491 research outputs found
Publisher Correction: Tracing the transitions from pluripotency to germ cell fate with CRISPR screening
No full textTracing the Transitions from Pluripotency to Germ Cell Fate with CRISPR Screening
No full textEarly mammalian development entails transit through naïve pluripotency towards post-implantation epiblast, which subsequently gives rise to primordial germ cells (PGC), the founding germline population. To investigate these cell fate transitions, we developed a compound-reporter to track cellular identity in a model of PGC specification (PGC-like cells;PGCLC), and coupled it with genome-wide CRISPR-screening. We identify key genes both for exit from pluripotency and for acquisition of PGC fate, and characterise a central role for the transcription-regulators Nr5a2 and Zfp296 in germline ontogeny. Abrogation of these genes results in widespread activation (Nr5a2-/-) or inhibition (Zfp296-/-) of WNT-pathway factors in PGCLC. This leads to aberrant upregulation of the somatic programme or failure to activate germline-genes, respectively, and consequently loss of germ cell identity. Our study places Zfp296 and Nr5a2 as key components of an expanded PGC gene regulatory network, and outlines a transferable strategy for identifying critical regulators of complex cell fate decisions
Non-resonant and resonant X-ray emission at high pressure using a von Hámos setup: the case of FeO
No full textAbstractWe present a setup exploiting a von Hámos spectrometer in order to study (resonant) X-ray emission of matter exposed to high pressure. The capabilities of this setup are demonstrated for the case of FeO at pressures between 13 GPa and 75 GPa. The setup provides high-quality Kβ
1,3 X-ray emission spectra at high pressures for iron spin state analysis within minutes and iron valence-to-core spectra in less than one hour. Resonant X-ray emission maps can be obtained on a timescale of one hour with 1.0 eV and in approximately 3 hours with 0.2 eV incident energy resolution. Both Kα and Kβ emission can be utilized to gain L-edge and M-edge-like information, respectively, with the option of measuring both simultaneously. The spin state results on FeO between 13 GPa and 75 GPa are in accordance with recent literature. The structural distortion is reflected in both, valence-to-core spectra and resonant X-ray emission maps, which showcase the great potential of the presented setup. The achieved data acquisition times are promising to couple pressure with temperature by laser heating
Anomalous Impact of Mechanochemical Treatment on the Na-ion Conductivity of Sodium Closo-Carbadodecaborate Probed by X-Ray Raman Scattering Spectroscopy
No full textSolid-state sodium ion conductors are crucial for the next generation of all-solid-state sodium batteries with high capacity, low cost, and improved safety. Sodium closo-carbadodecaborate (NaCB11H12) is an attractive Na-ion conductor owing to its high thermal, electrochemical, and interfacial stability. Mechanical milling has recently been shown to increase conductivity by five orders of magnitude at room temperature, making it appealing for application in all-solid-state sodium batteries. Intriguingly, milling longer than 2 h led to a significant decrease in conductivity. In this study, X-ray Raman scattering (XRS) spectroscopy is used to probe the origin of the anomalous impact of mechanical treatment on the ionic conductivity of NaCB11H12. The B, C, and Na K-edge XRS spectra are successfully measured for the first time, and ab initio calculations are employed to interpret the results. The experimental and computational results reveal that the decrease in ionic conductivity upon prolonged milling is due to the increased proximity of Na to the CB11H12 cage, caused by severe distortion of the long-range structure. Overall, this work demonstrates how the XRS technique, allowing investigation of low Z elements such as C and B in the bulk, can be used to acquire valuable information on the electronic structure of solid electrolytes and battery materials in general. Mechanochemical milling is a common technique to achieve high ionic conductivity in solid electrolytes. In this work, X-ray Raman scattering (XRS) spectroscopy reveals that the structural defects introduced by milling are beneficial to the ionic conductivity of sodium closo-carbadodecaborate (NaCB11H12). However, extended milling destroys the structure by increasing the proximity of Na+ to the CB11H12- cage, leading to a profound decrease in the Na-ion conductivity.imag
Magnetic excitation spectrum of Na2IrO3 probed with resonant inelastic x-ray scattering
