Optimization Based Self-localization for IoT Wireless Sensor Networks

In this paper we propose an embedded optimization framework for the simultaneous self-localization of all sensors in wireless sensor networks making use of range measurements from ultra-wideband (UWB) signals. Low-power UWB radios, which provide time-of-arrival measurements with decimeter accuracy over large distances, have been increasingly envisioned for realtime localization of IoT devices in GPS-denied environments and large sensor networks. In this work, we therefore explore different non-linear least-squares optimization problems to formulate the localization task based on UWB range measurements. We solve the resulting optimization problems directly using non-linear-programming algorithms that guarantee convergence to locally optimal solutions. This optimization framework allows the consistent comparison of different optimization methods for sensor localization. We propose and demonstrate the best optimization approach for the self-localization of sensors equipped with off-the-shelf microcontrollers using state-of-the-art code generation techniques for the plug-and-play deployment of the optimal localization algorithm. Numerical results indicate that the proposed approach improves localization accuracy and decreases computation times relative to existing iterative methods

Photophoretic Strength on Chondrules. 2. Experiment

Photophoretic motion can transport illuminated particles in protoplanetary disks. In a previous paper we focused on the modeling of steady state photophoretic forces based on the compositions derived from tomography and heat transfer. Here, we present microgravity experiments which deviate significantly from the steady state calculations of the first paper. The experiments on average show a significantly smaller force than predicted with a large variation in absolute photophoretic force and in the direction of motion with respect to the illumination. Time-dependent modeling of photophoretic forces for heat-up and rotation show that the variations in strength and direction observed can be well explained by the particle reorientation in the limited experiment time of a drop tower experiment. In protoplanetary disks, random rotation subsides due to gas friction on short timescales and the results of our earlier paper hold. Rotation has a significant influence in short duration laboratory studies. Observing particle motion and rotation under the influence of photophoresis can be considered as a basic laboratory analog experiment to Yarkovsky and YORP effects

Institutionelle Untersuchungen zum Bewässerungsfeldbau in einer südmarokkanischen Flussoase

Werden Defizite in Bewässerungssystemen als rein technisches Problem betrachtet, führt dies zur Ausblendung sozialer und kultureller Aspekte der Ressourcenverwaltung. Als Konsequenz werden sinnvolle technische Innovationen von der Bevölkerung nicht angenommen und verbleiben letztendlich ungenutzt. Bisherige Studien über das südmarokkanische Oasengebiet im Ziz-Tal hatten überwiegend ökologische und ingenieurtechnische Ansätze verfolgt. Das Forschungsinteresse dieser Arbeit liegt stärker auf den kollektiven Handlungsmustern, Regelsystemen und spezifischen Variationen sozialer Vereinbarungen in Form von formellen und informellen Institutionen der traditionellen und der heutigen Bewässerung. Zum Verständnis der gegenwärtigen Situation werden die rechtlichen und politischen Rahmenbedingungen, der soziokulturelle Kontext sowie die naturräumlichen Voraussetzungen und Umweltveränderungen – mit besonderem Blick auf die verfügbaren Wasserressourcen in dieser ariden Region – analysiert und das institutionelle Gefüge in einer auf Methoden der qualitativen Sozialforschung basierenden Fallstudie in einem Oasendorf untersucht

Verhuellia is a segregate lineage in Piperaceae: more evidence from flower, fruit and pollen morphology, anatomy and development

Background and Aims The perianthless Piperales, i.e. Saururaceae and Piperaceae, have simple reduced flowers strikingly different from the other families of the order (e.g. Aristolochiaceae). Recent molecular phylogenies proved Verhuellia to be the first branch in Piperaceae, making it a promising object to study the detailed structure and development of the flowers. Based on recently collected material, the first detailed study since 1872 was conducted with respect to morphology, anatomy and development of the inflorescence, pollen ultrastructure and fruit anatomy. Methods Original Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Light Microscopy (LM) observations on Verhuellia lunaria were compared with Piperaceae, Saururaceae and fossils. Key results The inflorescence is an indeterminate spike with sessile flowers, each in the axil of a bract, developing in acropetal, helical succession. Flowers consist of two (occasionally three) stamens with basifixed tetrasporangiate anthers and latrorse dehiscence by a longitudinal slit. The gynoecium lacks a style but has three to four stigma branches and a single, basal orthotropous, and unitegmic ovule. The fruit is a drupe with large multicellular epidermal protuberances. The pollen is very small, inaperturate, and areolate with hemispherical microechinate exine elements. Conclusions Despite the superficial similarities with different genera of Piperaceae and Saururaceae, the segregate position of Verhuellia revealed by molecular phylogenetics is supported by morphological, developmental and anatomical data presented here. Unitegmic ovules and inaperturate pollen, which are synapomorphies for the genus Peperomia, are also present in Verhuellia

