Calculation Of Distribution Function Research Articles

MPS-ATLAS: A fast all-in-one code for synthesising stellar spectra

Context. Stellar spectral synthesis is essential for various applications, ranging from determining stellar parameters to comprehensive stellar variability calculations. New observational resources as well as advanced stellar atmosphere modelling, taking three dimensional effects from radiative magnetohydrodynamics calculations into account, require a more efficient radiative transfer. Aims. For accurate, fast and flexible calculations of opacity distribution functions (ODFs), stellar atmospheres, and stellar spectra, we developed an efficient code building on the well-established ATLAS9 code. The new code also paves the way for easy and fast access to different elemental compositions in stellar calculations. Methods. For the generation of ODF tables, we further developed the well-established DFSYNTHE code by implementing additional functionality and a speed-up by employing a parallel computation scheme. In addition, the line lists used can be changed from Kurucz’s recent lists. In particular, we implemented the VALD3 line list. Results. A new code, the Merged Parallelised Simplified ATLAS, is presented. It combines the efficient generation of ODF, atmosphere modelling, and spectral synthesis in local thermodynamic equilibrium, therefore being an all-in-one code. This all-in-one code provides more numerical functionality and is substantially faster compared to other available codes. The fully portable MPS-ATLAS code is validated against previous ATLAS9 calculations, the PHOENIX code calculations, and high-quality observations.

Physical Origin of Distinct Mechanical Properties of Polymer Tethered Graphene Nanosheets Reinforced Polymer Nanocomposites Revealed by Nonequilibrium Molecular Dynamics Simulations

AbstractA non‐equilibrium deformation simulation based on standard molecular dynamics is employed to reveal the physical origin of distinct mechanical properties of polymer nanocomposites (PNCs) reinforced by polymer tethered graphene nanosheets (P/G‐T). The effect of tethered polymer length (L) and interaction strength on the mechanical properties, including tensile stress, modulus, and yield strength, are examined. The simulation results show that the P/G‐T systems exhibit improved mechanical properties as L and interaction strength increases. The strengthening in attractive interaction between matrix polymer and tethered polymer has a better effect on mechanical properties than that between P and graphene nanosheets. It is found that the bond orientation and nonbonding potential is of crucial importance in determining the mechanical properties of the P/G‐T nanocomposite systems. The calculations of radial distribution functions and mean‐squared displacement are further performed to reveal the physical origin of enhanced mechanical properties, suggesting that the stronger interfacial interactions will induce the closer packing distance with smaller free volume, higher polymer chain entanglement, and higher restriction of polymer chain movement, which synergistically contribute to the improvement in the mechanical properties. The results may provide useful guidance for promoting the development and practical application of the advanced PNCs with excellent performance.

The longitudinal structure function in the presence of QED effects

The highest precision for theoretical predictions at the high LHC energy requires the calculation of parton distribution function (PDFs) and the structure functions which include heavy quarks that include perturbative QCD and QED corrections. In this paper, the first, we review calculation of PDFs with QED corrections that we obtain them from the QCD⊗QED DGLAP evolution equations in Mellin space in NLO QCD and NLO QED approximations. We give a detailed explanation of the approach that we follow to determine the longitudinal structure functions up to O(αs2) in QCD, O(ααs) and O(α2) in QED approximations. We show how our method gives an exact representation for the total longitudinal structure functions, FL(x,Q2), including the heavy quark structure functions in terms of the PDFs based on the Mellin transform techniques, valid to all orders in QED and QCD. In this work, we investigate the effects of the O(ααs) and O(α2) corrections to PDFs on the longitudinal structure functions. We compare our results with APFEL and experimental data in the different values of Q2. The results are shown that the QED corrections have a small but non-negligible impact on the structure functions.

Tribological Behavior of Poly(tetrafluoroethylene) and Its Composites Reinforced by Carbon Nanotubes and Graphene Sheets: Molecular Dynamics Simulation

Low‐dimensional fillers play an important role in improving the tribological properties of poly(tetrafluoroethylene) (PTFE) composites. However, the reinforcement mechanism is not fully understood, since few in situ experiments are able to capture the dynamics evolution and interfacial behavior of fillers. Herein, the tribological behavior of PTFE composites filled with graphene (Gr) sheets and carbon nanotubes (CNT) at the nanoscale is investigated. The results demonstrate that the composites filled with the CNT and Gr fillers have much better wear resistance than that of the pure PTFE, and the wear amounts are reduced by 76.2% and 85.7%, respectively. The relative bond and angle energy of PTFE indicate less deformation in the reinforced composite matrices. The calculations of interfacial interaction energy and radial distribution function reveal that the Gr fillers have better reinforcements than CNT due to stronger interactions at the Gr/PTFE interfaces.

