Agricultural and forestry biomass can be converted to biochar through pyrolysis gasification,making it a significant carbon source for soil.Applying biochar to soil is a carbon-negative process that helps combat clima...Agricultural and forestry biomass can be converted to biochar through pyrolysis gasification,making it a significant carbon source for soil.Applying biochar to soil is a carbon-negative process that helps combat climate change,sustain soil biodiversity,and regulate water cycling.However,quantifying soil carbon content conventionally is time-consuming,labor-intensive,imprecise,and expensive,making it difficult to accurately measure in-field soil carbon’s effect on storage water and nutrients.To address this challenge,this paper for the first time,reports on extensive lab tests demonstrating non-intrusive methods for sensing soil carbon and related smart biochar applications,such as differentiating between biochar types from various biomass feedstock species,monitoring soil moisture,and biochar water retention capacity using portable microwave and millimeter wave sensors,and machine learning.These methods can be scaled up by deploying the sensor in-field on a mobility platform,either ground or aerial.The paper provides details on the materials,methods,machine learning workflow,and results of our investigations.The significance of this work lays the foundation for assessing carbon-negative technology applications,such as soil carbon content accounting.We validated our quantification method using supervised machine learning algorithms by collecting real soil mixed with known biochar contents in the field.The results show that the millimeter wave sensor achieves high sensing accuracy(up to 100%)with proper classifiers selected and outperforms the microwave sensor by approximately 10%–15%accuracy in sensing soil carbon content.展开更多
A model for the mechanics of woven fabrics is developed in the framework of two-dimensional elastic surface theory. Thickness effects are modeled indirectly in terms of appropriate constitutive equations. The model ac...A model for the mechanics of woven fabrics is developed in the framework of two-dimensional elastic surface theory. Thickness effects are modeled indirectly in terms of appropriate constitutive equations. The model accounts for the strain of the fabric and additional effects associated with the normal bending, geodesic bending, and twisting of the constituent fibers.展开更多
A high-g beam-mass structure accelerometer was designed.In this structure,by means of KOH back etching on the mass,V-groove structure was fabricated on the backside of the mass,so the weight of the mass and also the r...A high-g beam-mass structure accelerometer was designed.In this structure,by means of KOH back etching on the mass,V-groove structure was fabricated on the backside of the mass,so the weight of the mass and also the relative distance between the mass center and the neutral plane were all decreased.With the thin mass structure,we can take advantage of both beam-mass structure and flat film structure;the fabrication process is also simple.By means of Hopkinson shock test system,we did the accelerometer calibration.According to the test result,the sensitivity of the MEMS accelerometer is 0.71 μV/g,which keeps in accordance with the theoretical calculation.After a 200 000 g shocking test,the micro structure worked as usual,so this design can satisfy the requirements of high shock,seriously vibration test environment.展开更多
The structure and measurement theory of a single-axis integrated inertia measurement device are discussed in this paper.The acceleration and angle velocity can be detected by the proposed sensor at the same time.The k...The structure and measurement theory of a single-axis integrated inertia measurement device are discussed in this paper.The acceleration and angle velocity can be detected by the proposed sensor at the same time.The ki- netic model of the device is also established.In addition,the signal generation of the single-axis integrated inertia measurement device is analyzed and simulated.The results of the model are consistent with simulation result.展开更多
The authors have developed a two-dimensional model for the extension and flexure response of electroelastic plates under biasing fields in a curvilinear coordinate system. Applications of the model in analyzing buckli...The authors have developed a two-dimensional model for the extension and flexure response of electroelastic plates under biasing fields in a curvilinear coordinate system. Applications of the model in analyzing buckling of two circular piezoelectric plates, one single-layered and the other double-layered, are included. The analysis indicates that the piezoelectric coupling has a strengthening effect against buckling.展开更多
A highly efficient "hybrid integral-equation method" for computing hydrodynamic added-mass, wave-damping, and wave-exciting force of general body geometries with a vertical axis of symmetry is presented. The...A highly efficient "hybrid integral-equation method" for computing hydrodynamic added-mass, wave-damping, and wave-exciting force of general body geometries with a vertical axis of symmetry is presented. The hybrid method utilizes a numerical inner domain and a semi-infinite analytical outer domain separated by a vertical cylindrical matching boundary.Eigenfunction representation of velocity potential is used in the outer domain;the three-dimensional potential in the inner domain is solved using a "two-dimensional" boundary element method with ring sources and ring dipoles to exploit the body symmetry for efficiency. With proper solution matching at the common boundary, both radiation and diffraction potentials can be solved efficiently while satisfying the far-field radiation condition exactly. This method is applied to compute the hydrodynamic properties of two different body geometries: a vertical-walled moonpool with a bottom plate that restricts the opening and a spar-like structure with a diverging bottom opening inspired by designs of floating Oscillating Water Columns. The effects of the size of the bottom opening on the hydrodynamic properties of the body are investigated for both geometries. The heave motion of the floater as well as the motion of the internal free surface under incident wave excitation are computed and studied for the spar-like structure.展开更多
