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In this work, a calibration of ruby, samarium-doped strontium tetraborate (Sm2+: SrB4O7), and samarium-doped yttrium aluminum garnet (Sm3+: YAG) using Raman and fluorescence spectra was conducted within the temperature range of 296–850 K and pressure range of 0–55 GPa. The obtained calibration can be applied independently for high-temperature or high-pressure conditions and described as the unit form of P = (A′/B′) × [(λ/λT)B′ − 1] with A′ = A (296 K) + A1 × (T − 296) + A2 × (T − 296)2, B′ = B(296 K) + B1 × (T – 296), and λT = λT (296 K) + ΔλT, where the specific parameters are provided in the main text. It was observed that for the λ1 line (5D0 → 7F0 transition, about 685.2 nm under ambient conditions, also known as the 0-0 line) of Sm2+: SrB4O7, the neglect of the temperature effect on the pressure coefficient may lead to an underestimation of pressure above 35–40 GPa, with a maximum deviation of approximately 2.5 GPa within the range of 55 GPa and 850 K. For Sm3+: YAG, it may introduce significant errors under the whole high temperature and high pressure range if the effect of temperature is ignored, that is, about 3.9 GPa for Y1 line (4G5/2 → 6H7/2 transition, about 617.8 nm under ambient conditions) and 4.6 GPa for Y2 line (4G5/2 → 6H7/2 transition, about 616.0 nm under ambient conditions) at 850 K. Comparing the three fluorescence pressure sensors, the ruby has the strongest signal intensity and highest temperature sensitivity, and the Sm2+: SrB4O7 and the Sm3+: YAG possess lower temperature sensibility, wider used temperature range, and better spectral quality under high temperature and high pressure (HTHP), especially Sm2+: SrB4O7, which has a sharp high-intensity single peak λ1, perhaps the most promising sensor for high P–T experiments. Therefore, in view of the potential deflections of fluorescence peaks of each pressure sensor under HTHP, we recommend utilizing the HTHP-corrected relationships for pressure calibration. [ABSTRACT FROM AUTHOR]

Ultrahigh-temperature–pressure experiments are crucial for understanding the physical and chemical properties of matter. The recent development of boron-doped diamond (BDD) heaters has made such melting experiments possible in large-volume presses. However, estimates of temperatures above 2600 K and of the temperature distributions inside BDD heaters are not well constrained, owing to the lack of a suitable thermometer. Here, we establish a three-dimensional finite element model as a virtual thermometer to estimate the temperature and temperature field above 2600 K. The advantage of this virtual thermometer over those proposed in previous studies is that it considers both alternating and direct current heating modes, the actual sizes of cell assemblies after compression, the effects of the electrode, thermocouple and anvil, and the heat dissipation by the pressure-transmitting medium. The virtual thermometer reproduces the power–temperature relationships of ultrahigh-temperature–pressure experiments below 2600 K at press loads of 2.8–7.9 MN (∼19 to 28 GPa) within experimental uncertainties. The temperatures above 2600 K predicted by our virtual thermometer are within the uncertainty of those extrapolated from power–temperature relationships below 2600 K. Furthermore, our model shows that the temperature distribution inside a BDD heater (19–26 K/mm along the radial direction and <83 K/mm along the longitudinal direction) is more homogeneous than those inside conventional heaters such as graphite or LaCrO3 heaters (100–200 K/mm). Our study thus provides a reliable virtual thermometer for ultrahigh-temperature experiments using BDD heaters in Earth and material sciences. [ABSTRACT FROM AUTHOR]

