall have gained much research attention, RH studies have received scant attention in the research literature. This study investigated the trends and variability of RH levels in Bangladesh and the influence of other meteorological factors over the past 40 years. Variabilities in the meteorological factors were identified by calculating descriptive statistics. Innovative trend analysis (ITA) and Mann-Kendall test (MK-test) methods were utilized to assess monthly, seasonal, and annual trends. The magnitude of temperature, rainfall, and windspeed influences on RH variability were identified using Pearson's correlation, Spearman rank correlation, and Kendall correlation model. Variability analysis showed higher spatial variations in RH levels across the country, and RH skewed negatively in all stations. Results reveal that daily, monthly, seasonal, and annual trends of RH exhibited positive trends in all stations, with an increasing rate of 0.083-0.53% per year in summer, 0.43-0.68% per year in winter, and 0.58-0.31% per year in the rainy season. Both ITA and MK-test provided consistent results, indicating no discrepancies in trend results. All three models indicate that temperature, rainfall, and windspeed have weak to moderate positive influences on changing RH levels in Bangladesh. The study will contribute to decision-making to improve crop yields, health outcomes, and infrastructure efficiency.

7.
Heliyon ; 9(7): e18255, 2023 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-37501996

RESUMEN

The Rohingya crisis in Myanmar's Rakhine state has resulted in a significant influx of refugees into Cox's Bazar, Bangladesh. However, the ecological impact of this migration has received limited attention in research. This study aimed to address this gap by utilizing remote sensing data and machine learning techniques to model the ecological quality (EQ) of the region before and after the refugee influx. To quantify changes in land use and land cover (LULC), three supervised machine learning classification methods, namely artificial neural networks (ANN), support vector machines (SVM), and random forests (RF), were applied. The most accurate LULC maps obtained from these methods were then used to assess changes in ecosystem service valuation and function resulting from the land use changes. Furthermore, fuzzy logic models were employed to examine the EQ conditions before and after the Rohingya influx. The findings of the study indicate that the increased number of Rohingya refugees has led to a 9.58% decrease in forest area, accompanied by an 8.25% increase in settlement areas. The estimated total ecosystem services value (ESV) in the research area was $67.83 million in 2017 and $67.78 million in 2021, respectively. The ESV for forests experienced a significant decline of 21.97%, equivalent to a decrease of $5.33 million. Additionally, the reduction in forest lands has contributed to a 13.58% decline in raw materials and a 14.57% decline in biodiversity. Furthermore, utilizing a Markovian transition probability model, our analysis reveals that the EQ conditions in the area have deteriorated from "very good" or "good" to "bad" or "very bad" following the Rohingya influx. The findings of this study emphasize the importance of integrating ecological considerations into decision-making processes and developing proactive measures to mitigate the environmental impact of such large-scale migrations.

8.
Neural Netw ; 166: 236-247, 2023 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-37517358

RESUMEN

Graph Neural Networks (GNNs) are powerful in learning rich network representations that aid the performance of downstream tasks. However, recent studies showed that GNNs are vulnerable to adversarial attacks involving node injection and network perturbation. Among these, node injection attacks are more practical as they do not require manipulation in the existing network and can be performed more realistically. In this paper, we propose a novel problem statement - a class-specific poison attack on graphs in which the attacker aims to misclassify specific nodes in the target class into a different class using node injection. Additionally, nodes are injected in such a way that they camouflage as benign nodes. We propose NICKI, a novel attacking strategy that utilizes an optimization-based approach to sabotage the performance of GNN-based node classifiers. NICKI works in two phases - it first learns the node representation and then generates the features and edges of the injected nodes. Extensive experiments and ablation studies on four benchmark networks show that NICKI is consistently better than four baseline attacking strategies for misclassifying nodes in the target class. We also show that the injected nodes are properly camouflaged as benign, thus making the poisoned graph indistinguishable from its clean version w.r.t various topological properties.


