Search, Costly Price Adjustment and the Frequency of Price Changes - Theory and Evidence

We establish a new empirical finding that the intensity of search for the best price affects the frequency of nominal price changes. This relationship holds in very different economies and for various proxies for search intensity. We derive this relationship from a model of monopolistically competitive firms that face menu costs of changing nominal prices and heterogeneous consumers who search for the best price. We discuss alternative explanations and argue that they do not explain the observed correlations. Our results establish that pricing policies differ endogenously in the cross-section. This may be an important feature missing in many macroeconomic models based on nominal rigidities with exogenous frequency of price changes.Nominal rigidity; search; price adjustment

Regular Adjustment - Theory and Evidenc

We ask why, in many circumstances and many environments, decision-makers choose to act on a time-regular basis (e.g. adjust every six weeks, etc.) or on a state-regular basis (e.g. change an interest rate by 0.25%, etc.), even though such an approach appears suboptimal. The paper attributes regular behaviour to adjustment cost heterogeneity. The reasons for this heterogeneity are discussed. We show that, given the cost heterogeneity, the likelihood of adopting regular policies depends on the shape of the benefit function: the flatter it is, the more likely, ceteris paribus, is regular adjustment. In general, however, there is no clear relationship between the degree of cost and benefit function heterogeneity and the incidence of regular adjustment. We provide sufficient conditions under which the less frequent are adjustments, the greater is the incidence of regular policies. To test the model we use a large Austrian data set, which consists of the direct price information collected by the statistical office and covers 80% of the CPI over eight years. We run cross-sectional tests, regressing the proportion of attractive prices and, separately, the excess proportion of price changes at the beginning of a year and at the beginning of a quarter, on various conditional frequencies of adjustment, inflation and its variability, dummies for good types, and other relevant variables. The results provide strong support for the model: the lower is, in a given market, the conditional frequency of price changes, the higher is the incidence of time- and state-regular adjustment.Optimal pricing; attractive prices; menu costs

Inhomogeneity effect in Wainwright-Marshman space-times

Green and Wald have presented a mathematically rigorous framework to study, within general relativity, the effect of small scale inhomogeneities on the global structure of space-time. The framework relies on the existence of a one-parameter family of metrics that approaches the effective background metric in a certain way. Although it is not necessary to know this family in an exact form to predict properties of the backreaction effect, it would be instructive to find explicit examples. In this paper, we provide the first example of such a family of exact non-vacuum solutions to the Einstein's equations. It belongs to the Wainwright-Marshman class and satisfies all of the assumptions of the Green-Wald framework.Comment: 10 pages; revised version, as published in PR

Soft effective interactions between weakly charged polyelectrolyte chains

We apply extensive Molecular Dynamics simulations and analytical considerations in order to study the conformations and the effective interactions between weakly charged, flexible polyelectrolyte chains in salt-free conditions. We focus on charging fractions lying below 20%, for which case there is no Manning condensation of counterions and the latter can be thus partitioned in two states: those that are trapped within the region of the flexible chain and the ones that are free in the solution. We examine the partition of counterions in these two states, the chain sizes and the monomer distributions for various chain lengths, finding that the monomer density follows a Gaussian shape. We calculate the effective interaction between the centers of mass of two interacting chains, under the assumption that the chains can be modeled as two overlapping Gaussian charge profiles. The analytical calculations are compared with measurements from Molecular Dynamics simulations. Good quantitative agreement is found for charging fractions below 10%, where the chains assume coil-like configurations, whereas deviations develop for charge fraction of 20%, in which case a conformational transition of the chain towards a rodlike configuration starts to take place.Comment: 38 pages, 12 figures, 2 tables. Revised version of the manuscript. Selected for publication in the V\irtual Journal of Biological Physics Research, issue of 1 september, 200

Fluid-fluid demixing transitions in colloid--polyelectrolyte star mixtures

We derive effective interaction potentials between hard, spherical colloidal particles and star-branched polyelectrolytes of various functionalities and smaller size than the colloids. The effective interactions are based on a Derjaguin-like approximation, which is based on previously derived potentials acting between polyelectrolyte stars and planar walls. On the basis of these interactions we subsequently calculate the demixing binodals of the binary colloid--polyelectrolyte star mixture, employing standard tools from liquid-state theory. We find that the mixture is indeed unstable at moderately high overall concentrations. The system becomes more unstable with respect to demixing as the star functionality and the size ratio grow.Comment: 24 pages, 9 figures, submitted to Journal of Physics: Condensed Matte

A broadband noise prediction scheme for low-noise centrifugal blowers

In this paper we outline a semi-empirical procedure for predicting the broadband sound power spectrum radiated by any member of a family of geometrically similar, centrifugal blowers. The prediction scheme is based on the use of a normalized sound power spectrum that is obtained by measuring the sound power radiated by one member of the blower family. In the present instance, a low noise blower design has been identified by conducting a large scale parametric study of blower noise as a function of geometrical design parameters and operating point; the resulting optimum design served to define the geometrical parameters of the blower family considered here. The prediction procedure allows calculation of either 1/3-octave band spectral levels or overall A-weighted levels. In addition it is possible to calculate noise surfaces, i.e., plots of A-weighted sound power level versus design parameters and operating condition; in this way it is easy to identify optimally quiet blower designs that satisfy specified pumping requirements. It has been found, for example, that large diameter impellers of relatively small width operating at low speeds tend to result in the lowest noise level at a given pumping requirement

Experimental design of a low noise centrifugal fan

The effect of various design parameters on broadband noise generation by centrifugal fans has been studied. The parameters varied included: blade type, radial and axial inlet clearance, scroll development angle, scroll development length and cutoff clearance. Scaling laws for pressure, flow and noise were applied to allow the A-weighted sound power levels of different fans to be compared at the same operating points. That approach has allowed an optimum low noise fan design to be identified. To extend the usefulness of that design, a semi-empirical procedure for predicting the broadband sound power spectrum of any member of a family of geometrically similar centrifugal fans has also been developed. The prediction procedure allows the calculation of 1/3-octave band sound power levels based on a measurement of the sound power radiated by a single member of the fan family. By the use of the prediction procedure, it is straightforward to identify optimally quiet fans that satisfy a range of pumping requirements

Directional approach to spatial structure of solutions to the Navier-Stokes equations in the plane

We investigate a steady flow of incompressible fluid in the plane. The motion is governed by the Navier-Stokes equations with prescribed velocity $u_\infty$ at infinity. The main result shows the existence of unique solutions for arbitrary force, provided sufficient largeness of $u_\infty$. Furthermore a spacial structure of the solution is obtained in comparison with the Oseen flow. A key element of our new approach is based on a setting which treats the directino of the flow as \emph{time} direction. The analysis is done in framework of the Fourier transform taken in one (perpendicular) direction and a special choice of function spaces which take into account the inhomogeneous character of the symbol of the Oseen system. From that point of view our technique can be used as an effective tool in examining spatial asymptotics of solutions to other systems modeled by elliptic equations