94,041 research outputs found
Zinc calixarene complexes for the ring opening polymerization of cyclic esters
Reaction of Zn(C₆F₅)₂·toluene (two equivalents) with 1,3-dipropoxy-p-tert-butyl-calix[4]arene (L¹H₂) led to the isolation of the complex [{Zn(C₆F₅)}₂L¹] (1), whilst similar use of Zn(Me)₂ resulted in the known complex [{Zn(Me)}₂L¹] (2). Treatment of L¹H₂ with in situ prepared Zn{N(SiMe₃)₂}₂ in refluxing toluene led to the isolation of the compound [(Na)ZnN(SiMe₃)₂L¹] (3). The stepwise reaction of L¹H₂ and sodium hydride, followed by ZnCl₂ and finally NaN(SiMe₃)₂ yielded the compound [Zn{N(SiMe₃)₂}₂L¹] (4). The reaction between three equivalents of Zn(C₆F₅)₂·toluene and oxacalix[3]arene (L²H₃) at room temperature formed the compound {[Zn(C₆F₅)]₃L²} (5); heating of 5 in acetonitrile caused the ring opening of the parent oxacalix[3]arene and rearrangement to afford the complex [(L²)Zn₆(C₆F₅)(R)(RH)OH]·5MeCN R = C₆F₅CH₂-(p-ᵗBuPhenolate-CH₂OCH₂–)₂–p-ᵗBuPhenolate-CH₂O⁻)³⁻ (6). The molecular structures of the new complexes 1, 3 and 6, together with that of the known complex 2, whose solid state structure has not previously been reported, have been determined. Compounds 1, 3–5 have been screened for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and rac-lactide. Compounds featuring a Zn–C₆F₅ fragment were found to be poor ROP pre-catalysts as they did not react with benzyl alcohol to form an alkoxide. By contrast, compound 4, which contains a zinc silylamide linkage, was the most active of the zinc-based calix[4]arene compounds screened and was capable of ROP at ambient temperature with 65% conversion over 4 h
The Baryonic Fraction in Groups of Galaxies from X-Ray Measurements
The recent {\sl ROSAT \/} X-ray detections of hot intergalactic gas in three
groups of galaxies are reviewed and the resulting baryonic fraction in these
groups is reevaluated. We show that the baryonic fraction obtained, assuming
hydrostatic equilibrium, should depend, perhaps sensitively, on the radius out
to which the X-rays are detected, and the temperature profile of the gas. We
find that the NGC 2300 group has a baryonic fraction out to of at least
20\%, thus over five times higher than in the original analysis of Mulchaey
\etal\ (1993), and also much higher than one would obtain from big-bang
nucleosynthesis, but similar to the other two groups as well as rich clusters.
With this baryonic fraction, groups would be fair tracers of the distribution
of baryons in the Universe if . A baryonic fraction that
increases with radius is consistent with the X-ray data from all three groups.
However, a detailed analysis of the NGC 2300 group shows that the dependence of
baryonic fraction on radius is not well constrained by the data, in part
because of uncertainties in the estimated background.Comment: ApJ Lett 421 (Feb 1 1994), in press. 4 pages of uuencoded compressed
Postscript (extract on UNIX with 'csh' after removing header: 1st line should
be '#/bin/csh -f') with 3 figures. POP-DAEC-9306
Estimating the Impact of the Medical Loss Ratio Rule: A State-by-State Analysis
Outlines the healthcare reform law's requirement that insurers spend a minimum ratio of 80 to 85 percent of premiums on medical care expenses or rebate the difference to policy holders. Estimates rebates in each state if it had been in effect in 2010
Insurers' Responses to Regulation of Medical Loss Ratios
The Affordable Care Act's medical loss ratio (MLR) rule requires health insurers to pay out at least 80 percent of premiums for medical claims and quality improvement, as opposed to administrative costs and profits. This issue brief examines whether insurers have reduced administrative costs and profit margins in response to the new MLR rule. In 2011, the first year under the rule, insurers reduced administrative costs nationally, with the greatest decrease -- over 200 million each. In the individual market, insurers passed these savings on to consumers by reducing their profits even more than administrative costs. But in the large- and smallgroup markets, lower administrative costs were offset by increased profits of a similar amount. Stronger measures may be needed if consumers are to benefit from reduced overhead costs in the group insurance markets
How well can we estimate a sparse vector?
The estimation of a sparse vector in the linear model is a fundamental
problem in signal processing, statistics, and compressive sensing. This paper
establishes a lower bound on the mean-squared error, which holds regardless of
the sensing/design matrix being used and regardless of the estimation
procedure. This lower bound very nearly matches the known upper bound one gets
by taking a random projection of the sparse vector followed by an
estimation procedure such as the Dantzig selector. In this sense, compressive
sensing techniques cannot essentially be improved
The Ubiquity and Dual Nature of Ultra Compact Dwarfs
We present the discovery of several Ultra Compact Dwarfs (UCDs) located in
field/group environments. Examination of these objects, plus literature
objects, confirms the existence of two distinct formation channels for UCDs. We
find that the UCDs we have discovered around the group elliptical NGC3923 (and
UCDs generally) have properties consistent with their being the most luminous
members of the host galaxy's globular cluster (GC) system. We describe UCDs of
this type as giant GCs (GGCs). In contrast, the UCD we have found associated
with the isolated S0 NGC4546 is clearly the result of the stripping of a
nucleated companion galaxy. The young age (~3.4 Gyr) of the UCD, the lack of a
correspondingly young GC population, the apparently short dynamical friction
decay timescale (~0.5 Gyr) of the UCD, and the presence of a counterrotating
gas disc in the host galaxy (co-rotating with the UCD) together suggest that
this UCD is the liberated nucleus remaining after the recent stripping of a
companion by NGC4546. We suggest a general scheme that unifies the formation of
GCs, UCDs, and galaxy nuclei. In this picture "normal" GCs are a composite
population, composed of GCs formed in situ, GCs acquired from accreted
galaxies, and a population of lower mass stripped dwarf nuclei masquerading as
GCs. Above a "scaling onset mass" of 2x10^6 Msun (Mv ~ -10), UCDs emerge
together with a mass-size relation and a likely mass-metallicity relation (the
"blue tilt"). In the mass range up to 7x10^7 Msun (Mv ~ -13) UCDs comprise a
composite population of GGCs and stripped nuclei. Above 7x10^7 Msun, UCDs must
be almost exclusively stripped nuclei, as no sufficiently rich GC systems exist
to populate such an extreme of the GCLF.Comment: 23 pages, 16 figures, accepted for publication in MNRA
How Has the Affordable Care Act Affected Health Insurers' Financial Performance?
Starting in 2014, the Affordable Care Act transformed the market for individual health insurance by changing how insurance is sold and by subsidizing coverage for millions of new purchasers. Insurers, who had no previous experience under these market conditions, competed actively but faced uncertainty in how to price their products. This issue brief uses newly available data to understand how health insurers fared financially during the ACA's first year of full reforms. Overall, health insurers' financial performance began to show some strain in 2014, but the ACA's reinsurance program substantially buffered the negative effects for most insurers. Although a quarter of insurers did substantially worse than others, experience under the new market rules could improve the accuracy of pricing decisions in subsequent years
- …