When Protest Doesn\u27t Quite Fit the Mold

White people protesting is powerful. It is a privilege to be guaranteed that someone will listen to us, as pointed out by Jerome Clarke in a piece about last year’s “Won’t Stand For Hate” protest. With that privilege comes a responsibility that has been neglected on this campus. I agree with the students who protested on the steps of Penn Hall and spoke out during the Student Senate meeting about the way our administration is handling the mold situation in Hanson Hall. The response was insufficient and it directly contradicts the College’s verbal commitment to promoting a healthy living and learning environment. However, as I walked by the students protesting on Friday, I was hit with irony and felt ashamed of the way many of us have responded to this issue. Perhaps I wouldn’t feel that way if every issue facing the students of this campus, specifically those most marginalized, were met with similar outcry from the majority population here. [excerpt

Multiphase modelling of vascular tumour growth in two spatial dimensions

In this paper we present a continuum mathematical model of vascular tumour growth which is based on a multiphase framework in which the tissue is decomposed into four distinct phases and the principles of conservation of mass and momentum are applied to the normal/healthy cells, tumour cells, blood vessels and extracellular material. The inclusion of a diffusible nutrient, supplied by the blood vessels, allows the vasculature to have a nonlocal influence on the other phases. Two-dimensional computational simulations are carried out on unstructured, triangular meshes to allow a natural treatment of irregular geometries, and the tumour boundary is captured as a diffuse interface on this mesh, thereby obviating the need to explicitly track the (potentially highly irregular and ill-defined) tumour boundary. A hybrid finite volume/finite element algorithm is used to discretise the continuum model: the application of a conservative, upwind, finite volume scheme to the hyperbolic mass balance equations and a finite element scheme with a stable element pair to the generalised Stokes equations derived from momentum balance, leads to a robust algorithm which does not use any form of artificial stabilisation. The use of a matrix-free Newton iteration with a finite element scheme for the nutrient reaction-diffusion equations allows full nonlinearity in the source terms of the mathematical model. Numerical simulations reveal that this four-phase model reproduces the characteristic pattern of tumour growth in which a necrotic core forms behind an expanding rim of well-vascularised proliferating tumour cells. The simulations consistently predict linear tumour growth rates. The dependence of both the speed with which the tumour grows and the irregularity of the invading tumour front on the model parameters are investigated

Effect of Particle-Hole Asymmetry on the Mott-Hubbard Metal-Insulator Transition

The Mott-Hubbard metal-insulator transition is one of the most important problems in correlated electron systems. In the past decade, much progress has been made on examining a particle-hole symmetric form of the transition in the Hubbard model with dynamical mean field theory where it was found that the electronic self energy develops a pole at the transition. We examine the particle-hole asymmetric metal-insulator transition in the Falicov-Kimball model, and find that a number of features change when the noninteracting density of states has a finite bandwidth. Since, generically particle-hole symmetry is broken in real materials, our results have an impact on understanding the metal-insulator transition in real materials.Comment: 5 pages, 3 figure

Federal Government Debt and Interest Rates

Does government debt affect interest rates? Despite a substantial body of empirical analysis, the answer based on the past two decades of research is mixed. While many studies suggest, at most, a single-digit rise in the interest rate when government debt increases by one percent of GDP, others estimate either much larger effects or find no effect. Comparing results across studies is complicated by differences in economic models, definitions of econometric approaches, and sources of data. Using a standard set of data and a simple analytical framework, we reconsider and add to empirical evidence on the effect of federal government debt and interest rates. We begin by deriving analytically the effect of government debt on the real interest rate and find that an increase in government debt equivalent to one percent of GDP would be predicted to increase the real interest rate by about two to three basis points. While some existing studies estimate effects in this range, others find larger effects. In almost all cases, these larger estimates come from specifications relating federal deficits (as opposed to debt) and the level of interest rates or from specifications not controlling adequately for macroeconomic influences on interest rates that might be correlated with deficits. We present our own empirical analysis in two parts. First, we examine a variety of conventional reduced-form specifications linking interest rates and government debt and other variables. In particular, we provide estimates for three types of specifications to permit comparisons among different approaches taken in previous research; we estimate the effect of: an expected, or projected, measure of federal government debt on a forward-looking measure of the real interest rate; an expected, or projected, measure of federal government debt on a current measure of the real interest rate; and a current measure of federal government debt on a current measure of the real interest rate. Most of the statistically significant estimated effects are consistent with the prediction of the simple analytical calculation. Second, we provide evidence using vector autoregression analysis. In general, these results are similar to those found in our reduced-form econometric analysis and consistent with the analytical calculations. Taken together, the bulk of our empirical results suggest that an increase in federal government debt equivalent to one percent of GDP, all else equal, would be expected to increase the long-term real rate of interest by about three basis points, though one specification suggests a larger impact, while some estimates are not statistically significantly different from zero. By presenting a range of results with the same data, we illustrate the dependence of estimation on specification and definition differences.

