Weak dynamical effects in the Uranian ring system

1984 ◽  
Vol 75 ◽  
pp. 457-458
Author(s):  
Adam P. Freedman ◽  
Scott Tremaine ◽  
James L. Elliot
Keyword(s):  
Close Association ◽  
Ring System ◽  
Convincing Evidence ◽  
Gravitational Forces ◽  
Ring Model ◽  
Maximum Change ◽  
Uranian Ring ◽  
The Masses ◽  
Three Body ◽  
Residual Errors

ABSTRACTA number of weak gravitational forces were examined for their kinematic effects on the Uranian ring system, in an attempt to account for residual errors of ~2 km in the ring positions and a few times 10-3deg/day in the apse precession rates. The principal conclusions are as follows: (1) perturbations by the five known satellites are too small to have observable effects with the best current estimates of the satellite masses. (2) Limits can be set on the masses of inter-ring “shepherd” satellites from their influence on precession rates and their radial perturbations on the rings. For example, the maximum mass of a shepherd satellite between rings 4 and 5 is ~ 1019gm. (3) Using the best available ring parameters, there is no convincing evidence that the rings are associated with resonances with known satellites. The only close association is of rings 5, α and γ with three-body resonances due to Miranda and Ariel. It is more likely that the putative shepherd satellites may occupy resonances. (4) The known satellites can cause anomalous residuals by changing the position of Uranus relative to the system barycenter during the occultation. The maximum change, so far, during the 1977 March 10 event, was 1.6 km. This effect will be investigated with the MIT Uranus ring model.

Tidal breakup and origin of the Uranian ring system

1984 ◽  
Vol 75 ◽  
pp. 687-689
Author(s):  
P. Farinella ◽  
A. Milani ◽  
A.M. Nobili ◽  
P. Paolicchi
Keyword(s):  
Observational Data ◽  
Ring System ◽  
Dissipative Processes ◽  
Gravitational Torque ◽  
Gravitational Forces ◽  
Uranian Ring ◽  
Interparticle Collisions ◽  
Ring Material

The peculiar features of the Uranian ring system have posed several difficult dynamical problems. The mutual gravitational forces among the ring particles can ensure stability against the spreading due to differential precession of the orbits, but are not able to provide an effective confinement mechanism against dissipative processes like interparticle collisions (Farinella et al., 1978, 1980a). The existence of small undiscovered satellites inside the orbit of Miranda is not ruled out by the presently available observational data, and has been proposed by Goldreich and Tremaine (1979) as a possible solution for the confinement problem: each ring is supposed to lie between two different satellites exerting a gravitational torque which tends to repel ring material and prevents the collisional spreading.

scholarly journals Studies of Strained Ring Systems: Cyclopropa[1]Phenanthrenes

2021 ◽  
Author(s):  
◽  
Barry Roy Dent
Keyword(s):  
Carboxylic Acid ◽  
Model Compound ◽  
Structural Type ◽  
Ring System ◽  
Convincing Evidence ◽  
Conclusive Evidence ◽  
Oxidative Decarboxylation ◽  
Fluoride Ion ◽  
Allyl Cation ◽  
Dichloro Derivative

<p>The aim of the present study has been the synthesis of 1H-cyclo-Propa[1]phenanthrene (16a) and its derivatives, the sole remaining unknown structural type of the cycloproparenes. Established procedures for cycloproparene synthesis are not readily adaptable to this ring system, and routes based upon new bridge-head-substituted 1a,9b-dihydrocyclopropa[1]phenanthrenes are examined. 1, 1-Dichloro-1a-phenylseleno-1a, 9b-dihydrocyclopropa [1] phenanthrene (73) is prepared by the addition of dichlorocarbene to the corresponding phenanthrenyl selenide (72). syn-Selenoxide elimination of PhSeOH from the derived selenoxide (74) gives 1,1-dichloro-1H-cyclopropa[1]phenanthrene (76) which is intercepted by methanolysis. Labelling studies provide convincing evidence for the intermediacy of the 1H-cycloproparene. The viability of an oxidative decarboxylation route to 1,1-dialkyl-1H-cyclopropa[1]phenanthrenes is investigated for the model compound 7,7-dimethylbicyclo[4.1.0]hept-3-ene-1-carboxylic acid (122). A product of formal cyclopropyl-allyl cation rearrangement, is isolated. 1a-Methylseleno-1a,9b-dihydrocyclopropa[1]phenanthrenes (174) is prepared by the unprecedented addition of methylselenide anion to 1aH-cyclopropa[1]phenanthrene (63) (generated by a new route involving the fluoride ion-promoted elimination of the elements of chlorotrimethylsilane from the isomeric 1-chloro-1a-trimethylsilyl-1a, 9b-dihydrocyclopropa[1]phenanthrenes (170) and (171)). Treatment of the drived dimethylselenonium tetra-fluoroborate (179) with base in the presence of furan gives the endo- and exo-furan cycloadducts (180) and (181) of 1H-cyclopropa[1]phenanthrene (16a). The results presented herein provide the first conclusive evidence for the existence of the 1H-cyclopropa[1]phenanthrene ring system, both as the parent hydrocarbon (16a) and the 1,1-dichloro-derivative(76).</p>

scholarly journals MINIMIZATION OF REAL POWER LOSS BY ENHANCED GRAVITATIONAL SEARCH ALGORITHM

