The European Physical Journal E最新文献

For a static granular system, the constitutive equation of its stress tensor is of great significance for understanding its mechanical behaviors. Under isostatic state, it can have the form of stress-geometry equation. To investigate the force moment tensor and the stress-geometry equation of a two-dimensional (2D) granular system in theory, we propose some algebraic theories such as the decomposition formula of a second-order tensor and the cross-product of two symmetric tensors for the dyadic space (mathbb {T}^{2}(mathbb {R}^{2})). For a 2D frictionless disk packing, the local stress-geometry equation for a disk with three or four contacts is derived based on the definition of force moments tensor and the equilibrium equation of contact forces. The definition of the geometry tensor in the stress-geometry equation shows complex associations between the contact branch vectors of a disk with three or four contacts. For a disk with four contacts, its local Janssen coefficient can be given from the eigenvalues of its geometry tensor. Discrete element method (DEM) simulations for random frictionless disk packings are performed to verify two local stress-geometry equations in this paper, and the numerical results are in good agreement with the theoretical predictions. The local stress-geometry equations are convenient for obtaining some information about the stress tensors according to the contact structures without knowing the details of the deformations and the intergranular interactions.

 We study the formation of propagating large-scale density waves of mixed polar-nematic symmetry in a colony of self-propelled agents that are bound to move along the planar surface of a thin viscous film. The agents act as an insoluble surfactant, i.e. the surface tension of the liquid depends on their density. Therefore, density gradients generate a Marangoni flow. We demonstrate that for active matter in the form of self-propelled surfactants with local (nematic) aligning interactions such a Marangoni flow nontrivially influences the propagation of the density waves. Upon gradually increasing the Marangoni parameter, which characterises the relative strength of the Marangoni flow as compared to the self-propulsion speed, the density waves broaden while their speed may either increase or decrease depending on wavelength and overall mean density. A further increase in the Marangoni parameter eventually results in the disappearance of the density waves. This may occur either discontinuously at finite wave amplitude via a saddle-node bifurcation or continuously with vanishing wave amplitude at a wave bifurcation, i.e. a finite-wavelength Hopf bifurcation.

Two-dimensional monodisperse linear polymer chains are known to adopt for sufficiently large chain lengths N and surface fractions (phi ) compact configurations with fractal perimeters. We show here by means of Monte Carlo simulations of reversibly connected hard disks (without branching, ring formation and chain intersection) that polydisperse self-assembled equilibrium polymers with a finite scission energy E are characterized by the same universal exponents as their monodisperse peers. Consistently with a Flory-Huggins mean-field approximation, the polydispersity is characterized by a Schulz–Zimm distribution with a susceptibility exponent (gamma =19/16) for all not dilute systems and the average chain length (left<N right>propto exp (delta E) phi ^{alpha }) thus increases with an exponent (delta = 16/35). Moreover, it is shown that (alpha =3/5) for semidilute solutions and (alpha approx 1) for larger densities. The intermolecular form factor F(q) reveals for sufficiently large (left<N right>) a generalized Porod scattering with (F(q) propto 1/q^{11/4}) for intermediate wavenumbers q consistently with a fractal perimeter dimension (d_s=5/4).

Snapshot of a subvolume of a much larger configuration of strictly two-dimensional equilibrium polymers as considered in this study for a broad range of surface fractions and scission energies. Despite the low dimensionality and the strong polydispersity of the annealed chain systems, the same univeral scaling relations and asymptotic exponents as for their monodisperse quenched peers are found as suggested by a simple Flory-Huggins type mean-field approximation. This holds especially for semidilute solutions and dense melts where the chains are demonstrated to adopt compact configurations of a fractal perimeter dimension 5/4. The intermolecular form factor F(q) thus reveals a generalized Porod scattering with (F(q) propto 1/q^{11/4}) for intermediate wavenumbers q Snapshot of a subvolume of a much larger configuration of strictly two-dimensional equilibrium polymers as considered in this study for a broad range of surface fractions and scission energies. Despite the low dimensionality and the strong polydispersity of the annealed chain systems, the same univeral scaling relations and asymptotic exponents as for their monodisperse quenched peers are found as suggested by a simple Flory-Huggins type mean-field approximation. This holds especially for semidilute solutions and dense melts where the chains are demonstrated to adopt compact configurations of a fractal perimeter dimension 5/4. The intermolecular form factor F(q) thus reveals a generalized Porod scattering with (F(q) propto 1/q^{11/4}) for intermediate wavenumbers q

