The generation of offshore tidal sand banks and sand waves

A simple morphological model is considered which describes the interaction between a tidal flow and an erodible bed in a shallow sea. The basic state of this model describes a spatially uniform tide over a flat bottom where the flow vector is represented as a tidal ellipse. The linear stability of this solution is analysed with respect to bed form perturbations. Results are presented for both a uni-directional and circular tide. In the former case the wave-length and the orientation of the fastest growing bed mode agree well with those of tidal sand banks. However, this model only predicts the growth of large-scale sand ridges. With a simplified numerical model we tentatively show that the effects of secondary currents on the sediment transport trigger the formation of instabilities at an essentially smaller scale, viz, sand waves. Another limitation of a model with uni-directional tides is that no selective modes found are the first to become unstable if the model parameters are varied. In the case of a circular tide, critical model parameters are found below which the basic state is stable. We conclude that this provides a starting point for the development of a weakly non-linear analysis, which will yield information on the amplitude behaviour of marginally growing bed forms

Partial-Wave Analyses of all Proton-Proton and Neutron-Proton Data Below 500 MeV

In 1993 the Nijmegen group published the results of energy-dependent partial-wave analyses (PWAs) of the nucleon-nucleon (NN) scattering data for laboratory kinetic energies below Tlab=350 MeV (PWA93). In this talk some general aspects, but also the newest developments on the Nijmegen NN PWAs are reported. We have almost finished a new energy-dependent PWA and will discuss some typical aspects of this new PWA; where it differs from PWA93, but also what future developments might be, or should be.Comment: Presentation at the 19th European Conference on Few-Body Problems in Physics, Groningen, The Netherlands, 23-27 August 2004. 4 pages REVTeX4, no figure

The Status of the Pion-Nucleon Coupling Constant

A review is given of the various determinations of the different piNN coupling constants in analyses of the low-energy pp, np, pbarp, and pi-p scattering data. The most accurate determinations are in the energy-dependent partial-wave analyses of the NN data. The recommended value is f^2 = 0.075 . A recent determination of f^2 by the Uppsala group from backward np cross sections is shown to be model dependent and inaccurate, and therefore completely uninteresting. We also argue that an accurate determination of f^2 using pp forward dispersion relations is not a realistic option.Comment: 19 pages, latex2e with a4wide.sty, more information is available at http://NN-OnLine.sci.kun.nl . Invited talk at FBXV, Groningen, The Netherlands, July 22-26, 1997. Invited talk at MENU97, Vancouver, B.C., Canada, July 28 - August 1, 199

Renormalization of the Deuteron with One Pion Exchange

We analyze the deuteron bound state through the One Pion Exchange Potential. We pay attention to the short distance peculiar singularity structure of the bound state wave functions in coordinate space and the elimination of short distance ambiguities by selecting the regular solution at the origin. We determine the so far elusive amplitude of the converging exponential solutions at the origin. All bound state deuteron properties can then be uniquely deduced from the deuteron binding energy, the pion-nucleon coupling constant and pion mass. This generates correlations among deuteron properties. Scattering phase shifts and low energy parameters in the 3S1-3D1 channel are constructed by requiring orthogonality of the positive energy states to the deuteron bound state, yielding an energy independent combination of boundary conditions. We also analyze from the viewpoint of short distance boundary conditions the weak binding regime on the light of long distance perturbation theory and discuss the approach to the chiral limit.Comment: 22 pages, 11 figure

The nucleon-sigma coupling constant in QCD Sum Rules

The external-field QCD Sum Rules method is used to evaluate the coupling constant of the light isoscalar-scalar meson (``$\sigma$'' or \epsilon) to the nucleon. The contributions that come from the excited nucleon states and the response of the continuum threshold to the external field are calculated. The obtained value of the coupling constant is compatible with the large value required in one-boson exchange potential models of the two-nucleon interaction.Comment: 11 pages, 4 figure

Circulation, Sediment Concentration and Oxygen Depletion in the Tidal Ems River

We present measurements which show that the tidal Ems River in Germ any is extremely muddy over a 30 km + turbid zone, with fluid mud o f 1-2 m thickness covering the bed with suspended sediment concentrations (SSC) o f greater than 50 kg.m-3. Moreover, we show that these elevated SSC contain large quantities of organic material which deplete dissolved oxygen (DO) and produce summertime hypoxic zones. Using mathematical modeling, we develop simplified representations o f the estuary physics that reproduce the tidally-averaged circulation, SSC distribution, and oxygen depletion. These models show that SSC and oxygen concentrations are extremely sensitive to factors such as the mean depth, the mixing due to bottom friction (turbulence), and river flow. The observed increase in SSC and decrease in DO over the past 25 years is linked to the progressive deepening o f the tidal Em s from 4-5 m to 7 m between 1985- 1994, which moved the turbid zone upstream and decreased mixing. A review of scientific literature and data from the Em s suggests that hum an intervention (dyking,channel modification) combines with more gradual natural changes (sea level rise, climate variation) to continually modify sediment transport

