Papers

Large single crystals of graphene and hexagonal boron nitride (hBN) remain difficult to manufacture because batch growth and transfer limit area, throughput, and quality. This Perspective asks whether an atomically thin film could instead be grown, hot-delaminated, and regrown repeatedly on a long, reusable single-crystal metal surface. No integrated process is demonstrated. Once rapid full-area growth is available, hot film removal is likely to become the rate-limiting step, whereas usable single-crystal growth area sets the material produced per cycle. Two experiments determine whether the concept merits further development: rapid, damage-free delamination at or near the growth temperature, and acceptable film growth through repeated complete growth-dwell-peel-regrowth cycles. The analysis then examines the crystalline growth surface, layer control, interface and gas chemistries, product capture, quality criteria, energy, and scale. These provisional analyses expose known requirements, define early stop criteria, and guide experiments; they cannot anticipate every coupled constraint or failure mode. Graphene is the quantitative baseline. hBN requires its own M(111), product thickness, apparatus, and scaling strategy. Pilot-scale development is justified only if the two central experiments succeed and the remaining gates can then be refined experimentally.

Accurate and efficient simulation of ultrasound pressure fields and pulse-echo responses is essential for transducer design, beamforming optimization, and model-based imaging research. Conventional Spatial Impulse Response methods compute acoustic fields by explicitly sampling trapezoidal impulse responses for each rectangular aperture subdivision, which leads to high computational cost for large apertures, dense spatial grids, and high sampling frequencies. We introduce Sparse Delta Integration, a mathematical framework for the far-field SIR of rectangular apertures that expresses the trapezoidal spatial impulse response as the double integration of a sparse set of Dirac delta distributions. This formulation yields compact expressions for time-domain and frequency-domain SIRs and enables vectorized implementations whose computational cost is independent of the trapezoid duration. We further derive a spectral formulation for pulse-echo simulation that removes part of the conventional Fourier-domain convolution pipeline. Implemented in the open-source Python package eSDIva, these methods achieve speedups of up to 180x for temporal SIR computation and up to 20x for pulse-echo RF simulation relative to Field II, while maintaining high numerical accuracy with mean squared errors below 1e-5 and correlation coefficients close to unity.

The realization of large-scale quantum networks requires more than advances in quantum repeaters, memories, and processors, it requires a framework explaining how heterogeneous quantum technologies evolve from isolated deployments into interconnected infrastructures. While the classical Internet evolved under strong utility incentives associated with resource sharing and communication demands, quantum networking currently lacks dominant applications capable of generating comparable incentives. As a consequence, contemporary quantum networks are largely formed through technology-driven decisions motivated by technical feasibility, experimental validation, and expected future value. This work argues that the absence of utility-driven network formation is not solely a consequence of immature applications, but also of insufficient abstraction. In particular, heterogeneous quantum platforms remain tightly coupled to the functionalities they provide, preventing the definition of technology-independent utility functions. A hierarchical architecture consisting of Physical Platforms (PP), Functionalities (F), Services (S), Applications (A), and Use-Cases (UC) is proposed, together with the argument that quantum interconnects constitute the enabling technology required to decouple physical implementations from network functionalities. Such decoupling permits the definition of utility functions at the functionality level and establishes the conditions under which strategic (agent-based) network formation becomes applicable. Quantum interconnects should therefore be viewed not only as interoperability devices, but also as fundamental enablers of strategic quantum network evolution.

The Hydrotope gives a geometric representation of tree-level water-wave amplitudes with two negative spatial momenta as the volume of a hyperplane slice of a box. We trace the origin of this geometry directly to the water-wave action. Writing the $n$-point contact interaction as $\mathcal{V}_n=\sum_{i<j}w_iw_jh_{ij}^{(n)}$, we show that when the two marked momenta have the same sign and every spectator has the opposite sign, the corresponding coefficient is $h_{ij}^{(n)}=2H_n$, where $H_n/(n{-}3)!$ is the Hydrotope volume. More generally, every fixed-pair coefficient admits a denominator-free ordered-flag representation as an oriented sum of $(n{-}3)$-dimensional box volumes. We then sum all two-minus trees by cutting each at the unique vertex joining its two minus branches. The coefficients multiplying minus-minus, minus-plus, and plus-plus frequency bilinears reduce, respectively, to $(2^{n{-}1}{-}2)H_n$, $0$, and $2H_n$, and immediately reproduce the known amplitude $2^{n{-}1}w_1w_2H_n$. Thus, the Hydrotope-and a broader class of related box-slice geometries-is already encoded locally in the water-wave action. This points to further hidden simplicity and geometric structure in general water-wave amplitudes.

