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1.
《Solid State Ionics》2006,177(35-36):3199-3203
A co-dopant strategy is used to investigate the effect that the elastic strain in the lattice has on the grain ionic conductivity of doped ceria electrolytes. Based on critical dopant ionic radius (rc), different compositions in the LuxNdyCe1−xyO2−δ (x + y = 0.05, 0.10, 0.15, and 0.20) system are studied. Dopants are added such that the weighted average dopant ionic radius matches rc for all the compositions. Dense ceramic discs are prepared using conventional solid oxide route and sintering methods. Precise lattice parameter measurements are used to calculate the lattice strain. The ionic conductivity of the samples is measured in the temperature range of 250 °C to 700 °C using two-probe electrochemical impedance spectroscopy technique. The elastic strain present in LuxNdyCe1−xyO2−δ system is found to be negligible when compared to LuxCe1−xO2−δ (negative) and NdxCe1−xO2−δ (positive) systems. Grain ionic conductivity of LuxNdyCe1−xyO2−δ (where x + y = 0.05) at 500 °C is observed to be 1.9 × 10 3 S/cm which is twice as high as that of Lu0.05Ce0.95O2−δ. These results extend the validity of the rc concept as a strategy for co-doping ceria electrolytes and open new designing avenues for solid oxide electrolytes with enhanced ionic conductivity.  相似文献   

2.
Pyrochlore-free lead zirconate titanate – lead zinc niobate ceramics have been systematically investigated in the as-sintered condition as well as after annealing. The ceramics were characterized by dielectric spectroscopy and Sawyer–Tower polarization (PE) measurements. The powders of Pb[(Zr1/2Ti1/2)(1−x)–(Zn1/3Nb2/3)x]O3, where x = 0.1, 0.3 and 0.5 were prepared using the columbite–(wolframite) precursor method. The general trend seems to indicate that the annealed samples become more normal-ferroelectric-like behavior as opposed to the relaxor-ferroelectric-like behavior observed in the as-sintered state. The as-sintered 0.9PZT–0.1PZN ceramic exhibited weak relaxor-ferroelectric behavior, with a relatively low dielectric constant maximum of 14,000 measured at 1 kHz. Annealing resulted in a transition to normal-ferroelectric-like behavior, a shift in the dielectric maximum temperature from 360 °C to 350 °C, and a dramatic increase in the dielectric constant at 1 kHz to a maximum value of 35,000 for the longer anneal. After thermal annealing at 900 °C for one week a strong enhancement of remanent polarization (Pr) was observed.  相似文献   

3.
Phase formation study in lead-free piezoelectric ceramics based on lanthanum doped bismuth sodium titanate (Bi0.4871Na0.4871La0.0172TiO3:BNLT) and zirconium doped barium titanate (BaZr0.05Ti0.95O3:BZT), has been carried out in the system of (1−x)BNLT–xBZT where x = 0.0–1.0, by two-step mixed oxide method. It was observed that the addition of BZT in the BNLT ceramics developed the dielectric and piezoelectric properties of the ceramics with the optimum piezoelectric constant (d33) and dielectric constant (εr) at room temperature of about 138 pC/N and 1651, respectively, from the 0.2 BNLT to 0.8 BZT ceramic sample. The Curie temperature (TC) of this ceramic was found at 295 °C which is 195 °C higher than that of pure BZT ceramics, promising the use of this ceramic in a higher range of temperature.  相似文献   

4.
Flame spreading over pure methane hydrate in a laminar boundary layer is investigated experimentally. The free stream velocity (U) was set constant at 0.4 m/s and the surface temperature of the hydrate at the ignition (Ts) was varied between ?10 and ?80 °C. Hydrate particle sizes were smaller than 0.5 mm. Two types of flame spreading were observed; “low speed flame spreading” and “high speed flame spreading”. The low speed flame spreading was observed at low temperature conditions (Ts = ?80 to ?60 °C) and temperatures in which anomalous self-preservation took place (Ts = ?30 to ?10 °C). In this case, the heat transfer from the leading flame edge to the hydrate surface plays a key role for flame spreading. The high speed flame spreading was observed when Ts = ?50 and ?40 °C. At these temperatures, the dissociation of hydrate took place and the methane gas was released from the hydrate to form a thin mixed layer of methane and air with a high concentration gradient over the hydrate. The leading flame edge spread in this premixed gas at a spread speed much higher than laminar burning velocity, mainly due to the effect of burnt gas expansion.  相似文献   

