Papers

Many biological machines function through controlled conformational transitions, yet designing synthetic nanostructures with prescribed dynamical behavior remains a major challenge. Here, we develop a modular inverse-design framework for bistable nanostructures whose function is controlled by an energy profile along a geometric reaction coordinate. Inspired by proteins with rigid domains connected by flexible hinges, we introduce a hinge-arm paradigm in which a small bistable hinge controls the energetics of a conformational transition, while rigid arms map this transition onto the separation between external binding sites. Specifically, we ask which features of a target energy profile can be programmed under different design constraints. We find that the energy barriers and the binding-site separations in the two metastable states can be readily designed, while controlling the location of the transition state or the full shape of the energy profile requires additional design freedom. Using a differentiable design framework, we find that some optimized solutions are numerically inexact but still display the functional behavior for which the target profile was selected, emphasizing the importance of function-based evaluation criteria. These results establish a practical hierarchy of designability for bistable nanostructures and provide a route toward synthetic nanomachines that couple conformational transitions to target behavior.

Understanding stellar magnetic activity is central to exoplanet science in two ways: it sets the dynamic astrospheric boundary condition governing planetary space environments, and it is the primary obstacle to exoplanet detection and characterisation, since magnetically driven variability imprints correlated quasi-periodic signals across detection time series. In cool stars, MHD-dynamo-generated fields emerge at the photosphere as bipolar regions, drive chromospheric and coronal heating, modulate irradiance and wind, and power flares and coronal mass ejections. Spatial scales range from individual flux tubes to global coronal configurations, and temporal scales from minutes to decades and beyond, requiring observational and theoretical tools of correspondingly wide scope. We review observational manifestations and physical models of magnetic activity in stars with outer convective envelopes, addressed to the exoplanet community. We develop the solar-stellar connection through the 'Sun in Time' framework and a sequence of solar analogues serving as evolutionary snapshots of a solar-mass star over several Gyr. We survey photospheric, chromospheric, and coronal activity diagnostics across timescales, together with forward-modelling tools translating surface field distributions into signals at or above the level of exoplanet detection. Empirical rotation-activity relationships and their physical interpretation are examined across all three atmospheric layers. Surface reconstruction techniques are assessed for their diagnostic reach and limitations. The evolution of magnetism in solar-like stars is discussed as context for habitability and as a window to other worlds. We close with an account of how stellar magnetism sculpts the astrospheric environment and affects close-in exoplanets, followed by a synthesis of outstanding issues and an outlook on future prospects.

Exceptionally, a bunched electron beam can get trapped by its own spontaneously emitted synchrotron undulator radiation in the self-interaction scheme of TES (Tapering Enhanced Superradiance). In this scheme, excess radiative energy is extracted from the beam by tapering the undulator after the bunch trapping. To avoid slippage of the radiation wavepacket away from the bunch, the interaction takes place in a waveguide with a slow group velocity mode. Here we study the time domain waveform of the Electric Field and the radiation energy buildup in this scheme. We compare its analytical theory and numerical simulations in an ideal exemplary setup based on a rectangular waveguide and a planar undulator

Molecular gas in galaxies is shaped by both star formation and active galactic nuclei. In NGC 1068, the circumnuclear disk and the starburst ring offer a nearby case to study these effects with many molecular tracers. Earlier work has shown strong outflow activity and complex chemistry, which motivates the use of methods that combine radiative transfer with time-dependent chemistry. Our aim is to map the physical conditions across the circumnuclear disk and the starburst ring of NGC 1068 and to test whether the nuclear outflow influences the molecular gas in the ring. We also examine whether the heating or the quiescent cloud scenario better matches the observations. We use archival ALMA observations obtained in Bands 3, 4, and 5, covering molecular species including HCN, HCO+, HNC, CS, CN and C2H. All data cubes are convolved to a common resolution of 0.8" and are sampled into 56 pc hexagons with a signal-to-noise threshold of three. We perform hierarchical Bayesian inference that links a non-LTE radiative transfer module SpectralRadex with chemical modelling. To make the analysis efficient, we replace direct UCLCHEM calculations with a neural network emulator trained on a large model grid. Sampling is done with Nautilus. We also compare our results with previous studies that used RADEX and UCLCHEM for selected regions. The emulator reproduces the UCLCHEM abundances with low error and allows inference at modest computational cost. We find clear radial and azimuthal variations in gas density, temperature, column density, and cosmic-ray ionization rate.

