scholarly journals ELECTROMAGNETIC DUALITY ON THE LIGHT-FRONT IN THE PRESENCE OF EXTERNAL SOURCES

2000 ◽  
Vol 15 (30) ◽  
pp. 4739-4748 ◽  
Author(s):  
ASMITA MUKHERJEE ◽  
SOMDATTA BHATTACHARYA
Keyword(s):  
Degrees Of Freedom ◽  
Transverse Field ◽  
Light Front ◽  
Duality Transformation ◽  
Hamiltonian Density ◽  
Free Theory ◽  
External Sources ◽  
Normal Light ◽  
The Right ◽  
Dynamical Field

We investigate the issue of electromagnetic duality on the light-front. We work with Zwanziger's theory of electric and magnetic sources which is appropriate for treating duality. When quantized on the light-front in the light-front gauge, this theory yields two independent phase space degrees of freedom, namely the two transverse field components, the right number to describe the gauge field sector of normal light-front QED and also the appropriate commutator between them. The electromagnetic duality transformation formulated in terms of them is similar in form to the Susskind transformation proposed for the free theory, provided one identifies them as the dynamical field components of the photon on the light-front in the presence of magnetic sources. The Hamiltonian density written in terms of these components is invariant under the duality transformation.

scholarly journals Slow scrambling in extremal BTZ and microstate geometries

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Ben Craps ◽  
Marine De Clerck ◽  
Philip Hacker ◽  
Kévin Nguyen ◽  
Charles Rabideau
Keyword(s):  
Field Theory ◽  
Black Holes ◽  
Degrees Of Freedom ◽  
Average Power ◽  
Nonzero Temperature ◽  
Time Intervals ◽  
Conformal Field ◽  
Btz Black Holes ◽  
The Right ◽  
Extremal Black Holes

Abstract Out-of-time-order correlators (OTOCs) that capture maximally chaotic properties of a black hole are determined by scattering processes near the horizon. This prompts the question to what extent OTOCs display chaotic behaviour in horizonless microstate geometries. This question is complicated by the fact that Lyapunov growth of OTOCs requires nonzero temperature, whereas constructions of microstate geometries have been mostly restricted to extremal black holes.In this paper, we compute OTOCs for a class of extremal black holes, namely maximally rotating BTZ black holes, and show that on average they display “slow scrambling”, characterized by cubic (rather than exponential) growth. Superposed on this average power-law growth is a sawtooth pattern, whose steep parts correspond to brief periods of Lyapunov growth associated to the nonzero temperature of the right-moving degrees of freedom in a dual conformal field theory.Next we study the extent to which these OTOCs are modified in certain “superstrata”, horizonless microstate geometries corresponding to these black holes. Rather than an infinite throat ending on a horizon, these geometries have a very deep but finite throat ending in a cap. We find that the superstrata display the same slow scrambling as maximally rotating BTZ black holes, except that for large enough time intervals the growth of the OTOC is cut off by effects related to the cap region, some of which we evaluate explicitly.

Interstitial Nucleus of Cajal Encodes Three-Dimensional Head Orientations in Fick-Like Coordinates

2007 ◽  
Vol 97 (1) ◽  
pp. 604-617 ◽  
Author(s):  
Eliana M. Klier ◽  
Hongying Wang ◽  
J. Douglas Crawford
Keyword(s):  
Coordinate System ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Semicircular Canals ◽  
Head Rotation ◽  
Head Orientation ◽  
Interstitial Nucleus Of Cajal ◽  
The Gaze ◽  
Behavioral Constraints ◽  
The Right

