Neighbor Sites Research Articles

Электронная структура и спектры оптического поглощения золотых фуллеренов Au-=SUB=-16-=/SUB=- и Au-=SUB=-20-=/SUB=-

AbstractThe electronic and optical properties of gold fullerenes are studied in the framework of the Hubbard model. The expressions of the Fourier transforms of anticommutator Green functions have been obtained for gold fullerenes Au_16 and Au_20, the poles of which determine the energy spectrum of the system under consideration. The calculations are performed for the thermodynamic means that characterize jumps of electrons from a nanosystem site to a neighboring site, the correlation functions demonstrating the possibility of existing two d electrons with oppositely oriented spin projections on the same site of the fullerenes consisting of gold atoms. The optical absorption spectra are presented. The optical absorption peaks of ions $${\text{Au}}_{{20}}^{ - }$$ and $${\text{Au}}_{{16}}^{ - }$$ correspond to a near-infrared spectral region, where the light absorption by blood or a soft tissue is vanishingly small; thus, these ions can be used as a new class of contrast improvements and phototherapeutic means for diagnostics and treatment of cancer.

Competitive exchange interaction and noncollinear magnetic structure in Mn-based Ni2In type alloys

Novel magnetic skyrmion state has recently been identified in the centrosymmetric hexagonal MnNiGa alloy, rendering it interesting for the exploration of the origin of noncollinear magnetism in MnNiGa and related Ni2In-type MnMX alloys. In this work, we investigate the magnetic interaction and noncollinear magnetic structure in MnNiGa, MnFeGe and MnCoSn alloys, mainly by the method of first principles studies. It is revealed that in these systems, the shortest Mn-Mn separation, denoted by the parameter d1, plays the dominant role in determining the magnetic state. The calculation of the exchange parameters Jij shows that they exhibit a competing ferromagnetic and antiferromagnetic interaction along the c axis. A noncollinear calculation that considers a canting Mn moment on the neighbour sites reveals a stable state at a specific tilting angle. Preliminary experimental results for MnFeGe1-xSnx (x = 0, 0.05 and 0.1) alloys demonstrate a reduced saturated magnetization with a growing value of d1, proving the validity of our calculation. The calculation of the magnetocrystalline anisotropy and quality factor further rationalize the possibility of hosting magnetic skyrmions or bubbles in Mn-based Ni2In alloys.

Dispersal of Hydrothermal Vent Larvae at East Pacific Rise 9–10°N Segment

AbstractA three‐dimensional, primitive‐equation, ocean circulation model coupled with a Lagrangian particle‐tracking algorithm is used to investigate the dispersal and settlement of planktonic larvae released from discrete hydrothermal habitats on the East Pacific Rise segment at 9–10°N. Model outputs show that mean circulation is anticyclonic around the ridge segment, which consists of a northward flow along the western flank and a southward flow along the eastern flank. Those flank jets are dispersal expressways for the along‐ridge larval transport and strongly affect its overall direction and spatial‐temporal variations. It is evident from model results that the transform faults bounding the ridge segment and off axis topography (the Lamont Seamount Chain) act as topographic barriers to larval dispersal in the along‐ridge direction. Furthermore, the presence of an overlapping spreading center and an adjacent local topographic high impedes the southward along‐ridge larval transport. The model results suggest that larval recolonization within ridge‐crest habitats is enhanced by the anticyclonic circulation around the ridge segment, and the overall recolonization rate is higher for larvae having a short precompetency period and an altitude above the bottom sufficient to avoid influence by the near‐bottom currents Surprisingly, for larvae having a long precompetency period (>10 days), the prolonged travel time allowed some of those larvae to return to their natal vent clusters, which results in an unexpected increase in connectivity among natal and neighboring sites. Overall, model‐based predictions of connectivity are highly sensitive to the larval precompetency period and vertical position in the water column.

