Inhibition of cholesterol synthesis by cyclopropylamine derivatives of squalene in human hepatoblastoma cells in culture

Two squalene derivatives, trisnorsqualene cyclopropylamine and trisnorsqualeneN-methylcyclopropylamine, were synthesized and tested for inhibition of lanosterol and squalene epoxide formation from squalene in rat hepatic microsomes, and for the inhibition of cholesterol syntheses in human cultured hepatoblastoma (HepG2) cells. Trisnorsqualene cyclopropylamine inhibited [³H]-squalene conversion to [³H]squalene epoxide in microsomes (IC₅₀=5.0 μM), indicating that this derivative inhibited squalene mono-oxygenase. Trisnorsqualenen-methylcyclopropylamine inhibited [³H]squalene conversion to [³H]lanosterol (IC₅₀=12.0 μM) and caused [³H]-squalene epoxide to accumulate in microsomes, indicating that this derivative inhibited 2,3-oxidosqualene cyclase. Cholesterol biosynthesis from [¹⁴C]acetate in HepG2 cells was inhibited by both derivatives (IC₅₀=1.0 μM for trisnorsqualene cyclopropylamine; IC₅₀=0.5 μM for trisnorsqualeneN-methylcyclopropylamine). Cells incubated with trisnorsqualene cyclopropylamine accumulated [¹⁴C]squalene, while cells incubated with trisnorsqualeneN-methylcyclopropylamine accumulated [¹⁴C]squalene epoxide and [¹⁴C]squalene diepoxide. The concentration range of inhibitor which caused these intermediates to accumulate coincided with that which inhibited cholesterol synthesis. The results indicate that cyclopropylamine derivatives of squalene are effective inhibitors of cholesterol synthesis, and that substitutions at the nitrogen affect enzyme selectivity and thus the mechanism of action of the compounds.     

Estimates of N2O and CH4 fluxes from agricultural lands in various regions in Europe

According to the revised 1996 IPCC guidelines, several emission factors are needed to calculate national inventories of N₂O emissions from agriculture. To estimate the direct N₂O emissions from mineral soils, an emission factor of 0.0125 kg N₂O-N per kg N applied is currently being used. From recent literature data it was clearly shown that real N₂O emissions could differ substantially from this value. Based on the IPCC methodology an inventory of N₂O emission from agriculture in Europe (EU-15) has been made. In 1996, the N₂O emission was estimated at 672 Gg N₂O-N. The N₂O emission per country varied between 10 and 177 Gg N₂O-N. The N₂O emission per ha agricultural land in the various countries varied between 1.7 and 14.2 kg N₂O-N ha⁻¹. Highest N₂O emissions per ha were found in countries with a high agricultural intensity, such as the Netherlands, Belgium-Luxembourg, Denmark and Germany. Agricultural soils are a sink for atmospheric methane. An oxidation capacity of 2.5 and 1.5 kg CH₄ ha⁻¹ yr⁻¹ was put forward for grasslands and arable land, respectively. Based on land use data of 1993, the CH₄ sink of agricultural lands in EU-15 was estimated at 303.5 Gg CH₄. In general, it could be concluded that N₂O emissions from soils (327 Tg CO₂ equivalents) are far more important than its sink function for CH₄ (6.3 Tg CO₂ equivalents). This revised version was published online in August 2006 with corrections to the Cover Date.     

Theoretical analysis of the effects of asymmetric membrane structure on fouling during microfiltration

