Online discussion compensates for suboptimal timing of supportive information presentation in a digitally supported learning environment

This study used a sequential set-up to investigate the consecutive effects of timing of supportive information presentation (information before vs. information during the learning task clusters) in interactive digital learning materials (IDLMs) and type of collaboration (personal discussion vs. online discussion) in computer-supported collaborative learning (CSCL) on student knowledge construction. Students (N = 87) were first randomly assigned to the two information presentation conditions to work individually on a case-based assignment in IDLM. Students who received information during learning task clusters tended to show better results on knowledge construction than those who received information only before each cluster. The students within the two separate information presentation conditions were then randomly assigned to pairs to discuss the outcomes of their assignments under either the personal discussion or online discussion condition in CSCL. When supportive information had been presented before each learning task cluster, online discussion led to better results than personal discussion. When supportive information had been presented during the learning task clusters, however, the online and personal discussion conditions had no differential effect on knowledge construction. Online discussion in CSCL appeared to compensate for suboptimal timing of presentation of supportive information before the learning task clusters in IDLM

Soil moisture control of NO turnover and N₂O release in nitrogen-saturated subtropical forest soils

Acid forest soils in South China experience a chronically elevated input of atmospheric nitrogen (N), turning them into hot spots for gaseous N emissions. Soil moisture is known to be a major controller for the partitioning of gaseous N loss to nitric (NO) and nitrous oxide (N2O), which may be of particular relevance in the monsoonal climate of South China. To study this partitioning in more detail, we determined gas phase kinetics of NO and N2O release during laboratory dry-out of acidic surface soils from the headwater catchment TieShanPing (TSP), situated close to Chongqing, SW China. Soils were sampled from two hydrologically distinct environments, a well-drained hill slope (HS), and a periodically flooded groundwater discharge zone (GDZ). Production and consumption of NO were studied in an automated flow-through system purged with NO-free or NO-spiked air. Production rates peaked at 21% and 18% water filled pore space (WFPS) in HS and GDZ soils, respectively, suggesting nitrification as the dominant process of NO formation in both landscape units. In HS soils, maximum production and consumption occurred at the same WFPS, whereas GDZ soils displayed maximum NO consumption at higher WFPS than maximum production, suggesting that denitrification is an important NO sink in GDZ soils. Net N2O release was largest at 100% WFPS and declined steadily during drying. Integrated over the entire range of soil moisture, potential NO-N loss outweighed potential N2O-N loss, suggesting that N-saturated, acid forest soil is an important NO source

Stilling basin optimization for a combined inlet-outlet sluice in the framework of the Sigmaplan

Within the framework of the so-called Actualised Sigmaplan, i.e. the masterplan to create a sustainable Schelde estuary, flood control areas (FCA) are setup in well-chosen polders along the tidal part of the river Scheldeand its tributaries. In some of these FCAs a semi-diurnal, controlled reduced tide (CRT) is introduced, by means of simple inlet and outlet sluices. Nowadays, it is preferred to combine in- let and outlet sluices in one single structure, in which the inlet culverts are situated on top of the outlet culverts. At inflow, energy is dissipated by means of a vertical drop and a stilling basin. In this paper, results are presented of a physical model study (scale 1:8) aiming at the optimization of the inlet configuration, i.e. the stilling basin, starting from the desktop design of the in- and outlet construction for FCACRT Bergenmeersen

Looking up and down: Strong collaboration is only the first step in tackling parachute science

Abstract Critiques of parachute science argue for closer collaborations among local and international scientists. Here, building on such a collaboration, we highlight further challenges when outsiders, typically working through international nongovernmental organizations, fail to respect both the governance framework within which they are working and the realities on the ground. Specifically, we emphasize the importance of observing governance structures, maintaining transparency, and responding flexibly to national and regional priorities (?looking up?), as well as stressing the need to keep a close focus on local cultural context when designing interventions such as educational programs (?looking down?). Addressing the shortcomings for conservation practice contingent on parachute science interventions requires nimble, creative, and respectful actions, which at least in the context of Tanzania, we all still struggle to put into action