Enabling optimization-based localization for IoT devices

In this paper, we propose an embedded optimization approach for the localization of Internet of Things (IoT) devices making use of range measurements from ultra-wideband (UWB) signals. Low-cost, low-power UWB radios provide time-of-arrival measurements with decimeter accuracy over large distances. UWB-based localization methods have been envisioned to enable feedback control in IoT applications, particularly, in GPS-denied environments, and large wireless sensor networks. In this paper, we formulate the localization task as a nonlinear least-squares optimization problem based on two-way time-of-arrival measurements between the IoT device and several UWB radios installed in a 3-D environment. For the practical implementation of large-scale IoT deployments we further assume only approximate knowledge of the UWB radio locations. We solve the resulting optimization problem directly on IoT devices equipped with off-the-shelf microcontrollers using state-of-the-art code generation techniques for plug-and-play deployment of the nonlinear-programming algorithms. This paper further provides practical implementation details to improve the localization accuracy for feedback control in experimental IoT applications. The experimental results finally show that subdecimeter localization accuracy can be achieved using the proposed optimization-based approach, even when the majority of the UWB radio locations are unknown

«Revolving Doors» – Manager in Politics and Politicians in Business. An Introduction

Dieser Beitrag ist mit Zustimmung des Rechteinhabers (De Gruyter) frei zugänglich.Peer Reviewe

Eine schmale Brücke in die Zukunft?: Stellungnahme zum Förderprogramm des Freistaates Sachsen

„800 Millionen Euro für Schulen, Straßen, Sportstätten und ÖPNV“ konnte man im Februar 2016 einer Pressemitteilung der sächsischen Staatsregierung entnehmen. Von Investitionen, welche „direkt vor Ort in Sachsens Städten und Gemeinden spürbar sein [sollen]“, war auf der Homepage der CDU-Fraktion Sachsen die Rede. Sachsens Ministerpräsident Tillich sprach von einem Konjunkturpaket mit „Einmaligkeitscharakter“, CDU-Fraktionschef Frank Kupfer vom größten Sonderprogramm in der Geschichte des Landes Sachsen. Bei diesem Paket handelt es sich um das Investitionsprogramm „Brücken in die Zukunft“, welches der Freistaat Sachsen auf Grundlage des Gesetzes zur Stärkung der kommunalen Investitionskraft aufgesetzt hat. Die finanziellen Mittel sollen demnach den sächsischen Kommunen zur Finanzierung von Infrastrukturprojekten zur Verfügung gestellt werden

CFD Simulation of a Twin Screw Expander including Leakage Flows

The numerical simulation of rotary positive displacement (PD) machines has proven to be a very challenging task characterized by complex geometries with a time dependent change of the chamber volume along with complex flow physics. In addition, the leakage flow caused by housing clearances, front gaps and the intermesh clearance is of particular interest. The resulting losses have a severe impact on the overall machine efficiency. This paper shows workflow and results for Computational Fluid Dynamics (CFD) simulations of the Screw Expander SE-51 of TU Dortmund University. The simulation is performed using ANSYS CFX, where the computational grids for the rotary parts are derived from the grid generator TwinMesh. The SE-51 is a gearless, dry running twin screw expander that converts thermal into mechanical energy by decompressing air with pressure-ratios up to 6:1 by a rotational speed range up to 20,000 rev/min. The volume ratio of the expander is 2.5 at a shaft distance of 51 mm with a displaced volume per male rotor revolution of 285 cm³. The Numerical model of this machine includes fully resolved clearances along with the meshing of the rotor solid end faces whereas a contact point between the rotors is neglected. For several rotational speeds, CFD results are compared to measurements at 4 bar at the high pressure side, expanding air down to 1 bar. The validation is based on integral values, e.g. mass flow, torque and power, all averaged over a certain time period for several operating points. Moreover, time- and space-resolved pressure measurements for distinct positions are compared to simulation results. Besides direct evaluation against experimental data, tendencies are analyzed by varying the numerical model with respect to mesh resolution or changing the size of clearances. Apart from local changes in the flow field, it is shown that also global values like torque or mass flow are clearly affected. In addition, flow regimes not captured by measurements, like leakage flows within clearances between rotors and housing, are evaluated and illustrated based on CFD results. While the simulation allows reliable analysis of dry running screw machines and their complex flow characteristics, oil- or water-injected machines are also commonly used in the industry, allowing higher pressure-ratios. The liquid fluid acts as a sealing for clearances and can also be used as lubricant. From the simulation point of view, multiphase calculations with corresponding multiphase-effects are required in order to cope with injected screw machines. Further investigation also involves heat transfer and resulting deformations of rotary and stationary parts. Clearances can vary due to deformations, eventually resulting in different machine characteristics and efficiency. Thus, fluid-structure interaction is of high demand. For both of these issues, a prospect is given to extend the scope of application, using CFD for screw machine analysis

