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Rapid disc settling and the transition from bursty to steady star formation in Milky Way-mass galaxies
No full textRecent observations and simulations indicate substantial evolution in the properties of galaxies with time, wherein rotationally supported and steady thin discs (like those frequently observed in the local Universe) emerge from galaxies that are clumpy, irregular, and have bursty star formation rates (SFRs). To better understand the progenitors of local disc galaxies, we carry out an analysis of three FIRE-2 simulated galaxies with a mass similar to the Milky Way at redshift z = 0. We show that all three galaxies transition from bursty to steady SFRs at a redshift between z = 0.5 and z = 0.8, and that this transition coincides with the rapid (≲1 Gyr) emergence of a rotationally supported interstellar medium (ISM). In the late phase with steady SFR, the rotational energy comprises ≳90 per cent of the total kinetic + thermal energy in the ISM, and is roughly half the gravitational energy. By contrast, during the early bursty phase, the ISM initially has a quasi-spheroidal morphology and its energetics are dominated by quasi-isotropic in- and outflows out of virial equilibrium. The subdominance of rotational support and out-of-equilibrium conditions at early times challenge the application of standard equilibrium disc models to high-redshift progenitors of Milky Way-like galaxies. We further find that the formation of a rotationally-supported ISM coincides with the onset of a thermal pressure supported inner circumgalactic medium (CGM). Before this transition, there is no clear boundary between the ISM and the inner CGM
Dynamics of eddying abyssal mixing layers over sloping rough topography
No full textThe abyssal overturning circulation is thought to be primarily driven by small-scale turbulent mixing. Diagnosed watermass transformations are dominated by rough topography “hotspots”, where the bottom-enhancement of mixing causes the diffusive buoyancy flux to diverge, driving widespread downwelling in the interior—only to be overwhelmed by an even stronger up-welling in a thin Bottom Boundary Layer (BBL). These watermass transformations are significantly underestimated by one-dimensional (1D) sloping boundary layer solutions, suggesting the importance of three-dimensional physics. Here, we use a hierarchy of models to generalize this 1D boundary layer approach to three-dimensional eddying flows over realistically rough topography. When applied to the Mid-Atlantic Ridge in the Brazil Basin, the idealized simulation results are roughly consistent with available observations. Integral buoyancy budgets isolate the physical processes that contribute to realistically strong BBL upwelling. The downwards diffusion of buoyancy is primarily balanced by upwelling along the sloping canyon sidewalls and the surrounding abyssal hills. These flows are strengthened by the restratifying effects of submesoscale baroclinic eddies and by the blocking of along-ridge thermal wind within the canyon. Major topographic sills block along-thalweg flows from restratifying the canyon trough, resulting in the continual erosion of the trough’s stratification. We propose simple modifications to the 1D boundary layer model which approximate each of these three-dimensional effects. These results provide local dynamical insights into mixing-driven abyssal overturning, but a complete theory will also require the non-local coupling to the basin-scale circulation
Dry heterometallic resist processing based on thermal sublimation deposition and development
No full textA negative tone heterometallic ring resist (HRR) based on a supramolecular assembly [NH₂(allyl)₂][Cr₇NiF₈(piv)₁₆] with previously demonstrated resolution down to sub 10-nm lines is evaluated in terms of its flexibility to be processed either “wet” (spin cast and solvent developed) or “dry” (deposition and development by vacuum sublimation). The implemented sublimation hardware fits easily in the wafer load-lock chamber of extreme ultraviolet and electron beam exposure systems dedicated to research and development activities and allows for HRR films to be uniformly deposited or developed in the same vacuum environment. The HRR shows a sublimation rate dependence on temperature that obeys a Clausius–Clapeyron relation, with thermal stability up to 275°C. Flood exposures of the HRR show identical sensitivity between wet- and dry-deposited films, whereas contrast degradation is observed when dry development is initiated by increasing the temperature prior to system pump down. A modified sublimation setup allows for the dry development of exposed HRR samples inside the electron beam tool without breaking vacuum. In this case, nominally patterned 25 nm L/S are identically resolved at 30 keV for wet- or dry-developed HRR
Data-driven model of glycolysis identifies the role of allostery in maintaining ATP homeostasis
