In this paper we investigate the implementation of contact angles in the pseudopotential lattice Boltzmann modeling of wetting at a large density ratio ρ_{L}/ρ_{V}=500. The pseudopotential lattice ...Boltzmann model X. Shan and H. Chen, Phys. Rev. E 49, 2941 (1994)10.1103/PhysRevE.49.2941 is a popular mesoscopic model for simulating multiphase flows and interfacial dynamics. In this model the contact angle is usually realized by a fluid-solid interaction. Two widely used fluid-solid interactions, the density-based interaction and the pseudopotential-based interaction, as well as a modified pseudopotential-based interaction formulated in the present paper are numerically investigated and compared in terms of the achievable contact angles, the maximum and the minimum densities, and the spurious currents. It is found that the pseudopotential-based interaction works well for simulating small static (liquid) contact angles θ<90^{∘}, however, it is unable to reproduce static contact angles close to 180^{∘}. Meanwhile, it is found that the proposed modified pseudopotential-based interaction performs better in light of the maximum and the minimum densities and is overall more suitable for simulating large contact angles θ>90^{∘} as compared with the two other types of fluid-solid interactions. Furthermore, the spurious currents are found to be enlarged when the fluid-solid interaction force is introduced. Increasing the kinematic viscosity ratio between the vapor and liquid phases is shown to be capable of reducing the spurious currents caused by the fluid-solid interactions.
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A hybrid thermal lattice Boltzmann (LB) model is presented to simulate thermal multiphase flows with phase change based on an improved pseudopotential LB approach (Li et al., 2013). ...The present model does not suffer from the spurious term caused by the forcing-term effect, which was encountered in some previous thermal LB models for liquid–vapor phase change. Using the model, the liquid–vapor boiling process is simulated. The boiling curve together with the three boiling stages (nucleate boiling, transition boiling, and film boiling) is numerically reproduced in the LB community for the first time. The numerical results show that the basic features and the fundamental characteristics of boiling heat transfer are well captured, such as the severe fluctuation of transient heat flux in the transition boiling and the feature that the maximum heat transfer coefficient lies at a lower wall superheat than that of the maximum heat flux. Furthermore, the effects of the heating surface wettability on boiling heat transfer are investigated. It is found that an increase in contact angle promotes the onset of boiling but reduces the critical heat flux, and makes the boiling process enter into the film boiling regime at a lower wall superheat, which is consistent with the findings from experimental studies.
Reactive transport equations are solved at the pore scale using the lattice Boltzmann (LB) method, and the results are upscaled using volume averaging over a representative elemental volume and are ...fit to a multiscale continuum model. The multiscale continuum model accounts for local concentration gradients within diffusion‐dominated matrix domains that are coupled to the primary continuum fluid. In general it is found that a multiscale continuum formulation is required to fit the upscaled pore‐scale results. However, it is also demonstrated that in some cases, multiscale processes may be represented by a single‐continuum model employing effective parameters that are not directly measurable. Provided that sufficient resolution of the pore‐scale geometry can be obtained, the pore‐scale model can be used to determine the most appropriate form of continuum formulation (single, dual, or multiple continua) that best fits the upscaled pore‐scale simulation and, simultaneously, to provide parameters needed for constitutive relations appearing in the multiscale continuum formulation. It is suggested that a multiscale continuum approach may help explain the observed discrepancy between laboratory and field‐derived reaction rates by explicitly representing distinct transport domains through separate interacting continua which could be responsible for the formation of preferential pathways. An example is presented on the basis of a multiscale, synthetic, structured porous medium describing transport of a tracer and linear reaction kinetics.
