252 research outputs found
Comment on "Probing the equilibrium dynamics of colloidal hard spheres above the mode-coupling glass transition"
In the Letter [PRL 102, 085703 (2009)] Brambilla, et al. claimed to observe
activated dynamics in colloidal hard spheres above the critical packing
fraction of mode coupling theory (MCT). By performing microscopic MCT
calculations, we show that polydispersity in their system shifts the critical
packing fraction above the value determined by van Megen et al. for less
polydisperse samples, and that the data agree with theory except for, possibly,
the highest packing fraction.Comment: Comment in print in Phys. Rev. Lett.; for accompanying reply see
arXiv Brambilla et al. (Monday 18.10.2010
XPP: X-ray Pump Probe station at BESSY II
The X-ray Pump-Probe (XPP) experimental station predominantly aims at investigating hard and soft matter under a broad range of ambient conditions using time-resolved X-ray diffraction
Contactless 2-dimensional laser sensor for 3-dimensional wire position and tension measurements
We have developed a contact-free 2-dimensional laser sensor with which the
position of wires can be measured in 3 dimensions with an accuracy of better
than 10 micrometer and with which the tension of the wires can be determined
with an accuracy of 0.04 N. These measurements can be made from a distance of
15 cm. The sensor consists of commercially available laser pointers, lenses,
color filters and photodiodes. In our application we have used this laser
sensor together with an automated 3 dimensional coordinate table. For a single
position measurement, the laser sensor is moved by the 3-dimensional coordinate
table in a plane and determines the coordinates at which the wires intersect
with this plane. The position of the plane itself (the third coordinate) is
given by the third axis of the measurement table which is perpendicular to this
plane. The control and readout of the table and the readout of the laser sensor
were realized with LabVIEW. The precision of the position measurement in the
plane was determined with wires of 0.2 mm and 0.3 mm diameter. We use the
sensor for the quality assurance of the wire electrode modules for the KATRIN
neutrino mass experiment. We expect that the precision is at least comparable
or better if the wires are thinner. Such a device could be well suited for the
measurement of wire chamber geometries even with more than one wire layer.Comment: 15 pages, 8 figure
Primordial Earth mantle heterogeneity caused by the Moon-forming giant impact
The giant impact hypothesis for Moon formation successfully explains the
dynamic properties of the Earth-Moon system but remains challenged by the
similarity of isotopic fingerprints of the terrestrial and lunar mantles.
Moreover, recent geochemical evidence suggests that the Earth's mantle
preserves ancient (or "primordial") heterogeneity that predates the
Moon-forming giant impact. Using a new hydrodynamical method, we here show that
Moon-forming giant impacts lead to a stratified starting condition for the
evolution of the terrestrial mantle. The upper layer of the Earth is
compositionally similar to the disk, out of which the Moon evolves, whereas the
lower layer preserves proto-Earth characteristics. As long as this predicted
compositional stratification can at least partially be preserved over the
subsequent billions of years of Earth mantle convection, the compositional
similarity between the Moon and the accessible Earth's mantle is a natural
outcome of realistic and high-probability Moon-forming impact scenarios. The
preservation of primordial heterogeneity in the modern Earth not only
reconciles geochemical constraints but is also consistent with recent
geophysical observations. Furthermore, for significant preservation of a
proto-Earth reservoir, the bulk composition of the Earth-Moon system may be
systematically shifted towards chondritic values.Comment: Comments are welcom
EpiScanGIS: an online geographic surveillance system for meningococcal disease
<p>Abstract</p> <p>Background</p> <p>Surveillance of infectious diseases increasingly relies on Geographic Information Systems (GIS). The integration of pathogen fine typing data in dynamic systems and visualization of spatio-temporal clusters are a technical challenge for system development.</p> <p>Results</p> <p>An online geographic information system (EpiScanGIS) based on open source components has been launched in Germany in May 2006 for real time provision of meningococcal typing data in conjunction with demographic information (age, incidence, population density). Spatio-temporal clusters of disease detected by computer assisted cluster analysis (SaTScan™) are visualized on maps. EpiScanGIS enables dynamic generation of animated maps. The system is based on open source components; its architecture is open for other infectious agents and geographic regions. EpiScanGIS is available at <url>http://www.episcangis.org</url>, and currently has 80 registered users, mostly from the public health service in Germany. At present more than 2,900 cases of invasive meningococcal disease are stored in the database (data as of June 3, 2008).</p> <p>Conclusion</p> <p>EpiScanGIS exemplifies GIS applications and early-warning systems in laboratory surveillance of infectious diseases.</p
