10,227 research outputs found
An Endolithic Microbial Community in Dolomite Rock in Central Switzerland: Characterization by Reflection Spectroscopy, Pigment Analyses, Scanning Electron Microscopy, and Laser Scanning Microscopy
A community of endolithic microorganisms dominated by phototrophs was found as a distinct band a few millimeters below the surface of bare exposed dolomite rocks in the Piora Valley in the Alps. Using in situ reflectance spectroscopy, we detected chlorophyll a (Chl a), phycobilins, carotenoids, and an unknown type of bacteriochlorophyll-like pigment absorbing in vivo at about 720nm. In cross sections, the data indicated a defined distribution of different groups of organisms perpendicular to the rock surface. High-performance liquid chromatography analyses of pigments extracted with organic solvents confirmed the presence of two types of bacteriochlorophylls besides chlorophylls and various carotenoids. Spherical organisms of varying sizes and small filaments were observed in situ with scanning electron microscopy and confocal laser scanning microscopy (one- and two-photon technique). The latter allowed visualization of the distribution of phototrophic microorganisms by the autofluorescence of their pigments within the rock. Coccoid cyanobacteria of various sizes predominated over filamentous ones. Application of fluorescence-labeled lectins demonstrated that most cyanobacteria were embedded in an exopolymeric matrix. Nucleic acid stains revealed a wide distribution of small heterotrophs. Some biological structures emitting a green autofluorescence remain to be identifie
Visibility in space - Target description subroutine
Computer subroutine for use in calculating visibility of Lunar Excursion Module /LEM/ ASCENT stage during moon orbit rendezvous with Command Service Module /CSM
Induced tungsten melting events in the divertor of ASDEX Upgrade and their influence on plasma performance
Exhaustion of Nucleation in a Closed System
We determine the distribution of cluster sizes that emerges from an initial
phase of homogeneous aggregation with conserved total particle density. The
physical ingredients behind the predictions are essentially classical:
Super-critical nuclei are created at the Zeldovich rate, and before the
depletion of monomers is significant, the characteristic cluster size is so
large that the clusters undergo diffusion limited growth. Mathematically, the
distribution of cluster sizes satisfies an advection PDE in "size-space".
During this creation phase, clusters are nucleated and then grow to a size much
larger than the critical size, so nucleation of super-critical clusters at the
Zeldovich rate is represented by an effective boundary condition at zero size.
The advection PDE subject to the effective boundary condition constitutes a
"creation signaling problem" for the evolving distribution of cluster sizes
during the creation era.
Dominant balance arguments applied to the advection signaling problem show
that the characteristic time and cluster size of the creation era are
exponentially large in the initial free-energy barrier against nucleation, G_*.
Specifically, the characteristic time is proportional to exp(2 G_*/ 5 k_B T)
and the characteristic number of monomers in a cluster is proportional to
exp(3G_*/5 k_B T). The exponentially large characteristic time and cluster size
give a-posteriori validation of the mathematical signaling problem. In a short
note, Marchenko obtained these exponentials and the numerical pre-factors, 2/5
and 3/5. Our work adds the actual solution of the kinetic model implied by
these scalings, and the basis for connection to subsequent stages of the
aggregation process after the creation era.Comment: Greatly shortened paper. Section on growth model removed. Added a
section analyzing the error in the solution of the integral equation. Added
reference
A low-loss, broadband antenna for efficient photon collection from a coherent spin in diamond
We report the creation of a low-loss, broadband optical antenna giving highly
directed output from a coherent single spin in the solid-state. The device, the
first solid-state realization of a dielectric antenna, is engineered for
individual nitrogen vacancy (NV) electronic spins in diamond. We demonstrate a
directionality close to 10. The photonic structure preserves the high spin
coherence of single crystal diamond (T2>100us). The single photon count rate
approaches a MHz facilitating efficient spin readout. We thus demonstrate a key
enabling technology for quantum applications such as high-sensitivity
magnetometry and long-distance spin entanglement.Comment: 5 pages, 4 figures and supplementary information (5 pages, 8
figures). Comments welcome. Further information under
http://www.quantum-sensing.physik.unibas.c
Monopolelike probes for quantitative magnetic force microscopy: calibration and application
A local magnetization measurement was performed with a Magnetic Force
Microscope (MFM) to determine magnetization in domains of an exchange coupled
[Co/Pt]/Co/Ru multilayer with predominant perpendicular anisotropy. The
quantitative MFM measurements were conducted with an iron filled carbon
nanotube tip, which is shown to behave like a monopole. As a result we
determined an additional in-plane magnetization component of the multilayer,
which is explained by estimating the effective permeability of the sample
within the \mu*-method.Comment: 3 pages, 3 figure
Laboratory astrophysics on ASDEX Upgrade: Measurements and analysis of K-shell O, F, and Ne spectra in the 9 - 20 A region
High-resolution measurements of K-shell emission from O, F, and Ne have been performed at the ASDEX Upgrade tokamak in Garching, Germany. Independently measured temperature and density profiles of the plasma provide a unique test bed for model validation. We present comparisons of measured spectra with calculations based on transport and collisional-radiative models and discuss the reliability of commonly used diagnostic line ratios
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