Quantum phase transitions (QPTs) are usually associated with many-body systems in the thermodynamic limit when their ground states show abrupt changes at zero temperature with variation of a ...parameter in the Hamiltonian. Recently it has been realized that a QPT can also occur in a system composed of only a two-level atom and a single-mode bosonic field, described by the quantum Rabi model (QRM). Here we report an experimental demonstration of a QPT in the QRM using a
Yb
ion in a Paul trap. We measure the spin-up state population and the average phonon number of the ion as two order parameters and observe clear evidence of the phase transition via adiabatic tuning of the coupling between the ion and its spatial motion. An experimental probe of the phase transition in a fundamental quantum optics model without imposing the thermodynamic limit opens up a window for controlled study of QPTs and quantum critical phenomena.
The primary challenges for simulating a turbulent flow over a micro‐structured surface arise from the two hugely disparate spatial length scales. For fluid–solid coupled conjugate heat transfer ...(CHT), there is also a time‐scale disparity. The present work addresses the scale disparities based on a two‐scale framework. For the spatial scale disparity, a dual meshing is employed to couple a global coarse‐mesh domain with local fine‐mesh blocks around micro‐structures through source terms generated from the local fine‐mesh and propagated to the global coarse‐mesh domain. The convergence and robustness of the source terms driven coarse‐mesh solution is enhanced by a balanced eddy‐viscosity damping. In this work, the two‐scale method previously developed only for a fluid‐domain is extended to a solid domain so that thermal conduction around micro‐elements can now be resolved accurately and efficiently. The fluid–solid timescale disparity is dealt with by a frequency domain approach. The time‐averaged (zeroth harmonic) is effectively obtained in the same way as steady CHT. And remarkably, wall temperature unsteadiness can be simply obtained from the fluid temperature harmonics through a wall fluid–solid temperature harmonic transfer‐function at minimal computational cost. The developed CHT capability is validated for an experimental internal cooling channel with multiple surface rib‐elements. For a test configuration with 100 micro‐structures, the fluid domain‐only, the solid domain‐only and the fluid–solid coupled CHT solutions are analyzed respectively to examine and demonstrate the validity of the present framework and implementation methods. Some of the results also serve to illustrate the primary underlying working of the methodology.
The two‐scale method previously developed for turbulent flow solution is extended to a solid domain, enabling LES conjugate heat transfer solutions for micro‐structured surface. The wall temperature unsteadiness is resolved efficiently through a harmonic transfer function. The method is validated against experimental data. The two‐scale capability indicates the potential for the cost of conjugate heat transfer solutions for micro‐structured surfaces to be largely independent of the number of microstructure elements.
•A non-partitioned moving-average based interface method is developed for conjugate heat transfer (CHT) with scale-resolved (LES) turbulence flow models.•Stability analyses indicate that the ...interface treatment is stable at no more stringent conditions than those for the stability of interior domain solutions.•Impact of heat transfer on near wall turbulence flow is indicated by comparing the adiabatic and CHT solutions.•Advantages of the method over the conventional method are highlighted, numerically and analytically aided by an interface response analysis.•Both wall temperature fluctuation and its sensitivity to the interface treatment are augmented for Thermal Barrier Coating (TBC).
Fluid–solid coupled Conjugate Heat Transfer (CHT) simulations are relevant to many practical problems. Most existing interfacing methods have been developed for Reynolds averaged Navier-Stokes solvers. For high fidelity turbulence scale-resolved flow solvers however, the CHT interface methods face significant challenges arisen from a wide frequency spectrum of unsteady disturbances to be dealt with, compounded by the huge time scale disparity between fluid and solid domains.
In this paper, a closely coupled non-partitioned (monolithic) CHT method is presented. The main issues of interest are the prohibitive time costs of direct time domain CHT methods and an extra mesh dependency in the solid domain when resolving high frequency turbulence disturbances. Based on a temporal Fourier spectral framework, the present CHT interface method entails a moving-average for the time-mean flow and a discrete Fourier transform on-the-fly at each time step. Taking advantage of a semi-analytical transfer function and harmonic balancing for the CHT interface, we can achieve solving the solid domain completely in its own time step (3–5 orders of magnitude larger than that of the fluid domain). The present interface method can effectively circumvent aliasing errors and extra solid domain mesh-dependence encountered by other time-domain coupling methods when applied to turbulence scale-resolved CHT solutions. Illustrative stability analyses also show that the numerical stability of the present CHT interface should require no more stringent conditions than that in either fluid or solid domain. The computational results and analyses highlight the advantages of the present methodology in terms of both the computational efficiency and accuracy, in comparison with a conventional directly coupled interface method. Furthermore, a case study aided by a simple interface response analysis highlights much augmented wall temperature fluctuations and higher sensitivity to the interface treatment when a low conductivity protection layer (Thermal Barrier Coating, TBC) is added. The present study underlines the relevance of accounting for fluid disturbances over a range of frequencies in an effective and accurate CHT interface treatment.
