717 research outputs found
Biphasic Culture of Arcobacter spp.
Arcobacter spp. have recently been genetically differentiated as a genus distinct from Campylobacter. Physiologically, Arcobacter spp. are aerotolerant bacteria, while Campylobacter spp. are microaerophilic. However, since Arcobacter spp. have been difficult to grow to high population densities in broth media, alternative culture techniques were investigated. A biphasic culture system was developed in 25 cm2 tissue culture flasks. Biphasic culture, consisting of a solid phase of 10% bovine blood agar and a liquid phase of Brain Heart Infusion broth, was found to increase bacterial population densities by more than 2 log10 cycles for strains of A. butzleri and A. skirrowii. A strain of A. cryaerophilus, which was non-culturable in broth culture, attained population densities of 109 cells ml-1 in biphasic culture. Neither the addition of fetal bovine serum to the liquid nor an increase in the surface area from 25 to 75 cm2 resulted in increased cell densities
Neutron tomography in modern archaeology
The search for non invasive and non destructive techniques is fundamental when dealing with samples of great historical, cultural and artistic value as well as with samples strongly degraded. Among different techniques, Neutron Tomography NT allows a close analysis of samples of Archaeological interest without damaging them. In what follows, a few cases in which the Neutron Tomography instrument of the BENSC at HMI Berlin has been successfully applied will be show
Impact of catalyst layer morphology on the operation of high temperature PEM fuel cells
Electrochemical impedance spectroscopy (EIS) is a well-established method to analyze a polymer electrolyte membrane fuel cell (PEMFC). However, without further data processing, the impedance spectrum yields only qualitative insight into the mechanism and individual contribution of transport, kinetics, and ohmic losses to the overall fuel cell limitations. The distribution of relaxation times (DRT) method allows quantifying each of these polarization losses and evaluates their contribution to a given electrocatalyst\u27s depreciated performances. We coupled this method with a detailed morphology study to investigate the impact of the 3D-structure on the processes occurring inside a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC). We tested a platinum catalyst (Pt/C), a platinum-cobalt alloy catalyst (PtCo/C), and a platinum group metal-free iron-nitrogen-carbon (Fe–N–C) catalyst. We found that the hampered mass transport in the latter is mainly responsible for its low performance in the MEA (along with its decreased intrinsic performances for the ORR reaction). The better performance of the alloy catalyst can be explained by both improved mass transport and a lower ORR resistance. Furthermore, single-cell tests show that the catalyst layer morphology influences the distribution of phosphoric acid during conditioning
In situ radiographic investigation of de lithiation mechanisms in a tin electrode lithium ion battery.
The lithiation and delithiation mechanisms of multiple Sn particles in a customized flat radiography cell were investigated by in amp; 8197;situ synchrotron radiography. For the first time, four de lithiation phenomena in a Sn electrode battery system are highlighted 1 amp; 8197;the de lithiation behavior varies between different Sn particles, 2 amp; 8197;the time required to lithiate individual Sn particles is markedly different from the time needed to discharge the complete battery, 3 amp; 8197;electrochemical deactivation of originally electrochemically active particles is reported, and 4 amp; 8197;a change of electrochemical behavior of individual particles during cycling is found and explained by dynamic changes of de lithiation pathways amongst particles within the electrode. These unexpected findings fundamentaly expand the understanding of the underlying de lithiation mechanisms inside commercial lithium ion batteries LIBs and would open new design principles for high performance next generation LIB
Charmonium Spectrum from Quenched Anisotropic Lattice QCD
We present a detailed study of the charmonium spectrum using anisotropic
lattice QCD. We first derive a tree-level improved clover quark action on the
anisotropic lattice for arbitrary quark mass. The heavy quark mass dependences
of the improvement coefficients, i.e. the ratio of the hopping parameters
and the clover coefficients , are examined at the tree
level. We then compute the charmonium spectrum in the quenched approximation
employing anisotropic lattices. Simulations are made with
the standard anisotropic gauge action and the anisotropic clover quark action
at four lattice spacings in the range =0.07-0.2 fm. The clover
coefficients are estimated from tree-level tadpole improvement. On
the other hand, for the ratio of the hopping parameters , we adopt both
the tree-level tadpole-improved value and a non-perturbative one. We calculate
the spectrum of S- and P-states and their excitations. The results largely
depend on the scale input even in the continuum limit, showing a quenching
effect. When the lattice spacing is determined from the splitting, the
deviation from the experimental value is estimated to be 30% for the
S-state hyperfine splitting and 20% for the P-state fine structure. Our
results are consistent with previous results at obtained by Chen when
the lattice spacing is determined from the Sommer scale . We also address
the problem with the hyperfine splitting that different choices of the clover
coefficients lead to disagreeing results in the continuum limit.Comment: 43 pages, 49 eps figures, revtex; minor changes, version to appear in
Physical Review
Capturing 3D Water Flow in Rooted Soil by Ultra fast Neutron Tomography
AbstractWater infiltration in soil is not only affected by the inherent heterogeneities of soil, but even more by the interaction with plant roots and their water uptake. Neutron tomography is a unique non-invasive 3D tool to visualize plant root systems together with the soil water distribution in situ. So far, acquisition times in the range of hours have been the major limitation for imaging 3D water dynamics. Implementing an alternative acquisition procedure we boosted the speed of acquisition capturing an entire tomogram within 10 s. This allows, for the first time, tracking of a water front ascending in a rooted soil column upon infiltration of deuterated water time-resolved in 3D. Image quality and resolution could be sustained to a level allowing for capturing the root system in high detail. Good signal-to-noise ratio and contrast were the key to visualize dynamic changes in water content and to localize the root uptake. We demonstrated the ability of ultra-fast tomography to quantitatively image quick changes of water content in the rhizosphere and outlined the value of such imaging data for 3D water uptake modelling. The presented method paves the way for time-resolved studies of various 3D flow and transport phenomena in porous systems.</jats:p
Reduzierung von Missing Wedge Artefakten mit DIRECTT
Wir stellen eine Prozedur vor, mit der typische Missing Wedge MW Artefakte in CT Rekonstruktionen effektiv unterdrückt werden können. Dazu wird der iterative DIRECTT Algorithmus Direkte Iterative Rekonstruktion Computertomographischer Trajektorien mit einigen Zyklen diskreter Rekonstruk tion eingesetzt. Die Kernfunktionen des Algorithmus , die wiederholte Auswahl und Gewichtung von Elementen einer Zwischenrekonstruktion, werden beibehalten. Abgesehen von Sonderfällen der Röntgen und Neutronentomographie tritt die MW Restriktion neben einer Vielzahl anderer in Standardkonfigurationen der Elektronentomographie auf. Um den MW Effekt isoliert zu untersuchen und beurteilen zu können, werden hier vollständige experimentelle Datensätze einer bekannten Porenstruktur um einen Sektor beschnitten sowie MW Rekonstruktionen von Porenmodellen erzeugt. Die Ergebnisse werden mit zurzeit verbreiteten Algorithmen Gefilterte Rückprojektion FBP und ART Varianten verglichen. Die Bewertung im Fourierraum zeigt, dass DIRECTT die fehlende Information im MW erfolgreich ergänzt. Zur quantitativen Bewertung der lokalen Rekonstruktions qualität werden Methoden der räumlichen Statistik eingesetz
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