A novel directional coupler utilizing a left-handed material

A novel directional coupler with a left-handed material (LHM) layer between two single-mode waveguides of usual material is introduced. The coupling system is analyzed with the supermode theory. It is shown that such a LHM layer of finite length can shorten significantly the coupling length for the two single-mode waveguides. A LHM layer with two slowly tapered ends is used to avoid the reflection loss at the ends.Comment: 3 pages, 2 figure

Virtual Knowledge Graphs: An Overview of Systems and Use Cases

In this paper, we present the virtual knowledge graph (VKG) paradigm for data integration and access, also known in the literature as Ontology-based Data Access. Instead of structuring the integration layer as a collection of relational tables, the VKG paradigm replaces the rigid structure of tables with the flexibility of graphs that are kept virtual and embed domain knowledge. We explain the main notions of this paradigm, its tooling ecosystem and significant use cases in a wide range of applications. Finally, we discuss future research directions

The complete chloroplast genome sequence of Gentiana triflora and comparative analysis with its congeneric species

Gentiana triflora is an important medicinal plant in China with economic and medicinal value. Here, we report the complete chloroplastsequences of G. trifloral. The cp genome of G. triflora of 149, 125 bp contains 130 unique genes, including 85 protein-coding genes,8 rRNA genes, and 37 tRNA genes. The analysis of repeat showed that palindromic had the highest frequency. Besides, a total numberof 45 SSR were identified, most of which were mononucleotide adenine-thymine. Comparative genome analysis of Gentiana speciesrevealed that the pair of the inverted repeat was more conserved than the single-copy region. This analysis resulted in identification of 8 hypervariable regions (trnH-GUG, trnG-UCC-intron, atpI, trnD-GUC, trnL-UAA, rpl32-trnL-UAG, petA and ycf1). Phylogenetic analysis revealed that G. triflora was most closely related to Gentiana manshurica. In conclusion, this study enriched the genomic resources of the Gentiana genus and provided a basis for evolution and phylogeny analyses

Path following control for underactuated AUV based on feedback gain backstepping

U svrhu razvoja regulatora praćenja putanje podvodno pogonjenog AUV u horizontalnoj ravnini, predlažemo da se jednadžbe grešaka praćenja postave na osnovu virtualnog cilja te je razvijena nova metoda povratnog koraka (backstepping method) na temelju Lyapunovog teorema stabilnosti i tehnike interaktivnog pojačanja. Nelinearni izrazi u modelu dinamičke greške mogu se kompenzirati podešavajući interaktivno pojačanje regulatora, čime se može izbjeći derivacija visokog reda varijable virtualnog regulatora kod uobičajenog povratnog koraka i smanjiti složenost regulatora te poboljšati podesivost parametara regulatora. Konačno, provedena su simulacijska ispitivanja na WL-II podvodno pogonjenom AUV. Rezultati pokazuju da regulator može precizno pratiti očekivanu horizontalnu putanju te ima teorijsku i praktičnu vrijednost.In order to achieve path following control for the underactuated AUV in the horizontal plane, we propose that the tracking error equations are established based on virtual target and a novel backstepping method is designed based on Lyapunov stability theorem and feedback gain technique. The nonlinear terms in the error dynamic model can be compensated by adjusting feedback gain of the controller, which can avoid the high-order derivative of the virtual control variable in common backstepping and reduce the complexity of controller and improve adjustability of the controller parameters. Finally, simulation experiments are carried out on WL-II under actuated AUV. The results show that the controller can follow the expected horizontal path precisely, and has theoretical and practical value

Integrating 3D City Data through Knowledge Graphs

CityGML is a widely adopted standard by the Open Geospatial Consortium (OGC) for representing and exchanging 3D city models. The representation of semantic and topological properties in CityGML makes it possible to query such 3D city data to perform analysis in various applications, e.g., security management and emergency response, energy consumption and estimation, and occupancy measurement. However, the potential of querying CityGML data has not been fully exploited. The official GML/XML encoding of CityGML is only intended as an exchange format but is not suitable for query answering. The most common way of dealing with CityGML data is to store them in the 3DCityDB system as relational tables and then query them with the standard SQL query language. Nevertheless, for end users, it remains a challenging task to formulate queries over 3DCityDB directly for their ad-hoc analytical tasks, because there is a gap between the conceptual semantics of CityGML and the relational schema adopted in 3DCityDB. In fact, the semantics of CityGML itself can be modeled as a suitable ontology. The technology of Knowledge Graphs (KGs), where an ontology is at the core, is a good solution to bridge such a gap. Moreover, embracing KGs makes it easier to integrate with other spatial data sources, e.g., OpenStreetMap and existing (Geo)KGs (e.g., Wikidata, DBPedia, and GeoNames), and to perform queries combining information from multiple data sources. In this work, we describe a CityGML KG framework to populate the concepts in the CityGML ontology using declarative mappings to 3DCityDB, thus exposing the CityGML data therein as a KG. To demonstrate the feasibility of our approach, we use CityGML data from the city of Munich as test data and integrate OpenStreeMap data in the same area