13,621 research outputs found
HEAL-SWIN: A Vision Transformer On The Sphere
High-resolution wide-angle fisheye images are becoming more and more
important for robotics applications such as autonomous driving. However, using
ordinary convolutional neural networks or vision transformers on this data is
problematic due to projection and distortion losses introduced when projecting
to a rectangular grid on the plane. We introduce the HEAL-SWIN transformer,
which combines the highly uniform Hierarchical Equal Area iso-Latitude
Pixelation (HEALPix) grid used in astrophysics and cosmology with the
Hierarchical Shifted-Window (SWIN) transformer to yield an efficient and
flexible model capable of training on high-resolution, distortion-free
spherical data. In HEAL-SWIN, the nested structure of the HEALPix grid is used
to perform the patching and windowing operations of the SWIN transformer,
resulting in a one-dimensional representation of the spherical data with
minimal computational overhead. We demonstrate the superior performance of our
model for semantic segmentation and depth regression tasks on both synthetic
and real automotive datasets. Our code is available at
https://github.com/JanEGerken/HEAL-SWIN.Comment: Main body: 10 pages, 7 figures. Appendices: 4 pages, 2 figure
Technology for Low Resolution Space Based RSO Detection and Characterisation
Space Situational Awareness (SSA) refers to all activities to detect, identify and track objects in Earth orbit. SSA is critical to all current and future space activities and protect space assets by providing access control, conjunction warnings, and monitoring status of active satellites. Currently SSA methods and infrastructure are not sufficient to account for the proliferations of space debris. In response to the need for better SSA there has been many different areas of research looking to improve SSA most of the requiring dedicated ground or space-based infrastructure. In this thesis, a novel approach for the characterisation of RSO’s (Resident Space Objects) from passive low-resolution space-based sensors is presented with all the background work performed to enable this novel method. Low resolution space-based sensors are common on current satellites, with many of these sensors being in space using them passively to detect RSO’s can greatly augment SSA with out expensive infrastructure or long lead times. One of the largest hurtles to overcome with research in the area has to do with the lack of publicly available labelled data to test and confirm results with. To overcome this hurtle a simulation software, ORBITALS, was created. To verify and validate the ORBITALS simulator it was compared with the Fast Auroral Imager images, which is one of the only publicly available low-resolution space-based images found with auxiliary data. During the development of the ORBITALS simulator it was found that the generation of these simulated images are computationally intensive when propagating the entire space catalog. To overcome this an upgrade of the currently used propagation method, Specialised General Perturbation Method 4th order (SGP4), was performed to allow the algorithm to run in parallel reducing the computational time required to propagate entire catalogs of RSO’s. From the results it was found that the standard facet model with a particle swarm optimisation performed the best estimating an RSO’s attitude with a 0.66 degree RMSE accuracy across a sequence, and ~1% MAPE accuracy for the optical properties. This accomplished this thesis goal of demonstrating the feasibility of low-resolution passive RSO characterisation from space-based platforms in a simulated environment
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
On the importance of low-frequency signals in functional and molecular photoacoustic computed tomography
In photoacoustic computed tomography (PACT) with short-pulsed laser
excitation, wideband acoustic signals are generated in biological tissues with
frequencies related to the effective shapes and sizes of the optically
absorbing targets. Low-frequency photoacoustic signal components correspond to
slowly varying spatial features and are often omitted during imaging due to the
limited detection bandwidth of the ultrasound transducer, or during image
reconstruction as undesired background that degrades image contrast. Here we
demonstrate that low-frequency photoacoustic signals, in fact, contain
functional and molecular information, and can be used to enhance structural
visibility, improve quantitative accuracy, and reduce spare-sampling artifacts.
