122 research outputs found
SELF-ASSEMBLED HETEROLEPTIC CHIRAL LIGANDS, ASYMMETRIC CATALYST SYSTEMS AND METHODS
A method of synthesizing a heteroleptic, multiple metal containing metallocyclic catalyst, particularly Suited for asymmetric catalysis, comprising combining a plurality of plural functional group-containing, monodentate ligands of complementary chirality, said plural functional groups being tethered to each other by tethers in the presence of a scaffold structural metal Ms or derivative thereof, wherein at least one functional group on each ligand combines to ligate M to form a bidentate, Ms centered ligand scaffold containing the remaining functional groups and combining said bidentate ligand scaffold with a catalytic metal Mc or derivative thereof whereby the remaining functional groups combine to ligate Mc, thereby forming said catalyst
Facile access to functionalized chiral secondary benzylic boronic esters via catalytic asymmetric hydroboration
Allylic and homoallylic phosphonates bearing an aryl or heteroaryl substituent at the Îł- or ÎŽ-position undergo rhodium-catalyzed asymmetric hydroboration by pinacolborane to give functionalized chiral secondary benzylic boronic esters in yields up to 86% and enantiomer ratios up to 99â:â1. Compared to minimally-functionalized terminal and 1,1-disubstituted vinyl arenes, there are relatively few reports of efficient catalytic asymmetric hydroboration (CAHB) of more highly functionalized internal alkenes. Phosphonate substrates bearing a variety of common heterocyclic ring systems, including furan, indole, pyrrole and thiophene derivatives, as well as those bearing basic nitrogen substituents (e.g., morpholine and pyrazine) are tolerated, although donor substituents positioned in close proximity of the alkene can influence the course of the reaction. Stereoisomeric (E)- and (Z)-substrates afford the same major enantiomer of the borated product. Deuterium-labelling studies reveal that rapid (Z)- to (E)-alkene isomerization accounts for the observed (E/Z)-stereoconvergence during CAHB. The synthetic utility of the chiral boronic ester products is illustrated by stereospecific CâB bond transformations including stereoretentive electrophile promoted 1,2-B-to-C migrations, stereoinvertive SE2 reactions of boron-ate complexes with electrophiles, and stereoretentive palladium- and rhodium-catalyzed cross-coupling protocols
Towards Precision LSST Weak-Lensing Measurement - I: Impacts of Atmospheric Turbulence and Optical Aberration
The weak-lensing science of the LSST project drives the need to carefully
model and separate the instrumental artifacts from the intrinsic lensing
signal. The dominant source of the systematics for all ground based telescopes
is the spatial correlation of the PSF modulated by both atmospheric turbulence
and optical aberrations. In this paper, we present a full FOV simulation of the
LSST images by modeling both the atmosphere and the telescope optics with the
most current data for the telescope specifications and the environment. To
simulate the effects of atmospheric turbulence, we generated six-layer phase
screens with the parameters estimated from the on-site measurements. For the
optics, we combined the ray-tracing tool ZEMAX and our simulated focal plane
data to introduce realistic aberrations and focal plane height fluctuations.
Although this expected flatness deviation for LSST is small compared with that
of other existing cameras, the fast f-ratio of the LSST optics makes this focal
plane flatness variation and the resulting PSF discontinuities across the CCD
boundaries significant challenges in our removal of the systematics. We resolve
this complication by performing PCA CCD-by-CCD, and interpolating the basis
functions using conventional polynomials. We demonstrate that this PSF
correction scheme reduces the residual PSF ellipticity correlation below 10^-7
over the cosmologically interesting scale. From a null test using HST/UDF
galaxy images without input shear, we verify that the amplitude of the galaxy
ellipticity correlation function, after the PSF correction, is consistent with
the shot noise set by the finite number of objects. Therefore, we conclude that
the current optical design and specification for the accuracy in the focal
plane assembly are sufficient to enable the control of the PSF systematics
required for weak-lensing science with the LSST.Comment: Accepted to PASP. High-resolution version is available at
http://dls.physics.ucdavis.edu/~mkjee/LSST_weak_lensing_simulation.pd
Electronic Structure Evidence for All-Trans Poly(methylvinylidene cyanide)
On the basis of a comparison of theoretical quantum calculations, by both semiempirical and ab initio methods, with photoemission and inverse photoemission results, we suggest that polymethylvinylidenecyanide (PMVC) adopts an all-trans conformation with few, if any, alternating trans-gauche carbonâcarbon bond arrangements. The comparison of theory with the available photoemission and inverse photoemission excludes the presence of a significant fraction of gauche bonds in the polymer chains, indicative of the all-trans conformation, with dipoles all aligned
ÆŽ-Selective directed catalytic asymmetric hydroboration of 1,1-disubstituted alkenes
Directed catalytic asymmetric hydroborations of 1,1-disubstituted alkenes afford ÆŽ
-dioxaborato amides and esters in high enantiomeric purity (90â95% ee)
Rhodium-catalyzed asymmetric hydrogenation using self-assembled chiral bidentate ligands
A Next-generation Marker Genotyping Platform (AmpSeq) in Heterozygous Crops: A Case Study for Marker-assisted Selection in Grapevine
Marker-assisted selection (MAS) is often employed in crop breeding programs to accelerate and enhance cultivar development, via selection during the juvenile phase and parental selection prior to crossing. Next-generation sequencing and its derivative technologies have been used for genome-wide molecular marker discovery. To bridge the gap between marker development and MAS implementation, this study developed a novel practical strategy with a semi-automated pipeline that incorporates traitassociated single nucleotide polymorphism marker discovery, low-cost genotyping through amplicon sequencing (AmpSeq) and decision making. The results document the development of a MAS package derived from genotyping-by-sequencing using three traits (flower sex, disease resistance and acylated anthocyanins) in grapevine breeding. The vast majority of sequence reads ( â©Ÿ99%) were from the targeted regions. Across 380 individuals and up to 31 amplicons sequenced in each lane of MiSeq data, most amplicons (83 to 87%) had o10% missing data, and read depth had a median of 220â244 Ă . Several strengths of the AmpSeq platform that make this approach of broad interest in diverse crop species include accuracy, flexibility, speed, high-throughput, lowcost and easily automated analysis
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
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