The return to education in the mid-20th century: evidence from twins

What was the return to education in the US at mid-century? In 1940, the correlation between years of schooling and earnings was relatively low. In this paper, we estimate the causal return to schooling in 1940, constructing a large linked sample of twin brothers to account for differences in unobserved ability and family background. We find that each additional year of schooling increased labor earnings by approximately 4%, about half the return found for more recent cohorts in contemporary twins studies. These returns were evident both within and across occupations and were higher for sons from lower SES families.First author draf

Algorithmic Algebraic Geometry and Flux Vacua

We develop a new and efficient method to systematically analyse four dimensional effective supergravities which descend from flux compactifications. The issue of finding vacua of such systems, both supersymmetric and non-supersymmetric, is mapped into a problem in computational algebraic geometry. Using recent developments in computer algebra, the problem can then be rapidly dealt with in a completely algorithmic fashion. Two main results are (1) a procedure for calculating constraints which the flux parameters must satisfy in these models if any given type of vacuum is to exist; (2) a stepwise process for finding all of the isolated vacua of such systems and their physical properties. We illustrate our discussion with several concrete examples, some of which have eluded conventional methods so far.Comment: 41 pages, 4 figure

Compressive sampling for accelerometer signals in structural health monitoring

In structural health monitoring (SHM) of civil structures, data compression is often needed to reduce the cost of data transfer and storage, because of the large volumes of sensor data generated from the monitoring system. The traditional framework for data compression is to first sample the full signal and, then to compress it. Recently, a new data compression method named compressive sampling (CS) that can acquire the data directly in compressed form by using special sensors has been presented. In this article, the potential of CS for data compression of vibration data is investigated using simulation of the CS sensor algorithm. For reconstruction of the signal, both wavelet and Fourier orthogonal bases are examined. The acceleration data collected from the SHM system of Shandong Binzhou Yellow River Highway Bridge is used to analyze the data compression ability of CS. For comparison, both the wavelet-based and Huffman coding methods are employed to compress the data. The results show that the values of compression ratios achieved using CS are not high, because the vibration data used in SHM of civil structures are not naturally sparse in the chosen bases

Exploring the Vacuum Geometry of N=1 Gauge Theories

Using techniques of algorithmic algebraic geometry, we present a new and efficient method for explicitly computing the vacuum space of N=1 gauge theories. We emphasize the importance of finding special geometric properties of these spaces in connecting phenomenology to guiding principles descending from high-energy physics. We exemplify the method by addressing various subsectors of the MSSM. In particular the geometry of the vacuum space of electroweak theory is described in detail, with and without right-handed neutrinos. We discuss the impact of our method on the search for evidence of underlying physics at a higher energy. Finally we describe how our results can be used to rule out certain top-down constructions of electroweak physics.Comment: 35 pages, 2 figures, LaTe

Exploring Positive Monad Bundles And A New Heterotic Standard Model

A complete analysis of all heterotic Calabi-Yau compactifications based on positive two-term monad bundles over favourable complete intersection Calabi-Yau threefolds is performed. We show that the original data set of about 7000 models contains 91 standard-like models which we describe in detail. A closer analysis of Wilson-line breaking for these models reveals that none of them gives rise to precisely the matter field content of the standard model. We conclude that the entire set of positive two-term monads on complete intersection Calabi-Yau manifolds is ruled out on phenomenological grounds. We also take a first step in analyzing the larger class of non-positive monads. In particular, we construct a supersymmetric heterotic standard model within this class. This model has the standard model gauge group and an additional U(1)_{B-L} symmetry, precisely three families of quarks and leptons, one pair of Higgs doublets and no anti-families or exotics of any kind.Comment: 48 page

Vacuum Geometry and the Search for New Physics

We propose a new guiding principle for phenomenology: special geometry in the vacuum space. New algorithmic methods which efficiently compute geometric properties of the vacuum space of N=1 supersymmetric gauge theories are described. We illustrate the technique on subsectors of the MSSM. The fragility of geometric structure that we find in the moduli space motivates phenomenologically realistic deformations of the superpotential, while arguing against others. Special geometry in the vacuum may therefore signal the presence of string physics underlying the low-energy effective theory.Comment: 8 pages, LaTeX; v2: revised title, minor changes in wording, reference adde

Thermal analysis of high-bandwidth and energy-efficient 980 nm VCSELs with optimized quantum well gain peak-to-cavity resonance wavelength offset

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 111, 243508 (2017) and may be found at https://doi.org/10.1063/1.5003288.The static and dynamic performance of vertical-cavity surface-emitting lasers (VCSELs) used as light-sources for optical interconnects is highly influenced by temperature. We study the effect of temperature on the performance of high-speed energy-efficient 980 nm VCSELs with a peak wavelength of the quantum well offset to the wavelength of the fundamental longitudinal device cavity mode so that they are aligned at around 60 °C. A simple method to obtain the thermal resistance of the VCSELs as a function of ambient temperature is described, allowing us to extract the active region temperature and the temperature dependence of the dynamic and static parameters. At low bias currents, we can see an increase of the −3 dB modulation bandwidth f−3dB with increasing active region temperature, which is different from the classically known situation. From the detailed analysis of f−3dB versus the active region temperature, we obtain a better understanding of the thermal limitations of VCSELs, giving a basis for next generation device designs with improved temperature stability

Immigrant Entrepreneurs Creating Jobs and Strengthening the U.S. Economy in Growing Industries

The focus of this report evolved from a 2010 conference at Babson College on "Immigrant Entrepreneurship in Massachusetts" sponsored by The Immigrant Learning Center, Inc. (ILC) from which two key ideas emerged. One is that there is an "immigrant entrepreneurship ecology" that includes immigrant neighborhood storefront businesses; immigrant high-tech and health science entrepreneurs; immigrant non-tech growth businesses; and immigrant transnational businesses. A second idea was that these growing, non-tech industries (including transportation, food and building services) have not attracted much attention. Interestingly, these sectors can be crucial to the expansion of the green economy. Within this context, The ILC decided to look at these three sectors in Massachusetts as well as in New York and Pennsylvania.Moreover, the report dramatically illustrates how immigrant entrepreneurs look for niches in underserved markets. For example, vans and other alternatives to mass transit serve unmet transportation needs in urban areas. Food intended to be a "taste of home" for compatriots in local restaurants and grocery stores becomes popular and influences the eating habits of other Americans. Workers who enter industries like landscaping or cleaning because they don't require much English gain experience and see opportunities to start their own companies. Businesses like these add value to American life by expanding the economy rather than taking away from native businesses