Number Of Atoms Research Articles

Massive-vortex realization of a Bosonic Josephson Junction

We study the mass exchange between two rotating, quantum massive vortices in a two-component Bose-Einstein condensate. The vortices, in the majority component, exhibit a filled core, where the in-filling minority component undergoes a quantum tunneling effect. Remarkably, we observe that the two-vortex system features stable Josephson oscillations, as well as all the nonlinear phenomena, including the macroscopic quantum self-trapping, that characterize a Bosonic Josephson Junction. We propose an analytical model for describing the intervortex tunneling, obtained by implementing the coherent-state representation of the two-mode Bose-Hubbard model. This allows us to give the explicit expression of the model's parameters in terms of the physical macroscopic parameters of the two-vortex system. The comparison of the dynamical scenario predicted by the model with that emerging from the Gross–Pitaevskii equations is very good for sufficiently small atom numbers, while at larger atom numbers it grows less precise, presumably due to the partial exclusion of the many-body interactions from our model. The definition of an effective self-interaction parameter allows us to include the many-body effects, thus restoring a quite good agreement with the numerical results. Interestingly, the recognition of the bosonic Josephson dynamics paves the way to the investigation of new dynamical behaviors in multivortex configurations. Published by the American Physical Society 2024

Stable Truncated Trigonometric Moment Problems

Let , be an one dimensional complex sequence of degree at most 2n. In the present paper we give a necessary condition such that admits on an atomic representing measure with a finite number of atoms. The necessary condition is expressed in terms of "stability" of the Riesz linear non-negative functional, , associated to the given sequence. We also give a necessary and sufficient condition such that the extended sequence to admit on an unique atomic representing measure with a finite number of atoms. The "stability" condition of the introduced Riesz functional is an adaption of the concept "dimension stability" by Vasilescu introduced for solving Hamburger moment problems in [5]. In section 3 of the present paper, we apply the main existence theorem for determining representing measures with 1, 2, 3 atoms, according to the rank of the moment matrix. The representing measures of the data of the quadratic moment problem have the support in the unit circle.

Unravelling the intricacies of fluorescence enhancement in heptamethine cyanine dyes induced by heavy halogen atoms

The classic heavy-atom effect refers to the photophysical phenomenon observed in fluorophores, where the interaction with heavy atoms quenches fluorescence emission. Many fluorophores containing heavy halogen atoms, such as xanthenes, BODIPYs, porphyrins, and anthracenes, adhere to this effect, while the photophysical behavior of others, e.g. halogenated heptamethine cyanine dyes, is poorly studied having contradicting results. In this study, we explored for the first time unexpected fluorescence enhancement induced by heavy halogen atoms in heptamethine dyes, contrasting the classic heavy-atom effect. To this end, a series of novel heptamethine cyanine dyes were synthesized and their photophysical properties were experimentally and theoretically investigated. Heavy halogen atoms were found to significantly affect the fluorescence behaviour of heptamethine dyes depending on the number and position of the attached halogens. Thus, the introduction of bromine and iodine atoms at the non-conjugated positions to the chromophore moieties led to an increase in the fluorescence quantum yields, which contradicts the classic principle and could be explained by heavy halogen-induced vibration restrictions. The value of halogen atom-promoted singlet oxygen generation quantum yield ΦΔ is also not straightforward and depends on the number, position and weight of the halogen atom. The breaking of the classic heavy-atom effect in halogenated heptamethine dyes provides an effective strategy to substantially increase the fluorescence intensity of long-wavelength cyanine dyes, providing new functional advantages for fluorescence imaging, diagnostics, and photodynamic therapy, among other applications.

Measurements and kinetic modeling of O2 vibrational Kknetics in O2-Ar mixtures partially dissociated by a Ns pulse discharge

