Multi-field modelling and simulation of large deformation ductile fracture

In the present contribution we focus on a phase-field approach to ductile fracture applied to large deformation contact problems. Phase-field approaches to fracture allow for an efficient numerical investigation of complex three-dimensional fracture problems, as they arise in contact and impact situations. To account for large deformations the underlying formulation is based on a multiplicative decomposition of the deformation gradient into an elastic and plastic part. Moreover, we make use of a fourth-order crack regularization combined with gradient plasticity. Eventually, a demonstrative example shows the capability of the proposed framework

On the Apparent Orbital Inclination Change of the Extrasolar Transiting Planet TrES-2b

On June 15, 2009 UT the transit of TrES-2b was detected using the University of Arizona's 1.55 meter Kuiper Telescope with 2.0-2.5 millimag RMS accuracy in the I-band. We find a central transit time of $T_c = 2454997.76286 \pm0.00035$ HJD, an orbital period of $P = 2.4706127 \pm 0.0000009$ days, and an inclination angle of $i = 83^{\circ}.92 \pm 0.05$, which is consistent with our re-fit of the original I-band light curve of O'Donovan et al. (2006) where we find $i = 83^{\circ}.84 \pm0.05$. We calculate an insignificant inclination change of $\Delta i = -0^{\circ}.08 \pm 0.07$ over the last 3 years, and as such, our observations rule out, at the $\sim 11 \sigma$ level, the apparent change of orbital inclination to $i_{predicted} = 83^{\circ}.35 \pm0.1$ as predicted by Mislis and Schmitt (2009) and Mislis et al. (2010) for our epoch. Moreover, our analysis of a recently published Kepler Space Telescope light curve (Gilliland et al. 2010) for TrES-2b finds an inclination of $i = 83^{\circ}.91 \pm0.03$ for a similar epoch. These Kepler results definitively rule out change in $i$ as a function of time. Indeed, we detect no significant changes in any of the orbital parameters of TrES-2b.Comment: 19 pages, 1 table, 7 figures. Re-submitted to ApJ, January 14, 201

Mixed variational formulations for multi-field problems

General thermoelastic material models have been investigated over the past decades, see e.g. Reese and Govindjee [1], Holzapfel and Simo [2] and Miehe [3] among many oth- ers. In this paper we present a novel computational framework for large strain thermo- elasticity. The ideas of a new formulation for polyconvex large strain elasticity originally introduced by Ball [4] and recently resumed by Bonet et al. [5] are extended to non-linear coupled thermoelasticity, see also Dittmann [6]. In particular, the deformation gradient (line map), its co-factor (area map) and its determinant (volume map) along with the absolute temperature are formulated as independent variables to obtain a polyconvex free energy function. Moreover, we introduce work conjugate stresses to the extended kine- matic set to define a complementary energy principle of Hellinger-Reissner type, where the introduced conjugate stresses along with the deformed geometry and the absolute tem- perature constitute the set of primal variables, see also Hesch condensed.Eventually,quasi-staticaswellastransientnumericalexamplesareinvesti-gatedtodemonstratethecapabilityoftheproposedframework. et al. [7] for the application of a mixed Hu-Washizu type variational principle in the context of coupled phase-field fracture problems. The finite element discretization relies on a quadratic approximation of the deformed geometry and the absolute temperature, whereas discontinuous linear interpolations are used for the conjugate stresses such that the stress unknowns can b

Trigonometric Parallaxes for 1,507 Nearby Mid-to-Late M-dwarfs

The MEarth survey is a search for small rocky planets around the smallest, nearest stars to the Sun as identified by high proper motion with red colors. We augmented our planetary search time series with lower cadence astrometric imaging and obtained two million images of approximately 1800 stars suspected to be mid-to-late M dwarfs. We fit an astrometric model to MEarth's images for 1507 stars and obtained trigonometric distance measurements to each star with an average precision of 5 milliarcseconds. Our measurements, combined with the 2MASS photometry, allowed us to obtain an absolute K_s magnitude for each star. In turn, this allows us to better estimate the stellar parameters than those obtained with photometric estimates alone and to better prioritize the targets chosen to monitor at high cadence for planetary transits. The MEarth sample is mostly complete out to a distance of 25 parsecs for stars of type M5.5V and earlier, and mostly complete for later type stars out to 20 parsecs. We find eight stars that are within ten parsecs of the Sun for which there did not exist a published trigonometric parallax distance estimate. We release with this work a catalog of the trigonometric parallax measurements for 1,507 mid-to-late M-dwarfs, as well as new estimates of their masses and radii.Comment: ApJ, accepted. 36 pages, 8 figures, 2 tables. Please find our data table here: http://www.cfa.harvard.edu/MEarth/DataDR2.htm

