Controlled detonation initiation in hypersonic flow

Experimental evidence of controlled detonation initiation and propagation in a hypersonic flow of premixed hydrogen-air is presented. This controlled detonation initiation is created in a hypersonic facility capable of producing a Mach 5 flow of hydrogen-air. Flow diagnostics such as high-speed schlieren and OH* chemiluminescence results show that a flame deflagration-to-detonation transition occurs as a combined result of turbulent flame acceleration and shock-focusing. The experimental results define three new distinct regimes in a Mach 5 premixed flow: deflagration-to-detonation transition (DDT), unsteady compressible turbulent flames, and shock-induced combustion. A two-dimensional implicit-LES (ILES) simulation, which solves the compressible, reactive Navier-Stokes equations on an adapting grid is conducted to provide additional insight into the local physical mechanism of detonation transition and propagation.     

Trace metal detection in Šibenik Bay, Croatia: Cadmium, lead and copper with anodic stripping voltammetry and manganese via sonoelectrochemistry. A case study

The vertical profiles of the concentration of reactive Mn and total concentrations of Cd, Pb, and Cu ions in the water column of the ?ibenik Bay (Krka river estuary) were determined. The measured ranges of concentrations are: 60–1300 ng l^?1 for Mn, 5–13 ng l^?1 for Cd, 70–230 ng l^?1 for Pb, and 375–840 ng l^?1 for Cu. These values are comparable with the concentrations found in the unpolluted estuaries. The Krka river estuary is highly stratified, with the measured salinity gradient of 20% within a half meter of the freshwater-seawater interface (FSI). The main changes in the vertical profiles of the measured parameters occur in the FSI: the temperature increases for 1 °C and the pH decreases for 0.1 unit, whereas the metal concentrations show different behaviour. Generally, Mn, Pb, and Cd ions show the increase of concentrations in the FSI, while copper concentration profile indicates anthropogenic pollution in the brackish layer caused by agriculture activities and by the paint with copper basis used as an antifoulant biocide for the ships. UV-digested samples show an increase in manganese concentrations for at least 3.5 times comparing to non UV-digested. This suggests that in natural water manganese exists mainly in the form of inert complexes and as associated to particulate matter (about 70–80%). UV irradiation has no influence on the concentration of cadmium, while for lead an increase of 50% in the seawater layer is observed. The twofold increase of the copper concentration in the upper freshwater layer and at least the fourfold one in the seawater layer were measured in the UV-digested samples. These results show that copper is strongly bound to inert complexes, and that UV-digestion is necessary step in determination of the total metal concentrations in natural water samples. No significant increase of the metal concentrations in the deeper seawater layer was observed, indicating the absence of the processes of remobilization or dissolution of metals from the sediment. Presented results confirm that the new method for the determination of manganese by CSV on boron-doped diamond electrode with ultrasound enhanced accumulation can be successfully applied to natural waters.     

Structural formulas and explanation in organic chemistry

Organic chemists have been able to develop a robust, theoretical understanding of the phenomena they study; however, the primary theoretical devices employed in this field are not mathematical equations or laws, as is the case in most other physical sciences. Instead it is diagrams, and in particular structural formulas and potential energy diagrams, that carry the explanatory weight in the discipline. To understand how this is so, it is necessary to investigate both the nature of the diagrams employed in organic chemistry and how these diagrams are used in the explanations of the discipline. I will begin this paper by characterizing some of the major ways that structural formulas used in organic chemistry. Next I will present a model of the explanations in organic chemistry and describe how both structural formulas and potential energy diagrams contribute to these explanations. This will be followed by several examples that support my abstract account of the role of diagrams in the explanations of organic chemistry. In particular, I will consider both the appeal to ‘hyperconjugation’ in the explanation of alkene stability and how the idea of ‘ring strain’ was developed to explain the relative stability of cyclic compounds.

