903 research outputs found
Sharp rate of average decay of the Fourier transform of a bounded set
We prove that the spherical mean of the Fourier transform of the
characteristic function of a bounded convex set (without any additional
assumptions) or a bounded set with a C^{3/2} boundary decays at infinity at the
same rate as the Fourier transform of the characteristic function of the ball.Comment: 10 pages. GAFA (to appear
Upper bounds for the eigenvalues of Hessian equations
We prove some upper bounds for the Dirichlet eigenvalues of a class of fully
nonlinear elliptic equations, namely the Hessian equationsComment: 15 pages, 1 figur
Papia civitas gloriosa: urban geomorphology for a thematic itinerary on geocultural heritage in Pavia (Central Po Plain, N Italy)
The interaction between geomorphological processes and anthropogenic activities produces an impressive association of geomorphological and archaeological heritage in urban contexts. We analyzed the urban geomorphology and the geo- and cultural heritage in the town of Pavia (N Italy). The city is located in a strategic position, on a series of fluvial terraces where the Romans founded a colony, probably in the place of an Iron Age Gaul settlement. In Medieval Times and the Modern Era, Pavia sprawled outside the Roman walls, creating new urban areas and modifying the landscape. Geomorphological and GIS-spatial analyses integrated with anthropic landform surveying, archaeological data and historical cartography were performed. This multi-disciplinary approach allowed an investigation into how urban development was firstly adapted and then superimposed onto fluvial landforms. As a result, a flexible geocultural itinerary is proposed for linking geoheritage with cultural heritage, and for disseminating urban geomorphology key-concepts
49Cr: Towards full spectroscopy up to 4 MeV
The nucleus 49Cr has been studied analysing gamma-gamma coincidences in the
reaction 46Ti(alpha,n)49Cr at the bombarding energy of 12 MeV. The level scheme
has been greatly extended at low excitation energy and several new lifetimes
have been determined by means of the Doppler Shift Attenuation Method.
Shell model calculations in the full pf configuration space reproduce well
negative-parity levels. Satisfactory agreement is obtained for positive parity
levels by extending the configuration space to include a nucleon-hole either in
the 1d3/2 or in the 2s1/2 orbitals.
A nearly one-to-one correspondence is found between experimental and
theoretical levels up to an excitation energy of 4 MeV.
Experimental data and shell model calculations are interpreted in terms of
the Nilsson diagram and the particle-rotor model, showing the strongly coupled
nature of the bands in this prolate nucleus. Nine values of K(pi) are proposed
for the levels observed in this experiment.
As a by-result it is shown that the values of the experimental magnetic
moments in 1f7/2 nuclei are well reproduced without quenching the nucleon
g-factors.Comment: 13 pages, 8 figure
CaracterÃsticas fÃsico-quÃmicas y estabilidad oxidativa de aceites de diferentes ecotipos de ricino peruano
The aim of this research was to assess the physico-chemical properties and shelf-life of oils press-extracted at two temperatures (60 °C and 80 °C) from five Peruvian castor bean ecotypes. A wide variation for all traits was observed. Low acidity index, low peroxide index and absence of p-anisidine were recorded. The total tocopherol contents ranged from 798 to 1040 mg/kg. A higher antioxidant capacity was detected in methanolic extracts than in hexane extract. From the Rancimat performed at 150-170 °C, the predicted shelf-life at 25 °C ranged from 0.15 to 8.93 years; the higher extraction temperature led to a longer shelf-life, probably because of enzyme inactivation.El objetivo de esta investigación fue estudiar las propiedades fisicoquÃmicas y la vida útil de aceite de ricino extraido a presión a dos temperaturas (60 y 80 °C) de cinco ecotipos peruanos. Se notó una amplia variación para todas las caracterÃsticas. Se observaron bajos Ãndice de acidez, bajo Ãndice de peróxido y ausencia de p-anisidina. El contenido total de tocoferoles osciló entre 798 y 1040 mg/kg. Se detectó una mayor capacidad antioxidante en los extractos en metanol que en los extractos en hexano. A partir del Rancimat realizado a 150-170 °C, la vida útil prevista a 25 °C osciló entre 0.15 y 8.93 años; la mayor temperatura de extracción condujo a una vida útil más larga, probablemente debido a inactivación de las enzimas.
 
Solutions of elliptic equations with a level surface parallel to the boundary: stability of the radial configuration
Positive solutions of homogeneous Dirichlet boundary value problems or initial-value problems for certain elliptic or parabolic equations must be radially symmetric and monotone in the radial direction if just one of their level surfaces is parallel to the boundary of the domain. Here, for the elliptic case, we prove the stability counterpart of that result. In fact, we show that if the solution is almost constant on a surface at a fixed distance from the boundary, then the domain is almost radially symmetric, in the sense that is contained in and contains two concentric balls Bre and Bri, with the difference re 12ri (linearly) controlled by a suitable norm of the deviation of the solution from a constant. The proof relies on and enhances arguments developed in a paper by Aftalion, Busca and Reichel
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