Defects in graphene can profoundly impact its extraordinary properties,ultimately influencing the performances of graphene-based nanodevices.Methods to detect defects with atomic resolution in graphene can be technica...Defects in graphene can profoundly impact its extraordinary properties,ultimately influencing the performances of graphene-based nanodevices.Methods to detect defects with atomic resolution in graphene can be technically demanding and involve complex sample preparations.An alternative approach is to observe the thermal vibration properties of the graphene sheet,which reflects defect information but in an implicit fashion.Machine learning,an emerging data-driven approach that offers solutions to learning hidden patterns from complex data,has been extensively applied in material design and discovery problems.In this paper,we propose a machine learning-based approach to detect graphene defects by discovering the hidden correlation between defect locations and thermal vibration features.Two prediction strategies are developed:an atom-based method which constructs data by atom indices,and a domain-based method which constructs data by domain discretization.Results show that while the atom-based method is capable of detecting a single-atom vacancy,the domain-based method can detect an unknown number of multiple vacancies up to atomic precision.Both methods can achieve approximately a 90%prediction accuracy on the reserved data for testing,indicating a promising extrapolation into unseen future graphene configurations.The proposed strategy offers promising solutions for the non-destructive evaluation of nanomaterials and accelerates new material discoveries.展开更多
Objective:To assess the biomechanical properties of a new design configuration for zirconia dental implants. Methods: The new design has a cylindrical shape that is partially hollow and porous in the bottom, which per...Objective:To assess the biomechanical properties of a new design configuration for zirconia dental implants. Methods: The new design has a cylindrical shape that is partially hollow and porous in the bottom, which permits the implants to be locked into the alveolar bone over time. It also utilizes bioactive glass coatings to increase adhesion to surrounding bone structure. Samples of the new design were fabricated in the laboratory and their material strength, hardness, and fracture toughness were evaluated. In addition, biocompatibility of the new design was evaluated through testing in dogs. Results: Results of mechanical tests indicate that structural properties of the new design exceed the usual requirements for implants. Moreover, animal tests suggest that there is appreciable improvement in lock-in strength and osteointegration. Conclusion: The new design configuration is biomechanically feasible and further research is warranted to improve the design for human use.展开更多
This study describes a multidimensional 3D/lumped parameter(LP) model which contains appropriate inflow/outflow boundary conditions in order to model the entire human arterial trees. A new extensive LP model of the ...This study describes a multidimensional 3D/lumped parameter(LP) model which contains appropriate inflow/outflow boundary conditions in order to model the entire human arterial trees. A new extensive LP model of the entire arterial network(48 arteries) was developed including the effect of vessel diameter tapering and the parameterization of resistance, conductor and inductor variables. A computer aided-design(CAD) algorithm was proposed to effciently handle the coupling of two or more 3D models with the LP model, and substantially lessen the coupling processing time. Realistic boundary conditions and Navier-Stokes equations in healthy and stenosed models of carotid artery bifurcation(CAB) were used to investigate the unsteady Newtonian blood flow velocity distribution in the internal carotid artery(ICA). The present simulation results agree well with previous experimental and numerical studies. The outcomes of a pure LP model and those of the coupled 3D healthy model were found to be nearly the same in both cases. Concerning the various analyzed 3D zones, the stenosis growth in the ICA was not found as a crucial factor in determining the absorbing boundary conditions.This paper demonstrates the advantages of coupling local and systemic models to comprehend physiological diseases of the cardiovascular system.展开更多
Motivated by an animal territoriality model,we consider a centroidal Voronoi tessellation algorithm from a dynamical systems perspective.In doing so,we discuss the stability of an aligned equilibrium configuration for...Motivated by an animal territoriality model,we consider a centroidal Voronoi tessellation algorithm from a dynamical systems perspective.In doing so,we discuss the stability of an aligned equilibrium configuration for a rectangular domain that exhibits interesting symmetry properties.We also demonstrate the procedure for performing a center manifold reduction on the system to extract a set of coordinates which capture the long term dynamics when the system is close to a bifurcation.Bifurcations of the system restricted to the center manifold are then classified and compared to numerical results.Although we analyze a specific set-up,these methods can in principle be applied to any bifurcation point of any equilibrium for any domain.展开更多
