Asymptotic Behavior of Traveling Wave Solutions to Reaction-Diffusion Equations

We will discuss travelling wave solutions to reaction-diffusion equations of the form: ut=uxx+ up (1-uq) which can be used as a mathematical model for various biological phenomena, as well as to model problems in combustion theory. We identify conditions on the wave speed so that travelling wave solutions exist for the case p ≥1 and q ≥1. Moreover, we estimate the rate of decay of the travelling wave solutions. When p \u3e 1 and q ≥1, this estimate requires center manifold theory because the typical linear methods fail to work. Through the mathematical analysis of reaction diffusion equations, the results of this research create further studies and application in physical and industrial chemistry

Instability in U.S. inflation: 1967-2005

Maintaining stables prices and keeping inflation in check have become key policy objectives of the Federal Reserve and other central banks. Evidence indicates that inflation has become less persistent and volatile since the early 1980s. Although economists have examined the implications for inflation modeling and forecasting, little information exists about whether changes or instabilities in inflation dynamics coincide with specific economic events such as oil price shocks or recessions. ; This article studies U.S. monthly inflation, inflation growth, and price level dynamics from January 1967 to September 2005. The author employs four price level measures—two versions of the monthly consumer price index and two versions of the monthly personal consumption expenditure deflator—with the goal of identifying possible instabilities in these dynamics. ; Autoregressive, moving average, and unobserved components models provide estimates on various aspects of inflation and price levels. Two rolling samples spanning the 1967–2005 period are constructed to uncover evidence about possible instability in mean inflation and the persistence and volatility of inflation and inflation growth. ; One way to summarize the empirical results is that this instability coincides with different economic events such as the oil price shocks of the 1970s or the end of the 1990–91 recession. An unresolved question is whether such changes are one-time events or can be expected to be repeated systematically in the future.Inflation (Finance)

The p_T Spectrum in Heavy-Flavour Photoproduction

We consider the transverse-momentum distribution of heavy flavours in photon-hadron collisions. We present a formalism in which large transverse-momentum logarithms are resummed to the next-to-leading level, and mass effects are included exactly up to order alpha_em alpha_s^2, so as to retain predictivity at both small and large transverse momenta. Phenomenological applications relevant to charm photoproduction at HERA are given.Comment: 26 pages, Latex, epsfig, 15 figures. Submitted to JHE

Is There a Significant Excess in Bottom Hadroproduction at the Tevatron?

We discuss the excess in the hadroproduction of B mesons at the Tevatron. We show that an accurate use of up-to-date information on the B fragmentation function reduces the observed excess to an acceptable level. Possible implications for experimental results reporting bottom quark cross sections, also showing an excess with respect to next-to-leading order theoretical predictions, are discussed.Comment: 5 pages, Latex, 4 figures. Submitted to Phys. Rev. Let

The \pt spectrum of heavy quarks in photoproduction

We illustrate a formalism that allows to match the next-to-leading order cross section for the photoproduction of heavy quarks to the cross section obtained by resumming logarithms of \pt/m to the next-to-leading accuracy, thus giving a sensible prediction for any value of \pt. We present a comparison between our predictions and H1 and ZEUS data.Comment: 4 pages Latex; 3 figures included. Talk given at DIS01, 27 April - 1 May 2001, Bologna, Ital

Business cycle implications of internal consumption habit for New Keynesian models

This paper studies the implications of internal consumption habit for propagation and monetary transmission in New Keynesian dynamic stochastic general equilibrium (NKDSGE) models. We use Bayesian methods to evaluate the role of internal consumption habit in NKDSGE model propagation and monetary transmission. Simulation experiments show that internal consumption habit often improves NKDSGE model fit to output and consumption growth spectra by dampening business cycle periodicity. Nonetheless, habit NKDSGE model fit is vulnerable to nominal rigidity, the choice of monetary policy rule, the frequencies used for evaluation, and spectra identified by permanent productivity shocks.

Business Cycle Implications of Internal Consumption Habit for New Keynesian Model

This paper studies the implications of internal consumption habit for propagation and monetary transmission in new Keynesian dynamic stochastic general equilibrium (NKDSGE) models. Bayesian methods are employed to evaluate the role of internal consumption habit in NKDSGE model propagation and monetary transmission. Simulation experiments show that internal consumption habit often improves NKDSGE model fit to output and consumption growth spectra by dampening business cycle periodicity. Nonetheless, habit NKDSGE model fit is vulnerable to the nominal rigidity, to the choice of monetary policy rule, to the frequencies used for evaluation, and to spectra identified by permanent productivity shocks.

"Business Cycle Implications of Internal Consumption Habit for New Keynesian Models"

This paper studies the implications of internal consumption habit for new Keynesian dynamic stochastic general equilibrium (NKDSGE) models. Bayesian Monte Carlo methods are employed to evaluate NKDSGE model fit. Simulation experiments show that consumption habit often improves the ability of NKDSGE models to match output and consumption growth spectra. Nonetheless, the fit of NKDSGE models with consumption habit is susceptible to the source of the nominal rigidity, to spectra identified by permanent productivity shocks, to the frequencies used for evaluation, and to the choice of monetary policy rule. These vulnerabilities suggest that NKDSGE model specification is fragile.

Business Cycle Implications of Habit Formation

The inability of a wide array of dynamic stochastic general equilibrium (DSGE) models to generate fluctuations that resemble actual business cycles has lead to the use of habit formation in consumption. For example, habit formation has been shown to help explain the negative response of labour input to a positive, permanent technology shock, several asset pricing puzzles, and the impact of monetary shocks on real variables. Investigating four different DSGE models with the Bayesian calibration approach, this paper observes that, especially in a new Keynesian monetary business cycle model with both staggered price and wage, habit formation fails to mimic the shape of output growth in the frequency domain: it counterfactually emphasizes low frequency fluctuations in output growth, compared to the U.S. data. On the other hand, habit formation has no clear implications on other business cycle aspects including impulse responses and forecast error variance decompositions of output to permanent and transitory shocks. These observations cast doubt on habit formation as an important ingredient of the DSGE model with a rich set of internal propagation mechanisms.Business Cycle; Habit Formation; Frequency Domain; Bayesian Calibration