A discrete version of the Darboux transform for isothermic surfaces

We study Christoffel and Darboux transforms of discrete isothermic nets in 4-dimensional Euclidean space: definitions and basic properties are derived. Analogies with the smooth case are discussed and a definition for discrete Ribaucour congruences is given. Surfaces of constant mean curvature are special among all isothermic surfaces: they can be characterized by the fact that their parallel constant mean curvature surfaces are Christoffel and Darboux transforms at the same time. This characterization is used to define discrete nets of constant mean curvature. Basic properties of discrete nets of constant mean curvature are derived.Comment: 30 pages, LaTeX, a version with high quality figures is available at http://www-sfb288.math.tu-berlin.de/preprints.htm

Efficacy of plant protection substances against virus transmission by aphids infesting potato

Mit Hilfe von zeitgekoppelten Video-Aufzeichnungen wurde das Verhalten von Blattläusen auf Kartoffel-Blattscheiben untersucht. In den Experimenten wurden sowohl Geflügelte als auch Ungeflügelte von Aphis frangulae und Aulacorthum solani berücksichtigt. Als Parameter für die Beeinflussung des Verhaltens von Aphiden durch Insektizide (Ripcord 10 und Confidor) wurden die Anzahl der Probestiche, die Zeit bis zum Beginn des ersten Probestichs, die mittlere Dauer der Probestiche und die mittlere Gesamtdauer aller Probestiche in der Versuchszeit von 15 Minuten registriert. Zwischen dem Verhalten der geprüften Blattlausarten und dem der beiden Morphen ließen sich Unterschiede nachweisen. Die meisten Probestiche setzten im unteren Temperaturbereich (16°C) ungeflügelte Weibchen von A. solani. Die geringste Anzahl von Probestichen wurde für geflügelte A. frangulae ermittelt. Nach Applikation von Insektiziden reagieren die Blattläuse artspezifisch unterschiedlich. Bei beiden Arten werden die aufeinander folgenden Probestiche während der Prüfung auf Blattscheiben immer kürzer. Dieses Verhalten wird sonst bei Blattläusen auf Nichtwirtspflanzen beobachtet. Ripcord 10 verursachte eine starke Beunruhigung beider Arten, die letztlich durch eine „Schmerzhaltung“ beantwortet wird. Mit Ausnahme von ungeflügelten A. frangulae führte die Anwendung von Ripcord 10 bei den geprüften Morphen zu einer Verringerung der Anzahl von Probestichen und zumindest in der Tendenz zu einer Reduktion der Dauer der Probestiche. Die wenigsten Probestiche setzten die Blattläuse unter Einwirkung von Ripcord 10 im höheren Temperaturbereich. Der Wirkstoff Imidacloprid verursachte keine Beunruhigung der Versuchstiere, wie sie für Ripcord 10 beschrieben wurde. Während bei höheren Temperaturen die Ungeflügelten von A. solani die wenigsten Probestiche setzten, zeigten die Geflügelten dieser Art bei geringerer Temperatur die stärkste Reduktion der Anzahl der Probestiche. Die Geflügelten von A. frangulae zeigten eine entgegengesetzte Reaktion, sie führten die wenigsten Probestiche bei höherer Temperatur aus. Die Ungeflügelten dieser Art realisierten im höheren Temperaturbereich unter Einfluss von Confidor mehr Probestiche als in der Kontrolle und erhöhten auch die mittlere Gesamtdauer der Probestiche. Die Experimente mit reduzierten Aufwandmengen von Ripcord 10 ließen keine Beeinflussung der Aphiden erkennen, die zu einer verstärkten Infektionsrate von nicht persistenten Viren beiträgt.The behaviour of aphids on potato leaf-discs was analysed using time-lapse video-recording. In these experiments the behaviour of both apterous and alate Aphis frangulae and Aulacorthum solani were studied. The number of probes, the time to the onset of probing, the mean duration and the mean total duration of all probes made within a period of 15 minutes were used to characterize the effect of two insecticides (Ripcord 10 and Confidor). The behaviour of the two aphid species and the two morphs differed. At a low temperature (16°C) most probes were made by apterae of A. solani and the fewest by alate A. frangulae. After exposure to insecticides the aphids showed species specific responses. While testing the leaf surface the successive probes became shorter in both aphid species. This is typical behaviour for aphids on non host plants. Ripcord 10 induces a strong reaction in both species, which finally adopt a “pain position”, in apparent attempt to reduce body contact with the treated leaf surface. The application of Ripcord 10 caused a reduction in number of probes and duration of probes made by all the morphs except apterous A. frangulae. The lowest number of probes was made by the aphids exposed to Ripcord 10 at 25°C. Confidor did not induce the aphids to adopt a “pain position”. However, at 25°C apterous A. solani treated with this insecticide made the fewest probes, whereas the alatae made the fewest probes at 16°C. The opposite was found for alate A. frangulae, which made the fewest probes at 25°C. Exposure of apterous aphids of this species to Confidor at 25°C resulted in more and more prolonged probes than in the control, indicating such treatment might increase the risk of transmission of non-persistent viruses like PVY