The motion of a particle in vacuum near macroscopic bodies gives rise to a Magnus-like contribution to the nonequilibrium Casimir-Polder force. This effect originates from the interplay between particle dynamics and material-modified electromagnetic quantum fluctuations, inducing in the particle a direction-dependent angular momentum coupled to the electromagnetic field spin. The resulting drift force is proportional to the cross product of the particle's angular and translational velocities, revealing a rotational transport component in the nonequilibrium Casimir-Polder interaction. Our results establish a striking connection between quantum fluctuations-induced forces and the classical Magnus effect in fluid dynamics.

In light of the increasing supply chain concerns regarding silver for solar cell metallization, the replacement of the silver contacts by copper is desirable. As copper diffuses readily in silicon, deposition of an additional diffusion barrier to protect the respective absorber material stacks is required. We investigate multifunctional layers of transparent conductive oxides (TCOs) from the In-Zn-O system to serve as front electrode and Cu diffusion barrier coating, focusing on purely amorphous layers without grain boundaries to impede copper diffusion. We employ a 2D combinatorial approach to simultaneously screen the Zn/(In+Zn) ratio and the oxygen content in a single materials library deposited by magnetron sputtering without intentional substrate heating. Cu diffusion barrier performance was evaluated by depositing Cu on top of intentionally ultrathin In-Zn-O libraries of 7 nm on silicon wafers and annealing them at temperatures of 200-450{\deg}C. Both the formation of copper silicides, as well as the silicon photoluminescence signal were monitored. The first was detected only after the crystallization of the In-Zn-O films and required annealing temperatures of 450{\deg}C and above. Even for extended dwell times of 20 h at a relevant process temperature of 200{\deg}C, we find no evidence of Cu ingress for most of our fabricated In-Zn-O compositions, whereas Si/Cu stacks without In-Zn-O barriers showed a reduction of their photo-luminescence intensity already after less than 1 h. These results suggest thin amorphous In-Zn-O films with an optimal Zn/(In+Zn) ratio of ~0.12 and intermediate oxygen deficiency as effective transparent conductive Cu diffusion barriers for solar cell applications.

Quasiperiodic systems usually interpolate between extended, critical, and localized states as the quasiperiodic modulation is increased. Here we show that the magnetic Qi-Wu-Zhang Chern-insulator model realizes a distinct full-spectrum transition in which localization is avoided. For an irrational magnetic flux, the two-dimensional model reduces to a spinor quasiperiodic chain with a matrix onsite modulation controlled by the hopping amplitude $t_x$. When $|m+2|>t_y$, increasing $t_x$ produces the conventional extended-critical-localized sequence with a critical line at $t_x=t_y$. In contrast, when $|m+2|\le t_y$, the system changes from an extended phase to a critical phase at $t_x=|m+2|$ and remains critical even for stronger quasiperiodic modulation. Finite-size scaling of the average inverse participation ratio gives $\overline{\mathrm{IPR}}\sim q^{-\alpha}$ with $0<\alpha<1$ throughout this persistent critical regime. A dual transformation exchanging $t_x$ and $t_y$, together with a Lyapunov-exponent analysis, explains the phase diagram. Wave-packet dynamics further distinguish ballistic, anomalous-diffusive, and localized regimes. These results identify magnetic Chern-insulator systems as a natural platform for robust criticality and anomalous quantum transport.

The core step in quantum simulations is typically matrix vector multiplication $\phi = \Hmat \psi$. Executing this step is limited by memory requirement to store the Hamiltonian. We present a memory-scalable, hardware-adaptive matrix-free framework for applying large operators on vectors without materializing the full matrix on a single accelerator. The operator is represented through a block-procedural interface: blocks may be generated, loaded, cached, distributed, or applied directly only when their action is needed. For quantum simulation, it provides the core kernel for quantum operations. An adaptive planner selects block size, cache strategy, GPU grouping, row distribution, and task parallelization from memory and workload estimates. We describe analytic, measured, and learned planning strategies that choose between procedural generation, partial caching, full caching, and row-distributed caching. The method removes the requirement that the full dense matrix fit in the accelerator memory. This shifts large simulations from a fixed memory barrier to a tunable balance between block generation, cache reuse, data movement, parallel scheduling, and numerical accuracy.