In this paper, the effects of second-order difference-frequency wave forces on the global motion of an offshore wind turbine system with a large displacement under the survival condition are studied. In this case, the...In this paper, the effects of second-order difference-frequency wave forces on the global motion of an offshore wind turbine system with a large displacement under the survival condition are studied. In this case, the hydrodynamic force is the main force because the blades are feathered to reduce the lifting force. The first-order hydrodynamic forces are calculated by WADAM, while the second-order wave forces are calculated by a customized MATLAB module. Then the hydrodynamic coefficients are transferred to the wind turbine analytical code FAST. Through the comparisons of dynamic responses between the first-and second-order numerical models, it is found that the second-order wave forces significantly influence the motion of floating wind turbine under the survival condition. Moreover, neglecting the second-order force significantly underestimates the tension forces in the mooring lines.展开更多
A new and computationally efficient version of the immersed boundary method,which is combined with the coarse-graining method,is introduced for modeling inextensible filaments immersed in low-Reynolds number flows.Thi...A new and computationally efficient version of the immersed boundary method,which is combined with the coarse-graining method,is introduced for modeling inextensible filaments immersed in low-Reynolds number flows.This is used to represent actin biopolymers,which are constituent elements of the cytoskeleton,a complex network-like structure that plays a fundamental role in shape morphology.An extension of the traditional immersed boundary method to include a stochastic stress tensor is also proposed in order to model the thermal fluctuations in the fluid at smaller scales.By way of validation,the response of a single,massless,inextensible semiflexible filament immersed in a thermally fluctuating fluid is obtained using the suggested numerical scheme and the resulting time-averaged contraction of the filament is compared to the theoretical value obtained from the worm-like chain model.展开更多
We report on the results of numerical models of the(i)initial growth and(ii)steady state phases of atmospheric-pressure homogeneous dielectric barrier discharge in argon.We employ our new inhouse code called Py DBD,wh...We report on the results of numerical models of the(i)initial growth and(ii)steady state phases of atmospheric-pressure homogeneous dielectric barrier discharge in argon.We employ our new inhouse code called Py DBD,which solves continuity equations for both particles and energy,shows exceptional stability,is accelerated by adaptive time stepping and is openly available to the scientific community.Modeling argon plasma is numerically challenging due to the lower speeds of more inertial ions compared to more commonly modeled neon and helium,but its common use for plasma jets in medicine makes its modeling compelling.Py DBD is here applied to modeling two setups:(i)the exponential growth from natural electron-ion seeds(onset phase)until saturation is reached and(ii)the multiple current pulses that naturally appear during the steady state phase.We find that the time required for the onset phase,when the plasma density grows from 10^(9)m^(-3)to 10^(17)m^(-3),varies from 80μs at 4.5 k V down to a fewμs above 6.5 k V,for voltage frequency f=80 k Hz and gap width d_(g)=0.9 mm.At the steady state,our model reproduces two previously observed features of the current in dielectric barrier discharge reactors:(1)an oscillatory behavior associated to the capacitative character of the circuit and(2)several(N_(p))current pulses occurring every half sinusoidal cycle.We show that the oscillations are present during the exponential growth,while current pulses appear approaching the steady state.After each micro-discharge,the gas voltage decreases abruptly and charged particles rapidly accumulate at the dielectric boundaries,causing avalanches of charged particles near the reactor boundaries.Finally,we run a parametric study finding that N_(p)increases linearly with voltage amplitude V_(amp),is inversely proportional to dielectric gap d_(g)and decreases when voltage frequency f increases.The code developed for this publication is freely available at the address https://github.com/gabersyd/PyDBD.展开更多
Tungsten(W)is an important material in tokamak walls and divertors.The W ion charge state distribution and the dynamic behavior of ions play important roles in the investigation of plasma–wall interactions using lase...Tungsten(W)is an important material in tokamak walls and divertors.The W ion charge state distribution and the dynamic behavior of ions play important roles in the investigation of plasma–wall interactions using laser-ablation-based diagnostics such as laser-induced breakdown spectroscopy and laser-induced ablation spectroscopy.In this work,we investigate the temporal and spatial evolutions of differently charged ions in a nanosecond-laser-produced W plasma in vacuum using time-of-flight mass spectroscopy.Ions with different charge states from 1 to 7(W+to W7+)are all observed.The temporal evolutions of the differently charged ions show that ions with higher charge states have higher velocities,indicating that space separation occurs between the differently charged ion groups.Spatially-resolved mass spectroscopy measurements further demonstrate the separation phenomenon.The temporal profile can be accurately fitted by a shifted Maxwell–Boltzmann distribution,and the velocities of the differently charged ions are also obtained from the fittings.It is found that the ion velocities increase continuously from the measured position of 0.75 cm to 2.25 cm away from the target surface,which indicates that the acceleration process lasts through the period of plasma expansion.The acceleration and space separation of the differently charged ions confirm that there is a dynamic plasma sheath in the laser-produced plasma,which provides essential information for the theoretical laser-ablation model with plasma formation and expansion.展开更多
