Clusters Of Different Sizes Research Articles

Real-world evidence for patient phenotypes in heart failure with preserved ejection fraction

Abstract Background Heart failure (HF) with preserved ejection fraction (HFpEF) presents a high mortality risk due to its heterogeneous and multifactorial nature, coupled with limited treatment options. The incompletely understood pathophysiology is influenced by various comorbidities, resulting in different clinical phenotypes. Identifying these could be crucial for tailored HFpEF treatments. While previous studies focused on small, well-characterized patient populations, electronic health records (EHRs) offer the potential to unveil HFpEF phenotypes in larger real-world patient groups. Purpose We aimed to establish a sizable, unselected HFpEF patient population using real-world data. Employing cluster analysis, we intended to uncover distinct groups with varied disease aetiology and medical needs based on comorbidity profiles and prognoses. Methods From EHRs of n = 1,610,101 HF patients, we identified an HFpEF cohort of n = 32,009 patients, by applying thresholds for the LVEF and data availability, and by excluding confounding conditions. Clustering by the relative frequency of common comorbidities aimed to reveal patient populations with unique prognoses, comorbidity profiles, and clinical and demographic characteristics. Results Six clusters of different sizes, comorbidity prevalence, clinical presentation, and all-cause mortality were identified. About 50% of patients (n = 15,445) were predominantly hypertensive, with varying extents of coronary heart disease and diabetes mellitus (DM), and a 5-year mortality of about 30%. Around 22% (n = 7,089) exhibited a cardiometabolic comorbidity profile, with an increased prevalence of obesity and sleep apnea, but also DM and hypertension, and a 5-year mortality of 22.5%. Over 15% of patients (n = 5,298) had a 5-year mortality rate of 45.0%, marked by highest rates of anaemia and chronic kidney disease (CKD) but also DM, elevated N-terminal prohormone of brain natriuretic peptide levels, and a reduced estimated glomerular filtration rate. Conclusion Despite the favourable prognosis, a significant proportion of patients represent a cardiometabolic HFpEF phenotype with notable unmet medical needs regarding cohort size and multimorbidity. Patients simultaneously suffering from CKD, anaemia, and the highest mortality rates may represent a previously underrecognized phenotype. Our study demonstrates that distinct medical needs can be identified in a large, unselected real-world HFpEF cohort. In contrast to clinical trials, this approach enabled access to a broader patient population, revealing novel phenotypes to be targeted by precision medicine in the future.

Comprehensive genetic analysis reveals the genetic structure and diversity of Calanthe hoshii (Orchidaceae), an endemic species of the Ogasawara Islands: Implications for appropriate conservation of a critically endangered species

AbstractThe Ogasawara Islands, isolated from the continent throughout their geological history, harbor abundant endemic species. However, 32% of the native plant species are on the Japanese Red List, signaling their endangered status. Among these endangered species, Calanthe hoshii stands out as highly susceptible to extinction. Two wild and 89 ex situ individuals were alive in 2020, but the last known wild individual died in October 2021, indicating this species may have become extinct in the wild. Despite the conservation efforts under the Act for the Conservation of Endangered Species of Wild Fauna and Flora, the lack of essential information regarding genetic diversity and population structure among the remaining individuals poses a significant obstacle to developing effective conservation measures. In this research, we conducted a genetic analysis of the wild and ex situ individuals, which revealed notably reduced genetic diversity between individuals, with individual heterozygosity levels (1.0 × 10−5) measuring one‐ninth of those observed within a closely related species Calanthe triplicata (1.5 × 10−4). Comprehensive genetic analysis revealed that C. hoshii consisted of three genetic clusters of different sizes: cluster 1 comprised 95% of the total population, while clusters 2 and 3, with few individuals, were only found in the ex situ populations at Koishikawa Botanical Garden. Since extant C. hoshii maintains a remarkably low genetic diversity at both individual and population levels, it is necessary to consider future management strategies, such as artificial breeding among different clades identified in this study, to safeguard the stability and resilience of this species.