Vector mesons in qqˉqˉq\bar q\bar q systems

A new selection rule is described for the vector mesons in the decuplet representations of flavor SU(3)Comment: 7 pages and 1 figur

Hydrodynamics and Morphology in the Ems/Dollard Estuary: Review of Models, Measurements, Scientific Literature, and the Effects of Changing Conditions

The Ems estuary has constantly changed over the past centuries both from man-made and natural influences. On the time scale of thousands of years, sea level rise has created the estuary and dynamically changed its boundaries. More recently, storm surges created the Dollard sub-basin in the 14th -15th centuries. Beginning in the 16th century, diking and reclamation of land has greatly altered the surface area of the Ems estuary, particularly in the Dollard. These natural and anthropogenic changes to the surface area of the Ems altered the flow patterns of water, the tidal characteristics, and the patterns of sediment deposition and erosion. Since 1945, reclamation of land has halted and the borders of the Ems estuary have changed little. Sea level rise has continued, and over the past 40 years the rate of increase in mean high water (MHW) along the German coast has accelerated to 40 cm/ century. Climate has varied on a decadal time scale due to long-term variations in the North Atlantic Oscillation (NAO), which controls precipitation, temperature, and the direction and magnitude of winds. Between 1960 and 1990 the most intense variation in the NAO index on record was observed. As a result the magnitude and frequency of storm surges increased, and mean wave heights increased at 1-2 cm/year. Currently the NAO index—and therefore storminess—is trending downwards. Over the longer term, global warming models predict an average temperature rise of 2 degrees Celsius over the next century. A doubling of CO2 is expected to increase sea level by 30 cm, while the significant wind speed and wave heights in the North Sea are predicted to increase by 50 cm/s and 50 cm, respectively. Beginning in the late 1950’s, dredging activity and construction measures in harbours and shipping channels greatly altered the physical processes in the Ems. Deepening and streamlining the Ems River and shipping channel between the 1960s and 1990s decreased the hydraulic roughness and increased the tidal range in the river above Emden by as much as 1.5 m. At the turbidity maximum between Emden and Papenburg, concentrations of sediment are currently between 1-2 orders of magnitude larger than in the 1950’s, and fluid mud layers of several meters thickness occur. Other man-made changes, such as gas pipelines and the expansion of harbours, have often caused significant, but more localized, changes to the estuary. Between the mid 19th century and the 1970’s, dumping of organic waste—agricultural, industrial, and human—severely stressed the ecology of the Dollard sub-basin in particular. Since then the input of organic waste has been greatly reduced and anoxic conditions eliminated. However, the increase in turbidity at the turbidity maximum has caused depleted oxygen concentrations and periodic anoxia between Pogum and Papenburg during the summer months (personal communication, H. Juergens; Talke et al, 2005). The Ems is a relatively well studied estuary. Significant research projects have included the BOEDE project in the 1970’s --1980’s and the BOA and INTRAMUD projects in the 1990’s. These projects and other efforts have amassed a deep literature in the knowledge of tidal flats, fluid mud and flocculation, and mixing and dispersion processes. Projects currently underway are focusing on tidal dynamics and the affects of dredging in the high turbidity zone between Emden and Herbrum. Optimal management of the estuary is the goal of the HARBASINS project. Many analytical and numerical models have been applied to the Ems estuary to estimate tidal range, storm surges, wave fields, sediment transport, and mixing and dispersion processes. Analytical models to estimate mixing of scalars and sediment fluxes (Sediment Trend Analysis) have been extensively used. Numerical models such as WAQUA, unTRIM, MIKE3, Telemac 2D, SWAN, Delft 3D –Sed, and others have been applied to the Ems. While reasonable results are found for short term processes (order of days), long-term morphological change cannot yet be predicted. For the Ems catchement basin, the numerical models REGFLUD and FLUMAGIS are used to estimate nutrient inputs from diffuse sources and to visualize and evaluate the effects of land-use change

An interacting quark-diquark model of baryons

A simple quark-diquark model of baryons with direct and exchange interactions is constructed. Spectrum and form factors are calculated and compared with experimental data. Advantages and disadvantages of the model are discussed.Comment: 13 pages, 3 eps-figures, accepted by Phys.Rev. C Rapid Communication