Polylactic acid(PLA)possesses good mechanical and biodegradability properties which make it a suitable material for polymer composites whereas brittleness and high costs limit its utilization in various applications.T...Polylactic acid(PLA)possesses good mechanical and biodegradability properties which make it a suitable material for polymer composites whereas brittleness and high costs limit its utilization in various applications.The reinforcement of natural fibres with biopolymers has been formed to be an efficient technique to develop composites having the ability to be fully biodegradable.This study concerns with the incorporation of various percentages of untreated and alkali-treated Coir Fibres(CF)and pineapple leaf fibres(PALF)in PLA biocomposites and characterizations of flexural,morphological and dynamic mechanical properties.Flexural properties showed that the treated C1P1 hybrid composites(C1P1A)displayed highest flexural strength(35.81 MPa)and modulus(5.28 GPa)among all hybrid biocomposites.Scanning Electron Microscopy(SEM)revealed a behaviour of fibre-matrix adhesion in untreated treated biocomposites.SEM observation revealed good dispersion of the fillers in PLA.Dynamic mechanical analysis revealed that C1P1A showed highest glass transition temperature(Tg)and storage modulus(E')while untreated C3P7 displayed the least Tg and E'.Overall findings showed that alkali-treated hybrid biocomposites(CF/PALF/PLA)especially C1P1A have improved flexural properties,dynamic and morphological properties over untreated biocomposites.Success of these findings will provide attracting consideration of these hybrid biocomposites for various lightweight uses in a broad selection of industrial applications such as biomedical sectors,automobile,construction,electronics equipment,and hardware tools.展开更多
The energy system of the future will transform from the current centralised fossil based to a decentralised, clean, highly efficient, and intelligent network. This transformation will require innovative technologies a...The energy system of the future will transform from the current centralised fossil based to a decentralised, clean, highly efficient, and intelligent network. This transformation will require innovative technologies and ideas like trigeneration and the crowd energy concept to pave the way ahead. Even though trigeneration systems are extremely energy efficient and can play a vital role in the energy system, turning around their deployment is hindered by various barriers. These barriers are theoretically analysed in a multiperspective approach and the role decentralised trigeneration systems can play in the crowd energy concept is highlighted. It is derived from an initial literature research that a multiperspective （technological, energy-economic, and user） analysis is necessary for realising the potential of trigeneration systems in a decentralised grid. And to experimentally quantify these issues we are setting up a microseale trigeneration lab at our institute and the motivation for this lab is also briefly introduced.展开更多
Ringing, i.e. the emergence of an oscillatory tail behind a wave pulse as it propagates through a medium, is a pervasive artefact in FE and FDTD calculated waveforms. It is known to be a consequence of numerical dispe...Ringing, i.e. the emergence of an oscillatory tail behind a wave pulse as it propagates through a medium, is a pervasive artefact in FE and FDTD calculated waveforms. It is known to be a consequence of numerical dispersion arising from the discretization of the equations of motion. The use of an irregular mesh in a FE code has the further consequence of rendering the displacement field increasingly noisy with distance behind the wave front. In this paper these effects are illustrated using the commercial FE package ABAQUS with square and irregular triangular meshes to calculate the progress of a longitudinally polarized Ricker pulse along the axis of a cylindrically shaped aluminium specimen. We are able to give a precise analytical account of the evolution of ringing on the basis of a low order approximation for the dispersion relation of the discretized equations of motion. A qualitative account is provided of the generation of noise in the use of an irregular triangular mesh.展开更多
The velocity profiles and separation efficiency curves of a hydrocyclone were predicted by an Euler-Euler approach using a computational fluid dynamics tool ANSYS-CFX 14.5. The Euler-Euler approach is capable of consi...The velocity profiles and separation efficiency curves of a hydrocyclone were predicted by an Euler-Euler approach using a computational fluid dynamics tool ANSYS-CFX 14.5. The Euler-Euler approach is capable of considering the particle-particle interactions and is appropriate for highly laden liquid-solid mixtures. Pre- dicted results were compared and validated with experi- mental results and showed a considerably good agreement. An increase in the particle cut size with increasing solid concentration of the inlet mixture flow was observed and discussed. In addition to this, the erosion on hydrocyclone walls constructed from stainless steel 410, eroded by sand particles （mainly SiOz）, was predicted with the Euler-La- grange approach. In this approach, the abrasive solid particles were traced in a Lagrangian reference frame as discrete particles. The increases in the input flow velocity, solid concentration, and the particle size have increased the erosion at the upper part of the cylindrical body of the hydrocyclone, where the tangential inlet flow enters the hydrocyclone. The erosion density in the area between the cylindrical to conical body area, in comparison to other parts of the hydrocyclone, also increased considerably. Moreover, it was observed that an increase in the particle shape factor from 0.1 to 1.0 leads to a decrease of almost 70 % in the average erosion density of the hydrocyclone wall surfaces.展开更多