Density Waves Inside Inner Lindblad Resonance: Nuclear Spirals in Disk Galaxies

We analyze formation of grand-design two-arm spiral structure in the nuclear regions of disk galaxies. Such morphology has been recently detected in a number of objects using high-resolution near-infrared observations. Motivated by the observed (1) continuity between the nuclear and kpc-scale spiral structures, and by (2) low arm-interarm contrast, we apply the density wave theory to explain the basic properties of the spiral nuclear morphology. In particular, we address the mechanism for the formation, maintenance and the detailed shape of nuclear spirals. We find, that the latter depends mostly on the shape of the underlying gravitational potential and the sound speed in the gas. Detection of nuclear spiral arms provides diagnostics of mass distribution within the central kpc of disk galaxies. Our results are supported by 2D numerical simulations of gas response to the background gravitational potential of a barred stellar disk. We investigate the parameter space allowed for the formation of nuclear spirals using a new method for constructing a gravitational potential in a barred galaxy, where positions of resonances are prescribed.Comment: 18 pages, 9 figures, higher resolution available at http://www.pa.uky.edu/~ppe/papers/nucsp.ps.g

Large Eddy Simulation of the water flow around a cylindrical pier mounted in a flat and fixed bed

In the present work, a numerical model based upon the Large Eddy Simulation approach has been set up for predicting the three-dimensional flow around a cylindrical pier, mounted on a flat and fixed bed, a generic case that is relevant for the study of flow and scour around bridge piers. This turbulent flow configuration was studied experimentally by Nogueira et al. (2008) with Particle Image Velocimetry (PIV). The main goal of this paper is a first validation of the numerical model, based upon the available data. The numerical tool is capable to qualitatively reproduce the characteristic flow features around the pier, like e.g. the horseshoe vortex system and the vortex shedding in the wake. The predicted extent of the initial scour hole, based upon the bed shear stress magnitudes, agrees well with the observations at the onset of the souring process during the lab experiments. Further quantitative validation of the numerical model will benefit from additional measurement efforts in the experiments

Physical model for the emptying and filling system of the third set of Panama locks

The Panama Canal Authority (ACP) extension plan includes the construction of a third lane with new locks at both sides of the Canal. The design ship is a so-called Post- Panamax 12 000 TEU container carrier. In order to maximize the transit throughput of the new locks, and at the same time, to limit hawser forces under an acceptable maximum threshold, many numerical studies and two physical model studies have been carried out. In a first phase, the filling and emptying (F/E) system of the locks has been preoptimized with numerical models (1D, 2D and 3D models). Then, to complete the design, a study have been carried out on a 1/30 physical scale model at Compagnie Nationale du Rhône Hydraulic Laboratory, Lyon, France, operating as member of the consortium CPP. The F/E system is a “double culverts” sidewall and ports system composed of: a main culvert connected by a central flow divider to two secondary culverts in middle section of the lock chamber; each secondary culvert is equipped with 10 ports which feed the lock on 80% of its length. In order to limit water consumption, each lock includes 3 Water Saving Basins (WSB). The scale model represents two locks chambers, 3 WSB associated with the lower chamber, a fore and a tail bay. The Post-Panamax container ship vessel is also modelled. A special emphasis is put on the hawser forces measurements and in the definition of a threshold value for them as no standard values presently exists for Post-Panamax locks given such operating conditions (use of water saving basins or not, hydraulic heads ranging from 3.5 m to 20 m). The experimental setup and the scenarios of tests are described and an overview of the main results (F/E times, times series of water levels with and without ship in the lock chamber, time series of hydraulic efforts on the ship hull) are given. The results of this physical model are an input for the design-build tender for the construction of the third set of locks, presently in progress

Tuning the tide: creating ecological conditions for tidal marsh development in a flood control area

The Schelde estuary, characterised as a turbid, polluted and eutrophic system, has nowadays reached a turning point in the restoration of its water quality. During the past century, human activities have reduced the intertidal areas, essential in the estuarine ecosystem for nutrient cycling and the self-cleaning capacity. Today, in combination with a master plan to protect the population from storm surges, an opportunity rises to restore areas with a tidal influence. One specific option of combining safety and ecology is the creation of flood control areas (FCA) under the influence of a controlled reduced tide (CRT). These specific areas will differ in many ways from fully tidal areas. However, these areas can fulfill important ecological functions with effects on aeration, nitrification, denitrification, sedimentation and primary production in the estuary. Opportunities for ecological development within a CRT have been investigated for a specific case. The ecology within a CRT showed to be very case specific, depending e.g. on the morphology of the area, the sluice design and the local water quality. Depending on the sluice design, water quality can be improved and sedimentation can be influenced. Possible measures to design a CRT with a rich habitat variation are discussed