Vibrational Frequencies for Model Silicates: Extensions Beyond Molecular Properties

1990 ◽  
Vol 209 ◽  
Author(s):  
Kim F. Ferris ◽  
Steven M. Risser
Keyword(s):  
Molecular Complexes ◽  
Ceramic Materials ◽  
Vibrational Frequencies ◽  
Molecular Properties ◽  
Model Systems ◽  
Surface Absorption ◽  
Reaction Field ◽  
Silica Surfaces ◽  
Surrounding Matrix ◽  
Structure Calculations

The investigation of surface properties for ceramic materials often focuses on molecular properties, both in terms of model systems and methods. Typically, we use molecular species (i.e. SiO4H4 , H3SiOH) to represent silica surfaces, often resulting in poor prediction of absorption phenomena. Dielectric effects, even when approximated by electrostatic and dipolar interactions, can have significant effects on the charge distribution and surface absorption characteristics of model molecular complexes. In this paper, we report on the effect of the surrounding matrix on the harmonic vibrational frequencies by employing reaction field techniques in electronic structure calculations. Comparisons of molecular-based to reaction field affected properties will be made to illustrate the extensions of the molecular to the extended network domain.

scholarly journals Relativistic Effects on the Equation-of-State of the Light Actinides

2005 ◽  
Vol 893 ◽  
Author(s):  
Alexander Landa ◽  
Per Söderlind
Keyword(s):  
Electronic Structure ◽  
Equation Of State ◽  
Density Functional ◽  
Relativistic Effects ◽  
Model Systems ◽  
Face Centered Cubic ◽  
Electronic Structure Methods ◽  
The Face ◽  
Face Centered ◽  
Structure Calculations

AbstractThe effect of the relativistic spin-orbit (SO)interaction on the bonding in the early actinides has been investigated by means of electronic-structure calculations. Specifically, the equation of state (EOS) for the face-centered cubic (fcc) model systems of these metals has been calculated from the first-principles density-functional (DFT) theory. Traditionally, the SO interaction in electronic-structure methods is implemented as a perturbation to the Hamiltonian that is solved for basis functions that explicitly do not depend on SO coupling. Here this approximation is shown to compare well with the fully relativistic Dirac treatment. It is further shown that SO coupling has a gradually increasing effect on the EOS as one proceeds through the actinides and the effect is diminished as density increases.

scholarly journals Dielectric and Absorbate Effects on the Optical Properties of Phosphazenes

1993 ◽  
Vol 328 ◽  
Author(s):  
KIM F. Ferris ◽  
W. D. Samuels ◽  
Y. Morita ◽  
G. J. Exarhos
Keyword(s):  
Optical Properties ◽  
Electronic Structure ◽  
Nonlinear Optical ◽  
Electronic Structure Calculations ◽  
Model Systems ◽  
Cyclic Molecules ◽  
Out Of Plane ◽  
Linear And Nonlinear ◽  
Bonding Systems ◽  
Structure Calculations

ABSTRACTThe optical response of polyphosphazenes can be directly related to the π (out-of-plane) and π′ (in-plane) bonding interactions intrinsic to the electronic structure of these Materials. Altering this structure either by hydrogen bonding or absórbate effects, affects both the linear and nonlinear optical susceptibilities. In this paper, we have performed electronic structure calculations on the cyclic Molecules, P3N3 (NHCH3)6, P3N3(SCH3)6, P3N3 (OCH3)6 and P4N4 (NHCH3)8 as model systems for the polymer. Charge distribution arguments are discussed to explain the influence of a polarizing electric field on the π bonding systems, and are used to suggest methods to enhance their nonlinearities.

scholarly journals Cell contraction induces long-ranged stress stiffening in the extracellular matrix

2018 ◽  
Vol 115 (16) ◽  
pp. 4075-4080 ◽  
Author(s):  
Yu Long Han ◽  
Pierre Ronceray ◽  
Guoqiang Xu ◽  
Andrea Malandrino ◽  
Roger D. Kamm ◽  
...  
Keyword(s):  
Extracellular Matrix ◽  
Optical Tweezers ◽  
Model Systems ◽  
Animal Cells ◽  
Surrounding Matrix ◽  
Highly Nonlinear ◽  
Nonlinear Stress ◽  
Nonlinear Mechanical ◽  
The Matrix ◽  
3D Matrix

Animal cells in tissues are supported by biopolymer matrices, which typically exhibit highly nonlinear mechanical properties. While the linear elasticity of the matrix can significantly impact cell mechanics and functionality, it remains largely unknown how cells, in turn, affect the nonlinear mechanics of their surrounding matrix. Here, we show that living contractile cells are able to generate a massive stiffness gradient in three distinct 3D extracellular matrix model systems: collagen, fibrin, and Matrigel. We decipher this remarkable behavior by introducing nonlinear stress inference microscopy (NSIM), a technique to infer stress fields in a 3D matrix from nonlinear microrheology measurements with optical tweezers. Using NSIM and simulations, we reveal large long-ranged cell-generated stresses capable of buckling filaments in the matrix. These stresses give rise to the large spatial extent of the observed cell-induced matrix stiffness gradient, which can provide a mechanism for mechanical communication between cells.

The Origin of Biological Information

1997 ◽  
Vol 161 ◽  
pp. 443-453 ◽  
Author(s):  
Manfred Eigen
Keyword(s):  
Natural Selection ◽  
Genetic Information ◽  
Charles Darwin ◽  
Molecular Model ◽  
Molecular Complexes ◽  
Living System ◽  
Model Systems ◽  
Biological Information ◽  
Equilibrium Process ◽  
Controlled Reproduction

What is the distinguishing feature of a living system that singularizes it from every non-living chemical ensemble, regardless of the extent of the complexity? The differentiable characteristic of the living system is information. Information assures the controlled reproduction of all the constituents, thereby ensuring the conservation of viability. Information – unlike energy – is not subject to a conservation law. Hence the fundamental question behind the origin of life is: How can information originate?Information theory, which was pioneered by Claude Shannon, cannot answer this question: this theory is most successful in dealing with problems of coding and transmission. In principle, the answer was formulated 130 years ago by Charles Darwin: The information that is unique for life evolves by virtue of natural selection. Today we can be more specific: natural selection is a non-equilibrium process. It is an inherent consequence of mutagenous self-replication at several levels of organization: for instance it is evident in molecules such as nucleic acids, in molecular complexes such as viruses and in autonomous formes of life such as micro- or higher organisms. New physical concepts have been introduced in order to deal quantitatively with the dynamics of the molecular generation of genetic information. They provide a physical foundation for Darwinian behaviour, yet they introduce major modifications in its interpretation. The lecture deals with these physical concepts, such as «sequence space», «quasi-species» and «hypercycles» and will scrutinize their adequacy for rationalizing experimental results obtained with molecular model systems and with viruses under natural conditions. Elucidating the principles of molecular self-organization has made possible to construct automated machines that make it possible for genetic information to evolve under controlled conditions in an abridged time scale.

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