No full textThe specific roles of allostery in regulating metabolism are not well understood. Here, we develop a data-driven mathematical model of mammalian glycolysis that uses enzyme rate equations and coupled ordinary differential equations. The key components of our model are the rate equations for allosterically regulated enzymes based on the Monod-Wyman-Changeux model that we derive using a rigorous analysis of thousands ofin vitrokinetic measurements. The resulting model recapitulates the properties of glycolysis observed in live cells and shows that the specific function of allosteric regulation is to maintain high and stable concentrations of ATP, while glycolysis without allosteric regulation is fully capable of producing ATP and ensuring that ATP hydrolysis generates energy. Our data-based modeling approach provides a roadmap for a better understanding of the role of allostery in metabolism regulation.One-Sentence SummaryThe glycolysis model based on allosteric enzyme rate equations recapitulates properties of glycolysis observed in live cells
Quantum Biology in Cellular Migration
No full textThe impact of magnetic fields on cellular function is diverse but can be described at least in part by the Radical Pair Mechanism (RPM), where magnetic field intervention alters reactive oxygen species (ROS) populations and downstream cellular signaling. Here, cellular magnetophoresis within three-dimensional scaffolds was monitored in an applied oscillating 1.4 MHz radiofrequency (RF) magnetic field with an amplitude of 10 μT and a static 50 μT magnetic field. Given that cellular respiration or glycolysis can be increased based on the orientation of the RF magnetic field, this study focused on the parallel orientation to increase ATP synthesis. Results suggest that RF accelerated clustering and elongation after 1 day with increased levels of clustering and cellular linkage after 7 days. Electron microscopy provided additional topological information and verified the development of fibrous networks and extracellular matrix were visualized after 7 days in samples maintained in RF. Analysis of the distribution of cells within the scaffolds revealed that the clustering rate during the first day was increased nearly five times in the RF environment. This work demonstrates time-dependent cellular magnetophoresis that may be influenced by quantum biology (QB) processes and signaling that can further attenuate or enhance cellular bioenergetics and behavior
A cryogenic, coincident fluorescence, electron and ion beam microscope
No full textCryogenic electron tomography (cryo-ET) combined with sub-tomogram averaging, allows in-situ visualisation and structure determination of macromolecular complexes at sub-nanometre resolution. Cryogenic focused ion beam (cryo-FIB) micromachining is used to prepare a thin lamella-shaped sample out of a frozen-hydrated cell for cryo-ET imaging, but standard cryo-FIB fabrication is blind to the precise location of the structure or proteins of interest. Fluorescence-guided focused ion beam (FIB) milling at target locations requires multiple sample transfers prone to contamination, and relocation and registration accuracy is often insufficient for 3D targeting. Here, we present in-situ fluoresence microscopy-guided FIB fabrication of a frozen-hydrated lamella to solve this problem: we built a coincident 3-beam cryogenic correlative microscope by retrofitting a compact cryogenic microcooler, custom positioning stage, and an inverted widefield fluorescence microscope (FM) on an existing focused ion-beam scanning electron microscope (FIB-SEM). We show FM controlled targeting at every milling step in the lamella fabrication process, validated with transmission electron microscope (TEM) tomogram reconstructions of the target regions. The ability to check the lamella during and after the milling process results in a higher success rate in the fabrication process and will increase the throughput of fabrication for lamellae suitable for high-resolution imaging
Photochemistry of thymine in solution and DNA revealed by an electrostatic embedding QM/MM combined with mixed-reference spin-flip TDDFT
No full textThe photochemistry of nucleobases, important for their role as building blocks of DNA, is largely affected by the electrostatic environment in which they are soaked. For example, despite the numerous studies of thymine in solution and DNA, there is still a debate on the photochemical deactivation pathways after UV absorption. Many theoretical models are oversimplified due to the lack of computationally accurate and efficient electronic structure methodologies that capture excited state electron correlation effects when nucleobases are embedded in large electrostatic media. Here, we combine mixed-reference spin-flip time-dependent density-functional theory (MRSF-TDDFT) with electrostatic embedding QM/MM using electrostatic potential fitting (ESPF) atomic charges, as a strategy to accurately and efficiently describe the electronic structure of chromophores polarized by an electrostatic medium. In particular, we develop analytic expressions for the energy and gradient of MRSF/MM based on the ESPF coupling using atom-centered grids and total charge conservation. We apply this methodology to the study of solvation effects on thymine photochemistry in water and thymine dimers in DNA. In the former, the combination of trajectory surface hopping (TSH) non-adiabatic molecular dynamics (NAMD) with MRSF/MM remarkably revealed the accelerated deactivation decay pathways, which is consistent with the experimental decay time of ~ 400 fs. The enhanced hopping rate can be explained by the preferential stabilization of corresponding conical interactions due to their increased dipole moments. Structurally, it is a consequence of characteristic methyl puckered geometries near the conical intersection region. For the thymine dimer in B-DNA, we found new photochemical pathways through conical intersections that could explain the formation of cyclobutadiene dimers and 6-4 photoproducts