 A topological index is a numerical value that correlates with a chemical structure. A degree-based topological index of drug molecular structures is beneficial for researchers investigating in the fields of medicals and pharmaceuticals because it is significant for testing the physicochemical properties of drugs. Graph theory has proven to be quite useful in this field of study. Graph analysis reveals insights into chemical structures. In physical chemistry, a line graph has multiple applications. This article focuses on the topological characterization of a line graph for antiviral COVID-19 drugs, namely Nirmatrelvir, Molnupiravir, Thalidomide, Theaflavin, Remdesivir, Ritonavir, Chloroquine, Hydroxychloroquine, Arbidol and Lopinavir. The computation of degree-based topological indices is carried out using their M-polynomials. Numerical values of topological indices of line graphs and geometric representations of the polynomials are shown graphically. A comparative study between the obtained values of the line graph and the values of an actual graph is presented through numerical and graphical representation. Furthermore, we conduct a QSPR analysis between the degree-based topological indices of the line graph of certain COVID-19 drugs and their physicochemical properties using curvilinear regression models. A comparison is made between the squared correlation coefficients derived from our curvilinear regression models and those obtained from earlier research. These findings may aid the applicability of newly developed drugs of similar kind, in predicting their physicochemical properties and in improving the associated QSPR studies and hence pave a way to improve treatments against the COVID-19 disease.

This study advances the quantitative structure–property relationship analysis by leveraging novel vertex–edge-weighted (VEW) molecular graphs to investigate 19 drug molecules commonly used to treat cardiovascular diseases and diabetes. The graphs are constructed by assigning weights to vertices and edges based on atomic properties, enabling a detailed and chemically meaningful representation of molecular structures. Python-based programs were developed to compute degree-based topological indices, which were then analyzed through robust linear regression models to uncover correlations with key physicochemical properties. The results reveal strong and consistent relationships between the computed indices and the physicochemical properties, validating the predictive capability of the proposed approach. Notably, the VEW model demonstrates significant improvements in accuracy and correlation strength over traditional unweighted molecular graph models, underscoring its enhanced ability to capture intricate molecular interactions. This work provides novel insights into the utility of degree-based topological indices in drug design, particularly for cardiovascular and diabetic treatments. By bridging theoretical modeling with practical pharmaceutical applications, it lays a solid foundation for optimizing molecular properties, improving drug efficacy, and accelerating the drug development pipeline. These findings reaffirm the growing significance of computational strategies in advancing precision medicine and pharmaceutical innovation.

Droplet generation under steady conditions is a common microfluidic method for producing biphasic systems. However, this process works only over a limited range of imposed pressure: beyond a critical value, a stable liquid jet can instead form. Furthermore, for a given geometry, the pressure conditions set both the generation rate of droplets and their volume. Here, we report on-demand droplet production using a positive pressure pulse to the dispersed-phase inlet of a flow-focusing geometry. This strategy enables confined droplet generation within and beyond the pressure range observed under steady conditions, and decouples volume and production rate. In particular, elongated plugs not possible under steady conditions may be formed when the maximal pressure during the pulse reaches the jet regime. The measured volume of droplets-on-demand as well as the onset of droplet generation are both captured with a simple model that considers hydraulic resistances. This work provides a strategy and design rules for processes that require individual droplets or elongated plugs in a simple microfluidic chip design.