Recent Submissions

Article

Interior a priori estimates for supersolutions of fully nonlinear subelliptic equations under geometric conditions

(Wiley, 2024-02-17) Goffi, Alessandro; Dipartimento di Matematica “Tullio Levi-Civita” Università degli Studi di Padova Padua Italy

In this note, we prove interior a priori first- and second-order estimates for solutions of fully nonlinear degenerate elliptic inequalities structured over the vector fields of Carnot groups, under the main assumption that is semiconvex along the fields. These estimates for supersolutions are new even for linear subelliptic inequalities in nondivergence form, whereas in the nonlinear setting they do not require neither convexity nor concavity on the second derivatives. We complement the analysis exhibiting an explicit example showing that horizontal regularity of Calderón–Zygmund type for fully nonlinear subelliptic equations posed on the Heisenberg group cannot be in general expected in the range , being the homogeneous dimension of the group.

Article

Enhanced damage tolerance and fracture toughness of lightweight carbon-Kevlar fiber hybrid laminate

(SAGE Publications, 2024-02-17) Wagih, Ahmed; Junaedi, Harri; Mahmoud, Hassan; Lubineau, Gilles; Kumar, Ajay; Sebaey, Tamer A; Mechanics of Composites for Energy and Mobility Lab, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia; Mechanical Engineering Program; Physical Science and Engineering (PSE) Division; Mechanical Design and Production Department, Faculty of Engineering, Zagazig University, Zagazig, Egypt; Engineering Management Department, College of Engineering, Prince Sultan University, Riyadh, Saudi Arabia; Department of Mechanical Engineering, School of Engineering and Technology, JECRC University, Jaipur, India

Low damage tolerance and residual strength are the main drawbacks of carbon fiber composite laminates that limit their application in many lightweight structures. This study demonstrates the exceptional damage tolerance and high fracture toughness of carbon-Kevlar hybrid laminate, where Kevlar plies are placed between two carbon fiber face sheets. Flexural strength after damage and mode I translaminar fracture toughness of carbon and Kevlar and the hybrid laminates were evaluated using three-point bending and single-edge notched bending tests, respectively. The damage mechanisms in the three configurations were investigated using micro-computed tomography and correlated with their mechanical responses. The results showed that the hybrid laminate could sustain 70% of the laminate strength after fiber damage occurs and can sustain the same strength for large strains, unlike carbon and Kevlar fiber laminates, where they both lose their mechanical integrity after fiber breakage. Moreover, this laminate showed 200% and 170% larger specific absorbed energy than carbon and Kevlar laminates, respectively. The improvement can be justified by the propagation of fiber breakage at three different positions in the Kevlar core and the delamination at the carbon-Kevlar interface that allowed larger energy dissipation during fracture. Additionally, it showed 21% and 42.7% larger absolute and specific fracture toughness, respectively, than the carbon fiber laminate.

Article

Bolgiano-Obukhov scaling in two-dimensional Rayleigh-Bénard convection at extreme Rayleigh numbers

(American Physical Society (APS), 2024-02-16) Samuel, Roshan; Verma, Mahendra K.; Department of Mechanical Engineering, Indian Institute of Technology, Kanpur 208016, India; Department of Physics, Indian Institute of Technology, Kanpur 208016, India

Understanding the behavior of the kinetic energy spectrum and flux in two-dimensional (2D) turbulent thermal convection remains a challenge. In this paper, using highresolution direct numerical simulation of Rayleigh-Bénard convection for Rayleigh numbers 1011–1014 and unit Prandtl number, we show that 2D turbulent convection exhibits Bolgiano-Obukhov scaling. At small wave numbers, where buoyancy feeds energy to the velocity field, kinetic energy exhibits inverse cascade. Consequently, the kinetic energy spectrum scales as k−11/5 and the kinetic energy flux shows k−4/5 scaling at small wave numbers. Buoyancy is weakened at large wave numbers, and this leads to a constant enstrophy cascade and k−3 kinetic energy spectrum, similar to 2D hydrodynamic turbulence. However, the entropy spectrum exhibits a bispectrum with the upper branch varying as k−2. We also observe constant entropy flux in the inertial range. Finally, we also draw a connection between the entropy flux in the dissipation range and the entropy dissipation rate in the bulk.

