A simple panel-CADF test for unit roots

Copyright © Blackwell Publishing Ltd and the Department of Economics, University of Oxford 2012. This is the accepted version of the following article: Costantini, M. and Lupi, C. (2013), A Simple Panel-CADF Test for Unit Roots. Oxford Bulletin of Economics and Statistics, 75: 276–296, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/j.1468-0084.2012.00690.x/abstract.In this paper, we propose a simple extension to the panel case of the covariate-augmented Dickey–Fuller (CADF) test for unit roots developed in Hansen (1995). The panel test we propose is based on a P values combination approach that takes into account cross-section dependence. We show that the test has good size properties and gives power gains with respect to other popular panel approaches. An empirical application is carried out for illustration purposes on international data to test the purchasing power parity (PPP) hypothesis

Platform Competition and Broadband Uptake: Theory and Empirical Evidence from the European Union

Broadband access provides users with high speed, always-on connectivity to the Internet. Due to its superiority, broadband is seen as the way for consumers and firms to exploit the great potentials of new applications. This has generated a policy debate on how to stimulate adoption of broadband technology. One of the most disputed issues is about competition policies: these may be intended to promote competition in the Digital Subscriber Line (DSL) segment of the market (intra- platform competition), or to stimulate entry into the market for alternative platforms such as cable access or fiber optics (inter- platform competition). Using a model of oligopoly competition between differentiated products, our paper explicitly studies the effect of inter and intra platform competition on the diffusion of broadband access. The implications of the model are then tested using data from 14 European countries. The econometric evidence confirms the results of the theoretical model and indicates that while inter-platform competition drives broadband adoption, competition in the market for DSL services does not play a significant role. The results also confirm that lower unbundling prices stimulate broadband uptake.Broadband, inter-platform and intra-platform competition, local loop unbundling

Public's Willingness to Pay for Ecosystem Service Improvements From Agriculture

Consumer/Household Economics, Demand and Price Analysis,

Combining Supply and Demand Estimates for Ecosystem Services from Cropland

Payment-for-Ecosystem-Services (PES) programs are gaining appeal as flexible approaches to inducing the voluntary provision of ecosystem services (ES). Farmers, who manage agricultural ecosystems, provide important nonmarket ecosystem services to the public by their choice of production inputs and management practices. Although there exist various PES programs in the United States and Europe, we are aware of none that was designed based on a comprehensive understanding of the underlying supply and demand of ecosystem services. Taking advantage of unique, coupled datasets of stated preferences, this paper combines a supply-side cost function of farmers’ willingness to adopt practices that provide increased ES with a demand-side social benefit function of residents’ willingness to pay (WTP) for these ES. The result is an empirically based, welfare-maximizing price and quantity of ES that can inform the design of future PES programs.Payment-for-Ecosystem-Services (PES), Contingent valuation, Aggregate supply and demand, Cropland, Eutrophication, Greenhouse gas, Agricultural and Food Policy, Environmental Economics and Policy, Q11, Q51, Q57, Q58,

Reflectivity measurements in uniaxial superconductors: a methodological discussion applied to the case of La(2-x)Sr(x)CuO(4)

Most of the novel superconductors are uniaxial crystals, with metallic planes ($ab$) orthogonal to an insulating axis ($c$). Far-infrared measurements of the reflectivity $R_{ab} (\omega)$ provide valuable information on their low-energy electrodynamics, but involve delicate experimental issues. Two of them are a possible contamination of $R_{ab} (\omega)$ from the c axis and the extrapolation of the $R_{ab}$ data to $\omega$ =0, both above and below $T_c$. Here we discuss quantitatively these issues with particular regard to La$_{2-x}$Sr$_x$CuO$_{4+y}$, one of the most studied high-$T_c$ materials.Comment: 13 pages with 3 Fig

Incentives to Supply Enhanced Ecosystem Services from Cropland

This paper examines the willingness of farmers to participate in hypothetical programs that would pay them to adopt cropping practices that enhance provision of ecosystem services from agriculture. A survey of 3,000 Michigan corn and soybean farmers elicited willingness to adopt four sets of cropping practices that reflected increasing levels of environmental stewardship. Acreage enrollments in the programs were modeled using hurdle models. The acreage that farmers would be willing to enroll depends chiefly on farm size and the perception of environmental improvements from the practices. For farms over 500 acres, the payment offered was also a significant inducement to acreage enrollment in all systems examined. This paper advances the literature on adoption of agro-environmental practices by developing a supply function for crop acreage managed for environmental stewardship. Like prior studies of environmental technology adoption in agriculture, we find that environmental attitudes and affiliations, age, education and current farming practices are influential. But we find that the low cost suppliers of environmental services are the largest farms. Agricultural policies based on payment for environmental services that aim for cost-effective environmental impact will likely achieve most of their impact from larger farms.Willingness to participate, willingness to accept, stated preference, supply response, ecosystem services, payment for environmental services, agricultural policy, agro-environmental policy, environmental policy, corn, soybean, Environmental Economics and Policy, Q18, Q51, Q57,

Temperature dependence of the optical spectral weight in the cuprates: Role of electron correlations

We compare calculations based on the Dynamical Mean-Field Theory of the Hubbard model with the infrared spectral weight $W(\Omega,T)$ of La$_{2-x}$Sr$_x$CuO$_4$ and other cuprates. Without using fitting parameters we show that most of the anomalies found in $W(\Omega,T)$ with respect to normal metals, including the existence of two different energy scales for the doping- and the $T$-dependence of $W(\Omega,T)$, can be ascribed to strong correlation effects.Comment: 4 pages, 3 figures. Minor corrections, corrected some typos and added reference

Resonant plasma excitation by single-cycle THz pulses

In this paper, an alternative perspective for the generation of millimetric high-gradient resonant plasma waves is discussed. This method is based on the plasma-wave excitation by energetic single-cycle THz pulses whose temporal length is comparable to the plasma wavelength. The excitation regime discussed in this paper is the quasi-nonlinear regime that can be achieved when the normalized vector potential of the driving THz pulse is on the order of unity. To investigate this regime and determine the strength of the excited electric elds, a Particle-In-Cell (PIC) code has been used. It has been found that by exploiting THz pulses with characteristics currently available in laboratory, longitudinal electron plasma waves with electric gradients up to hundreds MV/m can be obtained. The mm-size nature of the resonant plasma wave can be of great utility for an acceleration scheme in which high-brightness electron bunches are injected into the wave to undergo a strong acceleration. The long-size nature of the acceleration bucket with respect to the short length of the electron bunches can be handled in a more robust manner in comparison with the case when micrometric waves are employed