Nonlinear stabilitty for steady vortex pairs

In this article, we prove nonlinear orbital stability for steadily translating vortex pairs, a family of nonlinear waves that are exact solutions of the incompressible, two-dimensional Euler equations. We use an adaptation of Kelvin's variational principle, maximizing kinetic energy penalised by a multiple of momentum among mirror-symmetric isovortical rearrangements. This formulation has the advantage that the functional to be maximized and the constraint set are both invariant under the flow of the time-dependent Euler equations, and this observation is used strongly in the analysis. Previous work on existence yields a wide class of examples to which our result applies.Comment: 25 page

Master agreement task order 2 - Analyses and limited evaluations of payload and landing system structures for the survivable soft landing of instrument payloads

Computer programs for analysis and evaluation of payload and landing system structures for soft landing of instrument package

(Mis)understanding alcohol use disorder: Making the case for a public health first approach

‘Alcohol use disorder’ (AUD) is used by several contemporary conceptualizations to identify, treat and prevent problems associated with alcohol use. Such conceptualizations encompass diagnostic classifications and broader frameworks for policy and practice. However, current AUD concepts are subject to multiple tensions and limitations in capturing and responding to the complex and heterogeneous nature of alcohol problems. Further, public understandings of alcohol problems are heavily divergent from professional AUD concepts and remain embedded within an ‘alcoholism’ master narrative in which disease model stereotypes come with multiple costs for prevention and ‘recovery’. The persistence of a problematic ‘alcoholism’ paradigm reflects the coalescing of multiple forces including the cognitive appeal of reductionism, motives to stigmatize and ‘other’, and an over-emphasis on AUD as an individually located biomedical problem. Public misperceptions of AUD as a matter of the individual, the individual’s essence, and misconceived notions of responsibility and control have been bolstered by industry interests and the ascension of neuroscience and genetics, in turn diverting attention from the importance of the environmental and commercial determinants of health and the effectiveness of under-utilized public health policies. We call for multiple stakeholders to support efforts to prioritize a public health first approach to advancing AUD research, policy and treatment in order to make significant advances in AUD prevention and treatment. We offer several recommendations to assist in shifting public understanding and scientific limitations in AUD concepts and responses

The inexorable resistance of inertia determines the initial regime of drop coalescence

Drop coalescence is central to diverse processes involving dispersions of drops in industrial, engineering and scientific realms. During coalescence, two drops first touch and then merge as the liquid neck connecting them grows from initially microscopic scales to a size comparable to the drop diameters. The curvature of the interface is infinite at the point where the drops first make contact, and the flows that ensue as the two drops coalesce are intimately coupled to this singularity in the dynamics. Conventionally, this process has been thought to have just two dynamical regimes: a viscous and an inertial regime with a crossover region between them. We use experiments and simulations to reveal that a third regime, one that describes the initial dynamics of coalescence for all drop viscosities, has been missed. An argument based on force balance allows the construction of a new coalescence phase diagram

Heat exchanger test experimental apparatus. Section I - Helium heater. Section II - Helium circulator Summary report

Molybdenum heater tube for heating helium to operating temperature of high temperature heat exchanger facility - performance of helium circulato

A Detailed Investigation of Staged Normal Injection into a Mach 2 Flow

A study of the staged injection of two jets of air behind a rearward facing step into a Mach 2 flow was performed using the SPARK 3-D Navier-Stokes code. Calculated mole fraction distributions were compared with an extensive set of planar mole fraction measurements made with a laser induced iodine fluorescence technique. A statistical measure, the standard deviation, was used to help assess agreement between calculation and experiment. Overall, good agreement was found between calculated and measured values. Generally, agreement was better in the far field of the injectors. The effect of grid resolution was investigated by calculating solutions on grids of 60,000, 200,000, and 450,000 points. Differences in the solutions on the two finer grids were small. However, the mole fraction distributions were distinguishable. The effect of turbulence modeling was investigated by employing three different algebraic models for the jet turbulence: the Baldwin-Lomax model, the Prandtl mixing length model, and the Eggers mixing length model. Overall, the Eggers mixing length model was found to be superior for this case. Finally, the effect of the jet exit conditions was examined. A recently proposed Mach number distribution at the jet exit was found to slightly improve agreement between measurement and calculation