Background:Internal tibial loading is influenced by modifiable factors with implications for the risk of stress injury.Runners encounter varied surface steepness(gradients)when running outdoors and may adapt their spe...Background:Internal tibial loading is influenced by modifiable factors with implications for the risk of stress injury.Runners encounter varied surface steepness(gradients)when running outdoors and may adapt their speed according to the gradient.This study aimed to quantify tibial bending moments and stress at the anterior and posterior peripheries when running at different speeds on surfaces of different gradients.Methods:Twenty recreational runners ran on a treadmill at 3 different speeds(2.5 m/s,3.0 m/s,and 3.5 m/s)and gradients(level:0%;uphill:+5%,+10%,and+15%;downhill:-5%,-10%,and-15%).Force and marker data were collected synchronously throughout.Bending moments were estimated at the distal third centroid of the tibia about the medial-lateral axis by ensuring static equilibrium at each 1%of stance.Stress was derived from bending moments at the anterior and posterior peripheries by modeling the tibia as a hollow ellipse.Two-way repeated-measures analysis of variance were conducted using both functional and discrete statistical analyses.Results:There were significant main effects for running speed and gradient on peak bending moments and peak anterior and posterior stress.Higher running speeds resulted in greater tibial loading.Running uphill at+10%and+15%resulted in greater tibial loading than level running.Running downhill at-10%and-15%resulted in reduced tibial loading compared to level running.There was no difference between+5%or-5%and level running.Conclusion:Running at faster speeds and uphill on gradients≥+10%increased internal tibial loading,whereas slower running and downhill running on gradients≥-10%reduced internal loading.Adapting running speed according to the gradient could be a protective mechanism,providing runners with a strategy to minimize the risk of tibial stress injuries.展开更多
Three-dimensional compressible flow simulationswere conducted to develop a Hyperloop pod. Thenovelty is the usage of Gamma transition model, in whichthe transition from laminar to turbulent flow can be predicted.First...Three-dimensional compressible flow simulationswere conducted to develop a Hyperloop pod. Thenovelty is the usage of Gamma transition model, in whichthe transition from laminar to turbulent flow can be predicted.First, a mesh dependency study was undertaken,showing second-order convergence with respect to themesh refinement. Second, an aerodynamic analysis for twodesigns, short and optimized, was conducted with thetraveling speed 125 m/s at the system pressure 0.15 bar.The concept of the short model was to delay the transitionto decrease the frictional drag;meanwhile that of theoptimized design was to minimize the pressure drag bydecreasing the frontal area and introduce the transitionmore toward the front of the pod. The computed resultsshow that the transition of the short model occurred moreon the rear side due to the pod shape, which resulted in 8%smaller frictional drag coefficient than that for the optimizedmodel. The pressure drag for the optimized designwas 24% smaller than that for the short design, half ofwhich is due to the decrease in the frontal area, and theother half is due to the smoothed rear-end shape. The totaldrag for the optimized model was 14% smaller than that forthe short model. Finally, the influence of the systempressure was investigated. As the system pressure and theReynolds number increase, the frictional drag coefficientincreases, and the transition point moves toward the front,which are the typical phenomena observed in the transitionregime.展开更多
This study demonstrates that two-and three-dimensional spatially graded,truss-based polymeric-material metamaterials can be designed for beneficial impact mitigation and energy absorption capabilities.Through a combin...This study demonstrates that two-and three-dimensional spatially graded,truss-based polymeric-material metamaterials can be designed for beneficial impact mitigation and energy absorption capabilities.Through a combination of numerical and experimental techniques,we highlight the broad property space of periodic viscoelastic trusses,realized using 3D printing via selective laser sintering.Extending beyond periodic designs,we investigate the impact response of spatially variant viscoelastic lattices in both two and three dimensions.Our result reveal that introducing spatial variations in lattice topology allows for redirecting of the impact trajectory,opening new opportunities for engineering and tailoring lightweight materials with target impact functionality.This is achieved through the combined selection of base material and metamaterial design.展开更多
We investigate primal and mixed u−p isogeometric collocation methods for application to nearly-incompressible isotropic elasticity.The primal method employs Navier’s equations in terms of the displacement unknowns,an...We investigate primal and mixed u−p isogeometric collocation methods for application to nearly-incompressible isotropic elasticity.The primal method employs Navier’s equations in terms of the displacement unknowns,and the mixed method employs both displacement and pressure unknowns.As benchmarks for what might be considered acceptable accuracy,we employ constant-pressure Abaqus finite elements that are widely used in engineering applications.As a basis of comparisons,we present results for compressible elasticity.All the methods were completely satisfactory for the compressible case.However,results for low-degree primal methods exhibited displacement locking and in general deteriorated in the nearly-incompressible case.The results for the mixed methods behaved very well for two of the problems we studied,achieving levels of accuracy very similar to those for the compressible case.The third problem,which we consider a“torture test”presented a more complex story for the mixed methods in the nearly-incompressible case.展开更多
In this work, investigation of particle rebound characteristics due to impact with surface of a target material is presented. The rebound of a spherical particle after impact on a planar surface was analyzed in detail...In this work, investigation of particle rebound characteristics due to impact with surface of a target material is presented. The rebound of a spherical particle after impact on a planar surface was analyzed in detail. Specifically, the coefficient of restitution of the particle under various impact conditions was investigated numerically. This study has been conducted by carrying out a series of FEM-based (finite element method) simulations using ANSYS Autodyn software. First, a summary about the state of the art and the theoretical models for the elastic collisions were reviewed. Afterwards, the impact of an aluminum oxide particle on an aluminum alloy target surface was modeled. Using the Autodyn tool, the results were compared and validated by the experimental results of Gorham and Kharaz [1]. Selection of an appropriate equation of state (EOS) and a strength model for each material had a strong effect on the results. For both materials, the Shock EOS was applied for the final simulations. As the strength model, the Johnson-Cook and the elastic model were used, respectively. The agreement of the obtained numerical results with the experimental data confirmed that the proposed model can precisely predict the real behavior of the particle after the impact, when the material models are properly chosen. Furthermore, the effects of impact velocity and impact angle on the rebound characteristics of the particle were analyzed in detail. It was found that the selection of the exact value of friction coefficient has a drastic effect on the prediction of restitution coefficient values, especially the tangential restitution coefficient.展开更多
