Organizations, Social Structure, and Historical Change: Toward an Historical Sociology of Organizations

http://deepblue.lib.umich.edu/bitstream/2027.42/50955/1/180.pd

A Response

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69076/2/10.1177_009770047700300402.pd

Organic management and soil health promote nutrient use efficiency

Introduction: Nitrogen is a key nutrient for plants. Often less than 50% of the applied nitrogen fertilisers is acquired by crops and nitrogen can be easily lost into the environment causing environmental pollution. Thus, to make agriculture more sustainable, it is important to investigate which factors determine nitrogen use efficiency (NUE). We investigated whether NUE was higher in organically managed soils compared to conventionally managed soils. Materials and Methods: To test this, we carried out a pot experiment in a greenhouse using soils from 16 fields. The soils were collected from conventionally (eight fields) or organically managed fields (eight fields). In addition, plants received two different 15N enriched N sources (mineral 15N or an organic fertiliser source, namely 15N enriched plant litter). Plants were harvested at three time points, and growth and nitrogen uptake were assessed at each time point. Results: NUE depended on management type and harvest time and the higher NUE of organically managed soils became more evident towards the second and third harvest. The average NUE at the end of the experiment was 93% and 55% for mineral fertiliser and litter application, respectively. This indicated that mineral fertilisers were immediately acquired by the plants, while nutrients in organic amendments had a lower availability and probably would be supplied later but steadier. Further, NUE was positively linked to microbial biomass, soil organic carbon content, and aggregate size, indicating that enhanced soil quality and soil health leads to a more efficient use of fertilisers. Conclusion: Our results indicate that organic management and soil health promote a more efficient use of nutrients and contribute to a more sustainable agriculture

One-dimensional thermal pressure-driven expansion of a pair cloud into an electron-proton plasma

Recently a filamentation instability was observed when a laser-generated pair cloud interacted with an ambient plasma. The magnetic field it drove was strong enough to magnetize and accelerate the ambient electrons. It is of interest to determine if and how pair cloud-driven instabilities can accelerate ions in the laboratory or in astrophysical plasma. For this purpose, the expansion of a localized pair cloud with the temperature 400 keV into a cooler ambient electron-proton plasma is studied by means of one-dimensional particle-in-cell (PIC) simulations. The cloud's expansion triggers the formation of electron phase space holes that accelerate some protons to MeV energies. Forthcoming lasers might provide the energy needed to create a cloud that can accelerate protons.Comment: 5 pages 4 figures, accepted for publication in Physics of Plasma

Interstellar Turbulence and Star Formation

We provide a brief overview of recent advances and outstanding issues in simulations of interstellar turbulence, including isothermal models for interior structure of molecular clouds and larger-scale multiphase models designed to simulate the formation of molecular clouds. We show how self-organization in highly compressible magnetized turbulence in the multiphase ISM can be exploited in simple numerical models to generate realistic initial conditions for star formation.Comment: 8 pages, 5 color figures; submitted to Proceedings of IAU Symposium 270 "Computational Star Formation" held in Barcelona, May 31 - June 4, 201

Marxism, Maoism, and Social Change

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68502/2/10.1177_009770047700300201.pd

Luminosity- and morphology-dependent clustering of galaxies

How does the clustering of galaxies depend on their inner properties like morphological type and luminosity? We address this question in the mathematical framework of marked point processes and clarify the notion of luminosity and morphological segregation. A number of test quantities such as conditional mark-weighted two-point correlation functions are introduced. These descriptors allow for a scale-dependent analysis of luminosity and morphology segregation. Moreover, they break the degeneracy between an inhomogeneous fractal point set and actual present luminosity segregation. Using the Southern Sky Redshift Survey~2 (da Costa et al. 1998, SSRS2) we find both luminosity and morphological segregation at a high level of significance, confirming claims by previous works using these data (Benoist et al. 1996, Willmer et al. 1998). Specifically, the average luminosity and the fluctuations in the luminosity of pairs of galaxies are enhanced out to separations of 15Mpc/h. On scales smaller than 3Mpc/h the luminosities on galaxy pairs show a tight correlation. A comparison with the random-field model indicates that galaxy luminosities depend on the spatial distribution and galaxy-galaxy interactions. Early-type galaxies are also more strongly correlated, indicating morphological segregation. The galaxies in the PSCz catalog (Saunders et al. 2000) do not show significant luminosity segregation. This again illustrates that mainly early-type galaxies contribute to luminosity segregation. However, based on several independent investigations we show that the observed luminosity segregation can not be explained by the morphology-density relation alone.Comment: aastex, emulateapj5, 20 pages, 13 figures, several clarifying comments added, ApJ accepte