scholarly journals The Lanczos Equation on Light-Like Hypersurfaces in a Cosmologically Viable Class of Kinetic Gravity Braiding Theories

Symmetry ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 616
Author(s):  
Bence Racskó ◽  
László Á. Gergely
Keyword(s):  
Wave Propagation ◽  
The Other ◽  
Kinetic Term ◽  
Density Current ◽  
Junction Condition ◽  
Junction Conditions ◽  
Isotropic Pressure ◽  
Field Dependent ◽  
Gauge Fixing ◽  
Linear Kinetic

We discuss junction conditions across null hypersurfaces in a class of scalar–tensor gravity theories (i) with second-order dynamics, (ii) obeying the recent constraints imposed by gravitational wave propagation, and (iii) allowing for a cosmologically viable evolution. These requirements select kinetic gravity braiding models with linear kinetic term dependence and scalar field-dependent coupling to curvature. We explore a pseudo-orthonormal tetrad and its allowed gauge fixing with one null vector standing as the normal and the other being transversal to the hypersurface. We derive a generalization of the Lanczos equation in a 2 + 1 decomposed form, relating the energy density, current, and isotropic pressure of a distributional source to the jumps in the transverse curvature and transverse derivative of the scalar. Additionally, we discuss a scalar junction condition and its implications for the distributional source.

scholarly journals Finite BRST–anti-BRST transformations in generalized Hamiltonian formalism

2014 ◽  
Vol 29 (27) ◽  
pp. 1450159 ◽  
Author(s):  
Pavel Yu. Moshin ◽  
Alexander A. Reshetnyak
Keyword(s):  
Dynamical Systems ◽  
Path Integral ◽  
Hamiltonian Path ◽  
Hamiltonian Formalism ◽  
Lagrangian Formalism ◽  
Yang Mills ◽  
Gauge Dependence ◽  
Field Dependent ◽  
Gauge Fixing ◽  
Constrained Dynamical Systems

We introduce the notion of finite BRST–anti-BRST transformations for constrained dynamical systems in the generalized Hamiltonian formalism, both global and field-dependent, with a doublet λa, a = 1, 2, of anticommuting Grassmann parameters and find explicit Jacobians corresponding to these changes of variables in the path integral. It turns out that the finite transformations are quadratic in their parameters. Exactly as in the case of finite field-dependent BRST–anti-BRST transformations for the Yang–Mills vacuum functional in the Lagrangian formalism examined in our previous paper [arXiv:1405.0790 [hep-th]], special field-dependent BRST–anti-BRST transformations with functionally-dependent parameters λa= ∫ dt(saΛ), generated by a finite even-valued function Λ(t) and by the anticommuting generators saof BRST–anti-BRST transformations, amount to a precise change of the gauge-fixing function for arbitrary constrained dynamical systems. This proves the independence of the vacuum functional under such transformations. We derive a new form of the Ward identities, depending on the parameters λaand study the problem of gauge dependence. We present the form of transformation parameters which generates a change of the gauge in the Hamiltonian path integral, evaluate it explicitly for connecting two arbitrary Rξ-like gauges in the Yang–Mills theory and establish, after integration over momenta, a coincidence with the Lagrangian path integral [arXiv:1405.0790 [hep-th]], which justifies the unitarity of the S-matrix in the Lagrangian approach.

scholarly journals Effects of Central Tube on Shape of Modal Duct of a Helicoid in a Simple Expansion Chamber

2018 ◽  
Vol 2018 ◽  
pp. 1-6
Author(s):  
Daniel Omondi Onyango ◽  
Robert Kinyua ◽  
Abel Nyakundi Mayaka
Keyword(s):  
Wave Propagation ◽  
Acoustic Wave ◽  
Plane Wave ◽  
Acoustic Pressure ◽  
Three Dimensional ◽  
The Other ◽  
Expansion Chamber ◽  
Central Tube ◽  
Simple Expansion ◽  
Plane Wave Propagation

