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Classical Gravitational Spinning-Spinless Scattering at O(G²S^∞)
No full textMaking use of the recently derived, all-spin, opposite-helicity Compton amplitude, we calculate the classical gravitational scattering amplitude for one spinning and one spinless object at O(G²) and all orders in spin. By construction, this amplitude exhibits the spin structure that has been conjectured to describe Kerr black holes. This spin structure alone is not enough to fix all deformations of the Compton amplitude by contact terms, but when combined with considerations of the ultrarelativistic limit we can uniquely assign values to the parameters remaining in the even-in-spin sector. Once these parameters are determined, much of the spin dependence of the amplitude resums into hypergeometric functions. Finally, we derive the eikonal phase for aligned-angular-momentum scattering
Resolving the Chemical Formula of Nesquehonite via NMR Crystallography, DFT Computation, and Complementary Neutron Diffraction
No full textNesquehonite is a magnesium carbonate mineral relevant to carbon sequestration envisioned for carbon capture and storage of CO₂. Its chemical formula remains controversial today, assigned as either a hydrated magnesium carbonate [MgCO₃)OH ⋅ 2H₂O]. The resolution of this controversy is central to understanding this material‘s thermodynamic, phase, and chemical behavior. In an NMR crystallography study, using rotational-echo double-resonance ¹³C{¹H} (REDOR), ¹³C−¹H distances are determined with precision, and the combination of ¹³C static NMR lineshapes and density functional theory (DFT) calculations are used to model different H atomic coordinates. [MgCO₃ ⋅ 3H₂O] is found to be accurate, and evidence from neutron powder diffraction bolsters these assignments. Refined H positions can help understand how H-bonding stabilizes this structure against dehydration to MgCO₃. More broadly, these results illustrate the power of NMR crystallography as a technique for resolving questions where X-ray diffraction is inconclusive
Fe Substitutions Improve Spectral Response of Bi₂WO₆-Based Photoanodes
No full textThe quest for a scalable solar fuel technology has stimulated a concerted effort to develop a metal oxide semiconductor for solar-driven photoelectrochemical water oxidation (oxygen evolution reaction) in an efficient and durable manner. So far, the search for such a metal oxide photoanode has highlighted the promise of Bi-based oxides, which have also been extensively studied for other photocatalyst applications. Bi₂WO₆ is a durable photocatalyst whose primary shortcoming is a 2.8 eV band gap that limits utilization of the solar spectrum. Improvements in visible photoresponse upon incorporation of Fe have been reported in the photocatalysis literature, motivating our use of high-throughput synthesis and photoelectrochemistry to determine the spectral photoresponse for Bi–W–Fe oxides synthesized under nonequilibrium conditions based on thermal oxidation of metallic films. Photoactivity down to 2 eV was achieved over a broad range of compositions, with detailed characterization of optimal compositions revealing that Fe incorporation increases the valence band position by 0.75 eV. Density functional theory calculations of Fe substitutions on W sites in Bi₂WO₆ re consistent with this valence band shift, providing a plausible explanation for the experiments. This Fe-mediated band tuning yields a ca. 2 eV band gap while retaining a turn-on potential for photoanodic current near 0.4 V versus RHE, which combined with the operational durability motivates continuous study and development of this promising class of metal oxide photoanodes
Trait impressions from faces depend on the goals of the perceiver
No full textTrait impressions from faces formed in the real world likely depend on the circumstances in which a face is seen, in particular, on the goal of the perceiver in that circumstance. This goal dependency is typically not incorporated into laboratory studies, an omission that has limited our understanding of trait impressions from faces
3D-Printable Cellular Composites for the Production of Recombinant Proteins
No full textThe incorporation of living cells into materials promises both significant challenges and new possibilities. Although recent years have seen important advances in this field, there is still much to be learned about engineering interfaces between cells and materials. Here, we present a new class of 3D-printable materials, based on poly(N-hydroxymethylacrylamide) (PNHMAA), in which the spore-forming bacterium Bacillus subtilis is effectively cross-linked into the surrounding polymeric scaffold. After dehydration and subsequent re-swelling in nutrient-rich media, embedded cells and spores become metabolically active and are capable of heterologous protein production and secretion. Strikingly, the leak-free scaffold allows protein production while preventing escape of embedded cells. The successful construction of complex three-dimensional structures by stereolithographic printing of living PNHMAA composite materials suggests utility in a broad range of applications
15000 Ellipsoidal Binary Candidates in TESS: Orbital Periods, Binary Fraction, and Tertiary Companions
No full textWe present a homogeneously-selected sample of 15779 candidate binary systems with main sequence primary stars and orbital periods shorter than 5 days. The targets were selected from TESS full-frame image lightcurves on the basis of their tidally-induced ellipsoidal modulation. Spectroscopic follow-up suggests a sample purity of 83 ± 13 per cent. Injection-recovery tests allow us to estimate our overall completeness as 28 ± 3 per cent with P_(orb) < 3 days and to quantify our selection effects. We estimate that 39 ± 4 per cent of our sample are contact binary systems, and we disentangle the period distributions of the contact and detached binaries. We derive the orbital period distribution of the main sequence binary population at short orbital periods, finding a distribution continuous with the log-normal distribution previously found for solar-type stars at longer periods, but with a significant steepening at P_(orb) ≲ 3 days, and a pile-up of contact binaries at P_(orb) ≈ 0.4 days. Companions in the period range 1--5 days are found to be an order of magnitude more frequent around stars hotter than ≈6250K (the Kraft break) when compared to cooler stars, suggesting that magnetic braking plays an important role in shaping the temperature and period distributions. We detect resolved tertiary companions to 9.0 ± 0.2 per cent of our binaries with a median separation of 3200 AU. The frequency of tertiary companions rises to 29 ± 5 per cent among the systems with the shortest ellipsoidal periods. This large binary sample with quantified selection effects will be a powerful resource for future studies of detached and contact binary systems with P_(orb) < 5 days
