1,223 research outputs found
Turbulent drag reduction by hydrophobic surfaces with shear-dependent slip length
No full textThe stabilisation of a parabolic equilibrium profile in a three-dimensional (3D) turbulent channel flow for an incompressible fluid is addressed with the objective of achieving drag reduction. The formulation of this problem stems from Balogh’s work [1] where Lyapunov stability analysis was used to devise prototype feedback laws and prove global stability of the solutions. This treatment only considers the controller as a mathematical artefact, but it can actually be linked to physical control strategies modelling hydrophobic surfaces and porous media. In the former, only linear slip velocity boundary conditions (BC) were considered [8]. However, experiments [2] have suggested that the slip length may be shear-dependent. Motivated by these, the effect on drag reduction of a shear-dependent slip length surface is examined in the present study using Direct Numerical Simulations (DNS) at Re τ0 = u τ0 δ/ν ≃ 180. δ is the channel half height, u τ0 the wall-shear velocity for regular no-slip walls channel and ν the kinematic viscosity. The theoretical analysis in [5], is extended to this new model. The proposed formulation shows that the skin-friction coefficient can be reduced by tuning the parameters in the shear-dependent slip length model. The results, which verified by DNS simulations, show that by taking a slip length value based on a constant slip model [8] and combining it within a shear-dependent model, up to 50% drag reduction can be obtained. The effect of control is further assessed by formulating the Fukagata identity [4] with general boundaries; the weighted Reynolds shear-stress for each quadrant shows an enhanced reduction in the sweep/ejection events compared to the constant slip model
Hydrodynamical turbulence by fractal fourier decimation
No full textWe present a systematic numerical investigation of high-resolution 3D isotropic and homogeneous turbulence resolved on a decimated set of Fourier modes. Fractal decimation acts to decrease the effective dimensionality of the flow by allowing triadic interactions only in a set of Fourier modes N(k) proportional to k^DF for large k. While keeping the symmetries of the original 3D Navier-Stokes equations unchanged, a dramatic change in small-scale statistics is detected at decreasing the fractal dimension DF . Already at fractal dimension DF = 2.8, a global self-similar behaviour is observed in the inertial range of scales, the consequence of such transition are the restoration of the scaling symmetry and vorticity distribution that becomes close to Gaussian. We relate the results to the different roles of local vs non-local interactions in the energy transfer range
Estimating the Greenhouse Gas Emissions of a Typical Wildlife Safari Tour: A Case Study from Yala National Park in the Dry Zone of Sri Lanka
No full textTourists are increasingly becoming environmentally conscious, driven by growing awareness of climate change and the environmental impact of tourism. This shift has led to a growing preference for low-carbon tourism options. Many travelers now seek destinations and experiences that prioritize renewable energy, eco-friendly transportation, and minimal waste generation. Wildlife tourism is a key component in Sri Lanka’s tourism mix. With Sri Lanka's tourism sector experiencing a significant resurgence in 2025, low-carbon wildlife tourism represents a sustainable approach to experiencing nature, while opening new opportunities. This study attempts to understand the GHG emission dynamics in a wildlife tourism setting with special reference to safari tours to identify decarbonizing opportunities. We estimated the carbon footprint of a typical safari tour at Yala National Park; one of the highly visited National Parks in Sri Lanka, using a combination of primary and secondary data. We surveyed 50 safari jeep drivers to gather emission-related details of vehicles/jeeps used for safari tours as well as tour routes, duration and passenger numbers. For this study, following the guidelines in ISO 14067:2018, the boundary of a safari tour was set from the point of entry to the point of exit through the gate of the Yala National Park. We used DEFRA/BEIS emission factors and IPCC guidelines for calculations. Secondary data such as monthly visitor numbers and numbers of vehicles entered the park were gathered from Department of Wildlife Conservation records from June 2023 to June 2024. Results suggest that a typical safari tour in Yala NP generates 24.7 kgCO2e emissions. The average number of persons per safari jeep is 5, hence this translates to 4.94 kgCO2e per tourist for a safari tour. We further analyzed the emissions associated with the hypothetical scenario of safari tour operation with 8 persons per jeep as a low carbon option. Under this scenario, the per tourist emission is 3 kgCO2e for a safari tour. This option can achieve 202,007.5 kgCO2e potential emission reductions per year. Overall, this study's findings provide important insights to the GHG emission profile of a wildlife tourism destination and support informed policy decisions to transform NPs to low-carbon tourism destinations.
