scholarly journals Quadratic gravity and restricted Weyl symmetry

2021 ◽  
pp. 2150139
Author(s):  
Arata Kamimura ◽  
Ichiro Oda
Keyword(s):  
Gauge Symmetry ◽  
Degrees Of Freedom ◽  
Minkowski Spacetime ◽  
Static Condition ◽  
Gauge Parameter ◽  
Zero Energy ◽  
Quadratic Gravity ◽  
Weyl Symmetry ◽  
Dynamical Degrees ◽  
The Relationship

In this paper, we investigate the relationship between quadratic gravity and a restricted Weyl symmetry where a gauge parameter [Formula: see text] of Weyl transformation satisfies a constraint [Formula: see text] in a curved spacetime. First, we briefly review a model with a restricted gauge symmetry on the basis of QED, where a [Formula: see text] gauge parameter [Formula: see text] obeys a similar constraint [Formula: see text] in a flat Minkowski spacetime, and explain that the restricted gauge symmetry removes one on-shell mode of gauge field, which together with the Feynman gauge leaves only two transverse polarizations as physical states. Next, it is shown that the restricted Weyl symmetry also eliminates one component of a dipole field in quadratic gravity around a flat Minkowski background, leaving only a single scalar state. Finally, we show that the restricted Weyl symmetry cannot remove any dynamical degrees of freedom in static background metrics by using the zero-energy theorem of quadratic gravity. This fact also holds for the Euclidean background metrics without imposing the static condition.

scholarly journals Membrane paradigm from near-horizon soft hair

2018 ◽  
Vol 27 (14) ◽  
pp. 1847006 ◽  
Author(s):  
D. Grumiller ◽  
M. M. Sheikh-Jabbari
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Boundary Conditions ◽  
Degrees Of Freedom ◽  
Black Hole Entropy ◽  
Heisenberg Algebra ◽  
Zero Energy ◽  
Shear Deformations ◽  
Dynamical Degrees ◽  
Area Preserving

The membrane paradigm posits that black hole microstates are dynamical degrees of freedom associated with a physical membrane vanishingly close to the black hole’s event horizon. The soft hair paradigm postulates that black holes can be equipped with zero-energy charges associated with residual diffeomorphisms that label near-horizon degrees of freedom. In this paper we argue that the latter paradigm implies the former. More specifically, we exploit suitable near-horizon boundary conditions that lead to an algebra of “soft hair charges” containing infinite copies of the Heisenberg algebra, associated with area-preserving shear deformations of black hole horizons. We employ the near-horizon soft hair and its Heisenberg algebra to provide a formulation of the membrane paradigm and show how it accounts for black hole entropy.

COMPLEX MASS FERMIONIC FIELDS

1994 ◽  
Vol 09 (12) ◽  
pp. 2103-2115 ◽  
Author(s):  
D.G. BARCI ◽  
L.E. OXMAN
Keyword(s):  
Degrees Of Freedom ◽  
Order Equation ◽  
Complex Conjugate ◽  
Zero Energy ◽  
Natural Representation ◽  
Symmetric State ◽  
Fermionic Field ◽  
Fermionic Fields ◽  
Real Mass ◽  
Mass Case

We consider a fermionic field obeying a second order equation containing a pair of complex conjugate mass parameters. After obtaining a natural representation for the different degrees of freedom, we are able to construct a unique vacuum as the more symmetric state (zero energy-momentum, charge and spin). This representation, unlike the real mass case, is not holomorphic in the Grassmann variables. The vacuum eigenstate allows the calculation of the field propagator which turns out to be half advanced plus half retarded.

Footbridges as an important part of a system: the context as an experience

2021 ◽  
Author(s):  
Toon Maas ◽  
Mohamad Tuffaha ◽  
Laurent Ney
Keyword(s):  
Design Process ◽  
Degrees Of Freedom ◽  
The Other ◽  
Infrastructure Projects ◽  
Good Design ◽  
Cultural Processes ◽  
The Relationship