Understanding the structures and interactions in gaseous mixtures of water-alcohol by high-resolution infrared spectroscopy

Interactions of water and chemical or bio-compound have a universal concern and have been extensively studied. For spectroscopic analysis, the complexity and the low resolution of the spectra make it difficult to obtain the spectral features showing the interactions. In this work, the structures and interactions in gaseous water and water-alcohol mixtures were studied using high-resolution infrared (HR-IR) spectroscopy. The spectral features of water clusters of different sizes, including dimer, trimer, tetramer and pentamer, were observed from the measured spectra of the samples in different volume concentrations, and the interactions of water and methanol/ethanol in the mixtures were obtained. In the analysis, a method based on principal component analysis was used to separate the overlapping spectra. In water-alcohol mixtures, when water is less, water molecules tend to interact with the OH groups on the exterior of the alcohol aggregate, and with the increase of water, a water cage forms around the aggregates. Furthermore, the ratio of the molecule number of methanol in the aggregate to that of water in the cage is around 1:2.3, and the ratio for ethanol is about 1:3.2.

MODIFICATION OF PINDIGA BENTONITE CLAY WITH DIDODECYLDIMETHYLAMMONIUM BROMIDES SURFACTANT FOR FOUNDRY USE

Bentonite clay from Pindiga, Gombe State, Nigeria, was surface modified with didodecyldimethylammonium bromides (DDAB) by the Base Exchange (cation exchange capacity) method for its possible use in foundries. The surfaces of the unmodified and modified Pindiga bentonite clay were characterised by means of spectroscopic, diffraction, and scanning methods (X-Ray fluorescence spectrometry (XRF)Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM).XRF showed that unmodified sample was rich of montmorillonite (MMt) with ca +2 as exchangeable cation, FTIR analysis revealed that unmodified water absorption causes stretching and bending vibrations for hydroxyl groups, with the most intense bands in the low-frequency region, while DDAB organo-bentonites showed slight changes in wave bands, with a strong methyl band and a weak methyl band indicative of long-chain linear aliphatic structure. The basal spacing of the unmodified bentonite sample was 1.52 nm, and after modification with DDAB, it improved to 2.1 nm as determined from the X-ray diffraction (XRD) analysis. Results of the SEM images revealed rougher surfaces with uniformly dispersed small particles of grain-like structures characteristic of the unmodified, while theorgano-modified bentoniterevealed clusters of different sizes and shapes, larger Fe 3+ ions replacing smaller Al 3+ ions at octahedral sites, discontinuous layers enveloping large grains, polygonal growth foams with octahedral and tetrahedral shapes, mixed layers of calcium bentonite, and particle sizes less than 200nm. The study concluded that modified bentonite with didodecyldimethylammonium bromides gives good microstructure, increases rigidity, and improve thermal stability, to the organoclays. Therefore, it is recommended that DDAB bentonite be used as binder for foundries.

Probing Isolated Water Molecules in Aqueous Acetonitrile Solutions Using Oxygen K-Edge X-ray Absorption Spectroscopy.

Oxygen K-edge X-ray absorption spectroscopy (XAS) of an aqueous acetonitrile solution exhibited a sharp peak at approximately 537 eV, which was similar to that of water vapor and was not observed in liquid water. The inner-shell spectra of isolated water molecules and water clusters of different sizes surrounded by acetonitrile molecules were obtained by extracting these water structures from the liquid structures of aqueous acetonitrile solutions, as calculated using molecular dynamics simulations. The sharp peak profiles of the O K-edge XAS spectra were derived not from water clusters but from isolated water molecules surrounded by acetonitrile molecules. The present study proposes that isolated water molecules are easily formed in aqueous acetonitrile solutions and that the electronic structures of the isolated water molecules can be analyzed using O K-edge XAS spectra, which separates the contributions of small water clusters.

HST Survey of the Orion Nebula Cluster in ACS/Visible and WFC3/IR Bands. IV. A Bayesian Multiwavelength Study of Stellar Parameters in the Orion Nebula Cluster

We have performed a comprehensive study of the Orion Nebula Cluster (ONC) combining the photometric data obtained by the two Hubble Space Telescope Treasury programs that targeted this region. To consistently analyze the rich data set obtained in a wide variety of filters, we adopted a Bayesian approach to fit the spectral energy distribution of the sources, deriving mass, age, extinction, distance, and accretion for each source in the region. The three-dimensional study of mass distribution for bona fide cluster members shows that mass segregation in the ONC extends to subsolar masses, while the age distribution strongly supports the idea that star formation in the ONC is best described by a major episode of star formation that happened ∼1 Myr ago. For masses ≳0.1 M ⊙, our derived empirical initial mass function (IMF) is in good agreement with a Chabrier system IMF. Both the accretion luminosity (L acc) and mass accretion rates ( Ṁacc ) are best described by broken power-law relations. This suggests that for the majority of young circumstellar disks in this cluster the excess emission may be dominated by X-ray-driven photoevaporation by the central star rather than external photoevaporation. If this is the case, the slopes of the power-law relations may be largely determined by the initial conditions set at the onset of the star formation process, which may be quite similar between regions that eventually form clusters of different sizes.

