Thermodynamics and Spin Tunneling Dynamics in Ferric Wheels with Excess Spin

We study theoretically the thermodynamic properties and spin dynamics of a class of magnetic rings closely related to ferric wheels, antiferromagnetic ring systems, in which one of the Fe (III) ions has been replaced by a dopant ion to create an excess spin. Using a coherent-state spin path integral formalism, we derive an effective action for the system in the presence of a magnetic field. We calculate the functional dependence of the magnetization and tunnel splitting on the magnetic field and show that the parameters of the spin Hamiltonian can be inferred from the magnetization curve. We study the spin dynamics in these systems and show that quantum tunneling of the Neel vector also results in tunneling of the total magnetization. Hence, the spin correlation function shows a signature of Neel vector tunneling, and electron spin resonance (ESR) techniques or AC susceptibility measurements can be used to measure both the tunneling and the decoherence rate. We compare our results with exact diagonalization studies on small ring systems. Our results can be easily generalized to a wide class of nanomagnets, such as ferritin.Comment: 15 pages, 5 figure

Push is Fast on Sparse Random Graphs

We consider the classical push broadcast process on a large class of sparse random multigraphs that includes random power law graphs and multigraphs. Our analysis shows that for every $\varepsilon>0$, whp $O(\log n)$ rounds are sufficient to inform all but an $\varepsilon$-fraction of the vertices. It is not hard to see that, e.g. for random power law graphs, the push process needs whp $n^{\Omega(1)}$ rounds to inform all vertices. Fountoulakis, Panagiotou and Sauerwald proved that for random graphs that have power law degree sequences with $\beta>3$, the push-pull protocol needs $\Omega(\log n)$ to inform all but $\varepsilon n$ vertices whp. Our result demonstrates that, for such random graphs, the pull mechanism does not (asymptotically) improve the running time. This is surprising as it is known that, on random power law graphs with $2<\beta<3$, push-pull is exponentially faster than pull

Spin-Photon Dynamics of Quantum Dots in Two-mode Cavities

A quantum dot interacting with two resonant cavity modes is described by a two-mode Jaynes-Cummings model. Depending on the quantum dot energy level scheme, the interaction of a singly doped quantum dot with a cavity photon generates entanglement of electron spin and cavity states or allows one to implement a SWAP gate for spin and photon states. An undoped quantum dot in the same structure generates pairs of polarization entangled photons from an initial photon product state. For realistic cavity loss rates, the fidelity of these operations is of order 80%.Comment: 6 pages, 4 figures; extended discussion of experimental implementatio

The age of cheap money and passive investing: Are pro forma earnings value relevant?

This study investigates the impact of pro forma earnings on stock misvaluation. In light of a decade of substantial changes in the market and investment environment since 2008 that are challenging the traditional primacy of accounting disclosures for valuation, I link mispriced shares to voluntary firm disclosures. Using a hand-collected sample of pro forma earnings from quarterly earnings press releases of the constituent firms of the US Dow Jones 30 between 2011 and 2017, I find that providing pro forma earnings reduces overvaluation for the most overvalued stocks. Further analysis indicates, however, that for firms with higher analyst earnings forecast dispersion, disclosing pro forma earnings increases these firms' overvaluation. In addition, different types of expenses excluded to meet or beat analyst earnings forecasts affect misvaluation differently. These findings suggest that pro forma earnings still play an important role and are value relevant in the new market conditions. JEL classification numbers: G38, M40, M4

Transferable Ageing Provisions in Individual Health Insurance Contracts

We consider lifetime health insurance contracts in which ageing provisions are used tosmooth the premium profile. The capital stock accumulated for each individual can bedecomposed into two parts: a premium insurance and an annuitised life insurance, onlythe latter being transferable between insurers without triggering premium changesthrough risk segmentation. In a simulation based on German data, the transferable sharedeclines in age and falls with an increasing age of entry into the contract. In spite ofdifferent benefit profiles, it is almost identical for women and men.Health insurance, lifetime contracts, ageing provisions, premium insurance, simulations

Transferable Ageing Provisions in Individual Health Insurance Contracts

We consider lifetime health insurance contracts in which ageing provisions are used to smooth the premium profile. The stock of capital accumulated for each individual can be split into two parts: a premium insurance and an annuitised life insurance, where the latter would be transferable between insurers without triggering premium changes through risk segmentation. In a simulation based on German data, the transferable share declines in age. It is smaller for women than for men, and it falls with an increasing age of entry into the contract.health insurance, lifetime contracts, ageing provisions premium insurance, simulations