We consider a family of continuous-time Markov chains with finite strongly connected transition graph and rates $\left(r_N\right)_{N>0}$ depending on a parameter $N$, so that, when $N$ is large, transitions may happen on different time scales. Under suitable general assumptions on the asymptotic behavior of the rates, we give a recursive characterization of the limiting invariant measure. The recursion is encoded in a forest structure equivalent to the one recently developed in the analysis of dynamical aspects of metastability \cite{BL,LX}. Our proof is based on a combinatorial representation of the invariant measure, given by the Markov chain tree theorem. Basic steps are the reduction of the chain by a trace process, the introduction of an effective dynamics, and a careful analysis of the set of relevant arborescences in the expansion. In particular we use a factorization of fast arborescences. As a byproduct we obtain properties of the arborescences of generalized star-delta reductions of weighted digraphs.

We explore approaches to numerically optimize a segment of the perturbative series for physical quantities using the QCD renormalization group. We apply these methods to the perturbative series for the coefficient function $C_{Bjps}$ of the Bjorken polarized sum rule and the Adler function $D_A$. Using various techniques proposed in the literature, we discuss the consequences of “optimization.”

We study scattering in noninteracting multi-terminal quantum wire junctions and show that junctions with dihedral symmetry can exhibit exact zero-reflection points for $N \ge 4$ terminals. By analyzing the scattering matrix, we identify these reflectionless points in the $(E,t')$ parameter space, where $E$ is the incident particle energy and $t'$ is the junction hopping amplitude. These points exhibit an even-odd dependence on $N$ and converge asymptotically to a common limiting value in the large-$N$ limit. We show that the reflectionless points are characterized by an integer winding number associated with the phase of the reflection amplitude, providing a topological description for their stability against weak on-site disorder. We also consider junctions with broken time-reversal symmetry and find that a magnetic flux can induce additional reflectionless points, including for the $N = 3$ case. For a four-terminal junction threaded by a $\pi$-flux, we identify a unique parameter regime in which the reflection amplitude vanishes over the entire energy band. Finally, we discuss experimental signatures through the behavior of Friedel oscillations and examine the stability of these reflectionless points in the presence of weak interactions.

Strong gravitational lensing is a powerful tool for investigating the universe's large-scale structure and understanding the properties of dark matter and dark energy. The magnification and distortion of distant background sources by cluster lenses have enabled detailed studies of both lens and source populations, making these systems promising probes for precision cosmology. While classical strong-lenses are well understood, much remains to be explored for hyperbolic-umbilic (HU) exotic lenses, which produce unique telescopic effects and uncommon images with potentially very high magnifications. Identifying and quantifying these objects, along with characterising their geometric configurations, could have broad implications for studies of galaxy clusters and lensed galaxy populations. Using parametric cluster mass models, we mapped regions in the source plane where HU exotic images can form and integrate these areas over redshift to define an exotic comoving volume (V_z<10). We validated this approach on confirmed exotic systems (RXJ0437.1+0043 and Abell 1703), then applied it to a sample of 74 cluster models. We show HU-region contours for the most promising clusters, assess both systematic and stochastic uncertainties on exotic area and volume estimates, and confirm that our error remains sufficiently small to support robust conclusions. Next, we explore correlations between six cluster parameters and (V_z<10), finding that pairs of parameters, especially ellipticity with Einstein radius or cuspiness, best distinguish high-(V_z<10) systems. Finally, we estimate that each cluster contributes ~0.125 galaxies to its exotic volume on average (as a conservative lower bound), meaning that observing 19 clusters yields a 90% chance of detecting at least one HU system in a random sample.

