Engineering Commons^™

Ordination And Mapping Of Wetland Communities In Nebraska's Rainwater Basin Region, Michael C. Gilbert

US Army Corps of Engineers

Forty-seven Rainwater Basin wetlands of south-central Nebraska were evaluated to provide information on vegetation composition, species assemblages determined from direct and indirect ordination methodology, and community characteristics derived from wetlands mapping. Vegetation/soil relationships were evaluated from both vegetational stand and mapping data. Seasonal and year to year vegetation dynamics were evaluated for one study site, Harvard Marsh.

Ordination of vegetational data was accomplished by use of weighted averaging and detrended correspondence analysis. Weighted average ordination results indicated wetland status for the Fillmore, Scott and Massie soil series. Occurrence of upland vegetation on hydric soils and wetland vegetation on non-hydric soils …

Subsurface Transport Of Contaminants, John E. Mccarthy, John M. Zachara

US Department of Energy Publications

Contaminants originating from human activities have entered the subsurface environment through waste disposal practices, spills, and land application of chemicals. The establishment of effective disposal and isolation procedures for chemical wastes, the protection of public health, and the amelioration of subsurface contamination rely on the ability to predict the velocity at which contaminants move through the vadose (unsaturated) and saturated zones. However, attempts to describe and predict contaminant transport cannot succeed if major pathways and mechanisms for transport are not defined.

Most approaches to describing and predicting the movement of contaminants treat groundwater as a two-phase system in which contaminants …

Review Of Radial Dose Measurement Technique And Data, Matesh N. Varma

US Department of Energy Publications

Radial dose is the average energy deposited in a short length of cylindrical shell formed between radii r and r + dr, per unit mass. Here, r is the distance perpendicular to the trajectory of an incident charged particle. Radial dose profiles as a function of radial distance for charged particles have been used to interpret radiobiological data. This article reviews the technique for measuring radial dose distributions and the available data.

Energetic Electron Tracks And Dna Strand Breaks, A. Chatterjee, W. R. Holley

US Department of Energy Publications

A theoretical model with no adjustable parameters is presented to evaluate the strand break yields for incident electrons between 100 eV and 1 MeV. Indirect mechanisms as well as direct mechanisms are included for the production of strand breaks. The model includes the following features: (i) multiple scattering of low energy electrons; (ii) decay of hydroxyl radicals in an aqueous solution containing Tris buffer; (iii) Monte Carlo simulation of the motion of hydroxyl radicals for interaction with the DNA sites; and (iv) stochastic aspects of the direct ionization on the DNA sites and the use of oscillator strength of a …

The Katz Cell-Survival Model And Beams Of Heavy Charged Particles, Stanley B. Curtis

US Department of Energy Publications

In this paper, we describe how the Katz cell-survival model has been used to predict survival along the central axis of the dose vs depth curve of beams of heavy charged particles. Unmodified beams with sharp Bragg peaks as well as ridge-filter-modulated beams with spread Bragg peaks have been studied. The analysis in terms of this model leads to the definition of two coefficients, "ion kill" and "gamma kill", which characterize the radiation quality of the beams. In this way, the relative importance of the primary lind secondary (fragmentation) contributions can be assessed easily.

Setting the model parameter m equal …

Physical Aspects Of Charged Particle Track Structure, R. H. Ritchie, R. N. Hamm, J. E. Turner, H. A. Wright, J. C. Ashley, G. J. Banks

US Department of Energy Publications

A plasmon generated by a swift charged particle constitutes a coherent excitation about the particle track. We discuss the physics of the plasmon in condensed matter and its effects on electron transport in liquid water. Criteria for the existence of the plasmon III a given substance, Its characteristics when generated by a swift charged particle, its representation in impact parameter space, and its decay into localized excitations are described. We describe how plasmon excitation and decay are implemented in our Monte Carlo code, OREC, and how track structure calculations are affected by this mode.