2017 ◽  
Vol 5 (7) ◽  
pp. 623-630
Author(s):  
K. Lenin
Keyword(s):  
Local Minimum ◽  
Global Minimum ◽  
Reactive Power ◽  
Search Algorithm ◽  
Gravitational Search Algorithm ◽  
Gravitational Forces ◽  
Bee Colony ◽  
Gravitational Search ◽  
The Masses ◽  
Power Problem

In this paper, Enhanced Gravitational Search (EGS) algorithm is proposed to solve the reactive power problem. Gravitational search algorithm (GSA) results are improved by using artificial bee colony algorithm (ABC). In GSA, solutions are fascinated towards each other by applying gravitational forces, which depending on the masses assigned to the solutions, to each other. The heaviest mass will move slower than other masses and pull others. Due to nature of gravitation, GSA may pass global minimum if some solutions stuck to local minimum. ABC updates the positions of the best solutions that have obtained from GSA, preventing the GSA from sticking to the local minimum by its strong penetrating capability. The proposed algorithm improves the performance of GSA in greater level. In order to evaluate the performance of the proposed EGS algorithm, it has been tested on IEEE 57,118 bus systems and compared to other standard algorithms.

scholarly journals A note on the existence of invariant punctured tori in the planar circular restricted three-body problem

1988 ◽  
Vol 8 (8) ◽  
pp. 63-72 ◽  
Keyword(s):  
Body Problem ◽  
Small Mass ◽  
Connected Components ◽  
Restricted Three Body Problem ◽  
Three Body Problem ◽  
Jacobi Constant ◽  
Hill Region ◽  
The Masses ◽  
Three Body ◽  
Collision Orbits

AbstractThe existence of transversal ejection—collision orbits in the restricted three-body problem is shown to imply, via the KAM theorem, the existence, for certain intervals of (large) values of the Jacobi constant, of an uncountable number of invariant punctured tori in the corresponding (non-compact) energy surface. The proof is based on a comparison between Levi-Civita and McGehee regularizing variables. That these transversal ejection-collision orbits do actually exist was proved in [5] in the case where one of the primaries has a small mass and the zero-mass body revolves around the other (and for all values of the Jacobi constant compatible with the existence of three connected components for the Hill region); it is proved here without any restriction on the masses, well in the spirit of Conley's thesis [3].

scholarly journals An Analysis of Jack Mapanje’s Poetry with Particular Reference to his use of Obscuring Devices

2017 ◽  
Vol 6 (7) ◽  
pp. 30
Author(s):  
Theophilus T Mukhuba
Keyword(s):  
Life Experiences ◽  
Close Association ◽  
Literary Work ◽  
Political Resistance ◽  
Intended Audience ◽  
Abuse Of Power ◽  
Animal Imagery ◽  
Wide Range ◽  
The Masses ◽  
The Relationship

Jack Mapanje’s poetry is a true reflection of his society through the use of obscuring devices. These obscuring devices are necessary to ensure that the literary work reaches its intended audience in a totalitarian society. Overall, Jack Mapanje’s poetry exploits creatures from the world of nature—mammals, birds, amphibians, reptiles and insects—for close association with life experiences in various contexts and situations and with people he viewed with contempt and disgust and those he regarded with tenderness and compassion. He utilises them to conceptualize and construct a wide range of ideas that respond to questions of justice, identity and belonging. It all thus becomes part of ecocriticism which is defined by various authors as ‘the study of the relationship between literature and the physical environment’. This eco-critical reading, the use of animal imagery in his poetry makes it stand apart and ahead of other resistance poetry and makes new statements about the relationships between animals, poetry and political resistance in African literature. Mapanje’s poetry is a direct response and a stance of resistance to social injustice, especially the debasement of culture, abuse of power, despotism, oppression and exploitation of the masses by the hegemonic regime of Dr. Hastings in Malawi that leads to his incarceration and final forced flight from his motherland. This paper attempts to showcase the nature of poetic expressions produced in a repressive society.

scholarly journals Three-Body Stability Criteria

1999 ◽  
Vol 172 ◽  
pp. 441-442
Author(s):  
J.R. Donnison
Keyword(s):  
Major Axis ◽  
Quantitative Agreement ◽  
Separation Distance ◽  
Critical Distance ◽  
Third Body ◽  
Semi Major Axis ◽  
Distance Ratio ◽  
The Third ◽  
The Masses ◽  
Three Body

Progress has been made in understanding the stability of hierarchical three-body systems where the third body moves on an approximately Keplerian orbit about the centre of mass of the binary, at a distance large compared to the binary separation. Harrington (1968,1969) showed analytically that provided the third body was sufficiently distant from the binary no secular terms appeared in the semi-major axis and the system was stable. Harrington (1972,1975,1977) established numerically a critical minimum separation distance (or period) for a stable system in terms of the masses, unaffected by the relative inclinations of the orbits, except for angles close to 90°. Most subsequent investigations have therefore used planar configurations. Graziani & Black (1981), Black (1982) and Pendleton & Black (1983) again using long-term integration of the orbits obtained a criterion for high and low mass binaries. Donnison & Mikulskis (1992,1994,1995) carried out numerical integrations on prograde, retrogade, planetary and stellar triple systems and found for prograde systems very good quantitative agreement with the c2H method. Eggleton & Kieselva (1995) suggested a critical distance ratio approximation determined by the masses in the system. Systems with eccentric orbits are covered using the period ratio determined by Kepler’s third law.

