66 research outputs found
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
Being Earnest with Collections â Collection Development from the Library Services Vendorâs Point of View
Precision spectra of A\, ^2\Sigma^+,v'=0 \leftarrow X\, ^2\Pi_{3/2},v''=0,J''=3/2 transitions in OH and 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 OH, as well as to the 16
lowest levels of the same vibronic state in OD. The absolute frequencies
of these transitions have been determined with a relative uncertainty of a few
parts in , representing a 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-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
transitions, resulting in typical deviations of the predicted optical
transition frequencies of 150 MHz, but they generally agree quite well
with the constants determined using hyperfine-resolved measurements of
splittings within the 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 Energyâs (DOE) aircraft during the Two-Column Aerosol Project (TCAP). Namely, these data types are: (1) size distributions measured by a suite of OPCâs; (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 âreason to,â âcan do,â and âenergized toâ 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
- âŠ