The wastes and the by-products of food industrial technologies are suitable for bioenergy generating because of the high organic matter content. Anaerobic digestion is the eldest technology for waste stabilization and...The wastes and the by-products of food industrial technologies are suitable for bioenergy generating because of the high organic matter content. Anaerobic digestion is the eldest technology for waste stabilization and however by controlled decomposition a high value and marketable energy source can be produced. Whey is normally used as a component of dairy products or as an additive for food product. In our work we focused on another utilization method： biogas generating from membrane separated fractions i.e.： permeate and concentrate of whey. The effect of the pH, thermal, microwave pre-treatment and their combinations on the biogas yield were investigated. Our results showed that the applied pre-treatments had significant effect on biogas production. In consequence of the hydrolysis of large molecules the biodegradability of the pre-treated whey fractions was enhanced, therefore the biogas and methane production yield increased significantly.展开更多
In the present study,a combined bonded multi-sphere model was developed,validated,and applied to simulate the motion and breakage behavior of wet fibers in a fluidized bed.The effects of particle resolution,bond numbe...In the present study,a combined bonded multi-sphere model was developed,validated,and applied to simulate the motion and breakage behavior of wet fibers in a fluidized bed.The effects of particle resolution,bond number,and humidity coefficient(γ)on fiber breakage rate,breakage location,and fragment size distribution were systematically investigated.Results show that increasing particle resolution from 3 to 6 generally reduces fiber breakage.While a higher bond number lowers the probability of breakage.Two different breakage modes are identified under varyingγvalues:Mode 1,characterized by breakage due to collisions between rapidly falling individual fibers and fiber clusters,and Mode 2,arising from impacts between fiber clusters and the bed bottom.Asγincreases within a certain range,the dominant breakage mechanism transitions from Mode 1 to a mixed mode involving both Modes 1 and 2,accompanied by a shift in the primary breakage location from the corner region toward the center region of the bed.All these findings provide valuable insights into the dynamics of wet fiber fluidization and offer guidance for optimizing wet fiber breakage behavior in real applications.展开更多
This short review describes the capabilities of magnetic resonance （MR） to image opaque single- and two-phase granular systems, such as rotating cylinders and gas-fluidized beds operated in different fluidization re...This short review describes the capabilities of magnetic resonance （MR） to image opaque single- and two-phase granular systems, such as rotating cylinders and gas-fluidized beds operated in different fluidization regimes. The unique capability of MR to not only image the solids＇ distribution （voidage） but also the velocity of the particulate phase is clearly shown. It is demonstrated that MR can provide measurements over different length and time scales. With the MR equipment used for the studies summarized here, temporal and spatial scales range from sub-millisecond to hours and from a few hundred micrometres to a few centimetres, respectively. Besides providing crucial data required for an improved understanding of the underlying physics of granular flows, multi-scale MR measurements were also used to validate numerical simulations of granular systems. It is shown that predictions of time-averaged properties, such as voidage and velocity of the particulate phase, made using the Discrete Element Model agree very well with MR measurements.展开更多
The identification of nanomaterials with the properties required for energy-efficient electronic systems is usually a tedious human task.A workflow to rapidly localize and characterize nanomaterials at the various sta...The identification of nanomaterials with the properties required for energy-efficient electronic systems is usually a tedious human task.A workflow to rapidly localize and characterize nanomaterials at the various stages of their integration into large-scale fabrication processes is essential for quality control and,ultimately,their industrial adoption.In this work,we develop a high-throughput approach to rapidly identify suspended carbon nanotubes(CNTs)by using high-speed Raman imaging and deep learning analysis.Even for Raman spectra with extremely low signal-to-noise ratios(SNRs)of 0.9,we achieve a classification accuracy that exceeds 90%,while it reaches 98%for an SNR of 2.2.By applying a threshold on the output of the softmax layer of an optimized convolutional neural network(CNN),we further increase the accuracy of the classification.Moreover,we propose an optimized Raman scanning strategy to minimize the acquisition time while simultaneously identifying the position,amount,and metallicity of CNTs on each sample.Our approach can readily be extended to other types of nanomaterials and has the potential to be integrated into a production line to monitor the quality and properties of nanomaterials during fabrication.展开更多
Magnetic resonance imaging （MRI） gave images of air jets from orifices in the distributor plate of a bed of poppy seeds. Attention focused on two features： （1） The interaction between nearby vertical jets from tw...Magnetic resonance imaging （MRI） gave images of air jets from orifices in the distributor plate of a bed of poppy seeds. Attention focused on two features： （1） The interaction between nearby vertical jets from two, three or four orifices; （2） Wall effects, where one or more orifices created vertical jets near the vertical wall of the cylinder containing the particle bed. The results show that nearby jets are mutually attracted. Likewise a jet near a wall bends out of the vertical, towards the wall, For multiple adjacent jets, the jet lengths show dependence on orifice layout： the lengths are in reasonable agreement with published measurements, by other methods, for single jets. The MRI gives three-dimensional images of the single jets and of multiple jets, separate or merging.展开更多