We provide an in-depth theoretical analysis of low-frequency signals in PACT,
and experimentally evaluate their impact on several representative PACT
applications, such as mapping temperature in photothermal treatment, measuring
blood oxygenation in a hypoxia challenge, and detecting photoswitchable
molecular probes in deep organs. Our results strongly suggest that
low-frequency signals are important for functional and molecular PACT
Modelling, Monitoring, Control and Optimization for Complex Industrial Processes
This reprint includes 22 research papers and an editorial, collected from the Special Issue "Modelling, Monitoring, Control and Optimization for Complex Industrial Processes", highlighting recent research advances and emerging research directions in complex industrial processes. This reprint aims to promote the research field and benefit the readers from both academic communities and industrial sectors
A review of coarse mineral dust in the Earth system
Mineral dust particles suspended in the atmosphere span more than three orders of magnitude in diameter, from <0.1 µm to more than 100 µm. This wide size range makes dust a unique aerosol species with the ability to interact with many aspects of the Earth system, including radiation, clouds, hydrology, atmospheric chemistry, and biogeochemistry. This review focuses on coarse and super-coarse dust aerosols, which we respectively define as dust particles with a diameter of 2.5–10 µm and 10–62.5 µm. We review several lines of observational evidence indicating that coarse and super-coarse dust particles are transported farther than previously expected and that the abundance of these particles is substantially underestimated in current global models. We synthesize previous studies that used observations, theories, and model simulations to highlight the impacts of coarse and super-coarse dust aerosols on the Earth system, including their effects on dust-radiation interactions, dust-cloud interactions, atmospheric chemistry, and biogeochemistry. Specifically, coarse and super-coarse dust aerosols produce a net positive direct radiative effect (warming) at the top of the atmosphere and can modify temperature and water vapor profiles, influencing the distribution of clouds and precipitation. In addition, coarse and super-coarse dust aerosols contribute a substantial fraction of ice-nucleating particles, especially at temperatures above –23 °C. They also contribute a substantial fraction to the available reactive surfaces for atmospheric processing and the dust deposition flux that impacts land and ocean biogeochemistry by supplying important nutrients such as iron and phosphorus. Furthermore, we examine several limitations in the representation of coarse and super-coarse dust aerosols in current model simulations and remote-sensing retrievals. Because these limitations substantially contribute to the uncertainties in simulating the abundance and impacts of coarse and super-coarse dust aerosols, we offer some recommendations to facilitate future studies. Overall, we conclude that an accurate representation of coarse and super-coarse properties is critical in understanding the impacts of dust aerosols on the Earth system
The electron-gamma coincidence set-up at the S-DALINAC
This work describes the development, construction and commissioning of a new setup for (e,e'γ)-coincidence measurements at the superconducting Darmstadt linear accelerator S-DALINAC. (e,e'γ) reactions are characterized by the pure electromagnetic interaction in the excitation and in the decay channels and thereby allow nuclear physics investigations with high precision. In contrast to inclusive electron scattering, this measurement method is directly sensitive to the interference of longitudinal and transverse form factors, which affects the angular distribution of the emitted photons.
To establish the new (e,e’γ) setup, the existing large acceptance QCLAM electron spectrometer was combined with a new setup consisting of LaBr_3:Ce detectors. For the readout of the γ-ray detectors, a new data acquisition system was developed and combined with the existing QCLAM data acquisition system to form a coincidence data acquisition. A software package for data analysis was developed.
In the first commissioning experiment on the 2_1^+ and 1_2^+ states of 12C, the functionality of the (e,e'γ)-setup could be demonstrated. Findings from this and from a second commissioning experiment on 96Ru, together with GEANT4 simulations, were used to optimize the setup with a particular focus on the reduction of background radiation in the γ-ray detectors. The full and optimized setup was used in a first production run on a 96Ru target to measure the γ-decay behavior below and above the neutron separation threshold. Isolated states were observed to decay via the 2_1^+ state of 96Ru. Above the neutron separation threshold, 96Ru decays by emission of a neutron to 95Ru. Depopulations of the low-lying states of 95Ru were observed
Edge-resolved non-line-of-sight imaging
Over the past decade, the possibility of forming images of objects hidden from line-of-sight (LOS) view has emerged as an intriguing and potentially important expansion of computational imaging and computer vision technology. This capability could help soldiers anticipate danger in a tunnel system, autonomous vehicles avoid collision, and first responders safely traverse a building. In many scenarios where non-line-of-sight (NLOS) vision is desired, the LOS view is obstructed by a wall with a vertical edge. In this thesis we show that through modeling and computation, the impediment to LOS itself can be exploited for enhanced resolution of the hidden scene.
