Thermo-chemical manifold reduction for tabulated chemistry modeling. Temperature and dilution constraints for smooth combustion reactors

New scenarios for energy systems pointed out the importance of designing innovative combustion systems. In this context, high levels of internal dilution and preheating show interesting features related to low emissions, smooth temperature gradients, absence of visible flame and large fuel and load flexibility. Those characteristics are very difficult to obtain simultaneously with conventional combustion processes in the same device.The large-scale utilization of such novel concepts relies on the developments of proper modeling tools that should consider the multiple physical phenomena involved under distributed ignition. A challenging modeling aspect is related to the strong coupling between fluid-dynamics and kinetic time scales that implies the use of detailed mechanisms. Moreover, the heat transfer mechanisms and the heat loss at walls play key roles.In this context, tabulated chemistry methods are viable solutions to represent the thermo-chemical pattern in combustion systems with internal recirculation. However, the identification of adequate controlling variables for these systems is not trivial. In fact, in addition to mixture fraction and progress variable, an internal dilution and a heat loss parameter must be considered, leading to a 4-dimensional thermo-chemical manifold, with an inherent increase of computational costs.In this work a novel tabulation procedure is proposed in order to represent such comprehensive manifold taking into account the primary role of the internal recirculation on system reactivity.Moreover, a reduction of the thermo-chemical manifold was carried out by exploiting active interconnections between experiments and computations and embedding physical and process constraints based on measurable quantities obtained from experiments. These constrains are related to minimum ignition and maximum attainable process temperatures, heat loss through the surroundings and recirculation rate. The reliability of the proposed approach was assessed by comparing the reduced manifolds to the measured data for a cyclonic burner operating under massive internal dilution levels.     

5‐Benzoyl­amino‐3‐bromo‐4‐(4‐methoxy­phenyl)‐4,5‐di­hydro­isoxazole‐5‐carboxyl­ic acid

The title compound, C₁₈H₁₅BrN₂O₅, a promising N‐protected α‐amino acid, was synthesized directly from an unusual bromo dipole and a 4‐(aryl­methyl­ene)­oxazolone. The crystal packing of the title compound is a racemic mixture. Peculiar graph‐set motifs driven by the most important hydrogen bonds are described.     

Comparative LC Enantioseparation of Novel PPAR Agonists on Cellulose- and Amylose-Based Chiral Stationary Phases

The LC enantiomeric separation of several dual PPARα/γ agonists on the commercially available Chiralcel OD and Chiralpak AD columns has been evaluated in normal phase mode using a mobile phase consisting in a mixture of n-hexane, 2-propanol and trifluoroacetic acid at constant volume ratio. Most compounds were separated as underivatized acids without requiring time consuming analysis. Some complementary selectivity was evidenced on the two investigated chiral stationary phases related to the different accessibility of the active sites of the helical cavities. Additional information on the chiral recognition mechanism were deduced from the chromatographic behaviour of some selected methyl esters.     

NF-κB is Not Directly Responsible for Photoresistance Induced by Fractionated Light Delivery in HT-29 Colon Adenocarcinoma Cells

Our recent study follows up an earlier one which demonstrated hypericin-mediated photocytotoxic effects on HT-29 adenocarcinoma cells by light fractionation with a longer dark pause between two unequal light doses (Sackova, A. [2005] Photochem. Photobiol. 81 , 1411–1416). Here, we present closer study on events invoked by sublethal light dose (1 J cm⁻²) during the period of 6 h that is sufficient to invoke resistance to second lethal dose (11 J cm⁻²). First, we proved that the dark pause of 6 h, but not 1 h, resulted in better cell survival with suppressed phosphatidylserine externalization, decreased reactive oxygen species production and hypericin content as well as altered expression of HSP70, GRP94, clusterin, nuclear factor (NF)-κB, IκB-α or Mcl-1. NF-κB activity assay confirmed activation of this early-response pathway. However, inhibition of IκB (IKK) kinase by parthenolide by stopping NF-κB release from the complex with IκB did not prevent onset of resistance, but it invoked some resistance even in groups with shorter, 1 h dark pause. Therefore, we predict involvement of another signaling pathway, located upstream from NF-κB, responsible for onset of resistance to photodynamic therapy with hypericin in colon adenocarcinoma cells HT-29.