Background:Hypertrophic scarring after burn injury is one of the greatest unmet challenges in patients with burn injuries.A better understanding of the characteristics of scar maturation and early prediction of the lo...Background:Hypertrophic scarring after burn injury is one of the greatest unmet challenges in patients with burn injuries.A better understanding of the characteristics of scar maturation and early prediction of the long-term outcome of scarring are prerequisites for improving targeted therapies and pivotal for patient counselling.Methods:Repeated measurements of scar stiffness in 11 pediatric patients were performed over the course of 1 year using 2 suction devices,the Cutometer and the Nimble.In addition,the observer pliability score of the Patient and Observer Scar Assessment Scale was applied.This longitudinal study allowed quantification of the ability of each of the measured parameters to reflect scar maturation,as indicated by change in skin pliability/stiffness,over time(using linear regression);the ability to distinguish individual patients(intraclass correlation coefficient(ICC));the correlation of the devices(Spearman correlation coefficient);and the ability to predict longterm scar maturation based on early scar assessment(using receiver operating characteristic).Results:All the tools used showed significant longitudinal decrease of scar stiffness from 3 months until 12 months after the injury.The Nimble(ICC_(patient)^(Nimble)=0.99)and the Cutometer(ICC_(patient)^(Cuto)=0.97)demonstrated an excellent ability to distinguish between individual patients.The Nimble seemed to be able to predict the 12-month pliability of scars based on early(3-month)measurements(area under the curve(AUC)_(12m)^(POSAS)=0.67;AUC_(12m)^(C)=0.46;AUC_(12m)^(N)=0.79).Conclusions:The results of this preliminary study suggest that all 3 tools provide suitable means to quantify alterations in scar stiffness over time.Initial evidence suggests the Nimble is most favorable for predicting changes in stiffness associated with long-term scar maturation.Further studies with a larger sample size are required to validate tissue suction as a clinical tool for analysis of changes of scar stiffness over time.展开更多
All biological processes use or produce heat.Traditional microcalorimeters have been utilized to study the metabolic heat output of living organisms and heat production of exothermic chemical processes.Current advance...All biological processes use or produce heat.Traditional microcalorimeters have been utilized to study the metabolic heat output of living organisms and heat production of exothermic chemical processes.Current advances in microfabrication have made possible the miniaturization of commercial microcalorimeters,resulting in a few studies on the metabolic activity of cells at the microscale in microfluidic chips.Here we present a new,versatile,and robust microcalorimetric differential design based on the integration of heat flux sensors on top of microfluidic channels.We show the design,modeling,calibration,and experimental verification of this system by utilizing Escherichia coli growth and the exothermic base catalyzed hydrolysis of methyl paraben as use cases.The system consists of a Polydimethylsiloxane based flow-through microfluidic chip with two 46µl chambers and two integrated heat flux sensors.The differential compensation of thermal power measurements allows for the measurement of bacterial growth with a limit of detection of 1707 W/m^(3),corresponding to 0.021OD(2·10^(7) bacteria).We also extracted the thermal power of a single Escherichia coli of between 1.3 and 4.5 pW,comparable to values measured by industrial microcalorimeters.Our system opens the possibility for expanding already existing microfluidic systems,such as drug testing lab-on-chip platforms,with measurements of metabolic changes of cell populations in form of heat output,without modifying the analyte and minimal interference with the microfluidic channel itself.展开更多
In this paper,we present a new precipitation model based on a multi-factor Ornstein-Uhlenbeck approach of pure-jump type.In this setup,we derive a representation for the related precipitation swap price process and in...In this paper,we present a new precipitation model based on a multi-factor Ornstein-Uhlenbeck approach of pure-jump type.In this setup,we derive a representation for the related precipitation swap price process and infer its risk-neutral time dynamics.We further deduce a pricing formula for European options written on the prccipitation swap and obtain the minimal variance hedging portfolio in the underlying weather market.In the second part of the paper,we provide a precipitation swap price representation under future information modeled by an initially enlarged filtration.We finally derive a formula for the associated information premium and investigate minimal variance hedging of prccipitation dcrivatives undcr futurc information.展开更多
In this paper,we propose a new way to construct the distribution function through the second-order polynomial approximation in terms of particle mass,momentum and energy.The new construction holds three distinguished ...In this paper,we propose a new way to construct the distribution function through the second-order polynomial approximation in terms of particle mass,momentum and energy.The new construction holds three distinguished features.First,the formulations are more concise as compared with the third-order truncated Hermite polynomial expansion which yields Grad’s 13-moment distribution function;Second,all moments of the present distribution function are determined from conservation laws;Third,these moments are closely linked to the most desirable variables,such as mass,momentum and energy.Then,this new distribution function is applied to construct a new gas kinetic flux solver.Numerical validations show that the proposed method recovers the Navier-Stokes solutions in the continuum regime.In addition,it outperforms Grad’s 13-moment distribution function in the transition regime,especially in the prediction of temperature and heat flux.展开更多
基金gratitude to Institute of Tropical Forestry and Forest Products(INTROP),Universiti Putra Malaysia for supporting the funding of research through Grant No:6369108funded by Researchers Supporting Project number(RSP-2021/117),King Saud University,Riyadh,Saudi Arabia.
