Range Of Plausible Parameter Values Research Articles

A Time‐resolved Photometric Study of the Eclipsing Dwarf Nova RX J0909+1849

ABSTRACTMulticolor (BVRI) light curves have been obtained for the newly discovered, 4.21 hr eclipsing dwarf nova RX J0909+1849. The eclipse profiles have been analyzed with a parameter‐fitting model to constrain properties of the system. The model assumes four sources of luminosity: the white dwarf primary star and the secondary star (both assumed to radiate as blackbodies) and an accretion disk characterized as a blackbody whose temperature follows a radial power‐law distribution:T(r) = Td(Rd/r)α, where Td and Rd are the outer disk temperature and radius, respectively. The model also includes an optically thick bright spot at the intersection of the mass transfer stream and the disk periphery. A matrix of model solutions is computed, which covers an extensive range of plausible parameter values. The solution matrix is then explored to determine the optimum values for the fitting parameters and their associated errors.The mass ratio of RX J0909+1849 is unknown, thus the orbital inclination is not tightly constrained by the model. Five mass ratios have been considered spanning a range of plausible values,0.3≤q(= M2/M1)≤0.7. Over this range of q, the inclination varies between roughly 74° and 80°. Model parameters include the temperatures of the white dwarf (T1) and the secondary star (T2), the radius (Rd) and temperature (Td) of the disk periphery, the disk power‐law temperature exponent (α), and the bright spot temperature (Ts). With the exception of the q = 0.3 models, which required a relatively hot white dwarf (80,000 K), the optimum values of the parameters are nearly constant with mass ratio. For a representative mass ratio of q = 0.5, values of T1 = 26,000 ± 14,000 K,Ts = 18,000 ± 7000 K,Td = 3200 ± 600 K,Rd/RL1 = 0.54 ± 0.08,α = 0.53 ± 0.11, and B−V = 0.45 ± 0.07 are found. A value of T2 = 3400 K has been adopted for all models based on the spectral type of the secondary star (M3–M4).The observed color (B−V = 0.4 ± 0.2) is consistent with the colors given by the model; thus, it is unlikely that RX J0909+1849 suffers significant interstellar absorption. The observed spectral type of the secondary star suggests an absolute magnitude in the range 10.6<MV(2)<11.0. After correcting the apparent V magnitude at mideclipse by the fraction of light originating from the secondary star (∼94%), a distance of ∼200–250 pc is derived for the RX J0909+1849 system.

Could Condoms Stop the AIDS Epidemic?

Although therapeutic treatment strategies appear promising for retarding the progression of HIV‐related diseases, prevention remains the most effective strategy against the HIV/AIDS epidemic. This paper focuses on the effect of condom use as a single‐strategy approach in HIV prevention in the absence of any treatment. There are two primary factors in the use of condoms to halt the HIV/AIDS epidemic: condom efficacy and compliance. Our study is focused on the effect of these factors in stopping the epidemic by constructing a new deterministic mathematical model. The current estimate of condom effectiveness against HIV transmission, based on the latest meta‐analysis, is 60–96%, with a mean of 87%. Since the parameter estimates are subject to different kinds of uncertainty, to achieve adequate quality assurance in predictions, uncertainty and sensitivity analyses are carried out using latin hypercube sampling (LHS) and partial rank correlation coefficients (PRCCs). Using stability and sensitivity analyses, based on a plausible range of parameter values, key parameters that govern the persistence or eradication of HIV are identified. This analysis shows that the product of efficacy and compliance, which we call ‘preventability’ (p), has a negative effect on the epidemic; as increasing p decreases the level of epidemicity. It is also shown that the threshold preventability (pc) increases with increasing average number of HIV‐infected partners of susceptible individuals, especially those in the AIDS stage. For populations where the average number of HIV‐infected partners is large, the associated preventability threshold is high and perhaps unattainable, suggesting that for such a population, HIV may not be controlled using condoms alone. On the other hand, for a population where the average number of HIV‐infected partners is low (within a reasonable range), it is shown that pc is about 75%, suggesting that the epidemic could be stopped using condoms. Thus, for such a population, public health measures that can bring preventability above the threshold and continuous quantitative monitoring to make sure it stays there, are what would be necessary. In other words, for populations with reasonable average numbers of HIV‐infected partners, given the will and effort, it is within our means to halt this epidemic using condoms.

