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

Calculation of the stochastic pulsed Rossi-alpha formula and its experimental verification

The Rossi-alpha formula for subcritical systems driven by a pulsed neutron source was derived with a solution technique that can effectively take different shape functions of the pulsed neutron source into account. The result of derivation showed that the present formula consists of the correlated and uncorrelated terms and an oscillating term whose period was identical to that of the pulsed neutron source.To investigate the validity of the pulsed Rossi-alpha formula and its applicability for the evaluation of the prompt neutron decay constant alpha from measurements, an experiment was performed at the Kyoto University Critical Assembly with a pulsed D-T neutron source. Although it seemed that fitting the present formula to the experimental curves was not practical because of an infinite-series expansion structure of the oscillating term, it was possible to extract only the correlated term, that explicitly includes the alpha value, by a simple data handling procedure. It was found that the measured alpha values agreed with those obtained by the pulsed neutron source method very well. This finding means that the pulsed Rossi-alpha method will be an attractive candidate for the monitoring method of the subcritical reactivity of future accelerator driven systems

Calculation of the stochastic pulsed Rossi-alpha formula and its experimental verification

The Rossi-alpha formula for subcritical systems driven by a pulsed neutron source was derived with a solution technique that can effectively take different shape functions of the pulsed neutron source into account. The result of derivation showed that the present formula consists of the correlated and uncorrelated terms and an oscillating term whose period was identical to that of the pulsed neutron source.To investigate the validity of the pulsed Rossi-alpha formula and its applicability for the evaluation of the prompt neutron decay constant alpha from measurements, an experiment was performed at the Kyoto University Critical Assembly with a pulsed D-T neutron source. Although it seemed that fitting the present formula to the experimental curves was not practical because of an infinite-series expansion structure of the oscillating term, it was possible to extract only the correlated term, that explicitly includes the alpha value, by a simple data handling procedure. It was found that the measured alpha values agreed with those obtained by the pulsed neutron source method very well. This finding means that the pulsed Rossi-alpha method will be an attractive candidate for the monitoring method of the subcritical reactivity of future accelerator driven systems