scholarly journals Particle Ejection Contributions to the Rotational Acceleration and Orbit Evolution of Asteroid (101955) Bennu

2020 ◽  
Vol 125 (3) ◽  
Author(s):  
D. J. Scheeres ◽  
J. W. McMahon ◽  
D. N. Brack ◽  
A. S. French ◽  
S. R. Chesley ◽  
...  
Keyword(s):  
Rotational Acceleration ◽  
Orbit Evolution ◽  
Particle Ejection

The E-ring: interactions with plasma and implications for its evolution

1984 ◽  
Vol 75 ◽  
pp. 599-602
Author(s):  
T.V. Johnson ◽  
G.E. Morfill ◽  
E. Grun
Keyword(s):  
Time Scale ◽  
Particle Density ◽  
High Energy ◽  
Particle Removal ◽  
Density Region ◽  
Drag Forces ◽  
Orbit Evolution ◽  
History Of ◽  
Ring Particle ◽  
Ring Material

A number of lines of evidence suggest that the particles making up the E-ring are small, on the order of a few microns or less in size (Terrile and Tokunaga, 1980, BAAS; Pang et al., 1982 Saturn meeting; Tucson, AZ). This suggests that a variety of electromagnetic and plasma affects may be important in considering the history of such particles. We have shown (Morfill et al., 1982, J. Geophys. Res., in press) that plasma drags forces from the corotating plasma will rapidly evolve E-ring particle orbits to increasing distance from Saturn until a point is reached where radiation drag forces acting to decrease orbital radius balance this outward acceleration. This occurs at approximately Rhea's orbit, although the exact value is subject to many uncertainties. The time scale for plasma drag to move particles from Enceladus' orbit to the outer E-ring is ~104yr. A variety of effects also act to remove particles, primarily sputtering by both high energy charged particles (Cheng et al., 1982, J. Geophys. Res., in press) and corotating plasma (Morfill et al., 1982). The time scale for sputtering away one micron particles is also short, 102 - 10 yrs. Thus the detailed particle density profile in the E-ring is set by a competition between orbit evolution and particle removal. The high density region near Enceladus' orbit may result from the sputtering yeild of corotating ions being less than unity at this radius (e.g. Eviatar et al., 1982, Saturn meeting). In any case, an active source of E-ring material is required if the feature is not very ephemeral - Enceladus itself, with its geologically recent surface, appears still to be the best candidate for the ultimate source of E-ring material.

Head Impact Biomechanics in Youth Flag Football: A Prospective Cohort Study

2021 ◽  
pp. 036354652110266
Author(s):  
Landon B. Lempke ◽  
Rachel S. Johnson ◽  
Rachel K. Le ◽  
Melissa N. Anderson ◽  
Julianne D. Schmidt ◽  
...  
Keyword(s):  
Mixed Model ◽  
Linear Acceleration ◽  
Cross Sectional Study ◽  
Head Impact ◽  
Rotational Acceleration ◽  
Event Type ◽  
Level Of Evidence ◽  
Cross Sectional ◽  
Head Impact Biomechanics ◽  
Impact Biomechanics

Background: Youth flag football participation has rapidly grown and is a potentially safer alternative to tackle football. However, limited research has quantitatively assessed youth flag football head impact biomechanics. Purpose: To describe head impact biomechanics outcomes in youth flag football and explore factors associated with head impact magnitudes. Study Design: Cross-sectional study; Level of evidence, 3. Methods: We monitored 52 player-seasons among 48 male flag football players (mean ± SD; age, 9.4 ± 1.1 years; height, 138.6 ± 9.5 cm; mass, 34.7 ± 9.2 kg) across 3 seasons using head impact sensors during practices and games. Sensors recorded head impact frequencies, peak linear ( g) and rotational (rad/s2) acceleration, and estimated impact location. Impact rates (IRs) were calculated as 1 impact per 10 player-exposures; IR ratios (IRRs) were used to compare season, event type, and age group IRs; and 95% CIs were calculated for IRs and IRRs. Weekly and seasonal cumulative head impact frequencies and magnitudes were calculated. Mixed-model regression models examined the association between player characteristics, event type, and seasons and peak linear and rotational accelerations. Results: A total of 429 head impacts from 604 exposures occurred across the study period (IR, 7.10; 95% CI, 4.81-10.50). Weekly and seasonal cumulative median head impact frequencies were 1.00 (range, 0-2.63) and 7.50 (range, 0-21.00), respectively. The most frequent estimated head impact locations were the skull base (n = 96; 22.4%), top of the head (n = 74; 17.2%), and back of the head (n = 66; 15.4%). The combined event type IRs differed among the 3 seasons (IRR range, 1.45-2.68). Games produced greater IRs (IRR, 1.24; 95% CI, 1.01-1.53) and peak linear acceleration (mean difference, 5.69 g; P = .008) than did practices. Older players demonstrated greater combined event–type IRs (IRR, 1.46; 95% CI, 1.12-1.90) and increased head impact magnitudes than did younger players, with every 1-year age increase associated with a 3.78 g and 602.81-rad/s2 increase in peak linear and rotational acceleration magnitude, respectively ( P≤ .005). Conclusion: Head IRs and magnitudes varied across seasons, thus highlighting multiple season and cohort data are valuable when providing estimates. Head IRs were relatively low across seasons, while linear and rotational acceleration magnitudes were relatively high.

scholarly journals Football concussion case series using biomechanical and video analysis

