scholarly journals Energy dissipation of a particle colliding on a flat surface

2021 ◽  
Vol 249 ◽  
pp. 06007
Author(s):  
Fabricio Éric Fernández ◽  
Marcelo Fabián Piva ◽  
Román Gustavo Martino ◽  
María Alejandra Aguirre
Keyword(s):  
Kinetic Energy ◽  
Degrees Of Freedom ◽  
Flat Surface ◽  
Coefficient Of Restitution ◽  
Normal Direction ◽  
Normal Velocity ◽  
Factors Affecting ◽  
Different Types ◽  
Before And After ◽  
The Impact

To gain an understanding of the factors affecting the interaction of one grain with its environment as it reaches equilibrium, we study a particle bouncing off a flat surface. The bouncing of the particle leads to dissipation that is usually characterized with t, the coefficient of restitution, defined as the ratio between the velocity component that is normal to the contact surface just before impact (Vn) and the same component, but immediately after the collision (Vn’), i.e. related to a kinetic energy corresponding to motion in the normal direction. We will show how d is affected by energy stored in other degrees of freedom and transferred to kinetic energy that leads to an increase in normal velocity after the impact Vn’, and therefore to, ɛ >1. For this purpose, the evolution of potential, translational kinetic energy and rotational kinetic energy is analysed during the whole relaxation process and just before and after each collision for two different types of particle, a disk and a faceted particle.

scholarly journals Motion Planning for a Mobile Humanoid Manipulator Working in an Industrial Environment

2021 ◽  
Vol 11 (13) ◽  
pp. 6209
Author(s):  
Iwona Pajak ◽  
Grzegorz Pajak
Keyword(s):  
Kinetic Energy ◽  
Collision Avoidance ◽  
Industry 4.0 ◽  
Degrees Of Freedom ◽  
Industrial Environment ◽  
Acceleration Level ◽  
Different Types ◽  
Manipulability Measure ◽  
Robotic Tasks ◽  
Primary Problem

This paper presents the usage of holonomic mobile humanoid manipulators to carry out autonomous tasks in industrial environments, according to the smart factory concept and the Industry 4.0 philosophy. The problem of transporting lengthy objects, taking into account mechanical limitations, the conditions for avoiding collisions, as well as the dexterity of the manipulator arms was considered. The primary problem was divided into three phases, leading to three different types of robotic tasks. In the proposed approach, the pseudoinverse Jacobian method at the acceleration level to solve each of the tasks was used. The redundant degrees of freedom were used to satisfy secondary objectives such as robot kinetic energy, the maximization of the manipulability measure, and the fulfillment mechanical and collision-avoidance limitations. A computer example involving a mobile humanoid manipulator, operating in an industrial environment, illustrated the effectiveness of the proposed method.

Deceleration of sliding motorcycles (mainly scooters) in accident reconstructions

2017 ◽  
Vol 232 (7) ◽  
pp. 866-876 ◽  
Author(s):  
Carlo Cialdai ◽  
Dario Vangi ◽  
Antonio Virga
Keyword(s):  
Urban Areas ◽  
Test Session ◽  
Road Accidents ◽  
Factors Affecting ◽  
Different Types ◽  
Energy Dissipated ◽  
Comparison Of The Results ◽  
Two Wheeler ◽  
The Impact ◽  
Good Agreement

This paper presents an analysis of the situation in which a two-wheeler (i.e. a motorcycle, where the term motorcycles includes scooters) falls over to the side and then successively slides; this typically occurs in road accidents involving this type of vehicle. Knowing the deceleration rate of the sliding phase allows the kinetic energy dissipated and the speed of the motorcycle just before the fall to the ground to be calculated. These parameters are very important in the analysis and reconstruction of accidents. The work presented in this paper was developed in two experimental test sessions on fully faired motorcycles which are mainly of the scooter type and widely used in urban areas. In the first session, sliding tests were carried out, with the speed in the range 10–50 km/h, on three different types of road surface. Analysis of the evidence allowed the dissipative main phases of motion of the motorcycle (the impact with the ground, the rebounds and the stabilized swiping) to be identified and some factors affecting the phenomenon to be studied. The coefficient of average deceleration was calculated using two typical equations. The second test session consisted of drag tests. In these tests, the motorcycle, which had previously laid on its side, was dragged for a few metres at a constant speed of about 20 km/h, while the drag force was measured. A comparison of the results obtained in these tests with those obtained in the sliding tests yielded very good agreement in the coefficients of deceleration.