There is a growing interest in the use of both asymmetric and composite membranes for microfiltration and ultrafiltration processes. This includes particle removal applications in the semiconductor industry and virus clearance in biopharmaceutical applications. Filter fouling plays an important role in these processes. Although flux decline models have been developed for homogeneous membranes, the effects of asymmetric membrane structure on flux decline behavior remain poorly understood on a fundamental level. Here, we develop a theoretical model to describe the effects of asymmetric membrane structure on flux decline. The asymmetric structure was described by the spatial variation in Darcy permeability in the directions normal to and parallel to the membrane surface. The velocity profile and flux decline because of pore blockage were described using Darcy's law and a pore blockage and cake filtration model. Flux decline data were obtained using pseudocomposite membranes with highly interconnected polyvinylidene fluoride membranes (PVDF) and straight through pore polycarbonate track‐etched membranes (PCTE). Model composite membranes were formed by layering PCTE or PVDF membranes with different pore sizes on top of each other. Flux decline data for the composite membrane were in good agreement with model calculations. The results provide important insights into the effects of asymmetric membrane pore structures on flux decline. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

应用覆膜支架介入救治颈动脉破裂并假性动脉瘤

目的探讨应用覆膜支架介入治疗颈动脉破裂并假性动脉瘤.方法4例肿瘤所致颈动脉破裂并假性动脉瘤形成的患者,均出现颈部或口腔危及生命的出血,采用Seldinger方法,选用自膨式聚四氟乙烯覆膜支架治疗.结果4例成功施行血管内介入治疗,其中颈总动脉中段1例,颈动脉球2例,颈总动脉远段1例.共置入覆膜支架6枚.术后假性动脉瘤腔被隔绝,颈动脉通畅,患者的临床症状明显改善,无神经功能障碍.1例患者11 d后支架下缘颈总动脉与原瘤腔相通,再次置入覆膜支架,2个月的随访无再出血.1例患者经钢圈栓塞、放置覆膜支架及裸支架瘤腔     

Long-term tests of a Jülich planar short stack with reversible solid oxide cells in both fuel cell and electrolysis modes

A two-cell planar stack in the Jülich F-design with solid oxide cells has been built and the reversible operation between fuel cell and electrolysis modes has been demonstrated. The cells were anode supported cells (ASC) with yttria-stabilized zirconia (YSZ) electrolytes, Ni/YSZ hydrogen electrodes and perovskite oxygen electrodes with lanthanum strontium cobalt ferrite (LSCF). This paper summarizes and discusses the preliminary experimental results on the long-term aging tests of the reversible solid oxide planar short stack for fuel cell operation (4000 h) at a current density of 0.5 A cm⁻² which shows a degradation of 0.6% per 1000 h and for steam electrolysis operation (3450 h) and co-electrolysis operation of CO₂ and H₂O (640 h) under different current densities from −0.3 to −0.875 A cm⁻² which show different degradation rates depending on current density and on steam or co-electrolysis.     

A reaction mechanism for gasoline surrogate fuels for large polycyclic aromatic hydrocarbons

This work aims to develop a reaction mechanism for gasoline surrogate fuels (n-heptane, iso-octane and toluene) with an emphasis on the formation of large polycyclic aromatic hydrocarbons (PAHs). Starting from an existing base mechanism for gasoline surrogate fuels with the largest chemical species being pyrene (C₁₆H₁₀), this new mechanism is generated by adding PAH sub-mechanisms to account for the formation and growth of PAHs up to coronene (C₂₄H₁₂). The density functional theory (DFT) and the transition state theory (TST) have been adopted to evaluate the rate constants for several PAH reactions. The mechanism is validated in the premixed laminar flames of n-heptane, iso-octane, benzene and ethylene. The characteristics of PAH formation in the counterflow diffusion flames of iso-octane/toluene and n-heptane/toluene mixtures have also been tested for both the soot formation and soot formation/oxidation flame conditions. The predictions of the concentrations of large PAHs in the premixed flames having available experimental data are significantly improved with the new mechanism as compared to the base mechanism. The major pathways for the formation of large PAHs are identified. The test of the counterflow diffusion flames successfully predicts the PAH behavior exhibiting a synergistic effect observed experimentally for the mixture fuels, irrespective of the type of flame (soot formation flame or soot formation/oxidation flame). The reactions that lead to this synergistic effect in PAH formation are identified through the rate-of-production analysis.     