Background The Singapore national Advance Care Planning (ACP) programme was launched in 2011 with the purpose of ensuring that healthcare professionals are fully aware of patients' treatment ...preferences. There is little research assessing the performance of such programmes in ethnically diverse Asian countries; hence, the purpose of this study was to qualitatively examine patients and caregivers' experiences with the ACP programme. Method We conducted interviews with 28 participants, thirteen of whom identified as proxy decision makers (PDMs) and the remainder as patients. Interviews focused on respondents' experiences of chronic illness and of participating in the ACP programme. Textual data was analysed through a framework analysis approach. Results Participants' narratives focused on four major themes with 12 subthemes: a) Engagement with Death, factors influencing respondents' acceptance of ACP; b) Formation of Preferences, the set of concerns influencing respondents' choice of care; c) Choice of PDM, considerations shaping respondents' choice of nominated health spokesperson; and d) Legacy Solidification, how ACP is used to ensure the welfare of the family after the patient passes. These findings led to our development of the directive decision-making process framework, which delineates personal and sociocultural factors influencing participants' decision-making processes. Respondents' continual participation in the intervention were driven by their personal belief system that acted as a lens through which they interpreted religious doctrine and socio-cultural norms according to their particular needs. Conclusion The directive decision-making process framework indicated that ACP could be appropriate for the Asian context because participants displayed an awareness of the need for ACP and were able to develop a concrete treatment plan. Patients in this study made decisions based on their perceived long-term legacy for their family, who they hoped to provide with a solid financial and psychological foundation after their death.
Aberrant expression of long noncoding RNAs (lncRNAs) is associated with various human cancers. However, the role of lncRNAs in Bcr-Abl-mediated chronic myeloid leukemia (CML) is unknown. In this ...study, we performed a comprehensive analysis of lncRNAs in human CML cells using an lncRNA cDNA microarray and identified an lncRNA termed lncRNA-BGL3 that acted as a key regulator of Bcr-Abl-mediated cellular transformation. Notably, we observed that lncRNA-BGL3 was highly induced in response to disruption of Bcr-Abl expression or by inhibiting Bcr-Abl kinase activity in K562 cells and leukemic cells derived from CML patients. Ectopic expression of lncRNA-BGL3 sensitized leukemic cells to undergo apoptosis and inhibited Bcr-Abl-induced tumorigenesis. Furthermore, transgenic (TG) mice expressing lncRNA-BGL3 were generated. We found that TG expression of lncRNA-BGL3 alone in mice was sufficient to impair primary bone marrow transformation by Bcr-Abl. Interestingly, we identified that lncRNA-BGL3 was a target of miR-17, miR-93, miR-20a, miR-20b, miR-106a and miR-106b, microRNAs that repress mRNA of phosphatase and tensin homolog (PTEN). Further experiments demonstrated that lncRNA-BGL3 functioned as a competitive endogenous RNA for binding these microRNAs to cross-regulate PTEN expression. Additionally, our experiments have begun to address the mechanism of how lncRNA-BGL3 is regulated in the leukemic cells and showed that Bcr-Abl repressed lncRNA-BGL3 expression through c-Myc-dependent DNA methylation. Taken together, these results reveal that Bcr-Abl-mediated cellular transformation critically requires silence of tumor-suppressor lncRNA-BGL3 and suggest a potential strategy for the treatment of Bcr-Abl-positive leukemia.
The Helium Cooled Pebble Bed (HCPB) Breeding Blanket (BB) is one of the 4 BB concepts being investigated in the EU for their possible implementation in DEMO. During 2014 the former “beer-box” BB ...concept based on the ITER’s HCPB Test Blanket Module suffered several design changes so as to meet the different counteracting nuclear, thermohydraulic and thermomechanical requirements. These studies evidenced that the concept is too rigid to meet the tight TBR requirements imposed for the EU DEMO (i.e. TBR≥1.10). Additionally, the complex manifold system with unbalanced helium mass flow in each of the 2 parallel cooling loops made the concept thermohydraulically complex. However, parametric studies during 2015 revealed that the HCPB concept have potential for a better nuclear performance, as well as margin for a significant simplification of the cooling internals by redefining the cooling plates and the architecture of the blanket, building a symmetric flow scheme.
This paper describes the new HCPB concept based on an integrated FW with the breeding zone thermohydraulics and helium manifold systems. The former complex manifold backplates have been compacted and integrated in the cooling plates, releasing ≈300mm of radial space that can be used now to increase breeder zone, the neutron shielding, to reinforce the Back Supporting Structure (BSS) or basically to reduce the reactor size. Detailed neutronic analyses have yielded a TBR of ∼1.20 for the baseline design. Initial analyses show a correct thermohydraulic behavior. Preliminary thermomechanical analyses also indicate that the design can potentially withstand an in-box LOCA at 9 MPa at a level C according to the RCC-MRx code. Future consolidation activities are described, which shall lead to a concept meeting the BB requirements.
