Nitrogen-15 NMR studies of 1,4-benzodiazepines: 2—The triazolobenzodiazepines

Nitrogen-15 NMR data for a series of 21 triazolobenzodiazepines are presented, including ¹⁵N chemical shifts and substituent effects. The line assignments made by correlation to other model compounds were confirmed by a shift reagent and protonation study. A Yb(dpm)₃ study on alprazolam showed that the molar shifts of the four nitrogens ranged from 35 to 150 ppm.     

10 kHz detection of CO2 at 4.5 microm by using tunable diode-laser-based difference-frequency generation

A compact, high-speed tunable, diode-laser-based mid-infrared (MIR) laser source has been developed for absorption spectroscopy of CO2 at rates up to 10 kHz. Radiation at 4.5 microm with a mode-hop-free tuning range of 80 GHz is generated by difference-frequency mixing the 860 nm output of a distributed-feedback diode laser with the 1064 nm output of a diode-pumped Nd:YAG laser in a periodically poled lithium niobate crystal. MIR absorption spectroscopy of CO2 with a detection limit of 44 ppm m at 10 kHz is demonstrated in a C2H4-air laminar diffusion flame and in the exhaust of a liquid-fueled model gas-turbine combustor.     

Long waves in streamwise varying shear flows: new mechanisms for a weakly nonlinear instability

The weakly nonlinear dynamics of long waves embedded in marginally stable shear flows that vary in the streamwise direction are shown to be governed by a variable-coefficient Boussinesq equation. Depending on the local stability characteristics of the flow, new nonmodal or modal instabilities may emerge that serve as natural mechanisms for achieving amplitude thresholds necessary for weakly nonlinear instability and the transition to fully finite-amplitude states.     

Endpoint Fragmentation Index: A Method for Monitoring the Evolution of Microbial Degradation of Polysaccharide Feedstocks

We describe a simple method for tracking the course of microbial degradation of polysaccharide-rich feedstocks. The method involves determining total polysaccharides present in the feedstock, measured in glucose equivalents, relative to the fractional component of polysaccharides exhibiting 2,3-dinitrosalycylic acid aldehyde activity. The ratio of total polysaccharide to aldehyde activity, defined as the end-point fragmentation (EPF) index, is then calculated and tracked as it shifts as microbial degradation of polysaccharide-rich feedstock progresses. While degradation occurs, the EPF index falls. It bottoms out at an asymptotic limit marking the point in time where further degradation of the polysaccharide-rich feedstock has ceased. The EPF index can be used to follow the progressive breakdown of composting polysaccharide-rich waste. It may also have applicability as a means of tracking the turnover of polysaccharides in other complex environments including soil, sediments, wetlands, and peat bogs.     

New high permittivity tetragonal tungsten bronze dielectrics Ba2LaMNb4O15: M=Mn, Fe

The new phases Ba₂LaMNb₄O₁₅: M=Mn, Fe were prepared by solid state reaction at 1100 °C. They have the tetragonal tungsten bronze structure, space group P4/mbm, at room temperature. The two octahedral sites show partial order of M and Nb with preferential occupancy of the smaller B(1) sites by M. Both phases have high permittivities 90±15 over the range 10-320 K. Ba₂LaFeNb₄O₁₅ is highly insulating with bulk conductivity ?10⁻⁸ ohm⁻¹ cm⁻¹ at 25 °C and tan δ?0.001 over the range 100-320 K and at 10⁵ Hz. Solid solutions between these new phases and the compositionally and structurally related relaxor ferroelectric Ba₂LaTi₂Nb₃O₁₅ show gradual loss of ferroelectric behaviour attributed to replacement of polarisable Ti⁴⁺ by a mixture of (Mn, Fe)³⁺ and Nb⁵⁺.     

Entropy drives an attached water molecule from the C- to N-terminus on protonated proline

Results from infrared photodissociation (IRPD) spectroscopy and kinetics of singly hydrated, protonated proline indicate that the water molecule hydrogen bonds preferentially to the formally neutral carboxylic acid at low temperatures and at higher temperatures to the protonated N-terminus, which bears the formal charge. Hydration isomer populations obtained from IRPD kinetic data as a function of temperature are used to generate a van't Hoff plot that reveals that C-terminal binding is enthalpically favored by 4.2-6.4 kJ/mol, whereas N-terminal binding is entropically favored by 31-43 J/(mol K), consistent with a higher calculated barrier for water molecule rotation at the C-terminus.     

High-speed CH planar laser-induced fluorescence imaging using a multimode-pumped optical parametric oscillator

We report on high-speed CH planar laser-induced fluorescence (PLIF) imaging in turbulent diffusion flames using a multimode-pumped optical parametric oscillator (OPO). The OPO is pumped by the third-harmonic output of a multimode Nd:YAG cluster for direct signal excitation in the A-X (0,0) band of the CH radical. The lasing threshold, conversion efficiency, and linewidth are shown to depend on the number of pump passes in the ring cavity of the OPO. Single-shot CH PLIF images are acquired at 10 kHz with excitation energy up to 6 mJ/pulse at 431.1 nm. Signal-to-noise ratios of ~25-35 are the highest yet reported for high-speed CH PLIF.     

A method for separation of Po,Th, Pa and U in high yields from various matrices

We give a new general method of separation of the title radionuclides, using ferric hydroxide precipitations, cation exchange chromatography followed by anion exchange for U, further cation exchange for Pa and direct elution for Th. Electrodeposition for all three elements is from sulfate medium. Yields for Pa, Th, Pa, U are mostly about 98%. Matrices analyzed include calcite, dolomite, phosphorite, sediments, organic material, and mineral fractions from rock.