Nucleation of isolated PO4 units on CeO2 driven by high temperatures and the effect on its oxygen storage and release properties

The chemical nature of P-containing species of varying concentration present in CeO₂ after impregnation with (NH₄)₂HPO₄ and calcination at 1273 K, and their effects on the oxygen storage and release (OSR) properties of ceria are reported for the first time. The samples were characterized by different techniques and the results were compared with those recently reported on the same samples but calcined at 873 K. When P-containing ceria solids were calcined at 1273 K, CePO₄ (monazite) was the predominant P-containing species on the surface of ceria, confirming previous studies that showed that monazite exists for those samples in which the surface P loading (P atoms per nm⁻²) is larger than 5.5. For lower surface P concentrations, isolated orthophosphate units are present at the surface and within the subsurface region of the solid. Severe sintering of CeO₂ after calcination at 1273 K resulted in P concentrations >5.5 P atoms·nm⁻² in all samples. Isolated PO₄ units that could initially be present in the samples calcined at 873 K nucleated and CePO₄ was formed when samples were calcined at 1273 K. OSR properties of CeO₂ deteriorated progressively when P loading increased due to the presence of larger crystals of the very stable Ce(III) phase of CePO₄ at the surface of the P-containing ceria solids.     

Assessment of accuracy of the Doppler pressure half-time method in the estimation of the mitral valve area immediately after balloon mitral valvuloplasty

AIM: The reliability of Doppler echocardiography in determining the mitral valve area after balloon mitral valvuloplasty has been questioned, as discrepancies were noted between measurements obtained by the pressure half-time method and those derived haemodynamically, immediately following completion of the procedure. Recent investigations, however, have indicated that these discrepancies may be attributable to the over-estimation of the mitral valve area by haemodynamic measurements, caused by the presence of the iatrogenic atrial septal defect complicating transseptal catheterization. The aim of the present study was to further test this hypothesis. METHODS AND RESULTS: Measurements of the mitral valve area by the Doppler pressure half-time method and the Gorlin formula were obtained and compared in 238 consecutive patients before and immediately after retrograde non-transseptal balloon mitral valvuloplasty, which does not involve puncture and/or dilatation of the inter-atrial septum. No significant difference was found between Doppler- and Gorlin-derived measurements, neither before (1.04 +/- 0.23 vs 1.03 +/- 0.23 cm2, P = ns) nor immediately after (2.14 +/- 0.47 vs 2.12 +/- 0.49 cm2, P = ns) valvuloplasty. Linear regression analysis demonstrated a high degree of correlation between Doppler and Gorlin measurements before (r = 0.778) and after (r = 0.886) the procedure. Good agreement was confirmed by the Bland-Altman method. CONCLUSION: Doppler echocardiography yields accurate measurements of the mitral valve area immediately after retrograde non-transseptal balloon mitral valvuloplasty. This finding supports the hypothesis that the creation of an iatrogenic atrial septal defect during transseptal catheterization may contribute to the poor agreement between Doppler and Gorlin data after balloon mitral valvuloplasty.     

Exploiting Mobility for Efficient Coverage in Sparse Wireless Sensor Networks

Reliable monitoring of a large area with a Wireless Sensor Network (WSN) typically requires a very large number of stationary nodes, implying a prohibitive cost and excessive (radio) interference. Our objective is to develop an efficient system that will employ a smaller number of stationary nodes that will collaborate with a small set of mobile nodes in order to improve the area coverage. The main strength of this collaborative architecture stems from the ability of the mobile sensors to sample areas not covered (monitored) by stationary sensors. An important element of the proposed system is the ability of each mobile node to autonomously decide its path based on local information (i.e. a combination of self collected measurements and information gathered by stationary sensors in the mobile’s communication range), which is essential in the context of large, distributed WSNs. The contribution of the paper is the development of a simple distributed algorithm that allows mobile nodes to autonomously navigate through the field and improve the area coverage. We present simulation results based on a real sparse stationary WSN deployment for the coverage improvement scenario.     

