Novel probes and evaluation procedures to assess field magnitudeand polarization

The immense development rate of wireless technologies has also brought new requirements for the RF design of transmitters. The design challenge is to optimize multiband devices with minimal dimensions and weight as well as an appealing appearance, which nevertheless operate well within varyingly complex environments such as frequently changing positions within the closest vicinity of the human body. The optimization of such transceivers requires new analysis tools providing precise measurement of electric and magnetic field strength distributions, even in the closest proximity of RF transmitters. In this study, novel field probes were analyzed optimized, and constructed enabling not only the assessment of the local field strength, but also information on the polarization of the field. The ellipse parameters are reconstructed by a combination of a downhill simplex and a Givens updating algorithm, which has proven to be fast and robust. The developed probes and procedures greatly enhance the quality of the information needed for analysis and optimization of antennas and transmitters     

Impact of powder morphology on quality of low-pressure injection moulded reaction-bonded net shape oxide ceramics

Low-pressure injection moulding is a very efficient process for net shape manufacturing of ceramic micro parts. In order to obtain sintered ceramic specimens without shape distortion or damages, density gradients in the green bodies have to be avoided. Especially feedstocks with a solid loading near the critical powder volume content often tend to segregate the binder while flowing. However, the value of critical powder content can be significantly influenced by particle size, particle size distribution and particle morphology. This paper compares two powder mixtures of identical chemical compositions with different specific surfaces and morphology and evaluates their workability for low-pressure injection moulding. The aim of this paper is to identify the influence of morphology on feedstock rheology as well as on accuracy, mechanical properties and microstructure of net shape manufactured reaction-bonded zircon ceramics.     

A novel feedback control system – Controlling the material flow in deep drawing using distributed blank-holder force

The performance of a feedback control system is often limited by the quality of the model on which it is based, and often the controller design is based on trial and error due to insufficient modeling capabilities. A framework is proposed where the controller design is based on classical state space control theory and time series. The system plant has been modeled using non-linear finite element and the gain factors for the control loop were identified by solving the optimal control problem using a non-linear least square optimization algorithm.The proposed design method has been applied on a deep drawing operation where the objective was to control material flow throughout the part using only spatial information regarding flange draw-in. The control system controls both the magnitude and distribution of the blank-holder force.The methodology proved stable and flexible with respect to controlling the dynamic behavior of the system and the numerical tests showed that it is possible to control the material flow.Preliminary experimental results show that the proposed control system can eliminate process instability when the process is subject to a systematic error.     

Phosphate uptake from water on a Surfactant-Modified Zeolite and Ca-zeolites

The phosphate adsorption kinetics are determined in batch-wise (noted B) and fixed-bed column (noted C) experiments on a Surfactant-Modified Zeolite (SMZ) and various Ca-zeolites. The influence of phosphate concentration (0.08 or 0.8?mmol/L), presence of NO₃ ^?, HCO₃ ^?, SO₄ ^2? and Cl^? competing anions (individual concentration?=?0.8?meq/L) and flow rate Q (1?C30?mL/min) is studied. Preliminary experiments lead to the selection of the most efficient Ca-LTA and SMZ samples for the subsequent studies. In B experiments, the nature of the used system does not influence the equilibrium removal rate R (??80%) but affects the adsorption kinetics. The equilibrium times are shorter on SMZ than on Ca-LTA, increasing with the phosphate concentration and the presence of competing anions, respectively in the ~0.5?C6 or ~3?C24?h ranges. In C experiments, the phosphate uptake performances on SMZ are higher than in the corresponding B experiments, with in particular higher final q/q_m values. The deterioration of the performances on SMZ in presence of competing anions or with increase of Q is due to the effect of the slow phosphate ion-exchange kinetics and the short used contact time. For similar reasons, sorption on Ca-LTA is lower than on SMZ. For instance, with a 0.8?mmol/L phosphate concentration and a 10?mL/min flow rate, the time-decreasing R values become close to 50 and 10% after filtration of 10 bed-volumes respectively in presence of SMZ and Ca-LTA. Globally, SMZ is clearly more efficient than Ca-LTA, being furthermore a versatile and easily regenerable material.     

