Position Of Transition Research Articles

Topological extension including quantum jump

Non-Hermitian (NH) systems and the Lindblad form master equation have always been regarded as reliable tools in dissipative modeling. Intriguingly, existing literature often obtains an equivalent NH Hamiltonian by neglecting the quantum jumping terms in the master equation. However, there lacks investigation into the effects of discarded terms as well as the unified connection between these two approaches. In this study, we study the Su–Schrieffer–Heeger model with collective loss and gain from a topological perspective. When the system undergoes no quantum jump events, the corresponding shape matrix exhibits the same topological properties in contrast to the traditional NH theory. Conversely, the occurrence of quantum jumps can result in a shift in the positions of the phase transition. Our study provides a qualitative analysis of the impact of quantum jumping terms and reveals their unique role in quantum systems.

Experimental study on the heat flux of transitional shock wave–boundary layer interaction at Mach 6

The shock wave–boundary layer interaction (SWBLI) phenomenon was investigated experimentally to explore the heat flux distribution characteristics of SWBLIs under different boundary layer flow regimes and the influence/mechanism of different transition positions on peak heat flux of SWBLI. Experiments were conducted in a flow of Mach number 6. The shock generator deflected the flow by 20 °, 22 °, 25 ° and 30 ° resulting in an oblique shock impinging on a flat plate. The rough elements with different heights were arranged to achieve different transition positions. The influence of the relative position of transition and interference zone on the peak heat flux and its physical mechanism are revealed. The results demonstrated that the transitional SWBLI has a higher peak heat flux than the turbulent SWBLI, however the overshoot phenomenon is not reflected in the peak pressure. The increment of heat flux peak in transitional SWBLI is related to the relative positions of transition and interference zones. The increment of heat flux peak of transitional SWBLI compared to turbulent SWBLI can reach 25.5–38.9% and 51.9–65.1% when transition approaches the separation zone and reattachment zone, respectively. This overshoot phenomenon is caused by the streamwise vortex in transitional and so-called laminar SWBLIs, which enhances the energy exchange in the boundary layer and leads to an increase in heat flux. However, in the turbulent SWBLI, the energy mixing in the boundary layer is not significantly enhanced due to the breakup of the large scale streamwise vortex into turbulent small-scale structure.

Synthesis and structural characterization of CaMg0.5CoxNi0.5-xSi2O6 (0 ≤ x ≤ 0.5) solid solutions as a colouring substance

In this study, CaMg0.5CoxNi0.5-xSi2O6 (0.0 ≤ x ≤ 0.5) solid solutions with a diopside structure were prepared to reduce the cobalt and nickel amounts compared to M2SiO4 or MgMSiO4 (M = Co, Ni) compounds or CaCoxNi1-xSi2O6 solid solutions. Colloidal gels were obtained by adding an ammonia aqueous solution to the suspensions of precursors in aqua until pH = 10. Diopside structure began to develop at 800 °C and at 1000–1200 °C crystallinity and pink colour of materials (x ≠ 0) are optimal. In both CaMg0.5CoxNi0.5-xSi2O6 (0.0 ≤ x ≤ 0.5) and MgCoxNi1-xSiO4 (0.0 ≤ x ≤ 1.0) solid solutions with diopside and olivine structures the position of the third transition of octahedral Co(II), 4T1 → 4T1(P), is centred into the green absorption range and the observed colour is pink. A higher red amount in diopside than in olivine structure can be explained by the minor width of band of this third transition (minor distortion of octahedral M1 site) and shorter mean M1-O distances (M = Ni, Co).