Investigation of the reactivity properties of a thiourea derivative with anticancer activity by DFT and MD simulations.

Spectroscopic analysis of 1-(2-fluorophenyl)-3-[3-(trifluoromethyl)phenyl]thiourea (FPTT) is reported. Experimental and theoretical analyses of FPTT, with molecular dynamics (MD) simulations, are reported for finding different parameters like identification of suitable excipients, interactions with water, and sensitivity towards autoxidation. Molecular dynamics and docking show that FPTT can act as a potential inhibitor for new drug. Additionally, local reactivity, interactivity with water, and compatibility of FPTT molecule with frequently used excipients have been studied by combined application of density functional theory (DFT) and MD simulations. Analysis of local reactivity has been performed based on selected fundamental quantum-molecular descriptors, while interactivity with water was studied by calculations of radial distribution functions (RDFs). Compatibility with excipients has been assessed through calculations of solubility parameters, applying MD simulations. Graphical abstract Reactive sites identified.

Highly-concentrated electrolyte incorporating Li-ion solvation sheath interphase for encapsulation-free organic electrochromic devices

Electrolytes play an essential role in boosting the performance of electrochromic devices (ECDs), nevertheless, the detailed impact of highly-concentrated electrolytes (HCEs) on electrochromism remains elusive. In this work, we creatively report an eco-friendly, aqueous HCE based on lithium bis (trifluoromethanesul-phonyl)-imide (TFSILi), and investigate the potential of developed electrolyte for ECD applications through combining experimental and molecular dynamic simulation approaches. The radial distribution function calculations reveal that the primary solvation sheath of Li-ion is greatly alterd by the concentration of electrolyte. The formation of Li-ion solvation sheath containing TFSI− in electrolyte protects the electrochromic (EC) layer from being destroyed by free water. Mean squared displacement shows that the diffusion coefficient of Li-ion in 15 M HCE reaches up to 8.5 × 10−11 m2/s, indicating that high ion mobility enables faster charge transfer and efficient transport of Li-ion promotes interfacial reaction kinetics, which correlates-well with the experimental conductivity results. These findings demonstrate that HCEs can substantially improve the performance of organic ECDs, especially in terms of device stability, optical memory and switching rate. Notably, the solvation sheath nature of the developed HCE enables the development of encapsulation-free devices, which is greatly attractive for the industrialization of EC technology.

MATHEMATICAL MODEL FOR CALCULATING THE STRUCTURE OF A LIQUID (MELT) USING DISTRIBUTION FUNCTIONS

This article considers a spatio-temporal study of the structure of melts using the correlation functions of the distribution of physical and chemical analysis. The authors consider the properties of metallic melts and their dependence on the physical state of the melt. The dynamic structure of the melt is considered, the numerical description is given. The binary distribution function is distinguished as the one that best corresponds to the structure of the fluid. With the help of the atomic distribution function, if the interaction potentials are known, it is possible to find the equation of state of a system fluid, to determine its energy, compression, and a number of other kinetic and thermodynamic quantities. The atomic distribution function allows you to quantify the parameters of the short order in a liquid. The authors indicate two approaches for the theoretical calculation of the atomic distribution function to quantify short-range parameters in a fluid based on integro-differential equations that relate correlation functions to interaction potentials.
 For real systems, the most common methods of finding the radial distribution function are the method of diffraction of X-rays, neurons or electrons. This paper presents the results of X-ray diffraction by Pb-Cd melts, calculated functions of radial distribution of atomic density, presents the main parameters of the radial distribution function and the results of model interpretation.
 The article proves that the implementation of the mathematical model is possible through the theoretical calculation of distribution functions. The authors took as a basis the solutions of integro-differential equations, which include both the equation of the complete and correlation functions, and the equation that connects the distribution functions with the even interaction potential. The proposed mathematical model is implemented using the function of radial distribution of atomic density on the basis of physicochemical analysis. As a result of realization, the dependences of the percentage of atoms on the coordination numbers calculated in two ways in the graphical results are obtained.

