Urban Governance and Infrastructure: Coping with Diversity, Complexity and Uncertainty

In this concluding chapter, we discuss how these two perspectives on urban infrastructures and urban performance could be linked to each other. For this purpose, the next section proposes a framework for an integrated approach. Section 'Learning from theoretical and practical experiences' combines the most important issues raised in the contributions to this book. In the concluding section, we formulate some suggestions for research in the near futur

Surface code architecture for donors and dots in silicon with imprecise and nonuniform qubit couplings

A scaled quantum computer with donor spins in silicon would benefit from a viable semiconductor framework and a strong inherent decoupling of the qubits from the noisy environment. Coupling neighbouring spins via the natural exchange interaction according to current designs requires gate control structures with extremely small length scales. We present a silicon architecture where bismuth donors with long coherence times are coupled to electrons that can shuttle between adjacent quantum dots, thus relaxing the pitch requirements and allowing space between donors for classical control devices. An adiabatic SWAP operation within each donor/dot pair solves the scalability issues intrinsic to exchange-based two-qubit gates, as it does not rely on sub-nanometer precision in donor placement and is robust against noise in the control fields. We use this SWAP together with well established global microwave Rabi pulses and parallel electron shuttling to construct a surface code that needs minimal, feasible local control.Comment: Published version - more detailed discussions, robustness to dephasing pointed out additionall

Epistatic interactions between sex chromosomes and autosomes can affect the stability of sex determination systems

Sex determination (SD) is an essential and ancient developmental process, but the genetic systems that regulate this process are surprisingly variable. Why SD mechanisms vary so much is a longstanding question in evolutionary biology. SD genes are generally located on sex chromosomes which also carry genes that interact epistatically with autosomes to affect fitness. How this affects the evolutionary stability of SD mechanisms is still unknown. Here, we explore how epistatic interactions between a sexually antagonistic (SA) non‐SD gene, located on either an ancestral or novel sex chromosome, and an autosomal gene affect the conditions under which an evolutionary transition to a new SD system occurs. We find that when the SD gene is linked to an ancestral sex‐chromosomal gene which engages in epistatic interactions, epistasis enhances the stability of the sex chromosomes so that they are retained under conditions where transitions would otherwise occur. This occurs both when weaker fitness effects are associated with the ancestral sex chromosome pair or stronger fitness effects associated with a newly evolved SD gene. However, the probability that novel SD genes spread is unaffected if they arise near genes involved in epistasis. This discrepancy occurs because, on autosomes, SA allele frequencies are typically lower than on sex chromosomes. In our model, increased frequencies of these alleles contribute to a higher frequency of epistasis which may therefore more readily occur on sex chromosomes. Because sex chromosome–autosome interactions are abundant and can take several forms, they may play a large role in maintaining sex chromosomes

Local formation of nitrogen-vacancy centers in diamond by swift heavy ions

We exposed nitrogen-implanted diamonds to beams of swift uranium and gold ions (~1 GeV) and find that these irradiations lead directly to the formation of nitrogen vacancy (NV) centers, without thermal annealing. We compare the photoluminescence intensities of swift heavy ion activated NV- centers to those formed by irradiation with low-energy electrons and by thermal annealing. NV- yields from irradiations with swift heavy ions are 0.1 of yields from low energy electrons and 0.02 of yields from thermal annealing. We discuss possible mechanisms of NV-center formation by swift heavy ions such as electronic excitations and thermal spikes. While forming NV centers with low efficiency, swift heavy ions enable the formation of three dimensional NV- assemblies over relatively large distances of tens of micrometers. Further, our results show that NV-center formation is a local probe of (partial) lattice damage relaxation induced by electronic excitations from swift heavy ions in diamond.Comment: to be published in Journal of Applied Physic

Generalized genetic association study with samples of related individuals

Genetic association study is an essential step to discover genetic factors that are associated with a complex trait of interest. In this paper we present a novel generalized quasi-likelihood score (GQLS) test that is suitable for a study with either a quantitative trait or a binary trait. We use a logistic regression model to link the phenotypic value of the trait to the distribution of allelic frequencies. In our model, the allele frequencies are treated as a response and the trait is treated as a covariate that allows us to leave the distribution of the trait values unspecified. Simulation studies indicate that our method is generally more powerful in comparison with the family-based association test (FBAT) and controls the type I error at the desired levels. We apply our method to analyze data on Holstein cattle for an estimated breeding value phenotype, and to analyze data from the Collaborative Study of the Genetics of Alcoholism for alcohol dependence. The results show a good portion of significant SNPs and regions consistent with previous reports in the literature, and also reveal new significant SNPs and regions that are associated with the complex trait of interest.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS465 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Effects of low energy electron irradiation on formation of nitrogen-vacancy centers in single-crystal diamond

Exposure to beams of low energy electrons (2 to 30 keV) in a scanning electron microscope locally induces formation of NV-centers without thermal annealing in diamonds that have been implanted with nitrogen ions. We find that non-thermal, electron beam induced NV-formation is about four times less efficient than thermal annealing. But NV-center formation in a consecutive thermal annealing step (800C) following exposure to low energy electrons increases by a factor of up to 1.8 compared to thermal annealing alone. These observations point to reconstruction of nitrogen-vacancy complexes induced by electronic excitations from low energy electrons as an NV-center formation mechanism and identify local electronic excitations as a means for spatially controlled room-temperature NV-center formation

Absence of complementary sex determination in two <i>Leptopilina</i> species (Figitidae, Hymenoptera) and a reconsideration of its incompatibility with endosymbiont-induced thelytoky

Complementary sex determination (CSD) is a widespread sex determination mechanism in haplodiploid Hymenoptera. Under CSD, sex is determined by the allelic state of one or multiple CSD loci. Heterozygosity at one or more loci leads to female development, whereas hemizygosity of haploid eggs and homozygosity of diploid eggs results in male development. Sexual (arrhenotokous) reproduction normally yields haploid male and diploid female offspring. Under asexual reproduction (thelytoky), diploidized unfertilized eggs develop into females. Thelytoky is often induced by bacterial endosymbionts that achieve egg diploidization by gamete duplication. As gamete duplication leads to complete homozygosity, endosymbiont-induced thelytokous reproduction is presumed to be incompatible with CSD, which relies on heterozygosity for female development. Previously, we excluded CSD in four Asobara (Braconidae) species and proposed a two-step mechanism for Wolbachia-induced thelytoky in Asobara japonica. Here, we conclusively reject CSD in two cynipid wasp species, Leptopilina heterotoma and Leptopilina clavipes. We further show that thelytoky in L. clavipes depends on Wolbachia titer but that diploidization and feminization steps cannot be separated, unlike in A. japonica. We discuss what these results reveal about the sex determination mechanism of L. clavipes and the presumed incompatibility between CSD and endosymbiont-induced thelytoky in the Hymenoptera

Financing Complexity and Sophistication in Nascent Ventures

Although scholars have considered the financing challenges facing small businesses for some time, little work has focused on financing issues at the venture's nascent stage. In this study, we investigate the sources of funding sought by nascent entrepreneurs and the relationship between the complexity of these funding sources, business plan formalization, and expectations of future firm growth. Using data from the Entrepreneurship Research Consortium/Panel Study of Entrepreneurial Dynamics, we find that nascent entrepreneurs, even those associated with high-growth ventures, favor simple rather than complex sources of funding at the nascent stage. Funding complexity and business plan formalization are also found related to expectation of firm growth. An additional contribution is the development of a funding complexity continuum scale, which should be useful in future studies of nascent as well as later stage entrepreneurial finance and firm growth