The Formation of Fragments at Corotation in Isothermal Protoplanetary Disks

Numerical hydrodynamics simulations have established that disks which are evolved under the condition of local isothermality will fragment into small dense clumps due to gravitational instabilities when the Toomre stability parameter $Q$ is sufficiently low. Because fragmentation through disk instability has been suggested as a gas giant planet formation mechanism, it is important to understand the physics underlying this process as thoroughly as possible. In this paper, we offer analytic arguments for why, at low $Q$, fragments are most likely to form first at the corotation radii of growing spiral modes, and we support these arguments with results from 3D hydrodynamics simulations.Comment: 21 pages, 1 figur

Electronic Data Interchange Agreements: Private Contracting Toward a Global Environment

With the growth in the use of electronic communications technologies to communicate important business and trade information, the size of the earth, although it may remain at the present 7,900 miles in diameter, is rapidly shrinking. In a matter of seconds, commercial trade data can be exchanged between parties thousands of miles apart, leading to the establishment of new business relationships. In the emerging new global economy, data, information, goods, and services are being exchanged internationally. No longer are parties to a commercial transaction bound by artificial national boundaries with their accompanying sets of domestic legal rules. Over the past few years, rule-making on the international scene the drafting or crafting of several international codifications - has contributed to the evolution of a commercial code to govern international commercial transactions

Electronic Data Interchange Agreements: Private Contracting Toward a Global Environment

With the growth in the use of electronic communications technologies to communicate important business and trade information, the size of the earth, although it may remain at the present 7,900 miles in diameter, is rapidly shrinking. In a matter of seconds, commercial trade data can be exchanged between parties thousands of miles apart, leading to the establishment of new business relationships. In the emerging new global economy, data, information, goods, and services are being exchanged internationally. No longer are parties to a commercial transaction bound by artificial national boundaries with their accompanying sets of domestic legal rules. Over the past few years, rule-making on the international scene the drafting or crafting of several international codifications - has contributed to the evolution of a commercial code to govern international commercial transactions

Validation of the particle size distribution obtained with the laser in-situ scattering and transmission (LISST) meter in flow-through mode

High spatial and temporal resolution estimates of the particle size distribution (PSD) in the surface ocean can enable improved understanding of biogeochemistry and ecosystem dynamics. Oceanic PSD measurements remain rare due to the time-consuming, manual sampling methods of common particle sizing instruments. Here, we evaluate the utility of measuring particle size data at high spatial resolution with a commercially-available submersible laser di raction particle sizer (LISST-100X, Sequoia Scientific), operating in an automated mode with continuously flowing seawater. The LISST PSD agreed reasonably well with discrete PSD measurements obtained with a Coulter Counter and data from the flow-through sampling Imaging Flow-Cytobot, validating our methodology. Total particulate area and Volume derived from the LISST PSD agreed well with beam-attenuation and particulate organic carbon respectively, further validating the LISST PSD. Furthermore, When compared to the measured spectral characteristics of particulate beam attenuation, we find a significant correlation. However, no significant relationship between the PSD and spectral particulate backscattering was found

Turbulence-plankton interactions : a new cartoon

Author Posting. © John Wiley & Sons, 2009. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Marine Ecology 30 (2009): 133-150, doi:10.1111/j.1439-0485.2009.00288.x.Climate change will alter turbulence intensity, motivating greater attention to mechanisms of turbulence effects on organisms. Many analytic and analog models used to simulate and assess effects of turbulence on plankton rely on a one-dimensional simplification of the dissipative scales of turbulence, i.e., simple, steady, uniaxial shears, as produced in Couette vessels. There shear rates are constant and spatially uniform, and hence so is vorticity. Studies in such Couette flows have greatly informed, spotlighting stable orientations of nonspherical particles and predictable, periodic, rotational motions of steadily sheared particles in Jeffery orbits that steepen concentration gradients around nutrient-absorbing phytoplankton and other chemically (re)active particles. Over the last decade, however, turbulence research within fluid dynamics has focused on the structure of dissipative vortices in space and time and on spatially and temporally varying 2 vorticity fields in particular. Because steadily and spatially uniformly sheared flows are exceptional, so therefore are stable orientations for particles in turbulent flows. Vorticity gradients, finite net diffusion of vorticity and small radii of curvature of streamlines are ubiquitous features of turbulent vortices at dissipation scales that are explicitly excluded from simple, steady Couette flows. All of these flow components contribute instabilities that cause rotational motions of particles and so are important to simulate in future laboratory devices designed to assess effects of turbulence on nutrient uptake, particle coagulation and predatorprey encounter in the plankton. The Burgers vortex retains these signature features of turbulence and provides a simplified “cartoon” of vortex structure and dynamics that nevertheless obeys the Navier-Stokes equations. Moreover, this idealization closely resembles many dissipative vortices observed in both the laboratory and the field as well as in direct numerical simulations of turbulence. It is simple enough to allow both simulation in numerical models and fabrication of analog devices that selectively reproduce its features. Exercise of such numerical and analog models promises additional insights into mechanisms of turbulence effects on passive trajectories and local accumulations of both living and nonliving particles, into solute exchange with living and nonliving particles and into more subtle influences on sensory processes and swimming trajectories of plankton, including demersal organisms and settling larvae in turbulent bottom boundary layers. The literature on biological consequences of vortical turbulence has focused primarily on the smallest, Kolmogorov-scale vortices of length scale η. Theoretical dissipation spectra and direct numerical simulation, however, indicate that typical dissipative vortices with radii of 7η to 8η, peak azimuthal speeds of order 1 cm s-1 and lifetimes of order 10 s as a minimum (and much longer for moderate pelagic turbulence intensities) deserve new attention in studies of biological effects of turbulence.This research was supported by collaborative U.S. National Science Foundation grant (OCE- 0724744) to Jumars and Karp-Boss