Covariant phase space with boundaries Harlow, Daniel; Wu, Jie-qiang
The journal of high energy physics,
10/2020, Volume:
2020, Issue:
10
Journal Article
Peer reviewed
Open access
A
bstract
The covariant phase space method of Iyer, Lee, Wald, and Zoupas gives an elegant way to understand the Hamiltonian dynamics of Lagrangian field theories without breaking covariance. The ...original literature however does not systematically treat total derivatives and boundary terms, which has led to some confusion about how exactly to apply the formalism in the presence of boundaries. In particular the original construction of the canonical Hamiltonian relies on the assumed existence of a certain boundary quantity “
B
”, whose physical interpretation has not been clear. We here give an algorithmic procedure for applying the covariant phase space formalism to field theories with spatial boundaries, from which the term in the Hamiltonian involving
B
emerges naturally. Our procedure also produces an additional boundary term, which was not present in the original literature and which so far has only appeared implicitly in specific examples, and which is already nonvanishing even in general relativity with sufficiently permissive boundary conditions. The only requirement we impose is that at solutions of the equations of motion the action is stationary modulo future/past boundary terms under arbitrary variations obeying the spatial boundary conditions; from this the symplectic structure and the Hamiltonian for any diffeomorphism that preserves the theory are unambiguously constructed. We show in examples that the Hamiltonian so constructed agrees with previous results. We also show that the Poisson bracket on covariant phase space directly coincides with the Peierls bracket, without any need for non-covariant intermediate steps, and we discuss possible implications for the entropy of dynamical black hole horizons.
A low‐cost phased array antenna, consisting of waveguide radiators, dielectric phase shifters and a cooperated feeding network, is proposed and experimentally validated in this paper. The required ...progressive phases are obtained by controlling the loading depths of dielectric laminas, which are axially inserted into the rectangular channels. The phase difference among channels is determined by the lamina length, the loading depth and the dielectric constant. Theoretically arbitrary phases can be achieved with these design freedoms. A validation prototype of a 1 × 4 array antenna operating around 10 GHz with an element spacing of 0.735λ0 demonstrates a continuous beam steering range of ±23°, which is consistent with theoretical predictions.
In recent years, emulsions stabilized by micro‐ or nanoparticles (known as Pickering emulsions) have attracted much attention. Micro‐ or nanoparticles, as the main components of the emulsion, play a ...key role in the preparation and application of Pickering emulsions. The existence of particles at the interface between the oil and aqueous phases affects not only the preparation, but also the properties of Pickering emulsions, affording superior stability, low toxicity, and stimuli‐responsiveness compared to classical emulsions stabilized by surfactants. These advantages of Pickering emulsions make them attractive, especially in biomedicine. In this review, the effects of the characteristics of micro‐ and nanoparticles on the preparation and properties of Pickering emulsions are introduced. In particular, the preparation methods of Pickering emulsions, especially uniform‐sized emulsions, are listed. Uniform Pickering emulsions are convenient for both mechanistic research and applications. Furthermore, some biomedical applications of Pickering emulsions are discussed and the problems hindering their clinical application are identified.
Pickering emulsions, stabilized by particles, have attracted much attention in recent years. Due to the introduction of particles at the interface between oil and aqueous phases, Pickering emulsions possess many distinctive properties such as high stability and low toxicity, when compared with classical emulsions stabilized by surfactants. These properties also affect their applications, especially in biomedical fields, such as oral or topical delivery systems.
Pure organic room temperature phosphorescence (RTP) is highly preferable because of its long lifetime and potential applications. However, these kinds of materials are still very scarce due to the ...weak spin–orbit coupling between singlet and triplet states and easily nonradiative decay of the excited states. Achieving room temperature phosphorescence under visible light excitation is particularly challenging in aqueous solution. Herein, a micelle‐assisted assembling strategy has been developed to realize pure organic RTP in water by using donor–acceptor molecules. A visible‐light responsive long‐lived RTP in water with a lifetime more than 3 ms is obtained by the prepared nanocrystals. However, the same molecules show no RTP as rigid bulk crystals. Spectroscopic studies, single‐crystal structure analysis, X‐ray diffraction patterns, and density functional theory calculations reveal that the intermolecular interactions, heavy atom effect, and the molecular packing way play critical role to the long‐lived RTP character for the assembled nanocrystals in water and thermally activated delayed fluorescence for crystals in solid.
A micelle‐assisted assembly strategy to realize long‐lived pure organic room temperature phosphorescence under visible light excitation in water is reported. The molecular packing plays a critical role to the room temperature phosphorescence character in the assembled nanocrystals and delayed fluorescence in the crystals.