Spin point groups classify magnetic phases in the weak spin-orbit coupling regime and characterize the static properties of altermagnetic phases, but their dynamical consequences remain largely unexplored. Here, we derive selection rules for high-harmonic generation of charge and spin currents by extending dynamical symmetry to include spin point group operations. Since spin currents transform under both real and spin space operations, whereas charge currents transform only under real space operations, spin current selection rules can reveal magnetic information that is inaccessible to charge current harmonics. In a minimal altermagnetic model, an axis-aligned linearly polarized drive is non-diagnostic for distinguishing ferromagnetic and altermagnetic phases, although the antiferromagnetic phase is distinguished by the absence of the corresponding spin-current harmonics. A diagonal linearly polarized drive distinguishes the three spin-point-group phases within the weak-coupling spin-group description, whereas a single-helicity circularly polarized drive provides a sharper spin-current-harmonic criterion for distinguishing them from magnetic-point-group mimics. These results establish spin current harmonics as a dynamical probe of spin group symmetry. Finite spin-orbit coupling lifts these zeros only perturbatively: the forbidden harmonics acquire amplitudes analytic in the coupling strength, so that the fingerprint becomes a small same-order helicity contrast, below $3\times10^{-2}$ at low orders for couplings up to $10^{-2}$ of the hopping in our model.

We perform the first three-dimensional hydrodynamical simulations of cosmological first-order phase transitions in an expanding background. These simulations consistently incorporate the effects of the evolving phase transition strength throughout the full nucleation process of slow phase transitions. We find that, in addition to reducing mean bubble separations via an effectively enhanced nucleation rate, cosmic expansion unexpectedly induces highly nonlinear growth in the gravitational wave energy fraction, ultimately leading to a significant $\mathcal{O}(10)$ to $\mathcal{O}(100)$ amplification of the gravitational wave spectra. This amplification is more pronounced for initially weak transitions than for those of initially intermediate strength. Our results highlight the challenge and importance of accurately modelling slow phase transitions while accounting for cosmic expansion.

Recent Scanning Tunneling Microscopy (STM) experiments measuring the superconducting gap features in thin films of superconducting bilayer nickelates La2PrNi2O7 at ambient pressure and compressive strain paved the way to study the Cooper-pairing models and the band-selective identification of the gap features in these systems. Here, using the realistic two-orbital bilayer model and the continuum Green's function formalism, we theoretically analyze orbital and band-selective local density of states as well as the corresponding STM spectra. We find that the multiorbital character and the spatial dependence of the Wannier functions leads to the spectra developing characteristic features depending on the position of the scanning tunneling microscope's tip. This allows for a band-resolved analysis of the superconducting coherence peaks and scattering momenta. We identify a clear path for experimental measurements to not only identify the debated incipiency of the gamma-band, but also identification of the coherence peaks' band origins via distance dependent measurements of the local density of states and its corrections through impurity scattering.

Three ingredients of the elementary Landau-Zener problem determine the familiar expression $a_{LZ}\equiv\exp\left[-\pi/(2\epsilon)\right]$ for the asymptotic value of the probability amplitude for remaining in the initial level: (i) A wave whose phase is determined by the product of a contour integral over a simple pole at the origin of the complex plane and the inverse of twice the scaled chirp parameter $\epsilon$. (ii) An asymptotic limit of the associated path connecting the points $\pm 1$ along the real axis and circumventing the pole in the upper half-plane, and (iii) a half-circle in the lower half plane enclosing together with the asymptotic path the pole. The Cauchy theorem immediately provides us with the value $\ii\pi$ of the asymptotic contour, and thus with $a_{LZ}$. Our analysis demonstrates not only that $a_{LZ}$ is the consequence of a logarithmic phase singularity but also explains why the Markov approximation also leads to $a_{LZ}$.

