743 research outputs found
Composition Operators and Endomorphisms
If is an inner function, then composition with induces an
endomorphism, , of that leaves
invariant. We investigate the structure of the
endomorphisms of and that implement
through the representations of and
in terms of multiplication operators on
and . Our analysis, which is based on work
of R. Rochberg and J. McDonald, will wind its way through the theory of
composition operators on spaces of analytic functions to recent work on Cuntz
families of isometries and Hilbert -modules
Evidence for electromagnetic granularity in polycrystalline Sm1111 iron-pnictides with enhanced phase purity
We prepared polycrystalline SmFeAsO1-xFx (Sm1111) bulk samples by sintering
and hot isostatic pressing (HIP) in order to study the effects of phase purity
and relative density on the intergranular current density. Sintered and HIPped
Sm1111 samples are denser with fewer impurity phases, such as SmOF and the
grain boundary wetting phase, FeAs. We found quite complex magnetization
behavior due to variations of both the inter and intragranular current
densities. Removing porosity and reducing second phase content enhanced the
intergranular current density, but HIPping reduced Tc and the intragranular
current density, due to loss of fluorine and reduction of Tc. We believe that
the HIPped samples are amongst the purest polycrystalline 1111 samples yet
made. However, their intergranular current densities are still small, providing
further evidence that polycrystalline pnictides, like polycrystalline cuprates,
are intrinsically granular.Comment: 14 pages, 6 figure
Influence of growth temperature on the vortex pinning properties of pulsed laser deposited YBa(2)Cu(3)O(7-x) thin films
Epitaxial high-temperature superconducting YBa(2)Cu(3)O(7-x) thin films grown on 2 degrees miscut (001) (LaAlO(3))(0.3)-(SrAl(0.5)Ta(0.5)O(3))(0.7) substrates by pulsed laser deposition show significant and systematic changes in flux pinning properties on changing the substrate temperature from 730 to 820 degrees C. The bulk pinning force is highest for the 760 degrees C growth, rising to a maximum of 4.4 GN/m(3) at 77 K, though there are indications that vortex pinning strength is even higher for the 730 degrees C growth once allowance for the current-blocking effects of a-axis oriented grains is made. Cross-sectional transmission electron microscope images show that the density of antiphase boundaries, stacking faults, and edge dislocations increases strongly with decreasing growth temperature, and is highest at 730 degrees C. In spite of the enhanced density of the pinning defects mentioned above, their vortex pinning effect is still much smaller than for insulating nanoparticles of high density and optimum size, where pinning forces can be four to five times higher.open121
Neutron Irradiation of Sm-1111
SmFeAsOF was irradiated in a fission reactor to a fast (E > 0.1
MeV) neutron fluence of 4x10^ m. The introduced defects increase
the normal state resistivity due to a reduction in the mean free path of the
charge carriers. This leads to an enhancement of the upper critical field at
low temperatures. The critical current density within the grains, Jc, increases
upon irradiation. The second maximum in the field dependence of Jc disappears
and the critical current density becomes a monotonically decreasing function of
the applied magnetic field
Preparation of amino-substituted indenes and 1,4-dihydronaphthalenes using a one-pot multireaction approach: total synthesis of oxybenzo[c]phenanthridine alkaloids
Allylic trichloroacetimidates bearing a 2-vinyl or 2-allylaryl group have been designed as substrates for a one-pot, two-step multi-bond-forming process leading to the general preparation of aminoindenes and amino-substituted 1,4-dihydronaphthalenes. The synthetic utility of the privileged structures formed from this one-pot process was demonstrated with the total synthesis of four oxybenzo[c]phenanthridine alkaloids, oxychelerythrine, oxysanguinarine, oxynitidine, and oxyavicine. An intramolecular biaryl Heck coupling reaction, catalyzed using the Hermann–Beller palladacycle was used to effect the key step during the synthesis of the natural products
Desulfation of Heparan Sulfate by Sulf1 and Sulf2 Is Required for Corticospinal Tract Formation
Heparan sulfate (HS) has been implicated in a wide range of cell signaling. Here we report a novel mechanism in which extracellular removal of 6-O-sulfate groups from HS by the endosulfatases, Sulf1 and Sulf2, is essential for axon guidance during development. In Sulf1/2 double knockout (DKO) mice, the corticospinal tract (CST) was dorsally displaced on the midbrain surface. In utero electroporation of Sulf1/2 into radial glial cells along the third ventricle, where Sulf1/2 mRNAs are normally expressed, rescued the CST defects in the DKO mice. Proteomic analysis and functional testing identified Slit2 as the key molecule associated with the DKO phenotype. In the DKO brain, 6-O-sulfated HS was increased, leading to abnormal accumulation of Slit2 protein on the pial surface of the cerebral peduncle and hypothalamus, which caused dorsal repulsion of CST axons. Our findings indicate that postbiosynthetic desulfation of HS by Sulfs controls CST axon guidance through fine-tuning of Slit2 presentation
Search for dinucleon decay into pions at Super-Kamiokande
A search for dinucleon decay into pions with the Super-Kamiokande detector
has been performed with an exposure of 282.1 kiloton-years. Dinucleon decay is
a process that violates baryon number by two units. We present the first search
for dinucleon decay to pions in a large water Cherenkov detector. The modes
O C, O
N, and O
O are investigated. No significant excess in the
Super-Kamiokande data has been found, so a lower limit on the lifetime of the
process per oxygen nucleus is determined. These limits are:
years,
years, and
years. The lower
limits on each mode are about two orders of magnitude better than previous
limits from searches for dinucleon decay in iron.Comment: 20 pages, 17 figures. Accepted for publication in Physical Review D
on March 30, 201
Analysis of microstructure effects on edge crack of thin strip during cold rolling
Edge cracks in cold rolling of the thin strip affect the strip quality and productivity significantly. In this study, an experimental and mechanical investigation on microstructures has been carried out to study the edge crack formation during cold rolling of the thin strip. The effects of the feed material microstructures on the edge crack evolution were studied employing optical microscopy and scanning electron microscopy (SEM). Experimental observation indicates that fine grain occurs in hot-rolled microstructure and coarse grain is produced in ferritic rolled microstructure. Different grain sizes affect significantly the formation mechanics of the microcrack, crack initiation, and orientation of crack extension. The grain size and grain boundaries effects on crack retardation are discussed also during edge crack initiation. During the crack growth in coarse grain, most edge crack tips will blunt, which improves the crack toughness by causing less stress concentration. Overall, the fine microstructure shows a good crack initiation resistance, whereas the coarse microstructure has a better resistance to crack propagation. This research provides additional understanding of the mechanism of microstructure influence on edge crack evolution of cold strip rolling, which could be helpful for developing defect-free thin strip
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