•Delta-SPH model is extended for simulating strongly-compressible multiphase flows.•A new Volume Adaptive Scheme is proposed.•Governing equations are discretized with corrected SPH operators.•Strict ...numerical validations are carried out using challenging benchmarks.
In the present work, the single-phase and weakly-compressible δ-SPH model is further extended to simulate multiphase and strongly-compressible flows. This is motivated by the fact that traditional SPH models can meet some difficulties when modeling strongly-compressible flows with large volume variations (e.g. expansion and collapse of cavitation bubbles). Due to the strong compressibility of the fluid, the energy equation should be considered in the governing equations. In that case, the pressure is solved based on both density and internal energy. To stabilize the pressure field, density and energy diffusive terms should be applied. Large variations of particle volumes in the compressible phase would result in large variations of particle spacing. Therefore, particle smoothing lengths are adjusted in time to maintain appropriate neighboring particles. To ensure good properties of accuracy and conservation when particles with different smoothing lengths interact, corrected SPH operators are utilized to discretize the governing equations. Moreover, in order to limit the particle volume variations and maintain a homogeneous volume distribution in the entire flow field, especially near the interface between different phases of different compressibility, a new volume adaptive scheme is proposed to control particle volumes. The volumes which are over-expanded or over-compressed will be split or merged with others, maintaining a small particle volume variation in the flow. Finally, the proposed SPH model is validated with several challenging benchmarks including expansion and collapse of underwater-explosion bubbles or cavitation bubbles. All the SPH results are compared with other numerical solutions with good agreements.
At ambient pressure, CrAs undergoes a first-order transition into a double-helical magnetic state atTN=265K, which is accompanied by a structural transition. The recent discovery of pressure-induced ...superconductivity in CrAs makes it important to clarify the nature of quantum phase transitions out of the coupled structural/helimagnetic order in this system. Here, we show, via neutron diffraction on the single-crystal CrAs under hydrostatic pressure (P), that the combined order is suppressed atPc≈10kbar, near which bulk superconductivity develops with a maximal transition temperatureTc≈2K. We further show that the coupled order is also completely suppressed by phosphorus doping inCrAs1−xPxat a criticalxc≈0.05, above which inelastic neutron scattering evidenced persistent antiferromagnetic correlations, providing a possible link between magnetism and superconductivity. In line with the presence of antiferromagnetic fluctuations nearPc(xc), theAcoefficient of the quadratic temperature dependence of resistivity exhibits a dramatic enhancement asP(x) approachesPc(xc), around whichρ(T)has a non-Fermi-liquid form. Accordingly, the electronic specific-heat coefficient ofCrAs1−xPxpeaks aroundxc. These properties provide clear evidence for quantum criticality, which we interpret as originating from a nearly second-order helimagnetic quantum phase transition that is concomitant with a first-order structural transition. Our findings in CrAs highlight the distinct characteristics of quantum criticality in bad metals, thereby bringing out new insights into the physics of unconventional superconductivity such as those occurring in the high-Tciron pnictides.
AIMS: The aim of this study was to characterize anaerobic ammonium oxidation (anammox) community in sediments of the Dongjiang River, a drinking water source of Hong Kong. METHODS AND RESULTS: The ...diversity and distribution of the anammox community were investigated based on a comparative analyses of 16S rRNA and hydrazine oxidation (hzo) genes of anammox bacteria. Candidatus Brocadia and two new anammox bacterial clusters were detected based on phylogenetic analysis of 16S rRNA genes. In contrast, the targeting of hzo genes indicated the presence of only Candidatus Jettenia with four different clusters. It was found that the sequence diversities of hzo genes were higher than those of the 16S rRNA genes. The abundance of anammox bacteria varied significantly among the sediment samples based on qPCR. Pearson correlation analysis indicated that nitrite concentration was the key factor influencing the abundance of anammox bacteria. The redundance analysis (RDA) confirmed that the combination of the contents of nitrite and nitrate, and the ratio of total nitrogen vs total carbon (TN/TC) had significant impact on the anammox bacterial community structure. CONCLUSIONS: The results revealed that the diverse anammox bacteria were present in sediments of the Dongjiang River, and the community structures were associated with varied environmental factors caused by urban pollutant invasion. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report about the distribution of anammox bacterial community in sediments of the Dongjiang River, which provides helpful information of anammox niche specificity and influencing factors in the river ecosystem.
