Skyline-based localisation for aggressively manoeuvring robots using UV sensors and spherical harmonics

Place recognition is a key capability for navigating robots. While significant advances have been achieved on large, stable platforms such as robot cars, achieving robust performance on rapidly manoeuvring platforms in outdoor natural conditions remains a challenge, with few systems able to deal with both variable conditions and large tilt variations caused by rough terrain. Taking inspiration from biology, we propose a novel combination of sensory modality and image processing to obtain a significant improvement in the robustness of sequence-based image matching for place recognition. We use a UV-sensitive fisheye lens camera to segment sky from ground, providing illumination invariance, and encode the resulting binary images using spherical harmonics to enable rotation-invariant image matching. In combination, these methods also produce substantial pitch and roll invariance, as the spherical harmonics for the sky shape are minimally affected, providing the sky remains visible. We evaluate the performance of our method against a leading appearance-invariant technique (SeqSLAM) and a leading viewpoint-invariant technique (FAB-MAP 2.0) on three new outdoor datasets encompassing variable robot heading, tilt, and lighting conditions in both forested and urban environments. The system demonstrates improved condition- and tilt-invariance, enabling robust place recognition during aggressive zigzag manoeuvring along bumpy trails and at tilt angles of up to 60 degrees

Snapshot navigation in the wavelet domain

Many animals rely on robust visual navigation which can be explained by snapshot models, where an agent is assumed to store egocentric panoramic images and subsequently use them to recover a heading by comparing current views to the stored snapshots. Long-range route navigation can also be explained by such models, by storing multiple snapshots along a training route and comparing the current image to these. For such models, memory capacity and comparison time increase dramatically with route length, rendering them unfeasible for small-brained insects and low-power robots where computation and storage are limited. One way to reduce the requirements is to use a compressed image representation. Inspired by the filter bank-like arrangement of the visual system, we here investigate how a frequency-based image representation influences the performance of a typical snapshot model. By decomposing views into wavelet coefficients at different levels and orientations, we achieve a compressed visual representation that remains robust when used for navigation. Our results indicate that route following based on wavelet coefficients is not only possible but gives increased performance over a range of other models

Computer simulation of correlated self-diffusion via randomly migrating vacancies in cubic crystals

Abstract Title of program: RANDOM VACANCY MIGRATION Catalog number: ACKO Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland (see application form in this issue) Computer: CDC 6600; Installation: University of Stuttgart Operating system: Scope 3.4 Programming language used: FORTRAN IV High speed storage required: 58 000 words No. of bits in a word: 60 Overlay structure: none No. of magnetic tapes required: none Other peripherals used: card reader, line printer No of... Title of program: RANDOM VACANCY MIGRATION Catalogue Id: ACKO_v1_0 Nature of problem Computer simulation of the relative jumps of atoms induced by a randomly migrating single or double vacancy in a face-centered cubic, body-centered cubic, or simple cubic crystal lattice. ADAPTATION SUMMARY: Vol:Year:Page 13:1977:183 "0001 CORRELATION FACTOR AND NMR" "Determination of correlation factor and NMR diffusion parameters from the computer-simulated random motion of vacancies in cubic crystals." D. Wolf; K. Differt; H. Mehrer Note: adaptation instructions are contained in source code Versions of this program held in the CPC repository in Mendeley Data ACKO_v1_0; RANDOM VACANCY MIGRATION; 10.1016/0010-4655(77)90011-X This program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2019

Scanning internal photoemission microscopy for the identification of hot carrier transport mechanisms

Differt D, Pfeiffer W, Diesing D. Scanning internal photoemission microscopy for the identification of hot carrier transport mechanisms. Applied Physics Letters. 2012;101(11): 111608.Linear and nonlinear internal photoemission in a thin-film metal-insulator-metal heterosystem, i.e., a Ta-TaOx-Ag junction, together with surface reflectivity are mapped with a lateral resolution of better than 5 mu m. The spatial correlation of the different signals and time-resolved internal photoemission spectroscopy reveal excitation mechanisms and ballistic hot carrier injection. The internal photoemission yield variation with Ag layer thickness is quantitatively explained by above-barrier injection. The hot-spot-like behavior of the two-photon induced internal photoemission observed for short pulse excitation is attributed to local field enhancements because of Ag-film thickness reduction and plasmonic effects at structural defects. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752734

Modification of a-Si: H Films via Non-linear Femtosecond Laser Pulse Absorption

AbstractThe modification of a-Si:H via non-linear femtosecond laser pulse absorption was studied and the characteristic thresholds for hydrogen diffusion/effusion, crystallization and material ablation were determined. To consider the impact of the hydrogen content on laser materials processing, a-Si:H was deposited at different temperatures (25°C, 200°C, 520°C) resulting in different hydrogen contents (30%, 13%, and <1%). Essential information for device applications such as the degree of crystallization and the Si-H dissociation are obtained from micro-Raman spectroscopy of the laser treated areas. The prospects of a flexible non-linear fs laser material processing of a-Si:H for bulk and surface modification will be discussed

Time Domain Characterization of Light Trapping States in Thin Film Solar Cells

Spectral interferometry of the backscattered radiation reveals coherence lifetimes of about 150 fs for nanolocalized electromagnetic modes in textured layered nanostructures as they are commonly used in thin film photovoltaics to achieve high cell efficiencies