Exoplanets discovered with the radial velocity method suffer from a mass-inclination degeneracy: only the minimum mass $M_{\rm min} = M \sin i$ is measured. An exoplanet with an Earth-sized minimum mass could actually therefore be a sub-Neptune, or even a gas giant. However, for compact multi-planet systems, the inclination angle cannot be too low, as this would imply masses so large that the system would be dynamically unstable on time-scales shorter than the age of the system. We present CINEMAS, a Bayesian framework to constrain the inclinations - and hence true masses - of radial-velocity exoplanets in flat multi-planet systems, by accounting for dynamical stability. Applying this framework to five compact exoplanetary systems, we cut upper limits on the true masses of their planets by as much as 45%. As two examples, the masses of the four Barnard's Star planets are constrained to all be below $0.6~M_{\oplus}$ to at least 95% confidence; and the three gas giants orbiting HD 184010 are found to be intermediate in mass between Saturn and Jupiter. With only ~1% of planetary systems being inclined enough to transit, methods of studying non-transiting systems are vital for constraining the properties of nearby exoplanets.

In this essay I will make a non-exhaustive survey of the role of scientists, politicians, and the military in the development and use of the Bomb in the thirty years following the beginning of the United States Manhattan Project. I will be mainly focusing on facts or documents that have gradually fallen into oblivion, but that in my opinion are important to develop a critical view of the past responsibilities, and to consciously address the present dramatic situation of worldwide wars, that may yield again to the use of the Bomb.

Utilizing quantum second-order nonlinear transport for practical junction-free devices require materials with large and tunable nonlinearites at room temperature – a current materials platform challenge. Here, we report the nonlinear Hall effect (NLHE) in double-ionic gated bilayer graphene devices that enable unusually strong inversion breaking. We observe NLHE that are readily switchable (on, off, and sign reversed) with second order nonlinear susceptibilities $\chi^{(2)}_{yxx}$ that reaches giant room-temperature values of $3\,10^{-3}\,\mu\mathrm{m}\,\mathrm{S/V}$, comparable to values commonly observed at low temperature in WTe$_2$ or in graphene-based moiré superlattices, and three-to-four orders of magnitude larger than values reported in material systems recently employed in search of a room-temperature NLHE. Our devices produce corresponding THz voltage responsivities $\simeq 4\,10^{4}\,\mathrm{V/W}$, comparable to commercially available Schottky diodes. These are orders of magnitude better than for previously reported room-temperature NLHE devices rendering double-ionic gated bilayer graphene a choice platform for junction-free nonlinear technology.

Artificial confinement encodes continuum scattering information in discrete, bound-state-like spectra, allowing reaction observables to be extracted with finite-basis or finite-domain methods. We apply this strategy to a two-channel cluster model of $^4$He with open $^3$H+p and $^3$He+n channels. We extract coupled-channel observables from spectra generated by a harmonic-oscillator (HO) trap, a spherical hard wall, and, within a single-partial-wave truncation, a periodic cubic box. The three geometries are formulated in a unified quantization-condition framework and benchmarked against a continuum $R$-matrix calculation. Above the second-channel threshold, several confined levels at a common scattering energy are combined in an overdetermined fit to determine two phase shifts and an inelasticity. Without Coulomb interactions, all three geometries yield consistent results for the $^1S_0$ and $^3P_1$ partial waves. With Coulomb interactions in the charged $^3$H+p channel, the HO and spherical-wall results also agree closely with the continuum reference. A Monte Carlo propagation study shows that spectral uncertainties are amplified near trap-function poles and along poorly conditioned directions associated with the inelasticity and phase-shift difference, whereas the phase-shift sum remains comparatively robust. These results provide a controlled benchmark for confinement-based scattering methods and delineate their strengths and limitations for future few-body and ab initio reaction calculations.