The epidemiology of candidaemia varies between hospitals and geographic regions. Although there are many studies from Asia, a large-scale cross-sectional study across Asia has not been performed. We ...conducted a 12-month, laboratory-based surveillance of candidaemia at 25 hospitals from China, Hong Kong, India, Singapore, Taiwan and Thailand. The incidence and species distribution of candidaemia were determined. There were 1601 episodes of candidaemia among 1.2 million discharges. The overall incidence was 1.22 episodes per 1000 discharges and varied among the hospitals (range 0.16–4.53 per 1000 discharges) and countries (range 0.25–2.93 per 1000 discharges). The number of Candida blood isolates and the total number of fungal isolates were highly correlated among the six countries (R² = 0.87) and 25 hospitals (R² = 0.77). There was a moderate correlation between incidence of candidaemia and the intensive care unit (ICU)/total bed ratio (R² = 0.47), although ICUs contributed to only 23% of candidaemia cases. Of 1910 blood isolates evaluated, Candida albicans was most frequently isolated (41.3%), followed by Candida tropicalis (25.4%), Candida glabrata (13.9%) and Candida parapsilosis (12.1%). The proportion of C. tropicalis among blood isolates was higher in haemato-oncology wards than others wards (33.7% versus 24.5%, p 0.0058) and was more likely to be isolated from tropical countries than other Asian countries (46.2% versus 18.9%, p 0.04). In conclusion, the ICU settings contribute, at least in part, to the incidence variation among hospitals. The species distribution is different from Western countries. Both geographic and healthcare factors contribute to the variation of species distribution.
The newly emerging monolayer phosphorene was recently predicted to be a promising thermoelectric material. In this work, we propose to further enhance the thermoelectric performance of phosphorene ...using the strain-induced band convergence. The effect of the uniaxial strain on the thermoelectric properties of phosphorene was investigated by using the first-principles calculations combined with the semiclassical Boltzmann theory. When the zigzag-direction strain is applied, the Seebeck coefficient and electrical conductivity in the zigzag direction can simultaneously be greatly enhanced at the critical strain of 5%, at which the band convergence is achieved. The largest ZT value of 1.65 at 300 K is then conservatively estimated by using the bulk lattice thermal conductivity. When the armchair-direction strain of 8% is applied, the room-temperature ZT value can reach 2.12 in the armchair direction of phosphorene. Our results indicate that strain-induced band convergence could be an effective method to enhance the thermoelectric performance of phosphorene.
The finite-time dynamics, apart from its fundamental importance in nonequilibrium thermodynamics, is of great significance in designing heat engine cycles. We build an experimental apparatus to test ...the predicted long-time 1/τ scaling of the irreversible entropy generation in the finite-time (τ) thermodynamic process by compressing dry air in a temperature-controlled water bath. We present the first direct experimental validation of the scaling, utilized in many finite-time thermodynamic models at the long-time regime. The experimental data also demonstrate a clear deviation from the scaling at the short-time regime. We show the optimal control scheme to minimize the irreversible entropy generation in finite-time process. Such optimization shall bring new insight to the practical design of heat engine cycles.
•The strongly-compressible SPH model is extended to cylindrical coordinate.•A convenient and effective way of avoiding singularity at the axis is adopted.•VAS is important for both strongly- and ...weakly-compressible flow simulations.•Axisymmetric-SPH results are validated with 3D experimental data.
The present work is dedicated to extending the strongly-compressible multiphase SPH Volume Adaptive Scheme (see 22) from Cartesian to cylindrical polar coordinates for addressing axisymmetric problems. By omitting the gradient in the circumferential direction, an Axisymmetric-SPH model is developed. Three-dimensional axisymmetric problems including rising bubbles, expanding or collapsing bubbles are conveniently and efficiently simulated using the proposed Axisymmetric-SPH model. Contrary to the purely three-dimensional SPH model established in Cartesian coordinates, with the axisymmetric model, sufficient particle resolutions can be easily adopted to reach converged simulations of complex problems. Axisymmetric-SPH results are validated either using experimental data or other numerical results. In the Axisymmetric-SPH model, a convenient and effective way of avoiding singularity at the axis is presented. In addition, the Volume Adaptive Scheme (VAS), originally developed for compressible flow simulations with large volume variations in Cartesian coordinates, is shown to be a crucial tool to adjust particle volumes in the Axisymmetric-SPH model for all flow cases, including both weakly-compressible and strongly-compressible flows.
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