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We report that it was successful to use thermal and UV embossing techniques for the fabrication of 1310/1550nm directional coupler demultiplexer and 1x4 MMI optical power splitter, respectively. The mold was prepared with a poly-dimethylsiloxane (PDMS) elastomer, and the pattern was transferred from the photoresist. We experimented also on the durability of the PDMS mold and successfully fabricated 50th replica with thermal curable polymer and 17th replica with UV curable polymer, respectively.

AC susceptibility of the Rb3C60 superconductor shows a weak dependence on ac magnetic-field frequency f. The temperature, Tp where χ″ is maximum, rises with increasing frequency and the effect is enhanced as the dc magnetic-field amplitude Hdc is increased. The temperature is found to obey a scaling law (1 − T p /T c ) 3 2 = 1.9 × 10 −4 H dc [ ln (f 0 /f) + 23] + 8 × 10 −5 [ ln (f 0 /f) + 23] , where f0 (≈ 1010 s−1) is a characteristic frequency and Hdc is in tesla. The scaling relationship is in good agreement with the predicted equation based on the model of thermally activated flux motion.

Temperature-dependent magnetization and magnetic-hysteresis curves for the zero-field cooled and the field-cooled processes of Rb 3 C 60 superconducting fullerene with T c of 30.5±0.1 K were measured between 5 and 30 K in magnetic fields up to 1 T. Small field-cooled diamagnetism and flux jumps were observed at low temperatures and in low fields. Both results strongly suggest the existence of a rather large pinning strength in our sample. This suggestion is further confirmed by the field-cooled hysteresis curve and high critical current densities, J c ( H , T ), at low temperatures. Based on the major hysteresis loops and the Bean critical-state model, the J c at T = 5 K are 2.1 × 10 6 A/cm 2 for H = 0 T and 5.2 × 10 5 A/cm 2 for H = 0.9 T. These J c values are larger than other powdered superconductors with comparable sample sizes, except for YBa 2 Cu 3 O y . For T >10 K, J c versus H agrees well with the expression: J c ( H , T )= k 1 /(1+ H / H 01 ) n . On the other hand, for T J c ( H , T ) may be expressed as J c ( H , T )= k 2 exp(− H / H 02 ). Here k 1 , k 2 , H 01 , H 02 and n are temperature-dependent parameters. The dependence of J c on temperature thus obeys the empirical scaling relation, J c ( H , T )= J c0 ( H )(1− T / T c ) m , where J c0 and m are field-dependent parameters. For 0.4 T H m equals about 2.

We report the magnetic J c ( T ) in K 3 C 60 and Rb 3 C 60 powder samples for temperatures from 5 K to T c . J c near T c was obtained from AC measurements whereas J c at low temperatures was obtained from DC measurements. In the AC measurements, two χ″ peaks were observed on some of the samples. This is attributed to weak links in granular superconductors. The intragranular J c is much larger than the intergranular J c . The J c ( T ) data are fitted by J c ( T ) = J c (0)(1 − T / T c ) γ , with J c (0) and γ as fitting parameters. In the DC measurements on Rb 3 C 60 , J c depends approximately linearly on temperature. Extrapolating the zero-field DC data to 0 K yields J c (0) = 3.1 × 10 6 A/cm 2 . This is a rather large J c for a powdered superconductor, suggesting strong pinning in these materials. Finally, the values of γ for the intergranular and intragranular components are compared with the predictions of theories.

Numerical simulations and a mean-field analysis of a sandpile model of earthquake aftershocks in 1d, 2d and 3d euclidean lattices determine that the average stress decays in a punctuated fashion after a main shock, with events occurring at characteristic times increasing as a geometrical series with a well-defined multiplicative factor which is a function of the stress corrosion exponent, the stress drop ratio and the degree of dissipation. These results are independent of the discrete nature of the lattice and stem from the interplay between the threshold dynamics and the power law stress relaxation., 5 pages, 6 figures (revtex)

Hydrogen (H) absorption by YBa 2 Cu 3 O 7− δ (YBCO) was carried out by exposing the superconducting powders to rf-generated H plasma. We find that both the field-cooled (FC) and zero-field-cooled (ZFC) susceptibilities increase after hydrogenation. The largest enhancement is about 24% for the FC susceptibility at 5K.

Far infrared measurements on detwinned single crystals at 2 K give an anisotropic absorptivity for the a and b polarizations. A ≊ 0.5% for the axis from ≊ 100cm −1 up to the optical edge at 400cm −1 . The a axis conductivity shows low frequency absorption bands of electronic strength.