Vehicle impacts on the environment at different spatial scales: observations in west central Georgia, USA

Roads and vehicles change the environmental conditions in which they occur. One way to categorize these effects is by the spatial scale of the cause and the impacts. Roads may be viewed from the perspective of road segments, the road network, or roads within land ownership or political boundaries such as counties. This paper examines the hypothesis that the observable impacts of roads on the environment depend on spatial resolution. To examine this hypothesis, the environmental impacts of vehicles and roads were considered at four scales in west central Georgia in and around Fort Benning: a second-order catchment, a third-order watershed, the entire military installation, and the five-county region including Fort Benning. Impacts from an experimental path made by a tracked vehicle were examined in the catchment. Land-cover changes discerned through remote sensing data over the past three decades were considered at the watershed and installation scales. A regional simulation model was used to project changes in land cover for the five-county region. Together these analyses provide a picture of the how environmental impacts of roads and vehicles can occur at different spatial scales. Following tracked vehicle impact with a D7 bulldozer, total vegetation cover responded quickly, but the plant species recovered differently. Soils were compacted in the top 10 cm and are likely to remain so for some time. Examining the watershed from 1974 to 1999 revealed that conversion from forest to nonforest was highest near unpaved roads and trails. At the installation scale, major roads as well as unpaved roads and trails were associated with most of the conversion from forest to nonforest. For the five-county region, most of the conversion from forest to nonforest is projected to be due to urban spread rather than direct road impacts. The study illustrates the value of examining the effects of roads at several scales of resolution and shows that road impacts in west central Georgia are most important at local to subregional scales. The insights from these analyses led to several questions about resource management at different spatial scales.     

Simultaneous velocity and concentration field measurements of passive-scalar mixing in a confined rectangular jet

Simultaneous velocity and concentration fields in a confined liquid-phase rectangular jet with a Reynolds number based on the hydraulic diameter of 50,000 (or 10,000 based on the velocity difference between streams and the jet exit dimension) and a Schmidt number of 1,250 were obtained by means of a combined particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) system. Data were collected at the jet exit and six further downstream locations. The velocity and concentration field data were analyzed for flow statistics such as turbulent fluxes, turbulent viscosity and diffusivity, and turbulent Schmidt number (Sc _T ). The streamwise turbulent flux was found to be larger than the transverse turbulent flux, and the mean concentration gradient was not aligned with the turbulent flux vector. The average Sc _T was found to vary both in streamwise and in cross stream directions and had a mean value around 0.8, a value consistent with the literature. Spatial correlation fields of turbulent fluxes and concentration were then determined. The R _u′ϕ′ correlation was elliptical in shape with a major axis tilted downward with respect to the streamwise axis, whereas the R _v′ϕ′ correlation was an ellipse with a major axis aligned with the cross-stream direction. Negative regions of R _u′ϕ′ were observed in the outer streams, and these negatively correlated regions decayed with downstream distance and finally disappeared altogether. The R _ϕ′ϕ′ correlation field was found to be an ellipse with the major axis inclined at about 45° with respect to the streamwise direction. Linear stochastic estimation was used to interpret spatial correlation data and to determine conditional flow structures. It is believed that a vortex street formed near the splitter plate is responsible for the negatively correlated region observed in the R _u′ϕ′ spatial correlations of turbulent fluxes. A positive concentration fluctuation event was observed to correspond to a finger of nearly uniform concentration fluid reaching out into the outer stream, whereas a negative event corresponds to a pocket of nearly uniform fluid being entrained from the outer stream into the center jet region. Large-scale vortical structures were observed in the conditional velocity fields with an elliptical shape and a streamwise major axis. The growth of the structure size increased linearly initially but then grew more slowly as the flow transitioned toward channel flow. Support of this work was provided by the National Science Foundation through grants CTS-9985678 and CTS-0336435 and by the Dow Chemical Company. The author greatly acknowledge Charles Lipp at Dow Chemical and Ken Junk at Emerson Fisher for their valuable assistance in the design and construction of the flow system.     

What''s new with the XYZ mesons?

I review some of the recent experimental results on the so-called XYZ mesons.     

Na2TiGeO5: Crystal structure stability at low temperature and high pressure

The temperature evolution of the lattice parameters measured from 295 to 125 K exhibits a small instability below T_c≈278 K, indicating ferroelastic properties of Na₂TiGeO₅. The behavior is related to the specific crystal structure built of polyhedral layers with shared TiO₅ pyramids and GeO₄ tetrahedra, alternating with layers of Na⁺ cations. Antiparallel alignment of the short apical titanyl bond in adjacent rows of the polyhedral layer gives rise to spontaneous strain, when a distortion of the TiO₅ groups occurs. Single-crystal structures determined at room temperature and 120 K suggest that {1 1 0} domains, developing below T_c, entail a tetragonal-to-orthorhombic symmetry change. The mechanism is attributed to a shortening of the O–O distance between the polyhedral layers, and to minor shifts of the positions of the Ti atoms and the correlated oxygen atoms along the c-axis. The structure distortion, however, is too small to allow any unambiguous determination of the symmetry-breaking effects. The bulk modulus and its pressure derivative have been determined as B₀=89(2) GPa and . A pressure-induced phase transformation takes place at P_c≈12.5 GPa, presumably to an orthorhombic structure. The pressure effect on the transition temperature is given by ΔT_c/ΔP≈1.76 K/GPa.     

Measurement and imaging of supersonic combustion in a model scramjet engine

Results of tests performed in a free-piston shock tunnel on a model scramjet engine are presented. Two conditions which differed in Mach number were tested. Flow at the lower Mach number condition was achieved using a variable-angle diffuser. Shadowgraph images and floor static pressure measurements were obtained, the latter used as the basis of a finite-difference calculation of flow properties in the scramjet. Received 9 May 1998 / Accepted 30 September 1998     

Bottom-Up Design of a Copper–Ruthenium Nanoparticulate Catalyst for Low-Temperature Ammonia Oxidation

A novel nanoparticulate catalyst of copper (Cu) and ruthenium (Ru) was designed for low-temperature ammonia oxidation at near-stoichiometric mixtures using a bottom-up approach. A synergistic effect of the two metals was found. An optimum CuRu catalyst presents a reaction rate threefold higher than that for Ru and forty-fold higher than that for Cu. X-ray absorption spectroscopy suggests that in the most active catalyst Cu forms one or two monolayer thick patches on Ru and the catalysts are less active once 3D Cu islands form. The good performance of the tuned Cu/Ru catalyst is attributed to changes in the electronic structure, and thus the altered adsorption properties of the surface Cu sites.     

Dimensions of prevalent continuous functions

Let K be a compact subset of ${\mathbb{R}^{d}}$ and write C(K) for the family of continuous functions on K. In this paper we study different fractal and multifractal dimensions of functions in C(K) that are generic in the sense of prevalence. We first prove a number of general results, namely, for arbitrary ??dimension?? functions ${\Delta:C(K) \to \mathbb{R}}$ satisfying various natural scaling conditions, we obtain formulas for the ??dimension?? ??(f) of a prevalent function f in C(K); this is the contents of Theorems 1.1?C1.3. By applying Theorems 1.1?C1.3 to appropriate choices of ?? we obtain the following results: we compute the (lower and upper) local dimension of a prevalent function f in C(K); we compute the (lower or upper) H?lder exponent at a point x of a prevalent function f in C(K); finally, we compute the (lower or upper) Renyi dimensions of a prevalent function f in C(K). Perhaps surprisingly, in many cases our results are very different from the corresponding results for continuous functions that are generic in the sense of Baire category.