Acceleration of an initially moving electron by a copropagation ultra-short ultra-intense laser pulse in vacuum is studied. It is shown that when appropriate laser pulse parameters and focusing conditions axe imposed,...Acceleration of an initially moving electron by a copropagation ultra-short ultra-intense laser pulse in vacuum is studied. It is shown that when appropriate laser pulse parameters and focusing conditions axe imposed, the acceleration of electron by ascending front of laser pulse can be much stronger compared to the deceleration by descending part. Consequently, the electron can obtain significantly high net energy gain. We also report the results of the new scheme that enables a second-step acceleration of electron using laser pulses of peak intensity in the range of 1019 - 1020 Wμm^2/cm^2. In the first step the electron acceleration from rest is limited to energies of a few MeV, while in the second step the electron acceleration can be considerably enhanced to about 100 MeV energy.展开更多
This article summarizes work at the Laser Thermal Laboratory and discusses related studies on the laser synthesis and functionalization of semiconductor nanostructures and two-dimensional(2D)semiconductor materials.Re...This article summarizes work at the Laser Thermal Laboratory and discusses related studies on the laser synthesis and functionalization of semiconductor nanostructures and two-dimensional(2D)semiconductor materials.Research has been carried out on the laser-induced crystallization of thin films and nanostructures.The in situ transmission electron microscopy(TEM)monitoring of the crystallization of amorphous precursors in nanodomains is discussed herein.The directed assembly of silicon nanoparticles and the modulation of their optical properties by phase switching is presented.The vapor-liquid-solid mechanism has been adopted as a bottom-up approach in the synthesis of semiconducting nanowires(NWs).In contrast to furnace heating methods,laser irradiation offers high spatial selectivity and precise control of the heating mechanism in the time domain.These attributes enabled the investigation of NW nucleation and the early stage of nanostructure growth.Site-and shape-selective,on-demand direct integration of oriented NWs was accomplished.Growth of discrete silicon NWs with nanoscale location selectivity by employing near-field laser illumination is also reported herein.Tuning the properties of 2D transition metal dichalcogenides(TMDCs)by modulating the free carrier type,density,and composition can offer an exciting new pathway to various practical nanoscale electronics.In situ Raman probing of laser-induced processing of TMDC flakes was conducted in a TEM instrument.展开更多
Large single crystal colloidal copper particles with diameters between 0.5 - 2 μm were created using a green synthesis process. The process used ascorbic acid to reduce Schweizer’s reagent created in situ using copp...Large single crystal colloidal copper particles with diameters between 0.5 - 2 μm were created using a green synthesis process. The process used ascorbic acid to reduce Schweizer’s reagent created in situ using copper salts in the presence of various concentrations of gum arabic. The Schweizer’s reagents were created by varying the concentrations of ammonium hydroxide and copper nitrate solutions, copper hydroxide, or copper sulfate. The pH of the solution was controlled by the addition of ascorbic acid. Particle formation was favored at high temperature using copper sulfate at pH values ranging from 7.5 to 9, while the optimal formation occurred at a pH value of 8.5. At high concentrations, copper particle formation was found to occur from the aggregation of smaller particles which continued to nucleate once aggregated, and this resulted in the creation of globular particles and large aggregates of micron-sized particles. The addition of gum arabic resulted in the creation of large single crystal particles that did not aggregate. SEM was used to observe the effect of increasing gum arabic concentrations and EDX was used to confirm the elemental purity of the particles.展开更多
Optimization of composition and microstructure is important to enhance performance of solid oxide fuel cells (SOFC) and lithium-ion batteries (LIB). For this, the porous electrode structures of both SOFC and LIB a...Optimization of composition and microstructure is important to enhance performance of solid oxide fuel cells (SOFC) and lithium-ion batteries (LIB). For this, the porous electrode structures of both SOFC and LIB are modeled as a binary mixture of electronic and ionic conducting particles to estimate effective transport properties. Particle packings of 10000 spherical, binary sized and randomly positioned particles are created numerically and densified considering the different manufacturing processes in SOFC and LIB: the sintering of SOFC electrodes is approximated geometrically, whereas the calendering process and volume change due to intercalation in LIB are modeled physically by a discrete el- ement approach. A combination of a tracking algorithm and a resistor network approach is developed to predict the con- nectivity and effective conductivity for the various densified structures. For SOFC, a systematic study of the influence of morphology on connectivity and conductivity is performed on a large number of assemblies with different compositions and particle size ratios between 1 and 10. In comparison to percolation theory, an enlarged percolation area is found, es- pecially for large size ratios. It is shown that in contrast to former studies the percolation threshold correlates to varying coordination numbers. The effective conductivity shows not only an increase with volume fraction as expected but also with size ratio. For LIB, a general increase of conductivity during the intercalation process was observed in correlation with increasing contact forces. The positive influence of cal- endering on the percolation threshold and the effective conductivity of carbon black is shown. The anisotropy caused by the calendering process does not influence the carbon black phase.展开更多
