170 research outputs found
Birational automorphisms of a three-dimensional double quadric with an elementary singularity
It is proved that the group of birational automorphisms of a
three-dimensional double quadric with a singular point arising from a double
point on the branch divisor is a semidirect product of the free group generated
by birational involutions of a special form and the group of regular
automorphisms. The proof is based on the method of `untwisting' maximal
singularities of linear systems.Comment: 18 page
Birational rigidity of a three-dimensional double cone
It is proved that a three-dimensional double cone is a birationally rigid
variety. We also compute the group of birational automorphisms of such a
variety. This work is based on the method of "untwisting" maximal singularities
of linear system.Comment: 20 pages; AmsLaTe
Mineralogical and geochemical features of the Manus Basin hydrothermal sulfide ores, Bismarck Sea
Paragenetic mineral assemblages have been established based on
mineralogical, chemical, and isotope (S, Pb) studies, and the sequence
of deposition has been defined in hydrothennal sulfide structures in a
typical back-arc basin. The ores in the Manus basin have a prominent
Zn specialization (sphalerite, würtzite, and fe-sphalerite). An association
of Fe-spbalerite and galena with Ag sulfosalts is noted that is not
characteristic of typical midocean ridge hydrothennal systems. The
average 34S in the sulfide minerals is 3.5%o, which corresponds to the
medium-temperature sphalerite stage in hydrothermal mineral fonnation.
It is suggested that the metal source is located in the relatively acid
rocks of the island-arc tholeiitic series and possibly in sediments
Extended Magnetic Dome Induced by Low Pressures in Superconducting FeSeS
We report muon spin rotation (SR) and magnetization measurements under
pressure on FeSeS with x
.Above GPa we find microscopic coexistence of
superconductivity with an extended dome of long range magnetic order that spans
a pressure range between previously reported separated magnetic phases. The
magnetism initially competes on an atomic scale with the coexisting
superconductivity leading to a local maximum and minimum of the superconducting
. The maximum of corresponds to the onset of
magnetism while the minimum coincides with the pressure of strongest
competition. A shift of the maximum of for a series of single
crystals with x up to 0.14 roughly extrapolates to a putative magnetic and
superconducting state at ambient pressure for x .Comment: 10 pages, 6 figures, including supplemental materia
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