scholarly journals On the stability of spinning asteroids

2021 ◽  
Author(s):  
Bo Persson
Keyword(s):  
Surface Roughness ◽  
Centrifugal Force ◽  
Critical Period ◽  
Gravitational Force ◽  
Interaction Force ◽  
Solid Object ◽  
Adhesive Interaction ◽  
Interaction Forces ◽  
The Stability ◽  
Almost All

Abstract Most asteroids with a diameter larger than ∼ 300 m are rubble piles i.e. consisting of more than one solid object. All asteroids are rotating but almost all asteroids larger than ∼ 300 m rotate with a period longer than 2.3 hours, which is the critical period where the centrifugal force equals the gravitational force. This indicates that there are nearly no adhesive interaction forces between the asteroid fragments. We show that this is due to the surface roughness of the asteroid particles which reduces the van der Waals interaction between the particles by a factor of 100 for micrometer sized particles and even more for larger particles. We show that surface roughness results in an interaction force which is independent of the size of the particles, in contrast to the linear size dependency expected for particles with smooth surfaces. Thus, two stone fragments of size 100 nm attract each other with the same non-gravitational force as two fragments of size 10 m.

scholarly journals An Optimization-Based Impedance Approach for Robot Force Regulation with Prescribed Force Limits

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
R. de J. Portillo-Vélez ◽  
A. Rodriguez-Angeles ◽  
C. A. Cruz-Villar
Keyword(s):  
Dynamic Optimization ◽  
Optimization Problem ◽  
Gradient Flow ◽  
Interaction Force ◽  
Convergence Properties ◽  
Dynamic Optimization Problem ◽  
Interaction Forces ◽  
End Effector ◽  
Impedance Model ◽  
The Stability

An optimization based approach for the regulation of excessive or insufficient forces at the end-effector level is introduced. The objective is to minimize the interaction force error at the robot end effector, while constraining undesired interaction forces. To that end, a dynamic optimization problem (DOP) is formulated considering a dynamic robot impedance model. Penalty functions are considered in the DOP to handle the constraints on the interaction force. The optimization problem is online solved through the gradient flow approach. Convergence properties are presented and the stability is drawn when the force limits are considered in the analysis. The effectiveness of our proposal is validated via experimental results for a robotic grasping task.

THE NATURE OF THE INTERACTION FORCES BETWEEN PARTICLES IN SUSPENSIONS OF GLASS SPHERES IN ORGANIC LIQUID MEDIA

1955 ◽  
Vol 33 (7) ◽  
pp. 1189-1196 ◽  
Author(s):  
P. G. Howe ◽  
D. P. Benton ◽  
I. E. Puddington
Keyword(s):  
Surface Roughness ◽  
Particle Size ◽  
Simple Model ◽  
Solid Phase ◽  
Organic Liquid ◽  
Liquid Media ◽  
Interaction Forces ◽  
Glass Spheres ◽  
Yield Value ◽  
The Stability

Electrostatic agglomeration can be induced in suspensions of glass beads in organic liquid media. The stability of the agglomerates is markedly dependent on temperature. The influence of surface roughness and the presence of small quantities of water on the interparticle interaction is discussed. Assuming a simple model the observed relationship between yield value and particle size for systems containing the same concentration of solid phase is derived.

Resistance of cherry varieties to spring return frozes in the conditions of Astrakhan region

2020 ◽  
Author(s):  
A.A. Dronic A.A. ◽  
Keyword(s):  
Weather Conditions ◽  
Damage Score ◽  
The Stability ◽  
Almost All ◽  
Total Damage ◽  
Continental Climate ◽  
Unfavorable Weather

The article presents an assessment of the stability of introduced cherry varieties to spring return frosts in 2020 in the conditions of the sharply continental climate of the Astrakhan region. As a result of unfavorable weather conditions, the total damage score of all varieties was 2-5 points. Almost all the studied varieties showed an insufficient level of resistance to recurrent frosts.

Effect of Surface Roughness on Slip Resistance of Rubber

2011 ◽  
Vol 189-193 ◽  
pp. 1538-1542
Author(s):  
Li Xiao Jia ◽  
Yong Zhen Zhang ◽  
Yong Ping Niu ◽  
San Ming Du ◽  
Jian Li
Keyword(s):  
Surface Roughness ◽  
Correlation Coefficient ◽  
Correlation Coefficients ◽  
Roughness Parameters ◽  
Test Conditions ◽  
Slip Resistance ◽  
Materials Used ◽  
Almost All ◽  
Effect Of Surface

In order to decrease accidents of slips and falls, COFs of rubber samples with different surface roughness were measured by Brungraber Mark II. And the correlation coefficients between roughness parameters and COF were calculated. The rusults have shown that the COF increases with surface roughness and the correlation coefficient between Sq and COF is highest. In general, almost all the roughness parameters used in the study have high correlation with COF. Parameters had the highest correlation with COF depends on the materials used and test conditions.

