Prediction of boundary-layer characteristics of an oscillating airfoil

The evolution of unsteady boundary layers on oscillating airfoils is investigated by solving the governing equations by the Characteristic Box scheme. The difficulties associated with computing the first profile on a given time line, and the velocity profiles with partial flow reversal are solved. A sample calculation is performed for an external velocity distribution typical of those found near the leading edge of thin airfoils. The viability of the calculation procedure is demonstrated

Calculation of boundary layers near the stagnation point of an oscillating airfoil

The results of an investigation of boundary layers close to the stagnation point of an oscillating airfoil are reported. Two procedures for generating initial conditions, the characteristics box scheme and a quasi-static approach, were investigated, and the quasi-static approach was shown to be appropriate provided the initial region was far from any flow separation. With initial conditions generated in this way, the unsteady boundary layer equations were solved for the flow in the leading edge region of a NACA 0012 airfoil oscillating from 0 to 5 deg. Results were obtained for both laminar and turbulent flow, and, in the latter case, the effect of transition was assessed by specifying its occurrence at different locations. The results demonstrate the validity of the numerical scheme and suggest that the procedures should be applied to calculation of the entire flow around oscillating airfoils

Stability criterion for self-similar solutions with a scalar field and those with a stiff fluid in general relativity

A stability criterion is derived in general relativity for self-similar solutions with a scalar field and those with a stiff fluid, which is a perfect fluid with the equation of state $P=\rho$. A wide class of self-similar solutions turn out to be unstable against kink mode perturbation. According to the criterion, the Evans-Coleman stiff-fluid solution is unstable and cannot be a critical solution for the spherical collapse of a stiff fluid if we allow sufficiently small discontinuity in the density gradient field in the initial data sets. The self-similar scalar-field solution, which was recently found numerically by Brady {\it et al.} (2002 {\it Class. Quantum. Grav.} {\bf 19} 6359), is also unstable. Both the flat Friedmann universe with a scalar field and that with a stiff fluid suffer from kink instability at the particle horizon scale.Comment: 15 pages, accepted for publication in Classical and Quantum Gravity, typos correcte

The Structuration of Identification on Organizational Members’ Social Media

The structurational model of identification is applied to test structures that may lead to sharing organizational membership on social media and increased organizational identification. We propose and test how antecedents (e.g., social media use, organizational prestige) relate to acts of identification on social media and promote organizational identification. United States working adults (N = 303) responded to an online survey about hypothesized motivational structures, online disclosures of organizational affiliation, and organizational identification. Results show three specific structures significantly predicted one’s willingness to share her or his organizational affiliation across social media: personae overlap, social media use, and organizational prestige. Commitment and turnover intentions were, surprisingly, not direct predictors of organizational affiliation disclosure. Implications for individuals, organizations, and both organizational and computer-mediated theory are presented

Employer reviews may say as much about the employee as they do the employer: Online disclosures, organizational attachments, and unethical behavior

This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Applied Communication Research on 02 Sep 202002 Sep 2020, available online: http://www.tandfonline.com/10.1080/00909882.2020.1812692.Do reviews on organizational review websites (e.g., Indeed.com, GlassDoor.com) speak to the employer or the employee? This study tests the structural relationship between cognitive and affective organizational attachments and three outcomes: willingness to disclose one’s workplace online, unethical pro-organizational behavior (UPB), and workplace reviews. Using a national sample of U.S. workers (N = 304), we examine how organizational identification and commitment relate to publicly posting about one’s organization. Self-presentation and organizational attachment are used to hypothesize how individuals selectively self-present organizational identities online. Structural equation modeling shows identification and commitment both positively relate to review ratings. While identification positively predicts online disclosure and UPB, commitment is unrelated to disclosure and has a buffering effect whereby it negatively predicts UPB and interacts with UPB to predict organizational review ratings. Findings illustrate that online reviews and disclosures of one's workplace may say as much about the worker as the workplace itself

Near-Critical Gravitational Collapse and the Initial Mass Function of Primordial Black Holes

The recent discovery of critical phenomena arising in gravitational collapse near the threshold of black hole formation is used to estimate the initial mass function of primordial black holes (PBHs). It is argued that the universal scaling relation between black hole mass and initial perturbation found for a variety of collapsing space-times also applies to PBH formation, indicating the possibility of the formation of PBHs with masses much smaller than one horizon mass. Owing to the natural fine-tuning of initial conditions by the exponential decline of the probability distribution for primordial density fluctuations, sub-horizon mass PBHs are expected to form at all epochs. This result suggests that the constraints on the primordial fluctuation spectrum based on the abundance of PBHs at different mass scales may have to be revisited.Comment: 4 pages, uses revtex, also available at http://bigwhirl.uchicago.edu/jcn/pub_pbh.html . To appear in Phys. Rev. Let

Intensity to frequency conversion technique in intensity modulated fiber optic sensing systems

A novel sensing technique based on intensity-to-frequency conversion is explained and demonstrated. Experimental data are presented and a comparison with a theoretical model is made

Growth of primordial black holes in a universe containing a massless scalar field

The evolution of primordial black holes in a flat Friedmann universe with a massless scalar field is investigated in fully general relativistic numerical relativity. A primordial black hole is expected to form with a scale comparable to the cosmological apparent horizon, in which case it may go through an initial phase with significant accretion. However, if it is very close to the cosmological apparent horizon size, the accretion is suppressed due to general relativistic effects. In any case, it soon gets smaller than the cosmological horizon and thereafter it can be approximated as an isolated vacuum solution with decaying mass accretion. In this situation the dynamical and inhomogeneous scalar field is typically equivalent to a perfect fluid with a stiff equation of state $p=\rho$. The black hole mass never increases by more than a factor of two, despite recent claims that primordial black holes might grow substantially through accreting quintessence. It is found that the gravitational memory scenario, proposed for primordial black holes in Brans-Dicke and scalar-tensor theories of gravity, is highly unphysical.Comment: 24 pages, accepted for publication in Physical Review

Computation of unsteady turbulent boundary layers with flow reversal and evaluation of two separate turbulence models

A procedure which solves the governing boundary layer equations within Keller's box method was developed for calculating unsteady laminar flows with flow reversal. This method is extended to turbulent boundary layers with flow reversal. Test cases are used to investigate the proposition that unsteady turbulent boundary layers also remain free of singularities. Turbulent flow calculations are performed. The governing equations for both models are solved. As in laminar flows, the unsteady turbulent boundary layers are free from singularities, but there is a clear indication of rapid thickening of the boundary layer with increasing flow reversal. Predictions of both turbulence models are the same for all practical purposes