Background estimation in experimental spectra

A general probabilistic technique for estimating background contributions to measured spectra is presented. A Bayesian model is used to capture the defining characteristics of the problem, namely, that the background is smoother than the signal. The signal is allowed to have positive and/or negative components. The background is represented in terms of a cubic spline basis. A variable degree of smoothness of the background is attained by allowing the number of knots and the knot positions to be adaptively chosen on the basis of the data. The fully Bayesian approach taken provides a natural way to handle knot adaptivity and allows uncertainties in the background to be estimated. Our technique is demonstrated on a particle induced x-ray emission spectrum from a geological sample and an Auger spectrum from iron, which contains signals with both positive and negative components.     

A multifaceted phosphate tether: application to the C1-C14 subunit of dolabelides A-D

A phosphate tether approach to the C1-14 subunit of dolabelide is described. The phosphate tether serves a multifaceted role mediating several processes, including (i) diastereotopic differentiation via RCM, (ii) selective CM by imparting Type III behavior to the exocyclic olefin, (iii) regioselective hydrogenation, and (iv) regioselective Pd(0)-catalyzed reductive opening of the bicyclic phosphate. Overall, this strategy uses orthogonal protecting- and leaving-group properties innate to phosphate esters to rapidly assembly the titled subunit.     

Synthesis, characterization, and photodegradation behavior of single-phase anatase TiO2 materials synthesized from Ti-oxychloride precursors

Single-phase anatase-TiO2 nanomaterials with a size of ca. 10 nm and variable quantities of anion impurities were prepared using a novel pathway based on the use of amorphous ammonium Ti-oxychloride precursors synthesized using Ti/Cl initial ratios between 1 and 6. The precursor nature and evolution under thermal treatment were studied using chemical analysis, XRD, XPS, DRIFTS, and mass spectrometry. The nature and concentration of anatase-TiO2 materials anion impurities were analyzed by XPS and DRIFTS. It is shown that negatively charged impurities located in substitutional positions of the anatase network are maximized for a sample synthesized using a Ti/Cl 1:1 atomic ratio and are responsible for the elimination of liquid-phase (phenol) and gas-phase (isopropanol or methylcyclohexane) pollutants under sunlight excitation. A link is established among the initial chemical characterization of the precursors, the final morphological, structural, and chemical composition of the oxide materials, and their photochemical properties.     

High-load, oligomeric dichlorotriazine: a versatile ROMP-derived reagent and scavenger

A new high-load, soluble oligomeric dichlorotriazine (ODCT) reagent derived from ring-opening metathesis polymerization (ROMP) is reported as an effective coupling reagent, scavenger of nucleophilic species, and activator of DMSO for the classic Swern oxidations. Two variants of this reagent (2G)ODCT 4 and (1G)ODCT 16, possessing theoretical loads of 5.3 and 7.3 mmol/g, respectively, have been synthesized. Preparation was accomplished via simple synthetic protocols affording free flowing powders, amenable for large-scale production. Removal of the spent oligomeric reagent was achieved via either precipitation of the spent reagent or simple filtration utilizing a silica SPE, followed by solvent removal, to deliver products in excellent yield and purity. In addition, the corresponding norbornenyl monomer 3 was successfully demonstrated in a couple-ROMP-filter protocol utilizing in situ polymerization, achieving comparable results versus the corresponding oligomeric variant.     

Effects of arc3, arc5 and arc6 mutations on plastid morphology and stromule formation in green and nongreen tissues of Arabidopsis thaliana

Mutations in the ARC3, ARC5 and ARC6 genes of Arabidopsis thaliana affect chloroplast division. We investigated whether ARC3, ARC5 and ARC6 are also involved in determining plastid morphology in nongreen tissues, where stromules, stroma-filled tubular extensions of the plastid envelope membrane, are more abundant than in mesophyll cells. Using plastid-targeted green fluorescent protein to observe plastids throughout the organs of these mutants, we have discovered a number of new mutant phenotypes. The size of arc3 plastids was heterogeneous in various tissues. arc5 plastids appeared wild-type in the majority of nongreen tissues examined. However, in cells of stamen filaments, the arc5 mutant showed an increase in the frequency of stromules. Increased stromule frequency was observed for a number of organs in the arc6 mutant. Some arc6 cells contained heterogeneous mixtures of plastids; epidermal cells of hypocotyls, stamen filaments and the bases of petals possessed both very large chloroplasts as well as much smaller nongreen plastids. Quantitative analysis in hypocotyl cells revealed that the alteration in stromule length in arc3 and arc6 mutants occurred despite wild-type plastid densities. Thus, in hypocotyls, the effects of the arc3 and arc6 mutations on stromule length and frequency are independent of changes in plastid division. Although electron micrographs of stromules emanating from chloroplasts have rarely been reported, within the arc3 mutant, narrow, 40-50 nm diameter, recoiled stromules could be followed for about 10 microm in electron micrographs of leaf tissue.     