文摘Polylactic acid(PLA)possesses good mechanical and biodegradability properties which make it a suitable material for polymer composites whereas brittleness and high costs limit its utilization in various applications.The reinforcement of natural fibres with biopolymers has been formed to be an efficient technique to develop composites having the ability to be fully biodegradable.This study concerns with the incorporation of various percentages of untreated and alkali-treated Coir Fibres(CF)and pineapple leaf fibres(PALF)in PLA biocomposites and characterizations of flexural,morphological and dynamic mechanical properties.Flexural properties showed that the treated C1P1 hybrid composites(C1P1A)displayed highest flexural strength(35.81 MPa)and modulus(5.28 GPa)among all hybrid biocomposites.Scanning Electron Microscopy(SEM)revealed a behaviour of fibre-matrix adhesion in untreated treated biocomposites.SEM observation revealed good dispersion of the fillers in PLA.Dynamic mechanical analysis revealed that C1P1A showed highest glass transition temperature(Tg)and storage modulus(E')while untreated C3P7 displayed the least Tg and E'.Overall findings showed that alkali-treated hybrid biocomposites(CF/PALF/PLA)especially C1P1A have improved flexural properties,dynamic and morphological properties over untreated biocomposites.Success of these findings will provide attracting consideration of these hybrid biocomposites for various lightweight uses in a broad selection of industrial applications such as biomedical sectors,automobile,construction,electronics equipment,and hardware tools.
基金supported by the "Industry on Campus" at HS Offenburg and by the Baden-Württemberg Ministry of Science,Research and Arts(MWK) under the "DENE" Project
文摘The energy system of the future will transform from the current centralised fossil based to a decentralised, clean, highly efficient, and intelligent network. This transformation will require innovative technologies and ideas like trigeneration and the crowd energy concept to pave the way ahead. Even though trigeneration systems are extremely energy efficient and can play a vital role in the energy system, turning around their deployment is hindered by various barriers. These barriers are theoretically analysed in a multiperspective approach and the role decentralised trigeneration systems can play in the crowd energy concept is highlighted. It is derived from an initial literature research that a multiperspective （technological, energy-economic, and user） analysis is necessary for realising the potential of trigeneration systems in a decentralised grid. And to experimentally quantify these issues we are setting up a microseale trigeneration lab at our institute and the motivation for this lab is also briefly introduced.
文摘Ringing, i.e. the emergence of an oscillatory tail behind a wave pulse as it propagates through a medium, is a pervasive artefact in FE and FDTD calculated waveforms. It is known to be a consequence of numerical dispersion arising from the discretization of the equations of motion. The use of an irregular mesh in a FE code has the further consequence of rendering the displacement field increasingly noisy with distance behind the wave front. In this paper these effects are illustrated using the commercial FE package ABAQUS with square and irregular triangular meshes to calculate the progress of a longitudinally polarized Ricker pulse along the axis of a cylindrically shaped aluminium specimen. We are able to give a precise analytical account of the evolution of ringing on the basis of a low order approximation for the dispersion relation of the discretized equations of motion. A qualitative account is provided of the generation of noise in the use of an irregular triangular mesh.
基金“Stiftung Rheinland-Pfalz fur Innovation,Mainz,Germany,”for financial support
文摘The velocity profiles and separation efficiency curves of a hydrocyclone were predicted by an Euler-Euler approach using a computational fluid dynamics tool ANSYS-CFX 14.5. The Euler-Euler approach is capable of considering the particle-particle interactions and is appropriate for highly laden liquid-solid mixtures. Pre- dicted results were compared and validated with experi- mental results and showed a considerably good agreement. An increase in the particle cut size with increasing solid concentration of the inlet mixture flow was observed and discussed. In addition to this, the erosion on hydrocyclone walls constructed from stainless steel 410, eroded by sand particles （mainly SiOz）, was predicted with the Euler-La- grange approach. In this approach, the abrasive solid particles were traced in a Lagrangian reference frame as discrete particles. The increases in the input flow velocity, solid concentration, and the particle size have increased the erosion at the upper part of the cylindrical body of the hydrocyclone, where the tangential inlet flow enters the hydrocyclone. The erosion density in the area between the cylindrical to conical body area, in comparison to other parts of the hydrocyclone, also increased considerably. Moreover, it was observed that an increase in the particle shape factor from 0.1 to 1.0 leads to a decrease of almost 70 % in the average erosion density of the hydrocyclone wall surfaces.
