Total Number Of Bonds Research Articles

Investigating agglomeration behavior of recycled asphalt mixtures in mixing stage using discrete element method

The inclusion of clusters in recycled asphalt pavement (RAP) materials has a substantial negative impact on the mechanical properties, particularly affecting the homogeneity formation in recycled asphalt mixtures. Hence, it is imperative to gain insight into the agglomeration and dispersion of RAP materials during the mixing stage. Due to experimental limitations, this study opted for the discrete element method (DEM) as an alternative approach to simulate the mixing process of hot recycled asphalt mixtures containing RAP clusters. The impact of RAP cluster sizes and aging degree was examined. Parameters for the parallel bond model were determined through static loading and stacking angle tests, while contact bond number and dispersion coefficients were calculated to assess the agglomeration and dispersion behaviors of hot recycled asphalt mixtures. The results indicated that an increase in total bond number and a decrease in RAP-RAP bonds demonstrated the formation of new clusters during the mixing process. A critical cluster size (7.1 mm in this study) was identified, requiring more mixing effort for dispersion. Although following the same principle, the influence of aging degree on RAP materials was found to be significant.

Hydrogen Bonding and Infrared Spectra of Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide/Water Mixtures: A View from Molecular Dynamics Simulations

Simulations of ab initio molecular dynamics have been performed for mixtures of ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) ionic liquid and water. Statistics of donors and acceptors of hydrogen bonds has revealed that with increasing water content, hydrogen bonds between EMIM cations and TFSI anions are replaced by bonds to water molecules. In the mixture of liquids, the total number of bonds (from EMIM cations or water molecules) formed by TFSI acceptors increases. IR spectra obtained from ab initio molecular dynamics trajectories are in good agreement with literature data for ionic liquid/water systems. Analysis of oscillations of individual C-H and O-H bonds has shown correlations between vibrational frequencies and hydrogen bonds formed by an EMIM cation or water molecule and has indicated that the changes in the IR spectrum result from the decreased number of water-water hydrogen bonds in the mixture. The tests of DFTB methodology with tailored parameterizations have yielded reasonably good description of the IR spectrum of bulk water, whereas available parameterizations have failed in satisfactory reproduction of the IR spectrum of EMIM-TFSI/water mixtures in the region above 3000 cm-1.

Chemometric QSAR modeling of acute oral toxicity of Polycyclic Aromatic Hydrocarbons (PAHs) to rat using simple 2D descriptors and interspecies toxicity modeling with mouse

The information of the acute oral toxicity for most polycyclic aromatic hydrocarbons (PAHs) in mammals are lacking due to limited experimental resources, leading to a need to develop reliable in silico methods to evaluate the toxicity endpoint. In this study, we developed the quantitative structure-activity relationship (QSAR) models by genetic algorithm (GA) and multiple linear regression (MLR) for the rat acute oral toxicity (LD50) of PAHs following the strict validation principles of QSAR modeling recommended by OECD. The best QSAR model comprised eight simple 2D descriptors with definite physicochemical meaning, which showed that maximum atom-type electrotopological state, van der Waals surface area, mean atomic van der Waals volume, and total number of bonds are main influencing factors for the toxicity endpoint. A true external set (554 compounds) without rat acute oral toxicity values, and 22 limit test compounds, were firstly predicted along with reliability assessment. We also compared our proposed model with the OPERA predictions and recently published literature to prove the prediction reliability. Furthermore, the interspecies toxicity (iST) models of PAHs between rat and mouse were also established, validated and employed for filling data gap. Overall, our developed models should be applicable to new or untested or not yet synthesized PAHs falling within the applicability domain (AD) of the models for rapid acute oral toxicity prediction, thus being important for environmental or personal exposure risk assessment under regulatory frameworks.

Effect of lead and zinc oxides on the thermal properties of tellurite glass systems

Thermal properties of binary (PbO)x(TeO2)1-x, x = 0, 0.10, 0.15, 0.20, 0.25, 0.30 mol% and ternary [ZnO]y[(TeO2)0.7-(PbO)0.3]1-y with y = 0.15, 0.17, 0.20, 0.22, 0.25 mol% were measured. The glass systems were prepared using the conventional melt-quenching technique. The thermal properties of the glasses were investigated using differential scanning calorimetry (DSC) analysis. Thermal analysis of the glasses was realized regarding the glass transition temperature (Tg), glass crystallization temperature (Tc), and glass stability against crystallization (∆T). Quantitative analysis of the Tg of the glass samples was discussed based on the total number of bonds per unit volume and average stretching force constant of each bond in each glass composition. Debye temperature, softening temperature and thermal expansion coefficient, (αP) of the glass samples were calculated based on the measured ultrasonic velocities and densities data. The addition of PbO improved the thermal properties in the binary PbO-TeO2 glasses, while the addition of ZnO showed the different trend to the thermal properties of the ternary ZnO-PbO-TeO2 glasses.

