Influence of excited electron lifetimes on the electronic structure of carbon nanotubes

We have studied the dynamics of electrons in single wall carbon nanotubes using femtosecond time-resolved photoemission. The lifetime of electrons excited to the pi* bands is found to decrease continuously from 130 fs at 0.2 eV down to less than 20 fs at energies above 1.5 eV with respect to the Fermi level. This should lead to a significant lifetime--induced broadening of the characteristic van Hove singularities in the nanotube DOS.Comment: 6 pages, 4 figure

Local heights of toric varieties over non-archimedean fields

We generalize results about local heights previously proved in the case of discrete absolute values to arbitrary non-archimedean absolute values of rank 1. First, this is done for the induction formula of Chambert-Loir and Thuillier. Then we prove the formula of Burgos--Philippon--Sombra for the toric local height of a proper normal toric variety in this more general setting. We apply the corresponding formula for Moriwaki's global heights over a finitely generated field to a fibration which is generically toric. We illustrate the last result in a natural example where non-discrete non-archimedean absolute values really matter.Comment: 67 pages. v2: Assumption in Theorem 2.5.8 corrected to support function; other minor change

Potential gains from reducing trade barriers in manufacturing, services and agriculture

Trade barriers

Examining Pinterest as a Curriculum Resource for Negative Integers: An Initial Investigation

This paper reports an investigation of mathematical resources available on the social media site Pinterest. Pinterest is an online bulletin board where users create visual bookmarks called pins in order to share digital content (e.g., webpages, images, videos). Although recent surveys have shown that Pinterest is a popular reference for teachers, understanding of the mathematical resources available on the site is lacking. To take initial steps in investigating the curriculum resources provided by Pinterest, we used keyword searches to gather a database of pins related to the topic of negative integers. A content analysis was conducted on the pins with a focus on several characteristics including mathematical operations, mathematical models, use of real-world context, and whether mathematical errors were present in source material. Results show a dominance of addition and subtraction over other operations, use of mathematical models in half of pins, infrequent use of real-world context, and mathematical errors in roughly one-third of pins. We provide a breakdown of these results and discuss implications of the findings for mathematics teacher education and professional development

A GLOBAL PERSPECTIVE ON REGIONAL INTEGRATION IN NORTH AMERICA

International Relations/Trade,

A Survey of Findings on the Poverty Impacts of Agricultural Trade Liberalization

The purpose of this survey is to review the available empirical evidence on the impacts of agricultural trade liberalization on poverty – considering both the impact of domestic and international liberalization. Since trade liberalization is generally an economywide phenomenon, with tariff cuts occurring across a wide range of commodities, we do not restrict ourselves to episodes where only agricultural trade was liberalized, although emphasis in this survey is given to agricultural trade policies. Furthermore, given the difficulty of isolating the effects of trade policies alone, we will also consider the impact of other types of external shocks which have the effect of changing the relative prices of tradeable and non-tradeable goods. By examining the way in which households adjust to such external shocks, we can learn a great deal about how they would respond to sharp reductions in tariffs, or significant changes in a country’s international terms of trade engendered by multilateral trade liberalization.Poverty, rural development, agriculture, Food Security and Poverty, International Relations/Trade,