NLOS methods may be active, where controlled illumination of the hidden scene is used, or passive, relying only on already present light sources. In both active and passive NLOS imaging, measured light returns to the sensor after multiple diffuse bounces. Each bounce scatters light in all directions, eliminating directional information. When the scene is hidden behind a wall with a vertical edge, that edge occludes light as a function of its incident azimuthal angle around the edge. Measurements acquired on the floor adjacent to the occluding edge thus contain rich azimuthal information about the hidden scene. In this thesis, we explore several edge-resolved NLOS imaging systems that exploit the occlusion provided by a vertical edge. In addition to demonstrating novel edge-resolved NLOS imaging systems with real experimental data, this thesis includes modeling, performance bound analyses, and inversion algorithms for the proposed systems.
We first explore the use of a single vertical edge to form a 1D (in azimuthal angle) reconstruction of the hidden scene. Prior work demonstrated that temporal variation in a video of the floor may be used to image moving components of the hidden scene. In contrast, our algorithm reconstructs both moving and stationary hidden scenery from a single photograph, without assuming uniform floor albedo. We derive a forward model that describes the measured photograph as a nonlinear combination of the unknown floor albedo and the light from behind the wall. The inverse problem, which is the joint estimation of floor albedo and a 1D reconstruction of the hidden scene, is solved via optimization, where we introduce regularizers that help separate light variations in the measured photograph due to floor pattern and hidden scene, respectively.
Next, we combine the resolving power of a vertical edge with information from the relationship between intensity and radial distance to form 2D reconstructions from a single passive photograph. We derive a new forward model, accounting for radial falloff, and propose two inversion algorithms to form 2D reconstructions from a single photograph of the penumbra. The performances of both algorithms are demonstrated on experimental data corresponding to several different hidden scene configurations. A Cramer-Rao bound analysis further demonstrates the feasibility and limitations of this 2D corner camera.
Our doorway camera exploits the occlusion provided by the two vertical edges of a doorway for more robust 2D reconstruction of the hidden scene. This work provides and demonstrates a novel inversion algorithm to jointly estimate two views of change in the hidden scene, using the temporal difference between photographs acquired on the visible side of the doorway. A Cramer-Rao bound analysis is used to demonstrate the 2D resolving power of the doorway camera over other passive acquisition strategies and to motivate the novel biangular reconstruction grid.
Lastly, we present the active corner camera. Most existing active NLOS methods illuminate the hidden scene using a pulsed laser directed at a relay surface and collect time-resolved measurements of returning light. The prevailing approaches are inherently limited by the need for laser scanning, a process that is generally too slow to image hidden objects in motion. Methods that avoid laser scanning track the moving parts of the hidden scene as one or two point targets. In this work, based on more complete optical response modeling yet still without multiple illumination positions, we demonstrate accurate reconstructions of objects in motion and a `map’ of the stationary scenery behind them. This new ability to count, localize, and characterize the sizes of hidden objects in motion, combined with mapping of the stationary hidden scene could greatly improve indoor situational awareness in a variety of applications
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Dynamics, Pathways, and Regulation of Exocytotic Release
Exocytosis involves fusion between a membrane-bound vesicle containing signaling moleculesand the plasma membrane of the cell. Cells use exocytosis to release membrane-impermeant bioactive molecules to the extracellular space, and to deliver lipids and proteins to the plasma membrane. Exocytosis is essential to many fundamental processes including neurotransmission and hormone secretion. Exocytosis is triggered and regulated by a range of cellular components including calcium, SNARE proteins, and the actin cortex. Despite of the accumulative discovery of molecules involved in exocytosis, a unified physical landscape that these molecules act on is missing. The biophysical forces driving exocytosis haven’t been identified, and the mechanisms by which these biophysical forces regulate exocytosis are not established.