文摘Background:Internal tibial loading is influenced by modifiable factors with implications for the risk of stress injury.Runners encounter varied surface steepness(gradients)when running outdoors and may adapt their speed according to the gradient.This study aimed to quantify tibial bending moments and stress at the anterior and posterior peripheries when running at different speeds on surfaces of different gradients.Methods:Twenty recreational runners ran on a treadmill at 3 different speeds(2.5 m/s,3.0 m/s,and 3.5 m/s)and gradients(level:0%;uphill:+5%,+10%,and+15%;downhill:-5%,-10%,and-15%).Force and marker data were collected synchronously throughout.Bending moments were estimated at the distal third centroid of the tibia about the medial-lateral axis by ensuring static equilibrium at each 1%of stance.Stress was derived from bending moments at the anterior and posterior peripheries by modeling the tibia as a hollow ellipse.Two-way repeated-measures analysis of variance were conducted using both functional and discrete statistical analyses.Results:There were significant main effects for running speed and gradient on peak bending moments and peak anterior and posterior stress.Higher running speeds resulted in greater tibial loading.Running uphill at+10%and+15%resulted in greater tibial loading than level running.Running downhill at-10%and-15%resulted in reduced tibial loading compared to level running.There was no difference between+5%or-5%and level running.Conclusion:Running at faster speeds and uphill on gradients≥+10%increased internal tibial loading,whereas slower running and downhill running on gradients≥-10%reduced internal loading.Adapting running speed according to the gradient could be a protective mechanism,providing runners with a strategy to minimize the risk of tibial stress injuries.
基金The authors acknowledge all the members of the Swissloop Team for their great endeavor to compete in the Hyperloop pod Competition and to push the Hyperloop technology forward.The authors gratefully acknowledge Connova AG for their support in manufacturing of the pod.
文摘Three-dimensional compressible flow simulationswere conducted to develop a Hyperloop pod. Thenovelty is the usage of Gamma transition model, in whichthe transition from laminar to turbulent flow can be predicted.First, a mesh dependency study was undertaken,showing second-order convergence with respect to themesh refinement. Second, an aerodynamic analysis for twodesigns, short and optimized, was conducted with thetraveling speed 125 m/s at the system pressure 0.15 bar.The concept of the short model was to delay the transitionto decrease the frictional drag;meanwhile that of theoptimized design was to minimize the pressure drag bydecreasing the frontal area and introduce the transitionmore toward the front of the pod. The computed resultsshow that the transition of the short model occurred moreon the rear side due to the pod shape, which resulted in 8%smaller frictional drag coefficient than that for the optimizedmodel. The pressure drag for the optimized designwas 24% smaller than that for the short design, half ofwhich is due to the decrease in the frontal area, and theother half is due to the smoothed rear-end shape. The totaldrag for the optimized model was 14% smaller than that forthe short model. Finally, the influence of the systempressure was investigated. As the system pressure and theReynolds number increase, the frictional drag coefficientincreases, and the transition point moves toward the front,which are the typical phenomena observed in the transitionregime.
文摘This study demonstrates that two-and three-dimensional spatially graded,truss-based polymeric-material metamaterials can be designed for beneficial impact mitigation and energy absorption capabilities.Through a combination of numerical and experimental techniques,we highlight the broad property space of periodic viscoelastic trusses,realized using 3D printing via selective laser sintering.Extending beyond periodic designs,we investigate the impact response of spatially variant viscoelastic lattices in both two and three dimensions.Our result reveal that introducing spatial variations in lattice topology allows for redirecting of the impact trajectory,opening new opportunities for engineering and tailoring lightweight materials with target impact functionality.This is achieved through the combined selection of base material and metamaterial design.
基金FF and LDL gratefully acknowledge the financial support of the German Research Foundation(DFG)within the DFG Priority Program SPP 1748“Reliable Simulation Techniques in Solid Mechanics”.AR has been partially supported by the MIUR-PRIN project XFAST-SIMS(No.20173C478 N).
文摘We investigate primal and mixed u−p isogeometric collocation methods for application to nearly-incompressible isotropic elasticity.The primal method employs Navier’s equations in terms of the displacement unknowns,and the mixed method employs both displacement and pressure unknowns.As benchmarks for what might be considered acceptable accuracy,we employ constant-pressure Abaqus finite elements that are widely used in engineering applications.As a basis of comparisons,we present results for compressible elasticity.All the methods were completely satisfactory for the compressible case.However,results for low-degree primal methods exhibited displacement locking and in general deteriorated in the nearly-incompressible case.The results for the mixed methods behaved very well for two of the problems we studied,achieving levels of accuracy very similar to those for the compressible case.The third problem,which we consider a“torture test”presented a more complex story for the mixed methods in the nearly-incompressible case.
文摘In this work, investigation of particle rebound characteristics due to impact with surface of a target material is presented. The rebound of a spherical particle after impact on a planar surface was analyzed in detail. Specifically, the coefficient of restitution of the particle under various impact conditions was investigated numerically. This study has been conducted by carrying out a series of FEM-based (finite element method) simulations using ANSYS Autodyn software. First, a summary about the state of the art and the theoretical models for the elastic collisions were reviewed. Afterwards, the impact of an aluminum oxide particle on an aluminum alloy target surface was modeled. Using the Autodyn tool, the results were compared and validated by the experimental results of Gorham and Kharaz [1]. Selection of an appropriate equation of state (EOS) and a strength model for each material had a strong effect on the results. For both materials, the Shock EOS was applied for the final simulations. As the strength model, the Johnson-Cook and the elastic model were used, respectively. The agreement of the obtained numerical results with the experimental data confirmed that the proposed model can precisely predict the real behavior of the particle after the impact, when the material models are properly chosen. Furthermore, the effects of impact velocity and impact angle on the rebound characteristics of the particle were analyzed in detail. It was found that the selection of the exact value of friction coefficient has a drastic effect on the prediction of restitution coefficient values, especially the tangential restitution coefficient.