Studies on Polyaniline: Polyethyleneterephthalate Films

2006 ◽  
Vol 111 ◽  
pp. 99-102 ◽  
Author(s):  
A.A. Ahmed ◽  
Faiz Mohammad
Keyword(s):  
Electrical Conductivity ◽  
Electrical Properties ◽  
Arrhenius Equation ◽  
Great Increase ◽  
Thermooxidative Stability ◽  
Ambient Conditions ◽  
Dc Electrical Conductivity ◽  
The Stability ◽  
Almost All ◽  
Conductivity Retention

The films of polyaniline:polyethyleneterephthalate films were prepared by polymerizing aniline soaked in polyethyleneterephthalate films of different thicknesses. The films were characterized by FTIR as well as for their electrical properties. The electrical properties of the films were observed to be of good quality as almost all the films showed a great increase in their electrical conductivity from insulator to semiconductor region after doping with hydrochloric acid. All the films in their doped state follow the Arrhenius equation for the temperature dependence of electrical conductivity from 35 to 115oC. The thermooxidative stability was studied by thermogravimetry and differential thermal analysis. The stability in terms of dc electrical conductivity retention was also studied under ambient conditions by two slightly different techniques viz. isothermal and cyclic techniques. The dc electrical conductivity of the films was found to be stable below 90oC for all the films under ambient conditions.

Research on chatter stability in milling and parameter optimization based on process damping

2017 ◽  
Vol 24 (12) ◽  
pp. 2642-2655 ◽  
Author(s):  
Lida Zhu ◽  
Baoguang Liu ◽  
Hongyu Chen
Keyword(s):  
Surface Roughness ◽  
Frequency Method ◽  
Processing Efficiency ◽  
Machined Surface ◽  
Process Damping ◽  
Analysis Methodology ◽  
Optimization Of Process Parameters ◽  
Orthogonal Experiments ◽  
Cutting Chatter ◽  
The Stability

Cutting stability is the prerequisite to ensure efficient and high-precision machining, resulting in poor surface quality and damaged tool, which is the basis for the optimization of process parameters and improvement of processing efficiency. Aiming at process damping caused by interference between a tool flank face and a machined surface of part, the dynamic model and critical condition of stability is proposed in the paper. The frequency method is applied to solve the stability of the cutting chatter, and the correctness of the model is validated by experiments. Moreover, through orthogonal experiments, regression analysis methodology are adopted to establish a prediction model of surface roughness and finally combined with the study findings on milling stability based on process damping and surface roughness, achieved optimization of the milling parameters by genetic optimization algorithm. This conclusion provides a theoretical foundation and reference for the milling mechanism research.

OPTIMIZATION OF THE REPAIR AND MAINTENANCE BASE OF THE AGRO-INDUSTRIAL COMPLEX

2021 ◽  
Vol 3 (144) ◽  
pp. 64-71
Author(s):  
Yuriy V. Katayev ◽  
◽  
Valeriy S. Gerasimov ◽  
Vladimir I. Ignatov ◽  
Zoya N. Mishina ◽  
...  
Keyword(s):  
Critical Period ◽  
The State ◽  
Research Purpose ◽  
Industrial Complex ◽  
Resource Saving ◽  
Technical Literature ◽  
Lack Of Information ◽  
Technological Level ◽  
Almost All ◽  
Technical Readiness

The repair industry in almost all countries has entered a critical period, characterized by the need to combine and use various strategies and technologies for maintenance and repair of new equipment, as well as equipment produced many years ago. (Research purpose) The research purpose is in analyzing the state of the repair and maintenance base of the agro-industrial complex and justifying the possibilities of its modernization using intelligent technologies. (Materials and methods) Authors used methods of generalizing data from various services of agro- industrial formations of individual regions, materials of scientific and technical literature and research developments, studied data on the practical use of modern resource-saving technologies by engineering services of the agro-industrial complex of the regions when carrying out repairs and service and technological services. (Results and discussion) The lack of information about the state of the repair and maintenance base makes it difficult to determine all the criteria associated with the transition of manufacturers to a contract of the entire life cycle. Obtaining information about the state of the repair and maintenance base of the agro-industrial complex is a very important stage that contributes to the modernization of this base and attracting not only the governments, but also agricultural machinery manufacturers to modernization. (Conclusions) The technological level of the enterprises of the repair and maintenance base of agriculture has significantly decreased in recent years, and this has affected the decline in technical readiness indicators, which confirms the need to conduct research and implement in practice the main measures related to the modernization of the specified repair and maintenance base.