Pt and Ru dispersed on LiCoO2 for hydrogen generation from sodium borohydride solutions

Nano-sized platinum and ruthenium dispersed on the surface LiCoO₂ as catalysts for borohydride hydrolysis are prepared by microwave-assisted polyol process. The catalysts are characterized by transmission electron microscopy (TEM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). Very uniform Pt and Ru nanoparticles with sizes of <10 nm are dispersed on the surface of LiCoO₂. XRD patterns show that the Pt/LiCoO₂ and Ru/LiCoO₂ catalysts only display the characteristic diffraction peaks of a LiCoO₂ crystal structure. Results obtained from XPS analysis reveal that the Pt/LiCoO₂ and Ru/LiCoO₂ catalysts contain mostly Pt(0) and Ru(0), with traces of Pt(IV) and Ru(IV), respectively. The hydrogen generation rates using low noble metal loading catalysts, 1 wt.% Pt/LiCoO₂ and 1 wt.% Ru/LiCoO₂, are very high. The hydrogen generation rate using Ru/LiCoO₂ as a catalyst is slightly higher compared with that of Pt/LiCoO₂.     

Transport, chemical and electrochemical processes in a planar solid oxide fuel cell: Detailed three-dimensional modeling

A detailed numerical three-dimensional (3D) model for a planar solid oxide fuel cell (SOFC) is developed in this paper. The 3D model takes into account detailed processes including transport, chemical and electrochemical processes taking place in the cell. Moreover, effects of the composite electrodes are taken into account by considering an electrochemically active layer of finite thickness in each of the electrodes. The developed model is applied to a repeating unit of an anode-supported SOFC working under direct internal reforming conditions. Detailed results for chemical species, temperature, current density and electric potential distribution are presented and discussed. It was found that the temperature distribution across the cell is more uniform in the interconnects than in the inner part of the cell. However, only small differences in the electric potential between the electrode and the corresponding interconnect are found. The current density in the electrodes is found to be high near the electrolyte and low deep into the electrochemically active layer. The current density is also low under the ribs of the interconnects.     

Evaporation heat transfer and pressure drop characteristics of R-290 (propane), R-600 (butane), and a mixture of R-290/R-600 in the three-lines serpentine small-tube bank

This paper reports an experimental investigation of heat-transfer and pressure-drop behavior of R-290, R-600, and R-290/R-600 in the three-lines serpentine small-diameter (2.46 mm) tube bank. Heat transfer coefficients and pressure drop characteristics are measured for a range of heat flux (5–21 kW/m²), mass flux (250–500 kg/m² s), equilibrium mass quality (0–0.86), and the fixed mixture composition ((R-290/R-600 (55 wt.%/45 wt.%)). The results show that the flow boiling heat transfer coefficients for R-290, R-600, and R-290/R-600 are 1.66–1.96-fold, 1.28–1.38-fold and 1.57–1.88-fold greater as compared with those for R-134a under equal heat and mass fluxes. Also, the two-phase flow frictional pressure drop for R-600, R-290/R-600 and R-290 are 1.41–1.60-fold, 1.32–1.50-fold and 1.22–1.40-fold smaller as compared with that for R-134a. A new heat transfer correlation was presented by using a superposition model to predict the experimental data for both pure refrigerants and refrigerant mixtures. Experimental results were compared with several correlations which predict the evaporative heat transfer, which are in good agreement with experimental data.     

Separation of oligonucleotides by reversed-phase high performance liquid chromatography

The use of Reversed-Phase High Performance Liquid Chromatography (RP-HPLC) was investigated for the separation of oligonucleotides. By the gradient elution with the mobile phase of methanol, 0.1 M KH₂PO₄ and 0.02 M MaCl₂, the mixtures could be separated in a 250 mm × 4.6 mm I.D. column. The number of theoretical plates and resolution were compared belween this technique and Micellar Electrokinetic Capillary Chromatography (MECC). The charged nucleic acid constituents in the RP-HPLC were relatively better separated than in the MECC.