The electrical transport property of layered MoSe2 has a strong response to high pressure by enhancing the inter-layer interaction. However, the narrowed bandgap under high pressure will cause the bipolar effect (i.e., the thermally excited minority carriers contribute to a Seebeck coefficient with the opposite sign to the majority carriers) at high temperatures to degrade the thermoelectric (TE) performance. Hence, suppressing the bipolar effect is important to optimize the TE performance of MoSe2 under high pressure and high temperature (HPHT). In this study, the degradation of TE performance caused by the bipolar effect under HPHT in MoSe2 is investigated. It is found that in MoSe2, the electrical conductivity was improved significantly by pressure; however, the bipolar effect led to a significantly degraded Seebeck coefficient at high temperatures. By injecting massive carriers beforehand, the bipolar effect was suppressed to make a dominant type of p-type charge carries, achieving an increased Seebeck coefficient with increasing temperature, resulting in an improved power factor from 29.3 μW m−1 K−2 in MoSe2 to 285.7 μW m−1 K−2 in Mo0.98Nb0.02Se2 at 5.5 GPa, 1110 K. Combined with the reduced thermal conductivity by point defect scattering on phonons, a maximum Z T value of 0.11 at 5.5 GPa, 1110 K. This work highlights the significance of suppressing the bipolar effect under HPHT for optimizing TE performance in such layered semiconductors. [ABSTRACT FROM AUTHOR]

Pattern-illuminated Fourier ptychography (piFP) is an elegant combination of structured illumination imaging and a Fourier ptychographic algorithm with the ability to image beyond the diffraction limit of the employed optics. Artifact-free piFP super-resolution reconstruction requires a high level of stability in the illumination pattern. However, unpredictable pattern variation occurs in the presence of environment perturbation, intensity fluctuation, and pointing instability at the source, leading to declines in image reconstruction quality. To address this issue, we present an efficient and robust piFP algorithm based on low-rank approximation (LRA-piFP), which relaxes the requirement for the stability of illumination patterns. This LRA-piFP method can model frame-wise pattern variation during a full scan, thus improve the reconstruction quality significantly. We take numerical simulations and proof-of-principle experiments with both long-range imaging and microscopy for demonstrations. Results show that the LRA-piFP method can handle different kinds of pattern variation and outperforms other state-of-the-art techniques in terms of reconstruction quality and resolution improvement. Our method provides effective experimental robustness to piFP with a natural algorithmic extension, paving the way for its application in both macroscopic and microscopic imaging. [ABSTRACT FROM AUTHOR]

This work focuses on the transient process of thermoacoustic oscillation in a standing-wave thermoacoustic engine with gas–liquid coupling oscillation. Observing the transient evolution of the pressure amplitude shows that the on-off phenomenon can occur through adjusting the location of the stack in the acoustic field, and there exists a critical distance from the stack center to the pressure antinode for this phenomenon to occur. The analysis from the perspective of energy balance indicates that energy dissipation induced by liquid surface instability is a key factor contributing to the occurrence of on-off phenomenon. Through installing a submerged float into the liquid column to stabilize the liquid surface, the on-off phenomenon can be suppressed. Besides, the temperature difference for achieving steady thermoacoustic oscillation is decreased and the steady-state pressure amplitude is increased. In this work, the significance of liquid surface instability on the transient process of thermoacoustic oscillation is revealed and should be considered for better characterizing the dynamics of gas–liquid thermoacoustic engines. [ABSTRACT FROM AUTHOR]

High pressure is an effective means to optimize the thermoelectric (TE) performance by sharply improving the electrical properties of materials. Studying the carrier effective mass (m*) is a feasible way to uncover the basic reason for superior electrical properties under high pressure. However, it is still difficult to obtain the m* under pressure in experiments. Thus, in this work, the m* of α-PbSe (F m 3 ̄ m) under high pressure is calculated by band dispersion relation based on the density functional theory. It is found that the high pressure decreases m* of α-PbSe, which is the cause for excellent electrical properties. Moreover, the isotropy of m* enhances with the increase in the pressure, which means the high pressure further optimizes the isotropy of the carrier migration in the structure. It is reveled that the higher the pressure, the more beneficial to improve the electrical properties of α-PbSe, thus optimizing the TE performance before the phase transition pressure (4.5 GPa). This work is of great significance for exploring the mechanism of in situ high-pressure TE properties in the future, as well as the prediction and selection of high-performance TE materials under high pressure. [ABSTRACT FROM AUTHOR]