Dilute magnetic semiconductor and half-metal behaviors in C-codoped BeO nanotubes: A first principles simulations

The geometric, electronic and magnetic properties of C-codoped single walled BeO nanotubes (SWBeONTs) are systematically explored by using ab-initio density functional theory calculations. We performed our calculations for C codoping BeO nanotube in two different chiralities: (8,0) and (5,5). In each case, two different configurations are considered, first the two oxygen atoms replaced by two carbon atoms are on first nearest neighbor sites in the plane of codoping and second they are far from each other. We found when C atoms are at the nearest-neighboring positions; the antiferromagnetism (AFM) phase is stable while increasing the distance between the two C atoms, the ferromagnetism stability increases. In the AFM phase the structures are nonmagnetic semiconductors, but in the FM phase all these systems are half-metallic systems with high magnetic moment and 100% spin polarization which can be used as magnetic nanostructure and possible future applications in permanent magnetism, magnetic recording, and spintronics.

Colonization and Collapse on Homogeneous Trees

We investigate a metapopulation model referring to populations that are spatially structured in colonies. Each colony thrives during a random time until a catastrophe when only a random amount of individuals of that colony survives. These survivors try independently establishing new colonies at neighbour sites, randomly. If the chosen site is occupied, that individual dies, otherwise the individual founds there a new colony. Here we consider this metapopulation model subject to two schemes: (i) Poisson growth, during an exponential time, for each colony and geometric catastrophe, and (ii) Yule growth, during an exponential time, for each colony and binomial catastrophe. We study conditions on the set of parameters for these processes to survive, present relevant bounds for the probability of survival, for the number of vertices that were colonized and for the reach of the colonies compared to the starting point. As a byproduct we study convergence of sequence of branching processes.

Influence of surface charge density on ligand-metal bonding: A DFT study of NH3 and HCOOH on Mg (0 0 0 1) surface

Activation of the ligand binding to substrate is a highly desirable, yet challenging reaction for biomolecular coating on the biomedical material surface. One advantage of this process is their modular construction on the surface as the biomolecular linkers, allowing for flexible design and detailed control of certain properties. In this work, we studied the binding properties of NH3 and HCOOH on Mg (0 0 0 1) surface and tried to understand the effect of alloy elements in the binding process. First principles within density functional theory (DFT) has been used to investigate the adsorption of NH3 and HCOOH molecules on Mg (0 0 0 1) and Zn-(Y-) doped surfaces. The electron redistribution, effect of alloy element and changes in the density of states of interaction systems are analyzed. Our results revealed that NH3 and HCOOH interact with the Mg (0 0 0 1) surface through dative bond with the adsorption energy (Eads) −0.70 and −0.64 eV, and the Zn/Y alloy element can improve the adsorption process which accompanied by charge-transfer between substrate and adsorbate. Calculated results of the nudged elastic band (NEB) show that the energy barrier of 0.14 eV need to be overcome for NH3 from the neighbor site to Y atom. Our findings provide insight for the binding mechanism of ligand on Mg and Mg-based alloy surfaces and also point out some directions for future experimental efforts.

Temporal disorder in discontinuous nonequilibrium phase transitions: General results

We develop a general theory for discontinuous non-equilibrium phase transitions into an absorbing state in the presence of temporal disorder. We focus in two paradigmatic models for discontinuous transitions: the quadratic contact process (in which activation is only spread when two nearest- neighbor sites are both active) and the contact process with long-range interactions. Using simple stability arguments (supported by Monte Carlo simulations), we show that temporal disorder does not destroy the discontinuous transition in the former model. For the latter one, the first-order transition is turned into a continuous one only in the strong-disorder limit, with critical behavior belonging to the infinite-noise universality class of the contact process model. Finally, we have found that rare temporal fluctuations dramatically changes the behavior of metastable phase turning it into a temporal Griffiths inactive phase characterized by an exponentially large decay time.

