Analytic structure of the Landau gauge gluon propagator

The analytic structure of the non-perturbative gluon propagator contains information on the absence of gluons from the physical spectrum of the theory. We study this structure from numerical solutions in the complex momentum plane of the gluon and ghost Dyson-Schwinger equations in Landau gauge Yang-Mills theory. The resulting ghost and gluon propagators are analytic apart from a distinct cut structure on the real, timelike momentum axis. The propagator violates the Osterwalder-Schrader positivity condition, confirming the absence of gluons from the asymptotic spectrum of the theory.Comment: 5 pages, 7 figure

Cosmic rays in astrospheres

Cosmic rays passing through large astrospheres can be efficiently cooled inside these "cavities" in the interstellar medium. Moreover, the energy spectra of these energetic particles are already modulated in front of the astrospherical bow shocks. We study the cosmic ray flux in and around lambda Cephei as an example for an astrosphere. The large-scale plasma flow is modeled hydrodynamically with radiative cooling. We studied the cosmic ray flux in a stellar wind cavity using a transport model based on stochastic differential equations. The required parameters, most importantly, the elements of the diffusion tensor, are based on the heliospheric parameters. The magnetic field required for the diffusion coefficients is calculated kinematically. We discuss the transport in an astrospheric scenario with varying parameters for the transport coefficients. We show that large stellar wind cavities can act as sinks for the galactic cosmic ray flux and thus can give rise to small-scale anisotropies in the direction to the observer. Small-scale cosmic ray anisotropies can naturally be explained by the modulation of cosmic ray spectra in huge stellar wind cavities

Three-Fermion Bound States on the Light Front

We investigate the stability of the relativistic three-fermion system with a zero-range force in the light front form. In particular, introducing an invariant cut-off, we study the dependence of the bound state on the coupling strength also for cases where the two-fermion system is unbound. The relativistic Thomas collapse is discussed by solving the fully coupled integral equation system. Furthermore, we explicitly investigate the ground state mass of the three-fermion system and compare to previous simplified calculations.Comment: 23 pages, 6 figure

Upcoming Public Lecture: Nick Couldry on the Myth of Big Data

In the past year, the LSE Media Policy Project blog has contained a lot of discussion of “big data”. Stefan Strauss and Monica Horten wrote about the EU’s Data Protection Directive and the protection of personal data from mass collection by corporate interests. Oxford’s Ian Brown explained how big data is accessed by government agencies, and our Internet Governance Series covered recent attempts by Brazil and other countries to take control over where big data is stored and transferred. But have we been perpetuating flawed assumptions about the nature of big data

The Seasonal Fluctuation of Fatigue in Multiple Sclerosis.

Background Fatigue is a common symptom in patients with multiple sclerosis. Several studies suggest that outdoor temperature can impact fatigue severity, but a systematic study of seasonal variations is lacking. Methods Fatigue was assessed with the Fatigue Scale for Motor and Cognitive Functions (FSMC) in a temperate climatic zone with an average outdoor temperature of 8.8°C. This study included 258 patients with multiple sclerosis from 572 visits temporally distributed over the year. The data were adjusted for age, sex, cognition, depression, disease severity, and follow-up time. Linear regression models were performed to determine whether the temporal course of fatigue was time-independent, linearly time dependent, or non-linearly time dependent. Results Fatigue was lowest during January (mean FSMC: 49.84) and highest during August (mean FSMC: 53.88). The regression analysis showed the best fit with a model that included months + months2, which was a non-linear time dependency. Mean FSMC per month correlated significantly with the average monthly temperature (ρ = 0.972; p < 0.001). Conclusion In multiple sclerosis, fatigue showed a natural temporal fluctuation. Fatigue was higher during summer compared to winter, with a significant relationship of fatigue with outdoor temperature. This finding should be carefully taken into account when clinically monitoring patients over time to not interpret higher or lower scores independent of seasonal aspects

Automation in Surgery: The Impact of Navigated-Control Assistance on the Performance, Workload and Situation Awareness of Surgeons