Networks of Hydrogen Bond Networks in Water Clusters.

Water clusters play a prominent role in atmospheric and solution chemistry. Numerous arrangements of protons, H-bond configurations or networks, shape the cluster properties. Studies of small water clusters by cryogenic scanning tunneling microscopy and high-resolution rovibrational spectroscopy have established proton rearrangement mechanisms forming pathways between H-bond networks. The mechanisms, concerted tunneling in particular, describe the local processes connecting pairs of configurations. Here, proton rearrangement networks mapping these transformations are defined and explored to provide a global view of the H-bond configurations in clusters. The networks are constructed for clusters of different sizes and structures. Their analysis reveals an odd-even effect with respect to the number of water molecules, exponential growth of the small-world character, bimodality of the degree distributions, and gapped assortativity of the networks. The last two properties signify the unexpected division of H-bond configurations into two classes according to their network connectivity. The results demonstrate qualitative differences between proton rearrangement mechanisms, suggest a strong influence of the cluster structure. The generated networks are of interest as real-world models for network rewiring; they establish an alternative platform for studies of proton rearrangements in H-bonded systems.

Effect of transmutation rhenium on tensile properties of tungsten by molecular dynamics simulation

The tensile properties of W-Re alloys are studied using molecular dynamics method. Two forms of transmutation Re uniform distribution and cluster distribution in W-Re alloys are systematically explored, W-xRe alloys and W-nRe clusters, respectively. The effects of Re concentration, Re cluster number density, and temperature on the tensile properties are discussed. Findings suggest that Young’s modulus of W-xRe alloys decreases with increasing Re concentration, reaching only 323 GPa when the Re concentration is 50 at.%. The ultimate stress of W-xRe alloys is lower than that of pure tungsten, indicating that the presence of Re would accelerates the fracture of W-xRe alloys. Additionally, Re clusters of different sizes and number density are constructed in tungsten, forming the W-nRe cluster system. Interestingly Re clusters can reduce tensile strength, and the strain hardening modulus (E sh) is independent of the single Re cluster size. With an increase in Re cluster number density, Young’s modulus, ultimate stress, and ultimate strain decrease gradually, leading to fracture in the Re cluster position. Non-coherent and semi-coherent interfaces between Re cluster (χ- and σ-phases) and W lattice cause Re cluster to undergo imbalance stress. For example, in W-12.5 at.% Re alloys, stress–strain curves are studied at different temperatures, revealing that Young’s modulus decreases with increasing temperature, reaching 292 GPa at 1300 K. A linear formula is obtained by fitting Young’s modulus-temperature curve. These results provide important theoretical references for the design of W-Re alloys as the PFMs in the ITER.

CO2 activation by copper oxide clusters: size, composition, and charge state dependence.

The interaction of CO2 with copper oxide clusters of different size, composition, and charge is investigated via infrared multiple-photon dissociation (IR-MPD) spectroscopy and density functional theory (DFT) calculations. Laser ablation of a copper target in the presence of an O2/He mixture leads to the preferred formation of oxygen-rich copper oxide cluster cations, CuxOy+ (y > x; x ≤ 8), while the anionic cluster distribution is dominated by stoichiometric (x = y) and oxygen-deficient (y < x; x ≤ 8) species. Subsequent reaction of the clusters with CO2 in a flow tube reactor results in the preferred formation of near-stoichiometric CuxOy(CO2)+/- complexes. IR-MPD spectroscopy of the formed complexes reveals the non-activated binding of CO2 to all cations while CO2 is activated by all anions. The great resemblance of spectra for all sizes investigated demonstrates that CO2 activation is largely independent of cluster size and Cu/O ratio but mainly determined by the cluster charge state. Comparison of the IR-MPD spectra with DFT calculations of the model systems Cu2O4(CO2)- and Cu3O4(CO2)- shows that CO2 activation exclusively results in the formation of a CO3 unit. Subsequent CO2 dissociation to CO appears to be unfavorable due to the instability of CO on the copper oxide clusters indicating that potential hydrogenation reactions will most likely proceed via formate or bicarbonate intermediates.

