Quantum slow motion

We simulate the center of mass motion of cold atoms in a standing, amplitude modulated, laser field as an example of a system that has a classical mixed phase-space. We show a simple model to explain the momentum distribution of the atoms taken after any distinct number of modulation cycles. The peaks corresponding to a classical resonance move towards smaller velocities in comparison to the velocities of the classical resonances. We explain this by showing that, for a wave packet on the classical resonances, we can replace the complicated dynamics in the quantum Liouville equation in phase-space by the classical dynamics in a modified potential. Therefore we can describe the quantum mechanical motion of a wave packet on a classical resonance by a purely classical motion

Zur Interpretation der Dosiswirkungsbeziehungen in der Strahlenbiologie

Der Zufallscharakter zellulärer Strahleneffekte muß nicht stets auf einer Variabilität der Strahlenempfindlichkeit oder auf einer inhomogenen Verteilung der absorbierten Energie auf die Einheiten einer bestrahlten Population oder ihre ldquorTreffbereicheldquo beruhen, sondern kann auch bei einer kontinuierlich mit der Dosis zunehmenden ldquordispersen Vorschädigungldquoaller Einheiten zustandekommen, wenn diese die inhärente Labilität des lebenden Systems erhöht. Das zufallsartige ldquorkritische Ereignisldquo, das über das Eintreten der Testreaktion entscheidet, muß daher nicht unbedingt schon durch die Energieabsorption gegeben sein, sondern kann in einem späteren Glied der Ursachenkette liegen. Charakteristisch für den Verlauf von Überlebenskurven ist ihre Neigung in halblogarithmischer Darstellung; wir bezeichnen diese Größe als ldquorReaktivitätldquo. Kurvenformen, die bisher durch den Mehrtreffer- oder Mehrbereichsansatz gedeutet wurden, ergeben sich auch, wenn man allein die Tatsache berücksichtigt, daß die Reaktivität mit der Dosis ansteigen kann. Strebt die Reaktivität mit steigender Dosis einem Endwert zu, so kann dies darauf beruhen, daß eine dem vitalen Objekt inhärente Kompensationsfähigkeit sich mit der Dosis erschöpft. In einigen Fällen wird die biochemische Natur einer solchen Kompensationsfähigkeit bereits deutlich

Pure hydrogen low-temperature plasma exposure of HOPG and graphene: Graphane formation?

Single- and multilayer graphene and highly ordered pyrolytic graphite (HOPG) were exposed to a pure hydrogen low-temperature plasma (LTP). Characterizations include various experimental techniques such as photoelectron spectroscopy, Raman spectroscopy and scanning probe microscopy. Our photoemission measurement shows that hydrogen LTP exposed HOPG has a diamond-like valence-band structure, which suggests double-sided hydrogenation. With the scanning tunneling microscopy technique, various atomic-scale charge-density patterns were observed, which may be associated with different C-H conformers. Hydrogen-LTP-exposed graphene on SiO₂ has a Raman spectrum in which the D peak to G peak ratio is over 4, associated with hydrogenation on both sides. A very low defect density was observed in the scanning probe microscopy measurements, which enables a reverse transformation to graphene. Hydrogen-LTP-exposed HOPG possesses a high thermal stability, and therefore, this transformation requires annealing at over 1000 °C

Identification and characterization of novel factors that act in the nonsense-mediated mRNA decay pathway in nematodes, flies and mammals

Nonsense-mediated mRNA decay (NMD) is a surveillance mechanism that degrades mRNAs harboring premature termination codons (PTCs). We have conducted a genome-wide RNAi screen in Caenorhabditis elegans that resulted in the identification of five novel NMD genes that are conserved throughout evolution. Two of their human homologs, GNL2 (ngp-1) and SEC13 (npp-20), are also required for NMD in human cells. We also show that the C. elegans gene noah-2, which is present in Drosophila melanogaster but absent in humans, is an NMD factor in fruit flies. Altogether, these data identify novel NMD factors that are conserved throughout evolution, highlighting the complexity of the NMD pathway and suggesting that yet uncovered novel factors may act to regulate this process

Anisotropic Etching of Graphite and Graphene in a Remote Hydrogen Plasma

We investigate the etching of a pure hydrogen plasma on graphite samples and graphene flakes on SiO$_2$ and hexagonal Boron-Nitride (hBN) substrates. The pressure and distance dependence of the graphite exposure experiments reveals the existence of two distinct plasma regimes: the direct and the remote plasma regime. Graphite surfaces exposed directly to the hydrogen plasma exhibit numerous etch pits of various size and depth, indicating continuous defect creation throughout the etching process. In contrast, anisotropic etching forming regular and symmetric hexagons starting only from preexisting defects and edges is seen in the remote plasma regime, where the sample is located downstream, outside of the glowing plasma. This regime is possible in a narrow window of parameters where essentially all ions have already recombined, yet a flux of H-radicals performing anisotropic etching is still present. At the required process pressures, the radicals can recombine only on surfaces, not in the gas itself. Thus, the tube material needs to exhibit a sufficiently low H radical recombination coefficient, such a found for quartz or pyrex. In the remote regime, we investigate the etching of single layer and bilayer graphene on SiO$_2$ and hBN substrates. We find isotropic etching for single layer graphene on SiO$_2$, whereas we observe highly anisotropic etching for graphene on a hBN substrate. For bilayer graphene, anisotropic etching is observed on both substrates. Finally, we demonstrate the use of artificial defects to create well defined graphene nanostructures with clean crystallographic edges.Comment: 7 pages, 4 color figure

The common feeder cockroach Blaptica dubia shows increased transmission distance based on mode of acquisition of environmental bacteria

Although some researchers claim that cockroaches are masters of disease transmission, these claims have little to no scientific support. Most studies concerning cockroaches as a vector of disease only focus on the bacteria found on the body surface, not on whether cockroaches have actually transferred pathogenic bacteria via surface contact. We set out to determine if cockroaches would act as a mechanical vector for the transfer of the opportunistic pathogen, E. coli. Roaches were contaminated with Green fluorescent protein expressing E. coli (GFP-E.coli) broth by either walking the roach through a broth culture or by complete immersion in the culture.. We then ran the roaches down a sterile agar track and measured the length of the glowing trail. Roaches were able to transmit E.coli, but only for a continuous distance of less than 50 cm, with the occasional sporadic colony growing after that. Roaches that were immersed in bacterial broth tracked the bacterium further than those that only walked through the solution. This suggests that while cockroaches are capable of acting as a mechanical vector, they are not capable of transporting transient flora over long distances. Future studies should explore this mechanism