scholarly journals The Λ-BMS4 charge algebra

2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
Geoffrey Compère ◽  
Adrien Fiorucci ◽  
Romain Ruzziconi
Keyword(s):  
Boundary Conditions ◽  
Surface Charge ◽  
Central Extension ◽  
Symplectic Structure ◽  
Lorentz Transformations ◽  
Dirac Bracket ◽  
Surface Charges ◽  
Null Infinity ◽  
Boundary Measure ◽  
Flat Spacetimes

Abstract The surface charge algebra of generic asymptotically locally (A)dS4 spacetimes without matter is derived without assuming any boundary conditions. Surface charges associated with Weyl rescalings are vanishing while the boundary diffeomorphism charge algebra is non-trivially represented without central extension. The Λ-BMS4 charge algebra is obtained after specifying a boundary foliation and a boundary measure. The existence of the flat limit requires the addition of corner terms in the action and symplectic structure that are defined from the boundary foliation and measure. The flat limit then reproduces the BMS4 charge algebra of supertranslations and super-Lorentz transformations acting on asymptotically locally flat spacetimes. The BMS4 surface charges represent the BMS4 algebra without central extension at the corners of null infinity under the standard Dirac bracket, which implies that the BMS4 flux algebra admits no non-trivial central extension.

scholarly journals A Note on the Newman-Unti Group and the BMS Charge Algebra in Terms of Newman-Penrose Coefficients

2012 ◽  
Vol 2012 ◽  
pp. 1-16 ◽  
Author(s):  
Glenn Barnich ◽  
Pierre-Henry Lambert
Keyword(s):  
Riemann Sphere ◽  
Symmetry Algebra ◽  
Conformal Killing ◽  
Surface Charges ◽  
Null Infinity ◽  
Asymptotically Flat ◽  
Four Dimensions ◽  
Abelian Algebra ◽  
Conformal Killing Vectors ◽  
Flat Spacetimes

The symmetry algebra of asymptotically flat spacetimes at null infinity in four dimensions in the sense of Newman and Unti is revisited. As in the Bondi-Metzner-Sachs gauge, it is shown to be isomorphic to the direct sum of the abelian algebra of infinitesimal conformal rescalings with𝔟𝔪𝔰4. The latter algebra is the semidirect sum of infinitesimal supertranslations with the conformal Killing vectors of the Riemann sphere. Infinitesimal local conformal transformations can then consistently be included. We work out the local conformal properties of the relevant Newman-Penrose coefficients, construct the surface charges, and derive their algebra.

scholarly journals Actions, topological terms and boundaries in first-order gravity: A review

2016 ◽  
Vol 25 (04) ◽  
pp. 1630011 ◽  
Author(s):  
Alejandro Corichi ◽  
Irais Rubalcava-García ◽  
Tatjana Vukašinac
Keyword(s):  
Boundary Conditions ◽  
Symplectic Structure ◽  
Equations Of Motion ◽  
Hamiltonian Formalism ◽  
Action Principle ◽  
Internal Boundary ◽  
Four Dimensions ◽  
First Order ◽  
Conserved Charges ◽  
Boundary Terms

In this review, we consider first-order gravity in four dimensions. In particular, we focus our attention in formulations where the fundamental variables are a tetrad [Formula: see text] and a [Formula: see text] connection [Formula: see text]. We study the most general action principle compatible with diffeomorphism invariance. This implies, in particular, considering besides the standard Einstein–Hilbert–Palatini term, other terms that either do not change the equations of motion, or are topological in nature. Having a well defined action principle sometimes involves the need for additional boundary terms, whose detailed form may depend on the particular boundary conditions at hand. In this work, we consider spacetimes that include a boundary at infinity, satisfying asymptotically flat boundary conditions and/or an internal boundary satisfying isolated horizons boundary conditions. We focus on the covariant Hamiltonian formalism where the phase space [Formula: see text] is given by solutions to the equations of motion. For each of the possible terms contributing to the action, we consider the well-posedness of the action, its finiteness, the contribution to the symplectic structure, and the Hamiltonian and Noether charges. For the chosen boundary conditions, standard boundary terms warrant a well posed theory. Furthermore, the boundary and topological terms do not contribute to the symplectic structure, nor the Hamiltonian conserved charges. The Noether conserved charges, on the other hand, do depend on such additional terms. The aim of this manuscript is to present a comprehensive and self-contained treatment of the subject, so the style is somewhat pedagogical. Furthermore, along the way, we point out and clarify some issues that have not been clearly understood in the literature.