Abstract Vibrational kinetics of O2 is studied during the O atom recombination in an O2-Ar mixture, partially dissociated by a burst of ns discharge pulses in a heated plasma flow reactor. The time-resolved temperature in the discharge afterglow is determined by Rayleigh scattering. Time-resolved O atom number density is measured by ps Two-Photon absorption Laser Induced Fluorescence (TALIF), calibrated in xenon. Time-resolved vibrational level populations of molecular oxygen, O2(v=8-20), are measured by ps Laser Induced Fluorescence (LIF), with the absolute calibration by NO LIF. Time-resolved ozone number density is monitored by broadband UV absorption. The results are compared with the predictions of a state-specific kinetic model. The experimental data indicate a rapid initial decay of O2(v) populations generated by electron impact in the discharge, due to the vibration-translation (V-T) relaxation by O atoms. This is followed by a slower population reduction, on the time scale much longer compared to that for V-T relaxation or vibration-vibration (V-V) exchange. Both O atoms and the O2(v) populations decay on the same time scale, indicating that chemical reactions initiated by the O atom recombination result in the generation of vibrationally excited O2 molecules. These trends are reproduced by the kinetic model, which shows that the reaction of O atoms with ozone is the dominant pathway of O2(v) generation at the present conditions. The predicted relative O2(v) populations are close to the experimental results, but absolute number densities differ from the experimental data. This is likely due to uncertainties in the absolute calibration of LIF measurements and in the spectroscopic model used in the data reduction. The present work demonstrates the capability for the absolute, time-resolved measurements of vibrationally excited O2 in recombining gas flows, to quantify the energy partition in the recombination reactions.

Effect of Doped Carbon Atoms on Electronic Structure and Optical Properties of Monolayer 1T-ZrS2

In this paper, a method based on density functional theory is used to replace varying numbers of sulfur atoms with carbon atoms in the original monolayer ZrS2 system, resulting in a new doped system. The theory is based on the First Principle. The photovoltaic properties of the new carbon-atom doping systems have been calculated and investigated. The pristine system and the carbon-atom doped systems were structurally optimized using the automatic optimization method. It was found that the stability of the structure decreases as the number of carbon atoms increases. Pristine monolayer 1T-ZrS2 is an indirect bandgap material. The results show that after doping carbon atoms in monolayer 1T-ZrS2, the p-type conductivity of the system increases and exhibits metallicity. The density of states analysis shows that the conduction band consists mainly of S-3p, Zr-4d, Zr-4p, Zr-5s and C-2p orbitals, while the valence band consists mainly of S-3p, S-3s, Zr-4d, C-2p and C-2s orbitals. It is concluded that strong hybridization between Zr-d and S-p orbitals is exhibited by both the pristine and doped systems. The analysis of the optical properties shows that the peak absorption coefficient and reflectivity peaks are blue-shifted in the doped system, and these peaks are lower than in the pristine system. The peaks of the real and imaginary parts of the dielectric function are also blue shifted. With the increase of doping concentration, the system’s energy loss decreases, indicating that proper doping can effectively reduce the system’s energy loss. The above studies provide theoretical support for applying ZrS2 in nano-optoelectronics.

Molecular dynamics study of the microstamping of TiAl6V4 alloy.

Microstamping has been shown to enhance the surface strength of alloy materials by improving interatomic density. This paper delves into the damage mechanism of TiAl6V4(TC4), which has been processed using high-speed stamping with varying overlap ratios at the atomic level. Additionally, the general trend of stress variation between loading and unloading is discussed. The mechanical properties of the substrate and the changes in microstructure resulting from varying overlap rates in microstamping were investigated. The impact of different machining overlap ratios on the depth of the damaged layer, the number of dislocation density lines, and the density of the matrix is also explored. The results indicate that the dislocation density remains relatively unchanged due to material hardening, while the overlap ratio increases continuously. Based on this analysis, a more optimal microstamping overlay ratio parameter is proposed to effectively enhance the surface strength of the substrate and reduce processing time. First, an alloy model with titanium, aluminum, and vanadium was created in ATOMSK and LAMMPS software. The model was divided into three layers: fixed, constant temperature, and Newton. To ensure the accuracy of the simulation, the system was annealed in order to minimize energy and replicate real-world conditions. Zhou's EAM alloy potential was employed to represent the interaction between the alloy atoms, while the Tersoff potential was used to represent the interatomic interaction of the diamond indenter. Additionally, the LJ potential function was selected to depict the interaction between the metal atom and the diamond indenter. The construct surface mesh method in OVITO software was then utilized to construct a surface mesh and analyze the impact of different machining overlap rates on surface topography. The common neighborhood analysis (CNA) module in OVITO was used to calculate the number of defective atoms and the depth of the damaged layer. Finally, the DXA (dislocation extraction analysis) module in OVITO was used to calculate the dislocation density length and dislocation density.

