Zero field spin polarization in a 2D paramagnetic resonant tunneling diode

We study I-V characteristics of an all-II-VI semiconductor resonant tunneling diode with dilute magnetic impurities in the quantum well layer. Bound magnetic polaron states form in the vicinity of potential fluctuations at the well interface while tunneling electrons traverse these interface quantum dots. The resulting microscopic magnetic order lifts the degeneracy of the resonant tunneling states. Although there is no macroscopic magnetization, the resulting resonant tunneling current is highly spin polarized at zero magnetic field due to the zero field splitting. Detailed modeling demonstrates that the local spin polarization efficiency exceeds 90% without an external magnetic field.Comment: 7 pages, 10 figures (including supplementary information

Characterizing a Meta-CDN

CDNs have reshaped the Internet architecture at large. They operate (globally) distributed networks of servers to reduce latencies as well as to increase availability for content and to handle large traffic bursts. Traditionally, content providers were mostly limited to a single CDN operator. However, in recent years, more and more content providers employ multiple CDNs to serve the same content and provide the same services. Thus, switching between CDNs, which can be beneficial to reduce costs or to select CDNs by optimal performance in different geographic regions or to overcome CDN-specific outages, becomes an important task. Services that tackle this task emerged, also known as CDN broker, Multi-CDN selectors, or Meta-CDNs. Despite their existence, little is known about Meta-CDN operation in the wild. In this paper, we thus shed light on this topic by dissecting a major Meta-CDN. Our analysis provides insights into its infrastructure, its operation in practice, and its usage by Internet sites. We leverage PlanetLab and Ripe Atlas as distributed infrastructures to study how a Meta-CDN impacts the web latency

A First Look at QUIC in the Wild

For the first time since the establishment of TCP and UDP, the Internet transport layer is subject to a major change by the introduction of QUIC. Initiated by Google in 2012, QUIC provides a reliable, connection-oriented low-latency and fully encrypted transport. In this paper, we provide the first broad assessment of QUIC usage in the wild. We monitor the entire IPv4 address space since August 2016 and about 46% of the DNS namespace to detected QUIC-capable infrastructures. Our scans show that the number of QUIC-capable IPs has more than tripled since then to over 617.59 K. We find around 161K domains hosted on QUIC-enabled infrastructure, but only 15K of them present valid certificates over QUIC. Second, we analyze one year of traffic traces provided by MAWI, one day of a major European tier-1 ISP and from a large IXP to understand the dominance of QUIC in the Internet traffic mix. We find QUIC to account for 2.6% to 9.1% of the current Internet traffic, depending on the vantage point. This share is dominated by Google pushing up to 42.1% of its traffic via QUIC

Learning and teaching with video games: Toward theoretical progress and educational practice

Learning with video games has been related to several beneficial educational effects, indicating that teaching with video games could also be a promising teaching approach to foster student learning. However, more theoretical guidance and more insights from educational practice are needed to better evaluate potentials of learning and teaching with video games. Therefore, this dissertation presents a reference framework that aims to support theoretical progress in the field of e-learning and the general workflow of e-learning projects (Article 1). Then, with a focus on educational practice and teaching with video games, three field studies were conducted that illustrate how video games could be integrated into two different educational contexts. The results of these studies show that teaching with video games can foster students’ dance skills (Article 2) and reflection processes (Article 3). Considering that teachers decide whether they teach with video games, pre-service teachers were surveyed to examine their intention to teach with digital games in their future school teaching (Article 4). The results indicate that teachers’ intention to teach with video games is related to a small set of key personal characteristics that could be specifically considered in teacher education. Given pandemic restrictions, it was also outlined how video games could provide educational experiences at home and foster physical and mental health (Article 5). In addition, findings from experimental studies show that mobile learning with quiz apps can benefit student learning in terms of cognitive and metacognitive outcomes (Article 6). Overall, this dissertation emphasizes the relevance of theoretical progress and illustrates how learning and teaching with video games can be effective in educational practice

MUST, SHOULD, DON'T CARE: TCP Conformance in the Wild

Standards govern the SHOULD and MUST requirements for protocol implementers for interoperability. In case of TCP that carries the bulk of the Internets' traffic, these requirements are defined in RFCs. While it is known that not all optional features are implemented and nonconformance exists, one would assume that TCP implementations at least conform to the minimum set of MUST requirements. In this paper, we use Internet-wide scans to show how Internet hosts and paths conform to these basic requirements. We uncover a non-negligible set of hosts and paths that do not adhere to even basic requirements. For example, we observe hosts that do not correctly handle checksums and cases of middlebox interference for TCP options. We identify hosts that drop packets when the urgent pointer is set or simply crash. Our publicly available results highlight that conformance to even fundamental protocol requirements should not be taken for granted but instead checked regularly

How Do Income and the Debt Position of Households Propagate Public into Private Spending?

We study the household sector’s post-tax income and debt position as propagation mechanisms of public into private spending, in postwar U.S. data. In structural VARs, we obtain the consumption “crowding-in puzzle” for surges in public spending and show this consumption response to be accompanied by a persistent increase in disposable income. Endogenously reacting income, however, is insufficient to rationalize conditional comovement of private and public spending: once we hypothetically force (dis)aggregate measures of income to their pre-shock paths, consumption still rises. Corroborating these findings within an external-instruments-identified VAR, which constitutes an adequate laboratory for the simultaneous interplay of financial and macroeconomic time-series, we provide causal evidence of fiscal stimulus prompting households to take on more credit. This favorable debt cycle is paralleled by dropping interest rates, narrowing credit spreads, and inflating collateral prices, e.g., real estate prices, suggesting that softening borrowing constraints support the accumulation of debt and help rationalizing the absence of crowding-out