Spectral, spatial and temporal characteristics of a millisecond pulsed glow discharge: metastable argon atom production

Time resolved atomic emission, atomic absorbance, and laser-induced atomic fluorescence measurements of a millisecond pulsed glow discharge, made perpendicular to the insertion probe, provide temporal profiles of 1s₅ (³P₂) and 1s₃ (³P₀) metastable argon atom populations. Acquisition of these profiles at different spatial positions in the plasma provides data from which two-dimensional spatial plots of relative populations are constructed. Each map, the result of 368 individual pulse profiles, provides insight into the production of metastable argon atoms as a function of time and position within the plasma. During power application, intensities plateau after 3 ms as the plasma reaches a steady state condition. Metastable argon atoms are most abundant 1–2 mm above the cathode surface during this time. Excitation mechanisms such as electron excitation and fast atom/ion impact appear to dominate in this temporal regime. In contrast, argon ion–electron recombination dominates metastable formation after pulse termination. The relative population maximum for metastable argon atoms in the afterpeak shifts to 5–9 mm above the cathode surface. This shift should impact signals for analyte species generated by Penning processes in the plasma. Absorption and fluorescence measurements of the ³P₂ (11.55 eV) and the ³P₀ (11.72 eV) metastable argon atom states indicate possible differences in the populations of these two states between the plateau and afterpeak time regimes.     

Soil compaction and over-winter changes to tracked-vehicle ruts, Yakima Training Center, Washington

We monitored two experimental areas at the Yakima Training Center (YTC) in central Washington to measure changes to M1A2 Abrams (M1) tank-rut surface geometry and in- and out-of-rut saturated hydraulic conductivity (K_fs), soil penetration resistance (SPR) and soil bulk density (BD). Profile-meter data show that rut cross-sectional profiles smoothed significantly and that turning ruts did so more than straight ruts. Rut edges were zones of erosion and sidewall bases were zones of deposition. K_fs values were similar in and out of ruts formed on soil with 0–5% moisture by volume, but were lower in ruts formed on soil with about 15% water. Mean SPR was similar in and out of ruts from 0- to 5-cm depth, increased to 2 MPa outside ruts and 4 MPa inside ruts at 10- to 15-cm depth, and decreased by 10–38% outside ruts and by 39–48% inside ruts at the 30-cm depth. Soil BD was similar in and out of ruts from 0- to 2.5-cm depth, and below 2.5 cm, it was generally higher in ruts formed on moist soil with highest values between 10- and 20-cm depth. Conversely, BD in ruts formed on dry soil was similar to out-of-rut BD at all depths. This information is important for determining impacts of tank ruts on water infiltration and soil erosion and for modifying the Revised Universal Soil Loss Equation (RUSLE) and the Water Erosion Prediction Project (WEPP) models to more accurately predict soil losses on army training lands.     

CO(2) fixation by Rubisco: computational dissection of the key steps of carboxylation, hydration, and C-C bond cleavage.

Despite intensive experimental and computational studies, some important features of the mechanism of the photosynthetic CO(2)-fixing enzyme, Rubisco, are still not understood. To complement our previous investigation of the first catalytic step, the enolization of D-ribulose-1,5-bisphosphate (King et al., Biochemistry 1998, 44, 15414-15422), we present the first complete computational dissection of subsequent steps of the carboxylation reaction that includes the roles of the central magnesium ion and modeled residues of the active site. We investigated carboxylation, hydration, and C-C bond cleavage using the density functional method and the B3LYP/6-31G(d) level to perform geometry optimizations. The energies were determined by B3LYP/6-311+G(2d,p) single-point calculations. We modeled a fragment of the active site and substrate, taking into account experimental findings that the residues coordinated to the Mg ion, especially the carbamylated Lys-201, play critical roles in this reaction sequence. The carbamate appears to act as a general base, not only for enolization but also for hydration of the beta ketoacid formed by addition of CO(2) and, as well, cleavage of the C2-C3 bond of the hydrate. We show that CO(2) is added directly, without assistance of a Michaelis complex, and that hydration of the resultant beta ketoacid occurs in a separate subsequent step with a discrete transition state. We suggest that two conformations of the hydrate (gem-diol), with different metal coordination, are possible. The step with the highest activation energy during the carboxylation cycle is the C-C bond cleavage. Depending on the conformations of the gem-diol, different pathways are possible for this step. In either case, special arrangements of the metal coordination result in bond breaking occurring at remarkably low activation energies (between 28 and 37 kcal mol(-1)) which might be reduced further in the enzyme environment.     

Reorganizing freshman business mathematics II: authentic assessment in mathematics through professional memos

The first part of this two-part paper (13) described the developmentof a new freshman business mathematics (FBM) course at our college.In this paper, we discuss our assessment tool, the businessmemo, as a venue for students to apply mathematical skills,via mathematical modelling, to realistic business problems.These memos have proven a crucial step in turning our FBM coursearound from a dreaded course with little connection to students’intended careers into a course where students experience thepower of mathematics for solving problems and informing decisions.Comments from students in the course throughout its 6-year historyclearly point to the course's value and importance.     

Nachweis und Bestimmung des Eisens, sowie seine Trennung von anderen Elementen

Ohne Zusammenfassung     

Frobenius formula for the characters of hecke algebras of type An−1 at roots of unity

A Frobenius formula is found for the (m, k)-standard characters φ^σ _ρ, of the Hecke algebras H_n(q) of type A_n-1, where q is a primitive pth root of unity, with p=m+k.     

Textilien

Ohne Zusammenfassung     

Surface-tension-driven flow in a slender cone

After a droplet has broken away from a slender thread or jetof liquid, the tip of the thread or jet recoils rapidly. Atthe moment of break-off, the tip of the thread/jet is observedto have the shape of a cone close to the bifurcation point.In this paper, we study the evolution of an ideal fluid whichis initially conical, where the only force acting on the fluidis due to surface tension. We find an asymptotic solution tothe problem in terms of the aspect ratio of the cone which isassumed to be small. Using a similarity transformation, whichis valid for small times after the bifurcation, we identifya rapidly oscillating non-linear wave which propagates awayfrom the tip, as observed in experiments.