The shape of the modal duct of an acoustic wave propagating in a muffling system varies with the internal geometry. This shape can be either as a result of plane wave propagation or three-dimensional wave propagation. These shapes depict the distribution of acoustic pressure that may be used in the design or modification of mufflers to create resonance at cut-off frequencies and hence achieve noise attenuation or special effects on the output of the noise. This research compares the shapes of acoustic duct modes of two sets of four pitch configurations of a helicoid in a simple expansion chamber with and without a central tube. Models are generated using Autodesk Inventor modeling software and imported into ANSYS 18.2, where a fluid volume from the complex computer-aided-design (CAD) geometry is extracted for three-dimensional (3D) analysis. Mesh is generated to capture the details of the fluid cavity for frequency range between 0 and 2000Hz. After defining acoustic properties, acoustic boundary conditions and loads were defined at inlet and outlet ports before computation. Postprocessed acoustic results of the modal shapes and transmission loss (TL) characteristics of the two configurations were obtained and compared for geometries of the same helical pitch. It was established that whereas plane wave propagation in a simple expansion chamber (SEC) resulted in a clearly defined acoustic pressure pattern across the propagation path, the distribution in the configurations with and without the central tube depicted three-dimensional acoustic wave propagation characteristics, with patterns scattering or consolidating to regions of either very low or very high acoustic pressure differentials. A difference of about 80 decibels between the highest and lowest acoustic pressure levels was observed for the modal duct of the geometry with four turns and with a central tube. On the other hand, the shape of the TL curve shifts from a sinusoidal-shaped profile with well-defined peaks and valleys in definite multiples of π for the simple expansion chamber, while that of the other two configurations depended on the variation in wavelength that affects the location of occurrence of cut-on or cut-off frequency. The geometry with four turns and a central tube had a maximum value of TL of about 90 decibels at approximately 1900Hz.

Mobile Integrated Profiler System (MIPS) Observations of Low-Level Convergent Boundaries during IHOP

2006 ◽  
Vol 134 (1) ◽  
pp. 92-112 ◽  
Author(s):  
Haldun Karan ◽  
Kevin Knupp
Keyword(s):  
Boundary Layer ◽  
Cold Front ◽  
The Other ◽  
Density Current ◽  
Wind Profiler ◽  
Density Currents ◽  
General Increase ◽  
Convective Boundary ◽  
Convective Initiation ◽  
Slow Moving

Abstract Characteristics of convergent boundary zones (CBZs) sampled by the Mobile Integrated Profiling System (MIPS) during the 2002 International H2O Project (IHOP_2002) are presented. The MIPS sensors (915-MHz wind profiler, 12-channel microwave profiling radiometer, ceilometer, and surface instrumentation) provide very fine temporal kinematic and thermodynamic profiles of the atmospheric boundary layer and CBZ properties, including enhanced 915-MHz backscatter within the CBZ updraft (equivalent to the radar fine line), a general increase in integrated water vapor within the updrafts of the CBZ, an increase in the convective boundary layer (CBL) depth, and changes in ceilometer backscatter that are typically coincident with arrival of cooler, moister air (the case for density current CBZ). Three contrasting CBZs are analyzed. Convective initiation was associated with a slow-moving dryline as it passed over the MIPS on 19 June. Updrafts up to 6 m s−1 were measured, and the CBL attained its greatest depth within the CBZ. The CBZ in the other two cases were quite similar to density currents. The retrograding dryline of 18 June produced an enhancement in preexisting convection within 30 km of the MIPS. On 24 May, a shallow cold front, about 800 m deep, was sampled.

Finite-amplitude deep-water waves on currents

1979 ◽  
Vol 292 (1392) ◽  
pp. 371-390 ◽  
Keyword(s):  
Wave Propagation ◽  
Deep Water ◽  
Water Waves ◽  
Large Scale ◽  
Finite Amplitude ◽  
The Other ◽  
Wave Trains ◽  
Deep Water Waves

Accurate integral properties of plane periodic deep-water waves of amplitudes up to the steepest are tabulated by Longuet-Higgins (1975). These are used to define an averaged Lagrangian which, following Whitham, is used to describe the properties of slowly varying wave trains. Two examples of waves on large-scale currents are examined in detail. One flow is that of a shearing current, V ( x ) j , which causes waves to be refracted. The other flow, U ( x ) i , varies in the direction of wave propagation and causes waves to either steepen or become more gentle. Some surprising features are found.

