Estimating the cell density and invasive radius of three-dimensional glioblastoma tumor spheroids grown in vitro

To gain insight into brain tumor invasion, experiments are conducted on multicellular tumor spheroids grown in collagen gel. Typically, a radius of invasion is reported, which is obtained by human measurement. We present a simple, heuristic algorithm for automated invasive radii estimation (AIRE) that uses local fluctuations of the image intensity. We then derive an analytical expression relating the image graininess to the cell density for a model imaging system. The result agrees with the experiment up to a multiplicative constant and thus describes a novel method for estimating the cell density from bright-field images.     

电力电子中的碳化硅（SiC）

SiC是提高功率模块中功率密度的一种理想材料,SiC功率器件具有非常低的开关损耗,热传导率很低。本文介绍了SiC混合模块（传统IGBT和SiC肖特基二极管）和全SiC模块的性能,并与传统硅续流二极管（CALHD）和快速硅二极管进行比较。．     

Opposite effects of plasma homocysteine and the methylenetetrahydrofolate reductase C677T mutation on carotid artery geometry in asymptomatic adults

Studies of symptomatic patients have identified hyperhomocysteinemia as an independent risk factor for vascular disease. In case-control studies, a point mutation (C677T) in the gene encoding 5,10-methylenetetrahydrofolate reductase (MTHFR) has also been linked to an increased risk of vascular disease through its effect on homocysteinemia. Our aim was to extend these observations to asymptomatic subjects by studying the influence of both homocysteinemia and its mutation on carotid artery geometry. We examined 144 subjects free of atherosclerotic lesions. Fasting homocysteinemia was measured by high-performance liquid chromatography with fluorometric detection. MTHFR genotype was analyzed by polymerase chain reaction followed by HinfI digestion. Carotid artery geometry was characterized by internal diameter and intima-media thickness, as assessed by a high-resolution echo-tracking system. Subjects in the upper homocysteine tertile had a greater carotid internal diameter than did subjects in the middle and lower tertiles (6516+/-770 versus 6206+/-641 and 5985+/-558 microm, respectively; P<0.001). Subjects homozygous for the mutation had a smaller carotid artery internal diameter than did subjects heterozygous or homozygous for the wild-type allele (5846+/-785 versus 6345+/-673 and 6199+/-671 microm, respectively; P<0.05). Homocysteinemia was not significantly increased in subjects homozygous for the mutation. In multivariate regression analysis, homocysteinemia was independently and positively associated with lumen diameter (P=0.0008) and wall thickness (P=0.020). Conversely, homozygosity for the mutation was negatively associated with internal diameter (P=0.009). These preliminary data suggest that mildly elevated homocysteinemia and homozygosity for the MTHFR C677T mutation are associated with opposite preclinical modifications of carotid artery geometry. If confirmed, these results may have important implications for new treatment strategies for vascular disease before the onset of clinical manifestations.     

Phosphatidylinositol-specific phospholipase C from Listeria monocytogenes contributes to intracellular survival and growth of Listeria innocua

Listeria monocytogenes is a facultative intracellular organism that is capable of replicating within macrophage and macrophage-like cells. The species secretes a phosphatidylinositol-specific phospholipase C (PI-PLC) encoded by the plcA gene. A plcA gene from L. monocytogenes was cloned downstream of a gram-positive promoter in the plasmid pWS2-2. To determine what effect plcA would have on intracellular survival when introduced into Listeria innocua, a species that does not growth intracellularly or contain plcA, transformation with the recombinant pWS2-2 plasmid was performed. Phospholipase C activity in Listeria innocua/pWS2-2 was confirmed on a brain heart infusion-phosphatidylinositol agar plate, whereas wild-type L. innocua did not produce PI-PLC activity. Intracellular growth of L. innocua/pWS2-2 was subsequently measured in the macrophage-like cell line J774 by Giemsa staining and viable count determinations at specific time points following infection. The J774 cells infected with wild-type L. innocua showed a falling viable count through 8 h postinfection. Although J774 cells infected with L. innocua/pWS2-2 also initially displayed reduced viable counts, the viable count rose after 6 h postinfection and increased further at 8 h postinfection before a subsequent decline again at 16 h postinfection. Giemsa staining revealed fewer than 6 bacteria in individual macrophage cells at 2 h postinfection, and yet approximately 15% of the J774 cells had 6 to 12 bacteria localized to one area of the macrophage cell after 6 h; moreover, electron micrographs showed that the L. innocua/pWS2-2 cells were replicating inside the phagosome of the host cell. Furthermore, Thoria Sol labeling demonstrated that lysosomes had fused with these phagosomes, and acridine orange staining revealed that the compartments were acidified. These results demonstrate that L. innocua cells transformed with the plasmid-borne plcA gene, and expressing functional PI-PLC, are able to grow intracellularly in what appear to be phagolysosomes, although between 3 and 6 h is needed for this to manifest itself. Intracellular growth specifically in L. innocua may be a secondary function associated with the plcA gene product. The addition of this one gene, plcA, to a species of Listeria that in the wild-type state does not replicate intracellularly apparently can now allow some of the bacteria to transiently multiply inside the phagosomes of host macrophage cells.     