Analysis of the Antenna＇s Setup Errors at the Global Navigation Satellite System Measurements

Today, the GNSS （global navigation satellite system） is used for more complicate and accurate applications such as monitoring or stake out works. The truth lies in the fact that in the most of the times not enough attention is paid to the antenna＇s setup. Usually, gross errors are found in the antenna＇s centering, leveling and in the measurement of its height, which are significant. In this paper, a thoroughly analysis of the above mentioned errors is carried out. The influence of these errors in the calculation of the X, Y, Z Cartesian geocentric coordinates and the ~, 2, h ellipsoid geodetic coordinates of a point P on the earth＇s surface, is analyzed and is presented in several diagrams. Also a new convenient method for the accurate measurement of the antenna＇s height is presented and it is strongly proposed. The conclusions outline the magnitude of these errors and prove the significance of the antenna＇s proper setup at the accurate GNSS applications.     

The effect of Fe on the catalytic behavior of model Pd-Rh/CeO2-Al2O3 three-way catalyst

The present work attempts to address the issue whether iron (Fe) which is accumulated on the surface of “three-way” catalysts (TWCs) used in gasoline-driven cars is a true chemical poison of their catalytic activity. This important issue from a scientific and technological point of view is addressed via catalytic activity, temperature-programmed surface reaction (TPSR), and X-ray photoelectron spectroscopy (XPS) measurements over a model TWC (1 wt% Pd–Rh/20 wt% CeO₂–Al₂O₃). It was found that deposition of Fe up to the level of 0.4 wt% (an average concentration found in aged commercial TWCs) on the model TWC does not deteriorate its activity towards CO and C₃H₆ oxidation, and reduction of NO by H₂. Instead it was found that iron improves significantly the T₅₀ parameter in the activity versus temperature profile. Small Fe clusters in contact with the noble metal (Pd and Rh) particles due to the lower work function of Fe compared to Pd and Rh act likely as a source of electron flow towards the noble metals (as evidenced by XPS measurements), thus altering their surface work function and adsorption energetics of reaction intermediates. The latter have increased significantly the activity of the model TWC towards oxidation of CO and propylene, and to a lesser extent the activity towards the reduction of NO by H₂. The presence of Fe on the surface of the model TWC provided and/or created also new active catalytic sites for the reactions investigated. According to previous work from this laboratory, iron up to the level of 0.4 wt% was shown not to deteriorate the oxygen storage capacity (OSC) of the same model TWC used in the present work. Thus, it could be concluded that Fe when deposited on a commercial TWC at least up to the level of 0.4 wt% acts likely as a promoter than a poison of its catalytic activity.     

Novel approaches to the measurement of arterial blood flow from dynamic digital X-ray images

We have developed two new algorithms for the measurement of blood flow from dynamic X-ray angiographic images. Both algorithms aim to improve on existing techniques. First, a model-based (MB) algorithm is used to constrain the concentration-distance curve matching approach. Second, a weighted optical flow algorithm (OP) is used to improve on point-based optical flow methods by averaging velocity estimates along a vessel with weighting based on the magnitude of the spatial derivative. The OP algorithm was validated using a computer simulation of pulsatile blood flow. Both the OP and the MB algorithms were validated using a physiological blood flow circuit. Dynamic biplane digital X-ray images were acquired following injection of iodine contrast medium into a variety of simulated arterial vessels. The image data were analyzed using our integrated angiographic analysis software SARA to give blood flow waveforms using the MB and OP algorithms. These waveforms were compared to flow measured using an electromagnetic flow meter (EMF). In total 4935 instantaneous measurements of flow were made and compared to the EMF recordings. It was found that the new algorithms showed low measurement bias and narrow limits of agreement and also out-performed the concentration-distance curve matching algorithm (ORG) and a modification of this algorithm (PA) in all studies.     