5.
The formation of complex species of dioxouranium(VI) ion with EDTA was studied in the pH range of 1–3.5 and at 25 °C using a combination of potentiometric and spectrophotometric techniques. Results showed evidence for formation of the following species: [UO2H4EDTA]2+, [UO2H3EDTA]+, and [UO2H2EDTA]. Investigations were performed in sodium perchlorate as background electrolyte at 0.1, 0.3, 0.5, 0.7, and 1.0 mol dm? 3. The parameters based on the formation constants were calculated, and the dependences of protonation and the stability constants on ionic strength are described. The dependence on ionic strength of the formation constants was analyzed using the specific ion interaction theory (SIT) model. The stability constant values at infinite dilution, obtained using SIT model, are log β°141 = 6.77, log β°131 = 5.99 and log β°121 = 9.29, where indexes for the overall stability constant, βpqr, refer to the equilibrium pUO22+ + qH+ + rL4? ? MpHqLr(2p + q ? 4r). The specific interaction coefficients are also reported.  相似文献   

6.
《Solid State Ionics》2006,177(7-8):669-676
The electrical conductivity of sintered samples of Ce1−xNdxO2−x / 2 (0.01  x  0.2) was investigated in air as a function of temperature between 150 and 600 °C using AC impedance spectroscopy. The individual contribution of the bulk and grain boundary conductivities has been discussed in detail. In the low temperature range (< 350 °C), the activation enthalpy for bulk conductivity exhibited a shallow minimum at 3 mol% Nd, with a value of 0.68 eV. The activation enthalpy also produced a shallow minimum at 5 mol% Nd in the high temperature range (> 350 °C), with a value of 0.56 eV. It was shown that Ce1−xNdxO2−x / 2 is an electrolyte that obeys the Meyer Neldel rule. The bulk conductivity data measured by others for the same system has also been recalculated and re-evaluated to facilitate easier comparison with our own data.  相似文献   

7.
PurposeTo evaluate the biophysical processes that generate specific T2 values and their relationship to specific cerebrospinal fluid (CSF) content.Materials and methodsCSF T2s were measured ex vivo (14.1 T) from isolated CSF collected from human, rat and non-human primate. CSF T2s were also measured in vivo at different field strength in human (3 and 7 T) and rodent (1, 4.7, 9,4 and 11.7 T) using different pulse sequences. Then, relaxivities of CSF constituents were measured, in vitro, to determine the major molecule responsible for shortening CSF T2 (2 s) compared to saline T2 (3 s). The impact of this major molecule on CSF T2 was then validated in rodent, in vivo, by the simultaneous measurement of the major molecule concentration and CSF T2.ResultsEx vivo CSF T2 was about 2.0 s at 14.1 T for all species. In vivo human CSF T2 approached ex vivo values at 3 T (2.0 s) but was significantly shorter at 7 T (0.9 s). In vivo rodent CSF T2 decreased with increasing magnetic field and T2 values similar to the in vitro ones were reached at 1 T (1.6 s). Glucose had the largest contribution of shortening CSF T2 in vitro. This result was validated in rodent in vivo, showing that an acute change in CSF glucose by infusion of glucose into the blood, can be monitored via changes in CSF T2 values.ConclusionThis study opens the possibility of monitoring glucose regulation of CSF at the resolution of MRI by quantitating T2.  相似文献   

8.
Fluorinated ceramics with initial composition (1−x)CaTiO3+xPbF2+xLiF were sintered at 950 °C. The X-ray diffraction (XRD) patterns of the samples showed the formation of a novel solid solution in the initial composition range 0⩽x⩽0.125. SEM observations were performed on fractured ceramics and DSC analyses were carried out from room temperature up to 600 °C. Three second-order phase transitions were detected for all the samples. Capacitors were prepared from the pre-sintered ceramics then dielectric measurements were performed as a function of temperature in the frequency range 102–4×107 Hz. The ε′r−T curves exhibit the profile of dielectrics for class I capacitors, however the values of tan δ are too high (tan δ⩾1%).  相似文献   

