719 research outputs found
Time-frequency analysis of 3D ship-wave fields in martime waterways
In the last 15 years an increased number of serious damages of protective structures such as groins and revetments have been observed in maritime waterways. The analyses of these damages have shown that the current design approaches for the rubble mound layers of such structures are not sufficient to ensure sufficient stability against ship-induced wave loads. Since these approaches are determined for wind-induced waves, they do not consider the long-period ship-wave components. Within a joint research project, the design loads of ship-induced long-period waves on rubble mound structures in maritime waterways are investigated. By means of first project results, the knowledge gaps with respect to the classification and parameterization of ship waves have been identified. The project has clearly shown the need for a 3D analysis of three-dimensional, nonlinear ship-wave fields. Therefore, another research project was initiated in order to generate the scientific knowledge for the parameterization of ship-induced 3D wave fields as required for the hydraulic design of rubble mound structures in maritime waterways with a special focus on the spatial and nonlinear properties of ship waves
Anomalous Lattice Response at the Mott Transition in a Quasi-2D Organic Conductor
Discontinuous changes of the lattice parameters at the Mott metal-insulator
transition are detected by high-resolution dilatometry on deuterated crystals
of the layered organic conductor -(BEDT-TTF)Cu[N(CN)]Br.
The uniaxial expansivities uncover a striking and unexpected anisotropy,
notably a zero-effect along the in-plane c-axis along which the electronic
interactions are relatively strong. A huge thermal expansion anomaly is
observed near the end-point of the first-order transition line enabling to
explore the critical behavior with very high sensitivity. The analysis yields
critical fluctuations with an exponent 0.8 0.15
at odds with the novel criticality recently proposed for these materials
[Kagawa \textit{et al.}, Nature \textbf{436}, 534 (2005)]. Our data suggest an
intricate role of the lattice degrees of freedom in the Mott transition for the
present materials.Comment: 4 pages, 4 figure
Nature of the spin dynamics and 1/3 magnetization plateau in azurite
We present a specific heat and inelastic neutron scattering study in magnetic
fields up into the 1/3 magnetization plateau phase of the diamond chain
compound azurite Cu(CO)(OH). We establish that the
magnetization plateau is a dimer-monomer state, {\it i.e.}, consisting of a
chain of monomers, which are separated by dimers on the
diamond chain backbone. The effective spin couplings K
and K are derived from the monomer and dimer
dispersions. They are associated to microscopic couplings K,
K and a ferromagnetic K, possibly as
result of orbitals in the Cu-O bonds providing the superexchange
pathways.Comment: 5 pages, 4 figure
Effects of Two Energy Scales in Weakly Dimerized Antiferromagnetic Quantum Spin Chains
By means of thermal expansion and specific heat measurements on the
high-pressure phase of (VO)PO, the effects of two energy scales of
the weakly dimerized antiferromagnetic = 1/2 Heisenberg chain are explored.
The low energy scale, given by the spin gap , is found to manifest
itself in a pronounced thermal expansion anomaly. A quantitative analysis,
employing T-DMRG calculations, shows that this feature originates from changes
in the magnetic entropy with respect to , . This term, inaccessible by specific heat, is visible only in the
weak-dimerization limit where it reflects peculiarities of the excitation
spectrum and its sensitivity to variations in .Comment: 4 pages, 4 figures now identical with finally published versio
Inelastic Diffraction and Spectroscopy of Very Weakly Bound Clusters
We study the coherent inelastic diffraction of very weakly bound two body
clusters from a material transmission grating. We show that internal
transitions of the clusters can lead to new separate peaks in the diffraction
pattern whose angular positions determine the excitation energies. Using a
quantum mechanical approach to few body scattering theory we determine the
relative peak intensities for the diffraction of the van der Waals dimers
(D_2)_2 and H_2-D_2. Based on the results for these realistic examples we
discuss the possible applications and experimental challenges of this coherent
inelastic diffraction technique.Comment: 15 pages + 5 figures. J. Phys. B (in press
Tribological Properties of SiNx Films on PH Stainless Steel with and Without Nitriding as a Pre-treatment
AbstractIn this work, the tribological behavior and adhesion of SiNx films deposited by PACVD on nitrided and non-nitrided Corraẍ PH stainless steel were evaluated. The films were characterized by FTIR and EDS, hardness was assessed with a nanoindenter and the microstructure was analyzed by Optical Microscopy, SEM and FIB. To evaluate the tribological behavior, fretting and linear sliding tests were performed using WC and alumina balls as counterparts, and the adhesion of the SiNx films was characterized using the Scratch Test and Rockwell C indentation methods. Erosion tests were conducted in sea water and sand flux. Corrosion behavior was evaluated by the Salt Spray Fog Test. The film reached a hardness of 2300 HV and a thickness of about 1.4 microns. The duplex coated sample had a better tribological behavior than the simple coated sample, the nitrided layer allowed a graded interlayer which improved the wear resistance. Regarding the film adhesion, the duplex coating had an acceptable adhesion; the nitrided layer reduced the interface stress and enhanced the adhesion. Additionally, the films evidenced good corrosion resistance in a saline environment
Neural correlates of ‘pessimistic' attitude in depression
Background Preparing for potentially threatening events in the future is essential for survival. Anticipating the future to be unpleasant is also a cognitive key feature of depression. We hypothesized that ‘pessimism'-related emotion processing would characterize brain activity in major depression. Method During functional magnetic resonance imaging, depressed patients and a healthy control group were cued to expect and then perceive pictures of known emotional valences - pleasant, unpleasant and neutral - and stimuli of unknown valence that could have been either pleasant or unpleasant. Brain activation associated with the ‘unknown' expectation was compared with the ‘known' expectation conditions. Results While anticipating pictures of unknown valence, activation patterns in depressed patients within the medial and dorsolateral prefrontal areas, inferior frontal gyrus, insula and medial thalamus were similar to activations associated with expecting unpleasant pictures, but not with expecting positive pictures. The activity within a majority of these areas correlated with the depression scores. Differences between healthy and depressed persons were found particularly for medial and dorsolateral prefrontal and insular activations. Conclusions Brain activation in depression during expecting events of unknown emotional valence was comparable with activation while expecting certainly negative, but not positive events. This neurobiological finding is consistent with cognitive models supposing that depressed patients develop a ‘pessimistic' attitude towards events with an unknown emotional meaning. Thereby, particularly the role of brain areas associated with the processing of cognitive and executive control and of the internal state is emphasized in contributing to major depressio
Decoherence in a Talbot Lau interferometer: the influence of molecular scattering
We study the interference of C70 fullerenes in a Talbot-Lau interferometer
with a large separation between the diffraction gratings. This permits the
observation of recurrences of the interference contrast both as a function of
the de Broglie wavelength and in dependence of the interaction with background
gases. We observe an exponential decrease of the fringe visibility with
increasing background pressure and find good quantitative agreement with the
predictions of decoherence theory. From this we extrapolate the limits of
matter wave interferometry and conclude that the influence of collisional
decoherence may be well under control in future experiments with proteins and
even larger objects.Comment: 8 pages, 5 figure
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