Energy storage technologies, which enable demand response, are being explored throughout the world as a component of strategies for switching to renewable intermittent energy sources and reducing peak loads. This stud...Energy storage technologies, which enable demand response, are being explored throughout the world as a component of strategies for switching to renewable intermittent energy sources and reducing peak loads. This study examines thermal storage refrigeration (TSR) technology as a case study for the potential value of demand response in California and Denmark. Using technical specifications from a TSR prototype developed at UC Davis and market data from California and Denmark, the analysis examines possible business models for the TSR refrigerators and highlights market characteristics that are important to its adoption. Results suggest that the TSR technology is not a viable option in the current market environment in Denmark, but could payback in less than 6 years in California if a part of a demand response based virtual power plant. In a hypothetical future scenario involving real-time pricing in the retail market, a high degree of price volatility would be needed to make TSR technology appealing to residential consumers. Based on this analysis, an interesting area of future work would focus on the market potential of TSR technology for commercial and industrial applications.展开更多
Biopsy is a method commonly used for early cancer diagnosis.However,bleeding complications of widely available biopsy are risky for patients.Safer biopsy will result in a more accurate cancer diagnosis and a decrease ...Biopsy is a method commonly used for early cancer diagnosis.However,bleeding complications of widely available biopsy are risky for patients.Safer biopsy will result in a more accurate cancer diagnosis and a decrease in the risk of complications.In this article,we propose a novel biopsy needle that can reduce bleeding during biopsy procedures and achieve stable hemostasis.The proposed biopsy needle features a compact structure and can be operated easily by left and right hands.A predictive model for puncture force and tip deflection based on coupled Eulerian–Lagrangian(CEL)method is developed.Experimental results show that the biopsy needle can smoothly deliver the gelatin sponge hemostatic plug into the tissue.Although the hemostatic plug bends,the overall delivery process is stable,and the hemostatic plug retains in the tissue without being affected by the withdrawal of the needle.Further experiments indicate that the specimens are well obtained and evenly distributed in the groove of the outer needle without scattering.Our proposed design of biopsy needle possesses strong ability of hemostasis,tissue cutting,and tissue retention.The CEL model accurately predicts the peak of puncture force and produces close estimation of the insertion force at the postpuncture stage and tip position.展开更多
基金supported by SGC project5 entitled"Mobile Biochar Production for Methane Emission Reduction and Soil Amendment".Grant Agreement#CCR20014supported in part by NSF CBET#1856112supported in part by an F3 R&D GSR Award (Farms Food Future Innovation Initiative (or F3),as funded by US Dept.of Commerce,Economic Development Administration Build Back Better Regional Challenge).
文摘Agricultural and forestry biomass can be converted to biochar through pyrolysis gasification,making it a significant carbon source for soil.Applying biochar to soil is a carbon-negative process that helps combat climate change,sustain soil biodiversity,and regulate water cycling.However,quantifying soil carbon content conventionally is time-consuming,labor-intensive,imprecise,and expensive,making it difficult to accurately measure in-field soil carbon’s effect on storage water and nutrients.To address this challenge,this paper for the first time,reports on extensive lab tests demonstrating non-intrusive methods for sensing soil carbon and related smart biochar applications,such as differentiating between biochar types from various biomass feedstock species,monitoring soil moisture,and biochar water retention capacity using portable microwave and millimeter wave sensors,and machine learning.These methods can be scaled up by deploying the sensor in-field on a mobility platform,either ground or aerial.The paper provides details on the materials,methods,machine learning workflow,and results of our investigations.The significance of this work lays the foundation for assessing carbon-negative technology applications,such as soil carbon content accounting.We validated our quantification method using supervised machine learning algorithms by collecting real soil mixed with known biochar contents in the field.The results show that the millimeter wave sensor achieves high sensing accuracy(up to 100%)with proper classifiers selected and outperforms the microwave sensor by approximately 10%–15%accuracy in sensing soil carbon content.
基金support provided by the Powley Fund for Ballistics Research
文摘A model for the mechanics of woven fabrics is developed in the framework of two-dimensional elastic surface theory. Thickness effects are modeled indirectly in terms of appropriate constitutive equations. The model accounts for the strain of the fabric and additional effects associated with the normal bending, geodesic bending, and twisting of the constituent fibers.
基金Shanxi province young leaders on science and by program for New Century Excellent Talents in University(NCET)
文摘A high-g beam-mass structure accelerometer was designed.In this structure,by means of KOH back etching on the mass,V-groove structure was fabricated on the backside of the mass,so the weight of the mass and also the relative distance between the mass center and the neutral plane were all decreased.With the thin mass structure,we can take advantage of both beam-mass structure and flat film structure;the fabrication process is also simple.By means of Hopkinson shock test system,we did the accelerometer calibration.According to the test result,the sensitivity of the MEMS accelerometer is 0.71 μV/g,which keeps in accordance with the theoretical calculation.After a 200 000 g shocking test,the micro structure worked as usual,so this design can satisfy the requirements of high shock,seriously vibration test environment.
