10 research outputs found
Analysis of acoustic emission during the melting of embedded indium particles in an aluminum matrix: a study of plastic strain accommodation during phase transformation
Acoustic emission is used here to study melting and solidification of
embedded indium particles in the size range of 0.2 to 3 um in diameter and to
show that dislocation generation occurs in the aluminum matrix to accommodate a
2.5% volume change. The volume averaged acoustic energy produced by indium
particle melting is similar to that reported for bainite formation upon
continuous cooling. A mechanism of prismatic loop generation is proposed to
accommodate the volume change and an upper limit to the geometrically necessary
increase in dislocation density is calculated as 4.1 x 10^9 cm^-2 for the
Al-17In alloy. Thermomechanical processing is also used to change the size and
distribution of the indium particles within the aluminum matrix. Dislocation
generation with accompanied acoustic emission occurs when the melting indium
particles are associated with grain boundaries or upon solidification where the
solid-liquid interfaces act as free surfaces to facilitate dislocation
generation. Acoustic emission is not observed for indium particles that require
super heating and exhibit elevated melting temperatures. The acoustic emission
work corroborates previously proposed relaxation mechanisms from prior internal
friction studies and that the superheat observed for melting of these
micron-sized particles is a result of matrix constraint.Comment: Presented at "Atomistic Effects in Migrating Interphase Interfaces -
Recent Progress and Future Study" TMS 201
Advances in Global and Local Helioseismology: an Introductory Review
Helioseismology studies the structure and dynamics of the Sun's interior by
observing oscillations on the surface. These studies provide information about
the physical processes that control the evolution and magnetic activity of the
Sun. In recent years, helioseismology has made substantial progress towards the
understanding of the physics of solar oscillations and the physical processes
inside the Sun, thanks to observational, theoretical and modeling efforts. In
addition to the global seismology of the Sun based on measurements of global
oscillation modes, a new field of local helioseismology, which studies
oscillation travel times and local frequency shifts, has been developed. It is
capable of providing 3D images of the subsurface structures and flows. The
basic principles, recent advances and perspectives of global and local
helioseismology are reviewed in this article.Comment: 86 pages, 46 figures; "Pulsation of the Sun and Stars", Lecture Notes
in Physics, Vol. 832, Rozelot, Jean-Pierre; Neiner, Coralie (Eds.), 201
Nonlinear Analysis of a High-Resolution Optical Wave-Front Control System
A class of feedback systems for high-resolution optical wave-front control (or adaptive optic wave-front distortion suppression) is modeled and analyzed. Under certain conditions, the nonlinear dynamical system models obtained are shown to be gradient systems, with energy functions that also serve as Lyapunov functions. The approach taken here to a problem of nonlinear control system design and analysis might also be applicable to other problems involving high-resolution control of physical fields, particularly if the field sensing is performed optically. 1 Introduction The idea of using sensor and actuator arrays to manipulate physical fields is most developed in the area of adaptive optics (i.e., feedback control for optical wavefront phase distortion suppression). Cameras serve as sensor arrays, and spatial light modulators, such as liquid-crystal or MEMS micro-mirror devices, provide the actuation for manipulating optical beams. The control problem involves determining how the se..
Sensitivity of composites based on gelatin and nanoparticles Cu2S and CdS to vapors of some organic compounds
Effect of helical edge states on the tunneling conductance in ferromagnet/noncentrosymmetric superconductor junction
‘Good fences make good neighbours’: Concepts and records of range dynamics in ground squirrels and geographical barriers in the Pleistocene of the Circum-Black Sea area
Observations of Photospheric Dynamics and Magnetic Fields: From Large-Scale to Small-Scale Flows
International audienceThis paper reviews solar flows and magnetic fields observed at the photospheric level. We first present the context in which these observations are performed. We describe the various temporal and spatial scales involved, and the coupling between them. Then we present small-scale flows, mainly supergranulation and flows around active regions. Flows at the global scale are then reviewed, again with emphasis on the flows, i.e. differential rotation, torsional oscillation and meridional circulation. In both small- and global-scale we discuss the coupling between flow fields and magnetic field and give an overview of observational techniques. Finally, the possible connection between studies of solar activity and stellar activity is briefly discussed