Experimental investigation on the vortex-induced vibration response of a lazy-wave flexible riser filled with different fluid media

This paper reports the experimental results of the vortex-induced vibration (VIV) of a lazy-wave flexible riser filled with different fluid media, including the water and helium as typical liquid and light gas examples. The lazy-wave configuration was produced by mounting a buoyancy module of approximately triple the riser diameter on the one-third of the riser length measured from the riser base. The VIV tests were carried out in the depth-averaged reduced velocity (U¯r) range of 9.32–23.19 using the non-intrusive optical measurement with a couple of high-speed cameras. The experimental results indicate that not only the excited mode of in-plane response but also the response amplitude is significantly adjusted when the internal fluid changes, while the excited mode of the out-of-plane response has no obvious modification. Both the water- and helium-filled risers experience the space-varying dominant frequency. However, the helium-filled riser segment possessing a higher dominant frequency is significantly shortened as compared to the water-filled one. When the internal fluid shifts from water to helium, the in-plane mode transition from the first to second becomes incomplete, and the mode transition becomes smoother as U¯r grows. It is found that the starting position of the mode transition is related to the dominant mode as well as the response direction. Then, the influenced length of the riser response from the buoyancy module and the affecting length of the riser on the buoyancy module response are quantified in terms of the spatial distribution of the dominant frequency in comparison with the natural frequencies. The in-plane response of the helium-filled riser is more vulnerable to the oscillation of the buoyancy module, and hence, the coupling between the in-plane and out-of-plane responses is weaker than the water-filled riser. When the impact of buoyancy module on the riser response is enhanced, the reverse effect is weakened.

Magnetic and dielectric properties of the Co-defective Ca3Co2-xO6 compounds

The Ca3Co2-xO6 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) samples were prepared by reducing the stoichiometric ratio of Co atoms. Their structure, magnetic properties, dielectric and magnetodielectric properties were investigated. XRD results show that the presence of a small number of vacancies does not change the crystalline structure. The positive Curie-Weiss temperature θ and interchain exchange constants J indicate that ferromagnetic interactions are stronger than the antiferromagnetic interactions in Co-defective Ca3Co2-xO6. The Co-vacancies could weaken the Co-Co exchange interactions, it has an obvious dilution effect on the ferromagnetic interactions within the chain. The magnetization steps move to low field accompanying the defects increase. Simultaneously, Co defects could also release part of the magnetic frustration. The competition of the released magnetic frustration and the dilution effect of the vacancies to the ferromagnetic chains and low doping concentration make the Co-defective Ca3Co2-xO6 present similar magnetic property with the parent Ca3Co2O6. At the positions of magnetic phase transition and the critical magnetic field of magnetization steps, clear dielectric anomalies can be detected. This result suggests the strong magnetodielectric coupling effect in Ca3Co2-xO6 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) samples.

Influence of distributed hydrogen injection and combustion on supersonic boundary layer stability and transition

This theoretical study recorded the influence of the distributed injection of hydrogen through a permeable surface and its combustion on the stability and transition of a supersonic boundary layer (BL). The laminar base flow for a multicomponent flat-plate BL was computed using the computational fluid dynamics solver with finite-rate chemistry for free-stream Mach number (M) = 2. Linear stability theory (LST) equations for a reactive gas mixture were derived in the local parallel base flow approximation. Stability calculations based on the developed theory revealed the possibility of a decrease in the local spatial amplification rates of unstable perturbations. A double reversal in the maximal amplification rate magnitudes of perturbations was obtained, wherein at first, they increased, then decreased to zero, and then rose again. The influence of the distributed injection and combustion of hydrogen in the supersonic BL on the position of the laminar-turbulent transition was estimated using the LST-based eN-method. Calculated and experimentally obtained dependencies of the relative transition Reynolds number on the relative mass flow rate of injected hydrogen were compared. It was found that depending upon the flow conditions, the hydrogen diffusion flame could accelerate or decelerate the transition in the supersonic M = 2 BL, when compared to absence of hydrogen burning. Two counteracting effects compete: heat supply by combustion exerts stabilizing influence, while low-molecular-weight gas blowing from the surface exerts destabilizing influence. Depending on the interplay of these two factors, it would be possible to obtain acceleration or deceleration of transition.

