The Influence of Adhesion and Sub-Newton Pull-Off Forces on the Release of Objects in Outer Space

2006 ◽  
Vol 128 (4) ◽  
pp. 828-840 ◽  
Author(s):  
M. Benedetti ◽  
D. Bortoluzzi ◽  
M. Da Lio ◽  
V. Fontanari
Keyword(s):  
Outer Space ◽  
Space Mission ◽  
Theoretical Background ◽  
Contact Forces ◽  
Zero Gravity ◽  
Adhesion Forces ◽  
Fractal Surface ◽  
Element Analysis ◽  
Interaction Forces

The theoretical background and the numerical modeling results of a ground-based verification activity of a critical space mission phase affected by adhesion issues are presented. Tribological models are first reviewed with an emphasis on the contact forces assessment and their relationship to the geometrical, material, and mechanical properties of the contacting metal bodies. An approach based on a finite element analysis of the contact, accounting for the adhesion forces, is then proposed for studying the contact behavior of smooth surfaces in vacuum. Some solutions aimed at reducing adhesion pull-off forces are discussed. Special emphasis is placed on the role of surface roughness in reducing adhesion. To this purpose, a fractal surface theory is used to estimate interaction forces. The obtained results are applied to discuss the role of adhesion on the release of a test mass under zero gravity as well as to suggest an appropriate detachment procedure that finds a specific application in a scientific space mission.

The Role of Adhesion and Sub-Newton Pull-Off Forces on the Test Mass Release for the LISA Experiment

2005 ◽  
Author(s):  
M. Benedetti ◽  
D. Bortoluzzi ◽  
P. Bosetti ◽  
M. Da Lio ◽  
V. Fontanari
Keyword(s):  
Space Mission ◽  
Test Mass ◽  
Zero Gravity ◽  
Adhesion Forces ◽  
Fractal Surface ◽  
Element Analysis ◽  
Interaction Forces ◽  
Surface Theory ◽  
Mass Release

The present paper illustrates the problematic of precise release of objects in weightless conditions. Under these circumstances, the role of weak bonds (electrostatic and van der Waals attractive forces) is not obscured by the gravity force. A finite-element analysis approach has been presented with the aim to quantify the adhesion forces between smooth surfaces in vacuum. On the basis of the obtained results, some solutions aimed at reducing adhesion pull-off forces have been discussed. Special emphasis has been placed on the role of surface roughness in reducing adhesion. To this purpose, a fractal surface theory has been used to estimate interaction forces. The obtained results have been used to discuss the role of adhesion on the release of a gold test mass under zero gravity conditions for the scientific space mission LISA.

Making Space for Islam: Religion, Science, and Politics in Contemporary Malaysia

2010 ◽  
Vol 69 (4) ◽  
pp. 1143-1166 ◽  
Author(s):  
Darren C. Zook
Keyword(s):  
International Space Station ◽  
International Politics ◽  
Outer Space ◽  
Space Station ◽  
Religious Practice ◽  
Space Mission ◽  
International Space ◽  
Science And Politics ◽  
Cooperative Venture

In October 2007, Malaysia celebrated sending its first astronaut into space, as part of a cooperative venture on board a Russian space mission. As Malaysia's first astronaut was a Muslim, the Malaysian government commissioned, through its Department of Islamic Development, a project to create a definitive set of guidelines for the practice of Islam in outer space, specifically on board the International Space Station. What may on the surface appear to be a practical exercise in clarifying religious practice reveals upon closer examination to be a complex restructuring of Malaysia's domestic and international politics, with the role of Islam as the catalytic and somewhat controversial centerpiece.

scholarly journals Calculators as Facilitators of Understanding Computational and Mathematical Contexts

2019 ◽  
Vol 1 (1) ◽  
pp. 177-183
Author(s):  
Jan Guncaga ◽  
Lilla Korenova ◽  
Jozef Hvorecky
Keyword(s):  
Soft Skills ◽  
Real Life ◽  
Theoretical Background ◽  
Learning Processes ◽  
Complex Phenomenon ◽  
Learning To Learn ◽  
Life Problems ◽  
The Subject ◽  
The Relationship

