Faces of weight polytopes and a generalization of a theorem of Vinberg

The paper is motivated by the study of graded representations of Takiff algebras, cominuscule parabolics, and their generalizations. We study certain special subsets of the set of weights (and of their convex hull) of the generalized Verma modules (or GVM's) of a semisimple Lie algebra \lie g. In particular, we extend a result of Vinberg and classify the faces of the convex hull of the weights of a GVM. When the GVM is finite-dimensional, we ask a natural question that arises out of Vinberg's result: when are two faces the same? We also extend the notion of interiors and faces to an arbitrary subfield \F of the real numbers, and introduce the idea of a weak \F-face of any subset of Euclidean space. We classify the weak \F-faces of all lattice polytopes, as well as of the set of lattice points in them. We show that a weak \F-face of the weights of a finite-dimensional \lie g-module is precisely the set of weights lying on a face of the convex hull.Comment: Statement changed in Section 4. Typos fixed and some proofs updated. Submitted to "Algebra and Representation Theory." 18 page

Encouraging Individual Contributions to Net-Zero Organizations: Effects of Behavioral Policy Interventions and Social Norms

To contribute to a better understanding of the determinants of climate-friendly organizational behavior, we study the potential of behavioral policy interventions and social norms to foster individual contributions to organizational decarbonization initiatives. We investigate the effects of different types of behavioral policy interventions (default nudges vs. short-term boosts) in isolation and when they are combined with normative appeals to adopt climate-friendly behaviors in an organizational context. In a 2 × 2 between-subjects experiment, we find that default nudges generally induced higher individual contributions to organizational carbon compensation programs than short-term boosts. Moreover, injunctive social norm information decreased the effectiveness of both types of behavioral interventions but affected the effectiveness of short-term boosts to a stronger extent than the effectiveness of default nudges. Contributing to the nascent literature on motivating climate change mitigating behaviors in organizational contexts, we additionally explore whether factors such as personality traits, pro-social and pro-environmental beliefs, attitudes, and behaviors, and the degree of organizational identification exert an influence on the effectiveness of the interventions and provide qualitative insights into participants’ reasoning for their decisions

Spectral Control via Multi-Species Effects in PW-Class Laser-Ion Acceleration

Laser-ion acceleration with ultra-short pulse, PW-class lasers is dominated by non-thermal, intra-pulse plasma dynamics. The presence of multiple ion species or multiple charge states in targets leads to characteristic modulations and even mono-energetic features, depending on the choice of target material. As spectral signatures of generated ion beams are frequently used to characterize underlying acceleration mechanisms, thermal, multi-fluid descriptions require a revision for predictive capabilities and control in next-generation particle beam sources. We present an analytical model with explicit inter-species interactions, supported by extensive ab initio simulations. This enables us to derive important ensemble properties from the spectral distribution resulting from those multi-species effects for arbitrary mixtures. We further propose a potential experimental implementation with a novel cryogenic target, delivering jets with variable mixtures of hydrogen and deuterium. Free from contaminants and without strong influence of hardly controllable processes such as ionization dynamics, this would allow a systematic realization of our predictions for the multi-species effect.Comment: 4 pages plus appendix, 11 figures, paper submitted to a journal of the American Physical Societ

Probability of Physical Association of 104 Blended Companions to Kepler Objects of Interest Using Visible and Near-Infrared Adaptive Optics Photometry

We determine probabilities of physical association for stars in blended Kepler Objects of Interest (KOIs), and find that 14.5%_(-3.4%)^(+3.8%) of companions within ~ 4" are consistent with being physically unassociated with their primary. This produces a better understanding of potential false positives in the Kepler catalog and will guide models of planet formation in binary systems. Physical association is determined through two methods of calculating multi-band photometric parallax using visible and near-infrared adaptive optics observations of 84 KOI systems with 104 contaminating companions within ~ 4". We find no evidence that KOI companions with separations of less than 1" are more likely to be physically associated than KOI companions generally. We also reinterpret transit depths for 94 planet candidates, and calculate that 2.6% ± 0.4% of transits have R > 15R_⊕, which is consistent with prior modeling work

Robo-AO Kepler Survey IV: the effect of nearby stars on 3857 planetary candidate systems

We present the overall statistical results from the Robo-AO Kepler planetary candidate survey, comprising of 3857 high-angular resolution observations of planetary candidate systems with Robo-AO, an automated laser adaptive optics system. These observations reveal previously unknown nearby stars blended with the planetary candidate host star which alter the derived planetary radii or may be the source of an astrophysical false positive transit signal. In the first three papers in the survey, we detected 440 nearby stars around 3313 planetary candidate host stars. In this paper, we present observations of 532 planetary candidate host stars, detecting 94 companions around 88 stars; 84 of these companions have not previously been observed in high-resolution. We also report 50 more-widely-separated companions near 715 targets previously observed by Robo-AO. We derive corrected planetary radius estimates for the 814 planetary candidates in systems with a detected nearby star. If planetary candidates are equally likely to orbit the primary or secondary star, the radius estimates for planetary candidates in systems with likely bound nearby stars increase by a factor of 1.54, on average. We find that 35 previously-believed rocky planet candidates are likely not rocky due to the presence of nearby stars. From the combined data sets from the complete Robo-AO KOI survey, we find that 14.5\pm0.5% of planetary candidate hosts have a nearby star with 4", while 1.2% have two nearby stars and 0.08% have three. We find that 16% of Earth-sized, 13% of Neptune-sized, 14% of Saturn-sized, and 19% of Jupiter-sized planet candidates have detected nearby stars.Comment: Accepted to the Astronomical Journa

