Numerical Study of Three-dimensional Spatial Instability of a Supersonic Flat Plate Boundary Layer

The behavior of spatially growing three-dimensional waves in a supersonic boundary layer was studied numerically by solving the complete Navier-Stokes equations. Satisfactory comparison with linear parallel and non-parallel stability theories, and experiment are obtained when a small amplitude inflow disturbance is used. The three-dimensional unsteady Navier-Stokes equations are solved by a finite difference method which is fourth-order and second-order accurate in the convection and viscous terms respectively, and second-order accurate in time. Spanwise periodicity is assumed. The inflow disturbance is composed of eigenfunctions from linear stability theory. By increasing the amplitude of the inflow disturbance, nonlinear effects in the form of a relaxation type oscillation of the time signal of rho(u) are observed

Some unpleasant arithmetics of regional unemployment in the EU. Are there any lessons for EMU?

Several studies have documented the weak response of regional wage differentials and labour mobility following region-specific (“idiosyncraticâ€) shocks in the average of the EU countries. This has been often taken as evidence of the rigidity of labour markets in European countries, as opposed to the flexibility of the USA. However, as such shocks by definition average to zero, one cannot make an explicit link between the (lack of) adjustment at regional level and aggregate unemployment. Moreover, the emphasis on the reaction to short-run idiosyncratic shocks is unlikely to explain the permanent differentials across regions, which characterise the regional distribution of unemployment in many EU countries. This paper tries to provide a better understanding of the regional distribution of unemployment and why region-specific shocks can matter for aggregate unemployment. It does so by explicitly considering the possibility of asymmetric reactions, so that unemployment rises more in poorer areas suffering an adverse shock than it declines in richer regions experiencing a favourable shock. The reason behind such asymmetries is the presence of a wage floor in the poorer regions resulting from policy centralisation, as for instance in the case of a national unemployment compensation system, which provides benefits that are uniform across regions. If such a mechanism is at work, aggregate unemployment tends to be “inflated†by region-specific shocks that are inequality- increasing. After presenting an illustrative model of the mechanism, the paper proposes a simple measure of the resulting “excess unemploymentâ€, based on the difference between the average (national) unemployment rate and the unemployment rate of the median region. It also examines the relationship between regional asymmetries in unemployment and the dispersion of productivity across regions, taken as proxy of the inequality-increasing shocks. The evidence, while not entirely conclusive, justifies two tentative policy conclusions, which are particularly relevant in the context of EMU: a) to avoid centralisation of labour market institutions at the EU level that may end up inflating aggregate unemployment; b) to effectively deploy regional policies to combat inequality- increasing shocks.regional policy, unemployment, disparities

On the gap-opening criterion of migrating planets in protoplanetary disks

We perform two-dimensional hydrodynamical simulations to quantitatively explore the torque balance criterion for gap-opening (as formulated by Crida et al. 2006) in a variety of disks when considering a migrating planet. We find that even when the criterion is satisfied, there are instances when planets still do not open gaps. We stress that gap-opening is not only dependent on whether a planet has the ability to open a gap, but whether it can do so quickly enough. This can be expressed as an additional condition on the gap-opening timescale versus the crossing time, i.e. the time it takes the planet to cross the region which it is carving out. While this point has been briefly made in the previous literature, our results quantify it for a range of protoplanetary disk properties and planetary masses, demonstrating how crucial it is for gap-opening. This additional condition has important implications for the survival of planets formed by core accretion in low mass disks as well as giant planets or brown dwarfs formed by gravitational instability in massive disks. It is particularly important for planets with intermediate masses susceptible to Type III-like migration. For some observed transition disks or disks with gaps, we expect that estimates on the potential planet masses based on the torque balance gap-opening criterion alone may not be sufficient. With consideration of this additional timescale criterion theoretical studies may find a reduced planet survivability or that planets may migrate further inwards before opening a gap.Comment: Accepted by ApJ, 22 pages, 13 figures, 6 table

Zeno and anti-Zeno polarization control of spin-ensembles by induced dephasing

We experimentally and theoretically demonstrate the purity (polarization) control of qubits entangled with multiple spins, using induced dephasing in nuclear magnetic resonance (NMR) setups to simulate repeated quantum measurements. We show that one may steer the qubit ensemble towards a quasi-equilibrium state of certain purity, by choosing suitable time intervals between dephasing operations. These results demonstrate that repeated dephasing at intervals associated with the anti-Zeno regime lead to ensemble purification, whereas those associated with the Zeno regime lead to ensemble mixing.Comment: Main Text: 5 pages, 2 figures. Sup. Inf.: 5pages, 1 figur

Reaching the millennium development goal for child mortality : improving equity and efficiency in Ecuador's health budget

health care; infant mortality; health policy;