Twisted bilayers of two-dimensional (2D) transition metal dichalcogenides are promising systems for achieving tunable quasicrystalline orders with emergent properties. The underpinning electronic structure and scattering processes in 2D quasicrystals with multiorbital dodecagonal replica bands have so far not been determined. Here, we utilize angle-resolved photoemission spectroscopy (ARPES) with micrometer spatial resolution to directly observe replica bands in 30$^{\circ}$-twisted bilayer WSe$_2$. The symmetry and intensity distribution of the observed replicas are explained by interlayer Umklapp scattering from bottom to top WSe$_2$ layers. Our spectral function measurements are consistent with the presence of a van Hove singularity adjacent to the $\mathrm{K}$-valleys, which underlines the possibility of inducing electronic reconstructions in bilayers with a large interlayer twist angle.

We present a detailed NLO+PS study of Higgs-boson production in association with charm and bottom quarks, with particular focus on the modelling of the H+c final state. We systematically compare predictions in massive and massless flavour schemes, quantify scale and flavour-scheme uncertainties, and assess the impact of interference and loop-induced contributions. Special emphasis is placed on the Higgs production via charm Yukawa fusion, for which we compare NLO+PS predictions with a NNLO+PS calculation of $c\bar{c}H$ production in the four-flavour scheme at 13.6 TeV. Based on these results, we provide the first practical recommendations for the simulation of $c\bar{c}H$ production in LHC analyses.

Remote charging of a quantum battery (QB) is hindered by radiative leakage of the excitation into the photonic environment that acts as a mediator for energy transfer. We consider a charger-battery model consisting of two two-level systems (TLSs) that are locally coupled to two sites of a one-dimensional coupled cavity array. When their transition frequency lies outside the propagation band, the system forms atom-photon bound states with localized photonic components, and the overlap of these components lifts the degeneracy of the even- and odd-parity bound states, yielding an energy splitting that drives coherent energy transfer from the charger to the QB. In this way, the band gap suppresses resonant emission and the localized bound states mediate remote charging. From the parity-resolved spectrum, we relate the charging time to the energy splitting and the charged ergotropy to the fraction of TLS population on the bound states. Bound states closer to the band edge extend the interaction range of the TLSs but contain a large photonic fraction and are consequently more susceptible to photon loss.

Fast radio bursts (FRBs) are widely considered to be associated with magnetars, motivated by the detection of an FRB-like radio burst from the Galactic magnetar SGR~1935+2154. However, constraining the magnetic field strength of extragalactic FRB sources remains challenging. In this work, we develop a Bayesian framework that models FRB time–energy sequences as a marked point process, combining burst waiting-time statistics with energy distributions to quantify the magnetic field strengths required to sustain the observed bursting activity under the magnetar powered scenario. Applying this method to a sample of repeating FRBs, we derive constraints on their magnetic fields by incorporating an empirical prior on the radio emission efficiency calibrated from the Galactic event. Under a conservative assumption for the activity duty cycle, most sources require magnetic energy reservoirs consistent with magnetar strength fields, with characteristic field strengths of order $10^{13}$–$10^{15}$ G, although the constraints remain sensitive to the poorly known efficiency and duty-cycle parameters. FRB~20200120E provides an interesting case with a substantially lower field requirement, highlighting the importance of source environment and evolutionary history in interpreting FRB activity. Our framework provides a statistical approach for connecting transient burst properties with magnetic energy reservoirs, with potential applications to FRBs and other magnetically powered transients.

Site-selective nanostructure growth and material incorporation at the atomic scale offer a promising pathway for engineering quantum materials and nanodevices. Here, GaAs nanowires (NWs) with an axial heterostructure of alternating zinc blende (Zb) and wurtzite (Wz) crystal phases are employed as templates for site-selective Ga and Bi overgrowth. Using X-ray photoemission electron microscopy (XPEEM) with nanoscale spatial resolution, we map elemental distribution and local chemical bonding to reveal the incorporation behavior of Bi atoms in {110} Zb and {11-20} Wz facets. Bi incorporation proceeds through an anion-exchange process, where Bi atoms replace As, forming local Ga-Bi bonds and producing a thin GaAs1-xBix shell. We observe crystal-phase-dependent Bi incorporation, with higher Bi concentration in the Zb segments than in the neighboring Wz segments within the same NW. Furthermore, the Zb segment with higher Bi content exhibits reduced susceptibility to oxidation compared with the Wz segment, resulting in increased Ga-oxide in the Wz surfaces. This study highlights GaAs NW Zb/Wz heterostructures as a template for controlled growth of GaBi and GaAs1-xBix nanostructures with tailored functionalities for quantum applications

