Characterisation of retained energised fragments from explosive devices in military personnel

IntroductionCharacterising the shapes, dimensions and overall numbers of fragments produced by explosive devices is important for determining methods of potential mitigation, such as personal armour. The aim of this investigation was to compare the mass of excised fragments with that predicted from CT to ascertain the validity of using such an approach to measure retained fragments for multiple body areas using CT alone.Method27 retained fragments excised from consecutive patients treated at a US Role 3 Medical Treatment Facility in Afghanistan were examined. Each fragment was measured in three dimensions and the mass was obtained to estimate the density and thereby probable composition. These same excised fragments were identified radiologically and their predicted masses calculated and compared with the known masses with a paired t-test. The total numbers of retained fragments in each of four body areas for 20 casualties were determined radiographically and the mass of the largest fragment in each body region estimated.ResultsExcised fragments were most commonly metallic (17/27, 63%), with masses ranging from 0.008 to 37.6 g. Mean mass predicted from CT was significantly different from than that measured (p=0.133), with CT underestimating true mass by 5%–17%. 889/958 (93%) retained fragments appeared metallic on imaging, with the most commonly affected body areas being the torso and upper extremity (45% of casualties).ConclusionsPredicting the mass of metallic fragments from CT was possible with an error margin of up to 5%, but was less accurate for non-metallic fragments such as stone. Only 3% of fragments were removed through debridement or purposeful excision; these were not just the largest or most superficial. This suggests that future retrospective analysis of the dimensions and predicted masses of retained fragments in larger casualty cohorts of service personnel is potentially feasible within a small margin of error.

Taming the Janssen effect

We investigate both experimentally and theoretically the apparent mass of a ferromagnetic granular assembly filling a cylindrical container and submitted to a magnetic field B, aligned vertically along the silo. We show that the mass of the ferromagnetic granular column depends strongly on the applied magnetic field. Notably, our measurements deviate strongly from the exponential saturation of the measured mass as a function of the true mass of the grain packing, as predicted by Janssen [H.A. Janssen, Vereins Eutscher Ingenieure Zeitschrift, 1045 (1895)]. In particular, the measured mass of tall columns decreases systematically as the amplitude of the magnetic field increases. We rationalize our experimental findings by considering the induced magnetic dipole-dipole interactions within the whole packing. We show the emergence of a global magnetic radial force along the walls of the silos, fully determined by the external magnetic field. The resulting tunable frictional interactions allows a full control of the effective mass of the ferromagnetic granular column.

CODEX Weak Lensing Mass Catalogue and implications on the mass-richness relation

The COnstrain Dark Energy with X-ray clusters (CODEX) sample contains the largest flux limited sample of X-ray clusters at 0.35 < z < 0.65. It was selected from ROSAT data in the 10,000 square degrees of overlap with BOSS, mapping a total number of 2770 high-z galaxy clusters. We present here the full results of the CFHT CODEX program on cluster mass measurement, including a reanalysis of CFHTLS Wide data, with 25 individual lensing-constrained cluster masses. We employ lensfit shape measurement and perform a conservative colour-space selection and weighting of background galaxies. Using the combination of shape noise and an analytic covariance for intrinsic variations of cluster profiles at fixed mass due to large scale structure, miscentring, and variations in concentration and ellipticity, we determine the likelihood of the observed shear signal as a function of true mass for each cluster. We combine 25 individual cluster mass likelihoods in a Bayesian hierarchical scheme with the inclusion of optical and X-ray selection functions to derive constraints on the slope α, normalization β, and scatter σln λ|μ of our richness–mass scaling relation model in log-space: <ln λ|μ > =αμ + β, with μ = ln (M200c/Mpiv), and Mpiv = 1014.81M⊙. We find a slope $\alpha = 0.49^{+0.20}_{-0.15}$, normalization $\exp (\beta ) = 84.0^{+9.2}_{-14.8}$ and $\sigma _{\ln \lambda | \mu } = 0.17^{+0.13}_{-0.09}$ using CFHT richness estimates. In comparison to other weak lensing richness-mass relations, we find the normalization of the richness statistically agreeing with the normalization of other scaling relations from a broad redshift range (0.0 < z < 0.65) and with different cluster selection (X-ray, Sunyaev-Zeldovich, and optical).

Determining the true mass of radial-velocity exoplanets with Gaia

Mass is one of the most important parameters for determining the true nature of an astronomical object. Yet, many published exoplanets lack a measurement of their true mass, in particular those detected as a result of radial-velocity (RV) variations of their host star. For those examples, only the minimum mass, or m sin i, is known, owing to the insensitivity of RVs to the inclination of the detected orbit compared to the plane of the sky. The mass that is given in databases is generally that of an assumed edge-on system (~90°), but many other inclinations are possible, even extreme values closer to 0° (face-on). In such a case, the mass of the published object could be strongly underestimated by up to two orders of magnitude. In the present study, we use GASTON, a recently developed tool taking advantage of the voluminous Gaia astrometric database to constrain the inclination and true mass of several hundreds of published exoplanet candidates. We find nine exoplanet candidates in the stellar or brown dwarf (BD) domain, among which six were never characterized. We show that 30 Ari B b, HD 141937 b, HD 148427 b, HD 6718 b, HIP 65891 b, and HD 16760 b have masses larger than 13.5 MJ at 3σ. We also confirm the planetary nature of 27 exoplanets, including HD 10180 c, d and g. Studying the orbital periods, eccentricities, and host-star metallicities in the BD domain, we found distributions with respect to true masses consistent with other publications. The distribution of orbital periods shows of a void of BD detections below ~100 d, while eccentricity and metallicity distributions agree with a transition between BDs similar to planets and BDs similar to stars in the range 40–50 MJ.

