3,056 research outputs found
Glass-to-metal seals comprising relatively high expansion metals
A glass suitable for glass-to-metal seals that has a resistance to attack by moisture and a high coefficient of linear thermal expansion is introduced. Linear expansion covers the range from 12 to 14 x 10 to the minus 6 C between room temperature and 500 C. The glass is essentially composed of, by molar percent, about 9% of K2O, about 10% of Na2O, about 70% of SiO2, about 6% Al2O3, and about 5% of MgO
High temperature glass coatings for superalloys and refractory metals
New glasses are used as protective coatings on metals and alloys susceptible to oxidation at high temperatures in oxidizing atmospheres. Glasses are stable and solid at temperatures up to 1000 deg C, adhere well to metal surfaces, and are usable for metals with broad range of expansion coefficients
Measurement of the Noise Spectrum Using a Multiple-Pulse Sequence
A method is proposed for obtaining the spectrum for noise that causes the
phase decoherence of a qubit directly from experimentally available data. The
method is based on a simple relationship between the spectrum and the coherence
time of the qubit in the presence of a pi-pulse sequence. The relationship is
found to hold for every system of a qubit interacting with the classical-noise,
bosonic, and spin baths.Comment: 8 pages (4 pages + 4 pages Supplemental material), 1 figur
Comment on ``Reduction of static field equation of Faddeev model to first order PDE'', arXiv:0707.2207
The authors of the article Phys. Lett. B 652 (2007) 384, (arXiv:0707.2207),
propose an interesting method to solve the Faddeev model by reducing it to a
set of first order PDEs. They first construct a vectorial quantity , depending on the original field and its first derivatives, in terms of which
the field equations reduce to a linear first order equation. Then they find
vectors and which identically obey this linear
first order equation. The last step consists in the identification of the with the original as a function of the original field.
Unfortunately, the derivation of this last step in the paper cited above
contains an error which invalidates most of its results
Decomposition of meron configuration of SU(2) gauge field
For the meron configuration of the SU(2) gauge field in the four dimensional
Minkowskii spacetime, the decomposition into an isovector field \bn,
isoscalar fields and , and a U(1) gauge field is
attained by solving the consistency condition for \bn. The resulting \bn
turns out to possess two singular points, behave like a monopole-antimonopole
pair and reduce to the conventional hedgehog in a special case. The
field also possesses singular points, while and are regular
everywhere.Comment: 18 pages, 5 figures, Sec.4 rewritten. 5 refs. adde
A Class of Exact Solutions of the Faddeev Model
A class of exact solutions of the Faddeev model, that is, the modified SO(3)
nonlinear sigma model with the Skyrme term, is obtained in the four dimensional
Minkowskian spacetime. The solutions are interpreted as the isothermal
coordinates of a Riemannian surface. One special solution of the static vortex
type is investigated numerically. It is also shown that the Faddeev model is
equivalent to the mesonic sector of the SU(2) Skyrme model where the baryon
number current vanishes.Comment: 20 pages, 7 figures, refs. adde
High expansion coefficient glasses can be sealed to common metals
New series of high expansion coefficient glasses can be sealed by fusion onto hot surfaces of metals and alloys. Glasses have relatively low working temperatures, good chemical durability, and can be used in electrical insulators and feedthroughs to fluid or vacuum systems
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Enzyme-catalyzed cationic epoxide rearrangements in quinolone alkaloid biosynthesis.
Epoxides are highly useful synthons and biosynthons for the construction of complex natural products during total synthesis and biosynthesis, respectively. Among enzyme-catalyzed epoxide transformations, a reaction that is notably missing, in regard to the synthetic toolbox, is cationic rearrangement that takes place under strong acid. This is a challenging transformation for enzyme catalysis, as stabilization of the carbocation intermediate upon epoxide cleavage is required. Here, we discovered two Brønsted acid enzymes that can catalyze two unprecedented epoxide transformations in biology. PenF from the penigequinolone pathway catalyzes a cationic epoxide rearrangement under physiological conditions to generate a quaternary carbon center, while AsqO from the aspoquinolone pathway catalyzes a 3-exo-tet cyclization to forge a cyclopropane-tetrahydrofuran ring system. The discovery of these new epoxide-modifying enzymes further highlights the versatility of epoxides in complexity generation during natural product biosynthesis
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