Numerical Investigation on Suction Flow Control Technology for a Blunt Trailing Edge Hydrofoil

The generation of hydro-mechanical resonance is related to the transition of the boundary layer and the development of vortex shedding. The application effect of suction control in hydrodynamics is equally deserving of consideration as an active control technique in aerodynamics. This study examines how suction control affects the flow field of the NACA0009 blunt trailing edge hydrofoil using the γ transition model. Firstly, the accuracy of the numerical method is checked by performing a three-dimensional hydrofoil numerical simulation. Based on this, three-dimensional hydrofoil suction control research is conducted. According to the results, the suction control increases the velocity gradient in the boundary layer and delays the position of transition. The frequency of vortex shedding in the wake region lowers, and the peak value of velocity fluctuation declines. The hydrofoil hydrodynamic performance may be successfully improved with a proper selection of the suction coefficient via research of the suction coefficient and suction position on the flow field around the hydrofoil. The lift/drag ratio goes up as the suction coefficient goes up. The boundary layer displacement thickness and momentum thickness are at their lowest points, and the velocity fluctuation amplitude in the wake region is at its lowest point as the suction coefficient Cμ = 0.003. When the suction slots are at the leading edge, the momentum loss in the boundary layer is minimal and the velocity fluctuation in the wake zone is negligible.

Shift of the semimetal-dielectric phase transition boundary in case of violation of sublattice symmetry in the extended Hubbard model

Within the framework of the extended Hubbard model on a hexagonal lattice, the effect of sublattice symmetry breaking on the position of the semimetal-antiferromagnet phase transition is studied. The study is carried out using the Quantum Monte Carlo method with five auxiliary Hubbard fields. It is shown that the difference in the intensity of the on-site interaction of electrons on the sublattices leads to a shift of the phase transition point towards lower values of the interaction parameter. An antiferromagnetic condensate is considered.

Quantifying Soil Goethite/Hematite Ratios: A New Method Based on Diffuse Reflectance Spectra

AbstractGoethite/hematite ratios in soils are widely used to reconstruct past climatic changes, but their accurate measurements have remained challenging due to the matrix effect. Here we present a new method for measuring soil goethite/hematite ratios by characterizing the band position of electron pair transition (EPT) based on the diffuse reflectance spectra processed by continuum removal. We introduce a “half‐band‐area wavelength”, λ1/2, to characterize the EPT band position and validate the method using synthetic standards made from mixing pure goethite and hematite and four sets of goethite‐ and hematite‐free matrices derived from arid aeolian deposits and tropical saprolite. A consistent λ1/2‐goethite/hematite relation across four matrices demonstrates that our method eliminates the matrix effect. We further validate our method by applying it to quantify goethite/hematite ratios in 180‐Kyr loess‐paleosol sequences and comparing the results to the reported paleoclimatic records. Our new method is promising for improving the measurement of goethite/hematite ratios in sediments.

Locomotor and postural diversity among reptiles viewed through the prism of femoral microanatomy: Palaeobiological implications for some Permian and Mesozoic taxa.

The water-to-land transition by the first tetrapod vertebrates represents a key stage in their evolution. Selection pressures exerted by this new environment on animals led to the emergence of new locomotor and postural strategies that favoured access to different ecological niches and contributed to their evolutionary success. Today, amniotes show great locomotor and postural diversity, particularly among Reptilia, whose extant representatives include parasagittally locomoting erect and crouched bipeds (birds), sub-parasagittal 'semi-erect' quadrupeds (crocodylians) and sprawling quadrupeds (squamates and turtles). But the different steps leading to such diversity remain enigmatic and the type of locomotion adopted by many extinct species raises questions. This is notably the case of certain Triassic taxa such as Euparkeria and Marasuchus. The exploration of the bone microanatomy in reptiles could help to overcome these uncertainties. Indeed, this locomotor and postural diversity is accompanied by great microanatomical disparity. On land, the bones of the appendicular skeleton support the weight of the body and are subject to multiple constraints that partly shape their external and internal morphology. Here we show how microanatomical parameters measured in cross-section, such as bone compactness or the position of the medullocortical transition, can be related to locomotion. We hypothesised that this could be due to variations in cortical thickness. Using statistical methods that take phylogeny into account (phylogenetic flexible discriminant analyses), we develop different models of locomotion from a sample of femur cross-sections from 51 reptile species. We use these models to infer locomotion and posture in 7 extinct reptile taxa for which they remain debated or not fully clear. Our models produced reliable inferences for taxa that preceded and followed the quadruped/biped and sprawling/erect transitions, notably within the Captorhinidae and Dinosauria. For taxa contemporary with these transitions, such as Terrestrisuchus and Marasuchus, the inferences are more questionable. We use linear models to investigate the effect of body mass and functional ecology on our inference models. We show that body mass seems to significantly impact our model predictions in most cases, unlike the functional ecology. Finally, we illustrate how taphonomic processes can impact certain microanatomical parameters, especially the eccentricity of the section, while addressing some other potential limitations of our methods. Our study provides insight into the evolution of enigmatic locomotion in various early reptiles. Our models and methods could be used by palaeontologists to infer the locomotion and posture in other extinct reptile taxa, especially when considered in combination with other lines of evidence.