Improving Molecular Catalyst Activity using Strain-Inducing Carbon Nanotube Supports
No full textSupport-induced strain engineering is a powerful strategy to modulate the electronic structure of two-dimensional materials. However, controlling strain of planar molecules such as metallophthalocyanines and metalloporphyrins is technically challenging due to their sub–2 nm lateral size. In addition, the effect of strain on molecular properties remains poorly understood. Starting with cobalt phthalocyanine (CoPc), a model CO₂ reduction reaction (CO₂RR) catalyst, we show that carbon nanotubes (CNTs) are ideal substrates for inducing optimum properties through molecular curvature. Using a tandem-flow electrolyzer with monodispersed CoPc on single-walled CNTs (CoPc/SWCNT) as the catalyst, we achieve a methanol partial current density of >90 mA cm⁻² with a selectivity of >60%. CoPc on wide multi-walled CNTs (MWCNTs) leads to only 16.6% selectivity. We report X-ray spectroscopic characterizations to unravel the distinct local coordinations and electronic structures induced by the strong molecule-support interactions. These results agree with our Grand Canonical Density Functional Theory that calculates the energetics as a function of applied potential. We find that SWCNTs induce curvature in CoPc, which improves *CO binding to enable subsequent formation of methanol, while wide MWCNTs favor CO desorption. Thus, we demonstrate that the SWCNT-induced molecular strain increases methanol formation. We also show that induced strain can accelerate the oxygen reduction reaction and CO2RR for other catalysts. Our results show the important role of SWCNTs beyond catalyst dispersion and electron conduction
Robust Safe Control Synthesis with Disturbance Observer-Based Control Barrier Functions
No full textIn a complex real-time operating environment, external disturbances and uncertainties adversely affect the safety, stability, and performance of dynamical systems. This paper presents a robust stabilizing safety-critical controller synthesis framework with control Lyapunov functions (CLFs) and control barrier functions (CBFs) in the presence of disturbance. A high-gain input observer method is adapted to estimate the time-varying unmodelled dynamics of the CBF with an error bound using the first-order time derivative of the CBF. This approach leads to an easily tunable low order disturbance estimator structure with a design parameter as it utilizes only the CBF constraint. The estimated unknown input and associated error bound are used to ensure robust safety and exponential stability by formulating a CLF-CBF quadratic program. The proposed method is applicable to both relative degree one and higher relative degree CBF constraints. The efficacy of the proposed approach is demonstrated using a numerical simulations of an adaptive cruise control system and a Segway platform with an external disturbance
Exploring metallicity-dependent rates of Type Ia supernovae and their impact on galaxy formation
No full textType Ia supernovae play a critical role in stellar feedback and elemental enrichment in galaxies. Recent transient surveys like the All-Sky Automated Survey for Supernova (ASAS-SN) and the Dark Energy Survey (DES) find that the specific Ia rate at z ~ 0 may be ~ 15-50 times higher in lower-mass galaxies than at Milky Way-mass. Independently, Milky Way observations show that the close-binary fraction of solar-type stars is higher at lower metallicity. Motivated by these observations, we use the FIRE-2 cosmological zoom-in simulations to explore the impact of varying Ia rate models, including metallicity dependence, on galaxies across a range of stellar masses: 10⁷ M_⊙ - 10¹¹ M_⊙. First, we benchmark our simulated star-formation histories (SFHs) against observations. We show that assumed SFHs and stellar mass functions play a major role in determining the degree of tension between observations and metallicity-independent Ia rate models, and potentially cause ASAS-SN and DES observations to be much more consistent with each other than might naively appear. Models in which the Ia rate increases with decreasing metallicity (as ~ Z^(-0.5) to Z⁻¹) provide significantly better agreement with observations. Encouragingly, these increases in Ia rate (> 10x in low-mass galaxies) do not significantly impact galaxy stellar masses and morphologies: effective radii, axis ratios, and ν/σ remain largely unaffected except for our most extreme rate models. We explore implications for both [Fe/H] and [α/Fe] enrichment: metallicity-dependent Ia rate models can improve agreement with observed stellar mass-metallicity relations in low-mass galaxies. Our results demonstrate that a wide range of metallicity-dependent Ia models are viable for galaxy formation and motivate future work in this area