A Water Quality Survey of the Big Blue River, Nebraska

Physiochemical and bacteriological conditions along with the macroinvertebrate community structure were studied to evaluate water quality of the Big Blue River, in southeastern Nebraska. Samples were taken between November 7, 1978, and December 19, 1979, at six stations from the headwaters to lower reaches of the river. Some sample sites were below specific municipal and industrial effluents to evaluate better their impact on water quality. Parameters measured included pH, temperature, dissolved oxygen, suspended solids, conductivity, biochemical oxygen demand, nitrate, ammonia, and fecal coliforms. Dissolved oxygen and nitrate were significantly different (p\u3c0.05) between stations, with the headwaters station exhibiting the greatest difference in water quality. Fecal coliforms were substantially higher at stations below Crete. The macroinvertebrate fauna comprised 42 and 66 taxa collected with Ekman grabs and multiplate artificial substrates, respectively. Average diversity values, using the Shannon-Weaver index, indicated all stations would be categorized as moderately polluted. Taxa collected at the stations showed a great deal of homogeneity. An exception was the headwaters site where pollution-associated taxa were found in abundance. Seasonal changes were an apparent factor affecting diversity of the macro invertebrates. The results collected provide useful baseline information for future evaluation of water quality trends of the Big Blue River

A Water Quality Survey of the Big Blue River, Nebraska

Physiochemical and bacteriological conditions along with the macroinvertebrate community structure were studied to evaluate water quality of the Big Blue River, in southeastern Nebraska. Samples were taken between November 7, 1978, and December 19, 1979, at six stations from the headwaters to lower reaches of the river. Some sample sites were below specific municipal and industrial effluents to evaluate better their impact on water quality. Parameters measured included pH, temperature, dissolved oxygen, suspended solids, conductivity, biochemical oxygen demand, nitrate, ammonia, and fecal coliforms. Dissolved oxygen and nitrate were significantly different (p\u3c0.05) between stations, with the headwaters station exhibiting the greatest difference in water quality. Fecal coliforms were substantially higher at stations below Crete. The macroinvertebrate fauna comprised 42 and 66 taxa collected with Ekman grabs and multiplate artificial substrates, respectively. Average diversity values, using the Shannon-Weaver index, indicated all stations would be categorized as moderately polluted. Taxa collected at the stations showed a great deal of homogeneity. An exception was the headwaters site where pollution-associated taxa were found in abundance. Seasonal changes were an apparent factor affecting diversity of the macro invertebrates. The results collected provide useful baseline information for future evaluation of water quality trends of the Big Blue River

Avalanche statistics and time-resolved grain dynamics for a driven heap

We probe the dynamics of intermittent avalanches caused by steady addition of grains to a quasi-two dimensional heap. To characterize the time-dependent average avalanche flow speed v(t), we image the top free surface. To characterize the grain fluctuation speed dv(t), we use Speckle-Visibility Spectroscopy. During an avalanche, we find that the fluctuation speed is approximately one-tenth the average flow speed, and that these speeds are largest near the beginning of an event. We also find that the distribution of event durations is peaked, and that event sizes are correlated with the time interval since the end of the previous event. At high rates of grain addition, where successive avalanches merge into smooth continuous flow, the relationship between average and fluctuation speeds changes to dv Sqrt[v]

Non-collinear magnetism in Al-Mn topologically disordered systems

We have performed the first ab-initio calculations of a possible complex non-collinear magnetic structure in aluminium-rich Al-Mn liquids within the real-space tight-binding LMTO method. In our previous work we predicted the existence of large magnetic moments in Al-Mn liquids [A.M. Bratkovsky, A.V. Smirnov, D. N. Manh, and A. Pasturel, \prb {\bf 52}, 3056 (1995)] which has been very recently confirmed experimentally. Our present calculations show that there is a strong tendency for the moments on Mn to have a non-collinear (random) order retaining their large value of about 3~$\mu_B$. The d-electrons on Mn demonstrate a pronounced non-rigid band behaviour which cannot be reproduced within a simple Stoner picture. The origin of the magnetism in these systems is a topological disorder which drives the moments formation and frustrates their directions in the liquid phase.Comment: 10 pages, RevTex 3.0, 24kb. 3 PS figures available on request from [email protected] The work has been presented at ERC ``Electronic Structire of Solids'' (Lunteren, The Netherlands, 9-14 September 1995