We study collective slow flavor conversion (SFC) of supernova neutrinos with multi-energy, multi-angle simulations for three representative neutrino spectra in the early accretion, late accretion, and cooling phases, in which multiple crossings between the initial electron- and heavy-lepton-flavor spectra are present. By numerically solving the neutrino quantum kinetic equations in a local periodic box, we find that SFC triggered predominantly by the spatially inhomogeneous instabilities drives the system toward a spatially coarse-grained, quasi-stationary state, whose flavor conversion probability depends strongly on energy, angle, and the neutrino mass ordering. While we find that not all of the initial spectral crossings are completely erased in the final state, a simple, box-like analytical prescription inspired by studies of fast flavor conversions, which eliminates the spectral crossings, can reasonably approximate the post-SFC spectra. Using the initial and post-SFC spectra, we also evaluate the changes of the corresponding $\nu_e$ and $\bar\nu_e$ heating rates as well as the absorption equilibrium electron fraction ($Y_e$). Within the considered scenarios, we find that the heating rates are generally enhanced by up to $\sim 80\%$ due to the net conversion of $\nu_x$ to $\nu_e$ (and $\bar\nu_x$ to $\bar\nu_e$) above their crossing energy, provided that the energy spectra above the crossing energy differ substantially. For the absorption equilibrium $Y_e$, spectra changes due to SFC increase it by $\sim 0.03$ due to the relatively more enhanced $\nu_e$ absorption rate than $\bar\nu_e$, which potentially drives supernova materials to be more proton-rich. These results highlight the importance of energy-dependent treatments of SFC for supernova neutrinos.

Energy-ordered occupation is deeply embedded in quantum physics, from the Aufbau principle governing the filling of electronic states in atoms and molecules to the emergence of low-energy configurations in quantum many-body systems. However, the dynamical mechanism by which a generic quantum state develops such an energy hierarchy remains a fundamental question. Here we show that such an energy hierarchy can emerge dynamically from nonlinear quantum dissipation. Rather than being imposed as a principle or generated through coupling to a thermal reservoir, an Aufbau-like ordering of energy levels emerges intrinsically under quantum Landau-Lifshitz-Gilbert dynamics from a generic initial mixed state. This convergence is a nontrivial consequence of Lyapunov monotonicity and instability of disordered population configurations. The resulting dynamics establish an intrinsic nonlinear mechanism for organizing density-matrix populations and provides a route toward selective preparation of low-energy subspaces. Numerical simulations confirm analytical predictions and illustrate convergence toward low-energy sectors.

The maximum energy dissipation principle is employed to nonlinear chemical thermodynamics in terms of distance variable (generalized displacement) from the global equilibrium, applying the optimal control interpretation to develop a variational formulation. The cost-like functional was chosen to support the suggestion that such a formulation corresponds to the maximum energy dissipation principle. Using this approach, the variational framework was proposed for a nonlinear chemical thermodynamics, including general cooperative kinetics model. The formulation is in good agreement with standard linear non-equilibrium chemical thermodynamics.

Muon acceleration is a key technology for producing low-emittance muon beams over a wide energy range. Various acceleration schemes have been proposed for applications ranging from low-energy $\mu$SR and precision particle-physics measurements to neutrino factories and muon colliders. Experimental demonstrations of muon acceleration, however, have so far been limited. At J-PARC, a positive-muon accelerator based on the production and acceleration of ultraslow muons is being developed, and in 2024 the first RF acceleration of positive muons was demonstrated. In this review, we provide a brief overview of muon-acceleration methods and related experiments, and then review the acceleration method, current status, and future prospects at J-PARC.