<p>“A bridge has to be designed”. Every bridge is the exploration of all degrees of a freedom of a project: the context, cultural processes, technology, engineering and industrial skills. A successful bridge aims to dialogue with these degrees of freedom to achieve a delicate equilibrium, one that invites the participation of its users and emotes new perceptions for its viewers. In short, a good design “makes the bridge talk.”</p><p>Too often, the bridge, as an object, is reduced to its functionality. Matters of perceptions and experiences of the users are often not considered in the design process; they are relegated to levels of chance or treated as simple decorative matter. The longevity of infrastructure projects, in general, and bridges, in particular, highlights the deficiencies of such an approach. The framework to design bridges must include historical, cultural, and experiential dimensions. Technology and engineering are of paramount importance but cannot be considered as “an end in themselves but a means to an end”. This paper proposes to discuss three projects by Ney &amp; Partners that illustrate such a comprehensive exploration approach to footbridge design: the Poissy and Albi crossings and the Tintagel footbridge.</p><p>The footbridges of Poissy and Albi dialogue most clearly with their historical contexts, reconfiguring the relationship between old and new in the materiality and typology use. In Tintagel, legend replaces history. Becoming a metaphor for the void it crosses, the Tintagel footbridge illustrates the delicate dialogue of technology and engineering on one side and imagination and experience on the other.</p>

DEONTOLOGY, THRESHOLDS, AND EFFICIENCY

Legal Theory ◽  
2011 ◽  
Vol 17 (4) ◽  
pp. 301-317 ◽  
Author(s):  
Christopher T. Wonnell
Keyword(s):  
Decision Making ◽  
Degrees Of Freedom ◽  
Moral Judgments ◽  
Rule Following ◽  
Threshold Functions ◽  
Ex Post ◽  
Ex Ante ◽  
The Many ◽  
The Relationship ◽  
Public Decision

This article explores four topics raised by Eyal Zamir and Barak Medina's treatment of constrained deontology. First, it examines whether mathematical threshold functions are the proper way to think about limits on deontology, given the discontinuities of our moral judgments and the desired phenomenology of rule-following. Second, it asks whether constrained deontology is appropriate for public as well as private decision-making, taking issue with the book's conclusion that deontological options are inapplicable to public decision-making, whereas deontological constraints are applicable. Third, it examines the issue of the relationship between deontology and efficiency, asking whether deontological constraints should yield in situations where everyone would expect to benefit from their suspension, either ex ante or ex post. Finally, the article concludes that constrained deontology is susceptible to political abuse because of the many degrees of freedom involved in identifying constrained actions and the point at which those constraints yield to consequentialist benefits.

EMBODIMENT DESIGN OF NOVEL 5-SPEED REAR DRIVE HUBS FOR BICYCLES

2015 ◽  
Vol 39 (3) ◽  
pp. 431-441 ◽  
Author(s):  
Yi-Chang Wu ◽  
Tze-Cheng Wu
Keyword(s):  
Power Flow ◽  
Degrees Of Freedom ◽  
Planetary Gear ◽  
Gear Train ◽  
Main Body ◽  
Direct Drive ◽  
Drive Gear ◽  
Planetary Gear Train ◽  
Embodiment Design ◽  
The Relationship

This paper presents embodiment design of 5-speed rear drive hubs for bicycles. A 7-link, 2-degrees of freedom (DOF) compound planetary gear train as the main body of a rear drive hub is introduced. The relationship between the number of coaxial links of a planetary gear train and the number of gear stages that a drive hub can provide with is discussed. By means of kinematic analysis, four speed ratios of the planetary gear train are derived, which represents four forward gears of the rear drive hub. By adding a direct-drive gear, five forward gears can be provided and two feasible clutching sequence tables are synthesized. Manual translational-type gear-shifting mechanisms are further designed to incorporate with the planetary gear train for appropriately controlling the gear stage. The power-flow path at each gear stage is checked to verify the feasibility of the proposed design. Finally, two novel 5-speed bicycle rear drive hubs are presented.

scholarly journals Multiple choice of gauge generators and consistency of interactions

2014 ◽  
Vol 29 (31) ◽  
pp. 1450167 ◽  
Author(s):  
S. L. Lyakhovich ◽  
A. A. Sharapov
Keyword(s):  
Gauge Symmetry ◽  
Simple Model ◽  
Degrees Of Freedom ◽  
Multiple Choice ◽  
Gravity Models ◽  
Coupling Constant ◽  
Free Theory ◽  
Gauge Symmetries

It is usually assumed that any consistent interaction either deforms or retains the gauge symmetries of the corresponding free theory. We propose a simple model where an obvious irreducible gauge symmetry does not survive an interaction, while the interaction is consistent as it preserves the number of physical degrees of freedom. The model turns out admitting a less obvious reducible set of gauge generators which is compatible with the interaction and smooth in coupling constant. Possible application to gravity models is discussed.

