Thermal and electric conductivity of near-zero thermal expansion ZrW 2O8//ZrO2 composites

In this work, the microstructure, thermal and electric conductivity properties of near-zero thermal expansion ZrW2O8/ZrO2 and Al2O3 added ZrW2O8/ZrO2 composites were studied. Both the two composites exhibit very low thermal conductivity and the thermal conductivity decreases slightly as the temperature increases. The electric conductivity of the two composites increases with the increasing of the measurement temperature. The Al2O3 added ZrW2O8/ZrO2 composite has higher thermal and electric conductivity than ZrW2O8/ZrO2 composite. The most important factor which causes the difference of the thermal and electric conductivity of the composites is the porosity. (C) 2008 The Ceramic Society of Japan. All rights reserved.

Interplay of Substrate Conductivity, Cellular Microenvironment, and Pulsatile Electrical Stimulation toward Osteogenesis of Human Mesenchymal Stem Cells in Vitro

The influences of physical stimuli such as surface elasticity, topography, and chemistry over mesenchymal stem cell proliferation and differentiation are well investigated. In this context, a fundamentally different approach was adopted, and we have demonstrated the interplay of inherent substrate conductivity, defined chemical composition of cellular microenvironment, and intermittent delivery of electric pulses to drive mesenchymal stem cell differentiation toward osteogenesis. For this, conducting polyaniline (PANI) substrates were coated with collagen type 1 (Coll) alone or in association with sulfated hyaluronan (sHya) to form artificial extracellular matrix (aECM), which mimics the native microenvironment of bone tissue. Further, bone marrow derived human mesenchymal stem cells (hMSCs) were cultured on these moderately conductive (10(-4)10(-3) S/cm) aECM coated PANI substrates and exposed intermittently to pulsed electric field (PEF) generated through transformer-like coupling (TLC) approach over 28 days. On the basis of critical analysis over an array of end points, it was inferred that Coll/sHya coated PANI (PANI/Coll/sHya) substrates had enhanced proliferative capacity of hMSCs up to 28 days in culture, even in the absence of PEF stimulation. On the contrary, the adopted PEF stimulation protocol (7 ms rectangular pulses, 3.6 mV/cm, 10 Hz) is shown to enhance osteogenic differentiation potential of hMSCs. Additionally, PEF stimulated hMSCs had also displayed different morphological characteristics as their nonstimulated counterparts. Concomitantly, earlier onset of ALP activity was also observed on PANI/Coll/sHya substrates and resulted in more calcium deposition. Moreover, real-time polymerase chain reaction results indicated higher mRNA levels of alkaline phosphatase and osteocalcin, whereas the expression of other osteogenic markers such as Runt-related transcription factor 2, Col1A, and osteopontin exhibited a dynamic pattern similar to control cells that are cultured in osteogenic medium. Taken together, our experimental results illustrate the interplay of multiple parameters such as substrate conductivity, electric field stimulation, and aECM coating on the modulation of hMSC proliferation and differentiation in vitro.

Electrical properties of the SnO2-based varistor

The non-linear electrical properties of CoO-doped and Nb205-doped SnO2 ceramics were characterized. X-ray diffraction and scanning electron microscopy indicated that the system is single phase. The electrical conduction mechanism for low applied electrical field was associated with thermionic emission of the Schottky type. An atomic defect model based on the Schottky double-barrier formation was proposed to explain the origin of the potential barrier at the ceramic grain boundaries. These defects create depletion layers at grain boundaries, favouring electron tunnelling at high values of applied electrical field. © 1998 Chapman & Hall.

Dynamic behavior of a linear induction motor

Although conventional rotating machines have been largely used to drive underground transportation systems, linear induction motors are also being considered for future applications owing to their indisputable advantages. A mathematical model for the transient behavior analysis of linear induction motors, when operating with constant r.m.s. currents, is presented in this paper. Operating conditions, like phase short-circuit and input frequency variations and also some design characteristics, such as air-gap and secondary resistivity variations, can be considered by means of this modeling. The basis of the mathematical modeling is presented. Experimental results obtained in the laboratory are compared with the corresponding simulations and discussed in this paper.

Dielectric behavior of XLPE aged under multi-stressing conditions

In this work fresh cables were laboratory aged under multi-stressing conditions at room temperature. Foils were peeled from cables, with approximately 150 ?m thickness, from the outer, middle and inner positions of the XLPE cable insulating layer. For samples obtained from the outer cable layer position, an increasing near-permanent electrical conduction process with aging time was observed. At the middle and inner cable layer positions a flat-loss relaxation process was observed becoming a dominating process on the ageing. In addition, PEA results confirmed that degradation in the outer region of the XLPE cables arises from the simultaneous presence of dipoles and injected space charge that distorts the internal electric field on the ageing.

