2,811 research outputs found
Vertical liquid controlled adiabatic waveguide coupler
A broadband vertical liquid controlled optical waveguide coupler (LCC) is demonstrated. The fabricated vertical LCC with silicon nitride (SiN) waveguides can switch light between 2 stacked photonic circuit layers with zero energy consumption in a steady switch state. In combination with low-loss interlayer waveguide crossovers they enable large scale non-volatile switch circuits with low loss. The fabricated vertical LCC has a loss less than 2.0 dB in bar state and less than 2.6 dB in cross state over the telecommunication wavelength range 1260 nm to 1630 nm. Interlayer waveguide crossovers with the same interlayer oxide thickness as the LCC have a loss less than 0.06 dB over the same wavelength range. The crosstalk of the LCC is less than 21 dB over the wavelength range 1500 nm to 1630 nm for both bar and cross state. (c) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen
Laser scanning imaging and local characterization of superconducting properties in high-Tc thin film multiturn coil
Low-temperature scanning laser microscopy has been used to investigate the spatial variation of the critical temperature Tc and critical current Ic in thin-film high-Tc multilayer structures that include dielectric layers. The method is described and measurements are presented on an YBa2Cu3O7-x-based multiturn coil with SrTiO3 insulating layer. We found that the critical temperature Tc of the YBa2Cu3O7-x top layer, from which the return strip of the coil is formed, is higher than that of the YBa2Cu3O7-x base layer. The critical current of the coil is limited by the quality of the YBa2Cu3O7-x base layer and not by the edges of the crossovers
PushPush is NP-hard in 2D
We prove that a particular pushing-blocks puzzle is intractable in 2D,
improving an earlier result that established intractability in 3D [OS99]. The
puzzle, inspired by the game *PushPush*, consists of unit square blocks on an
integer lattice. An agent may push blocks (but never pull them) in attempting
to move between given start and goal positions. In the PushPush version, the
agent can only push one block at a time, and moreover, each block, when pushed,
slides the maximal extent of its free range. We prove this version is NP-hard
in 2D by reduction from SAT.Comment: 18 pages, 13 figures, 1 table. Improves cs.CG/991101
A Seeded Genetic Algorithm for RNA Secondary Structural Prediction with Pseudoknots
This work explores a new approach in using genetic algorithm to predict RNA secondary structures with pseudoknots. Since only a small portion of most RNA structures is comprised of pseudoknots, the majority of structural elements from an optimal pseudoknot-free structure are likely to be part of the true structure. Thus seeding the genetic algorithm with optimal pseudoknot-free structures will more likely lead it to the true structure than a randomly generated population. The genetic algorithm uses the known energy models with an additional augmentation to allow complex pseudoknots. The nearest-neighbor energy model is used in conjunction with Turner’s thermodynamic parameters for pseudoknot-free structures, and the H-type pseudoknot energy estimation for simple pseudoknots. Testing with known pseudoknot sequences from PseudoBase shows that it out performs some of the current popular algorithms
The effects of kinematic condensation on internally resonant forced vibrations of shallow horizontal cables
This study aims at comparing non-linear modal interactions in shallow horizontal cables with kinematically non-condensed vs. condensed modeling, under simultaneous primary external and internal resonances. Planar 1:1 or 2:1 internal resonance is considered. The governing partial-differential equations of motion of non-condensed model account for spatio-temporal modification of dynamic tension, and explicitly capture non-linear coupling of longitudinal/ vertical displacements. On the contrary, in the condensed model, a single integro-differential equation is obtained by eliminating the longitudinal inertia according to a quasi-static cable stretching assumption, which entails spatially uniform dynamic tension. This model is largely considered in the literature. Based on a multi-modal discretization and a second-order multiple scales solution accounting for higher-order quadratic effects of a infinite number of modes, coupled/uncoupled dynamic responses and the associated stability are evaluated by means of frequency- and force-response diagrams. Direct numerical integrations confirm the occurrence of amplitude-steady or -modulated responses. Non-linear dynamic configurations and tensions are also examined. Depending on internal resonance condition, system elasto-geometric and control parameters, the condensed model may lead to significant quantitative and/or qualitative discrepancies, against the non-condensed model, in the evaluation of resonant dynamic responses, bifurcations and maximal/minimal stresses. Results of even shallow cables reveal meaningful drawbacks of the kinematic condensation and allow us to detect cases where the more accurate non-condensed model has to be used