Treating Afro hair loss: signs, symptoms and specialist interest

2021 ◽  
Vol 10 (5) ◽  
pp. 190-197
Author(s):  
Ingrid Wilson
Keyword(s):  
Black Women ◽  
Hair Loss ◽  
Factors Affecting ◽  
Different Types ◽  
Recent Developments ◽  
Hair Care ◽  
Care Practices ◽  
The Aesthetic ◽  
The Impact ◽  
Symptoms And Signs

This article explores the different types of hair loss that black women may experience more than other groups of patients. Properties of African hair and the impact of hair care practices are discussed, as well as factors affecting the presentation of other hair loss conditions. It is important for the aesthetic practitioner to be able to distinguish between the temporary forms of hair loss that they can help to treat and the permanent or scarring forms of hair loss, which need a prompt referral to a dermatologist with a specialist interest in hair. Prompt recognition and referral can help to delay the progression of hair loss. The symptoms and signs that patients and practitioners should be alerted to are explored, as well as the treatments that can help and where referrals may be necessary. Recent developments and gaps in knowledge are summarised.

scholarly journals The Role of Non-Rubber Components on Molecular Network of Natural Rubber during Accelerated Storage

Polymers ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 2880
Author(s):  
Huifeng Zhang ◽  
Lu Zhang ◽  
Xu Chen ◽  
Yueqiong Wang ◽  
Fuchun Zhao ◽  
...  
Keyword(s):  
Natural Rubber ◽  
Network Formation ◽  
Crosslinking Density ◽  
Factors Affecting ◽  
Hardening Mechanism ◽  
Accelerated Storage ◽  
Before And After ◽  
The Impact ◽  
Vital Factor

Though the non-rubber components have long been recognized to be a vital factor affecting the network of natural rubber (NR), the authentic role of non-rubber components on the network during accelerated storage has not been fully illuminated. This work attempts to clarify the impact of non-rubber components on the network for NR during accelerated storage. A natural network model for NR was proposed based on the gel content, crosslinking density, and the non-rubber components distribution for NR before and after centrifugation. Furthermore, the effect of non-rubber components on the network was investigated during accelerated storage. The results show that terminal crosslinking induced by non-rubber components and entanglements are primary factors affecting the network formation during accelerated storage. By applying the tube model to analyze the stress-strain curves of NR, we found that the contribution of the entanglements to the network formation is larger than that of terminal crosslinking during accelerated storage. The work highlights the role of non-rubber components on the network during accelerated storage, which is essential for understanding the storage hardening mechanism of NR.

scholarly journals The Effect of the Contact Model on the Design of Mechanical Systems

2012 ◽  
Author(s):  
M. R. Brake ◽  
D. S. Aragon ◽  
D. J. VanGoethem ◽  
H. Sumali
Keyword(s):  
Constant Coefficient ◽  
Degrees Of Freedom ◽  
Mechanical Systems ◽  
Constitutive Models ◽  
Coefficient Of Restitution ◽  
Rigid Body Dynamics ◽  
Contact Model ◽  
Elastic Plastic ◽  
Contact Models ◽  
The Impact

