Journal Staff

Multi-decadal studies of community and ecosystemdynamics are rare; however, this time frame is most relevant for assessing the impact of anthropogenic influences and climate change on ecosystems. For this reason, we investigated changes in vegetation and microtopography over 52 years in two contrasting mire ecosystems, one ombrotrophic (bog) and one minerotrophic (fen), representing different successional stages and contrasting hydrological settings. In both peatlands, floristic composition was recorded in the same permanent plots (n = 55-56, 0.25 m(2)) in both 1960 and 2012 and microtopography was mapped over a large area (ca. 2500 m(2)) that encompassed these same plots. We quantified and compared the community-level changes and internal spatial dynamics, tested associations between pH/microtopography and community/species change, and examined how the area and location of hummock microforms had changed over time. The bog exhibited little site level change in vegetation, where few species changed significantly in cover and plot frequency. However, detailed analyses revealed some large within-plot changes over time in the bog, illustrating that bogs can be highly dynamic systems at a fine scale. In contrast, the rich fen experienced a clear directional change; specifically, bryophyte abundance decreased by 70% and brown mosses were almost extinct. Although pH had decreased over time at the rich fen, this decrease at the plot-level was not associated with the decline of brown moss abundance. The microtopographic structure did not change substantially at the bog where similar to 70% was covered by lawn/hummocks; however, in the rich fen hummocks expanded (from 10% to 16% cover) and moved or expanded down slope. Our study suggests, that at the site-level, the bog ecosystem was more resistant to environmental changes over time compared to the rich fen, as evidenced by shifts in vegetation and microtopography. The contrasting scales of vegetation dynamics observed within a bog (i.e., within-plot changes vs. site-level) indicate that plant-environment feedbacks contribute to the peatland level stability. While in rich fens, internal feedbacks may be weaker and the ecosystem's vegetation and microtopographic structure are vulnerable to shifting hydrological fluxes

The Dynamical Mean Field Theory phase space extension and critical properties of the finite temperature Mott transition

We consider the finite temperature metal-insulator transition in the half filled paramagnetic Hubbard model on the infinite dimensional Bethe lattice. A new method for calculating the Dynamical Mean Field Theory fixpoint surface in the phase diagram is presented and shown to be free from the convergence problems of standard forward recursion. The fixpoint equation is then analyzed using dynamical systems methods. On the fixpoint surface the eigenspectra of its Jacobian is used to characterize the hysteresis boundaries of the first order transition line and its second order critical end point. The critical point is shown to be a cusp catastrophe in the parameter space, opening a pitchfork bifurcation along the first order transition line, while the hysteresis boundaries are shown to be saddle-node bifurcations of two merging fixpoints. Using Landau theory the properties of the critical end point is determined and related to the critical eigenmode of the Jacobian. Our findings provide new insights into basic properties of this intensively studied transition.Comment: 11 pages, 12 figures, 1 tabl

Superconductivity in hole-doped C60 from electronic correlations

We derive a model for the highest occupied molecular orbital band of a C60 crystal which includes on-site electron-electron interactions. The form of the interactions are based on the icosahedral symmetry of the C60 molecule together with a perturbative treatment of an isolated C60 molecule. Using this model we do a mean-field calculation in two dimensions on the [100] surface of the crystal. Due to the multi-band nature we find that electron-electron interactions can have a profound effect on the density of states as a function of doping. The doping dependence of the transition temperature can then be qualitatively different from that expected from simple BCS theory based on the density of states from band structure calculations

Distribution of spectral weight in a system with disordered stripes

The ``band-structure'' of a disordered stripe array is computed and compared, at a qualitative level, to angle resolved photoemission experiments on the cuprate high temperature superconductors. The low-energy states are found to be strongly localized transverse to the stripe direction, so the electron dynamics is strictly one-dimensional (along the stripe). Despite this, aspects of the two dimensional band-structure Fermi surface are still vividly apparent.Comment: 10 pages, 11 figure

The fermi arc and fermi pocket in cuprates in a short-range diagonal stripe phase

In this paper we studied the fermi arc and the fermi pocket in cuprates in a short-range diagonal stripe phase with wave vectors $(7\pi/8, 7\pi/8)$, which reproduce with a high accuracy the positions and sizes of the fermi arc and fermi pocket and the superstructure in cuprates observed by Meng et al\cite{Meng}. The low-energy spectral function indicates that the fermi pocket results from the main band and the shadow band at the fermi energy. Above the fermi energy the shadow band gradually departs away from the main band, leaving a fermi arc. Thus we conclude that the fermi arc and fermi pocket can be fully attributed to the stripe phase but has nothing to do with pairing. Incorporating a d-wave pairing potential in the stripe phase the spectral weight in the antinodal region is removed, leaving a clean fermi pocket in the nodal region.Comment: 5 pages, 6 figure

Quantal phases, disorder effects and superconductivity in spin-Peierls systems

In view of recent developments in the investigation on cuprate high-T${}_{\rm c}$ superconductors and the spin-Peierls compound CuGeO${}_{3}$, we study the effect of dilute impurity doping on the spin-Peierls state in quasi-one dimensional systems. We identify a common origin for the emergence of antiferromagnetic order upon the introduction of static vacancies, and superconductivity for mobile holes.Comment: 4 pages revtex; revised versio

Genetic link between renal birth defects and congenital heart disease

Structural birth defects in the kidney and urinary tract are observed in 0.5% of live births and are a major cause of end-stage renal disease, but their genetic aetiology is not well understood. Here we analyse 135 lines of mice identified in large-scale mouse mutagenesis screen and show that 29% of mutations causing congenital heart disease (CHD) also cause renal anomalies. The renal anomalies included duplex and multiplex kidneys, renal agenesis, hydronephrosis and cystic kidney disease. To assess the clinical relevance of these findings, we examined patients with CHD and observed a 30% co-occurrence of renal anomalies of a similar spectrum. Together, these findings demonstrate a common shared genetic aetiology for CHD and renal anomalies, indicating that CHD patients are at increased risk for complications from renal anomalies. This collection of mutant mouse models provides a resource for further studies to elucidate the developmental link between renal anomalies and CHD

Antiferromagnetic spin ladders effectively coupled by one-dimensional electron liquids

We study a model of the stripe state in strongly correlated systems consisting of an array of antiferromagnetic spin ladders, each with $n_{leg}$ legs, coupled to each other through the spin-exchange interaction to charged stripes in between each pair of ladders. The charged stripes are assumed to be Luttinger liquids in a spin-gap regime (Luther-Emery). An effective interaction for a pair of neighboring ladders is calculated by integrating out the gapped spin degree of freedom in the charged stripe. The low energy effective theory of each ladder is the usual nonlinear $\sigma$-model with additional cross couplings of neighboring ladders. These interactions are found to favor either in-phase or anti-phase short range spin orderings depending on whether the charge stripe is site-centered or bond-centered as well as on its filling factor and other physical parameters of the charged stripe.Comment: 4 pages with 1 figure, revised introduction and discussion section