Evaluating stream CO2 outgassing via drifting and anchored flux chambers in a controlled flume experiment

Carbon dioxide (CO2) emissions from running waters represent a key component of the global carbon cycle. However, quantifying CO2 fluxes across air-water boundaries remains challenging due to practical difficulties in the estimation of reach-scale standardized gas exchange velocities (k(600)) and water equilibrium concentrations. Whereas craft-made floating chambers supplied by internal CO2 sensors represent a promising technique to estimate CO2 fluxes from rivers, the existing literature lacks rigorous comparisons among differently designed chambers and deployment techniques. Moreover, as of now the uncertainty of k(600) estimates from chamber data has not been evaluated. Here, these issues were addressed by analysing the results of a flume experiment carried out in the Summer of 2019 in the Lunzer:::Rinnen - Experimental Facility (Austria). During the experiment, 100 runs were performed using two different chamber designs (namely, a standard chamber and a flexible foil chamber with an external floating system and a flexible sealing) and two different deployment modes (drifting and anchored). The runs were performed using various combinations of discharge and channel slope, leading to variable turbulent kinetic energy dissipation rates (1.5 x 10(-3) epsilon < 1 x 10(-1) m(2) s(-3)). Estimates of gas exchange velocities were in line with the existing literature (4 < k(600) < 32 m(2) s(-3)), with a general increase in k(600) for larger turbulent kinetic energy dissipation rates. The flexible foil chamber gave consistent k600 patterns in response to changes in the slope and/or the flow rate. Moreover, acoustic Doppler velocimeter measurements indicated a limited increase in the turbulence induced by the flexible foil chamber on the flow field (22 % increase in 8, leading to a theoretical 5 % increase in k(600)). The uncertainty in the estimate of gas exchange velocities was then estimated using a generalized likelihood uncertainty estimation (GLUE) procedure. Overall, uncertainty in k(600) was moderate to high, with enhanced uncertainty in high-energy set-ups. For the anchored mode, the standard deviations of k 6 00 were between 1.6 and 8.2 m d(-1), whereas significantly higher values were obtained in drifting mode. Interestingly, for the standard chamber the uncertainty was larger (+ 20 %) as compared to the flexible foil chamber. Our study suggests that a flexible foil design and the anchored deployment might be useful techniques to enhance the robustness and the accuracy of CO2 measurements in low-order streams. Furthermore, the study demonstrates the value of analytical and numerical tools in the identification of accurate estimations for gas exchange velocities. These findings have important implications for improving estimates of greenhouse gas emissions and reaeration rates in running waters

Ponderomotive light squeezing with atomic cavity optomechanics

Accessing distinctly quantum aspects of the interaction between light and the position of a mechanical object has been an outstanding challenge to cavity-optomechanical systems. Only cold-atom implementations of cavity optomechanics have indicated effects of the quantum fluctuations in the optical radiation pressure force. Here we use such a system, in which quantum photon-number fluctuations significantly drive the center of mass of an atomic ensemble inside a Fabry-Perot cavity. We show that the optomechanical response both amplifies and ponderomotively squeezes the quantum light field. We also demonstrate that classical optical fluctuations can be attenuated by 26 dB or amplified by 20 dB with a weak input pump power of < 40 pW, and characterize the optomechanical amplifier's frequency-dependent gain and phase response in both the amplitude and phase-modulation quadratures

UltraSail - Ultra-Lightweight Solar Sail Concept

UltraSail is a next-generation high-risk, high-payoff sail system for the launch, deployment, stabilization and control of very large (sq km class) solar sails enabling high payload mass fractions for high (Delta)V. Ultrasail is an innovative, non-traditional approach to propulsion technology achieved by combining propulsion and control systems developed for formation-flying micro-satellites with an innovative solar sail architecture to achieve controllable sail areas approaching 1 sq km, sail subsystem area densities approaching 1 g/sq m, and thrust levels many times those of ion thrusters used for comparable deep space missions. Ultrasail can achieve outer planetary rendezvous, a deep space capability now reserved for high-mass nuclear and chemical systems. One of the primary innovations is the near-elimination of sail supporting structures by attaching each blade tip to a formation-flying micro-satellite which deploys the sail, and then articulates the sail to provide attitude control, including spin stabilization and precession of the spin axis. These tip micro-satellites are controlled by 3-axis micro-thruster propulsion and an on-board metrology system. It is shown that an optimum spin rate exists which maximizes payload mass