基金Supported by Shanxi Province Young Leaders on Science and by Program for New Century Excellent Talents in University(NCET)
文摘The structure and measurement theory of a single-axis integrated inertia measurement device are discussed in this paper.The acceleration and angle velocity can be detected by the proposed sensor at the same time.The ki- netic model of the device is also established.In addition,the signal generation of the single-axis integrated inertia measurement device is analyzed and simulated.The results of the model are consistent with simulation result.
基金the National Natural Science Foundation of China(No.10172036)the Office of US Naval Research(Contract No.ONR N00014-96-1-0884)
文摘The authors have developed a two-dimensional model for the extension and flexure response of electroelastic plates under biasing fields in a curvilinear coordinate system. Applications of the model in analyzing buckling of two circular piezoelectric plates, one single-layered and the other double-layered, are included. The analysis indicates that the piezoelectric coupling has a strengthening effect against buckling.
文摘A highly efficient "hybrid integral-equation method" for computing hydrodynamic added-mass, wave-damping, and wave-exciting force of general body geometries with a vertical axis of symmetry is presented. The hybrid method utilizes a numerical inner domain and a semi-infinite analytical outer domain separated by a vertical cylindrical matching boundary.Eigenfunction representation of velocity potential is used in the outer domain;the three-dimensional potential in the inner domain is solved using a "two-dimensional" boundary element method with ring sources and ring dipoles to exploit the body symmetry for efficiency. With proper solution matching at the common boundary, both radiation and diffraction potentials can be solved efficiently while satisfying the far-field radiation condition exactly. This method is applied to compute the hydrodynamic properties of two different body geometries: a vertical-walled moonpool with a bottom plate that restricts the opening and a spar-like structure with a diverging bottom opening inspired by designs of floating Oscillating Water Columns. The effects of the size of the bottom opening on the hydrodynamic properties of the body are investigated for both geometries. The heave motion of the floater as well as the motion of the internal free surface under incident wave excitation are computed and studied for the spar-like structure.
基金This work used the Extreme Science and Engineering Discovery Environment(XSEDE)Bridges system,which is supported by National Science Foundation Grant Number ACI-1548562.
文摘Defects in graphene can profoundly impact its extraordinary properties,ultimately influencing the performances of graphene-based nanodevices.Methods to detect defects with atomic resolution in graphene can be technically demanding and involve complex sample preparations.An alternative approach is to observe the thermal vibration properties of the graphene sheet,which reflects defect information but in an implicit fashion.Machine learning,an emerging data-driven approach that offers solutions to learning hidden patterns from complex data,has been extensively applied in material design and discovery problems.In this paper,we propose a machine learning-based approach to detect graphene defects by discovering the hidden correlation between defect locations and thermal vibration features.Two prediction strategies are developed:an atom-based method which constructs data by atom indices,and a domain-based method which constructs data by domain discretization.Results show that while the atom-based method is capable of detecting a single-atom vacancy,the domain-based method can detect an unknown number of multiple vacancies up to atomic precision.Both methods can achieve approximately a 90%prediction accuracy on the reserved data for testing,indicating a promising extrapolation into unseen future graphene configurations.The proposed strategy offers promising solutions for the non-destructive evaluation of nanomaterials and accelerates new material discoveries.
文摘Objective:To assess the biomechanical properties of a new design configuration for zirconia dental implants. Methods: The new design has a cylindrical shape that is partially hollow and porous in the bottom, which permits the implants to be locked into the alveolar bone over time. It also utilizes bioactive glass coatings to increase adhesion to surrounding bone structure. Samples of the new design were fabricated in the laboratory and their material strength, hardness, and fracture toughness were evaluated. In addition, biocompatibility of the new design was evaluated through testing in dogs. Results: Results of mechanical tests indicate that structural properties of the new design exceed the usual requirements for implants. Moreover, animal tests suggest that there is appreciable improvement in lock-in strength and osteointegration. Conclusion: The new design configuration is biomechanically feasible and further research is warranted to improve the design for human use.
基金the Iranian National Science Foundation (INSF) for the financial support to this project (87040150)
文摘This study describes a multidimensional 3D/lumped parameter(LP) model which contains appropriate inflow/outflow boundary conditions in order to model the entire human arterial trees. A new extensive LP model of the entire arterial network(48 arteries) was developed including the effect of vessel diameter tapering and the parameterization of resistance, conductor and inductor variables. A computer aided-design(CAD) algorithm was proposed to effciently handle the coupling of two or more 3D models with the LP model, and substantially lessen the coupling processing time. Realistic boundary conditions and Navier-Stokes equations in healthy and stenosed models of carotid artery bifurcation(CAB) were used to investigate the unsteady Newtonian blood flow velocity distribution in the internal carotid artery(ICA). The present simulation results agree well with previous experimental and numerical studies. The outcomes of a pure LP model and those of the coupled 3D healthy model were found to be nearly the same in both cases. Concerning the various analyzed 3D zones, the stenosis growth in the ICA was not found as a crucial factor in determining the absorbing boundary conditions.This paper demonstrates the advantages of coupling local and systemic models to comprehend physiological diseases of the cardiovascular system.