Nearly Antiferromagnetic Fermi Liquids: A Progress Report
I describe recent theoretical and experimental progress in understanding the
physical properties of the two dimensional nearly antiferromagnetic Fermi
liquids (NAFL's) found in the normal state of the cuprate superconductors. In
such NAFL's, the magnetic interaction between planar quasiparticles is strong
and peaked at or near the commensurate wave vector, . For
the optimally doped and underdoped systems, the resulting strong
antiferromagnetic correlations produce three distinct magnetic phases in the
normal state: mean field above , pseudoscaling between and
, and pseudogap below . I present arguments which suggest that the
physical origin of the pseudogap found in the quasiparticle spectrum below
is the formation of a precursor to a spin-density-wave-state, describe
the calculations based on this scenario of the dynamical spin susceptibility,
Fermi surface evolution, transport, and Hall effect, and summarize the
experimental evidence in its support.Comment: LATEX + PS figures. To appear in the proceedings of the
Euroconference on "Correlations in Unconventional Quantum Liquids," Evora,
Portugal, October 199
Nearly Antiferromagnetic Fermi Liquids: A Progress Report
I describe recent theoretical and experimental progress in understanding the
physical properties of the two dimensional nearly antiferromagnetic Fermi
liquids (NAFL's) found in the normal state of the cuprate superconductors. In
such NAFL's, the magnetic interaction between planar quasiparticles is strong
and peaked at or near the commensurate wave vector, . For
the optimally doped and underdoped systems, the resulting strong
antiferromagnetic correlations produce three distinct magnetic phases in the
normal state: mean field above , pseudoscaling between and
, and pseudogap below . I present arguments which suggest that the
physical origin of the pseudogap found in the quasiparticle spectrum below
is the formation of a precursor to a spin-density-wave-state, describe
the calculations based on this scenario of the dynamical spin susceptibility,
Fermi surface evolution, transport, and Hall effect, and summarize the
experimental evidence in its support.Comment: LATEX + PS figures. To appear in the proceedings of the
Euroconference on "Correlations in Unconventional Quantum Liquids," Evora,
Portugal, October 199
Josephson effect in double-barrier superconductor-ferromagnet junctions
We study the Josephson effect in ballistic double-barrier SIFIS planar
junctions, consisting of bulk superconductors (S), a clean metallic ferromagnet
(F), and insulating interfaces (I). We solve the scattering problem based on
the Bogoliubov--de Gennes equations and derive a general expression for the dc
Josephson current, valid for arbitrary interfacial transparency and Fermi wave
vectors mismatch (FWVM). We consider the coherent regime in which quasiparticle
transmission resonances contribute significantly to the Andreev process. The
Josephson current is calculated for various parameters of the junction, and the
influence of both interfacial transparency and FWVM is analyzed. For thin
layers of strong ferromagnet and finite interfacial transparency, we find that
coherent (geometrical) oscillations of the maximum Josephson current are
superimposed on the oscillations related to the crossover between 0 and
states. For the same case we find that the temperature-induced
transition occurs if the junction is very close to the crossovers at zero
temperature.Comment: 13 pages, 6 figure
Genetic embedded matching approach to ground states in continuous-spin systems
Due to an extremely rugged structure of the free energy landscape, the
determination of spin-glass ground states is among the hardest known
optimization problems, found to be NP-hard in the most general case. Owing to
the specific structure of local (free) energy minima, general-purpose
optimization strategies perform relatively poorly on these problems, and a
number of specially tailored optimization techniques have been developed in
particular for the Ising spin glass and similar discrete systems. Here, an
efficient optimization heuristic for the much less discussed case of continuous
spins is introduced, based on the combination of an embedding of Ising spins
into the continuous rotators and an appropriate variant of a genetic algorithm.
Statistical techniques for insuring high reliability in finding (numerically)
exact ground states are discussed, and the method is benchmarked against the
simulated annealing approach.Comment: 17 pages, 12 figures, 1 tabl
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