Lehigh University

About: Lehigh University is a education organization based out in Bethlehem, Pennsylvania, United States. It is known for research contribution in the topics: Catalysis & Fracture mechanics. The organization has 12684 authors who have published 26550 publications receiving 770061 citations.

The boundary layer induced by a convected two-dimensional vortex

Abstract: The response of a wall boundary layer to the motion of a convected vortex is investigated. The principal cases considered are for a rectilinear filament of strength –κ located a distance a above a plane wall and convected to the right in a uniform flow of speed U∞*. The inviscid solution predicts that such a vortex will remain at constant height a above the wall and be convected with constant speed αU∞*. Here α is termed the fractional convection rate of the vortex, and cases in the parameter range 0 [les ] α < 1 are considered. The motion is initiated at time t* = 0 and numerical calculations of the developing boundary-layer flow are carried out for α = 0, 0.2, 0.4, 0.55, 0.7, 0.75 and 0.8. For α < 0.75, a rapid lift-up of the boundary-layer streamlines and strong boundary-layer growth occurs in the region behind the vortex; in addition an unusual separation phenomenon is observed for α [les ] 0.55. For α [ges ] 0.75, the boundary-layer development is more gradual, but ultimately substantial localized boundary-layer growth also occurs. In all cases, it is argued that a strong inviscid–viscous interaction will take place in the form of an eruption of the boundary-layer flow. The generalization of these results to two-dimensional vortices with cores of finite dimension is discussed.

Empirical Accurate Masses and Radii of Single Stars with TESS and Gaia

Abstract: We present a methodology for the determination of empirical masses of single stars through the combination of three direct observables with Gaia and Transiting Exoplanet Survey Satellite (TESS): (i) the surface gravity via granulation-driven variations in the TESS light curve, (ii) the bolometric flux at Earth via the broadband spectral energy distribution, and (iii) the distance via the Gaia parallax. We demonstrate the method using 525 Kepler stars for which these measures are available in the literature, and show that the stellar masses can be measured with this method to a precision of ~25%, limited by the surface-gravity precision of the granulation "flicker" method (~0.1 dex) and by the parallax uncertainties (~10% for the Kepler sample). We explore the impact of expected improvements in the surface gravity determinations—through the application of granulation background fitting and the use of recently published granulation-metallicity relations—and improvements in the parallaxes with the arrival of the Gaia second data release. We show that the application of this methodology to stars that will be observed by TESS should yield radii good to a few percent and masses good to ≈10%. Importantly, the method does not require the presence of an orbiting, eclipsing, or transiting body, nor does it require spatial resolution of the stellar surface. Thus, we can anticipate the determination of fundamental, accurate stellar radii and masses for hundreds of thousands of bright single stars—across the entire sky and spanning the Hertzsprung–Russell diagram—including those that will ultimately be found to host planets.

Columns Under Combined Bending and Thrust

Abstract: Interaction curves relating axial thrust, applied end bending moment, and slenderness ratio, developed for ultimate carrying capacity of pin ended, wide flange beam columns; assumed symmetrical residual stress pattern considered in calculations; interaction curves are fitted into approximate equations; comparison with various column test results.

If you spoke as she does, sir, instead of the way you do: a sociolinguistics perspective of gender differences in virtual communities

Abstract: This study examines virtual community quality through sociolinguistics theory. According to sociolinguistics, in oral discourse men communicate to establish superior social standing, while women communicate with the undertone of rapport, compassion, and empathy. The study shows that these differences carry over to the asynchronous written environment of virtual communities and affect men's and women's respective perceptions of community quality. Women go to virtual communities to give and to get social support and have a more favorable assessment of the capability of others. This pattern generally holds even when comparing mostly single-gender communities and mixed-gender communities. However, a closer look at these differences reveals a more complex picture, with undertones in mixed-gender communities being less than in their respective mostly single-gender communities.