RNA participates both in functional aspects of the cell and in gene regulation. The interactions of these molecules are mediated by their secondary structure which can be viewed as a planar circle graph with arcs for all the chemical bonds between pairs of bases in the RNA sequence. The problem of predicting RNA secondary structure, specifically the chemically most probable structure, has many useful and efficient algorithms. This leaves RNA folding, the problem of predicting the dynamic behavior of RNA structure over time, as the main open problem. RNA folding is important for functional understanding because some RNA molecules change secondary structure in response to interactions with the environment. The full RNA folding model on at most O(3 n ) secondary structures is the gold standard. We present a new subset approximation model for the full model, give methods to analyze its accuracy and discuss the relative merits of our model as compared with a pre-existing subset approximation. The main advantage of our model is that it generates Monte Carlo folding pathways with the same probabilities with which they are generated under the full model. The pre-existing subset approximation does not have this property.

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In a toy model of gauge and gravitational interactions in D ≥ 4 dimensions, endowed with an invariant UV cut-off Λ, and containing a large number N of non-selfinteracting matter species, the physical gauge and gravitational couplings at the cut-off, α g ≡ g 2 Λ D−4 and α G ≡ G N Λ D−2 , are shown to be bounded by appropriate powers of 1/N . This implies that the infinite-bare-coupling (so-called compositeness) limit of these theories is smooth, and can even resemble our world. We argue that such a result, when extended to more realistic situations, can help avoid large-N violations of entropy bounds, solve the dilaton stabilization and GUT-scale problems in superstring theory, and provide a new possible candidate for quintessence.

Ag addition to YBa2Cu3O7-x superconducting films prepared using electrophoretic deposition on Cu substrates was investigated. The electrical characteristics of the films, such as zero-resistance temperature (T c), critical current density (J c), and resistivity at room temperature (ρ) were greatly improved by Ag doping. The T c of 94 K was attained with the electrophoretic Ag-doped film on Cu substrate. By doping with Ag, the grain growth was enhanced but no shift in YBa2Cu3O7-x peaks was observed in X-ray diffraction patterns. From the electron probe microanalysis of the sample cross section, the doped Ag was found to exist in the region devoid of YBa2Cu3O7-x grains.