What constrains Africa's exports?

This paper examines the effects of transit, documentation, and ports and customs delays on Africa’s exports. The authors find that transit delays have the most economically and statically significant effect on exports. A one-day reduction in inland travel times leads to a 7 percent increase in exports. Put another way, a one-day reduction in inland travel times translates to a 1.5 percentage point decrease in all importing-country tariffs. By contrast, longer delays in the other areas have a far smaller impact on trade. The analysis controls for the possibility that greater trade leads to shorter delays in three ways. First, it examines the effect of trade times on exports of new products. Second, it evaluates the effect of delays in a transit country on the exports of landlocked countries. Third, it examines whether delays affect time-sensitive goods relatively more. The authors show that large transit delays are relatively more harmful because of high within-country variation

Dynamic Crack Tip Equation of Motion: High-speed Oscillatory Instability

A dynamic crack tip equation of motion is proposed based on the autonomy of the near-tip nonlinear zone of scale $\ell_{nl}$, symmetry principles, causality and scaling arguments. Causality implies that the asymptotic linear-elastic fields at time $t$ are determined by the crack path at a {\bf retarded time} $t-\tau_d$, where the delay time $\tau_d$ scales with the ratio of $\ell_{nl}$ and the typical wave speed $c_{nl}$ within the nonlinear zone. The resulting equation is shown to agree with known results in the quasi-static regime. As a first application in the fully dynamic regime, an approximate analysis predicts a high-speed oscillatory instability whose characteristic scale is determined by $\ell_{nl}$. This prediction is corroborated by experimental results, demonstrating the emergence of crack tip inertia-like effects.Comment: 4 pages, 2 figures; minor change

QCD evolution and skewedness effects in color dipole description of DVCS

We show the role played by QCD evolution and skewedness effects in the DVCS cross section at large $Q^2$ within the color dipole description of the process at photon level. The dipole cross section is given by the saturation model, which can be improved by DGLAP evolution at high photon virtualities. We investigate both possibilities as well as the off-forward effect through a simple phenomenological parametrisation. The results are compared to the recent ZEUS DVCS data.Comment: LaTeX, 6 pages, 5 Figs. Vers 2: Minor modifications. Accepted by EPJ

Raising household energy prices in Poland : who gains? who loses?

The authors examine the welfare effects of increasing household energy prices in Poland. Their main finding is that the policy of subsidizing household energy prices, common in the transition economies of Eastern Europe and the former Soviet Union, is regressive. Such programs do help the poor by providing them with lower-cost energy, but they are more useful to the rich, who consume more energy. What is surprising is the extent to which Poland's nonpoor have benefited from lower energy prices. Non only do the wealthy consume more energy in absolute terms than the poor, but they also spend a larger portion of their income on energy. Their analysis allowed the authors to rule out the oft-used social welfare argument for delaying increases in household energy prices, but they do not try to recommend a dynamically efficient pricing path. The first-best response would be to raise energy prices while targeting cash relief to the poor through a social assistance program. This is far more efficient than the present go-slow price adjustment policies, which imply energy subsidies that provide across-the-board relief to all consumers. But if governments want to provide some relief for consumers to ease the adjustment, several options are available: in-kind transfers to the poor, vouchers, cash transfers, and lifeline pricing for a small block of electricity combined with significant price increases. Simulations show that if raising prices to efficient levels for all consumers is not now politically feasible, it may be socially better to use lifeline pricing and a large price increase rather than an overall (but smaller) price increase. Lifeline pricing for electricity in combination with an 80 percent price increase has better distributional effects than a 50 percent across-the-board price increase. Ideally, the public utility would be compensated from the budgtet for any reduced-price sales, rather than having to finance them through internal cross-subsidies. In-kind transfers to poor households are also effective in terms of efficiency, but may be harder to administer in some countries than lifeline pricing.Engineering,Environmental Economics&Policies,Economic Theory&Research,Markets and Market Access,Payment Systems&Infrastructure,Environmental Economics&Policies,Economic Theory&Research,Markets and Market Access,Access to Markets,Energy Demand

Full-field optical measurement of curvatures in ultra-thin-film–substrate systems in the range of geometrically nonlinear deformations

This article describes coherent gradient sensing (CGS) as an optical, full-field, real-time, nonintrusive, and noncontact technique for the measurement of curvatures and nonuniform curvature changes in film-substrate systems. The technique is applied to the study of curvature fields in thin Al films (6 mum) deposited on thin circular silicon wafers (105 mum) of "large" in-plane dimensions (50.8 mm in diameter) subjected to thermal loading histories. The loading and geometry is such that the system experiences deformations that are clearly within the nonlinear range. The discussion is focused on investigating the limits of the range of the linear relationship between the thermally induced mismatch strain and the substrate curvature, on the degree to which the substrate curvature becomes spatially nonuniform in the range of geometrically nonlinear deformation, and finally, on the bifurcation of deformation mode from axial symmetry to asymmetry with increasing mismatch strain. Results obtained on the basis of both simple models and more-detailed finite-element simulations are compared with the full-field CGS measurements with the purpose of validating the analytical and numerical models

Drip and Mate Operations Acting in Test Tube Systems and Tissue-like P systems

The operations drip and mate considered in (mem)brane computing resemble the operations cut and recombination well known from DNA computing. We here consider sets of vesicles with multisets of objects on their outside membrane interacting by drip and mate in two different setups: in test tube systems, the vesicles may pass from one tube to another one provided they fulfill specific constraints; in tissue-like P systems, the vesicles are immediately passed to specified cells after having undergone a drip or mate operation. In both variants, computational completeness can be obtained, yet with different constraints for the drip and mate operations

The Evolution of Securitization in Multifamily Mortgage markets and Its Effect on lending Rates

Loan purchase and securitization by Freddie Mac, Fannie Mae and private-label commercial mortgage-backed securities (CMBS) grew rapidly during the 1990s and accounted for more than one-half of the net growth in multifamily debt over the decade. By facilitating the integration of the multifamily mortgage market into the broader capital markets, securitization helped to create new sources of credit as some traditional portfolio investors—savings institutions and life insurers—reduced their share of loan holdings. A model of commercial mortgage rates at life insurers, expressed relative to a comparable-term Treasury yield, was estimated over a twenty-two-year period. The parameter estimates supported an option-based pricing model of rate determination; proxies for CMBS activity showed no significant effect.

The DVCS Measurement at HERA

The recent results of the studies of Deeply Virtual Compton Scattering (DVCS) events at HERA are presented. The possibility offered by this process to gain information about skewed parton distributions (SPD) is emphasized.Comment: Talk given at New Trends in HERA Physics 2001, Ringberg Castle, Tegernsee, Germany, 17-22 Jun 2001, 13 pages, 10 figures, recent ZEUS data discussed, references update