Quantum amplitude estimation can reduce the sampling cost of rare-event probability estimation, but applying it to correlated Ising graphical models is limited by the difficulty of preparing the target distribution and building a practical event oracle. This work explores two approximate strategies for mitigating these challenges. We introduce a sample-free state-preparation method combining loopy belief propagation with the Chow–Liu algorithm. The resulting tree approximation is compiled into a quantum circuit with linear gate count and depth, and its accuracy is evaluated across graph families spanning different topologies, coupling strengths, and coupling signs. We also construct a structural oracle that evaluates threshold rules with reversible Boolean gates. Using a twenty-node supply-chain disruption model as a case study, we compare maximum likelihood amplitude estimation against four classical Monte Carlo baselines. Under the fixed-depth schedule used throughout this work, the quantum estimator has the same asymptotic error scaling as the classical methods but achieves lower estimation error by a constant factor. This reduction narrows when amplitude-encoding queries replace raw shots as the resource metric. We separate statistical error from the deterministic errors caused by approximate state preparation and oracle construction, and identify the requirements for achieving an improvement beyond a constant factor.

Within the Clifford algebra of spacetime, a covariant electrodynamics is formulated in which the derivative of the four-potential contains a scalar field (S) in addition to the electromagnetic bivector. A generalized system of Maxwell equations is derived that reduces to the classical Maxwell system when S=0. The energy-momentum tensor, the corresponding conservation laws, and a generalized Lorentz force density are obtained. It is shown that, in free space, the field S admits wave solutions, termed scalar S-waves. The structure and energy characteristics of a free S-wave, as well as its possible sources and the conditions for its experimental detection, are determined.

We clarify some mathematical features of the density of a dilute particle flow on a body surface in a two-fluid model, with a view toward its application to icing simulations. Inviscid solutions in the vicinity of a front stagnation point are obtained in exact and perturbed forms for small and large Stokes numbers, respectively, and the behavior of the density of the dispersed phase is clarified over the entire range of Stokes numbers. The viscous effect of the laminar boundary layer in the carrier phase on the particle-free thin layer appearing in the low-Stokes-number regime is also investigated based on the incompressible Navier-Stokes equations. An order-of-magnitude estimation of the velocity field of the dispersed phase reveals the cause of this layer and the criterion for its appearance. In particular, the latter result provides an improved form of Michael's criterion.

The European XFEL accelerator produces high-brightness X-ray pulses using relativistic electron beams. Beam characterization is performed at multiple diagnostic stations using scintillator screens, where beam images are analyzed to extract key parameters such as emittance, energy spread, and current profile. Accurate detection of the region of interest in these images is essential for reliable beam diagnostics and stable accelerator operation. Conventional methods, such as bounding-box-based beam localization, can become less reliable for complex or non-ideal beam profiles, such as low-intensity signals, tilted or streaked beams, and multiple beam structures. In this work, we develop machine learning-based approaches for region of interest detection directly from beam images. These ML methods adapt to variations in beam shape and intensity and enable more precise, pixel-level identification of beam regions. Experimental results demonstrate improved robustness and accuracy in challenging conditions compared to traditional techniques. The proposed methodology is validated at the European XFEL and is broadly applicable to image-based beam diagnostics across accelerator facilities.

Krylov state complexity, or spread complexity, has emerged as a sharp and versatile diagnostic of quantum chaos, information spreading, and many-body dynamics. Built from the Lanczos algorithm and grounded in the optimal-basis theorem, Krylov complexity thereby provides a robust spectroscopic window into quantum dynamics. A central theme is the characteristic overshoot observed in chaotic systems: a complexity peak in which chaotic evolution drives the state deeper into the Krylov chain than in integrable systems before relaxing to equilibrium. This behavior, tied to random-matrix universality classes of spectral statistics, is illustrated across a broad range of models, including quantum billiards, quantum spin chains, and variants of the SYK model. We also discuss proposed holographic descriptions of Krylov complexity in Einstein gravity, and conclude by outlining future directions and open problems, including time-dependent systems and quantum-field-theoretic formulations. A Mathematica notebook is provided for numerical exploration of Krylov complexity and spectral statistics across models.