Impact of coating type on structure and magnetic properties of biocompatible iron oxide nanoparticles: insights into cluster organization and oxidation stability.

Superparamagnetic iron oxide nanoparticles (SPIONs) are a promising tool for biomedical applications, including drug delivery, imaging, and magnetic hyperthermia. However, their tendency to agglomerate limits their performance efficiency. To overcome this limitation, a coating can be applied during or after synthesis. This work investigates the effect of three biocompatible coatings, namely sodium citrate, (3-aminopropyl)triethoxysilane (APTES), and dextran, on controlling the agglomeration of iron oxide nanoparticles. Various experimental techniques were used to characterize the structural and magnetic properties of the coated nanoparticles, including cryogenic transmission electron microscopy (cryo-TEM), magnetometry, Mössbauer spectroscopy, and small-angle X-ray and neutron scattering. The results indicate that the coatings effectively stabilize the nanoparticles, leading to clusters of different sizes that modify their magnetic behaviour due to magnetic inter-particle interactions. The oxidation kinetics of the nanoparticles prepared with the various coating materials were investigated to characterize their oxidation behaviour and stability over time. This research provides valuable insights into the design of an optimized nanoparticle functionalization strategy for biomedical applications.

Karyotypes and Physical Mapping of Ribosomal DNA with Oligo-Probes in Eranthis sect. Eranthis (Ranunculaceae).

A comparative karyotype analysis of four species of yellow-flowered Eranthis sect. Eranthis, i.e., E. bulgarica, E. cilicica, E. hyemalis, and E. longistipitata from different areas, has been carried out for the first time. All the studied specimens had somatic chromosome number 2n = 16 with basic chromosome number x = 8. Karyotypes of the investigated plants included five pairs of metacentric chromosomes and three pairs of submetacentric/subtelocentric chromosomes. The chromosome sets of the investigated species differ mainly in the ratio of submetacentric/subtelocentric chromosomes, their relative lengths, and arm ratios. A new oligonucleotide probe was developed and tested to detect 45S rDNA clusters. Using this probe and an oligonucleotide probe to 5S rDNA, 45S and 5S rDNA clusters were localized for the first time on chromosomes of E. cilicica, E. hyemalis, and E. longistipitata. Major 45S rDNA clusters were identified on satellite chromosomes in all the species; in E. cilicica, minor clusters were also identified in the terminal regions of one metacentric chromosome pair. The number and distribution of 5S rDNA clusters is more specific. In E. cilicica, two major clusters were identified in the pericentromeric region of a pair of metacentric chromosomes. Two major clusters in the pericentromeric region of a pair of submetacentric chromosomes and two major clusters in the interstitial region of a pair of metacentric chromosomes were observed in E. longistipitata. E. hyemalis has many clusters of different sizes, localized mainly in the pericentromeric regions. Summarizing new data on the karyotype structure of E. sect. Eranthis and previously obtained data on E. sect. Shibateranthis allowed conclusions to be formed about the clear interspecific karyological differences of the genus Eranthis.

Areas with high HIV prevalence: A spatial analysis of nationwide claims data in Germany.