文摘The wastes and the by-products of food industrial technologies are suitable for bioenergy generating because of the high organic matter content. Anaerobic digestion is the eldest technology for waste stabilization and however by controlled decomposition a high value and marketable energy source can be produced. Whey is normally used as a component of dairy products or as an additive for food product. In our work we focused on another utilization method： biogas generating from membrane separated fractions i.e.： permeate and concentrate of whey. The effect of the pH, thermal, microwave pre-treatment and their combinations on the biogas yield were investigated. Our results showed that the applied pre-treatments had significant effect on biogas production. In consequence of the hydrolysis of large molecules the biodegradability of the pre-treated whey fractions was enhanced, therefore the biogas and methane production yield increased significantly.
文摘In the present study,a combined bonded multi-sphere model was developed,validated,and applied to simulate the motion and breakage behavior of wet fibers in a fluidized bed.The effects of particle resolution,bond number,and humidity coefficient(γ)on fiber breakage rate,breakage location,and fragment size distribution were systematically investigated.Results show that increasing particle resolution from 3 to 6 generally reduces fiber breakage.While a higher bond number lowers the probability of breakage.Two different breakage modes are identified under varyingγvalues:Mode 1,characterized by breakage due to collisions between rapidly falling individual fibers and fiber clusters,and Mode 2,arising from impacts between fiber clusters and the bed bottom.Asγincreases within a certain range,the dominant breakage mechanism transitions from Mode 1 to a mixed mode involving both Modes 1 and 2,accompanied by a shift in the primary breakage location from the corner region toward the center region of the bed.All these findings provide valuable insights into the dynamics of wet fiber fluidization and offer guidance for optimizing wet fiber breakage behavior in real applications.
基金Financial support from the EPSRC (EP/C547195/1and GR/S20789/01)
文摘This short review describes the capabilities of magnetic resonance （MR） to image opaque single- and two-phase granular systems, such as rotating cylinders and gas-fluidized beds operated in different fluidization regimes. The unique capability of MR to not only image the solids＇ distribution （voidage） but also the velocity of the particulate phase is clearly shown. It is demonstrated that MR can provide measurements over different length and time scales. With the MR equipment used for the studies summarized here, temporal and spatial scales range from sub-millisecond to hours and from a few hundred micrometres to a few centimetres, respectively. Besides providing crucial data required for an improved understanding of the underlying physics of granular flows, multi-scale MR measurements were also used to validate numerical simulations of granular systems. It is shown that predictions of time-averaged properties, such as voidage and velocity of the particulate phase, made using the Discrete Element Model agree very well with MR measurements.
基金We acknowledge financial support from Strategic Focus Area(SFA)Advanced Manufacturing(Project NanoAssembly)M.L.P.and J.Z.acknowledge funding by the EMPAPOSTDOCS-II program,which has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska–Curie Grant Agreement no.754364M.L.P.also acknowledges funding from the Swiss National Science Foundation under Spark grant no.196795。
文摘The identification of nanomaterials with the properties required for energy-efficient electronic systems is usually a tedious human task.A workflow to rapidly localize and characterize nanomaterials at the various stages of their integration into large-scale fabrication processes is essential for quality control and,ultimately,their industrial adoption.In this work,we develop a high-throughput approach to rapidly identify suspended carbon nanotubes(CNTs)by using high-speed Raman imaging and deep learning analysis.Even for Raman spectra with extremely low signal-to-noise ratios(SNRs)of 0.9,we achieve a classification accuracy that exceeds 90%,while it reaches 98%for an SNR of 2.2.By applying a threshold on the output of the softmax layer of an optimized convolutional neural network(CNN),we further increase the accuracy of the classification.Moreover,we propose an optimized Raman scanning strategy to minimize the acquisition time while simultaneously identifying the position,amount,and metallicity of CNTs on each sample.Our approach can readily be extended to other types of nanomaterials and has the potential to be integrated into a production line to monitor the quality and properties of nanomaterials during fabrication.
基金the Engineering and Physical Sciences Research Council(Grant number EP/F041772/1)
文摘Magnetic resonance imaging （MRI） gave images of air jets from orifices in the distributor plate of a bed of poppy seeds. Attention focused on two features： （1） The interaction between nearby vertical jets from two, three or four orifices; （2） Wall effects, where one or more orifices created vertical jets near the vertical wall of the cylinder containing the particle bed. The results show that nearby jets are mutually attracted. Likewise a jet near a wall bends out of the vertical, towards the wall, For multiple adjacent jets, the jet lengths show dependence on orifice layout： the lengths are in reasonable agreement with published measurements, by other methods, for single jets. The MRI gives three-dimensional images of the single jets and of multiple jets, separate or merging.
