Electronic Hong-Ou-Mandel interferometry in two-dimensional topological insulators

The edge states of a two-dimensional topological insulator are characterized by their helicity, a very remarkable property which is related to the time-reversal symmetry and the topology of the underlying system. We theoretically investigate a Hong-Ou-Mandel like setup as a tool to probe it. Collisions of two electrons with the same spin show a Pauli dip, analogous to the one obtained in the integer quantum Hall case. Moreover, the collisions between electrons of opposite spin also lead to a dip, known as $\mathbb{Z}_{2}$ dip, which is a direct consequence of the constraints imposed by time-reversal symmetry. In contrast to the integer quantum Hall case, the visibility of these dips is reduced by the presence of the additional edge channels, and crucially depends on the properties of the quantum point contact. As a unique feature of this system, we show the possibility of three-electron interference, which leads to a total suppression of the noise independently of the point contact configuration. This is assured by the peculiar interplay between Fermi statistics and topology. This work intends to extend the domain of applicability of electron quantum optics.Comment: 12 pages, 7 figure

Sinusoidal nanotextures for light management in silicon thin film solar cells

Recent progresses in liquid phase crystallization enabled the fabrication of thin wafer quality crystalline silicon layers on low cost glass substrates enabling conversion efficiencies up to 12.1 . Because of its indirect band gap, a thin silicon absorber layer demands for efficient measures for light management. However, the combination of high quality crystalline silicon and light trapping structures is still a critical issue. Here, we implement hexagonal 750 nm pitched sinusoidal and pillar shaped nanostructures at the sun facing glass silicon interface into 10 m thin liquid phase crystallized silicon thin film solar cell devices on glass. Both structures are experimentally studied regarding their optical and optoelectronic properties. Reflection losses are reduced over the entire wavelength range outperforming state of the art anti reflective planar layer systems. In case of the smooth sinusoidal nanostructures these optical achievements are accompanied by an excellent electronic material quality of the silicon absorber layer enabling open circuit voltages above 600 mV and solar cell device performances comparable to the planar reference device. For wavelengths smaller than 400 nm and higher than 700 nm optical achievements are translated into an enhanced quantum efficiency of the solar cell devices. Therefore, sinusoidal nanotextures are a well balanced compromise of optical enhancement and maintained high electronic silicon material quality which opens a promising route for future optimizations in solar cell designs for silicon thin film solar cells on glas

Mitigating optical losses in crystalline silicon thin film solar cells on glass

Liquid phase crystallized silicon thin film solar cells on glass provide efficiencies up to 14.2 . While open circuit voltage and fill factor are already comparable to wafer based devices, short circuit current density is reduced due to incomplete light absorption. This paper analyzes the losses of current device designs in experiment and one dimensional simulations, revealing the low absorber thickness of 15 20 amp; 956;m as well as the planar glass silicon interface as the main cause of non absorption. Interface textures, in particular a sinusoidal texture and a smooth anti reflective three dimensional SMART texture, are discussed concerning their potential to mitigate these losses, allowing to reduce losses at the glass silicon interface by at least 40 relative. Taking the electronic interface quality into account, the SMART texture is identified as the most promising texture for light management in liquid phase crystallized silicon thin film solar cells on glas

Técnicas laboratoriais para isolamento de Campylobacter em material avícola.

Projeto/Plano de Ação: 03.08.06.004

Improved Light Management in Crystalline Silicon Thin Film Solar Cells by Advanced Nano Texture Fabrication

We present a texturing method for liquid phase crystallized silicon thin film solar cells enabling a maximum achievable short circuit current density of 36.5mA cm 2 due to optimized light management compared to current textured device

Tailoring nano textures for optimized light in coupling in liquid phase crystallized silicon thin film solar cells

Thin film solar cells based on liquid phase crystallized silicon LPC Si with 8 20 m thick absorber layers demand for advanced light management to achieve high photocurrent densities. Open circuit voltages Voc gt;600 mV underline the high silicon material quality of LPC silicon thin films on nano textured glass superstrates. We present a 500 nm pitched sinusoidal nano texture which outperforms larger pitched gratings with respect to light in coupling at the buried glass silicon interface. In the wavelength range of interest reflection of incident light is minimized to values close to 4 , which is the reflection at the sun facing air glass interface. Further, the electronic material quality of sinusoidally textured devices is analyzed on basis of a comparison of maximum achieved open circuit voltages on different texture types. The Voc on sinusoidally textured glass superstrates could be raised to 630 mV by changing the interlayer deposition method from a PVD to a PECVD process. Thus, we are able to unify high optical and electronic properties of silicon absorber layers on sinusoidal textured glass substrates. These results constitute a crucial step towards fully exploiting the optical potential of LPC silicon thin film solar cell

Building Neural Network Models for Time Series: A Statistical Approach

This paper is concerned with modelling time series by single hidden layer feedforward neural network models. A coherent modelling strategy based on statistical inference is presented. Variable selection is carried out using existing techniques. The problem of selecting the number of hidden units is solved by sequentially applying Lagrange multiplier type tests, with the aim of avoiding the estimation of unidentified models. Misspecification tests are derived for evaluating an estimated neural network model. A small-sample simulation experiment is carried out to show how the proposed modelling strategy works and how the misspecification tests behave in small samples. Two applications to real time series, one univariate and the other multivariate, are considered as well. Sets of one-step-ahead forecasts are constructed and forecast accuracy is compared with that of other nonlinear models applied to the same series.

Additives incorporated into urea to reduce nitrogen losses after application to the soil.

The objective of this work was to develop urea-based fertilizers with internal incorporation of urease inhibitors and other additives in the granule. The effects of the incorporation of NBPT, copper (Cu+2), boric acid (H3BO3), elemental sulphur (Sº), and a clay mineral from the zeolite group in powder urea - with ten different combinations of these additives - were evaluated as to N losses by volatilization and leaching. The losses in laboratory-developed formulations were compared with those of commercial fertilizers coated with the same additives (Super N, FH Nitro Mais, and FH Nitro Gold). The evaluations were made in greenhouse conditions, using a Ultisol accommodated in PVC columns. Nitrate and ammonium leaching was evaluated in the solution percolated through the soil columns. Ammonia volatilization was measured with a semi-open static chamber. The incorporation of urease inhibitors (NBPT, H3BO3, and Cu+2) into the urea granules was efficient to reduce N volatilization. Ammonia volatilization in the laboratory-developed ureas was lower than in commercial fertilizers coated with the same additives, while ammonium sulfate losses by leaching were similar. The addition of zeolite does not reduce N volatilization. Mineral N leaching in the soil profile is not affected by urease inhibitors.Título em português: Aditivos incorporados à ureia para reduzir perdas de nitrogênio após aplicação ao solo

Imprinted Nanostructures for Light Management in Crystalline Silicon Thin Film Solar Cells on Glass

We present various imprinted nanostructures for light management in liquid phase crystallized silicon thin film solar cells enabling both, increased jsc by enhanced absorption and excellent electronic material quality with Voc values above 640 m