Convectively driven shear and decreased heat flux

We report on direct numerical simulations of two-dimensional, horizontally periodic Rayleigh-B\'enard convection, focusing on its ability to drive large-scale horizontal flow that is vertically sheared. For the Prandtl numbers ($Pr$) between 1 and 10 simulated here, this large-scale shear can be induced by raising the Rayleigh number ($Ra$) sufficiently, and we explore the resulting convection for $Ra$ up to $10^{10}$. When present in our simulations, the sheared mean flow accounts for a large fraction of the total kinetic energy, and this fraction tends towards unity as $Ra\to\infty$. The shear helps disperse convective structures, and it reduces vertical heat flux; in parameter regimes where one state with large-scale shear and one without are both stable, the Nusselt number of the state with shear is smaller and grows more slowly with $Ra$. When the large-scale shear is present with $Pr\lesssim2$, the convection undergoes strong global oscillations on long timescales, and heat transport occurs in bursts. Nusselt numbers, time-averaged over these bursts, vary non-monotonically with $Ra$ for $Pr=1$. When the shear is present with $Pr\gtrsim3$, the flow does not burst, and convective heat transport is sustained at all times. Nusselt numbers then grow roughly as powers of $Ra$, but the growth rates are slower than any previously reported for Rayleigh-B\'enard convection without large-scale shear. We find the Nusselt numbers grow proportionally to $Ra^{0.077}$ when $Pr=3$ and to $Ra^{0.19}$ when $Pr=10$. Analogies with tokamak plasmas are described.Comment: 25 pages, 12 figures, 5 video

Socio-cultural, environmental and health challenges facing women and children living near the borders between Afghanistan, Iran and Pakistan (AIP region)

For hundreds of years, people in the AIP region (the Afghanistan-Iran-Pakistan borders) have been challenged by conflict and political and civil instability, mass displacement, human rights abuses, drought and famine. Given this sad history, it not surprising that in this region health and quality of life of vulnerable groups are among the worst in the world. In spite of national and international efforts to improve health status of vulnerable populations in this region, the key underlying socio-cultural determinants of health and disparities, i.e. gender, language, ethnicity, residential status, and socio-economic status (SES), have not been addressed or even systematically studied, nor have their relationship to environmental challenges. Overall, the health problems faced by this under-developed region can be categorized into those resulting from lack of essential supplies and services, as well as those stemming from the existing cultural practices in the area

Stellar Hydrodynamics in Radiative Regions

We present an analysis of the response of a radiative region to waves generated by a convective region of the star; this wave treatment of the classical problem of ``overshooting'' gives extra mixing relative to the treatment traditionally used in stellar evolutionary codes. The interface between convectively stable and unstable regions is dynamic and nonspherical, so that the nonturbulent material is driven into motion, even in the absence of ``penetrative overshoot.'' These motions may be described by the theory of nonspherical stellar pulsations, and are related to motion measured by helioseismology. Multi-dimensional numerical simulations of convective flow show puzzling features which we explain by this simplified physical model. Gravity waves generated at the interface are dissipated, resulting in slow circulation and mixing seen outside the formal convection zone. The approach may be extended to deal with rotation and composition gradients. Tests of this description in the stellar evolution code TYCHO produce carbon stars on the asymptotic giant branch (AGB), an isochrone age for the Hyades and three young clusters with lithium depletion ages from brown dwarfs, and lithium and beryllium depletion consistent with observations of the Hyades and Pleiades, all without tuning parameters. The insight into the different contributions of rotational and hydrodynamic mixing processes could have important implications for realistic simulation of supernovae and other questions in stellar evolution.Comment: 27 pages, 5 figures, accepted to the Astrophysical Journa

Bridging psychology and biology - the analysis of individuals in groups

Biological systems are particularly prone to variation, and the authors argue that such variation must be regarded as important data in its own right. The authors describe a method in which individual differences are studied within the framework of a general theory of the population as a whole and illustrate how this method can be used to address three types of issues: the nature of the mechanisms that give rise to a specific ability, such as mental imagery; the role of psychological or biological mediators of environmental challenges, such as the biological bases for differences in dispositional mood; and the existence of processes that have nonadditive effects with behavioral and physiological variables, such as factors that modulate the response to stress and its effects on the immune response. Variation occurs around every central tendency, bu

The Quantity Theory of Money is Valid. The New Keynesians are Wrong!

We test the quantity theory of money (QTM) using a novel approach and a large new sample. We do not follow the usual approach of first differentiating the logarithm of the Cambridge equation to obtain an equation relating the growth rate of real GDP, the growth rate of money and inflation. These variables must then again be ‘integrated’ by averaging in order to obtain stable relationships. Instead we suggest a much simpler procedure for testing directly the stability of the coefficient of the Cambridge equation. For 125 countries and post-war data we find the coefficient to be surprisingly stable. We do not select for high inflation episodes as was done in most empirical studies; inflation rates do not even appear in our data set. Much work supporting the QTM has been done by economic historians and at the University of Chicago by Milton Friedman and his associates. The QTM was a foundation stone of the monetarist revolution. Subsequently belief in it waned. The currently dominant New Keynesian School, implicitly or explicitly denies the validity of the QTM. We survey this history and argue that the QTM is valid and New Keynesians are wrong

CHARIS Science: Performance Simulations for the Subaru Telescope's Third-Generation of Exoplanet Imaging Instrumentation

We describe the expected scientific capabilities of CHARIS, a high-contrast integral-field spectrograph (IFS) currently under construction for the Subaru telescope. CHARIS is part of a new generation of instruments, enabled by extreme adaptive optics (AO) systems (including SCExAO at Subaru), that promise greatly improved contrasts at small angular separation thanks to their ability to use spectral information to distinguish planets from quasistatic speckles in the stellar point-spread function (PSF). CHARIS is similar in concept to GPI and SPHERE, on Gemini South and the Very Large Telescope, respectively, but will be unique in its ability to simultaneously cover the entire near-infrared $J$, $H$, and $K$ bands with a low-resolution mode. This extraordinarily broad wavelength coverage will enable spectral differential imaging down to angular separations of a few $\lambda/D$, corresponding to $\sim$0.\!\!''1. SCExAO will also offer contrast approaching $10^{-5}$ at similar separations, $\sim$0.\!\!''1--0.\!\!''2. The discovery yield of a CHARIS survey will depend on the exoplanet distribution function at around 10 AU. If the distribution of planets discovered by radial velocity surveys extends unchanged to $\sim$20 AU, observations of $\sim$200 mostly young, nearby stars targeted by existing high-contrast instruments might find $\sim$1--3 planets. Carefully optimizing the target sample could improve this yield by a factor of a few, while an upturn in frequency at a few AU could also increase the number of detections. CHARIS, with a higher spectral resolution mode of $R \sim 75$, will also be among the best instruments to characterize planets and brown dwarfs like HR 8799 cde and $\kappa$ And b.Comment: 13 pages, 7 figures, proceedings from SPIE Montrea

Kepler-424 b: A "lonely" hot Jupiter that found a companion

Peer reviewedFinal Accepted Versio