Thermodynamic properties of non-Hermitian Nambu–Jona-Lasinio models

We investigate the impact of non-Hermiticity on the thermodynamic properties of interacting fermions by examining bilinear extensions to the $3+1$ dimensional $SU(2)$-symmetric Nambu--Jona-Lasinio (NJL) model of quantum chromodynamics at finite temperature and chemical potential. The system is modified through the anti-$PT$-symmetric pseudoscalar bilinear $\bar{\psi}\gamma_5 \psi$ and the $PT$-symmetric pseudovector bilinear $iB_\nu \,\bar{\psi}\gamma_5\gamma^\nu \psi$, introduced with a coupling $g$. Beyond the possibility of dynamical fermion mass generation at finite temperature and chemical potential, our findings establish model-dependent changes in the position of the chiral phase transition and the critical end-point. These are tunable with respect to $g$ in the former case, and both $g$ and $|B|/B_0$ in the latter case, for both lightlike and spacelike fields. Moreover, the behavior of the quark number, entropy, pressure, and energy densities signal a potential fermion or antifermion excess compared to the standard NJL model, due to the pseudoscalar and pseudovector extension respectively. In both cases regions with negative interaction measure $I = \epsilon-3p$ are found. Future indications of such behaviors in strongly interacting fermion systems, for example in the context of neutron star physics, may point toward the presence of non-Hermitian contributions. These trends provide a first indication of curious potential mechanisms for producing non-Hermitian baryon asymmetry. In addition, the formalism described in this study is expected to apply more generally to other Hamiltonians with four-fermion interactions and thus the effects of the non-Hermitian bilinears are likely to be generic.

Effects of unstable thermal stratification on the flow characteristics in an idealized rural-to-urban transition region: A large-eddy simulation study

Large-eddy simulations are performed to study the impacts of unstable thermal stratification on the mean wind and turbulence in an idealized rural-to-urban surface transition region. In the unstable stratification case, a convective boundary layer is developed over the urban region and much longer adjustment distances for the mean wind and turbulence within the canopy are identified compared with that in the neutral case. Moreover, the flow recirculation and turbulence within the canopy are substantially enhanced by the unstable stratification. Specifically, at the far downstream positions of the surface transition, the mean wind is observed to flow at oblique angles through the street channels under the effects of buoyancy, which is qualitatively different from that in the neutral stratification case. Despite the magnitudes of the turbulent and dispersive stresses are significantly larger in the unstable case, the horizontally space-averaged mean streamwise velocity component within the canopy shows similar magnitudes as those in the neutral case. At the downstream region where the flow is already adjusted to the urban surface, the turbulent viscosity and Prandtl mixing length calculated from the horizontally space-averaged quantities are found to be significantly larger in the unstable case than those in the neutral case, while the turbulent Prandtl number is approximately uniform with height with a value of 0.5.

