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71.
Femtosecond laser direct writing is employed for the fabrication of buried tubular waveguides in bulk poly(methyl methacrylate). A novel technique using selective chemical etching is presented to resolve the two-dimensional refractive-index profile of the fabrication structures. End-to-end coupling in the waveguides reveals a near-field intensity distribution that results from the superimposition of several propagating modes with different azimuthal symmetries. Mode analysis of the tubular waveguides is performed using the finite-difference method, and the possible propagating mode profiles are compared with the experimental data. 相似文献
72.
Particles moving along curved trajectories will diffuse if the curvature fluctuates sufficiently in either magnitude or orientation. We consider particles moving at a constant speed with either a fixed or a Gaussian distributed magnitude of curvature. At small speeds the diffusivity is independent of the speed. At larger particle speeds, the diffusivity depends on the speed through a novel exponent. We apply our results to intracellular transport of vesicles. In sharp contrast to thermal diffusion, the effective diffusivity increases with vesicle size and so may provide an effective means of intracellular transport. 相似文献
73.
74.
Direct detection of ultrafast thermal transients by use of a chirped, supercontinuum white-light pulse 总被引:1,自引:0,他引:1
An experimental technique is demonstrated that permits direct optical measurement of ultrafast material transients during a single excitation-relaxation cycle. Reflection of a linearly chirped, supercontinuum optical pulse from a gold film with changing surface temperature induced by an ultrafast pump pulse allows the thermal transients to be encoded onto the spectrum of the probe pulse. Calibrating the chirp of the probe pulse and the wavelength sensitivity of the sample permits mapping of the measured transient into the time domain. Measurements are completed over the course of 100 ps with subpicosecond time resolution. Results obtained with this technique are compared with similar measurements obtained with conventional pump-probe correlation techniques. 相似文献
75.
B. B. Bhattacharyya X. Li M. Pensky G. D. Richardson 《Annals of the Institute of Statistical Mathematics》2000,52(1):71-83
The limiting distribution of the normalized periodogram ordinate is used to test for unit roots in the first-order autoregressive model st= s-1,t+s,t-1- s-1,t-1+st. Moreover, for the sequence
n
= e
c/n
,
n
= e
d/n
of local Pitman-type alternatives, the limiting distribution of the normalized periodogram ordinate is shown to be a linear combination of two independent chi-square random variables whose coefficients depend on c and d. This result is used to tabulate the asymptotic power of a test for various values of c and d. A comparison is made between the periodogram test and a spatial domain test. 相似文献
76.
Broderick NG Ross GW Offerhaus HL Richardson DJ Hanna DC 《Physical review letters》2000,84(19):4345-4348
We report on the fabrication of what we believe is the first example of a two-dimensional (2D) nonlinear photonic crystal [Berger, Phys. Rev. Lett. 81, 4136 (1998)], where the refractive index is constant but where the 2nd order nonlinear susceptibility is spatially periodic. Such crystals allow for efficient quasi-phase-matched 2nd harmonic generation using multiple reciprocal lattice vectors. External 2nd harmonic conversion efficiencies >60% were measured with picosecond pulses. The fabrication technique is extremely versatile and should allow for the fabrication of a broad range of 2D crystals including quasicrystals. 相似文献
77.
The response to drying and storage at -20 degrees C or in liquid nitrogen was studied in seeds of the freshwater aquatic plant Najas flexilis. The seeds of this species show some desiccation sensitivity, although post-harvest storage in water at 16 degrees C resulted in improvements in desiccation tolerance. There was 63% germination of seeds dried to 9.5% moisture content (30% RH) following this maturation period. Optimum moisture contents for seeds stored at -20 degrees C for 3 months and in liquid nitrogen for 1 week were ~11% and ~15%, respectively. 相似文献
78.
High-energy, high-power ytterbium-doped Q-switched fiber laser 总被引:8,自引:0,他引:8
Alvarez-Chavez JA Offerhaus HL Nilsson J Turner PW Clarkson WA Richardson DJ 《Optics letters》2000,25(1):37-39
We report on a Q -switched, cladding-pumped, ytterbium-doped large-mode-area fiber laser operating at 1090 nm that is capable of generating 2.3 mJ of output pulse energy at a 500-Hz repetition rate and more than 5 W of average output power at higher repetition rates in a high-brightness beam (M(2) = 3) . Using a similar fiber with a smaller core, we generated >0.5-mJ pulses in a diffraction-limited beam. Our results represent a threefold increase in pulse energy over previously published values for Q-switched fiber lasers and firmly establish fiber lasers as compact, multiwatt, multimillijoule pulse sources with large scope for both industrial and scientific applications. 相似文献
79.
Albanis V Bratfalean RT Dhanjal S Zheludev NI Emel'yanov VI Petropoulos P Richardson DJ 《Optics letters》2000,25(21):1594-1596
The reflectivity of a gallium/silica interface formed on an optical flat or at the tip of a cleaved optical fiber can be reduced in a reversible fashion when the interface is excited by a few milliwatts of laser power. This phenomenon occurs at temperatures just below gallium's melting point. We believe that the effect can be attributed to light-induced structuring at the interface. 相似文献
80.
We present a new approach for the simulation of beyond standard model (BSM) physics within the Herwig++ event generator. Our
approach is more generic than previous methods with the aim of minimising the effort of implementing further new physics models.
Spin correlations, which are important for BSM models due to new heavy fermions and bosons, are discussed and their effects
demonstrated for the minimal supersymmetric standard model (MSSM) and Randall–Sundrum model using our new framework. 相似文献