Systolic geometry of translation surfaces

Let $S$ be a translation surface of genus $g > 1$ with $n$ cone points $(p_i)_{i=1,\ldots,n}$ with cone angle $2\pi \cdot (k_i+1)$ at $p_i$, where $k_i \in \mathbb{N}$. In this paper we investigate the systolic landscape of these translation surfaces for fixed genus.Comment: 25 pages, 4 figures. Added explicit computations of systoles in the graph of saddle connections for origamis in H(1,1) and a criterion to decide whether such systoles define systoles on the translation surfac

Irreversible Structural Transformation of five fold i-AlPdMn Quasicrystals after Ion Bombardment and Annealing

Five fold i-AlPdMn surface prepared under UHV by ion bombardment and annealing was so far considered to be bulk terminated. This result was substantially based on a quantitative LEED analyses [1]. Analysis of the specular rod in a X ray diffraction experiment at grazing incidence supported this result [2]. We present a new study of this surface by high resolution X ray diffraction at normal incidence. In this Bragg configuration the diffraction peak 18 – 29 for instance is at a photon energy of 2.873keV, the 72 – 116 reflection at 5.725keV. This results in an analyzed thickness of the sample surface of a few micrometers. The surface was cleaned by ion bombardment. During annealing (T≅880K), we clearly observed the progressive disappearance of the initial Bragg peak characteristic of the as cast bulk sample. Conversely a new Bragg peak grows at an energy position shifted by 1eV compared to the position of the original Bragg peak. This is a clear signature for an irreversible structural transformation which takes place on at least the micron thickness. On the transformed surface, both, a LEED pattern and a RHEED pattern, characteristic for a five fold surface were easily obtained. This high resolution experiment (the relative Bragg peak shift is 3ׁ10−4) was reproduced on samples from different initial compositions. This shows that five fold i-AlPdMn surface changes after preparation by ion bombardment and annealing at 900K on a micrometer thickness. This is not consistent with the conclusion that the surface is simply terminated by a cut of the original bulk. We conclude that a reorganization process of the quasicrystalline structure during annealing proceeds in the surface vicinity (probed depth is close to a few microns)

Ordre à courte et à longue distance dans le quasicristal Al-Pd-Mn

Nous avons d'abord sondé l'excellent ordre rotationnel (holographie de rayons X) et l'ordre à longue distance (ondes stationnaires X) de la phase icosaédrique Al-Pd-Mn après croissance. En effet, nous avons analysé ces deux expériences sur la base d'une structure quasicristalline parfaite. L'expérience d'holographie de rayons X nous a permis d'obtenir des images 3d de l'environnement moyen local d'une espèce atomique sans connaissances a priori de la structure. Pour un échantillon fracturé nous avons obtenu une cohérence parfaite entre une onde stationnaire périodique et la structure du quasicristal. Nos résultats montrent que le polissage détruit cette cohérence pour les profondeurs sondées. Ensuite, nous avons mis en évidence une condensation des lacunes vers la surface lors des traitements thermiques des échantillons. Ceci se traduit par un changement violent de la morphologie à grande échelle suite à la création de pores facetés en surface lors du premier recuit d'un échantillon poli après croissance. Lors de mêmes traitements thermiques nous avons observé une variation du paramètre de maille en voisinage de la surface. Il ne s'agit pas d'une relaxation de surface standard connue pour des systèmes cristallins, mais d'une variation du paramètre de maille relative de 3.10-4 qui s'étend sur une épaisseur de 6[mu]m. Nous attribuons cette modification structurale à un changement de la densité des lacunes. Nos résultats montrent que les surfaces préparées par recuit ne peuvent pas être analysées comme simple coupe de l'échantillon après croissance.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Meteorological observations during POLARSTERN cruise PS124

The meteorological observatory Polarstern issues synoptical reports every 3 hours during times of ship operation. The reports are distritubed via global networks of the World Meteorological Organisation. When designated weather observers are onboard manual observations are included in the reports. For times that are not covered by an observer automatic reports are issued. All observations are made in compliance with standards of the World Meteorological Organisation and those of the German Weather Service (DWD). This dataset compiles all synoptical reports issued during Polarstern cruise PS124

Irreversible Structural Transformation of five fold i-AlPdMn Quasicrystals after Ion Bombardment and Annealing

Five fold i-AlPdMn surface prepared under UHV by ion bombardment and annealing was so far considered to be bulk terminated. This result was substantially based on a quantitative LEED analyses [1]. Analysis of the specular rod in a X ray diffraction experiment at grazing incidence supported this result [2]. We present a new study of this surface by high resolution X ray diffraction at normal incidence. In this Bragg configuration the diffraction peak 18 – 29 for instance is at a photon energy of 2.873keV, the 72 – 116 reflection at 5.725keV. This results in an analyzed thickness of the sample surface of a few micrometers. The surface was cleaned by ion bombardment. During annealing (T≅880K), we clearly observed the progressive disappearance of the initial Bragg peak characteristic of the as cast bulk sample. Conversely a new Bragg peak grows at an energy position shifted by 1eV compared to the position of the original Bragg peak. This is a clear signature for an irreversible structural transformation which takes place on at least the micron thickness. On the transformed surface, both, a LEED pattern and a RHEED pattern, characteristic for a five fold surface were easily obtained. This high resolution experiment (the relative Bragg peak shift is 3ׁ10−4) was reproduced on samples from different initial compositions. This shows that five fold i-AlPdMn surface changes after preparation by ion bombardment and annealing at 900K on a micrometer thickness. This is not consistent with the conclusion that the surface is simply terminated by a cut of the original bulk. We conclude that a reorganization process of the quasicrystalline structure during annealing proceeds in the surface vicinity (probed depth is close to a few microns).This article is from MRS Proceedings 643 (2000): K11.4.1, doi:10.1557/PROC-643-K11.2 .</p

Morphological evolution of the fivefold surface of i-AlPdMn quasicrystals

Morphology of the fivefold symmetric quasicrystal surface of AlPdMn was investigated by x-ray reflectivity and by x-ray diffraction. X-ray experiments revealed two different morphologies depending on the surface preparation. Sputtering and annealing up to 900 K, under UHV conditions, produced a rough and facetted quasicrystal surface. These features were confirmed by atomic force microscopy and scanning tunnel microscopy measurements. We also observed that an annealing above 900 K induces a rapid and irreversible transition toward a flat surface.This article is from Physical Review B 65 (2002): 245405, doi:10.1103/PhysRevB.65.245405.</p