External-cavity diode laser at 2.6 µm and its frequency stabilization with a scanning Fabry-Pérot cavity

We report on the construction of an external cavity diode laser at 2.6 µm wavelength and its frequency stabilization with an external scanning Fabry-Pérot cavity using Pound-Drever-Hall (PDH) frequency stabilization technique. We discuss the frequency noise characteristics of the laser using the PDH residual error signal analysis and the locking performance. We have achieved a 2.5 x 105 suppression factor in the frequency noise power spectral density at Fourier frequencies lower than 100 Hz when the laser is stabilized. The laser is employed to observe resonant excitation on the 5s5p3P0 →5s4d3D1 transition in cold 88Sr atoms trapped in a magneto-optical trap. We have observed an enhancement in the trapped atom number by a factor of 8.3 compared to the case when a single laser at 707 nm is employed for repumping.

Lead‐Sulfide‐Based Hybrid Inorganic‐Organic Superlattice Particles for Prominent Nonlinear Optical Absorption

AbstractSimultaneously optimizing nonlinear absorption coefficient and modulation depth is a considerable challenge for nonlinear optical materials. Here we present an effective solution through constructing PbS2‐based inorganic‐organic superlattice. PbS2/Cn superlattice particles are synthesized, where n (4, 6, and 8) denotes the number of carbon atoms in the organic component. First‐principles simulations indicate the formation of covalent bonds and van der Waals interaction between PbS2 unit and interlayer organic molecules. All samples exhibit strong nonlinear absorption under femtosecond laser excitation with a wavelength range between 515 nm and 900 nm, and the nonlinear absorption coefficient increases with interlayer distance. The optimized sample, PbS2/C8, demonstrates outstanding nonlinear absorption and substantial modulation depth under 800 nm (the third‐order nonlinear absorption coefficient βeff, 10449 ± 609 cm GW−1; modulation depth, 39.1%) and 900 nm (the fifth‐order nonlinear absorption coefficient γeff, 6465 ± 68 cm3 GW−2; modulation depth, 88.1%), which exhibits saturable absorption under 515 nm (βeff, ‐4932 ± 818 cm GW−1; modulation depth, 48.1%). It exhibits a small optical limiting threshold of 1.23 mJ cm−2. These performances surpass those of typical single‐/few‐layer metal chalcogenides. Structural and spectral analyses elucidate that the remarkable optical nonlinearity can be attributed to quantum confinement in the inorganic layer and the dielectric enhancement of the superlattice.

Difference in the Catalytic Activity of Atoms in the Corners and at the Edges of Gold Nanoparticles: Hydrogen Isotope Exchange Reaction.

The goal of this work is to investigate the catalytic activities of low-coordination atoms located in gold nanoparticles. Gold nanoparticles with sizes from 0.7 to 40 nm deposited on γ-Al2O3 were used as a catalyst. Synthesized gold nanoparticles and prepared catalysts were characterized by HRTEM, SEM, XRD, DLS, and UV-Vis spectroscopy. The specific activity of gold nanoparticles towards the isotope exchange reaction at 77 K was studied as a function of nanoparticle size. The catalytic activity increases significantly when the particle size is less than 3 nm. The activities of low-coordination gold atoms located at the edges and in the corners are markedly different. Corner atoms (CN = 6) are more than 40 times more active in the reaction of hydrogen isotope exchange than edge atoms (CN = 7). TOF for atoms with coordination numbers CN = 6 and CN = 7 are 0.258 ± 0.020 and 0.006 ± 0.001 molecules site-1 s-1, respectively. An equation was proposed for the dependence of the catalytic activity of the reaction on the particle size, the number of atoms on the surface, and their activity.

Screening the organic materials database for superconducting metal-organic frameworks.

The increasing financial and environmental cost of many inorganic materials has motivated study into organic and "green" alternatives. However, most organic compounds contain a large number of atoms in the primitive unit cell, posing a significant barrier to high-throughput screening for functional properties. In this work, we attempt to overcome this challenge and identify superconducting candidates among the metal-organic-frameworks in the organic materials database using a recently proposed proxy for the electron-phonon coupling. We then isolate the most promising candidate for in-depth analysis, C9H8Mn2O11, providing evidence for superconductivity below 100mK.