Asunto(s)
Benchmarking , Aprendizaje , Redes Neurales de la Computación
9.
J Mol Graph Model ; 124: 108534, 2023 11.
Artículo en Inglés | MEDLINE | ID: mdl-37290240

RESUMEN

Transition metals doped semiconductors have been extensively used as a greener alternative to lead-based solar cell materials. In this work, we have investigated the structure, electronic, optical, and thermo-chemical properties of CuCrX2 (X = S, Se, Te) by using the Conceptual Density Functional Theory (CDFT) approach. Different suitable exchange correlations have been used for the process of geometry optimization of systems in the study. Applied exchange correlations namely B3LYP and WB97XD demonstrate that the energy gap shows a decline from the atom S to Se to Te. HOMO-LUMO obtained from level B3LYP/LANL2DZ is in accordance with the stated data. The attained band gap directs that studied materials could be beneficial for further utilization in optoelectronic and photovoltaic devices. A comparative study has been made based on the selected exchange correlations for the analysis of investigated materials, which has not been explored commonly. The study reveals that B3LYP/LANL2DZ could be a better choice for a combination set of level and basis set for studying these types of compounds. CDFT-based global reactivity descriptors are computed and analyzed. The obtained band gap range indicates the desirable nature of CuCrX2 for further exploration in the application of Intermediate Band Solar cells.


Asunto(s)
Energía Solar , Modelos Moleculares , Teoría Funcional de la Densidad , Electrónica , Electrones
10.
Appl Opt ; 62(13): 3284-3288, 2023 May 01.
Artículo en Inglés | MEDLINE | ID: mdl-37132828

RESUMEN

We explore the suitability of a virtually imaged phased array as a spectral-to-spatial mode-mapper (SSMM) for applications in quantum communication such as a quantum repeater. To this end, we demonstrate spectrally resolved Hong-Ou-Mandel (HOM) interference with weak coherent states (WCSs). Spectral sidebands are generated on a common optical carrier, and WCSs are prepared in each spectral mode and sent to a beam splitter followed by two SSMMs and two single-photon detectors, allowing us to measure spectrally resolved HOM interference. We show that the so-called HOM dip can be observed in the coincidence detection pattern of matching spectral modes with visibilities as high as 45% (maximum 50% for WCSs). For unmatched modes, the visibility drops significantly, as expected. Due to the similarity between HOM interference and a linear-optics Bell-state measurement (BSM), this simple optical arrangement figures as a candidate for the implementation of a spectrally resolved BSM. Finally, we simulate the secret key generation rate using current and state-of-the-art parameters in a measurement-device-independent quantum key distribution scenario and explore the trade-off between rate and complexity of a spectrally multiplexed quantum communication link.

11.
PNAS Nexus ; 2(3): pgad041, 2023 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-36926221

RESUMEN

Recent years have witnessed a swelling rise of hateful and abusive content over online social networks. While detection and moderation of hate speech have been the early go-to countermeasures, the solution requires a deeper exploration of the dynamics of hate generation and propagation. We analyze more than 32 million posts from over 6.8 million users across three popular online social networks to investigate the interrelations between hateful behavior, information dissemination, and polarized organization mediated by echo chambers. We find that hatemongers play a more crucial role in governing the spread of information compared to singled-out hateful content. This observation holds for both the growth of information cascades as well as the conglomeration of hateful actors. Dissection of the core-wise distribution of these networks points towards the fact that hateful users acquire a more well-connected position in the social network and often flock together to build up information cascades. We observe that this cohesion is far from mere organized behavior; instead, in these networks, hatemongers dominate the echo chambers-groups of users actively align themselves to specific ideological positions. The observed dominance of hateful users to inflate information cascades is primarily via user interactions amplified within these echo chambers. We conclude our study with a cautionary note that popularity-based recommendation of content is susceptible to be exploited by hatemongers given their potential to escalate content popularity via echo-chambered interactions.

