Theory of Drop Formation

We consider the motion of an axisymmetric column of Navier-Stokes fluid with a free surface. Due to surface tension, the thickness of the fluid neck goes to zero in finite time. After the singularity, the fluid consists of two halves, which constitute a unique continuation of the Navier-Stokes equation through the singular point. We calculate the asymptotic solutions of the Navier-Stokes equation, both before and after the singularity. The solutions have scaling form, characterized by universal exponents as well as universal scaling functions, which we compute without adjustable parameters

Membership in the Young Cluster Trumpler 37

Astrometric positions for 1387 stars and proper motions for a subset of 1135 stars brighter than V=15 in a 1.5 degree surrounding the young open cluster Trumpler 37 are presented. Membership probabilities are presented for those stars with measured proper motions, and 486 stars with probabilities of \u3e80% are identified

Origin and Evolution of Jupiter's Trojan Asteroids

The origin of the Jupiter Trojan asteroids has long been a mystery. Dynamically, the population, which is considerably smaller than the main asteroid belt, librates around Jupiter's stable L4 and L5 Lagrange points, 60 deg ahead and behind Jupiter. It is thought that these bodies were captured into these orbits early in solar system history, but any capture mechanism must also explain why the Trojans have an excited inclination distribution, with some objects reaching inclinations of 35 deg. The Trojans themselves, individually and in aggregate, also have spectral and physical properties that appear consistent with many small bodies found in the outer solar system (e.g., irregular satellites, Kuiper belt objects). In this review, we assemble what is known about the Trojans and discuss various models for their origin and collisional evolution. It can be argued that the Trojans are unlikely to be captured planetesimals from the giant planet zone, but instead were once denizens of the primordial Kuiper belt, trapped by the events taking place during a giant planet instability. The Lucy mission to the Trojans is therefore well positioned to not only answer questions about these objects, but also about their place in planet formation and solar system evolution studies.Comment: 30 pages, 4 figure

Analysis of the commutation error of filtering operators for the double-averaged equations of flows in porous media in a LES formalism

The continuum approach employing porous media models is an attractive solution method in the area of Computational Fluid Dynamics (CFD) simulation of fixed-bed reactors due to its robustness and efficiency. This paper applies the double-averaging methodology to refine the mathematical basis for the continuum approach, opening a way to alleviate its main limitations: space-invariant averaging volume and inaccurate treatment of the porous/non-porous interface. The averaging operator is recast as a general space-time filter and a detailed analysis of commutation errors is performed, using a classic Large Eddy Simulation (LES) formalism. An explicit filtering framework has been implemented in the open-source CFD library OpenFOAM to carry out an a-posteriori evaluation of the unclosed terms appearing in the Double-Averaged Navier-Stokes (DANS) equations also considering a space-varying filter width. Two resolved simulations have been performed. First, the flow around a single, stationary particle has been considered and used to validate derived equations and the filtering procedure. Second, an LES of the turbulent flow in a channel partly occupied with a porous medium has been conducted. The results have been filtered, and the commutation error at the porous-fluid interface has been evaluated and compared to the prediction of two models. The significance of the commutation error terms is also discussed and assessed. Finally, the solver for DANS equations has been developed and used to simulate both of the studied geometries. The magnitude of the error associated with neglecting the commutation errors has been investigated and an LES simulation combined with a porous drag model was performed. Very encouraging results have been obtained indicating that the inaccuracy of the drag closure overshadows the error related to the commutation of operators.Comment: This material has been submitted to Physics of Fluids. It contains 33 pages and 21 Figure

Photometry of the Young Open Cluster Trumpler 37

Photoelectric UBV observations of 120 stars in the young open cluster Trumpler 37 are presented, primarily in the magnitude range 10.0\u3c

Weekend diagnosis of Escherichia coli urinary tract infection does not predict poor outcome

It has been suggested that mortality is higher in patients admitted to hospitals during the weekend. The objective of this study was to compare outcomes in patients with E. coli urinary tract infection (UTI) depending on the hospital admission day. For this purpose, a secondary analysis of data from a prospective cohort of patients with E. coli UTI was conducted. Weekend diagnosis of UTI was not associated with higher mortality. However, mortality was associated with sepsis, sepsis-induced hypotension and intensive care unit (ICU) admission. Sepsis-induced hypotension and ICU admission were independent determinants of mortality. The results indicate that indicators of severity of illness are associated with higher mortality in patients with UTI rather than the time of diagnosis