Scaffold-aided repair of articular cartilage studied by MRI

OBJECTIVE: The objective of the study was to evaluate the ability of the noninvasive magnetic resonance techniques to monitor the scaffold-aided process of articular cartilage repair. MATERIALS AND METHODS: Defects of 4 mm in diameter and 3 mm in depth were created in right knees of 30 adolescent white New Zealand rabbits. Fourteen rabbits were implanted with poly(lactide-co-glycolic acid) (PLGA) scaffold trimmed to match the size and the shape of the defect (PLGA+ group). No procedure was applied to the remaining 16 animals (PLGA- group). Animals were sacrificed sequentially at 4, 12, and 24 weeks after the surgery and magnetic resonance T (2)-weighted images (400 MHz) of the dissected bone plugs at eight different echo times were taken to derive T (2) relaxation time. The images and the T (2) time dependencies versus the tissue depth were statistically analyzed. Histological results of bone plugs were evaluated using semiquantitative histological scales. RESULTS: The results obtained for PLGA repair tissue were evaluated versus the PLGA- group and the healthy tissue harvested from the opposite knee (reference group), and compared with histological results (hematoxylin and eosin staining). The magnetic resonance images and T (2) relaxation time profiles taken 4 weeks after surgery for both the PLGA- and PLGA+ group did not reveal the tissue reconstruction. After 12 weeks of treatment T (2) time dependence indicates a slight reconstruction for PLGA+ group. The T (2) time dependence obtained for PLGA+ samples taken after 24 weeks of treatment resembled the one observed for the healthy cartilage, indicating tissue reconstruction in the form of fibrous cartilage. The tissue reconstruction was not observed for PLGA- samples. CONCLUSION: The study revealed correlation between magnetic resonance and histology data, indicating the potential value of using MRI and spatial variation of T (2) as the noninvasive tools to evaluate the process of articular cartilage repair. It also suggested, that the PLGA scaffold-aided treatment could help to restore the proper architecture of collagen fibrils.     

The C2H2 gas effect on the growth behavior of remote plasma enhanced CVD SiC:H film

SiC:H films were produced in a remote plasma enhanced chemical vapor deposition (RPE-CVD) system. The HMDS was chosen as the primary source gas and was fixed at constant flow rate of 10 sccm. The C₂H₂ gas input amount was varied from 3 to 200 sccm for the study of carbon effect on the film stoichiometry and bonding properties. The deposition temperature of the substrate was fixed at 400^∘C, and the plasma power was fixed at 300 W. Using auger electron spectroscopy, the depth profile of the film was investigated with C₂H₂ flow rate changes. The C₂H₂ played an important role in the transition between sp² and sp³ carbon hybridization bonds, which affected the growth behavior and properties of the films.     

The role of relaxation time corrections for the evaluation of long and short echo time <Superscript>1</Superscript>H MR spectra of the hippocampus by NUMARIS and LCModel techniques

1H MR spectroscopy is routinely used for lateralization of epileptogenic lesions. The present study deals with the role of relaxation time corrections for the quantitative evaluation of long (TE=135 ms) and short echo time (TE=10 ms) 1H MR spectra of the hippocampus using two methods (operator-guided NUMARIS and LCModel programs). Spectra of left and right hippocampi of 14 volunteers and 14 patients with epilepsy were obtained by PRESS (TR/TE=5000/135 ms) and STEAM (TR/TE=5000/10 ms) sequences with a 1.5-T imager. Evaluation was carried out using Siemens NUMARIS software and the results were compared with data from LCModel processing software. No significant differences between the two methods of processing spectra with TE=135 ms were found. The range of relaxation corrections was determined. Metabolite concentrations in hippocampi calculated from spectra with TE=135 ms and 10 ms after application of correction coefficients did not differ in the range of errors and agreed with published data (135 ms/10 ms: NAA=10.2±0.6/10.4±1.3 mM, Cho=2.4±0.1/2.7±0.3 mM, Cr=12.2±1.3/11.3±1.3 mM). When relaxation time corrections were applied, quantitative results from short and long echo time evaluation with LCModel were in agreement. Signal intensity ratios obtained from long echo time spectra by NUMARIS operator-guided processing also agreed with the LCModel results.     

