Robust hybridization gap in the Kondo insulator YbB12 probed by femtosecond optical spectroscopy

In heavy fermions the relaxation dynamics of photoexcited carriers has been found to be governed by the low energy indirect gap Eg resulting from hybridization between localized moments and conduction band electrons. Here, carrier relaxation dynamics in a prototype Kondo insulator YbB12 is studied over a large range of temperatures and over three orders of magnitude. We utilize the intrinsic nonlinearity of dynamics to quantitatively determine microscopic parameters, such as electron-hole recombination rate. The extracted value reveals that hybridization is accompanied by a strong charge transfer from localized 4 f levels. The results imply the presence of a hybridization gap up to temperatures of the order of Eg/kB ≈ 200 K, which is extremely robust against electronic excitation. Finally, below 20 K the data reveal changes in the low energy electronic structure, attributed to short-range antiferromagnetic correlations between the localized levels

Exploring the links between star formation and minor companions around isolated galaxies

Previous studies have shown that galaxies with minor companions exhibit an elevated star formation rate. We reverse this inquiry, constructing a volume-limited sample of \simL\star (Mr \leq -19.5 + 5 log h) galaxies from the Sloan Digital Sky Survey that are isolated with respect to other luminous galaxies. Cosmological simulations suggest that 99.8% of these galaxies are alone in their dark matter haloes with respect to other luminous galaxies. We search the area around these galaxies for photometric companions. Matching strongly star forming (EW(H{\alpha})\geq 35 \AA) and quiescent (EW(H{\alpha})< 35 \AA) samples for stellar mass and redshift using a Monte Carlo resampling technique, we demonstrate that rapidly star-forming galaxies are more likely to have photometric companions than other galaxies. The effect is relatively small; about 11% of quiescent, isolated galaxies have minor photometric companions at radii \leq 60 kpc h$^{-1}$ kpc while about 16% of strongly star-forming ones do. Though small, the cumulative difference in satellite counts between strongly star-forming and quiescent galaxies is highly statistically significant (PKS = 1.350 \times10$^{-3}$) out to to radii of \sim 100 h$^{-1}$ kpc. We discuss explanations for this excess, including the possibility that \sim 5% of strongly star-forming galaxies have star formation that is causally related to the presence of a minor companion.Comment: 7 pages, 6 figures, submitted to MNRA

DESIGN FOR A FAST, XFEL-QUALITY WIRE SCANNER

Abstract RadiaBeam Technologies has designed and manufactured a new wire scanner for high-speed emittance measurements of XFEL-type beams of energy 139 MeV. Using three 25-micron thick tungsten wires, this wire scanner measures vertical and horizontal beam size as well as transverse spatial correlation in one pass. The intensity of the beam at a wire position is determined from emitted bremsstrahlung photons as measured by a BGO scintillator system. The wires are transported on a two-ended support structure moved by a ball-screw linear stage. The doubleended structure reduces vibrations in the wire holder, and the two-bellows design negates the effects of air pressure on the motion. The expected minimum beam size measurable by this system is on the order of 10 microns with 0.1-micron accuracy. To achieve this, new algorithms are presented that reduce the effect of the non-zero thickness of the wire on the wire scan output. In addition, novel calculations are presented for determining the elliptical geometric parameters (vertical and horizontal beam size and correlation, or alternatively, the axis lengths and rotation) of the beam from the wire scanner measurements

Time- and momentum-resolved photoemission studies using time-of-flight momentum microscopy at a free-electron laser

Time-resolved photoemission with ultrafast pump and probe pulses is an emerging technique with wide application potential. Real-time recording of nonequilibrium electronic processes, transient states in chemical reactions, or the interplay of electronic and structural dynamics offers fascinating opportunities for future research. Combining valence-band and core-level spectroscopy with photoelectron diffraction for electronic, chemical, and structural analyses requires few 10 fs soft X-ray pulses with some 10 meV spectral resolution, which are currently available at high repetition rate free-electron lasers. We have constructed and optimized a versatile setup commissioned at FLASH/PG2 that combines free-electron laser capabilities together with a multidimensional recording scheme for photoemission studies. We use a full-field imaging momentum microscope with time-of-flight energy recording as the detector for mapping of 3D band structures in (kx, ky, E) parameter space with unprecedented efficiency. Our instrument can image full surface Brillouin zones with up to 7 Å−1 diameter in a binding-energy range of several eV, resolving about 2.5 × 105 data voxels simultaneously. Using the ultrafast excited state dynamics in the van der Waals semiconductor WSe2 measured at photon energies of 36.5 eV and 109.5 eV, we demonstrate an experimental energy resolution of 130 meV, a momentum resolution of 0.06 Å−1, and a system response function of 150 fs

The globular cluster system of the Milky Way: accretion in a cosmological context

