Physical and electrical properties of band-engineered SiO2/(TiO2) x (SiO2)1−x stacks for nonvolatile memory applications

In our study, the physical properties of (TiO₂) _x (SiO₂)_1?x , including band-gap, band-offset, and thermal stability and the electrical properties of band-engineered SiO₂/(TiO₂) _x (SiO₂)_1?x tunnel barrier stacks, including the tunneling current and charge-trapping characteristics for applications to nonvolatile memory devices were investigated. It was observed that the band-gap and band-offset of (TiO₂) _x (SiO₂)_1?x can be controlled by adjustment in the composition of the (TiO₂) _x (SiO₂)_1?x films. Ti-silicate film with TiO₂:SiO₂ cycle ratio of 1:5 was maintained in an amorphous phase, even after annealing at 950 °C. The tunneling current of the band-engineered SiO₂/(TiO₂) _x (SiO₂)_1?x stacked tunnel barrier was larger than that of a single SiO₂ barrier under a higher external bias, while the tunneling current of a SiO₂/(TiO₂) _x (SiO₂)_1?x stacked tunnel barrier under a lower external bias was smaller. Charge-trapping tests showed that the voltage shift for SiO₂/(TiO₂) _x (SiO₂)_1?x is slightly larger than that for single SiO₂.     

Constructing connected bicritical graphs with edge-connectivity 2

A graph $G$ is said to be bicritical if the removal of any pair of vertices decreases the domination number of $G$. For a bicritical graph $G$ with the domination number $t$, we say that $G$ is $t$-bicritical. Let $\lambda \left(G\right)$ denote the edge-connectivity of $G$. In [2], Brigham et al. (2005) posed the following question: If $G$ is a connected bicritical graph, is it true that $\lambda \left(G\right)\ge 3?$In this paper, we give a negative answer toward this question; namely, we give a construction of infinitely many connected $t$-bicritical graphs with edge-connectivity $2$ for every integer $t\ge 5$. Furthermore, we give some sufficient conditions for a connected $5$-bicritical graph to have $\lambda \left(G\right)\ge 3$.     

Advances in digital holographic micro-PTV for analyzing microscale flows

The accurate three-dimensional (3D) velocity field measurement technique has been receiving large attention in the study of microfluidics. DHM-PTV technique was developed by combining the digital holographic microscopy and particle tracking velocimetry technique. DHM-PTV is an ideal method for measuring three-component-three-dimensional (3C-3D) velocity field in a microscale flow with a fairly good spatial resolution. The advances in the DHM-PTV technique enable the measurement of various microscale flows, such as transport of red blood cells in a microtube and 3D flows in microfluidic devices. DHM-PTV is also applied in studying the motile behavior of swimming microorganisms. DHM-PTV would play an important role in ascertaining the undiscovered basic physics in various microscale and biofluid flow phenomena. In the current study, the basic principle of the DHM-PTV technique and its typical applications to microscale flows are introduced and discussed.     

Understanding a time reversal process in Lamb wave propagation

This study investigates the time reversal process (TRP) of Lamb wave signals which are transmitted and received by piezoelectric transducers bonded on plate-like structures. A number of previous studies have paid attention to spatial and temporal refocusing capability of an original excitation through the TRP in highly dispersive and complex media. However, when the TRP is applied to Lamb waves in a homogeneous regular waveguide, the refocusing capability is limited due to permanent residual side bands even if the duration of the time reversed signal increases. Based on the reciprocity of elastodynamics and linear piezoelectricity, theoretical interpretation is conducted for the main and residual side bands of the reconstructed signal in the time domain. In particular, the interpretation includes the temporal effect of velocity and amplitude dispersions, the existence of multimodes, and the reflections from boundaries during the TRP. Then, numerical and experimental tests are conducted to validate the theoretical findings of this paper. Practical issues for the successful implementation of the TRP of Lamb waves are briefly addressed as well.     

Effect of apex strake incidence-angle on the vortex development and interaction of a double-delta wing

The vortex flow characteristics of a sharp-edged delta wing with an apex strake was investigated through the visualization and particle image velocimetry (PIV) measurement of the wing-leeward flow region, and the wing-surface pressure measurement. The wing model was a flat-plate, and 65°-sweep cropped-delta wing with sharp leading edges. The apex strake was also a flat-plate wing with a cropped-delta shape of 65°/90° sweep, and it can change its incidence angle. The flow Reynolds number was 2.2 × 10⁵ for the flow visualization and 8.2 × 10⁵ for the PIV and wing-surface pressure measurements. The physics of the vortex flow in the wing-leeward flow region and the suction-pressure distribution on the wing upper-surface were interrelated and analyzed. The effect of a positive (negative) strake incidence-angle was the upward movement of the strake and wing vortices away from (downward movement of the strake and wing vortices toward) the wing-upper surface and the delayed (enhanced) coiling interaction between them. This change of vortex flow characteristics projected directly on the suction pressure distribution on the wing upper-surface.     

Preparation and electrochemical performance of titanium nitride-graphene nanocomposite with high Ti contents and tailored morphology

Titanium nitride (TiN) - graphene (G) nanocomposites are promising for electrochemical charge storage where a high content of Ti species is desired. Herein, we propose an effective method for the preparation of TiN-G nanocomposites with a high concentration of Ti species. These nanocomposites can be successfully achieved through a further deposition of Ti on Ti-graphene oxide (GO) or a thermally exfoliated Ti-GO. Depending on the annealing condition employed (NH₃ and N₂), two types of TiN-G nanocomposites (NH₃ annealing for TiN/G and TiN/G-TE, TE: thermal exfoliation) and a TiO₂-G nanocomposite (N₂ annealing for TiO₂/G-TE) were prepared. These nanocomposites were then investigated for potential application as an electrochemical supercapacitor. Compare with TiO₂/G-TE, the TiN-G nanocomposites both exhibited a higher specific capacitance, although one of these nanocomposites had a lower surface area than TiO₂/G-TE. Among the nanocomposites prepared, TiN/G-TE delivered the best electrochemical performance. The relationship between the physical properties and the capacitive performance of the nanocomposites were systematically evaluated.     

Prüfung von Genussmilehsäure und Weinsäure

Analytical and Bioanalytical Chemistry -     

Characteristic polynomials of complement of graph bundles and their applications

We study the structure of the complement of an F-bundle over a graph G when it can be expressed as an F-bundle over another graph G. In particular, we compute the characteristie polynomial of the complement of an F-bundle when its voltages lie in and abelian subgroup Г of Aut(F) which acts freely and transitively on the vertices of the fiber F Some applications to regular embeddings of graph bundles into Euclidean spaces are also discussed