Two central, related questions in motor control are 1) how the brain represents movement directions of various effectors like the eyes and head and 2) how it constrains their redundant degrees of freedom. The interstitial nucleus of Cajal (INC) integrates velocity commands from the gaze control system into position signals for three-dimensional eye and head posture. It has been shown that the right INC encodes clockwise (CW)-up and CW-down eye and head components, whereas the left INC encodes counterclockwise (CCW)-up and CCW-down components, similar to the sensitivity directions of the vertical semicircular canals. For the eyes, these canal-like coordinates align with Listing’s plane (a behavioral strategy limiting torsion about the gaze axis). By analogy, we predicted that the INC also encodes head orientation in canal-like coordinates, but instead, aligned with the coordinate axes for the Fick strategy (which constrains head torsion). Unilateral stimulation (50 μA, 300 Hz, 200 ms) evoked CW head rotations from the right INC and CCW rotations from the left INC, with variable vertical components. The observed axes of head rotation were consistent with a canal-like coordinate system. Moreover, as predicted, these axes remained fixed in the head, rotating with initial head orientation like the horizontal and torsional axes of a Fick coordinate system. This suggests that the head is ordinarily constrained to zero torsion in Fick coordinates by equally activating CW/CCW populations of neurons in the right/left INC. These data support a simple mechanism for controlling head orientation through the alignment of brain stem neural coordinates with natural behavioral constraints.

An appropriate biomechanical model of seated human subjects exposed to whole-body vibration

2021 ◽  
pp. 146441932110394
Author(s):  
Raj Desai ◽  
Anirban Guha ◽  
Pasumarthy Seshu
Keyword(s):  
Degrees Of Freedom ◽  
Human Subjects ◽  
Computational Cost ◽  
Biomechanical Model ◽  
Whole Body ◽  
Body Parts ◽  
Lumped Parameter ◽  
Long Duration ◽  
The One ◽  
The Right

Long duration automobile-induced vibration is the cause of many ailments to humans. Predicting and mitigating these vibrations through seat requires a good model of seated human body. A good model is the one that strikes the right balance between modelling difficulty and simulation results accuracy. Increasing the number of body parts which have been separately modelled and increasing the number of ways these parts are connected to each other increase the number of degrees of freedom of the entire model. A number of such models have been reported in the literature. These range from simple lumped parameter models with limited accuracy to advanced models with high computational cost. However, a systematic comparison of these models has not been reported till date. This work creates eight such models ranging from 8 to 26 degrees of freedom and tries to identify the model which strikes the right balance between modelling complexity and results accuracy. A comparison of the models’ prediction with experimental data published in the literature allows the identification of a 12 degree of freedom backrest supported model as optimum for modelling complexity and prediction accuracy.

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.

Some New Effects: Phenomenal Glare, Luminous ‘Mist’ and Dark ‘Smoke’

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 58-58
Author(s):  
D Zavagno
Keyword(s):  
Light Source ◽  
Spreading Effect ◽  
Black Background ◽  
Black Smoke ◽  
Grey Scale ◽  
Intense Light ◽  
To Come ◽  
Normal Light ◽  
The Right ◽  
Background Brightness

The impression of glare is caused by a very intense light source. However, here I show that this impression can also be generated with normal light intensities. The strength of the effect depends on the number of elements used to produce it. The elements are 2 cm × 5 cm rectangles. A single horizontal achromatic rectangle is first used on a homogeneous white or black background. From left to right, the brightness of the rectangle varies smoothly from black to white. The left part of the rectangle appears to progressively bend toward the background when the background is black, while the rectangle appears straight and to fade into an apparent white mist near its right side when the background is white. When the background is black, two horizontal rectangles, mirror-shaded from black to white, so that their black ends face each other with a 2 cm gap between them, appear either to bend toward the background or to be straight and to fade into a sort of dark ‘smoke’. When the background is white with the left rectangle varying in brightness from black to white and the right one from white to black, the rectangles look straight with a sort of white glare appearing to come out from the gap. The black ‘smoke’ and the white glare look more compelling when there are four rectangles forming a cross with a central square gap. It can be argued that this and the neon spreading effect are unrelated. Instead, psychophysical experiments suggest that the glare and smoke effects depend on a relation between the grey scale gradient and the background brightness.

