Crystal structure of bis(1,3-bis[{4-methyl-pyridin-2-yl}amido]-1,1,3,3-tetramethyldisiloxane)dichromium dichloride, [(C16H24N4OSi2)CrCl]2

C32H48Cl2Cr2N8O2Si=, monoclinic, P121/n1 (no. 14), a = 12.416(2) Å, b = 13.668(3) Å, c = 13.172(3) Å, β = 113.83(3)°, V= 2044.8 A3, Z = 2, Rgt(F) = 0.052, wRref(F2) = 0.110, T = 200 K. © 2014 Oldenbourg Wissenschaftsverlag GmbH, Rosenheimer Str. 145, 81671 München. All rights reserved

Improving Atmospheric Angular Momentum Forecasts by Machine Learning

Earth angular momentum forecasts are naturally accompanied by forecast errors that typically grow with increasing forecast length. In contrast to this behavior, we have detected large quasi-periodic deviations between atmospheric angular momentum wind term forecasts and their subsequently available analysis. The respective errors are not random and have some hard to define yet clearly visible characteristics which may help to separate them from the true forecast information. These kinds of problems, which should be automated but involve some adaptation and decision-making in the process, are most suitable for machine learning methods. Consequently, we propose and apply a neural network to the task of removing the detected artificial forecast errors. We found that a cascading forward neural network model performed best in this problem. A total error reduction with respect to the unaltered forecasts amounts to about 30% integrated over a 6-days forecast period. Integrated over the initial 3-days forecast period, in which the largest artificial errors are present, the improvements amount to about 50%. After the application of the neural network, the remaining error distribution shows the expected growth with forecast length. However, a 24-hourly modulation and an initial baseline error of 2 × 10−8 became evident that were hidden before under the larger forecast error

The fastest unbound star in our Galaxy ejected by a thermonuclear supernova

Hypervelocity stars (HVS) travel with velocities so high, that they exceed the escape velocity of the Galaxy. Several acceleration mechanisms have been discussed. Only one HVS (US 708, HVS 2) is a compact helium star. Here we present a spectroscopic and kinematic analysis of US\,708. Travelling with a velocity of $\sim1200\,{\rm km\,s^{-1}}$, it is the fastest unbound star in our Galaxy. In reconstructing its trajectory, the Galactic center becomes very unlikely as an origin, which is hardly consistent with the most favored ejection mechanism for the other HVS. Furthermore, we discovered US\,708 to be a fast rotator. According to our binary evolution model it was spun-up by tidal interaction in a close binary and is likely to be the ejected donor remnant of a thermonuclear supernova.Comment: 16 pages report, 20 pages supplementary material

Reliability of measures of impairments associated with patellofemoral pain syndrome

BACKGROUND: The reliability and measurement error of several impairment measures used during the clinical examination of patients with patellofemoral pain syndrome (PFPS) has not been established. The purpose was to determine the inter-tester reliability and measurement error of measures of impairments associated with PFPS in patients with PFPS. METHODS: A single group repeated measures design was used. Two pairs of physical therapists participated in data collection. Examiners were blinded to each others' measurements. RESULTS: Thirty patients (age 29 +/- 8; 17 female) with PFPS participated in this study. Inter-tester reliability coefficients were substantial for measures of hamstrings, quadriceps, plantarflexors, and ITB/TFL complex length, hip abductors strength, and foot pronation (ICCs from .85 to .97); moderate for measures of Q-angle, tibial torsion, hip external rotation strength, lateral retinacular tightness, and quality of movement during a step down task (ICCs from .67 to .79); and poor for femoral anteversion (ICC of .45). Standard error of measurement (SEM) for measures of muscle length ranged from 1.6 degrees to 4.3 degrees. SEM for Q-angle, tibial torsion, and femoral anteversion were 2.4 degrees, 2.9 degrees, and 4.5 degrees respectively. SEM for foot pronation was 1 mm. SEM for measures of muscle strength was 1.8 Kg for abduction and 2.4 Kg for external rotation. CONCLUSION: Several of the impairments associated with PFPS had sufficient reliability and low measurement error. Further investigation is needed to test if these impairment measurements are related to physical function and whether or not they are useful for decision-making

Asteroseismology of massive stars with the TESS mission: the runaway Beta Cep pulsator PHL 346 = HN Aqr

We report an analysis of the first known Beta Cep pulsator observed by the TESS mission, the runaway star PHL 346 = HN Aqr. The star, previously known as a singly-periodic pulsator, has at least 34 oscillation modes excited, 12 of those in the g-mode domain and 22 p modes. Analysis of archival data implies that the amplitude and frequency of the dominant mode and the stellar radial velocity were variable over time. A binary nature would be inconsistent with the inferred ejection velocity from the Galactic disc of 420 km/s, which is too large to be survivable by a runaway binary system. A kinematic analysis of the star results in an age constraint (23 +- 1 Myr) that can be imposed on asteroseismic modelling and that can be used to remove degeneracies in the modelling process. Our attempts to match the excitation of the observed frequency spectrum resulted in pulsation models that were too young. Hence, asteroseismic studies of runaway pulsators can become vital not only in tracing the evolutionary history of such objects, but to understand the interior structure of massive stars in general. TESS is now opening up these stars for detailed asteroseismic investigation.Comment: accepted for ApJ

Hubble spectroscopy of LB-1: comparison with B+black-hole and Be+stripped-star models

LB-1 has variously been proposed as either an X-ray dim B-type star plus black hole (B+BH) binary, or a Be star plus an inflated stripped star (Be+Bstr) binary. The Space Telescope Imaging Spectrograph (STIS) on board HST was used to obtain a flux-calibrated spectrum that is compared with non-LTE spectral energy distributions (SED) and line profiles for the proposed models. The Hubble data, together with the Gaia EDR3 parallax, provide tight constraints on the properties and stellar luminosities of the system. In the case of the Be+Bstr model we adopt the published flux ratio for the Be and Bstr stars, re-determine the T$_{eff}$ of the Bstr using the silicon ionization balance, and infer Teff for the Be star from the fit to the SED. We derive stellar parameters consistent with previous results, but with greater precision enabled by the Hubble SED. While the Be+Bstr model is a better fit to the HeI lines and cores of the Balmer lines in the optical, the B+BH model provides a better fit to the Si iv resonance lines in the UV. The analysis also implies that the Bstr star has roughly twice solar silicon abundance, difficult to reconcile with a stripped star origin. The Be star on the other hand has a rather low luminosity, and a spectroscopic mass inconsistent with its possible dynamical mass. The fit to the UV can be significantly improved by reducing the T$_{eff}$ and radius of the Be star, though at the expense of leading to a different mass ratio. In the B+BH model, the single B-type spectrum is a good match to the UV spectrum. Adopting a mass ratio of 5.1$\pm$0.1 (Liu et al. 2020) implies a BH mass of $\sim$21$^{+9}_{-8}M_{\odot}$.Comment: 8 pages, 7 figures, 1 online table In press with Astronomy & Astrophysic