9.
《Solid State Ionics》2006,177(17-18):1395-1403
Solid state sintering has been used to prepare the cubic perovskite structured compounds BaZr1−xInxO3−δ (0.0  x  0.75). Analysis of X-ray powder diffraction (XRPD) data reveals that the unit cell parameter, a, increases linearly with an increased Indium concentration. XRPD data was also used to demonstrate the completion of sample hydration, which was reached when the materials showed a set of single-phase Bragg-peaks. Dynamic thermogravimetric analysis (TGA) data showed that approx. 89% of the total number of available oxygen vacancies can be filled in BaZr1−xInxO3−δ for x = 0.50, and that the maximum water uptake occurs below 300 °C. Rietveld analysis of the room temperature neutron powder diffraction (NPD) data confirmed the average cubic symmetry (space group Pm-3m), and an expansion of the unit cell parameter after the hydration reaction. The strong O–H stretch band, 2500–3500 cm 1, in the infrared absorbance spectrum clearly manifests the presence of protons in the hydrated material. Proton conductivity of hydrated BaZr1−xInxO3−δ, x = 0.75 was investigated during heating and cooling cycles under dry argon atmosphere. The total conductivity during the heating cycle was nearly two orders of magnitude greater than that of cooling cycle at 300 °C, whilst these values were similar at higher temperatures i.e. T > 600 °C.  相似文献   

10.
《Current Applied Physics》2009,9(5):1042-1045
The effect of Nd0.5Na0.5TiO3 addition on the microwave dielectric properties of Mg0.95Ni0.05TiO3 ceramics was investigated. The Nd0.5Na0.5TiO3 content plays a significant role in improving the dielectric properties. Microwave dielectric measurements show an increase in the dielectric constant (εr) and temperature coefficient of the resonant frequency (τf) and a decrease in the quality factor (Q × f value) with increasing Nd0.5Na0.5TiO3 content. By properly adjusting the Nd0.5Na0.5TiO3 content, a zero τf value can also be obtained, which make Mg0.95Ni0.05TiO3 a promising material in wireless systems. At 1300 °C, the 0.81Mg0.95Ni0.05TiO3–0.19Nd0.5Na0.5TiO3 ceramics possess excellent microwave dielectric properties: a dielectric constant (εr) of 25.61, a Q × f value of 69,100 GHz, and a τf value of −6 ppm/°C.  相似文献   

11.
《Solid State Ionics》2006,177(19-25):1807-1810
The crystal chemistry and mixed conductor properties of the n = 2 member of the Ruddlesden–Popper (R–P) phases Sr3−xLaxFe2−yNiyO7−δ with 0  x  0.3 and 0  y  1.0 have been studied at high temperature. High-temperature X-ray diffraction and thermogravimetric measurements of the equilibrium pO2 (10 5  pO2  1 atm) in the temperature range 400  T  1000 °C indicate that the Sr3FeNiO7−δ phase is able to accommodate a large oxygen non-stoichiometry (δ  1.5) without structural transformations. The electrical conductivity and oxygen permeability increase with the substitution of Ni for Fe in the range 550  T  1000 °C. The electrical transport of the Sr3FeNiO7−δ phase is thermally activated and the activation energy decreases with the substitution of Ni for Fe for a given oxygen content. The increase in the oxygen permeation flux with increasing Ni content is due to an increasing oxygen non-stoichiometry and a lower activation energy for permeation.  相似文献   