Impact is a wide-spread phenomenon in mechanical systems that can have a significant effect on the system’s dynamics, stability, wear, and damage. The simulation of impact in complex, mechanical systems, however, is often too computationally intensive for high fidelity finite element analyses to be useful as design tools. As a result, rigid body dynamics and reduced order model simulations are often used, with the impact events modeled by ad hoc methods such as a constant coefficient of restitution or a penalty stiffness. The consequences of the choice of contact model are studied in this paper for a representative multiple-degrees of freedom mechanical system. Four contact models are considered in the analysis: a constant coefficient of restitution model, two similar elastic-plastic constitutive models, and one dissimilar elastic-plastic constitutive model. The predictions of wear, mechanical failure, and stability are assessed for each of the contact models, and the subsequent effect on the system design is investigated. These results emphasize the importance of choosing a realistic contact model when simulations are being used to drive the design of a system.

Women and Chocolate Advertising: Exposure to Thin Models Exacerbates Ambivalence

2009 ◽  
Vol 24 (S1) ◽  
pp. 1-1 ◽  
Author(s):  
K. Durkin ◽  
K. Rae
Keyword(s):  
Three Dimensions ◽  
Exposure Condition ◽  
Approach And Avoidance ◽  
Different Types ◽  
Before And After ◽  
Advertising Exposure ◽  
And Control ◽  
Disordered Eating Patterns ◽  
The Impact ◽  
General Community

Chocolate craving is very common among women. It is known to be associated with ambivalent attitudes and with eating disorders.Aims:The present study investigated the impact of different types of media images (associating the product with thin versus overweight models) on females’ attitudes to chocolate.Method:Eighty-four female participants were recruited from the general community. Age ranged from 17 to 63 years (mean=35). Mean BMI was 23.4. Participants were allocated randomly to one of three conditions: Chocolate with thin models, Chocolate with overweight models, and Control (non-chocolate related products). Groups did not differ on age and BMI. They were assessed before and after exposure using the Orientation to Chocolate Questionnaire, which measures three dimensions of chocolate craving: guilt, approach and avoidance.Results:Participants in the thin exposure condition experienced more guilt and were more likely to report both heightened approach and avoidance of chocolate after exposure. In contrast, participants in the overweight exposure condition had lower guilt and lower approach to chocolate, with no change in avoidance, after exposure. No changes were obtained for the females in the control condition.Conclusion:These findings suggest that viewing thin images in association with chocolate intensifies women's ambivalence towards the product. It is argued that ambivalence is stressful and fosters disordered eating patterns.

Modeling Impacts Between a Continuous System and a Rigid Obstacle Using Coefficient of Restitution

2009 ◽  
Vol 77 (2) ◽  
Author(s):  
Chandrika P. Vyasarayani ◽  
John McPhee ◽  
Stephen Birkett
Keyword(s):  
Initial Conditions ◽  
Equations Of Motion ◽  
Continuous System ◽  
Coefficient Of Restitution ◽  
Continuous Systems ◽  
Rigid Obstacle ◽  
Unit Impulse ◽  
Before And After ◽  
System Equations ◽  
The Impact

In this work, we discuss the limitations of the existing collocation-based coefficient of restitution method for simulating impacts in continuous systems. We propose a new method for modeling the impact dynamics of continuous systems based on the unit impulse response. The developed method allows one to relate modal velocity initial conditions before and after impact without requiring the integration of the system equations of motion during impact. The proposed method has been used to model the impact of a pinned-pinned beam with a rigid obstacle. Numerical simulations are presented to illustrate the inability of the collocation-based coefficient of restitution method to predict an accurate and energy-consistent response. We also compare the results obtained by unit impulse-based coefficient of restitution method with a penalty approach.

scholarly journals Effects Of The Combined Heat And Cryogenic Treatment On The Stability Of Austenite In A High Co-Ni Steel

2015 ◽  
Vol 60 (3) ◽  
pp. 2131-2137 ◽  
Author(s):  
M. Gruber ◽  
S. Ploberger ◽  
G. Ressel ◽  
M. Wiessner ◽  
M. Hausbauer ◽  
...  
Keyword(s):  
Phase Distribution ◽  
Cryogenic Treatment ◽  
Tempering Temperature ◽  
Factors Affecting ◽  
Transmission Electron ◽  
Reverted Austenite ◽  
Before And After ◽  
Different Temperatures ◽  
The Stability ◽  
The Impact