Neurology ◽  
2018 ◽  
Vol 91 (23 Supplement 1) ◽  
pp. S2.2-S2
Author(s):  
Mirellie Kelley ◽  
Jillian Urban ◽  
Derek Jones ◽  
Alexander Powers ◽  
Christopher T. Whitlow ◽  
...  
Keyword(s):  
Video Analysis ◽  
Case Series ◽  
Linear Acceleration ◽  
The United States ◽  
Head Impact ◽  
Rotational Acceleration ◽  
Impact Location ◽  
Injury Mechanisms ◽  
The Mean ◽  
Impact Data

Approximately 1.1–1.9 million sport-related concussions among athletes ≤18 years of age occur annually in the United States, but there is limited understanding of the biomechanics and injury mechanisms associated with concussions among lower level football athletes. Therefore, the objective of this study was to combine biomechanical head impact data with video analysis to characterize youth and HS football concussion injury mechanisms. Head impact data were collected from athletes participating on 22 youth and 6 HS football teams between 2012 and 2017. Video was recorded, and head impact data were collected during all practices and games by instrumenting players with the Head Impact Telemetry (HIT) System. For each clinically diagnosed concussion, a video abstraction form was completed, which included questions concerning the context in which the injury occurred. Linear acceleration, rotational acceleration, and impact location were used to characterize the concussive event and each injured athlete's head impact exposure on the day of the concussion. A total of 9 (5 HS and 4 youth) concussions with biomechanics and video of the event were included in this study. The mean [range] linear and rotational acceleration of the concussive impacts were 62.9 [29.3–118.4] g and 3,056.7 [1,046.8–6,954.6] rad/s2, respectively. Concussive impacts were the highest magnitude impacts for 6 players and in the top quartile of impacts for 3 players on the day of injury. Concussions occurred in both practices (N = 4) and games (N = 5). The most common injury contact surface was helmet-to-helmet (N = 5), followed by helmet-to-ground (N = 3) and helmet-to-body (N = 1). All injuries occurred during player-to-player contact scenarios, including tackling (N = 4), blocking (N = 4), and collision with other players (N = 1). The biomechanics and injury mechanisms of concussions varied among athletes in our study; however, concussive impacts were among the highest severity for each player and all concussions occurred as a result of player-to-player contact.

Peculiarities of particle ejection in scattering and sputtering of single crystals

1976 ◽  
Vol 27 (3-4) ◽  
pp. 173-178 ◽  
Author(s):  
V. E. Yurasova ◽  
V. I. Shulga ◽  
I. G. Bunin ◽  
B. M. Mamaev ◽  
L. N. Nevzorova ◽  
...  
Keyword(s):  
Single Crystals ◽  
Particle Ejection

scholarly journals Rotational Acceleration Measurements - Evaluating Helmet Protection

2004 ◽  
Vol 31 (4) ◽  
pp. 499-503 ◽  
Author(s):  
M. Kis ◽  
F. Saunders ◽  
M.W. ten Hove ◽  
J.R. Leslie
Keyword(s):  
Horizontal Plane ◽  
Rotational Acceleration ◽  
Testing Device ◽  
Cerebral Concussion ◽  
Impact Simulation ◽  
Head Protection ◽  
Rotational Components ◽  
Protection Devices ◽  
Testing Standards ◽  
Testing Paradigm

Purpose:Current helmet testing standards do not address the rotational components of an impact to the head. We describe a new testing paradigm used to measure the rotational acceleration of a headform and a protective helmet following an impact to the head in the horizontal plane. This impact simulation allows for the testing of currently available head protection devices in conditions thought to be important for the generation of cerebral concussion. The degree to which a particular helmet dampens rotational acceleration, and thus protects against concussion, can be assessed.Methods:Our testing device consists of a pneumatic piston that provides a measured impact to a standard headform. Four different helmets were tested using the described paradigm.Results:Acceleration curves for each helmet and the corresponding headform are presented.Conclusion:Clear differences in rotational acceleration were demonstrated. Possible avenues of further investigation are discussed.

scholarly journals Space-Object Charging and Its Effect on Orbit Evolution

2017 ◽  
Vol 40 (12) ◽  
pp. 3180-3198 ◽  
Author(s):  
Smriti Nandan Paul ◽  
Carolin Frueh
Keyword(s):  
Space Object ◽  
Orbit Evolution

scholarly journals Orbit Evolution Analysis of DubaiSat-2 using Hall-effect Thruster

2015 ◽  
Vol 43 (4) ◽  
pp. 377-386
Author(s):  
Eun-Hyouek Kim ◽  
Youn-Ho Kim ◽  
Jong-Soo Park ◽  
Dong-Wook Koh ◽  
Yun-Hwang Jeong ◽  
...  
Keyword(s):  
Hall Effect ◽  
Hall Effect Thruster ◽  
Evolution Analysis ◽  
Orbit Evolution

scholarly journals Video: Particle ejection by a laser-induced bubble

2017 ◽  
Author(s):  
Shengji Wu ◽  
Zhigang Zuo ◽  
Howard Stone ◽  
Shuhong Liu
Keyword(s):  
Particle Ejection

A study of particle ejection by high-speed impacts

Shock Waves ◽  
2009 ◽  
pp. 803-808
Author(s):  
M. Anyoji ◽  
D. Numata ◽  
M. Sun ◽  
K. Takayama
Keyword(s):  
High Speed ◽  
Particle Ejection
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