Primordial Earth mantle heterogeneity caused by the Moon-forming giant impact

The giant impact hypothesis for Moon formation successfully explains the dynamic properties of the Earth-Moon system but remains challenged by the similarity of isotopic fingerprints of the terrestrial and lunar mantles. Moreover, recent geochemical evidence suggests that the Earth's mantle preserves ancient (or "primordial") heterogeneity that predates the Moon-forming giant impact. Using a new hydrodynamical method, we here show that Moon-forming giant impacts lead to a stratified starting condition for the evolution of the terrestrial mantle. The upper layer of the Earth is compositionally similar to the disk, out of which the Moon evolves, whereas the lower layer preserves proto-Earth characteristics. As long as this predicted compositional stratification can at least partially be preserved over the subsequent billions of years of Earth mantle convection, the compositional similarity between the Moon and the accessible Earth's mantle is a natural outcome of realistic and high-probability Moon-forming impact scenarios. The preservation of primordial heterogeneity in the modern Earth not only reconciles geochemical constraints but is also consistent with recent geophysical observations. Furthermore, for significant preservation of a proto-Earth reservoir, the bulk composition of the Earth-Moon system may be systematically shifted towards chondritic values.Comment: Comments are welcom

Gremlin is a novel agonist of the major pro-angiogenic receptor VEGFR2

The bone morphogenic protein antagonist gremlin is expressed during embryonic development and under different pathologic conditions, including cancer. Gremlin is a proangiogenic protein belonging to the cystine-knot superfamily that includes transforming growth factor-β proteins and the angiogenic vascular endothelial growth factors (VEGFs). Here, we demonstrate that gremlin binds VEGF receptor-2 (VEGFR2), the main transducer of VEGF-mediated angiogenic signals, in a bone morphogenic protein-independent manner. Similar to VEGF-A, gremlin activates VEGFR2 in endothelial cells, leading to VEGFR2-dependent angiogenic responses in vitro and in vivo. Gremlin thus represents a novel proangiogenic VEGFR2 agonist distinct from the VEGF family ligands with implications in vascular development, angiogenesis-dependent diseases, and tumor neovascularization

Optimal strategies for gravitational wave stochastic background searches in pulsar timing data

A low frequency stochastic background of gravitational waves may be detected by pulsar timing experiments in the next five to ten years. Using methods developed to analyze interferometric gravitational wave data, in this paper we lay out the optimal techniques to detect a background of gravitational waves using a pulsar timing array. We show that for pulsar distances and gravitational wave frequencies typical of pulsar timing experiments, neglecting the effect of the metric perturbation at the pulsar does not result in a significant deviation from optimality. We discuss methods for setting upper limits using the optimal statistic, show how to construct skymaps using the pulsar timing array, and consider several issues associated with realistic analysis of pulsar timing data.Comment: 20 pages, 6 figures. Added figure with sky sensitivity for Parkes Pulsar Timing Array, included dipole overlap reduction function and derivation in appendix, extended likelihood discussio

Substrate-transferred GaAs/AlGaAs crystalline coatings for gravitational-wave detectors: A review of the state of the art

In this Perspective we summarize the status of technological development for large-area and low-noise substrate-transferred GaAs/AlGaAs (AlGaAs) crystalline coatings for interferometric gravitational-wave (GW) detectors. These topics were originally presented in a workshop{\dag} bringing together members of the GW community from the laser interferometer gravitational-wave observatory (LIGO), Virgo, and KAGRA collaborations, along with scientists from the precision optical metrology community, and industry partners with extensive expertise in the manufacturing of said coatings. AlGaAs-based crystalline coatings present the possibility of GW observatories having significantly greater range than current systems employing ion-beam sputtered mirrors. Given the low thermal noise of AlGaAs at room temperature, GW detectors could realize these significant sensitivity gains, while potentially avoiding cryogenic operation. However, the development of large-area AlGaAs coatings presents unique challenges. Herein, we describe recent research and development efforts relevant to crystalline coatings, covering characterization efforts on novel noise processes, as well as optical metrology on large-area (~10 cm diameter) mirrors. We further explore options to expand the maximum coating diameter to 20 cm and beyond, forging a path to produce low-noise AlGaAs mirrors amenable to future GW detector upgrades, while noting the unique requirements and prospective experimental testbeds for these novel materials.Comment: 13pages, 3 figure