scholarly journals Water Dynamics in Hydrated Carboxylated Cellulose Nanofibril Membranes

2019 ◽  
Author(s):  
Shun Yu ◽  
Valentina Guccini ◽  
Franz Demmel ◽  
Germán Salazar-Alvarez
Keyword(s):  
Surface Charge ◽  
Network Formation ◽  
Water Movement ◽  
Polymer Electrolyte Membrane ◽  
Cellulose Nanofibrils ◽  
Bulk Water ◽  
Water Dynamics ◽  
Surface Charges ◽  
Tempo Oxidation ◽  
Elastic Neutron

Cellulose nanofibrils (CNF) are a class of materials with good mechanical properties, surface functionality and bio-/environmental friendliness. They have been used in many applications as loading material or function materials, where water-cellulose interaction determines the materials performance. Especially, CNF with carboxylated groups can be used as the separation membrane in polymer electrolyte membrane fuel cell. The water dynamics is closely related to the proton conductivity. The Non-destructive quasi-elastic neutron scattering (QENS) is used to characterized water movement in hydrated membrane made of CNF prepared by TEMPO-oxidation with different surface charges. However, neither surface charge nor the nanoconfinement due to membrane swelling has large impact on water dynamics mechanism. A slow diffusive motion is found with the diffusion coefficient close to bulk water and that in hydrated Nafion membrane regardless the surface charge, while a fast motion is rather localized with a correlation time increasing as temperature increase, which might related to the hydrogen bond network formation between water and CNF.

scholarly journals Local and correlated studies of humidity-mediated ferroelectric thin film surface charge dynamics

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Iaroslav Gaponenko ◽  
Loïc Musy ◽  
Neus Domingo ◽  
Nicolas Stucki ◽  
Albert Verdaguer ◽  
...  
Keyword(s):  
Surface Charge ◽  
Dictionary Learning ◽  
Film Surface ◽  
Ferroelectric Thin Film ◽  
Microscopy Study ◽  
Lateral Spread ◽  
Surface Charges ◽  
Kelvin Probe ◽  
Sensing Applications ◽  
Reaction Diffusion Model

AbstractElectrochemical phenomena in ferroelectrics are of particular interest for catalysis and sensing applications, with recent studies highlighting the combined role of the ferroelectric polarisation, applied surface voltage and overall switching history. Here, we present a systematic Kelvin probe microscopy study of the effect of relative humidity and polarisation switching history on the surface charge dissipation in ferroelectric Pb(Zr0.2Ti0.8)O3 thin films. We analyse the interaction of surface charges with ferroelectric domains through the framework of physically constrained unsupervised machine learning matrix factorisation, Dictionary Learning, and reveal a complex interplay of voltage-mediated physical processes underlying the observed signal decays. Additional insight into the observed behaviours is given by a Fitzhugh–Nagumo reaction–diffusion model, highlighting the lateral spread and charge passivation process contributors within the Dictionary Learning analysis.

scholarly journals Conduction through the Inward Rectifier Potassium Channel, Kir2.1, Is Increased by Negatively Charged Extracellular Residues

2005 ◽  
Vol 125 (5) ◽  
pp. 493-503 ◽  
Author(s):  
Nazzareno D'Avanzo ◽  
Hee Cheol Cho ◽  
Illya Tolokh ◽  
Roman Pekhletski ◽  
Igor Tolokh ◽  
...  
Keyword(s):  
Surface Charge ◽  
Single Channel ◽  
Molecular Model ◽  
Chinese Hamster ◽  
Fluctuation Analysis ◽  
Channel Measurements ◽  
Surface Charges ◽  
Charge Effects ◽  
Current Decay ◽  
Inward Rectifier Potassium Channel

