Sub-ppb measurement of a fundamental band rovibrational transition in HD

We report a direct measurement of the 0-1 R(0) vibrational transition frequency in ground-state hydrogen deuteride (HD) using infrared-ultraviolet double resonance spectroscopy in a molecular beam. Ground-state molecules are vibrationally excited using a frequency comb referenced continuous-wave infrared laser, and the excited molecules are detected via state-selective ionization with a pulsed ultraviolet laser. We determine an absolute transition frequency of 111 448 815 477(13) kHz. The 0.12 parts-per-billion (ppb) uncertainty is limited primarily by the residual first-order Doppler shift.Comment: 5 pages, 4 figure

Precision spectra of A\, ^2\Sigma^+,v'=0 \leftarrow X\, ^2\Pi_{3/2},v''=0,J''=3/2 transitions in 16^{16}OH and 16^{16}OD

We report absolute optical frequencies of electronic transitions from the X\, ^2\Pi_{3/2},v''=0,J''=3/2 rovibronic ground state to the 12 lowest levels of the A\, ^2\Sigma^+,v'=0 vibronic state in $^{16}$OH, as well as to the 16 lowest levels of the same vibronic state in $^{16}$OD. The absolute frequencies of these transitions have been determined with a relative uncertainty of a few parts in $10^{11}$, representing a $\sim$1000-fold improvement over previous measurements. To reach this level of precision, an optical frequency comb has been used to transfer the stability of a narrow-linewidth I$_2$-stabilized reference laser onto the 308-nm spectroscopy laser. The comb is also used to compare the optical frequency of the spectroscopy laser to an atomic clock reference, providing absolute accuracy. Measurements have been carried out on OH/OD molecules in a highly-collimated molecular beam, reducing possible pressure shifts and minimizing Doppler broadening. Systematic shifts due to retroreflection quality, the Zeeman effect, and the ac Stark effect have been considered during the analysis of the measured spectra; particularly in the case of the OD isotopologue, these effects can result in shifts of the fitted line positions of as much as 300 kHz. The transition frequencies extracted in the analysis were also used to determine spectroscopic constants for the A\, ^2\Sigma^+,v'=0 vibronic state. The constants fitted in this work differ significantly from those reported in previous works that measured the $A - X$ transitions, resulting in typical deviations of the predicted optical transition frequencies of $\sim$150 MHz, but they generally agree quite well with the constants determined using hyperfine-resolved measurements of splittings within the $A$ state.Comment: 13 pages, 4 figure

Promiscuous Partitioning of a Covalent Intermediate Common in the Pentein Superfamily

SummaryMany enzymes in the pentein superfamily use a transient covalent intermediate in their catalytic mechanisms. Here we trap and determine the structure of a stable covalent adduct that mimics this intermediate using a mutant dimethylarginine dimethylaminohydrolase and an alternative substrate. The interactions observed between the enzyme and trapped adduct suggest an altered angle of attack between the nucleophiles of the first and second half-reactions of normal catalysis. The stable covalent adduct is also capable of further reaction. Addition of imidazole rescues the original hydrolytic activity. Notably, addition of other amines instead yields substituted arginine products, which arise from partitioning of the intermediate into the evolutionarily related amidinotransferase reaction pathway. The enzyme provides both selectivity and catalysis for the amidinotransferase reaction, underscoring commonalities among the reaction pathways in this mechanistically diverse enzyme superfamily. The promiscuous partitioning of this intermediate may also help to illuminate the evolutionary history of these enzymes

Airborne Aerosol in Situ Measurements during TCAP: A Closure Study of Total Scattering

We present a framework for calculating the total scattering of both non-absorbing and absorbing aerosol at ambient conditions from aircraft data. Our framework is developed emphasizing the explicit use of chemical composition data for estimating the complex refractive index (RI) of particles, and thus obtaining improved ambient size spectra derived from Optical Particle Counter (OPC) measurements. The feasibility of our framework for improved calculations of total scattering is demonstrated using three types of data collected by the U.S. Department of Energy’s (DOE) aircraft during the Two-Column Aerosol Project (TCAP). Namely, these data types are: (1) size distributions measured by a suite of OPC’s; (2) chemical composition data measured by an Aerosol Mass Spectrometer and a Single Particle Soot Photometer; and (3) the dry total scattering coefficient measured by a integrating nephelometer and scattering enhancement factor measured with a humidification system. We demonstrate that good agreement (~10%) between the observed and calculated scattering can be obtained under ambient conditions (RH < 80%) by applying chemical composition data for the RI-based correction of the OPC-derived size spectra. We also demonstrate that ignoring the RI-based correction or using non-representative RI values can cause a substantial underestimation (~40%) or overestimation (~35%) of the calculated scattering, respectively

How does the social context fuel the proactive fire? A multilevel review and theoretical synthesis

© 2018 John Wiley & Sons, Ltd. The role of social context (e.g., leadership, team climate, and organizational support) in shaping employee proactive behavior has received considerable attention and has been investigated across multiple forms of proactive behavior. However, the research has not been well integrated. In this review, we adopt a multilevel approach to synthesize what is known about how social context factors influence employees' proactive behavior, as well as what mechanisms underpin these effects. Our analyses show that leader-, team-, and organization-related social context factors mainly influence employee proactivity through shaping “reason to,” “can do,” and “energized to” states (i.e., proactive motivational states) via individual-, team-, and cross-level processes. That has been most frequently investigated is the effect of the discretionary social context, particularly leadership, on proactive behavior. We also review the interaction effects between social context factors and other factors on employee proactive behavior and found inconsistent support for the motivational-fit perspective that stimuli with the same directions enhance each other's effect. We offer a research agenda to advance theoretical insights on this important topic

Fast, Edward Arthur

Interview on 5 February 1998, Apache Junction, Arizona. Conducted by Chris and Betty Maier