Interest For Many Applications Research Articles

Rutile-type dense ceramics fabricated by pressureless sintering of Ti 1− xRu xO 2 powders prepared by sol–gel

Materials in the TiO 2–RuO 2 system, in different shapes, as thin films, coatings, fine powders, xerogels and aerogels are of great interest for many applications, such as energy storage and production systems, solar cells, chemical sensors, electronics, gas separation processes, and industrial electrochemistry. However, a serious drawback in the processing of materials based on RuO 2 is the well-established chemical reactivity above ∼700 °C where RuO 2 becomes volatile and oxidizes to RuO 3/RuO 4 gases (in air) or reduces to Ru metal (in a vacuum). For this reason, it is not obvious to attain dense materials in the systems containing Ru. In this study, a novel method has been used to obtain rutile-type Ti 1− x Ru x O 2 ( x = 0.05, 0.08 and 0.10) as dense ceramics without the use of the hot-pressing for the sintering step. The relative densities of the materials prepared were higher than 99.0 ρ th %). This method combines the sol–gel synthesis, a pressureless fast-firing method (heating and cooling rate of 20 °C min −1) at 1350 °C for 10 min and the use of a buffer during the sintering that provides a RuO 3 + RuO 4 rich atmosphere.

Dynamic materials behavior of a porous pressureless sintered steel and a HIPped steel

Dampening of shock waves is of interest in many applications. The material studied is a low carbon steel alloy as it is usually used for sintered automotive parts. The low carbon steel alloy was in the initial state pressure less sintered with a density of about 83% of the theoretical density. Some specimens had been hot isostatically pressed (HIPped) at 1050 bar and 1120°C for 1 h. Dynamic compression tests revealed that no Pochhammer-Cree vibration occured for the porous material whereas strong vibration could be observed for the HIPped steel alloy. Planar plate impact tests had been performed in order to study the influence of the porous microstructure on shock waves. The results show that the shock wave velocity is drastically decreased compared to dense materials. It can be concluded that a microstructure with low porosity and small homogeneously distributed pores is an excellent dampening material for strong shock waves.

Strehl ratio and scintillation theory for uplink Gaussian-beam waves: beam wander effects

First-order weak-fluctuation Rytov theory predicts that the longitudinal (on-axis) component of the scintillation index of an uplink collimated beam will become significantly smaller as the size of the transmitter aperture increases up to around 100 cm. However, the results of recent computer simulations are at odds with this behavior, and we believe that this discrepancy is due to the fact that the conventional Rytov theory does not correctly account for the effects of beam wander on the scintillation index. We present a theoretical structure that accurately describes far-field irradiance fluctuations caused by uncorrected beam wander. This new theory is validated by demonstrating excellent agreement between the predicted scintillation index and computer code results for both tracked and untracked beams. For many applications of practical interest, such as free-space optical communications, a good understanding of the time-average Strehl ratio is also essential simulation results for this parameter are presented and shown to be in good agreement with the theory.

Temperature dependence of large-scale water-retention curves: a case study

A local-scale model for temperature-dependence of water-retention curves may be applicable to large scales. Consideration of this temperature dependence is important for modeling unsaturated flow and transport in the subsurface in numerous cases. Although significant progress has been made in understanding and modeling this temperature effect, almost all the previous studies have been limited to small scales (on the order of several centimeters). Numerical experiments were used to investigate the possibility of extending a local-scale model for the temperature-dependence of water retention curves to large scales (on the order of meters). Temperature effects on large-scale hydraulic properties are of interest in many practical applications. Numerical experiment results indicate that the local-scale model can indeed be applicable to large-scale problems for special porous media with high air entry values. A typical porous medium of this kind is the porous tuff matrix in the unsaturated zone of Yucca Mountain, Nevada, the proposed geologic disposal site for national high-level nuclear wastes. Whether this finding can approximately hold for general cases needs to be investigated in future studies.