We have studied spin-related transport in a polycrystalline NiCo2O4 (NCO) film on a MgAl2O4/Si(001) substrate, motivated by potential applications of the theoretical half-metallicity of NCO to Si-based high-performance spin-transport devices. Our approach is to systematically measure and analyze the temperature dependence of the film's resistivity ($\rho-T$) with various in-plane currents (100 nA$-$1 mA) and temperatures (4$-$290 K). With increasing current, the $\rho-T$ curve changes drastically from semiconducting ($d\rho/dT<0$) to non-monotonic and eventually toward metallic ($d\rho/dT>0$). A distinctive feature is that the single NCO film exhibits a $\rho-T$ characteristic of polycrystalline defective NCO at 100 nA, whereas it exhibits a $\rho-T$ characteristic of epitaxial less-defective NCO over a wide temperature range at 1 mA. This current-induced evolution of $\rho-T$ reflects the enhancement of the Curie temperature of defective regions near grain boundaries, accompanied by enhanced spin alignment there. We proposed a spin-related transport model that extends conventional hopping conduction models by incorporating the temperature- and current-dependent degree of spin alignment, as well as its spatial dependence inherent to polycrystalline NCO. This model comprehensively explains the interplay between the spin-alignment profile and transport mechanism. The analysis reveals that spin injection from grain bodies to grain boundaries enhances the spin alignment there and strengthens double-exchange interactions, facilitating conduction. This phenomenon strongly depends on both temperature and current. Our findings provide evidence of spin-polarized electrons inside the grain bodies, highlighting the potential of our polycrystalline NCO film as an efficient spin source. The present model is further supported by current$-$voltage and magnetoresistance features.

Kaluza-Klein (KK) Gravitons are the direct collider imprints of the higher dimensional bulk physics in our four dimensional universe, arising from the compactification of an extra spatial dimension. In this work, we consider a two-brane warped geometry with a 5D $f(\mathcal R) = \mathcal R + \alpha\mathcal R^2$ gravity along with cosmological constant $\Lambda$. The warped spacetime provides an elegant resolution of the gauge-hierarchy problem without introducing any intermediate scale, while the Planck-scale curvature of the underlying $AdS_5$ bulk naturally motivates the inclusion of higher-curvature corrections. For small values of higher-curvature parameter ($\alpha$), we obtain the leading-order back-reacted warp factors perturbatively from the modified gravitational field equations. In the backdrop of a warped braneworld model, we have solved the Schrödinger-like equation governing the graviton fluctuations using a Euclidean path integral formalism, yielding the KK graviton spectrum and normalized wavefunctions directly from the corresponding quantum-mechanical propagator. Treating these results as the unperturbed background, we analytically determine the higher curvature corrections to KK graviton spectrum and their couplings to Standard Model (SM) matter fields. We find that there is an appreciable upward shift in the KK graviton masses while leaving the graviton-SM couplings only mildly modified as compared to a model with only Einstein gravity in the bulk. However the net cross-section of processes involving virtual gravitons appears to be suppressed whereas the dilepton and diphoton decay widths of the gravitons are significantly enhanced because of the higher curvature corrections. Overall, these effects lead to observable modifications to both the production and decay signatures of massive KK gravitons and may be probed in some future precision collider experiments.

Quantum gravity suggests that spacetime may not be fundamental, and it has been argued that we can understand a theory without a fundamental spacetime if we are able to claim that spacetime `emerges' from some non-spatiotemporal entities. In this sense, strategies like functionalism have been deployed to claim that this emergence is possible and plausible, both in principle and in practice for current approaches to quantum gravity. In this article I argue that this analysis is incomplete, as it tends to overlook the way the dynamics of these theories is `quantum' in a way that differs from standard quantum theory. The challenge for the emergentist (and for the quantum gravity theorist) is to give an interpretation not only to the kinematical and classical aspects of these theories, but to the dynamical and quantum ones, and to show how the spacetime roles can be fulfilled, if possible at all. Therefore, I argue that some current approaches to quantum gravity seem to fail to provide meaningful theories, that spacetime functionalism is of no help, and that the position of the spacetime emergentists is weakened, as they lack any example of a successful reduction of spacetime to some truly quantum non-spatiotemporal stuff.

