32 research outputs found
Min-max theory for -invariant minimal hypersurfaces
In this paper, we consider a closed Riemannian manifold with
dimension , and a compact Lie group acting as isometries
on with cohomogeneity at least . After adapting the Almgren-Pitts
min-max theory to a -equivariant version, we show the existence of a
nontrivial closed smooth embedded -invariant minimal hypersurface
provided that the union of non-principal orbits forms a
smooth embedded submanifold of with dimension at most . Moreover, we
also build upper bounds as well as lower bounds of -width which are
analogs of the classical conclusions derived by Gromov and Guth. An application
of our results combined with the work of Marques-Neves shows the existence of
infinitely many -invariant minimal hypersurfaces when and
orbits satisfy the same assumption above
Min-max theory for free boundary G-invariant minimal hypersurfaces
Given a compact Riemannian manifold with dimension and , the free boundary min-max theory built by
Martin Man-Chun Li and Xin Zhou shows the existence of a smooth almost properly
embedded minimal hypersurface with free boundary in . In this
paper, we generalize their constructions into equivariant settings.
Specifically, let be a compact Lie group acting as isometries on with
cohomogeneity at least . Then we show that there exists a nontrivial smooth
almost properly embedded -invariant minimal hypersurface with free boundary.
Moreover, if the Ricci curvature of is non-negative and is
strictly convex, then there exist infinitely many properly embedded
-invariant minimal hypersurfaces with free boundary.Comment: Accepted by Advances in Mathematic
Min-max theory for free boundary minimal hypersurfaces in locally wedge-shaped manifolds
We develop a min-max theory for the area functional in the class of locally
wedge-shaped manifolds. Roughly speaking, a locally wedge-shaped manifold is a
Riemannian manifold that is allowed to have both boundary and certain types of
edges. Fix a dimension . As our main theorem, we prove that
every compact locally wedge-shaped manifold with acute wedge angles
contains a locally wedge-shaped free boundary minimal hypersurface
which is smooth in its interior and on its faces and is up to
and including its edge. We can also handle the case of 90 degree wedge angles
under an additional assumption.Comment: 47 pages, 6 figures, comments are welcome
Generalized -stability theorem
We use the equivariant -bubbles technique to prove that for any compact
manifold with non-empty boundary, , the Yamabe invariant
of is positive if and only if the Yamabe invariant of is
positive. This generalized the -stability conjecture of Rosenberg to
compact manifolds with boundary.Comment: 14 pages, comments are welcome
Curvature estimates for stable free boundary minimal hypersurfaces in locally wedge-shaped manifolds
In this paper, we consider locally wedge-shaped manifolds, which are
Riemannian manifolds that are allowed to have both boundary and certain types
of edges. We define and study the properties of free boundary minimal
hypersurfaces inside locally wedge-shaped manifolds. In particular, we show a
compactness theorem for free boundary minimal hypersurfaces with curvature and
area bounds in a locally wedge-shaped manifold. Additionally, using
Schoen-Simon-Yau's estimates, we also prove a Bernstein-type theorem indicating
that, under certain conditions, a stable free boundary minimal hypersurface
inside a Euclidean wedge must be a portion of a hyperplane. As our main
application, we establish a curvature estimate for sufficiently regular free
boundary minimal hypersurfaces in a locally wedge-shaped manifold. We expect
this curvature estimate will be useful for establishing a min-max theory for
the area functional in wedge-shaped spaces.Comment: 28 pages, 6 figures, comments are welcome
Stabilization of Fast Pyrolysis Liquids from Biomass by Mild Catalytic Hydrotreatment:Model Compound Study