Testing for Covariate Effects in the Fully Nonparametric Analysis of Covariance Model

Traditional inference questions in the analysis of covariance mainly focus on comparing different factor levels by adjusting for the continuous covariates, which are believed to also exert a significant effect on the outcome variable. Testing hypotheses about the covariate effects, although of substantial interest in many applications, has received relatively limited study in the semiparametric/nonparametric setting. In the context of the fully nonparametric analysis of covariance model of Akritas et al., we propose methods to test for covariate main effects and covariate–factor interaction effects. The idea underlying the proposed procedures is that covariates can be thought of as factors with many levels. The test statistics are closely related to some recent developments in the asymptotic theory for analysis of variance when the number of factor levels is large. The limiting normal distributions are established under the null hypotheses and local alternatives by asymptotically approximating a new class of quadratic forms. The test statistics bear similar forms to the classical F-test statistics and thus are convenient for computation. We demonstrate the methods and their properties on simulated and real data.

Nonlinear magneto-optical rotation with frequency-modulated light in the geophysical field range

Recent work investigating resonant nonlinear magneto-optical rotation (NMOR) related to long-lived $({\ensuremath{\tau}}_{\mathrm{rel}}\ensuremath{\sim}1\mathrm{s})$ ground-state atomic coherences has demonstrated potential magnetometric sensitivities exceeding ${10}^{\ensuremath{-}11}\phantom{\rule{0.3em}{0ex}}\mathrm{G}∕\sqrt{\mathrm{Hz}}$ for small $(\ensuremath{\lesssim}1\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{G}$) magnetic fields. In the present work, NMOR using frequency-modulated light (FM NMOR) is studied in the regime where the longitudinal magnetic field is in the geophysical range$(\ensuremath{\sim}500\mathrm{mG})$, of particular interest for many applications. In this regime a splitting of the FM NMOR resonance due to the nonlinear Zeeman effect is observed. At sufficiently high light intensities, there is also a splitting of the FM NMOR resonances due to ac Stark shifts induced by the optical field, as well as evidence of alignment-to-orientation conversion type processes. The consequences of these effects for FM-NMOR-based atomic magnetometry in the geophysical field range are considered.

Laser–plasma accelerator: status and perspectives

Laser-plasma accelerators deliver high-charge quasi-monoenergetic electron beams with properties of interest for many applications. Their angular divergence, limited to a few mrad, permits one to generate a small gamma ray source for dense matter radiography, whereas their duration (few tens of fs) permits studies of major importance in the context of fast chemistry for example. In addition, injecting these electron beams into a longer plasma wave structure will extend their energy to the GeV range. A GeV laser-based accelerator scheme is presented; it consists of the acceleration of this electron beam into relativistic plasma waves driven by a laser. This compact approach (centimetres scale for the plasma, and tens of meters for the whole facility) will allow a miniaturization and cost reduction of future accelerators and derived X-ray free electron laser (XFEL) sources.

Comparison of Common Segmentation Techniques Applied to Transmission Electron Microscopy Images

ABSTRACTNanoparticles are of interest in many applications since their decreased size may give them properties that are very different from bulk material. Often nanoparticle properties such as size (diameter) and size distribution are evaluated using transmission electron microscopy (TEM). These parameters, size and size distribution, can be more easily obtained from digitized TEM images by mapping particle signal to black and background pixel to white in a process known as thresholding then performing an algorithm known as a particle analysis. The goal of this study was to compare the ability of several popular thresholding algorithms to segment TEM images. Performance of the thresholding algorithms was evaluated through qualitative and quantitative measures. Results show that the choice of a thresholding algorithm will strongly affect the results obtained from particle analysis.

Optimal reproduction of spot colors on a digital press

Digital presses manufactured by companies such as Hewlett-Packard, NexPress, and Xerox are rapidly gaining acceptance in the marketplace. Since these devices typically use four or a few more colors in their printing processes, the degree to which they can accurately simulate the larger gamut of spot colors is of considerable interest in many applications. Pantone licenses printers at the end of an extensive color evaluation and analysis procedure, during which a lookup table is developed, giving the optimal inking values for matching or simulating each color of the PANTONE MATCHING SYSTEM®. The stability of the printing process over time gets a thorough test during this procedure, which uses both instrumental and visual matching techniques. Gamut mapping algorithms used in commercial profile-building software were developed for the reproduction of images, which are ensembles of colors; they do not usually yield optimal results for the case of individual colors. Development work at Pantone is aimed at a better understanding of how a skilled colorist makes the decisions leading to an optimal simulation of a color.