We examine the significance of a planar arrangement in the spatial distribution of the Milky Way's globular clusters (GCs). We find that, when separated on the basis of horizontal branch morphology and metallicity, the outer-most canonical young halo GC sample (at galactocentric radii in excess of 10 kpc) exhibit an anisotropic distribution that may be equated to a plane (24 +/- 4) kpc thick (rms) and inclined at 8 degrees +/- 5 degrees to the polar axis of the Milky Way disk. To quantify the significance of this plane we determine the fraction of times that an isotropic distribution replicates the observed distribution in Monte-Carlo trials. The plane is found to remain significant at the >95% level outside a galactocentric radius of 10 kpc, inside this radius the spatial distribution is apparently isotropic. In contrast, the spatial distribution of the old halo sample outside 10 kpc is well matched by an isotropic distribution. The plane described by the outer young halo globular clusters is indistinguishable in orientation from that presented by the satellite galaxies of the Milky Way. Simulations have shown that the planar arrangement of satellites can arise as filaments of the surrounding large scale structure feed into the Milky Way's potential. We therefore propose that our results are direct observational evidence for the accreted origin of the outer young halo globular cluster population. This conclusion confirms numerous lines of evidence that have similarly indicated an accreted origin for this set of clusters from the inferred cluster properties.Comment: 25 pages, 6 figures, ApJ accepte

The design of RIP belts impacts the reliability and quality of the measured respiratory signals.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked DownloadPurpose: Evaluate the effect of respiratory inductance plethysmography (RIP) belt design on the reliability and quality of respiratory signals. A comparison of cannula flow to disposable cut-to-fit, semi-disposable folding and disposable RIP belts was performed in clinical home sleep apnea testing (HSAT) studies. Methods: This was a retrospective study using clinical HSAT studies. The signal reliability of cannula, thorax, and abdomen RIP belts was determined by automatically identifying periods during which the signals did not represent respiratory airflow and breathing movements. Results were verified by manual scoring. RIP flow quality was determined by examining the correlation between the RIP flow and cannula flow when both signals were considered reliable. Results: Of 767 clinical HSAT studies, mean signal reliability of the cut-to-fit, semi-disposable, and disposable thorax RIP belts was 83.0 ± 26.2%, 76.1 ± 24.4%, and 98.5 ± 9.3%, respectively. The signal reliability of the cannula was 92.5 ± 16.1%, 87.0 ± 23.3%, and 85.5 ± 24.5%, respectively. The automatic assessment of signal reliability for the RIP belts and cannula flow had a sensitivity of 50% and a specificity of 99% compared with manual assessment. The mean correlation of cannula flow to RIP flow from the cut-to-fit, semi-disposable, and disposable RIP belts was 0.79 ± 0.24, 0.52 ± 0.20, and 0.86 ± 0.18, respectively. Conclusion: The design of RIP belts affects the reliability and quality of respiratory signals. The disposable RIP belts that had integrated contacts and did not fold on top of themselves performed the best. The cut-to-fit RIP belts were most likely to be unreliable, and the semi-disposable folding belts produced the lowest-quality RIP flow signals compared to the cannula flow signal. Keywords: Obstructive sleep apnea (OSA); Respiratory airflow; Respiratory inductance plethysmography (RIP) belts; Signal quality; Signal reliability.Icelandic Research Fund Horizon 2020 grant (H2020-SMEINST-2-2016-2017

The Halos of Satellite Galaxies: the Companion of the Massive Elliptical Lens SL2S J08544-0121

Strong gravitational lensing by groups or clusters of galaxies provides a powerful technique to measure the dark matter properties of individual lens galaxies. We study in detail the mass distribution of the satellite lens galaxy in the group-scale lens SL2S J08544-0121 by modelling simultaneously the spatially extended surface brightness distribution of the source galaxy and the lens mass distribution using Markov chain Monte Carlo methods. In particular, we measure the dark matter halo size of the satellite lens galaxy to be 6.0^{+2.9}_{-2.0} kpc with a fiducial velocity dispersion of 127^{+21}_{-12} km/s. This is the first time the size of an individual galaxy halo in a galaxy group has been measured using strong gravitational lensing without assumptions of mass following light. We verify the robustness of our halo size measurement using mock data resembling our lens system. Our measurement of the halo size is compatible with the estimated tidal radius of the satellite galaxy, suggesting that halos of galaxies in groups experience significant tidal stripping, a process that has been previously observed on galaxies in clusters. Our mass model of the satellite galaxy is elliptical with its major axis misaligned with that of the light by ~50 deg. The major axis of the total matter distribution is oriented more towards the centre of the host halo, exhibiting the radial alignment found in N-body simulations and observational studies of satellite galaxies. This misalignment between mass and light poses a significant challenge to modified Newtonian dynamics.Comment: 13 pages, 10 figures, minor revisions based on referee's comments, accepted for publication in A&