Assessment of coupled Zn concentration and natural stable isotope analyses of urine as a novel probe of Zn status

Zinc is a common trace metal in the human body, present in about 10% of proteins. Despite numerous roles of Zn in health and disease, there is still a need for a robust biomarker of Zn status. Many parameters have been proposed, with varying levels of success, with plasma Zn often favoured. This study investigates if Zn status can be assessed from the natural stable Zn isotope composition of urine. To this end, 60 urine samples were analysed from ten healthy participants. Remarkably, samples with lower Zn concentrations are systematically enriched in heavy Zn isotopes. Most of the low-Zn urine originated from individuals who omitted dairy, meat or both from their diets. When data for blood serum from age-matched, healthy individuals are compared with the urine results, the former plot at the extension of the urine trend at higher Zn concentrations and lighter isotope compositions. The observed co-variation of Zn isotope compositions with concentrations is indicative of an isotope fractionation system where both properties are controlled by the same processes. It is interpreted as arising from filtration and/or reabsorption processes within the kidney, which are associated with absorbed dietary Zn. The data suggest that the Zn in blood serum that is bound to low molecular weight molecules has an isotope composition distinct from total serum, due to the different affinities of molecular Zn-binding residues to heavy and light Zn isotopes. This technique provides additional information into an individual's Zn status compared to urine or plasma Zn levels alone

Elastic Behavior of a Two-dimensional Crystal near Melting

Using positional data from video-microscopy we determine the elastic moduli of two-dimensional colloidal crystals as a function of temperature. The moduli are extracted from the wave-vector-dependent normal mode spring constants in the limit $q\to 0$ and are compared to the renormalized Young's modulus of the KTHNY theory. An essential element of this theory is the universal prediction that Young's modulus must approach $16 \pi$ at the melting temperature. This is indeed observed in our experiment.Comment: 4 pages, 3 figure

An upper limit on the mass of the circumplanetary disk for DH Tau b

DH Tau is a young ($\sim$1 Myr) classical T Tauri star. It is one of the few young PMS stars known to be associated with a planetary mass companion, DH Tau b, orbiting at large separation and detected by direct imaging. DH Tau b is thought to be accreting based on copious H${\alpha}$ emission and exhibits variable Paschen Beta emission. NOEMA observations at 230 GHz allow us to place constraints on the disk dust mass for both DH Tau b and the primary in a regime where the disks will appear optically thin. We estimate a disk dust mass for the primary, DH Tau A of $17.2\pm1.7\,M_{\oplus}$, which gives a disk-to-star mass ratio of 0.014 (assuming the usual Gas-to-Dust mass ratio of 100 in the disk). We find a conservative disk dust mass upper limit of 0.42$M_{\oplus}$ for DH Tau b, assuming that the disk temperature is dominated by irradiation from DH Tau b itself. Given the environment of the circumplanetary disk, variable illumination from the primary or the equilibrium temperature of the surrounding cloud would lead to even lower disk mass estimates. A MCFOST radiative transfer model including heating of the circumplanetary disk by DH Tau b and DH Tau A suggests that a mass averaged disk temperature of 22 K is more realistic, resulting in a dust disk mass upper limit of 0.09$M_{\oplus}$ for DH Tau b. We place DH Tau b in context with similar objects and discuss the consequences for planet formation models.Comment: accepted for publication in A

Near-arcsecond resolution observations of the hot corino of the solar type protostar IRAS 16293-2422

Complex organic molecules have previously been discovered in solar type protostars, raising the questions of where and how they form in the envelope. Possible formation mechanisms include grain mantle evaporation, interaction of the outflow with its surroundings or the impact of UV/X-rays inside the cavities. In this Letter we present the first interferometric observations of two complex molecules, CH3CN and HCOOCH3, towards the solar type protostar IRAS16293-2422. The images show that the emission originates from two compact regions centered on the two components of the binary system. We discuss how these results favor the grain mantle evaporation scenario and we investigate the implications of these observations for the chemical composition and physical and dynamical state of the two components.Comment: 5 pages (apjemulate), 2 figures; accepted by ApJ