Three-Dimensional Microfabrication by Two-Photon Lithography

AbstractThe controlled formation of submicrometer-scale structures in three dimensions is of increasing interest in many applications. Not intended to produce the smallest structures, but instead aimed at complex topographies, two-photon lithography is an intrinsic 3D lithography technique that enables the fabrication of structures difficult to access by conventional single-photon processes with far greater spatial resolution than other 3D microfabrication techniques. By tightly focusing a femtosecond laser beam into a resin, subsequent photo-induced reactions such as polymerization occur only in the close vicinity of the focal point, allowing the fabrication of a 3D structure by directly writing 3D patterns. The current research effort in two-photon lithography is largely devoted to the design and synthesis of high-efficiency photoinitiators and sensitizers, as well as the development of new materials and systems. This article provides an overview of the progress in two-photon processes for the formation of complex images and the development of patterned structures.

A note on non-identifiability of mark survival function

The so-called mark variable which combines both quantity and quality of a patient's life is a tempting measure in evaluation of therapies. The survival function of such mark variable, referred to as mark survival function in this note, is a primary interest in many applications. Much effort has been made on the estimation for this survival function. Nevertheless, we show in this note that mark survival function is unidentifiable under conventional assumption. Illustrative examples are provided to confirm the non-identifiability of mark survival function.

A note on asymptotic approximations of distributions for maxima of wave crests

The distribution of maxima during a given time interval is of interest in many applications in risk analysis. Within the framework of stationary Gaussian processes, several theoretical results considering asymptotics from different aspects have been derived for this distribution. In this note, we review results from the theory and study the accuracy of these approximations by exemplifying with a model for wave heights from oceanography. It turns out that for high values and the time periods normally encountered for buoy measurements, care should be taken in use of approximation based on the Gumbel distribution.

Nanowires and 1D arrays fabrication: An overview

Since the discovery of M41S materials family in 1992, some special features like aligned pores perpendicularly to the substrate surface and long range order, have been looked for with great interest for many applications of these kind of nanomaterials. The growth of thin films displaying meso- and nano-porous structures have attracted the attention of many research groups in the last decade and, with that aim several techniques such as: MBE, CVD, AFM, ion beam lithography, etc., have been used. On the other hand, a lot of down–top techniques, particularly those in which, self-assembly processes play a relevant role in the growth mechanisms of that nanostructures have been reported. Among them, electrochemical techniques constitute one of the most used to fabricate highly ordered nanostructures to be used as templates for replicating other nanostructured materials and for growing functionalized material arrays. In this paper, a brief overview on the nanofabrication techniques is done mainly of those related with the nanowires and, in general, 1D nanostructures fabrication. In addition, we show some results on ordered and disordered nanoporous anodic alumina membranes (AAM) and anodic titania membranes (ATM), respectively. Besides some functionalized systems based on these membranes used as templates are presented such as, magnetic nanowire arrays, biosensors, and carbon nanotubes. The potentiality of these systems for applications on diverse field, such as, nanoelectronic, magneto-optic, biotechnology and optoelectronic is demonstrated.

Biphasic Janus particles with nanoscale anisotropy

Advances in the field of nanotechnology have fuelled the vision of future devices spawned from tiny functional components that are able to assemble according to a master blueprint. In this concept, the controlled distribution of matter or 'patchiness' is important for creating anisotropic building blocks and introduces an extra design parameter--beyond size and shape. Although the reliable and efficient fabrication of building blocks with controllable material distributions will be of interest for many applications in research and technology, their synthesis has been addressed only in a few specialized cases. Here we show the design and synthesis of polymer-based particles with two distinct phases. The biphasic geometry of these Janus particles is induced by the simultaneous electrohydrodynamic jetting of parallel polymer solutions under the influence of an electrical field. The individual phases can be independently loaded with biomolecules or selectively modified with model ligands, as confirmed by confocal microscopy and transmission electron microscopy. The fact that the spatial distribution of matter can be controlled at such small length scales will provide access to unknown anisotropic materials. This type of nanocolloid may enable the design of multicomponent carriers for drug delivery, molecular imaging or guided self-assembly.

Synthesis of high-quality semiconductor nanoparticles in a composite hot-matrix

Semiconductor nanocrystals are of a great interest for many practical applications which motivates the search of low cost and environmental-friendly methods for their manufacturing. Here we report the synthesis of CdSe and CdS nanoparticles utilizing composite matrix of liquid paraffin as a non-coordinating solvent and stearic acid as a coordinating ligand. The nanoparticle growth kinetics is compared to that of the classical synthesis in trioctylphosphine oxide matrix. It is found that the nucleation and crystal growth are remarkably affected by the coordinating ligand. The CdSe and CdS nanocrystals can be isolated and purified from the matrix which makes it possible their large-scale synthesis for applications.

