Experimental Test of a New Equality: Measuring Heat Dissipation in an Optically Driven Colloidal System

Measurement of energy dissipation in small nonequilibrium systems is generally a difficult task. Recently, Harada and Sasa [Phys.Rev.Lett. 95, 130602(2005)] derived an equality relating the energy dissipation rate to experimentally accessible quantities in nonequilibrium steady states described by the Langevin equation. Here, we show the first experimental test of this new relation in an optically driven colloidal system. We find that this equality is validated to a fairly good extent, thus the irreversible work of a small system is estimated from readily obtainable quantities.Comment: 4 pages, 6 figure

High Power Gamma-Ray Flash Generation in Ultra Intense Laser-Plasma Interaction

When high-intensity laser interaction with matter enters the regime of dominated radiation reaction, the radiation losses open the way for producing short pulse high power gamma ray flashes. The gamma-ray pulse duration and divergence are determined by the laser pulse amplitude and by the plasma target density scale length. On the basis of theoretical analysis and particle-in-cell simulations with the radiation friction force incorporated, optimal conditions for generating a gamma-ray flash with a tailored overcritical density target are found.Comment: 12 pages, 5 figures Accepted for publication in Physical Review Letters (this http://prl.aps.org/

ケンキュウ フセイ ヘノ タイオウ ヲ コエテ リサーチ インテグリティ アプローチ ト ソノ ガンイ

鷲田清一名誉教授　退職記念

Exchange stiffness proportional to power of magnetization in permalloy co-doped with Mo and Cu

The exchange stiffness of magnetic materials is one of the essential parameters governing magnetic texture and its dynamics in magnetic devices. The effect of single-element doping on exchange stiffness has been investigated for several doping elements for permalloy (NiFe alloy), a soft magnetic material whose soft magnetic properties can be controlled by doping. However, the impact of more practical multi-element doping on the exchange stiffness of permalloy is unknown. This study investigates the typical magnetic properties, including exchange stiffness, of permalloy systematically co-doped with Mo and Cu using broadband ferromagnetic resonance spectroscopy. We find that the exchange stiffness, which decreases with increasing doping levels, is proportional to a power of magnetization, which also decreases with increasing doping levels. The magnetization, $M_{\rm s}$, dependence of the exchange stiffness constant, $A$, of all the investigated samples, irrespective of the doping levels of each element, lies on a single curve expressed as $A\propto M_{\rm s}^n$ with exponent $n$ close to 2. This empirical power-law relationship provides a guideline for predicting unknown exchange stiffness in non-magnetic element-doped permalloy systems