A Comparative Study of Artificial Boundary Conditions in ABAQUS

2013 ◽  
Vol 671-674 ◽  
pp. 1386-1389
Author(s):  
Yan Wei Wang ◽  
Shan You Li ◽  
Qiang Ma ◽  
Wei Li
Keyword(s):  
Wave Propagation ◽  
Boundary Conditions ◽  
Element Model ◽  
The Other ◽  
Two Dimensional ◽  
Artificial Boundary ◽  
Artificial Boundary Conditions ◽  
Dimensional Finite Element ◽  
Viscous Boundary ◽  
Better Than

Viscous boundary, viscous spring boundary, infinite boundary have been widely used during the last decades to solve the wave propagation in the infinite ground. In this paper we evaluate the performance of the three boundary conditions focusing on their solution precision. The comparison is performed on a two dimensional finite element model built by ABAQUS. The results show that viscous spring boundary outperforms the other boundary conditions, and viscous boundary is better than infinite element.

scholarly journals EXPANSIONFREE FLUID EVOLUTION AND SKRIPKIN MODEL IN f(R) THEORY

2011 ◽  
Vol 20 (11) ◽  
pp. 2239-2252 ◽  
Author(s):  
M. SHARIF ◽  
H. RIZWANA KAUSAR
Keyword(s):  
General Relativity ◽  
The Self ◽  
Spherically Symmetric ◽  
Junction Conditions ◽  
Dynamical Equations ◽  
Constant Energy ◽  
Isotropic Pressure ◽  
Symmetric Star ◽  
Constant Energy Density ◽  
General Influence

We consider the modified f(R) theory of gravity whose higher-order curvature terms are interpreted as a gravitational fluid or dark source. The gravitational collapse of a spherically symmetric star, made up of locally anisotropic viscous fluid, is studied under the general influence of the curvature fluid. Dynamical equations and junction conditions are modified in the context of f(R) dark energy and by taking into account the expansionfree evolution of the self-gravitating fluid. As a particular example, the Skripkin model is investigated which corresponds to isotropic pressure with constant energy density. The results are compared with corresponding results in General Relativity.

Topological constraints on solar loop plasma instabilities and Alfvén waves

Open Physics ◽  
2009 ◽  
Vol 7 (1) ◽  
Author(s):  
Luiz Garcia de Andrade
Keyword(s):  
Differential Geometry ◽  
Wave Propagation ◽  
Imaginary Axis ◽  
The Other ◽  
Alfven Wave ◽  
Normal Vector ◽  
Frenet Frame ◽  
Topological Constraints ◽  
Classical Differential Geometry ◽  
Solar Loops

AbstractInhomogeneous plasmas-solar instabilities-are investigated by using the techniques of classical differential geometry for curves, where the Frenet torsion and curvature describe completely the motion of a curve. In our case, the Frenet frame changes in time and also depends upon the other coordinates, taking into account the inhomogeneity of the plasma. The exponential perturbation method, so commonly used to describe cosmological perturbations, is applied to the magnetohydrodynamic (MHD) plasma equations to find modes describing Alfvén wave propagation in the medium of planar loops. Stability is investigated in the imaginary axis of the spectra of complex frequencies ω, i.e. $$ \Im $$ m (ω) ≠ 0. A pratical guide for experimental solar physicists is given by computing the twist of force-free solar loops, which generalizes the Parker formula relating the twist to the Frenet torsion. In our expression the twist of the solar loops also depends on the abnormality of the normal vector of the frame.

scholarly journals POISSON BRACKET ALGEBRA FOR CHIRAL GROUP ELEMENTS IN THE WZNW MODEL

1992 ◽  
Vol 07 (24) ◽  
pp. 6159-6174 ◽  
Author(s):  
G. BIMONTE ◽  
P. SALOMONSON ◽  
A. SIMONI ◽  
A. STERN
Keyword(s):  
Poisson Bracket ◽  
Monodromy Matrix ◽  
The Other ◽  
Poisson Brackets ◽  
Arbitrary Boundary ◽  
Gauge Invariant ◽  
Wznw Model ◽  
Gauge Fixing ◽  
Left And Right ◽  
Bracket Algebra

We examine the Wess-Zumino-Novikov-Witten (WZNW) model on a circle and compute the Poisson bracket algebra for left- and right-moving chiral group elements. Our computations apply for arbitrary groups and arbitrary boundary conditions, the latter being characterized by the monodromy matrix. Unlike in previous treatments, the Poisson brackets do not require specifying a particular parametrization of the group valued fields in terms of angles spanning the group. We do however find it necessary to make a gauge choice, as the chiral group elements are not gauge invariant observables. (On the other hand, the quadratic form of the Poisson brackets may be defined independently of a gauge fixing.) Gauge invariant observables can be formed from the monodromy matrix and these observbles are seen to commute in the quantum theory.