Keywords: Sustainable tourism, GHG emissions, Wildlife tourism, Low-carbon tourism, Yala N
Least Squares Fitting of Chacón-Gielis Curves by the Particle Swarm Method of Optimization
No full textRicardo Chacón generalized Johan Gielis's superformula by introducing elliptic functions in place of trigonometric functions. In this paper an attempt has been made to fit the Chacón-Gielis curves (modified by various functions) to simulated data by the least squares principle. Estimation has been done by the Particle Swarm (PS) methods of global optimization. The Repulsive Particle Swarm optimization algorithm has been used. It has been found that although the curve-fitting exercise may be satisfactory, a lack of uniqueness of Chacón-Gielis parameters to data (from which they are estimated) poses an insurmountable difficulty to interpretation of findings.Least squares multimodal nonlinear curve-fitting; Ricardo Chacón; Jacobian Elliptic functions; Weierstrass ; Gielis super-formula; supershapes; Particle Swarm method; Repulsive Particle Swarm method of Global optimization; nonlinear programming; multiple sub-optima; global; local optima; fit; empirical; estimation; cellular automata; fractals
Introduction to mineralogy and petrology / S.K. Haldar.
No full textIncludes bibliographical references (p. 325-326) and index.xviii, 338 pages
Some Experiments on Fitting of Gielis Curves by Simulated Annealing and Particle Swarm Methods of Global Optimization
No full textIn this paper an attempt has been made to fit the Gielis curves (modified by various functions) to simulated data. The estimation has been done by two methods - the Classical Simulated Annealing (CSA) and the Particle Swarm (PS) methods - of global optimization. The Repulsive Particle Swarm (RPS) optimization algorithm has been used. It has been found that both methods are quite successful in fitting the modified Gielis curves to the data. However, the lack of uniqueness of Gielis parameters to data (from which they are estimated) is corroborated. From a technical viewpoint, this exercise may be considered as an application of CSA and RPS to extremely nonlinear least-squares curve-fitting to data that may exhibit a large number of local optima.Gielis curves; superformula; nonlinear curve-fitting; Least squares; multi-modal; local optima; global optimization; simulated annealing; particle swarm; parameters estimation
Symbols for Hijabs in The Proudest Blue The Story of Hijab and Family by Ibtihaj Muhammad and S.K. Ali
No full textThis study aimed at analyzing symbols that represent hijab as depicted in The Proudest Blue The Story of Hijab and Family written by Ibtihaj Muhammad and S.K. Ali and illustrated by Hatem Aly. This study was a qualitative study that analyze a text, so that the data were in the form of sentences and illustrations taken from the book. The data were collected by reading the book, identifying the data, and classifying the data. Then, the collected data were analyzed using the semiotic theory from Peirce. Based on the findings, there were five symbols representing hijab. The first two symbols are related to the authors’ choice of color. The author uses the pink to illustrate that hijabs are related to love and the blue color that is related to religious symbol of piety and chastity or sincerity. The blue color was the most dominant symbol in the book. In addition, the authors recommend that hijab is not a whisper, a laugh, and a tablecloth. These three symbols represent hijabs as something strong, not a joke to be laughed at and not only a thing to cover. All symbols used by the author are positive ones which challenge the negative stereotypes about hijab in which it is associated with radicalism and terrorism
CASESIAN : a knowledge-based system using statistical and experiential perspectives for improving the knowledge sharing in the medical prescription process
No full textAuthor name used in this manuscript: S.K. KwokAuthor name used in this manuscript: A.H.C. TsangAccepted ManuscriptPublishedGreen (AAM
Effective conductive and dielectric properties of matrix composites with inclusions of arbitrary shapes
No full textSuperior pre-osteoblast cell response of etched ultrafine-grained titanium with a controlled crystallographic orientation
No full textUltrafine-grained (UFG) Ti for improved mechanical performance as well as its surface modification enhancing biofunctions has attracted much attention in medical industries. Most of the studies on the surface etching of metallic biomaterials have focused on surface topography and wettability but not crystallographic orientation, i.e., texture, which influences the chemical as well as the physical properties. In this paper, the influences of texture and grain size on roughness, wettability, and pre-osteoblast cell response were investigated in vitro after HF etching treatment. The surface characteristics and cell behaviors of ultrafine, fine, and coarse-grained Ti were examined after the HF etching. The surface roughness during the etching treatment was significantly increased as the orientation angle from the basal pole was increased. The cell adhesion tendency of the rough surface was promoted. The UFG Ti substrate exhibited a higher texture energy state, rougher surface, enhanced hydrophilic wettability, and better cell adhesion and proliferation behaviors after etching than those of the coarse- and fine-grained Ti substrates. These results provide a new route for enhancing both mechanical and biological performances using etching after grain refinement of Ti. ? The Author(s) 2017.115Ysciescopu
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