Long-term qualitative changes in fish populations and aquatic habitat in San Mateo Creek Lagoon, northern San Diego County, southern California, USA.

Observations beginning in 1974 and later surveys of increasing intensity with small seines, traps, and dipnets (1991 to mid-2008) documented patterns of abundance, colonization, and extirpation of 15 species of native and non-native fishes as well as crayfishes, and amphibians in the lagoon at the mouth of San Mateo Creek, northern San Diego County, California. Fish populations varied with Mediterranean climate patterns of stream flow and breaching of the lagoon to the ocean through the barrier sand berm. Two near-record rainfall seasons occurred during this period; the 1997-1998 El Niño due to southern storms and the 2004-2005 winter wet season of more usual storms from the north and northwest. The lagoon stabilized as fresh to brackish in the dry season and for multiple years during successive dry winters. Closed conditions benefitted the native, federally endangered Southern Tidewater Goby, Eucyclogobius n. sp., but were unsuitable for other native estuarine species more common in wetter years. Wet year flows also brought down non-native freshwater species to the lagoon; some thrived and increased predation pressure on the tidewater goby. Historically these exotics were absent and two additional native species were present in the lagoon, Partially Armored Threespine Stickleback, Gasterosteus aculeatus, and the now federally endangered Southern Steelhead, Oncorhynchus mykiss. Restoring and maintaining a full suite of native species will require a combination of 1) habitat maintenance, 2) control or management of non-native species, and 3) reintroduction of some native fishes and amphibians to restore the faunal communities of remaining small coastal estuarine systems

Anomalies in the Low Frequency Vibrational Density of States for a Polymer with Intrinsic Microporosity – The Boson Peak of PIM-1

Polymers with intrinsic microporosity are promising candidates for the active separation layer in gas separation membranes. Here, the vibrational density of states (VDOS) for PIM-1, the prototypical polymer with intrinsic microporosity, is investigated by means of inelastic neutron scattering. The results are compared to data measured for a more conventional high-performance polyimide used in gas separation membranes (Matrimid). The measured data show the characteristic low frequency excess contribution to VDOS above the Debye sound wave level, generally known as the Boson peak in glass-forming materials. In comparison to the Boson peak of Matrimid, that of PIM-1 is shifted to lower frequencies. This shift is discussed considering the microporous, sponge-like structure of PIM-1 as providing a higher compressibility at the molecular scale than for conventional polymers. For an annealed PIM-1 sample, the Boson peak shifts to higher frequencies in comparison to the un-annealed sample. These changes in the VDOS of the annealed PIM-1 sample are related to changes in the microporous structure as confirmed by X-ray scattering

Long-term Qualitative Changes in Fish Populations and Aquatic Habitat in San Mateo Creek Lagoon, Northern San Diego County, California

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Investigating the Gas Sorption Mechanism in an <i>rht</i>-Metal–Organic Framework through Computational Studies

Grand canonical Monte Carlo (GCMC) simulations were performed to investigate CO₂ and H₂ sorption in an <i>rht</i>-metal–organic framework (MOF) that was synthesized with a ligand having a nitrogen-rich trigonal core through trisubstituted triazine groups and amine functional groups. This MOF was synthesized by two different groups, each reporting their own distinct gas sorption measurements and crystal structure. Electronic structure calculations demonstrated that the small differences in the atomic positions between each group’s crystal structure resulted in different electrostatic parameters about the Cu²⁺ ions for the respective unit cells. Simulations of CO₂ sorption were performed with and without many-body polarization effects and using our recently developed CO₂ potentials, in addition to a well-known bulk CO₂ model, in both crystallographic unit cells. Simulated CO₂ sorption isotherms and calculated isosteric heats of adsorption, <i>Q</i>_st, values were in excellent agreement with the results reported previously by Eddaoudi et al. for both structures using the polarizable CO₂ potential. For both crystal structures, the initial site for CO₂ sorption were the Cu²⁺ ions that had the higher positive charge in the unit cell, although the identity of this electropositive Cu²⁺ ion was different in each case. Simulations of H₂ sorption were performed with three different hydrogen potentials of increasing anisotropy in both crystal structures and the results, especially with the highest fidelity model, agreed well with Eddaoudi et al.’s experimental data. The preferred site of H₂ sorption at low loading was between two Cu²⁺ ions of neighboring paddlewheels. The calculation of the normalized hydrogen dipole distribution for the polarizable model in both crystal structures aided in the identification of four distinct sorption sites in the MOF, which is consistent to what was observed in the experimental inelastic neutron scattering (INS) spectra. Lastly, while the experimental results for the two groups are quantitatively different, the sorption mechanisms (for both crystal structures and sorbates) are broadly similar and not inconsistent with either set of experimental data; the theoretical sorption isotherms themselves resemble those by Eddaoudi et al