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Compact, eye-safe polarization light detection and ranging system at 1550 nm wavelength for aerosol anomaly detection
No full textThe study of atmospheric aerosols, which are defined as fine particles suspended in the atmosphere, using light detection and ranging (lidar) techniques is well-established. This work presents the real-time measurement of aerosol anomalies (i.e., concentration hotspots) using an eye-safe, portable polarization lidar system operating at a wavelength of 1550 nm. The system, mainly consisting of commercial off-the-shelf components, has a spatial resolution of about 3 m and a weight of less than 10 kg. As a proof of concept, this paper discusses the classification of aerosols and their physical characteristics, as well as the implications of their presence in the atmosphere. Therefore, the aerosols water mist, sand, and Arizona road dust were measured in a distance of 100 m
Assessing residential location and commuting preferences
No full textUnderstanding the interplay between residential location choices and commuting behavior is crucial for addressing urban mobility
and housing policies. This paper introduces a comprehensive survey conducted in Germany, integrating three discrete choice experiments to simultaneously measure preferences for residential locations, commuting distances, and transportation modes. The sample
comprises 1,169 employed respondents, recruited through a professional service provider with quotas based on age, gender, and
residential location. Experiment 1 focused on residential location preferences without considering commuting characteristics, utilizing a Multiple Discrete-Continuous Extreme Value (MDCEV) model to assess budget allocations for various dwelling attributes.
Results indicate that the quality of the residential area holds greater significance than the specific place of residence. Experiments
2 and 3 explored the trade-offs between dwelling characteristics and commuting time, alongside mode choice preferences. These
experiments revealed that while dwelling attributes are prioritized over commuting duration, commuting time remains a significant factor in residential decisions. Notably, teleworking scenarios were associated with a reduction in the Value of Travel Time
Savings (VTTS) for commuting, highlighting the diminishing burden of travel time for remote workers. The three experiments
build progressively from housing preferences to commuting trade-offs and mode choices. Together, they reveal how residential
and mobility decisions interact. The findings contribute valuable insights for integrating residential location and travel demand
models, emphasizing the impact of teleworking on future commuting patterns. Future work will focus on joint model estimations
and further integration into predictive models to inform integrated land-use and transport planning policies
Design of a rotary kiln solar particle receiver for pyrolysis application
No full textDesign of solar rotary kiln receiver for heating of particle heat carriers, which are coupled in a biomass pyrolysis proces
Design and Implementation of an alternative Azimuth Interpolation Scheme for Staggered-SAR FPGA Processing
No full textGround-based experimental study on the contamination potential of a freely expanding 10 N bi-propellant thruster plume
Full text linkSatellite thruster plume constituents pose a challenge when it comes to estimating their potential to degrade or contaminate spacecraft surfaces. Therefore, ESA has commissioned a study that covers the characterization of a European bi-propellant attitude control thruster plume and its potential contamination impact. In this regard, a freely expanding 10 N MMH/MON bi-propellant thruster plume is investigated in this ground-based experimental campaign. Methods of investigation include quartz-crystal microbalance (QCM) and mass spectrometry (MS) measurements. QCM experiments supply data on mass flux as well as desorption rates at temperatures ranging from 80 to 300K, which help to estimate the impact of plume gas on surfaces of different temperatures. Additionally, MS measurements map the chemical composition of gaseous plume species under a wide range of angles, spanning from plume centerline to the backflow region. The optical and chemical analysis of actual spacecraft surface material witness coupons that were exposed to the plume complements this study. Furthermore, high-speed imaging of the thruster nozzle supports the interpretation of results with information on ejected droplet velocities, trajectories and size distribution, especially regarding potential droplet impact features which were identified on witness materials in this on-going study
Engineering a large-scale data analytics and array computing library for research: Heat
Full text linkHeat is a Python library for massively-parallel and GPU-accelerated array computing and machine learning. It is developed by researchers for researchers, with the ultimate goal to make multi-dimensional array processing and machine learning for scientists (almost) as easy on a supercomputer as it is on a workstation with NumPy or scikit-learn. This paper highlights the relevance of this project to the research software engineering community by giving a short, but illustrative overview of Heat and discusses its role in the context of related libraries with a specific focus on its research software aspects
Comparison of high performance hybrid variable reluctance fast steering mirrors
Full text linkActuated mirrors are a key element in free-space
optical communications. This paper compares the two high
performance, commercially available actuators with a hybrid
variable reluctance drive principle. They feature a mechanical
range of up to 3 degrees and achieve closed-loop bandwidths
of more than 1 kHz in combination with eddy-current sensors.