The C/N ratio from FUV spectroscopy as a constraint upon the past evolution of HS0218+3229
No full textSome white dwarfs accreting from non-degenerate companions show anomalous carbon and nitrogen abundances in the photospheres of their stellar components which have been postulated to be descendants of supersoft X-ray binaries. Therefore the carbon-to-nitrogen ratio can provide constraints upon their past evolution. We fit far ultraviolet spectroscopy of the cataclysmic variable HS0218+3229 taken with the Cosmic Origins Spectrograph using Markov Chain Monte Carlo. While some parameters depend upon the amount of reddening, the carbon-to-nitrogen ratio is about one tenth of the Solar value (log C/N = −0.53^(+0.13)_(−0.14) and −0.58^(+0.16)_(−0.15) for almost no reddening and E(B-V) = 0.065, respectively, which are consistent within the uncertainties). We also provide estimates of the silicon and aluminum abundances, and upper limits for iron and oxygen. Using the measured parameters of HS0218+3229 we reconstruct its past using evolutionary simulations with MESA. We implemented Gaussian process fits to the MESA grid in order to determiner the most likely initial binary configuration of HS0218+3229. We found that an initial mass of the donor of M_(donor;i) = 0.90−0.98, M_⊙ and an initial orbital period of P_(orb;i) = 2.88 days (P_(orb;i) = 3.12−3.16 days) for an assumed white dwarf mass of M_(WD) = 0.83 M_⊙ (M_(WD) = 0.60 M_⊙) are needed to replicate the measured parameters. These configurations imply that the system did not go through a phase of quasi-steady hydrogen-burning on the white dwarf's surface. However, it could have experienced a phase of thermal timescale mass transfer in the past if the initial mass ratio was ≥1.5. We predict that HS0218+3229 will evolve into a CV with a period below the ≃80\,min period minimum for normal CVs, displaying helium and hydrogen in its spectrum
Reports From The Frontier-Strategies to Design Stable Layered Oxide Cathodes for Na-Ion Batteries
No full textThis feature page is intended to let ECS award winning students and post-docs write a primary-author perspective on their field, their work, and where they believe things are going. This month we highlight the work of Muhammad Mominur Rahman, the Battery Division 2021 Student Research Award winner
Molecular Level Sucrose Quantification: A Critical Review
No full textSucrose is a primary metabolite in plants, a source of energy, a source of carbon atoms for growth and development, and a regulator of biochemical processes. Most of the traditional analytical chemistry methods for sucrose quantification in plants require sample treatment (with consequent tissue destruction) and complex facilities, that do not allow real-time sucrose quantification at ultra-low concentrations (nM to pM range) under in vivo conditions, limiting our understanding of sucrose roles in plant physiology across different plant tissues and cellular compartments. Some of the above-mentioned problems may be circumvented with the use of bio-compatible ligands for molecular recognition of sucrose. Nevertheless, problems such as the signal-noise ratio, stability, and selectivity are some of the main challenges limiting the use of molecular recognition methods for the in vivo quantification of sucrose. In this review, we provide a critical analysis of the existing analytical chemistry tools, biosensors, and synthetic ligands, for sucrose quantification and discuss the most promising paths to improve upon its limits of detection. Our goal is to highlight the criteria design need for real-time, in vivo, highly sensitive and selective sucrose sensing capabilities to enable further our understanding of living organisms, the development of new plant breeding strategies for increased crop productivity and sustainability, and ultimately to contribute to the overarching need for food security
Asymptotically self-similar blowup of the Hou-Luo model for the 3D Euler equations
No full textInspired by the numerical evidence of a potential 3D Euler singularity [54, 55], we prove finite time singularity from smooth initial data for the HL model introduced by Hou-Luo in [54, 55] for the 3D Euler equations with boundary. Our finite time blowup solution for the HL model and the singular solution considered in [54, 55] share some essential features, including similar blowup exponents, symmetry properties of the solution, and the sign of the solution. We use a dynamical rescaling formulation and the strategy proposed in our recent work in [11] to establish the nonlinear stability of an approximate self-similar profile. The nonlinear stability enables us to prove that the solution of the HL model with smooth initial data and finite energy will develop a focusing asymptotically self-similar singularity in finite time. Moreover the self-similar profile is unique within a small energy ball and the C_γ norm of the density θ with γ ≈ 1/3 is uniformly bounded up to the singularity time.
[11] Chen, J., Hou, T.Y., Huang, D.: On the finite time blowup of the De Gregorio model for the 3D Euler equations. Communications on Pure and Applied Mathematics 74(6), 1282–1350 (2021)
[54] Luo, G., Hou, T.: Toward the finite-time blowup of the 3D incompressible Euler equations: a numerical investigation. SIAM Multiscale Modeling and Simulation 12(4), 1722–1776 (2014)
[55] Luo, G., Hou, T.Y.: Potentially singular solutions of the 3d axisymmetric euler equations. Proceedings of the National Academy of Sciences 111(36), 12968–12973 (2014