MADYMO Simulations of Occupant and Vehicle Kinematics in Offset and Oblique Barrier Tests

2005 ◽  
Author(s):  
Rex T. Shea ◽  
Jiri Kral
Keyword(s):  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Oblique Impact ◽  
Test Method ◽  
Vehicle Interior ◽  
Center Of Rotation ◽  
Frontal Impacts ◽  
Coordinate Origin ◽  
The Right

Oblique and offset impacts occur more frequently than full frontal impacts and the resulting occupant and vehicle kinematics are more complicated. Simulations of these test modes are more involved with added vehicle degrees of freedom. Additional occupant interactions with the vehicle interior need to be considered so that the occupant kinematics can be correlated more accurately. In order to capture the vehicle motion in an offset or oblique impact, a prescribed motion approach is preferred where the vehicle is given a three-dimensional motion with six degrees of freedom. With a planar motion assumption, the dominant angular motion about the vertical direction can be derived from linear accelerations measured at two locations where the vehicle deformation is a minimum. In a previous study the angular kinematics was given to a coordinate origin located on the vehicle centerline and longitudinally near the rear rocker. The instantaneous center of rotation was assumed to be fixed at this point during the event. This is referred to as Method I in this paper. A new approach, referred to as Method II, applied translational displacement to three bodies, which carried the passenger compartment through stiff spring elements. The displacements were integrated from measured accelerations, eliminating the uncertainty of a shifting center of rotation. Both methods assumed the vehicle frame between the front and rear rockers as a rigid body. The IP and steering column intrusions and floor deformations were neglected. The results from both methods were correlated to a pair of 40 kph 30 degree angle impact tests and an IIHS ODB test. Method II showed a slightly better timing correlation for the angle tests and the IIHS ODB test. However, both methods didn’t predict the lateral head contact for the driver in the left angle test and the passenger in the right angle test. More interior details have to be included in the model to capture the lateral motion of the occupants. The prescribed motion method is a more general approach than the commonly used inverse kinematics method, and can be applied to full frontal impact as well. The versatility of the method provides a basis for a modular approach in occupant simulations.

scholarly journals Modeling the Device Behavior of Biological and Synthetic Nanopores with Reduced Models

Entropy ◽  
2020 ◽  
Vol 22 (11) ◽  
pp. 1259
Author(s):  
Dezső Boda ◽  
Mónika Valiskó ◽  
Dirk Gillespie
Keyword(s):  
Ion Channels ◽  
Degrees Of Freedom ◽  
Ionic Currents ◽  
Response Functions ◽  
Reduced Models ◽  
Rules Of Thumb ◽  
Transport Of Ions ◽  
Current Rectification ◽  
The Right ◽  
Axial Concentration

Biological ion channels and synthetic nanopores are responsible for passive transport of ions through a membrane between two compartments. Modeling these ionic currents is especially amenable to reduced models because the device functions of these pores, the relation of input parameters (e.g., applied voltage, bath concentrations) and output parameters (e.g., current, rectification, selectivity), are well defined. Reduced models focus on the physics that produces the device functions (i.e., the physics of how inputs become outputs) rather than the atomic/molecular-scale physics inside the pore. Here, we propose four rules of thumb for constructing good reduced models of ion channels and nanopores. They are about (1) the importance of the axial concentration profiles, (2) the importance of the pore charges, (3) choosing the right explicit degrees of freedom, and (4) creating the proper response functions. We provide examples for how each rule of thumb helps in creating a reduced model of device behavior.

scholarly journals 3+1DMassless Weyl Spinors from Bosonic Scalar-Tensor Duality

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Andrea Amoretti ◽  
Alessandro Braggio ◽  
Giacomo Caruso ◽  
Nicola Maggiore ◽  
Nicodemo Magnoli
Keyword(s):  
Dirac Equation ◽  
Charge Density ◽  
Dimensional Reduction ◽  
Degrees Of Freedom ◽  
Planar Boundary ◽  
Weyl Spinor ◽  
Bf Theory ◽  
Free Theory ◽  
Tomographic Representation

We consider the fermionization of a bosonic-free theory characterized by the3+1Dscalar-tensor duality. This duality can be interpreted as the dimensional reduction, via a planar boundary, of the4+1Dtopological BF theory. In this model, adopting the Sommerfield tomographic representation of quantized bosonic fields, we explicitly build a fermionic operator and its associated Klein factor such that it satisfies the correct anticommutation relations. Interestingly, we demonstrate that this operator satisfies the massless Dirac equation and that it can be identified with a3+1DWeyl spinor. Finally, as an explicit example, we write the integrated charge density in terms of the tomographic transformed bosonic degrees of freedom.