It is shown, that the choice of driver is closely linked to their
achievable dynamics. In particular, the performance in the application area of optical communication on satellites is analyzed.
Therefore, in addition to the dynamic properties, the integration,
their power consumption and suppression of vibrations is also
being considered. To ensure comparability, a parameter tuning
algorithm is used. The breadboard utilizes the same control
software and hardware for both devices. The FSM20B shows
better passive rejection against external vibrations, a lower
average power consumption, and allows the exchange of its
angular sensors. The FSM3000 achieves a better steady-state
jitter, features a larger operating range and is more compact
in size with precalibrated, internal sensors
Isotopologue dependence of the CO2-air broadening and shifting coefficients: Experimental evidence and comparison with theory for 13CO2 and 12CO2
No full textFifteen transitions of the 20012-00001 band of 13CO2 in air have been recorded at 296 K using a cavity ring-down spectrometer linked to an optical frequency comb referenced to a GPS-disciplined Rb oscillator. In parallel, measurements of 12CO2 in air were made with a Fourier transform spectrometer for transitions belonging to the 20012-00001 band, enabling comparison of the air-induced half-width and line shift coefficients of both isotopologues. For that a multi-spectrum fit procedure is adopted with a Hartmann-Tran (HT) line profile. A decrease of about 0.4% is demonstrated for the 13CO2 air-broadening coefficients compared to the corresponding value of the main isotopologue. To the best of our knowledge, this observation is the first experimental evidence of an isotopic effect on the air-broadening coefficients in CO2 (which are generally assumed to be identical in spectroscopic databases).
On the theoretical side, a refinement to the simple model described in [Lamouroux et al. JQSRT 111;2010:2321] is proposed which enables the determination of γ(13CO2) from γ(12CO2). In addition, complex
Robert-Bonamy-Ma (CRBM) calculations have been performed for 12CO2 and 13CO2 in collision with N2 or O2 for the 20012-00001 band with J” values from 0 to 85. From these CRBM data, the 13CO2-air and 12CO2-air halfwidth and line shift coefficients were computed and the obtained isotopologue effect on these parameters was compared to the experimental data. A good average agreement is achieved for the CRBM calculations for the airbroadening coefficients while the simple model leads to slightly smaller isotopic effect. In contrast, for the airpressure shift coefficients, a quite large disagreement is observed between the calculations and the experimental data
The troublesome kernel: on hallucinations, no free lunches and the accuracy-stability trade-off in inverse problems
No full textMethods inspired by Artificial Intelligence (AI) are starting to fundamentally change computational science and engineering through breakthrough performances on challenging problems. However, reliability and trustworthiness of such techniques is a major concern. In inverse problems in imaging, the focus of this paper, there is increasing empirical evidence that methods may suffer from hallucinations, i.e., false, but realistic-looking artifacts; instability, i.e., sensitivity to perturbations in the data; and unpredictable generalization, i.e., excellent performance on some images, but significant deterioration on others. This paper provides a theoretical foundation for these phenomena. We give mathematical explanations for how and when such effects arise in arbitrary reconstruction methods, with several of our results taking the form of `no free lunch' theorems. Specifically, we show that (i) methods that overperform on a single image can wrongly transfer details from one image to another, creating a hallucination, (ii) methods that overperform on two or more images can hallucinate or be unstable, (iii) optimizing the accuracy-stability trade-off is generally difficult, (iv) hallucinations and instabilities, if they occur, are not rare events, and may be encouraged by standard training, (v) it may be impossible to construct optimal reconstruction maps for certain problems. Our results trace these effects to the kernel of the forward operator whenever it is nontrivial, but also apply to the case when the forward operator is ill-conditioned. Based on these insights, our work aims to spur research into new ways to develop robust and reliable AI-based methods for inverse problems in imaging
The Cognitive Challenges of Aviation: Exploring the Demands on Pilots and Air Traffic Controllers.
No full textThe field of aviation neuropsychology helps us to understand and improve human performance and safety in the aerospace industry, both for the estimated 300,000+ commercial pilots and the 4.5 billion passengers they transport every year. This handbook brings together a group of internationally renowned academic and industry experts to provide a comprehensive overview of the background, goals, principles, challenges, and associated practice skills and research themes of aviation neuropsychology