Nutrient Limitation of Periphyton in a Spring-Fed, Coastal Stream in Florida, USA.

There is strong evidence to suggest that ground-water nitrate concentrations have increased in recent years and further increases are expected along portions of the central Gulf coast of Florida. Much of the nitrate enriched groundwater is discharged into surface waters through numerous freshwater springs that are characteristic of the area and the potential for eutrophication of their receiving waters is a legitimate concern. To test the potential effects of elevated nutrient concentrations on the periphyton community an in situ nutrient addition experiment was conducted in the spring-fed Chassahowitzka River, FL, USA, during the summer of 1999. Plastic tubes housing arrays of glass microscope slides were suspended in the stream. Periphyton colonizing the microscope slides was subjected to artificial increases in nitrogen, phosphorus or a combination of both. Slides from each tube were collected at 3- to 4- day intervals and the periphyton communities were measured for chlorophyll concentration. The addition of approximately 10 μg/L of phosphate above ambient concentrations significantly increased the amount of periphyton on artificial substrates relative to controls; the addition of approximately 100 μg/L of nitrate above ambient concentrations did not. The findings from this experiment implicated phosphorus, rather than nitrogen, as the nutrient that potentially limits periphyton growth in this system.(PDF contains 4 pages.

Effects of Uniaxial Stress on Antiferromagnetic Moment in the Heavy Electron Compound URu_2Si_2

We have performed the elastic neutron scattering experiments under uniaxial stress \sigma along the tetragonal [100], [110] and [001] directions for URu2Si2. For \sigma // [100] and [110], the antiferromagnetic moment \mu_o is strongly enhanced from 0.02 \mu_B (\sigma=0) to 0.22 \mu_B (\sigma=2.5 kbar) at 1.5 K. The rate of increase d\mu_o/d\sigma is roughly estimated to be ~ 0.1 \mu_B/kbar, which is much larger than that for the hydrostatic pressure (~ 0.025 \mu_B/kbar). Above 2.5 kbar, \mu_o shows a tendency to saturate similar to the behavior in the hydrostatic pressure. For \sigma // [001], on the other hand, \mu_o shows only a slight increase to 0.028 \mu_B (\sigma = 4.6 kbar) with a rate of ~ 0.002 \mu_B/kbar. The observed anisotropy suggests that the competition between the hidden order and the antiferromagnetic state in URu2Si2 is strongly coupled with the tetragonal four-fold symmetry and the c/a ratio, or both.Comment: 3 pages, 3 eps figures, Proceedings of Int. Conf. on Strongly Correlated Electrons with Orbital Degrees of Freedom (Sendai, Japan, September 11-14, 2001

Student perceptions of laboratory classroom activities and experimental physics practice

We report results from a study designed to identify links between undergraduate students' views about experimental physics and their engagement in multiweek projects in lab courses. Using surveys and interviews, we explored whether students perceived particular classroom activities to be features of experimental physics practice. We focused on 18 activities, including maintaining lab notebooks, fabricating parts, and asking others for help. Interviewees identified activities related to project execution as intrinsic to experimental physics practice based on high prevalence of those activities in interviewees' own projects. Fabrication-oriented activities were identified as conditional features of experimentation based on differences between projects, which interviewees attributed to variations in project resources. Interpersonal activities were also viewed as conditional features of experimentation, dependent upon one's status as novice or expert. Our findings suggest that students' views about experimental physics are shaped by firsthand experiences of their own projects and secondhand experiences of those of others.Comment: 6 pages, 1 table, accepted for publication in 2020 Physics Education Research Conference Proceeding

Vitamin D with Calcium reduces mortality: patient level pooled analysis of 70,528 patients from eight major vitamin D trials

