Domestic factors, such as credit and preference shocks, can explain the negative correlation between house prices and the current account in the U.S. and several other countries before the recent ...crisis. These shocks, however, cannot account for the fall of world real interest rates observed in the data. Expansionary monetary policy shocks in the U.S., coupled with exchange rate pegs to the dollar in emerging economies, are crucial to understanding the evolution of the real interest rate. Yet, monetary policy factors play virtually no role for house prices and the current account.
The demographic transition can affect the equilibrium real interest rate through three channels. An increase in longevity—or expectations thereof—puts downward pressure on the real interest rate, as ...agents build up their savings in anticipation of a longer retirement period. A reduction in the population growth rate has two counteracting effects. On the one hand, capital per-worker rises, thus inducing lower real interest rates through a reduction in the marginal product of capital. On the other hand, the decline in population growth eventually leads to a higher dependency ratio (the fraction of retirees to workers). Because retirees save less than workers, this compositional effect lowers the aggregate savings rate and pushes real rates up. We calibrate a tractable life-cycle model to capture salient features of the demographic transition in developed economies, and find that its overall effect is a reduction of the equilibrium interest rate by at least one and a half percentage points between 1990 and 2014. Demographic trends have important implications for the conduct of monetary policy, especially in light of the zero lower bound on nominal interest rates. Other policies can offset the negative effects of the demographic transition on real rates with different degrees of success.
Supersonic inlets are a key component of present and future air-breathing propulsion systems for high-speed flight. The inlet design is challenging because of several phenomena that must be taken ...under control: shock waves, boundary layer separation and unsteadiness. Furthermore, the intensity of these phenomena is strongly influenced by the working conditions and so active control systems can be particularly useful in off-design conditions. In this work, a mixed compression supersonic inlet with a double wedge ramp is considered. The flow field was numerically investigated at different values of Mach number. The simulations show that large separations appear at the higher Mach numbers on both the upper and lower walls of the duct. In order to improve the performances of the inlet two different control strategies were investigated: plasma actuators and bleed. Different locations of the plasma actuator are considered in order to also apply this technology to configurations with a diverter which prevents boundary layer ingestion. The potential of the proposed solutions is investigated in terms of total pressure recovery, flow distortion and power consumption.
We introduce liquidity frictions into an otherwise standard DSGE model with nominal and real rigidities and ask: can a shock to the liquidity of private paper lead to a collapse in short-term nominal ...interest rates and a recession like the one associated with the 2008 US financial crisis? Once the nominal interest rate reaches the zero bound, what are the effects of interventions in which the government provides liquidity in exchange for illiquid private paper? We find that the effects of the liquidity shock can be large, and show some numerical examples in which the liquidity facilities of the Federal Reserve prevented a repeat of the Great Depression in the period 2008-2009.
Photon-counting detector (PCD) CT is a new CT technology utilizing a direct conversion X-ray detector, where incident X-ray photon energies are directly recorded as electronical signals. The design ...of the photon-counting detector itself facilitates improvements in spatial resolution (via smaller detector pixel design) and iodine signal (via count weighting) while still permitting multi-energy imaging. PCD-CT can eliminate electronic noise and reduce artifacts due to the use of energy thresholds. Improved dose efficiency is important for low dose CT and pediatric imaging. The ultra-high spatial resolution of PCD-CT design permits lower dose scanning for all body regions and is particularly helpful in identifying important imaging findings in thoracic and musculoskeletal CT. Improved iodine signal may be helpful for low contrast tasks in abdominal imaging. Virtual monoenergetic images and material classification will assist with numerous diagnostic tasks in abdominal, musculoskeletal, and cardiovascular imaging. Dual-source PCD-CT permits multi-energy CT images of the heart and coronary arteries at high temporal resolution. In this special review article, we review the clinical benefits of this technology across a wide variety of radiological subspecialties.
Interest rate decisions by central banks are universally discussed in terms of Taylor rules, which describe policy rates as responding to inflation and some measure of the output gap. We show that an ...alternative specification of monetary policy, in which the interest rate tracks the Wicksellian efficient rate of return as the primary indicator of real activity, fits the U.S. data better than otherwise identical Taylor rules. This result holds for a variety of specifications of the other ingredients of the policy rule, including the output gap, and of private agents׳ behavior.
•Taylor rules respond to the output gap as a measure of real activity.•W rules track the Wicksellian efficient rate of return instead.•W rules fit the U.S. data better than equivalent Taylor rules.•This result does not depend on the measurement of the output gap.•It is also robust across two different models of private agents׳ behavior.
The US external deficits have been the most striking manifestation of global imbalances. This paper investigates the contribution of productivity growth, demographics and fiscal policy in accounting ...for the evolution of the US external imbalances against industrialized countries during the last three decades. Productivity growth plays a dominant role. Demographics explain a non-negligible and nearly permanent component of the US trade deficit. Furthermore, the international demographic transition is crucial for large US external imbalances to be consistent with the persistent decline of world real interest rates observed in the data. Fiscal policy is of minor importance.
Highlights • Surgery leads to better results at an average follow-up of at least 6 months, followed by infiltrations. • Complications and failures for every treatment are not always reported in ...studies. • High level of evidence studies are needed.
Hybrid rocket engines are a green alternative to solid rocket motors and may represent a low-cost alternative to kerosene fueled rockets, while granting performance and control features similar to ...that of typical storable liquid rocket engines. In this work, the design of a three-stage hybrid launcher is optimized by means of a coupled procedure: an evolutionary algorithm optimizes the engine design, whereas an indirect optimization method optimizes the corresponding ascent trajectory. The trajectory integration also provides the vertical emission profiles required for the evaluation of the environmental impact of the launch. The propellants are a paraffin-based wax and liquid oxygen. The vehicle is launched from the ground and uses an electric turbo pump feed system. The initial mass is given (5000 kg) and the insertion of the payload into a 600-km circular, and polar orbit is considered as a reference mission. Clusters of similar hybrid rocket engines, with only few differences, are employed in all stages to reduce the development and operational costs of the launcher. Optimization is carried out with the aim of maximizing the payload mass and then minimizing the overall environmental impact of the launch. The results show that satisfactory performance is achievable also considering rocket polluting emissions: the carbon footprint of the launch can be reduced by one fourth at the cost of a 5-kg payload mass reduction.
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