K-classes of matroids and equivariant localization

To every matroid, we associate a class in the K-theory of the Grassmannian. We study this class using the method of equivariant localization. In particular, we provide a geometric interpretation of the Tutte polynomial. We also extend results of the second author concerning the behavior of such classes under direct sum, series and parallel connection and two-sum; these results were previously only established for realizable matroids, and their earlier proofs were more difficult.Comment: v2: added a starting point for combinatorialists in Section 2.4, + minor change

Resonant Elastic Soft X-Ray Scattering

Resonant (elastic) soft x-ray scattering (RSXS) offers a unique element, site, and valence specific probe to study spatial modulations of charge, spin, and orbital degrees of freedom in solids on the nanoscopic length scale. It cannot only be used to investigate single crystalline materials. This method also enables to examine electronic ordering phenomena in thin films and to zoom into electronic properties emerging at buried interfaces in artificial heterostructures. During the last 20 years, this technique, which combines x-ray scattering with x-ray absorption spectroscopy, has developed into a powerful probe to study electronic ordering phenomena in complex materials and furthermore delivers important information on the electronic structure of condensed matter. This review provides an introduction to the technique, covers the progress in experimental equipment, and gives a survey on recent RSXS studies of ordering in correlated electron systems and at interfaces

Matrix metalloproteinases-2,-3,-7,-9 and-10, but not MMP-11, are differentially expressed in normal, benign tumorigenic and malignant human keratinocyte cell lines

In order to investigate the correlations between constitutive proteinase expression and the degree of tumorigenicity of cancer cells we have studied a model system of three keratinocyte cell lines. RT-PCR studies showed that the cell lines express the genes of matrix metalloproteinase-2, -3, -7, -9, -10 and -11, indicating that they are able to synthesize the corresponding enzymes. Actual MMP synthesis was proven by zymography and Western blotting. In conditioned media gelatinolytic activities or immunoreactive forms of MMP-2, -3, -7, -9, -10 and -11 were detected. The signal intensities showed that MMP secretion increases in the order HaCaT < A5 less than or equal to II-4RT, whereas only MMP-11 is secreted by all cell lines in equal amounts, Intracellularly, enhanced levels of one or both of the tumorigenic variants were only found for MMP-3 -9 and -10, suggesting special functions of these intracellular MMP pools for the tumorigenic cell lines. For MMP-11 exclusive expression in stromal fibroblasts of tumor tissues is widely accepted; however, our results and three other recent reports demonstrate that this concept is not generally valid. In conclusion, the three keratinocyte cell lines investigated here represent an excellent model for studying constitutive expression and secretion of MMPs in correlation to the degree of in vivo tumorigenicity

Spectroscopic Observations of New Oort Cloud Comet 2006 VZ13 and Four Other Comets

Spectral data are presented for comets 2006 VZ13 (LINEAR), 2006 K4 (NEAT), 2006 OF2 (Broughton), 2P/Encke, and 93P/Lovas I, obtained with the Cerro-Tololo Inter-American Observatory 1.5-m telescope in August 2007. Comet 2006 VZ13 is a new Oort cloud comet and shows strong lines of CN (3880 angstroms), the Swan band sequence for C_2 (4740, 5160, and 5630 angstroms), C_3 (4056 angstroms), and other faint species. Lines are also identified in the spectra of the other comets. Flux measurements of the CN, C_2 (Delta v = +1,0), and C_3 lines are recorded for each comet and production rates and ratios are derived. When considering the comets as a group, there is a correlation of C_2 and C_3 production with CN, but there is no conclusive evidence that the production rate ratios depend on heliocentric distance. The continuum is also measured, and the dust production and dust-to-gas ratios are calculated. There is a general trend, for the group of comets, between the dust-to-gas ratio and heliocentric distance, but it does not depend on dynamical age or class. Comet 2006 VZ13 is determined to be in the carbon-depleted (or Tempel 1 type) class.Comment: 8 pages, 6 figures, 6 tables; Accepted by MNRA

The Graying of Global Population and Its Macroeconomic Consequences

Population aging is emerging as a major demographic trend in many countries, with potentially important implications for a variety of macroeconomic issues. Notwithstanding these challenges, population aging will likely have a comparatively modest effect on economic growth. Although the changed age distribution would be expected to cause the labor force participation rate to decrease, the ratio of labor force to population will actually increase in most countries. This will occur because the lower youth dependency rate and the increased rate of female labor force participation – both of which may reasonably be expected to follow from the fertility rate declines that are driving population aging – will counterbalance the shifting of adults toward older ages at which labor force participation and savings rates are lower. Behavioral and policy responses to population aging – including higher savings for retirement, a higher rate of human capital accumulation, alternate pension funding plans, and (possibly) increased migration from labor-abundant to labor-scarce countries – also suggest that population aging need not necessarily significantly impede economic growth.Global population, macroeconomics, aging

Urbanization and the Wealth of Nations

The proportion of a country's population living in urban areas is highly correlated with its level of income. Urban areas offer economies of scale and richer market structures, and there is strong evidence that workers in urban areas are individually more productive, and earn more, than rural workers. However, rapid urbanization is also associated with crowding, environmental degradation, and other impediments to productivity. Overall, we find no evidence that the level of urbanization affects the rate of economic growth. Our findings weaken the rationale for either encouraging or discouraging urbanization as part of a strategy for economic growth.urbanization, economic growth, development.

Disease and Development Revisited

In a recent paper, Acemoglu and Johnson (2007) argue that the large increases in population health witnessed in the 20th century may have lowered income levels. We argue that this result depends crucially on their assumption that initial health and income do not affect subsequent economic growth. Using their data we reject this assumption in favor of a model of conditional convergence, with income adjusting to its steady state over time. We show that, allowing for conditional convergence, exogenous improvements in health due to technical advances associated with the epidemiological transition appear to have increased income levels.Disease, development, economic growth, health

Fertility, Female Labor Force Participation, and the Demographic Dividend

We estimate the effect of fertility on female labor force participation in a cross-country panel data set using abortion legislation as an instrument for fertility. We find a large negative effect of the fertility rate on female labor force participation. The direct effect is concentrated among those aged 20–39, but we find that cohort participation is persistent over time giving an effect among older women. We present a simulation model of the effect of fertility reduction on income per capita, taking into account these changes in female labor force participation as well as population numbers and age structure.

Does Age Structure Forecast Economic Growth?

Increases in the proportion of the working age population can yield a "demographic dividend" that enhances the rate of economic growth. We estimate the parameters of an economic growth model with a cross section of countries over the period 1960 to 1980 and investigate whether the inclusion of age structure improves the model's forecasts for the period 1980 to 2000. We find that including age structure improves the forecast, although there is evidence of parameter instability between periods with an unexplained growth slowdown in the second period. We use the model to generate growth forecasts for the period 2000 to 2020.

Demographic Change, Institutional Settings, and Labor Supply

This paper analyzes cross-country panel data to examine the effect of key institutional features of social security systems on male labor supply. Our findings indicate that the labor supply of older males covaries negatively with replacement rates and system coverage, with the replacement rate effects being stronger for pay-as-you-go systems than for fully funded systems. The results also reveal a surprisingly small and often negative response of the labor supply of older males to improvements in life expectancy.Global health, labor, Aging, Economics, Demography.