Fault Tolerant Gradient Clock Synchronization

Synchronizing clocks in distributed systems is well-understood, both in terms of fault-tolerance in fully connected systems and the dependence of local and global worst-case skews (i.e., maximum clock difference between neighbors and arbitrary pairs of nodes, respectively) on the diameter of fault-free systems. However, so far nothing non-trivial is known about the local skew that can be achieved in topologies that are not fully connected even under a single Byzantine fault. Put simply, in this work we show that the most powerful known techniques for fault-tolerant and gradient clock synchronization are compatible, in the sense that the best of both worlds can be achieved simultaneously. Concretely, we combine the Lynch-Welch algorithm [Welch1988] for synchronizing a clique of $n$ nodes despite up to $f<n/3$ Byzantine faults with the gradient clock synchronization (GCS) algorithm by Lenzen et al. [Lenzen2010] in order to render the latter resilient to faults. As this is not possible on general graphs, we augment an input graph $\mathcal{G}$ by replacing each node by $3f+1$ fully connected copies, which execute an instance of the Lynch-Welch algorithm. We then interpret these clusters as supernodes executing the GCS algorithm, where for each cluster its correct nodes' Lynch-Welch clocks provide estimates of the logical clock of the supernode in the GCS algorithm. By connecting clusters corresponding to neighbors in $\mathcal{G}$ in a fully bipartite manner, supernodes can inform each other about (estimates of) their logical clock values. This way, we achieve asymptotically optimal local skew, granted that no cluster contains more than $f$ faulty nodes, at factor $O(f)$ and $O(f^2)$ overheads in terms of nodes and edges, respectively. Note that tolerating $f$ faulty neighbors trivially requires degree larger than $f$, so this is asymptotically optimal as well

Der Einfluss sozioökonomischer, kultureller und struktureller Faktoren auf den Kindertagesstättenbesuch von geflüchteten Kindern

Previous research has found that ethnic educational inequalities arise even before children enroll in primary school. It has been shown that especially for migrants, early participation in education has a positive impact on later educational outcomes, with the acquisition of the host-country language being one of the main mechanisms driving this effect. With the influx of over one million refugees into Germany in recent years, the integration of migrant children, especially refugee children, into the educational system is more salient in educational politics than ever. The first empirical findings on early and preschool education among refugees have shown that while a considerable share of refugee children attend a daycare center, they do so at lower rates than native and other migrant children. This paper aims to examine whether inequalities in the early education of refugee children can be explained by different socioeconomic and migration-related factors known to be associated with inequality in daycare attendance and to explore whether additional refugee-specific factors affect the likelihood of enrollment in preschool education. With data from the IAB-BAMF-SOEP Survey of Refugees in Germany and the study Refugees in the German Educational System (ReGES), we show that conventional explanatory variables do affect refugee children’s attendance of daycare centers. In addition to children’s age, the employment status of the mother, and the length of stay in Germany are particularly important. However, we see regional differences in participation in preschool education that cannot be explained by the municipal childcare supply. (DIPF/Orig.)Bisherige Studien haben gezeigt, dass ethnische Bildungsungleichheiten bereits vor der Einschulung entstehen. Es wurde gezeigt, dass insbesondere für Lernende mit Migrationshintergrund eine frühe Bildungsbeteiligung einen positiven Einfluss auf die späteren Bildungsergebnisse hat, wobei der Erwerb der Sprache des Aufnahmelandes einer der Hauptmechanismen für diesen Effekt ist. Mit der Zuwanderung von über einer Million Schutzsuchenden nach Deutschland in den letzten Jahren ist die Integration von Migrantenkindern, insbesondere von geflüchteten Kindern, in das Bildungssystem bildungspolitisch aktueller denn je. Erste empirische Befunde zur frühkindlichen und vorschulischen Bildung von Geflüchteten haben gezeigt, dass zwar ein erheblicher Anteil der geflüchteten Kinder eine Kindertagesstätte besucht, ihre Betreuungsquoten sind jedoch geringer als die von einheimischen und anderen Migrantenkindern. In diesem Beitrag soll untersucht werden, ob Ungleichheiten in der frühen Bildung von geflüchteten Kindern durch verschiedene sozioökonomische und migrationsspezifische Faktoren erklärt werden können, von denen aus der Literatur bekannt ist, dass sie mit Ungleichheiten im Kindertagesstättenbesuch einhergehen, und ob zusätzliche flüchtlingsspezifische Faktoren die Wahrscheinlichkeit den Besuch einer Kindertagesstätte beeinflussen. Mit Daten aus der IAB-BAMFSOEP-Befragung von Geflüchteten in Deutschland und der Studie Refugees in the German Educational System (ReGES) zeigen wir, dass bekannte Determinanten den Kindertagesstättenbesuch von geflüchteten Kindern tatsächlich beeinflussen. Neben dem Alter der Kinder sind vor allem der Erwerbsstatus der Mutter und die Dauer des Aufenthalts in Deutschland von Bedeutung. Wir sehen jedoch regionale Unterschiede in der frühkindlichen Bildungsbeteiligung, die nicht durch das kommunale Kinderbetreuungsangebot erklärt werden können. (DIPF/Orig.