Graphene Oxide-Enhanced Nucleation and Growth of Calcium-Silicate-Hydrate Gel at Nanoscale: A Molecular Dynamics Study.

Graphene oxide (GO) enhances the performance of cement-based materials by optimizing the microstructure of calcium-silicate-hydrate (C-S-H). However, the influence of GO on the nucleation and growth of C-S-H gel at nanoscale is unexplored. This study investigates this mechanism by molecular dynamics simulation at nano scale. Results show that GO can reduce the activation energy during the polymerization reaction of silicon oxide tetrahedra during the reaction process, and can increase the content of polymer Q3 and Q4. The influence of GO with epoxy (-O-), hydroxyl (-OH) and carboxyl (-COOH) groups on the radial distribution function (RDF), mean square displacement (MSD), and atomic spatial distribution of monomers are studied. Results show that GO-OH exhibits excellent performance, with the highest number of bridging oxygen atoms (about 0.6), the lowest Q0 monomer content (just 26.8%), the highest RDF (27.18), and the highest MSD (calcium and silicon content around 20,000 Å2). This paper elucidates the nucleation and growth mechanism of C-S-H influenced by GO to develop high performance cement.

NUMERICAL DESCRIPTION OF THE DISTRIBUTION OF n-PARAFFINS CONTENT IN VACUUM GAS OIL AND THEIR REACTIVITY IN THE HYDROCRACKING PROCESS

Currently, the process of hydrocracking of heavy petroleum feedstocks is one of the main processes that makes it possible to increase the depth of oil refining and to obtain high-quality motor fuel components, including diesel fuel components with improved low-temperature properties. In this paper, a review on the existing modelling approaches and models of the heavy oil feedstock hydrocracking process is presented. The object of the research is the process of vacuum gasoil hydrocracking. The work proposes the scheme of chemical transformations in the process of hydrocracking and the model of the process. The distinctive feature of the proposed chemical transformations scheme and a model is taking into account the hydrocracking reactions of individual n-paraffins. It is proposed to determine the content of individual n-paraffins in the feedstock of the process (vacuum gas oil) by the number of carbon atoms in the molecule based on the probability distribution, using the Gaussian function as a probability density function. The reactivity of individual n-paraffins in the hydrocracking reaction was taken into account via thermodynamic characteristics of the reactions of each individual n-paraffin determined using quantum-chemical methods. The calculation of the detailed composition of the target diesel product including the content of n-paraffins provides determination of cold filter plugging point, which is influenced by the content of n-paraffins to the most extent. The developed detailed model of vacuum gasoil hydrocracking process includes the equations for calculation of changes in concentrations of reacting component and change in the temperature of the process. The proposed approach to the modelling of the hydrocracking process makes it possible to optimize the process taking into account the detailed composition to get the maximum yield of low freezing diesel fuel. For citation: Belinskaya N.S. Numerical description of the distribution of n-paraffins content in vacuum gas oil and their reactivity in the hydrocracking process. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 11. P. 95-105. DOI: 10.6060/ivkkt.20246711.7039.

Limitation of single-repumping schemes for laser cooling of Sr atoms

We explore the efficacy of two single-repumping schemes, 5s5pP23−5p2P23 (481nm) and 5s5pP23−5s5dD23 (497nm), for a magneto-optical trap (MOT) of Sr atoms. We reveal that the enhancement in the MOT lifetime is limited to 26.9(2) for any single-repumping scheme. Our investigation indicates that the primary decay path from the 5s5pP11 state to the 5s5pP03 state proceeds via the 5s4dD13 state, rather than through the upper states accessed by the single-repumping lasers. We estimate that the branching ratio for the 5s5pP11→5s4dD13→5s5pP03 decay path is 1:3.9(1.5)×106 and the decay rate for the transition from the 5s5pP11 state to the 5s4dD13 state is 83(32)s−1. This outcome underscores the limitation on atom number in the MOT for long loading times (≳1s) when employing a single-repumping scheme. These findings will contribute to the construction of field-deployable optical lattice clocks. Published by the American Physical Society 2024

Correlative activation free energy (CAFE) model: Application to viscous processes in inorganic oxide glass-formers

