Relative equilibrium stability of a mechanical system with deformable elements in a circular orbit

2014 ◽  
Vol 69 (1) ◽  
pp. 16-20
Author(s):  
A. V. Il’inskaya
Keyword(s):  
Mechanical System ◽  
Circular Orbit ◽  
Relative Equilibrium ◽  
Equilibrium Stability

Role of DNA sequence in nucleosome stability and dynamics

2001 ◽  
Vol 34 (3) ◽  
pp. 269-324 ◽  
Author(s):  
J. Widom
Keyword(s):  
Free Energy ◽  
Dna Sequence ◽  
Dna Bending ◽  
Relative Equilibrium ◽  
Nucleosome Positioning ◽  
Equilibrium Stability ◽  
Core Particle ◽  
Nucleosome Core ◽  
Relative Free Energy ◽  
Nucleosome Stability

1. Introduction 2701.1 Overview of nucleosome structure 2712. Relative equilibrium stability (affinity) of histone–DNA interactions in nucleosomes 2722.1 Relative affinity equals relative equilibrium stability 2722.2 Competition assays for relative free-energy measurements 2732.3 Technical issues in relative free-energy measurements 2752.4 Range of affinities 2783. Relation of nucleosome stability to nucleosome positioning 2793.1 Translational nucleosome positioning 2793.2 Rotational positioning 2803.3 Unfavorable positioning 2813.4 Experiments 2814. Physical basis of DNA sequence preferences 2824.1 Free-energy cost of DNA bending 2834.2 Molecular mechanics of DNA bending and bendability 2844.3 Bent and bendable DNA sequences 2864.4 Parameter sets for prediction of DNA bending and bendability 2884.5 DNA twisting 2904.6 Energetics of nucleosomal DNA packaging 2915. DNA sequence motifs for nucleosome packaging 2925.1 Natural and designed nucleosomal DNAs 2935.2 New rules and reagents from physical selection studies 2945.3 Molecular basis of DNA sequence preferences 2995.4 Special properties of the TA step 3005.5 Unfavorable sequences 3025.6 Natural genomes 3035.7 Evolutionary approach toward an optimal sequence 3055.8 Optimization by design 3056. Dynamic nucleosome instability 3086.1 Site-exposure equilibria 3086.2 DNA sequence-dependence to site-exposure equilibria 3126.3 Nucleosome translocation 3156.4 Action of processive enzymes 3197. Conclusions 3198. Acknowledgements 3209. References 320The nucleosome core particle is the fundamental repeating subunit of chromatin. It consists of two molecules each of the four ‘core histone’ proteins, H2A, H2B, H3 and H4, and a 147 bp stretch of DNA. The lowest level of chromatin organization consists of a repeated array of nucleosome core particles separated by variable lengths of ‘linker DNA’. In many, but not all, cases, each core particle plus its linker DNA is associated with one molecule of a fifth ‘linker’ histone protein, H1. The complex of the core particle plus its linker DNA and H1 (when present) is called a ‘nucleosome’.

scholarly journals Application of software tools for symbolic description and modeling of mechanical systems

2020 ◽  
Author(s):  
A. Banshchikov ◽  
A. Vetrov
Keyword(s):  
Mechanical System ◽  
Software Package ◽  
Equations Of Motion ◽  
Relative Equilibrium ◽  
Mechanical Systems ◽  
Software Tools ◽  
Rigid Bodies ◽  
Symbolic Form ◽  
The Stability ◽  
Lagrange Formalism

The paper presents two software tools (graphical editor and software package). The editor is designed for the formation of a symbolic description of a mechanical system using the Lagrange formalism. A system of the absolutely rigid bodies connected by joints is considered as a mechanical system. The editor is a user interface by which one sets the structure of the interconnection of bodies (system configuration) as well as the geometric and kinematic characteristics for each body of the system. The created structure and the entered data are automatically presented in the form of a text file, which is used as an input file for the software package for modeling mechanical systems in a symbolic form with a computer. The use of these software tools is shown in detail in the example of the analysis of the dynamics of a satellite with a gravitational stabilizer in a circular orbit. For this system, the kinetic energy and force function of an approximate Newtonian gravitational field were obtained, nonlinear and linearized equations of motion were constructed, and the question of the stability of the relative equilibrium position was considered.

