The ELFIN mission

The Electron Loss and Fields Investigation with a Spatio-Temporal Ambiguity-Resolving option (ELFIN-STAR, or heretoforth simply: ELFIN) mission comprises two identical 3-Unit (3U) CubeSats on a polar (∼93∘ inclination), nearly circular, low-Earth (∼450 km altitude) orbit. Launched on September 15, 2018, ELFIN is expected to have a >2.5 year lifetime. Its primary science objective is to resolve the mechanism of storm-time relativistic electron precipitation, for which electromagnetic ion cyclotron (EMIC) waves are a prime candidate. From its ionospheric vantage point, ELFIN uses its unique pitch-angle-resolving capability to determine whether measured relativistic electron pitch-angle and energy spectra within the loss cone bear the characteristic signatures of scattering by EMIC waves or whether such scattering may be due to other processes. Pairing identical ELFIN satellites with slowly-variable along-track separation allows disambiguation of spatial and temporal evolution of the precipitation over minutes-to-tens-of-minutes timescales, faster than the orbit period of a single low-altitude satellite (Torbit ∼ 90 min). Each satellite carries an energetic particle detector for electrons (EPDE) that measures 50 keV to 5 MeV electrons with Δ E/E 1 MeV. This broad energy range of precipitation indicates that multiple waves are providing scattering concurrently. Many observed events show significant backscattered fluxes, which in the past were hard to resolve by equatorial spacecraft or non-pitch-angle-resolving ionospheric missions. These observations suggest that the ionosphere plays a significant role in modifying magnetospheric electron fluxes and wave-particle interactions. Routine data captures starting in February 2020 and lasting for at least another year, approximately the remainder of the mission lifetime, are expected to provide a very rich dataset to address questions even beyond the primary mission science objective.Published versio

Molecular basis of chiral acid recognition by Candida rugosa lipase: X-ray structure of transition state analog and modeling of the hydrolysis of methyl 2-methoxy-2-phenylacetate

Lipase from Candida rugosa shows high enantioselectivity toward \u3b1-substituted chiral acids such as 2-arylpropionic acids. To understand how Candida rugosa lipase (CRL) distinguishes between enantiomers of chiral acids, we determined the X-ray crystal structure of a transition-state analog covalently linked to CRL. CRL shows moderate enantioselectivity (E=23) toward methyl 2-methoxy-2-phenylacetate, 1-methyl ester, favoring the (S)-enantiomer. We synthesized phosphonate (RC,RPSP)-3, which, upon reaction with CRL, mimics the transition state for hydrolysis of (S)-1-methyl ester, the fast-reacting enantiomer. An X-ray crystal structure of this complex shows a catalytically productive orientation with the phenyl ring in the hydrophobic tunnel of the lipase. Phe345 crowds the region near the substrate stereocenter. Computer modeling of the slow-reacting enantiomer examined four possible conformations for the corresponding slow-reacting enantiomer: three conformations where two substituents at the stereocenter have been exchanged relative to the fast-reacting enantiomer and one conformation with an umbrella-like inversion orientation. Each of these orientations disrupts the orientation of the catalytic histidine, but the molecular basis for disruption differs in each case showing that multiple mechanisms are required for high enantioselectivity. Copyright \ua9 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Peer reviewed: YesNRC publication: Ye

Secondary lon mass spectrometry sims: proceedings of the fitth international conrefence, Washington D,C, September 30 October 4, 1985

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Scanning probe microscopy

During the past year, scanning probe microscopy, especially atomic force microscopy (AFM), has taken root in the biological sciences community, as is evident from the large number of publications and from the variety of specialized journals in which these papers appear. Furthermore, there is a strong indication that the technique is evolving from a qualitative imaging tool to a probe of the critical dimensions and properties of biomolecules and living cells. The next stage of the evolution involves the development of microinstruments for process control and sensing applications. Recent advances have been reported in AFM instrumentation and method. For example, the tapping mode of operation is becoming the method of choice to image biological molecules; work to extend tapping-mode operation in liquids has been reported. Biological molecules can also be imaged at low temperature in a cryo-AFM with improved resolution. The measurement of recognition forces between individual molecules continues to attract much attention and has spawned new concepts for ultra-sensitive biosensors. The AFM is being used increasingly for property measurements such as determining the viscoelastic properties of biological molecules. Finally, structural studies using the AFM abound. Some specific highlights include the mapping of DNA using restriction enzymes, imaging during DNA transcription and determining the mode of drug binding to DNA