We aimed to identify spatial clusters of high HIV prevalence in Germany. Using nationwide outpatient claims data comprising information of about 88% of the total German population (N = 72 041 683), we examined spatial variations and spatial clusters of high HIV prevalence at the district level (N = 401). People with HIV were identified using the International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10 codes) B20, B22, and B24 (HIV disease) documented as 'confirmed'. Among 72 041 683 people with statutory health insurance in Germany in 2021, 72 636 had diagnosed HIV, which corresponds to a prevalence of 101 per 100 000 individuals (0.10%). Of these, 56 895 were males (78%). At a district level, the HIV prevalence varied by a factor of 32 between 13 in a rural district in Bavaria and 417 per 100 000 individuals in the German capital, Berlin. The spatial autocorrelation coefficient was 0.24 (p < 0.0001, Global Moran's I). Several high-prevalence spatial clusters of different sizes were identified, mostly located in western Germany. The largest cluster comprised eight districts in the southern part of Hesse, including the city of Frankfurt and the city of Mainz in Rhineland-Palatinate. The second cluster consisted of four districts in North Rhine-Westphalia, including the cities of Cologne and Düsseldorf. Two districts in southern Germany (Mannheim and Ludwigshafen) formed the third cluster. Only urban districts were observed in spatial clusters of high HIV prevalence. The current study identified for the first time spatial clusters with high HIV prevalence in Germany. This understanding is of particular importance when planning the general and specialized medical care of patients with HIV and to support preventive measures.

Effect of contact inhibition locomotion on confined cellular organization

Experiments performed using micro-patterned one dimensional collision assays have allowed a precise quantitative analysis of the collective manifestation of contact inhibition locomotion (CIL) wherein, individual migrating cells reorient their direction of motion when they come in contact with other cells. Inspired by these experiments, we present a discrete, minimal 1D Active spin model that mimics the CIL interaction between cells in one dimensional channels. We analyze the emergent collective behaviour of migrating cells in such confined geometries, as well as the sensitivity of the emergent patterns to driving forces that couple to cell motion. In the absence of vacancies, akin to dense cell packing, the translation dynamics is arrested and the model reduces to an equilibrium spin model which can be solved exactly. In the presence of vacancies, the interplay of activity-driven translation, cell polarity switching, and CIL results in an exponential steady cluster size distribution. We define a dimensionless Péclet number Q—the ratio of the translation rate and directional switching rate of particles in the absence of CIL. While the average cluster size increases monotonically as a function of Q, it exhibits a non-monotonic dependence on CIL strength, when the Q is sufficiently high. In the high Q limit, an analytical form of average cluster size can be obtained approximately by effectively mapping the system to an equivalent equilibrium process involving clusters of different sizes wherein the cluster size distribution is obtained by minimizing an effective Helmholtz free energy for the system. The resultant prediction of exponential dependence on CIL strength of the average cluster size and Q1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Q^{1/2}$$\\end{document} dependence of the average cluster size is borne out to reasonable accuracy as long as the CIL strength is not very large. The consequent prediction of a single scaling function of Q, particle density and CIL interaction strength, characterizing the distribution function of the cluster sizes and resultant data collapse is observed for a range of parameters.

Identification of Critical Urban Clusters for Placating Urban Heat Island Effects over Fast-Growing Tropical City Regions: Estimating the Contribution of Different City Sizes in Escalating UHI Intensity

The incessant rise of artificial surfaces has increased the temperatures of cities, distressing urban health and sustainability. Fast-growing tropical cities particularly call for an understanding of this phenomenon, known as the urban heat island (UHI). The present study was conducted to detect UHI dynamics over the National Capital Region of India. Stretching over more than 32 000 km2, this region consists of urban centers of varying sizes. Landsat thermal bands were processed to extract temperature patterns between 1999 and 2019. Urban climate change was prominent, as a 2349-km2 expansion in UHI area was spotted. Urban clusters of different sizes were demarcated by applying the k-nearest neighbor algorithm on the normalized difference building index maps. This empirical analysis helped to form a logarithmic relation between city size and UHI intensity. Observed results set a framework to assess the thermal environment of numerous urban centers from any tropical country. UHI intensity values for various city sizes were computed, as they were crucial to decide the outdoor comfort zones based on the base temperature conditions of other cities. Further, the critical zones in each urban cluster were identified using the vegetation index, and scopes of landscaping were suggested based on the observed building morphologies of different local climate zones.

