Meshing highly regular structures: The case of super carbon nanotubes of arbitrary order

Mesh generation is an important step inmany numerical methods.We present the “HierarchicalGraphMeshing” (HGM)method as a novel approach to mesh generation, based on algebraic graph theory.The HGM method can be used to systematically construct configurations exhibiting multiple hierarchies and complex symmetry characteristics. The hierarchical description of structures provided by the HGM method can be exploited to increase the efficiency of multiscale and multigrid methods. In this paper, the HGMmethod is employed for the systematic construction of super carbon nanotubes of arbitrary order, which present a pertinent example of structurally and geometrically complex, yet highly regular, structures. The HGMalgorithm is computationally efficient and exhibits good scaling characteristics. In particular, it scales linearly for super carbon nanotube structures and is working much faster than geometry-based methods employing neighborhood search algorithms. Its modular character makes it conducive to automatization. For the generation of a mesh, the information about the geometry of the structure in a given configuration is added in a way that relates geometric symmetries to structural symmetries. The intrinsically hierarchic description of the resulting mesh greatly reduces the effort of determining mesh hierarchies for multigrid and multiscale applications and helps to exploit symmetry-related methods in the mechanical analysis of complex structures.

Praxisrelevante Auswirkungen des Vorschlages für eine EU-Verordnung KOM/2000/7/final, 2000/0212(COD) des europäischen Parlaments und des Rates von der Kommission der Europäischen Gemeinschaften auf die Verkehrsplanung des öffentlichen Personennahverkehrs

