equilibrium structure
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2022 ◽  
Belinda Boehm ◽  
David Huang

From classical molecular dynamics simulations, we identify a simple and general predictor of molecular orientation at solid and vapour interfaces of isotropic fluids of anisotropic particles based on their shape and interaction anisotropy. For a wide variety of inter-particle interactions, temperatures, and substrate types within the range of typical organic semiconductors and their processing conditions, we find remarkable universal scaling of the orientation at the interface with the free energy calculated from pair interactions between close-packed nearest neighbours and an empirically derived universal relationship between the entropy and the shape anisotropy and bulk volume fraction of the fluid particles. The face-on orientation of fluid particles at the solid interface is generally predicted to be the equilibrium structure, although the alignment can be controlled by tuning the particle shape and substrate type, while changing the strength of fluid--fluid interactions is likely to play a less effective role. At the vapour interface, only the side-on structure is predicted, and conditions for which the face-on structure may be preferred, such as low temperature, low interaction anisotropy, or low shape anisotropy, are likely to result in little orientation preference (due to the low anisotropy) or be associated with a phase transition to an anisotropic bulk phase for systems with interactions in the range of typical organic semiconductors. Based on these results, we propose a set of guidelines for the rational design and processing of organic semiconductors to achieve a target orientation at a solid or vapour interface.

Physics ◽  
2021 ◽  
Vol 3 (4) ◽  
pp. 1123-1132
Júlio C. Fabris ◽  
Túlio Ottoni ◽  
Júnior D. Toniato ◽  
Hermano Velten

A Newtonian-like theory inspired by the Brans–Dicke gravitational Lagrangian has been recently proposed by us. For static configurations, the gravitational coupling acquires an intrinsic spatial dependence within the matter distribution. Therefore, the interior of astrophysical configurations may provide a testable environment for this approach as long as no screening mechanism is evoked. In this work, we focus on the stellar hydrostatic equilibrium structure in such a varying Newtonian gravitational coupling G scenario. A modified Lane–Emden equation is presented and its solutions for various values of the polytropic index are discussed. The role played by the theory parameter ω, the analogue of the Brans–Dicke parameter, in the physical properties of stars is discussed.

A.K. Dorosh ◽  
N.M. Bilko ◽  
D.I. Bilko

The rheological properties of the gel-like material, the monomer of which is a crosslinked and modified 2-propenamide of acrylic acid, were determined by relaxation rheometry methods. The values of its elastic modulus and modulus of losses and complex viscosity depending on: deforming stress and its frequency are determined; relative deformation; temperature in the range (20-100) ° C and the regularities of these dependences are noted. It is established that: 1) the dependence of the modulus of elasticity (G'); modulus of loss (G'') and complex viscosity from: relative deformation; voltage; temperature; frequencies indicate that in the linear scale they change according to nonlinear dependencies, and in the transition to the logarithmic scale contain plateau-like areas; 2) analytical dependences of the above parameters on stress, strain rate and temperature are complex and difficult to establish; 3) in the range (20-80) ° C and relative deformations (10-100)% hydrogel has a virtually unchanged value of the modulus (G ') ten times greater than the modulus (G' '), whichdetermines the uniqueness of its rheological and biophysical properties ;  4) in the region (20-80) ° C hydrogel in terms of modulus of elasticity and tangent of the angle of loss is close to a completely elastic body; 5) when the frequency of the deforming voltage is more than 15.8 Hz and the relative deformation ≥100%, the gel is brittlely deformed; while the modulus of its elasticity decreases abruptly and the modulus of losses increases rapidly with increasing frequency of the deforming stress. 6) the dependence of the elastic-viscosity characteristics of the samples washed and unwashed in saline gel in the temperature range (20-80) ° C differ little and indicate that the equilibrium structure of the hydrogel 2-propenamide acrylic acid belongs to the typical colloidal dispersed structure of gelatinous substances.