Improving feature extraction by replacing the Fisher criterion by an upper error bound

A lot of alternatives and constraints have been proposed in order to improve the Fisher criterion. But most of them are not linked to the error rate, the primary interest in many applications of classification. By introducing an upper bound for the error rate a criterion is developed which can improve the classification performance.

Improving the Damping Properties of Composites Using Ferroelectric Inclusions

This paper presents a recently developed composite constructed in an attempt to improve damping properties by using ferroelectric inclusions in a constrained medium. Several samples of this new composite have been made and tests of their damping properties are presented here. Damping properties of materials are of great interest in many applications. The focus here is on the development of composites with ferroelastic components to develop a new class of materials having improved temperature-dependent damping properties. Typical damping materials, such as viscoelastic materials, have damping values that decrease with increasing temperature. The work presented here considers a material system consisting of fine particles of vanadium dioxide (VO2) and zinc oxide (ZnO) incorporated into matrix materials (tin and polymer adhesives) to produce composite materials with improved damping properties. A number of mechanical damping tests have been conducted on the prepared composites at a frequency range of 0-2000 Hz and over a broad temperature range using piezoceramic exciters and miniature accelerometers. The mechanical vibration test results show that VO2 and ZnO give significantly higher damping values at ≈68° C (155° F) and 29° C (85° F). For example, ≈15 and 12% damping is achieved at the first and second resonance frequencies, respectively. This significant improvement on the damping of the composite materials may be because of the ferroelasticity and/or viscoelasticity at those particular temperatures. It has also been observed that etching of substrate surfaces improves the adhesion between composite materials and surfaces for better damping results. These composites offer high damping at elevated temperatures and hence may provide useful solutions to applications requiring increased damping.

A cosine similarity-based negative selection algorithm for time series novelty detection

Detecting the new or anomalous signal sequences in the observed time series data is a problem of great practical interest for many applications. The bio-inspired negative selection algorithm, whose main idea is to discriminate the non-self pattern from self pattern, has drawn much attention because only normal information is needed for training. Most of the proposed algorithms are based on binary-valued string matching. A real-valued negative selection algorithm for novelty detection in vibration signal is implemented in this paper. The vector set for calculation is constructed by sampling the discrete time series from a moving time window. The matching affinity between two vectors is measured by cosine similarity. The calculated results show that the cosine similarity-based algorithm is more practical for potential applications in online signal monitoring.

Meshless Methods Coupled with Other Numerical Methods

Meshless or mesh-free (or shorten as MFree) methods have been proposed and achieved remarkable progress over the past few years. The idea of combining MFree methods with other existing numerical techniques such as the finite element method (FEM) and the boundary element method (BEM), is naturally of great interest in many practical applications. However, the shape functions used in some MFree methods do not have the Kronecker delta function property. In order to satisfy the combined conditions of displacement compatibility, two numerical techniques, using the hybrid displacement shape function and the modified variational form, are developed and discussed in this paper. In the first technique, the original MFree shape functions are modified to the hybrid forms that possess the Kronecker delta function property. In the second technique, the displacement compatibility is satisfied via a modified variational form based on the Lagrange multiplier method. Formulations of several coupled methods are presented. Numerical examples are presented to demonstrate the effectiveness of the present coupling methods.

Synthesis of TiO2 Nanoparticles Using Chemical Vapor Condensation

AbstractNano-sized TiO2 particles are of interest for many applications, including use as photocatalysts and in heat transfer fluids (nanofluids). In the present study, TiO2 nanoparticles with controllable phase and particle size have been obtained through homogeneous gas-phase nucleation using chemical vapor condensation (CVC). The phase and particle size of TiO2 nanoparticles under various processing conditions have been characterized using x-ray diffraction and transmission electron microscopy. Chamber temperature and pressure were found to be two key parameters affecting particle phase and size. Pure anatase phase was observed for synthesis temperatures as low as 600 °C with chamber pressure varying from 20-50 Torr. When the furnace temperature was increased to 1000 °C at a pressure of 50 Torr, a mixture of anatase and rutile phases was observed, with the predominant phase being anatase. The average particle size under all the experimental conditions was observed to be less than 20 nm.