scholarly journals Grativation origin

2021 ◽  
Author(s):  
Physicist Zheng shengming
Keyword(s):  
Gravitational Force ◽  
Interaction Force ◽  
Elementary Particles ◽  
Universal Gravitation ◽  
Classification Approach ◽  
Naturally Occurring ◽  
World Point ◽  
Origin Mechanism

<div>In the process of humanity searching for beauty and secret of nature; people have been gradually getting familiar with many interactions in nature. Today, the whole diversity of naturally occurring forces can be reduced to four fundamental types of interaction: gravitational, weak, electromagnetic, and strong. Obviously, this kind of classification approach is based on their interaction characteristics rather than based on the mechanism of what how give rise to these four types of force. Until today, people still have no notion of their origin mechanism. Namely humanity does not know what is responsible for the origin of these forces. In order to answer their origin, I did some experiments and discovered that moving photons generate gravitation. This discovery come to light the origin of gravitation. In a word, these experiments indicate that moving of elementary particles bring on interaction force what appearing behavior of gravitation, and this interaction lead to gravitational force in the macro world. Meanwhile these discoveries application in the macro world point out the meaning of law of Universal gravitation, and solve some enigmas which law of Universal gravitation have not solved until today. These works reveal the origin of gravitation.</div><div><br></div>

CONTROLLABLE WRINKLING OF THIN FILMS ON PRE-STRETCHED ELASTOMERS INDUCED BY GRAVITY

2014 ◽  
Vol 06 (03) ◽  
pp. 1450029
Author(s):  
FANG WANG ◽  
KAI LI ◽  
KAI LIU
Keyword(s):  
Gravitational Force ◽  
Periodic Array ◽  
Linear Perturbation ◽  
Tensile Direction ◽  
Elastic Film ◽  
Calculation Results ◽  
Surface Patterns ◽  
The Stability ◽  
Rod Structures ◽  
Soft Elastomer

We study wrinkling instability of a thin elastic film on a pre-stretched soft elastomer induced by the gravity of periodic array of the rods homogenously clamped on the surface of the film. By using linear perturbation analysis, we show that the periodic array of the rods can drive the wrinkling instability of the film when the gravitational force of the rods attains the threshold, and the film will wrinkle into stripes parallel to the tensile direction of the pre-stretched elastomer. Our calculation results give the stability criterion of the system, and the threshold of the gravitational force and the wavelength of the wrinkling patterns are obtained, which can be controlled by tuning the magnitude of the pre-stretch and properties of the thin film and the soft elastomer. These results may provide a regulating strategy for generating precise surface patterns in similar rod structures.

Climate Change

2017 ◽  
Author(s):  
Peter Mason
Keyword(s):  
Climate Change ◽  
Rain Forest ◽  
Fossil Fuels ◽  
Mass Tourism ◽  
Major Threat ◽  
The World ◽  
Tourism Activity ◽  
The Stability ◽  
Almost All ◽  
Main Attraction

Climate change poses a major threat to almost all forms of human activity on earth, including tourism. As Holden (2016: 227) argues: Of all the challenges facing tourism’s relationship with nature, it is not an exaggeration to state that climate change represents the greatest. Holden gives as his rationale for this statement that it is the stability and predictability of climate that is vital for the environments and ecosystems that are required for the continuation of current types of tourism, whether these are the traditional form of mass tourism, in terms of ‘sun, sea and sand’ holidays, or a niche activity which involves visiting a tropical rain forest with rare flora and fauna as the main attraction. Climate change also presents opportunities for tourism. If areas currently experiencing cool winters and mild summers get warmer, then new types of tourism may be possible including beach-based holidays where at present these are of little importance. Climate change is likely to lead to modifications in the weather at different times of the year so ‘seasonality’ which is currently a very important dimension to many forms of tourism will be affected, probably to the extent that seasons when there is high tourism activity will get longer in some parts of the world. Although tourism is likely to be significantly affected by climate change, it has also contributed to climate change through for example the burning of fossil fuels in transport for tourism as well through the use of power in hotel accommodation.

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