A
bstract
In this work, we study the inhomogeneous BMS free fermion theory, and show that it gives a free field realization of the BMS Ising model. We find that besides the BMS symmetry there exists ...an anisotropic scaling symmetry in BMS free fermion theory. As a result, the symmetry of the theory gets enhanced to an infinite dimensional symmetry generated by a new type of BMS-Kac-Moody algebra, different from the one found in the BMS free scalar model. Besides the different coupling of the
u
(1) Kac-Moody current to the BMS algebra, the Kac-Moody level is nonvanishing now such that the corresponding modules are further enlarged to BMS-Kac-Moody staggered modules. We show that there exists an underlying
W
(2, 2, 1) structure in the operator product expansion of the currents, and the BMS-Kac-Moody staggered modules can be viewed as highest-weight modules of this
W
-algebra. Moreover we obtain the BMS Ising model by a fermion-boson duality. This BMS Ising model is not a minimal model with respect to BMS
3
, since the minimal model construction based on BMS Kac determinant always leads to chiral Virasoro minimal models. Instead, the underlying algebra of the BMS Ising model is the
W
(2, 2, 1)-algebra, which can be understood as a quantum conformal BMS
3
algebra.
On Galilean conformal bootstrap Chen, Bin; Hao, Peng-xiang; Liu, Reiko ...
The journal of high energy physics,
06/2021, Volume:
2021, Issue:
6
Journal Article
Peer reviewed
Open access
A
bstract
In this work, we develop conformal bootstrap for Galilean conformal field theory (GCFT). In a GCFT, the Hilbert space could be decomposed into quasiprimary states and its global ...descendants. Different from the usual conformal field theory, the quasiprimary states in a GCFT constitute multiplets, which are block-diagonized under the Galilean boost operator. More importantly the multiplets include the states of negative norms, indicating the theory is not unitary. We compute global blocks of the multiplets, and discuss the expansion of four-point functions in terms of the global blocks of the multiplets. Furthermore we do the harmonic analysis for the Galilean conformal symmetry and obtain an inversion formula. As the first step to apply the Galilean conformal bootstrap, we construct generalized Galilean free theory (GGFT) explicitly. We read the data of GGFT by using Taylor series expansion of four-point function and the inversion formula independently, and find exact agreement. We discuss some novel features in the Galilean conformal bootstrap, due to the non-semisimpleness of the Galilean conformal algebra and the non-unitarity of the GCFTs.
Display omitted
•A procedure to pretreat electrocatalysts to study the ammonia oxidation is provided.•Nads and O/OHads were identified as the major deactivation species that prevent ammonia ...oxidatoin.•The electrocatalytic activity, thermodynamics, and possible deactivation mechanisms for ammonia oxidation were elucidated.•The onset potential for ammonia oxidation is related to the hydrogen binding energy of the catalyst.•Ammonia electro-oxidation involves a complex decoupled electron and proton transfer process.
The ammonia electro-oxidation reaction (AOR) has been studied due to its promising applications in ammonia electrolysis, wastewater remediation, direct ammonia fuel cells, and sensors. However, it is difficult to compare and analyze the reported electrocatalytic activity of AOR reliably, likely due to the variation in catalyst synthesis, electrode composition, electrode morphology, and testing protocol. In this paper, the electro-oxidation of ammonia on different carbon-supported precious metal nanoparticle catalysts was revisited. The effect of experimental conditions, electrochemical test parameters, electrocatalytic activity, thermodynamics, and possible deactivation mechanism of the catalysts were investigated. Pt/C catalyst possesses the highest electrocatalytic activity, while Ir/C and Rh/C show lower overpotential. The onset potential of the AOR is related to the hydrogen binding energy of the catalyst. Nads is one major cause of deactivation accompanied with the formation of surface O/OHads at high potentials. The coulombic efficiency of Nads formation on Pt is about 1% initially and gradually decreases with reaction time. Increase in ammonia concentration leads to increase in current density, while increase in hydroxyl ions concentration can enhance the current density and reduce the overpotential simultaneously. The slopes of AOR onset potential and hydrogen adsorption/desorption potential of Pt/C as a function of pH follow Nernst equation. In contrast, potentials measured at different current densities exhibit non-Nernstian behavior, suggesting a critical role of the local pH change.
Graphene/polyaniline (PANI) nanocomposites were prepared by reducing graphene oxide with hydrazine in the presence of different amounts of polyaniline nanoparticles. In situ cryo-transmission ...electron microscope (TEM) images of a graphene oxide (GO)/PANI solution revealed that the PANI nanoparticles were anchored on the surface of the GO sheets. During the reduction, the as-adsorbed PANI nanoparticles were sandwiched between layers of graphene sheets. These PANI nanoparticles acted as spacers to create gaps between neighboring graphene sheets, resulting in a higher surface area compared to pure graphene. Graphene/PANI nanocomposites exhibited the high specific surface area of 891 m2/g. Utilizing this composite material, a supercapacitor with a specific capacitance of 257 F/g at a current density of 0.1 A/g has been achieved.
A novel Sn4P3/graphite composite anode material with superior capacity and cycling performance (651 mA h g−1 after 100 cycles) is investigated by in situ X‐ray absorption spectroscopy. Extended X‐ray ...absorption fine structure modeling and detailed analysis of local environment changes are correlated to the cell capacity and reveal the mechanism of lithiation/delithiation process. Results show that in the first two lithiation/delithiation cycles crystalline Sn4P3 is fully converted to an amorphous SnPx phase, which in further cycles participates in reversible conversion and alloying reactions. The superior reversibility of this material is attributed to the highly dispersed SnPx in the graphite matrix, which provides enhanced electrical conductivity and prevents aggregation of Sn clusters during the lithiation/delithiation process. The gradual capacity fading in long‐term cycling is attributed to the observed increase in the size and the amount of metallic Sn clusters in the delithiated state, correlated to the reduced recovery of the SnPx phase. This paper reveals the mechanism responsible for the highly reversible tin phosphides and provides insights for improving the capacity and cycle life of conversion and alloying materials.
