10,416 research outputs found
On construction of optimal mixed-level supersaturated designs
Supersaturated design (SSD) has received much recent interest because of its
potential in factor screening experiments. In this paper, we provide equivalent
conditions for two columns to be fully aliased and consequently propose methods
for constructing - and -optimal mixed-level SSDs
without fully aliased columns, via equidistant designs and difference matrices.
The methods can be easily performed and many new optimal mixed-level SSDs have
been obtained. Furthermore, it is proved that the nonorthogonality between
columns of the resulting design is well controlled by the source designs. A
rather complete list of newly generated optimal mixed-level SSDs are tabulated
for practical use.Comment: Published in at http://dx.doi.org/10.1214/11-AOS877 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Double Coronal Hard and Soft X-ray Source Observed by RHESSI: Evidence for Magnetic Reconnection and Particle Acceleration in Solar Flares
We present data analysis and interpretation of an M1.4-class flare observed
with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) on April
30, 2002. This event, with its footpoints occulted by the solar limb, exhibits
a rarely observed, but theoretically expected, double-source structure in the
corona. The two coronal sources, observed over the 6-30 keV range, appear at
different altitudes and show energy-dependent structures with the higher-energy
emission being closer together. Spectral analysis implies that the emission at
higher energies in the inner region between the two sources is mainly
nonthermal, while the emission at lower energies in the outer region is
primarily thermal. The two sources are both visible for about 12 minutes and
have similar light curves and power-law spectra above about 20 keV. These
observations suggest that the magnetic reconnection site lies between the two
sources. Bi-directional outflows of the released energy in the form of
turbulence and/or particles from the reconnection site can be the source of the
observed radiation. The spatially resolved thermal emission below about 15 keV,
on the other hand, indicates that the lower source has a larger emission
measure but a lower temperature than the upper source. This is likely the
result of the differences in the magnetic field and plasma density of the two
sources.Comment: Accepted by ApJ (12/06/2007), scheduled for the 03/20/2008 Vol. 676
No. 1 Issue, 13 pages, 9 figure
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How did the introduction of managed care for the uninsured in Iowa affect the use of substance abuse services?
Concerns about access under managed care have been raised for vulnerable populations such as publicly funded patients with substance abuse problems. To estimate the effects of the Iowa Managed Substance Abuse Care Plan (IMSACP) on substance abuse service use by publicly funded patients, service use before and after IMSACP was compared; adjustments were made for changes in population sociodemographic and clinical characteristics. Between fiscal years 1994 and 1997, patient case mix was marked by a higher burden of illness and the use of inpatient, residential nondetox, outpatient counseling, and assessment services declined, while use of intensive outpatient and residential detox services increased. Findings were similar among women, children, and homeless persons. Thus, care moved away from high-cost inpatient settings to less costly venues. Without knowing the impact on treatment outcomes, these changes cannot be interpreted as improved provider efficiency versus simply cost containment and profit maximization
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Concerted [4 + 2] and Stepwise (2 + 2) Cycloadditions of Tetrafluoroethylene with Butadiene: DFT and DLPNO-UCCSD(T) Explorations.
Tetrafluoroethylene and butadiene form the 2 + 2 cycloadduct under kinetic control, but the Diels-Alder cycloadduct is formed under thermodynamic control. Borden and Getty showed that the preference for 2 + 2 cycloaddition is due to the necessity for syn-pyramidalization of the two CF2 groups in the 4 + 2 transition state. We have explored the full potential energy surface for the concerted and stepwise reactions of tetrafluoroethylene and butadiene with density functional theory, DFT (B3LYP and M06-2X), DLPNO-UCCSD(T), and CASSCF-NEVPT2 methods and with the distortion/interaction-activation strain model to explain the energetics of different pathways. The 2 + 2 cycloadduct is formed by an anti-transition state followed by two rotations and a final bond formation transition state. Energetics are compared to the reaction of maleic anhydride and ethylene
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