Effective Dielectric Constant of Two Phase Systems

Theoretical approaches to electrical characterization of two phase systems are mostly limited to the systems where the individual components exhibit the same type of conductivity (pure dielectric or pure conductive systems). In this article, the brick wall geometry is extended to the mixed conductive systems with percolation. Impedance spectroscopy techniques were used for experimental investigation of slurries. Various metal oxide powders and host liquids were analyzed using a wide range of solids loadings. Comparison of experimental results with theoretical predictions shows good fitting of the experimental data. Parameters (the values of permittivity for both phases and percolation threshold) calculated from this fitting match the corresponding values of components of two phase systems. Analysis of both low frequency (less than 10 kHz) as well as high frequency (10 kHz to 1 MHz) responses of impedance spectra allows determining of permittivity of dielectric powders suspended in various liquids. Low frequency response provides better accuracy for systems with high dielectric contrast between components, while high frequency response is more accurate for low contrast systems

Impedance Spectroscopy of BaTiO₃ Cubes Suspended in Lossy Liquids as a Physical Model of Two-phase System

Impedance spectroscopy techniques were used for analysis of the physical model in a two-phase system toward determining of dielectric constant of dielectric particles suspended in liquids at various solids loading (volume fraction) levels. Model experimental studies were conducted using BaTiO3 as a dielectric material that was prepared as small cubes of uniform size (2×2×1 mm). Barium titanate (BT) cubes having a dielectric constant of 3850 were immersed in liquids of low dielectric constant and moderate electrical conductivity. Measured impedance spectra consisted of two semicircles, which were fitted for (R∥C)(R∥C) equivalent circuit. The parameters obtained from fitting were compared with the data acquired from simulations of brick layer models and Maxwell-Wagner effective media model. In the investigated range of volume fractions the Maxwell-Wagner model correlates well with the data extracted from measurements

Microstructure and Electrical Properties of Fe,Cu Substituted (Co,Mn)₃O₄ Thin Films

In this work, thin films (~1000 nm) of a pure MnCo2O4 spinel together with its partially substituted derivatives (MnCo1.6Cu0.2Fe0.2O4, MnCo1.6Cu0.4O4, MnCo1.6Fe0.4O4) were prepared by spray pyrolysis and were evaluated for electrical conductivity. Doping by Cu increases the electrical conductivity, whereas doping by Fe decreases the conductivity. For Cu containing samples, rapid grain growth occurs and these samples develop cracks due to a potentially too high thermal expansion coefficient mismatch to the support. Samples doped with both Cu and Fe show high electrical conductivity, normal grain growth and no cracks. By co-doping the Mn, Co spinel with both Cu and Fe, its properties can be tailored to reach a desired thermal expansion coefficient/electrical conductivity value

Radiofrequency ablation of small renal masses as an alternative to nephron-sparing surgery : preliminary results

INTRODUCTION: Radical endoscopic minimal-invasive treatment methods, such as thermal ablation, are sought as an alternative to standard radical surgical treatment of kidney neoplasms. We analysed patients who could be qualified for radical treatment due to T1a renal tumour. MATERIAL AND METHODS: Twenty-three patients out of 129 who underwent radiofrequency thermal ablation of kidney tumours in the years 2003-2010 were analysed. The inclusion criteria were age below 70 years, lack of major comorbidities (ASA score 1, 2), and competent contralateral kidney. In all cases tumour size was below 4 cm. All patients were followed up with computed tomography (CT) and ultrasonography (USG) every 6 months for 3 years. RESULTS: In 20 patients kidney tumour was biopsied before radiofrequency ablation (RFA) and 10 of these biopsies were positive and revealed cancer. Six patients required additional treatment due to recurrence visible in CT – 3 with a positive biopsy result, 1 with negative and 2 without biopsy. Three of them were treated with a second session of RFA, 1 with radical nephrectomy and 2 with partial nephrectomy. No disease dissemination was observed and all patients who received additional treatment remain disease free. CONCLUSIONS: The RFA can be safely used in selected patients with T1a tumour as an alternative to partial nephrectomy. Careful follow-up is required after thermal ablation and allows early detection and successful treatment of recurrences