Experimental investigation on H2S and SO2 sulphur poisoning and regeneration of a commercially available Ni-catalyst during methane tri-reforming

H₂S and SO₂ poisoning during methane tri-reforming are the main degradation sources for nickel catalysts, especially when exhaust gases are used as reactants. To prolong the lifetime of such applications, it is of primary importance to find strategies which reduce the poisoning effects of sulphur or allow regeneration of poisoned catalysts. The specific feature of tri-reforming, oxygen addition to the reactants, offers possibilities for both of these objectives. This experimental study, based on a specific thermochemical recuperation process, thus scrutinizes three aspects of sulphur poisoning and regeneration during methane tri-reforming focusing on oxygen as key influencing factor: (I) Oxygen addition to the reactants is investigated. (II) A comparison between H₂S and SO₂ poisoning is made. (III) Catalyst regeneration by oxygen treatment is performed. The conclusions derived from the results allow significant improvements in terms of catalyst stability and regeneration and thus contribute to expand application possibilities of reforming catalysts.     

Sensitivity analysis of skeletal reaction mechanisms for use in CFD simulation of oxygen enhanced combustion systems

Oxygen enhanced combustion (OEC) techniques are supposed to be a fuel saving alternative to conventional air-fired combustion, due to the reduction or removal of nitrogen from the combustion system, which causes a higher flame temperature and radiation intensity. Therefore, more heat is available in OEC for heating, melting and annealing processes, and subsequently, increases the process efficiency. The main aim of the present study is the numerical investigation of different reaction mechanisms under air-fuel and oxy-fuel conditions using 1D simulation of laminar counter-flow diffusion flames. The mechanisms are further used in 3D CFD simulation with the steady laminar flamelet model for the development of a time efficient numerical approach, applicable in air-fuel and OEC. Three skeletal reaction mechanisms were tested and compared to the GRI3.0 mechanism. The calculated temperatures and species concentrations revealed that a skeletal mechanism with 17 species and 25 reversible reactions predicts a faster fuel conversion into the reaction products under oxy-fuel conditions, which leads to higher temperatures in the flame compared to the GRI3.0. Sensitivity analysis showed that two reversible reactions are mainly responsible for the faster fuel conversion. Furthermore, the reaction mechanisms investigated, were used for 3D CFD simulation of a lab-scale furnace under different OEC conditions and air-fuel combustion. Up to concentrations of 30% O₂ in the O₂/N₂ mixture, all reaction mechanisms were able to predict the temperatures in the furnace with a close accordance to measured data. With higher oxygen enrichment levels, only the mentioned skeletal mechanism with 25 reactions calculated good results, whereas the GRI3.0 failed for oxy-fuel combustion.     

The STM learning curve and where it may take us*

The scanning tunnelling microscope (STM) has proved to be an extraordinary method to investigate surfaces in vacuum, air and liquid environments. Several issues regarding the use of the STM for atomic resolution studies are discussed. These include electronic contributions to STM images, the role of the tip in resolution and spectroscopy, as well as the need for complementary information about chemical composition or sub-surface structure.     

How the coarse fraction influences the microstructure and the effective thermal conductivity of alumina castables – An experimental and numerical study

This study investigates the particle size distribution's effect on the microstructure and effective thermal conductivity (ETC) of alumina castables. The ETC was measured by the transient plane source method and predicted numerically based on a two-scale model describing the structure on a fine and coarse scale. The prediction considered particle and pore size distributions, porosity (around 20%) and grain morphology. The microstructure was investigated by scanning electron microscopy. For a constant fines content, increasing the coarse grain fraction while decreasing the medium fraction enhanced sintering of the matrix. Small pores (≤250 nm) increased the sintering activity. The densest castable contained the most small pores. The particles’ and pores’ contributions to the sintering activity led to intensified microcracking and a decreased ETC. The numerical model did not consider constituents ≤500 nm like the small pores and microcracks and the calculated ETC values consequently deviated from the measured values.