Die Arbeit behandelt den Vorschlag für eine EU-Verordnung KOM/2000/7/final, 2000/0212(COD) des europäischen Parlaments und des Rates von der Kommission der Europäischen Gemeinschaften als Grundlage einer Marktöffnungsverordnung und welche Veränderungen sich dadurch in Deutschland einstellen werden. Ausschreibungen von Verkehrsleistungen werden zunehmen. Die Ausschreibungsarten werden sich in ländlichen Regionen von denen in Verkehrszentren unterscheiden. In der Region werden sich Bedarfslösungen stärker durchsetzen. Kürzungen von Verkehrsleistungen werden hier stärker ausfallen als in den Zentren und damit zu einem kleineren Leistungsvolumen führen. Aufgrund des geringen Leistungsumfangs gibt es weniger Interessenten. Bei Standardausschreibungen werden deshalb auch häufig die Varianten der beschränkten oder die freihändige Vergabe gewählt. Funktionale Ausschreibungen haben nur eine untergeordnete Bedeutung. In den Verkehrszentren sind die Lose größer und damit für viele Anbieter interessant. Die Verkehrszusatzleistungen sind zudem komplexer. Standardausschreibungen in öffentlicher Vergabeart werden sich hier vermutlich als Norm durchsetzen. Die VOL/A wird sicherlich ihre Bedeutung und ihren dafür notwendigen Regelungsumfang in Deutschland als deutsches oder als europäisches Recht behalten. Ob der empfehlende Charakter der DIN EN 13816 Norm „ÖPNV: Definition, Festlegung von Leistungszielen und Messung der Servicequalität“ erhalten werden kann und nicht als Steuerungselement zur Standardisierung im ÖPNV beitragen wird, ist dabei zu bezweifeln. Durch diese Wettbewerbspflicht wird der Aufgabenträger zum Besteller von Verkehrsleistungen. Damit geht die Verkehrsplanung in die Verantwortung des Aufgabenträgers über und gerät stärker in den Einflussbereich der Politik. Die strategisch abstrakte und die konkrete Verkehrsplanung wachsen für den Normfall der Standardausschreibung zusammen. Die Hoffnung auf eine bessere Netzintegration und eine Standardisierung des ÖPNV Angebots und der ÖPNV Qualität entsteht. Es entwickelt sich dadurch aber auch die Gefahr der Abhängigkeit des Nahverkehrsangebots von der derzeitigen Haushaltslage oder der Interessenlage der Politik. Kontinuität in Angebot und Qualität werden zu erklärten Planungszielen. Der Verkehrsplaner auf der Bestellerseite muss die Planung in Ausschreibungsunterlagen umsetzen. Dies erfordert erweiterte Kompetenzen in den Bereichen Betriebswirtschaft, Logistik, Jura, Informatik und Führungskompetenzen. Ausbildende Institutionen müssen darauf bereits im Vorfeld der Umsetzung reagieren. Durch die zeitliche Verzögerung der Umsetzung der Planung durch die Ausschreibungsschritte sind in der Verkehrsplanung längere Planungsvorlaufzeiten einzukalkulieren. Vorausschauender zu planen, wird dabei wichtiger. Auch eventuelle Fehler in der Planung sind nicht mehr so einfach zu korrigieren. Durch den gestiegenen Einsatz von Technologien in den Fahrzeugen besteht für den Verkehrsplaner dafür häufiger die Möglichkeit, Planungsänderungen auf ihre Wirksamkeit im Hinblick auf Attraktivität für den Fahrgast anhand von den ermittelten Fahrgastzahlen zu kontrollieren. Dasselbe gilt auch für Marketing- und Vertriebsmaßnahmen, wie für die Tarifpolitik. Die Zahlen stehen nicht nur für diese Rückkopplung zur Verfügung, sondern dienen auch als Planungsgrundlage für zukünftige Maßnahmen. Dem Planer stehen konkretere Zahlen für die Planung zur Verfügung. Ein Aspekt, der aufgrund der Sanktionsmaßnahmen bei Ausschreibungen an Bedeutung gewinnen wird, ist die Möglichkeit, Qualität von Verkehrsleistungen möglichst objektiv beurteilen zu können. Praxisrelevante Auswirkungen auf die Verkehrsplanung des öffentlichen Personennahverkehrs ergeben sich hauptsächlich durch die gestiegene Komplexität in der Planung selbst und den dadurch unverzichtbaren gewordenen Einsatz von Computerunterstützung. Die Umsetzung in Ausschreibungsunterlagen der Planung und die Kontrolle stellen neue Elemente im Aufgabenbereich des Verkehrsplaners dar und erfordern damit breiter ausgelegte Kernkompetenzen. Es werden mehr Verkehrsplaner mit breiterer Ausbildung benötigt werden. Diese Arbeit hat aufgezeigt, dass sich mit der Integration des Ausschreibungsgedankens in den Ablauf der Verkehrsplanung eine sprunghafte Entwicklung in der Planungstätigkeit ergeben wird. Aufgrund der in Zukunft steigenden Qualität und Quantität der Planungsgrundlagen und der ebenfalls gestiegenen Ansprüche an die Bewertungsparameter ergeben sich Veränderungen und neue Anforderungen auf diesem Gebiet, die in erster Linie für die Hochschulen und andere ausbildende Einrichtungen, aber auch für die Verkehrsplanung unterstützende Industrie.

Content aggregation on knowledge bases using graph clustering

Recently, research projects such as PADLR and SWAP have developed tools like Edutella or Bibster, which are targeted at establishing peer-to-peer knowledge management (P2PKM) systems. In such a system, it is necessary to obtain provide brief semantic descriptions of peers, so that routing algorithms or matchmaking processes can make decisions about which communities peers should belong to, or to which peers a given query should be forwarded. This paper proposes the use of graph clustering techniques on knowledge bases for that purpose. Using this clustering, we can show that our strategy requires up to 58% fewer queries than the baselines to yield full recall in a bibliographic P2PKM scenario.

Agricultural practices and horizontal nutrient balances in urban gardens and the alternative use of urban agricultural land in Khartoum, Sudan

