Positive Measure Spectrum for Schroedinger Operators with Periodic Magnetic Fields

We study Schroedinger operators with periodic magnetic field in Euclidean 2-space, in the case of irrational magnetic flux. Positive measure Cantor spectrum is generically expected in the presence of an electric potential. We show that, even without electric potential, the spectrum has positive measure if the magnetic field is a perturbation of a constant one.Comment: 17 page

Induced Gamma-band Activity Elicited by Visual Representation of Unattended Objects

Peer reviewedPostprin

6sterreichische Wasser- und Abfallwirtschaft / Synthetisch hergestellte Nanomaterialien in Konsumprodukten und deren Verbleib am Ende ihrer Nutzungsphase

Seit geraumer Zeit finden k\ufcnstlich hergestellte und oberfl\ue4chenmodifizierte Nanomaterialien in diversen Alltagsprodukten Anwendung. F\ufcr die gegenst\ue4ndliche Materialflussanalyse wurden 6 Nanokonsumprodukte ausgew\ue4hlt, die am \uf6sterreichischen Markt erh\ue4ltlich sind und vorwiegend metallische Nanomaterialien enthalten (d. h.: Nano-SiO2, -TiO2, -Ag oder CdSe-Quantenpunkte). Ein Produktbeispiel enthielt Kohlenstoffnanor\uf6hrchen (kurz CNTs). F\ufcr die Materialflussanalysen mussten die Nanomaterial-Inputmengen auf Produktebene abgesch\ue4tzt werden. Anhand von Produktinformationen sowie wissenschaftlichen Publikationen wurden erste Hochrechnungen des \uf6sterreichweiten Verbrauchs durchgef\ufchrt. Beim Produktbeispiel \u201eTV-Ger\ue4te mit Quantenpunkt-Displays\u201c war die Datengrundlage so d\ufcrftig, dass keine Mengenabsch\ue4tzung m\uf6glich war. Dieses Szenario ist aber Beispiel daf\ufcr, dass bei vielen Produktkategorien mangelnde bis keine Produktinformationen vorliegen und f\ufcr diese daher derzeit keine quantitative Absch\ue4tzung des Verbleibs von Nanomaterialien in Abfallstr\uf6men m\uf6glich ist. Die ersten Mengenabsch\ue4tzungen zeigen, dass Nano-TiO2 bereits im Tonnenma fstab in Sonnencremen eingesetzt wird (in 6sterreich ca. 5,4 bis 40,8 t/a). Nano-SiO2 in Autoversiegelungen, Nano-Ag in Wandfarben oder Putzlappen sowie CNTs in Tennisschl\ue4gern werden hingegen eher im unteren einstelligen Kilogrammma fstab eingesetzt. Anhand der Materialflussanalysen l\ue4sst sich absch\ue4tzen, dass sich metallische/metalloxidische Nanomaterialien mit hoher Wahrscheinlichkeit im Zuge der Abfallbehandlung in Sekund\ue4rabf\ue4llen, wie Verbrennungsr\ufcckst\ue4nden, anreichern, welche wiederum gr\uf6 ftenteils deponiert werden. Kohlenstoffbasierte Nanomaterialien wie CNTs werden mit hoher Wahrscheinlichkeit w\ue4hrend der Abfallverbrennung vollst\ue4ndig oxidiert. Ihre Elimination kann aber nur dann gew\ue4hrleistet werden, wenn w\ue4hrend der Verbrennung eine entsprechend lange Verweildauer bei hohen Temperaturen sichergestellt ist. Die Unsicherheiten bzw. gro fen Schwankungsbreiten der hochgerechneten Nanomaterialfl\ufcsse verdeutlichen, dass es noch gro fe Wissens- und Informationsl\ufccken gibt und vor allem entsprechender Forschungsbedarf hinsichtlich des genauen Umweltverhaltens von Nanoprodukten \u2013 insbesondere \ufcber das Verhalten und potenzielle Freisetzungspfade in der Entsorgungsphase \u2013 besteht.For some time now, engineered and surface-modified nanomaterials have been used in various everyday products. For the material flow analyses presented in the following paper, six nano-based consumer products were selected that are available on the Austrian market and primarily contain metallic nanomaterials (nano-SiO2, -TiO2, -Ag or CdSe quantum dots); one sample product contained carbon nanotubes (CNTs). For the purpose of the material flow analyses, it was necessary to estimate the amounts of nanomaterial input at the product level. On the basis of available product information and academic publications, initial estimates of consumption in Austria were prepared. In the case of the sample product \u201ctelevisions with quantum dot displays,\u201d there was too little data available to do so. However, this scenario offers valuable proof of the fact that little to no product information is available for many product categories, making it impossible to quantitatively estimate the amount of nanomaterials in waste streams. The initial estimates show that tons of nano-TiO2 are already used in sun creams (ca. 5.4 to 40.8 t/year in Austria). In contrast, only several kilograms each of nano-SiO2 (in automotive paint sealants), nano-Ag (in indoor paints and washcloths), and CNTs (in tennis rackets) are used each year. Based on the material flow analyses it can be assumed that, in the course of waste treatment, metallic/metal oxide nanomaterials very likely enrich in secondary waste like combustion residues, which in turn predominantly end up in landfills. Carbon-based nanomaterials like CNTs are most likely completely oxidized in the course of incineration. However, their elimination can only be ensured if they are subjected to high temperatures for a sufficiently long time. The uncertainties/substantial variances in the projected nanomaterial flows clearly show that there are still considerable gaps in our knowledge and available information, and that research regarding the exact environmental fate of nano-products \u2013 especially into their behavior and potential emission pathways in the disposal phase \u2013 is urgently needed