Ceria based protective coatings for steel interconnects prepared by spray pyrolysis

AbstractStainless steels can be used in solid oxide fuel/electrolysis stacks as interconnects. For successful long term operation they require protective coatings, that lower the corrosion rate and block chemical reactions between the interconnect and adjacent layers of the oxygen or the hydrogen electrode. One of the promising coating materials for the hydrogen side is ceria. Using standard sintering techniques, ceria sinters at around 1400°C which even for a very short exposure would destroy the interconnect. Therefore in this paper a low temperature deposition method, i.e. spray pyrolysis, is used to deposit thin (∼400nm), continuous CeO2 layers on Crofer 22 APU steel substrates. Influence of the deposition parameters on layer quality is elucidated in this work

Electrical Properties of YSZ Films Prepared by Net Shape Technology

The preparation of dense electrolyte films for most electrochemical devices is a crucial technological process. Net shape technology is a new approach, which uses a combination of colloidal suspensions and polymer precursor techniques, to obtain the dense electrolyte layers. It allows the overlapping of the thickness range from 1 to 10 m in which other preparation techniques experience difficulties. Net shape processing is a low-temperature technology ͑preparation temperature can be as low as 400°C͒ and it eliminates shrinkage of the film during the densification stage, so chemical reactions between the substrate and the film can be minimized. In this study two types of dense substrates were used to confirm these features of the net shape technology: single-crystal sapphire and platinum foil. It was shown that dense yttria-stabilized zirconia ͑YSZ͒ layers can be obtained on both types of substrates at temperatures as low as 400°C. Moreover, further higher annealing temperature does not produce either shrinkage or cracking of the film. Electrical properties of YSZ films were measured in plane ͑on sapphire͒ and through the film ͑on platinum͒ using impedance spectroscopy and two-probe dc methods. Solid oxide fuel cells ͑SOFCs͒ are one of the most efficient energy conversion devices. 1 The main demand in the current SOFC development is lowering operation temperature to the range of 600-800°C. In order to lower operational temperature and increase or at least sustain performance comparable to that at high-temperature SOFCs, it is necessary to decrease the resistance of the electrolyte. One of the ways to achieve this goal is to decrease the thickness of the electrolyte. Yttria-stabilized zirconia ͑YSZ͒ is the most commonly used material as SOFC electrolyte, and several deposition techniques have been used to develop thin-film YSZ on either the anode or cathode. The methods include chemical and physical deposition, such as electrochemical vapor deposition ͑EVD͒ 2 or magnetron sputtering, 3 and liquid precursor and powder processing techniques such as polymer spin coating 4 or tape casting. The aim of this research was to develop a low-temperature method for deposition of 1-10 m thick YSZ electrolyte using a combination of YSZ powder and YSZ polymeric precursor ͑net shape processing͒. Experimental The YSZ (Zr 0.84 Y 0.16 O x ) films were prepared on platinum and sapphire substrates by net shape technology, which combines colloidal suspension and polymer precursor techniques. The colloidal suspension was prepared using commercially available YSZ powder ͑Zirconium Sales of America, Inc.͒ with an initial grain size of about 100 nm, which was dispersed ultrasonically in water and ethanol. The suspension contained about 50 wt % YSZ powder. The YSZ polymer was prepared using zirconium chloride and yttrium nitrate precursors ͑Alfa Aesar͒. Our previous studies of YSZ films derived from polymer precursor only shows that single-phase single YSZ structure is obtained at as low as 400°C. 8 A schematic diagram of film preparation is presented in Scanning electron microscopy ͑SEM͒ images were obtained using a field emission scanning electron microscope Hitachi S-4700, while the atomic force microscopy ͑AFM͒ images were obtained using a scanning probe microscopy Digital Instruments Nanoscope IIIa. Two-probe dc measurements were performed using a Keithley 6517A electrometer. The dc results were confirmed by two-probe impedance spectroscopy, which was performed using a Solartron 1296 dielectric interface together with a Solartron 1260 impedance * Electrochemical Society Active Member.