Recognition and Complexity of Point Visibility Graphs

A point visibility graph is a graph induced by a set of points in the plane, where every vertex corresponds to a point, and two vertices are adjacent whenever the two corresponding points are visible from each other, that is, the open segment between them does not contain any other point of the set. We study the recognition problem for point visibility graphs: given a simple undirected graph, decide whether it is the visibility graph of some point set in the plane. We show that the problem is complete for the existential theory of the reals. Hence the problem is as hard as deciding the existence of a real solution to a system of polynomial inequalities. The proof involves simple substructures forcing collinearities in all realizations of some visibility graphs, which are applied to the algebraic universality constructions of Mnev and Richter-Gebert. This solves a longstanding open question and paves the way for the analysis of other classes of visibility graphs. Furthermore, as a corollary of one of our construction, we show that there exist point visibility graphs that do not admit any geometric realization with points having integer coordinates

HEPchain: Novel Proof-of-Useful-Work blockchain consensus for High Energy Physics

Monte Carlo simulations play a crucial role in all stages of particle collider experiments. There has been a long-term trend in HEP of both increasing collision energies and the luminosity. As a result, the requirements for MC simulations have become more rigorous: Their computational complexity has increased due to higher accuracy requirements. Additionally, more simulation data is required to allow data analysts to spot Standard Model deviations in observations of real data and enable the filtering of rare events. In order to keep up with the computational complexity of simulations and analysis of real data, distributed computing approaches are commonly employed. For instance, CERN relies on the Worldwide LHC Computing Grid (WLCG) in order to be able to store, process, distribute and analyze collision data. Since not every HEP experiment has access to these resources and the addition of new Grid servers is a complex process, this publication explores a novel distributed computing approach for HEP which is based on blockchain technology. It features the description of a novel Proof-of-Useful-Work consensus algorithm which aims to both support real-world HEP experiments with the production of required MC data and to secure the underlying blockchain infrastructure at the same time. Instead of being an alternative to WLCG or BOINC projects that rely on volunteer computing, it aims to be a complementary source of additional computing power. This publication also features a brief introduction into blockchain fundamentals and comparisons to existing distributed computing approaches.Comment: This is a Draft version that might be subjected to changes in the futur

The Critical Role of PPARγ in Human Malignant Melanoma

The past 30 years have only seen slight improvement in melanoma therapy. Despite a wide variety of therapeutic options, current survival for patients with metastatic disease is only 6–8 months. Part of the reason for this treatment failure is the broad chemoresistance of melanoma, which is due to an altered survival capacity and an inactivation of apoptotic pathways. Several targetable pathways, responsible for this survival/apoptosis resistance in melanoma, have been described and current research has focused on mechanism inactivating these pathways. As PPARγ was shown to be constitutively active in several tumour entities and PPARγ agonists extent strong anticancer effects, the role of PPARγ as a possible target for specific anticancer strategy was investigated in numerous studies. However, only a few studies have focused on the effects of PPARγ agonists in melanoma, showing conflicting results. The use of PPARγ agonists in melanoma therapy has to be carefully weighted against considerable, undesirable side effects, as their mode of action is not fully understood and even pro-proliferative effects have been described. In the current review, we discuss the role of PPARs, in particular PPARγ in melanoma and their potential role as a molecular target for melanoma therapy

Effect of short-term storage on quality of wheat stored in large polyethylene bags

Abstract: The aim of this study was to compare the short-term storage of food grains in large polyethylene bag silos with the conventional bulk storage of grain regarding quality parameters.  This storage option provides the chance to get along fluctuations in prices without investment in building operations.75 t newly harvested wheat with a dry matter content of 89.1% was stored during a period of six months in two polyethylene bags and as control in a granary on the same farm.  After two weeks, one month, three and six months samples were collected off the first bag below the polyethylene film and in 1.20 m depth and at the same time samples were taken in the granary.  The second bag was kept closed over the six month. Results demonstrated that there are no differences between the measuring points within a bag, between the two bags and no differences between the storage systems regarding the parameters dry matter, pH, starch, crude protein, content of mesophilic microorganisms (bacteria, yeast, mould) and germination.  The temperature in the polyethylene bag silos resembled rapidly to the ambient temperature.  There was no local overheating due to microbiological activity.  The results demonstrate that the temporary grain storage in polyethylene bags does not lead to any grain quality loss compared to the conventional storage.  Because of the very low cost, the flexible bagging system represents an alternative to high investment in permanent storage structures for grain. Key words: wheat, storage, polyethylene bags, quality, costs

Solving Practical Railway Crew Scheduling Problems with Attendance Rates

Arising from a practical problem in German rail passenger transport, a prototype for a multi-period railway crew scheduling problem with attendance rates for conductors is developed and evaluated in this paper. The consideration of attendance rates is of increasing importance in regional transport networks and requires decision support. For this purpose business analytics is applied in order to offer an approach to transform real-world data to concrete operational decision support (action). The focus here is on the analysis step using a new set covering model with several essential restrictions integrated for the first time. A hybrid column generation approach is applied, which solves the pricing problem by means of a genetic algorithm. The artifact is evaluated with the help of a case study of three real-world transport networks. It is shown that the hybrid solution approach is able to solve the problem more effectively and efficiently compared to conventional approaches used in practice