Ex situ X-­Ray absorption study of Li-­rich layered cathode material Li[Li0.2Mn0.56Ni0.16Co0.08]O2

The Li-rich layered transition metal oxides (LLOs) Li2MnO3-LiMO2 (M=Mn, Co, Ni, etc.) have drawn considerable attention as cathode materials for rechargeable lithium batteries. They generate large reversible capacities but the fundamental reaction mechanism and structural perturbations during cycling remain controversial. In the present thesis, ex situ X-ray absorption spectroscopy (XAS) measurements were performed on Li[Li0.2Mn0.56Ni0.16Co0.08]O2 at different stage of charge during electrochemical oxidation/reduction. K-edge spectra of Co, Mn and Ni were recorded through a voltage range of 3.7-4.8V vs. Li/Li+, which consist of X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Oxidation states during initial charge were discussed based on values from literature as well as XANES analysis. Information about bond distance, coordination number as well as corresponding Debye-Waller factor were extracted from Gnxas analysis of raw data in the EXAFS region. The possibility of oxygen participation in the initial charge was discussed. Co and Ni prove to take part in the oxidation/reduction process while Mn remain in the tetravalent state. The cathode material appears to retain good structural short-range order during charge-discharge. A resemblance of the pristine sample and sample 4 was discovered which was firstly reported for similar compounds

Creating a Traversable Wormhole

We argue that one can nucleate a traversable wormhole via a nonperturbative process in quantum gravity. To support this, we construct spacetimes in which there are instantons giving a finite probability for a test cosmic string to break and produce two particles on its ends. One should be able to replace the particles with small black holes with only small changes to the spacetime away from the horizons. The black holes are then created with their horizons identified, so this is an example of nucleating a wormhole. Unlike previous examples where the created black holes accelerate apart, in our case they remain essentially at rest. This is important since wormholes become harder and harder to make traversable as their mouths become widely separated, and since traversability can be destroyed by Unruh radiation. In our case, back-reaction from quantum fields can make the wormhole traversable.Comment: 24 pages, 6 Figs, v2: comment added and a few typos correcte

Pole-skipping in holographic theories with bosonic fields

We study the phenomenon of pole-skipping in holographic CFTs dual to diffeomorphism invariant theories containing an arbitrary number of bosonic fields in the large $N$ limit. Defining a weight to organize the bulk equations of motion and field components, a set of general pole-skipping conditions are derived. In particular, the frequencies simply follow from general covariance and weight matching. Relating the highest-weight pole-skipping frequency to an exponential growth rate, i.e., the Lyapunov exponent, we show that the chaos bound is generally violated in the presence of finitely many higher spin fields, consistent with existing evidence. In the absence of such pathological fields, we show that the energy density Green's function has its highest-weight pole-skipping happening at a location related to the OTOC for arbitrary higher-derivative gravity, with a Lyapunov exponent saturating the chaos bound and a butterfly velocity matching that extracted from a shockwave calculation. We also suggest a physical explanation for this matching by obtaining the shockwave metric from a regularized limit of the metric perturbation at the skipped pole.Comment: 5 page

High-energy collision of black holes in higher dimensions

We compute the gravitational wave energy E_(rad) radiated in head-on collisions of equal-mass, nonspinning black holes in up to (D=8)-dimensional asymptotically flat spacetimes for boost velocities v up to about 90% of the speed of light. We identify two main regimes: weak radiation at velocities up to about 40% of the speed of light, and exponential growth of E_(rad) with v at larger velocities. Extrapolation to the speed of light predicts a limit of 12.9% (10.1, 7.7, 5.5, 4.5)% of the total mass that is lost in gravitational waves in D=4 (5, 6, 7, 8) spacetime dimensions. In agreement with perturbative calculations, we observe that the radiation is minimal for small but finite velocities, rather than for collisions starting from rest. Our computations support the identification of regimes with super-Planckian curvature outside the black-hole horizons reported by Okawa, Nakao, and Shibata [Phys. Rev. D 83, 121501(R) (2011)]

Pole skipping in holographic theories with gauge and fermionic fields

Using covariant expansions, recent work showed that pole skipping happens in general holographic theories with bosonic fields at frequencies $\mathrm{i}(l_b-s) 2\pi T$, where $l_b$ is the highest integer spin in the theory and $s$ takes all positive integer values. We revisit this formalism in theories with gauge symmetry and upgrade the pole-skipping condition so that it works without having to remove the gauge redundancy. We also extend the formalism by incorporating fermions with general spins and interactions and show that their presence generally leads to a separate tower of pole-skipping points at frequencies $\mathrm{i}(l_f-s)2\pi T$, $l_f$ being the highest half-integer spin in the theory and $s$ again taking all positive integer values. We also demonstrate the practical value of this formalism using a selection of examples with spins $0,\frac{1}{2},1,\frac{3}{2},2$.Comment: 40 page

Does China’s emission trading scheme affect corporate financial performance:Evidence from a quasi-natural experiment

Taking China’s emissions trading system (ETS) pilots as a quasi-natural experiment, we examine how the ETS affects firms’ financial performance. Previous studies highlight the impact of ETS on regional and industrial development; however, few studies focus on its potential impact on firms’ performance. Using a time-varying difference-in-differences model and data on Chinese listed firms from 2008 to 2020, we find that the ETS pilots have significant positive impacts on firms’ profitability and value and a negative impact on operating costs. We also find that the ETS pilots improve total factor productivity, but the technological changes indirectly suppress the relation between the ETS and financial performance. Finally, we find evidence that state-owned enterprises experience more significant improvements in their financial performance, led by ETS participation. Our findings have policy implications for firms’ sustainable development and the transition to a low-carbon economy

Holographic entanglement from the UV to the IR

In AdS/CFT, observables on the boundary are invariant under renormalization group (RG) flow in the bulk. In this paper, we study holographic entanglement entropy under bulk RG flow and find that it is indeed invariant. We focus on tree-level RG flow, where massive fields in a UV theory are integrated out to give the IR theory. We explicitly show that in several simple examples, holographic entanglement entropy calculated in the UV theory agrees with that calculated in the IR theory. Moreover, we give an argument for this agreement to hold for general tree-level RG flow. Along the way, we generalize the replica method of calculating holographic entanglement entropy to bulk theories that include matter fields with nonzero spin.Comment: 29 pages, 2 figure