The application performance of droplets, including the size and core-shell volumetric ratio of a double emulsion droplet, is investigated under various geometric sizes and flow rates in a flow-focusing capillary device. This study uses three-dimensional (3D) printing to create a novel substrate to assemble capillaries and make the inner dimension of the device tunable. Droplet generation is separated into two regions (uniform or non-uniform) based on the interface coupling shapes, where different generation modes are classified based on the rupture form of the multilayer interfaces. A map of the generation modes is established based on geometric size and flow conditions. In the dripping mode, interface coupling and its effect on generation are analyzed by the interface necking process for the two generation sub-modes (with/without a ball). The local capillary number of the double emulsion droplet is established for these sub-modes to analyze variations in the inner droplet volume, which helps propose the volume predictive model of inner and outer droplets. [ABSTRACT FROM AUTHOR]

Explosive welding can join a wide variety of both similar and dissimilar metals. However, because of the extremely fast welding process and micro-sized interfacial morphologies, it is a challenge to experimentally acquire the complete dynamic microscopic information. In this paper, the formation of the bonding interface was modeled through molecular dynamics simulations. Three significant phenomena, including a flat/wavy interface, wave formation, and fine grains, were investigated. The simulation results demonstrate that a flat interface is formed in the solid-state welding while a wavy interface is produced in the liquid-state welding. The wave formation can be explained by the jet that sequentially impacts the flyer plate and the base plate. There are two different pathways to form fine grains. At the regions of the bonding interface and the vortex, the fine grains are generated after the cooling process. Away from the bonding interface, the fine grains are produced by the drastic collision between the jet and the bonding surfaces. [ABSTRACT FROM AUTHOR]

Perovskite La2Ti2O7 nanocrystalline powder was obtained through the shock synthesis method. In the study, La2O3 and TiO2 powders were mixed through ball milling and, subsequently, shocked by a flyer at a velocity of 3.2 km/s. After shock treatment, the sample was recovered and characterized via various techniques, such as x-ray diffraction, Raman, scanning electron microscope, transmission electron microscope, and ultraviolet-visible diffuse reflection spectrum analysis, to find the presence of La2Ti2O7 nanocrystalline powder with an average grain size of approximately 30 nm in the recovered samples with different yields. Moreover, the results further confirm that the high shock temperature and long ball milling treatment induce higher activation of precursors to improve the La2Ti2O7 content in the recovered samples. By adjusting the relative density of precursor and the ball milling period, pure La2Ti2O7 nanocrystalline powder was obtained. The formation mechanism of La2Ti2O7 was carefully illustrated. This study presents a new method to synthesize La2Ti2O7 nanocrystalline powder by detonation-driven flyer impact. [ABSTRACT FROM AUTHOR]

In this work, we carry out direct numerical simulations of particle suspensions in the compressible turbulent vertical channel (TVC) flows with Mach number Ma = 1.5 and particle Stokes number St = 1–100. The compressibility effect is considered in the particle dynamic model for the first time in the study of compressible particle-laden wall turbulence. We find that in both incompressible and compressible flow, gravity weakens the wall-normal and spanwise fluctuations of particle velocities as the Stokes number increases. However, compared to the incompressible flow case, the compressible effect amplifies the mean velocity, fluctuations of velocity, and slip velocity of particle in the streamwise direction. The wall-normal and spanwise fluctuations of particle velocities are augmented by the compressible effect in the channel core region. Moreover, in the core region, the effect of fluid compressibility on the wall-normal and spanwise fluctuations of particle velocities attenuates as the Stokes number increases, indicating a competition between the compressible effect and the particle inertia effect. We, furthermore, conduct the quadrant analysis of the local fluctuation velocities of fluid at particle positions and observe preferential distributions in the second and the fourth quadrants at y+ = 12.5–13.5. For compressible TVC flows, the pattern of probability distributions is more elongated, and the percentage is slightly higher in the second and fourth quadrants than that of incompressible flows. This observation implies that more particles locate in the ejection and sweep events in compressible flows than that in incompressible flows, which is anticipated to influence the particle wall-normal transport. [ABSTRACT FROM AUTHOR]