Optimal guidance for hypersonic vehicle using analytical solutions and an intelligent reversal strategy

This paper presents a novel three-dimensional guidance law to quickly generate optimal commands in the gliding phase. Owing to the complicated trajectory constraints and highly uncertain disturbances, the novel gliding profile is developed for the longitudinal plane. Subsequently, this longitudinal profile is utilized to obtain analytical equations of motion for performance index and path constraints prediction. Moreover, stringent terminal constraints, which comprise the altitude, the flight path angle, and the position of transition from gliding phase to terminal diving phase, are integrated into the longitudinal profile. The proposed analytical expressions simplify the onboard generation of optimal gliding trajectory as it does not involve complicated nonlinear programming problems. In addition, to regulate the terminal velocity onboard and simultaneously eliminate the heading error, two bank-reversal opportunities are used in the lateral profile and determined using a reinforcement learning algorithm. In the proposed guidance law, the terminal deviations are first predicted in real-time using the analytical expressions; and then the three-dimensional trajectory is regenerated by addressing a simple optimization problem and planning bank-reversal positions. The computation of the guidance law is facilitated using analytical solutions and a reinforcement learning method; therefore, the frequency of replanning facilitates the robustness, accuracy, and optimality. We evaluated the effectiveness of our method using some representative scenarios.

Revisiting the reattachment regime: a closer look at tandem cylinder flow at

Tandem cylinder flow comprises several different flow regimes. Within the reattachment regime, the development of the gap shear layers is of utmost importance to the flow, but has received little attention so far. Through direct numerical simulations at$Re = 10^{4}$, for a gap ratio of 3.0, we have discovered that the shear layers are significantly altered with respect to a single cylinder. These differences include early onset of separation, crossflow stabilising, delayed transition to turbulence and little meandering of the transition region. Vortex pairing in the gap shear layers is reported for the first time. The interaction between the recirculating gap flow and the shear layers was investigated. Asymmetrical, large-scale gap vortices influence the position of transition to turbulence through direct contact and through secondary flows. The occurrence of transition in the gap shear layers has consequences for both the reattachment mechanism and the development of the downstream cylinder wake. The reattachment points are unsteady with large amplitude fluctuations on a fine time scale. Reattachment is seen to be a combination of impingement and modification of the upstream shear layers, which causes a double shear layer in the downstream cylinder near-wake. Buffeting by and interaction with the gap shear layers likely cause transition to turbulence in the downstream cylinder boundary layer. This leads to significant changes in the wake topology, compared with a single-cylinder wake.

Variational Ansatz for the Ground State of the Quantum Sherrington-Kirkpatrick Model.

We present an Ansatz for the ground states of the quantum Sherrington-Kirkpatrick model, a paradigmatic model for quantum spin glasses. Our Ansatz, based on the concept of generalized coherent states, very well captures the fundamental aspects of the model, including the ground state energy and the position of the spin glass phase transition. It further enables us to study some previously unexplored features, such as the nonvanishing longitudinal field regime and the entanglement structure of the ground states. We find that the ground state entanglement can be captured by a simple ensemble of weighted graph states with normally distributed phase gates, leading to a volume law entanglement, contrasting with predictions based on entanglement monogamy.

Large-Eddy Simulation of a Water Jet Exhausting into Quiescent Air

This study focuses on a water injection system, typical of those used to inject water in the motor jet plume of rocket engines to reduce noise, and particularly on the destabilization of the liquid jet that leads to a spray system. For that purpose, a large-eddy simulation is conducted for an experimental water jet of the literature. It is a sprinkler whose Reynolds number is and nozzle exit diameter is , similar to injectors used for jet noise reduction studies at a reduced scale. A diffuse interface method is used to calculate the dense liquid phase, and the dispersed phase containing droplets is calculated with an Eulerian solver. Transfers between the dense and the dispersed phases are modeled in the coupling procedure, including the atomization and impingement processes. The jet mean radius and initial instability frequency are consistent with the experimental data, while the position of the jet transition varies with the fluctuation levels at the nozzle exit. The droplets are created in the shear layer and accumulate on the jet center when only the atomization process is considered. When also implemented, the impingement phenomenon, however, is shown to absorb the droplets before they reach the center.