So far, one main shortcoming restricting the wide application of Ti2AlNb sheet is the poor ductility. To solve this problem, we hot packed rolled the Ti2AlNb compact prepared by ...spark-plasma-sintering the pre-alloyed powders at the α2+B2+O phase field in this work. The sheets were rolled by different thickness reductions and passes. Results showed that the packs made of 304 stainless steel effectively protected the Ti2AlNb sheet from cracking, and the obtained sheets had good surface formation quality. B2 grain size and the texture intensity increased with increasing the rolling pass. The sheets rolled by all schemes had excellent ductility and relative high strength without applying any post heat treatment. An extreme high elongation of 13.91% with a tensile strength of 1063.27 MPa was obtained after four rolling passes. The nano O phases had excellent ability to coordinate transformations and account for the excellent ductility of the sheet. The α2 phases mainly strengthen the strength of the sheet; maintaining its high strength. This work may provide a new insight to develop commercial high ductility Ti2AlNb alloys.
•Poor room-temperature ductility of Ti2AlNb sheet is overcome by hot packed rolling the SPS compact at α2+O+B2 phase field.•Elongation of 13.91 % with a strength of 1063.27 MPa is achieved without post heat treatment after four rolling passes.•The reasons underlying the high ductility of Ti2AlNb sheet are discussed in detail.
Understanding hydraulic fracturing: a multi-scale problem Hyman, J. D.; Jiménez-Martínez, J.; Viswanathan, H. S. ...
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
10/2016, Volume:
374, Issue:
2078
Journal Article
Peer reviewed
Open access
Despite the impact that hydraulic fracturing has had on the energy sector, the physical mechanisms that control its efficiency and environmental impacts remain poorly understood in part because the ...length scales involved range from nanometres to kilometres. We characterize flow and transport in shale formations across and between these scales using integrated computational, theoretical and experimental efforts/methods. At the field scale, we use discrete fracture network modelling to simulate production of a hydraulically fractured well from a fracture network that is based on the site characterization of a shale gas reservoir. At the core scale, we use triaxial fracture experiments and a finite-discrete element model to study dynamic fracture/crack propagation in low permeability shale. We use lattice Boltzmann pore-scale simulations and microfluidic experiments in both synthetic and shale rock micromodels to study pore-scale flow and transport phenomena, including multi-phase flow and fluids mixing. A mechanistic description and integration of these multiple scales is required for accurate predictions of production and the eventual optimization of hydrocarbon extraction from unconventional reservoirs. Finally, we discuss the potential of CO2 as an alternative working fluid, both in fracturing and re-stimulating activities, beyond its environmental advantages.
This article is part of the themed issue ‘Energy and the subsurface’.
Whispering gallery mode (WGM) resonators have become increasingly diverse in terms of both architecture and applications, especially as refractometric sensors, allowing for unprecedented levels of ...sensitivity. However, like every refractometric sensor, a single WGM resonator cannot distinguish temperature variations from changes in the refractive index of the surrounding environment. Here, we investigate how breaking the symmetry of an otherwise perfect fluorescent microsphere, by covering half of the resonator with a high-refractive-index (RI) glue, might enable discrimination of changes in temperature from variations in the surrounding refractive index. This novel approach takes advantage of the difference of optical pathway experienced by WGMs circulating in different equatorial planes of a single microsphere resonator, which induces mode-splitting. We investigated the influence of the surrounding RI of the microsphere on mode-splitting through an evaluation of the sphere's WGM spectrum and quality factor (Q-factor). Our results reveal that the magnitude of the mode-splitting increases as the refractive index contrast between the high-refractive-index (RI) glue and the surrounding environment increases, and that when they are equal no mode-splitting can be seen. Investigating the refractive index sensitivity of the individual sub modes resulting from the mode-splitting unveils a new methodology for RI sensing, and enables discrimination between surrounding refractive index changes and temperature changes, although it comes at the cost of an overall reduced refractive index sensitivity.
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