Effects of interstitial atoms (N/O) in bcc Fe from first-principle calculations

Based on the supercell structures of bcc-Fe alloys, the structural, electronic, and magnetic properties of bcc Fe with N/O atoms in octahedral interstices were investigated using first-principle calculations. Structural models with double atoms in the near neighbor sites were built; their combined action and the interactions between them were also analyzed. The effects of pressure on the properties of bcc Fe with one N (or O) atom or double N (or O) atoms in the octahedral sites were discussed. After N (O) solid solution, lattice distortion occurs in the bcc-Fe supercells. Interstitial N and O atoms increase the stability of the bcc-Fe supercells. The valence character and ionic character exist in the FeN and FeO bonds. The magnetic moments of the supercells increase after N/O dissolution. The ratios of B/G for Fe54 with N reduce more obviously than that for Fe54 with O. The interstitial atoms (N/O) increase the anisotropy of the mechanical properties of bcc Fe. The magnetic moments of the bcc-Fe supercells decrease with increasing pressure.

Effects of nano-confinement on Zn(II) adsorption to nanoporous silica

Nanopores (at least one dimension ≤100 nm and no dimension <1 nm) are commonly observed features of grain coatings and primary silicate minerals and can contribute substantially to the total surface area available for chemical reactions. Despite the ubiquity of nanopores in natural and synthetic porous media, a generalizable framework for evaluating the effects of nanopore confinement on both fluid and sorbate properties across the entire nanoscale has yet to emerge. As a result, we have a poor understanding of the effect of pore size on molecular-scale processes controlling nano-confinement phenomena in systems in which mineral surfaces are in contact with aqueous solutions.To address these knowledge gaps, we carried out batch experiments designed to reveal the molecular-level details of adsorption reaction products and attendant isotope fractionation of aqueous Zn(II) for synthetic, variably porous, amorphous silica (SiO2(am)) particles with average pore diameters ranging from 10 nm to 330 nm. Shell-by-shell fitting of Zn K-edge extended X-ray absorption fine structure (EXAFS) spectra reveals that Zn(II) (1) adsorbs as dominantly monodentate, corner-sharing complexes to silicate tetrahedra of all SiO2(am) particles examined, regardless of pore size, (2) is tetrahedrally coordinated by oxygen atoms in nanoporous silica with small pore sizes (≤10 nm), and (3) is present as a mixture of tetrahedrally and octahedrally coordinated surface complexes in silica with larger pore sizes (>10 nm). In addition, at low Zn(II) surface coverages (<0.9 μmol m−2) on macroporous SiO2(am), Zn(II) forms a mixture of octahedrally and tetrahedrally coordinated surface complexes, whereas tetrahedrally coordinated surface complexes predominate at higher Zn(II) coverages (>0.9 μmol m−2).Although molecular-level differences in Zn(II) adsorption complexes are apparent with respect to SiO2(am) pore size, we observed no quantifiable differences in attendant isotope fractionation or adsorption edge structure for Zn(II) uptake on nanoporous SiO2(am) surfaces. These results suggest that the differences in binding energy of tetrahedrally versus octahedrally coordinated Zn(II) complexes at the same site on SiO2(am) are small. Comparison of EXAFS spectra to the results of surface complexation modeling (SCM) of experimental Zn(II) uptake data indicates that monodentate Zn(II) adsorption on the SiO2(am) surface releases two protons through binding one site and passivating an adjacent site, which accounts for the modification of surface charge and surface complex structure during adsorption of Zn(II) cations.This study shows that adsorption of Zn(II) in variably porous SiO2(am) results in differences in surface complex geometry as pore size decreases and as surface coverage of Zn(II) increases. Although surface complexation modeling of Zn(II) adsorption edges on macroporous and nanoporous SiO2(am) does not independently identify these molecular-level differences, combination of SCM and molecular-level observations reveals unique insight into the overall adsorption reaction and neighboring surface site reactivity.

Graphdiyne Electrocatalyst

Graphdiyne Electrocatalyst

Electrochemical, Spectroelectrochemical, Mößbauer, and EPR Spectroscopic Studies on Ferrocenyl-Substituted Tritylium Dyes.