A dispersion-corrected DFT insight into the structural, electronic and CH4 adsorption properties of small tin-oxide clusters

The main goal of this paper is to investigate the structural and electronic properties of small tin-oxide clusters, SnxOy (x = 2–6), before and after methane (CH4) physisorption. To this end, we employ the dispersion-corrected density functional theory (DFT-D2). At first, we demonstrate the relative binding stability of SnxOy clusters with a fixed number of tin atoms via analysis of their binding energy per atom and second-order energy differences. Our results show that the highest relative stability occurs at y = 2, y = 3, y = 4, y = 6 and y = 8 for Sn2Oy, Sn3Oy, Sn4Oy, Sn5Oy and Sn6Oy clusters, respectively. Furthermore, with the cluster size increasing, the ring-shape to cube-like structural crossover is occurred. The higher average coordination and total number of bonds in cube-like clusters make their interatomic bonds weaker and longer. On the other hand, the cube-like clusters, in comparison with ring-shape ones, possess higher chemical potential and lower chemical hardness that lead to their more chemical reactivity. We then proceed to study the CH4 adsorption properties of the resulted most stable clusters. The lowest-energy structures of CH4-adsorbed clusters have been found by comparing the adsorption energy of different configurations. It is found that Van der Waals interactions lead to exothermic physisorption of CH4 on each tin-oxide cluster with the adsorption energy ranging from −101 to −191 meV. In addition, upon CH4 adsorption on SnxOy clusters, the energy gap is decreased which shows an enhancement in the conductivity of the clusters. As a result, the CH4 physisorption ability of these small studied tin-oxide clusters provides their application feasibility as the low-temperature CH4 gas sensors.

Chemical Bonds between Charged Atoms in the Even-Odd Rule and a Limitation to Eight Covalent Bonds per Atom in Centered-Cubic and Single Face-Centered-Cubic Crystals

A crystal is a highly organized arrangement of atoms in a solid, wherein a unit cell is periodically repeated to form the crystal pattern. A unit cell is composed of atoms that are connected to some of their first neighbors by chemical bonds. A recent rule, entitled the even-odd rule, introduced a new way to calculate the number of covalent bonds around an atom. It states that around an uncharged atom, the number of bonds and the number of electrons have the same parity. In the case of a charged atom on the contrary, both numbers have different parity. The aim of the present paper is to challenge the even-odd rule on chemical bonds in well-known crystal structures. According to the rule, atoms are supposed to be bonded exclusively through single-covalent bonds. A distinctive criterion, only applicable to crystals, states that atoms cannot build more than 8 chemical bonds, as opposed to the classical model, where each atom in a crystal is connected to every first neighbor without limitation. Electrical charges can be assigned to specific atoms in order to compensate for extra or missing bonds. More specifically the article considers di-atomic body-centered-cubic, tetra-atomic and dodeca-atomic single-face-centered-cubic crystals. In body-centered crystals, atoms are interconnected by 8 covalent bonds. In face-centered crystal, the unit cell contains 4 or 12 atoms. For di-element crystals, the total number of bonds for both elements is found to be identical. The neutrality of the unit cell is obtained with an opposite charge on the nearest or second-nearest neighbor. To conclude, the even-odd rule is applicable to a wide number of compounds in known cubic structures and the number of chemical bonds per atom is not related to the valence of the elements in the periodic table.

Monte Carlo Simulation Studies of the Size and Shape of Regular Three Generation Dendrimers

By the use of a dynamic Monte Carlo method, three‐generation dendrimers of type F1F2F2 with functionalities F1 = 3 to 6 and F2 = 2 to F1–1 are simulated and investigated as functions of spacer lengths, with a total chain length up to 200 000 segments. Highly diluted athermal and theta solutions are studied as well as properties of non‐reversal random walk dendrimers for comparison. For athermal conditions mean square dimensions obey the same scaling law regarding the total number of bonds as linear chains, irrespective of functionality and complexity. Likewise the theta parameter is the same for all systems investigated. Dimensions of theta systems are slightly expanded as compared to non‐reversal random walk data, the effect increasing with increasing F1 and F2 while shape data near to theta conditions fairly well coincide with those of non‐reversal random walks.