The Impact of Legal Status on Different Schooling Aspects of Adolescents in Germany

During the so-called refugee crisis of 2015, approximately 300,000 underage asylum seekers came to Germany. We examine whether their legal status and their subjective perception of their status are equally important for their educational integration. On the basis of rational choice theory, we hypothesize that refugees’ legal status should affect their educational outcomes. Our study finds no differences among students with different legal statuses in school placement. However, students who perceive their status as insecure report significantly worse GPA than students who feel rather secure. Concerning the objective legal status, we do find that students with an insecure legal status report better grades than those with a granted refugee status. These contrary results show the importance of additionally considering status perception in understanding and explaining educational outcomes of immigrants in further research. Educators should be aware of the potential divergence between objective and subjective status and their corresponding effects on educational trajectories. **** Note that the original PDF version of this article contained a production error, which has now been fixed. As a result, the original pagination has been adjusted. *** &nbsp;Pendant la soi-disant « crise des réfugiés » de 2015, approximativement 300 000 demandeurs d’asile d’âge mineur sont arrivés en Allemagne. Nous examinons si leur statut légal et la perception subjective qu’ils ont de leur statut ont une importance égale en ce qui concerne leur intégration éducative. Nous appuyant sur la théorie du choix rationnel, nous émettons des hypothèses sur la manière dont le statut légal des réfugiés affecte leurs résultats scolaires. Notre étude ne révèle aucune divergence entre les étudiants de statuts légaux différents dans le placement scolaire. Cependant, les étudiants qui perçoivent leur statut comme précaire rapportent des moyennes significativement plus basses que ceux qui ont un plus grand sentiment de sécurité. En ce qui concerne le statut légal objectif, nous constatons que les étudiants au statut précaire rapportent de meilleures notes que ceux qui ont reçu le statut de réfugié. Ces résultats contradictoires montrent qu’il est important de tenir compte de la manière dont les immigrants perçoivent leur statut afin de comprendre et d’expliquer leurs résultats scolaires lors de recherches ultérieures. Les éducateurs devraient être conscients des potentielles divergences entre le statut objectif et le statut subjectif ainsi que leurs effets sur les trajectoires éducatives. ***Notez que la version PDF d'origine de cet article contenait une erreur de production, qui a maintenant été corrigée. En conséquence, la pagination d'origine a été ajustée.**

