Study of air pollutant signatures for remote sensing

Experimental results are presented for a possible new, indirect signature for air pollutants: the spectral reflectivity of plant leaves. Sub-visual changes (up to 160%) in the spectral reflectivity of bean and tobacco leaves were observed over the range 475nm to 750nm in response to SO2 exposures such as 2ppm/4hrs or 4ppm/16hrs, or to O3 exposures such as 90pphm/21hrs or 7.5pphm/292hrs. Such changes might be observed from a satellite using either laser or sunlight as the illumination source. Inasmuch as the plants appear to become acclimated to some of these exposure doses, environmental changes may be most important for this type of plant-response

Diffusion and structural changes in microcircuit interconnections

The interdiffusion of platimum and gold films, a couple utilized in beam lead microcircuits, has been studied for temperatures up to 550 C. Gold-on-platinum couples and separate platimum and gold films 80-450 nm thick, were deposited by electron beam evaporation onto oxidized (111) silicon substrates. Diffusion was monitored by means of spectral reflectance versus wavelength in the band 500-1000 nm. The separate metal films showed good adhesion and stable reflectances (after an initial change) for at least 6 h at diffusion temperatures, in contrast to the couples. Analysis of platinum diffusion through the gold films yielded an activation energy about 38 kcal/g-atom and a pre-exponential factor of the order 0.001 sq cm/sec, values close to those for volume diffusion. The pre-exponential factor especially is dependent upon film deposition conditions

Singlet-triplet avoided crossings and effective gg factor versus spatial orientation of spin-orbit-coupled quantum dots

We study avoided crossings opened by spin-orbit interaction in the energy spectra of one- and two-electron anisotropic quantum dots in perpendicular magnetic field. We find that for simultaneously present Rashba and Dresselhaus interactions the width of avoided crossings and the effective $g$ factor depend on the dot orientation within (001) crystal plane. The extreme values of these quantities are obtained for [110] and [1$\bar{1}$0] orientations of the dot. The width of singlet-triplet avoided crossing changes between these two orientations by as much as two orders of magnitude. The discussed modulation results from orientation-dependent strength of the Zeeman interaction which tends to polarize the spins in the direction of the external magnetic field and thus remove the spin-orbit coupling effects

Time dependent configuration interaction simulations of spin swap in spin orbit coupled double quantum dots

We perform time-dependent simulations of spin exchange for an electron pair in laterally coupled quantum dots. The calculation is based on configuration interaction scheme accounting for spin-orbit (SO) coupling and electron-electron interaction in a numerically exact way. Noninteracting electrons exchange orientations of their spins in a manner that can be understood by interdot tunneling associated with spin precession in an effective SO magnetic field that results in anisotropy of the spin swap. The Coulomb interaction blocks the electron transfer between the dots but the spin transfer and spin precession due to SO coupling is still observed. The electron-electron interaction additionally induces an appearance of spin components in the direction of the effective SO magnetic field which are opposite in both dots. Simulations indicate that the isotropy of the spin swap is restored for equal Dresselhaus and Rashba constants and properly oriented dots

Levy--Brownian motion on finite intervals: Mean first passage time analysis

We present the analysis of the first passage time problem on a finite interval for the generalized Wiener process that is driven by L\'evy stable noises. The complexity of the first passage time statistics (mean first passage time, cumulative first passage time distribution) is elucidated together with a discussion of the proper setup of corresponding boundary conditions that correctly yield the statistics of first passages for these non-Gaussian noises. The validity of the method is tested numerically and compared against analytical formulae when the stability index $\alpha$ approaches 2, recovering in this limit the standard results for the Fokker-Planck dynamics driven by Gaussian white noise.Comment: 9 pages, 13 figure