Nonlinear Evolution of Instabilities Between Dust and Sound Waves

We study the non-linear evolution of the acoustic 'Resonant Drag Instability' (RDI) using numerical simulations. The acoustic RDI is excited in a dust-gas mixture when dust grains stream through gas, interacting with sound waves to cause a linear instability. We study this process in a periodic box by accelerating neutral dust with an external driving force. The instability grows as predicted by linear theory, eventually breaking into turbulence and saturating. As in linear theory, the non-linear behavior is characterized by three regimes - high, intermediate, and low wavenumbers - the boundary between which is determined by the dust-gas coupling strength and the dust-to-gas mass ratio. The high and intermediate wavenumber regimes behave similarly to one another, with large dust-to-gas ratio fluctuations while the gas remains largely incompressible. The saturated state is highly anisotropic: dust is concentrated in filaments, jets, or plumes along the direction of acceleration, with turbulent vortex-like structures rapidly forming and dissipating in the perpendicular directions. The low-wavenumber regime exhibits large fluctuations in gas and dust density, but the dust and gas remain more strongly coupled in coherent 'fronts' perpendicular to the acceleration. These behaviors are qualitatively different from those of dust 'passively' driven by external hydrodynamic turbulence, with no back-reaction force from dust onto gas. The virulent nature of these instabilities has interesting implications for dust-driven winds in a variety of astrophysical systems, including around cool-stars, in dusty torii around active-galactic-nuclei, and in and around giant molecular clouds.Comment: 11 pages, 9 figure

N-Fold Matrix Factorizations

The study of matrix factorizations began when they were introduced by Eisenbud; they have since been an important topic in commutative algebra. Results by Eisenbud, Buchweitz, and Yoshino relate matrix factorizations to maximal Cohen-Macaulay modules over hypersurface rings. There are many important properties of the category of matrix factorizations, as well as tensor product and hom constructions. More recently, Backelin, Herzog, Sanders, and Ulrich used a generalization of matrix factorizations -- so called N-fold matrix factorizations -- to construct Ulrich modules over arbitrary hypersurface rings. In this dissertation we build up the theory of N-fold matrix factorizations, proving analogues of many known properties of the classical setting. We also obtain tensor product and internal hom constructions using a special type of roots of unity and combinatorial results from Heller and Stephan. Finally, we prove generalizations of two of Eisenbud\u27s landmark results for the classical setting in the context of 3-fold matrix factorizations

Improving the Measurement and Analysis of African Agricultural Productivity: Promoting Complementarities between Micro and Macro Data

Productivity Analysis,

Non-linear evolution of instabilities between dust and sound waves

We study the non-linear evolution of the acoustic ‘resonant drag instability’ (RDI) using numerical simulations. The acoustic RDI is excited in a dust–gas mixture when dust grains stream through gas, interacting with sound waves to cause a linear instability. We study this process in a periodic box by accelerating neutral dust with an external driving force. The instability grows as predicted by linear theory, eventually breaking into turbulence and saturating. As in linear theory, the non-linear behaviour is characterized by three regimes – high, intermediate, and low wavenumbers – the boundary between which is determined by the dust–gas coupling strength and the dust-to-gas mass ratio. The high and intermediate wavenumber regimes behave similarly to one another, with large dust-to-gas ratio fluctuations while the gas remains largely incompressible. The saturated state is highly anisotropic: dust is concentrated in filaments, jets, or plumes along the direction of acceleration, with turbulent vortex-like structures rapidly forming and dissipating in the perpendicular directions. The low-wavenumber regime exhibits large fluctuations in gas and dust density, but the dust and gas remain more strongly coupled in coherent ‘fronts’ perpendicular to the acceleration. These behaviours are qualitatively different from those of dust ‘passively’ driven by external hydrodynamic turbulence, with no back-reaction force from dust on to gas. The virulent nature of these instabilities has interesting implications for dust-driven winds in a variety of astrophysical systems, including around cool stars, in dusty torii around active-galactic-nuclei, and in and around giant molecular clouds

Testing a prediction of the merger origin of early-type galaxies: a correlation between stellar populations and asymmetry

