Observations of Outflowing UV Absorbers in NGC 4051 with the Cosmic Origins Spectrograph

We present new Hubble Space Telescope (HST)/Cosmic Origins Spectrograph observations of the Narrow-Line Seyfert 1 galaxy NGC 4051. These data were obtained as part of a coordinated observing program including X-ray observations with the Chandra/High Energy Transmission Grating (HETG) Spectrometer and Suzaku. We detected nine kinematic components of UV absorption, which were previously identified using the HST/Space Telescope Imaging Spectrograph. None of the absorption components showed evidence for changes in column density or profile within the \sim 10 yr between the STIS and COS observations, which we interpret as evidence of 1) saturation, for the stronger components, or 2) very low densities, i.e., n_H < 1 cm^-3, for the weaker components. After applying a +200 km s^-1 offset to the HETG spectrum, we found that the radial velocities of the UV absorbers lay within the O VII profile. Based on photoionization models, we suggest that, while UV components 2, 5 and 7 produce significant O VII absorption, the bulk of the X-ray absorption detected in the HETG analysis occurs in more highly ionized gas. Moreover, the mass loss rate is dominated by high ionization gas which lacks a significant UV footprint.Comment: 41 pages, 10 Figures; accepted for publication in the Astrophysical Journa

Generalized Entropies

We study an entropy measure for quantum systems that generalizes the von Neumann entropy as well as its classical counterpart, the Gibbs or Shannon entropy. The entropy measure is based on hypothesis testing and has an elegant formulation as a semidefinite program, a type of convex optimization. After establishing a few basic properties, we prove upper and lower bounds in terms of the smooth entropies, a family of entropy measures that is used to characterize a wide range of operational quantities. From the formulation as a semidefinite program, we also prove a result on decomposition of hypothesis tests, which leads to a chain rule for the entropy.Comment: 21 page

The cognitive and neural dynamics of memory-based decisions

The recent years have seen the rise of neuroeconomics, a scientific discipline investigating the cognitive and neural principles of value-based decision making. While neuroeconomists made significant progress in characterizing basic computations of value-based decision making, the critical role of memory has all-too-often been neglected. Within this cumulative dissertation thesis, I present four manuscripts, which address the relation of memory and decision making. Manuscript 1 reviews empirical evidence which demonstrates that memory-based decisions are biased in favor of choice options which can be recalled from memory. Adopting cognitive process models, Manuscript 2 demonstrates that this memory bias is rather due to a single decision process, as compared to a dual-process account of memory-based decisions. Manuscript 3 focuses on the temporal dynamics of memory retrieval and choice formation, outlining altered evidence accumulation dynamics of memory-based versus standard value-based decisions. Finally, Manuscript 4 takes the first steps toward a cognitive process model which accounts for the temporal dynamics of both, memory retrieval and decision making. While every manuscript can be approached individually, the synopsis part of this dissertation thesis discusses them in a broader perspective, drawing on the neuroeconomic framework by Rangel et al. (2008). All in all, this dissertation thesis advocates for neuroeconomics to take memory processes more seriously. Future research will especially profit from a deeper understanding of the temporal dynamics of memory retrieval and its relation to decision making

Study of quasi-optical circuit techniques in varactor multipliers

Quasi-optical circuit techniques in varactor multiplier