Signature change induces compactification

It is shown -- using a FRW model with ${\bf S}^3 \times {\bf S}^6$ as spatial sections and a positive cosmological constant -- that classical signature change implies a new compactification mechanism. The internal scale factor is of the order $\Lambda^{-1/2}$, and the solutions are stable against small perturbatons. In the case of compactified ${\bf S}^6$, it is shown that the effective four-dimensional space-time metric has Lorentzian signature, undergoes exponential inflation in ${\bf S}^3$ and is unique. Speculations concerning relations to quantum cosmology and conceivable modifications are added.Comment: 31 pages, LaTeX, 4 Figures are available on request as hard copies. Some clarifications are included concerning the particular model of signature change considered; misprints corrected and some references adde

The site frequency spectrum of dispensable genes

The differences between DNA-sequences within a population are the basis to infer the ancestral relationship of the individuals. Within the classical infinitely many sites model, it is possible to estimate the mutation rate based on the site frequency spectrum, which is comprised by the numbers $C_1,...,C_{n-1}$, where n is the sample size and $C_s$ is the number of site mutations (Single Nucleotide Polymorphisms, SNPs) which are seen in $s$ genomes. Classical results can be used to compare the observed site frequency spectrum with its neutral expectation, $E[C_s]= \theta_2/s$, where $\theta_2$ is the scaled site mutation rate. In this paper, we will relax the assumption of the infinitely many sites model that all individuals only carry homologous genetic material. Especially, it is today well-known that bacterial genomes have the ability to gain and lose genes, such that every single genome is a mosaic of genes, and genes are present and absent in a random fashion, giving rise to the dispensable genome. While this presence and absence has been modeled under neutral evolution within the infinitely many genes model in previous papers, we link presence and absence of genes with the numbers of site mutations seen within each gene. In this work we derive a formula for the expectation of the joint gene and site frequency spectrum, denotes $G_{k,s}$ the number of mutated sites occurring in exactly $s$ gene sequences, while the corresponding gene is present in exactly $k$ individuals. We show that standard estimators of $\theta_2$ for dispensable genes are biased and that the site frequency spectrum for dispensable genes differs from the classical result.Comment: 24 pages, 8 figure

Local Economic Development Incentives in New York City

This report provides the first systematic and comprehensive analysis of datasets on economic development incentives in New York City over the last fifteen years