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Integrated Solar-Driven Device with a Front Surface Semitransparent Catalysts for Unassisted CO₂ Reduction
No full textMonolithic integrated photovoltaic-driven electrochemical (PV-EC) artificial photosynthesis is reported for unassisted CO₂ reduction. The PV-EC structures employ triple junction photoelectrodes with a front mounted semitransparent catalyst layer as a photocathode. The catalyst layer is comprised of an array of microscale triangular metallic prisms that redirect incoming light toward open areas of the photoelectrode to reduce shadow losses. Full wave electromagnetic simulations of the prism array (PA) structure guide optimization of geometries and length scales. An integrated device is constructed with Ag catalyst prisms covering 35% of the surface area. The experimental device has close to 80% of the transmittance with a catalytic surface area equivalent 144% of the glass substrate area. Experimentally this photocathode demonstrates a direct solar-to-CO conversion efficiency of 5.9% with 50 h stability. Selective electrodeposition of Cu catalysts onto the surface of the Ag triangular prisms allows CO2 conversion to higher value products enabling demonstration of a solar-to-C₂₊ product efficiency of 3.1%. This design featuring structures that have a semitransparent catalyst layer on a PV-EC cell is a general solution to light loss by shadowing for front surface mounted metal catalysts, and opens a route for the development of artificial photosynthesis based on this scalable design approach
On route to one-pot synthesis of delaminated Al-SSZ-70 zeolite via partial substitution of OSDA with CTAOH surfactant
No full textDirect one-pot synthesis of delaminated layered zeolitic materials aims to create two-dimensionally confined catalysts for reactions involving sterically bulky reactants, which are too large to benefit from conventional three-dimensional confinement in micropores. As a prototypical system, several efforts have focused on the development of post-synthetic approaches for delamination of silica-rich MWW layered zeolite precursors, but to date this has required either harsh (halide) multi-step conditions, or the need for gemini quaternary ammonium organic surfactants for direct-synthesis routes. The one-pot synthesis of silica-rich delaminated layered zeolites consisting of MWW layers with simple quaternary ammonium surfactants such as those consisting of cetyltrimethyl ammonium (CTA) head groups remains a challenge. In this study, we describe our attempts for one-pot synthesis of delaminated Al-SSZ-70 zeolite via partial replacement of the organic structure-directing agent (OSDA) with a simple surfactant, CTAOH. Leveraging on our prior demonstration of direct one-pot synthesis of delaminated B-SSZ-70, our goal is to use these dual organic additives in Al-SSZ-70 hydrothermal synthesis, to effectively restrain the MWW layer stacking by capping the external surface of the MWW layer with a surfactant. The synthetic approach reported in this work leads to high-silica delaminated MWW-type zeolite Al-SSZ-70, which benefits from postsynthetic high-shear mixing of the layered zeolite precursor for further delamination. The resulting delaminated zeolites exhibit a similar Brønsted/Lewis acid site distributions as characterized by FTIR spectroscopy of adsorbed pyridine at various temperatures, and enhanced acid catalytic properties over a non-delaminated control. However, we observe a minor amorphous-phase impurity when using the high surfactant loading required for optimum delamination, which is observable using TEM imaging and low-angle powder X-ray diffraction. The presence of this amorphous phase highlights the ongoing challenge of synthesizing a fully crystalline MWW-type delaminated material via direct hydrothermal synthesis, when using simple surfactants, which remains a target for future research
Data-Driven Synthesis of Broadband Earthquake Ground Motions Using Artificial Intelligence
No full textRobust estimation of ground motions generated by scenario earthquakes is critical for many engineering applications. We leverage recent advances in generative adversarial networks (GANs) to develop a new framework for synthesizing earthquake acceleration time histories. Our approach extends the Wasserstein GAN formulation to allow for the generation of ground motions conditioned on a set of continuous physical variables. Our model is trained to approximate the intrinsic probability distribution of a massive set of strong-motion recordings from Japan. We show that the trained generator model can synthesize realistic three-component accelerograms conditioned on magnitude, distance, and V_(S30). Our model captures most of the relevant statistical features of the acceleration spectra and waveform envelopes. The output seismograms display clear P- and S-wave arrivals with the appropriate energy content and relative onset timing. The synthesized peak ground acceleration estimates are also consistent with observations. We develop a set of metrics that allow us to assess the training process’s stability and to tune model hyperparameters. We further show that the trained generator network can interpolate to conditions in which no earthquake ground-motion recordings exist. Our approach allows for the on-demand synthesis of accelerograms for engineering purposes
