QCD Propagators at non-vanishing temperatures

We investigate the behaviour of the gluon and ghost propagators, especially their infrared properties, at non-vanishing temperatures. To this end we solve their Dyson-Schwinger equations on a torus and find an infrared enhanced ghost propagator and an infrared vanishing gluon propagator.Comment: 2 pages, 2 figures; talk given by B.G. at the Erice summer school on Nuclear Physics, Sept. 16 -- 24, 2003, Erice, Ital

Attractive internal wave patterns

This paper gives background information for the fluid dynamics video on internal wave motion in a trapezoidal tank.Comment: 2 pg, movie at two resolutions _low(Low-resolution) and _hr(High-resolution

A study of the influence of the gauge group on the Dyson-Schwinger equations for scalar-Yang-Mills systems

The particular choice of the gauge group for Yang-Mills theory plays an important role when it comes to the influence of matter fields. In particular, both the chosen gauge group and the representation of the matter fields yield structural differences in the quenched case. Especially, the qualitative behavior of the Wilson potential is strongly dependent on this selection. Though the algebraic reasons for this observation is clear, it is far from obvious how this behavior can be described besides using numerical simulations. Herein, it is investigated how the group structure appears in the Dyson-Schwinger equations, which as a hierarchy of equations for the correlation functions have to be satisfied. It is found that there are differences depending on both the gauge group and the representation of the matter fields. This provides insight into possible truncation schemes for practical calculations using these equations.Comment: 47 page

The Age and Origin of the Gelderse IJssel

Historic trading cities are located on the Gelderse IJssel and flourished in the late Middle Ages. Little is known about this river in the early Middle Ages and before, and there is considerable debate on the age and origin of the Gelderse IJssel as a Rhine distributary. A small river draining the surrounding Pleistocene uplands must have been present in the IJssel valley during most of the Holocene, but very diverse opinions exist as to when this local river became connected to the Rhine system (and thereby to a vast hinterland), and whether this was human induced or a natural process. We collected new AMS radiocarbon evidence on the timing of beginning overbank sedimentation along the lower reach of the Gelderse IJssel. Our data indicate onset of overbank sedimentation at about 950 AD in this reach. We attribute this environmental change to the establishment of a connection between the precursor of the IJssel and the Rhine system by avulsion. Analysis of previous conventional radiocarbon dates from the upper IJssel floodplain yields that this avulsion may have started ~600 AD. Our results contradict earlier suppositions, based on interpretation of archaeological data and historical accounts, that the Gelderse IJssel is much older and originated as a canal, dug under supervision of the Roman general DrususThe Gelderse IJssel is the third major distributary of the Rhine in the Netherlands and diverts on average similar to 15% of the Rhine discharge northward. Historic trading cities are located on the Gelderse IJssel and flourished in the late Middle Ages. Little is known about this river in the early Middle Ages and before, and there is considerable debate on the age and origin of the Gelderse IJssel as a Rhine distributary. A small river draining the surrounding Pleistocene uplands must have been present in the IJssel valley during most of the Holocene, but very diverse opinions exist as to when this local river became connected to the Rhine system (and thereby to a vast hinterland), and whether this was human induced or a natural process. We collected new AMS radiocarbon evidence on the timing of beginning overbank sedimentation along the lower reach of the Gelderse IJssel. Our data indicate onset of overbank sedimentation at about 950 AD in this reach. We attribute this environmental change to the establishment of a connection between the precursor of the IJssel and the Rhine system by avulsion. Analysis of previous conventional radiocarbon dates from the upper IJssel floodplain yields that this avulsion may have started similar to 600 AD. Our results contradict earlier suppositions, based on interpretation of archaeological data and historical accounts, that the Gelderse IJssel is much older and originated as a canal, dug under supervision of the Roman general Drusus

Thermal evidence for the structural instability in Ni3 Al alloys

The thermal expansion coefficient (¿) and calorimetric data were obtained as a function of temperature in order to clarify some of the significant variations reported with regard to these values in the literature. Stoichiometric and off-stoichiometric compositions of Ni3Al alloys (with and without boron addition) were investigated. Dilatometric experiments were performed on all the alloys and the ¿ values were estimated over the temperature range from ambient to 1000°C. Two runs were made on each sample under different initial conditions and differences in ¿ values were noticed. The results were analysed based on our earlier X-ray diffraction results. Additional isothermal dilatometric tests were also carried out and a significant volume change was noticed (0.45% contraction) when the alloy quenched from 1000°C was heated to 600°C and held for a long duration. The calorimetric data were obtaindd over the same range of temperature and enthalpy changes, though less distinct, were noticed at around 360, 660 and 900°C. The variations seen further augment our earlier results on the instability of the L12 structure and the existence of a structural transformatio