A novel Sn4P3/graphite composite anode for Li‐ion batteries with high reversible capacity and cycle life is investigated with in situ X‐ray absorption spectroscopy. The mechanism for reversible conversion and alloying reactions due to the amorphous SnPx phase and graphite matrix is proposed based on extended X‐ray absorption fine structure (EXAFS) modeling results.
A
bstract
In this work, we continue our work on two dimensional Galilean conformal field theory (GCFT
2
). Our previous work (2011.11092) focused on the
ξ
≠ 0 sector, here we investigate the more ...subtle
ξ
= 0 sector to complete the discussion. The case
ξ
= 0 is degenerate since there emerge interesting null states in a general
ξ
= 0 boost multiplet. We specify these null states and work out the resulting selection rules. Then, we compute the
ξ
= 0 global GCA blocks and find that they can be written as a linear combination of several building blocks, each of which can be obtained from a
sl
(2
,
ℝ) Casimir equation. These building blocks allow us to give an Euclidean inversion formula as well. As a consistency check, we study 4-point functions of certain vertex operators in the BMS free scalar theory. In this case, the
ξ
= 0 sector is the only allowable sector in the propagating channel. We find that the direct expansion of the 4-point function reproduces the global GCA block and is consistent with the inversion formula.
A
bstract
In this work, we study the tensionless (super)string in the formalism of path-integral quantization. We introduce BMS
bc
and
βγ
ghosts intrinsically by accounting for the Faddeev-Popov ...determinants appeared in fixing the gauges. We then do canonical quantization and obtain the critical dimensions for different tensionless strings. We find that among four kinds of tensionless superstrings, the 𝒩 = 2 homogeneous and inhomogeneous doublet tensionless superstrings have the same critical dimension as the usual superstrings. Taking the BMS
bc
and
βγ
ghosts as new types of BMS free field theories, we find that their enhanced underlying symmetries are generated by BMS-Kac-Moody algebras, with the Kac-Moody subalgebras being built from a three-dimensional non-abelian and non-semi-simple Lie algebra.
In this work, we study two-dimensional Galilean field theories with global translations and anisotropic scaling symmetries. We show that such theories have enhanced local symmetries, generated by the ...infinite dimensional spin-ℓ Galilean algebra with possible central extensions, under the assumption that the dilation operator is diagonalizable and has a discrete and non-negative spectrum. We study the Newton-Cartan geometry with anisotropic scaling, on which the field theories could be defined in a covariant way. With the well-defined Newton-Cartan geometry we establish the state-operator correspondence in anisotropic Galilean conformal field theory and determine the two-point functions of primary operators.
The enhancement of Pt nanoparticle anchoring strength and dispersion on carbon supports is highly desirable in polymer electrolyte membrane fuel cells (PEMFCs) as well as in other catalysis ...processes. Presented here is a comprehensive study of the interaction between catalyst nanoparticles and carbon supports in terms of the electronic structure change and its effects on the electrocatalytic performance of supported catalysts. Graphene was chosen as an ideal model support because the unique 2-D structure allows the direct investigation of the interaction with supported metal nanoparticles at their interface. We developed a facile strategy to covalently graft p-phenyl SO3Hor p-phenyl NH2groups onto the graphene surface. The functional groups were found to not only facilitate the homogeneous distribution of Pt nanoparticles on the surface of graphene supports and reduce the Pt average particle size but also strengthen the interaction of the Pt atoms with the functional groups and, consequently, minimize the migration/coalescence of the Pt nanoparticles in the course of accelerated durability tests. The experimental results from both X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) demonstrate the electron density shift from Pt to graphene supports with the strength of the Pt–graphene interaction following the trend of Pt/p-phenyl NH2-graphene > Pt/p-phenyl SO3H-graphene > Pt/graphene. This study will shed light on strategies to improve not only the durability but also the activity of the metal nanoparticles via the functionalization of the catalyst supports in the catalysis field.
A simple method to fabricate graphene-encapsulated pyrolyzed polyaniline-grafted Si nanoparticles has been developed. Instead of using Si nanoparticles with a native oxide layer, HF-treated Si ...nanoparticles were employed in this work. The uniqueness of this method is that, first, a PANI layer over the Si nanoparticles was formed via the surface-initiated polymerization of aniline on the surface of aniline-functionalized Si nanoparticles; then, the PANI-grafted Si nanoparticles were wrapped by the GO sheets via π–π interaction and electrostatic attraction between the GO and the PANI. Finally, the GO and PANI were pyrolyzed, and this pyrolyzed PANI layer tightly binds the graphene sheets and the Si nanoparticles together in the composite. The composite materials exhibit better cycling stability and Coulombic efficiency as anodes in lithium ion batteries, as compared to pure Si nanoparticles and physically mixed graphene/Si composites. After 300 cycles at a current density of 2 A/g, the composite electrodes can still deliver a specific capacity of about 900 mAh/g, which corresponds to ∼76% capacity retention. The enhanced performance can be attributed to the absence of surface oxides, the better electronic conductivity, faster ion diffusion rate, and the strong interaction between the graphene sheets and the tightly bound carbon-coated Si nanoparticles.
PDF