"Success Taxes," Entrepreneurial Entry, and Innovation

Interest in the role of entrepreneurial entry in innovation raises the question of the extent to which tax policy encourages or discourages entry. We find that, while the level of the marginal tax rate has a negative effect in entrepreneurial entry, the progressivity of the tax also discourages entrepreneurship, and significantly so for some groups of households. These effects are principally traceable to the upside' or success' convexity of the household tax schedule. Prospective entrants from a priori innovative industries and occupations are no less affected by the considerations we examine than other prospective entrants. In terms of destination-based industry and occupation measures of innovative entrepreneurs, we find mixed evidence on whether innovative entrepreneurs differ from the general population; the results for entrepreneurs moving to innovative industries suggest that they may be unaffected by tax convexity but the possible endogeneity of this measure of innovative entrepreneurs confounds interpreting this specification. Using education as a measure of potential for innovation, we find that tax convexity discourages entry into self-employment for people of all educational backgrounds. Overall, we find little evidence that the tax effects are focused simply on the employment changes of less skilled or less promising potential entrants.

A chemical model for lunar non-mare rocks

Nearly all rocks returned from the moon are readily divided into three broad categories on the basis of their chemical compositions: (1) mare basalts, (2) non-mare rocks of basaltic composition (KREEP, VHA), and (3) anorthositic rocks. Only mare basalts may unambiguously be considered to have original igneous textures and are widely understood to have an igneous origin. Nearly all other lunar rocks have lost their original textures during metamorphic and impact processes. For these rocks one must work primarily with chemical data in order to recognize and define rock groups and their possible modes of origin. Non-mare rocks of basaltic composition have chemical compositions consistent with an origin by partial melting of the lunar interior. The simplest origin for rocks of anorthositic chemical composition is the crystallization and removal of ferromagnesian minerals. It is proposed that the rock groups of anorthositic and non-mare basaltic chemical composition could have been generated from a single series of original, but not necessarily primitive, lunar materials

A chemical model for lunar non-mare rocks

Nearly all rocks returned from the moon are readily divided into three broad categories on the basis of their chemical compositions: (1) mare basalts, (2) non-mare rocks of basaltic composition (KREEP, VHA), and (3) anorthositic rocks. Only mare basalts may unambiguously be considered to have original igneous textures and are widely understood to have an igneous origin. Nearly all other lunar rocks have lost their original textures during metamorphic and impact processes. It is shown that for these rocks one must work primarily with chemical data in order to recognize and define rock groups and their possible modes of origin. Non-mare rocks of basaltic composition have chemical compositions consistent with an origin by partial melting of the lunar interior. The simplest origin for rocks of anorthositic chemical composition is the crystallization and removal of ferromagnesian minerals. It is proposed that the rock groups of anorthositic and non-mare basaltic chemical composition could have been generated from a single series of original but not necessarily primitive lunar materials

The Effects of Progressive Income Taxation on Job Turnover

We examine whether the level of the income tax rate and the convexity of the income tax schedule affect job mobility, as measured by moving to a better job. While the predicted effect of the level of the tax rate is ambiguous, we predict that an increase in the convexity of the tax schedule decreases job search activity by taxing away some of the benefits of a successful job search. Using data from the Panel Study of Income Dynamics, we estimate that both higher tax rates and increased tax rate progressivity decrease the probability that a head of household will move to a better job during the coming year. Our estimates imply that a five-percentage-point reduction in the marginal tax rate increases the average probability of moving to a better job by 0.79 percentage points (a 8.0 percent increase in the turnover propensity) and that a onestandard- deviation in our measure of tax progressivity would increase this probability by 0.86 percentage points (a 8.7 percent increase in the turnover propensity).