Attenuation of stress waves in single and multi-layered structures

Analytical and experimental studies were made of the attenuation of the stress waves during passage through single and multilayer structures. The investigation included studies on elastic and plastic stress wave propagation in the composites and those on shock mitigating material characteristics such as dynamic stress-strain relations and energy absorbing properties. The results of the studies are applied to methods for reducing the stresses imposed on a spacecraft during planetary or ocean landings

Optimum design of structures of composite materials in response to aerodynamic noise and noise transmission

Elastic wave propagation and attenuation in a model fiber matrix was investigated. Damping characteristics in graphite epoxy composite materials were measured. A sound transmission test facility suitable to incorporate into NASA Ames wind tunnel for measurement of transmission loss due to sound generation in boundary layers was constructed. Measurement of transmission loss of graphite epoxy composite panels was also included

A Multivariate GARCH Model with Time-Varying correlations

In this paper we propose a new multivariate GARCH model with time- varying correlations. We adopt the vech representation based on the conditional variances and the conditional correlations. While each conditional-variance term is assumed to follow a univariate GARCH formulation, the conditional-correlation matrix is postulated to follow an autoregressive moving average type of analogue. By imposing some suitable restrictions on the conditional-correlation-matrix equation, we construct a MGARCH model in which the conditional-correlation matrix is guaranteed to be positive definite during the optimisation. Thus, our new model retains the intuition and interpretation of the univariate GARCH model and yet satisfies the positive-definite condition as found in the constant-correlation and BEKK models. We report some Monte Carlo results on the finite-sample distributions of the MLE of the varying- correlation MGARCH model. The new model is applied to some real data sets. It is found that extending the constant-correlation model to allow for time-varying correlations provides some interesting time histories that are not available in a constant-correlation model.BEKK model, constant correlation, Monte Carlo method, multivariate GARCH model, maximum likelihood estimate, varying correlation

Medical Savings Accounts in Singapore: How much is adequate?

While many studies have examined the cost-containment aspect of Medical savings accounts (MSA), few have investigated the adequacy of MSA to finance the health care expenditure. This paper estimates the present value of lifetime healthcare expenses (PVHE) of the Singaporean male and female elderly upon retirement at age 62. The estimation involves calibrating the stream of future healthcare expenditure; stochastic forecasting of cohort survival probabilities; and discounting the projected lifetime healthcare expenditure. Estimated values of the PVHE under various scenarios are used to assess the adequacy of the government-decreed minimum saving to be maintained in the MSA.medical savings accounts, present value of lifetime health care expense, cohort survival probabilities

A Multivariate GARCH Model with Time-Varying Correlations

In this paper we propose a new multivariate GARCH model with time-varying correlations. We adopt the vech representation based on the conditional variances and the conditional correlations. While each conditional-variance term is assumed to follow a univariate GARCH formulation, the conditional-correlation matrix is postulated to follow an autoregressive moving average type of analogue. By imposing some suitable restrictions on the conditional-correlation-matrix equation, we manage to construct a MGARCH model in which the conditional-correlation matrix is guaranteed to be positive definite during the optimisation. Thus, our new model retains the intuition and interpretation of the univariate GARCH model and yet satisfies the positive-definite condition as found in the constant-correlation and BEKK models. We report some Monte Carlo results on the finite-sample distributions of the QMLE of the varying-correlation MGARCH model. The new model is applied to some real data sets. It is found that extending the constant-correlation model to allow for time-varying correlations provides some interesting time histories that are not available in a constant-correlation model.

Monetizing Housing Equity to Generate Retirement Incomes

The public housing program and the unique way of financing housing through the mandatory savings system in Singapore have created a class of homeowners. This paper compares the instruments available to different flat owners to monetize their assets, including the Lease Buyback Scheme (LBS), subletting, downsizing and reverse mortgage. We estimate the present value of retirement incomes derived from these options by incorporating the survival probability which is forecasted using the Lee-Carter demographic model. We compare the monthly payouts that can be unlocked and discuss the tradeoffs of adequate retirement with the elderly preference for leaving a bequest and ageing in place. Our results show that LBS is the most attractive option. It allows the elderly to age-inplace while generating a steady stream of monthly drawdown and possibility of leaving a bequest. Subletting releases housing equity while retaining the asset. This helps the elderly to fulfill their bequest motive. Reverse mortgage is the least attractive option, yielding the lowest retirement income due to high loading factors.