Optimal saving policy for exhaustible resource economies

The paper examines the optimal saving policy for a small exhaustible resource-exporting economy (ERE) that has an exhaustible asset and a reproducible capital stock. It shows that, both in magnitude and time profile, the optimal saving policy for an ERE sharply differs from (a) that of a nonextractive economy and (b) that derived from the conventional models of growth with exhaustible resources. These differences arise from the specific economic features that distinguish the small resource-exporting developing economies both from other developing economies and from mature industrial ones. For a wide range of plausible parameter values, comparisons of computed optimal saving paths with actual savings rates of selected EREs suggest substantial deficiencies in their savings rates.

Chaotic Behaviour in a Simple Model of Inflation

A simple model of inflation is proposed. The model is set in discrete time and consists of a demand for money equation, a government budget constraint and two alternative mechanisms for the formation of expectations of the inflation rate—adaptive expectations and rational expectations. It is shown that when expectations are adaptive the model can exhibit chaotic behaviour for a range of plausible parameter values, but with rational expectations chaotic behaviour is not possible.

On the existence of a hole-hole bound state in ceramic superconductors due to the high polarizability of oxygen ions

Real-space pairing of two holes in strontium titanate is investigated, depending on various model parameters. The net attraction is mediated by the high polarizability of the oxygen ions in the crystal. Pairing is found to happen for quite a wide range of plausible parameter values. Based on the fact that there are similar oxygen octahedra in the ceramic superconductors, we conjecture that this electronic pairing mechanism may well be important in these materials.

Estimating bivariate errors-in-variables models with instrumental variables

The bivariate errors-in-variables model is considered with a new choice of instrumental variables. A new estimate of the regression coefficient, based on these instrumental variables, has attractive properties over the ordinary least square estimator and Wald's estimator. Monte Carlo simulation studies indicate that the proposed estimator is than its competitors over a range of plausible parameter values, where better is defined in terms of mean square error and Pitman's nearness criterion. Finally, we use actual data from an assessment equity study to show that our proposed method produces estimators that, appear superior to those produced by the ordinary least square estimator and Wald's estimator

Global warming and the evaluation of fuel substitution strategies: on why policy should be left to the politicians

It is often taken for granted that substituting natural gas for oil will serve to reduce the greenhouse emissions of the energy sector, and executing such substitution is thus seen as a coherent policy response to the problem of global warming. In this paper we argue that such a policy is ill–founded because the supposition on which it rests is based on an incomplete consideration of the comparative pollution characteristics of the two fuels. The consideration is incomplete in two senses: (i) authors focus on emissions of carbon dioxide to the virtual exclusion of the secondary greenhouse gases, and (ii) attention is paid only to those emissions which result from fuel combustion, rather than to emissions from the entire fuel cycle (including extraction, distribution and storage). In this paper we adopt a simple, empirical 'emissions–accounting' framework [28]. Using a range of plausible parameter values it is demonstrated that the 'greenhouse friendliness' ranking of natural gas and oil is highly ambiguous. We cite very recent engineering estimates of methane leakage associated with commercial natural gas distribution and go on to demonstrate that natural gas usage may result in the emission of more greenhouse gases than oil usage. The ambiguity in the ranking is driven by two major uncertainties, one technological and one political. The most significant implication is that the resolution of the technical uncertainty surrounding the greenhouse effect and man's impact upon global climate will not be sufficient to determine what constitutes an effective policy response. The determination of policy will be an essentially political problem. Policy formulation and determination should, as the title suggests, be left to the politicians.