Density functional theory study the mechanism of two CO* forming *OC-CO on different size of Cun (n = 3 to 20) clusters supported on TiO2

Cun@TiO2 nanocatalytic materials are widely used in experiments to catalyze the reduction of CO2 to hydrocarbon fuels and oxygenated alcohols. However, due to the complexity of the coupling reaction of the Cun@TiO2 catalyst to form key CC bonds to C2 products, it is unclear. In this paper, the density functional theory (DFT) is employed to systematically study the influence of the size of Cun clusters on the CC bond formation with the Cun cluster supporting on the TiO2 surface. It was discovered that the adsorption of Cu metal clusters of different sizes on TiO2 was primarily determined by the bonding of TiO2 oxygen atoms. Subsequently, in the CO*+CO* → COOC* coupling reaction on each different Cun cluster size, we found that the active site was the interface position, when the Cun cluster showed a three-dimensional configuration, with the increase of the Cu cluster, that is, the coordination number increased, the activation energy barrier gradually decreased, and when the coordination of Cu cluster reached saturation, the coupling energy barrier size also stabilized. This work provides new sight of the size of co-catalyst in the CO2 reduction reaction and may guide to synthesis higher efficiency co-catalyst.

Characterization of the effects of wettability and pore pressure on the interfacial behavior of CO2 interacting with oil-water two-phase on pore walls

To date, research studies on film-like residual oil have mainly focused on reservoirs in the late stage of water flooding development. However, there have been relatively few studies on film-like residual oil on pore walls after gas flooding. In this study, a molecular dynamics simulation method was used to investigate the behavior characteristics of fluid-fluid and fluid-solid interfaces and the exploitation potential of film-like remaining oil in water-wet, mixed-wet and oil-wet systems under different pore pressures after CO2 flooding. The results indicated that in the oil-in-water system, the cohesive energy density (CED) of the water films was much greater than that of the CO2 and decane components, and the CED of water films in the water-wet systems was slightly greater than the CED of water films in the mixed-wet systems. Regardless of the water-wet or mixed-wet systems, Einter(CO2−decane) was the strongest between the components. Therefore, CO2 molecules could easily enter the oil films and divide the oil phase into clusters of different sizes. The interfacial tension at the CO2 + decane/H2O and H2O/SiO2 interfaces in both the water-wet and mixed-wet systems decreased with increasing pressure. Under the same pressure, the degree of decrease in interfacial tension at the CO2 + decane/H2O interface in the mixed-wet systems was smaller than that in the water-wet systems. The degree of decrease in interfacial tension at the H2O/SiO2 interfaces in the mixed-wet systems was generally greater than that in the water-wet systems. In the water-in-oil system, because the water films isolated the oil films from the CO2 molecules, the interaction energy between the CO2 molecules and oil phase was weak, so the oil films remained on the quartz surfaces. Due to the existence of the hydrogen bond network inside the water phase, the morphological changes in water films were also small when the CO2 molecules interacted with the water phase. At the CO2/H2O interfaces, under the same pressure, the resistance of CO2 molecules to pass through the water films in the oil-wet systems was greater than that in the mixed-wet systems, and the CO2 molecules in the mixed-wet systems were more likely to enter into the water films. The interfacial tension reduction at the interfaces in the mixed-wet systems was smaller than that in the oil-wet systems. At the H2O/decane interfaces, the power of CO2 molecules breaking through the oil-water interfaces and entering into the oil phase in both the mixed-wet and oil-wet systems was basically equal under the same pressure. The interfacial tension reduction at the interfaces in the mixed-wet systems was almost equal to that of the oil-wet systems. At the decane/SiO2 interfaces, the CED of the oil films in the oil-wet systems was greater than that in the oil-wet systems under the same pressures, and the Einter(CO2−SiO2) in the mixed-wet systems was greater than the Einter(CO2−SiO2) in the oil-wet systems, indicating that CO2 molecules were more easily adsorbed on the quartz surfaces in the mixed-wet systems, and the interfacial tension reduction at the interfaces in the mixed-wet systems was greater than that of the oil-wet systems. The interfacial tension at the CO2/H2O, H2O/decane and decane/SiO2 interfaces in both the mixed-wet and oil-wet systems decreased with increasing pressure. The research results provide a reference for understanding the fluid-fluid and fluid-solid interface behaviors and the exploitation potential of film-like residual oil during CO2 gas flooding.