12.
ObjectiveTo determine accurate quantitative transverse relaxation times (T2) using retrospective clinical images and apply it to examine 7-year changes in multiple sclerosis (MS) brain.MethodsA method for T2 mapping from retrospective proton density (PD) and T2-weighted fast spin echo images was recently introduced, but requires measurement of flip angles. We examined whether 1.5 T flip angle variation in brain can be predicted, thus enabling T2 analysis of historical PD and T2-weighted images without a concurrent flip angle map. After method validation in healthy volunteers, retrospective longitudinal T2 analysis was performed in 14 MS subjects over seven years. Changes in patient T2 values were compared with brain atrophy, T2 lesion load and disability score in MS.ResultsSimilar flip angle maps across volunteers enabled retrospective T2 from PD and T2-weighted images even when different refocusing angles were used. Over seven years, significant T2 changes of 2–4% were observed when using T2 modelling and the 7-year effect size for globus pallidus T2 was 0.56, which was more significant than brain atrophy. No significant T2 results were found when using exponential fit, which cannot account for refocusing angle variation. Moreover, change is T2 in globus pallidus and internal capsule correlated with MS disability score over time when using T2 modelling.ConclusionsAccurate quantitative T2 can be extracted from standard clinical 1.5 T MRI exams that include PD and T2-weighted imaging even when no flip angle map is available. This method was applied retrospectively to examine seven year changes in MS.  相似文献   

13.
Stoichiometric Ni-bearing ferrite was formed by air oxidation of an iron(II) hydroxide suspension at an initial Ni : Fetot mol ratio (rNi) of 0.20 : 2.80 at pH 10.0 and 65°C. Most of products formed at rNi=0.40 : 2.60 and 0.60 : 2.40 were Ni-bearing ferrites, of which vacancies of Fe3+ ion on the lattice points may be considered. Only Ni, Zn-bearing ferrites were formed in the suspensions at initial (Ni + Zn)  : Fetot mol ratios (rNi + Zn) of 0.20 : 2.80–0.60 : 2.40 at pH 10.0 and 65°C. At higher rNi or rNi + Zn by-products containing Ni, Fe and O42− were formed. The formation of the by-products was depressed in the suspensions containing chloride ions in the place of sulfate ions.  相似文献   

14.
PurposeTo investigate the in-vivo precision and clinical feasibility of 3D-QALAS - a novel method for simultaneous three-dimensional myocardial T1- and T2-mapping.MethodsTen healthy subjects and 23 patients with different cardiac pathologies underwent cardiovascular 3 T MRI examinations including 3D-QALAS, MOLLI and T2-GraSE acquisitions. Precision was investigated in the healthy subjects between independent scans, between dependent scans and as standard deviation of consecutive scans. Clinical feasibility of 3D-QALAS was investigated for native and contrast enhanced myocardium in patients. Data were analyzed using mean value and 95% confidence interval, Pearson correlation, Paired t-tests, intraclass correlation and Bland-Altman analysis.ResultsAverage myocardial relaxation time values and SD from eight repeated acquisitions within the group of healthy subjects were 1178 ± 18.5 ms (1.6%) for T1 with 3D-QALAS, 52.7 ± 1.2 ms (2.3%) for T2 with 3D-QALAS, 1145 ± 10.0 ms (0.9%) for T1 with MOLLI and 49.2 ± 0.8 ms (1.6%) for T2 with GraSE.Myocardial T1 and T2 relaxation times obtained with 3D-QALAS correlated very well with reference methods; MOLLI for T1 (r = 0.994) and T2-GraSE for T2 (r = 0.818) in the 23 patients. Average native/post-contrast myocardial T1 values from the patients were 1166.2 ms/411.8 ms for 3D-QALAS and 1174.4 ms/438.9 ms for MOLLI. Average native myocardial T2 values from the patients were 53.2 ms for 3D-QALAS and 54.4 ms for T2-GraSE.ConclusionsRepeated independent and dependent scans together with the intra-scan repeatability, demonstrated all a very good precision for the 3D-QALAS method in healthy volunteers. This study shows that 3D T1 and T2 mapping in the left ventricle is feasible in one breath hold for patients with different cardiac pathologies using 3D-QALAS.  相似文献   