Dynamics of eccentric and inclined ringlets

1984 ◽  
Vol 75 ◽  
pp. 341-343
Author(s):  
N. Borderies ◽  
P. Goldreich ◽  
S. Tremaine
Keyword(s):  
Semimajor Axis ◽  
Ring System ◽  
The Self ◽  
Uranian Ring ◽  
Self Gravity

The Saturn and Uranian ring system contain a number of narrow eccentric ringlets. Several of the Uranian ringlets are also inclined to the planet's equator. We show that the self-gravity is probably responsible for maintaining apse and node alignment across these ringlets. This hypothesis leads to the prediction that within each ringlet both the eccentricity and the inclination increase with semimajor axis.

A Region of Association and Turbulence

2016 ◽  
pp. 1-27
Author(s):  
Meha Pant
Keyword(s):  
Indian Subcontinent ◽  
Close Association ◽  
The Political ◽  
Regional Power ◽  
Important Place ◽  
Bilateral Relations ◽  
War And Conflict ◽  
The Times ◽  
The Masses ◽  
The Cold War

The areas in and around India have always had a close association in building up of events which with time have attained historical and cultural prominence. In this study of cultural association the today's neighboring countries of Pakistan and Afghanistan have served as a passage of the influx of various cultures into the Indian subcontinent. The end of the Cold War highlighted the new threats which had emerged, not bound in the notions of safeguarding the integrity and sovereignty; they were way beyond territorial demarcations. These new threats were transnational in form with a much larger impact on the masses of the state. The rise and fall of Taliban in Afghanistan and the Anti India Islamic forces in Pakistan with the rise of India as a new regional power has led to new perspectives in concerns for the diplomatic and bilateral relations between these countries. What remains to be pointed is the level of porosity of borders and the ancient passes which have been routes for trade and inter cultural affiliations among these countries. The period of 2009-2015 was marked by various incidents which rocked the subcontinent bringing in strategic concerns to a new level. This article would study the historical linkages and cultural affiliations which binds the area of Afghanistan, Pakistan and India into a deeper relationship. Along with dwelling into the political scenario defined by bilateral and diplomatic ties which has taken up an important place in the times of changing perspectives of war and conflict.

Synthetic Studies toward Tubiferal A: Asymmetric Synthesis of a Model ABC-ring Compound

Synlett ◽  
2021 ◽  
Author(s):  
Yuki Yukutake ◽  
Takahiro Hiramatsu ◽  
Ryusei Itoh ◽  
Kazutada Ikeuchi ◽  
Takahiro Suzuki ◽  
...  
Keyword(s):  
Asymmetric Synthesis ◽  
Claisen Rearrangement ◽  
Ring System ◽  
Alkylation Reaction ◽  
Ring Model ◽  
Stereoselective Addition ◽  
Stereogenic Centers ◽  
Rearrangement Reaction ◽  
Synthetic Studies ◽  
Ab Ring

Synthetic studies on an ABC-ring model of Tubiferal A, a triterpenoid isolated from the fruit bodies of the Tubifera dimorphotheca myxomycete, are described. The stereogenic centers at the angular positions were constructed through the stereoselective addition of a C-ring allylborane followed by an Eschenmoser–Claisen rearrangement reaction prior to the formation of the AB-ring system by a double intramolecular alkylation reaction of a dichloro nitrile intermediate.

Psychoneuroimmunology and Related Mechanisms in Understanding Health Disparities in Vulnerable Populations

2007 ◽  
Vol 25 (1) ◽  
pp. 219-256 ◽  
Author(s):  
Teresita L. Briones
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Acute Infection ◽  
Relevant Literature ◽  
Endocrine System ◽  
Convincing Evidence ◽  
Immune Functions ◽  
Parasympathetic Nerves ◽  
Three Body ◽  
State Of The Science

The nervous system as well as the endocrine system maintain extensive communication with the immune system through the influence of hormones and neurotransmitters and also by way of the hardwiring of sympathetic and parasympathetic nerves to the lymphoid organs. There is now convincing evidence that the communication between these three body systems is bidirectional. This chapter will provide a succinct review of how neuroendocrine and immune functions are affected in factors that impact vulnerability, such as aging, acute infection, and central nervous system injury. Given that the relevant literature on these topics is vast, the presentation in this chapter will serve to highlight primary references that reflect state of the science in these systems of focus.

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