Many matrices in computational chemistry are neither sparse nor low-rank, making the design of low-scaling algorithms difficult. In this Perspective, we point out that many important matrices in computational chemistry, such as the Coulomb matrix, the electronic repulsion integral tensor, the density matrix, the localized molecular orbital (LMO) coefficient matrix, the Fock matrix, and the nuclear Hessian matrix share the same property: when their basis functions are suitably ordered, their off-diagonal blocks have low numerical ranks (despite that they as a whole have high numerical ranks). This property, termed off-diagonal low rank (ODLR), has been extensively studied in the mathematics community, but has surprisingly found very little use in computational chemistry. This Perspective reviews the existing mathematical literature on how to use the ODLR property of matrices to compactly store, as well as efficiently calculate or use them. Subsequently, we review the use of the ODLR property in computational chemistry, and point out possible future opportunities of devising new low-scaling methods for dense, full-rank matrices, exploiting the ODLR property. In particular, we prove for the first time that Fock matrices and LMO coefficient matrices satisfy the ODLR property, even if the system is gapless (in which case the matrices are dense). This paves the way to linear scaling electronic structure calculations of gapless systems at zero electronic temperature.

The National Oceanic and Atmospheric Administration (NOAA) employs independent prediction systems for distinct forecast products. While some separation is practical, we argue that combining short- and medium-range weather into a single prediction system would provide the public with a useful distillation of global weather and its impacts. To this end, we present Nested-EAGLE (Experimental Artificial intelligence Global and Limited-area Ensemble): a 0.25{\deg} global weather model with a 6 km refinement over the Contiguous United States (CONUS). The model achieves significantly lower mean-squared error in near-surface and low-level quantities over CONUS compared to NOAA's Global Forecast System and High-Resolution Rapid Refresh (HRRR), while remaining competitive throughout the rest of the global atmosphere. We show that the skill gains for near-surface fields stem from incorporating high-resolution regional analysis data into training through the nesting process. Forecasts of precipitation amounts are less skillful than those from HRRR, owing to deterministic training. However, we show that Nested-EAGLE provides the most accurate forecasts of storm locations at longer leads, despite blurred extrema. Our results motivate future work to extend the skill gains beyond CONUS and improve precipitation representation.

We investigate the form of the Saito metric on quotients of the reflection representation of an extended affine Weyl group, restricted to an arbitrary stratum of its discriminant. We compute the Saito determinant for all strata and Dynkin types and show that it is divisible by a product of q-analogues of restricted roots for the associated hyperplane arrangement. Our results simultaneously generalise the factorisation in the Weyl denominator formula to higher codimension strata, and provide q-analogue refinements of results of Antoniou-Feigin-Strachan for Coxeter groups.

It is well known that the Einstein equations are tensor equations for a Lorentzian metric. Hence, choosing a suitable gauge condition is crucial for solving them. As a powerful gauge condition, maximal foliations have played a pivotal role in two groundbreaking works in general relativity: the global stability of Minkowski spacetime and the bounded L^2 curvature conjecture. Nevertheless, if the initial hypersurface fails to be maximal, the usual elliptic approach for constructing maximal foliations encounters fundamental difficulties when solving the Einstein equations. The purpose of the paper is to provide a construction of maximal foliations around any initial asymptotically flat Cauchy surface satisfying vacuum Einstein constraint equations, under a suitable smallness condition on the mean curvature.

We introduce the Split Coaxial Cable Medium (SCCM), a mechanically tunable, capacitively loaded wire medium supporting artificial-dielectric and artificial-plasma Bloch regimes with high in-plane isotropy. Its unit cell comprises coaxial conductors interrupted by axial gaps. Relative axial displacement continuously varies their capacitive overlap and series capacitance while preserving the transverse lattice geometry and leaving the unit-cell inductance approximately unchanged. Equivalent RLC parameters are derived directly from the geometry and incorporated into complementary analytical models. A spatially dispersive local-field model predicts the Bloch dispersion and isofrequency contours, whereas a multilayer homogenization model provides the modal impedance, closed-form estimates of the low-frequency Bloch refractive index and plasma frequency, and loss-inclusive finite-slab scattering. Full-wave eigenmode and finite-slab simulations validate the predictions. Over the investigated displacement range, simulations yield tunabilities of $46\%$ in the low-frequency Bloch refractive index, from $n_{0,\min}=1.42$ to $n_{0,\max}=2.28$, and $21\%$ in the plasma frequency, from $f_{\mathrm{p},\min}=9.45~\mathrm{GHz}$ to $f_{\mathrm{p},\max}=11.61~\mathrm{GHz}$, while confirming high in-plane isotropy near the $\Gamma$ point in both regimes. These characteristics make the SCCM promising for gradient-index devices, directive antennas, and tunable plasma haloscopes.