Four monoferrocenyl tritylium derivatives with donor-substituted (OMe, NMe2 ) aryl rings are reported, along with their spectroscopic and electrochemical properties. All the complexes show a one-electron reduction and a quasi-reversible ferrocene oxidation at a very positive potential. Small quadrupole splittings, ΔEQ , in Mößbauer spectra agree with highly electron-deficient ferrocenes. Comparison of the experimental half-wave potentials for ferrocene oxidation, E1/2 (Fc/Fc+ ), with those estimated from established correlations of E1/2 (Fc/Fc+ ) with ΔEQ indicates that the E1/2 values of the anisyl-substituted congeners FcOMe+ and FcMeOMe+ are affected by Coulombic repulsion between the positive charges at the Fe ion and the neighboring methylium site. Electronic spectra are recorded and interpreted with the aid of quantum chemical calculations. UV/Vis spectroelectrochemical measurements as well as chemical reduction provide insight into the redox-induced color changes upon ferrocene oxidation or upon reduction to the neutral trityl radicals. The neutral radicals reversibly form EPR-silent dimers. This process is studied by temperature-dependent EPR spectroscopy, and thermodynamic data for their dimerization are determined. Experimental and quantum chemical data suggest that the dimers assume classical hexaarylethane structures as opposed to normal or "offset" Jacobson-Nauta-type structures.

(Invited) Electrochemistry of Solid-State Inorganic Polymer Electrolyte

Electrochemistry explores the charge transfer reaction across the interfaces, such as solid/liquid interface, liquid/liquid interface and also solid/solid interface. Most reported charge transfer behaviours across the “solid/solid” interface are involved liquid electrolyte. For example, in the lithium-ion batteries, the redox of cobalt-based active material is coupled by the heterogeneous intercalation/deintercalation of Li+ ions, which is existed in the electrolyte solution. In another words, the electron transfer occurs at the solid/solid interface while the ion transfer occurs at the solid/electrolyte solution. We employ SECM to construct the solid-solid interface and to study the electron transfer phenomena therein. That means there is no liquid electrolyte environment. When the electron transfer occurs at the solid/solid interface, the counterion transfer will occur in the crystal due to the crystalline defects. For example, we cultured the NaCl microcrystals, which are doped with iron oxides, between the pair electrodes on a microchip. The multi-step electron transfer processes of iron from Fe(0) to Fe(VI) through Fe(II) and Fe(III) were observed. The solid-state electrolyte solution just like an inorganic polymer. The electron transfer is wired through hopping between the neighboring redox lattice sites, coupling with the counterion transfer in the crystalline defects. The electrochemical behavior in the solid-state inorganic “polymer” electrolyte will be discussed in this presentation.

Local Hamiltonians for one-dimensional critical models

Conformal field theory has turned out to be a powerful tool to derive interesting lattice models with analytical ground states. Here, we investigate a class of critical, one-dimensional lattice models of fermions and hardcore bosons related to the Laughlin states. The Hamiltonians of the exact models involve interactions over long distances that are difficult to realize experimentally. This motivates us to study the properties of models with the same type of interactions, but now only between nearest and possibly next-nearest neighbor sites. Based on computations of wavefunction overlaps, entanglement entropies, and two-site correlation functions for systems of up to 32 sites, we find that the ground state is close to the ground state of the exact model. There is also a high overlap per site between the lowest excited states for the local and the exact models, although the energies of the low-lying excited states are modified to some extent for the system sizes considered. We also briefly discuss possibilities for realizing the local models in ultracold atoms in optical lattices.

Mechanistic Insights into the Activity of Mo-Carbide Clusters for Methane Dehydrogenation and Carbon–Carbon Coupling Reactions To Form Ethylene in Methane Dehydroaromatization

Methane dehydrogenation and C–C coupling reactions to form ethylene on two different carbide clusters of molybdenum (Mo4C2 and Mo2C6) were studied. Density functional theory (DFT) calculations were performed to understand the reactivity of the two clusters, linking it to the overall methane dehydroaromatization (MDA) process. The electronic effect of catalyst reduction procedures and anchoring of the cluster on the zeolite framework was captured in simulations with varying positive charge on the cluster. In general, with one exception, DFT calculations suggested a reduction in dehydrogenation activation energies with more reduced (lesser positive charge) clusters. Similarly, activation barriers for the transfer of a H atom from the carbon to the neighboring Mo site were calculated to be lower on more reduced clusters. In contrast, the coupling reactions of the two CH3 and the two H atoms on the surface showed a reverse trend. The activation energies of the C–C and the H–H coupling steps were observed to b...