To address these unsolved questions, we built mathematical model to study exocytosis on the single-vesicle level and the cell level. In the first chapter of the thesis we modeled the shape evolution of dense-core vesicles in chromaffin cells during exocytosis. Emerged from the model, we discovered a novel mechanism that drives vesicles to merge into the plasma membrane. Following fusion, the osmotic pressure of the cell squeezes the vesicle and abolishes the vesicle membrane tension, and the high plasma membrane tension reels the vesicle onto the adjacent cytoskeleton. With no fitting parameters, the model predicted remarkable vesicle shapes consistent with real-time visualizations by super-resolution microscopy from the Wu lab. Interestingly, we predicted vesicles to adopt elongated tubular shapes under mildly high osmotic pressure, which was confirmed by visualizations from the Wu lab, providing a vivid illustration of osmotic squeezing.
In the second chapter of the thesis we investigated fusion pores, the membrane connection between a fused vesicle and the plasma membrane. As commonly observed in amperometric traces, the initially small pore may subsequently dilate for full contents release. Here using formalisms of differential geometry, we obtained exact solutions for fusion pores between two membranes. We found three families: a narrow pore, a wide pore and an intermediate tether-like pore. We suggest membrane fusion initially generates a stable narrow pore, and the dilation pathway is a transition to the stable wide pore family. The unstable intermediate pore is the transition state that sets the energy barrier for this dilation pathway. Pore dilation is mechanosensitive, as the energy barrier is lowered by increased membrane tension. Finally, we showed fusion pores are locked into the narrow pore family in nanodisc-based experiments, powerful systems for the study of individual pores.
In the third chapter of the thesis we investigated the mechanism of spatiotemporal regulation of exocytosis on the cell level. By analyzing the spatiotemporal profile of exocytosis events in chromaffin cells observed by confocal microcopy from the Wu lab, we discovered a novel mechanism of exocytosis regulation via release site availability. We found vesicle fusion can happen repeatedly at hotspots, which generated a membrane reservoir consisting of unmerged and slowly merged vesicles that are spatially close to hotspots. In turn, unmerged vesicles occupy release sites and locally suppress exocytosis frequency. We developed a mathematical model to demonstrate that such membrane reservoir requires sufficiently low local membrane tension that abolishes the driving force of vesicle merger.
Finally, in the fourth chapter of the thesis we studied virus entry, a process similar to exocytosis but involves membrane fusion between the virus and the host cell. SARS-CoV-2 entry in to host cells is accomplished by the S2 subunit of the spike S protein by capture of the host cell membrane and fusion with the viral envelope. Membrane capture requires the native S2 to transit to its potent, fusogenic form, the fusion intermediate, whose structure is unknown. Here, we computationally constructed a full-length model of the CoV-2 fusion intermediate by extrapolating from known CoV-2 pre- and postfusion structures. In atomistic and coarse-grained molecular dynamics simulations the fusion intermediate was remarkably flexible and executed large bending and extensional fluctuations due to three hinges in the C-terminal base. The large configurational fluctuations of the fusion intermediate generated a substantial exploration volume that aided capture of the target membrane. Simulations suggested a host cell membrane capture time of ~ 2 ms. Our simulated structures of the fusion intermediate showed good agreement with cryo-electron tomography data from the Moscona’s lab
Safe Autonomous Driving in Adverse Weather: Sensor Evaluation and Performance Monitoring
The vehicle's perception sensors radar, lidar and camera, which must work
continuously and without restriction, especially with regard to
automated/autonomous driving, can lose performance due to unfavourable weather
conditions. This paper analyzes the sensor signals of these three sensor
technologies under rain and fog as well as day and night. A data set of a
driving test vehicle as an object target under different weather conditions was
recorded in a controlled environment with adjustable, defined, and reproducible
weather conditions. Based on the sensor performance evaluation, a method has
been developed to detect sensor degradation, including determining the affected
data areas and estimating how severe they are. Through this sensor monitoring,
measures can be taken in subsequent algorithms to reduce the influences or to
take them into account in safety and assistance systems to avoid malfunctions.Comment: Accepted for the 35th IEEE Intelligent Vehicles Symposium (IV 2023),
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