4,474 research outputs found

    Nonlinear magnetization dynamics of antiferromagnetic spin resonance induced by intense terahertz magnetic field

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    We report on the nonlinear magnetization dynamics of a HoFeO3 crystal induced by a strong terahertz magnetic field resonantly enhanced with a split ring resonator and measured with magneto-optical Kerr effect microscopy. The terahertz magnetic field induces a large change (~40%) in the spontaneous magnetization. The frequency of the antiferromagnetic resonance decreases in proportion to the square of the magnetization change. A modified Landau-Lifshitz-Gilbert equation with a phenomenological nonlinear damping term quantitatively reproduced the nonlinear dynamics

    Initial POLAR MFE observation of substorm signatures in the polar magnetosphere

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    This paper studies substorm influences in the polar magnetosphere using data from the POLAR magnetic field experiment (MFE). The POLAR spacecraft remains in the high altitude polar magnetosphere for extended periods around apogee. There it can stay at nearly constant altitude through all phases of a substorm, which was not possible on previous missions. We report such an event on March 28, 1996. Ground magnetometers monitored substorm activity, while the POLAR spacecraft, directly over the pole at (−0.8, −0.6, 8.5) RE in GSM coordinates, observed a corresponding perturbation in the total magnetic field strength. The total magnetic field first increased, then recovered toward quiet levels, consistent with erosion of magnetic flux from the dayside magnetosphere, followed by transport of that flux to the magnetotail, and eventual onset of tail reconnection and the return of that magnetic flux to the dayside magnetosphere

    A new measurement of thermal conductivity of amorphous ice and its implications for the thermal evolution of comets

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    Very slowly deposited amorphous ice has a thermal conductivity about four orders of magnitude or more smaller than hitherto estimated. Using the exceedingly low value of the thermal conductivity of comets deduced from the properties of amorphous ice leads to the expectation that internal heating of comets is negligible below the outer several tens of centimeters

    Valley current characterization of high current density resonant tunnelling diodes for terahertz-wave applications

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    We report valley current characterisation of high current density InGaAs/AlAs/InP resonant tunnelling diodes (RTDs) grown by metal-organic vapour phase epitaxy (MOVPE) for THz emission, with a view to investigate the origin of the valley current and optimize device performance. By applying a dual-pass fabrication technique, we are able to measure the RTD I-V characteristic for different perimeter/area ratios, which uniquely allows us to investigate the contribution of leakage current to the valley current and its effect on the PVCR from a single device. Temperature dependent (20 – 300 K) characteristics for a device are critically analysed and the effect of temperature on the maximum extractable power (PMAX) and the negative differential conductance (NDC) of the device is investigated. By performing theoretical modelling, we are able to explore the effect of typical variations in structural composition during the growth process on the tunnelling properties of the device, and hence the device performance

    GEOTAIL observation of tilted X-line formation during flux transfer events (FTEs) in the dayside magnetospheric boundary layers

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    International audienceThe magnetic field and plasma structures during two successive crossings of the subsolar magnetospheric boundary layers (i.e. MagnetoPause Current Layer (MPCL) and Low-Latitude Boundary Layer (LLBL)) under the southward-dawnward IMF are examined on the basis of the data obtained by the GEOTAIL spacecraft. A significant and interesting feature is found, that is, Flux Transfer Events (FTEs) occur in association with the formation of the tilted X-line. During the first inbound MPCL/LLBL crossing, the ion velocity enhancement (in particular, the Vl component negatively increases) can be observed in association with simultaneous typical bipolar signature (positive followed by negative) in the Bn component. In addition, a clear D-shaped ion distribution whose origin is the magnetosheath can also be found in the dawnward direction. A few minutes later, the satellite experiences outbound MPCL crossing. The negative enhancement of the Vm component can be found as well as the positive enhancement of the Vl component. Simultaneously, a typical bipolar signature with the polarity (negative followed by positive) opposite that observed in the first encounter can also be observed. The ions from the magnetosheath flow predominantly in the duskward direction, although the D-shaped ion distribution cannot be observed. These results indicate that the satellite initially observes one part of a reconnected flux tube formed by FTEs whose magnetospheric side is anchored to the Southern Hemisphere. The ions confined in this partial flux tube are flowing in the south-dawnward direction. Then, the satellite observes the other part of the reconnected flux tube whose magnetospheric side is anchored to the Northern Hemisphere. The ions confined in this flux tube flow dominantly in the north-duskward direction. Furthermore, it can be considered that the second MPCL crossing is a direct cut through the diffusion region of FTEs because the LLBL is absent in the vicinity of the MPCL. On the basis of these results, it can be concluded that the satellite was passing near the tilted X-line. The information obtained through this study is expected to be of great use in discriminating between the anti-parallel (steady-state) reconnection and tilted X-line models on the dayside MPCL

    A classification of some S3-bundles

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    Article信州大学理学部紀要 31(2): 55-58(1997)departmental bulletin pape


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    Five collegiate baseball pitchers, who have different types of delivery, were videotaped and analyzed using three-dimensional videography and ground reaction force (GRF) anaysis. Just before stride foot contact, a peak vertical GRF of 1.28 BW for pivot foot was produced, resulting from the joint torques for the knee and hip extensors. A peak forward GRF of 0.67 BW also appeared. This GRF may result in the ankle plantar flexors. Immediately after stride foot contact, the joint torques of hip’s extension, abduction and internal rotation, knee’s extension and valgus, ankle’s plantar flexion for the striding leg were generated in order to resist the resultant of vertical and backward GRFs