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This thesis represents a significant advance in our understanding of the synthesis and propertiesof two-dimensional (2D) materials. The author’s work breaks new ground in the understanding of a number of 2D crystals, including atomically thin transition metal dichalcogenides, graphene, and their heterostructures, that are technologically important to next-generation electronics. In addition to critical new results on the direct growth of 2D heterostructures, it also details growth mechanisms, surface science, and device applications of “epi-grade” 2D semiconductors, which are essential to low-power electronics, as well as for extending Moore’s law. Most importantly, it provides an effective alternative to mechanically exfoliate 2D layers for practical applications. .
Heterostructures. --- Crystals --- Superlattices as materials --- Nanotechnology. --- Optical materials. --- Surfaces (Physics). --- Crystallography. --- Semiconductors. --- Optical and Electronic Materials. --- Surfaces and Interfaces, Thin Films. --- Crystallography and Scattering Methods. --- Molecular technology --- Nanoscale technology --- High technology --- Optics --- Materials --- Leptology --- Physical sciences --- Mineralogy --- Physics --- Surface chemistry --- Surfaces (Technology) --- Electronic materials. --- Materials—Surfaces. --- Thin films. --- Films, Thin --- Solid film --- Solid state electronics --- Solids --- Coatings --- Thick films --- Electronic materials --- Crystalline semiconductors --- Semi-conductors --- Semiconducting materials --- Semiconductor devices --- Electrical engineering --- Electronics
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This thesis represents a significant advance in our understanding of the synthesis and propertiesof two-dimensional (2D) materials. The author’s work breaks new ground in the understanding of a number of 2D crystals, including atomically thin transition metal dichalcogenides, graphene, and their heterostructures, that are technologically important to next-generation electronics. In addition to critical new results on the direct growth of 2D heterostructures, it also details growth mechanisms, surface science, and device applications of “epi-grade” 2D semiconductors, which are essential to low-power electronics, as well as for extending Moore’s law. Most importantly, it provides an effective alternative to mechanically exfoliate 2D layers for practical applications. .
Optics. Quantum optics --- Electronics and optics of solids --- Solid state physics --- Physics --- Surface chemistry --- Chemical and physical crystallography --- Rocks. Minerals --- Electronics --- Electrical engineering --- kristallografie --- oppervlakte-onderzoek --- nanotechniek --- fysica --- kristallen --- transistoren --- halfgeleiders --- microwaves
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In recent years, there has been widespread concern that misinformation on social media is damaging societies and democratic institutions. In response, social media platforms have announced actions to limit the spread of false content. We measure trends in the diffusion of content from 569 fake news websites and 9,540 fake news stories on Facebook and Twitter between January 2015 and July 2018. User interactions with false content rose steadily on both Facebook and Twitter through the end of 2016. Since then, however, interactions with false content have fallen sharply on Facebook while continuing to rise on Twitter, with the ratio of Facebook engagements to Twitter shares decreasing by 60 percent. In comparison, interactions with other news, business, or culture sites have followed similar trends on both platforms. Our results suggest that the relative magnitude of the misinformation problem on Facebook has declined since its peak.
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In recent years, there has been widespread concern that misinformation on social media is damaging societies and democratic institutions. In response, social media platforms have announced actions to limit the spread of false content. We measure trends in the diffusion of content from 569 fake news websites and 9,540 fake news stories on Facebook and Twitter between January 2015 and July 2018. User interactions with false content rose steadily on both Facebook and Twitter through the end of 2016. Since then, however, interactions with false content have fallen sharply on Facebook while continuing to rise on Twitter, with the ratio of Facebook engagements to Twitter shares decreasing by 60 percent. In comparison, interactions with other news, business, or culture sites have followed similar trends on both platforms. Our results suggest that the relative magnitude of the misinformation problem on Facebook has declined since its peak.
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Physicians, judges, teachers, and agents in many other settings differ systematically in the decisions they make when faced with similar cases. Standard approaches to interpreting and exploiting such differences assume they arise solely from variation in preferences. We develop an alternative framework that allows variation in both preferences and diagnostic skill, and show that both dimensions may be identified in standard settings under quasi-random assignment. We apply this framework to study pneumonia diagnoses by radiologists. Diagnosis rates vary widely among radiologists, and descriptive evidence suggests that a large component of this variation is due to differences in diagnostic skill. Our estimated model suggests that radiologists view failing to diagnose a patient with pneumonia as more costly than incorrectly diagnosing one without, and that this leads less-skilled radiologists to optimally choose lower diagnostic thresholds. Variation in skill can explain 39 percent of the variation in diagnostic decisions, and policies that improve skill perform better than uniform decision guidelines. Failing to account for skill variation can lead to highly misleading results in research designs that use agent assignments as instruments.
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Concerned about the low academic ability of public school teachers, in the 1990s and 2000s, some states increased licensing stringency to weed out low-quality candidates, while others decreased restrictions to attract high-quality candidates. We offer a theoretical model justifying both reactions. Using data from 1991-2007 on licensing requirements and teacher quality--as measured by the selectivity of teachers' undergraduate institutions--we find that stricter licensing requirements, especially those emphasizing academic coursework, increase the left tail of the quality distribution for secondary school teachers without significantly decreasing quality for high-minority or high-poverty districts.
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This paper uses detailed data on sequential offers from seven vastly different real-world bargaining settings to document a robust pattern: agents favor offers that split the difference between the two most recent offers on the table. Our settings include negotiations for used cars, insurance injury claims, a TV game show, auto rickshaw rides, housing, international trade tariffs, and online retail. We demonstrate that this pattern can arise in a perfect Bayesian equilibrium of an alternating-offer game with two-sided incomplete information, but this equilibrium is far from unique. We then provide a robust-inference argument to explain why agents may view the two most recent offers as corresponding to the potential surplus. Split-the-difference offers under this weaker, robust inference can then be viewed as fair. We present a number of other patterns in each data setting that point to split-the-difference offers as a strong social norm, whether in high-stakes or low-stakes negotiations.
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