Temperature Dependence of Gluon and Ghost Propagators in Landau-Gauge Yang-Mills Theory below the Phase Transition

The Dyson-Schwinger equations of Landau-gauge Yang-Mills theory for the gluon and ghost propagators are investigated. Numerical results are obtained within a truncation scheme which has proven to be successful at vanishing temperature. For temperatures up to 250 MeV we find only minor quantitative changes in the infrared behaviour of the gluon and ghost propagators. The effective action calculated from these propagators is temperature-independent within the numerical uncertainty.Comment: 9 pages, 14 figures, submitted to EPJ C, typos corrected, reference and 2 minor clarifications added, in v3: one paragraph extended, some references added, version to appear in EPJ

Keplerian discs around post-AGB stars: a common phenomenon?

Aims: We aim at showing that the broad-band SED characteristics of our sample of post-AGB stars are best interpreted, assuming the circumstellar dust is stored in Keplerian rotating passive discs. Methods: We present a homogeneous and systematic study of the Spectral Energy Distributions (SEDs) of a sample of 51 post-AGB objects. The selection criteria to define the whole sample were tuned to cover the broad-band characteristics of known binary post-AGB stars. The whole sample includes 20 dusty RV Tauri stars from the General Catalogue of Variable Stars (GCVS). We supplemented our own Geneva optical photometry with literature data to cover a broad range of fluxes from the UV to the far-IR. Results: All the SEDs display very similar characteristics: a large IR excess with a dust excess starting near the sublimation temperature, irrespective of the effective temperature of the central star. Moreover, when available, the long wavelength fluxes show a black-body slope indicative of the presence of a component of large mm sized grains. Conclusions: We argue that in all systems, gravitationally bound dusty discs are present. The discs must be puffed-up to cover a large opening angle for the central star and we argue that the discs have some similarity with the passive discs detected around young stellar objects. We interpret the presence of a disc to be a signature for binarity of the central object, but this will need confirmation by long-term monitoring of the radial velocities. We argue that dusty RV Tauri stars are those binaries which happen to be in the Population II instability strip.Comment: 29 pages, 5 figures, accepted for publication in A&

Bouwsteen riviermorfologie en -dynamiek Rijntakken t.b.v. het koepelbeheerplan natura2000 rivierengebied

Voor de Natura2000 gebieden Rijntakken wordt een koepelbeheerplan opgesteld. Dit koepelbeheerplan betreft de habitat- en vogelrichtlijngebieden in het rivierengebied. Specifieke kenmerken van het rivierengebied, zoals de relatie tussen rivierdynamiek, morfologie en de Natura2000 doelen worden uitgewerkt in het koepelplan. Dit document is één van de bouwstenen daarvoor. De volgende onderdelen komen in deze bouwsteen achtereenvolgens aan de orde: * Een indeling van de Rijntakken in riviertrajecten met een korte beschrijving van de belangrijkste morfologische en hydraulische kenmerken; * de kansrijke gebieden voor morfodynamische processen (sedimentatie-erosie); * betekenis van deze specifieke kenmerken (rivierdynamiek) voor de realisatie van de natura2000doelen (abiotische randvoorwaarden); * vanuit de specifieke kenmerken van de riviertakken het aangeven van de potenties voor de belangrijkste N2000-doelstellingen: hardhoutooibos, zachthoutooibos, stroomdalgraslanden, moeras en moerasruigten, pioniervegetaties op slikoever

Optimalisering recirculatie voedingswater

Binnen het project Schone Bronnen is optimalisatie van recirculatie in glastuinbouw aan de orde gesteld, als zijnde een belangrijke oplossingsrichting om de emissie door spui en drainagewater te reduceren. Op verzoek van de stuurgroep van het project Schone Bronnen is binnen het emissiereductie onderzoek voor LNV deze notitie opgesteld. Deze geeft in het kort antwoord op de onderzoekvragen: Wat zijn de grootste knelpunten om tot volledige recirculatie te komen? Hoe bepaalt men in de praktijk wanneer wel/niet gerecirculeerd kan worden? Wat is nodig om de mate van recirculatie te verhogen

Electromagnetic radiative corrections in parity-violating electron-proton scattering

QED radiative corrections have been calculated for leptonic and hadronic variables in parity-violating elastic ep scattering. For the first time, the calculation of the asymmetry in the elastic radiative tail is performed without the peaking-approximation assumption in hadronic variables configuration. A comparison with the PV-A4 data validates our approach. This method has been also used to evaluate the radiative corrections to the parity-violating asymmetry measured in the G0 experiment. The results obtained are here presented.Comment: 12 pages, 11 figure