Finite pseudo orbit expansions for spectral quantities of quantum graphs

We investigate spectral quantities of quantum graphs by expanding them as sums over pseudo orbits, sets of periodic orbits. Only a finite collection of pseudo orbits which are irreducible and where the total number of bonds is less than or equal to the number of bonds of the graph appear, analogous to a cut off at half the Heisenberg time. The calculation simplifies previous approaches to pseudo orbit expansions on graphs. We formulate coefficients of the characteristic polynomial and derive a secular equation in terms of the irreducible pseudo orbits. From the secular equation, whose roots provide the graph spectrum, the zeta function is derived using the argument principle. The spectral zeta function enables quantities, such as the spectral determinant and vacuum energy, to be obtained directly as finite expansions over the set of short irreducible pseudo orbits.

Effect of dopants on alumina grain boundary sliding: implications for creep inhibition

We investigate by means of periodic density functional theory the mechanism of grain boundary sliding along the α-alumina Σ11 tilt grain boundary. We identify minimum and maximum energy structures along a preferential sliding pathway for the pure grain boundary, as well as for grain boundaries doped with a series of early transition metals, as well as barium, gadolinium, and neodymium. We predict that the segregation of those dopants results in a considerable increase in the grain boundary sliding barrier. Grain boundary sliding occurs by a series of bond breaking and forming across the grain boundary. Our results suggest that the presence of large cations inhibits the regeneration of bonds during sliding, which results in a decrease in total number of bonds across the grain boundary interface, thereby raising the barrier to sliding. Trends in predicted grain boundary sliding energies are in good agreement with recently measured creep activation energies in polycrystalline alumina, lending further credence to the notion that grain boundary sliding plays a dominant role in alumina creep.

Atomic bond fluctuations and crossover to potential-energy-landscape-influenced regime in supercooled liquid

The ideas related to potential-energy landscape and cooperativity of atomic rearrangements are widely discussed in the research field of glass transition. The crossover transition from high-temperature regime to potential-energy-landscape-influenced regime was extensively studied using the concept of inherent structure. However, the interpretation of this crossover behavior in terms of microscopic changes in real structures is still lacking. In this paper we present several observations on the crossover behavior on real structures. We compare fluctuations in the global properties (total number of bonds, total potential energy, pressure) versus fluctuations in the local properties (coordination number, atomic potential energy, local atomic pressure) by means of molecular dynamics simulations. We then show that the total and local fluctuations in the number of atomic bonds in the system depend on temperature differently above and below the temperature of crossover to the landscape-influenced regime. Similarly, the ratio between the global and local fluctuations in the potential energy and pressure changes in the vicinity of the crossover temperature, whereas the change is less distinct than in the case of the bond fluctuations. Our results indicate that local fluctuations become more correlated below the crossover temperature, most likely via the interaction through the dynamic shear elastic field.

Percolation of a collection of finite random walks: a model for gas permeation through thin polymeric membranes

Motivated by recent studies of gas permeation through polymer networks, we consider a collection of ordinary random walks of fixed length l, placed randomly on the bonds of a square lattice. These walks model polymers, each with l segments. Using computer simulations, we find the critical concentration of occupied bonds (i.e., the critical occupation probability) for such a network to percolate the system. Though this threshold decreases monotonically with l, the critical “mass” density, defined as the total number of segments divided by total number of bonds in the system, displays a more complex behavior. In particular, for fixed mass densities, the percolation characteristics of the network can change several times, as shorter polymers are linked to form longer ones.

Simulating Effects of Fiber Crimp, Flocculation, Density, and Orientation on Structure Statistics of Stochastic Fiber Networks

The Neyman-Scott process is adapted to the problem of simulating the statistical properties of stratified stochastic fibrous materials. The simulations suggest a relationship between the mean number of fibers per zone and mean voids, independent of the nature of the stochastic fibrous structure: the characteristic shape of the transfer function curve persists whether or not the structure contains crimped fibers or if it is random or flocculated, isotropic or anisotropic. This could be an important universal effect. The mean and standard deviation turn out to be positively related for some fiber network parameters, such as mean voids, fiber density, and mean number of fiber bounds. Also, the simulations suggest that fiber crimp has a higher impact on isotropic structures. As crimp is increased, isotropic structures tend to present smaller mean voids, higher mean number of fibers per zone, and higher total number of bonds per fiber than anisotropic structures.

Small-world phenomena in physics: the Ising model

The Ising system with a small fraction of random long-range interactions is the simplest example of small-world phenomena in physics. Considering the latter both in an annealed and in a quenched state we conclude that: (a) the existence of random long-range interactions leads to a phase transition in the one-dimensional case and (b) there is a minimal average number p of these interactions per site (p<1 in the annealed state, and p1 in the quenched state) needed for the appearance of the phase transition. Note that the average number of these bonds, pN/2, is much smaller than the total number of bonds, N2/2.

