Nutrient cycling and field-based partial nutrient balances in two mountain oases of Oman

Little is known about nutrient fluxes as a criterion to assess the sustainability of traditional irrigation agriculture in eastern Arabia. In this study GIS-based field research on terraced cropland and groves of date palm (Phoenix dactylifera L.) was conducted over 2 years in two mountain oases of northern Oman to determine their role as hypothesized sinks for nitrogen (N), phosphorus (P) and potassium (K). At Balad Seet 55% of the 385 fields received annual inputs of 100–500 kg N ha^-1 and 26% received 500–1400 kg N ha^-1. No N was applied to 19% of the fields which were under fallow. Phosphorus was applied annually at 1–90 kg ha^-1 on 46% of the fields, whereas 27% received 90–210 kg ha^-1. No K was applied to 27% of the fields, 32% received 1–300 kg K ha^-1, and the remaining fields received up to 1400 kg ha^-1. At Maqta N-inputs were 61–277 kg ha^-1 in palm groves and 112–225 kg ha^-1 in wheat (Triticum spp.) fields, respective P inputs were 9–40 and 14–29 kg ha^-1, and K inputs were 98–421 and 113–227 kg ha^-1. For cropland, partial oasis balances (comprising inputs of manure, mineral fertilizers, N2-fixation and irrigation water, and outputs of harvested products) were similar for both oases, with per hectare surpluses of 131 kg N, 37 kg P, and 84 kg K at Balad Seet and of 136 kg N, 16 kg P and 66 kg K at Maqta. This was despite the fact that N2-fixation by alfalfa (Medicago sativa L.), estimated at up to 480 kg ha^-1 yr^-1 with an average total dry matter of 22 t ha^-1, contributed to the cropland N-balance only at the former site. Respective palm grove surpluses, in contrast were with 303 kg N, 38 kg P, and 173 kg K ha^-1 much higher at Balad Seet than with 84 kg N, 14 kg P, and 91 kg K ha^-1 at Maqta. The data show that both oases presently are large sinks for nutrients. Potential gaseous and leaching losses could at least partly be controlled by a decrease in nutrient input intensity and careful incorporation of manure.

Evolving Classifiers - Evolutionary Algorithms in Data Mining

Data mining means to summarize information from large amounts of raw data. It is one of the key technologies in many areas of economy, science, administration and the internet. In this report we introduce an approach for utilizing evolutionary algorithms to breed fuzzy classifier systems. This approach was exercised as part of a structured procedure by the students Achler, Göb and Voigtmann as contribution to the 2006 Data-Mining-Cup contest, yielding encouragingly positive results.

Algorithmen für regelmäßige Kettenbrüche

Die Arbeit soll einen Einblick in die Theorie der Kettenbrüche geben. Wir haben gesehen, dass schwer greifbare Zahlen als Kettenbrüche ausgedrückt werden können. Es ist besonders hervorzuheben, dass irrationale Zahlen mit Hilfe einer Abschätzung vereinfacht durch Kettenbrüche dargestellt werden können. Weiter sind wir auch darauf eingegangen, wie wir Kettenbrüche wieder in eine rationale Darstellung umwandeln können. Es wurde gezeigt, wie wir rationale Zahlen als endlichen Kettenbrüche schreiben können. Die endlichen Kettenbrüche lieferten uns dann die Grundlage, um unendliche zu betrachten, wobei das größte Augenmerk darauf gerichtet war, dass wir eine irrationale Zahl durch einen unendlichen Kettenbruch abschätzen können. Den Kern der Arbeit bildet der Kettenbruch-Algorithmus, mit dessen Hilfe wir irrationale Zahlen in einen Kettenbruch umwandeln können. Ein wichtiger Aspekt sind auch die Abschätzungen, die wir vorgenommen haben. Mit ihrer Hilfe können wir sehen, wie dicht die letzte Konvergente der Kettenbruchentwicklung an der gesuchten irrationalen Zahl liegt. Da die Konvergenten immer aus teilerfremden Zählern und Nennern bestehen, können wir sogar sagen, dass eine Konvergente die beste Approximation an eine irrationale Zahl bietet. Es ist die beste Approximation in dem Sinne, dass keine rationale Zahl mit kleinerem oder gleichem Nenner existiert, die die irrationale Zahl besser annähert. Ein weiterer wichtiger Aspekt der Kettenbruchtheorie ist, dass quadratische Irrationalitäten endlich durch einen periodischen Kettenbruch dargestellt werden können. Es ist bemerkenswert, dass Kettenbrüche von quadratischen Irrationalitäten eine Regelmäßigkeit aufweisen, so dass sie endlich als periodicher Kettenbruch geschrieben werden können.