Search for gravitational waves associated with the August 2006 timing glitch of the Vela pulsar

The physical mechanisms responsible for pulsar timing glitches are thought to excite quasinormal mode oscillations in their parent neutron star that couple to gravitational-wave emission. In August 2006, a timing glitch was observed in the radio emission of PSR B0833-45, the Vela pulsar. At the time of the glitch, the two colocated Hanford gravitational-wave detectors of the Laser Interferometer Gravitational wave observatory (LIGO) were operational and taking data as part of the fifth LIGO science run (S5). We present the first direct search for the gravitational-wave emission associated with oscillations of the fundamental quadrupole mode excited by a pulsar timing glitch. No gravitational-wave detection candidate was found. We place Bayesian 90% confidence upper limits of 6.3 x 10^(-21) to 1.4 x 10^(-20) on the peak intrinsic strain amplitude of gravitational-wave ring-down signals, depending on which spherical harmonic mode is excited. The corresponding range of energy upper limits is 5.0 x 10^(-44) to 1.3 x 10^(-45) erg

Plume–ridge interactions: ridgeward versus plate-drag plume flow

The analysis of mid-ocean ridges and hotspots that are sourced by deep-rooted mantle plumes allows us to get a glimpse of mantle structure and dynamics. Dynamical interaction between ridge and plume processes have been widely proposed and studied, particularly in terms of ridgeward plume flow. However, the effects of plate drag on plume–lithosphere and plume–ridge interaction remain poorly understood. In particular, the mechanisms that control plume flow towards vs. away from the ridge have not yet been systematically studied. Here, we use 2D thermomechanical numerical models of plume–ridge interaction to systematically explore the effects of (i) ridge-spreading rate, (ii) initial plume head radius and (iii) plume–ridge distance. Our numerical experiments suggest two different geodynamic regimes: (1) plume flow towards the ridge is favored by strong buoyant mantle plumes, slow spreading rates and small plume–ridge distances; (2) plume drag away from the ridge is in turn promoted by fast ridge spreading for small-to-intermediate plumes and large plume–ridge distances. We find that the pressure gradient between the buoyant plume and spreading ridge at first drives ridgeward flow, but eventually the competition between plate drag and the gravitational force of plume flow along the base of the sloping lithosphere controls the fate of plume (spreading towards vs. away from the ridge). Our results highlight that fast-spreading ridges exert strong plate-dragging force, which sheds new light on natural observations of largely absent plume–lithosphere interaction along fast-spreading ridges, such as the East Pacific Rise.</p

All-sky search for periodic gravitational waves in LIGO S4 data

We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50-1000 Hz and with the frequency's time derivative in the range -1.0E-8 Hz/s to zero. Data from the fourth LIGO science run (S4) have been used in this search. Three different semi-coherent methods of transforming and summing strain power from Short Fourier Transforms (SFTs) of the calibrated data have been used. The first, known as "StackSlide", averages normalized power from each SFT. A "weighted Hough" scheme is also developed and used, and which also allows for a multi-interferometer search. The third method, known as "PowerFlux", is a variant of the StackSlide method in which the power is weighted before summing. In both the weighted Hough and PowerFlux methods, the weights are chosen according to the noise and detector antenna-pattern to maximize the signal-to-noise ratio. The respective advantages and disadvantages of these methods are discussed. Observing no evidence of periodic gravitational radiation, we report upper limits; we interpret these as limits on this radiation from isolated rotating neutron stars. The best population-based upper limit with 95% confidence on the gravitational-wave strain amplitude, found for simulated sources distributed isotropically across the sky and with isotropically distributed spin-axes, is 4.28E-24 (near 140 Hz). Strict upper limits are also obtained for small patches on the sky for best-case and worst-case inclinations of the spin axes.Comment: 39 pages, 41 figures An error was found in the computation of the C parameter defined in equation 44 which led to its overestimate by 2^(1/4). The correct values for the multi-interferometer, H1 and L1 analyses are 9.2, 9.7, and 9.3, respectively. Figure 32 has been updated accordingly. None of the upper limits presented in the paper were affecte