Hong-Jie Bai ◽  
Long-Qing Chen ◽  
Hao Deng ◽  
Xian-Bo Liu ◽  
Xiao-Rong Qin ◽  

A new high-pressure structure of hafnium monocarbide (HfC) has been predicted by particle swarm optimization (PSO) algorithm based on first principles calculations. The newly found phase AuCu (L1[Formula: see text] belongs to the tetragonal P4/mmm space group. The transition pressure of NaCl (B1)[Formula: see text]L10 is predicted to be 387.6 GPa, which is much lower than that of B1[Formula: see text]CsCl (B2). L10 phase is found to transform to B2 structure at [Formula: see text]896.7 GPa. The structural stability criterion for tetragonal crystal was successfully deduced, which confirms the mechanical stability of L10 phase according to the calculated elastic constants. Thus, the equilibrium structure of HfC under high pressure was predicted to be L10 phase instead of B2. Furthermore, the bulk modulus, shear modulus, Young’s modulus and the compressional and shear wave velocities of HfC in B1 and L10 phases are found to increase monotonically as the pressure increases.

2021 ◽  
Vol 118 (38) ◽  
pp. e2110995118
Yuechuan Xu ◽  
Kaitlin Knapp ◽  
Kyle N. Le ◽  
Nicholas P. Schafer ◽  
Mohammad S. Safari ◽  

Amyloid fibrillization is an exceedingly complex process in which incoming peptide chains bind to the fibril while concertedly folding. The coupling between folding and binding is not fully understood. We explore the molecular pathways of association of Aβ40 monomers to fibril tips by combining time-resolved in situ scanning probe microscopy with molecular modeling. The comparison between experimental and simulation results shows that a complex supported by nonnative contacts is present in the equilibrium structure of the fibril tip and impedes fibril growth in a supersaturated solution. The unraveling of this frustrated state determines the rate of fibril growth. The kinetics of growth of freshly cut fibrils, in which the bulk fibril structure persists at the tip, complemented by molecular simulations, indicate that this frustrated complex comprises three or four monomers in nonnative conformations and likely is contained on the top of a single stack of peptide chains in the fibril structure. This pathway of fibril growth strongly deviates from the common view that the conformational transformation of each captured peptide chain is templated by the previously arrived peptide. The insights into the ensemble structure of the frustrated complex may guide the search for suppressors of Aβ fibrillization. The uncovered dynamics of coupled structuring and assembly during fibril growth are more complex than during the folding of most globular proteins, as they involve the collective motions of several peptide chains that are not guided by a funneled energy landscape.

2021 ◽  
Vol 155 (5) ◽  
pp. 054302
Brian J. Esselman ◽  
Maria A. Zdanovskaia ◽  
Andrew N. Owen ◽  
John F. Stanton ◽  
R. Claude Woods ◽  

G.P. Kolomiychuk ◽  
V.G. Kolomiichuk ◽  
V.G. Kolomiichuk ◽  

To create fundamentally new innovative large-span structures of buildings and structures coverings, modern design solutions of prestressed cable domes of the Tensegrity type are considered. The service life of the first built Tensigrity domes is only 35 years. These are fairly new, effective structures that require careful study and use of modern scientific approaches for their design using software systems, since their work under load and the construction process are quite complex. The design analysis and erection of self-stressed structures is based on the invention of an equilibrium structure, the so-called tensegrity form. The search for the shape is multidimensional and consists of the stage of computational analysis of a self-stressed dome for the equilibrium position of elements and their nodes, selection of the most stable and rigid structure, as well as taking into account possible unfavorable loads during operation and the initial load in the elements from the application of prestressing. To determine the shape of cable domes, a nonlinear programming problem with given axial forces is formulated, which can be considered as the problem of minimizing the difference in the total strain energy between the elements of the cables and struts under constraints on the compatibility conditions. The first step in calculating the prestressing of a cable dome is to assess the feasibility of its geometry. The possibility of forming a cable dome of negative Gaussian curvature is considered and a method for calculating the prestressing for this new shape is investigated. The proposed method is effective and accurate in determining the allowable prestressing for a cable dome with negative Gaussian curvature and can be used for other types of prestressed structures. The new directions for the development of effective constructive solutions for large-span coatings are presented, including a suspended-dome structure, which combines the advantages of a mesh shell and a cable dome. Special attention should be paid to experimental studies on models of tensegrity domes, the results of which demonstrate the positive and negative aspects of the behavior of structures under load, the process of their erection, as well as the possibility of control and restoration during operation.

2021 ◽  
Vol 154 (24) ◽  
pp. 244310
Vanessa L. Orr ◽  
Yotaro Ichikawa ◽  
Aatmik R. Patel ◽  
Samuel M. Kougias ◽  
Kaori Kobayashi ◽  

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