Towards A Representation of Vertically Resolved Ozone Changes in Reanalyses

The Solar Backscatter Ultraviolet Radiometer (SBUV) instruments on NASA and NOAA spacecraft provide a long-term record of total-column ozone and deep-layer partial columns since about 1980. These data have been carefully processed to extract long-term trends and offer a valuable resource for ozone monitoring. Studies assimilating limb-sounding observations in the Goddard Earth Observing System (GEOS) data assimilation system (DAS) demonstrate that vertical ozone gradients in the upper troposphere and lower stratosphere (UTLS) are much better represented than with the deep-layer SBUV observations. This is exemplified by the use of retrieved ozone from the EOS Microwave Limb Sounder (EOS-MLS) instrument in the MERRA-2 reanalysis, for the period after 2004. This study examines the potential for extending the use of limb-sounding observations at earlier times and into the future, so that future reanalyses may be more applicable to the study of long-term ozone changes.Historical data are available from NASA instruments: the Limb Infrared Monitor of the Stratosphere (LIMS: 1978-1979); the Upper Atmospheric Research Satellite (UARS: 1991-1995); Sounding of the Atmosphere using Broadband Emission Radiometry (SABER: 2000-onwards). For the post EOS-MLS period, the joint NASA-NOAA Ozone Monitoring and Profiling Suite Limb Profiler (OMPS-LP) instrument was launched on the Suomi-NPP platform in 201x and is planned for future platforms. This study will examine two aspects of these data pertaining to future reanalyses. First, the feasibility of merging the EOS-MLS and OMPS-LP instruments to provide a long-term record that extends beyond the potential lifetime of EOS-MLS. If feasible, this would allow for long-term monitoring of ozone recovery in a three-dimensional reanalysis context. Second, the skill of the GEOS DAS in ingesting historical data types will be investigated. Because these do not overlap with EOS-MLS, use will be made of system statistics and evaluation using independent datasets. Impacts of using a complete ozone chemistry module will also be considered

Can electric vehicle charging be carbon neutral? Uniting smart charging and renewables

Growing numbers of plug-in electric vehicles in Europe will have an increasing impact on the electricity system. Using the agent-based simulation model PowerACE for ten electricity markets in Central Europe, we analyze how different charging strategies impact price levels and production- as well as consumption-based carbon emissions in France and Germany. The applied smart charging strategies consider spot market prices and/or real-time production from renewable energy sources. While total European carbon emissions do not change significantly in response to the charging strategy due to the comparatively small energy consumption of the electric vehicle fleet, our results show that all smart charging strategies reduce price levels on the spot market and lower total curtailment of renewables. Here, charging processes optimized according to hourly prices have the strongest effect. Furthermore, smart charging strategies reduce electricity purchasing costs for aggregators by about 10% compared to uncontrolled charging. In addition, the strategies allow aggregators to communicate near-zero allocated emissions for charging vehicles. An aggregator’s charging strategy expanding classic electricity cost minimization by limiting total national PEV demand to 10% of available electricity production from renewable energy sources leads to the most favorable results in both metrics, purchasing costs and allocated emissions. Finally, aggregators and plug-in electric vehicle owners would benefit from the availability of national, real-time Guarantees of Origin and the respective scarcity signals for renewable production

Obstacle scanning by technical vibrissae with compliant support

Rodents, like mice and rats, use tactile hairs in the snout region (mystacial vibrissae) to acquire information about their environment, e.g. the shape or contour of obstacles. For this, the vibrissa is used for the perception of stimuli due to an object contact. Mechanoreceptors are processing units of this stimuli measured in the compliant support (follicle sinus complex). We use this behavior from biology as an inspiration to set up a mechanical model for object contour scanning. An elastic bending rod interacts with a rigid obstacle in the plane. Analyzing only one quasi-static sweep of the rod along the obstacle (in contrast to literature), we determine a) the support reactions (the only observables of the problem), and then b) the (discrete) obstacle contour in form of a set of contact points. In doing this, we first assume a stiff support (clamping) of the vibrissa, but in a next step we increase the elasticity of the support in focussing on a bearing with a rotational spring (also to control or delimitate the bending moment at the support). Thereby, we present a fully analytical treatment of the non-linear differential equations emerging from Bernoulli’s rod theory and a representation by Standard Elliptic Integrals

Mathematical model of vibrissae for surface texture detection

The plane elastic bending rod serves as a model of biological and artificial vibrissae. One task of vibrissae is to scan surfaces in order to detect their textures. We sketch the theory of static bending rod problems with a view to this field of applications. The solutions of the respective autonomous boundary value problems are given analytically. Numerical simulations are done in some worked out examples. Being aware of the fact that (1) in papers, object detecting by means of touch is seemingly exclusively investigated under the assumption of ideal contact (no stiction or friction), and (2) our present omission of this assumption is based upon simplifying model properties, the conclusions give some corresponding discussions and proposals for improvements and necessary work in future