Comparing Transient and Steady-State Analysis of Single-Ring Infiltrometer Data for an Abandoned Field Affected by Fire in Eastern Spain

This study aimed at determining the field-saturated soil hydraulic conductivity, Kfs, of an unmanaged field affected by fire by means of single-ring infiltrometer runs and the use of transient and steady-state data analysis procedures. Sampling and measurements were carried out in 2012 and 2017 in a fire-affected field (burnt site) and in a neighboring non-affected site (control site). The predictive potential of different data analysis procedures (i.e., transient and steady-state) to yield proper Kfs estimates was investigated. In particular, the transient WU1 method and the BB, WU2 and OPD methods were compared. The cumulative linearization (CL) method was used to apply the WU1 method. Values of Kfs ranging from 0.87 to 4.21 mm·h−1 were obtained, depending on the considered data analysis method. The WU1 method did not yield significantly different Kfs estimates between the sampled sites throughout the five-year period, due to the generally poor performance of the CL method, which spoiled the soil hydraulic characterization. In particular, good fits were only obtained in 23% of the cases. The BB, WU2 and the OPD methods, with a characterization based exclusively on a stabilized infiltration process, yielded an appreciably lower variability of the Kfs data as compared with the WU1 method. It was concluded that steady-state methods were more appropriate for detecting slight changes of Kfs in post-fire soil hydraulic characterizations. Our results showed a certain degree of soil degradation at the burnt site with an immediate reduction of the soil organic matter and a progressive increase of the soil bulk density during the five years following the fire. This general impoverishment resulted in a slight but significant decrease in the field-saturated soil hydraulic conductivity.

Effect of Fourier transform on the streaming in quantum lattice gas algorithms

ABSTRACTAll our previous quantum lattice gas algorithms for nonlinear physics have approximated the kinetic energy operator by streaming sequences to neighboring lattice sites. Here, the kinetic energy can be treated to all orders by Fourier transforming the kinetic energy operator with interlaced Dirac-based unitary collision operators. Benchmarking against exact solutions for the 1D nonlinear Schrodinger equation shows an extended range of parameters (soliton speeds and amplitudes) over the Dirac-based near-lattice-site streaming quantum algorithm.

Integrated geochronology of Acheulian sites from the southern Latium (central Italy): Insights on human-environment interaction and the technological innovations during the MIS 11-MIS 10 period

We have explored the multimethod approach combining 40Ar/39Ar on single crystal, ESR on bleached quartz, and ESR/U-series on teeth to improve the age of four neighbours “Acheulian” sites of the Frosinone Province (Latium, Italy): Fontana Ranuccio, Cava Pompi (Pofi), Isoletta, and Lademagne. Ages obtained by the three methods are in mutual agreement and confirm the potential of dating with confidence Middle Pleistocene sites of Italy using these methods.At Fontana Ranuccio, the 40Ar/39Ar age (408 ± 10 ka, full external error at 2σ) obtained for the archaeological level (unit FR4) and geochemical analyses of glass shards performed on the Unit FR2a layer allow us to attribute the studied volcanic material to the Pozzolane Nere volcanic series, a well-known caldera-forming event originated from the Colli Albani volcanic district. These new data ascribe the Fontana Ranuccio site, as well as the eponym faunal unit, to the climatic optimum of Marine Isotope Stage (MIS) 11. Ages obtained for the Cava Pompi, Isoletta, and Lademagne sites cover a relatively short period of time between 408 ka and 375 ka, spanning MIS 11 climatic optimum to the MIS 11–10 transition. Analysis of small collections of lithic industries, bifacial tools, and small cores technologies from Isoletta, Lademagne, and the neighbour site of Ceprano-Campogrande shows common technical strategies for the period comprised between MIS 11 and MIS 9 (410–325 ka), such as the elaboration of flaked elephant bone industries found over the whole Latium region. However, some features found only in the Frosinone province area, like large-sized bifaces, suggest particular regional behaviours. The presence of one Levallois core in the oldest layer of Lademagne (i.e. > 405 ± 9 ka) suggests a punctual practice of this technology, also proposed as early as MIS 10/11 in the neighbour site of Guado San Nicola (Molise) in central Italy.