Rare-earth quantum materials provide a promising platform for emergent phenomena ranging from quantum spin liquids with long-range entanglement to topological magnetic textures. However, the strong spin-orbit coupling that stabilizes their low-energy pseudospin degrees of freedom also tends to generate strongly anisotropic exchange interactions, complicating the realization of quasi-isotropic Heisenberg magnetism. Here we investigate the microscopic origin of superexchange in $\mathrm{Ce}^{3+}$- and $\mathrm{Yb}^{3+}$-based insulators with edge-sharing octahedral geometry. Using degenerate perturbation theory for a multiorbital Hubbard model, we show that isotropic exchange originates predominantly from virtual hopping within the ground-state Kramers doublet, whereas anisotropic interactions arise primarily from processes involving excited multiplets. This leads to a simple orbital design principle: quasi-isotropic exchange is promoted when the ground-state doublet has a strong maximal-angular-momentum character with respect to the quantization axis perpendicular to the superexchange plane spanned by rare-earth and ligand ions. We demonstrate this mechanism for both ideal and distorted geometries and show that it is broadly consistent with experimentally studied Yb-based insulators. Our results establish a practical framework for engineering quasi-isotropic interactions in rare-earth quantum materials.

Motivated by the quest for active quantum matter, we investigate the dynamics of an impurity immersed in a quantum gas – a polaron – whose coupling to the surrounding medium is periodically modulated in time, alternating in sign. By integrating out the bath degrees of freedom, we derive an effective velocity-dependent drag force acting on the impurity. Above a critical modulation frequency, the corresponding drag coefficient becomes negative at low velocities, signaling the onset of self-propulsion. In the classical limit, we characterize this transition as a function of the modulation frequency and the bath chemical potential. We then compute the leading-order quantum corrections to the impurity dynamics and show that, while the transition remains robust, it can be suppressed by sufficiently precise measurements of the impurity position.

We investigate the emergence of topological superconductivity at the two-dimensional heterostructure interface between a $p$-wave magnet (pWM) and an $s$-wave superconductor. By analyzing nodal gap closings, we identify seven distinct nodal topological phases, each characterized by the presence of Majorana zero-energy flat bands and quantized zero-bias conductance peaks. We demonstrate that the effective $p$-wave nature of the system gives rise to spin-triplet pairing correlations with even-frequency, odd-parity and odd-frequency, even-parity symmetries. Notably, the introduction of inter-orbital hopping induces an exotic orbital-singlet term characterized by simultaneous odd-parity and odd-frequency. Furthermore, we explore the transition from static phases to Floquet topological regimes through periodic driving. These driven phases host both zero and $\pi$ Majorana flat bands, with transport signatures governed by the Floquet sum rule. Most significantly, we show that periodic driving fundamentally reshapes the topological and superconducting landscape by generating multiple nodal points that support higher winding numbers and multiple Majorana flat bands, while the emergent Floquet degree of freedom doubles the number of symmetry-allowed Cooper-pair correlations. The first class of correlations is hosted by the even-Floquet sectors and has a direct counterpart in the static limit. In contrast, the second is a distinct Floquet-generated class that confines to the odd-Floquet sectors, representing a fundamentally nonequilibrium pairing channel that cannot exist in static systems. Finally, we demonstrate the robustness of these topological modes against strong disorder, confirming their potential for stable fault-tolerant applications.

Direct electron-density measurements at high redshift are usually limited to galaxies with individually strong density-sensitive doublets, and therefore may not trace the average interstellar medium of ordinary low-mass galaxies. We stack public JWST/NIRSpec medium-resolution spectra from the DAWN JWST Archive to measure [SII]-based electron densities $n_e$ for low-mass galaxies at $2<z<7$. The stacks yield $n_e\simeq100$–$150\ {\rm cm^{-3}}$ at $2<z<5$ and $n_e=381^{+104}_{-89}\ {\rm cm^{-3}}$ at $5<z<7$, corresponding to an evolution $n_e=n_{e,0}[(1+z)/(1+2.3)]^\alpha$ with $n_{e,0}=76^{+22}_{-23}\ {\rm cm^{-3}}$ and $\alpha=1.88^{+0.60}_{-0.64}$. A mass-matched stacking test gives a consistent rising trend, indicating that the increase is not driven solely by changing stellar-mass distributions. Individually measurable galaxies with both [SII] components detected at ${\rm S/N}>5$ have a higher normalization, $n_{e,0}=211^{+36}_{-31}\ {\rm cm^{-3}}$, showing that individual-doublet samples select a denser subset. Stacking archival JWST spectra therefore provides a direct route to measuring the average gas density of low-mass galaxies below the individual-doublet detection threshold.

