Northwestern University

About: Northwestern University is a education organization based out in Evanston, Illinois, United States. It is known for research contribution in the topics: Population & Transplantation. The organization has 75430 authors who have published 188857 publications receiving 9463252 citations. The organization is also known as: Northwestern & NU.

Measurements of near-ultimate strength for multiwalled carbon nanotubes and irradiation-induced crosslinking improvements.

Abstract: The excellent mechanical properties of carbon nanotubes are being exploited in a growing number of applications from ballistic armour to nanoelectronics. However, measurements of these properties have not achieved the values predicted by theory due to a combination of artifacts introduced during sample preparation and inadequate measurements. Here we report multiwalled carbon nanotubes with a mean fracture strength >100 GPa, which exceeds earlier observations by a factor of approximately three. These results are in excellent agreement with quantum-mechanical estimates for nanotubes containing only an occasional vacancy defect, and are ∼80% of the values expected for defect-free tubes. This performance is made possible by omitting chemical treatments from the sample preparation process, thus avoiding the formation of defects. High-resolution imaging was used to directly determine the number of fractured shells and the chirality of the outer shell. Electron irradiation at 200 keV for 10, 100 and 1,800 s led to improvements in the maximum sustainable loads by factors of 2.4, 7.9 and 11.6 compared with non-irradiated samples of similar diameter. This effect is attributed to crosslinking between the shells. Computer simulations also illustrate the effects of various irradiation-induced crosslinking defects on load sharing between the shells. The mechanical properties of carbon nanotubes rarely match the values predicted by theory owing to a combination of artefacts introduced during sample preparation and inadequate measurements. However, by avoiding chemical treatments and using high-resolution imaging, it is possible to obtain values of the mean fracture strength that exceed previous values by approximately a factor of three.

The national lung screening trial: Overview and study design

Abstract: The National Lung Screening Trial (NLST) is a randomized multicenter study comparing low-dose helical computed tomography (CT) with chest radiography in the screening of older current and former heavy smokers for early detection of lung cancer, which is the leading cause of cancer-related death in the United States Five-year survival rates approach 70% with surgical resection of stage IA disease; however, more than 75% of individuals have incurable locally advanced or metastatic disease, the latter having a 5-year survival of less than 5% It is plausible that treatment should be more effective and the likelihood of death decreased if asymptomatic lung cancer is detected through screening early enough in its preclinical phase For these reasons, there is intense interest and intuitive appeal in lung cancer screening with low-dose CT The use of survival as the determinant of screening effectiveness is, however, confounded by the well-described biases of lead time, length, and overdiagnosis Despite previous attempts, no test has been shown to reduce lung cancer mortality, an endpoint that circumvents screening biases and provides a definitive measure of benefit when assessed in a randomized controlled trial that enables comparison of mortality rates between screened individuals and a control group that does not undergo the screening intervention of interest The NLST is such a trial The rationale for and design of the NLST are presented

Developments in Nanostructured Cathode Materials for High‐Performance Lithium‐Ion Batteries

Abstract: Nanostructured materials lie at the heart of fundamental advances in efficient energy storage and/or conversion, in which surface processes and transport kinetics play determining roles. This Review describes some recent developments in the synthesis and characterization of nanostructured cathode materials, including lithium transition metal oxides, vanadium oxides, manganese oxides, lithium phosphates, and various nanostructured composites. The major goal of this Review is to highlight some new progress in using these nanostructured materials as cathodes to develop lithium batteries with high energy density, high rate capability, and excellent cycling stability resulting from their huge surface area, short distance for mass and charge transport, and freedom for volume change in nanostructured materials.

The Role of Social Capital in Financial Development

Abstract: To identify the effect of social capital on financial development, we exploit the well-known differences in social capital (Banfield (1958), Putnam (1993)) across different parts of Italy. In areas of the country with high levels of social capital, households invest less in cash and more in stock, are more likely to use checks, have higher access to institutional credit, and make less use of informal credit. The effect of social capital is stronger where legal enforcement is weaker and among less-educated people. These results are not driven by omitted environmental variables, since we show that the behavior of movers is still affected by the level of social capital present in the province where they were born.

Portfolio Choice and Asset Prices: The Importance of Entrepreneurial Risk

Abstract: Using cross-sectional data from the SCF and Tax Model, we show that entrepreneurial income risk has a significant inf luence on portfolio choice and asset prices. We find that households with high and variable business income hold less wealth in stocks than other similarly wealthy households, although they constitute a significant fraction of the stockholding population. Similarly for nonentrepreneurs, holding stock in the firm where one works reduces the portfolio share of other common stocks. Finally, we show that adding proprietary income to a linear asset pricing model improves its performance over a similar model that includes only wage income. IN CONSTRUCTING INVESTMENT PORTFOLIOS, it appears that many if not most households fail to behave in a manner consistent with simple economic theory. Even among relatively wealthy households, the share of financial assets held in different asset classes varies widely, and there is evidence that among those who hold common stock, there is often little diversification ~e.g., King and Leape ~1987!, Blume and Zeldes ~1994!!. We begin this paper with an empirical investigation into some of the risk factors and demographic variables that might explain these cross-sectional differences in portfolio composition. A number of previous studies focus on the level and variability of wage income growth as one of the largest sources of undiversifiable income risk. Here we present evidence that, for the subset of the population that has significant stockholdings, income from entrepreneurial ventures ~which we refer to as proprietary business income) represents a large source of undiversifiable risk that is more highly correlated with common stock returns. These findings motivate the investigation in the second part of the paper of a linear asset pricing model that incorporates proprietary income from pri