Proximal business intelligence on the semantic web

This is the post-print version of this article. The official version can be accessed from the link below - Copyright @ 2010 Springer.Ubiquitous information systems (UBIS) extend current Information System thinking to explicitly differentiate technology between devices and software components with relation to people and process. Adapting business data and management information to support specific user actions in context is an ongoing topic of research. Approaches typically focus on providing mechanisms to improve specific information access and transcoding but not on how the information can be accessed in a mobile, dynamic and ad-hoc manner. Although web ontology has been used to facilitate the loading of data warehouses, less research has been carried out on ontology based mobile reporting. This paper explores how business data can be modeled and accessed using the web ontology language and then re-used to provide the invisibility of pervasive access; uncovering more effective architectural models for adaptive information system strategies of this type. This exploratory work is guided in part by a vision of business intelligence that is highly distributed, mobile and fluid, adapting to sensory understanding of the underlying environment in which it operates. A proof-of concept mobile and ambient data access architecture is developed in order to further test the viability of such an approach. The paper concludes with an ontology engineering framework for systems of this type – named UBIS-ONTO

The 1999 Hercules X-1 Anomalous Low State

A failed main-on in the 35d cycle of Her X-1 was observed with the Rossi X-Ray Timing Explorer (RXTE) on 1999 April 26. Exceptions to the normal 35d cycle have been seen only twice before; in 1983 and again 1993. We present timing and spectral results of this latest Anomalous Low State (ALS) along with comparisons to the main-on and normal low states. Pulsations were observed in the 3-18 keV band with a fractional RMS variation of (0.037+-0.003). Spectral analysis indicates that the ALS spectrum has the same shape as the main-on but is modified by heavy absorption and scattering. We find that 70% of the observed emission has passed through a cold absorber (N_H=5.0x10^{23}cm^{-2}). This partially absorbing spectral fit can be applied to the normal low state with similar results. We find that the ALS observations may be interpreted as a decrease in inclination of the accretion disk causing the central X-Ray source to be obscured over the entire 35d cycle.Comment: revised text, 6 revised figures, accepted for publication in Ap

The average X-ray/gamma-ray spectrum of radio-quiet Seyfert 1s

We have obtained the average 1--500 keV spectrum of radio-quiet Seyfert 1s using data from EXOSAT, Ginga, HEAO, and GRO/OSSE. The spectral fit to the combined average EXOSAT and OSSE data is fully consistent with that for Ginga and OSSE, confirming results from an earlier Ginga/OSSE sample. The average spectrum is well-fitted by a power-law X-ray continuum with an energy spectral index of $\alpha \simeq 0.9$ moderately absorbed by an ionized medium and with a Compton reflection component. A high-energy cutoff (or a break) in the the power-law component at a few hundred keV or more is required by the data. We also show that the corresponding average spectrum from HEAO A1 and A4 is fully compatible with that obtained from EXOSAT, Ginga and OSSE. These results confirm that the apparent discrepancy between the results of Ginga (with $\alpha \simeq 0.9$) and the previous results of EXOSAT and HEAO (with $\alpha \simeq 0.7$) is indeed due to ionized absorption and Compton reflection first taken into account for Ginga but not for the previous missions. Also, our results confirm that the Seyfert-1 spectra are on average cut off in gamma-rays at energies of at least a few hundred keV, not at $\sim 40$ keV (as suggested earlier by OSSE data alone). The average spectrum is compatible with emission from either an optically-thin relativistic thermal plasma in a disk corona, or with a nonthermal plasma with a power-law injection of relativistic electrons.Comment: 7 pages, 3 Postscript figures, MNRAS accepte

The Use of Gamma-ray Bursts as Direction and Time Markers in SETI Strategies

When transmitting a signal over a large distance it is more efficient to send a brief beamed signal than a continuous omni-directional transmission but this requires that the receiver knows where and when to look for the transmission. For SETI, the use of various natural phenomena has previously been suggested to achieve the desired synchronization. Here it is proposed that gamma-ray bursts may well the best ``synchronizers'' of all currently known phenomena due to their large intrinsic luminosities, high occurrence rate, isotropic sky distribution, large distance from the Galaxy, short duration, and easy detectability. For targeted searches, precise positions for gamma-ray bursts are required together with precise distance measurements to a target star. The required burst position determinations are now starting to be obtained, aided in large part by the discovery of optical afterglows. Good distance measurements are currently available from Hipparcos and even better measurements should be provided by spacecraft now being developed. For non-targeted searches, positional accuracies simply better than a detector's field of view may suffice but the time delay between the detection of a gamma-ray burst and the reception of the transmitted signal cannot be predicted in an obvious way.Comment: 8 pages, accepted for publication in PAS