Forming gas annealing effects on the microstructure and ferroelectricity of SrBi2Ta2O9 thin films prepared by metalorganic decomposition

Abstract

Ferroelectric SrBi₂Ta₂O₉(SBT) thin films prepared by metalorganic decomposition (MOD) method were annealed in forming gas (5% hydrogen + 95% nitrogen) at different temperatures for 60 min. SEM analysis results showed that an amount of columnar structures appeared on SBT surface when the annealing temperature was up to 450°C. When the annealing temperature raised up to 500°C, these columnar structures grew along one dimension and changed into wire structures. The EDX micro-area mapping analysis result showed that Bi was concentrated in the columnar or wire structures on SBT surface. The ferroelectric property analysis results showed that the hysteresis loops still existed after 5 min forming gas processing (350°C or 400°C), but when the annealing time was longer than 10 min, the resistance of the SBT samples became too low to measure the hysteresis loops.     

I~2控制Buck变换器稳定性的研究

研究了电感电流检测电阻对电流模式控制开关变换器稳定性的改善作用。以I2控制Buck变换器为例,建立了含有输出电容等效串联电阻ESR(equivalent series resistance)的二阶离散迭代映射模型。在此基础上,通过分析输出电容时间常数和电感电流检测电阻变化时的分岔图、特征根轨迹、最大Lyapunov指数、稳定边界,深入研究了电感电流检测电阻对变换器动力学特征的影响。研究结果表明,增大电感电流检测电阻,可以使变换器在较小输出电容时间常数时稳定工作,拓宽稳定工作范围。最后,通过仿真和实验,验证了理论分析的正确性。研究结果可以推广到其他开关变换器,对开关变换器的设计和优化具有指导意义。     

Contribution of various substrates to total citric acid cycle flux and ]anaplerosis as determined by13C isotopomer analysis and O2 consumption in the heart

A simple relationship between parameters derived from a¹³C NMR isotopomer analysis and O₂ consumption is presented that allows measurement of the absolute rate of acetyl-CoA oxidation and anaplerotic flux in tissues oxidizing a mixture of four substrates. The method was first applied in a study of the effects of work state and -adrenergic stimulation on net acetate oxidation and anaplerosis in the isolated working rat heart. The results demonstrate that the anticipated ratio of 2 between O₂ consumption and TCA cycle flux for hearts oxidizing only acetate holds at low workload when anaplerosis is low, but deviates toward a factor of 3 under high workload conditions when anaplerosis is increased. This analysis was also extended to hearts that oxidize a more physiological mixture of substrates including long-chain fatty acids, acetoacetate, lactate, pyruvate, and glucose. We show that the contribution each substrate makes to total TCA cycle flux can be determined by combined¹³C NMR and O₂ consumption measurements. The present study also demonstrates that stimulation of anaplerosis (by addition of propionate) can significantly alter the relative contribution each substrate makes to total TCA cycle flux. We conclude that if¹³C labeling patterns are selected appropriately, a comprehensive picture of flux through all major metabolic pathways feeding the cycle can be determined in a single experiment even when complex physiological mixtures of substrates are provided.     

Influence of process conditions on the ferroelectric characteristics of SrBi2Ta2O9 films prepared by rf magnetron sputtering

Abstract

The effects of sputtering conditions on the SrBi₂Ta₂O₉ films deposited via a single-target RF-sputtering process were investigated in this study. It was found that the composition of targets significantly affected the phases and the composition of the deposited films. When the target contained high bismuth content, SrBi₂Ta₂O₉ and a secondary Bi₂O₃ phase were formed. When the bismuth content in the targets was insufficient, a pyrochlore phase was produced. SEM images revealed that the composition of the targets also affected the surface morphology of the obtained films. When the target-to-substrate distance was increased, bismuth oxide was formed, which resulted in an increase in the leakage current. By optimizing the deposition conditions, the ferroelectric properties of SrBi₂Ta₂O₉ films were improved.     

The effect of alumina addition on the electrical conductivity of Gd-doped ceria

Acceptor doped-ceria is a possible electrolyte material for the IT-SOFC (intermediate temperature solid oxide fuel cell) due to its high oxygen-ion conductivity. However, its use has been limited by its mechanical weakness and the appearance of electronic conductivity in reducing condition. In this study, alumina was selected as an additive in the doped-ceria to see if it increases the oxygen-ion conductivity and mechanical strength. Effects of alumina addition in doped ceria were studied as a function of alumina content and acceptor (Gd) content. The electrical conductivity of (Ce_1−x Gd _x O_2−δ)_1−y + (Al₂O₃) _y (x = 0–0.35, y = 0–0.10) was measured by using impedance spectroscopy. The grain conductivity of Ce_0.8Gd_0.2O_2-δ (GDC20) with 5 mol% alumina increased ∼3 times from that of GDC20 at 300^∘C. The grain conductivity was even ∼2 times higher than that of Ce_0.9Gd_0.1O_2−δ (GDC10) at 300^∘C. The electrical conductivity of GDC20 without alumina addition, measured at 500^∘C in air, rapidly decreased after exposure to reducing condition (Po₂∼10⁻²² atm) at 800^∘C. However, the decrease was much slower in GDC20 with alumina addition, indicating the improved mechanical strength. Among the examined compositions, (Ce_0.75Gd_0.25 O_2-δ)_0.95 + (Al₂O₃)_0.05 (GDC25A5) showed the highest conductivity at most temperatures.     

