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Conformer-Dependent Chemistry: Experimental Product Branching of the Vinyl Alcohol + OH + O₂ Reaction
No full textThe concentration of formic acid in Earth’s troposphere is underestimated by detailed chemical models compared to field observations. Phototautomerization of acetaldehyde to its less stable tautomer vinyl alcohol, followed by the OH-initiated oxidation of vinyl alcohol, has been proposed as a missing source of formic acid that improves the agreement between models and field measurements. Theoretical investigations of the OH + vinyl alcohol reaction in excess O₂ conclude that OH addition to the α carbon of vinyl alcohol produces formaldehyde + formic acid + OH, whereas OH addition to the β site leads to glycoaldehyde + HO₂. Furthermore, these studies predict that the conformeric structure of vinyl alcohol controls the reaction pathway, with the anti-conformer of vinyl alcohol promoting α OH addition, whereas the syn-conformer promotes β addition. However, the two theoretical studies reach different conclusions regarding which set of products dominate. We studied this reaction using time-resolved multiplexed photoionization mass spectrometry to quantify the product branching fractions. Our results, supported by a detailed kinetic model, conclude that the glycoaldehyde product channel (arising mostly from syn-vinyl alcohol) dominates over formic acid production with a 3.6:1.0 branching ratio. This result supports the conclusion of Lei et al. that conformer-dependent hydrogen bonding at the transition state for OH-addition controls the reaction outcome. As a result, tropospheric oxidation of vinyl alcohol creates less formic acid than recently thought, increasing again the discrepancy between models and field observations of Earth’s formic acid budget
Investigation of the shocked Viñales ordinary chondrite (L6) meteorite fall – Implications for shock classification, fragmentation, and collision dynamics
No full textThe effects of collisions on the evolution of asteroids, ranging from local fracturing to brecciation or even to catastrophic disruption, depend primarily on the encounter velocities. Here we present a refined view of the mineralogy and texture of the recent fall Viñales, an L6 ordinary chondrite meteorite. It preserves features that require at least one energetic impact, including numerous shock melt veins of variable thickness. We report the identification of two high-pressure phases, majorite and albitic jadeite, limited to just one of these shock melt veins. Viñales is a moderately shocked sample, shock stage S4, that experienced a complex and spatially variable pressure-temperature-time history with a low (but non-zero) probability of preservation of high-pressure phases
High-accuracy numerical models of Brownian thermal noise in thin mirror coatings
No full textBrownian coating thermal noise in detector test masses is limiting the sensitivity of current gravitational-wave detectors on Earth. Therefore, accurate numerical models can inform the ongoing effort to minimize Brownian coating thermal noise in current and future gravitational-wave detectors. Such numerical models typically require significant computational resources and time, and often involve closed-source commercial codes. In contrast, open-source codes give complete visibility and control of the simulated physics, enable direct assessment of the numerical accuracy, and support the reproducibility of results. In this article, we use the open-source SpECTRE numerical relativity code and adopt a novel discontinuous Galerkin numerical method to model Brownian coating thermal noise. We demonstrate that SpECTRE achieves significantly higher accuracy than a previous approach at a fraction of the computational cost. Furthermore, we numerically model Brownian coating thermal noise in multiple sub-wavelength crystalline coating layers for the first time. Our new numerical method has the potential to enable fast exploration of realistic mirror configurations, and hence to guide the search for optimal mirror geometries, beam shapes and coating materials for gravitational-wave detectors
Asymptotics of singular values for quantum derivatives
No full textWe obtain Weyl type asymptotics for the quantised derivative \dj ƒ of a function ƒ from the homgeneous Sobolev space Ẇ^(1)_(d) on (ℝᵈ). The asymptotic coefficient ||∇ƒ||_[L_(d)(ℝᵈ)] is equivalent to the norm of \dj ƒ in the principal ideal L_(d,∞), thus, providing a non-asymptotic, uniform bound on the spectrum of \dj ƒ. Our methods are based on the C*-algebraic notion of the principal symbol mapping on ℝᵈ, as developed recently by the last two authors and collaborators
The Type 1 and Type 2 AGN dichotomy according to their ZTF optical variability
No full textThe scarce optical variability studies in spectrally classified Type 2 active galactic nuclei (AGNs) have led to the discovery of anomalous objects that are incompatible with the simplest unified models (UMs). This paper focuses on the exploration of different variability features that allow to distinguish between obscured, Type 2 AGNs and the variable, unobscured Type 1s. We analyse systematically the Zwicky Transient Facility, 2.5-yr-long light curves of ∼15 000 AGNs from the Sloan Digital Sky Survey Data Release 16, which are generally considered Type 2s due to the absence of strong broad emission lines (BELs). Consistent with the expectations from the UM, the variability features are distributed differently for distinct populations, with spectrally classified weak Type 1s showing one order of magnitude larger variances than the Type 2s. We find that the parameters given by the damped random walk model lead to broader H α equivalent width for objects with τ_g > 16 d and long-term structure function SF_(∞, g) > 0.07 mag. By limiting the variability features, we find that ∼11 per cent of Type 2 sources show evidence for optical variations. A detailed spectral analysis of the most variable sources (∼1 per cent of the Type 2 sample) leads to the discovery of misclassified Type 1s with weak BELs and changing-state candidates. This work presents one of the largest systematic investigations of Type 2 AGN optical variability to date, in preparation for future large photometric surveys
Radio observations of the tidal disruption event AT2020opy: a luminous non-relativistic outflow encountering a dense circumnuclear medium
