Photoassociative Production and Trapping of Ultracold KRb Molecules

We have produced ultracold heteronuclear KRb molecules by the process of photoassociation in a two-species magneto-optical trap. Following decay of the photoassociated KRb*, the molecules are detected using two-photon ionization and time-of-flight mass spectroscopy of KRb$^+$. A portion of the metastable triplet molecules thus formed are magnetically trapped. Photoassociative spectra down to 91 cm$^{-1}$ below the K(4$s$) + Rb (5$p_{1/2}$) asymptote have been obtained. We have made assignments to all eight of the attractive Hund's case (c) KRb* potential curves in this spectral region.Comment: 4 pages, 4 figure

The effect of pH, aluminum, and chelator manipulations on the growth of acidic and circumneutral species of Asterionella

The growth rates of two diatoms, acidophilic Asterionella ralfsii and circumneutral A. formosa , were differentially affected by varying pH, Al, and EDTA in chemically defined media. Free Al ion concentration increased as pH and EDTA concentration decreased. Free trace metal ion concentration decreased as EDTA levels increased but increased by orders of magnitude upon addition of Al. pH had an overriding species specific effect on growth rate; at low pH A. ralfsii had higher growth rates than A. formosa and vice versa at high pH. For both species higher EDTA levels depressed growth rates. Moderate additions of Al generally resulted in growth stimulation. The growth rate stimulations, especially at 200 and 400 μg L −1 Al additions, correlate to increases in free trace metal ion concentrations. The EDTA-AI interaction effects on growth rate were both pH and concentration dependent: at pH 7 both species were stimulated by addition of Al at all EDTA levels (except A. ralfsii at 5.0 mM EDTA and A. formosa at 0.5 mNM EDTA); at pH 6 Al addition either stimulated or had no effect on the growth rates of both species (except at low EDTA and high Al levels); at pH 5 A. formosa did not grow and additions of 200 μg L −1 Al stimulated growth of A. ralfsii . It is likely that the effect of pH, Al, and EDTA on speciation of essential or toxic trace metals affects growth rates of these diatoms in a species specific manner.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43905/1/11270_2004_Article_BF00282626.pd

Resonant control of elastic collisions in an optically trapped Fermi gas of atoms

We have loaded an ultracold gas of fermionic atoms into a far off resonance optical dipole trap and precisely controlled the spin composition of the trapped gas. We have measured a magnetic-field Feshbach resonance between atoms in the two lowest energy spin-states, |9/2, -9/2> and |9/2, -7/2>. The resonance peaks at a magnetic field of 201.5 plus or minus 1.4 G and has a width of 8.0 plus or minus 1.1 G. Using this resonance we have changed the elastic collision cross section in the gas by nearly 3 orders of magnitude.Comment: 4 pages, 3 figure

Evaluation of Exposure-Effects Relationships of Metals in the Benthic Macroinvertebrate Community in the Upper Clark Fork River, Montana

Previously published studies conducted on the Upper Clark Fork River (UCFR) suggest adverse effects due to metals-enriched sediments found in the depositional areas that comprise approximately 4% of the riverbed. While these studies measure exposure concentrations from depositional areas, effects measurements (e.g., benthic invertebrate abundance and diversity measures and tissue residues) have been predominantly obtained from coarse substrate riffle areas. Comparing exposure data from one habitat to effects data from another is problematic. An integrated approach was conducted to assess effects data by sampling benthic macroinvertebrates for community composition measurements, tissue residues, and sediment contaminant concentrations. Thirteen co-located sampling sites along the UCFR were sampled in both depositional and riffle habitats in 1996. Metals concentrations in bulk sediments and benthic invertebrate tissues decreased with distance from metals sources in the headwaters, but sediment porewater concentrations did not. Although there were some significant relationships between bulk sediment metals concentrations and tissue metals residues, BMI community metrics did not appear to vary along this gradient, or with exposure concentrations. This is consistent with an evaluation of sediment toxicity tests performed using sediments from Warm Springs Ponds, as well as the UCFR, which do not suggest that metals are of potential concern to benthic macroinvertebrates

Evaluating the Bioavailability of Metals in Sediments from the Upper Clark Fork River Basin, Montana

A sediment quality assessment was developed to evaluate the potential bioavailability of metals from riverbed sediments. The proposed approach consisted of multiple assessment methods using bulk sediment metals concentrations, equilibrium partitioning measures, and bulk sediment and pore water toxicity tests. Metals bioavailability was evaluated using: 1) EPA’s theoretical guidelines which compare acid-volatile sulfide concentrations to simultaneously extractable metals concentrations, and compare sediment pore water metals concentrations to ambient water quality criteria; 2) correlative guidelines, which compare bulk sediment metals concentrations against sediment no-effect concentrations (NECs), and 3) sediment toxicity tests. Sediment toxicity studies were also used to derive site-specific NEC values. The study site chosen for this assessment was the metals-enriched upper Clark Fork River (UCFR) located in southwestern Montana, USA. Results of this assessment indicate only nominal risk to most aquatic organisms posed by sediment metals concentrations in depositional areas in the UCFR. The uncertainty associated with using only one of the approaches for evaluating sediment contamination should be reduced by using the combined approach outlined here