Variable labour supply and the pure theory of international trade: An empirical note

Previous writers have shown that variable labour supply may lead to perverse price output responses in the two-sector Heckscher-Ohlin model. This note attempts to assess the empirical likelihood, as opposed to the theoretical possibility, of such perversities. Using a range of plausible parameter values, we conclude that cases of a perverse price-output response consistent with dynamic stability of the model, though theoretically possible, are unlikely to arise in practice.

Long-Run Tax Incidence: A Comparative Dynamic Approach

The long-run incidence of tax changes has typically been analysed from a comparison of steady states. The recent contributions of Feldstein (1974) and Grieson (1975) consider the comparative steady-state effects of substituting a tax on capital income for a tax on income in standard single-sector neo-classical growth models with a constantly growing supply.' This is a natural extension of the comparative stationary-state tax incidence studies of Harberger (1962), Mieszkowski (1967) and many subsequent authors,2 and it has the merit that it is algebraically quite simple to analyse. The results obtained in the long-run models are in striking contrast to those obtained in the models with fixed capital stocks. In a static model with fixed factor supplies, a general-factor tax is entirely borne by the factor whose income is taxed.3 Under reasonable assumptions about elasticities of substitution in production and demand, a partial factor tax (e.g. corporate income tax) will also be largely borne by the owners of the partially-taxed factor. In the long run, however, radically different results can occur owing to the ability of the taxed factor to shift the tax by an induced change in factor proportions in the economy. Thus, Feldstein finds that for a wide range of plausible parameter values, a substantial fraction of the burden of a general profits tax is borne by labour (page 505). Similarly, Grieson finds that substitution of a wage for a profits tax may well make wage earners better off since the increased capital-labour ratio may cause the gross-of-tax wage rate to rise by more than tax payments on wages. It would be premature to derive policy prescriptions from these results based on a comparison of steady states. The difficulty is that economies may never reach the steady state either before or after the tax changes under consideration and, therefore, at best comparative steady-state analysis may indicate only long-run tendencies.4 Since the process of tax shifting through a change in capital accumulation takes time, comparative steadystate analysis may be quite inappropriate for considering the effects of tax changes over more limited time horizons. In this paper, we shall analyse the effect of tax changes on the growth path of an economy between two arbitrary points of time in a single-sector neoclassical model similar to those used by Feldstein and Grieson. The method of analysis, which we may call comparative dynamics, allows us to study the process of tax shifting over time. While the analysis is not restricted to the steady state, we can use it to study the movement of the economy from one steady state to another in response to a tax change. The results that we obtain indicate that, indeed, comparative steady-state analysis is likely to be misleading in analysing tax incidence over finite periods of time.

Incidence of a Capital Income Tax in a Growing Economy with Variable Savings Rates

The theory of economic growth has emphasized that the capital stock, unlike the labour force, is not an original factor of production but represents the accumulation of past incomes.2 Any analysis of the incidence of a tax on capital income should therefore begin by considering how the tax affects the stock of capital. Although a comparative static analysis with a varying capital stock can be instructive, the process of capital accumulation is represented best by a model of economic growth. The purpose of this paper is to examine how savings behaviour affects the long-run incidence of a tax on profits 3 in a growing economy. The analysis is in terms of a general tax on all capital income but the results are obviously relevant to understanding the incidence of the corporate income tax. With a fixed capital stock, owners of capital would bear the entire burden of a general tax on profits 4 and would avoid some of the burden of a partial tax on capital (such as the corporate income tax) to the extent that capital can shift away from the taxed sector to the untaxed sector without significantly reducing the marginal product of capital in the untaxed sector. Harberger's [4] analysis of such a model has shown that, with reasonable parameter values, the US corporate income tax is borne almost entirely by capital and is therefore quite similar in incidence to a general tax on capital income with a fixed capital stock. The current paper shows that replacing the usual static model and fixed capital stock by a model of a growing economy with variable savings rates substantially alters the conclusions about the incidence of a general tax on profits. For a wide range of plausible parameter values, a substantial fraction of the burden of a general profits tax is borne by labour. The assumption of a fixed capital stock may, therefore, also yield quite misleading conclusions in the analysis of the corporate income tax.