Transgenic human HOXB1-9 directs anterior-posterior axial skeleton pattern in Hoxb1-9 deficient mice

The cervical and anterior thoracic regions of mammals generally exhibit similar vertebral numbers and identities along the anterior-posterior axis. The position of the forelimbs along the axial skeleton is also generally conserved. In contrast, the number of lumbar and sacral vertebrae and pelvic position exhibit more variation, correlating with posture and locomotion. The molecular mechanisms that lead to these conserved and variable axial skeletal patterns between species are not fully understood. Here we use a human HOXB1-9 transgene to complement a HoxB1-9 deficiency in the mouse. In TgHOXB1-9 mice, human HOXB1, B2, B3, and B4 (HOXB1-4) genes were expressed in mouse embryos in patterns similar to mouse Hoxb1-4 genes. Human transgene expression rescued the cervical and anterior thoracic vertebral patterning defects of HoxB1-9Δ/Δ mice. In addition, the posterior shift in forelimb position of HoxB1-9Δ/Δ mice was rescued by the transgene. Interestingly, the position of the lumbar-sacral transition in both TgHOXB1-9; HoxB1-9Δ/Δ and TgHOXB1-9; HoxB1-9+/+ mice was altered from six lumbar and four sacral vertebrae found in wild-type controls to five lumbar and five sacral vertebrae. The change in the position of the lumbar-sacral transition consequently altered the position of the pelvis. In contrast to the conserved expression of human HOXB1-4 genes in TgHOXB1-9 mouse embryos, the anterior border of human HOXB9 expression in the neural tube and paraxial mesoderm was shifted posteriorly by 2–3 somites compared to the anterior boundary of endogenous Hoxb9 expression. These findings suggest that conservation and variation in Hoxb/HOXB expression contributes to conserved and species-specific vertebral pattern and limb position.

Semiclassical and quantum nonlinear spectra of a strongly coupled single Λ-type three-level atom-cavity QED system

We present detailed numerical simulations of semiclassical and quantum spectra of a cavity QED system consisting of a single three-level atom in Λ-configuration interacting with a quantized cavity mode through one of its transitions while its other transition is driven by a coherent classical field. We compute the semiclassical and quantum spectra of the system under various levels of external driving field strengths. In the semiclassical approach, we neglect the correlations between the cavity and atomic operators, whereas in the quantum case no such assumption is made. Our results show that the two approaches yield identical results under sufficiently weak driving field conditions. However, the two approaches yield starkly different results at stronger driving field intensities: the fully quantum approach yields a well-defined multiphoton spectrum whereas the semiclassical approach results in a bistable spectrum. Furthermore, our calculations reveal a complex Raman structure at the position of the dark-state transition.

Optical and Hot-Film Measurements of the Boundary Layer Transition on a Naca Airfoil

This study explores the possibilities of identifying position of a boundary layer transition using hot film measurements complemented by classical optical methods i.e. interferometry and schlieren method. The subject of the measurement is a NACA 0010-64 airfoil with varying leading edge surface quality corresponding to smooth surface and rough surface with Ra ~ 50 and Ra ~ 100. Measurements are performed at several subsonic regimes and a transonic regime. Despite several shortcomings of the experimental setup, the method proved to be useful in providing information on the boundary layer transition. Measurements show that in the case of smooth leading edge, the onset of the boundary layer transition shifts upstream with increasing inlet Mach number and the major portion of the boundary layer is transitional. This is in accordance with other published results on the boundary layer transition on this kind of airfoils [1]. In all cases with the rough leading edge, the complete transition takes place on the rough portion of the surface already.

Compressibility of quark matter under strong magnetic field in the NJL model

The compressibility of magnetized quark matter is investigated in the SU(2) NJL model. The increases of the chemical potential and the temperature can reduce the compressibility, and lead to the much stiffer equation of state. The variation of the compressibility with the magnetic field will depend on the phase region. Due to the anisotropic structure, the compressibility is different in the directions parallel and perpendicular to the field. The discontinuity of longitudinal compressibility with the chemical potential and the temperature captures the signature of a first-order chiral phase transition and the crossover at high temperature. Moreover, the magnetic-field-and-temperature running coupling would have an important effect on the position of the phase transition. Under the lowest landau level approximation at zero temperature, the longitudinal compressibility has a direct inverse proportional relation to the magnetic field strength and the chemical potential square as ${\ensuremath{\kappa}}_{\mathrm{LLL},\ensuremath{\chi}}^{\ensuremath{\parallel}}\ensuremath{\propto}1/(eB{\ensuremath{\mu}}^{2})$.