Atmospheric entry processes are characterized by high-enthalpy gas flows in strong thermo-chemical non-equilibrium. Accurate simulations of such conditions remain challenging due to the extreme conditions and the complex influence of internal energy modes. In particular, the common assumption of uncoupled harmonic vibrations may break down, and excited internal energy states can directly influence reaction rates. Previously, an anharmonic oscillator model has been developed by Civrais et al. to improve the accuracy of the Direct Simulation Monte Carlo (DSMC) method under such conditions. However, this extension has so far been limited to diatomic molecules. To increase the accuracy of the DSMC method in the open-source code PICLas, the anharmonic oscillator model is extended to include polyatomic species. The proposed model explicitly considers anharmonic effects and intramolecular energy redistribution. Vibrational degrees of freedom are treated in a local mode basis, in which anharmonic stretching modes are harmonically coupled by harmonic bending modes. The coupling allows for the redistribution of localized vibrational excitation. Dissociation can occur by the strong excitation of a stretching mode, and specific modes can be coupled to the reaction coordinate of the transition state in bimolecular exchange reactions. The newly developed model is evaluated by the comparison to high-fidelity calculations for a set of representative processes. Investigated are different dissociation reactions, which exhibit a high degree of energy redistribution, and the hydrogen-exchange reaction between methane and a hydrogen radical, in which only selected modes contribute to the reactive process. In addition, the recombination-dissociation equilibrium system has been investigated for methane.

Observing the 21-cm HI line in absorption provides a powerful means of tracing the cold neutral gas in normal and active galaxies across cosmic time. The frequency coverage and sensitivity of SKAO will allow us to detect HI in absorption from z = 0 to beyond z = 6, enabling the characterisation of the properties of cold gas in and around galaxies at all epochs. This chapter summarises recent advances in absorption-line studies, lessons learned from precursor surveys, and updates the science case presented in Kanekar and Briggs (2004) and Morganti et al. (2015), focusing on the capabilities enabled by the SKA design baseline, Array Assembly 4 (AA4). We expand on these earlier works by presenting new opportunities to simultaneously search for OH 18-cm absorption, an efficient tracer of diffuse molecular gas that complements the atomic gas traced by HI absorption, as well as the need for sub-arcsecond scale spectroscopic imaging and multi-wavelength data from large surveys. These advances will allow SKAO absorption surveys to address key questions surrounding the fuelling and feedback cycles of AGN and the evolution of the cold neutral gas across cosmic time.

We investigate how cooperative feedback shapes global oscillatory dynamics in a glycolysis model with product recycling and allosteric phosphofructokinase regulation. Using bifurcation theory and numerical continuation, we analyze the stability of equilibria and characterize Hopf and generalized Hopf bifurcations, using the Hill exponent as an effective measure of cooperativity. We show that a codimension-2 cusp-of-cycles point governs the creation and annihilation of detached branches of limit cycles (isolas) and, together with saddle-node bifurcations of limit cycles, organizes a regime map of six qualitatively distinct dynamical regions. In the birhythmic regime two stable oscillatory states coexist on connected branches; in the isola regime a stable oscillation exists on a fully disconnected branch, producing threshold-dependent onset of rhythmic activity. Time-domain simulations confirm coexistence of distinct rhythms and illustrate how the choice of initial condition determines which attractor is reached. Together, these results show how variations in cooperative feedback strength can generate isolated oscillatory modes and multistability in metabolic networks, highlighting isola dynamics as a general mechanism for rhythm selection and switching in nonlinear biological oscillators.

We introduce a squeezed-state pulse-position modulation (S-PPM) format, where the empty slots are squeezed vacuum states and the pulse slot is a displaced squeezed state. Based on this property, we propose an inverse-squeezing conditional pulse-nulling (IS-CPN) receiver. In the ideal case, inverse squeezing maps S-PPM into an equivalent coherent-state PPM signal with a large pulse energy, leading to a closed-form expression for the receiver error probability. We further analyze IS-CPN under common phase diffusion using a finite-path MAP formulation with phase-averaged likelihoods. Numerical results show that IS-CPN outperforms conventional CPN under the same energy constraint and remains advantageous under phase noise and finite photon-number resolution. These results demonstrate that combining squeezed-state modulation with inverse-squeezing conditional nulling can improve photon-efficient optical communication.

