Topological restrictions for circle actions and harmonic morphisms

Let $M^m$ be a compact oriented smooth manifold which admits a smooth circle action with isolated fixed points which are isolated as singularities as well. Then all the Pontryagin numbers of $M^m$ are zero and its Euler number is nonnegative and even. In particular, $M^m$ has signature zero. Since a non-constant harmonic morphism with one-dimensional fibres gives rise to a circle action we have the following applications: (i) many compact manifolds, for example $CP^{n}$, $K3$ surfaces, $S^{2n}\times P_g$ ($n\geq2$) where $P_g$ is the closed surface of genus $g\geq2$ can never be the domain of a non-constant harmonic morphism with one-dimensional fibres whatever metrics we put on them; (ii) let $(M^4,g)$ be a compact orientable four-manifold and $\phi:(M^4,g)\to(N^3,h)$ a non-constant harmonic morphism. Suppose that one of the following assertions holds: (1) $(M^4,g)$ is half-conformally flat and its scalar curvature is zero, (2) $(M^4,g)$ is Einstein and half-conformally flat, (3) $(M^4,g,J)$ is Hermitian-Einstein. Then, up to homotheties and Riemannian coverings, $\phi$ is the canonical projection $T^4\to T^3$ between flat tori.Comment: 18 pages; Minor corrections to Proposition 3.1 and small changes in Theorem 2.8, proof of Theorem 3.3 and Remark 3.

Inversion of Randomly Corrugated Surfaces Structure from Atom Scattering Data

The Sudden Approximation is applied to invert structural data on randomly corrugated surfaces from inert atom scattering intensities. Several expressions relating experimental observables to surface statistical features are derived. The results suggest that atom (and in particular He) scattering can be used profitably to study hitherto unexplored forms of complex surface disorder.Comment: 10 pages, no figures. Related papers available at http://neon.cchem.berkeley.edu/~dan

Erscheinungsjahr: 2009.

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TESTING LASER-STRUCTURED SURFACES AS ANTIMICROBIAL COUNTERMEASURE ON ISS – INSIGHTS INTO THE BIOFILMS & TOUCHING SURFACES PROJECTS

Long term space missions and space habitat design require efficient strategies to sustain crew’s health as well as material integrity. While many microorganisms are essential to our health, there are also pathogenic microorganisms which cause infections and opportunistic pathogens which can cause infections given the right circumstances such as a weakened immune system. Due to the conditions in space, astronauts often have a compromised immune system. Due to limited treatment options as well as the inability to return to Earth, hence opportunistic pathogens can cause a threat to the crew’s health. Frequently touched surfaces can pose a key niche for microorganisms, but with the help of antimicrobial surfaces, the microbial burden could be reduced. With the introduction of antimicrobial surfaces for medical, pharmaceutical and industrial purposes the unique potential for reducing and preventing biofilm formation has been shown. Within the DLR-ESA BIOFILMS experiment on the International Space Station (ISS), we evaluate biofilm formation on various antimicrobial surfaces under spaceflight conditions. These surfaces are composed of different metals with and without specified surface texture modifications. All surfaces have undergone specific surface modification by Ultrashort Pulsed Direct Laser Interference Patterning (USP-DLIP). The BIOFILMS experiment studies the biofilm formation potential of different microbial species in microgravity on the ISS. In the scope of this, the interaction between the surfaces and bacteria, which is highly determined by topography and surface chemistry, will be investigated. Beside actively growing microorganisms on surfaces as done in BIOFILMS - another approach to monitor and reduce microbial contamination is tested in the spaceflight experiment Touching Surfaces, where different chemically and topographically surfaces including stainless steel as inert surface, brass and copper are tested. The different surfaces are placed in so-called Touch Arrays, which are installed on the ISS, schools in Germany as well as a university hospital in Germany. Here, the antimicrobial materials were touched in regular (controlled) fashion by the astronauts, participating scientists and volunteers (e.g., teachers and pupils) to determine material longevity and (short/long-term) antimicrobial functionality and efficiency as well as (public) acceptance/utilization. The data generated will be indispensable for the future selection of antimicrobial materials in support of human- and robotic-associated activities in space exploration