Electron Swarm Parameters and Dielectric Properties of the Superconducting Binary Mixtures of He-H2

In this study, the electron energy distribution function EEDF, the electron swarm parameters, the effective ionization coefficients, and the critical field strength (dielectric strength) in binary He-H2 gas mixture which used as cryogenic for high-temperature superconducting power application, are evaluated by using two-term approximation of the Boltzmann equation over the range of E/N ( the electric field to gas density) from 1 to 100 Td ( 1 Td=10-17 Vcm2) at temperature 77 K and pressure 2MPa, taking into account elastic and inelastic cross-section. Using the calculated EEDF, the electron swarm parameters (electron drift velocity, mean electron energy, diffusion coefficient, electron mobility, ionization and attachment coefficient) are calculated. At low reduced electric field E/N, the EEDF close Maxwellian distribution, at high E/N, due to vibrational excitation of H2 the calculated distribution function is non-Maxwellian. Besides, in the He-H2 mixture, it is found that increasing small amount of H2 enhances to shift the tail of EEDF to the lower energy region, the reduced ionization coefficient α/N. reduced effective ionization coefficient (α-η)/N) decreases, while, reduced attachment coefficient η/N, reduced critical electric field strength (E/N)crt. and critical electric field Ecrt. Increases, because of hydrogen’s large ionization cross-sections. The dielectric strength of 5% H2 in mixture is in good agreement with experimental values, it is found that dielectric strength depend on pressure and temperature. The electron swarm parameters in pure gaseous helium (He) and hydrogen (H2), in satisfying agreement with previous available theoretical and experimental values. The validity of the calculated values has been confirmed by two-term approximation of the Boltzmann equation analysis.

QCD factorization for twist-three axial-vector parton quasidistributions

The transverse component of the axial-vector correlation function of quark fields is a natural starting object for lattice calculations of twist-3 nucleon parton distribution functions. In this work we derive the corresponding factorization expression in terms of twist-2 and twist-3 collinear distributions to one-loop accuracy. The results are presented both in position space, as the factorization theorem for Ioffe-time distributions, and in momentum space, for the axial-vector quasi- and pseudodistributions.

SELECTION OF OPTIMAL AL–SI COMBINATIONS IN CAST IRON FOR CASTINGS FOR ENGINEERING PURPOSES

In this work, the optimal combinations of Al – Si in cast iron for cast parts for machine-building purposes were determined with the aim of subsequent selection of rational modes of modification and alloying, and the possibility of their implementation under industrial smelting conditions was checked.
 The graphical dependence Si=f (Al) is obtained, which is a set of optimal combinations of the content of Al and Si in cast iron, providing the maximum ultimate tensile strength UTS≈245 ... 334 MPa.
 The technological audit of the results of serial industrial smelting included the analysis of actual indicators, the calculation of sample distribution functions (mathematical expectation and dispersion) of the Al and Si content in the alloy, as well as the UTS value. The correspondence of the indicators of the content of Al and Si and the value of σ to the optimal values was assessed by testing the statistical hypotheses: H: M(Al)=Alopt, M(Si)=Siopt, M(σв)=σвopt.On the basis of the obtained results of the assessment of statistical characteristics and verification of hypotheses, it was established that at the chosen significance level α=0.05, the technological process of smelting satisfies the requirements of optimality in terms of the Si content, but in terms of the Al content, the technological process does not meet the requirements of optimality.
 The proposed procedure for choosing the optimal combinations of Al and Si makes it possible to choose the amount of correcting additives depending on the actual indicators of the chemical composition during the smelting process. To do this, it is necessary to assess the closeness of the actual composition to the optimal curve Si=f(Al) and choose the one that most satisfies the criteria of rationality. The latter can be the cost of ferroalloys, through which Al and Si are introduced

ViewSq, a Visual Molecular Dynamics (VMD) module for calculating, analyzing, and visualizing X-ray and neutron structure factors from atomistic simulations

viewSq, a Visual Molecular Dynamics (VMD) module for calculating, analyzing, and visualizing X-ray and neutron structure factors from atomistic simulations

Microscopic Study on the Mechanism of Tool Bond Wear in Cutting Ni–Fe-Cr-Co–Cu Series Nickel-Base Superalloy

