A Baltimore Oriole Census

The question with which this article is concerned is one that was under discussion, in the Ornithology Class at Iowa Wesleyan College. The original problem was to discover how many pairs of Baltimore orioles nest yearly in the town of Mount Pleasant where the college is located. As the investigation was carried on and interest deepened, the scope of the problem was enlarged somewhat to include a study of the determining factors in an oriole\u27s selection of a nesting place. When the problem was first undertaken, the town, which has a population of about four thousand and covers an area of one and one-fourth square miles, was divided into six districts of about equal extent and two students were appointed to search each district for orioles\u27 nests and to note the species of tree in which they were found. This work was done in February, and, as there were no leaves on the trees, each swinging pouch was quite conspicuous and the matter was not one of great difficulty

Constraining the Distribution of L- & T-Dwarfs in the Galaxy

We estimate the thin disk scale height of the Galactic population of L- & T-dwarfs based on star counts from 15 deep parallel fields from the Hubble Space Telescope. From these observations, we have identified 28 candidate L- & T- dwarfs based on their (i'-z') color and morphology. By comparing these star counts to a simple Galactic model, we estimate the scale height to be 350+-50 pc that is consistent with the increase in vertical scale with decreasing stellar mass and is independent of reddening, color-magnitude limits, and other Galactic parameters. With this refined measure, we predict that less than 10^9 M_{sol} of the Milky Way can be in the form L- & T- dwarfs, and confirm that high-latitude, z~6 galaxy surveys which use the i'-band dropout technique are 97-100% free of L- & T- dwarf interlopers.Comment: 4 pages, 4 figures, accepted to ApJ

Overcoming the su(2^n) sufficient condition for the coherent control of n-qubit systems

We study quantum systems with even numbers N of levels that are completely state-controlled by unitary transformations generated by Lie algebras isomorphic to sp(N) of dimension N(N+1)/2. These Lie algebras are smaller than the respective su(N) with dimension N^2-1. We show that this reduction constrains the Hamiltonian to have symmetric energy levels. An example of such a system is an n-qubit system. Using a geometric representation for the quantum wave function of a finite system, we present an explicit example that shows a two-qubit system can be controlled by the elements of the Lie algebra sp(4) (isomorphic to spin(5) and so(5)) with dimension ten rather than su(4) with dimension fifteen. These results enable one to envision more efficient algorithms for the design of fields for quantum-state engineering, and they provide more insight into the fundamental structure of quantum control.Comment: 13 pp., 2 figure

Quantum-to-Classical Correspondence and Hubbard-Stratonovich Dynamical Systems, a Lie-Algebraic Approach

We propose a Lie-algebraic duality approach to analyze non-equilibrium evolution of closed dynamical systems and thermodynamics of interacting quantum lattice models (formulated in terms of Hubbard-Stratonovich dynamical systems). The first part of the paper utilizes a geometric Hilbert-space-invariant formulation of unitary time-evolution, where a quantum Hamiltonian is viewed as a trajectory in an abstract Lie algebra, while the sought-after evolution operator is a trajectory in a dynamic group, generated by the algebra via exponentiation. The evolution operator is uniquely determined by the time-dependent dual generators that satisfy a system of differential equations, dubbed here dual Schrodinger-Bloch equations, which represent a viable alternative to the conventional Schrodinger formulation. These dual Schrodinger-Bloch equations are derived and analyzed on a number of specific examples. It is shown that deterministic dynamics of a closed classical dynamical system occurs as action of a symmetry group on a classical manifold and is driven by the same dual generators as in the corresponding quantum problem. This represents quantum-to-classical correspondence. In the second part of the paper, we further extend the Lie algebraic approach to a wide class of interacting many-particle lattice models. A generalized Hubbard-Stratonovich transform is proposed and it is used to show that the thermodynamic partition function of a generic many-body quantum lattice model can be expressed in terms of traces of single-particle evolution operators governed by the dynamic Hubbard-Stratonovich fields. Finally, we derive Hubbard-Stratonovich dynamical systems for the Bose-Hubbard model and a quantum spin model and use the Lie-algebraic approach to obtain new non-perturbative dual descriptions of these theories.Comment: 25 pages, 1 figure; v2: citations adde