scholarly journals A Novel Method for Prediction of Attenuation of Millimeter Waves by Fog and Smoke

2019 ◽  
Vol 8 (3) ◽  
pp. 2080-2085
Keyword(s):  
Wave Propagation ◽  
Water Vapor ◽  
Radio Wave ◽  
Millimeter Wave ◽  
Millimeter Waves ◽  
The Other ◽  
Radio Waves ◽  
Weather Phenomenon ◽  
Novel Method ◽  
And Diffusion

Terrestrial radio wave link faces various challenges like attenuation caused by gases, water vapor and other weather phenomenon like rain, storms, snow, fog, cloud etc. These challenges are responsible for absorption and diffusion of energy. Another kind of obstacles observed by the radio waves on terrestrial path is vegetation, lamppost, grills and other urban constructions. Different phenomenon is studied under these conditions like reflection, diffraction, refraction, scattering, depolarization etc. In case of millimeter waves various propagation studies has been performed under different scenarios. More propagation studies are needed to be done especially for fog. In this paper radio wave propagation studies are performed for fog using proposed fog model and results are compared with the other model proposed in the Literature. Another propagation study is performed for smoke which is unique of its kind. This study indicates that even smoke can causes attenuation for millimeter wave frequencies.

scholarly journals KARAKTERISTIK BERPIKIR KREATIF SISWA KELAS VII SMP N 1 KRAGAN DALAM MEMECAHKAN DAN MENGAJUKAN MASALAH MATEMATIKA MATERI PERBANDINGAN DITINJAU DARI GAYA KOGNITIF

2014 ◽  
Vol 4 (2) ◽  
Author(s):  
Dian Fitri Argarini ◽  
Budiyono Budiyono ◽  
Imam Sujadi
Keyword(s):  
Cognitive Style ◽  
Creative Thinking ◽  
Sampling Technique ◽  
The Other ◽  
Incubation Stage ◽  
Embedded Figures Test ◽  
Field Independent ◽  
Field Dependent ◽  
Preparation Stage ◽  
Thinking Process

<p><strong>Abstract:</strong> The research objectives were to determine and to describe creative thinking characteristic of 7<sup>th</sup> grade students of SMP N 1 Kragan in solving and proposing problem at comparative case seen from the cognitive style. This research belonged to descriptive research by qualitative-explorative approach. The sample was taken by purposive sampling technique. The subjects being used in this research were 4, those were 2 students with field dependent cognitive style and 2 students with field independent cognitive style. The subject grouping based on cognitive style was taken by group embedded figures test. There were two instruments that were used to collect the data of this research. The first instrument was solving and proposing problem test instrument. The second was interview guidance. They were validated by using the time triangulation test and the reference fulfillment. The data were analyzed using a Miles and Huberman’s concept, that was data reduction, presentation, and conclusion.. The results of this research show as follows, (1) Creative thinking characteristics of students who had field dependent cognitive style in solving and proposing problem were as follows. The fluency aspect was shown by the students through 4 stages of creative thinking process, both in solving and proposing the problem. The four stages were preparation stage, incubation stage, illumination stage, and verification stage. The flexibility aspect in solving problems appeared when the students gave the other alternative answer, whereas this aspect was not fulfilled in proposing the problems.  The originality aspect was not fulfilled in solving and proposing problems. (2) Creative thinking characteristics of students who had field independent cognitive style in solving and proposing problem were as follows. The fluency aspect was shown by the students through 4 stages of creative thinking process, both in solving and proposing the problem. The four stages were preparation stage, incubation stage, illumination stage, and verification stage. The flexibility aspect in solving problems was shown when the students gave the other alternative answer, while in proposing the problem this aspect was not completed because students were able to make only one question. The originality aspect in solving the problem could be seen when the students gave a new way solution and this  was different from the previous one. Meanwhile in proposing the problems, aspet of originality was not fulfilled.</p><p><strong>Keywords</strong>:   creative thinking characteristics, solving  problems, proposing problems, cognitive style</p>

Sign in / Sign up

Export Citation Format

Share Document