Ion channel conductance can be influenced by electrostatic effects originating from fixed “surface” charges that are remote from the selectivity filter. To explore whether surface charges contribute to the conductance properties of Kir2.1 channels, unitary conductance was measured in cell-attached recordings of Chinese hamster ovary (CHO) cells transfected with Kir2.1 channels over a range of K+ activities (4.6–293.5 mM) using single-channel measurements as well as nonstationary fluctuation analysis for low K+ activities. K+ ion concentrations were shown to equilibrate across the cell membrane in our studies using the voltage-sensitive dye DiBAC4(5). The dependence of γ on the K+ activity (aK) was fit well by a modified Langmuir binding isotherm, with a nonzero intercept as aK approaches 0 mM, suggesting electrostatic surface charge effects. Following the addition of 100 mM N-methyl-d-glucamine (NMG+), a nonpermeant, nonblocking cation or following pretreatment with 50 mM trimethyloxonium (TMO), a carboxylic acid esterifying agent, the γ–aK relationship did not show nonzero intercepts, suggesting the presence of surface charges formed by glutamate or aspartate residues. Consistent with surface charges in Kir2.1 channels, the rates of current decay induced by Ba2+ block were slowed with the addition of NMG or TMO. Using a molecular model of Kir2.1 channels, three candidate negatively charged residues were identified near the extracellular mouth of the pore and mutated to cysteine (E125C, D152C, and E153C). E153C channels, but not E125C or D152C channels, showed hyperbolic γ–aK relationships going through the origin. Moreover, the addition of MTSES to restore the negative charges in E53C channels reestablished wild-type conductance properties. Our results demonstrate that E153 contributes to the conductance properties of Kir2.1 channels by acting as a surface charge.

Surface charges of anionic and cationic polyelectrolytes and their effects on the nucleation and the growth of CaCO3 crystals

e-Polymers ◽  
2009 ◽  
Vol 9 (1) ◽  
Author(s):  
Amane Jada ◽  
Arnaud Verraes ◽  
Alexandrine Aue ◽  
Céline Ducroquetz
Keyword(s):  
Surface Charge ◽  
Calcium Ions ◽  
Polymer Concentration ◽  
Free Calcium ◽  
Precipitation Reaction ◽  
Surface Charges ◽  
Strong Reduction ◽  
Interaction Efficiency ◽  
Cationic Polyelectrolytes ◽  
Positively Charged

AbstractStreaming Induced Potential (SIP) of polystyrene sulfonate, PSS, and poly(ethylenimine), PEI, in the presence of monovalent (NaCl) and divalent (CaCl2) electrolytes, were measured at ambient temperature. The data indicate that screening of polyelectrolyte surface charge, i.e. the reduction of SIP amplitude, is more efficient by divalent CaCl2, as compared to monovalent NaCl electrolytes. The screening of polyelectrolyte surface charge leads to reduction of the mutual repulsion between the polyelectrolyte segments. In the case of CaCl2 electrolyte, since PSS and PEI are, respectively, negatively and positively charged, sequestration of calcium ions by the polyelectrolyte leads to strong reduction of the free calcium ions concentration in the medium in the presence of the PSS when compared to the PEI. Further, the preparation of CaCO3 particles through a precipitation reaction, at room temperature, by using PSS and PEI polyelectrolytes as crystal modifiers were investigated. The final CaCO3 particles are found to result from the aggregation of nanocrystals, and have various shapes and sizes depending on polymer concentration and structure. It comes out that the properties of CaCO3 particles prepared in the presence of the polymer are function of the interaction efficiency between the polymer-repeating units and the calcium ions. Such interaction is found to affect the free calcium ions concentration in the medium.