Quantification of small molecule organic acids from Mycobacterium tuberculosis culture supernatant using ion exclusion liquid chromatography/mass spectrometry

Quantitative analysis of cellular small molecule organic acids of intermediary metabolism can provide critical insight into bacterial metabolic pathways. The concentration of these metabolites in culture supernatant varies at different growth stages or under particular environmental conditions reflecting both the energy and the biosynthetic needs, yielding metabolic information about the microorganism. The method described here utilizes ion exclusion chromatography with formic acid, coupled with a mass-selective detector using selective ion monitoring with negative mode electrospray ionization (SIM ES-), to detect and quantify several small organic acids in culture supernatants. The microM limits of quantitation (LOQs) were found to be 5.5 +/- 0.9 for pyruvate, 7.0 +/- 0.4 for malate, 2.5 +/- 0.5 for succinate, 12.7 +/- 0.8 for lactate, and 6.6 +/- 0.2 for fumarate. The method was used to detect and quantify these acids in the culture supernatants from Mycobacterium tuberculosis. Supernatant samples were spiked with stable-isotope-labeled internal standards, and the organic acids were quantified by isotope ratiometry.     

Co-occurrence of boundary and resonance ejection in a multiplexed rectilinear ion trap mass spectrometer

A method is reported for evaluating ion trap mass analyzers by selection of operating conditions under which both boundary and resonance ejection peaks occur in a single mass scan. The choice of frequency and amplitude of the auxiliary waveform applied for resonance ejection can be such as to produce a resonance ejection mass spectrum with unit resolution or, under selected conditions, signals attributable to both boundary and resonance ejection in a single mass scan. The contrasting mass resolution associated with these two ejection processes is evident in these data. The co-occurrence of the two ejection phenomena is ascribed to the effects of higher-order fields; it is more marked in some rectilinear ion traps (RITs) than in other nominally identical devices, leading to the possibility of using it to compare individual mass analyzers in multiplexed instruments. The method is used to compare multiple ion traps driven by the same RF signal in a fully-multiplexed mass spectrometer, composed of parallel ion source/mass analyzer/detector channels each housed in one quadrant of a specialized vacuum chamber.     

Nitric Oxide Dioxygenation Reaction by Oxy-Coboglobin Models: In-situ Low-Temperature FTIR Characterization of Coordinated Peroxynitrite

The oxy-cobolglobin models of the general formula (NH(3))Co(Por)(O(2)) (Por = meso-tetra-phenyl and meso-tetra-p-tolylporphyrinato dianions) were constructed by sequential low temperature interaction of NH(3) and dioxygen with microporous layers of Co-porphyrins. At cryogenic temperatures small increments of NO were introduced into the cryostat and the following reactions were monitored by the FTIR and UV-visible spectroscopy during slow warming. Upon warming the layers from 80 to 120 K a set of new IR bands grows with correlating intensities along with the consumption of the ν(O(2)) band. Isotope labeling experiments with (18)O(2), (15)NO and N(18)O along with DFT calculations provides a basis for assigning them to the six-coordinate peroxynitrite complexes (NH(3))Co(Por)(OONO). Over the course of warming the layers from 140 to 170 K these complexes decompose and there are spectral features suggesting the formation of nitrogen dioxide NO(2). Upon keeping the layers at 180-210 K the bands of NO(2) gradually decrease in intensity and the set of new bands grows in the range of 1480, 1270, and 980 cm(-1). These bands have their isotopic counterparts when (15)NO, (18)O(2) and N(18)O are used in the experiments and certainly belong to the 6-coordinate nitrato complexes (NH(3))Co(Por)(η(1)-ONO(2)) demonstrating the ability of oxy coboglobin models to promote the nitric oxide dioxygenation (NOD) reaction similar to oxy-hemes. As in the case of Hb, Mb and model iron-porphyrins, the six-coordinate nitrato complexes are not stable at room temperature and dissociate to give nitrate anion and oxidized cationic complex Co(III)(Por)(NH(3))(1,2).     

Concurrent changes of crystallographic and Mössbauer effect parameters at the high-spin(5T2) ⤥ low-spin(1A1) transition in compounds of iron (II)

Distinct and different X-ray diffraction patterns are found for the ⁵T₂ and ¹A₁ phases at the high-spin(⁵T₂) ? low-spin(¹A₁) transition in Fe(bt)₂(NCS)₂ (I) and Fe(phy)₂(ClO₄)₂ (II) (bt = 2,2′-bi-2-thiazoline; phy = 1,10-phenanthroline-2-carbaldehydephenylhydrazone). The peak profiles show the same temperature dependence and the same hysteresis behaviour as the ⁵T₂ and ¹A₁ fractions determined on the basis of Mössbauer effect or magnetism. At the transition temperature T_c, both phases are coexistent.