Two‐Dimensional Local Modeling of Thermospheric Heating and Neutral Mass Density Enhancement Driven by Alfvén Waves

In the cusp region, a significantly enhanced thermospheric mass density is commonly observed around 400 km altitude. Despite a number of studies, the enhancement mechanism has not been fully characterized. In order to determine how the Joule heating and resultant mass density enhancements are generated in the region of the ionosphere during a few hours after the Alfvén resonator modes are set up, we have developed a new efficient method to calculate Alfvén waves. In this method, the Fourier transform was used, and Alfvén waves were solved as frequency-domain boundary value problems. We employed a two-dimensional local model and performed five modeling runs. The result from the modeling runs shows that the Alfvén resonator modes generate significant neutral upwelling at ∼300 km altitude, which creates a “cell” of the neutral mass density enhancement at altitudes centered between 350 and 400 km. This cell becomes evident roughly 1 hr after the Alfvén resonator modes are set up, and this region continues to exist stably for 2 more hours. A fractional mass density enhancement at 400 km altitude 3 hr after the Alfvén resonator modes having an Alfvénic field-aligned current of 20 μAm⁻² at the top boundary are set up reaches ∼30%, which is consistent with the result obtained from satellite observations. In terms of the Poynting flux, this corresponds to ∼20 mWm⁻², which is also consistent with previous satellite observations

An observation of spin-valve effects in a semiconductor field effect transistor: a novel spintronic device

We present the first spintronic semiconductor field effect transistor. The injector and collector contacts of this device were made from magnetic permalloy thin films with different coercive fields so that they could be magnetized either parallel or antiparallel to each other in different applied magnetic fields. The conducting medium was a two dimensional electron gas (2DEG) formed in an AlSb/InAs quantum well. Data from this device suggest that its resistance is controlled by two different types of spin-valve effect: the first occurring at the ferromagnet-2DEG interfaces; and the second occuring in direct propagation between contacts.Comment: 4 pages, 2 figure

Optical pump-probe scanning tunneling microscopy for probing ultrafast dynamics on the nanoscale

The development of a method for exploring the ultrafast transient dynamics in small organized structures with high spatial resolution is expected to be a basis for further advances in current science and technology. Recently, we have developed a new microscopy technique by combining scanning tunneling microscopy (STM) with ultrashort-pulse laser technology, which enables the visualization of ultrafast carrier dynamics even on the single-atomic level. A nonequilibrium carrier distribution is generated using ultrashort laser pulses and its relaxation processes are probed by STM using the optical pump-probe method realized in STM by the pulse-picking technique. In this paper, the fundamentals of the new microscopy technique are overviewed

A feasibility study of H sup - beam extraction technique using YAG laser

Under a framework of JAERI-KEK joint project of high intensity proton accelerator, as for research and develop of the accelerator driven nuclear transmutation of the long lived radioactive nuclide, it is planed to built the Transmutation Physics Experiment Facility (TEF-P) and the Transmutation Engineering Experiment Facility (TEF-E). The TEF-P is used for the experiments for subcritical system coupled with a spallation neutron target bombarded with 600-MeV proton beam accelerated by the LINAC. To limit the maximum thermal power less than 500 W at the TEF-P, an incident beam power should be less than 10 W. On the contrary, at the TEF-E, high power beam of 200 kW is requested. Both high and low power beams are demanded for the transmutation facilities. It is difficult to deliver a low power beam to the TEF-P. Conventional beam extraction technique with a thin foil, is not desirable because the scattering of the beam at the foil requires the massive shield. Therefore, we study a new technique to extract a small portion of the beam precisely from the high intensity beam by using a laser beam. By a laser beam, H sup - in the beam from LINAC is partially changed to H sup 0 beam so that a low current H sup 0 beam can be obtained. As the cross section of the charge exchange reaction for H sup - ions has a peak around at a wave length of 1 mu m for photons, YAG laser is suitable for this charge exchange because of its 1.06 mu m wave length. It is derived that 10 W beam for 600-MeV proton can be extracted by the YAG laser with power of 2 J for each pulse of 25 Hz. By this technique, the pulse width for the extracted beam can be controlled by changing the time width of laser irradiation. When a charge exchanger having the beam collide point existing in straight section, a background beam current of projectile, however, will be increased due to the interaction with the residual gas in the beam duct. Thus, a charge exchanger is devised having the beam collide point in a by changing this charge exchanger, it is demonstrated that the possibility of the charge exchange due to interactions with residual gas can be drastically decrease. By the above studies, it is recognized that feasibility of the technique of beam extraction with the laser

The GNSS for Meteorology (G4M) Procedure and Its Application to Four Significant Weather Events

The authors conceived the GNSS for Meteorology (G4M) procedure to remote-sense the Precipitable Water Vapor (PWV) content in atmosphere with the aim to detect severe meteorological phenomena. It can be applied over an orographically complex area, exploiting existing networks of Global Navigation Satellite System (GNSS) Permanent Stations (PSs) and spread meteorological sensors, not necessarily co-located. The results of a posteriori analysis of four significant meteorological events are here presented, also in comparison with rain gauge data, to show the effectiveness of the method. The potentiality of G4M to detect and locate in space and time intense rainfall events is highlighted. The upcoming application of G4M in near-real time could provide a valuable support to existing Decision Support System for meteorological alerts