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The present study investigates performance consequences of a new approach of automated support for surgeons. “Navigated-Control” (NC) represents an advancement of image-guided navigation that does not only support the surgeon in navigating through a patient's anatomy, but also can stop the surgical device if it comes too close to risk structures which need to be protected to ensure patient safety. It is explored, how NC affects different aspects of surgical outcome, workload and stress, and situation awareness. Fourteen advanced students of medicine performed a simulated Mastoidectomy with and without NC support. The results reveal that NC support can reduce both, the risk of intra-operative injuries, as well as the physiological stress level of surgeons. However, “cost effects” emerged with respect to subjective workload, and a reduced spare capacity compared to unsupported surgeries. These latter effects do not seem to be related to the principle of NC but technical constraints of current implementations

The Quest for Stability: the macro view

On September 3-4, 2009 SUERF and Utrecht University School of Economicsorganized the Colloquium "The Quest for Stability" in Utrecht, the Netherlands. The papers included in this SUERF Study are based on contributions to the Colloquium.asset prices, bubbles, financial institutions, global recession, interest rates, liquidity, monetary policy, regulation, stability, supervision.

Automation in Surgery : The Impact of Navigated-Control Assistance on Performance, Workload, Situation Awareness, and Acquisition of Surgical Skills

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Objective: Human performance consequences of a new technology of image-guided navigation (IGN) support for surgeons are investigated. Background: Navigated control (NC) represents an advancement of IGN technology. In contrast to currently available pointer-based systems, it represents a higher degree of automation that supports processes not only of information analysis and integration but also of intraoperative decision making. Method: In the first experiment, 14 surgical novices performed a simulated mastoidectomy with and without NC support. Effects of provision of the system were analyzed with respect to different measures of surgical performance and outcome, workload, and situation awareness. In the second experiment, 21 advanced medical students were trained to perform a mastoidectomy by practicing it either with or without NC support. It was investigated to what extent the provision of the system during practice would affect the acquisition of surgical skills. Results: The results reveal that NC support can reduce both the risk of intraoperative injuries and complications as well as the physiological effort of surgeons. “Cost effects” compared to a conventional (i.e., not supported) surgery emerged with respect to the time needed for the surgery, increased subjective workload, reduced spare capacity, and a reduced level of situation awareness. However, no significant effects on processes of skill acquisition were found. Conclusion: NC systems can contribute to improved patient safety. Most of the cost effects seem to be related not to the basic principle of NC but to its current technological implementation. Application: The results have consequences for the design and clinical use of automated navigation support

First results of the SA Agulhas II mobile mini-neutron monitor: Instrumental characterization and environmental sensitivity

We present the first results of a new redesigned version of the mini-neutron monitor installed on the South African Research vessel, the SA Agulhas II. Measurements taken from the 2019/2020 relief voyages are presented. We show that the instrument is very sensitive to temperature variations when the ambient temperature is below 3oC. This is believed to be an instrumental effect. Additionally, we show the presence of high-frequency interference in the calculated waiting time distributions when the vessel reaches polar latitudes. We show that these periodic variations are only present in the intensity of secondary atmospheric particles and most likely related to the operation of the vessel’s ice radar. We are currently looking at moving the instrument to a more suitable location on board the SA Agulhas II where we will hopefully be able to operate the instrument in a continuous fashion for several years to come

Growth Histories in Bimetric Massive Gravity

We perform cosmological perturbation theory in Hassan-Rosen bimetric gravity for general homogeneous and isotropic backgrounds. In the de Sitter approximation, we obtain decoupled sets of massless and massive scalar gravitational fluctuations. Matter perturbations then evolve like in Einstein gravity. We perturb the future de Sitter regime by the ratio of matter to dark energy, producing quasi-de Sitter space. In this more general setting the massive and massless fluctuations mix. We argue that in the quasi-de Sitter regime, the growth of structure in bimetric gravity differs from that of Einstein gravity.Comment: 28 pages + appendix, 11 figure