AbstractLearning is a complex phenomenon. Contemporary theories of education underline active participation of learners in their learning processes. One of the key arguments supporting this approach is the learner’s simultaneous and unconscious development of their ability of “learning to learn”. This ability belongs to the soft skills highly valued by employers today.For Mathematics Education, it means that teachers have to go beyond making calculations and memorizing formulas. We have to teach the subject in its social context. When the students start understanding the relationship between real-life problems and the role of numbers and formulas for their solutions, their learning becomes a part of their tacit knowledge. Below we explain the theoretical background of our approach and provide examples of such activities.

Dynamic Splints, Functionally-Customized With Nitinol, Can Reduce Joint Rigidity in Pediatric Subjects With Spasticity

2013 ◽  
Author(s):  
Lorenzo Garavaglia ◽  
Elena Beretta ◽  
Sandra Strazzer ◽  
Felice Sala ◽  
Morena Delle Fave ◽  
...  
Keyword(s):  
Niti Alloy ◽  
Neuromuscular Diseases ◽  
Contact Forces ◽  
Muscle Rigidity ◽  
Cortical Function ◽  
Paretic Limb ◽  
Limb Posture ◽  
Joint Rigidity ◽  
Complex Phenomena

Neuromuscular diseases as a consequence of brain damage are complex phenomena involving disuse, immobility, brain tissue remodeling and cortical function remapping. They may have various causes and strike any part of the population. The vicious circle leading to a worsening of the patients’ conditions proceeds through muscle shortening by contractures, disruption of the normal reflex behavior and sensory problems, development of spasticity [1]. Physical rehabilitation alone or in association with surgery or pharmacological treatments can be useful in limiting those degenerations. Besides manual rehabilitation, splints and braces are prescribed to control the limb posture and obtain stretching of the muscles. The role of those orthoses is to maintain the paretic limb in a set ‘physiological’ position and let it relax into that posture, in an attempt to reduce muscle rigidity and contractures. However applying a fixed constraint to the limb and waiting for relaxation to take place, may cause discomfort, pain, skin rash, and sundry different complications [2]. Also, any residual voluntary movement is prevented by a fixed-angle splinting. In addition, all these negative characteristics limit tolerability and daily application times. This work presents a different way to promote limb repositioning, based on the application of NiTi-alloy-based dynamic splints, which favor mobility and any residual use of the affected limb. Furthermore it suggests that application of mild contact forces prolonged in time has the advantage of feeling less painful and uncomfortable for the patients, improving overall treatment tolerability.

Finite Element Analysis of Large-Size Yaw Bearings with Supporting Structure in Wind Turbine

2014 ◽  
Vol 672-674 ◽  
pp. 1550-1553
Author(s):  
Zhen Guo Shang ◽  
Zhong Chao Ma ◽  
Zhen Sheng Sun
Keyword(s):  
Finite Element ◽  
Wind Turbine ◽  
Point Contact ◽  
Element Model ◽  
Contact Forces ◽  
Element Analysis ◽  
Supporting Structure ◽  
Rolling Elements ◽  
Yaw Bearing ◽  
Compression Springs

A procedure for obtaining the load distribution in a four point contact wind turbine yaw bearing considering the effect of the structure’s elasticity is presented. The inhomogeneous stiffness of the supporting structures creates a variation in the results obtained with a rigid model. A finite element model substituting the rolling elements with nonlinear compression springs has been built to evaluate the effect of the supporting structure elasticity on the contact forces between the rolling elements and the raceways.

scholarly journals A nudge in the right direction: the role of food choice architecture in changing populations' diets

2021 ◽  
pp. 1-12
Author(s):  
H. Ensaff
Keyword(s):  
Food Choice ◽  
Empirical Studies ◽  
Food Selection ◽  
Theoretical Background ◽  
Choice Architecture ◽  
Different Populations ◽  
The Right ◽  
Care Costs