Diode laser measurements of temperature-dependent collisional-narrowing and broadening parameters of Ar-perturbed H2O transitions at 1391.7 and 1397.8 nm

High-resolution absorption lineshapes of two H₂O transitions near 7185.60 and 7154.35 cm⁻¹ have been recorded in a heated static cell as a function of temperature (296-1100 K) and pressure (6-830 Torr) using two distributed-feedback diode lasers. The measured absorption spectra are least squares fit to both Voigt and Galatry profiles. Strong collisional-narrowing effects are observed in the Ar-broadened H₂O spectra at near-atmospheric pressure due to the relatively weak collisional broadening induced by Ar-H₂O collisions, while collisional narrowing is not significant for pure H₂O absorption lineshapes. Line strengths and self-broadening coefficients are inferred from the pure H₂O absorption spectra and compared with published data. Temperature dependences of the Ar-induced broadening, narrowing, and shift coefficients are determined using Galatry fits to the absorption data. The measured collisional-narrowing parameters have similar temperature dependence to the collisional-broadening coefficients.     

Sensitive detection of NH2 in shock tube experiments using frequency modulation spectroscopy

Frequency modulation detection of NH₂ in shock tube kinetic experiments is demonstrated with sensitivities of 0.5 ppm in a single pass and 0.25 ppm in a double pass configuration (1500 K, 1.3 atm, detection bandwidth 1 MHz, 15 cm shock tube diameter). This corresponds to a minimum detectable absorption of 0.01% and 0.005%, respectively, which represents an improvement of more than a factor of 20 when compared to conventional laser absorption detection. The feasibility of quantitative absolute concentration measurements is demonstrated using CH₃NH₂ as a precursor for the preparation of known NH₂ concentrations. The uncertainty for absolute concentration measurements is estimated to be ±10% if a suitable precursor for direct shock tube calibration measurements can be used, and ±15% if an alternative calibration scheme based on the detection of the signal generated by a scanning etalon in reflective mode is used. FM detection has been applied to determine the rate coefficient of the thermal decomposition of CH₃NH₂: CH₃NH₂ + M → CH₃+NH₂+M over the temperature range 1530–1975 K and at pressures near 1.3 atm. The rate coefficient was found to be: k₁=8.17×10¹⁶ exp(−30710/T) (±20%) [cm³ mol⁻¹ s⁻¹] This is in good agreement with a recent determination using conventional laser absorption detection of the NH₂ radical. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 445–453, 1999     

Shock tube study of monomethylamine thermal decomposition and NH2 high temperature absorption coefficient

CH₃NH₂ thermal decomposition is shown to provide a suitable NH₂ radical source for spectroscopic and kinetic shock tube studies. Using this precursor, the absorption coefficient of the NH₂ radical at a detection wavelength of 16739.90 cm⁻¹ has been determined. In the temperature range 1600–2000K the low‐pressure absorption coefficient is described by the polynominal equation: k_NH2=3.953×10¹⁰/T ³+7.295×10⁵/T ²−1.549×10³/T [atm⁻¹ cm⁻¹] The uncertainty of the determined absorption coefficient is estimated to be ±10%. The rate of the thermal decomposition reaction CH₃NH₂+M → CH₃+NH₂+M is determined over the temperature range 1550–1900 K and at pressures near 1.6 atm. The rate coefficient was found to be: k₁=2.51×10¹⁶ exp(−28430/T) [cm³ mol⁻¹ s⁻¹] The uncertainty of the determined rate coefficients is estimated to be ±20%. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 323–330, 1999     

Study of the dependency of spectral radiance factor and colorimetric values on geometric tolerances

The CIE has recommended geometric tolerances for the illumination and collection of light in the measurement of reflectance and radiance factor for colorimetry. This investigation is a pilot study to examine the range of results obtained from the measurement of the radiance factor and colour of reflectance standards over these geometric tolerances.