Manipulator Task-Based Performance Optimization

2004 ◽  
Author(s):  
Chalongrath Pholsiri ◽  
Chetan Kapoor ◽  
Delbert Tesar
Keyword(s):  
Performance Optimization ◽  
Degrees Of Freedom ◽  
Performance Criteria ◽  
Redundancy Resolution ◽  
Task Constraints ◽  
Output Constraints ◽  
Definition Of ◽  
Joint Limits ◽  
Relationship Of ◽  
The Relationship

This research uses new developments in redundancy resolution and real-time capability analysis to improve the ability of an articulated arm to satisfy task constraints. Task constraints are specified using numerical values of position, velocity, force, and accuracy. Inherent in the definition of task constraints is the number of output constraints that the system needs to satisfy. The relationship of this with the input space (degrees of freedom) defines the ability to optimize manipulator performance. This is done through a Task-Based Redundancy Resolution (TBRR) scheme that uses the extra resources to find a solution that avoids system constraints (joint limits, singularities, etc.) and satisfies task constraints. To avoid system constraints, we use well-understood criteria associated with the constraints. For task requirements, the robot capabilities are estimated based on kinematic and dynamic manipulability analyses. We then compare the robot capabilities with the user-specified requirement values. This eliminates a confusing chore of selecting a proper set of performance criteria for a task at hand. The breakthrough of this approach lies in the fact that it continuously evaluates the relationship between task constraints and system resources, and when possible, improves system performance. This makes it equally applicable to redundant and non-redundant systems. The scheme is implemented using an object-oriented operational software framework and its effectiveness is demonstrated in computer simulations of a 10-DOF manipulator.

scholarly journals SOLUTION TO 2+1 GRAVITY IN DREIBEIN FORMALISM

1994 ◽  
Vol 03 (01) ◽  
pp. 131-137 ◽  
Author(s):  
W.G. UNRUH
Keyword(s):  
General Relativity ◽  
Degrees Of Freedom ◽  
Closed Timelike Curves ◽  
Original Theory ◽  
Arbitrary Genus ◽  
Genus 2 ◽  
Genus Two ◽  
Dynamical Degrees

This paper outlines the reduction of the dreibein formalism of 2+1 General Relativity to the dynamical degrees of freedom for a genus 2 (and by extension for an arbitrary genus) two space. The resulting dynamical variables of the reduced theory are global holonomies and are constants of the motion of the original theory. The relation to geometry and closed timelike curves is briefly described.

Modelling of Continuous Contact-Based Skating Technique

2018 ◽  
Author(s):  
Varan Gupta ◽  
Rohit Patel ◽  
Jitendra P. Khatait ◽  
I. N. Kar
Keyword(s):  
Degrees Of Freedom ◽  
Ground Plane ◽  
Humanoid Robots ◽  
Equivalent Model ◽  
Continuous Contact ◽  
Additional Equipment ◽  
Input Signals ◽  
Speed Up ◽  
The Relationship ◽  
Three Degrees Of Freedom

Quick locomotion has always been a challenge for humanoid robots. Most of the work has been done to improve the efficiency of the walking gaits. Recently, additional equipment like skates are increasingly being used to speed up location, but they also make the system highly unstable. This paper describes the development of a statically stable skating gait to facilitate movement across plain surfaces, such as roads and hard ice. The new gait utilises the non-holonomic nature of a wheel (or blade of an ice skate). The proposed motion of the skates on the ground plane enables it to propel the robot forward without lifting its leg. Kinematic and dynamic equations of an equivalent model are formulated. Further, the paper discusses the relationship between different input signals and their corresponding output gaits. Multibody dynamics software is then used to simulate and verify the results for various scenarios. The design of an equivalent model with three degrees of freedom is then analysed and discussed for practical testing. Finally, the algorithm was tested on a fabricated robot.

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