scholarly journals Relative equilibria of dynamically symmetric CubeSat nanosatellite under the action of aerodynamic and gravitational torques

2019 ◽  
Vol 18 (2) ◽  
pp. 21-32
Author(s):  
E. V. Barinova ◽  
I. A. Timbai
Keyword(s):  
Circular Orbit ◽  
Aerodynamic Drag ◽  
Relative Equilibrium ◽  
Relative Equilibria ◽  
Mass Center ◽  
Atmospheric Density ◽  
Force Coefficient ◽  
Aerodynamic Moment ◽  
Gravitational Moment ◽  
Proper Rotation

Motion of a dynamically symmetric CubeSat nanosatellite around the mass center on the circular orbit under the action of aerodynamic and gravitational torques is considered. We determined the nanosatellite equilibrium positions in the flight path axis system. We took into account the fact that the CubeSat nanosatellite has a rectangular parallelepiped shape and, therefore, the aerodynamic drag force coefficient depends on the angles of attack and proper rotation. We obtained formulae which allow calculating the values of the angles of attack, precession and proper rotation that correspond to the equilibrium positions, depending on the mass-inertia and geometric parameters of the nanosatellite, the orbit altitude, and the atmospheric density. It is shown that if the gravitational moment predominates over the aerodynamic one, there are 16 equilibrium positions, if the aerodynamic moment predominates over the gravitational one, there are 8 equilibrium positions, and in the case when both moments have comparable values there are 8, 12 or 16 equilibrium positions. Using the formulae obtained, we determined the equilibrium positions of the SamSat-QB50 nanosatellite. We calculated the ranges of altitudes where SamSat-QB50 nanosatellite has 8, 12, or 16 relative equilibrium positions.

Study of the dynamics of ТПА 350 automatic mill working stand elements

2020 ◽  
Vol 76 (8) ◽  
pp. 830-840
Author(s):  
S. R. Rakhmanov ◽  
V. V. Povorotnii
Keyword(s):  
Mechanical System ◽  
Dynamic Model ◽  
Maximum Amplitude ◽  
Calculation Scheme ◽  
Dynamic Loads ◽  
Forced Oscillations ◽  
Mass Model ◽  
Automatic Mill ◽  
Hollow Billet ◽  
Oscillation Movement

To form a necessary geometry of a hollow billet to be rolled at a pipe rolling line, stable dynamics of the base equipment of the automatic mill working stand has a practical meaning. Among the forces, acting on its parts and elements, significant by value short-time dynamic loads are the least studied phenomena. These dynamic loads arise during transient interaction of the hollow billet, rollers, mandrel and other mill parts at the forced grip of the hollow billet. Basing of the calculation scheme and dynamic model of the mechanical system of the ТПА 350 automatic mill working stand was accomplished. A mathematical model of dynamics of the system “hollow billet (pipe) – working stand” within accepted calculation scheme and dynamic model of the mechanical system elaborated. Influence of technological load of the rolled hollow billet variation in time was accounted, as well as variation of the mechanical system mass, and rigidity of the ТПА 350 automatic mill working stand. Differential equations of oscillation movement for four-mass model of forked sub-systems of the automatic mill working stand were made up, results of their digital calculation quoted. Dynamic displacement of the stand elements in the inter-roller gap obtained, which enabled to estimate the results of amplitude and frequency characteristics of the branches of the mill rollers setting. It was defined by calculation, that the maximum amplitude of the forced oscillations of elements of the ТПА 350 automatic mill working stand within the inter-roller gap does not exceed 2 mm. It is much higher than the accepted value of adjusting parameters of the deformation center of the ТПА 350 automatic mill. A scheme of comprehensive modernization of the rollers setting in the ТПА 350 automatic mill working stand was proposed. It was shown, that increase of rigidity of rollers setting in the ТПА 350 automatic mill working stand enables to stabilize the amplitude of forced oscillations of the working stand elements within the inter-rollers gap and considerably decrease the induced nonuniform hollow billet wall thickness and increase quality of the rolled pipes at ТПА 350.

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