Phantom Black Holes and Sigma Models

We construct static multicenter solutions of phantom Einstein-Maxwell-dilaton theory from null geodesics of the target space, leading to regular black holes without spatial symmetry for certain discrete values of the dilaton coupling constant. We also discuss the three-dimensional gravitating sigma models obtained by reduction of phantom Einstein-Maxwell, phantom Kaluza-Klein and phantom Einstein-Maxwell-dilaton-axion theories. In each case, we generate by group transformations phantom charged black hole solutions from a neutral seed.Comment: 19 page

The Physical Basis for Long-lived Electronic Coherence in Photosynthetic Light Harvesting Systems

The physical basis for observed long-lived electronic coherence in photosynthetic light-harvesting systems is identified using an analytically soluble model. Three physical features are found to be responsible for their long coherence lifetimes: i) the small energy gap between excitonic states, ii) the small ratio of the energy gap to the coupling between excitonic states, and iii) the fact that the molecular characteristics place the system in an effective low temperature regime, even at ambient conditions. Using this approach, we obtain decoherence times for a dimer model with FMO parameters of $\approx$ 160 fs at 77 K and $\approx$ 80 fs at 277 K. As such, significant oscillations are found to persist for 600 fs and 300 fs, respectively, in accord with the experiment and with previous computations. Similar good agreement is found for PC645 at room temperature, with oscillations persisting for 400 fs. The analytic expressions obtained provide direct insight into the parameter dependence of the decoherence time scales.Comment: 5 figures; J. Phys. Chem. Lett. (2011

On the relation between E(5)−E(5)-models and the interacting boson model

The connections between the $E(5)-$models (the original E(5) using an infinite square well, $E(5)-\beta^4$, $E(5)-\beta^6$ and $E(5)-\beta^8$), based on particular solutions of the geometrical Bohr Hamiltonian with $\gamma$-unstable potentials, and the interacting boson model (IBM) are explored. For that purpose, the general IBM Hamiltonian for the $U(5)-O(6)$ transition line is used and a numerical fit to the different $E(5)-$models energies is performed, later on the obtained wavefunctions are used to calculate B(E2) transition rates. It is shown that within the IBM one can reproduce very well all these $E(5)-$models. The agreement is the best for $E(5)-\beta^4$ and reduces when passing through $E(5)-\beta^6$, $E(5)-\beta^8$ and E(5), where the worst agreement is obtained (although still very good for a restricted set of lowest lying states). The fitted IBM Hamiltonians correspond to energy surfaces close to those expected for the critical point. A phenomenon similar to the quasidynamical symmetry is observed

A Comparison of the Chemical Evolutionary Histories of the Galactic Thin Disk and Thick Disk Stellar Populations

We have studied 23 long-lived G dwarfs that belong to the thin disk and thick disk stellar populations. Abundances have been derived for 24 elements: O, Na, Mg, Al, Si, Ca, Ti, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, and Eu. We find that the behavior of [alpha/Fe] and [Eu/Fe] vs. [Fe/H] are quite different for the two populations. As has long been known, the thin disk O, Mg, Si, Ca, and Ti ratios are enhanced relative to iron at the lowest metallicities, and decline toward solar values as [Fe/H] rises above -1.0. For the thick disk, the decline in [alpha/Fe] and [Eu/Fe] does not begin at [Fe/H] = -1.0, but at -0.4. Other elements share this behavior, including Sc, Co, and Zn, suggesting that at least in the chemical enrichment history of the thick disk, these elements were manufactured in similar-mass stars. Combining our results for the oldest and longest-lived stars with prior work, we find clear signs for an independent origin for the Galactic thick disk. (Abridged)Comment: 48 pages and 20 figures, accepted for publication in the Astronomical Journa