The surge in the urban population evident in most developing countries is a worldwide phenomenon, and often the result of drought, conflicts, poverty and the lack of education opportunities. In parallel with the growth of the cities is the growing need for food which leads to the burgeoning expansion of urban and peri-urban agriculture (UPA). In this context, urban agriculture (UA) contributes significantly to supplying local markets with both vegetable and animal produce. As an income generating activity, UA also contributes to the livelihoods of poor urban dwellers. In order to evaluate the nutrient status of urban soils in relation to garden management, this study assessed nutrient fluxes (inputs and outputs) in gardens on urban Gerif soils on the banks of the River Nile in Khartoum, the capital city of Sudan. To achieve this objective, a preliminary baseline survey was carried out to describe the structure of the existing garden systems. In cooperation with the author of another PhD thesis (Ms. Ishtiag Abdalla), alternative uses of cow dung in brick making kilns in urban Khartoum were assessed; and the socio-economic criteria of the brick kiln owners or agents, economical and plant nutritional value of animal dung and the gaseous emission related to brick making activities were assessed. A total of 40 household heads were interviewed using a semi-structured questionnaire to collect information on demographic, socio-economic and migratory characteristics of the household members, the gardening systems used and the problems encountered in urban gardening. Based on the results of this survey, gardens were divided into three groups: mixed vegetable-fodder gardens, mixed vegetable-subsistence livestock gardens and pure vegetable gardens. The results revealed that UA is the exclusive domain of men, 80% of them non-native to Khartoum. The harvested produce in all gardens was market oriented and represented the main source of income for 83% of the gardeners. Fast growing leafy vegetables such as Jew’s mallow (Corchorous olitorius L.), purslane (Portulaca oleracea L.) and rocket (Eruca sativa Mill.) were the dominant cultivated species. Most of the gardens (95%) were continuously cultivated throughout the year without any fallow period, unless they were flooded. Gardeners were not generally aware of the importance of crop diversity, which may help them overcome the strongly fluctuating market prices for their produce and thereby strengthen the contributions of UA to the overall productivity of the city. To measure nutrient fluxes, four gardens were selected and their nutrients inputs and outputs flows were monitored. In each garden, all plots were monitored for quantification of nutrient inputs and outputs. To determine soil chemical fertility parameters in each of the studied gardens, soil samples were taken from three selected plots at the beginning of the study in October 2007 (gardens L1, L2 and H1) and in April 2008 (garden H2) and at the end of the study period in March 2010. Additional soil sampling occurred in May 2009 to assess changes in the soil nutrient status after the River Nile flood of 2008 had receded. Samples of rain and irrigation water (river and well-water) were analyzed for nitrogen (N), phosphorus (P), potassium (K) and carbon (C) content to determine their nutrient inputs. Catchment traps were installed to quantify the sediment yield from the River Nile flood. To quantify the nutrient inputs of sediments, samples were analyzed for N, P, K and organic carbon (Corg) content, cation exchange capacity (CEC) and the particle size distribution. The total nutrient inputs were calculated by multiplying the sediment nutrient content by total sediment deposits on individual gardens. Nutrient output in the form of harvested yield was quantified at harvest of each crop. Plant samples from each field were dried, and analyzed for their N, P, K and Corg content. Cumulative leaching losses of mineral N and P were estimated in a single plot in garden L1 from December 1st 2008 to July 1st 2009 using 12 ion exchange resins cartridges. Nutrients were extracted and analyzed for nitrate (NO3--N), ammonium (NH4+-N) and phosphate PO4-3-P. Changes in soil nutrient balance were assessed as inputs minus outputs. The results showed that across gardens, soil N and P concentrations increased from 2007 to 2009, while particle size distribution remained unchanged. Sediment loads and their respective contents of N, P and Corg decreased significantly (P < 0.05) from the gardens of the downstream lowlands (L1 and L2) to the gardens of the upstream highlands (H1 and H2). No significant difference was found in K deposits. None of the gardens received organic fertilizers and the only mineral fertilizer applied was urea (46-0-0). This equaled 29, 30, 54, and 67% of total N inputs to gardens L1, L2, H1, and H2, respectively. Sediment deposits of the River Nile floods contributed on average 67, 94, 6 and 42% to the total N, P, K and C inputs in lowland gardens and 33, 86, 4 and 37% of total N, P, K and C inputs in highland gardens. Irrigation water and rainfall contributed substantially to K inputs representing 96, 92, 94 and 96% of total K influxes in garden L1, L2, H1 and H2, respectively. Following the same order, total annual DM yields in the gardens were 26, 18, 16 and 1.8 t ha-1. Annual leaching losses were estimated to be 0.02 kg NH4+-N ha-1 (SE = 0.004), 0.03 kg NO3--N ha-1 (SE = 0.002) and 0.005 kg PO4-3-P ha-1 (SE = 0.0007). Differences between nutrient inputs and outputs indicated negative nutrient balances for P and K and positive balances of N and C for all gardens. The negative balances in P and K call for adoptions of new agricultural techniques such as regular manure additions or mulching which may enhance the soil organic matter status. A quantification of fluxes not measured in our study such as N2-fixation, dry deposition and gaseous emissions of C and N would be necessary to comprehensively assess the sustainability of these intensive gardening systems. The second part of the survey dealt with the brick making kilns. A total of 50 brick kiln owners/or agents were interviewed from July to August 2009, using a semi-structured questionnaire. The data collected included general information such as age, family size, education, land ownership, number of kilns managed and/or owned, number of months that kilns were in operation, quantity of inputs (cow dung and fuel wood) used, prices of inputs and products across the production season. Information related to the share value of the land on which the kilns were built and annual income for urban farmers and annual returns from dung for the animal raisers was also collected. Using descriptive statistics, budget calculation and Gini coefficient, the results indicated that renting the land to brick making kilns yields a 5-fold higher return than the rent for agriculture. Gini coefficient showed that the kiln owners had a more equal income distribution compared to farmers. To estimate emission of greenhouse gases (GHGs) and losses of N, P, K, Corg and DM from cow dung when used in brick making, samples of cow dung (loose and compacted) were collected from different kilns and analyzed for their N, P, K and Corg content. The procedure modified by the Intergovernmental Panel on Climate Change (IPCC, 1994) was used to estimate the gaseous emissions of cow dung and fuel wood. The amount of deforested wood was estimated according to the default values for wood density given by Dixon et al. (1991) and the expansion ratio for branches and small trees given by Brown et al. (1989). The data showed the monetary value of added N and P from cow dung was lower than for mineral fertilizers. Annual consumption of compacted dung (381 t DM) as biomass fuel by far exceeded the consumption of fuel wood (36 t DM). Gaseous emissions from cow dung and fuel wood were dominated by CO2, CO and CH4. Considering that Gerif land in urban Khartoum supports a multifunctional land use system, efficient use of natural resources (forest, dung, land and water) will enhance the sustainability of the UA and brick making activities. Adoption of new kilns with higher energy efficiency will reduce the amount of biomass fuels (cow dung and wood) used the amount of GHGs emitted and the threat to the few remaining forests.