The gas–liquid interface plays a crucial role in reducing the flow resistance of superhydrophobic surfaces. However, this interface is highly unstable and prone to collapse under flow shear, environmental pressure fluctuations, phase transitions, and diffusion between dissolved gases and free gases. Once the gas–liquid interface collapses, the flow resistance increases rapidly. Therefore, it is necessary to study the stability of the gas–liquid interface. This paper considers a three-dimensional-printed composite structure combining transverse posts and reentrant structures in a microchannel. This structure effectively improves the stability of the gas–liquid interface, allowing it to maintain stability even on surfaces made of hydrophilic materials. Under the effect of the transverse posts, the length of the gas–liquid interface above the groove increases from micrometers to millimeters. The lattice Boltzmann method is applied to analyze how the composite structure effectively improves the stability of the gas–liquid interface. Through analysis of the interface collapse process, the factors affecting the stability of the gas–liquid interface in this structure are explored, providing a theoretical foundation for structural optimization. [ABSTRACT FROM AUTHOR]

During the pyrolysis and gasification processes inside fluidized bed reactors, a single reactive particle is generally surrounded by multiple inert heat carrier particles. In this work, we focus on the simplest mixed particle pair (one reactive particle: P1, and one inert particle: P2) to investigate the joint effects of the Stefan Reynolds number (Resf), the particle Reynolds number (Re), separation distance normalized by particle diameter (L), and relative orientation (α) on the drag force exerting on each particle by particle-resolved direct numerical simulations. The results show that when particles are placed in a tandem arrangement, the blocking effect on P2 is weakened/strengthened with negative/positive Stefan flow since the effective diameter of P1 is smaller/larger than its real diameter. When L = 1.25, Re = 3, and particles are placed in tandem, the drag force of P1 decreases as Resf increases, but the reduction of the drag force decreases as Re increases. Under such conditions, the positive Stefan flow induces the repulsion between the two particles; thus, the drag force of P2 increases as Resf increases. When Resf = 3 and P2 is located downstream, the repulsive force felt by P1 can partially offset the drag force at L = 1.25, Re = 3. Moreover, the negative/positive Stefan flow enhances/weakens the drag force of P2 when it is located upstream. The Stefan flow has a negligible effect on the drag force of P2 when L = 3. [ABSTRACT FROM AUTHOR]

The chemical reaction mechanism of Ni/Al composites, referring to the exothermic mechanism and intermetallic-forming mechanism, is investigated by using molecular dynamics simulation. During the exothermic process, the influences of Ni/Al atomic ratios and crystallographic orientations on the exothermic reaction are systematically investigated. The exothermic mechanism can be explained by the atomic diffusion that increases the quantity of Ni–Al chemical bonds. There are two pathways to form the intermetallic phase during the chemical reaction. One is the atomic diffusion that forms the B2 NiAl phase at the interface. The other way is quenching the sample to the room temperature, but the type of intermetallic phases depends on the Ni/Al atomic ratio and ignition temperature. [ABSTRACT FROM AUTHOR]

Shock-induced consolidation of tungsten nanoparticles to form a bulk material was modeled using molecular dynamics simulation. By arranging the nanoparticles in a three-dimensional model of body-centered cubic super-lattice, the calculated shock velocity-particle velocity Hugoniot data are in good agreement with the experiments. Three states, including solid-undensified, solid-densified, and liquid-densified, can be sequentially obtained with the increase of the impact velocity. It is due to the flow deformation at the particle surface that densifies the cavity, and the high pressure and temperature that join the particles together. Melting is not a necessary factor for shock consolidation. Based on whether or not melting takes place, the consolidation mechanisms are liquid-diffusion welding or solid-pressure welding. [ABSTRACT FROM AUTHOR]

We have performed high pressure-temperature Brillouin scattering measurements on single crystal hydrogen sulfide using externally heated diamond anvil cell techniques. The pressure dependences of the acoustic velocities, isothermal elastic constants, and moduli of single crystal hydrogen sulfide have been determined along four isotherms. Both elastic constants and moduli increase monotonously with pressure along each isotherm, while they show a decreased tendency with temperature elevated under the same pressure points. The experimental equation of state of single crystal hydrogen sulfide is obtained by fitting with a third-order Birch-Murnaghan and Tait equation. It is proposed that the effect of hydrogen bonds contributes to the unique tendency of elastic anisotropy in single crystal hydrogen sulfide. Through our work, we have extended the melting curve and phase diagram of hydrogen sulfide up to 12 GPa and 580 K. [ABSTRACT FROM AUTHOR]

