Optimal branching asymmetry of hydrodynamic pulsatile trees

Most of the studies on optimal transport are done for steady state regime conditions. Yet, there exists numerous examples in living systems where supply tree networks have to deliver products in a limited time due to the pulsatile character of the flow. This is the case for mammals respiration for which air has to reach the gas exchange units before the start of expiration. We report here that introducing a systematic branching asymmetry allows to reduce the average delivery time of the products. It simultaneously increases its robustness against the unevitable variability of sizes related to morphogenesis. We then apply this approach to the human tracheobronchial tree. We show that in this case all extremities are supplied with fresh air, provided that the asymmetry is smaller than a critical threshold which happens to fit with the asymmetry measured in the human lung. This could indicate that the structure is adjusted at the maximum asymmetry level that allows to feed all terminal units with fresh air.Comment: 4 pages, 4 figure

Spatial information retrieval and geographical ontologies: an overview of the SPIRIT project

A large proportion of the resources available on the world-wide web refer to information that may be regarded as geographically located. Thus most activities and enterprises take place in one or more places on the Earth's surface and there is a wealth of survey data, images, maps and reports that relate to specific places or regions. Despite the prevalence of geographical context, existing web search facilities are poorly adapted to help people find information that relates to a particular location. When the name of a place is typed into a typical search engine, web pages that include that name in their text will be retrieved, but it is likely that many resources that are also associated with the place may not be retrieved. Thus resources relating to places that are inside the specified place may not be found, nor may be places that are nearby or that are equivalent but referred to by another name. Specification of geographical context frequently requires the use of spatial relationships concerning distance or containment for example, yet such terminology cannot be understood by existing search engines. Here we provide a brief survey of existing facilities for geographical information retrieval on the web, before describing a set of tools and techniques that are being developed in the project SPIRIT : Spatially-Aware Information Retrieval on the Internet (funded by European Commission Framework V Project IST-2001-35047)

A note on compactly generated co-t-structures

The idea of a co-t-structure is almost "dual" to that of a t-structure, but with some important differences. This note establishes co-t-structure analogues of Beligiannis and Reiten's corresponding results on compactly generated t-structures.Comment: 10 pages; details added to proofs, small correction in the main resul

Safety Considerations for Operation of Unmanned Aerial Vehicles in the National Airspace System

There is currently a broad effort underway in the United States and internationally by several organizations to craft regulations enabling the safe operation of UAVs in the NAS. Current federal regulations governing unmanned aircraft are limited in scope, and the lack of regulations is a barrier to achieving the full potential benefit of UAV operations. To inform future FAA regulations, an investigation of the safety considerations for UAV operation in the NAS was performed. Key issues relevant to operations in the NAS, including performance and operating architecture were examined, as well as current rules and regulations governing unmanned aircraft. In integrating UAV operations in the NAS, it will be important to consider the implications of different levels of vehicle control and autonomous capability and the source of traffic surveillance in the system. A system safety analysis was performed according to FAA system safety guidelines for two critical hazards in UAV operation: midair collision and ground impact. Event-based models were developed describing the likelihood of ground fatalities and midair collisions under several assumptions. From the models, a risk analysis was performed calculating the expected level of safety for each hazard without mitigation. The variation of expected level of safety was determined based on vehicle characteristics and population density for the ground impact hazard, and traffic density for midair collisions. The results of the safety analysis indicate that it may be possible to operate small UAVs with few operational and size restrictions over the majority of the United States. As UAV mass increases, mitigation measures must be utilized to further reduce both ground impact and midair collision risks to target levels from FAA guidance. It is in the public interest to achieve the full benefits of UAV operations, while still preserving safety through effective mitigation of risks with the least possible restrictions. Therefore, a framework was presented under which several potential mitigation measures were introduced and could be evaluated. It is likely that UAVs will be significant users of the future NAS, and this report provides an analytical basis for evaluating future regulatory decisions

Geographic data science

Data science methods and approaches address all stages of transition from data to knowledge and action. Visualization of this data is essential for human understanding of the subject under study, analytical reasoning about it, and generating new knowledge. Geographic data science deals with data that incorporates spatial and, often, temporal elements. The articles selected for this special issue represent a mix of theoretical approaches and novel applications of geographic data science

Introduction to the special section on Visual Movement Analytics

PostprintNon peer reviewe

Kongenitale Nävi im Kindesalter

Zusammenfassung: Nävi stellen kongenitale hamartomatöse Fehlbildungen unterschiedlicher Bestandteile der Haut dar. Am häufigsten treten kongenitale melanozytäre Nävi (CMN) auf, gefolgt von Nävi epithelialen Ursprungs (epidermale und organoide Nävi). Insbesondere große CMN können zu schwerwiegenden Komplikationen führen, und das Management der Betroffenen stellt ab Geburt eine Herausforderung dar. Entgegen früheren Annahmen ist das Risiko einer malignen Entartung von CMN insgesamt als eher gering anzusehen, steigt jedoch in speziellen Situationen relevant an. Nicht zu vernachlässigen sind mögliche extrakutane Symptome im Falle einer ZNS-Beteiligung, und frühe bildgebende Untersuchungen gehören heute zur Routinediagnostik. Chirurgische Maßnahmen haben noch immer einen hohen Stellenwert in der Behandlung von CMN, die Indikation dazu ist jedoch von Fall zu Fall individuell abzuwägen. Nicht zuletzt leiden die Patienten häufig stark an der ästhetischen Beeinträchtigung durch ihr Muttermal, sodass in der Behandlung auch diesem Punkt Rechnung getragen werden muss. Der Naevus sebaceus ist der häufigste Vertreter der epithelialen Nävi. In 2-13% treten darin Zusatztumoren auf, und eine frühe chirurgische Exzision ist in den meisten Fällen nicht zuletzt auch aus ästhetischen Überlegungen sinnvoll. Epidermale Nävi erfordern bei generalisierter Ausdehnung Zusatzuntersuchungen zum Ausschluss von assoziierten ophthalmologischen, kardialen oder neurologischen Fehlbildunge