One of the key predictions of the merger hypothesis for the origin of early-type (elliptical and lenticular) galaxies is that tidally-induced asymmetric structure should correlate with signatures of a relatively young stellar population. Such a signature was found by Schweizer and Seitzer (1992; AJ, 104, 1039) at roughly 4sigma confidence. In this paper, we revisit this issue with a nearly ten-fold larger sample of 0.01<z<0.03 galaxies selected from the Two Micron All-Sky Survey and the Sloan Digital Sky Survey. We parameterize tidal structure using a repeatable algorithmic measure of asymmetry, and correlate this with color offset from the early-type galaxy color-magnitude relation. We recover the color offset-asymmetry correlation; furthermore, we demonstrate observationally for the first time that this effect is driven by a highly-significant trend towards younger ages at higher asymmetry values. We present a simple model for the evolution of early-type galaxies through gas-rich major and minor mergers that reproduces their observed build-up from z=1 to the present day and the distribution of present-day colors and ages. We show using this model that if both stellar populations and asymmetry were ideal `clocks' measuring the time since last major or minor gas-rich interaction, then we would expect a rather tight correlation between age and asymmetry. We suggest that the source of extra scatter is natural diversity in progenitor star formation history, gas content, and merger mass ratio, but quantitative confirmation of this conjecture will require sophisticated modeling. We conclude that the asymmetry-age correlation is in basic accord with the merger hypothesis, and indicates that an important fraction of the early-type galaxy population is affected by major or minor mergers at cosmologically-recent times.Comment: Astrophysical Journal, in press. 20 pages, 18 figure

5 steps to buying meat direct from the farm

Written by Jennifer Lutes (Field Specialist in Agricultural Business), Kyle Whittaker (County Engagement Specialist in Agriculture and Environment), Eric Meusch (Field Specialist in Livestock), Rachel Hopkins, (County Engagement Specialist in Agriculture and Environment), Amie Breshears (County Engagement Specialist in Agriculture and Environment)."If you plan to buy an animal to have processed into packaged meat, then the process can present some learning curves. This publication can help you navigate that process in five steps. Identify desired meat products. Purchase animal from livestock producer. Find a processor that fits your needs. Understand your costs. Consider timing."--Page 1.Jennifer Lutes (Field Specialist in Agricultural Business), Kyle Whittaker (County Engagement Specialist in Agriculture and Environment), Eric Meusch (Field Specialist in Livestock), Rachel Hopkins (County Engagement Specialist in Agriculture and Environment), Amie Breshears (County Engagement Specialist in Agriculture and Environment)New 5/22Includes bibliographical reference

Polyacrylamide in Glycerol Solutions From an Atomistic Perspective of the Energetics, Structure, and Dynamics

All-atom molecular dynamics is used to investigate the structural, energetic, and dynamical properties of polyacrylamide (PAM) oligomers of different lengths solvated in pure glycerol, a 90:10 glycerol–water mixture, and pure water. We predict that the oligomers’ globular structure is obtained only when the modeling strategy considers the solvent as a continuous background. Meanwhile, for all-atom modeled solvents, the glycerol solutions display a strong tendency of trapping the oligomers in instantaneous elongated random coiled structures that remain locked-in over tens of nanoseconds. In pure water, the oligomers acquire considerably shorter random coiled structures of increased flexibility. The all-atom force field, generalized amber force field, is modified by including restrained electrostatic potential atomic charges for both glycerol and PAM. Three PAM oligomer lengths containing 10, 20, and 30 monomers are considered in detail by monitoring the radius of gyration, end-to-end distance, intra-potential energy, and solvent–oligomer interaction energies for decades of nanoseconds. The density and radial distribution function of glycerol solutions are calculated when modeled with the modified atomic charges, showing a very good agreement with the experimental results at temperatures around 300 K. Glycerol has multiple applications, including its use in gel formation for PAM gel electrophoresis. Our findings are relevant for the design of sensors based on microfluidics and tailored pharmaceutical buffer solutions

The merger-driven evolution of massive galaxies

We explore the rate and impact of galaxy mergers on the massive galaxy population using the amplitude of the two-point correlation function on small scales for M > 5e10 M_sun galaxies from the COSMOS and COMBO-17 surveys. Using a pair fraction derived from the Sloan Digital Sky Survey as a low-redshift benchmark, the large survey area at intermediate redshifts allows us to determine the evolution of the close pair fraction with unprecedented accuracy for a mass-selected sample: we find that the fraction of galaxies more massive than 5e10M_sun in pairs separated by less than 30 kpc in 3D space evolves as F(z) = (0.0130+/-0.0019)x(1+z)^1.21+/-0.25 between z = 0 and z = 1.2. Assuming a merger time scale of 0.5 Gyrs, the inferred merger rate is such that galaxies with mass in excess of 1e11 M_sun have undergone, on average, 0.5 (0.7) mergers involving progenitor galaxies both more massive than 5e10 M_sun since z = 0.6 (1.2). We also study the number density evolution of massive red sequence galaxies using published luminosity functions and constraints on the M/L evolution from the fundamental plane. Moreover, we demonstrate that the measured merger rate of massive galaxies is sufficient to explain this observed number density evolution in massive red sequence galaxies since z = 1.Comment: Accepted in Ap