The Puzzling Collapse of Electronic Sliding Friction on a Superconductor Surface

In a recent paper [Phys. Rev. Lett. 80 (1998) 1690], Krim and coworkers have observed that the friction force, acting on a thin physisorbed layer of N_2 sliding on a lead film, abruptly decreases by a factor of ~2 when the lead film is cooled below its superconductivity transition temperature. We discuss the possible mechanisms for the abruptness of the sliding friction drop, and also discuss the relevance of these results to the problem of electronic friction.Comment: 5 pages, no figure

Photoheliograph requirements for a spectrograph, November 1967 - June 1968

Preliminary design requirements and constraints for ATM photoheliograp

Debt, Cash Flow and Inflation Incentives: A Swedish Example

The fiscal gains from, and hence the political incentives to, an increase in inflation rate of ten percentage points may be substantial: with Swedish data from 1994, these gains would have been an annual real flow of 3-4 percent of GDP, or a capitalized value of nearly 100 percent of GDP. They would mainly have arisen from the nominalistic features of the tax and transfer systems rather than from the traditional sources: seignorage and real depreciation of the public debt. The welfare costs of such an inflation increase would have been even larger, however, and would thus have reduced net welfare. Possible institutional reforms, aimed at making the political costs of inflation more equal to the social costs, are presented and discussed

Spectroscopic studies in open quantum systems

The spectroscopic properties of an open quantum system are determined by the eigenvalues and eigenfunctions of an effective Hamiltonian H consisting of the Hamiltonian H_0 of the corresponding closed system and a non-Hermitian correction term W arising from the interaction via the continuum of decay channels. The eigenvalues E_R of H are complex. They are the poles of the S-matrix and provide both the energies and widths of the states. We illustrate the interplay between Re(H) and Im(H) by means of the different interference phenomena between two neighboured resonance states. Level repulsion along the real axis appears if the interaction is caused mainly by Re(H) while a bifurcation of the widths appears if the interaction occurs mainly due to Im(H). We then calculate the poles of the S-matrix and the corresponding wavefunctions for a rectangular microwave resonator with a scatter as a function of the area of the resonator as well as of the degree of opening to a guide. The calculations are performed by using the method of exterior complex scaling. Re(W) and Im(W) cause changes in the structure of the wavefunctions which are permanent, as a rule. At full opening to the lead, short-lived collective states are formed together with long-lived trapped states. The wavefunctions of the short-lived states at full opening to the lead are very different from those at small opening. The resonance picture obtained from the microwave resonator shows all the characteristic features known from the study of many-body systems in spite of the absence of two-body forces. The poles of the S-matrix determine the conductance of the resonator. Effects arising from the interplay between resonance trapping and level repulsion along the real axis are not involved in the statistical theory.Comment: The six jpg files are not included in the tex-fil

The effect of surface roughness on the adhesion of elastic solids

We study the influence of surface roughness on the adhesion of elastic solids. Most real surfaces have roughness on many different length scales, and this fact is taken into account in our analysis. We consider in detail the case when the surface roughness can be described as a self affine fractal, and show that when the fractal dimension D_f >2.5, the adhesion force may vanish, or be at least strongly reduced. We consider the block-substrate pull-off force as a function of roughness, and find a partial detachment transition preceding a full detachment one. The theory is in good qualitative agreement with experimental data.Comment: 15 pages, 16 figures. Submitted to J. Chem. Phy