Robo-AO Kepler Survey V: The effect of physically associated stellar companions on planetary systems

The Kepler light curves used to detect thousands of planetary candidates are susceptible to dilution due to blending with previously unknown nearby stars. With the automated laser adaptive optics instrument, Robo-AO, we have observed 620 nearby stars around 3857 planetary candidates host stars. Many of the nearby stars, however, are not bound to the KOI. In this paper, we quantify the association probability between each KOI and detected nearby stars through several methods. Galactic stellar models and the observed stellar density are used to estimate the number and properties of unbound stars. We estimate the spectral type and distance to 145 KOIs with nearby stars using multi-band observations from Robo-AO and Keck-AO. We find most nearby stars within 1" of a Kepler planetary candidate are likely bound, in agreement with past studies. We use likely bound stars as well as the precise stellar parameters from the California Kepler Survey to search for correlations between stellar binarity and planetary properties. No significant difference between the binarity fraction of single and multiple planet systems is found, and planet hosting stars follow similar binarity trends as field stars, many of which likely host their own non-aligned planets. We find that hot Jupiters are ~4x more likely than other planets to reside in a binary star system. We correct the radius estimates of the planet candidates in characterized systems and find that for likely bound systems, the estimated planetary candidate radii will increase on average by a factor of 1.77, if either star is equally likely to host the planet. We find that the planetary radius gap is robust to the impact of dilution, and find an intriguing 95%-confidence discrepancy between the radius distribution of small planets in single and binary systems.Comment: 19 pages, 12 figures, submitted to AAS Journal

Einfluss agiler Methoden auf den Erfolgsfaktor. Benutzerakzeptanz in IT-Projekten

Ein zentraler Erfolgsfaktor, der für den Nutzen einer IT-Entwicklung maßgeblich sein kann, ist die Akzeptanz des zu entwickelnden Produkts durch die Benutzer. Vor dem Hintergrund dieses wichtigen Erfolgsfaktors wird die Fragestellung untersucht, inwiefern agile IT-Projektentwicklungsmethoden die Akzeptanz der späteren Benutzer, aber auch der am Entwicklungsprozess beteiligten Personen fördern können. Dabei wird insbesondere ermittelt, welche Voraussetzungen agile Methoden schaffen, damit während des Projekts und nach Projektende eine möglichst hohe Benutzerakzeptanz erreicht werden kann. Das Ziel dieser Arbeit ist demnach eine eingehende Betrachtung der Benutzerakzeptanz im Umfeld agiler Methoden sowie eine Beurteilung der Förderung dieses Erfolgsfaktors durch die neuen leichtgewichtigen Ansätze.The user acceptance represents an important success factor for the usefulness of IT development projects. This thesis analyses how agile software development influences the user acceptance of end-users and software producers. Furthermore the author examines the conditions for achieving this important success factor with regard to the development phase but also with regard to the final product. In the end this scientific research presents a detailed analysis of agile development methods and their overall impact on the success factor user acceptance. The author uses several approaches in different categories to point out the importance of user acceptance in all stages of a development process

The Robo-AO KOI survey: laser adaptive optics imaging of every Kepler exoplanet candidate

The Robo-AO Kepler Planetary Candidate Survey is observing every Kepler planet candidate host star (KOI) with laser adaptive optics imaging to hunt for blended nearby stars which may be physically associated companions. With the unparalleled efficiency provided by the first fully robotic adaptive optics system, we perform the critical search for nearby stars (0.15" to 4.0" separation with contrasts up to 6 magnitudes) that dilute the observed planetary transit signal, contributing to inaccurate planetary characteristics or astrophysical false positives. We present 3313 high resolution observations of Kepler planetary hosts from 2012-2015, discovering 479 nearby stars. We measure an overall nearby star probability rate of 14.5±0.8%. With this large data set, we are uniquely able to explore broad correlations between multiple star systems and the properties of the planets which they host, providing insight into the formation and evolution of planetary systems in our galaxy. Several KOIs of particular interest will be discussed, including possible quadruple star systems hosting planets and updated properties for possible rocky planets orbiting with in their star's habitable zone

Coherent, time-shifted patterns of microstructural plasticity during motor-skill learning

Motor skill learning relies on neural plasticity in the motor and limbic systems. However, the spatial and temporal characteristics of these changes-and their microstructural underpinnings-remain unclear. Eighteen healthy males received 1 hour of training in a computer-based motion game, 4 times a week, for 4 consecutive weeks, while 14 untrained participants underwent scanning only. Performance improvements were observed in all trained participants. Serial myelin- and iron-sensitive multiparametric mapping at 3T during this period of intensive motor skill acquisition revealed temporally and spatially distributed, performance-related microstructural changes in the grey and white matter across a corticospinal-cerebellar-hippocampal circuit. Analysis of the trajectory of these transient changes suggested time-shifted cascades of plasticity from the dominant sensorimotor system to the contralateral hippocampus. In the cranial corticospinal tracts, changes in myelin-sensitive metrics during training in the posterior limb of the internal capsule were of greater magnitude in those who trained their upper limbs vs. lower limb trainees. Motor skill learning is associated with waves of grey and white matter plasticity, across a broad sensorimotor network