Abstract The stability of austenite is one of the most dominant factors affecting the toughness properties of high Co-Ni steels such as Aermet 100 and AF1410. Thus, the aim of this work was to get a deeper understanding on the impact of combined heat and cryogenic treatment on the stability of retained and reverted austenite. In order to characterize the evolution of the phase fraction of austenite during tempering at different temperatures and times, X-ray diffraction analyses were carried out. The stability of austenite, which was formed during tempering, was analyzed with dilatometric investigations by studying the transformation behavior of the austenite during cooling from tempering temperature down to −100°C. Additionally, transmission electron microscopy investigations were performed to characterize the chemical composition and phase distribution of austenite and martensite before and after tempering.

scholarly journals The Impact of Coating Ingredients on the Aging Resistance of Topcoat Paints by Model Trees

2020 ◽  
Author(s):  
Tzu-Tsung Wong ◽  
Shih-Hsuan Hung
Keyword(s):  
Linear Regression ◽  
Regression Models ◽  
Prediction Method ◽  
Linear Regression Models ◽  
Key Factors ◽  
Model Trees ◽  
Factors Affecting ◽  
Aging Resistance ◽  
Before And After ◽  
The Impact

Topcoat paint is mainly composed of resin and pigment and hence its quality highly depends on the type and proportion of these two ingredients. This study aims at testing the formula of the topcoat paint for finding one that can achieve better quality for anti-aging. Various formulas of paint are applied on boards that will be put into ultraviolet accelerated test machines to simulate weathering tests. The gloss and color, before and after the tests, are collected and numerical prediction method M5P is used to grow model trees for discovering the key factors affecting aging. Based on the structure and the linear regression models in the trees, a better topcoat paint should be composed of a high proportion of resin and generally a low proportion of pigment. Good types of resin and pigment are also identified for keeping color and gloss.

The effects of conflict on risk perception and travelling intention of young tourists

2015 ◽  
Vol 10 (1) ◽  
pp. 118-130 ◽  
Author(s):  
Helena Desivilya ◽  
Sharon Teitler-Regev ◽  
Shosh Shahrabani
Keyword(s):  
Design Methodology ◽  
Priming Effect ◽  
Risk Estimation ◽  
Content Type ◽  
Factors Affecting ◽  
Conflict Area ◽  
Different Types ◽  
Travel Abroad ◽  
The Impact ◽  
Structured Questionnaire

Purpose – The purpose of this paper is to compare the evaluations of various risks by young Israelis living in conflict area and their Polish counterparts, who do not live in conflict area and how these perceptions affect their traveling intentions to destinations with different types of risks – Egypt, Turkey, India and Japan. Design/methodology/approach – The research participants were 713 Israeli and Polish students who responded to a structured questionnaire. Findings – The findings validate the assumption that contextual distinctions shape differently factors affecting traveling risk estimation and the intention of young people to travel abroad. The results indicated that the priming effect is substantial, reflected in Israelis’ significantly higher assessments of risks concerning destinations with terror, health and natural disasters hazards in comparison to Poles’ evaluations. As predicted, Israeli students exhibit lesser intentions to travel to Turkey, Egypt and India than their Polish counterparts. The study also showed similarities between Israeli and Polish students. Young tourists’ with strong aversion to health hazards exhibit low intention to travel to India and those refraining from economic crisis are reluctant to travel to Egypt. The intention to travel to Japan and India decreased with high perception of destination risks. Originality/value – The current study constitutes a new departure in studying the contextual effects on travel-related decision making. It focusses on the impact of conflict ridden environment on intentions, attitudes and risks perception of young tourists with respect to traveling to risky destinations, previously hardly studied.

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