Sustaining star formation rates in spiral galaxies - Supernova-driven turbulent accretion disk models applied to THINGS galaxies

Gas disks of spiral galaxies can be described as clumpy accretion disks without a coupling of viscosity to the actual thermal state of the gas. The model description of a turbulent disk consisting of emerging and spreading clumps (Vollmer & Beckert 2003) contains free parameters, which can be constrained by observations of molecular gas, atomic gas and the star formation rate for individual galaxies. Radial profiles of 18 nearby spiral galaxies from THINGS, HERACLES, SINGS, and GALEX data are used to compare the observed star formation efficiency, molecular fraction, and velocity dispersion to the model. The observed radially decreasing velocity dispersion can be reproduced by the model. In the framework of this model the decrease in the inner disk is due to the stellar mass distribution which dominates the gravitational potential. Introducing a radial break in the star formation efficiency into the model improves the fits significantly. This change in star formation regime is realized by replacing the free fall time in the prescription of the star formation rate with the molecule formation timescale. Depending on the star formation prescription, the break radius is located near the transition region between the molecular-gas-dominated and atomic-gas-dominated parts of the galactic disk or closer to the optical radius. It is found that only less massive galaxies (log (M (M_solar)) <~ 10) can balance gas loss via star formation by radial gas accretion within the disk. These galaxies can thus access their gas reservoirs with large angular momentum. On the other hand, the star formation of massive galaxies is determined by the external gas mass accretion rate from a putative spherical halo of ionized gas or from satellite accretion.Comment: 26 pages, 5 figures, full figures 1 and 2 as ancillary pdf files available; accepted by A

Concert recording 2016-11-15

[Track 1]. Subjugation. Connection [Track 2]. Captivation / Durgan Maxey -- [Track 3]. Fight / Bryce Owens -- [Track 4]. Overture to Stay / Joshua Bland -- [Track 5]. A cellist\u27s legacy. Part I [Track 6]. Part II / Eric Dreggors -- [Track 7]. Evening prayer / Robbie Baker -- [Track 8]. Elegy / Brandon Wade -- [Track 9]. The grotesques trio. Gargoyles [Track 10]. Chimera [Track 11]. Grotesques / Marissa Johnson -- [Track 12]. Crosshair / Joshua Bland -- [Track 13]. Nightwind sings / L. Coley Pitchford -- [Track 14]. Six reflections through poetry. Memories (Walt Whitman) [Track 15]. The musician\u27s wife (Weldon Kees) [Track 16]. The road not taken (Robert Frost) [Track 17]. Lessons (Whitman) [Track 18]. Stronger lessons (Whitman) [Track 19]. O me! O life! (Whitman) / Nick Vecchio -- [Tracks 20-21]. String quartet #1 / Jeremiah Flannery -- [Track 22]. Tides. Morning tide [Track 23]. Bore tide / Elizabeth Greener -- [Track 24]. Shepherd\u27s contemplation / Robbie Baker -- Green grass / arranged by Eva Martin -- [Track 25]. Urbe fracta est II. A prayer for Jerusalem / Joshua Bland

Information content and reward processing in the human striatum during performance of a declarative memory task

Negative feedback can signal poor performance, but it also provides information that can help learners reach the goal of task mastery. The primary aim of this study was to test the hypothesis that the amount of information provided by negative feedback during a paired-associate learning task influences feedback-related processing in the caudate nucleus. To do this, we manipulated the number of response options: With two options, positive and negative feedback provide equal amounts of information, whereas with four options, positive feedback provides more information than does negative feedback. We found that positive and negative feedback activated the caudate similarly when there were two response options. With four options, the caudate’s response to negative feedback was reduced. A secondary goal was to investigate the link between brain-based measures of feedback-related processing and behavioral indices of learning. Analysis of the posttest measures showed that trials with positive feedback were associated with higher posttest confidence ratings. Additionally, when positive feedback was delivered, caudate activity was greater for trials with high than with low posttest confidence. This experiment demonstrated the context sensitivity of feedback processing and provided evidence that feedback processing in the striatum can contribute to the strengthening of the representations available within declarative memory

Human Processing of Behaviorally Relevant and Irrelevant Absence of Expected Rewards: A High-Resolution ERP Study

Acute lesions of the posterior medial orbitofrontal cortex (OFC) in humans may induce a state of reality confusion marked by confabulation, disorientation, and currently inappropriate actions. This clinical state is strongly associated with an inability to abandon previously valid anticipations, that is, extinction capacity. In healthy subjects, the filtering of memories according to their relation with ongoing reality is associated with activity in posterior medial OFC (area 13) and electrophysiologically expressed at 220–300 ms. These observations indicate that the human OFC also functions as a generic reality monitoring system. For this function, it is presumably more important for the OFC to evaluate the current behavioral appropriateness of anticipations rather than their hedonic value. In the present study, we put this hypothesis to the test. Participants performed a reversal learning task with intermittent absence of reward delivery. High-density evoked potential analysis showed that the omission of expected reward induced a specific electrocortical response in trials signaling the necessity to abandon the hitherto reward predicting choice, but not when omission of reward had no such connotation. This processing difference occurred at 200–300 ms. Source estimation using inverse solution analysis indicated that it emanated from the posterior medial OFC. We suggest that the human brain uses this signal from the OFC to keep thought and behavior in phase with reality