Vienna University of Technology

About: Vienna University of Technology is a education organization based out in Vienna, Austria. It is known for research contribution in the topics: Laser & Context (language use). The organization has 16723 authors who have published 49341 publications receiving 1302168 citations.

Extending object-oriented systems with roles

Abstract: In many class-based object-oriented systems the association between as instance and a class is exclusive and permanent Therefore these systems have serious difficulties in representing objects taking on different roles over time Such objects must be reclassified any time they evolve (eg, if a person becomes a student and later an employee) Class hierarchies must be planned carefully and may grow exponentially if entities may take on serveral independent roles The problem is even more servere for object-oriented databases than for common object-oriented programming Databases store objects over longer periods, during which the represented entities evolve This article shows how class-based object-oriented systems can be extended to handle evolving objects well Class hierarchies are complemented by role hierarchies, whose nodes represent role types an object classified in the root may take on At any point in time, an entity is represented by an instance of the root and an instance of every role type whose role it currently plays In a natural way, the approach extends traditional object-oriented concepts, such as classification, object identity, specialization, inheritance, and polymorphism in a natural way The practicability of the approach is demonstrated by an implementation in Smalltalk Smalltalk was chosen because it is widely known, which is not true for any particular class-based object-oriented database programming language Roles can be provided in Smalltalk by adding a few classes There is no need to modify the semantics of Smalltalk itself Role hierarchies are mapped transparently onto ordinary classes The presented implementation can easily be ported to object-oriented database programming languages based on Smalltalk, such as Gemstone's OPAL hierarchies are complemented by role hierarchies, whose nodes represent role types an object classified in the root may take on At any point in time, an entity is represented by an instance of the root and an instance of every role type whose role in currently plays

Afternoon rain more likely over drier soils

Abstract: Analysis of observations on six continents reveals a global preference for afternoon rain to fall on locally drier soils—contrary to the predictions of large-scale climate models, and suggesting that such models may exaggerate the occurrence of droughts. Soil moisture is known to influence precipitation across a range of scales in time and space, and most models suggest that wetter soils promote higher atmospheric moisture content and favour the local development of storms. But this analysis of global precipitation data from a combination of weather satellites shows that — especially in semi-arid regions — afternoon precipitation is more likely over dry soil than over wet soil. The findings suggest that current climate models may be missing fundamental processes regulating convection and land–atmosphere interactions. Land surface properties, such as vegetation cover and soil moisture, influence the partitioning of radiative energy between latent and sensible heat fluxes in daytime hours. During dry periods, soil-water deficit can limit evapotranspiration, leading to warmer and drier conditions in the lower atmosphere1,2. Soil moisture can influence the development of convective storms through such modifications of low-level atmospheric temperature and humidity1,3, which in turn feeds back on soil moisture. Yet there is considerable uncertainty in how soil moisture affects convective storms across the world, owing to a lack of observational evidence and uncertainty in large-scale models4. Here we present a global-scale observational analysis of the coupling between soil moisture and precipitation. We show that across all six continents studied, afternoon rain falls preferentially over soils that are relatively dry compared to the surrounding area. The signal emerges most clearly in the observations over semi-arid regions, where surface fluxes are sensitive to soil moisture, and convective events are frequent. Mechanistically, our results are consistent with enhanced afternoon moist convection driven by increased sensible heat flux over drier soils, and/or mesoscale variability in soil moisture. We find no evidence in our analysis of a positive feedback—that is, a preference for rain over wetter soils—at the spatial scale (50–100 kilometres) studied. In contrast, we find that a positive feedback of soil moisture on simulated precipitation does dominate in six state-of-the-art global weather and climate models—a difference that may contribute to excessive simulated droughts in large-scale models.

Repeated double cross validation

Abstract: Repeated double cross validation (rdCV) is a strategy for (a) optimizing the complexity of regression models and (b) for a realistic estimation of prediction errors when the model is applied to new cases (that are within the population of the data used). This strategy is suited for small data sets and is a complementary method to bootstrap methods. rdCV is a formal, partly new combination of known procedures and methods, and has been implemented in a function for the programming environment R, providing several types of plots for model evaluation. The current version of the software is dedicated to regression models obtained by partial least-squares (PLS). The applied methods for repeated splits of the data into test sets and calibration sets, as well as for estimation of the optimum number of PLS components, are described. The relevance of some parameters (number of segments in CV, number of repetitions) is investigated. rdCV is applied to two data sets from chemistry: (1) determination of glucose concentrations from near infrared (NIR) data in mash samples from bioethanol production; (2) modeling the gas chromatographic retention indices of polycyclic aromatic compounds from molecular descriptors. Models using all original variables and models using a small subset of the variables, selected by a genetic algorithm (GA), are compared by rdCV.

Ultrastrong light-matter coupling regime with polariton dots.

Abstract: The regime of ultrastrong light-matter interaction has been investigated theoretically and experimentally, using zero-dimensional electromagnetic resonators coupled with an electronic transition between two confined states of a semiconductor quantum well. We have measured a splitting between the coupled modes that amounts to 48% of the energy transition, the highest ratio ever observed in a light-matter coupled system. Our analysis, based on a microscopic quantum theory, shows that the nonlinear polariton splitting, a signature of this regime, is a dynamical effect arising from the self-interaction of the collective electronic polarization with its own emitted field.

A Survey on Application Layer Protocols for the Internet of Things

Abstract: It has been more than fifteen years since the term Internet of Things (IoT) was introduced. However, despite the efforts of research groups and innovative corporations, still today it is not possible to say that the IoT is upon us. This is mainly due to the fact that a unified IoT architecture has not yet been clearly defined and there is no common agreement in defining communication protocols and standards for all the IoT parts. The framework that current IoT platforms use consists mostly in technologies that partially fulfill the IoT requirements. While developers employ existing technologies to build the IoT, research groups are working on adapting protocols to the IoT in order to optimize communications. In this paper, we present and compare existing IoT application layer protocols as well as protocols that are utilized to connect the “things” but also end-user applications to the Internet. We highlight IETF’s CoAP, IBM’s MQTT, HTML 5’s Websocket among others, and we argue their suitability for the IoT by considering reliability, security, and energy consumption aspects. Finally, we provide our conclusions for the IoT application layer communications based on the study that we have conducted.