The Discovery of Davemaoite, the CaSiO₃ Perovskite, in a Diamond from Earth’s Lower Mantle
No full textCommon silicate minerals such as olivine and garnet convert to other phases when brought to great depths in the planet, where they are subjected to extreme pressures. It has long been thought that two of the most common phases at depth in Earth have the perovskite structure. They have long been known from experimental studies in which they have been called magnesium silicate perovskite (MgSiO3) and calcium silicate perovskite (CaSiO3). Only recently has the magnesium silicate perovskite been found in nature, in a meteorite, where it was characterized and named bridgmanite (O. Tschauner et al., “Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked meteorite,” Science, Vol. 346, 2014, pp. 1100–1102). More recently, the calcium silicate perovskite has been found in a diamond and sufficiently characterized to be given a mineral species name (O. Tschauner et al., “Discovery of davemaoite, CaSiO3-perovskite, as a mineral from the lower mantle,” Science, Vol. 374, 2021, pp. 891–894)
Forced microrheology of active colloids
No full textParticle-tracking microrheology of dilute active (self-propelled) colloidal suspensions is studied by considering the external force required to maintain the steady motion of an immersed constant-velocity colloidal probe. If the probe speed is zero, the suspension microstructure is isotropic but exhibits a boundary accumulation of active bath particles at contact due to their self-propulsion. As the probe moves through the suspension, the microstructure is distorted from the nonequilibrium isotropic state, which allows us to define a microviscosity for the suspension using the Stokes drag law. For a slow probe, we show that active suspensions exhibit a swim-thinning behavior in which their microviscosity is gradually lowered from that of passive suspensions as the swim speed increases. When the probe speed is fast, the suspension activity is obscured by the rapid advection of the probe and the measured microviscosity is indistinguishable from that of passive suspensions. Generally for finite activity, the suspension exhibits a velocity-thinning behavior—though with a zero-velocity plateau lower than passive suspensions—as a function of the probe speed. These behaviors originate from the interplay between the suspension activity and the hard-sphere excluded-volume interaction between the probe and a bath particle
Relianceite-(K), a new phosphate-oxalate mineral related to davidbrownite-(NH₄) from the Rowley mine, Arizona, USA
No full textAbstractRelianceite-(K), K4Mg(V4+O)2(C2O4)(PO3OH)4(H2O)10, is a new mineral species from the Rowley mine, Maricopa County, Arizona, USA. It occurs in an unusual bat-guano-related, post-mining assemblage of phases. Other secondary minerals associated with relianceite-(K) are antipinite, dendoraite-(NH4), fluorite, mimetite, mottramite, rowleyite, salammoniac, struvite, vanadinite, willemite, wulfenite and at least one other new mineral. Crystals of relianceite-(K) are sky blue prisms up to ~0.1 mm in length. The streak is very pale blue and lustre is vitreous, Mohs hardness is 2½, tenacity is brittle and fracture is splintery. The calculated density is 2.111 g⋅cm–3. Relianceite-(K) is optically biaxial (+) with α = 1.528(2), β = 1.529(2), γ = 1.562(2) (white light); 2Vmeas = 22(1)°; orientation Z = b; pleochroism: X = colourless, Y = pale blue, Z = pale blue; X Y ≈ Z. Electron microprobe analysis gave the empirical formula [K2.21(NH4)1.79]Σ4.00Mg0.96(V4+0.95O)2(C2O4)[P1.03O3.03(OH)0.97]4(H2O)10, with the C, N and H contents constrained by the crystal structure. Raman spectroscopy confirmed the presence of NH4 and C2O4. Relianceite-(K) is monoclinic, Pc, with a = 12.404 (7) Å, b = 9.014 (6), c = 13.260 (8) Å, β = 100.803(10)°, V = 1456 (2) Å3 and Z = 2. The structural unit in the crystal structure of relianceite-(K) (R1 = 0.0540 for 3751 Io > 2σI reflections) is a (V4+O)2(C2O4)(PO3OH)4 chain in which VO6 octahedra are bridged by an oxalate group to form [V2C2O12] dimers, PO3OH tetrahedra form a double bridge between the VO6 octahedra of the dimers, and additional PO3OH tetrahedra decorate the chain. Topologically, this is the same chain found in the structure of davidbrownite-(NH4). The MgO(H2O)5 octahedron can be considered a distant decoration on the chain. The chains are linked to each other through an extensive system of K/NH4–O bonds and hydrogen bonds