15.
K. Russel Raj  P. Murugakoothan 《Optik》2012,123(12):1082-1086
Single crystals of semiorganic material 3-aminophenol orthophosphoric acid (denoted as 3-amphph) of size 29 × 17 × 4 mm3 have been grown by the slow evaporation of an aqueous solution of deionized water at 50 °C. The crystal belongs to orthorhombic system with the non centrosymmetric space group P212121. The lattice parameter values of 3-amphph crystal are a = 4.481(2) Å, b = 9.782(4) Å and c = 18.326(4) Å. The grown crystals are subjected to single crystal XRD studies to identify its morphology and structure. Optical transmittance and second harmonic generation of the grown crystals have been studied by UV–Vis–NIR spectrum and Kurtz powder technique respectively. The transmittance of 3-amphph crystal has been used to calculate the refractive index n, the extinction coefficient k, reflectance R and both the real (?r) and imaginary (?i) components of the dielectric constant as a function of wavelength. The optical band gap of 3-amphph is 4.05 eV with direct transition. The anisotropic mechanical behavior of 3-amphph has been analyzed using Vickers microhardness test. The mechanism of growth is revealed by carrying out chemical etching using water as etchant.  相似文献   

16.
PurposeTo quantify the differential plasma flow- (Fp-) and permeability surface area product per unit mass of tissue- (PS-) weighting in forward volumetric transfer constant (Ktrans) estimates by using a low molecular (Gd-DTPA) versus high molecular (Gadomer) weight contrast agent in dynamic contrast enhanced (DCE) MRI.Materials and methodsDCE MRI was performed using a 7T animal scanner in 14 C57BL/6J mice syngeneic for TRAMP tumors, by administering Gd-DTPA (0.9 kD) in eight mice and Gadomer (35 kD) in the remainder. The acquisition time was 10 min with a sampling rate of one image every 2 s. Pharmacokinetic modeling was performed to obtain Ktrans by using Extended Tofts model (ETM). In addition, the adiabatic approximation to the tissue homogeneity (AATH) model was employed to obtain the relative contributions of Fp and PS.ResultsThe Ktrans values derived from DCE-MRI with Gd-DTPA showed significant correlations with both PS (r2 = 0.64, p = 0.009) and Fp (r2 = 0.57, p = 0.016), whereas those with Gadomer were found only significantly correlated with PS (r2 = 0.96, p = 0.0003) but not with Fp (r2 = 0.34, p = 0.111). A voxel-based analysis showed that Ktrans approximated PS (< 30% difference) in 78.3% of perfused tumor volume for Gadomer, but only 37.3% for Gd-DTPA.ConclusionsThe differential contributions of Fp and PS in estimating Ktrans values vary with the molecular weight of the contrast agent used. The macromolecular contrast agent resulted in Ktrans values that were much less dependent on flow. These findings support the use of macromolecular contrast agents for estimating tumor vessel permeability with DCE-MRI.  相似文献   

17.
《Ultrasonics sonochemistry》2014,21(6):2010-2019
This paper concerns a preliminary study for a new copper recovery process from ionic solvent. The aim of this work is to study the reduction of copper in Deep Eutectic Solvent (choline chloride–ethylene glycol) and to compare the influence of temperature and the ultrasound effects on kinetic parameters. Solutions were prepared by dissolution of chloride copper salt CuCl2 (to obtain Copper in oxidation degree II) or CuCl (to obtain Copper in oxidation degree I) and by leaching metallic copper directly in DES. The spectrophotometry UV–visible analysis of the leached solution showed that the copper soluble form obtained is at oxidation degree I (Copper I). Both cyclic voltammetry and linear voltammetry were performed in the three solutions at three temperatures (25, 50 and 80 °C) and under ultrasonic conditions (F = 20 kHz, PT = 5.8 W) to calculate the mass transfer diffusion coefficient kD and the standard rate coefficient k°. These parameters are used to determine that copper reduction is carried out via a mixed kinetic-diffusion control process. Temperature and ultrasound have the same effect on mass transfer for reduction of CuII/CuI. On the other hand, temperature is more beneficial than ultrasound for mass transfer of CuI/Cu. Standard rate constant improvement due to temperature increase is of the same order as that obtained with ultrasound. But, by combining higher temperature and ultrasound (F = 20 kHz, PT = 5.6 W at 50 °C), reduction limiting current is increased by a factor of 10 compared to initial conditions (T = 25 °C, silent), because ultrasonic stirring is more efficient in lower viscosity fluid. These values can be considered as key-parameters in the design of copper recovery in global processes using ultrasound.  相似文献   

