Changes in fish populations in the Lower Canyons of the Rio Grande

The Lower Canyons of the Rio Grande suffer from environmental degradation that has negatively impacted native fish populations and their distributions. Macrhybopsis aestivalis (speckled chub), Notropis jemezanus (Rio Grande shiner), Rhinichthys cataractae (longnose dace) and Cycleptus elongatus (blue sucker) populations appear to have suffered recent declines. Although diminished water quantity is likely an important factor in these declines, related changes in channel morphology precipitated by massive stands of Arundo donax (giant reed) and Tamarix sp. (salt cedar) may also be responsible. These invasive exotics have essentially channelized the river, disrupted normal sediment distribution and reduced shallow, low-velocity habitats. Much of the Lower Canyons of the Rio Grande are devoid of sandy sediment and most riffles are now composed of gravel and cobble.Integrative Biolog

Two Photon Decays of Charmonia from Lattice QCD

We make the first calculation in lattice QCD of two-photon decays of mesons. Working in the charmonium sector, using the LSZ reduction to relate a photon to a sum of hadronic vector eigenstates, we compute form-factors in both the space-like and time-like domains for the transitions $\eta_c \to \gamma^* \gamma^*$ and $\chi_{c0} \to \gamma^* \gamma^*$. At the on-shell point we find approximate agreement with experimental world-average values.Comment: Replaced with version to be published in PRL. Expanded discussion of possible systematic error

Trade flows and the exchange rate in South Africa

The exchange rate plays a central role in public debate around trade and trade policy in South Africa. The general view is that depreciation enhances export competitiveness, encourages export diversification, protects domestic industries from imports and ultimately improves the trade balance. This paper reviews the theoretical and empirical relationship between the exchange rate and trade flows in South Africa. Trade volumes are found to be sensitive to real exchange rate movements but nominal depreciations have a limited long-run impact on trade volumes and the trade balance, as real effects are offset by domestic inflation. Policy should not focus on the exchange rate, but on the fundamental determinants of the profitability and competitiveness of domestic exporters and import competing industries: productivity enhancement, infrastructure, constraints to business operations and production costs, including labour costs.Exchange rate; South Africa; international trade

An Annotated Checklist of the Freshwater Fishes of Texas, with Keys to Identification of Species

Forty-five families and 247 species of fishes are known to inhabit the freshwaters of Texas. We report on the distribution and status of these fishes and provide a key to their identification. Of the native fishes originally found in Texas, five taxa, Notropis orca (phantom shiner), Notropis simus simus (Rio Grande bluntnose shiner), Cyprinella lutrensis blairi (Maravillas red shiner), Gambusia amistadensis (Amistad gambusia) and Gambusia georgei (San Marcos gambusia) are apparently extinct, and three, Oncorhynchus clarki virginalis (Rio Grande cutthroat trout), Hybognathus amarus (Rio Grande silvery minnow) and Gambusia senilis (blotched gambusia) appear to be extirpated from the state. More than 20 percent of the remaining primary freshwater species appear to be in some need of protection.Integrative Biolog

On the temperature of surfaces

The concept of the temperature of a surface is introduced from the viewpoint of the physical chemistry of surfaces. The surface, near surface and microlayer regions of the interface are defined. Most methods measure the temperature of the microlayer or at best the near surface region and may err in representing the surface temperature. Methods based on capillary ripples actually measure the surface temperature since surface tension (or surface tension tensor when a monolayer has been spread or absorbed at the interface) is the main restoring force that controls their propagation. Light scattering methods are described for determining the elevation of very small amplitude capillary waves through the computation of various correlation functions from which the surface tension can be estimated. Procedures for estimating the surface temperature are described

Isoscalar ππ,KK‾,ηη\pi\pi, K\overline{K}, \eta\eta scattering and the σ,f0,f2\sigma, f_0, f_2 mesons from QCD

We present the first lattice QCD study of coupled isoscalar $\pi\pi,K\overline{K},\eta\eta$ $S$- and $D$-wave scattering extracted from discrete finite-volume spectra computed on lattices which have a value of the quark mass corresponding to $m_\pi\sim391$ MeV. In the $J^P=0^+$ sector we find analogues of the experimental $\sigma$ and $f_0(980)$ states, where the $\sigma$ appears as a stable bound-state below $\pi\pi$ threshold, and, similar to what is seen in experiment, the $f_0(980)$ manifests itself as a dip in the $\pi\pi$ cross section in the vicinity of the $K\overline{K}$ threshold. For $J^P=2^+$ we find two states resembling the $f_2(1270)$ and $f_2'(1525)$, observed as narrow peaks, with the lighter state dominantly decaying to $\pi\pi$ and the heavier state to $K\overline{K}$. The presence of all these states is determined rigorously by finding the pole singularity content of scattering amplitudes, and their couplings to decay channels are established using the residues of the poles