Linear Embedding-based High-dimensional Batch Bayesian Optimization without Reconstruction Mappings

The optimization of high-dimensional black-box functions is a challenging problem. When a low-dimensional linear embedding structure can be assumed, existing Bayesian optimization (BO) methods often transform the original problem into optimization in a low-dimensional space. They exploit the low-dimensional structure and reduce the computational burden. However, we reveal that this approach could be limited or inefficient in exploring the high-dimensional space mainly due to the biased reconstruction of the high-dimensional queries from the low-dimensional queries. In this paper, we investigate a simple alternative approach: tackling the problem in the original high-dimensional space using the information from the learned low-dimensional structure. We provide a theoretical analysis of the exploration ability. Furthermore, we show that our method is applicable to batch optimization problems with thousands of dimensions without any computational difficulty. We demonstrate the effectiveness of our method on high-dimensional benchmarks and a real-world function

Observation of Antarctic ice sheet change by Synthetic Aperture Radar

第3回極域科学シンポジウム/第32回極域地学シンポジウム 11月29日（木） 統計数理研究所 ３階セミナー

Directional cell expansion requires NIMA-related kinase 6 (NEK6)-mediated cortical microtubule destabilization;

　Plant cortical microtubules align perpendicular to the growth axis to determine the direction of cell growth. However, it remains unclear how plant cells form well-organized cortical microtubule arrays in the absence of a centrosome. In this study, we investigated the functions of Arabidopsis NIMA-related kinase 6 (NEK6), which regulates microtubule organization during anisotropic cell expansion. Quantitative analysis of hypocotyl cell growth in the nek6-1 mutant demonstrated that NEK6 suppresses ectopic outgrowth and promotes cell elongation in different regions of the hypocotyl. Loss of NEK6 function led to excessive microtubule waving and distortion, implying that NEK6 suppresses the aberrant cortical microtubules. Live cell imaging showed that NEK6 localizes to the microtubule lattice and to the shrinking plus and minus ends of microtubules. In agreement with this observation, the induced overexpression of NEK6 reduced and disorganized cortical microtubules and suppressed cell elongation. Furthermore, we identified five phosphorylation sites in β-tubulin that serve as substrates for NEK6 in vitro. Alanine substitution of the phosphorylation site Thr166 promoted incorporation of mutant β-tubulin into microtubules. Taken together, these results suggest that NEK6 promotes directional cell growth through phosphorylation of β-tubulin and the resulting destabilization of cortical microtubules

A case study of generating a digital elevation model for the Soya Coast area, Antarctica, using JERS-1 SAR interferometry

The three-pass synthetic aperture radar (SAR) interferometry method has been applied to three time-serial scenes (two SAR pairs) over the Soya Coast area, Antarctica, observed by the Japanese Earth Resources Satellite 1 (JERS-1). For simplicity, we assumed that the ice flow during 88 days (2 repeat periods of JERS-1) was constant. Interferometric fringes associated with ice flow/deformation were removed using the two SAR pairs to leave the topographic fringes. The resultant topographic fringes were converted to the relative surface elevations above sea level. There are 23 suitable ground control points (GCPs) in the region concerned, covering the height range from 0 to 600 m. A digital elevation model (DEM) was created in order that the model heights fit the GCP heights in a least squares sense. The obtained DEM grids with a spatial resolution of 50 m by 50 m have a root-mean-square (rms) error of 15.3 m. As for the GTOPO30 model grids with a 30 arc-second resolution in the same region, similar comparison of the model heights with the GCP heights resulted in a bias of -66.2 m and rms error of 131.7 m, which is worse than the SAR derived DEM by one order of magnitude. It is also noted that 12 GCPs on the islands and coastal outcropped areas are incorrectly located outside of the land area when mapped in the GTOPO30 contours. In spite of several remaining problems to be solved, SAR interferometry can effectively be applied to generate DEMs on the vast inaccessible ice sheet of Antarctica

Detection of grounding line and vertical displacement of ice shelf by SAR interferometry -A case study for the Stanjukovicha Ice Shelf, East Antarctica, using ERS tandem SAR data-

Synthetic Aperture Radai (SAR) interfeiometiy was applied to the Stanjukovicha Ice Shelf, East Antarctica, to detect its grounding lines and vertical motion and to monitoi the ice shelf behavior The ERS-1 and -2 tandem mission data were used Fringes were clearly revealed on the obtained interferograms By tracing the inland side of the dense fringes, the grounding lines weie obtained not only for the boundary between the continental ice sheet and the ice shelf, but also foi the boundaries around the small "islands" The grounding lines derived from SAR interferometry were not always accompanied by cleai changes in surface pioperties of SAR intensity images Since the displacement fringes include the component of horizontal ice flow, the component of vertical displacement was extiacted by counting only the phase difference along the ice flow lines not absolute phase difference The derived vertical displacements agreed well with modeled sea surface height changes with a standaid deviation of 4 9 cm Thus the SAR inteiferometry demonstrated its ability and applicability in monitoimg the Antarctic ice shel

Preliminary study to generate a DEM of Amundsen Bay, Antarctica by interferometric SAR

A SAR interferogram was obtained from two JERS-1 SAR data sets around Amundsen Bay, west Enderby Land, received at Syowa Station on November 26, 1996 and January 9, 1997. Fringes were found in the interferogram related to topographic height and surface displacements. However, we could not generate a digital elevation model for the area because we did not succeed in carrying out phase unwrapping to estimate absolute phase. We compared the fringe patterns obtained for Tonaugh Island with the topographic map derived from the aerial photographs. Relative heights in the area of flat topography were estimated from the interferogram; the interferogram\u27s fringes agreed with the contour line shapes on the topographic map