Pair correlation functions and limiting distributions of iterated cluster point processes

We consider a Markov chain of point processes such that each state is a super position of an independent cluster process with the previous state as its centre process together with some independent noise process. The model extends earlier work by Felsenstein and Shimatani describing a reproducing population. We discuss when closed term expressions of the first and second order moments are available for a given state. In a special case it is known that the pair correlation function for these type of point processes converges as the Markov chain progresses, but it has not been shown whether the Markov chain has an equilibrium distribution with this, particular, pair correlation function and how it may be constructed. Assuming the same reproducing system, we construct an equilibrium distribution by a coupling argument

Unusual corrections to scaling in the 3-state Potts antiferromagnet on a square lattice

At zero temperature, the 3-state antiferromagnetic Potts model on a square lattice maps exactly onto a point of the 6-vertex model whose long-distance behavior is equivalent to that of a free scalar boson. We point out that at nonzero temperature there are two distinct types of excitation: vortices, which are relevant with renormalization-group eigenvalue 1/2; and non-vortex unsatisfied bonds, which are strictly marginal and serve only to renormalize the stiffness coefficient of the underlying free boson. Together these excitations lead to an unusual form for the corrections to scaling: for example, the correlation length diverges as \beta \equiv J/kT \to \infty according to \xi \sim A e^{2\beta} (1 + b\beta e^{-\beta} + ...), where b is a nonuniversal constant that may nevertheless be determined independently. A similar result holds for the staggered susceptibility. These results are shown to be consistent with the anomalous behavior found in the Monte Carlo simulations of Ferreira and Sokal.Comment: LaTeX, 25 pages, includes 9 figures. Version 2 includes a new footnote 3. To appear in J. Stat. Phy

A Careers Perspective on Entrepreneurship

[Excerpt] What if being an entrepreneur were treated like any other occupation—teacher, nurse, manager? What if the decision to found a new venture were thought of as one of many options that individuals consider as they try to structure a meaningful and rewarding career? How would the field of entrepreneurship research be different? In our view, there is much to be learned by conceiving of entrepreneurship not solely as a final destination, but as a step along a career trajectory. Doing so opens the study of entrepreneurship to a wider range of scholarly insights, and promises important insights for entrepreneurial practice, training, and policy. This special issue takes an important step in this direction

Resource curse or not: A question of appropriability

This paper shows that whether natural resources are good or bad for a country’s development crucially depends on the interaction between institutional setting and the type of resources possessed by the country. Some natural resources are, for economical and technical reasons, more likely to cause problems such as rent-seeking and conflicts than others. This potential problem can, however, be countered by good institutional quality. In contrast to the traditional resource curse hypothesis, we show the impact of natural resources on economic growth to be non-monotonic in institutional quality. Countries rich in minerals are cursed only if they have low quality institutions, while the curse is reversed if institutions are sufficiently good.Natural Resources, Appropriability, Property Rights, Institutions, Economic Growth, Development

Optical Hall conductivity in bulk and nanostructured graphene beyond the Dirac approximation

We present a perturbative method for calculating the optical Hall conductivity in a tight-binding framework based on the Kubo formalism. The method involves diagonalization only of the Hamiltonian in absence of the magnetic field, and thus avoids the computational problems usually arising due to the huge magnetic unit cells required to maintain translational invariance in presence of a Peierls phase. A recipe for applying the method to numerical calculations of the magneto-optical response is presented. We apply the formalism to the case of ordinary and gapped graphene in a next-nearest neighbour tight-binding model as well as graphene antidot lattices. In both case, we find unique signatures in the Hall response, that are not captured in continuum (Dirac) approximations. These include a non-zero optical Hall conductivity even when the chemical potential is at the Dirac point energy. Numerical results suggest that this effect should be measurable in experiments.Comment: 7 pages, 4 figures, accepted in Physical Review

C3TM: CEI CCD charge transfer model for radiation damage analysis and testing

Radiation induced defects in the silicon lattice of Charge Couple Devices (CCDs) are able to trap electrons during read out and thus create a smearing effect that is detrimental to the scientific data. To further our understanding of the positions and properties of individual radiation-induced traps and how they affect space- borne CCD performance, we have created the Centre for Electronic Imaging (CEI) CCD Charge Transfer Model (C3TM). This model simulates the physical processes taking place when transferring signal through a radiation damaged CCD. C3TM is a Monte Carlo model based on Shockley-Read-Hall theory, and it mimics the physical properties in the CCD as closely as possible. It runs on a sub-electrode level taking device specific charge density simulations made with professional TCAD software as direct input. Each trap can be specified with 3D positional information, emission time constant and other physical properties. The model is therefore also able to simulate multi-level clocking and other complex clocking schemes, such as trap pumping

Importance of charge capture in interphase regions during readout of charge-coupled devices

The current understanding of charge transfer dynamics in charge-coupled devices (CCDs) is that charge is moved so quickly from one phase to the next in a clocking sequence and with a density so low that trapping of charge in the interphase regions is negligible. However, simulation capabilities developed at the Centre for Electronic Imaging, which includes direct input of electron density simulations, have made it possible to investigate this assumption further. As part of the radiation testing campaign of the Euclid CCD273 devices, data have been obtained using the trap pumping method, a method that can be used to identify and characterize single defects within CCDs. Combining these data with simulations, we find that trapping during the transfer of charge among phases is indeed necessary to explain the results of the data analysis. This result could influence not only trap pumping theory and how trap pumping should be performed but also how a radiation-damaged CCD is readout in the most optimal way

p-Wave Polaron

We consider the properties of a single impurity immersed in a Fermi sea close to an interspecies p-wave Feshbach resonance. We calculate its dispersion and spectral response to a radiofrequency pulse. In the presence of a magnetic field, dipolar interactions split the resonance and lead to the appearance of two novel features with respect to the s-wave case: a third polaron branch in the excitation spectrum, in addition to the usual attractive and repulsive ones; and an anisotropic dispersion of the impurity characterized by different effective masses perpendicular and parallel to the magnetic field. The anisotropy can be tuned as a function of the field strength and the two effective masses may have opposite signs, or become smaller than the bare mass

Avid 18F-FDG Uptake in Idiopathic Tumoral Calcinosis Mimicking Lymph Node Metastasis

Tumoral calcinosis is a benign condition characterized by periarticular calcified lesions that is frequently observed in patients with chronic renal failure. Tumoral calcinosis often presents with subcutaneous masses and joint swelling. We present a case of tumoral calcinosis with dramatically increased 18F-fluoro-2-deoxy-d-glucose (18F-FDG) uptake on positron emission tomography/computed tomography (PET/CT) that mimicked lymphoma or lymph node metastases