Low-mass and sub-stellar eclipsing binaries in stellar clusters

We highlight the importance of eclipsing double-line binaries in our understanding on star formation and evolution. We review the recent discoveries of low-mass and sub-stellar eclipsing binaries belonging to star-forming regions, open clusters, and globular clusters identified by ground-based surveys and space missions with high-resolution spectroscopic follow-up. These discoveries provide benchmark systems with known distances, metallicities, and ages to calibrate masses and radii predicted by state-of-the-art evolutionary models to a few percent. We report their density and discuss current limitations on the accuracy of the physical parameters. We discuss future opportunities and highlight future guidelines to fill gaps in age and metallicity to improve further our knowledge of low-mass stars and brown dwarfs.Comment: 30 pages, 5 figures, no table. Review pape

Harmonic Forcing of Damped Non-homogeneous Elastic Rods

This work is one of an ongoing series of investigations on the motions of non-homogeneous structures. In the series, natural frequencies, mode shapes and frequency response functions (FRFs) were determined for undamped segmented rods and beams, using analytic and numerical approaches. These structures are composed of stacked cells, which may have distinct geometric and material properties. Here, the steady state response, due to harmonic forcing, of a segmented damped rod is investigated. The objective is the determination of FRFs for the system. Two methods are employed. The first uses the displacement differential equations for each segment, where boundary and interface continuity conditions are used to determine the constants involved in the solutions. Then the response as a function of forcing frequency can be obtained. This procedure is unwieldy and may become unpractical for arbitrary spatial forcing functions. The second approach uses logistic functions to model the segment discontinuities. This leads to a single partial differential equation with variable coefficients, which is solved numerically using MAPLE® software. For free-fixed boundary conditions and spatially constant force good agreement is found between the methods. The continuously varying functions approach is then used to obtain the response for a spatially varying force

Transverse vibrations of tapered materially inhomogeneous axially loaded shafts

Shafts loaded by axial compressive constant forces constitute an area of considerable technical importance. The transverse vibration of such shafts is the subject of the current work. Occasionally the shafts are tapered and of interest is the effect of employing functionally graded materials (FGM), with properties varying in the axial direction, on the buckling load and lowest natural frequency. The shaft cross section is circular and two types of taper are treated, namely, linear and sinusoidal. All shafts have the same volume and length and are subjected to a constant axial force below the static buckling load. Euler-Bernoulli theory is used with the axial force handled by a buckling type model. The problems that arise are computationally challenging but an efficient strategy employing MAPLE®’s two-point boundary value solver has been developed. Typical results for a linear tapered pin-pin shaft where one end radius is twice the other, and the FGM model varies in a power law fashion with material properties increasing in the direction of increasing area, include doubling of the buckling load and first bending frequency increase of approximately 43%, when compared to a homogeneous tapered shaft. For the same material and boundary conditions, a sinusoidal shaft, with mid-radius twice the value of the end ones, increases the buckling load by about 118% and the first frequency by 26%, when compared to a homogeneous sinusoidal shaft

Emergency coronary artery bypass grafting using minimized versus standard extracorporeal circulation--a propensity score analysis

BACKGROUND: The impact of minimized extracorporeal circulation (MECC) for emergency revascularization remains controversial. METHODS: A total of 348 patients underwent emergency CABG with MECC (n=146) or conventional extracorporeal circulation (CECC; n=175) between January 2005 and December 2010. Using propensity score matching after binary logistic regression, 100 patients, who underwent CABG with MECC could be matched with 100 patients, who underwent CABG with CECC. Primary outcome was 30-day mortality. RESULTS: Unadjusted 30-day mortality was 14.8% in patients with CECC and 6.9% in those with MECC (mean difference -7.9%; p=0.03). The adjusted mean difference (average treatment effect of the treated, ATT) after matching was -1.0% (95% CI -8.6 to 7.6; p=1.0). Intensive care unit stay (adjusted mean difference 1.0; 95% CI -0.2 to 3.2; p=0.70) and hospital stay (adjusted mean difference 1.0; 95% CI -2.0 to 3.6; p=0.40) did not show significant differences between both groups. The adjusted mean difference for postoperative low cardiac output syndrome was -1.1% (95% CI -7.3 to 7.1; p=0.83) without significant differences between CECC and MECC. Postoperative mechanical ventilation time, drain loss, postoperative rethoracotomy, postoperative neurological events, new onset renal replacement therapy and respiratory failure also had insignificant average treatment effects of the treated. In addition, all average treatment effects (ATEs) did not significantly differ between both groups. CONCLUSION: Using propensity score estimation and matching, we did not observe significant differences in terms of survival and further outcomes in patients who undergo emergency CABG with CECC or MECC, but our results call for further analysis