18.
ObjectiveThe purpose of this study was to correlate brain metabolism assessed shortly after therapeutic hyperthermia by 1H magnetic resonance spectroscopy (MRS), with neurodevelopmental outcome.MethodsAt the age of 6.0 ± 1.8 days, brain metabolites of 35 term asphyxiated newborns, treated with therapeutic hypothermia, were quantified by multivoxel proton MRS of a volume cranial to the corpus callosum, containing both gray and white matter. At the age of 30 months the Bayley Scale of Infant Development-III was performed.ResultsInfants that died had lower gray matter NAA levels than infants that survived (P = 0.005). In surviving infants (28 of 35) there was a trend of negative correlation between gray matter choline levels and gross motor outcome (r =  0.45). In the white matter, choline correlated negatively with fine motor skills (r =  0.40), and creatine positively with gross motor skills (r = 0.58, P = 0.02). There was no relationship between lactate levels and outcome.ConclusionMRS of asphyxiated neonates treated by therapeutic hypothermia can serve as predictor of outcome. Unlike previously reported associations in untreated asphyxiates, lactate levels had no relationship with outcome, which indicates that one of the working mechanisms of therapeutic hypothermia is reduction of the metabolic rate.  相似文献   

19.
《Current Applied Physics》2010,10(5):1349-1353
Single crystals of semiorganic material calcium dibromide bis(glycine) tetrahydrate were grown from aqueous solution. The crystal belongs to monoclinic system, with a = 13.261(5) Å, b = 6.792(2) Å, c = 15.671(9) Å and β = 91.68(4)°. The presence of the elements in the title compound was confirmed by energy dispersive X-ray analysis. The solubility and metastable zone width were found. The grown crystals were tested by powder XRD, FTIR, Thermo Gravimetric and Differential Thermal Analysis, UV–vis–NIR analysis, dielectrical and mechanical studies. The transmittance of calcium dibromide bis(glycine) tetrahydrate crystal has been used to calculate the refractive index n, the extinction coefficient K and both the real ɛr and imaginary ɛi components of the dielectric constant as functions of wavelength. The optical band gap of calcium dibromide bis(glycine) tetrahydrate is 3.23 eV.  相似文献   

20.
A. Jablonski  C.J. Powell 《Surface science》2010,604(21-22):1928-1939
We present an analysis of the dependence of the backscattering correction factor (BCF) in Auger-electron spectroscopy (AES) on the analyzer acceptance angle. Illustrative BCF calculations are presented for Pd M5N45N45 Auger electrons as a function of primary-electron energy for primary-electron angles of incidence, θ0, of 0° and 80° and for various values of the analyzer acceptance angle. It was necessary to generalize the BCF definition for the case of an analyzer with an arbitrarily large acceptance angle; this was done with a new function, the integral emission depth distribution function. BCFs calculated from an advanced model of electron transport in the surface region of the Pd sample varied weakly with analyzer half-cone angle for θ0 = 0° but more strongly for θ0 = 80° where there were BCF differences varying between 19% at a primary energy of 1 keV and 6% at a primary energy of 5 keV. These BCF differences are due in part to variations of the BCF with emission angle and in part to variations of the density of inner-shell ionizations within the information depth for the detected Auger electrons. The latter variations are responsible for differences larger than 10% between BCFs from the widely used simplified BCF model and those from the more accurate advanced model for primary energies less than about 5 keV for θ0 = 80°. For normal incidence of the primary beam, differences greater than 10% between BCFs from the simplified and advanced models were found for primary energies between 1 keV and 4 keV. These BCF differences indicate that the simplified model can provide only approximate BCF values. In addition, the simplified model does not provide any BCF dependence on Auger-electron emission angle or analyzer acceptance angle.  相似文献   

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