Introduction: Vitamin D may affect multiple health outcomes. If so, an effect on mortality is to be expected. Using pooled data from randomized controlled trials, we performed individual patient data (IPD) and trial level meta-analyses to assess mortality among participants randomized to either vitamin D alone or vitamin D with calcium. Subjects and Methods: Through a systematic literature search, we identified 24 randomized controlled trials reporting data on mortality in which vitamin D was given either alone or with calcium. From a total of 13 trials with more than 1000 participants each, eight trials were included in our IPD analysis. Using a stratified Cox regression model, we calculated risk of death during 3 yr of treatment in an intention-to-treat analysis. Also, we performed a trial level meta-analysis including data from all studies. Results: The IPD analysis yielded data on 70,528 randomized participants (86.8% females) with a median age of 70 (interquartile range, 62–77) yr. Vitamin D with or without calcium reduced mortality by 7% [hazard ratio, 0.93; 95% confidence interval (CI), 0.88–0.99]. However, vitamin D alone did not affect mortality, but risk of death was reduced if vitamin D was given with calcium (hazard ratio, 0.91; 95% CI, 0.84–0.98). The number needed to treat with vitamin D plus calcium for 3 yr to prevent one death was 151. Trial level meta-analysis (24 trials with 88,097 participants) showed similar results, i.e. mortality was reduced with vitamin D plus calcium (odds ratio, 0.94; 95% CI, 0.88–0.99), but not with vitamin D alone (odds ratio, 0.98; 95% CI, 0.91–1.06). Conclusion: Vitamin D with calcium reduces mortality in the elderly, whereas available data do not support an effect of vitamin D alone

Shoot growth of woody trees and shrubs is predicted by maximum plant height and associated traits

1. The rate of elongation and thickening of individual branches (shoots) varies across plant species. This variation is important for the outcome of competition and other plant-plant interactions. Here we compared rates of shoot growth across 44 species from tropical, warm temperate, and cool temperate forests of eastern Australia.2. Shoot growth rate was found to correlate with a suite of traits including the potential height of the species, xylem-specific conductivity, leaf size, leaf area per xylem cross-section, twig diameter (at 40 cm length), wood density and modulus of elasticity.3. Within this suite of traits, maximum plant height was the clearest correlate of growth rates, explaining 50 to 67% of the variation in growth overall (p p 4. Growth rates were not strongly correlated with leaf nitrogen or leaf mass per unit leaf area.5. Correlations between growth and maximum height arose both across latitude (47%, p p p p < 0.0001), reflecting intrinsic differences across species and sites

Moments of the Virtual Photon Structure Function

The photon structure function is a useful testing ground for QCD. It is perturbatively computable apart from a contribution from what is usually called the hadronic component of the photon. There have been many proposals for this nonperturbative part of the real photon structure function. By studying moments of the virtual photon structure function, we explore the extent to which these proposed nonperturbative contributions can be identified experimentally.Comment: LaTeX, 16 pages + 14 compressed and uuencoded postscript figures, UMN-TH-1111/9

Neutron Scattering Study on Competition between Hidden Order and Antiferromagnetism in U(Ru_{1-x}Rh_x)_2Si_2 (x <= 0.05)

We have performed elastic and inelastic neutron scattering experiments on the solid solutions U(Ru_{1-x}Rh_x)_2Si_2 for the Ru rich concentrations: x=0, 0.01, 0.02, 0.025, 0.03, 0.04 and 0.05. Hidden order is suppressed with increasing x, and correspondingly the onset temperature T_m (~ 17.5 K at x=0) of weak antiferromagnetic (AF) Bragg reflection decreases. For x=0.04 and 0.05, no magnetic order is detected in the investigated temperature range down to 1.4 K. In the middle range, 0.02 <= x <= 0.03, we found that the AF Bragg reflection is strongly enhanced. At x=0.02, this takes place at ~ 7.7 K (=T_M), which is significantly lower than T_m (~ 13.7 K). T_M increases with increasing x, and seems to merge with T_m at x=0.03. If the AF state is assumed to be homogeneous, the staggered moment \mu_o estimated at 1.4 K increases from 0.02(2) \mu_B/U (x=0) to 0.24(1) \mu_B/U (x=0.02). The behavior is similar to that observed under hydrostatic pressure (\mu_o increases to ~ 0.25 \mu_B/U at 1.0 GPa), suggesting that the AF evolution induced by Rh doping is due to an increase in the AF volume fraction. We also found that the magnetic excitation observed at Q=(1,0,0) below T_m disappears as T is lowered below T_M.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp

Effect of Pressure on Tiny Antiferromagnetic Moment in the Heavy-Electron Compound URu_2Si_2

We have performed elastic neutron-scattering experiments on the heavy-electron compound URu_2Si_2 for pressure P up to 2.8 GPa. We have found that the antiferrmagnetic (100) Bragg reflection below T_m ~ 17.5 K is strongly enhanced by applying pressure. For P < 1.1 GPa, the staggered moment mu_o at 1.4 K increases linearly from ~ 0.017(3) mu_B to ~ 0.25(2) mu_B, while T_m increases slightly at a rate ~ 1 K/GPa, roughly following the transition temperature T_o determined from macroscopic anomalies. We have also observed a sharp phase transition at P_c ~ 1.5 GPa, above which a 3D-Ising type of antiferromagnetic phase (mu_o ~ 0.4 mu_B) appears with a slightly reduced lattice constant.Comment: RevTeX, 4 pages, 4 eps figures, accepted for publication in Phys. Rev. Let

Forest structure, diversity, and primary production in relation to disturbance severity

Differential disturbance severity effects on forest vegetation structure, species diversity, and net primary production (NPP) have been long theorized and observed. Here, we examined these factors concurrently to explore the potential for a mechanistic pathway linking disturbance severity, changes in light environment, leaf functional response, and wood NPP in a temperate hardwood forest.Using a suite of measurements spanning an experimental gradient of tree mortality, we evaluated the direction and magnitude of change in vegetation structural and diversity indexes in relation to wood NPP. Informed by prior observations, we hypothesized that forest structural and species diversity changes and wood NPP would exhibit either a linear, unimodal, or threshold response in relation to disturbance severity. We expected increasing disturbance severity would progressively shift subcanopy light availability and leaf traits, thereby coupling structural and species diversity changes with primary production.Linear or unimodal changes in three of four vegetation structural indexes were observed across the gradient in disturbance severity. However, disturbance‐related changes in vegetation structure were not consistently correlated with shifts in light environment, leaf traits, and wood NPP. Species diversity indexes did not change in response to rising disturbance severity.We conclude that, in our study system, the sensitivity of wood NPP to rising disturbance severity is generally tied to changing vegetation structure but not species diversity. Changes in vegetation structure are inconsistently coupled with light environment and leaf traits, resulting in mixed support for our hypothesized cascade linking disturbance severity to wood NPP.We examined multiple metrics of vegetation structural and biological diversity concurrently to explore the potential for a mechanistic pathway linking disturbance severity, changes in light environment, leaf functional response, and wood NPP in a temperate hardwood forest. Significant linear or unimodal changes in three of four vegetation structural indexes were observed across the gradient in disturbance severity, although disturbance‐related changes in vegetation structure were not consistently correlated with shifts in light environment, leaf traits, and wood NPP. We conclude that, in our study system, the sensitivity of wood NPP to rising disturbance severity is generally tied to changing vegetation structure but not species diversity.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155474/1/ece36209.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155474/2/ece36209_am.pd

Evolution of Star Forming and Active Galaxies in Nearby Clusters

(Abridged) We have used optical spectroscopy to investigate the radio- selected active galaxy populations in a sample of 20 nearby Abell clusters. The spectra were used to characterize the galaxies as AGN or galaxies forming stars at rates comparable to or greater than the Milky Way. A significant population of star forming galaxies with large amounts of nuclear dust extinction were revealed. This extinction eliminates bluer emission lines such as [OII], meaning their star formation could easily be overlooked in studies which focus on such features. Around 20% of cluster star forming galaxies have such spectra, and their radial distribution suggests they are the consequence of some cluster environmental effect. We note that galaxies of this type may be identified using their 4000-Angstrom break strengths. We also find that discrepancies in reported radio luminosity functions for AGN are likely the result of classification differences. There exists a large population of cluster galaxies whose radio fluxes, FIR fluxes, and optical magnitudes suggest their radio emission may be powered by stars, yet their spectra lack emission lines. Understanding the nature of these galaxies is critical to assessing the importance of AGN in the radio luminosity function at low luminosities.Comment: 36 pages with figures, to appear in the Astronomical Journa