12.
Mol Divers ; 27(3): 1271-1283, 2023 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-35781180

RESUMEN

A detailed computational analysis of acridine derivatives viz. acridone, 9-amino acridine hydrochloride hydrate, proflavin, acridine orange and acridine yellow is done in terms of conceptual density functional theory (CDFT). CDFT-based global descriptors-ionization potential, electron affinity, HOMO-LUMO gap, hardness, softness, electronegativity and electrophilicity index of acridine derivatives for ground state as well as excited state are estimated with the help of different hybrid functionals B3LYP/6-31G (d, p), B3LYP/6-311G (d, p), B3LYP/DGDZVP and B3LYP/LANL2DZ. Acridine derivatives show higher values of ionization potential and electron affinity in excited state as compared to ground state, indicating that these compounds are willing to accept electrons in excited state rather than donating electron. Acridone shows the maximum HOMO-LUMO energy gap in ground and excited state which implies that one-way electron transfer is most feasible with this compound. Our computed results emphasize the pronounced electron acceptor behaviour of the acridine derivatives in the excited state which has already been experimentally verified. It is observed that the trend in the computed values of the descriptors is not much improved on refinement of the basis set.


Asunto(s)
Acridinas , Teoría Funcional de la Densidad , Acridinas/química
13.
Genes (Basel) ; 13(12)2022 12 09.
Artículo en Inglés | MEDLINE | ID: mdl-36553589

RESUMEN

Acute myocardial infarction (AMI) is a severe disease with elevated morbidity and mortality rate worldwide. This is attributed to great losses of cardiomyocytes, which can trigger the alteration of gene expression patterns. Although several attempts have been made to assess the AMI biomarkers, to date their role in rescuing myocardial injury remains unclear. Therefore, the current study investigated three independent microarray-based gene expression datasets from AMI patients (n = 85) and their age-sex-matched healthy controls (n = 70), to identify novel gene signatures that might be involved in cardioprotection. The differentially expressed genes (DEGs) were analyzed using 'GEO2R', and weighted gene correlation network analysis (WGCNA) was performed to identify biomarkers/modules. We found 91 DEGs, of which the number of upregulated and downregulated genes were 22 and 5, respectively. Specifically, we found that the deregulated genes such as ADOR-A3, BMP6, VPS8, and GPx3, may be associated with AMI. WGCNA revealed four highly preserved modules among all datasets. The 'Enrichr' unveiled the presence of miR-660 and STAT1, which is known to affect AMI severity. Conclusively, these genes and miRNA might play a crucial role the rescue of cardiomyocytes from severe damage, which could be helpful in developing appropriate therapeutic strategies for the management of AMI.


Asunto(s)
MicroARNs , Infarto del Miocardio , Humanos , Transcriptoma/genética , Perfilación de la Expresión Génica , Infarto del Miocardio/genética , Infarto del Miocardio/metabolismo , Biomarcadores/metabolismo , Biología Computacional
14.
Struct Chem ; 33(6): 2195-2204, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-36097582

RESUMEN

The pandemic, COVID-19, has caused social and economic disruption at a larger pace all over the world. Identification of an effective drug for the deadliest disease is still an exigency. One of the most promising approaches to combat the lethal disease is use of repurposed drugs. This study provides insights into some of the potential repurposed drugs viz. camostat mesylate, hydroxychloroquine, nitazoxanide, and oseltamivir in terms of the computational quantum chemical method. Properties of these compounds have been elucidated in terms of Conceptual Density Functional Theory (CDFT)-based descriptors, IR spectra, and thermochemical properties. Computed results specify that hydroxychloroquine is the most reactive drug among them. Thermochemical data reveals that camostat mesylate has the utmost heat capacity, entropy, and thermal energy. Our findings indicate that camostat mesylate and hydroxychloroquine may be investigated further as potential COVID-19 therapeutics. We anticipate that the current study will aid the scientific community to design and develop viable therapeutics against COVID-19.

