Luttinger liquid superlattices: realization of gapless insulating phases

We investigate Luttinger Liquid superlattices, a periodic structure composed of two kinds of one-dimensional systems of interacting electrons. We calculate several properties of the low-energy sector: the effective charge and spin velocities, the compressibility, various correlation functions, the Landauer conductance and the Drude weight. The low-energy properties are subsumed into effective parameters, much like homogeneous one-dimensional systems. A generic result is the weighted average nature of these parameters, in proportion to the spatial extent of the underlying subunits, pointing to the possibility of ``engineered'' structures. As a specific realization, we consider a one-dimensional Hubbard superlattice, which consists of a periodic arrangement of two long Hubbard chains with different coupling constants and different hopping amplitudes. This system exhibits a rich phase diagram with several phases, both metallic and insulating. We have found that gapless insulating phases are present over a wide range of parameters.Comment: 16 pages, 15 figures, RevTeX

Discretized Miller approach to assess effects on boundary layer ingestion induced distortion

The performance of propulsion configurations with boundary layer ingestion (BLI) is affected to a large extent by the level of distortion in the inlet flow field. Through flow methods and parallel compressor have been used in the past to calculate the effects of this aerodynamic integration issue on the fan performance; however high-fidelity through flow methods are computationally expensive, which limits their use at preliminary design stage. On the other hand, parallel compressor has been developed to assess only circumferential distortion. This paper introduces a discretized semi-empirical performance method, which uses empirical correlations for blade and performance calculations. This tool discretizes the inlet region in radial and circumferential directions enabling the assessment of deterioration in fan performance caused by the combined effect of both distortion patterns. This paper initially studies the accuracy and suitability of the semi-empirical discretized method by comparing its predictions with CFD and experimental data for a baseline case working under distorted and undistorted conditions. Then a test case is examined, which corresponds to the propulsor fan of a distributed propulsion system with BLI. The results obtained from the validation study show a good agreement with the experimental and CFD results under design point conditions

Predicción del punto de fusión de indoles con base en la estructura molecular usando redes neuronales artificiales

Mediante la aplicación del método de relación cuantitativa de estructura propiedad se determinó un modelo para predecir la temperatura del punto de fusión de indoles a partir de su estructura molecular (n = 86). Usando los programas de computadora Gaussian 98 y PCDM 2.0, se calcularon una serie de descriptores moleculares; descriptores electrónicos, topológicos y geométricos. Para la elaboración del modelo de predicción se empleó la regresiónlinear múltiple entre los descriptores moleculares y la temperatura de los puntos de fusión de los indoles presentes en la base de datos. Dando como resultados un coeficiente de determinación (R2) y un error estándar de estimación (EEE) de 0.73 y 27.42°C respectivamente. Por medio de una red neuronal retropropagación (5: 4: 1) se optimizó el modelo de regresión lineal múltiple, pudiéndose incluir relaciones no lineales entre la estructura molecular y la temperatura del punto de fusión de los indoles, obteniendo mejores resultados en la predicción del puntode fusión para el grupo de entrenamiento (R2 =0.9978) y el grupo de validación (R2 =0.9987). El error cuadrático promedio (MSE) asociado al grupo de entrenamiento y de validación para el modelo de con la red fue 0.006 y 0.006 respectivamente

Tunable beam displacer

We report the implementation of a tunable beam displacer, composed of a polarizing beam splitter (PBS) and two mirrors, that divides an initially polarized beam into two parallel beams whose separation can be continuously tuned. The two output beams are linearly polarized with either vertical or horizontal polarization and no optical path difference is introduced between them. The wavelength dependence of the device as well as the maximum separation between the beams achievable is limited mainly by the PBS characteristics.Comment: 3 pages, 2 figure

Quantum anisotropic Heisenberg chains with superlattice structure: a DMRG study

Using the density matrix renormalization group technique, we study spin superlattices composed of a repeated pattern of two spin-1/2 XXZ chains with different anisotropy parameters. The magnetization curve can exhibit two plateaus, a non trivial plateau with the magnetization value given by the relative sizes of the sub-chains and another trivial plateau with zero magnetization. We find good agreement of the value and the width of the plateaus with the analytical results obtained previously. In the gapless regions away from the plateaus, we compare the finite-size spin gap with the predictions based on bosonization and find reasonable agreement. These results confirm the validity of the Tomonaga-Luttinger liquid superlattice description of these systems.Comment: 6 pages, 6 figure