A
bstract
In this paper we use the covariant Peierls bracket to compute the algebra of a sizable number of diffeomorphism-invariant observables in classical Jackiw-Teitelboim gravity coupled to ...fairly arbitrary matter. We then show that many recent results, including the construction of traversable wormholes, the existence of a family of SL(2
,
ℝ) algebras acting on the matter fields, and the calculation of the scrambling time, can be recast as simple consequences of this algebra. We also use it to clarify the question of when the creation of an excitation deep in the bulk increases or decreases the boundary energy, which is of crucial importance for the “typical state” versions of the firewall paradox. Unlike the “Schwarzian” or “boundary particle” formalism, our techniques involve no unphysical degrees of freedom and naturally generalize to higher dimensions. We do a few higher-dimensional calculations to illustrate this, which indicate that the results we obtain in JT gravity are fairly robust.
•Our analyses are based on 96 publicly listed high-tech Chinese enterprises over the 2001–2012 period.•OFDI acts as a vehicle for the organization learning for EMEs.•EMEs’ OFDI positively affects ...innovation performance.•The innovation-enhancing effect of OFDI is higher when it is undertaken in developed host countries.
Although prior research conceptualizes how knowledge-seeking motivates the internationalization of emerging-market enterprises (EMEs), whether outward foreign direct investment (OFDI) indeed leads to enhanced innovation performance has received limited attention. We address this subject by conceptualizing how Chinese EMEs’ OFDI enhances their subsidiaries’ organizational learning and innovation performance and whether geographic location choices influence this relationship. Our panel data analysis of Chinese EMEs shows that OFDI has a positive effect on innovation performance of Chinese EMEs’ subsidiaries and that this effect is stronger when the OFDI is directed towards developed rather than emerging countries. These findings advance the notion that EMEs can use OFDI as a strategy to globalize R&D and enhance their innovation performance and demonstrate that certain established assumptions regarding organizational learning are not valid for EMEs.
A catalyst‐free approach for the generation of sulfonyl radicals from aryldiazonium tetrafluoroborates in the presence of DABCO⋅(SO2)2 is realized. The combination of aryldiazonium ...tetrafluoroborates, DABCO⋅(SO2)2, and aryl propiolates affords 3‐sulfonated coumarins in good to excellent yields. This tandem reaction process involves radical addition, spirocyclization, and 1,2‐migration of esters. Additionally, the in situ diazotization of a number of anilines allows the directional synthesis of desired 3‐sulfonated coumarins in a one‐pot, two‐step process.
A dab of radicals: A catalyst‐free approach enables the generation of sulfonyl radicals from aryldiazonium tetrafluoroborates in the presence of DABCO⋅(SO2)2. The reaction affords 3‐sulfonated coumarins in good to excellent yields. Additionally, the in situ diazotization of a number of anilines allows the directional synthesis of 3‐sulfonated coumarins in a one‐pot, two‐step process. DABCO=1,4‐diazabicyclo2.2.2octane.
Nitriles are widely existed in many bioactive compounds, and they can be easily transformed into other functional groups. Therefore, the synthesis of nitriles under cyanide-free conditions is of ...significant importance. Recent advances for the synthesis of nitriles through photoinduced C—C bond cleavage of cycloketone oximes classified by the type of C—X bond forming are summarized. Various compounds possessing nitriles can be efficiently accessed via this method.
A visible-light-mediated radical Smiles rearrangement has been achieved using neutral eosin Y as a direct hydrogen atom transfer (HAT) photocatalyst. Novel N-heterocycles as single diastereomers ...featuring an isothiazolidin-3-one 1,1-dioxide moiety are directly accessed by this method. A wide range of functional groups can be incorporated in the products by employing diverse aldehydes and N-(hetero)arylsulfonyl propiolamides. The transformation proceeds through a cascade of visible-light-induced HAT, 1,4-addition, Smiles rearrangement, 5-endo-trig cyclization, and a reverse HAT process. Preliminary biological studies of the highly functionalized heterocyclic compounds suggest potential anticancer activity with some of the synthesized compounds.
As heavy metal ions severely harm human health, it is important to develop simple, sensitive and accurate methods for their detection in environment and food. Electrochemical detection featured with ...short analytical time, low power cost, high sensitivity and easy adaptability for in-situ measurement is one of the most developed methods. This review introduces briefly the recent achievements in electrochemical sensing of heavy metal ions with inorganic, organic and bio-materials modified electrodes. In particular, the unique properties of inorganic nanomaterials, organic small molecules or their polymers, enzymes and nucleic acids for detection of heavy metal ions are highlighted. By employing some representative examples, the design and sensing mechanisms of these electrodes are discussed.
•Recent achievements in electrochemical sensing of heavy metal ions are introduced.•Inorganic, organic and bio-materials modified electrodes are highlighted.•The design of sensors for heavy metal ions and their sensing mechanisms are discussed.•Sensing mechanisms for indirect detection of heavy metal ions are summarized.
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