Attoyac Bayou GIS Inventory, Source Survey and Land Use Cover Report

The Attoyac Bayou watershed is one of many rural watersheds included in the Texas Water Quality Inventory and 303(d) List as an impaired water body due to excessive E. coli levels. In many cases the assessed data in these waterbodies is limited and information regarding potential sources of pollution or other factors that may influence the presence of pollutant sources is not readily available. To address this need, a comprehensive geographic information system (GIS) inventory of the watershed will be developed and will integrate numerous existing information resources into a single location. Generally, the GIS will illustrate waterbodies, roadways, permitted point-source dischargers, and other points of concern. Additionally, current land use/land cover (LULC) maps for the watershed will be updated. Existing LULC layers will be utilized as a starting point and will be re-delineated utilizing groundtruthed data points collected for the GIS inventory to verify the accuracy of the LULC map. Through the development of the GIS and update of the LULC maps, a physical source survey will also be conducted across the watershed to document the primary sources of bacteria in the watershed

Mixing by microorganisms in stratified fluids

We examine the vertical mixing induced by the swimming of microorganisms at low Reynolds and Péclet numbers in a stably stratified ocean, and show that the global contribution of oceanic microswimmers to vertical mixing is negligible. We propose two approaches to estimating the mixing efficiency, η, or the ratio of the rate of potential energy creation to the total rate-of-working on the ocean by microswimmers. The first is based on scaling arguments and estimates η in terms of the ratio between the typical organism size, a, and an intrinsic length scale for the stratified flow, l = (νκ/N2)1/4, where ν is the kinematic viscosity, κ the diffusivity, and N the buoyancy frequency. In particular, for small organisms in the relevant oceanic limit, a/l \u3c\u3c 1, we predict the scaling η ∼ (a/l)3. The second estimate of η is formed by solving the full coupled flow-stratification problem by modeling the swimmer as a regularized force dipole, and computing the efficiency numerically. Our computational results, which are examined for all ratios a/l, validate the scaling arguments in the limit a/l \u3c\u3c 1 and further predict η ≈ 1.2(a/l)3 for vertical swimming and η ≈ 0.15 (a/l)3 for horizontal swimming. These results, relevant for any stratified fluid rich in biological activity, imply that the mixing efficiency of swimming microorganisms in the ocean is at very most 8% and is likely smaller by at least two orders of magnitude

Aviation Safety as a Function of Pilot Experience: Rationale or Rationalization?

Editor\u27s Note: This article originally appeared in the Spring 1992 issue. It is reprinted due to its continuing value and timeliness. This study tests the effectiveness of an experience model in predicting aviation safety behavior. The elements comprising the model include: (a) flight hours, (b) ratings and flight characteristics, (c) career status, and (d) malfunction history. Data were derived from a random sample of U.S. pilots in Fall 1990 by means of a survey instrument. Significant variance in aviation safety is not explained by the model. The key predictor of safety behavior is the career status (i.e., certificate duration) of the pilot. Flight hours, ratings, and malfunction history are negatively and non-significantly associated with aviation safety. The research: (a) questions the use of these variables in ex post facto explanations of aviation safety, and (b) suggests a topology for examining safety behavior

Aviation Safety as a Function of Pilot Experience: Rationale or Rationalization?

This study tests the effectiveness of an experience model in predicting aviation safety behavior. The elements comprising the model include: (a) flight hours, (b) ratings and flight characteristics, (c) career status, and (d) malfunction history. Data were derived from a random sample of U.S. pilots in the fall of 1990 by means of a survey instrument. Significant variance in aviation safety is not explained by the model. The key predictor of safety behavior is the career status (i.e., certificate duration) of the pilot. Flight hours, ratings, and malfunction history are negatively and non-significantly associated with aviation safety. The research: (a) questions the use of these variables in ex post facto “explanations” of aviation safety, and (b) suggests a topology for examining safety behavior

Crawling scallop: Friction-based locomotion with one degree of freedom

c We demonstrate that friction-based locomotion with one-degree of freedom is possible. c Locomotion depends on breaking symmetry in both physical properties and kinematics. c This behavior is explained intuitively and through the system's equations of motion. c System locomotion is characterized for a range of physical and kinematic parameters. Fluid-based locomotion at low Reynolds number is subject to the constraints of the scallop theorem, which dictate that body kinematics identical under a time-reversal symmetry (in particular, those with a single degree of freedom) cannot display locomotion on average. The implications of the theorem naturally compel one to ask whether similar symmetry constraints exist for locomotion in different environments. In this work we consider locomotion along a surface where forces are described by isotropic Coulomb friction. To address whether motions with a single degree of freedom can lead to transport, we analyze a model system consisting of two bodies whose separation distance undergoes periodic time variations. The behavior of the two-body system is entirely determined by the kinematic specification of their separation, the friction forces, and the mass of each body. We show that the constraints of the scallop theorem can be escaped in frictional media if two asymmetry conditions are met at the same time: the frictional forces of each body against the surface must be distinct and the time-variation of the body-body separation must vary asymmetrically in time (so quick-slow or slowquick in the extension-contraction phases). Our results are demonstrated numerically and interpreted using asymptotic expansions

Attoyac Bayou Bacterial Source Tracking Report

The Attoyac Bayou, a sub-watershed within the Upper Neches River Watershed, extends approximately 82 miles through Rusk, Nacogdoches, San Augustine and Shelby counties before emptying into Sam Rayburn Reservoir. With several rural communities in the area, the majority of the land in the watershed is used for cattle and poultry operations, forestry or recreational and wildlife uses. The bayou is listed as an impaired water body on the Texas Integrated Report for Clean Water Act Sections 305(b) and 303(d) due to high levels of E. coli. Three monitoring stations managed by the Angelina & Neches River Authority, U.S. Geological Survey, and Texas Commission on Environmental Quality have provided water quality data on the bayou for a number of years. Beginning in 2000, data collected for E. coli have consistently shown elevated E. coli levels that exceed the applicable Texas Water Quality Standards. Through the Development of a Watershed Protection Plan for Attoyac Bayou project, additional water quality and stream flow data was collected to better understand E. coli loadings to the water body

Meson vacuum phenomenology in a three-flavor linear sigma model with (axial-)vector mesons

We study scalar, pseudoscalar, vector, and axial-vector mesons with non-strange and strange quantum numbers in the framework of a linear sigma model with global chiral $U(N_f)_L \times U(N_f)_R$ symmetry. We perform a global fit of meson masses, decay widths, as well as decay amplitudes. The quality of the fit is, for a hadronic model that does not consider isospin-breaking effects, surprisingly good. We also investigate the question whether the scalar $\bar{q}q$ states lie below or above 1 GeV and find the scalar states above 1 GeV to be preferred as $\bar{q}q$ states. Additionally, we also describe the axial-vector resonances as $\bar{q}q$ states.Comment: 29 pages, 4 figures, 3 tables. v2 is the updated version after referee remarks (dilaton field discussed, a new figure added