The Influence of Excess Precipitate on the Non-Ohmic Properties of SnO2-Based Varistors

Based on our background in the field of nonlinear electrical properties of SnO₂-based varistors, we have been observing the influence of microstructural heterogeneities, e.g., the precipitate phase at triple points of the grain boundary region. In this study, we have prepared a SnO₂-based varistor system with excess precipitates at triple points in the grain boundary region in order to discuss their influence on the system's non-ohmic properties, including thermal treatment at oxidizing atmospheres. Our results indicate that an excessive amount of such precipitates may be deleterious to the non-ohmic properties because they may create adjacent regions at grain boundaries with lower concentrations of segregated metal atoms, thus increasing the presence of a non-active potential barrier and increasing leakage current paths. Under these circumstances, the effect of thermal treatment in oxidizing atmospheres is to decrease the leakage current density instead of increasing the nonlinear coefficient.     

The effect of transition-metal addition on the non-equilibrium E.M.F.-type gas sensor

In this study, we made single chamber gas sensor which had two SnO₂ electrodes pasted onto either side of zirconia electrolyte. Transition metal (TM) was added in one of two SnO₂ electrodes to induce and thus confirm the catalytic effect of transition-metal. Since 1 mol% TM-doped SnO₂ showed the negligible change in microstructure, the effect of microstructure change could be ignored. The Co addition increased the e.m.f. of working electrode (TM-added SnO₂) in air, implying the enhanced oxygen adsorption. The addition of TM to SnO₂ was also effective in changing the e.m.f. values in H₂ balanced by air. Fe and Ni addition exhibited decreased e.m.f. in H₂ from that in air. Thus, Fe and Ni addition improved the catalytic activity for H₂ oxidation. Cu addition slightly improved the catalytic activity for CO oxidation. The results show that Co is expected to be a good additive for the cathode of solid-oxide-fuel-cell (SOFC) at low temperature. On the other hand, Fe, Cu, or Ni is good additives for anode.     

Effects of the O2/Ar gas flow ratio on the electrical and transmittance properties of ZnO:Al films deposited by RF magnetron sputtering

ZnO:Al thin films for transparent conductors were deposited on sapphire (0001) substrates by using an RF magnetron sputtering technique. Effects of the O₂/Ar flow ratio in the sputtering process on the crystallinity, carrier concentration, carrier mobility, and transmittance of the films were investigated. The FWHM of the (002) XRD intensity peak is minimal at the O₂/Ar flow ratio of 0.5. According to the Hall measurement results the carrier concentration and mobility of the film decrease and thus the resistivity increases as the O₂/Ar flow ratio increases. The transmittance of the ZnO:Al film deposited on the glass substrate is characteristic of standing wave. The transmittance increases as the O₂/Ar flow ratio in-RF magnetron sputtering increases up to 0.5. Considering the effects of the the O₂/Ar flow ratio on the electrical resistivity and transmittance of the ZnO:Al film the optimum O₂/Ar flow ratio is 0.5 in the RF magnetron sputter deposition of the ZnO:Al film.     

The influence of nuclear generation on CO2 emissions and on the cost of the Spanish system in long-term generation planning

This paper presents the influence of a nuclear generation option on CO₂ emissions and on the cost of the Spanish long-term generation system by means of the development of a stochastic linear model, based on the software GAMS, where multiple aspects have been contemplated: the uncertainty regards fossil fuel and CO₂ emission allowance prices by analysing different scenarios, the stability and supply security of the system by considering different restrictions, the maximum grade of penetration of the different technologies by means of commissioning plans, etc. Only two of the conclusions drawn are focused on here. First, it is possible to get a clean system without nuclear power generation but the cost would be higher than in the case where the existing nuclear power plants continue to operate. Second, the development of clean coal technologies could be affected negatively by the development of nuclear generation.