No full textThe low energy excitations in Na2IrO3 have been investigated using resonant inelastic x-ray scattering (RIXS). A magnetic excitation branch can be resolved, whose dispersion reaches a maximum energy of about 35 meV at the Gamma point. The momentum dependence of the excitation energy is much larger along the Gamma-X direction compared to that along the Gamma-Y direction. The observed dispersion relation is consistent with a recent theoretical prediction based on the Heisenberg-Kitaev model. At high temperatures, we find large contributions from lattice vibrational modes to our RIXS spectra, suggesting that a strong electron-lattice coupling is present in Na2IrO3.NSERC; CFI; OMRI; U.S. DOE [DE-AC02-06CH11357
Gretarsson, Experimental measurements of coating mechanical loss factors, Class. Quantum Grav
No full textAbstract All current gravitational wave detectors use test masses coated with alternating layers of two different dielectric materials to form highly reflective mirrors. The thermal noise from mechanical dissipation associated with such coatings may be significant for future detectors such as advanced LIGO. We have measured the mechanical dissipation of a number of types of coatings formed from SiO 2 (silica) and Ta 2 O 5 (tantala). The frequency dependence of the dissipation has been determined, taking into account the contribution of thermoelastic loss
High-efficiency X-ray emission spectroscopy of cold-compressed Fe<sub>2</sub>O<sub>3</sub> and laser-heated pressurized FeCO<sub>3</sub> using a von Hámos spectrometer
No full textX-ray spectroscopy of iron-bearing compounds under high pressure and high temperature is an important tool to understand geological processes in the deep Earth. However, the sample environment using a diamond anvil cell complicates spectroscopic measurements and leads to long data acquisition times. We present a setup for resonant and non-resonant X-ray emission spectroscopy and showcase its capabilities for in situ studies at high pressure and high temperature. Spin-state imaging of laser-heated FeCO3 at 75 GPa via Kβ1,3 emission spectroscopy demonstrates the great potential of this setup with measurement times within seconds for robust spin-state analysis results. The results of Kβ1,3 emission spectroscopy of cold-compressed Fe2O3 reveal a two-step spin transition with the ζ-phase between 57 GPa and 64 GPa, having iron in different spin states at the different iron sites. The phase transition via ζ- to Θ-phase causes a delocalization of the electronic states, which is supported by 1s2p resonant X-ray emission spectroscopy. © 2023 The Royal Society of Chemistry
Progress and Challenges Developing a Coating for Next Generation Gravitational-wave Detectors
No full textOrientation of the ground-state orbital in CeCoIn<sub>5</sub> and CeRhIn<sub>5</sub>
No full textWe present core level nonresonant inelastic x-ray scattering (NIXS) data of the heavy-fermion compounds CeCoIn5 and CeRhIn5 measured at the Ce N-4,N-5 edges. The higher than dipole transitions in NIXS allow determining the orientation of the Gamma(7) crystal-field ground-state orbital within the unit cell. The crystal-field parameters of the CeMIn5 compounds and related substitution phase diagrams have been investigated in great detail in the past; however, whether the ground-state wave function is the Gamma(+)(7) ((x2) - y(2)) or Gamma(-)(7) (xy orientation) remained undetermined. We show that the Gamma(-)(7) doublet with lobes along the (110) direction forms the ground state in CeCoIn5 and CeRhIn5. For CeCoIn5, however, we find also some contribution of the first excited state crystal-field state in the ground state due to the stronger hybridization of 4 f and conduction electrons, suggesting a smaller alpha(2) value than originally anticipated from x-ray absorption. A comparison is made to the results of existing density functional theory plus dynamical mean-field theory calculations
GW190521: a binary black hole merger with a total mass of 150 M⊙
No full textOn May 21, 2019 at 03:02:29 UTC Advanced LIGO and Advanced Virgo observed a short duration gravitational-wave signal, GW190521, with a three-detector network signal-to-noise ratio of 14.7, and an estimated false-alarm rate of 1 in 4900 yr using a search sensitive to generic transients. If GW190521 is from a quasicircular binary inspiral, then the detected signal is consistent with the merger of two black holes with masses of 85+21−14 M⊙ and 66+17−18 M⊙ (90% credible intervals). We infer that the primary black hole mass lies within the gap produced by (pulsational) pair-instability supernova processes, with only a 0.32% probability of being below 65 M⊙. We calculate the mass of the remnant to be 142+28−16 M⊙, which can be considered an intermediate mass black hole (IMBH). The luminosity distance of the source is 5.3+2.4−2.6 Gpc, corresponding to a redshift of 0.82+0.28−0.34. The inferred rate of mergers similar to GW190521 is 0.13+0.30−0.11 Gpc−3 yr−1
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