文摘Motivated by an animal territoriality model,we consider a centroidal Voronoi tessellation algorithm from a dynamical systems perspective.In doing so,we discuss the stability of an aligned equilibrium configuration for a rectangular domain that exhibits interesting symmetry properties.We also demonstrate the procedure for performing a center manifold reduction on the system to extract a set of coordinates which capture the long term dynamics when the system is close to a bifurcation.Bifurcations of the system restricted to the center manifold are then classified and compared to numerical results.Although we analyze a specific set-up,these methods can in principle be applied to any bifurcation point of any equilibrium for any domain.
基金supported by National Natural Science Foundation of China (No. 51479134)Fund for Creative Research Groups (No. 51321065)
文摘In this paper, the effects of second-order difference-frequency wave forces on the global motion of an offshore wind turbine system with a large displacement under the survival condition are studied. In this case, the hydrodynamic force is the main force because the blades are feathered to reduce the lifting force. The first-order hydrodynamic forces are calculated by WADAM, while the second-order wave forces are calculated by a customized MATLAB module. Then the hydrodynamic coefficients are transferred to the wind turbine analytical code FAST. Through the comparisons of dynamic responses between the first-and second-order numerical models, it is found that the second-order wave forces significantly influence the motion of floating wind turbine under the survival condition. Moreover, neglecting the second-order force significantly underestimates the tension forces in the mooring lines.
文摘A new and computationally efficient version of the immersed boundary method,which is combined with the coarse-graining method,is introduced for modeling inextensible filaments immersed in low-Reynolds number flows.This is used to represent actin biopolymers,which are constituent elements of the cytoskeleton,a complex network-like structure that plays a fundamental role in shape morphology.An extension of the traditional immersed boundary method to include a stochastic stress tensor is also proposed in order to model the thermal fluctuations in the fluid at smaller scales.By way of validation,the response of a single,massless,inextensible semiflexible filament immersed in a thermally fluctuating fluid is obtained using the suggested numerical scheme and the resulting time-averaged contraction of the filament is compared to the theoretical value obtained from the worm-like chain model.
基金funded by the Louisiana Board of Regents,project LEQSF(2014-17)-RD-A-14。
文摘We report on the results of numerical models of the(i)initial growth and(ii)steady state phases of atmospheric-pressure homogeneous dielectric barrier discharge in argon.We employ our new inhouse code called Py DBD,which solves continuity equations for both particles and energy,shows exceptional stability,is accelerated by adaptive time stepping and is openly available to the scientific community.Modeling argon plasma is numerically challenging due to the lower speeds of more inertial ions compared to more commonly modeled neon and helium,but its common use for plasma jets in medicine makes its modeling compelling.Py DBD is here applied to modeling two setups:(i)the exponential growth from natural electron-ion seeds(onset phase)until saturation is reached and(ii)the multiple current pulses that naturally appear during the steady state phase.We find that the time required for the onset phase,when the plasma density grows from 10^(9)m^(-3)to 10^(17)m^(-3),varies from 80μs at 4.5 k V down to a fewμs above 6.5 k V,for voltage frequency f=80 k Hz and gap width d_(g)=0.9 mm.At the steady state,our model reproduces two previously observed features of the current in dielectric barrier discharge reactors:(1)an oscillatory behavior associated to the capacitative character of the circuit and(2)several(N_(p))current pulses occurring every half sinusoidal cycle.We show that the oscillations are present during the exponential growth,while current pulses appear approaching the steady state.After each micro-discharge,the gas voltage decreases abruptly and charged particles rapidly accumulate at the dielectric boundaries,causing avalanches of charged particles near the reactor boundaries.Finally,we run a parametric study finding that N_(p)increases linearly with voltage amplitude V_(amp),is inversely proportional to dielectric gap d_(g)and decreases when voltage frequency f increases.The code developed for this publication is freely available at the address https://github.com/gabersyd/PyDBD.
基金supported by the National Key R&D Program of China(No.2017YFE0301304)National Natural Science Foundation of China(No.12005034)the China Postdoctoral Science Foundation(No.2019M661087)supported by the US Department of Energy,Office of Defense Nuclear Nonproliferation Research and Development,under contract number DE-AC02-05CH11231 at the Lawrence Berkeley National Laboratory。
文摘Tungsten(W)is an important material in tokamak walls and divertors.The W ion charge state distribution and the dynamic behavior of ions play important roles in the investigation of plasma–wall interactions using laser-ablation-based diagnostics such as laser-induced breakdown spectroscopy and laser-induced ablation spectroscopy.In this work,we investigate the temporal and spatial evolutions of differently charged ions in a nanosecond-laser-produced W plasma in vacuum using time-of-flight mass spectroscopy.Ions with different charge states from 1 to 7(W+to W7+)are all observed.The temporal evolutions of the differently charged ions show that ions with higher charge states have higher velocities,indicating that space separation occurs between the differently charged ion groups.Spatially-resolved mass spectroscopy measurements further demonstrate the separation phenomenon.The temporal profile can be accurately fitted by a shifted Maxwell–Boltzmann distribution,and the velocities of the differently charged ions are also obtained from the fittings.It is found that the ion velocities increase continuously from the measured position of 0.75 cm to 2.25 cm away from the target surface,which indicates that the acceleration process lasts through the period of plasma expansion.The acceleration and space separation of the differently charged ions confirm that there is a dynamic plasma sheath in the laser-produced plasma,which provides essential information for the theoretical laser-ablation model with plasma formation and expansion.
