Search

This paper reports on the design, fabrication and test of an integrated colloid micropropulsion system for spacecraft attitude control using the ionic liquid EMI-BF4 as fuel. The principle of operation of the thruster is identical to electrospray ionization. The objective of the project was to demonstrate the feasibility and operability of arrays of microfabricated capillary emitters with individual extractor electrodes. This design approach results in an identical electric field distribution from one capillary to the other, avoids crosstalk and therefore allows for a more finely modulated thrust control. Spraying tests with different thruster configurations were conducted under vacuum conditions. Tests were performed with different thruster configurations and starting voltages around 700 V were observed.

In this paper, an investigation into the use of Flexible ac Transmission Systems (FACTS) devices to aid damping of low-frequency inter-area oscillations in longitudinal power systems is presented. A linear model of VSC-based FACTS devices that takes into account the dynamics of dc links is developed and incorporated into a production-grade software for small signal analysis of large power systems. Based on this representation, a unified framework for modal power oscillation flow studies is then developed to analyze the sensitivity of modal behavior to FACTS control action. With this method, the transmission corridors and system parameters having a large contribution to critical system oscillations modes are determined. The method is particularly well suited for investigating inter-system oscillations in large-scale power systems with embedded FACTS controllers The utilized methodology is tested on a practical 45-machine Mexican system that includes several major static VAR compensators. Control mode implementations are discussed and tested and comparisons with existing technologies are presented.

In this paper, the decomposition of fully polarimetric SAR data into three canonical scattering mechanisms is investigated with respect to forest biomass retrieval. It is demonstrated that the dominant backscattering contribution depends strongly on the frequency, incidence angle, and stand condition. The relation between in-situ biomass measurements and the individual decomposition components is examined.

This paper presents the conceptual design of a compact 2x2 array receiver for GNSS applications. Besides mere miniaturization, the goal of this work is also investigation on novel techniques for coping with the strong mutual coupling imposed in electrically small antenna arrays and RF front ends, by means of eigenmode reception and digital beamforming in the beam space.

With growing availability and popularity of user generated content, the discipline of sentiment analysis has come to the attention of many researchers. Existing work has mainly focused on either knowledge based methods or standard machine learning techniques. In this paper we investigate sentiment polarity classification based on adaptive statistical data compression models. We evaluate the classification performance of the lossless compression algorithm Prediction by Partial Matching (PPM) as well as compression based measures using PPM-like character n-gram frequency statistics. Comprehensive experiments on three corpora show that compression based methods are efficient, easy to apply and can compete with the accuracy of sophisticated classifiers such as support vector machines.

Very high resolution satellite imagery used to be a rare commodity, with infrequent satellite pass-over times over a specific area-of-interest obviating many useful applications. Today, more and more such satellite systems are available, with visual analysis and interpretation of imagery still important to derive relevant features and changes from satellite data. In order to allow efficient, robust and routine image analysis for humanitarian purposes, semi-automated feature extraction is of increasing importance for operational emergency mapping tasks. In the frame of the European Earth Observation program COPERNICUS and related research activities under the European Union's Seventh Framework Program, substantial scientific developments and mapping services are dedicated to satellite based humanitarian mapping and monitoring. In this paper, recent results in methodological research and development of routine services in satellite mapping for humanitarian situational awareness are reviewed and discussed. Ethical aspects of sensitivity and security of humanitarian mapping are deliberated. Furthermore methods for monitoring and analysis of refugee/internally displaced persons camps in humanitarian settings are assessed. Advantages and limitations of object-based image analysis, sample supervised segmentation and feature extraction are presented and discussed.

In this paper we present our work on enabling Balloon launched high altitude UAV Missions for an autopilot system previously used only at lower levels in visual line of sight conditions. One field of our research in the context of flying robotics is focused on high altitude pseudo satellites (HAPS). To gain operational experience in high altitude flying and for system and payload testing, a balloon launched small UAV (sub 10kg) system was designed including building an optimized airframe. Balloon launching was chosen because it offers fast and clearly regulated access to the desired altitudes. Our autopilot system has proven its capabilities in many years of flight experiments with different platforms (helicopter and fixed wing). The main characteristics are modularity and easy use for scientists. On the hardware level the task was to integrate the existing segmented systems of the research autopilot in a compact form factor, with the possible use in larger platforms in mind. The design was driven by the special thermal requirements resulting from flying in stratospheric conditions. In the autopilot software, several mission specific functions had to be added, which only required moderate effort due to the modular system design. Major changes included adding a flight termination manager. A launch routine was developed allowing a safe transition from free-fall to stable horizontal flight in thin air after being dropped from the balloon. Extensive testing was performed to validate the design. Simulating the mission, including balloon ascend, was used to check the mission software. Thermal and pressure conditions at altitude were replicated in a thermal vacuum chamber with additional sensors applied to identify problems. The simulation and control laws were verified by means of low altitude test flights.

