Weak invariance principle in Besov spaces for stationary martingale differences

The classical Donsker weak invariance principle is extended to a Besov spaces framework. Polygonal line processes build from partial sums of stationary martingale differences as well independent and identically distributed random variables are considered. The results obtained are shown to be optimal

Multifunctional Nanomaterials for Energy Applications

In the last few decades, global energy requirements have grown exponentially, and increased demand is expected in the upcoming decades [...

ZnO nanowire application in chemoresistive sensing: A review

This article provides an overview of the recent development of ZnO nanowires (NWs) for chemoresistive sensing. Working mechanisms of chemoresistive sensors are unified for gas, ultraviolet (UV) and bio sensor types: single nanowire and nanowire junction sensors are described, giving the overview for a simple sensor manufacture by multiple nanowire junctions. ZnO NW surface functionalization is discussed, and how this effects the sensing is explained. Further, novel approaches for sensing, using ZnO NW functionalization with other materials such as metal nanoparticles or heterojunctions, are explained, and limiting factors and possible improvements are discussed. The review concludes with the insights and recommendations for the future improvement of the ZnO NW chemoresistive sensing

Non-catalytic growth of metal oxide nanowires : properties and growth mechanism investigations

This thesis is devoted to the non-catalytic syntheses of metal oxide nanowires (NWs), and investigations of their properties and growth mechanisms. Two different approaches were applied for the syntheses - metal resistive heating and vapor growth methods. The products were thoroughly characterized by electron microscopy, optical and X-ray characterization techniques. The synthesized NWs were examined for field emission (FE) and ultraviolet (UV) sensing applications. The resistive heating of various metals was demonstrated to be an efficient, simple and rapid method for the synthesis of CuO, Fe2O3, V2O5 and ZnO NWs under ambient air conditions. Fe2O3 NW formation was detected after just 2 s of heating; other metal oxide NWs were grown after 10 s. The NW growth mechanism during metal oxidation was explained based on observations of ZnO and Fe2O3 NW growth. The mechanism is based on the diffusion of metal ions to the surface through grain boundaries and to the tip of the growing NW through defect diffusion and by surface diffusion. FE from NWs grown by the resistive heating method exibited promising results for applications in vacuum electronic devices. Cold electron FE measurements showed that CuO NWs have a very low threshold electric field of 4 V/µm at a current density of 0.01 mA/cm². For the vapor growth of ZnO tetrapods (ZnO-Ts) a vertical flow reactor was designed and constructed. It was shown that the morphology of ZnO-Ts could be adjusted via the Zn vapor pressure in the reactor. The highest aspect ratio of ZnO-T legs was obtained at 700 °C, at a Zn partial pressure of 0.08 atm. ZnO-Ts demonstrated application possibilities for transparent and flexible UV sensors. Sensors based on ZnO-Ts showed a 45-fold current increase under UV irradiation with an intensity of 30 µW/cm² at a wavelength of 365 nm, and a response time of 0.9 s. The high performance of the device was explained by the multiple contact barriers

ZnO Nanowires for Dye Sensitized Solar Cells

This chapter provides a broad review of the latest research activities focused on the synthesis and application of ZnO nanowires (NWs) for dye‐sensitized solar cells (DSCs) and composed of three main sections. The first section briefly introduces DSC‐working principles and ZnO NW application advantages and stability issues. The next section reviews ZnO NW synthesis methods, demonstrating approaches for controlled synthesis of different ZnO NW morphology and discussing how this effects the overall efficiency of the DSC. In the last section, the methods for ZnO NW interface modification with various materials are discussed, which include ZnO core‐shell structures with semiconductive or protective layers, ZnO NW hybrid structures with other materials, such as nanoparticles, quantum dots and carbon nanomaterials and their benefit for charge and light transport in DSCs. The review is concluded with some perspectives and outlook on the future developments in the ZnO nanowire application for DSCs

Piezoelectric actuators and their application in precise-positioning systems and space structures

Complex piezoelectric actuators are frequently used in mechanisms of optical systems. They can be bimorph, axial and complex- combined stacks. This paper deals with axial piezostacks used in piezoconverters. They make it possible to develop and unipolar or bipolar motion which ensures the displacement dependent on each piezoelement of the compound stack section. The bifurcation problem of a piezodrive has been solved by evaluating physical properties of piezoelements in piezostacs and sealing material. It has made it possible to prove that piezostacs have a lot of static operation possibilities. The original solution of the actuator enabled the choice of optimal initial stresses in piezostacs. The experimental investigation of piezodrives with combined piezostacs have revealed the possibilities to optimize the design and materials for obtaining maximum displacement. These piezoelectric actuators may be applied in various systems like gyroscopes, telescopes

A Central Limit Theorem, and related results, for a two-color randomly reinforced urn

We prove a Central Limit Theorem for the sequence of random compositions of a two-color randomly reinforced urn. As a consequence, we are able to show that the distribution of the urn limit composition has no point masses.Comment: typos correcte