15.
Disaster Med Public Health Prep ; 17: e241, 2022 06 08.
Artículo en Inglés | MEDLINE | ID: mdl-35673800

RESUMEN

OBJECTIVE: The objective of this study is to map vulnerability of Asian countries to the COVID-19 pandemic. METHOD: According to the Intergovernmental Panel on Climate Change (IPCC) 2007 framework for natural hazards, vulnerability is a function of exposure, sensitivity, and adaptive capacity. From an extensive literature review, we identified 16 socioeconomic, meteorological, environmental, and health factors that influence coronavirus disease 2019 (COVID-19) cases and deaths. The underlying factors of vulnerability were identified using principal component analysis. RESULTS: Our findings indicate that the percentage of the urban population, obesity rate, air connectivity, and the population aged 65 and over, diabetes prevalence, and PM2.5 levels all contributed significantly to COVID-19 sensitivity. Subsequently, governance effectiveness, human development index (HDI), vaccination rate, and life expectancy at birth, and gross domestic product (GDP) all had a positive effect on adaptive capacity. The estimated vulnerability was corroborated by a Pearson correlation of 0.615 between death per million population and vulnerability. CONCLUSION: This study demonstrates the application of universal indicators for assessing pandemic vulnerability for informed policy interventions such as the COVAX vaccine roll-out priority. Despite data limitations and a lack of spatiotemporal analysis, this study's methodological framework allows for ample data incorporation and replication.


Asunto(s)
COVID-19 , Humanos , Cambio Climático , COVID-19/epidemiología , Salud Global , Esperanza de Vida , Pandemias
16.
Disaster Med Public Health Prep ; 17: e198, 2022 06 27.
Artículo en Inglés | MEDLINE | ID: mdl-35757871

RESUMEN

OBJECTIVE: The objective of the research is to estimate the cost of ecosystem service value (ESV) due to the Rohingya refugee influx in Ukhiya and Teknaf upazilas of Bangladesh. METHODS: Artificial neural network (ANN) supervised classification technique was used to estimate land use/land cover (LULC) dynamics between 2017 (ie, before the Rohingya refugee influx) and 2021. The ESV changes between 2017 and 2021 were assessed using the benefit transfer approach. RESULTS: According to the findings, the forest lost 54.88 km2 (9.58%) because of the refugee influx during the study. Around 47.26 km2 (8.25%) of settlement was increased due to the need to provide shelter for Rohingya refugees in camp areas. Due to the increase in Rohingya refugee settlements, the total ESV increased from US $310.13 million in 2017 to US $332.94 million in 2021. Because of the disappearance of forest areas, the ESV for raw materials and biodiversity fell by 13.58% and 14.57%, respectively. CONCLUSION: Natural resource conservation for long-term development will benefit from the findings of this study.


Asunto(s)
Ecosistema , Refugiados , Humanos , Bangladesh
17.
Acta Chim Slov ; 68(1): 178-184, 2021 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-34057528

RESUMEN

A new principle known as Minimum Magnetizability Principle has recently been introduced in the context of Density Functional Theory. In order to validate this principle, changes in the magnetizability (Δξ) and its cube-root (Δξ1/3) are computed at B3LYP/LanL2DZ level of theory for some elementary chemical reactions. The principle is found to be valid for 77% of reactions under study. It is observed that the molecules with the lowest sum of ξ or ξ1/3 are generally the most stable. The principle fails to work in the presence of hard species. A comparative study is also made with change in hardness (Δη), electrophilicity index (Δω), polarizability (Δα) and their cube-roots (Δη1/3, Δω1/3, Δα1/3). It is observed that the Minimum Magnetizability Principle is nearly as reliable as Minimum Electrophilicity Principle. It appears that this principle could be helpful in predicting the direction of diverse reactions as well as stable geometrical arrangements.