Shallow strained Ge quantum wells have gained recent attention for realizing scalable, high-performance hybrid superconductor/semiconductor-based qubits. Epitaxial superconducting contacts can improve the quality and consistency of the superconductor/semiconductor interface. The growth of Ge quantum wells by molecular beam epitaxy is then motivating due to the relative ease of integration with epitaxial superconductor growth. However, the performance of Ge quantum wells grown by molecular beam epitaxy (MBE) has been limited. To improve the properties of MBE-grown Ge quantum wells, the growth conditions were systematically optimized. Thick buffer layers are utilized to eliminate certain defects, and an optimal growth temperature is found. A peak hole mobility of 105,000 cm\textsuperscript{2}/Vs at 2 K is obtained in a 22-nm deep Ge quantum well, demonstrating that the Ge quantum wells grown in this study represent the highest mobilities for shallow MBE-grown samples. Mobility modeling indicates that the increase in mobility due to growth temperature optimization are likely due to a reduction in interface roughness scattering, and further improvements in mobility are expected through improved surface passivation.

The FAST All Sky HI Survey (FASHI) conducted with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) has mapped $\sim 19500\,\mathrm{deg}^2$ of the sky north of DEC $= -14^{\circ}$, detecting $156411$ extragalactic HI sources at $z< 0.09$ with a median sensitivity of $0.57\,\mathrm{mJy}\,\mathrm{beam}^{-1}$ at a velocity resolution of $6.4\,\mathrm{km}\,\mathrm{s}^{-1}$. The survey achieves unprecedented depth and area coverage, significantly improving upon previous single-dish surveys. Through a detailed completeness analysis that accounts for the survey's non-uniform sensitivity and line-width dependence, we construct a robust HI mass function (HIMF) using a completeness-corrected sample of over $109000$ sources. The HIMF is robustly constrained down to $M_{\mathrm{HI}}\sim 10^{6.2}\,M_{\odot}$. When systematic uncertainties are included, the HIMF is well described by a single-Schechter function with a characteristic mass $\log (M_{*} / h_{70}^{-2}M_{\odot}) = 9.89\pm 0.02$, low-mass end slope $\alpha = -1.31\pm 0.02$, and amplitude $\phi_{*} = (6.38\pm 0.49)\times 10^{-3}\,h_{70}^{3}\,\mathrm{Mpc}^{-3}\,\mathrm{dex}^{-1}$. The derived cosmic HI density is $\Omega_{\mathrm{HI}} = (4.71\pm 0.03_{\mathrm{stat}}\pm 0.40_{\mathrm{sys}})\times 10^{-4}\,h_{70}^{-1}$. FASHI provides the most extensive and sensitive HI catalog to date, establishing an important benchmark for studies of gas accretion, galaxy evolution, and large-scale structure in the local universe.

The relationship between plastic deformation accommodation structures and residual elastic strain fields in deformed metals is poorly understood at the intragranular scale, largely because no experimental technique has provided simultaneous, three-dimensional, bulk-sensitive access to both fields at the length scale of dislocation boundaries. Here we use dark-field X-ray microscopy (DFXM) to map intragranular misorientation and residual elastic strain simultaneously in three dimensions within a grain of 50% cold-rolled Fe 3%Si alloy. We resolve geometrically necessary boundaries (GNBs) and incidental dislocation boundary (IDB) cell structures in the bulk non-destructively. Correlating the elastic strain field with the segmented plastically deformed substructure reveals that GNBs act as the primary carriers and distributors of long range residual elastic strain. GNBs separate subdomains of distinct mean d-spacing, across the grain volume. The plastic misorientation associated with IDBs and dislocation cells develops within GNB-delimited subdomains that carry comparatively similar values of elastic strain. This supports a mechanistic picture in which GNBs accommodate nearly all the long-range residual elastic strain in the deformed state, while plastic slip propagates into GNB interiors to organize into IDB cells with similar strain levels. The three-dimensional misorientation and strain gradients quantified here provide direct experimental input for recovery and recrystallization modelling in ferritic steels, such as electrical steels.