Resolving the sharp interface between the dilute and dense phases in gas–solid flows is a bottleneck in fine-grid simulations. This study addresses this issue through the theoretical analysis of an infinite gas–structure interface with arbitrary flow directions. The drag force at the interface is decomposed into three parts: the homogeneous drag forces of the dilute and dense regions and a stress divergence difference term. All the three parts are expressed as the functions of the solid volume fractions, particle Reynolds numbers, and stress divergences of the interface grid and its adjacent grids. The developed theoretical drag models at the interface are verified and improved based on particle-resolved direct numerical simulations (PR-DNSs) of flows past plug-like structures. The models are then tested against PR-DNSs of flows past bubble-containing, spherical, ellipsoidal structures. They yield significantly better performance than the traditional Beetstra et al.'s model [Beetstra et al., "Drag force of intermediate Reynolds number flow past mono‐ and bidisperse arrays of spheres," AIChE J. 53(2), 489–501 (2007)]. [ABSTRACT FROM AUTHOR]

Black phosphorus quantum dots (BPQDs) have recently obtained great attention owing to their outstanding properties, such as high hole mobility, quantum confinement effect, and edge effect. At present, several methods have been applied to prepare BPQDs using black phosphorus as precursor. In this study, BPQDs are obtained via shock-induced phase transformation using ball-milled red phosphorus nanopowder as precursor. The red phosphorus powder was ball-milled and shocked to induce phase transformation at transient high pressure and temperature. Multiple techniques are applied to characterize the recovered samples, including x-ray diffraction, Raman spectroscopy, transmission electron microscopy, and atomic force microscope. The characterization results demonstrate that the majority of recovered sample is BPQDs with a lateral size of 2–10 nm and a thickness of 0.9–2 nm. In addition, the formation mechanism of BPQDs under shock treatment was carefully analyzed, consisting of phase transformation induced by shock loading and exfoliation by tensile and shear effects. Furthermore, this study also confirms that the micromorphology of precursor is critical to the formation of BPQDs. This research provides an efficient one-step path to prepare BPQDs using ball-milled red phosphorus nanopowder as precursor. [ABSTRACT FROM AUTHOR]

Seagull optimization algorithm (SOA) has the disadvantages of low convergence accuracy, weak population diversity, and tendency to fall into local optimum, especially for high dimensional and multimodal problems. To overcome these shortcomings, initially, in this study, a shared SOA (SSOA) is proposed based on the combination of a sharing multi-leader strategy with a self-adaptive mutation operator. In addition, seven new variants of the SSOA algorithm are proposed employing the Gaussian mutation operator, Cauchy mutation operator, Lévy flights mutation operator, improved Tent chaos mutation operator, neighborhood centroid opposition-based learning mutation operator, elite opposition-based learning mutation operator, and simulated annealing algorithm combined with other mutation operators, namely, GSSOA, CSSOA, LFSSOA, ITSSOA, ESSOA, NSSOA, and CMSSOA, respectively. Then, the performance of these variants was evaluated on 23 benchmark functions, and the various performances of the best variant were evaluated on a comprehensive set of 43 benchmark problems and three real-world problems compared to other optimizers. Experimental and statistical results demonstrate that the proposed CMSSOA algorithm outperforms other variants of the SSOA algorithm and competitor approaches. [ABSTRACT FROM AUTHOR]

In-plane propagation of excited light in layered materials boosts the observation of novel phenomena, which differ from out-of-plane propagation. In this work, we perform the Raman study with light propagation parallel to the plane of layered MoS2. The Raman signal is unveiled at least an order of magnitude larger than that perpendicular to the plane when the excitation photon energy at ∼2.81 eV. We attribute this high-yield Raman spectra to the stronger photon–exciton coupling with in-plane propagation of light. Furthermore, we show that the exciton-mediated phonon excitation in the first-order Raman process is dominant with consideration of angular momentum transfer between phonons and photons through the measurements of the circularly polarized Raman spectra. This experimental setup configuration paves a way with high efficiency to investigate the phonon information in layered materials. [ABSTRACT FROM AUTHOR]

