Exploration of the High Entropy Alloy Space as a Constraint Satisfaction Problem

High Entropy Alloys (HEAs), Multi-principal Component Alloys (MCA), or Compositionally Complex Alloys (CCAs) are alloys that contain multiple principal alloying elements. While many HEAs have been shown to have unique properties, their discovery has been largely done through costly and time-consuming trial-and-error approaches, with only an infinitesimally small fraction of the entire possible composition space having been explored. In this work, the exploration of the HEA composition space is framed as a Continuous Constraint Satisfaction Problem (CCSP) and solved using a novel Constraint Satisfaction Algorithm (CSA) for the rapid and robust exploration of alloy thermodynamic spaces. The algorithm is used to discover regions in the HEA Composition-Temperature space that satisfy desired phase constitution requirements. The algorithm is demonstrated against a new (TCHEA1) CALPHAD HEA thermodynamic database. The database is first validated by comparing phase stability predictions against experiments and then the CSA is deployed and tested against design tasks consisting of identifying not only single phase solid solution regions in ternary, quaternary and quinary composition spaces but also the identification of regions that are likely to yield precipitation-strengthened HEAs.Comment: 14 pages, 13 figure

Identifying Optimal Equivalent Area Changes to Reduce Sonic Boom Loudness

This work explores the design space created from modeling the effect of localized geometric changes on a supersonic aircraft’s near-field pressure signature. These geometric changes are used to alter the aircraft’s near-field pressure signature in a way that reduces its sonic boom loudness at the ground. The aircraft used in this work is the NASA 25D concept and its near-field pressure signature is modeled using two separate methods. The first method uses the PANAIR panel code to obtain a near-field pressure signature for an axisymmetric representation of the 25D. This near-field signature is propagated to the ground using the NASA sBOOM propagation code and the perceived level in decibels is calculated using an in-house loudness code called PyLdB. The second method uses the equivalent area distribution of the 25D which is passed directly to sBOOM and the perceived level is again found using PyLdB. To model the geometric changes, the axisymmetric geometry and the equivalent area distributions are independently modified with a parameterized Gaussian deformation. These methods are fast enough to quickly explore the design space and find the change in loudness for different deformation parameters. This design space exploration is used to study loudness changes for both on-design conditions and the effects of deviations from on-design angle of attack, Mach number, and azimuth angle. A genetic algorithm is used in subsequent studies to explore the effects of different atmospheric conditions. These results can be used to inform higher fidelity CFD studies and structural adaptation design on the aircraft

A Constraint Satisfaction Algorithm for the Generalized Inverse Phase Stability Problem

Researchers have used the (calculation of phase diagram) CALPHAD method to solve the forward phase stability problem of mapping from specific thermodynamic conditions (material composition, temperature, pressure, etc.) to the associated phase constitution. Recently, optimization has been used to solve the inverse problem: mapping specific phase constitutions to the thermodynamic conditions that give rise to them. These pointwise results, however, are of limited value since they do not provide information about the forces driving the point to equilibrium. In this paper, we investigate the problem of mapping a desirable region in the phase constitution space to corresponding regions in the space of thermodynamic conditions. We term this problem the generalized inverse phase stability problem (GIPSP) and model the problem as a continuous constraint satisfaction problem (CCSP). In this paper, we propose a new CCSP algorithm tailored for the GIPSP. We investigate the performance of the algorithm on Fe-Ti binary alloy system using ThermoCalc with the TCFE7 database against a related algorithm. The algorithm is able to generate solutions for this problem with high performance

Microwave observations of spinning dust emission in NGC6946

We report new cm-wave measurements at five frequencies between 15 and 18GHz of the continuum emission from the reportedly anomalous "region 4" of the nearby galaxy NGC6946. We find that the emission in this frequency range is significantly in excess of that measured at 8.5GHz, but has a spectrum from 15-18GHz consistent with optically thin free-free emission from a compact HII region. In combination with previously published data we fit four emission models containing different continuum components using the Bayesian spectrum analysis package radiospec. These fits show that, in combination with data at other frequencies, a model with a spinning dust component is slightly preferred to those that possess better-established emission mechanisms.Comment: submitted MNRA

Further Sunyaev-Zel'dovich observations of two Planck ERCSC clusters with the Arcminute Microkelvin Imager

We present follow-up observations of two galaxy clusters detected blindly via the Sunyaev-Zel'dovich (SZ) effect and released in the Planck Early Release Compact Source Catalogue. We use the Arcminute Microkelvin Imager, a dual-array 14-18 GHz radio interferometer. After radio source subtraction, we find a SZ decrement of integrated flux density -1.08+/-0.10 mJy toward PLCKESZ G121.11+57.01, and improve the position measurement of the cluster, finding the centre to be RA 12 59 36.4, Dec +60 04 46.8, to an accuracy of 20 arcseconds. The region of PLCKESZ G115.71+17.52 contains strong extended emission, so we are unable to confirm the presence of this cluster via the SZ effect.Comment: 4 tables, 3 figures, revised after referee's comments and resubmitted to MNRA

High resolution AMI Large Array imaging of spinning dust sources: spatially correlated 8 micron emission and evidence of a stellar wind in L675

We present 25 arcsecond resolution radio images of five Lynds Dark Nebulae (L675, L944, L1103, L1111 & L1246) at 16 GHz made with the Arcminute Microkelvin Imager (AMI) Large Array. These objects were previously observed with the AMI Small Array to have an excess of emission at microwave frequencies relative to lower frequency radio data. In L675 we find a flat spectrum compact radio counterpart to the 850 micron emission seen with SCUBA and suggest that it is cm-wave emission from a previously unknown deeply embedded young protostar. In the case of L1246 the cm-wave emission is spatially correlated with 8 micron emission seen with Spitzer. Since the MIR emission is present only in Spitzer band 4 we suggest that it arises from a population of PAH molecules, which also give rise to the cm-wave emission through spinning dust emission.Comment: accepted MNRA