Tunneling potentials for the tunneling action: gauge invariance
No full textWe formulate a procedure to obtain a gauge-invariant tunneling rate at zero temperature using the recently developed tunneling potential approach. This procedure relies on a consistent power counting in gauge coupling and a derivative expansion. The tunneling potential approach, while numerically more efficient than the standard bounce solution method, inherits the gauge-dependence of the latter when naïvely implemented. Using the Abelian Higgs model, we show how to obtain a tunneling rate whose residual gauge-dependence arises solely from the polynomial approximations adopted in the tunneling potential computation
The Chromium Dimer: Closing a Chapter of Quantum Chemistry
No full textThe complex electronic structure and unusual potential energy curve of the chromium dimer have fascinated scientists for decades, with agreement between theory and experiment so far elusive. Here, we present a new ab initio simulation of the potential energy curve and vibrational spectrum that significantly improves on all earlier estimates. Our data support a shift in earlier experimental assignments of a cluster of vibrational frequencies by one quantum number. The new vibrational assignment yields an experimentally derived potential energy curve in quantitative agreement with theory across all bond lengths and across all
measured frequencies. By solving this long-standing problem, our results raise the possibility of quantitative quantum chemical modeling of transition metal clusters with spectroscopic accuracy
A deep survey of short GRB host galaxies over z ∼ 0-2: implications for offsets, redshifts, and environments
No full textA significant fraction (30 per cent) of well-localized short gamma-ray bursts (sGRBs) lack a coincident host galaxy. This leads to two main scenarios: (i) that the progenitor system merged outside of the visible light of its host, or (ii) that the sGRB resided within a faint and distant galaxy that was not detected by follow-up observations. Discriminating between these scenarios has important implications for constraining the formation channels of neutron star mergers, the rate and environments of gravitational wave sources, and the production of heavy elements in the Universe. In this work, we present the results of our observing campaign targeted at 31 sGRBs that lack a putative host galaxy. Our study effectively doubles the sample of well-studied sGRB host galaxies, now totaling 72 events of which 28% lack a coincident host to deep limits (r ≳ 26 or F110W ≳ 27 AB mag), and represents the largest homogeneously selected catalogue of sGRB offsets to date. We find that 70 per cent of sub-arcsecond localized sGRBs occur within 10 kpc of their host’s nucleus, with a median projected physical offset of 5.6 kpc. Using this larger population, we discover an apparent redshift evolution in their locations: bursts at low-z occur at 2 × larger offsets compared to those at z > 0.5. This evolution could be due to a physical evolution of the host galaxies themselves or a bias against faint high-z galaxies. Furthermore, we discover a sample of hostless sGRBs at z ≳ 1 that are indicative of a larger high-z population, constraining the redshift distribution and disfavoring lognormal delay time models
Review of Particle Physics
No full textThe Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,143 new measurements from 709 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 120 reviews are many that are new or heavily revised, including a new review on Machine Learning, and one on Spectroscopy of Light Meson Resonances.
The Review is divided into two volumes. Volume 1 includes the Summary Tables and 97 review articles. Volume 2 consists of the Particle Listings and contains also 23 reviews that address specific aspects of the data presented in the Listings.
The complete Review (both volumes) is published online on the website of the Particle Data Group (pdg.lbl.gov) and in a journal. Volume 1 is available in print as the PDG Book. A Particle Physics Booklet with the Summary Tables and essential tables, figures, and equations from selected review articles is available in print, as a web version optimized for use on phones, and as an Android app