The coupling between the multilayer interfaces in compound jets has notable effects on the structure and generation sequence of the formed double emulsions. These effects are important for the performance of double emulsions, such as the capacity, release rate, and controlled release threshold in medical and chemical applications. In this work, the influence of the inner droplet on the necking of compound jets is investigated in a horizontally placed capillary flow-focusing device based on microfluidics. Three types of interface coupling modes are explored. Scaling laws that describe the time evolution of the neck radius for these different coupling modes are analyzed, and the reasons for transitions between such scaling laws are discussed. The results show that the motion and deformation of the droplet have a large impact on the neck breakup in the inertial regime, causing the scaling law to change, but only a slight effect in the viscous regime. Moreover, the inner droplet can prevent the jet from breaking up owing to interface coupling. These findings could help us to understand the role of interface coupling in compound jets and provide a reference for controlling the generation of compound droplets. [ABSTRACT FROM AUTHOR]

High-pressure Raman scattering and angle dispersive synchrotron x-ray diffraction studies have been carried out on magnesium tantalate (MgTa2O6) up to 41 GPa at room temperature. A pressure-induced phase transition at pressures above 10 GPa accompanied by softening of the internal ν11 (Eg) modes has been observed. Another phase transition took place at 20.2 GPa, which indicates that the edge shared TaO6 octahedra are distorted. The equation of state for MgTa2O6 in low pressure phase I was obtained by the second-order Birch–Murnaghan method, yielding a zero-pressure bulk modulus B0 of 205.8 ± 8.4 GPa. The pressure dependencies of the lattice vibration mode were extracted, and it is suggested that the instability of the trirutile structure at high pressure is related to the strong deformation of the TaO6 octahedra. Decompression measurements suggest that the pressure-induced transformation is irreversible. [ABSTRACT FROM AUTHOR]

The flow topology inside a droplet acts directly on the cells or substances enclosed therein and is, therefore, of great significance in controlling the living environment of cells and the biochemical reaction process. In this paper, the flow characteristics inside droplets moving in rectangular microchannels are studied experimentally by particle image velocimetry for capillary numbers ranging from 10−5 to 10−2. In order to decouple the effects of total flow, droplet spacing, viscosity ratio, droplet size, and the depth-to-width ratio of the channel on the flow field, the droplet trains with a designed initial state are first produced by controlling the two-phase flow rate and setting up an auxiliary inlet, which is used to adjust the droplet size and spacing, and then run at a set flow rate. As the total flow increases, the flow topologies inside the plunger droplet gradually change from four eddies to two at relatively high viscosity ratios, whereas the opposite transition direction is observed in the low-viscosity-ratio system. The flow topology inside spherical droplets is unaffected by the total flow or capillary number, invariably producing double vortices. The effect of the channel wall on the droplet boundary decreases as the droplet spacing increases or the droplet size decreases. Assuming the continuity of the fluid mass, the competition between the gutter-flow driving stress and the oil-film resistance determines the boundary velocity of the droplet. The oil-film resistance dominates the motion of the droplet boundary in high-aspect-ratio channels, resulting in the negative rotation of the boundary velocity vectors and six vortices in the interior of the droplet. The results are conducive to the further development of microfluidic flow cytometry, particle concentration control, and droplet micromixers. [ABSTRACT FROM AUTHOR]

We determined the shock equation of state of CaF2 at pressures of ∼0.4–1.5 TPa using high-power laser shock techniques. The shock velocity-particle velocity was approximated by the universal Hugoniot relationship known to metallic fluids. Our results do not support the incompressible behavior above ∼100 GPa claimed previously. Warm dense CaF2 is a bonded liquid above the melting point and approaches an ideal fluid above ∼1 TPa. The measured reflectivity change of CaF2 at the shock front, similar to the other semiconducting liquids in the warm dense region, suggests a gradual metallization process due to the presence of delocalized electrons at high shock-front temperatures. [ABSTRACT FROM AUTHOR]