In the process of nickel-based alloy machining, chips are easy to bond on the tool surface, which weaken the tool performance and make the tool wear. Therefore, it is very important to study the mechanism of tool bond wear in the process of nickel-based superalloy machining. In order to reflect the wear process of the tool from the perspective of micro cutting, the molecular dynamics simulation model for cutting Ni–Fe-Cr-Co–Cu nickel-based alloy with SiC tool was established. The Morse potential functions between the tool and workpiece are calculated, and the simulation results are analyzed visually. It is found that the bond wear is the main wear form of tool in the process of cutting nickel-based alloy, and the wear processes are divided into three stages: contact, adhesion and shedding. The stress and strain in the cutting area are calculated and it is found that the bond occurs when the tool-workpiece extrusion is strong. Through the calculation of radial distribution function and formation energy, it is found that Ni-Si compound is formed on the tool surface, and the newly generated Ni-Si compound reduces the tool performance compared with the silicon carbide structure. This study provides a more complete microscopic explanation of the tool wear mechanism, which is helpful to find a method to prolong tool life.

Next-to-Next-to-Leading Order Calculation of Quasiparton Distribution Functions.

We present the next-to-next-to-leading order (NNLO) calculation of quark quasiparton distribution functions (PDFs) in the large momentum effective theory. The nontrivial factorization at this order is established explicitly and the full analytic matching coefficients between the quasidistribution and the light-cone distribution are derived. We demonstrate that the NNLO numerical contributions can improve the behavior of the extracted PDFs sizably. With the unprecedented precision study of nucleon tomography at the planned electron-ion collider, high precision lattice QCD simulations with our NNLO results implemented will enable to test the QCD theory and more precise results on the PDFs of nucleons will be obtained.

Gluon distributions and their applications to Ioffe-time distributions

We investigate unpolarized and polarized gluon distributions and their applications to the Ioffe-time distributions, which are related to lattice QCD calculations of parton distribution functions. Guided by the counting rules based on the perturbative QCD at large momentum fraction $x$ and the color coherence of gluon couplings at small $x$, we parametrize gluon distributions in the helicity basis. By fitting the unpolarized gluon distribution, the inferred polarized gluon distribution from our parametrization agrees with the one from global analysis. A simultaneous fit to both unpolarized and polarized gluon distributions is also performed to explore the model uncertainty. The agreement with the global analysis supports the $(1-x)$ power suppression of the helicity-antialigned distribution relative to the helicity-aligned distribution. The corresponding Ioffe-time distributions and their asymptotic expansions are calculated from the gluon distributions. Our results of the Ioffe-time distributions can provide guidance to the extrapolation of lattice QCD data to the region lacking precise gluonic matrix elements. Therefore, they can help regulate the ill-posed inverse problem associated with extracting the gluon distributions from discrete data from first-principle calculations, which are available in a limited range of the nucleon momentum and the spatial separation between the gluonic currents. Given various limitations in obtaining lattice QCD data at large Ioffe time, phenomenological approaches can provide important complementary information to extract the gluon distributions in the entire $x$ region. The possibility of investigating higher-twist effects and other systematic uncertainties in the contemporary first-principle calculations of parton distributions from phenomenologically well-determined Ioffe-time distributions in the large Ioffe-time region is also discussed.

The x-dependence of hadronic parton distributions: A review on the progress of lattice QCD.

In this article, we review recent lattice calculations on the x-dependence of parton distributions, with the latter providing information on hadron structure. These calculations are based on matrix elements of boosted hadrons coupled to non-local operators and can be related to the standard, light-cone distribution functions via an appropriate factorization formalism. There is significant progress in several directions, including calculations of flavor-singlet parton distribution functions (PDFs), first calculations of generalized parton distributions (GPDs), as well as the implementation of some of the approaches for the transverse-momentum-dependent PDFs (TMD PDFs). This new direction of lattice calculations is particularly interesting for phenomenological fits on experimental data sets, as the lattice results can help improve the constraints on the distribution functions.

Valence-quark distribution of the kaon and pion from lattice QCD

We present the first lattice-QCD calculation of the kaon valence-quark distribution functions using the large-momentum effective theory (LaMET) approach. The calculation is performed with multiple pion masses with the lightest one around 220 MeV, 2 lattice spacings $a=0.06$ and 0.12 fm, $(M_\pi)_\text{min} L \approx 5.5$, and high statistics ranging from 11,600 to 61,312 measurements. We also calculate the valence-quark distribution of pion and find it to be consistent with the FNAL E615 experimental results, and our ratio of the $u$ quark PDF in the kaon to that in the pion agrees with the CERN NA3 experiment. We also make predictions of the strange-quark distribution of the kaon.

