357 research outputs found
Evidence for contact delocalization in atomic scale friction
We analyze an advanced two-spring model with an ultra-low effective tip mass
to predict nontrivial and physically rich 'fine structure' in the atomic
stick-slip motion in Friction Force Microscopy (FFM) experiments. We
demonstrate that this fine structure is present in recent, puzzling
experiments. This shows that the tip apex can be completely or partially
delocalized, thus shedding new light on what is measured in FFM and, possibly,
what can happen with the asperities that establish the contact between
macroscopic sliding bodies.Comment: 4 pages text and 3 figure
Improvement of Type 2 Diabetes Mellitus in Obese and Non-Obese Patients after the Duodenal Switch Operation
Introduction. Type 2 diabetes mellitus (T2DM) is one of the most important obesity-related comorbidities. This study was undertaken to characterise the effect of the biliopancreatic diversion with duodenal switch (BPD-DS) in morbidly obese and nonmorbidly obese diabetic patients. Methods. Outcome of 74 obese diabetic patients after BPD-DS and 16 non-obese diabetic patients after BPD or gastric bypass surgery was evaluated. Insulin usage, HbA1c-levels, and index of HOMA-IR (homeostasis model assessment of insulin resistence) were measured. Results. A substantial fraction of patients is free of insulin and shows an improved insulin sensitivity early after the operation, another fraction gets free of insulin in a 12-month period after the operation and a small fraction of long-term insulin users will not get free of insulin but nevertheless shows an improved metabolic status (less insulin needed, normal HbA1c-levels). Conclusion. BPD-DS leads to an improvement of T2DM in obese and non-obese patients. Nevertheless, more data is needed to clarify indications and mechanisms of action and to adjust our operation techniques to the needs of non-obese diabetic patients
Nothing moves a surface: vacancy mediated surface diffusion
We report scanning tunneling microscopy observations, which imply that all
atoms in a close-packed copper surface move frequently, even at room
temperature. Using a low density of embedded indium `tracer' atoms, we
visualize the diffusive motion of surface atoms. Surprisingly, the indium atoms
seem to make concerted, long jumps. Responsible for this motion is an ultra-low
density of surface vacancies, diffusing rapidly within the surface. This
interpretation is supported by a detailed analysis of the displacement
distribution of the indium atoms, which reveals a shape characteristic for the
vacancy mediated diffusion mechanism that we propose.Comment: 4 pages; for associated movie, see
http://www-lion.leidenuniv.nl/sections/cm/groups/interface/projects/therm
Roughening of close-packed singular surfaces
An upper bound to the roughening temperature of a close-packed singular
surface, fcc Al (111), is obtained via free energy calculations based on
thermodynamic integration using the embedded-atom interaction model. Roughening
of Al (111) is predicted to occur at around 890 K, well below bulk melting (933
K), and it should therefore be observable, save for possible kinetic hindering.Comment: RevTeX 4 pages, embedded figure
Temperature dependent surface relaxations of Ag(111)
The temperature dependent surface relaxation of Ag(111) is calculated by
density-functional theory. At a given temperature, the equilibrium geometry is
determined by minimizing the Helmholtz free energy within the quasiharmonic
approximation. To this end, phonon dispersions all over the Brillouin zone are
determined from density-functional perturbation theory. We find that the
top-layer relaxation of Ag(111) changes from an inward contraction (-0.8 %) to
an outward expansion (+6.3%) as the temperature increases from T=0 K to 1150 K,
in agreement with experimental findings. Also the calculated surface phonon
dispersion curves at room temperature are in good agreement with helium
scattering measurements. The mechanism driving this surface expansion is
analyzed.Comment: 6 pages, 7 figures, submitted to Phys. Rev. B (May 1998). Other
related publications can be found at
http://www.rz-berlin.mpg.de/th/paper.htm
Domain ontology for digital marketplaces
Recently the sharing economy has emerged as a viable alternative to fulfilling a variety of consumer needs. As there is no consensus on the definition of ‘sharing economy’ we use the term ‘marketplace’ to refer more specifically to Internet/software-based sharing economy platforms connecting two different market segments. In the field of sharing economy and marketplaces we found a research gap concerning the (socio)technological aspects and the development of marketplaces. A marketplace ontology can help to have a clear account of marketplace concepts which will facilitate communication, consensus and alignment. In this paper we design this marketplace ontology in four steps. First the selection of UFO as foundation and UFO-S as core ontology. Second the search for a set of minimal conditions and properties common for marketplaces and the derivation into competency questions. Third, use the competency questions to identify fragmented sub-ontology pieces called Domain-Related Ontology Patterns (DROPs) and apply them informally by extending UFO-S concepts to design a marketplace domain ontology. This marketplace domain ontology is represented in OntoUML. The last step is the validation of the OntoUML model using expert knowledge
Are Vicinal Metal Surfaces Stable?
Quantum Matter and Optic
- …