The capability to precisely rotate cells and other micrometer-sized biological samples is invaluable in biomedicine, bioengineering, and biophysics. We propose herein a novel on-chip cell rotation method using acoustic microstreaming generated by oscillating asymmetrical microstructures. When the vibration is applied to a microchip with our custom-designed microstructures, two different modes of highly localized microvortices are generated that are utilized to precisely achieve in-plane and out-of-plane rotational manipulation of microbeads and oocytes. The rotation mechanism is studied and verified using numerical simulations. Experiments of the microbeads are conducted to evaluate the claimed functions and investigate the effects of various parameters, such as the frequency and the driving voltage on the acoustically induced flows. Accordingly, it is shown that the rotational speed and direction can be effectively tuned on demand in single-cell studies. Finally, the rotation of swine oocytes is involved as further applications. By observing the maturation stages of M2 after the exclusion of the first polar body of operated oocytes, the proposed method is proved to be noninvasive. Compared with the conventional approaches, our acoustofluidic cell rotation approach can be simple-to-fabricate and easy-to-operate, thereby allowing rotations irrespective of the physical properties of the specimen under investigation. [ABSTRACT FROM AUTHOR]

Three-dimensional large eddy simulations were carried out to investigate the flow over two tandem square cylinders for a fixed spacing ratio of L/D = 4 and a Reynolds number of 5.3 × 103, where L is the cylinder center-to-center distance between the cylinders and D is the cylinder width. The corners of each cylinder were chamfered with a ratio of ξ = B/D = 0%, 5%, 10%, and 15%, where B is the chamfered corner dimension. The focus is given on how ξ influences the flow structure, wake recirculation bubble, flow separation bubble, Strouhal number (St), aerodynamic force, and phase lag (ϕ) between vortex sheddings from the cylinders. With increasing ξ, the recirculation bubble length and minimum velocity in the wake of the upstream cylinder remain more or less constant and are close to those of a single cylinder, while the minimum velocity in the wake of the downstream cylinder dramatically drops between ξ = 0% and 5%. While the flow over the downstream remains attached on the side surfaces, that over the upstream cylinder forms primary and secondary side-surface bubbles on the side surface, and both shrink with increasing ξ. In addition, the leading chamfered corners are accompanied by corner bubbles that play an important role in the flow structure modification. Therefore, the time-mean drag and fluctuating lift of the upstream cylinder remarkably decrease for 0% ≤ ξ ≤ 5% and remain almost unchanged for 5% < ξ ≤ 15%, whereas those on the downstream cylinder diminish in the whole range of 0% ≤ ξ ≤ 15%. The Strouhal number (St) being identical for the two cylinders grows from 0.104 to 0.132 when ξ is increased from 0% to 15%. Overall, the influence of ξ on the wake structure and aerodynamics is remarkable for 0% ≤ ξ ≤ 5% because of the corner bubbles and is less for 5% < ξ ≤ 15%. [ABSTRACT FROM AUTHOR]

Three-dimensional large eddy simulations were carried out to investigate the flow around two tandem circular cylinders at a subcritical Reynolds number of Re = 103. The cylinder center-to-center spacing ratio L/D is varied from 1.25 to 6, where D is the cylinder diameter. In order to enhance the understanding of flow physics around two circular cylinders, particular attention is devoted to fluctuating forces, shear-layer reattachment, flow separation, wake recirculation, Strouhal number (St), and phase lag (ϕ) between the fluctuating lift of the two cylinders. The flow structure around the cylinders is highly sensitive to L/D. A change in L/D thus leads to overshoot flow (L/D ≤ 1.25), reattachment flow (1.5 ≤ L/D ≤ 3.5), and coshedding flow (L/D ≥ 4). The boundaries are characterized by drastic changes in the flow structure and a discontinuous drop/rise in St and forces. The St drops at the boundary between overshoot and reattachment flow regimes and jumps at the boundary between reattachment and coshedding flow regimes, while fluctuating forces and ϕ both jump at both boundaries. The flow separation on the downstream cylinder is much delayed (122°–128°) in the reattachment flow regime compared to that on the single cylinder (95°) or upstream cylinder (92°–95.5°). The fluctuating pressure on the entire surface of either cylinder is low for the overshoot flow because the two cylinders are enclosed by the upstream-cylinder-generated shear layers having the longest wake recirculation. The ϕ is almost zero in the overshoot flow. With increasing L/D, ϕ linearly increases in the reattachment and coshedding regimes with different gradients, larger in the latter regime than in the former, by nearly twice. [ABSTRACT FROM AUTHOR]

