Magnetic Environments of Young Stellar Objects

We report on early results of magnetic field measurements towards a sample of young stellar objects. The results show a variety of field configurations, some of which can be explained by conventional models, while others cannot. We find that the field in some cases is curved over large scales and influenced by the gas kinematics in the local environment. This implies that, at these scales at least, the magnetic field plays a passive rôle in the star formation process.     

Buckling analysis of 3D layered structures using a Cosserat continuum approach

This paper concerns the buckling analysis of three-dimensional (3D) layered continua using the Cosserat approach. The finite element method (FEM) is used to implement the adopted Cosserat formulation. As a result, the interfaces between the layers need not be explicitly modelled. Instead, the internal characteristic length, i.e., the layer thickness and also the interaction conditions between the layers are incorporated into the governing equations of the solution. This paper introduces a new 3D geometric stiffness matrix based on the principle of virtual work. The proposed geometric stiffness matrix is applied to the linear buckling analysis of a number of benchmark problems with various geometries, boundary conditions, and interaction conditions between the layers. In all cases, the FEM Cosserat solution exhibits a high level of consistency with the analytical solution.     

Proposing a coordinated environmental effects monitoring (EEM) program structure for the offshore petroleum industry,Nova Scotia,Canada

Environmental effects monitoring (EEM) identifies, quantifies, and compares predicted environmental impacts of a proposed industrial project to those observed after the project has been developed. Several EEM program structures exist, while the structure used by Environment Canada to monitor impacts of the pulp and paper industry has proven to be effective. The aim of this study is to provoke discussion on the development of an effective and coordinated petroleum EEM program structure for the offshore of Nova Scotia, Canada. A structure that supports development of a national EEM program for the petroleum industry is then proposed. Advantages of a coordinated EEM program structure include: (1) reduced cost of the EEM; (2) fewer gaps and less overlapping of responsibilities; (3) fewer calculated risks to the marine environment; and (4) improved environmental safeguards.     

Hydrology of stockpiled industrial coal exposed to rainfall

The movement of water and particulate matter through a simulated coal pile using a rainfall–coal‐pile simulator is investigated. In conjunction with coal‐pile management practices, this study indicates that coal‐pile systems change their internal and surficial structure with successive rainstorm events. This change in coal‐pile structure alters the proportions, rates and suspended solid concentrations within surface runoff and infiltration during subsequent storm events. Results demonstrate the need to determine the optimal coal‐pile slope that minimizes water contact time, but at the same time minimizes the potential for mass wasting and rill erosion. Promotion of a compacted surface is beneficial for the minimization of solids removal, and a stormwater detention pond with potential flocculant additive is suggested as a viable remedial measure for the containment and treatment of coal‐pile runoff. Copyright © 2002 John Wiley & Sons, Ltd.     

Annual stability in the use of coves near inlets as settlement areas for winter flounder (Pseudopleuronectes americanus)

Coves near an ocean inlet in Little Egg Harbor in southern New Jersey may be important settlement areas for winter flounder (Pseudopleuronectes americanus), based on the high abundance of small postlarval individuals. During 1994–1996 we sampled in two coves and adjacent areas of this same estuary to determine if this pattern was annually consistent. Collections in spring and early summer indicated that small, recently-settled winter flounder (10–45 mm TL) were abundant in the coves from May to mid-June in every year with maximum mean densities ranging from 1.5–2.5 ind m⁻² and that these same size individuals were never collected at these densities in other habitats in the same estuary. Densities in the coves declined soon after settlement, usually by late June to early July in each year. In order to determine factors that may influence these high settlement rates we examined aspects of habitat quality by determining habitat-specific growth rates in cages for recently-settled individuals (17.5–38.3 mm TL) both inside and outside the coves during 1995. These rates (3.7–9.1 wt d⁻¹) overlapped those of other estuarine habitats (3.1–10.5 wt d⁻¹) suggesting that habitat quality, based on growth, does not differentiate the coves from other potential settlement habitats. Mark/recapture experiments for recently settled individuals (range 13–70 mm TL) in 1994 and 1996 had low recapture rates (1% in both years) suggesting that dispersal from the cove occurred soon after settlement. This pattern confirms that these coves are used as settlement areas but they are probably not used as nurseries because winter flounder, at least in this system, do not settle and stay and, as a result, use other habitats as primary nursery areas.     

Regional and local controls on the spatial distribution of bedrock reaches in the Upper Guadalupe River, Texas

While studies on gravel mantled and mixed alluvial bedrock rivers have increased in recent decades, few field studies have focused on spatial distributions of bedrock and alluvial reaches and differences between reach types. The objective of this work is to identify the spatial distribution of alluvial and bedrock reaches in the Upper Guadalupe River. We compare reach length, channel and floodplain width, sinuosity, bar length and spacing, bar surface grain size, and slope in alluvial and bedrock reaches to identify whether major differences exist between channel reach types. We find that local disturbances, interaction of the channel and valley sides, variation in lithology, and regional structural control contribute to the distribution of bedrock reaches in the largely alluvial channel. Alluvial and bedrock channel reaches in the Upper Guadalupe River are similar, particularly with respect to the distribution of gravel bars, surface grain size distributions of bars, and channel slope and width. Our observations suggest that the fluvial system has adjusted to changes in base level associated with the Balcones Escarpment Fault Zone by phased incision into alluvial sediment and the underlying bedrock, essentially shifting from a fully alluvial river to a mixed alluvial bedrock river.     

How sediment composition and flow rate influence downstream channel morphodynamics upon dam removal

The process of dam removal establishes the channel morphology that is later adjusted by high-flow events. Generalities about process responses have been hypothesized, but broad applicability and details remain a research need. We completed laboratory experiments focused on understanding how processes occurring immediately after a sediment release upon dam removal or failure affect the downstream channel bed. Flume experiments tested three sediment mixtures at high and low flow rates. We measured changes in impounded sediment volume, downstream bed surface, and rates of deposition and erosion as the downstream bed adjusted. Results quantified the process responses and connected changes in downstream channel morphology to sediment composition, temporal variability in impounded sediment erosion, and spatial and temporal rates of bedload transport. Within gravel and sand sediments, the process response depended on sediment mobility. Dam removals at low flows created partial mobility with sands transporting as ripples over the gravel bed. In total, 37% of the reservoir eroded, and half the eroded sediment remained in the downstream reach. High flows generated full bed mobility, eroding sands and gravels into and through the downstream reach as 38% of the reservoir eroded. Although some sediment deposited, there was net erosion from the reach as a new, narrower channel eroded through the deposit. When silt was part of the sediment, the process response depended on how the flow rate influenced reservoir erosion rates. At low flows, reservoir erosion rates were initially low and the sediment partially exposed. The reduced sediment supply led to downstream bed erosion. Once reservoir erosion rates increased, sediment deposited downstream and a new channel eroded into the deposits. At high flows, eroded sediment temporarily deposited evenly over the downstream channel before eroding both the deposits and channel bed. At low flows, reservoir erosion was 17–18%, while at the high flow it was 31–41%.