A Geophysical Interpretation of the Secular Displacement and Gravity Rates Observed at Ny-Ålesund, Svalbard in the Arctic— Effects of Post-Glacial Rebound and Present-Day Ice Melting

We have analysed the Ny-Ålesund very long baseline interferometry (VLBI) data over the period 1994 August to 2004 May, and we obtain secular displacement rates relative to a NNR-NUVEL-1A reference frame of and for the north, east and vertical directions, respectively. The corresponding global positioning system (GPS) station displacement rates relative to the same reference frame for the north, east, and vertical directions are at NYA1 and at NALL, where these GPS rates were derived from the ITRF2000 velocity solution of Heflin. From the comparison at 25 globally distributed collocated sites, we found that the difference in uplift rate between VLBI and GPS at Ny-Ålesund is mainly due to a GPS reference frame scale rate error corresponding to 1.6 mm yr−1 in the GPS vertical rates. The uplift rate was estimated to be 5.2 ± 0.3 mm yr−1 from the analysis of the tide gauge data at Ny-Ålesund. Hence the uplift rates obtained from three different kinds of data are very consistent each other. The absolute gravity (AG) measurements at Ny-Ålesund, which were carried out four times (period: 1998–2002) by three different FG5 absolute gravimeters, lead to a decreasing secular rate of . In this analysis, the actual data obtained from a superconducting gravimeter at Ny-Ålesund were used in the corrections for the gravity tide (including the ocean tide effect) and for the air pressure effect. We have estimated three geophysical contributions to examine the observed rates: (1) the effect of the sea-level (SL) change on a timescale of a few decades, (2) the effect of the present-day ice melting (PDIM) in Svalbard and (3) the sensitivity of the computed post-glacial rebound (PGR) effects to different choices of the models of past ice history and Earth\u27s viscosity parameters. Our analysis indicates that the effect of SL change can be neglected as the main source of the discrepancy. On the other hand, the effect of PDIM cannot be ignored in explaining the mutual relation between the observed horizontal and vertical rates and the predicted ones. A large melting rate of the order of −75 cm yr11 (i.e. roughly 1.6 times larger than the mean rate derived from glaciology over Svalbard) would explain the observed uplift but only half of the gravity changes. Our comparison results clearly point out the importance of both the estimation accuracy of the elastic deformations and better observation accuracy to constrain the size of PGR effects in the northwestern Svalbard more tightly

Tolerance of spin-Seebeck thermoelectricity against irradiation by swift heavy ions

The ion-irradiation tolerance of thermoelectric devices based on the spin Seebeck effect (SSE) was investigated by using 320 MeV gold ion (Au24+) beams modeling cumulative damages due to fission products emitted from the surface of spent nuclear fuels. For this purpose, prototypical Pt/Y3Fe5O12/Gd3Ga5O12 SSE elements were irradiated with varying the dose level at room temperature and measured the SSE voltage of them. We confirmed that the thermoelectric and magnetic properties of the SSE elements are not affected by the ion-irradiation up to 1010 ions/cm2 fluence and that the SSE signal is extinguished around 1012 ions/cm2, in which the ion tracks almost fully cover the sample surface. We also performed the hard X-ray photoemission spectroscopy (HAXPES) measurements to understand the effects atthe interface of Pt/Y3Fe5O12. The HAXPES measurements suggest that the chemical reaction that diminishes the SSE signals is enhanced with the increase of the irradiation dose. The present study demonstrates that SSE-based devicesare applicable to thermoelectric generation even in harsh environments for a long time period

The damage analysis for irradiation tolerant spin-driven thermoelectric device based on single-crystalline Y_3Fe_5O_12/Pt heterostructures

Spin-driven thermoelectric (STE) generation based on the combination of the spin Seebeck effect and inverse spin Hall effect is alternative to conventional semiconductor-based thermocouples as it is large-scale, low-cost, and environment-friendly. The STE device is thought to be radiation hard, making it attractive for space and nuclear technology applications. By using magnetometry, transmission electron microscopy, and the hard X-ray photoemission spectroscopy (HAXPES) measurements, we show that a STE device made of single-crystalline Y3Fe5O12/Pt heterostructures has tolerance to irradiation of high-energy heavy ion beams. We used 200 MeV gold ion beams modeling cumulative damages due to fission products emitted from the surface of spent nuclear fuels. By varying the dose level, we confirmed that the thermoelectric and magnetic properties of the single-crystalline Y3Fe5O12/Pt STE device are finite at the ion-irradiation dose up to 1012 ions/cm2 fluence. In addition, the HAXPES measurements were performed to understand the effects at the interface of Y3Fe5O12/Pt. The HAXPES data suggest that the chemical reaction regarding Fe and O that diminishes the SSE signals is promoted with the increase of the irradiation dose. The understandings of the damage analysis in Y3Fe5O12/Pt are beneficial for developing better STE devices applicable to harsh environmental usages