Chalmers University of Technology

About: Chalmers University of Technology is a education organization based out in Gothenburg, Sweden. It is known for research contribution in the topics: Catalysis & Finite element method. The organization has 17191 authors who have published 53951 publications receiving 1520592 citations. The organization is also known as: Chalmers Tekniska Högskola & Chalmers.

A Machine Learning Approach to Ranging Error Mitigation for UWB Localization

Abstract: Location-awareness is becoming increasingly important in wireless networks. Indoor localization can be enabled through wideband or ultra-wide bandwidth (UWB) transmission, due to its fine delay resolution and obstacle-penetration capabilities. A major hurdle is the presence of obstacles that block the line-of-sight (LOS) path between devices, affecting ranging performance and, in turn, localization accuracy. Many techniques have been proposed to address this issue, most of which make modifications to the localization algorithm. Since many localization algorithms work with distance or angle estimates, rather than received waveforms, information inherent in the wideband waveform is lost, leading to sub-optimal ranging error mitigation. To avoid this information loss, we present a novel approach to mitigate ranging errors directly in the physical layer. In contrast to existing techniques, which detect the non-line-of-sight (NLOS) condition, our approach directly mitigates the bias incurred in both LOS and non-LOS conditions. In particular, we apply two classes of non-parametric regressors to form an estimate of the ranging error. Our work is based on, and validated by, an extensive indoor measurement campaign with FCC-compliant UWB radios. The results show that the proposed regressors provide significant performance improvements in various practical localization scenarios, compared to conventional approaches.

Characterization of indoor sources of fine and ultrafine particles: a study conducted in a full-scale chamber.

Abstract: Humans and their activities are known to generate considerable amounts of particulate matter indoors. Some of the activities are cooking, smoking and cleaning. In this study 13 different particle sources were for the first time examined in a 32 m3 full-scale chamber with an air change rate of 1.7 ± 0.1/h. Two different instruments, a condensation particle counter (CPC) and an optical particle counter (OPC) were used to quantitatively determine ultrafine and fine particle emissions, respectively. The CPC measures particles from 0.02 μm to larger than 1.0 μm. The OPC was adjusted to measure particle concentrations in eight fractions between 0.3 and 1.0 μm. The sources were cigarette side-stream smoke, pure wax candles, scented candles, a vacuum cleaner, an air-freshener spray, a flat iron (with and without steam) on a cotton sheet, electric radiators, an electric stove, a gas stove, and frying meat. The cigarette burning, frying meat, air freshener spray and gas stove showed a particle size distribution that changed over time towards larger particles. In most of the experiments the maximum concentration was reached within a few minutes. Typically, the increase of the particle concentration immediately after activation of the source was more rapid than the decay of the concentration observed after deactivation of the source. The highest observed concentration of ultrafine particles was approximately 241,000 particles/cm 3 and originated from the combustion of pure wax candles. The weakest generation of ultrafine particles (1.17 × 107 particles per second) was observed when ironing without steam on a cotton sheet, which resulted in a concentration of 550 particles/cm3 in the chamber air. The highest generation rate (1.47 × 1010 particles per second) was observed in the radiator test.

Monitoring of lipid storage in Caenorhabditis elegans using coherent anti-Stokes Raman scattering (CARS) microscopy.

Abstract: Better understanding of the fundamental mechanisms behind metabolic diseases requires methods to monitor lipid stores on single-cell level in vivo. We have used Caenorhabditis elegans as a model organism to demonstrate the limitations of fluorescence microscopy for imaging of lipids compared with coherent anti-Stokes Raman scattering (CARS) microscopy, the latter allowing chemically specific and label-free imaging in living organisms. CARS microscopy was used to quantitatively monitor the impact of genetic variations in metabolic pathways on lipid storage in 60 specimens of C. elegans. We found that the feeding-defective mutant pha-3 contained a lipid volume fraction one-third of that found in control worms. In contrast, mutants (daf-2, daf-4 dauer) with deficiencies in the insulin and transforming growth factors (IGF and TGF-beta) signaling pathways had lipid volume fractions that were 1.4 and 2 times larger than controls, respectively. This was observed as an accumulation of small-sized lipid droplets in the hypodermal cells, hosting as much as 40% of the total lipid volume in contrast to the 9% for the wild-type larvae. Spectral CARS microscopy measurements indicated that this is accompanied by a shift in the ordering of the lipids from gel to liquid phase. We conclude that the degree of hypodermal lipid storage and the lipid phase can be used as a marker of lipid metabolism shift. This study shows that CARS microscopy has the potential to become a sensitive and important tool for studies of lipid storage mechanisms, improving our understanding of phenomena underlying metabolic disorders.

Triplet supercurrents in clean and disordered half-metallic ferromagnets

Abstract: Interfaces between materials with differently ordered phases present unique opportunities to study fundamental problems in physics. One example is the interface between a singlet superconductor and a half-metallic ferromagnet, where Cooper pairing occurs between electrons with opposite spin on the superconducting side, whereas the other exhibits 100% spin polarization. The recent surprising observation of a supercurrent through half-metallic CrO2 therefore requires a mechanism for conversion between unpolarized and completely spin-polarized supercurrents. Here, we suggest a conversion mechanism based on electron spin precession together with triplet-pair rotation at interfaces with broken spin-rotation symmetry. In the diffusive limit (short mean free path), the triplet supercurrent is dominated by inter-related odd-frequency s-wave and even-frequency p-wave pairs. In the crossover to the ballistic limit, further symmetry components become relevant. The interface region exhibits a superconducting state of mixed-spin pairs with highly unusual symmetry properties that open up new perspectives for exotic Josephson devices.