Determining the mass of RV exoplanet candidates using Gaia

<p>Mass is one of the most important parameters for determining the true nature of an astronomical object. Yet, many published exoplanets in on-line database, such as exoplanet.eu or the NASA exoplanet archive, still lacks a measurement of their true mass, in particular those detected thanks to radial velocity (RV) variations of their host star. For those, only the minimum mass, or m sin(i), is known, owing to the insensitivity of RVs to the inclination of the detected orbit compared to the plane-of-the-sky. The mass that is given in database is generally that of an assumed edge-on system (90 degrees), but many other inclinations are likely, even extreme values closer to 0 degree (face-on configuration). In such case, the mass of the published object could be strongly underestimated, even by 1 or 2 orders of magnitude. We used a recently developed tool, called GASTON (Kiefer et al. 2019b & 2019c), to take advantage of the voluminous Gaia astrometric database, in order to constrain the inclination and true mass of several hundreds of published exoplanet candidates (Kiefer et al. 2020, submitted). In this presentation, we will present the method and report on several exoplanet candidates reclassified in the stellar domain, among which unknown brown/M-dwarf. We also confirm the planetary nature of a few tens of candidates.</p>

Discovery and characterization of the exoplanets WASP-148b and c

We present the discovery and characterization of WASP-148, a new extrasolar system that includes at least two giant planets. The host star is a slowly rotating inactive late-G dwarf with a V = 12 magnitude. The planet WASP-148b is a hot Jupiter of 0.72 RJup and 0.29 MJup that transits its host with an orbital period of 8.80 days. We found the planetary candidate with the SuperWASP photometric survey, then characterized it with the SOPHIE spectrograph. Our radial velocity measurements subsequently revealed a second planet in the system, WASP-148c, with an orbital period of 34.5 days and a minimum mass of 0.40 MJup. No transits of this outer planet were detected. The orbits of both planets are eccentric and fall near the 4:1 mean-motion resonances. This configuration is stable on long timescales, but induces dynamical interactions so that the orbits differ slightly from purely Keplerian orbits. In particular, WASP-148b shows transit-timing variations of typically 15 min, making it the first interacting system with transit-timing variations that is detected on ground-based light curves. We establish that the mutual inclination of the orbital plane of the two planets cannot be higher than 35°, and the true mass of WASP-148c is below 0.60 MJup. We present photometric and spectroscopic observations of this system that cover a time span of ten years. We also provide their Keplerian and Newtonian analyses; these analyses should be significantly improved through future TESS observations.

On the detectability of density change in steam-assisted gravity drainage reservoirs using muon tomography

Muon tomography is applied to realistic density models of a steam-assisted gravity drainage (SAGD) reservoir at 1.25 and 5 years after initial reservoir production. Forward models of muon count and opacity based on the density models are computed, as well as inverse models of the synthetic muon observations for various simulated detector arrays. The results demonstrate that both phases of reservoir development, namely the rising phase and the spreading phase, can be resolved by muon detectors placed 30 m below the bitumen reservoir at 230 m total vertical depth. The total mass change in the reservoir was recovered from the inversion model and differs from the true mass change by 20%–29%. The spatial distribution of density change shows very good agreement in the horizontal direction, while the vertical is less well constrained in this modeled sensor array configuration. The inverse models provide improved insights into reservoir depletion patterns and indicate muon tomography to be an applicable tool for continuous reservoir monitoring. The numerical modeling approach developed herein is able to model a wide range of SAGD reservoir geometries and detector arrays toward planning of optimized monitoring solutions.

A low-mass planet candidate orbiting Proxima Centauri at a distance of 1.5 AU

Our nearest neighbor, Proxima Centauri, hosts a temperate terrestrial planet. We detected in radial velocities evidence of a possible second planet with minimum mass mc sin ic = 5.8 ± 1.9M⊕ and orbital period Pc=5.21−0.22+0.26 years. The analysis of photometric data and spectro-scopic activity diagnostics does not explain the signal in terms of a stellar activity cycle, but follow-up is required in the coming years for confirming its planetary origin. We show that the existence of the planet can be ascertained, and its true mass can be determined with high accuracy, by combining Gaia astrometry and radial velocities. Proxima c could become a prime target for follow-up and characterization with next-generation direct imaging instrumentation due to the large maximum angular separation of ~1 arc second from the parent star. The candidate planet represents a challenge for the models of super-Earth formation and evolution.