1st Kassel Student Workshop on Security in Distributed Systems

With this document, we provide a compilation of in-depth discussions on some of the most current security issues in distributed systems. The six contributions have been collected and presented at the 1st Kassel Student Workshop on Security in Distributed Systems (KaSWoSDS’08). We are pleased to present a collection of papers not only shedding light on the theoretical aspects of their topics, but also being accompanied with elaborate practical examples. In Chapter 1, Stephan Opfer discusses Viruses, one of the oldest threats to system security. For years there has been an arms race between virus producers and anti-virus software providers, with no end in sight. Stefan Triller demonstrates how malicious code can be injected in a target process using a buffer overflow in Chapter 2. Websites usually store their data and user information in data bases. Like buffer overflows, the possibilities of performing SQL injection attacks targeting such data bases are left open by unwary programmers. Stephan Scheuermann gives us a deeper insight into the mechanisms behind such attacks in Chapter 3. Cross-site scripting (XSS) is a method to insert malicious code into websites viewed by other users. Michael Blumenstein explains this issue in Chapter 4. Code can be injected in other websites via XSS attacks in order to spy out data of internet users, spoofing subsumes all methods that directly involve taking on a false identity. In Chapter 5, Till Amma shows us different ways how this can be done and how it is prevented. Last but not least, cryptographic methods are used to encode confidential data in a way that even if it got in the wrong hands, the culprits cannot decode it. Over the centuries, many different ciphers have been developed, applied, and finally broken. Ilhan Glogic sketches this history in Chapter 6.

Intrinsic channel closing in strong-field single ionization of H2

Die Ionisation von H2 in intensiven Laserpulsen wird mit Hilfe der numerischen Integration der zeitabhängigen Schrödingergleichung für ein Einelektronenmodell untersucht, das die Vibrationsbewegung berücksichtigt. Die Spektren der kinetischen Elektronenenergie hängen stark von der Vibrationsquantenzahl des erzeugten H2+ Ions ab. Für bestimmte Vibrationszustände ist die Ausbeute der Elektronen in der Mitte des Plateaus stark erhöht. Der Effekt wird "channel closings" zugeschrieben, die in Atomen durch Variation der Laserintensität beobachtet wurden. The ionization of H2 in intense laser pulses is studied by numerical integration of the time-dependent Schrödinger equation for a single-active-electron model including the vibrational motion. The electron kinetic energy spectra in high-order above-threshold ionization are strongly dependent on the vibrational quantum number of the created H2+ ion. For certain vibrational states, the electron yield in the mid-plateau region is strongly enhanced. The effect is attributed to channel closings, which were previously observed in atoms by varying the laser intensity.

Precision laser spectroscopy of the ground state hyperfine splitting of hydrogenlike ^209 Bi^82+

The first direct observation of a hyperfine splitting in the optical regime is reported. The wavelength of the M1 transition between the F = 4 and F = 5 hyperfine levels of the ground state of hydrogenlike ^209 Bi^82+ was measured to be \lamda_0 = 243.87(4) nm by detection of laser induced fluorescence at the heavy-ion storage ring ESR at GSI. In addition, the lifetime of the laser excited F = 5 sublevel was determined to be \tau_0 = 0.351(16) ms. The method can be applied to a number of other nuclei and should allow a novel test of QED corrections in the previously unexplored combination of strong magnetic and electric fields in highly charged ions.