A Virtual Element Method for elastic and inelastic problems on polytope meshes

We present a Virtual Element Method (VEM) for possibly nonlinear elastic and inelastic problems, mainly focusing on a small deformation regime. The numerical scheme is based on a low-order approximation of the displacement field, as well as a suitable treatment of the displacement gradient. The proposed method allows for general polygonal and polyhedral meshes, it is efficient in terms of number of applications of the constitutive law, and it can make use of any standard black-box constitutive law algorithm. Some theoretical results have been developed for the elastic case. Several numerical results within the 2D setting are presented, and a brief discussion on the extension to large deformation problems is included

On Collision Course: The Nature of the Binary Star Cluster NGC 2006 / SL 538

The LMC hosts a rich variety of star clusters seen in close projected proximity. Ages have been derived for few of them showing differences up to few million years, hinting at being binary star clusters. However, final confirmation needs to be done through spectroscopic analysis. Here we focus on the LMC cluster pair NGC2006-SL538 and aim to determine whether the star cluster pair is a bound entity (binary star cluster) or a chance alignment. Using the MIKE echelle spectrograph at LCO we have acquired integrated-light spectra for each cluster. We have measured radial velocities by two methods: a) direct line profile measurement yields v$_r=300.3\pm5\pm6$ km/s for NGC2006 and $v_r=310.2\pm4\pm6$ km/s for SL538. b) By comparing observed spectra with synthetic bootstrapped spectra yielding $v_r=311.0\pm0.6$ km/s for NGC2006 and $v_r=309.4\pm0.5$ km/s for SL538. Finally when spectra are directly compared, we find a ${\Delta}v=1.08\pm0.47$ km/s. Full-spectrum SED fits reveal that the stellar population ages lie in the range 13-21 Myr with a metallicity of Z=0.008. We find indications for differences in the chemical abundance patterns as revealed by the helium absorption lines between the two clusters. The dynamical analysis shows that the two clusters are likely to merge within the next $\sim$150 Myr. The NGC2006-SL538 cluster pair shows radial velocities, stellar population and dynamical parameters consistent with a gravitational bound entity. We conclude that this is a genuine binary cluster pair, and we propose that their differences in ages and stellar population chemistry is most likely due to variances in their chemical enrichment history within their environment. We suggest that their formation may have taken place in a loosely bound star-formation complex which saw initial fragmentation but then had its clusters become a gravitationally bound pair by tidal capture.Comment: Accepted for publication in Astronomy & Astrophysics. 15 pages, 10 figures in low resolutio

Limits of sensing temporal concentration changes by single cells

Berg and Purcell [Biophys. J. 20, 193 (1977)] calculated how the accuracy of concentration sensing by single-celled organisms is limited by noise from the small number of counted molecules. Here we generalize their results to the sensing of concentration ramps, which is often the biologically relevant situation (e.g. during bacterial chemotaxis). We calculate lower bounds on the uncertainty of ramp sensing by three measurement devices: a single receptor, an absorbing sphere, and a monitoring sphere. We contrast two strategies, simple linear regression of the input signal versus maximum likelihood estimation, and show that the latter can be twice as accurate as the former. Finally, we consider biological implementations of these two strategies, and identify possible signatures that maximum likelihood estimation is implemented by real biological systems.Comment: 11 pages, 2 figure

Star clusters in unperturbed spiral galaxies

Stars do not form in isolation, they form in groups known as star clusters. Star clusters are seen in a wide range of galaxies and environments. Their presence reveals the history of the host galaxy and the processes of its star formation. During the last years star clusters have been deeply investigated in violent environments, while the properties of star clusters in more quiet environments have received less attention. Among all unperturbed environments we focus on 5 spiral galaxies with no signs of external perturbations: NGC 45, NGC 1313, NGC 4395, NGC 5236 and NGC 7793. Star clusters lying in these galaxies were observed through HST imaging and VLT spectroscopy. The analysis of star cluster masses, ages, sizes, and their positions on the galaxies, showed that star cluster formation is an ongoing process that depends on the local conditions. The observed star cluster luminosity functions show values consistent with the expected alpha~-2. We found an important number of globular clusters in NGC 45. Their properties are analyzed through photometry and spectroscopy. Photometry suggests that these globular clusters belong to a single metal poor population. Spectroscopy confirmed this for the 8 brightest ones. Velocities indicate halo or bulge kinematics. Absorption spectrum features indicate ages of the order of Gyr and [alpha/Fe] values lower than the Milky Way globular clusters, but similar to dwarf galaxies in the local group

Examining Trauma-Informed Care Knowledge, Skills, Dispositions, and Professional Development Needs of Special Educators and Paraprofessionals in Therapeutic Alternative Schools: An Exploratory Survey Study

Examining the use of trauma-informed care (TIC) in schools is necessary to support the academic, behavior, and social-emotional development of students with and without disabilities who encounter trauma. In Chapter One, a systematic literature review was conducted to examine TIC interventions implemented in schools. Nineteen publications were included. Review results identified P-12 school-based TIC intervention characteristics, school-based facilitators, implementation strategies, and professional development (PD) components. Limitations and future directions are discussed. In Chapter Two, an online survey was administered to special educators and paraprofessionals to assess their knowledge, skills, dispositions and PD needs regarding TIC implementation for students with disabilities (SWD) in therapeutic alternative schools. Data analysis consisted of an exploratory factor analysis (EFA), an independent sample t-test, and a one-way Analysis of Variance (ANOVA). A total of 164 surveys were completed by special education classroom personnel. The EFA results revealed a 3-factor solution for examining TIC in therapeutic alternative schools. The independent t-test results revealed no statistically significant difference on TIC knowledge and skills, TIC personal responsibility dispositions, or TIC PD need. The overall ANOVA findings revealed that TIC PD need was significantly different across years of experience in therapeutic alternative schools, but not across school location or grade level. These findings set the stage for TIC practice implementation and creating appropriate and relevant TIC PD for special educators and paraprofessionals in therapeutic alternative schools