Diffraction phases in atom interferometers

Diffraction of atoms by laser is a very important tool for matter wave optics. Although this process is well understood, the phase shifts induced by this diffraction process are not well known. In this paper, we make analytic calculations of these phase shifts in some simple cases and we use these results to model the contrast interferometer recently built by the group of D. Pritchard at MIT. We thus show that the values of the diffraction phases are large and that they probably contribute to the phase noise observed in this experiment.Comment: v3 11/03/0

Navigation Pattern Discovery from Internet Data

Electronic commerce sites need to learn as much as possible about their customers and those browsing their virtual premises, in order to maximize their marketing effort. The discovery of marketing related navigation patterns requires the development of data mining algorithms capable of discovering sequential access patterns from web logs. This paper introduces a new algorithm called MiDAS that extends traditional sequence discovery with a wide range of web-specific features. Domain knowledge is described as flexible navigation templates that can specify navigational behavior, as network structures for the capture of web site topologies, in addition to concept hierarchies and syntactic constraints. Unlike existing approaches, field dependency has been implemented, which allows the detection of sequences across monitored attributes, such as URLs and http referrers. Three different types of contained-in relationships are supported, which express different types of browsing behavior. The carried out experimental evaluation have shown promising results in terms of functionality as well as scalability.

Automated solid-state NMR resonance assignment of protein microcrystals and amyloids

Solid-state NMR is an emerging structure determination technique for crystalline and non-crystalline protein assemblies, e.g., amyloids. Resonance assignment constitutes the first and often very time-consuming step to a structure. We present ssFLYA, a generally applicable algorithm for automatic assignment of protein solid-state NMR spectra. Application to microcrystals of ubiquitin and the Ure2 prion C-terminal domain, as well as amyloids of HET-s(218-289) and α-synuclein yielded 88-97% correctness for the backbone and side-chain assignments that are classified as self-consistent by the algorithm, and 77-90% correctness if also assignments classified as tentative by the algorithm are include

Drought affects the heat-hardening capacity of alpine plants as indicated by changes in xanthophyll cycle pigments, singlet oxygen scavenging, α-tocopherol and plant hormones

AbstractAlpine environments in Europe are increasingly affected by more erratic precipitation patterns, and more frequent drought and heat waves. Heat-hardening capacity is a key feature for survival of these abiotic stress factors, but it is poorly understood how heat and drought affect plant performance when combined. The main objectives of this study were (1) to determine maximum heat hardening capacity in 14 selected plant species and (2) to study how alpine plants respond to combined heat and drought stress compared to heat alone. (3) For risk assessment maximum leaf temperatures were measured in the field and (4) important methodological aspects of testing heat tolerance were evaluated. Heat hardening capacity was assessed by Tc, the heat threshold of photosystem II (PS II), and by heat tolerance tests based on visual inspection of leaf tissue damage or potential quantum efficiency of PS II (Fv/Fm). A purpose-built Heat Tolerance Testing System (HTTS) was used, which allows for controlled heat exposure of whole plants under nearly natural conditions. Additionally, in two species from contrasting habitats, Senecio incanus and Primula minima, the dynamics of heat hardening was studied during and after 8days exposure to heat (H), or to a combination of heat and severe drought (H+D) within a light-transmissive heat hardening chamber at the alpine field site. In both species, H treatment significantly increased heat tolerance (LT50), determined by the HTTS, to 58.0°C and 54.9°C, respectively, and was accompanied by elevated production of abscisic acid (ABA) and salicylic acid (SA), whereas jasmonic acid (JA) levels decreased. Under H+D the LT50 was only 56.5°C and 51.6°C, respectively, and levels of ABA were higher in S. incanus and SA lower in both species in comparison to H. Changes in xanthophyll cycle pigments, α-tocopherol and carotenoids:chlorophyll ratio were more pronounced in P. minima than in S. incanus. In P. minima both H and H+D significantly increased singlet oxygen (1O2) scavenging capacity, determined by electron paramagnetic resonance spectroscopy (EPR). In the field, the maximum half-hourly mean (HHM) leaf temperature of P. minima (32.2°C) was significantly lower than of S. incanus (46.5°C, a potentially harmful temperature). We conclude that the investigated species are well adapted to the prevailing temperature conditions in the field. They also possess an outstanding heat hardening capacity, but this can be curtailed when heat is combined with drought. As drought further increases leaf temperatures, the risk of suffering lethal heat damage of some species may increase in the future, particularly at south exposed, ruderal alpine sites with uncertain water supply

Synthesis of a boronic acid anhydride based ligand and its application in beryllium coordination

The synthesis of a boronic acid anhydride‐based ligand containing one three‐ and one four‐coordinated boron atom is presented. This ligand was successfully employed as a tridentate κ¹N,κ²O‐ligand in the coordination of beryllium chloride and both the ligand and the resulting complex have been structurally characterized. While the boron‐element separations are within the typical range of related homo‐nuclear compounds, the corresponding beryllium‐element distances are rather long, suggesting unexpectedly high electron density at the beryllium center. Incorporation of a beryllium atom in a six‐membered ring causes no more distortion than the corresponding boron atom, suggesting that analogous ligand systems could be used in boron and beryllium coordination chemistry. The generated hetero‐tri‐nuclear complex enables the direct comparison of bond lengths and angles at beryllium and boron atoms in similar coordination environments and can act as a monomolecular model for beryllium borates

Anisotropic Polar Magneto-Optic Kerr Effect of Ultrathin Fe/GaAs (001) Layers du to Interfacial Spin-Orbit Interaction

We report the observation of the anisotropic polar magneto-optical Kerr effect in thin layers of epitaxial Fe/GaAs(001) at room temperature. A clear twofold symmetry of the Kerr rotation angle depending on the orientation of the linear polarization of the probing laser beam with respect to the crystallographic directions of the sample is detected for ultrathin magnetic films saturated out of the film plane. The amplitude of the anisotropy decreases with increasing Fe film thickness, suggesting that the interfacial region is the origin of the anisotropy. The twofold symmetry is fully reproduced by model calculations based on an interference of interfacial Bychkov-Rashba and Dresselhaus spin-orbit coupling