Dairy farms typology and management of animal genetic resources in the peri-urban zone of Bamako (Mali)

Facing growth in demand, dairy production in peri-urban areas of developing countries is changing rapidly. To characterise this development around Bamako (Mali), this study establishes a typology of dairy production systems with a special focus on animal genetic resources. The survey included 52 dairy cattle farms from six peri-urban sites. It was conducted in 2011 through two visits, in the dry and harvest seasons. The median cattle number per farm was 17 (range 5-118) and 42% of farmers owned cropland (8.3 +/- 7.3 ha, minimum 1 ha, maximum 25 ha). Feeding strategy was a crucial variable in farm characterisation, accounting for about 85% of total expenses. The use of artificial insemination and a regular veterinary follow-up were other important parameters. According to breeders’ answers, thirty genetic profiles were identified, from local purebreds to different levels of crossbreds. Purebred animals raised were Fulani Zebu (45.8%), Maure Zebu (9.2%), Holstein (3.0%), Azawak Zebu (1.3%), Mere Zebu (0.5%) and Kuri taurine (0.1%). Holstein crossbred represented 30.5% of the total number of animals (19.0% Fulani-Holstein, 11.2% Maure-Holstein and 0.3% Kuri-Holstein). Montbéliarde, Normande and Limousin crossbreds were also found (6.6%, 0.7% and 0.3%, respectively). A multivariate analysis helped disaggregate the diversity of management practices. The high diversity of situations shows the need for consideration of typological characteristics for an appropriate intervention. Although strongly anchored on local breeds, the peri-urban dairy systems included a diversity of exotic cattle, showing an uncoordinated quest of breeders for innovation. Without a public intervention, this dynamic will result in an irremediable erosion of indigenous animal genetic resources.