Preoperative quantification of aortic valve stenosis: comparison of 64-slice computed tomography with transesophageal and transthoracic echocardiography and size of implanted prosthesis

Precise measurements of aortic complex diameters are essential for preoperative examinations of patients with aortic stenosis (AS) scheduled for aortic valve (AV) replacement. We aimed to prospectively compare the accuracy of transthoracic echocardiography (TTE), transoesophageal echocardiography (TEE) and multi-slice computed tomography (MSCT) measurements of the AV complex and to analyze the role of the multi-modality aortic annulus diameter (AAd) assessment in the selection of the optimal prosthesis to be implanted in patients surgically treated for degenerative AS. 20 patients (F/M: 3/17; age: 69 ± 6.5 years) with severe degenerative AS were enrolled into the study. TTE, TEE and MSCT including AV calcium score (AVCS) assessment were performed in all patients. The values of AAd obtained in the long AV complex axis (TTE, TEE, MSCT) and in multiplanar perpendicular imaging (MSCT) were compared to the size of implanted prosthesis. The mean AAd was 24 ± 3.6 mm using TTE, 26 ± 4.2 mm using TEE, and 26.9 ± 3.2 in MSCT (P = 0.04 vs. TTE). The mean diameter of the left ventricle out-flow tract in TTE (19.9 ± 2.7 mm) and TEE (19.5 ± 2.7 mm) were smaller than in MSCT (24.9 ± 3.3 mm, P < 0.001 for both). The mean size of implanted prosthesis (22.2 ± 2.3 mm) was significantly smaller than the mean AAd measured by TTE (P = 0.0039), TEE (P = 0.0004), and MSCT (P < 0.0001). The implanted prosthesis size correlated significantly to the AAd: r = 0.603, P = 0.005 for TTE, r = 0.592, P = 0.006 for TEE, and r = 0.791, P < 0.001 for MSCT. Obesity and extensive valve calcification (AV calcium score ≥ 3177Ag.U.) were identified as potent factors that caused a deterioration of both TTE and MSCT performance. The accuracy of AAd measurements in TEE was only limited by AV calcification. In multivariate regression analysis the mean value of the minimum and maximum AAd obtained in MSCT-multiplanar perpendicular imaging was an independent factor (r = 0.802, P < 0.0001) predicting the size of implanted prosthesis. In patients with AS echocardiography remains the main diagnostics tool in clinical practice. MSCT as a 3-dimentional modality allows for accurate measurement of entire AV complex and facilitates optimal matching of prosthesis size

Nanoparticle Orientation to Control RNA Loading and Ligand Display on Extracellular Vesicles for Cancer Regression

Nanotechnology offers many benefits, and here we report an advantage of applying RNA nanotechnology for directional control. The orientation of arrow-shaped RNA was altered to control ligand display on extracellular vesicle membranes for specific cell targeting, or to regulate intracellular trafficking of small interfering RNA (siRNA) or microRNA (miRNA). Placing membrane-anchoring cholesterol at the tail of the arrow results in display of RNA aptamer or folate on the outer surface of the extracellular vesicle. In contrast, placing the cholesterol at the arrowhead results in partial loading of RNA nanoparticles into the extracellular vesicles. Taking advantage of the RNA ligand for specific targeting and extracellular vesicles for efficient membrane fusion, the resulting ligand-displaying extracellular vesicles were capable of specific delivery of siRNA to cells, and efficiently blocked tumour growth in three cancer models. Extracellular vesicles displaying an aptamer that binds to prostate-specific membrane antigen, and loaded with survivin siRNA, inhibited prostate cancer xenograft. The same extracellular vesicle instead displaying epidermal growth-factor receptor aptamer inhibited orthotopic breast cancer models. Likewise, survivin siRNA-loaded and folate-displaying extracellular vesicles inhibited patient-derived colorectal cancer xenograft