The JCMT BISTRO Survey: Studying the Complex Magnetic Field of L43

We present observations of polarized dust emission at 850 μm from the L43 molecular cloud, which sits in the Ophiuchus cloud complex. The data were taken using SCUBA-2/POL-2 on the James Clerk Maxwell Telescope as a part of the BISTRO large program. L43 is a dense (NH 10 22 2 ~ –1023 cm−2) complex molecular cloud with a submillimeter-bright starless core and two protostellar sources. There appears to be an evolutionary gradient along the isolated filament that L43 is embedded within, with the most evolved source closest to the Sco OB2 association. One of the protostars drives a CO outflow that has created a cavity to the southeast. We see a magnetic field that appears to be aligned with the cavity walls of the outflow, suggesting interaction with the outflow. We also find a magnetic field strength of up to ∼160 ± 30 μG in the main starless core and up to ∼90 ± 40 μG in the more diffuse, extended region. These field strengths give magnetically super- and subcritical values, respectively, and both are found to be roughly trans-Alfvénic. We also present a new method of data reduction for these denser but fainter objects like starless cores

The JCMT BISTRO Survey: Studying the Complex Magnetic Field of L43

We present observations of polarized dust emission at 850 μm from the L43 molecular cloud, which sits in the Ophiuchus cloud complex. The data were taken using SCUBA-2/POL-2 on the James Clerk Maxwell Telescope as a part of the BISTRO large program. L43 is a dense ( NH2∼1022 –1023 cm−2) complex molecular cloud with a submillimeter-bright starless core and two protostellar sources. There appears to be an evolutionary gradient along the isolated filament that L43 is embedded within, with the most evolved source closest to the Sco OB2 association. One of the protostars drives a CO outflow that has created a cavity to the southeast. We see a magnetic field that appears to be aligned with the cavity walls of the outflow, suggesting interaction with the outflow. We also find a magnetic field strength of up to ∼160 ± 30 μG in the main starless core and up to ∼90 ± 40 μG in the more diffuse, extended region. These field strengths give magnetically super- and subcritical values, respectively, and both are found to be roughly trans-Alfvénic. We also present a new method of data reduction for these denser but fainter objects like starless cores

The JCMT BISTRO Survey: A Spiral Magnetic Field in a Hub-filament Structure, Monoceros R2

We present and analyze observations of polarized dust emission at 850 μm toward the central 1 × 1 pc hub-filament structure of Monoceros R2 (Mon R2). The data are obtained with SCUBA-2/POL-2 on the James Clerk Maxwell Telescope (JCMT) as part of the B-fields in Star-forming Region Observations survey. The orientations of the magnetic field follow the spiral structure of Mon R2, which are well described by an axisymmetric magnetic field model. We estimate the turbulent component of the magnetic field using the angle difference between our observations and the best-fit model of the underlying large-scale mean magnetic field. This estimate is used to calculate the magnetic field strength using the Davis–Chandrasekhar–Fermi method, for which we also obtain the distribution of volume density and velocity dispersion using a column density map derived from Herschel data and the C18O (J = 3 − 2) data taken with HARP on the JCMT, respectively. We make maps of magnetic field strengths and mass-to-flux ratios, finding that magnetic field strengths vary from 0.02 to 3.64 mG with a mean value of 1.0 ± 0.06 mG, and the mean critical mass-to-flux ratio is 0.47 ± 0.02. Additionally, the mean Alfvén Mach number is 0.35 ± 0.01. This suggests that, in Mon R2, the magnetic fields provide resistance against large-scale gravitational collapse, and the magnetic pressure exceeds the turbulent pressure. We also investigate the properties of each filament in Mon R2. Most of the filaments are aligned along the magnetic field direction and are magnetically subcritical

Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Prévision de l'effet de la taille de grain sur les traitements thermochimiques

Les matériaux nanocristallins présentent des propriétés de diffusion accrues dues à leur forte densité de joints de grain. Afin de maitriser totalement le processus de diffusion lors de traitements thermochimiques de tels matériaux, ces travaux s'attachent à donner un modèle de coefficient de diffusion macroscopique en fonction de la taille et de la forme des grain dans un polycristal. Ils s'appuient sur une technique d'homogénéisation effectuée après une analyse par éléments finis sur des volumes élémentaires représentatifs. On construit ainsi une expression analytique du coefficient de diffusion macroscopique en fonction de la taille de grain et de la surface de joints de grain projetée sur la direction de diffusion. Par une analyse de schémas élémentaires en deux dimensions, on extrapole le modèle trouvé à toute microstructure périodique

Finite element analysis of the grain size effect on diffusion in polycrystalline materials

International audiencePolycrystalline materials with refined grain size are well known to have enhanced diffusion properties compared to coarse grain materials. Due to their high grain boundary density, the macroscopic diffusivity of such materials is increased. Indeed, grain boundaries are fast diffusion channels in the material. In this paper, a numerical method to calculate the diffusivity of polycrystalline materials as a function of their grain size is proposed. A homogenization technique is applied on polycrystalline representative volume elements on which diffusion calculations are performed with a finite element method. This technique allows to extract the effective diffusivity of the material for different grain sizes. A relationship is then built between the diffusivity and the grain size. It is shown that the extracted diffusivity follows a mixture law of both diffusivities in the grains and grain boundaries, as proposed by Hart [14], but taking into account grain boundaries randomly oriented compared to the diffusion direction

Effect of the nanocrystallization on pure iron nitriding kinetics

International audienceGas nitriding has been used to improve the mechanical properties and corrosion resistance of components made of steel. This thermochemical surface treatment is performed using a flowing NH3, N2 gas mixture. The gas nitriding is usually performed at a temperature between 500 to 580°C for typically durations of 20 to 80h which involve very long cycle times. A pre-treatment of the sample surface by shot peening can be applied to produce nanocrystalline grains. This surface treatment enhances the nitrogen diffusion.The purpose of our study is to investigate the effect of nanocrystallization of pure iron samples on nitriding kinetics. Pure iron samples obtained by cold crucible melting have been submitted to short duration or long duration NanoPeening&#174 treatments. The samples are cuts in 5 mm thick pins in the cylindrical ingots (diameter 11 mm). Both sides of the pins receive the shot peening treatment. The pins are then cutted under water into 1 mm thick disks. The untreated surface is polished with SiC abrasive paper. For comparison, untreated shot peening iron disks (NG) are also prepared. The gas nitriding isothermal tests are performed at 500°C under NH3, N2, He mixture in a SETARAM TAG 24 thermobalance. The nitriding durations vary from 10 to 210 minutes. After the gas nitriding, the samples are first analysed by XRD. The nitrogen profiles are measured by GDOES (Glow Discharge Optical Emission Spectrometry). Finally, the machining and cross sectional electronics views of the samples are achieved in a FIB (Focused Ion Beam)