A Tentative Detection of a Starspot During Consecutive Transits of an Extrasolar Planet from the Ground: No Evidence of a Double Transiting Planet System Around TrES-1

There have been numerous reports of anomalies during transits of the planet TrES-1b. Recently, Rabus and coworkers' analysis of HST observations lead them to claim brightening anomalies during transit might be caused by either a second transiting planet or a cool starspot. Observations of two consecutive transits are presented here from the University of Arizona's 61-inch Kuiper Telescope on May 12 and May 15, 2008 UT. A 5.4 +/- 1.7 mmag (0.54 +/- 0.17%) brightening anomaly was detected during the first half of the transit on May 12 and again in the second half of the transit on May 15th. We conclude that this is a tentative detection of a r greater than or equal to 6 earth radii starspot rotating on the surface of the star. We suggest that all evidence to date suggest TrES-1 has a spotty surface and there is no need to introduce a second transiting planet in this system to explain these anomalies. We are only able to constrain the rotational period of the star to 40.2 +22.9 -14.6 days, due to previous errors in measuring the alignment of the stellar spin axis with the planetary orbital axis. This is consistent with the previously observed P_obs = 33.2 +22.3 -14.3 day period. We note that this technique could be applied to other transiting systems for which starspots exist on the star in the transit path of the planet in order to constrain the rotation rate of the star. (abridged)Comment: 21 pages, 3 tables, 6 figures, Accepted to Ap

Isogeometric Analysis and thermomechanical Mortar contact problems

Cataloged from PDF version of article.Thermomechanical Mortar contact algorithms and their application to NURBS based Isogeometric Analysis are investigated in the context of nonlinear elasticity. Mortar methods are applied to both the mechanical field and the thermal field in order to model frictional contact, the energy transfer between the surfaces as well as the frictional heating. A series of simplifications are considered so that a wide range of established numerical techniques for Mortar methods such as segmentation can be transferred to IGA without modification. The performance of the proposed framework is illustrated with representative numerical examples. (C) 2014 Elsevier B.V. All rights reserved

Gutachterliche Risikoeinschätzung bei Sexualstraftätern: Anwendbarkeit von PCL-SV, HCR-20+3 und SVR-20

Zusammenfassung: Relativ hohe Rezidivraten bei Sexualstraftätern, steigender Bedarf an forensischen Prognosegutachten und generelle Zweifel an der Validität gutachterlicher Prognosen sowie ein fortbestehender Mangel an qualifizierten Gutachtern verlocken zur Anwendung vermeintlich einfach anwendbarer Prognoseinstrumente wie PCL-SV, HCR-20+3 oder SVR-20. Sie liefern einen numerischen Wert zur Quantifizierung des Rückfallrisikos und finden vermehrt Eingang in forensische Gutachten. Dabei birgt die Anwendung dieser Instrumente bei Kollektiven, für die bisher keine Überprüfung der Praktikabilität oder Validität vorliegt, erhebliche Fehlerquellen. Die hier vorgestellte Studie ist Teil einer größeren Kohortenstudie zur forensisch-psychiatrischen Risikoprognose und dient unter anderem der Untersuchung der Differenzialindikation der "Psychopathy Checklist Screening Version"(PCL-SV), des HCR-20+3 sowie des "Sexual Violence Risk 20" (SVR-20). Es wurden bei 64 strafrechtlichen Gutachten über Sexualstraftäter retrospektiv PCL-SV, HCR-20+3 und SVR-20 erhoben, nachdem primär die Risikoeinschätzung mit dem Basler "Kriterienkatalog zur Beurteilung des Rückfallrisikos besonders gefährlicher Straftäter" erfolgt war. PCL-SV, HCR-20+3 und SVR-20 wurden danach mit den auf dem Basler Kriterienkatalog basierenden gutachterlichen Beurteilungen verglichen, welche ihrerseits an Hand von Auszügen aus dem Strafregister validiert wurden. Die Ergebnisse der Studie lassen die Anwendung dieser Prognoseinstrumente (PCL-SV, HCR-20+3 und SVR-20) im deutschsprachigen Raum bei Sexualstraftätern angesichts des gegenwärtigen Wissensstands primär als wissenschaftliches Instrument sinnvoll erscheinen. Darüber hinaus spricht nichts gegen eine Anwendung als Checkliste im eigentlichen Sinne, ohne dabei eine Zuordnung zu einer Risikokategorie vorzunehmen. Eine Verwendung zur eigentlichen Quantifizierung der Risikoeinschätzung sollte aufgrund unserer Resultate auf die Gruppe der dissozialen und aggressiven Sexualstraftäterbeschränkt bleibe