Collective excitations in low-density 2D electron systems

We report the observation of sharp plasmon and magnetoplasmon modes in ultra-low-density 2D electron systems. Well defined dispersions for the modes are observed at densities as low as 1.1×10⁹ cm⁻² and with excitation wave vectors as large as 1.2×10⁵ cm⁻¹. Interestingly, both modes are found to be more easily measured in low-density systems than in high-density systems. The strength of the light scattering cross-sections at low density suggests potential applications to the study of quantum phase transitions at large r_s.     

Physical mechanism of ultrafast flame acceleration

We explain the physical mechanism of ultrafast flame acceleration in obstructed channels used in modern experiments on detonation triggering. It is demonstrated that delayed burning between the obstacles creates a powerful jetflow, driving the acceleration. This mechanism is much stronger than the classical Shelkin scenario of flame acceleration due to nonslip at the channel walls. The mechanism under study is independent of the Reynolds number, with turbulence playing only a supplementary role. The flame front accelerates exponentially; the analytical formula for the growth rate is obtained. The theory is validated by extensive direct numerical simulations and comparison to previous experiments.     

A simple extended cavity diode laser for spectroscopy around 640 nm

We report on an extended cavity diode laser for operation near 640 nm. The laser is continuously tunable in 10 GHz ranges with a maximum output power of 3 mW. The laser system has been constructed using off-the-shelf optoelectronic components and easily machinable mechanical parts. The constructed system has been used to study the saturated absorption of the closed 1s₅–2p₉ neon transition in a radio-frequency discharge that can be maintained at neon pressures down to 10⁻² Pa.     

Giant magnetic anisotropy in tetragonal FeCo alloys

In order to further increase the recording density in hard disk drives, new media materials are required. Two essential parameters of future recording media are a large uniaxial magnetic anisotropy energy (MAE) K(u) and a large saturation magnetization M(s). Based on first-principles theory, we predict that very specific structural distortions of FeCo alloys possess these desired properties. The discovered alloy has a saturation magnetization that is about 50% larger than that of FePt--a compound that has received considerable attention lately-with a uniaxial MAE that can easily be tailored reaching a maximum value that is 50% larger than that of FePt.     

Quality management education over the Internet

We describe a program for continuing education in Quality management and metrology. It may be followed by class lectures, by videoconference or by individual distance learning over the Internet. An important feature for students who attend classes is visits to selected institutions for demonstrations of quality management in practice. For students using distance learning, multimedia presentations containing a total of 2 h of video and supporting documentation is the alternative to the visits. The program is aimed at personnel from all fields, and its emphasis is on the generality of quality principles, attitudes and motivation for quality thinking, measurements in quality work, as well as the use of system audits and other elements of quality management in related fields.     

Neutron powder diffraction study of Pb(HfxTi1-x)O3 ceramics (0.10<or=x<or=0.50)

The crystal symmetries of lead hafnate titanate (Pb(HfxTi1-x)O3, PHT) powders with 0.10相似文献   

Ion acceleration during reconnection in MAST

Spontaneous acceleration of ions to suprathermal energies is observed during magnetic reconnection in the Mega-Ampere Spherical Tokamak (MAST). A high-energy tail is observed in the ion-distribution function following each internal reconnection event in Ohmic discharges. This phenomenon is explained in terms of runaway ion acceleration in the electric field induced by the reconnection.     

Geometry of the valence transition induced surface reconstruction of Sm(0001)

We present a structural determination of the surface reconstruction of the Sm(0001) surface using surface x-ray diffraction, scanning tunneling microscopy, and ab initio calculations. The reconstruction is associated with a large (22%) expansion of the atomic radius for the top monolayer surface Sm atoms. The mechanism driving the surface reconstruction in Sm is unique among all elements and is connected to the strong correlations of the 4f electrons in Sm and the intermediate valence observed in certain Sm compounds. The atoms constituting the top monolayer of Sm(0001) have vastly different chemical properties compared to the layer underneath and behave as if they were an adsorbate of a different chemical species.     

Forty years of nonlinear ultrasound

Nonlinear ultrasound forms an integrated discipline of nonlinear acoustics founded in 1755. A short outline of the state-of-the-art in nonlinear ultrasound in 1960 forms the introduction to this paper. Some of the most important contributions to the development in the theoretical, analytical and numerical basis of nonlinear ultrasound and in experimental investigations of nonlinear ultrasonic processes published during the period of 1960 through 2000 are discussed and their successes and failures in practical exploitation are illuminated. A more detailed treatment is given of research achievements in nonlinearity of fluids, in focused ultrasonic field, in parametric acoustic arrays and in thermoacoustics. An attempt is made to point out some fields of research in nonlinear ultrasound where future efforts should be concentrated.