As integrated circuits advance toward higher power densities, three-dimensional integration, and heterogeneous packaging, chip thermal management has become a key bottleneck limiting device performance, reliability, and lifetime. This article systematically reviews numerical simulation methods and experimental measurement techniques for chip thermal design, with particular emphasis on the technical challenges associated with multiscale and multiphysics coupling, thermal boundary resistance measurement, and high-heat-flux cooling. We first introduce macro- and device-scale thermal simulation methods, including equivalent thermal-circuit models, the finite element method, and computational fluid dynamics, and discuss the application of phonon transport theory and molecular dynamics at microscopic scales. We then examine the advantages and limitations of infrared thermography, thermoreflectance, Raman thermometry, and embedded sensors. Current limitations include the enormous computational cost, inaccurate multiscale coupling, expensive experimental facilities, and the physical limits of conventional cooling technologies. Finally, we discuss emerging directions, including AI-accelerated thermal simulation, embedded microchannel liquid cooling, two-phase cooling, advanced high-thermal-conductivity materials, and multiphysics co-design, with the aim of advancing chip thermal management toward greater efficiency and intelligence.

Alkali lines, in particular the sodium Na $D$ (5891$\AA$, 5897$\AA$) and potassium K $D$ (7667$\AA$, 7701$\AA$) resonance doublets, are dominant opacity sources in giant planets over a wide range of temperatures ($\gtrsim$1000K). Their strong pressure-broadened wings significantly influence the thermal structure of giant planets, especially at high pressures. Most detailed line-profile calculations have so far been limited to perturber densities up to $10^{21}$cm$^{-3}$. However, conditions in the deep atmospheres and interiors of giant planets can reach significantly higher densities, making the temperature gradients increasingly uncertain. We determined how physically consistent collisional broadening of the Na $D$ and K $D$ lines at extreme densities affects opacity calculations and consequently the inferred interior structure of giant planets. We computed detailed Na $D$ and K $D$ line profiles using unified line theory, extending to molecular hydrogen perturber densities of $n_{\rm H_2} = 5 \times 10^{22}$cm$^{-3}$, which translates to pressures up to $\sim$ 20kbar. The revised cross sections were incorporated into Rosseland mean opacity tables, which were then used to evaluate their effect on planetary thermal structures. At densities $n_{\rm H_2} > 10^{21}$cm$^{-3}$, the line profiles predicted by unified line theory exhibit significantly stronger wings than commonly used Voigt profiles, as well as density-dependent line shifts, which substantially increases Rosseland mean opacities. Consequently, the radiative-convective boundary of warm and hot giant planets can shift to lower pressures, producing warmer interior adiabats and increasing inferred core masses. We further find that Jupiter is unlikely to host a stable radiative layer at the present time or throughout most of its evolution, as the required Na and K abundances for this are well below observational constraints.

The ionosphere is a highly complex plasma containing electron density structures with a wide range of spatial scales. Coupling of the ionosphere with the Earth's magnetosphere and the solar wind, as well as to the neutral atmosphere, makes the ionosphere highly dynamic and highly dependent on the driving processes. Thus, modelling the ionosphere and capturing its full dynamic range considering all spatiotemporal scales is challenging. Swarm is the European Space Agency's (ESA) first constellation mission for Earth Observation, comprising multiple satellites in low Earth orbit. During the Swarm-VIP-Dynamic project, a suite of statistical models has been developed using observations from Swarm and proxies for heliogeophysical processes. The statistical modelling technique of Generalised Linear Modelling was used to create models for both the electron density and the variability of the plasma structures at horizontal spatial scales between 7.5 km and 100 km. Separate models were created for low, middle, auroral and polar latitudes. The models make predictions based on explanatory variables, which act as proxies for the underlying physical processes. The performance of the models of the electron density approached the theoretical best values for some of the goodness-of-fit statistics. This suggests that the modelling method is appropriate for the task undertaken. The models of ionospheric variability at larger spatial scales (about 100 km) also perform well, however the model performance decreases at smaller spatial scales. This suggests that there are physical processes missing from the models. Possible candidates are instability processes or driving forces of the ionosphere by wave activity from below, neither of which are captured by the models.