Effect of Strong Electron Correlation on the Efficiency of Photosynthetic Light Harvesting

Research into the efficiency of photosynthetic light harvesting has focused on two factors: (1) entanglement of chromophores, and (2) environmental noise. While chromophores are conjugated $\pi$-bonding molecules with strongly correlated electrons, previous models have treated this correlation implicitly without a mathematical variable to gauge correlation-enhanced efficiency. Here we generalize the single-electron/exciton models to a multi-electron/exciton model that explicitly shows the effects of enhanced electron correlation within chromophores on the efficiency of energy transfer. The model provides more detailed insight into the interplay of electron correlation within chromophores and electron entanglement between chromophores. Exploiting this interplay is assisting in the design of new energy-efficient materials, which are just beginning to emerge

X-Ray Evidence for Multiphase Hot Gas with Nearly Solar Fe Abundances in the Brightest Groups of Galaxies

We analyze the ASCA spectra accumulated within ~100 kpc radii of 12 of the brightest groups of galaxies. Upon fitting isothermal models (1T) jointly to the ASCA SIS and GIS spectra we obtain fits for most groups that are of poor or at best marginal quality and give very sub-solar metallicities similar to previous studies, = 0.29 +/- 0.12 Z_sun. Two-temperature models (2T) provide significantly better fits for 11 out of the 12 groups and in every case have metallicities that are substantially larger than obtained for the 1T models, = 0.75 +/- 0.24 Z_sun. Although not very well constrained, for most of the groups absorption in excess of the Galactic value is indicated for the cooler temperature component of the 2T models. A simple multiphase cooling flow model gives results analogous to the 2T models including large metallicities, = 0.65 +/- 0.17 Z_sun. The nearly solar Fe abundances and also solar alpha/Fe ratios indicated by the 2T and cooling flow models are consistent with models of the chemical enrichment of ellipticals, groups, and clusters which assume ratios of Type Ia to Type II supernova and an IMF similar to those of the Milky Way. Thus, we have shown that the very sub-solar Fe abundances and Si/Fe enhancements obtained from most previous studies within r ~100 kpc of galaxy groups are an artifact of their fitting isothermal models to the X-ray spectra which also has been recently demonstrated for the brightest elliptical galaxies. Owing to the importance of these results for interpreting X-ray spectra, in an appendix we use simulated ASCA observations to examine in detail the ``Fe bias'' and ``Si bias'' associated with the spectral fitting of ellipticals, groups, and clusters of galaxies.Comment: 26 pages (6 figures), To Appear in MNRAS. Revised version contains more discussion of abundance gradients (see new section 4.1

What Would Zero Look Like? A Treaty for the Abolition of Nuclear Weapons

Nuclear disarmament-the comprehensive, universal, and permanent abolition of all nuclear weapons, pursuant to a verifiable, legally binding international agreement-has long been one of the most ambitious, controversial, and urgent items on the agenda for arms control. To date, however, most of the discussion of getting to zero has highlighted the political, military, technical and diplomatic dimensions of this complex problem, and there has been relatively little attention to the legal requirements for drafting such a novel treaty. This Article fills that gap by offering two proposed agreements. The first, a non-legally-bindingfr amework accord, would be designedf or signature relatively soon (e.g., in 2015) to re-commit states to the goal of nuclear elimination and to energize their concerted individual and collective action on a set of prescribed steps in pursuit of it. The second, a legally-binding document, would be concluded at some point in the more distant future, when states had accomplished great reductions in their current nuclear arsenals and were ready, at last, to plunge forward to true abolition. The Article describes the conditions necessary for the further articulation of these two novel agreements, and the text of each instrument carries numerous annotations that identify competing options, describe the negotiating range, and illuminate the drafter\u27s choices. The hope is that something novel can be gained-fresh insights can be suggested, and new questions can be raised (even if answering them remains elusive)-by advancing the dialogue about nuclear disarmament to the concrete stage of treaty drafting

Constitutional Bait and Switch: Executive Reinterpretation of Arms Control Treaties

A new constitutional crisis has been thrust upon the American body politic. The crisis arises from a dispute concerning the allocation of legal authority for the interpretation, and especially for the reinterpretation, of international agreements. Once a sleepy backwater reserved for specialized scholars, the issue of treaty interpretation has drawn the President and Congress into stark confrontation and generated splashy headlines

On the rate of convergence to stationarity of the M/M/N queue in the Halfin-Whitt regime

We prove several results about the rate of convergence to stationarity, that is, the spectral gap, for the M/M/n queue in the Halfin-Whitt regime. We identify the limiting rate of convergence to steady-state, and discover an asymptotic phase transition that occurs w.r.t. this rate. In particular, we demonstrate the existence of a constant $B^*\approx1.85772$ s.t. when a certain excess parameter $B\in(0,B^*]$, the error in the steady-state approximation converges exponentially fast to zero at rate $\frac{B^2}{4}$. For $B>B^*$, the error in the steady-state approximation converges exponentially fast to zero at a different rate, which is the solution to an explicit equation given in terms of special functions. This result may be interpreted as an asymptotic version of a phase transition proven to occur for any fixed n by van Doorn [Stochastic Monotonicity and Queueing Applications of Birth-death Processes (1981) Springer]. We also prove explicit bounds on the distance to stationarity for the M/M/n queue in the Halfin-Whitt regime, when $B<B^*$. Our bounds scale independently of $n$ in the Halfin-Whitt regime, and do not follow from the weak-convergence theory.Comment: Published in at http://dx.doi.org/10.1214/12-AAP889 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Hausdorff measure of arcs and Brownian motion on Brownian spatial trees

A Brownian spatial tree is defined to be a pair $(\mathcal{T},\phi)$, where $\mathcal{T}$ is the rooted real tree naturally associated with a Brownian excursion and φ is a random continuous function from $\mathcal{T}$ into ℝd such that, conditional on $\mathcal{T}$, φ maps each arc of $\mathcal{T}$ to the image of a Brownian motion path in ℝd run for a time equal to the arc length. It is shown that, in high dimensions, the Hausdorff measure of arcs can be used to define an intrinsic metric $d_{\mathcal{S}}$ on the set $\mathcal{S}:=\phi(\mathcal{T})$. Applications of this result include the recovery of the spatial tree $(\mathcal{T},\phi)$ from the set $\mathcal{S}$ alone, which implies in turn that a Dawson–Watanabe super-process can be recovered from its range. Furthermore, $d_{\mathcal{S}}$ can be used to construct a Brownian motion on $\mathcal{S}$, which is proved to be the scaling limit of simple random walks on related discrete structures. In particular, a limiting result for the simple random walk on the branching random walk is obtained