14,945 research outputs found
Real-space Manifestations of Bottlenecks in Turbulence Spectra
No full textAn energy-spectrum bottleneck, a bump in the turbulence spectrum between the inertial and dissipation ranges, is shown to occur in the non-turbulent, one-dimensional, hyperviscous Burgers equation and found to be the Fourier-space signature of oscillations in the real-space velocity, which are explained by boundary-layer-expansion techniques. Pseudospectral simulations are used to show that such oscillations occur in velocity correlation functions in one- and three-dimensional hyperviscous hydrodynamical equations that display genuine turbulence
Turbulent stratified shear flow experiments: Length scale comparison
No full textStratified shear flows are ubiquitous in geophysical systems such as oceanic overflows, wind-driven thermoclines, and atmo- spheric inversion layers. The stability of such flows is governed by the Richardson Number Ri which represents a balance between the stabilizing influence of stratification and the destabilizing influence of shear. For a shear flow with velocity difference U, density difference ∆ρ and characteristic length H, one has Ri = g(∆ρ/ρ)H/U^2 which is often used when detailed information about the flow is not available. A more precise definition is the gradient Richardson Number Rig = N^2/S^2 where the buoyancy frequency N = ((g/ρ)∂ρ/∂z)^{1/2}, the mean strain S = ∂U/∂z in which z is parallel to gravity and suitable ensemble or time averages define the gradients. We explore the stability and mixing properties of a wall-bounded shear flow over a range 0.1< Rig <1 using simultaneous planar measurements of density and velocity fields using Planar Laser-Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV), respectively. The flow, confined from the top by glass horizontal boundary, is a lighter alcohol-water mixture injected from a nozzle into quiescent heavier salt-water fluid with velocity between 5 and 10 cm/s and with a relative fractional density difference of 0.0026 or 0.0052. The injected flow is turbulent with Taylor Reynolds number between 50 and 100. We compare a set of length scales that characterize the mixing properties of our turbulent stratified shear flow including the Thorpe Length L_T, the Ozmidov Length L_o, the Ellison Length L_E, and turbulent mixing lengths L_m and L_ρ
Aspect-ratio dependence of the transition to the ultimate state of turbulent Rayleigh-Bénard convection
No full textWe report on measurements of the ultimate-state transition in turbulent Rayleigh-B\'enard convection obtained in a large facility known as the ``Uboot of G\"ottingen" and using pressurized sulfur hexafluoride as the convecting fluid. We found that the transition occurs over a range of which becomes more narrow as increases, ranging from which is at most weakly dependent on and close to to which varies from about for to about for
The Göttingen rotating turbulent Rayleigh-Bénard convection facility
No full textThermally driven turbulent convection under the influence of global rotation is ubiquitous in nature. Well known examples are the outer convective shell of our Sun and the outer liquid core of the Earth. Trying to understand the underlying dynamics of such flows is highly challenging, not only because of the enormous range in length- and time-scales that are involved with these geo/astrophysical cases and the complex interaction of hydrodynamics with electromagnetism, but also because direct measurements on these systems are most often impossible to carry out. We gain access to direct measurements by isolating part of the problem: We focus solely on the hydrodynamical aspects of turbulent convection by performing experiments in the lab and making comparisons with direct numerical simulations (DNS). The canonical system that we use to study such flows is Rayleigh-B\'enard convection (RBC), the flow between a warm bottom plate and cold top plate, in a fluid-filled upright cylindrical cell that is rotating around its geometrical axis. This presentation will focus on the newly constructed rotating RBC facility at the Max Planck Institute for Dynamics and Self-Organization (MPIDS) in G\"ottingen
Macroeconomic and policy implications of population aging in Brazil
No full textThis paper analyzes the macroeconomic implications of population aging in Brazil. Three alternative yet complementary methodologies are adopted, and depending on policy responses to the fiscal implications of aging, there are two main findings: First, saving rates could increase and not necessarily fall as a consequence of aging in Brazil -- thus contradicting conventional views. Second, lifetime wealth across generations could increase -- as capital deepening generates a second demographic dividend. Two policy responses to aging are emphasized: First, a structural policy response of linking mandatory retirement (or entitlement) ages to increasing life expectancy would boost labor supply and reduce the fiscal costs of aging. Second, in terms of preferable parametric policy responses, the second demographic dividend will be promoted to the highest extent by keeping taxes and debt unchanged while allowing public pensions to adjust downward. Such a policy response would keep pensions from further crowding out private saving -- thus balancing capital accumulation with intergenerational income distribution. In conclusion, Brazil will not necessarily experience a fall in saving and growth, but if government policies are appropriately, adequately, and timely formulated, population aging is likely to lead to substantial capital deepening and increases in lifetime income, wealth, and welfare.Emerging Markets,Access to Finance,Population Policies,Economic Theory&Research,Debt Markets
RE-EXAMINATION OF THE TRANSITION OF
No full textAuthor Institution: National Bureau of Standards; Naval Research LaboratoryWe have re-examined the high resolution emission bands of the Second Negative System. Particular emphasis will be placed on the determination of the sign of the spin-splitting parameter in the state and on the variation of as a function of
The U-shape without controls
No full textThis paper is a continuation of results in Blanchflower and Oswald (2008). It provides new evidence that well-being follows a curve through life. We use data on half a million randomly sampled individuals across eight major European nations. Importantly, we show that in this set of countries there is a U-shape even in unadjusted data, that is, without the inclusion of control variables. But we also advise against a focus on elementary bivariate associations
The U-Shape without Controls
No full textThis paper is a continuation of results in Blanchflower and Oswald (2008). It provides new evidence that well-being follows a curve through life. We use data on half a million randomly sampled individuals across eight major European nations. Importantly, we show that in this set of countries there is a U-shape even in unadjusted data, that is, without the inclusion of control variables. But we also advise against a focus on elementary bivariate associations.Happiness ; aging ; well-being ; mental-health ; depression ; life-course
DIRECT OBSERVATION OF THE 2 STATE OF IN A PULSED MOLECULAR BEAM: ROTATIONAL-BRANCH INTENSITY ANOMALIES IN THE 2 BANDS
No full textAuthor Institution: Department of Chemistry, Korea Advanced Institute of Science and TechnologyThe first observation of 2 transitions is reported. Rotationally resolved transitions of the 2 and 2 are observed by resonance enhanced 2-photon ionization (RE2PI) method in a pulsed molecular beam. -doubling and interference induced rotational branch intensity anomalies are observed for 2 transitions. Both of 2 and 2 states are strongly mixed with singlet slates by spin-orbit coupling. The former with 2 and the latter with 2 . In relatively weak 2 bands P-branch rotational lines disappear and the intensities of R-branch rotational lines are enhanced. These intensity anomalies in 2 transition, due to an interference effect between parallel and perpendicular transition amplitudes, is caused by perturbation. The molecular constants of 2 transition are determined as for . The spin-orbit coupling constant A and -doubling parameters p and q are determined by simultaneous fitting of the rotational contours of both 2 and 2 transitions
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