Populations' diets typically fall short of recommendations. The implication of this on ill health and quality of life is well established, as are the subsequent health care costs. An area of growing interest within public health nutrition is food choice architecture; how a food choice is framed and its influence on subsequent food selection. In particular, there is an appeal to manipulating the choice architecture in order to nudge individuals' food choice. This review outlines the current understanding of food choice architecture, theoretical background to nudging and the evidence on the effectiveness of nudge strategies, as well as their design and implementation. Interventions emphasising the role of nudge strategies have investigated changes to the accessibility, availability and presentation of food and the use of prompts. Empirical studies have been conducted in laboratories, online and in real-world food settings, and with different populations. Evidence on the effectiveness of nudge strategies in shifting food choice is encouraging. Underpinning mechanisms, not yet fully explicated, are proposed to relate to salience, social norms and the principle of least effort. Emerging evidence points to areas for development including the effectiveness of choice architecture interventions with different and diverse populations, and the combined effect of multiple nudges. This, alongside further examination of theoretical mechanisms and guidance to engage and inspire across the breadth of food provision, is critical. In this way, the potential of choice architecture to effect meaningful change in populations' diets will be realised.

Finite element analysis of hydrogen effects on superelastic NiTi shape memory alloys: Orthodontic application

2018 ◽  
Vol 29 (16) ◽  
pp. 3188-3198 ◽  
Author(s):  
Wissem Elkhal Letaief ◽  
Aroua Fathallah ◽  
Tarek Hassine ◽  
Fehmi Gamaoun
Keyword(s):  
Finite Element ◽  
Coupled Model ◽  
Element Model ◽  
Orthodontic Wires ◽  
Niti Wire ◽  
Element Analysis ◽  
Finite Element Software ◽  
Orthodontic Wire ◽  
Niti Shape Memory Alloys

Thanks to its greater flexibility and biocompatibility with human tissue, superelastic NiTi alloys have taken an important part in the market of orthodontic wires. However, wire fractures and superelasticity losses are notified after a few months from being fixed in the teeth. This behavior is due to the hydrogen presence in the oral cavity, which brittles the NiTi arch wire. In this article, a diffusion-mechanical coupled model is presented while considering the hydrogen influences on the NiTi superelasticity. The model is integrated in ABAQUS finite element software via a UMAT subroutine. Additionally, a finite element model of a deflected orthodontic NiTi wire within three teeth brackets is simulated in the presence of hydrogen. The numerical results demonstrate that the force applied to the tooth drops with respect to the increase in the hydrogen amount. This behavior is attributed to the expansion of the NiTi structure after absorbing hydrogen. In addition, it is shown that hydrogen induces a loss of superelasticity. Hence, it attenuates the role of the orthodontic wire on the correction tooth malposition.

scholarly journals Impacts of Gratifications on Consumers’ Emotions and Continuance Use Intention: An Empirical Study of Weibo in China

2018 ◽  
Vol 10 (9) ◽  
pp. 3162 ◽  
Author(s):  
Ives Gogan ◽  
Ziqiong Zhang ◽  
Elizabeth Matemba
Keyword(s):  
User Satisfaction ◽  
Uses And Gratifications ◽  
Theoretical Background ◽  
Emotional States ◽  
Continuance Intention ◽  
Uses And Gratifications Theory ◽  
Emotional Commitment ◽  
Use Of Social Media ◽  
Individual Use

Recently, several studies on information systems have applied the Uses and Gratifications theory to investigate individual use of social media, and have reported the role of different gratifications in predicting users’ behaviors. However, no attention was given to the influence of these gratifications on users’ emotional states (satisfaction and emotional commitment). To address this research gap, the current study integrates the Uses and Gratifications theory and the Stimulus-Organism-Response theory to provide a theoretical background for the impacts of gratification on consumers’ emotional states and continuance use intention. The study has proposed a theoretical model that was tested on data collected from 252 Sina Weibo users in China. The results revealed that social gratification is the most important factor influencing users’ satisfaction and emotional commitment. In addition, we report the roles that user satisfaction and emotional state provide in predicting users’ continuance intention. The theoretical and practical implications of the proposed theory are also discussed.

Sign in / Sign up

Export Citation Format

Share Document