Effect of structural conduction and heat loss on combustion in micro-channels

This paper presents a simple analytical model for the effects of heat exchange within the structure of a micro-channel combustor, and heat loss from the structure to the environment. This is accomplished by extending reasoning similar to that employed by Mallard and Le Chatelier in their thermal theory for flame propagation. The model is used to identify some of the basic parameters that must be considered when designing an efficient micro-combustor and its predictions are compared with the results of a numerical simulation of stoichiometric premixed combustion of a hydrogen–air mixture stabilized between two parallel plates. The simulation incorporates a one-dimensional continuity/energy equation solver with full chemistry coupled with a model for thermal exchange in the structure. The results show that heat exchange through the structure of the micro-combustor can lead to a broadening of the reaction zone. Heat loss to the environment decreases the broadening effect and eventually results in flame quenching. This behaviour, which arises from the thermal coupling between the gas and the structure, influences the maximum achievable power density of microscale combustors.     

Rapid sequential injections of hyperpolarized [1-C]pyruvate in vivo using a sub-kelvin,multi-sample DNP polarizer

The development of hyperpolarized technology utilizing dynamic nuclear polarization (DNP) has enabled the rapid measurement of ¹³C metabolism in vivo with very high SNR. However, with traditional DNP equipment, consecutive injections of a hyperpolarized compound in an animal have been subject to a practical minimum time between injections governed by the polarization build-up time, which is on the order of an hour for [1-¹³C]pyruvate. This has precluded the monitoring of metabolic changes occurring on a faster time scale. In this study, we demonstrated the ability to acquire in vivo dynamic magnetic resonance spectroscopy (MRS) and 3D magnetic resonance spectroscopic imaging (MRSI) data in normal rats with a 5 min interval between injections of hyperpolarized [1-¹³C]pyruvate using a prototype, sub-Kelvin dynamic nuclear polarizer with the capability to simultaneously polarize up to 4 samples and dissolve them in rapid succession. There were minimal perturbations in the hyperpolarized spectra as a result of the multiple injections, suggesting that such an approach would not confound the investigation of metabolism occurring on this time scale. As an initial demonstration of the application of this technology and approach for monitoring rapid changes in metabolism as a result of a physiological intervention, we investigated the pharmacodynamics of the anti-cancer agent dichloroacetate (DCA), collecting hyperpolarized data before administration of DCA, 1 min after administration, and 6 min after administration. Dramatic increases in ¹³C-bicarbonate were detected just 1 min (as well as 6 min) after DCA administration.     

Coincidence studies of fluorescence and dissociation processes in electronic excited states of I2+, Br2+, IBr+ and ICl+

The PIFCO technique in which mass-selected photoion—fluorescence photon coincidences are counted, was used to investigate whether I₂⁺, IBr⁺ and ICl⁺ fluoresce. Measurements were made of lifetimes and fluorescence quantum yields of electronic excited states of these ions. Emission was discovered for I₂⁺ and IBr⁺, but ICl⁺ apparently does not fluoresce. Information on the radiative properties of Br₂⁺ was obtained as a by-product of the work on IBr⁺. Fragment ion kinetic energy releases were determined and provide information on dissociative ionization processes in the halogen and interhalogen ions studied.     

Cosmic strings in Bianchi III spacetime: Integrable cases

We investigate the integrability of cosmic strings in Bianchi III spacetime using a symmetry analysis. The behaviour of the model is reduced to the solution of a single second order nonlinear differential equation. We show that this equation has a rich structure and admits an infinite family of solutions. Our class of solutions extends special cases previously obtained by Tikekar and Patel [Gen. Relativ. Gravit. 24, 397 (1992)].     

Variation of triplet state properties of N-mTEG[60]fulleropyrrolidine bis-adducts as a function of the bond path between the addends

For a group of seven isomeric N-mTEG[60]fulleropyrrolidine bis-adducts (mTEG = CH₂CH₂OCH₂CH₂OCH₂CH₂OCH₃), the quantum yields of singlet oxygen (O₂, ¹Δ_g) production and the maximum triplet molar absorption coefficients were found to be separately correlated with the shortest distances and with the number of bonds connecting the two addends on the fullerene sphere.     

Laser pyrolysis: Effect of ambient gases on molecular spectral emission

Observations are reported on the emission spectra of molecules in luminous plumes produced by focussing a Q-switched ruby laser beam on various solids (mostly elements) in the following gases at various pressures; air, H₂, N₂, SF₆ and O₂.     

Concerted and two-step conformational ring-flipping in [2.2] (3,3′,4,4′) biphenylophanes1

The [2.2] (3,3′,4,4′)biphenylophanes ($\text{4}$) and ($\text{7}$) undergo conformational ring-flipping. The activation energy barriers have been determined and the possible conformational pathways are presented.     

Organopalladium approaches to prostaglandins. 1. Synthesis of thiophene-containing prostaglandin endoperoxide analogs via thienylpalladation of bicycle olefins

Thiophene-containing prostaglandin endoperoxide analogs are readily available by addition of thienylpalladium species to bicyclic olefins and subsequent treatment with alkenyl or alkynyl organometallics. Hydrogenation affords bicyclic and tricyclic prostanoic acid analogs.