Kinetic analyses using simultaneous TG/DSC measurements

Summary The thermal decomposition of CaCO₃was studied using simultaneous TG/DSC for two different ranges of particle size from the same source and a physical mixture of each. The difference in kinetic behavior was as expected qualitatively, but significantly different quantitatively. In addition, the mixture did not behave as a simple combination of its end members. These discrepancies are attributed to the problems associated with mass and thermal transport. The TG data again proved easier to fit than the DSC data.     

Ionization and plasma formation in high n cold Rydberg samples

The experiments reported here show that the dipole-dipole interaction, the fundamental interaction between the cold Rydberg atoms, is the dominant initial ionization mechanism for evolution from a frozen Rydberg gas into a plasma. The study also indicates that plasma formation follows a path of initial ionization, redistribution of Rydberg population to higher angular momentum states, and rapid avalanche ionization due to electron-Rydberg collisions.     

Estimation of trace vapor concentration-pathlength in plumes for remote sensing applications from hyperspectral images

A novel approach for quantification of chemical vapor effluents in stack plumes using infrared hyperspectral imaging are presented and examined. The algorithms use a novel application of the extended mixture model to provide estimates of background clutter in the on-plume pixel. These estimates are then used iteratively to improve the quantification. The final step in the algorithm employs either an extended least-squares (ELS) or generalized least-squares (GLS) procedure. It was found that the GLS weighting procedure generally performed better than ELS, but they performed similarly when the analyte spectra had relatively narrow features. The algorithms require estimates of the atmospheric radiance and transmission from the target plume to the imaging spectrometer and an estimate of the plume temperature. However, estimates of the background temperature and emissivity are not required which is a distinct advantage. The algorithm effectively provides a local estimate of the clutter, and an error analysis shows that it can provide superior quantification over approaches that model the background clutter in a more global sense. It was also found that the estimation error depended strongly on the net analyte signal for each analyte, and this quantity is scenario-specific.     

Mathematical analysis of a structure-preserving approximation of the bidimensional vorticity equation

Summary. We show the consistency and the convergence of a spectral approximation of the bidimensional vorticity equation, proposed by V. Zeitlin in[13] and studied numerically by I. Szunyogh, B. Kadar, and D. Dévényi in [12], whose main feature is that it preserves the Hamiltonian structure of the vorticity equation. Received February 22, 2000 / Revised version received October 23, 2000 / Published online June 20, 2001     

Aflatrem,a tremorgenic toxin from Aspergillus flavus

The structure of aflatrem, a tremorgenic toxin from $\text{A. flavus}$ is reported.     

Squaraines as unique reporters for SERRS multiplexing

Modified anilino squaraine dyes provide unique SERRS spectra that can be identified at low concentrations within any mixture of current reporters using longer, biologically compatible wavelengths of excitation.     

A structural systematic study of three isomers of difluoro‐N‐(4‐pyridyl)benzamide

The isomers 2,3‐, (I), 2,4‐, (II), and 2,5‐difluoro‐N‐(4‐pyridyl)benzamide, (III), all with formula C₁₂H₈F₂N₂O, all exhibit intramolecular C—H...O=C and N—H...F contacts [both with S(6) motifs]. In (I), intermolecular N—H...O=C interactions form one‐dimensional chains along [010] [N...O = 3.0181 (16) Å], with weaker C—H...N interactions linking the chains into sheets parallel to the [001] plane, further linked into pairs via C—H...F contacts about inversion centres; a three‐dimensional herring‐bone network forms via C—H...π(py) (py is pyridyl) interactions. In (II), weak aromatic C—H...N(py) interactions form one‐dimensional zigzag chains along [001]; no other interactions with H...N/O/F < 2.50 Å are present, apart from long N/C—H...O=C and C—H...F contacts. In (III), N—H...N(py) interactions form one‐dimensional zigzag chains [as C(6) chains] along [010] augmented by a myriad of weak C—H...π(arene) and O=C...O=C interactions and C—H...O/N/F contacts. Compound (III) is isomorphous with the parent N‐(4‐pyridyl)benzamide [Noveron, Lah, Del Sesto, Arif, Miller & Stang (2002). J. Am. Chem. Soc. 124 , 6613–6625] and the three 2/3/4‐fluoro‐N‐(4‐pyridyl)benzamides [Donnelly, Gallagher & Lough (2008). Acta Cryst. C 64 , o335–o340]. The study expands our series of fluoro(pyridyl)benzamides and augments our understanding of the competition between strong hydrogen‐bond formation and weaker influences on crystal packing.     

Thermal chemistry of bicyclo[4.2.0]oct-2-enes

At 300 degrees C, bicyclo[4.2.0]oct-2-ene (1) isomerizes to bicyclo[2.2.2]oct-2-ene (2) via a formal [1,3] sigmatropic carbon migration. Deuterium labels at C7 and C8 were employed to probe for two-centered stereomutation resulting from C1-C6 cleavage and for one-centered stereomutation resulting from C1-C8 cleavage, respectively. In addition, deuterium labeling allowed for the elucidation of the stereochemical preference of the [1,3] migration of 1 to 2. The two possible [1,3] carbon shift outcomes reflect a slight preference for migration with inversion rather than retention of stereochemistry; the si/sr product ratio is approximately 1.4. One-centered stereomutation is the dominant process in the thermal manifold of 1, with lesser amounts of fragmentation and [1,3] carbon migration processes being observed. All of these observations are consistent with a long-lived, conformationally promiscuous diradical intermediate.     

Phosphorus-functionalized multi-wall carbon nanotubes as flame-retardant additives for polystyrene and poly (methyl methacrylate)

The relationship between the properties with the composition of nickel–aluminium mixed oxides was investigated in this work. Ni–Al materials with Ni/Al molar ratios between 0.5 and 9 were synthesised via co-precipitation. The samples were characterised using the following techniques: surface area measurements (S _BET), thermogravimetry, X-ray diffraction and temperature-programmed reduction, desorption and oxidation (H₂-TPR, NH₃-TPD and TPO/DTA). Samples with Ni/Al ratio = 0.5 primarily formed the Al₂O₃ phase, whereas Ni/Al ratio = 9 mainly led to the bulk NiO phase. However, Ni/Al ratios between 1 and 3 favoured the formation of the mixed oxide phase with increased thermal stability and specific surface area and decreased crystallite sizes. The lower Ni/Al ratios led to the production of ethylene, which is likely related to the higher number of sites with stronger acidity. The samples with Ni/Al ratios of 2 and 3 promoted selectivity towards synthesis gas. For higher Ni/Al ratios, low thermal stability leading to sintering and deactivation due to coke formation was observed.     

Synthetic entries to substituted bicyclic pyridones

The synthesis of 6,6- and 5,6-bicyclic pyridone scaffolds has been completed using (i) an intramolecular Mitsunobu reaction and/or (ii) hydrolysis of a bicyclic pyridinium salt intermediate. Regioselective functionalization of the pyridone ring has been achieved via either direct lithiation or use of the "halogen dance" reaction. Suzuki coupling then allows introduction of aryl units at C(7)/C(9) or C(8) onto the bicyclic pyridone scaffold at either an early or late stage in the synthetic sequence. Suzuki couplings involving iodopyridinium intermediates are particularly effective.