Cavity Optomechanics in the Quantum Regime

An exciting scientific goal, common to many fields of research, is the development of ever-larger physical systems operating in the quantum regime. Relevant to this dissertation is the objective of preparing and observing a mechanical object in its motional quantum ground state. In order to sense the object's zero-point motion, the probe itself must have quantum-limited sensitivity. Cavity optomechanics, the interactions between light and a mechanical object inside an optical cavity, provides an elegant means to achieve the quantum regime. In this dissertation, I provide context to the successful cavity-based optical detection of the quantum-ground-state motion of atoms-based mechanical elements; mechanical elements, consisting of the collective center-of-mass (CM) motion of ultracold atomic ensembles and prepared inside a high-finesse Fabry-P'erot cavity, were dispersively probed with an average intracavity photon number as small as 0.1. I first show that cavity optomechanics emerges from the theory of cavity quantum electrodynamics when one takes into account the CM motion of one or many atoms within the cavity, and provide a simple theoretical framework to model optomechanical interactions. I then outline details regarding the apparatus and the experimental methods employed, highlighting certain fundamental aspects of optical detection along the way. Finally, I describe background information, both theoretical and experimental, to two published results on quantum cavity optomechanics that form the backbone of this dissertation. The first publication shows the observation of zero-point collective motion of several thousand atoms and quantum-limited measurement backaction on that observed motion. The second publication demonstrates that an array of near-ground-state collective atomic oscillators can be simultaneously prepared and probed, and that the motional state of one oscillator can be selectively addressed while preserving the near-zero-point motion of neighboring oscillators

Kvantifiering av bidrag av turbulens och bubblor till gasutbyte i vattendrag

Aquatic ecosystems exchange gases with the atmosphere and this exchange is critical for many ecosystem processes and the global greenhouse gas cycle. However, it is difficult to determine how fast gases exchange with the atmosphere, especially in running waters where bubbles can speed up the exchange of certain gases. Here, we provide a data set on air-water gas exchange velocities, collected during an outdoor flume experiment. We used experimental stream channels to create a wide range of flow conditions, and tested how these conditions effect the rate at which different gases in the water exchange with the atmosphere. Besides gas exchange velocities for direct air-water exchange and exchange mediated by bubbles, the data set also contains data on, among others, flow conditions, turbulent kinetic energy dissipation rate, bubble flux rate and ambient underwater sound pressure signatures. The experimental design and data are described in articles by Vingiani et al. (2021) and Klaus et al. (2022). main data contributions: (1) Gas exchange velocity estimates based on mass balance of various gases in flume water Concentrations of helium, xenon, argon och methane were measured in the in- and outlet water of the flumes using mass-spectrometry . A mass balance of the gases yielded air-water gas exchange velocities. (2) turbulent kinetic energy dissipation estimates based on Acoustic Doppler Velocimetry Three-dimensional flow velocities were measured at 24 locations per flume using an Acoustic Doppler Velocity meter. Spectral analysis was applied to derives turbulent kinetic energy dissipation rates. (3) sound pressure signatures derived from Hydrophone and microphone recordings Ambient sound was recorded at 12 locations per flume using a hydrophone and a microphone. Spectral analysis was used to derive sound signatures associated with water flow / turbulence and air bubbles.Vattendrag bidrar med viktiga ekosystemtjänster till samhället och många av dessa processer är kopplade till vattendragens utbyte av gaser med atmosfären. Detaljerad kunskap om vilka processer som reglerar detta gasutbyte är dock bristfällig, framförallt rollen av bubblor som kan snabba på utbytet för vissa gaser. Den här databasen innehåller resultat från ett utomhusexperiment i rännor. Vi simulerade ett brett spektrum av flödesförhållanden i dessa rännor och undersökte hur dessa förhållanden påverkar hur snabbt olika gaser släpps från vattnet till atmosfären. Databasen innehåller resultat på gasutbyteshastigheten både för det direkta utbytet mellan vattnet och atmosfären, och det indirekta utbytet genom bubblor. Dessutom finns resultat på bland annat turbulens-, flödes-, och ljudförhållanden i rännorna. Den experimentella designen och datat beskrivs i artiklar av Vingiani et al. (2021) och Klaus et al. (2022). huvudsakliga datakällor/metoder: (1) gasutbyteshastigheter tagit fram genom massbalansberäkningar i rännorna Koncentrationer av helium, xenon, argon och metan har mätts i in- och utloppsvattnet i rännorna med en masspektrometer. en massbalans av gaserna har gjorts för att ta fram gasutbyteshastigheter med atmosfären. (2) turbulens beräknat från tredimensionella flödesmätningar Tredimensionella flödeshastigheter har mätts vid 24 punkter per ränna med en Akustiskt Doppler Velocitymeter och spektralanalys har använts för att beräkna turbulens. (3) ljudtryck mätt med hydrofoner och mikrofoner Ljud har spelats in vid 12 punkter per ränna med hydrofoner och mikrofoner och spektralanalys har använts för att ta fram ljudsignaturer skapat av vattenflödet/turbulens och bubblor