Three-dimensional large eddy simulations were carried out to investigate the flow around two tandem circular cylinders at a subcritical Reynolds number of Re = 103. The cylinder center-to-center spacing ratio L/D is varied from 1.25 to 6, where D is the cylinder diameter. In order to enhance the understanding of flow physics around two circular cylinders, particular attention is devoted to fluctuating forces, shear-layer reattachment, flow separation, wake recirculation, Strouhal number (St), and phase lag (ϕ) between the fluctuating lift of the two cylinders. The flow structure around the cylinders is highly sensitive to L/D. A change in L/D thus leads to overshoot flow (L/D ≤ 1.25), reattachment flow (1.5 ≤ L/D ≤ 3.5), and coshedding flow (L/D ≥ 4). The boundaries are characterized by drastic changes in the flow structure and a discontinuous drop/rise in St and forces. The St drops at the boundary between overshoot and reattachment flow regimes and jumps at the boundary between reattachment and coshedding flow regimes, while fluctuating forces and ϕ both jump at both boundaries. The flow separation on the downstream cylinder is much delayed (122°–128°) in the reattachment flow regime compared to that on the single cylinder (95°) or upstream cylinder (92°–95.5°). The fluctuating pressure on the entire surface of either cylinder is low for the overshoot flow because the two cylinders are enclosed by the upstream-cylinder-generated shear layers having the longest wake recirculation. The ϕ is almost zero in the overshoot flow. With increasing L/D, ϕ linearly increases in the reattachment and coshedding regimes with different gradients, larger in the latter regime than in the former, by nearly twice. [ABSTRACT FROM AUTHOR]

(c) Linearly polarization-resolved Raman spectra. Helicity-resolved Raman spectra with the excitation light (a) perpendicular and (b) parallel to the plane of monolayer MoS2. Publisher's Note: "High-yield helicity-resolved Raman scattering with in-plane propagation of light in monolayer MoS2" [Appl. Phys. [Extracted from the article]

The ab initio evolutionary algorithm is used to search for all thermodynamically stable Na-Te compounds at extreme pressure. In our calculations, several new structures are discovered at high pressure, namely, Imma Na2Te, Pmmm NaTe, Imma Na8Te2 and P4/mmm NaTe3. Like the known structures of Na2Te (Fm-3m, Pnma and P63/mmc), the Pmmm NaTe, Imma Na8Te2 and P4/mmm NaTe3 structures also show semiconductor properties with band-gap decreases when pressure increased. However, we find that the band-gap of Imma Na2Te structure increases with pressure. We presume that the result may be caused by the increasing of splitting between Te p states and Na s, Na p and Te d states. Furthermore, we think that the strong hybridization between Na p state and Te d state result in the band gap increasing with pressure. [ABSTRACT FROM AUTHOR]

In-plane propagation of excited light in layered materials boosts the observation of novel phenomena, which differ from out-of-plane propagation. In this work, we perform the Raman study with light propagation parallel to the plane of layered MoS2. The Raman signal is unveiled at least an order of magnitude larger than that perpendicular to the plane when the excitation photon energy at ∼2.81 eV. We attribute this high-yield Raman spectra to the stronger photon–exciton coupling with in-plane propagation of light. Furthermore, we show that the exciton-mediated phonon excitation in the first-order Raman process is dominant with consideration of angular momentum transfer between phonons and photons through the measurements of the circularly polarized Raman spectra. This experimental setup configuration paves a way with high efficiency to investigate the phonon information in layered materials. [ABSTRACT FROM AUTHOR]

We report angle dispersive X-ray diffraction (XRD) measurements and Raman spectroscopy on NH4Br up to 70.0 GPa at room temperature. Three thermodynamically stable phases (phases II, IV, and V) are confirmed and a new possible phase (phase VI) of P21/m symmetry is proposed whose structure was established from Rietveld refinement of synchrotron XRD data for the first time. The phase sequence observed in NH4Br is in accordance with phase II → IV → V → VI. Phase V transforms into phase VI at about 57.8 GPa with a huge volume reduction of 30%. Still, the intramolecular distances are analyzed to better understand the nature of structures. The H-H interactions become markedly more important as the N-Br distances are compacted, which is probably the reason of the kink of symmetric stretching band (ν1) at the transition pressure.