Fixed-frequency cavity ringdown diagnostic for atmospheric particulate matter

A nonresonant cavity ringdown diagnostic to measure light attenuation from atmospheric particulate matter at 532- and 355-nm wavelengths is described. The presence of atmospheric particulate is clearly detectable with this technique, as demonstrated by experimental results. The extinction cross section is higher at 355 than at 532 nm, although we were able to purchase significantly higher-reflectivity optics at 532 nm. The expected advantage at 355 nm is thus lost. This new technique is compared with a commercially available instrument, and sensitivity limitations are discussed.     

Algebraically stable general linear methods and the <Emphasis Type="Italic">G</Emphasis>-matrix

The standard algebraic stability condition for general linear methods (GLMs) is considered in a modified form, and connected to a branch of Control Theory concerned with the discrete algebraic Riccati equation (DARE). The DARE theory shows that, for an algebraically stable method, there is a minimal G-matrix, G ^*, satisfying an equation, rather than an inequality. This result, and another alternative reformulation of algebraic stability, are applied to construct new GLMs with 2 steps and 2 stages, one of which has order p=4 and stage order q=3. The construction process is simplified by method-equivalence, and Butcher’s simplified order conditions for the case p≤q+1.      

On a multistep method approximating a linear sectorial evolution equation

This paper concerns the linear multistep approximation of anabstract dissipative linear sectorial evolution equation ona Banach space X. We study how well the semigroup generatedby a sectorial operator A is approximated by the numerical semigroupgenerated by a q-step, strictly A ()-stable multistep method.An optimal order error bound is obtained.     

The complex Frobenius theorem for rough involutive structures

We establish a version of the complex Frobenius theorem in the context of a complex subbundle of the complexified tangent bundle of a manifold having minimal regularity. If the subbundle defines the structure of a Levi-flat CR-manifold, it suffices that be Lipschitz for our results to apply. A principal tool in the analysis is a precise version of the Newlander-Nirenberg theorem with parameters, for integrable almost complex structures with minimal regularity, which builds on recent work of the authors.

     

Exact Timing of Returned Molecular Wavepacket

An ionizing wavepacket of electron will re-visit its parent molecular ion during photoionization by strong laser field. This scenario is associated with physical concepts such as molecular re-scattering/collision, interference, diffraction, molecular clock, and generation of XUV light via high-order harmonic generation. On the workbench of a reduced dimensionality model of molecular hydrogen ions irradiated by laser pulse of 0.01-10.0 a.u. intensities, one-cycle pulsewidth, and 800nm wavelength, by deploying a momentum operator on the time-dependent wavefunction of an ionizing wavepacket, we can determine, in a precise manner, the exact time instant for the re-visiting electron to come back to the cation position. The time value is 57.6% of an optical cycle of the exciting laser pulse. This result may be useful in attosecond pump-probe experiments or molecular clock applications.     

Influence of polydisperse distributions of both primary particle and aggregate size on soot temperature in low-fluence LII

An improved aggregate-based low-fluence laser-induced incandescence (LII) model has been developed. The shielding effect in heat conduction between aggregated soot particles and the surrounding gas was modeled using the concept of the equivalent heat transfer sphere. The diameter of such an equivalent sphere was determined from direct simulation Monte Carlo calculations in the free molecular regime as functions of the aggregate size and the thermal accommodation coefficient of soot. Both the primary soot particle diameter and the aggregate size distributions are assumed to be lognormal. The effective temperature of a soot particle ensemble containing different primary particle diameters and aggregate sizes in the laser probe volume was calculated based on the ratio of the total thermal radiation intensities of soot particles at 400 and 780 nm to simulate the experimentally measured soot particle temperature using two-color optical pyrometry. The effect of primary particle diameter polydispersity is in general important and should be considered. The effect of aggregate size polydispersity is relatively unimportant when the heat conduction between the primary particles and the surrounding gas takes place in the free-molecular regime; however, it starts to become important when the heat conduction process occurs in the near transition regime. The model developed in this study was also applied to the re-determination of the thermal accommodation coefficient of soot in an atmospheric pressure laminar ethylene diffusion flame. PACS 44.05.+e; 61.46.Df; 65.80.+n     

Competitive sorption between glyphosate and inorganic phosphate on clay minerals and low organic matter soils

Inorganic phosphate may influence the adsorption of glyphosate to soilsurface sites. It has been postulated that glyphosate sorption is dominatedby the phosphoric acid moiety, therefore, inorganic phosphate could competewith glyphosate for surface sorption sites. We examine sorption of glyphosatein low organic carbon systems where clay minerals dominate the available adsorptionsites using ³²P-labeled phosphate and ¹⁴C-labeled glyphosateto track sorption. We found glyphosate sorption strongly dependent on phosphateadditions. Isotherms were generally of the L type, which is consistent witha limited number of surface sites. Most sorption on whole soils could be accountedfor by sorption observed on model clays of the same mineral type as foundin the soils.     

The use of NMR for determination of new structures in irradiated TFE/PMVE fluoropolymers

The radiation chemistry of two TFE/PMVE copolymers with TFE mole fractions of 0.66 and 0.81 has been studied under vacuum using ⁶⁰Co γ-radiation over absorbed dose ranges up to 4.2 MGy. The radiolysis temperature was 313 K for both TFE/PMVE copolymers. New structure formation in the copolymers was identified by solid-state ¹⁹F NMR and the G-values for new chain ends of 2.1 and 0.5 and for branching sites of 0.9 and 0.2 have been obtained for the TFE/PMVE with TFE mole fractions of 0.66 and 0.81, respectively. The relative yields of –O–CF₃ and –CF₂–CF₃ chain ends were found to be proportional to the copolymer composition, but the yields of the –CF₂–CF₃ chain ends and –CF– branch points were not linearly related to the composition, rather they were correlated with the radical yields measured at 77 K.     

HPLC Coupled with in-line photolysis, hydride generation and flame atomic-absorption spectrometry for the speciation of tin in natural waters

The use of an in-line photolysis coil in a continuous-flow system of high-performance liquid chromatography coupled with hydride generation and flame atomic-absorption spectrometry for the speciation of tin in natural waters is described. Irradiation with ultraviolet light is shown to convert tributyltin into organic tin(IV), from which a volatile hydride can be produced in the conventional way. The effect of various conditions on the analytical performance is discussed. A detection limit of 2 ng for tin was obtained, and the tin species could be completely separated within 6 min. Use of the technique for quantification of tributyltin compounds in local coastal waters is described.