Corporate accelerators: fostering innovation while bringing together startups and large firms

2017 ◽  
Vol 38 (6) ◽  
pp. 47-53 ◽  
Author(s):  
Martin Kupp ◽  
Moyra Marval ◽  
Peter Borchers
Keyword(s):  
Success Factors ◽  
Information And Communications Technology ◽  
Large Firms ◽  
Content Type ◽  
Technology Industry ◽  
External Sources ◽  
Potential Success ◽  
And Performance ◽  
External Sources Of Knowledge ◽  
The Right

Purpose This paper aims to examine the experience of hub:raum, the accelerator program of Deutsche Telekom, to deduce potential success factors. In today’s fast-paced world, large companies strive to keep up with the disruptive changes in their markets brought by innovative startups. In face of these challenges, the paradigm of open innovation encourages firms to use internal ideas and external sources of knowledge to advance their innovation output (Chesbrough, 2003). Yet, in practice, this is much easier said than done, particularly when large firms engage in partnerships with startups. Design/methodology/approach This paper is based on interviews and academic collaboration with hub:raum. Findings From the five years of experience since the foundation of hub:raum, one of the first German corporate accelerators, the authors have seen five key success factors: transparent and aligned goals, an independent team of startup advocates, a large and committed external network, top-management backing, long-term objectives and performance indicators. Research limitations/implications This paper is based on the case study of hub:raum. There are several limitations to this approach. Hub:raum has a clear industry focus in the information and communications technology industry and also acting international has a strong German and European focus. Practical implications Based on the identified five success factors, executives working with or designing accelerator programs can significantly increase the chances of success of these kind of programs. Constantly working on the right alignment of these factors with the overall objective of the incubator program is the key task of the management. Social implications Designing and running corporate accelerator programs more successfully will also help to enable more startups to join forces with corporates, creating more jobs and developing successful product innovation. Originality/value The paper is based on working for five years closely with the hub:raum management, a series of interviews and longitudinal study of this specific accelerator program.

scholarly journals FROM BRICKS TO QUASINORMAL MODES: A NEW PERSPECTIVE ON BLACK HOLE ENTROPY

2013 ◽  
Vol 22 (12) ◽  
pp. 1342027 ◽  
Author(s):  
MICHELE ARZANO ◽  
STEFANO BIANCO ◽  
OLAF DREYER
Keyword(s):  
Black Hole ◽  
Short Distance ◽  
Degrees Of Freedom ◽  
Quasinormal Modes ◽  
Black Hole Entropy ◽  
Quantum Field ◽  
Extended Region ◽  
New Perspective ◽  
The Right ◽  
Dynamical Degrees

Calculations of black hole entropy based on the counting of modes of a quantum field propagating in a Schwarzschild background need to be regularized in the vicinity of the horizon. To obtain the Bekenstein–Hawking result, the short distance cut-off needs to be fixed by hand. In this note, we give an argument for obtaining this cut-off in a natural fashion. We do this by modeling the black hole by its set of quasinormal modes (QNMs). The horizon then becomes a extended region: the quantum ergosphere. The interaction of the quantum ergosphere and the quantum field provides a natural regularization mechanism. The width of the quantum ergosphere provides the right cut-off for the entropy calculation. We arrive at a dual picture of black hole entropy. The entropy of the black hole is given both by the entropy of the quantum field in the bulk and the dynamical degrees of freedom on the horizon.

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