Analysis of Twitter usage in an exploratory seminar setting
Despite the massive social and technological changes that have occurred due to the Web in the recent years, university courses often still emphasize time-honored teaching methods with classical learning tools and resources. During these courses students often acquire knowledge that is not up-to-date and detached from problem-based, realistic learning. The use of more recent tools and methods often remains out of student’s grasp. In this article we briefly report on an exploratory seminar setting at two German universities where the use of Social Media for communication and collaboration was firmly embedded in the educational setup. Furthermore, we illustrate the usage of Twitter during the seminar using techniques from Social Network Analysis
The impact of physiological noise on hemodynamic-derived estimates of directed functional connectivity
This work was supported by a grant of the BrainLinks-BrainTools Cluster of Excellence funded by the German Research Foundation (DFG, Grant Number EXC 1086).Peer reviewedPostprintPostprin
3D bioprinting of mineralizing cyanobacteria as novel approach for the fabrication of living building materials
Living building materials (LBM) are gaining interest in the field of sustainable alternative construction materials to reduce the significant impact of the construction industry on global CO2 emissions. This study investigated the process of three-dimensional bioprinting to create LBM incorporating the cyanobacterium Synechococcus sp. strain PCC 7002, which is capable of producing calcium carbonate (CaCO3) as a biocement. Rheology and printability of biomaterial inks based on alginate-methylcellulose hydrogels containing up to 50 wt% sea sand were examined. PCC 7002 was incorporated into the bioinks and cell viability and growth was characterized by fluorescence microscopy and chlorophyll extraction after the printing process. Biomineralization was induced in liquid culture and in the bioprinted LBM and observed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and through mechanical characterization. Cell viability in the bioprinted scaffolds was confirmed over 14 days of cultivation, demonstrating that the cells were able to withstand shear stress and pressure during the extrusion process and remain viable in the immobilized state. CaCO3 mineralization of PCC 7002 was observed in both liquid culture and bioprinted LBM. In comparison to cell-free scaffolds, LBM containing live cyanobacteria had a higher compressive strength. Therefore, bioprinted LBM containing photosynthetically active, mineralizing microorganisms could be proved to be beneficial for designing environmentally friendly construction materials
Poly-acrylic Acid Brushes and Adsorbed Proteins
Planar polyelectrolyte brushes are prepared by Langmuir-Schaefer based grafting of perdeuterated (styrene)49-b-(acrylic acid)222 block copolymer (dPS-b-PAA) to dPS pre-coated silicon supports with grafting density σPAA from 0.07 to 0.11 nm-2. The structure of the solvent-swollen brushes, i. e. the volume fraction profile of polymer segments, ϕPAA, as a function of altitude z from the grafting plane into the liquid phase is extracted from neutron reflectivity measurements. We find that for all cases investigated ϕPAA(z) resembles a Gaussian profile. Although very condensed, the PAA brushes can be loaded with bovine serum albumin (BSA). The integral amount of adsorbed BSA scales linearly with grafting density. We compare our z-resolved volume fraction profile ϕBSA(z) of BSA on PAA brushes with existing literature on that system. It is found that a cross-over takes place in the adsorption scheme from ternary compressive, where proteins can approach the grafting surface only by compressing the brush, to ternary insertive, where proteins enter the brush with only local perturbation of the concentration profile, as a function of RP/Hmax, where RP is the Stokes-Radius of the protein, and Hmax is the experimentally determined maximum height of the brush
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