Geometric Characterization of Polygonal Hydraulic Jumps and the Role of Weir Geometry

Hydraulic jumps are characterized by flows with an abrupt change in the fluid height, as seen in tidal basins, rivers, and dam spillways. They also occur on smaller scales and we have developed a small-scale table top experiment consisting of an impinging fluid jet impacting a horizontal plate to systematically study the geometry of the hydraulic jump. Striking polygonal shapes are observed which depend upon the flow of the impinging jet, fluid properties, weir geometry and the flow history. These steady shapes are reflective of a balance of inertial, pressure, and surface tension forces. The effect of weir height and geometry on the modal behavior and jump geometry is studied. Two experimental protocols are introduced that illustrate the effect of flow history and hysteresis in the formation of polygonal hydraulic jumps. This highlights the nonlinearity inherent in mode selection. We are able to collapse all of our experimental data with the Weber number using the downstream fluid height as the characteristic length scale. The critical wavelength is shown to be approximately constant which strongly implies the mode selection mechanism is related to Plateau-Rayleigh breakup. Our results highlight the complex multiphysics involved in this phenomena

The markers of wellbeing: A basis for a theory-neutral approach

Programmes for measuring national wellbeing are challenged by the fact that there are a number of competing theories of what wellbeing consists in, and there is no prospect that the debate between them will be resolved.Although different theories disagree about what constitutes wellbeing, I argue that there is substantial common ground on what I call the 'markers' of wellbeing: things that are either constitutive, productive or indicative of wellbeing. Whatever stands in one of these relations to wellbeing is potentially relevant to its measurement. Something that is constitutive of wellbeing according to one theory will often be productive or indicative of wellbeing according to another and thus, despite their differences, both theories may acknowledge it as a marker of wellbeing.This paper considers which markers of wellbeing are sufficiently widely shared between different mainstream theories that they could form the basis of a theory-neutral approach to the measurement of wellbeing for the purposes of public policy. The paper defines what would count as a marker of wellbeing in this context; sets out criteria that candidate markers would need to meet; and proposes a list of nine markers that I argue are consistent with a wide range of mainstream theories and with widely-held folk assumptions about wellbeing.

George Fox\u27s Preston Patrick Friends

Reprinted from the Friends\u27 Quarterly Examiner, 1924. Includes bibliographical references. 16 pages, 22 cm.https://digitalcommons.georgefox.edu/quakerbooks/1005/thumbnail.jp

True polar wander driven by late-stage volcanism and the distribution of paleopolar deposits on Mars

The areal centroids of the youngest polar deposits on Mars are offset from those of adjacent paleopolar deposits by 5-10 degrees. We test the hypothesis that the offset is the result of true polar wander (TPW), the motion of the solid surface with respect to the spin axis, caused by a mass redistribution within or on the surface of Mars. In particular, we consider TPW driven by late-stage volcanism during the late Hesperian to Amazonian. There is observational and qualitative support for this hypothesis: in both North and South, observed offsets lie close to a great circle 90 degrees from Tharsis, as expected for polar wander after Tharsis formed. We calculate the magnitude and direction of TPW produced by mapped late-stage lavas for a range of lithospheric thicknesses, lava thicknesses, eruption histories, and prior polar wander events. If Tharsis formed close to the equator, the stabilizing effect of a fossil rotational bulge located close to the equator leads to predicted TPW of <2 degrees, too small to account for observed offsets. If, however, Tharsis formed far from the equator, late-stage TPW driven by low-latitude, late-stage volcanism would be 6-33 degrees, similar to that inferred from the location of paleopolar deposits. 4.4+/-1.3x10^19 kg of young erupted lava can account for the offset of the Dorsa Argentea Formation from the present-day south rotation pole. This mass is consistent with prior mapping-based estimates and would imply a mass release of CO2 by volcanic degassing similar to that in the atmosphere at the present time. The South Polar Layered Deposits are offset from the spin axis in the opposite sense to the other paleopolar deposits. This can be explained by an additional contribution from a plume beneath Elysium. We conclude with a list of observational tests of the TPW hypothesis.Comment: Accepted by Earth and Planetary Science Letters. 3 tables, 8 figure

Adapting the International System of Units to the twenty-first century

We review the proposal of the International Committee for Weights and Measures (Comité International des Poids et Mesures, CIPM), currently being considered by the General Conference on Weights and Measures (Conférences Générales des Poids et Mesures, CGPM), to revise the International System of Units (Le Système International d’Unitès, SI). The proposal includes new definitions for four of the seven base units of the SI, and a new form of words to present the definitions of all the units. The objective of the proposed changes is to adopt definitions referenced to constants of nature, taken in the widest sense, so that the definitions may be based on what are believed to be true invariants. In particular, whereas in the current SI the kilogram, ampere, kelvin and mole are linked to exact numerical values of the mass of the international prototype of the kilogram, the magnetic constant (permeability of vacuum), the triple-point temperature of water and the molar mass of carbon-12, respectively, in the new SI these units are linked to exact numerical values of the Planck constant, the elementary charge, the Boltzmann constant and the Avogadro constant, respectively. The new wording used expresses the definitions in a simple and unambiguous manner without the need for the distinction between base and derived units. The importance of relations among the fundamental constants to the definitions, and the importance of establishing a mise en pratique for the realization of each definition, are also discussed