4,676 research outputs found
Pressure-induced phase transitions in AgClO4
AgClO4 has been studied under compression by x-ray diffraction and density
functional theory calculations. Experimental evidence of a structural phase
transition from the tetragonal structure of AgClO4 to an orthorhombic
barite-type structure has been found at 5.1 GPa. The transition is supported by
total-energy calculations. In addition, a second transition to a monoclinic
structure is theoretically proposed to take place beyond 17 GPa. The equation
of state of the different phases is reported as well as the calculated
Raman-active phonons and their pressure evolution. Finally, we provide a
description of all the structures of AgClO4 and discuss their relationships.
The structures are also compared with those of AgCl in order to explain the
structural sequence determined for AgClO4.Comment: 38 pages, 11 figures, 4 table
Sparse bounds for pseudodifferential operators
We prove sparse bounds for pseudodifferential operators associated to H\"ormander symbol classes. Our sparse bounds are sharp up to the endpoint and rely on a single scale analysis. As a consequence, we deduce a range of weighted estimates for pseudodifferential operators. The results naturally apply to the context of oscillatory Fourier multipliers, with applications to dispersive equations and oscillatory convolution kernels
Endpoint Sobolev continuity of the fractional maximal function in higher dimensions
We establish continuity mapping properties of the non-centered fractional maximal operator in the endpoint input space for in the cases for which its boundedness is known. More precisely, we prove that for the map is continuous from to for if is radial and for for general . The results for extend to the centered counterpart . Moreover, if , we show that the conjectured boundedness of that map for implies its continuity
Bilinear identities involving the -plane transform and Fourier extension operators
We prove certain bilinear estimates for Fourier extension operators associated to spheres and hyperboloids under the action of the -plane transform. As the estimates are -based, they follow from bilinear identities: in particular, these are the analogues of a known identity for paraboloids, and may be seen as higher-dimensional versions of the classical -bilinear identity for Fourier extension operators associated to curves in
Regularity of fractional maximal functions through Fourier multipliers
We prove endpoint bounds for derivatives of fractional maximal functions with either smooth convolution kernel or lacunary set of radii in dimensions . We also show that the spherical fractional maximal function maps into a first order Sobolev space in dimensions
Sharp local smoothing estimates for Fourier integral operators
The theory of Fourier integral operators is surveyed, with an emphasis on local smoothing estimates and their applications. After reviewing the classical background, we describe some recent work of the authors which established sharp local smoothing estimates for a natural class of Fourier integral operators. We also show how local smoothing estimates imply oscillatory
integral estimates and obtain a maximal variant of an oscillatory integral estimate of Stein. Together with an oscillatory integral counterexample of Bourgain, this shows that our local smoothing estimates are sharp in odd spatial dimensions. Motivated by related counterexamples, we formulate local smoothing conjectures which take into account natural geometric assumptions
arising from the structure of the Fourier integrals
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