2,219 research outputs found
Recommended from our members
Boron carboxylate catalysis of homoallylboration.
Boron tris(trifluoroacetate) is identified as the first effective catalyst for the homoallyl- and homocrotylboration of aldehydes by cyclopropylcarbinylboronates. NMR spectroscopic studies and theoretical calculations of key intermediates and transition states both suggest that a ligand-exchange mechanism, akin to our previously reported PhBCl2-promoted homoallylations, is operative. Our experimental and theoretical results also suggest that the catalytic activity of boron tris(trifluoroacetate) might originate from more facile catalytic turnover of the trifluoroacetate ligands (in agreement with DFT calculations) or from a lower propensity for formation of off-pathway reservoir intermediates (as observed by (1)H NMR). This work shows that carboxylates are viable catalytic ligands for homoallyl- and homocrotylations of carbonyl compounds and opens the door to the development of catalytic asymmetric versions of this transformation
Case Studies of Habitable Trojan Planets in the System of HD 23079
We investigate the possibility of habitable Trojan planets in the HD 23079
star-planet system. This system consists of a solar-type star and a
Jupiter-type planet, which orbits the star near the outer edge of the stellar
habitable zone in an orbit of low eccentricity. We find that in agreement with
previous studies Earth-mass habitable Trojan planets are possible in this
system, although the success of staying within the zone of habitability is
significantly affected by the orbital parameters of the giant planet and by the
initial condition of the theoretical Earth-mass planet. In one of our
simulations, the Earth-mass planet is captured by the giant planet and thus
becomes a habitable moon.Comment: 24 pages, 8 figures, 3 tables; International Journal of Astrobiology
(in press
Recommended from our members
Transient [3,3] Cope rearrangement of 3,3-dicyano-1,5-dienes: computational analysis and 2-step synthesis of arylcycloheptanes.
A simple and modular route to arylcycloheptene scaffolds is reported. The two-step route from Knoevenagel adducts and allylic electrophiles is made possible through the design of a Cope rearrangement that utilizes a "traceless" activating group to promote an otherwise thermodynamically unfavorable transformation. Experimentally, the [3,3] rearrangement occurrs transiently at room temperature with a computed barrier of 19.5 kcal mol-1, which ultimately allows for three-component bis-allylation. Ring-closing metathesis delivers the arylcycloheptane and removes the activating group. This report describes the design and optimization of the methodology, scope and mechanistic studies, and computational analysis
Early life-history studies of nearshore rockfishes and lingcod off Central California, 1987-92
This study focused on the physical and biological processes that influence the distribution, abundance, growth, and survival of young-of-the-year (YOY) rockfishes and lingcod along the central California coast. The annual somatic and reproductive condition of adult female blue rockfish corresponded to annual upwelling. Resulting larval production may correspond to the reproductive potential of adults; however, ultimate recruitment success of YOY is also effected by oceanographic conditions during their planktonic stage. Within a year, each species of settled YOY was observed concurrently and in relatively similar abundances at all study dive sites along the central coast. Most species of YOY exhibited similar growth patterns among
stations and years. We found a high degree of interannual variability in the condition of adults and relative
abundances of YOY. We believe a large part of this variability is due to annual oceanographic conditions,
specifically upwelling.
Marine reserves, which would protect populations of reproductively mature rockfishes and lingcod and insure 1arval production, have been suggested as an alternative to present management strategies for these species. However, a crucial question is whether or not larvae from adult fish in reserves would significantly contribute to replenishing stocks in other areas. This study was undertaken to assist in determining the feasibility of reserves to enhance nearshore rockfish and lingcod populations. (78pp.
Presynaptic Inhibition in the Striatum of the Basal Ganglia Improves Pattern Classification and Thus Promotes Superior Goal Selection
This review article takes a multidisciplinary approach to understand how presynaptic inhibition in the striatum of the basal ganglia (BG) contributes to pattern classification and the selection of goals that control behavior. It is a difficult problem both because it is multidimensional and because it is has complex system dynamics. We focus on the striatum because, as the main site for input to the BG, it gets to decide what goals are important to consider
Alternating magnetic anisotropy of Li(Li)N with = Mn, Fe, Co, and Ni
Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be
substituted for Li in single crystalline Li(Li)N. Isothermal and
temperature-dependent magnetization measurements reveal local magnetic moments
with magnitudes significantly exceeding the spin-only value. The additional
contributions stem from unquenched orbital moments that lead to rare-earth-like
behavior of the magnetic properties. Accordingly, extremely large magnetic
anisotropies have been found. Most notably, the magnetic anisotropy alternates
as easy-plane easy-axis easy-plane
easy-axis when progressing from = Mn Fe Co
Ni. This behavior can be understood based on a perturbation
approach in an analytical, single-ion model. The calculated magnetic
anisotropies show a surprisingly good agreement with the experiment and capture
the basic features observed for the different transition metals.Comment: 5 pages, 3 figures, published as PRB Rapid Communication, Fig. 3
update
ASAS Light Curves of Intermediate Mass Eclipsing Binaries and the Parameters of HI Mon
We present a catalog of 56 candidate intermediate mass eclipsing binary
systems extracted from the 3rd data release of the All Sky Automated Survey. We
gather pertinent observational data and derive orbital properties, including
ephemerides, for these systems as a prelude to anticipated spectroscopic
observations. We find that 37 of the 56, or ~66% of the systems are not
identified in the Simbad Astronomical Database as known binaries. As a specific
example, we show spectroscopic data obtained for the system HI Mon (B0 V + B0.5
V) observed at key orbital phases based on the computed ephemeris, and we
present a combined spectroscopic and photometric solution for the system and
give stellar parameters for each component.Comment: 83 pages, 63 figure
- …