18.
Phys Rev E ; 103(4-1): 042133, 2021 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-34005942

RESUMEN

We calculate the bulk-diffusion coefficient and the conductivity in nonequilibrium conserved-mass aggregation processes on a ring. These processes involve chipping and fragmentation of masses, which diffuse on a lattice and aggregate with their neighboring masses on contact, and, under certain conditions, they exhibit a condensation transition. We find that, even in the absence of microscopic time reversibility, the systems satisfy an Einstein relation, which connects the ratio of the conductivity and the bulk-diffusion coefficient to mass fluctuation. Interestingly, when aggregation dominates over chipping, the conductivity or, equivalently, the mobility of masses, is greatly enhanced. The enhancement in the conductivity, in accordance with the Einstein relation, results in large mass fluctuations and can induce a mobility-driven clustering in the systems. Indeed, in a certain parameter regime, we show that the conductivity, along with the mass fluctuation, diverges beyond a critical density, thus characterizing the previously observed nonequilibrium condensation transition [Phys. Rev. Lett. 81, 3691 (1998)10.1103/PhysRevLett.81.3691] in terms of an instability in the conductivity. Notably, the bulk-diffusion coefficient remains finite in all cases. We find our analytic results in quite good agreement with simulations.

19.
Adv Mater ; 33(20): e2100977, 2021 May.
Artículo en Inglés | MEDLINE | ID: mdl-33829572

RESUMEN

Solid-gas interactions at electrode surfaces determine the efficiency of solid-oxide fuel cells and electrolyzers. Here, the correlation between surface-gas kinetics and the crystal orientation of perovskite electrodes is studied in the model system La0.8 Sr0.2 Co0.2 Fe0.8 O3 . The gas-exchange kinetics are characterized by synthesizing epitaxial half-cell geometries where three single-variant surfaces are produced [i.e., La0.8 Sr0.2 Co0.2 Fe0.8 O3 /La0.9 Sr0.1 Ga0.95 Mg0.05 O3-δ /SrRuO3 /SrTiO3 (001), (110), and (111)]. Electrochemical impedance spectroscopy and electrical conductivity relaxation measurements reveal a strong surface-orientation dependency of the gas-exchange kinetics, wherein (111)-oriented surfaces exhibit an activity >3-times higher as compared to (001)-oriented surfaces. Oxygen partial pressure ( p O 2 )-dependent electrochemical impedance spectroscopy studies reveal that while the three surfaces have different gas-exchange kinetics, the reaction mechanisms and rate-limiting steps are the same (i.e., charge-transfer to the diatomic oxygen species). First-principles calculations suggest that the formation energy of vacancies and adsorption at the various surfaces is different and influenced by the surface polarity. Finally, synchrotron-based, ambient-pressure X-ray spectroscopies reveal distinct electronic changes and surface chemistry among the different surface orientations. Taken together, thin-film epitaxy provides an efficient approach to control and understand the electrode reactivity ultimately demonstrating that the (111)-surface exhibits a high density of active surface sites which leads to higher activity.

20.
Mol Divers ; 25(1): 249-262, 2021 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-32146657

RESUMEN

Recently, we have defined atomic polarizability, a Conceptual Density Functional Theory (CDFT)-based reactivity descriptor, through an empirical method. Though the method is empirical, it is competent enough to meet the criteria of periodic descriptors and exhibit relativistic effect. Since the atomic data are very accurate, we have applied them to determine molecular polarizability. Molecular polarizability is an electronic parameter and has an impact on chemical-biological interactions. Thus, it plays a pivotal role in explaining such interactions through Structure Activity Relationships (SAR). In the present work, we have explored the application of polarizability in the real field through investigation of chemical-biological interactions in terms of molecular polarizability. A Quantitative Structure-Activity Relationship (QSAR) model is constructed to account for electronic effects owing to polarizability in ligand-substrate interactions. The study involves the prediction of various biological activities in terms of minimum block concentration, relative biological response, inhibitory growth concentration or binding affinity. Superior results are presented for the predicted and observed activities which support the accuracy of the proposed polarizability-QSAR model. Further, the results are considered from a biological viewpoint in order to understand the mechanism of interactions. The study is performed to explore the efficacy of the computational model based on newly proposed polarizability and not to establish the finest QSAR. For future studies, it is suggested that the descriptor polarizability should be contrasted with the use of other drug-like descriptors.


Asunto(s)
Relación Estructura-Actividad Cuantitativa , Simulación por Computador , Ligandos , Modelos Químicos
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