We explore the concept of correlative activation free energy (CAFE) for the analysis and interpretation of viscosity data of a collection of 847 inorganic oxide glass formers that exhibit various degrees of non-Arrhenius behavior. The CAFE model formalism is strictly based on transition state theory and accounts for the variation in the activation barrier height for the viscous dissipation due to the structural evolution the system undergoes upon traversing the glass transition regime. Thus, fitting parameters are meaningful in a statistical thermodynamic context. Compared to the VFT and MYEGA equations, fits using the CAFE model are more robust when extrapolating to infinite temperature because the latter encodes non-enthalpic contributions to the rate coefficient more realistically. The CAFE model-based analysis reveals a strong connection between melt fragility and the degree of change in the potential energy landscape with temperature. Accordingly, while the average ground-state potential energy of the glass forming liquid gradually increases with temperature, the energy of the activated state remains relatively invariant. Our analysis also allows one to estimate the number of atoms involved in the viscous relaxation process, which ranges from approximately 10 to 50 atoms for the oxide glass formers studied. We observe that thermally activated dynamic phenomena exhibited by glassy networks, such as the mixed alkali effect, persist into the supercooled liquid state.

Conductivity Prediction Method of Solid Electrolyte Materials Based on Pearson Coefficient Method and Ensemble Learning

In order to screen solid electrolytic materials with high ionic conductivity more quickly and accurately, a conductivity prediction method for solid electrolyte materials based on logistic regression model and random forest regression model is constructed. The method first selects 20 characteristic descriptors related to ionic conductivity from material library according to four dimensions: structural stability, metal stability, electronic conductivity and oxidative decomposition stability. The enumeration method and feature selection method are used to combine different features. Then, the dimension reduction of the feature combinations is carried out by Pearson coefficient method, so as to screen the optimal feature combinations. Finally, according to the optimal feature combination and data subset, the constructed random forest ensemble learning model is utilized to predict the ionic conductivity of other solid-state electrolyte materials in the material library, in order to find the solid-state electrolyte materials that can meet the high conductivity. The results indicate that as the number of features in the combination increases, the prediction performance of the model shows a trend of first increasing and then decreasing. When the feature descriptor in the combination is 7, the maximum AUC (Accuracy) value is reached, and the optimal feature in this case contains 7 optimal feature subsets corresponding to feature descriptors, namely the standard deviation of the average adjacency number of Li atoms, the standard deviation of Li-X ion bonds, the average electronegativity of the straight path, the average width of the straight path, the average atomic volume, the average Li-Li bond, and the filling fraction of the sublattice. On the basis of the optimal feature screening, the average prediction accuracy of the logistic regression model is 87.13%, which has a high accuracy. Using the random forest regression model for prediction, the average absolute error and root mean square error obtained are only 0.237 and 0.134, and compared with classical classification methods such as KNN, SVM and Adaboost, they are smaller, which can better predict the ionic conductivity of solid electrolyte materials. This proves that the constructed method can quickly and accurately produce high ionic conductivity materials in solid electrolyte materials, which is worthy of further research and promotion.

The Reconstruction of Pt(001) Surface and the Shell-Like Reconstruction of the Vicinal Pt(001) Surfaces Revealed by Neural Network Potential.

In this work, a highly accurate neural network potential (NNP) is presented, named PtNNP, and the exploration of the reconstruction of the Pt(001) surface and its vicinal surfaces with it. Contrary to the most accepted understanding of the Pt(001) surface reconstruction, the study reveals that the main driving force behind Pt(001) quasi-hexagonal reconstruction is not the surface stress relaxation but the increased coordination number of the surface atoms resulting in stronger intralayer binding in the reconstructed surface layer. In agreement with experimental observations, the optimized supercell size of the reconstructed Pt(001) surface contains (5×20) unit cells. Surprisingly, the reconstruction of the vicinal Pt(001) surfaces leads to a smooth shell-like surface layer covering the whole surface and diminishing sharp step edges.