Mechanism of Methanol Synthesis from CO2 Hydrogenation over Cu/γ-Al2O3 Interface: Influences of Surface Hydroxylation

The adsorption and hydrogenation of carbon dioxide on γ-Al2O3(110) surface-supported copper clusters of different sizes are investigated using density functional theory calculations. Our results show that the activation of CO2 is most obvious at the Cu/γ-Al2O3 interface containing the size-selected Cu4 cluster. It is interesting that the CO2 activation is more pronounced at the partially hydroxyl-covered interface. The catalytic mechanisms of CO2 conversion to methanol at the dry and hydroxylated Cu4/γ-Al2O3 interfaces via the formate route and the pathway initiated through the hydrogenation of carbon monoxide produced by the reverse water–gas shift reaction are further explored. On both interfaces, the formate pathway is identified as the preferred reaction pathway, in which the hydrogenation of HCOO to H2COO is the rate-limiting step (RLS). However, since the surface OH group can act as a hydrogen source in some elementary reactions, unlike the dry surface, the production of H2COOH species along the formate pathway is found at the hydroxylated interface. In addition, the introduction of OH at the interface leads to an increase in the kinetic barrier of the RLS, indicating that surface hydroxylation has a negative effect on the catalytic activity of CO2 conversion to CH3OH at the Cu/γ-Al2O3 interface.

Typical and atypical solutions in nonconvex neural networks with discrete and continuous weights.

We study the binary and continuous negative-margin perceptrons as simple nonconvex neural network models learning random rules and associations. We analyze the geometry of the landscape of solutions in both models and find important similarities and differences. Both models exhibit subdominant minimizers which are extremely flat and wide. These minimizers coexist with a background of dominant solutions which are composed by an exponential number of algorithmically inaccessible small clusters for the binary case (the frozen 1-RSB phase) or a hierarchical structure of clusters of different sizes for the spherical case (the full RSB phase). In both cases, when a certain threshold in constraint density is crossed, the local entropy of the wide flat minima becomes nonmonotonic, indicating a breakup of the space of robust solutions into disconnected components. This has a strong impact on the behavior of algorithms in binary models, which cannot access the remaining isolated clusters. For the spherical case the behavior is different, since even beyond the disappearance of the wide flat minima the remaining solutions are shown to always be surrounded by a large number of other solutions at any distance, up to capacity. Indeed, we exhibit numerical evidence that algorithms seem to find solutions up to the SAT/UNSAT transition, that we compute here using an 1RSB approximation. For both models, the generalization performance as a learning device is shown to be greatly improved by the existence of wide flat minimizers even when trained in the highly underconstrained regime of very negative margins.

Low-Data Deep Quantum Chemical Learning for Accurate MP2 and Coupled-Cluster Correlations.

Accurate ab initio prediction of electronic energies is very expensive for macromolecules by explicitly solving post-Hartree-Fock equations. We here exploit the physically justified local correlation feature in a compact basis of small molecules and construct an expressive low-data deep neural network (dNN) model to obtain machine-learned electron correlation energies on par with MP2 and CCSD levels of theory for more complex molecules and different datasets that are not represented in the training set. We show that our dNN-powered model is data efficient and makes highly transferable predictions across alkanes of various lengths, organic molecules with non-covalent and biomolecular interactions, as well as water clusters of different sizes and morphologies. In particular, by training 800 (H2O)8 clusters with the local correlation descriptors, accurate MP2/cc-pVTZ correlation energies up to (H2O)128 can be predicted with a small random error within chemical accuracy from exact values, while a majority of prediction deviations are attributed to an intrinsically systematic error. Our results reveal that an extremely compact local correlation feature set, which is poor for any direct post-Hartree-Fock calculations, has however a prominent advantage in reserving important electron correlation patterns for making accurate transferable predictions across distinct molecular compositions, bond types, and geometries.

Gaussian expansion of Yukawa non‐local kinetic energy functionals: Application to metal clusters

AbstractThe development of kinetic energy (KE) functionals is one of the current challenges in density functional theory (DFT). The Yukawa non‐local KE functionals [Phys. Rev. B 103, 155127 (2021)] have been shown to describe accurately the Lindhard response of the homogeneous electron gas (HEG) directly in the real space, without any step in the reciprocal space. However, the Yukawa kernel employs an exponential function which cannot be efficiently represented in conventional Gaussian‐based quantum chemistry codes. Here, we present an expansion of the Yukawa kernel in Gaussian functions. We show that for the HEG this expansion is independent of the electronic density, and that for general finite systems the accuracy can be easily tuned. Finally, we present results for atomistic sodium clusters of different sizes, showing that simple Yukawa functionals can give superior accuracy as compared to semilocal functionals.