Modelling of plasma gamma ray sources in large tokamaks

• Methodology for creation of realistic plasma gamma ray source for Monte Carlo simulations. • Connection between plasma physics simulations and gamma ray Monte Carlo transport. • Methodologies for generation of position, energy and direction sampling distributions from plasma parameters. • Methodology testing with a simplified MCNP tokamak model. Understanding the physics of fast ions in a fusion plasma is widely considered as one of the crucial tasks for the reliable operation of fusion tokamak reactors. Measurements on tokamaks have shown that gamma rays are produced when fast ions react with either plasma fuel ions or with the plasma impurities such as beryllium, carbon and oxygen. The spectroscopy of these gamma rays can be used for measurement of fusion rates in plasma or behaviour and confinement of fusion reaction products, such as the alpha particles. To computationally support experiments a methodology has been developed for creation of a realistic plasma gamma ray source for Monte Carlo simulations. The methodology presented in this paper consists of several steps. First the generation of realistic plasma parameters with the code TRANSP on the basis of experimental measurements. Second the generation of sampling distribution functions from the calculated plasma parameters such as the calculation of the source position distribution function based on the rate densities for the gamma ray emitting reaction. Third the creation of realistic plasma gamma ray source for the code MCNP gamma ray transport simulation. The developed methodology was analysed on a MCNP tokamak model to demonstrate that the methodology generates a realistic plasma gamma ray source for Monte Carlo simulations.

Electron parameters in a hollow cathode discharge plasma in He and He:H2O mixture

The electron energy distribution functions (EEDFs) were measured in the discharge plasma in pure helium and in helium with the addition of water vapor He:H2O (2:1). The studies were carried out in the discharge gap between the rectangular hollow cathode and the mesh anode using the original probe measurement system. It was established, in particular, that the EEDF in He had pronounced maxima in the regions of ∼4 eV and ∼15 eV, while in the He:H2O mixture there was no local maximum in the high-energy region. The EEDF calculations in the local approximation for experimental conditions were performed. It turned out that the calculated distribution functions differ noticeably from the measured ones. The possible physical causes leading to the discrepancy between the measured and calculated EEDFs were discussed.

Molecular Dynamics Simulation Study of N2/CO2 Displacement Process of Methane Hydrate

AbstractIn this paper, we construct three kinds of hydrate replacement models: N2, CO2 and N2‐CO2. The molecular dynamics (MD) method is used to study the dynamic process of N2‐CO2 replacement for natural gas hydrate. The replacement efficiency of N2/CO2 is simulated, and the influence of gas replacement on the stability of the water cage is assessed. The results show that CH4 molecules in the driving hydrate are all enriched in the gas‐liquid interface or gas region. Compared with the replacement of methane hydrate with CO2, when N2‐CO2 mixed gas is used to replace methane hydrate, the diffusion rate of CO2 is increased by 2 times, and the replacement efficiency of hydrate is significantly improved. The radial distribution function and free energy calculation results show that although the barrier of the water cage is significantly reduced after replacement, the water molecules in the cage still have difficulty jumping over the free energy barrier compared with the thermal motion energy, so the water cage structure remains highly stable.

Electrolyte nanofluid performance on the oil detachment from an oil-wetted carbonate surface: Water channel formation using molecular dynamics simulation

In this research, molecular dynamics simulation is used to provide a molecular-scale insight into the working mechanisms of the silica nanoparticles in oil detachment from carbonate surface in absence and presence of ionic compounds. The oil model comprises of heptane, decane and toluene mixture. The contents of aqueous phase are variated in different cases: (I) water, (II) water and ions of Na+, Cl−, Mg2+and SO42−, (III) water and silica nanoparticles and (IV) water, silica nanoparticles and individual ions. In each simulation, an oil layer with a thickness of 15°A were placed between the calcite surface and the water phase to cut the interactions between calcite surface and oil phase and form an oil-wet surface. According to the results, in the absence of nanoparticles, the aqueous layer could not change the conformation of the oil layer. However, in presence of nanoparticles, water molecules could diffuse into the oil phase and move toward calcite surface. Contact angle measurement showed oil contact angle reaching to 112.5° and 120.5° for the systems of (III) and (IV), respectively. Radial distribution function calculation showed more nanoparticles approaching the calcite surface in the presence of ions yielding to more detachment of the oil molecules and also showed the Na+ and Cl− ions more effects than Mg2+ and SO42−.