Modulating the carbon chain length of organic phosphine for the selective Au(I) recovery from a copper-ammonia-thiosulfate leaching solution

The selective recovery of gold ions from gold leaching solutions limits the industrial application of the copper-ammonia (Cu2+–NH3)-thiosulfate system. Here, the influence of the carbon chain length of organic phosphines on the selective recovery of gold ions was studied, and an extractant (trihexylphosphine, THP) that is suitable for the selective recovery of gold ions from a Cu2+–NH3-thiosulfate leaching solution was screened. The selectivity of organic phosphines with different carbon chain lengths for gold ions was C8 = C6 > C4 > C3 > C2, and when the number of carbon atoms in a single carbon chain was at least six, the selective recovery of gold ions from the Cu2+–NH3-thiosulfate solution was realized. THP completely recovered low concentration gold ions (6.73 mg/L) in the Cu2+–NH3-thiosulfate gold leaching solution regardless of the pH. The mechanism of gold ion extraction into the organic phase mainly involved ligand exchange between THP and [Au(S2O3)2]3−. Job’s method and density functional theory calculations confirmed that the composition ratio of the complex formed by THP and Au was 2:1 at the practical and theoretical levels, respectively. Finally, Multiwfn and VMD were used to visually predict the possible reaction sites in THP. This study provides an exact method for the selective recovery of gold ions from thiosulfate-based gold leaching solutions, which will promote the development of thiosulfate-based gold leaching systems

Towards a new generation of solid total-energy detectors for neutron-capture time-of-flight experiments with intense neutron beams

Challenging neutron-capture cross-section measurements of small cross sections and samples with a very limited number of atoms require high-flux time-of-flight facilities. In turn, such facilities need innovative detection setups that are fast, have low sensitivity to neutrons, can quickly recover from the so-called γ-flash, and offer the highest possible detection sensitivity. In this paper, we present several steps toward such advanced systems. Specifically, we describe the performance of a high-sensitivity experimental setup at CERN n_TOF EAR2. It consists of nine sTED detector modules in a compact cylindrical configuration, two conventional used large-volume C6D6 detectors, and one LaCl3(Ce) detector. The performance of these detection systems is compared using 93Nb(n, γ) data. We also developed a detailed Geant4 Monte Carlo model of the experimental EAR2 setup, which allows for a better understanding of the detector features, including their efficiency determination. This Monte Carlo model has been used for further optimization, thus leading to a new conceptual design of a γ detector array, STAR, based on a deuterated-stilbene crystal array. Finally, the suitability of deuterated-stilbene crystals for the future STAR array is investigaged experimentally utilizing a small stilbene-d12 prototype. The results suggest a similar or superior performance of STAR with respect to other setups based on liquid-scintillators, and allow for additional features such as neutron-gamma discrimination and a higher level of customization capability.

Embedded Many‐Body Green's Function Methods for Electronic Excitations in Complex Molecular Systems

ABSTRACTMany‐body Green's function theory in the GW approximation with the Bethe–Salpeter equation (BSE) provides a powerful framework for the first‐principles calculations of single‐particle and electron–hole excitations in perfect crystals and molecules alike. Application to complex molecular systems, for example, solvated dyes, molecular aggregates, thin films, interfaces, or macromolecules, is particularly challenging as they contain a prohibitively large number of atoms. Exploiting the often localized nature of excitation in such disordered systems, several methods have recently been developed in which GW‐BSE is applied to a smaller, tractable region of interest that is embedded into an environment described with a lower‐level method. Here, we review the various strategies proposed for such embedded many‐body Green's functions approaches, including quantum–quantum and quantum–classical embeddings, and focus in particular on how they include environment screening effects either intrinsically in the screened Coulomb interaction in the GW and BSE steps or via extrinsic electrostatic couplings.

Synthesis of 1,2,3‐Triphospholenes, 1,2‐Diphosphetes, and Unsymmetric Phospholes by Rhodium‐catalyzed Cleavage of P−P Bonds and Addition to Alkynes

AbstractThe rhodium‐catalyzed addition reaction of cyclo‐(PPh)5 to alkynes in refluxing THF efficiently provide 1,2,3‐triphospholenes, in which the –PPh–PPh–PPh– group is transferred from cyclo‐(PPh)5 by the cleavage of P−P bonds. In refluxing chlorobenzene, the reactions are accompanied by the formation of 1,2‐diphosphetes. When the triphospholenes containing P−P bonds are reacted with reactive alkynes under rhodium‐catalyzed conditions, unsymmetric phospholes are obtained. The rhodium‐catalyzed reactions can be used to synthesize various phosphorus‐containing heterocycles with different numbers of phosphorus atoms.