Ion Beam Damage of Polymer Surfaces: Insights from Molecular-Dynamics Simulation

AbstractMolecular-dynamics simulations are used to model the bombardment of crystalline polyethylene by carbon and rare-gas atoms with kinetic energies between 20 eV and 80 eV. The simulations predict substantial near-surface damage, including radical formation via loss of hydrogen from the chains, insertion of carbon into the polymer backbone, and chain crosslinking. For the rare gas atoms, the observed chemical dynamics are dependent on the mass of bombarding species, with the ratio of broken carbon-hydrogen to carbon-carbon bonds decreasing with increasing mass. The total number of bonds broken, however, is a linear function of kinetic energy with the lighter species having a higher slope and lower threshold energy for inducing damage.

A MARKOVIAN MODEL FOR COOPERATIVE INTERACTIONS IN PROTEINS

A stochastic model for cooperative interactions in proteins is proposed. The description is based on the theory of Markov’s chains and of birth-and-death processes. Even if the model depends only on two parameters: the mean probability p and the coupling capacity∆p, it presents a surprising wealth of qualitative behaviors when the two parameters are varied. In particular we provide numerical evidence of change of concavity of the stationary distribution at a critical value of the coupling capacity ∆p. The main mathematical feature is that the probability of creating a new chemical bond depends on the total number of bonds already present in the system. In this sense, we speak of a cooperative behavior.

Estimations of the aggregation time of various colloidal systems

Scaling approximations for the time after which macroscopic aggregation becomes visible are derived for various colloidal systems. It is shown that the aggregation rate, which is generally used as a measure of stability, is not the only factor determining the aggregation time. The total number of bonds that have to be formed before aggregation becomes visible is at least as important. The aggregation rate increases abruptly when orthokinetic aggregation or sedimentation becomes dominant or just before gelation occurs. This enables the estimation of an aggregation time without the use of an arbitrary or operational definition of visibility. This aggregation time refers to macroscopic aggregation, e.g. visible sedimentation or gelation. Complications that hinder an accurate determination of the aggregation time are listed, and their effects on the aggregation time are predicted. The obtained scaling relations provide useful insights into the progress and results of colloidal aggregation phenomena.

Functionality dependence of the distribution of cyclic species in network formation

The functionality dependence of the ring-size distribution is examined for the branching process of the A–R–Bf– 1 model. It is shown that the equilibrium concentration of j-rings decreases as (∂[Rj]/∂f)k⩽ 0 with increasing functionality f, for a fixed total bond number k. This directly gives rise to another inequality related to the cluster number Ω: (∂Ω/∂f)k⩽ 0.

Geometrical characteristics of compact nanoclusters

The geometrical characteristics of icosahedral and cubo-octahedral clusters are studied. The various shells around the central atom that form the cluster, the number of atoms forming each shell, the number of nearest neighbors to each atom, the various surface sites and the total number of bonds are analyzed. General expressions for the total number of atoms, the total number of surface atoms and their distribution and the total number of bonds are given. Some considerations on the cluster shape stability are also discussed.

Pseudopotential approach to band structure and stability for GaAs/Ge superlattices

The energy-band structure and thermodynamic stability for various GaAs/Ge superlattices with different orientations or atomic configurations are systematically investigated using ab initio, semi-empirical and perturbation pseudopotential methods. The energy band structure and stability are found to strongly depend on n/ N, where n denotes the number of Ga-Ge and Ge-As bonds and N the total number of bonds in the superlattices. The calculated energy-band gap for GaAs/Ge superlattices decreases with an increase of n/ N and disappears in the range of n/ N ⩾ 0.5. The GaAs/Ge superlattices become less stable with an increase of n/ N, since Ga-Ge and Ge-As bonds are energetically unfavorable in the superlattice formation.

Free rotation dimensions of linear polyesters and polyamides

The mean square end-to-end distance 〈 r 2〉 of of several families of polyesters and polyamides in the unperturbed freely rotating state has been calculated. The free rotation dimensions [〈r 2〉 of /N] 1 2 and [〈r 2〉 of /M] 1 2 , where N is the total number of bonds in the chain and M is the chain molecular weight, have been calculated as a function of the number of methylene units for hydroxy-carboxylic acid polyesters, amino-carboxylic acid polyamides, glycol-dicarboxylic acid polyesters, diamino-dicarboxylic acid polyamides, aromatic polyesters and polyamides. Calculations have also been made for Ekanol, Kevlar and poly ( p-benzamide).