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  1. ABSTRACT Spirals in protoplanetary discs have been used to locate the potential planet in discs. Since only the spiral shape from a circularly orbiting perturber is known, most previous works assume that the planet is in a circular orbit. We develop a simple semi-analytical method to calculate the shape of the spirals launched by an eccentric planet. We assume that the planet emits wavelets during its orbit, and the wave fronts of these propagating wavelets form the spirals. The resulting spiral shape from this simple method agrees with numerical simulations exceptionally well. The spirals excited by an eccentric planet canmore »detach from the planet, bifurcate, or even cross each other, which are all reproduced by this simple method. The spiral’s bifurcation point corresponds to the wavelet that is emitted when the planet’s radial speed reaches the disc’s sound speed. Multiple spirals can be excited by an eccentric planet (more than five spirals when e ≳ 0.2). The pitch angle and pattern speed are different between different spirals and can vary significantly across one spiral. The spiral wakes launched by high-mass eccentric planets steepen to spiral shocks and the crossing of spiral shocks leads to distorted or broken spirals. With the same mass, a more eccentric planet launches weaker spirals and induces a shallower gap over a long period of time. The observed unusually large/small pitch angles of some spirals, the irregular multiple spirals, and the different pattern speeds between different spirals may suggest the existence of eccentric perturbers in protoplanetary discs.« less
    Free, publicly-accessible full text available January 13, 2023
  2. A novel laser absorption sensing strategy has been developed to evaluate combustion progress through quantitative measurements of carbon dioxide (CO2) in high-pressure (> 50 atm), high-temperature (> 3000 K) hydrocarbon-fueled rocket combustion flows. The sensor enables a broad range of operability by probing rovibrational transitions in the bandhead of CO2 near 4.2 m, accessed with an interband cascade laser. Under extreme rocket conditions, this targeted bandhead region experiences line-mixing effects that favorably distort the molecular spectra. A preliminary spectroscopic model of line-mixing effects has been developed utilizing a high-enthalpy shock tube to achieve scalability of spectral simulations over a rangemore »of high temperatures and high pressures. The model is employed for quantitative interpretation of measured absorption signals. The mid-infrared light source was fiber-coupled for remote light delivery at propulsion test facilities. A wavelength modulation spectroscopy technique utilizing normalized-second harmonic detection was implemented for acquiring differential absorption signals in a harsh rocket combustor environment. Using this method, measurements of CO2 concentration have been demonstrated over a range of operating conditions up to 83 bar in a single-element-injector RP-2/GOx rocket combustor at the Air Force Research Laboratory in Edwards, CA.« less
  3. Abstract The accurate simulation of additional interactions at the ATLAS experiment for the analysis of proton–proton collisions delivered by the Large Hadron Collider presents a significant challenge to the computing resources. During the LHC Run 2 (2015–2018), there were up to 70 inelastic interactions per bunch crossing, which need to be accounted for in Monte Carlo (MC) production. In this document, a new method to account for these additional interactions in the simulation chain is described. Instead of sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the inelastic interactions are presampled, independent of the hardmore »scatter, and stored as combined events. Consequently, for each hard-scatter interaction, only one such presampled event needs to be added as part of the simulation chain. For the Run 2 simulation chain, with an average of 35 interactions per bunch crossing, this new method provides a substantial reduction in MC production CPU needs of around 20%, while reproducing the properties of the reconstructed quantities relevant for physics analyses with good accuracy.« less
    Free, publicly-accessible full text available December 1, 2023
  4. Abstract The ATLAS experiment at the Large Hadron Collider has a broad physics programme ranging from precision measurements to direct searches for new particles and new interactions, requiring ever larger and ever more accurate datasets of simulated Monte Carlo events. Detector simulation with Geant4 is accurate but requires significant CPU resources. Over the past decade, ATLAS has developed and utilized tools that replace the most CPU-intensive component of the simulation—the calorimeter shower simulation—with faster simulation methods. Here, AtlFast3, the next generation of high-accuracy fast simulation in ATLAS, is introduced. AtlFast3 combines parameterized approaches with machine-learning techniques and is deployed tomore »meet current and future computing challenges, and simulation needs of the ATLAS experiment. With highly accurate performance and significantly improved modelling of substructure within jets, AtlFast3 can simulate large numbers of events for a wide range of physics processes.« less
    Free, publicly-accessible full text available December 1, 2023
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  6. Free, publicly-accessible full text available May 1, 2023