Ecological restoration in Hamilton City, North Island, New Zealand

Hamilton City (New Zealand) has less than 20 hectares of high-quality, indigenous species dominated ecosystems, and only 1.6% of the original indigenous vegetation remains within the ecological district. A gradual recognition of the magnitude of landscape transformation has gathered momentum to the stage that there is now a concerted public and private effort to retrofit the City by restoring and reconstructing indigenous ecosystems. The initial focus was on rehabilitating existing key sites, but has shifted to restoring parts of the distinctive gully landform that occupies some 750 ha or 8% of the City. A new initiative at Waiwhakareke (Horseshoe Lake) will involve reconstruction from scratch of a range of ecosystems characteristic of the ecological district over an area of 60 ha. This address will examine a vision for ecological restoration in Hamilton City within the context of policy, education, and community dimensions that have triggered a shift from traditional parks and gardens management to ecosystem management

Coping with speaker-related variation via abstract phonemic categories

Listeners can cope with considerable variation in the way that different speakers talk. We argue here that they can do so because of a process of phonological abstraction in the speech-recognition system. We review evidence that listeners adjust the bounds of phonemic categories after only very limited exposure to a deviant realisation of a given phoneme. This learning can be talker-specific and is stable over time; further, the learning generalizes to previously unheard words containing the deviant phoneme. Together these results suggest that the learning involves adjustment of prelexical phonemic representations which mediate between the speech signal and the mental lexicon during word recognition. We argue that such an abstraction process is inconsistent with claims made by some recent models of language processing that the mental lexicon consists solely of multiple detailed traces of acoustic episodes. Simulations with a purely episodic model without functional prelexical abstraction confirm that such a model cannot account for the evidence on lexical generalization of perceptual learning. We conclude that abstract phonemic categories form a necessary part of lexical access, and that the ability to store talker-specific knowledge about those categories provides listeners with the means to deal with cross-talker variation

Language-universal constraints on the segmentation of English

Two word-spotting experiments are reported that examine whether the Possible-Word Constraint (PWC) [1] is a language-specific or language-universal strategy for the segmentation of continuous speech. The PWC disfavours parses which leave an impossible residue between the end of a candidate word and a known boundary. The experiments examined cases where the residue was either a CV syllable with a lax vowel, or a CVC syllable with a schwa. Although neither syllable context is a possible word in English, word-spotting in both contexts was easier than with a context consisting of a single consonant. The PWC appears to be language-universal rather than language-specific

A Benefit Cost Analysis of a Soil Erosion Control Program for the Northern Watershed of Lake Chicot, Arkansas

Lake Chicot, a 5,025-acre oxbow lake created by the ancient meandering of the Mississippi River, is located near the town of Lake Village in Chicot County of southeastern Arkansas (Fig. 1). Today the lake is separated into a northern basin of 1,154 acres and a southern basin of 3,871 acres by a levee maintained by the Arkansas Game and Fish Commission (Fig. 2). The entire lake once offered excellent fishing and recreational benefits. But with channelization in the drainage basin and final closure of the Cypress Creek gap along the Mississippi River levee in 1920, drainage and flood waters from approximately 350 square miles of agricultural lands were diverted into Connerly Bayou and thus, ultimately, into Lake Chicot

Iron Displacements and Magnetoelastic Coupling in the Spin-Ladder Compound BaFe2Se3

We report long-range ordered antiferromagnetism concomitant with local iron displacements in the spin-ladder compound BaFe$_2$Se$_3$. Short-range magnetic correlations, present at room temperature, develop into long-range antiferromagnetic order below T$_N$ = 256 K, with no superconductivity down to 1.8 K. Built of ferromagnetic Fe$_4$ plaquettes, the magnetic ground state correlates with local displacements of the Fe atoms. These iron displacements imply significant magnetoelastic coupling in FeX$_4$-based materials, an ingredient hypothesized to be important in the emergence of superconductivity. This result also suggests that knowledge of these local displacements is essential for properly understanding the electronic structure of these systems. As with the copper oxide superconductors two decades ago, our results highlight the importance of reduced dimensionality spin ladder compounds in the study of the coupling of spin, charge, and atom positions in superconducting materials

Pseudogap Formation in the Symmetric Anderson Lattice Model

We present self-consistent calculations for the self-energy and magnetic susceptibility of the 2D and 3D symmetric Anderson lattice Hamiltonian, in the fluctuation exchange approximation. At high temperatures, strong f-electron scattering leads to broad quasiparticle spectral functions, a reduced quasiparticle band gap, and a metallic density of states. As the temperature is lowered, the spectral functions narrow and a pseudogap forms at the characteristic temperature $T_x$ at which the width of the quasiparticle spectral function at the gap edge is comparable to the renormalized activation energy. For $T << T_x$, the pseudogap is approximately equal to the hybridization gap in the bare band structure. The opening of the pseudogap is clearly apparent in both the spin susceptibility and the compressibility.Comment: RevTeX - 14 pages and 7 figures (available on request), NRL-JA-6690-94-002

Density of Phonon States in Superconducting FeSe as a Function of Temperature and Pressure

The temperature and pressure dependence of the partial density of phonon states of iron atoms in superconducting Fe1.01Se was studied by 57Fe nuclear inelastic scattering (NIS). The high energy resolution allows for a detailed observation of spectral properties. A sharpening of the optical phonon modes and shift of all spectral features towards higher energies by ~4% with decreasing temperature from 296 K to 10 K was found. However, no detectable change at the tetragonal - orthorhombic phase transition around 100 K was observed. Application of a pressure of 6.7 GPa, connected with an increase of the superconducting temperature from 8 K to 34 K, results in an increase of the optical phonon mode energies at 296 K by ~12%, and an even more pronounced increase for the lowest-lying transversal acoustic mode. Despite these strong pressure-induced modifications of the phonon-DOS we conclude that the pronounced increase of Tc in Fe1.01Se with pressure cannot be described in the framework of classical electron-phonon coupling. This result suggests the importance of spin fluctuations to the observed superconductivity

Orbital Selective Magnetism in the Spin-Ladder Iron Selenides Ba1−x_{1-x}Kx_{x}Fe2_2Se3_3

Here we show that the 2.80(8) {\mu}B/Fe block antiferromagnetic order of BaFe2Se3 transforms into stripe antiferromagnetic order in KFe2Se3 with a decrease in moment to 2.1(1) {\mu}B/Fe. This reduction is larger than expected from the change in electron count from Ba$^{2+}$ to K$^{+}$, and occurs with the loss of the displacements of Fe atoms from ideal positions in the ladders, as found by neutron pair distribution function analysis. Intermediate compositions remain insulating, and magnetic susceptibility measurements show a suppression of magnetic order and probable formation of a spin-glass. Together, these results imply an orbital-dependent selection of magnetic versus bonded behavior, driven by relative bandwidths and fillings.Comment: Final versio