Empirical Methods in the Economics of International Immigration

In this chapter we provide a brief overview of the main empirical tools used by economists to study international migration. We begin by exploring the three broad research areas that economists examine when researching immigration. We then explore the strengths and shortcomings of the standard methods, and highlight new methods that will likely become more common in future work in the field. We divide the most common tools used in the empirical literature into four broad categories: (1) Ordinary Least Squares and Inference, (2) Difference-in-Difference Estimation, (3) Instrumental Variables Techniques, and (4) Recent Developments and Distributional Estimators. We use recent empirical work to highlight and explain each method, and provide sources for researchers interested in further information on each topic.empirical methods, immigration

Self-assembled granular walkers

Mechanisms of locomotion in microscopic systems are of great interest not only for technological applications, but also for the sake of understanding, and potentially harnessing, processes far from thermal equilibrium. Down-scaling is a particular challenge, and has led to a number of interesting concepts including thermal ratchet systems and asymmetric swimmers. Here we present a system which is particularly intriguing, as it is self-assembling and uses a robust mechanism which can be implemented in various settings. It consists of small spheres of different size which adhere to each other, and are subject to an oscillating (zero average) external force eld. An inherent nonlinearity in the mutual force network leads to force rectication and hence to locomotion. We present a model that accounts for the observed behaviour and demonstrates the wide applicability and potential scalability of the concept.Comment: 17 pages, 4 figure

A Survey of Satellite Communications System Vulnerabilities

The U.S. military’s increasing reliance on commercial and military communications satellites to enable widely-dispersed, mobile forces to communicate makes these space assets increasingly vulnerable to attack by adversaries. Attacks on these satellites could cause military communications to become unavailable at critical moments during a conflict. This research dissected a typical satellite communications system in order to provide an understanding of the possible attacker entry points into the system, to determine the vulnerabilities associated with each of these access points, and to analyze the possible impacts of these vulnerabilities to U.S. military operations. By understanding these vulnerabilities of U.S. communications satellite systems, methods can be developed to mitigate these threats and protect future systems. This research concluded that the satellite antenna is the most vulnerable component of the satellite communications system’s space segment. The antenna makes the satellite vulnerable to intentional attacks such as: RF jamming, spoofing, meaconing, and deliberate physical attack. The most vulnerable Earth segment component was found to be the Earth station network, which incorporates both Earth station and NOC vulnerabilities. Earth segment vulnerabilities include RF jamming, deliberate physical attack, and Internet connection vulnerabilities. The most vulnerable user segment components were found to be the SSPs and PoPs. SSPs are subject to the vulnerabilities of the services offered, the vulnerabilities of Internet connectivity, and the vulnerabilities associated with operating the VSAT central hub. PoPs are susceptible to the vulnerabilities of the PoP routers, the vulnerabilities of Internet and Intranet connectivity, and the vulnerabilities associated with cellular network access

Move Forward and Tell: A Progressive Generator of Video Descriptions

We present an efficient framework that can generate a coherent paragraph to describe a given video. Previous works on video captioning usually focus on video clips. They typically treat an entire video as a whole and generate the caption conditioned on a single embedding. On the contrary, we consider videos with rich temporal structures and aim to generate paragraph descriptions that can preserve the story flow while being coherent and concise. Towards this goal, we propose a new approach, which produces a descriptive paragraph by assembling temporally localized descriptions. Given a video, it selects a sequence of distinctive clips and generates sentences thereon in a coherent manner. Particularly, the selection of clips and the production of sentences are done jointly and progressively driven by a recurrent network -- what to describe next depends on what have been said before. Here, the recurrent network is learned via self-critical sequence training with both sentence-level and paragraph-level rewards. On the ActivityNet Captions dataset, our method demonstrated the capability of generating high-quality paragraph descriptions for videos. Compared to those by other methods, the descriptions produced by our method are often more relevant, more coherent, and more concise.Comment: Accepted by ECCV 201

Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows

This research is involved with the implementations of advanced computational schemes based on large eddy simulations (LES) and direct numerical simulations (DNS) to study the phenomenon of mixing and its coupling with chemical reactions in compressible turbulent flows. In the efforts related to LES, a research program was initiated to extend the present capabilities of this method for the treatment of chemically reacting flows, whereas in the DNS efforts, focus was on detailed investigations of the effects of compressibility, heat release, and nonequilibrium kinetics modeling in high speed reacting flows. The efforts to date were primarily focussed on simulations of simple flows, namely, homogeneous compressible flows and temporally developing hign speed mixing layers. A summary of the accomplishments is provided

Cars, capitalism and ecological crises: understanding systemic barriers to a sustainability transition in the German car industry

In the face of climate and ecological crises, it is vital that car use be reduced, while simultaneously shifting towards different powertrains and reducing the size, weight and energy demand of vehicles. This poses a challenge to the global car industry, as its business model historically centres on selling more and larger cars. In this context, the purpose of this paper is to examine the social-ecological limits of industrial restructuring in Germany. A narrative literature review through the lens of Marxian political economy sheds light on intertwined system-immanent barriers to achieving social and ecological sustainability at the sectoral level. Consequently, powertrain electrification is structured by technological dynamism, which fuels appropriation in the quest for metals and rare earths, with significant social and ecological disadvantages. This generates an impasse for the industry’s transition strategies. Understanding how capitalist tendencies generate interlaced and mutually re-enforcing barriers to achieving social-ecological sustainability is key to understanding why industrial transitions are insufficient from a social-ecological perspective

Precision Timing of Two Anomalous X-Ray Pulsars

We report on long-term X-ray timing of two anomalous X-ray pulsars, 1RXS J170849.0-400910 and 1E 2259+586, using the Rossi X-ray Timing Explorer. In monthly observations made over 1.4 yr and 2.6 yr for the two pulsars, respectively, we have obtained phase-coherent timing solutions which imply that these objects have been rotating with great stability throughout the course of our observations. For 1RXS J170849.0-400910, we find a rotation frequency of 0.0909169331(5) Hz and frequency derivative -15.687(4) x 10^(-14) Hz/s, for epoch MJD 51215.931. For 1E 2259+586, we find a rotation frequency of 0.1432880613(2)Hz, and frequency derivative -1.0026(7) x 10^(-14) Hz/s, for epoch MJD 51195.583. RMS phase residuals from these simple models are only about 0.01 cycles for both sources. We show that the frequency derivative for 1E 2259+586 is inconsistent with that inferred from incoherent frequency observations made over the last 20 yr. Our observations are consistent with the magnetar hypothesis and make binary accretion scenarios appear unlikely.Comment: 12 pages including 3 figures. To appear in ApJ Letter