基金supported by grants from the Helmut Horten Foundation。
文摘Background:Hypertrophic scarring after burn injury is one of the greatest unmet challenges in patients with burn injuries.A better understanding of the characteristics of scar maturation and early prediction of the long-term outcome of scarring are prerequisites for improving targeted therapies and pivotal for patient counselling.Methods:Repeated measurements of scar stiffness in 11 pediatric patients were performed over the course of 1 year using 2 suction devices,the Cutometer and the Nimble.In addition,the observer pliability score of the Patient and Observer Scar Assessment Scale was applied.This longitudinal study allowed quantification of the ability of each of the measured parameters to reflect scar maturation,as indicated by change in skin pliability/stiffness,over time(using linear regression);the ability to distinguish individual patients(intraclass correlation coefficient(ICC));the correlation of the devices(Spearman correlation coefficient);and the ability to predict longterm scar maturation based on early scar assessment(using receiver operating characteristic).Results:All the tools used showed significant longitudinal decrease of scar stiffness from 3 months until 12 months after the injury.The Nimble(ICC_(patient)^(Nimble)=0.99)and the Cutometer(ICC_(patient)^(Cuto)=0.97)demonstrated an excellent ability to distinguish between individual patients.The Nimble seemed to be able to predict the 12-month pliability of scars based on early(3-month)measurements(area under the curve(AUC)_(12m)^(POSAS)=0.67;AUC_(12m)^(C)=0.46;AUC_(12m)^(N)=0.79).Conclusions:The results of this preliminary study suggest that all 3 tools provide suitable means to quantify alterations in scar stiffness over time.Initial evidence suggests the Nimble is most favorable for predicting changes in stiffness associated with long-term scar maturation.Further studies with a larger sample size are required to validate tissue suction as a clinical tool for analysis of changes of scar stiffness over time.
基金This work is a part of and was partially funded by the ETHeart initiative of the Swiss Federal Institute of Technology(ETH Zurich).M.A.was supported as a part of NCCR Microbiomes,a National Centre of Competence in Research,funded by the Swiss National Science Foundation(grant number 180575).We would like to especially acknowledge the support of Prof.Dr.Volkmar Falk and Nikola Cesarovic for the project.We would also like to acknowledge Prof.Emma Wetter Slack of the Laboratory for Food Immunology in the Department of Health Sciences and Technologies at ETHZ for support and the use of equipment.We would also like to acknowledge Lavinia Recchioni for her help in the work on the lumped element model.Furthermore,we would like to acknowledge the help of Alyson Hockenberry for all of her support regarding the microfluidics.Lastly,we would like to acknowledge all of the support by the members of the Micro-and Nanosystems at ETH Zürich.
文摘All biological processes use or produce heat.Traditional microcalorimeters have been utilized to study the metabolic heat output of living organisms and heat production of exothermic chemical processes.Current advances in microfabrication have made possible the miniaturization of commercial microcalorimeters,resulting in a few studies on the metabolic activity of cells at the microscale in microfluidic chips.Here we present a new,versatile,and robust microcalorimetric differential design based on the integration of heat flux sensors on top of microfluidic channels.We show the design,modeling,calibration,and experimental verification of this system by utilizing Escherichia coli growth and the exothermic base catalyzed hydrolysis of methyl paraben as use cases.The system consists of a Polydimethylsiloxane based flow-through microfluidic chip with two 46µl chambers and two integrated heat flux sensors.The differential compensation of thermal power measurements allows for the measurement of bacterial growth with a limit of detection of 1707 W/m^(3),corresponding to 0.021OD(2·10^(7) bacteria).We also extracted the thermal power of a single Escherichia coli of between 1.3 and 4.5 pW,comparable to values measured by industrial microcalorimeters.Our system opens the possibility for expanding already existing microfluidic systems,such as drug testing lab-on-chip platforms,with measurements of metabolic changes of cell populations in form of heat output,without modifying the analyte and minimal interference with the microfluidic channel itself.
文摘In this paper,we present a new precipitation model based on a multi-factor Ornstein-Uhlenbeck approach of pure-jump type.In this setup,we derive a representation for the related precipitation swap price process and infer its risk-neutral time dynamics.We further deduce a pricing formula for European options written on the prccipitation swap and obtain the minimal variance hedging portfolio in the underlying weather market.In the second part of the paper,we provide a precipitation swap price representation under future information modeled by an initially enlarged filtration.We finally derive a formula for the associated information premium and investigate minimal variance hedging of prccipitation dcrivatives undcr futurc information.
基金supported by the National Natural Science Foundation of China(No.12302376)Natural Science Foundation of Jiangsu Province(No.BK20230905)+2 种基金Fundamental Research Funds for the Central Universities(No.30923011033)National Natural Science Foundation of China(No.52201329)MOE Tier 1 project at National University of Singapore(A-0005235-01-00).
文摘In this paper,we propose a new way to construct the distribution function through the second-order polynomial approximation in terms of particle mass,momentum and energy.The new construction holds three distinguished features.First,the formulations are more concise as compared with the third-order truncated Hermite polynomial expansion which yields Grad’s 13-moment distribution function;Second,all moments of the present distribution function are determined from conservation laws;Third,these moments are closely linked to the most desirable variables,such as mass,momentum and energy.Then,this new distribution function is applied to construct a new gas kinetic flux solver.Numerical validations show that the proposed method recovers the Navier-Stokes solutions in the continuum regime.In addition,it outperforms Grad’s 13-moment distribution function in the transition regime,especially in the prediction of temperature and heat flux.