No full textTidal disruption events (TDEs) occur when a star passes too close to a supermassive black hole and is destroyed by tidal gravitational forces. Radio observations of TDEs trace synchrotron emission from outflowing material that may be ejected from the inner regions of the accretion flow around the supermassive black hole or by the tidal debris stream. Radio detections of TDEs are rare, but provide crucial information about the launching of jets and outflows from supermassive black holes and the circumnuclear environment in galaxies. Here, we present the radio detection of the TDE AT2020opy, including three epochs of radio observations taken with the Karl G. Jansky Very Large Array, MeerKAT, and upgraded Giant Metrewave Radio telescope. AT2020opy is the most distant thermal TDE with radio emission reported to date, and from modelling the evolving synchrotron spectra we deduce that the host galaxy has a more dense circumnuclear medium than other thermal TDEs detected in the radio band. Based on an equipartition analysis of the synchrotron spectral properties of the event, we conclude that the radio-emitting outflow was likely launched approximately at the time of, or just after, the initial optical flare. We find no evidence for relativistic motion of the outflow. The high luminosity of this event supports that a dense circumnuclear medium of the host galaxy produces brighter radio emission that rises to a peak more quickly than in galaxies with lower central densities
Entangling remote qubits using the single-photon protocol: an in-depth theoretical and experimental study
No full textThe generation of entanglement between remote matter qubits has developed into a key capability for fundamental investigations as well as for emerging quantum technologies. In the single-photon, protocol entanglement is heralded by generation of qubit-photon entangled states and subsequent detection of a single photon behind a beam splitter. In this work we perform a detailed theoretical and experimental investigation of this protocol and its various sources of infidelity. We develop an extensive theoretical model and subsequently tailor it to our experimental setting, based on nitrogen-vacancy centers in diamond. Experimentally, we verify the model by generating remote states for varying phase and amplitudes of the initial qubit superposition states and varying optical phase difference of the photons arriving at the beam splitter. We show that a static frequency offset between the optical transitions of the qubits leads to an entangled state phase that depends on the photon detection time. We find that the implementation of a Charge-Resonance check on the nitrogen-vacancy center yields transform-limited linewidths. Moreover, we measure the probability of double optical excitation, a significant source of infidelity, as a function of the power of the excitation pulse. Finally, we find that imperfect optical excitation can lead to a detection-arm-dependent entangled state fidelity and rate. The conclusion presented here are not specific to the nitrogen-vacancy centers used to carry out the experiments, and are therefore readily applicable to other qubit platforms
High-gain and high-speed wavefront shaping through scattering media
No full textWavefront shaping (WFS) is emerging as a promising tool for controlling and focusing light in complex scattering media. The shaping system’s speed, the energy gain of the corrected wavefronts and the control degrees of freedom are the most important metrics for WFS, especially for highly scattering and dynamic samples. Despite recent advances, current methods suffer from trade-offs that limit satisfactory performance to only one or two of these metrics. Here we report a WFS technique that simultaneously achieves high speed, high energy gain and high control degrees of freedom. By combining photorefractive crystal-based analogue optical phase conjugation and stimulated emission light amplification, our technique achieves an energy gain approaching unity; that is, more than three orders of magnitude larger than conventional analogue optical phase conjugation. The response time of ~10 μs with about 106 control modes corresponds to an average mode time of about 0.01 ns per mode, which is more than 50 times quicker than some of the fastest WFS systems so far. We anticipate that this technique will be instrumental in overcoming the optical diffusion limit in photonics and translate WFS techniques to real-world applications
Chemodivergent C(sp³)–H and C(sp²)–H cyanomethylation using engineered carbene transferases
No full textThe ubiquity of C–H bonds presents an opportunity to efficiently elaborate and build complexity in organic molecules. Methods for selective functionalization, however, must differentiate among multiple, chemically similar C–H bonds: enzymes are attractive because they can be finely tuned using directed evolution to achieve divergent reaction outcomes. Here we present engineered enzymes that effect a new-to-nature C–H alkylation (C–H carbene insertion) with distinct selectivities: cytochrome P450-based carbene transferases deliver an α-cyanocarbene either into the α-amino C(sp³)–H bonds or the ortho-arene C(sp²)–H bonds of N-substituted arenes. These two transformations proceed via different mechanisms, yet only minimal changes to the protein scaffold were needed to adjust the enzyme’s chemoselectivity. Structural studies of the C(sp³)–H alkylase reveal an active-site helical disruption, which alters the structure and electrostatics of the substrate-binding pocket compared to the native enzyme. Overall, this work demonstrates advantages of using highly tuneable enzymes as C–H functionalization catalysts for divergent molecular derivatization
Aging-associated HELIOS deficiency in naive CD4⁺ T cells alters chromatin remodeling and promotes effector cell responses
No full textImmune aging combines cellular defects in adaptive immunity with the activation of pathways causing a low-inflammatory state. Here we examined the influence of age on the kinetic changes in the epigenomic and transcriptional landscape induced by T cell receptor (TCR) stimulation in naive CD4⁺ T cells. Despite attenuated TCR signaling in older adults, TCR activation accelerated remodeling of the epigenome and induced transcription factor networks favoring effector cell differentiation. We identified increased phosphorylation of STAT5, at least in part due to aberrant IL-2 receptor and lower HELIOS expression, as upstream regulators. Human HELIOS-deficient, naive CD4⁺ T cells, when transferred into human-synovium-mouse chimeras, infiltrated tissues more efficiently. Inhibition of IL-2 or STAT5 activity in T cell responses of older adults restored the epigenetic response pattern to the one seen in young adults. In summary, reduced HELIOS expression in non-regulatory naive CD4⁺ T cells in older adults directs T cell fate decisions toward inflammatory effector cells that infiltrate tissue