Calculation of hyperfine interactions measured by magnetic decoupling in oxygen ions

Magnetic hyperfine interactions in highly stripped oxygen ions recoiling in vacuum have been measured with perturbed angular correlations. The second excited state of¹⁶O(I =3^–,E _X=6.13 MeV, =26.6 psec, |g|=0.55) was produced with the nuclear reactions¹⁹F(p,)¹⁶O and¹⁶O(,)¹⁶O and the angular correlation of the -rays observed in coincidence with particles emitted at 180°. Five recoil velocities between 1.0 and 3.3% c produced average ion charge states from 2.1 to 5.5. The perturbation of the angular correlation and hence the decoupling of the hyperfine interactions was observed as a function of an external axial magnetic field varied between 0 and 33 kG. The perturbation is expected to arise primarily from hyperfine interactions of unpaired 1s electrons with smaller contributions from 2s electrons and other configurations. The maximum external field was strong enough to decouple all hyperfine interactions except that of the 1s electrons. The decoupling curves obtained were successfully fitted by calculations using the hyperfine interactions of the pertinent atomic Hartree-Fock-Slater orbitals.Supported in part by the National Science Foundation.     

A theoretical study of some maximum likelihood algorithms for emission and transmission tomography

This paper has the dual purpose of introducing some new algorithms for emission and transmission tomography and proving mathematically that these algorithms and related antecedent algorithms converge. Like the EM algorithms for positron, single-photon, and transmission tomography, the algorithms provide maximum likelihood estimates of pixel concentration or linear attenuation parameters. One particular innovation we discuss is a computationally practical scheme for modifying the EM algorithms to include a Bayesian prior. The Bayesian versions of the EM algorithms are shown to have superior convergence properties in a vicinity of the maximum. We anticipate that some of the other algorithms will also converge faster than the EM algorithms.     

Wismut

Ohne Zusammenfassung     

Elektrometrie

Ohne Zusammenfassung     

Two high-throughput techniques for determining wood properties as part of a molecular genetics analysis of hybrid poplar and loblolly pine

Two new high-through put techniques, computer tomography X-ray densitometry (CT scan) and pyrolysis molecular beam mass spectrometry (pyMBMS), coupled with quantitative trait loci (QTL) analysis, were tested as a means to overcome the time and cost associated with conventional characterization of biomass feedstock components. Applications of these two techniques were evaluated using hybrid poplar for the CT scan and loblolly pine for the pyMBMS. Segregating progeny from hybrid poplar varied in specific gravity, with individual mean estimates ranging from 0.21–0.41. Progeny from loblolly pine varied in lignin, α cellulose, and mannan contents, with individual mean estimates of lignin content ranging from 28.7–33.1%, α cellulose content from 28.8–43.5% and mannan content from 4.2–10.1%. QTL analysis of the loblolly pine data suggested that eleven QTLs were associated with individual feedstock characteristics and that two QTLs for several feedstock components were linked to the same position on the loblolly pine genetic map. Each QTL individually accounted for 7–13% of the total phenotypic variation in associated loblolly pine feedstock components.     

New proofs of identities of Lebesgue and Göllnitz via tilings

In 1840, V.A. Lebesgue proved the following two series-product identities:

     

7,11-epi-thyrsiferol: completion of its synthesis, evaluation of its antimitotic properties, and the further development of an SAR model

We (a) describe the completion of a total synthesis of 7,11-epi-thyrsiferol (4), (b) compare the antimitotic activities of thyrsiferol (2), Delta15,28-dehydrothyrsiferol (3), and 7,11-epi-thyrsiferol (4), (c) evaluate the synergistic behavior of the title compound and colchicine to inhibit cell proliferation, and (d) describe the results of conformational searches that provide additional insight concerning the SAR profile of the thyrsiferol family of natural products.     

A novel concept for fault current tolerable contactors

It is critical in the development of new contactors and starters to enable the product to avoid or minimize contact welding during short circuit events. The IEC 60947-4-1 or UL 508E Type II coordination requires that a contact weld can be easily broken without significant deformation after short circuit events, and the new standard of IEC 60947-6-2 mandates no contact welds after short circuit events. In this paper, a novel concept has been developed and investigated to allow significant fault current tolerance improvement for next generation contactor and starter product lines. An innovative design of the movable contact bridge utilizes the magnetic force generated by the fault current to "latch" the contacts open until current zero and reclose after current zero. This delay of contact reclosing allows the molten contact surface to solidify and minimizes or even eliminates contact welding altogether. This design does not require a size increase of the product to achieve this performance and adds minimal cost. Test evaluation has been carried out to verify this concept. The test results show that the contacts close about 1.5 to 2ms after current zero and achieve no contact welding after short circuit events with proper current limiting by the upstream circuit protector.