The role of clay minerals and the effect of H+ ions on removal of heavy metal (Pb2+) from contaminated soils

2000 ◽  
Vol 37 (2) ◽  
pp. 296-307 ◽  
Author(s):  
Loretta Y Li ◽  
Raymond S Li
Keyword(s):  
Heavy Metals ◽  
Heavy Metal ◽  
Surface Charge ◽  
Clay Minerals ◽  
Contaminated Soils ◽  
Surface Charges ◽  
Buffer Solution ◽  
Soil System ◽  
Variable Charge ◽  
Acid Leach

The importance of the surface charge of clay minerals (fixed or variable) and the effect of H+ ions on the adsorption and removal of Pb2+ ions from contaminated soil are investigated using kaolinite (variable charge) and two illitic (fixed charge) soils with pH 3.9 and 9.2. The adsorption-desorption characteristics of Pb2+ ions were determined using batch equilibrium tests and acid leach tests with various acids used to leach the soils. Under the same adsorption conditions, illitic soil adsorbed much more Pb2+ ions than kaolinite. The difference is largely due to the surface charges on the clay minerals. Removal of Pb2+ ions from variable-charge minerals (e.g., kaolinite) requires much less effort than removal of Pb2+ ions from constant-charge minerals (e.g., illite). The surface charge of a clay mineral has an important effect. By increasing the number of H+ ions available in the soil system with a buffer solution such as NaOAc-HOAc, heavy metals adsorbed on the clay surface are expelled to pore water. The increase in H+ ions in the soil system also assists in dissolving any metal carbonates, thereby increasing the solubility of heavy metals in illitic soil. The more H+ ions available in the pore fluid, the more Pb2+ ions can be released from the system.Key words: clay minerals, sorption, desorption, heavy metal, hydrogen ion, electrokinetic, acid leach.

Effects of surface charge on the electrostatic energy of an ionic crystal

1982 ◽  
Vol 381 (1780) ◽  
pp. 241-247 ◽  
Keyword(s):  
Charge Density ◽  
Surface Charge ◽  
Ionic Crystal ◽  
Surface Charge Density ◽  
Electrostatic Energy ◽  
Excess Charge ◽  
Surface Charges

An earlier paper discussed the influence of the shape of a macroscopic piece of ionic crystal on the electrostatic energy of the whole piece of crystal. Some of the considerations of that paper are extended to include the effects on the bulk term in the energy of distributing excess charge on the surface of the piece of crystal. The bulk term in the electrostatic energy of the piece of crystal plus surface charges depends on the shape of the piece and the surface charge density. The minimum of this bulk term with respect to surface charge density occurs at a well defined surface charge density and is the usual (shape-independent) Madelung crystal energy.

Molecular Dynamics Simulations of Water and Ion Structures Near Charged Surfaces

2007 ◽  
Author(s):  
Dongyan Xu ◽  
Deyu Li ◽  
Yongsheng Leng
Keyword(s):  
Molecular Dynamics ◽  
Surface Charge ◽  
Molecular Dynamics Simulations ◽  
Single Molecule ◽  
Research Field ◽  
Water Molecules ◽  
Wall Region ◽  
Surface Charges ◽  
Ion Distribution ◽  
Dynamics Simulations

Extensive research has been devoted to nanofluidics in the past decade because of its potential applications in single molecule sensing and manipulations. Fundamental studies have attracted significant attention in this research field since the success of nanofluidic devices depends on a thorough understanding of the fluidic, ionic, and molecular behavior in highly confined nano-environments. In this paper, we report on molecular dynamics simulations of the effect of surface charge densities on the ion distribution and the water density profile close to a charged surface. We demonstrate that surface charges not only interact with mobile ions in the electrolyte, but also interact with water molecules due to their polarizability, and hence influence the orientation of water molecules in the near wall region. For the first time, we show that as the surface charge density increases, the water molecules within ∼ 5 Å of the {100} silicon surface will evolve from one layer into two layers. Meanwhile, the orientation of the water molecules is more aligned instead of randomly distributed. This layering effect may have important implications on electroosmotic flow through nanochannels and heat transfer across the solid-liquid interface.

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