Retrograde nontransseptal balloon mitral valvuloplasty: immediate results and intermediate long-term outcome in 441 cases--a multicenter experience

OBJECTIVES: Our aim was to present the immediate and intermediate long-term results of the application of retrograde nontransseptal balloon mitral valvuloplasty (RNBMV) in four cooperating centers from Greece and India. BACKGROUND: RNBMV is a purely transarterial method of balloon valvuloplasty, developed with the aim to avoid complications associated with transseptal catheterization. Only single-center experience with RNBMV has been previously reported. METHODS: The procedure was attempted in 441 patients with symptomatic mitral stenosis (320 women, 121 men, mean age [+/-SD] 44+/-11 years, mean echocardiographic score [+/-SD] 7.7+/-2.0) from 1988 to 1996. Three hundred eighty-five patients with successful immediate outcome were followed clinically for a mean [+/-SD] of 3.5+/-1.9 (range, 0.5-9.1) years. RESULTS: A technically successful procedure was achieved in 388 (88%) cases. The echocardiographic score (p < 0.001), male gender (p=0.005), preprocedural mitral regurgitation (p=0.007) and previous surgical commissurotomy (p=0.029) were unfavorable predictors of immediate outcome. Complications included death (0.2%), severe mitral regurgitation (3.4%) and injury of the femoral artery (1.1%). Event-free (freedom from cardiac death, mitral valve surgery, repeat valvuloplasty and NYHA class > II symptoms) survival rates (+/-SEM) were 100%, 96.9+/-0.9%, 89.8+/-1.9% and 75.5+/-5.5% at 1, 2, 4 and 9 years, respectively. The echocardiographic score (p < 0.001), NYHA class (p=0.008) and postprocedural mitral valve area (p=0.009) were significant independent predictors of intermediate long-term outcome. CONCLUSIONS: Multicenter experience indicates that RNBMV is a safe and effective technique for the treatment of symptomatic mitral stenosis. As with the transseptal approach, patients with favorable mitral valve anatomy derive the greatest immediate and intermediate long-term benefit from this procedure.     

Characterization of the neutron flux distribution at the Athens Tandem Accelerator NCSR “Demokritos”

Quasi-monoenergetic neutron beams, in the energy range 7-11.5 MeV, produced via the ²H(d,n) reaction, have been used at the 5.5 MV tandem T11/25 Accelerator Laboratory of NCSR “Demokritos”. The flux variation of the neutron beam is monitored with a BF₃ detector, while the absolute flux is obtained with respect to reference reactions. An investigation of the energy dependence of the neutron fluence has been carried out using two independent techniques: by a liquid scintillator BC501A detector and deconvolution of its recoil energy spectra performed by means of the DIFBAS code, as well as via the multiple foil activation technique in combination with the SULSA unfolding code. The neutron facility has also been characterized by means of Monte Carlo simulations with MCNP5.     

Supercritical carbon dioxide extraction of okra (Hibiscus esculentus L) seeds

Pilot‐scale supercritical fluid extraction of okra seeds was carried out, using carbon dioxide as solvent, at temperatures of 40, 50 and 60 °C and pressures of 150, 300 and 450 bar. Laboratory‐scale Soxhlet extraction of the ground seeds was carried out with ethanol and n‐hexane. The yields of supercritical fluid extraction and n‐hexane Soxhlet extractions were similar. The ethanol Soxhlet extraction gave the highest yield, but the concentrations of β‐sitosterol and tocopherols in this extract were lower than in the supercritical fluid extraction product. The fatty acid profiles of the extracts were determined, and a high unsaturated/saturated ratio was observed. The fatty acid compositions were only slightly different for oils obtained by the different extraction methods. Copyright © 2005 Society of Chemical Industry     

Combined MR imaging towards subject-specific knee contact analysis

A combined magnetic resonance (MR) imaging method has been proposed to investigate individual’s knee functionality quantitatively under weight-bearing condition. High resolution MR data were acquired first to reconstruct the subject-specific anatomical model. A dynamic MR acquisition was obtained afterwards to record the motion of knee joint. A tri-rigid registration was applied to retrieve the knee joint motion, leading to a 12 degree-of-freedom (DoF) knee functional model. Using this model, the tibiofemoral contact mechanism was studied and analysed in both 2D and 3D. A mathematical definition of contact points of cartilage surfaces is given by modelling these surfaces as manifolds. It is believed that such subject-specific motion of contact points on cartilage surfaces of femur and two tibia plateaus can provide valuable insights for clinical applications such as knee replacement surgery.