Article

Carboxyl-Decorated UiO-66 Supporting Pd Nanoparticles for Efficient Room-Temperature Hydrodeoxygenation of Lignin Derivatives

(Wiley, 2024-02-16) Yangcheng, Ruixue; Li, Jingwei; He, Jiadai; Zheng, Yuxin; Yu, Haijie; Chen, Cailing; Wang, Jianjian; Advanced Membranes and Porous Materials (AMPM) Center Physical Sciences and Engineering Division King Abdullah University of Science and Technology (KAUST) Thuwal 23955 Saudi Arabia; Advanced Membranes and Porous Materials Research Center; Physical Science and Engineering (PSE) Division; School of Chemistry and Chemical Engineering State Key Laboratory of Coal Mine Disaster Dynamics and Control Institute of Advanced Interdisciplinary Studies Multi-scale Porous Materials Center Chongqing University Chongqing 401331 China

Hydrodeoxygenation (HDO) of lignin derivatives at room-temperature (RT) is still of challenge due to the lack of satisfactory activity reported in previous literature. Here, it is successfully designed a Pd/UiO-66-(COOH)2 catalyst by using UiO-66-(COOH)2 as the support with uncoordinated carboxyl groups. This catalyst, featuring a moderate Pd loading, exhibited exceptional activity in RT HDO of vanillin (VAN, a typical model lignin derivative) to 2-methoxyl-4-methylpheonol (MMP), and >99% VAN conversion with >99% MMP yield is achieved, which is the first metal-organic framework (MOF)-based catalyst realizing the goal of RT HDO of lignin derivatives, surpassing previous reports in the literature. Detailed investigations reveal a linear relationship between the amount of uncoordinated carboxyl group and MMP yield. These uncoordinated carboxyl groups accelerate the conversion of intermediate such as vanillyl alcohol (VAL), ultimately leading to a higher yield of MMP over Pd/UiO-66-(COOH)2 catalyst. Furthermore, Pd/UiO-66-(COOH)2 catalyst also exhibits exceptional reusability and excellent substrate generality, highlighting its promising potential for further biomass utilization.

Article

Membrane distillation of wastewater: comparison of model and real organics

(IWA Publishing, 2024-02-16) Habib, Rasikh; Phuong, Mai; Asif, Muhammad; Jiang, Guangming; Sivakumar, Muttucumaru; Advanced Membranes & Porous Materials Centre and KAUST Catalysis Centre, Physical Science & Engineering, King Abdullah University of Science and Technology, Thuwal 23955, Saudi Arabia; Advanced Membranes and Porous Materials Research Center; Physical Science and Engineering (PSE) Division; School of Civil, Mining, Environmental and Architectural Engineering, Faculty of Engineering and Information Sciences, University of Wollongong, NSW 2525, Australia

Fouling behaviour in membrane distillation (MD) processes plays a crucial role in determining their widespread acceptability. Most studies have primarily focused on model organic foulants, such as humic acid (HA) and sodium alginate (SA). This study investigates the fouling of a polytetrafluoroethylene membrane in a direct contact MD (DCMD) using model organics (i.e., HA and SA) and real wastewater. The results indicated that the flux decline (5–60%) was only observed during the initial phase of the operation with model organic foulants. In contrast, real wastewater caused a gradual decline in flux throughout the experiment in both the concentrate (40%) and continuous (90%) modes. The study also found significant differences in the fouling layer morphology, composition, and hydrophobicity between the model organic foulants and real wastewater. Fourier transform infrared spectroscopy findings demonstrated that the fouling layer formed by real wastewater varied significantly from model organics, which primarily comprised of protein-like and polysaccharide-like functional groups. Finally, liquid chromatography–organic carbon detection revealed that the fouling layer of the MD membrane with real wastewater was composed of 40.7% hydrophobic and 59.3% hydrophilic organics. This study suggests that model organics may not accurately reflect real wastewater fouling.