Stars quenching stars: how photoionization by local sources regulates gas cooling and galaxy formation

Current models of galaxy formation lack an efficient and physically constrained mechanism to regulate star formation (SF) in low and intermediate mass galaxies. We argue that the missing ingredient could be the effect of photoionization by local sources on the gas cooling. We show that the soft X-ray and EUV flux generated by SF is able to efficiently remove the main coolants (e.g., HeII, OV and FeIX) from the halo gas via direct photoionization. As a consequence, the cooling and accretion time of the gas surrounding star-forming galaxies may increase by one or two orders of magnitude. For a given halo mass and redshift, the effect is directly related to the value of the star formation rate (SFR). Our results suggest the existence of a critical SFR above which "cold" mode accretion is stopped, even for haloes with virial masses well below the critical shock-heating mass suggested by previous studies.The evolution of the critical SFR with redshift, for a given halo mass, resembles the respective steep evolution of the observed SFR for z<1. This suggests that photoionization by local sources would be able to regulate gas accretion and star formation, without the need for additional, strong feedback processes.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter

Physical Fitness Training in Patients with Subacute Stroke (PHYS-STROKE): multicentre, randomised controlled, endpoint blinded trial

OBJECTIVE: To determine the safety and efficacy of aerobic exercise on activities of daily living in the subacute phase after stroke. DESIGN: Multicentre, randomised controlled, endpoint blinded trial. SETTING: Seven inpatient rehabilitation sites in Germany (2013-17). PARTICIPANTS: 200 adults with subacute stroke (days 5-45 after stroke) with a median National Institutes of Health stroke scale (NIHSS, range 0-42 points, higher values indicating more severe strokes) score of 8 (interquartile range 5-12) were randomly assigned (1:1) to aerobic physical fitness training (n=105) or relaxation sessions (n=95, control group) in addition to standard care. INTERVENTION: Participants received either aerobic, bodyweight supported, treadmill based physical fitness training or relaxation sessions, each for 25 minutes, five times weekly for four weeks, in addition to standard rehabilitation therapy. Investigators and endpoint assessors were masked to treatment assignment. MAIN OUTCOME MEASURES: The primary outcomes were change in maximal walking speed (m/s) in the 10 m walking test and change in Barthel index scores (range 0-100 points, higher scores indicating less disability) three months after stroke compared with baseline. Safety outcomes were recurrent cardiovascular events, including stroke, hospital readmissions, and death within three months after stroke. Efficacy was tested with analysis of covariance for each primary outcome in the full analysis set. Multiple imputation was used to account for missing values. RESULTS: Compared with relaxation, aerobic physical fitness training did not result in a significantly higher mean change in maximal walking speed (adjusted treatment effect 0.1 m/s (95% confidence interval 0.0 to 0.2 m/s), P=0.23) or mean change in Barthel index score (0 (-5 to 5), P=0.99) at three months after stroke. A higher rate of serious adverse events was observed in the aerobic group compared with relaxation group (incidence rate ratio 1.81, 95% confidence interval 0.97 to 3.36). CONCLUSIONS: Among moderately to severely affected adults with subacute stroke, aerobic bodyweight supported, treadmill based physical fitness training was not superior to relaxation sessions for maximal walking speed and Barthel index score but did suggest higher rates of adverse events. These results do not appear to support the use of aerobic bodyweight supported fitness training in people with subacute stroke to improve activities of daily living or maximal walking speed and should be considered in future guidelines. TRIAL REGISTRATION: ClinicalTrials.gov NCT01953549