Rapid increase in computing power has made a huge difference in scales and complexities of the problems in turbomachinery that we can tackle by use of computational fluid dynamics (CFD). It is ...recognised, however, that there is always a need for developing efficient methods for applications to blade designs. In a design cycle, a large number of flow solutions are sought to interact iteratively or concurrently with various options, opportunities and constraints from other disciplines. This basic requirement for fast prediction methods in a multi-disciplinary design environment remains unchanged, regardless of computer speed. And it must be recognised that the multi-disciplinary nature of blading design increasingly influences outcomes of advanced gas turbine and aeroengine developments. Recently there has been considerable progress in the Fourier harmonic modelling method development for turbomachinery applications. The main driver is to develop efficient and accurate computational methodologies and working methods for prediction and analysis of unsteady effects on aerothermal performance (loading and efficiency) and aeroelasticity (blade vibration due to flutter and forced response) in turbomachinery. In this article, the developments and applications of this type of methods in the past 20 years or so are reviewed. The basic modelling assumptions and various forms of implementations for the temporal Fourier modelling approach are presented and discussed. Computational examples for realistic turbomachinery configurations/flow conditions are given to illustrate the validity and effectiveness of the approach. Although the major development has been in the temporal Fourier harmonic modelling, some recent progress in use of the spatial Fourier modelling is also described with demonstration examples.
Summary
Many problems of interest are characterized by 2 distinctive and disparate scales and a huge multiplicity of similar small‐scale elements. The corresponding scale‐dependent solvability ...manifests itself in the high gradient flow around each element needing a fine mesh locally and the similar flow patterns among all elements globally. In a block spectral approach making use of the scale‐dependent solvability, the global domain is decomposed into a large number of similar small blocks. The mesh‐pointwise block spectra will establish the block‐block variation, for which only a small set of blocks need to be solved with a fine mesh resolution. The solution can then be very efficiently obtained by coupling the local fine mesh solution and the global coarse mesh solution through a block spectral mapping. Previously, the block spectral method has only been developed for steady flows. The present work extends the methodology to unsteady flows of short temporal and spatial scales (eg, those due to self‐excited unsteady vortices and turbulence disturbances). A source term–based approach is adopted to facilitate a two‐way coupling in terms of time‐averaged flow solutions. The global coarse base mesh solution provides an appropriate environment and boundary condition to the local fine mesh blocks, while the local fine mesh solution provides the source terms (propagated through the block spectral mapping) to the global coarse mesh domain. The computational method will be presented with several numerical examples and sensitivity studies. The results consistently demonstrate the validity and potential of the proposed approach.
A multiscale methodology is developed for unsteady flows. A global domain is decomposed into large number of small domain blocks. Only are a subset of fine mesh blocks solved for getting pointwise block‐block spectra to be mapped to the global domain. The global domain time‐averaged flow can be solved on a coarse mesh efficiently and accurately with unsteady source terms generated from the fine mesh blocks and propagated to the global domain by the block spectral mapping.
The strong spectral dependence of light absorption of brown carbon (BrC) aerosol is regarded to influence aerosol's radiative forcing significantly. The Absorption Angstrom Exponent (AAE) method has ...been widely used in previous studies to attribute light absorption of BrC at shorter wavelengths for ambient aerosols, with a theoretical assumption that the AAE of "pure" black carbon (BC) aerosol equals to 1.0. In this study, the AAE method was applied to both urban and rural environments in the Pearl River Delta (PRD) region of China, with an improvement of constraining the realistic AAE of "pure" BC through statistical analysis of on-line measurement data. A three-wavelength photo-acoustic soot spectrometer (PASS-3) and aerosol mass spectrometers (AMS) were used to explore the relationship between the measured AAE and the relative abundance of organic aerosol to BC. The regression and extrapolation analysis revealed that more realistic AAE values for "pure" BC aerosol (AAEBC) were 0.86, 0.82, and 1.02 between 405 and 781 nm, and 0.70, 0.71, and 0.86 between 532 and 781 nm, in the campaigns of urbanwinter, urbanfall, and ruralfall, respectively. Roadway tunnel experiments were conducted and the results further confirmed the representativeness of the obtained AAEBC values for the urban environment. Finally, the average light absorption contributions of BrC ( relative uncertainties) at 405 nm were quantified to be 11.7 % ( 5 %), 6.3 % ( 4 %), and 12.1 % ( 7 %) in the campaigns of urbanwinter, urbanfall, and ruralfall, respectively, and those at 532 nm were 10.0 % ( 2 %), 4.1 % ( 3 %), and 5.5 % ( 5 %), respectively. The relatively higher BrC absorption contribution at 405 nm in the ruralfall campaign could be reasonably attributed to the biomass burning events nearby, which was then directly supported by the biomass burning simulation experiments performed in this study. This paper indicates that the BrC contribution to total aerosol light absorption at shorter wavelengths is not negligible in the highly urbanized and industrialized PRD region.
