Wind tunnel flow generation section

A flow generation section for a wind tunnel test facility is described which provides a uniform flow for the wind tunnel test section over a range of different flow velocities. The throat of the flow generation section includes a pair of opposed boundary walls which are porous to the flowing medium in order to provide an increase of velocity by expansion. A plenum chamber is associated with the exterior side of each of such porous walls to separate the same from ambient pressure. A suction manifold is connected by suction lines with each one of the chambers. Valves are positioned in each of the lines to enable the suction manifold to be independently varied

Jet engine air intake system

An axisymmetric air intake system for a jet aircraft engine comprising a fixed cowl extending outwardly from the face of the engine, a centerbody coaxially disposed within the cowl, and an actuator for axially displacing the centerbody within the cowl was developed. The cowl and centerbody define a main airflow passageway therebetween, the configuration of which is changed by displacement of the centerbody. The centerbody includes a forwardly-located closeable air inlet which communicates with a centerbody auxiliary airflow passageway to provide auxiliary airflow to the engine. In one embodiment, a system for opening and closing the centerbody air inlet is provided by a dual-member centerbody, the forward member of which may be displaced axially with respect to the aft member

Aircraft engine nozzle

A variable area exit nozzle arrangement for an aircraft engine was a substantially reduced length and weight which comprises a number of longitudinally movable radial vanes and a number of fixed radial vanes. The movable radial vanes are alternately disposed with respect to the fixed radial vanes. A means is provided for displacing the movable vanes along the longitudinal axis of the engine relative to the fixed radial vanes which extend across the main exhaust flow of the engine

Advanced porous transonic wind-tunnel nozzles

Advances in the design and control of the porous bleed flow distribution along the nozzle walls solves the problem of nonuniform flow at off-design conditions. This is accomplished in a two dimensional nozzle with porous parallel sidewalls backed with a single plenum chamber and employing a sliding compartment wall or backed with multiple plenum chambers within which the pressure can be controlled

Incommensurability in the magnetic excitations of the bilinear-biquadratic spin-1 chain

We study the magnetic excitation spectrum of the S=1 quantum Heisenberg spin chain with Hamiltonian : H = sum_i cos(theta) S_i S_i+1 + sin(theta) (S_i S_i+1)^2. We focus on the range -pi/4 < theta < +pi/4 where the spin chain is in the gapped Haldane phase. The excitation spectrum and static structure factor is studied using direct Lanczos diagonalization of small systems and density-matrix renormalization group techniques combined with the single-mode approximation. The magnon dispersion has a minimum at q=pi until a critical value theta_c = 0.38 is reached at which the curvature (velocity) vanishes. Beyond this point, which is distinct from the VBS point and the Lifshitz point, the minimum lies at an incommensurate value that goes smoothly to 2pi/3 when theta approaches pi/4, the Lai-Sutherland point. The mode remains isolated from the other states: there is no evidence of spinon deconfinement before the point theta =+pi/4. These findings explain recent observation of the magnetization curve M approx (H -H_c)^1/4 for theta =theta_c.Comment: 14 pages, 8 encapsulated figures, REVTeX 3.

Is state fiscal policy asymmetric over the business cycle?

A number of stabilizers are thought to mute the business cycle. One key stabilizer is federal fiscal policy. The federal budget surplus tends to rise during economic booms and fall in downturns, helping to stabilize consumers’ disposable income and thereby mitigate economic fluctuations. During booms, for example, the budget surplus typically rises because tax revenues rise more than expenditures.> Another stabilizer that has traditionally received less attention is state fiscal policy. Like the federal budget surplus, state government surpluses tend to rise during economic expansions and decline during downturns. Moreover, like the federal budget, state budgets represent large shares of the economy. The stabilizing influence of state fiscal policy, however, may differ across business cycle expansions and downturns – making state fiscal policy asymmetric. For example, state budgets could be more effective at mitigating economic slumps than at muting booms if taxes fall more sharply during a slump than they rise in an expansion of equal magnitude. Asymmetry in fiscal policy could be caused by a number of factors, such as balanced budget rules, which are constitutionally imposed restrictions on a state government’s ability to incur debt.> Sorensen and Yosha examine the business cycle behavior of state fiscal policy to determine whether policy is asymmetric and, if so, to identify the causes. They conclude that state revenue and expenditure display significant asymmetry over the business cycle, with nearly offsetting effects on the budget surplus. As a result, state fiscal policy tends to mute economic booms to roughly the same degree it mitigates slowdowns. The asymmetries in revenue and expenditure appear to be associated with balanced budget rules, although their fundamental causes cannot be clearly identified.Fiscal policy ; Business cycles

Is risk sharing in the United States a regional phenomenon?

Regions within the United States routinely experience economic fluctuations that differ from those of other regions. For example, in the past few years, falling wheat prices have slowed growth in the value of total output in Kansas. Such developments can pose concerns for policymakers because macroeconomic tools like monetary policy affect all regions, not just specific regions. Fortunately, several mechanisms help insulate regional income and consumption from region-specific output fluctuations. Diversification of asset ownership across regions, made possible by national capital markets, smoothes regional income and, in turn, consumption. The federal tax system also helps protect regional income and consumption from region- specific changes in output. Finally, adjustments to saving further insulate consumption from variation in output. In effect, each of these mechanisms mitigates the effect of region-specific economic fluctuations by pooling risks across regions--by providing risk sharing.> Although earlier research has documented the pattern of risk sharing for the United States as a whole, patterns may differ across broad regions of the nation. Eastern states, for example, may benefit more from income smoothing through capital markets due to their proximity to Wall Street. Moreover, geographic distance may affect whether and how risk is shared. For instance, it may be easier for Kansas residents to own property, such as a farm or hotel, in Colorado than in Massachusetts. Similarly, business owners in Kansas are more likely to obtain loans in Missouri than in New York. In this case, geography may affect the ability of risk sharing to mitigate region-specific fluctuations in output. Because geography matters, this article examines whether risk sharing occurs more in some regions than in others and whether risk sharing is greater within large regions of the United States than between regions.> Sorensen and Yosha present the conceptual framework of risk sharing and develop a method for estimating the amount of risk sharing provided by different mechanisms. They report estimates of risk sharing patterns within and across a set of large U.S. regions. These estimates reveal some important regional differences. Moreover, the estimates indicate there is more overall risk sharing within regions than between regions. The risk sharing provided by capital markets and the federal tax system is essentially the same within and across regions, implying that these are nationwide mechanisms. In contrast, risk sharing through saving adjustments is more local, occurring just within regions.Risk

Risk Sharing among OECD and EU Countries: The Role of Capital Gains, Capital Income, Transfers, and Saving

We estimate the amount of income and consumption smoothing (risk sharing) between OECD countries during the period 1970{2003 with a particular focus on EU and EMU countries. Income smoothing from international factor income has increased in the EU and, in particular, the EMU but not in the non-EU OECD since the introduction of the Euro. Consumption smoothing from pro-cyclical government saving has declined in the EMU, but not in the non-EU OECD, since the signing of the Maastricht treaty. We find that when capital gains and losses on international asset positions are considered part of income, the magnitude of capital gains leads to huge amounts of income smoothing and dis-smoothing although, at the time horizons we examine, the capital gains or losses are only weakly reflected in consumption. Understanding the role of capital gains in risk sharing appears to be of first order importance.Government De¯cits, Income Insurance, International Capital Markets, International Integration, Risk Sharing, External Capital Gains

Electric arc device for heating gases Patent

Electric arc device for minimizing electrode ablation and heating gases to supersonic or hypersonic wind tunnel temperature