SnO 2 ceramics with low electrical resistivity obtained by microwave sintering

The main aim of this study was to develop dense and conducting SnO 2 ceramics without precipitated phases on the grain boundaries, which was verified using field emission scanning microscopy (FE-SEM) coupled with an energy-dispersive X-ray spectroscopy (FE-SEM/EDS). Two sample groups were investigated, where the first sample group was doped with zinc while the second one was doped with cobalt. The ceramics were prepared using the oxides mixture method and the sintering was carried out in a conventional muffle oven as well as in microwave oven. The results obtained were found to be similar regarding the relative density for the two sintering methods while time and temperature gains were observed for the microwave sintering method. The relative densities obtained were nearly 95%, for the two sintering methods. Concerning the electrical characterization measurements-electric field x current density as well as the environment temperature, the ceramics obtained through the conventional sintering method presented non-ohmic behavior. For the microwave sintered ceramics, we observed an ohmic behavior with electrical resistivity of 1.3 Ωcm for the samples doped with ZnO/Nb 2O 5 and 2.5 Ωcm for that of the samples doped with CoO/Nb 2O 5. The FE-SEM/EDS results for the microwave sintered ceramics indicated a structure with a reduced number of pores and other phases segregated at the grain boundaries, which leads to a better conductive ceramic than the conventional oven sintered samples. The dilatometry analysis determined the muffle sintering temperature and the difference between the densification of cobalt and zinc oxides. The addition of niobium oxide resulted in the decrease in resistivity, which thus led us to conclude that it is possible to obtain dense ceramics with low electrical resistivity based on SnO 2 using commercial oxides by the oxides mixture technique and the microwave oven sintering method. Copyright © 2011 American Scientific Publishers All rights reserved.

Effect of yttrium doping in barium zirconium titanate ceramics: A structural, impedance, modulus spectroscopy study

In the current article, we studied the effect of yttrium [Y3+] ions' substitution on the structure and electric behavior of barium zirconate titanate (BZT) ceramics with a general formula [Ba1-x Y 2x/3](Zr0.25Ti0.75)O3 (BYZT) with [x = 0, 0.025, 0.05] which were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that these ceramics have a single phase with a perovskite-type cubic structure. Rietveld refinement data confirmed [BaO 12], [ZrO6], [TiO6], [YO6] clusters in the cubic lattice. The Y3+ ions' effects on the electric conductivity behavior of BZT ceramics as a function of temperature and frequency are described, which are based on impedance spectroscopy analyses. The complex impedance plots display a double semicircle which highlights the influences of grain and grain boundary on the ceramics. Impedance analyses showed that the resistance decreased with the increasing temperature and resulted in a negative temperature coefficient of the resistance property in all compositions. Modulus plots represent a non-Debye-type dielectric relaxation which is related to the grain and grain boundary as well as temperature-dependent electric relaxation phenomenon and an enhancement in the mobility barrier by Y3+ ions. Moreover, the electric conductivity increases with the replacement of Ba 2+ by Y3+ ions may be due to the rise in oxygen vacancies. © 2013 The Minerals, Metals & Materials Society and ASM International.

Cultivares de gérbera (Gerbera jamesonii L.), em vaso, sob dois níveis de fertirrigação

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Efeito de adubos orgânicos provenientes de dejetos de bovinos confinados nos atributos físicos e químicos do solo e na produtividade do milho

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Oxygen Interstitial Dynamics in Bi(2)Sr(2)CaCu(2)O(8+delta) Oxides Measured by Mechanical Spectroscopy

Many researchers became interested in the discovery of Bi(2)Sr(2)CaCu(2)O(8+delta) oxides with critical temperature of around 80 K. It is known that the critical temperature is related to the CuO2 planes of the material. For this reason, the study of the interstitial oxygen in these oxides is of great relevance. The samples were prepared by means of conventional solid state reactions, through the stoichiometric mixture of precursory powders. After the sinterization, the samples were submitted to measurements of density, electrical resistivity, x-ray diffraction, scanning electron microscopy and energy dispersion spectroscopy, with the objective of performing their characterization. The measurements of mechanical spectroscopy were performed by a torsion pendulum. The results show three relaxation processes in the temperature range of 200 and 700 K, with activation energy of approximately 0.9 eV, which has been attributed to the dynamics of the interstitial oxygen present in the material.

Copper wire tables.

Mode of access: Internet.

A versatile high-voltage bias supply for extended range MIS C(V) and G(V) measurements /

Includes bibliographical references (p. 61).

A 25-kV bias-isolation unit for 1-MHz capacitance and conductance measurements /

Includes bibliographical references.

Synergistic effect of polymorphism, substrate conductivity and electric field stimulation towards enhancing muscle cell growth in vitro

Poly(vinylidene difluoride), a well-known candidate for artificial muscle patch applications is a semi-crystalline polymer with a host of attributes such as piezo- and pyroelectricity, polymorphism along with low dielectric constant and stiffness. The present work explores the unique interplay among the factors (conductivity, polymorphism and electrical stimulation) towards cell proliferation on poly(vinylidene difluoride) (PVDF)-based composites. In this regard, multi-walled carbon nanotubes (MWNTs) are introduced in the PVDF matrix (limited to 2%) through melt mixing to increase the conductivity of PVDF. The addition of MWNTs also led to an increase in the fraction of piezoelectric beta-phase, tensile strength and modulus. The melting and crystallization behaviour of PVDF-MWNT together with FT-IR confirms that the crystallization is found to be aided by the presence of MWNT. The conducting PVDF-MWNTs are used as substrates for the growth of C2C12 mouse myoblast cells and electrical stimulation with a range of field strengths (0-2 V cm(-1)) is intermittently delivered to the cells in culture. The cell viability results suggest that metabolically active cell numbers can statistically increase with electric stimulation up to 1 V cm(-1), only on the PVDF + 2% MWNT. Summarising, the current study highlights the importance of biophysical cues on cellular function at the cell-substrate interface. This study further opens up new avenues in designing conducting substrates, that can be utilized for enhancing cell viability and proliferation and also reconfirms the lack of toxicity of MWNTs, when added in a tailored manner.