What can be learned from the schematic mode-coupling approach to experimental data ?

We propose a detailed investigation of the schematic mode-coupling approach to experimental data, a method based on the use of simple mode-coupling equations to analyze the dynamics of supercooled liquids. Our aim here is to clarify different aspects of this approach that appeared so far uncontrolled or arbitrary, and to validate the results obtained from previous works. Analyzing the theoretical foundations of the approach, we first identify the parameters of the theory playing a key role and obtain simple requirements to be met by a schematic model for its use in this context. Then we compare the results obtained from the schematic analysis of a given set of experimental data with a variety of models and show that they are all perfectly consistent. A number of potential biases in the method are identified and ruled out by the choice of appropriate models. Finally, reference spectra computed from the mode-coupling theory for a model simple liquid are analyzed along the same lines as experimental data, allowing us to show that, despite the strong simplification in the description of the dynamics it involves, the method is free from spurious artifacts and provides accurate estimates of important parameters of the theory. The only exception is the exponent parameter, the evaluation of which is hindered, as for other methods, by corrections to the asymptotic laws of the theory present when the dynamics is known only in a limited time or frequency range.Comment: 13 pages, 5 figures, revtex4, to appear in J. Chem. Phy

A Relativistic Version of the Two-Level Atom in the Rest-Frame Instant Form of Dynamics

We define a relativistic version of the two-level atom, in which an extended atom is replaced by a point particle carrying suitable Grassmann variables for the description of the two-level structure and of the electric dipole. After studying the isolated system "atom plus the electro-magnetic field" in the electric-dipole representation as a parametrized Minkowski theory, we give its restriction to the inertial rest frame and the explicit form of the Poincar\'e generators. After quantization we get a two-level atom with a spin 1/2 electric dipole and the relativistic generalization of the Hamiltonians of the Rabi and Jaynes-Cummings models.Comment: 23 page

Study of the Depolarized Light Scattering Spectra of Supercooled Liquids by a Simple Mode-Coupling Model

By using simple mode coupling equations, we investigate the depolarized light scattering spectra of two so-called "fragile" glassforming liquids, salol (phenylsalicylate) and CKN (Ca_{0.4}K_{0.6}(NO_3)_{1.4}), measured by Cummins and coworkers. Nonlinear integrodifferential equations for the time evolution of the density-fluctuations autocorrelation functions are the basic input of the mode coupling theory. Restricting ourselves to a small set of such equations, we fit the numerical solution to the experimental spectra. It leads to a good agreement between model and experiment, which allows us to determine how a real system explores the parameter space of the model, but it also leads to unrealistic effective vertices in a temperature range where the theory makes critical asymptotic predictions. We finally discuss the relevance and the range of validity of these universal asymptotic predictions when applied to experimental data on supercooled liquids.Comment: 31 LaTeX pages using overcite.sty, 10 postscript figures, accepted in J. Chem. Phy

Exploring Household Saving and Consumption-Smoothing in the Philippines

This paper explores whether or not the saving behavior of Filipino households fits the life-cycle hypothesis. Using pseudo-panels, which are constructed from the public use data files of the Family Income and Expenditures Survey of 1988 to 2000, it shows that consumption rises with the age of the household head and that the consumption profile has been rising for younger cohorts. The regressions indicate that the cohort-independent age effects on consumption simply track those on income across all ages, suggesting that Filipino households do not behave as the life-cycle hypothesis prescribes, possibly because they are liquidity constrained or impatient.consumption smoothing, household savings, household consumption

Exploring Household Saving and Consumption-Smoothing in the Philippines

This paper explores whether or not the saving behavior of Filipino households fits the life-cycle hypothesis. Using pseudo-panels, which are constructed from the public use data files of the Family Income and Expenditures Survey of 1988 to 2000, it shows that consumption rises with the age of the household head and that the consumption profile has been rising for younger cohorts. The regressions indicate that the cohort-independent age effects on consumption simply track those on income across all ages, suggesting that Filipino households do not behave as the life-cycle hypothesis prescribes, possibly because they are liquidity constrained or impatient.consumption smoothing, household savings, household consumption

On the correlation between fragility and stretching in glassforming liquids

We study the pressure and temperature dependences of the dielectric relaxation of two molecular glassforming liquids, dibutyl phtalate and m-toluidine. We focus on two characteristics of the slowing down of relaxation, the fragility associated with the temperature dependence and the stretching characterizing the relaxation function. We combine our data with data from the literature to revisit the proposed correlation between these two quantities. We do this in light of constraints that we suggest to put on the search for empirical correlations among properties of glassformers. In particular, argue that a meaningful correlation is to be looked for between stretching and isochoric fragility, as both seem to be constant under isochronic conditions and thereby reflect the intrinsic effect of temperature

Simulating the Impact of Macroeconomic Policy Changes on Macronutrient Availability in Households

This study estimates a system of food demand equations utilizing nationally representative survey data. These estimates are then used to set-up a model that can use price and income changes from simulating a general equilibrium model to determine the impact of changes on macroeconomic policy on the nutritional status of households. Results indicate that the tariff reform program has a more progressive impact on nutrition than on income.computable general equilibrium (CGE)

Simulating the Impact of Macroeconomic Policy Changes on Macronutrient Availability in Households

This study estimates a system of food demand equations utilizing nationally representative survey data. These estimates are then used to set-up a model that can use price and income changes from simulating a general equilibrium model to determine the impact of changes on macroeconomic policy on the nutritional status of households. Results indicate that the tariff reform program has a more progressive impact on nutrition than on income.computable general equilibrium (CGE)

Motives and Giving Norms Behind Remittances: the Case of Filipino Overseas Workers and their Recipient Households

The literature has focused on motives to explain remittance behavior. But as non-anonymous transfers, remittances are liable to be influenced by giving norms as well. We formulate an empirical specification that takes account of remittance motives involving worker-household pairs. We find that altruism dominates the exchange motive among overseas workers who are likely to be the primary breadwinners of their recipient households. We also find that, in the subsample in which overseas workers are likely to be secondary breadwinners, (a) household labor income is an endogenous explanatory variable and (b) the error covariance of the household income and remittance selection equations is positive. A possible reason for (a) is that secondary breadwinners use household income as an imperfect signal of opportunity cost or to detect unobserved effort, i.e., moral hazard, in generating income. As for (b), we surmise that it indicates the presence of incentive-compatible mechanisms against moral hazard. On giving norms, we find that in samples that include overseas workers who are secondary breadwinners, remittance amounts are afflicted with negative selectivity. We present evidence that this is consistent with Filipino giving practices, in which everyone gives but in modest amounts.Remittances, remittance motives, giving norms

Disentangling density and temperature effects in the viscous slowing down of glassforming liquids

We present a consistent picture of the respective role of density and temperature in the viscous slowing down of glassforming liquids and polymers. Specifically, based in part upon a new analysis of simulation and experimental data on liquid ortho-terphenyl, we conclude that a zeroth-order description of the approach to the glass transition should be formulated in terms of a temperature-driven super-Arrhenius activated behavior rather than a density-driven congestion or jamming phenomenon. The density plays a role at a quantitative level, but its effect on the viscosity and the structural relaxation time can be simply described via a single parameter, an effective interaction energy that is characteristic of the high temperature liquid regime; as a result, density does not affect the ``fragility'' of the glassforming system.Comment: RevTeX4, 8 pages, 8 eps figure