Phase Space Structure and Transport in a Caldera Potential Energy Surface

We study phase space transport in a 2D caldera potential energy surface (PES) using techniques from nonlinear dynamics. The caldera PES is characterized by a flat region or shallow minimum at its center surrounded by potential walls and multiple symmetry related index one saddle points that allow entrance and exit from this intermediate region.We have discovered four qualitatively distinct cases of the structure of the phase space that govern phase space transport. These cases are categorized according to the total energy and the stability of the periodic orbits associated with the family of the central minimum, the bifurcations of the same family, and the energetic accessibility of the index one saddles. In each case we have computed the invariant manifolds of the unstable periodic orbits of the central region of the potential and the invariant manifolds of the unstable periodic orbits of the families of periodic orbits associated with the index one saddles. We have found that there are three distinct mechanisms determined by the invariant manifold structure of the unstable periodic orbits govern the phase space transport. The first mechanism explains the nature of the entrance of the trajectories from the region of the low energy saddles into the caldera and how they may become trapped in the central region of the potential. The second mechanism describes the trapping of the trajectories that begin from the central region of the caldera, their transport to the regions of the saddles, and the nature of their exit from the caldera. The third mechanism describes the phase space geometry responsible for the dynamical matching of trajectories originally proposed by Carpenter and described in Collins et al. (2014) for the two dimensional caldera PES that we consider.Comment: 24 pages, International Journal of Bifurcation and Chaos (in press

High-density functional diffuse optical tomography based on frequency-domain measurements improves image quality and spatial resolution

Measurements of dynamic Near Infrared (NIR) light attenuation across the human head together with model-based image reconstruction algorithms allow the recovery of three-dimensional spatial brain activation maps. Previous studies using high-density diffuse optical tomography (HD-DOT) systems have reported improved image quality over sparse arrays. These HD-DOT systems incorporated multi-distance overlapping continuous wave measurements that only recover differential intensity attenuation. In this study, we investigate the potential improvement in reconstructed image quality due to the additional incorporation of phase shift measurements, which reflect the time-of-flight of the measured NIR light, within the tomographic reconstruction from high-density measurements. To evaluate image reconstruction with and without the additional phase information we simulated point spread functions across a whole-scalp field of view in 24 subject specific anatomical models using an experimentally derived noise model. The addition of phase information improves the image quality by reducing localization error by up to 59% and effective resolution by up to 21% as compared to using the intensity attenuation measurements alone. Furthermore, we demonstrate that the phase data enable images to be resolved at deeper brain regions where intensity data fails, which is further supported by utilizing experimental data from a single subject measurement during a retinotopic experiment

Identification of a Loan Supply Function: A Cross-Country Test for the Existence of a Bank Lending Channel

Using the theoretical predictions of the Bernanke-Blinder (1988) model, we seek to examine the existence of a bank lending channel through the empirical identification of a loan supply function and to assess the impact of differential bank characteristics on banks’ ability to supply loans. To this end, we estimate a loan supply model and test for the restrictions implied by perfect substitutability between loans and bonds in bank portfolios. Estimations are carried out on bank panel data for 16 OECD countries, the results showing that a bank lending channel is at work in only two of them. Moreover, and contrary to standard accounts, we find that the relevance of bank characteristics is hardly a decisive factor in the identification of a loan supply function.Bank lending channel; financial structure; dynamic panels

Bank-Specific, Industry-Specific and Macroeconomic Determinants of Bank Profitability

The aim of this study is to examine the effect of bank-specific, industry-specific and macroeconomic determinants of bank profitability, using an empirical framework that incorporates the traditional Structure-Conduct-Performance (SCP) hypothesis. To account for profit persistence, we apply a GMM technique to a panel of Greek banks that covers the period 1985-2001. The estimation results show that profitability persists to a moderate extent, indicating that departures from perfectly competitive market structures may not be that large. All bank-specific determinants, with the exception of size, affect bank profitability significantly in the anticipated way. However, no evidence is found in support of the SCP hypothesis. Finally, the business cycle has a positive, albeit asymmetric effect on bank profitability, being significant only in the upper phase of the cycle.Bank profitability; business cycles and profitability; dynamic panel data model

Εισαγωγή και διανομή του φυσικού αερίου στην Ελλάδα

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Διοίκηση Επιχειρήσεων (ΜΒΑ)

The dynamics of a spinning particle in a linear in spin Hamiltonian approximation

We investigate for order and chaos the dynamical system of a spinning test particle of mass $m$ moving in the spacetime background of a Kerr black hole of mass M. This system is approximated in our investigation by the linear in spin Hamiltonian function provided in [E. Barausse, and A. Buonanno, Phys.Rev. D 81, 084024 (2010)]. We study the corresponding phase space by using 2D projections on a surface of section and the method of color and rotation on a 4D Poincar\'e section. Various topological structures coming from the non-integrability of the linear in spin Hamiltonian are found and discussed. Moreover, an interesting result is that from the value of the dimensionless spin $S/(m M)=10^{-4}$ of the particle and below, the impact of the non-integrability of the system on the motion of the particle seems to be negligible.Comment: 11 pages, 8 figures, 1 table, to appear in Phys. Rev.

Technical and Allocative Efficiency in European Banking

This paper specifies an empirical framework for estimating both technical and allocative efficiency, which is applied to a large panel of European banks over the years 1996 to 2003. Our methodology allows for self-consistent measurement of technical and allocative inefficiency, in an effort to address the issue known in the literature as the Greene problem. The results suggest that, on average, European banks exhibit constant returns to scale, that technical and allocative efficiency are close to 80% and 75% respectively, and that overall economic efficiency shows a clearly improving trend. We also show through the comparison of various estimators that models incorporating only technical efficiency tend to overestimate it.Technical and allocative efficiency; Translog cost function; Maximum likelihood; European banking