University of Notre Dame

About: University of Notre Dame is a education organization based out in Notre Dame, Indiana, United States. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 22238 authors who have published 55201 publications receiving 2032925 citations. The organization is also known as: University of Notre Dame du Lac & University of Notre Dame, South Bend.

Transport and fate of nitrate in headwater agricultural streams in Illinois.

Abstract: Nitrogen inputs to the Gulf of Mexico have increased during recent decades and agricultural regions in the upper Midwest, such as those in Illinois, are a major source of N to the Mississippi River. How strongly denitrification affects the transport of nitrate (NO(3)-N) in Illinois streams has not been directly assessed. We used the nutrient spiraling model to assess the role of in-stream denitrification in affecting the concentration and downstream transport of NO(3)-N in five headwater streams in agricultural areas of east-central Illinois. Denitrification in stream sediments was measured approximately monthly from April 2001 through January 2002. Denitrification rates tended to be high (up to 15 mg N m(-2) h(-1)), but the concentration of NO(3)-N in the streams was also high (>7 mg N L(-1)). Uptake velocities for NO(3)-N (uptake rate/concentration) were lower than reported for undisturbed streams, indicating that denitrification was not an efficient N sink relative to the concentration of NO(3)-N in the water column. Denitrification uptake lengths (the average distance NO(3)-N travels before being denitrified) were long and indicated that denitrification in the streambed did not affect the transport of NO(3)-N. Loss rates for NO(3)-N in the streams were <5% d(-1) except during periods of low discharge and low NO(3)-N concentration, which occurred only in late summer and early autumn. Annually, most NO(3)-N in these headwater sites appeared to be exported to downstream water bodies rather than denitrified, suggesting previous estimates of N losses through in-stream denitrification may have been overestimated.

Spectroscopy and Dynamics of Nanometer-Sized Noble Metal Particles

Abstract: Electron−phonon coupling in 11 ± 2 nm diameter Au particles and 10 ± 3 nm and 50 ± 10 nm Ag particles has been examined by ultrafast pump−probe spectroscopy. The observed relaxation times are strongly dependent on the pump laser power. At the lowest pump powers used, the time constants for relaxation are 0.8 ± 0.1 ps for the 11 nm Au particles, 1.1 ± 0.1 ps for the 10 nm Ag particles, and 1.0 ± 0.1 ps for the 50 nm Ag particles. The measured relaxation times are similar to those for bulk metals, which implies that there are no size-dependent effects in the dynamics for particles in this size region. The transient absorption/bleach recovery signals for the particles were modeled using the theory developed by Rosei et al. (Surf. Sci. 1973, 37, 689). These calculations yield the transient absorption spectrum as a function of the temperature of the electron distribution. The time dependence of the electronic temperature after pump laser excitation was calculated using the two-temperature model for electron−ph...

Effect of Analysts' Optimism on Estimates of the Expected Rate of Return Implied by Earnings Forecasts

Abstract: Recent literature has used analysts' earnings forecasts, which are known to be optimistic, to estimate implied expected rates of return, yielding upwardly biased estimates. We estimate that the bias, computed as the difference between the estimates of the implied expected rate of return based on analysts' earnings forecasts and estimates based on current earnings realizations, is 2.84%. The importance of this bias is illustrated by the fact that several extant studies estimate an equity premium in the vicinity of 3%, which would be eliminated by the removal of the bias. We illustrate the point that cross-sample differences in the bias may lead to the erroneous conclusion that cost of capital differs across these samples by showing that analysts' optimism, and hence, bias in the implied estimates of the expected rate of return, differs with firm size and with analysts' recommendation. As an important aside, we show that the bias in a value-weighted estimate of the implied equity premium is 1.60% and that the unbiased value-weighted estimate of this premium is 4.43%.

The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10 to 100 au

Abstract: Author(s): Nielsen, EL; De Rosa, RJ; Macintosh, B; Wang, JJ; Ruffio, JB; Chiang, E; Marley, MS; Saumon, D; Savransky, D; Mark Ammons, S; Bailey, VP; Barman, T; Blain, C; Bulger, J; Burrows, A; Chilcote, J; Cotten, T; Czekala, I; Doyon, R; Duchene, G; Esposito, TM; Fabrycky, D; Fitzgerald, MP; Follette, KB; Fortney, JJ; Gerard, BL; Goodsell, SJ; Graham, JR; Greenbaum, AZ; Hibon, P; Hinkley, S; Hirsch, LA; Hom, J; Hung, LW; Ilene Dawson, R; Ingraham, P; Kalas, P; Konopacky, Q; Larkin, JE; Lee, EJ; Lin, JW; Maire, J; Marchis, F; Marois, C; Metchev, S; Millar-Blanchaer, MA; Morzinski, KM; Oppenheimer, R; Palmer, D; Patience, J; Perrin, M; Poyneer, L; Pueyo, L; Rafikov, RR; Rajan, A; Rameau, J; Rantakyro, FT; Ren, B; Schneider, AC; Sivaramakrishnan, A; Song, I; Soummer, R; Tallis, M; Thomas, S; Ward-Duong, K; Wolff, S | Abstract: We present a statistical analysis of the first 300 stars observed by the Gemini Planet Imager Exoplanet Survey. This subsample includes six detected planets and three brown dwarfs; from these detections and our contrast curves we infer the underlying distributions of substellar companions with respect to their mass, semimajor axis, and host stellar mass. We uncover a strong correlation between planet occurrence rate and host star mass, with stars M ∗ g1.5 M o more likely to host planets with masses between 2 and 13M Jup and semimajor axes of 3-100 au at 99.92% confidence. We fit a double power-law model in planet mass (m) and semimajor axis (a) for planet populations around high-mass stars (M ∗ g1.5 M o) of the form , finding α = -2.4 +0.8 and β = -2.0 +0.5, and an integrated occurrence rate of % between 5-13M Jup and 10-100 au. A significantly lower occurrence rate is obtained for brown dwarfs around all stars, with % of stars hosting a brown dwarf companion between 13-80M Jup and 10-100 au. Brown dwarfs also appear to be distributed differently in mass and semimajor axis compared to giant planets; whereas giant planets follow a bottom-heavy mass distribution and favor smaller semimajor axes, brown dwarfs exhibit just the opposite behaviors. Comparing to studies of short-period giant planets from the radial velocity method, our results are consistent with a peak in occurrence of giant planets between ∼1 and 10 au. We discuss how these trends, including the preference of giant planets for high-mass host stars, point to formation of giant planets by core/pebble accretion, and formation of brown dwarfs by gravitational instability.

What’s so Hot about Electrons in Metal Nanoparticles?

Abstract: Metal nanoparticles are excellent light absorbers. The absorption processes create highly excited electron–hole pairs, and recently there has been interest in harnessing these hot charge carriers for photocatalysis and solar energy conversion applications. The goal of this Perspective is to describe the dynamics and energy distribution of the charge carriers produced by photon absorption and the implications for the photocatalysis mechanism. We will also discuss how spectroscopy can be used to provide insight into the coupling between plasmons and molecular resonances. In particular, the analysis shows that the choice of material and shape of the nanocrystal can play a crucial role in hot electron generation and coupling between plasmons and molecular transitions. The detection and even calculation of many-body hot-electron processes in the plasmonic systems with continuous spectra of electrons and short lifetimes are challenging, but at the same time they are very interesting from the points of view of b...