The Value of Health and Longevity

We develop an economic framework for valuing improvements to health and life expectancy, based on individuals' willingness to pay. We then apply the framework to past and prospective reductions in mortality risks, both overall and for specific life-threatening diseases. We calculate (i) the social values of increased longevity for men and women over the 20th century; (ii) the social value of progress against various diseases after 1970; and (iii) the social value of potential future progress against various major categories of disease. The historical gains from increased longevity have been enormous. Over the 20th century, cumulative gains in life expectancy were worth over $1.2 million per person for both men and women. Between 1970 and 2000 increased longevity added about$3.2 trillion per year to national wealth, an uncounted value equal to about half of average annual GDP over the period. Reduced mortality from heart disease alone has increased the value of life by about $1.5 trillion per year since 1970. The potential gains from future innovations in health care are also extremely large. Even a modest 1 percent reduction in cancer mortality would be worth nearly$500 billion.

Why Has the Natural Rate of Unemployment Increased over Time?

macroeconomics, unemployment

Entry, Pricing and Product Design in an Initially Monopolized Market

We analyze entry, pricing and product design in a model with differentiated products. Under plausible conditions, entry into an initially monopolized market leads to higher prices for some, possibly all, consumers. Entry can induce a misallocation of goods to consumers, segment the market in a way that transfers surplus to producers and undermine aggressive pricing by the incumbent. Post entry, firms have strong incentives to modify product designs so as to raise price by strengthening market segmentation. Firms may also forego socially beneficial product improvements in the post-entry equilibrium, because they intensify price competition too much. Multi-product monopoly can lead to better design incentives than the non-cooperative pricing that prevails under competition.

A view of Estimation of Distribution Algorithms through the lens of Expectation-Maximization

We show that a large class of Estimation of Distribution Algorithms, including, but not limited to, Covariance Matrix Adaption, can be written as a Monte Carlo Expectation-Maximization algorithm, and as exact EM in the limit of infinite samples. Because EM sits on a rigorous statistical foundation and has been thoroughly analyzed, this connection provides a new coherent framework with which to reason about EDAs

Investigation of Reduced-Order Modeling for Aircraft Stability and Control Prediction

High-fidelity computational fluid dynamics tools offer the potential to approximate increments for ground-to-flight scaling effects, as well as to augment the dynamic damping derivative data for motion-based flight simulators. Unfortunately, the computational expense is currently prohibitive for populating a complete simulator database. This work investigates an existing surrogate-based, indicial response reduced-order model methodology as a means to efficiently augment a flight simulator database with high-fidelity nonlinear aerodynamic damping derivatives. Creation of the reduced-order model is based on the superposition integrals of the step response with the derivative of its corresponding input signal. Step responses are calculated using a computational grid motion approach that separates the effects of angle of attack and sideslip angle from angular rates, and rates from angle of attack and sideslip. It is demonstrated that the transients produced during the start of a forced-oscillation motion are captured by the reduced-order model to the level of fidelity of a comparable computational solution. Aerodynamic coefficients computed within minutes by the reduced-order model for an aircraft undergoing an 18-second half Lazy-8 maneuver and a 25-second Immelmann turn maneuver are compared with those from full computational flight solutions that required days to complete. Finally, a cost-benefit assessment is included that demonstrates a compelling advantage for this approach. d for maneuvering, flexible vehicles

Unsteady Model Estimation for Generic T-Tail Transport Aircraft Using Computational Data

Models including nonlinear and unsteady behaviors are developed for the longitudinal axis of the NASA Generic T-Tail Aircraft over a large range of angle of attack. These models are based on computational simulations of forced-oscillation tests in a wind tunnel. This work continues a recent study and an ongoing effort by NASA to improve aircraft simulations for pilot training in loss-of-control and stalled conditions. The objective of this work is to develop appropriate aerodynamic models that provide representative responses in simulation for a given class of aircraft. In the stall region, nonlinear unsteady responses are often present and may require an extended aerodynamic model compared to that used in the conventional flight envelope. In this study, two objectives are addressed. The first is to obtain representative models for the NASA Generic T-Tail aircraft over a wide range of angle of attack and the second is to continue development of a specialized CFD test technique that uses Schroeder sweeps to create information rich responses for unsteady aerodynamic model identification

