Seasonal stem loss and self-thinning in low marsh Spartina alterniflora in a New England tidal marsh

Dense monocultures of the grass Spartina alterniflora dominate the low marsh in typical New England tidal marshes. These marshes provide a number of important ecosystem services; thus, it is important to understand the factors that influence S. alterniflora productivity. End of season live biomass is often used to estimate S. alterniflora productivity, but this measure fails to account for stems lost within the growing season and may lead to a significant underestimate. We explored two possible factors that may influence S. alterniflora stem loss within the growing season: 1) density-dependent mortality (self-thinning), and 2) the physical force of moving water via tidal action. At four tidal creeks in the Plum Island Sound estuary, Massachusetts, we found that on average 34% of the S. alterniflora stems present in June were lost by August, but this varied from 11-44% among creeks. This stem loss accounted for at least 20% of the estimated annual productivity. We found little evidence that tidal action drives spatial variation in stem loss. Seasonal stem loss was greater in stands with higher early season density, consistent with self-thinning. As self-thinning occurred, density became more similar among creeks, meaning that end of the season density patterns are not reflective of early season stands. Adding a simple measure of early season stem density can improve productivity estimates by incorporating loss due to self-thinning

Decoherence and Programmable Quantum Computation

An examination of the concept of using classical degrees of freedom to drive the evolution of quantum computers is given. Specifically, when externally generated, coherent states of the electromagnetic field are used to drive transitions within the qubit system, a decoherence results due to the back reaction from the qubits onto the quantum field. We derive an expression for the decoherence rate for two cases, that of the single-qubit Walsh-Hadamard transform, and for an implementation of the controlled-NOT gate. We examine the impact of this decoherence mechanism on Grover's search algorithm, and on the proposals for use of error-correcting codes in quantum computation.Comment: submitted to Phys. Rev. A 35 double-spaced pages, 2 figures, in LaTe

Implementation of NMR quantum computation with para-hydrogen derived high purity quantum states

We demonstrate the first implementation of a quantum algorithm on a liquid state nuclear magnetic resonance (NMR) quantum computer using almost pure states. This was achieved using a two qubit device where the initial state is an almost pure singlet nuclear spin state of a pair of 1H nuclei arising from a chemical reaction involving para-hydrogen. We have implemented Deutsch's algorithm for distinguishing between constant and balanced functions with a single query.Comment: 7 pages RevTex including 6 figures. Figures 4-6 are low quality to save space. Submitted to Phys Rev

Duality, thermodynamics, and the linear programming problem in constraint-based models of metabolism

It is shown that the dual to the linear programming problem that arises in constraint-based models of metabolism can be given a thermodynamic interpretation in which the shadow prices are chemical potential analogues, and the objective is to minimise free energy consumption given a free energy drain corresponding to growth. The interpretation is distinct from conventional non-equilibrium thermodynamics, although it does satisfy a minimum entropy production principle. It can be used to motivate extensions of constraint-based modelling, for example to microbial ecosystems.Comment: 4 pages, 2 figures, 1 table, RevTeX 4, final accepted versio

A 600 year-long drought index for central Anatolia

We have used sediments from Nar lake in central Turkey to reconstruct climatic variability over timescales longer than can be obtained from direct meteorological observations. Because the sediments of this lake are annually layered and precisely dated, it has been possible to calibrate sedimentary climate proxies against meteorological records to derive a drought index; this has then been applied to time periods before instrumental data are available. In this study, δ18O from Nar lake carbonates have been used to generate a decadal average P/E index for central Anatolia, which highlights major drought events since 1400 AD