Numerical layout optimization provides a computationally efficient and generally applicable means of identifying the optimal arrangement of bars in a truss. When the plastic layout optimization ...formulation is used, a wide variety of problem types can be solved using linear programming. However, the solutions obtained are frequently quite complex, particularly when fine numerical discretizations are employed. To address this, the efficacy of two rationalization techniques are explored in this paper: (i) introduction of ‘joint lengths’, and (ii) application of geometry optimization. In the former case this involves the use of a modified layout optimization formulation, which remains linear, whilst in the latter case a non-linear optimization post-processing step, involving adjusting the locations of nodes in the layout optimized solution, is undertaken. The two rationalization techniques are applied to example problems involving both point and distributed loads, self-weight and multiple load cases. It is demonstrated that the introduction of joint lengths reduces structural complexity at negligible computational cost, though generally leads to increased volumes. Conversely, the use of geometry optimization carries a computational cost but is effective in reducing both structural complexity and the computed volume.
In this work, we report the design of topological filter and all-optical logic gates based on two-dimensional photonic crystals with robust edge states. All major logic gates, including OR, AND, NOT, ...NOR, XOR, XNOR, and NAND, are suitably designed by using the linear interference approach. Moreover, numerical simulations show that our designed all-optical logic devices can always work well even if significant disorders exist. It is expected that such robust and compact logic devices have potential applications in future photonic integrated circuits.
This study reports an efficient inoculation protocol that allowed cytological analysis of the infection process of the rice false smut pathogen Ustilaginoidea virens. Examination of serial semithin ...and ultrathin sections of infected spikelets showed that the primary infection sites for the pathogen were the upper parts of the three stamen filaments located between the ovary and the lodicules. The stigma and lodicules were also occasionally infected to a limited extent. The pathogen infected the filaments intercellularly and extended intercellularly along the filament base. The host cells were degraded gradually. The pathogen did not penetrate host cell walls directly and did not form haustoria. In the balls the ovary remained alive and was never infected. This suggests that the pathogen is a biotrophic parasite that grows intercellularly in vivo.
Recent findings on the Reynolds-number-dependent behaviour of near-wall turbulence in terms of the ‘foot-printing’ of outer large-scale structures call for a new modelling development. A two-scale ...framework was proposed to couple a local fine-mesh solution with a global coarse-mesh solution by He (Intl J. Numer. Meth. Fluids, vol. 86, 2018, pp. 655–677). The methodology was implemented and demonstrated by Chen & He (J. Fluid Mech, vol. 933, 2022, p. A47) for a canonical turbulent channel flow, where the mesh-count scaling with Reynolds number is potentially reduced from $O(R{e^2})$ for a conventional wall-resolved large-eddy simulation (WRLES) to $O(R{e^1})$. The present work extends the two-scale method to turbulent boundary layers. A two-dimensional roughness element is used to trip a turbulent boundary layer. It is observed that large-scale disturbances originating at the trip have a much shorter lifetime and weaker foot-printing signatures on near-wall flow compared to those long streaky coherent structures in well-developed wall-bounded turbulent flows. Modal analyses show that the impact of trip-induced large scales can be adequately captured by a locally embedded fine-mesh block. For the tripped turbulent boundary layer, a Chebyshev block-spectral mapping is adopted to propagate source terms from the local fine-mesh blocks to the global coarse-mesh domain, driving to a target solution for the upscaled equations. The computed mean statistics and energy spectra are in good agreement with corresponding experimental data, WRLES and direct numerical simulation (DNS) results. The overall mesh count–$Re$ scaling is estimated to reduce from $O(R{e^{1.8}})$ for the full wall-resolved LES to $O(R{e^{0.9}})$ for the present two-scale solution.
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