Retro-directive antenna systems are of special interest in satellite communications due to their self-tracking capabilities. Since frequency bands are regulated, a key issue is the realization of a large frequency gap between transmitted and received signal. In this paper, we present simulations of a novel phase-locked loop (PLL) based retro-directive antenna system for C-band which can realize arbitrary frequency translation between received and transmitted signal. It is also able to work with different array element spacings and can correct beam pointing errors.We show bistatic radiation patterns which are the response to plane waves impinging from different directions on a system with four element arrays. A frequency translation from 5.8 to 7.0 GHz is shown for different array element spacing. We demonstrate the suitability of the proposed system architecture for retro-directive applications. It can realize large frequency gaps while keeping system complexity on a reasonable level.

The phenomenon of crowdsourcing has emerged as a new pattern of digitally mediated collaboration. This novel socio-technical arrangement changes the organization of work as well as its general nature and takes place in information systems (IS) in which humans face many threats to their dignity. For this reason, the importance of ethical issues within this new form of employment arises. Hence, in this paper we focus on the ethical issues in crowd work – a perspective that has been largely neglected by current crowdsourcing research. We analyze recent crowdsourcing literature and extract ethical issues by following the PAPA (privacy, accuracy, property and accessibility of information) concept, a well-established approach in IS. The review focuses on the individual perspective of crowdworkers, which addresses their working conditions and benefits. Although, the literature review exhibits that there are PAPA dimensions in crowdsourcing, only few focus on the crowdworkers as individuals. Our findings contribute to further research in crowdsourcing by introducing an ethical framework and give practical insight into how to design sustainable and ethical crowd work.

International audience; In this digital age of the computer, Internet, and social media and Internet of Things, e-assessments have become an accepted method to determine if students have learned materials presented in a course. With acceptance of this electronic means of assessing students, many questions arise about this method. What should be the format of e-assessment? What amount of time? What kinds of questions should be asked (multiple choice, short answer, etc.)? These are only a few of the many different questions. In addition, educators have always had to contend with the possibility that some students might cheat on an examination. It is widely known that students are often times more technologically savvy than their professors. So how does one prevent students from cheating on an e-assessment? Understandably, given the amount of information available on e-assessments and the variety of formats to choose from, choosing to administer e-assessments over paper-based assessments can lead to confusion on the part of the professor. This paper presents helpful guidance for lecturers who want to introduce e-assessments in their class, and it provides recommendations about the technical infrastructure to implement to avoid students cheating. It is based on literature review, on an international survey that gathers insights and experiences from lecturers who are using e-assessment in their class, and on technological evaluation of e-assessment infrastructure.

This paper sheds light on the role of visualization methods within the design thinking process. It provides a conceptual framework showing illustrative examples of visualization for each phase indicating its functions and benefits. Based on a thorough understanding of the functions and benefits of knowledge visualization in general, this paper seeks to provide a first overview of the use of visualization in design thinking informing and supporting practitioners and researcher for more conscious selections of visualization methods in their design thinking efforts.

Building semantic segmentation is a crucial task for building information modeling (BIM). Current research generally exploits terrestrial image data, which provides only limited view of a building. By contrast, oblique imagery acquired by unmanned aerial vehicle (UAV) can provide richer information of both the building and its surroundings at a larger scale. In this paper, we present a novel pipeline for building semantic segmentation from oblique UAV images using a fully convolutional neural network (FCN). To cope with the lack of UAV image annotations at facade level, we leverage existing ground-view facades databases to simulate various aerial-view images based on estimated homography, yielding abundant synthetic aerial image annotations as training data. The FCN is trained end-to-end and tested on full-tile UAV images. Experiments demonstrate that the incorporation of simulated views can significantly boost the prediction accuracy of the network on UAV images and achieve reasonable segmentation performance.

Despite efforts to reduce them, traffic accidents continue to increase and bypass reduction targets. The costs of traffic accidents are enormous, killing 1.35 million people every year and costing 3% of most countries’ GDP. Recent research aims to target interventions at high-accident-density locations, called accident hotspots. New methods and technologies can systematically identify hotspots, but it remains unclear whether hotspots contribute to accident costs as well as volume. This paper investigates the monetary and human costs of accident hotspots. We analyze a dataset of all accidents from 2011 - 2017 in Switzerland. We identify hotspots, then analyze their contributions to traffic accident costs. We find that hotspot accidents are not different in monetary costliness or injury rates from non-hotspot accidents, so hotspots drive costs along with accident volume. However, hotspot accidents are less fatal, so hotspot targeting might not be best for fatalities. If hotspots are reduced to normal road conditions, total monetary costs can be reduced by up to 5% per year as a theoretical upper bound. Targeting the top 10% most frequent, costly, injurious, or deadly hotspots yeilds different results for different cost types, with accident number and monetary cost targets creating the highest reductions overall.

This paper presents an overview of established and innovative means and teaching approaches that contribute to higher students' attention during lecture. The results are based on an international survey among lecturers from eleven universities. This survey was initiated by three lecturers from different countries who met at EDUCON 2016. The objective was to collect teaching experiences about playful means that motivate students to be attentive during a lecture. The proposed teaching approaches fall into three categories: established teaching methods, unconventional extrinsic methods, and tools. We focus on the extrinsic methods and discuss 14 illustrative examples of these approaches.