Pilot Sensitivity to Simulator Flight Dynamics Model Formulation for Stall Training

A piloted simulation study was performed in the Cockpit Motion Facility at the National Aeronautics and Space Administration Langley Research Center. The research was motivated by the desire to reduce the commercial transport airplane fatal accident rate due to in-flight loss of control. The purpose of this study, which focused on a generic T-tail transport airplane, was to assess pilot sensitivity to flight dynamics model formulation used during a simulator stall recognition and recovery training/demonstration profile. To accomplish this, the flight dynamics model was designed with many configuration options. The model options were based on recently acquired static and dynamic stability and control data from sources that included wind tunnel, water tunnel, and computational fluid dynamics. The results, which are specific to a transport airplane stall recognition and recovery guided demonstration scenario, showed the two most important aerodynamic effects (other than stick pusher) to model were stall roll- off and the longitudinal static stability characteristic associated with the pitch break

Assessment of respiratory motor units in the mdx mouse model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a fatal neuromuscular disease characterised by the absence of the structural protein dystrophin. Respiratory failure is the leading cause of premature death in DMD. Although respiratory insufficiency is recognized as a hallmark of DMD, respiratory control is relatively understudied. We hypothesized that enhanced drive in respiratory motor pathways preserves ventilatory capacity compensating for severe respiratory muscle weakness. Male wild-type (n=23) and mdx (n=23) mice were studied. Breathing was examined during normoxia and chemo-challenge with hypercapnic-hypoxia. In urethane (1.7 g/kg i.p.) anaesthetised mice, diaphragm, external intercostal and genioglossus electromyogram (EMG) and motor unit recordings were performed during baseline conditions and in response to chemo-stimulation. Diaphragm muscle function was examined ex vivo. Diaphragm muscle function is severely impaired in young mdx mice. Despite substantial diaphragm muscle weakness, freely-behaving mdx mice can increase ventilation during chemostimulation with hypercapnic-hypoxia. Motor unit recordings revealed an increase in the number of active units for diaphragm and genioglossus muscle. There were no major differences in the firing frequency of motor units in the respiratory muscles. Diaphragm EMG activity was depressed in mdx mice during baseline and maximum chemostimulation, compared to wild-type. In conclusion, severe mechanical disadvantage of the diaphragm is evident across a range of stimulation frequencies, yet there is a preserved capacity to raise ventilation in young mdx mice indicating a significant ventilatory reserve. Motor unit remodelling is evident in the diaphragm of mdx mice, but ultimately diaphragm EMG activity is impaired. The combination of reduced neural activation of the diaphragm and intrinsic weakness reveals major compromise in the neuromuscular function of the diaphragm in mdx mice as early as 8 weeks of age. The novel observations of this study coupled with other work by our group suggest that support from accessory muscles is critical to the support of respiratory performance in mdx mice, which may have relevance to DMD

Efficient Unsteady Model Estimation Using Computational and Experimental Data

Improving aircraft simulations for pilot training in loss-of-control and stalled conditions is one goal of NASA research in the System Wide Safety Program. One part of this effort is to develop appropriate generic aerodynamic models that provide representative responses in simulation for a given class of aircraft. In this part of the flight envelope nonlinear unsteady responses are often present and may require an extended aerodynamic model compared to that used in the conventional flight envelope. In this preliminary study, two objectives are addressed. First, to obtain a representative model for a NASA generic aircraft at an unsteady condition in the flight envelope and second, to evaluate the techniques involved. To meet these objectives, two different generic aircraft configurations are modeled using both experimental and analytical data. With these results, an initial assessment of the efficiency and quality of the tools and test techniques are evaluated to develop guidance for analytical and experimental approaches to unsteady modeling