&lt;p class="HeadingRunIn"&gt;&lt;strong&gt;Urban Nature Gardens at the Natural History Museum of Los Angeles County attract “wildlife spectacle” of insect pollinators&lt;/strong&gt;&lt;/p&gt;

The newly-constructed Nature Gardens at the Natural History Museum of Los Angeles County (California, USA) were purposefully built to attract wildlife. In this study we wanted to find out to what extent this manufactured environment is successful in attracting native insect fauna to the urban core of the city when compared to the surrounding neighborhoods or natural areas on the periphery of Los Angeles. To determine this, a one-year Malaise trap catch from the Nature Gardens was compared with samples from four neighboring sites within a five-kilometer radius, as well as a site adjacent to natural habitat located sixteen kilometers away. Our analysis focused on the diversity and abundance of three pollinator groups: bees, flower flies and butterflies contrasted with a single non-pollinator group: scuttle flies. Our findings show that the Nature Gardens support greater abundance and diversity than any of the nearby sites or the natural site for all pollinator taxa examined. In contrast, the natural site supported much higher abundance and diversity of the non-pollinator scuttle flies when compared to the Nature Gardens. Calculated evenness of all taxa was lower in the Nature Gardens than at the natural site and Shannon Diversity indices were highest in the Nature Gardens for flower flies and butterflies, but lower in the Nature Gardens than at the natural site for bees and scuttle flies. These results indicate that biodiversity in an urban environment can be selectively manipulated through management of green spaces, but may not duplicate the communities found in natural spaces. Rather, targeted management (through plantings, ground cover and other substrates, watering, pest management techniques, etc.) can increase fauna predictively to create a “wildlife spectacle” of charismatic microfauna.

Temperature-dependence of electrical properties for the ceramic composites based on potassium polytitanates of different chemical composition

The samples of ceramic materials based on potassium polytitanate (PPT) characterized with various TiO2/K2O molar ratio, are produced by calcination at 900 °C and investigated. AC conductivity (σ ac ) of the obtained ceramics is measured at different temperatures between 200 and 800 °C in frequency range of 0.1 Hz–1 MHz. The method of combined impedance and modulus spectroscopy is used to analyze the obtained results. The activation energies of DC conductivity, bulk and grain-boundary conductivity as well as relaxation frequency for studied composites are estimated. Using the correlated barrier hopping (CBH) model, the energies of potential barrier between neighboring defect sites for all kinds of investigated materials are presented. The bulk and grain boundary parameters of the produced ceramic materials based on potassium polytitanates are calculated. The mechanism of different vacancies formation in the investigated ceramic system is discussed. The influence of precursor chemical composition on electrical properties for the ceramic composites based on potassium polytitanates is studied.

NH3 adsorption on anatase-TiO2(101).

The adsorption of ammonia on anatase TiO2 is of fundamental importance for several catalytic applications of TiO2 and for probing acid-base interactions. Utilizing high-resolution scanning tunneling microscopy (STM), synchrotron X-ray photoelectron spectroscopy, temperature-programmed desorption (TPD), and density functional theory (DFT), we identify the adsorption mode and quantify the adsorption strength on the anatase TiO2(101) surface. It was found that ammonia adsorbs non-dissociatively as NH3 on regular five-fold coordinated titanium surface sites (5f-Ti) with an estimated exothermic adsorption energy of 1.2 eV for an isolated ammonia molecule. For higher adsorbate coverages, the adsorption energy progressively shifts to smaller values, due to repulsive intermolecular interactions. The repulsive adsorbate-adsorbate interactions are quantified using DFT and autocorrelation analysis of STM images, which both showed a repulsive energy of ∼50 meV for nearest neighbor sites and a lowering in binding energy for an ammonia molecule in a full monolayer of 0.28 eV, which is in agreement with TPD spectra.