Repolymerization is a huge problem in the storage and processing of biomass pyrolysis liquid (PL). Herein, to solve the problem of repolymerization, mild catalytic hydrotreatment of PL was conducted to convert unstable PL model compounds (hydroxyacetone, furfural, and phenol) into stable alcohols. An Ni/SiO2 catalyst was synthesized by the deposition-precipitation method and used in a mild hydrotreatment process. The mild hydrotreatment of the single model compound was studied to determine the reaction pathways, which provided guidance for improving the selectivity of stable intermediate alcohols through the control of reaction conditions. More importantly, the mild hydrotreatment of mixed model compounds was evaluated to simulate the PL more factually. In addition, the effect of the interaction between hydroxyacetone, furfural, and phenol during the catalytic hydrotreatment was also explored. There was a strange phenomenon observed in that phenol was not converted in the initial stage of the hydrotreatment of mixed model compounds. Thermogravimetric analysis (TGA), Ultraviolet-Raman (UV-Raman), and Brunauer−Emmett−Teller (BET) characterization of catalysts used in the hydrotreatment of single and mixed model compounds demonstrated that this phenomenon did not mainly arise from the irreversible deactivation of catalysts caused by carbon deposition, but the competitive adsorption among hydroxyacetone, furfural, and phenol during the mild hydrotreatment of mixed model compounds
Rapid screening of Salmonella enterica serovars Enteritidis, Hadar, Heidelberg and Typhimurium using a serologically-correlative allelotyping PCR targeting the O and H antigen alleles
<p>Abstract</p> <p>Background</p> <p>Classical <it>Salmonella </it>serotyping is an expensive and time consuming process that requires implementing a battery of O and H antisera to detect 2,541 different <it>Salmonella enterica </it>serovars. For these reasons, we developed a rapid multiplex polymerase chain reaction (PCR)-based typing scheme to screen for the prevalent <it>S. enterica </it>serovars Enteritidis, Hadar, Heidelberg, and Typhimurium.</p> <p>Results</p> <p>By analyzing the nucleotide sequences of the genes for O-antigen biosynthesis including <it>wb</it>a operon and the central variable regions of the H1 and H2 flagellin genes in <it>Salmonella</it>, designated PCR primers for four multiplex PCR reactions were used to detect and differentiate <it>Salmonella </it>serogroups A/D1, B, C1, C2, or E1; H1 antigen types i, g, m, r or z<sub>10</sub>; and H2 antigen complexes, I: 1,2; 1,5; 1,6; 1,7 or II: e,n,x; e,n,z<sub>15</sub>. Through the detection of these antigen gene allele combinations, we were able to distinguish among <it>S. enterica </it>serovars Enteritidis, Hadar, Heidelberg, and Typhimurium. The assays were useful in identifying <it>Salmonella </it>with O and H antigen gene alleles representing 43 distinct serovars. While the H2 multiplex could discriminate between unrelated H2 antigens, the PCR could not discern differences within the antigen complexes, 1,2; 1,5; 1,6; 1,7 or e,n,x; e,n,z<sub>15</sub>, requiring a final confirmatory PCR test in the final serovar reporting of <it>S. enterica</it>.</p> <p>Conclusion</p> <p>Multiplex PCR assays for detecting specific O and H antigen gene alleles can be a rapid and cost-effective alternative approach to classical serotyping for presumptive identification of <it>S. enterica </it>serovars Enteritidis, Hadar, Heidelberg, and Typhimurium.</p
Photoemission Evidence of a Novel Charge Order in Kagome Metal FeGe
A charge order has been discovered to emerge deep into the antiferromagnetic
phase of the kagome metal FeGe. To study its origin, the evolution of the
low-lying electronic structure across the charge order phase transition is
investigated with angle-resolved photoemission spectroscopy. We do not find
signatures of nesting between Fermi surface sections or van-Hove singularities
in zero-frequency joint density of states, and there are no obvious energy gaps
at the Fermi level, which exclude the nesting mechanism for the charge order
formation in FeGe. However, two obvious changes in the band structure have been
detected, i.e., one electron-like band around the K point and another one
around the A point move upward in energy position when the charge order forms.
These features can be well reproduced by our density-functional theory
calculations, where the charge order is primarily driven by magnetic energy
saving via large dimerizations of a quarter of Ge1-sites (in the kagome plane)
along the c-axis. Our results provide strong support for this novel charge
order formation mechanism in FeGe, in contrast to the conventional nesting
mechanism.Comment: 6 pages, 4 figure