Properties of Cs-intercalated single wall carbon nanotubes investigated by 133Cs Nuclear Magnetic resonance

In the present study, we investigated Cs-intercalated single wall carbon nanotubes (SWCNTs) using ¹³³Cs Nuclear Magnetic resonance. We show that there are two types of Cs cations depending on the insertion level. Indeed, at low concentrations, Static spectra analysis shows that the Cs^(α)+ species are fully ionized, i.e. α equal ca.1, while at higher concentrations a second paramagnetically shifted line appears, indicating the formation of Cs^(β)+ ions with β < α ～ +1. At low concentrations and low temperatures the Cs^(α)+ ions exhibit a weak hyperfine coupling to the SWCNT conduction electrons, whereas, at higher temperatures, a thermally activated slow-motion diffusion process of the Cs^(α)+ ions occurs along the interstitial channels present within the carbon nanotube bundles. At high concentrations, the Cs^(β)+ ions seem to occupy well defined positions relative to the carbon lattice. As a matter of fact, the Korringa relaxation behavior suggests a strong hyperfine coupling between Cs nuclei and conduction electrons in the carbon nanotubes and a partial charge transfer, which suggest a plausible Cs(6s)–C(2p) hybridization.     

Investigation of Volatility Method for Measuring Aqueous Sulfuric Acid on Mixed Aerosols

The thermal discrimination or volatility technique is a widely used method exploiting differences in aerosol volatility to discriminate between particles of different chemical composition. In recent years numerous investigators applied this technique to determine the existence and the amount of sulfuric acid in the aerosol phase of aircraft contrails forming in the upper troposphere and lower stratosphere (UT/LS). Although the potential for systematic errors due to incomplete evaporation and recondensation of volatile material as well as internal wall losses was recognized by other investigators, we are not aware of any study on polydisperse aerosol (broad size distribution) incorporating these effects into the volatility technique. Here, a tandem differential mobility analyzer (TDMA) is employed to investigate the performance of a thermal discriminator designed at the University of Missouri-Rolla (UMR). Since sulfuric acid is of particular interest for atmospheric aerosol, this study focused on aqueous sulfuric acid (H 2 SO 4 /H 2 O) aerosol. For an operating temperature of 300°C and an aerosol residence time of more than 0.25 s, we found that complete evaporation of H 2 SO 4 /H 2 O aerosol occurred up to diameters of at least 1.9 w m, which is consistent with theoretical calculations. No evidence for recondensation was found for H 2 SO 4 /H 2 O particle surface area and mass concentrations typical for UT/LS background and aircraft plume conditions. Wall losses were measured and incorporated into a size-resolved version of the volatility method, allowing more accurate measurements of the volatile (H 2 SO 4 /H 2 O) volume fraction of polydisperse aerosol. The increased accuracy was demonstrated using well-characterized, mixed (partially volatile) H 2 SO 4 /H 2 O/NaCl aerosol.     

INFLUENCE OF THE PARTICLE SIZE AND SUPERFICIAL GAS VELOCITY ON THE SUBLIMATION OF PURE SUBSTANCES IN FLUIDIZED BEDS OF DIFFERENT SIZES

In the present study the sublimation of large solid carbon dioxide particles inside fluidized beds of fine particles is investigated. A model which takes the surface area of the sublimable particles into account is used to describe the sublimation kinetics. Based on this model, the results of different experiments, namely single particle experiments using a precision scale, batch experiments in a laboratory-scale fluidized bed and continuous experiments in a larger circulating fluidized bed are compared. The main focus of the study is to evaluate the influences of the particle size, of the inert bed material, of the bed temperature and of the superficial gas velocity, respectively.     

Structure of Duplex Multilayer Pb(Zr0.53Ti0.47)O3> Films Prepared by Sol-Gel Processing

Multilayer PZT films were prepared by sol-gel processing, and their structure and composition were investigated by cross-sectional TEM and EDX analyses. The films made by firing at 600°C (as-deposited films) are composed of alternating porous and dense layers, and the porosity increases by a factor of 2 through heating at 750°C. The pyrochlore phase observed in the as-deposited films turns to the perovskite phase by the heat treatment at 750°C. The Ti/Zr ratio along the film stacking direction is shown to change with the elevation of heat treatment temperature. The porous soft layers are considered to reduce the thermal stress and prevent the introduction of cracks during the firing process.