Mechanisms of wave transformation in finite-depth water

Mechanisms of wave transformation in finite-depth water are investigated. The linear mechanisms ex- amined are percolation, bottom motion, shoaling, and refraction. The nonlinear mechanisms examined are wave-wave interaction and bottom friction. New exact computations of the nonlinear transfer for fi- nite-depth waves are presented for some directional wave spectra. These mechanisms are found to ex- plain satisfactorily wave decay observations obtained at several sites with different bottom sediment properties. The decay rates at these sites are found to be dominated by different mechanisms which are determined by the bottom conditions. As an example, detailed calculations are presented for data ob- tained at the Jonswap site

Correlations of center flux in SU(2) Yang-Mills theory

By using the method of center projection the center vortex part of the gauge field is isolated and its propagator is evaluated in the center Landau gauge, which minimizes the open 3-dimensional Dirac volumes of non-trivial center links bounded by the closed 2-dimensional center vortex surfaces. The center field propagator is found to dominate the gluon propagator (in Landau gauge) in the low momentum regime and to give rise to an OPE correction to the latter of $\sqrt{\sigma} /p^3$.The screening mass of the center vortex field vanishes above the critical temperature of the deconfinement phase transition, which naturally explains the second order nature of this transition consistently with the vortex picture. Finally, the ghost propagator of maximal center gauge is found to be infrared finite and thus shows no signal of confinement.Comment: Presented at 23rd International Symposium on Lattice Field Field: Lattice 2005, Trinity College, Dublin, Ireland, 25-30 Jul 200

Ionization by bulk heating of electrons in capacitive radio frequency atmospheric pressure microplasmas

Electron heating and ionization dynamics in capacitively coupled radio frequency (RF) atmospheric pressure microplasmas operated in helium are investigated by Particle in Cell simulations and semi-analytical modeling. A strong heating of electrons and ionization in the plasma bulk due to high bulk electric fields are observed at distinct times within the RF period. Based on the model the electric field is identified to be a drift field caused by a low electrical conductivity due to the high electron-neutral collision frequency at atmospheric pressure. Thus, the ionization is mainly caused by ohmic heating in this "Omega-mode". The phase of strongest bulk electric field and ionization is affected by the driving voltage amplitude. At high amplitudes, the plasma density is high, so that the sheath impedance is comparable to the bulk resistance. Thus, voltage and current are about 45{\deg} out of phase and maximum ionization is observed during sheath expansion with local maxima at the sheath edges. At low driving voltages, the plasma density is low and the discharge becomes more resistive resulting in a smaller phase shift of about 4{\deg}. Thus, maximum ionization occurs later within the RF period with a maximum in the discharge center. Significant analogies to electronegative low pressure macroscopic discharges operated in the Drift-Ambipolar mode are found, where similar mechanisms induced by a high electronegativity instead of a high collision frequency have been identified

Vertical head rotation as major source of differences between time-separated digital cephalometric radiographs of patients acquired in one cephalostat X-ray device.

BACKGROUND The purpose of the retrospective study was to analyze the reliability and repeatability of specific landmark-positions used in cephalometry to determine the major sources of absolute landmark position differences for repeated, time-separated (time-point I and II) digital cephalometric radiographs (CEPH) of the same patients. METHODS 100 pairs of CPEHs from the database of a sample of adult patients (18 to 28 years) were analyzed by one calibrated observer and three landmark points (Sella: S, Nasion: N, Subspinale: A) were digitally marked using ImageJ-software. The coordinates of these points entered the evaluation using displacement vectors as primary endpoints between the coordinates of the landmarks in the two images as well as SNA-angles and the angle ω of SN relative to the floor. RESULTS Displacement vectors between CEPHI and CEPHII were rather large (N: 7.95 ± 4.85 mm, S: 5.34 ± 3.50 mm, A: 4.81 ± 3.95 mm. SNA was rather stable between the two sequential radiographs (mean difference: 0.002° ± 1.85°). and did not correlate with age of the patient (SNAI: spearman-Rho: 0.0239, p = 0.8134; SNAII : spearman-Rho: 0.0244, p = 0.8096). Although the vertical angle ω did not differ between CEPHI and CEPHII (mean difference: 0.4° ± 4.7°, pwilcoxon = 0.8155), it showed a quadratic relationship (pF-statistic: < 2.2e-16) with the length of the displacement vector N. CONCLUSION The significantly varying location of the reference points S, N and A between time-separated CEPHs of one patient can largely be explained by different angulation (head rotation within the sagittal plane) of the Frankfurt plane to the floor (horizontal plane)

Introduction to the special issue: multiple jobholding in Europe

In a number of European countries there is a clear trend towards increased multiple jobholding. As things stand, however, little is known about the structure and the potential consequences of this increase, notably in terms of quality of work and social protection. This special issue focuses on contemporary forms of multiple jobholding in Europe. Have the structure, nature and dynamics of multiple jobholding changed over time? What are the roles of labour market flexibility, technological change and work fragmentation in the development of multiple jobholding? And do multiple jobholders benefit from similar and adequate employment terms, conditions and protections compared with single jobholders, or are they worse off as a consequence of their (fragmented) employment situation? What implications do these findings have for unions, policy-makers and the regulation of work? The collection of articles in this special issue adds to the literature on emerging forms of employment in the digital age and challenges for social protection, also in light of the COVID-19 pandemic. This introduction initiates a discussion of central debates on multiple jobholding and presents a synopsis of the articles in this issue

Habitat width along a latitudinal gradient

We use the Chowdhury ecosystem model, one of the most complex agent-based ecological models, to test the latitude-niche breadth hypothesis, with regard to habitat width, i.e., whether tropical species generally have narrower habitats than high latitude ones. Application of the model has given realistic results in previous studies on latitudinal gradients in species diversity and Rapoport's rule. Here we show that tropical species with sufficient vagility and time to spread into adjacent habitats, tend to have wider habitats than high latitude ones, contradicting the latitude-niche breadth hypothesis.Comment: 13 pages including all figures, draft for a biology journa