基金Supported by the National High-Tech ICF Committee of China under Grant No 10335020/A0506, the National Natural Science Foundation of China under Grants Nos 10474137, 10676010, 10474081 and 10576035, and the National Basic Research Programme of China under Grant Nos 2007CB815100 and 2006CB806004, BRJH of CAS, and the TWAS, ICTP, Italy
文摘Acceleration of an initially moving electron by a copropagation ultra-short ultra-intense laser pulse in vacuum is studied. It is shown that when appropriate laser pulse parameters and focusing conditions axe imposed, the acceleration of electron by ascending front of laser pulse can be much stronger compared to the deceleration by descending part. Consequently, the electron can obtain significantly high net energy gain. We also report the results of the new scheme that enables a second-step acceleration of electron using laser pulses of peak intensity in the range of 1019 - 1020 Wμm^2/cm^2. In the first step the electron acceleration from rest is limited to energies of a few MeV, while in the second step the electron acceleration can be considerably enhanced to about 100 MeV energy.
基金The research was performed at the Laser Thermal Laboratory by Drs David J Hwang,Sang-gil Ryu,Eunpa Kim,Jung Bin In,and the current students,Letian Wang,Yoonsoo Rho and Matthew Eliceiri.Professors Andrew M Minor,Junqiao Wu,Oscar D Dubon,Drs Bin Xiang,Frances I Allen,and Changhyun Ko of UCB Materials Science and Engineering,and Dr Carlo Carraro of UCB Chem.Engineering contributed to the work.The research was supported by DARPA/MTO under TBN grant N66001-08-1-2041,the US Department of Energy SBIR grant(DE-FG02-07ER84813),Samsung GRO,and NSF CMMI-1363392.The in situ experiments were performed at the National Center for Electron Microscopy at the Lawrence Berkeley National Laboratory,which is supported by the Office of Science,Office of Basic Energy Sciences,Scientific User Facilities Division,of the US Department of Energy under Contract No.DE-AC02-05CH11231.The laser-induced nanowire growth and doping was conducted on the LACVD apparatus in the UC Berkeley Marvell Nanofabrication Laboratory.
文摘This article summarizes work at the Laser Thermal Laboratory and discusses related studies on the laser synthesis and functionalization of semiconductor nanostructures and two-dimensional(2D)semiconductor materials.Research has been carried out on the laser-induced crystallization of thin films and nanostructures.The in situ transmission electron microscopy(TEM)monitoring of the crystallization of amorphous precursors in nanodomains is discussed herein.The directed assembly of silicon nanoparticles and the modulation of their optical properties by phase switching is presented.The vapor-liquid-solid mechanism has been adopted as a bottom-up approach in the synthesis of semiconducting nanowires(NWs).In contrast to furnace heating methods,laser irradiation offers high spatial selectivity and precise control of the heating mechanism in the time domain.These attributes enabled the investigation of NW nucleation and the early stage of nanostructure growth.Site-and shape-selective,on-demand direct integration of oriented NWs was accomplished.Growth of discrete silicon NWs with nanoscale location selectivity by employing near-field laser illumination is also reported herein.Tuning the properties of 2D transition metal dichalcogenides(TMDCs)by modulating the free carrier type,density,and composition can offer an exciting new pathway to various practical nanoscale electronics.In situ Raman probing of laser-induced processing of TMDC flakes was conducted in a TEM instrument.
文摘Large single crystal colloidal copper particles with diameters between 0.5 - 2 μm were created using a green synthesis process. The process used ascorbic acid to reduce Schweizer’s reagent created in situ using copper salts in the presence of various concentrations of gum arabic. The Schweizer’s reagents were created by varying the concentrations of ammonium hydroxide and copper nitrate solutions, copper hydroxide, or copper sulfate. The pH of the solution was controlled by the addition of ascorbic acid. Particle formation was favored at high temperature using copper sulfate at pH values ranging from 7.5 to 9, while the optimal formation occurred at a pH value of 8.5. At high concentrations, copper particle formation was found to occur from the aggregation of smaller particles which continued to nucleate once aggregated, and this resulted in the creation of globular particles and large aggregates of micron-sized particles. The addition of gum arabic resulted in the creation of large single crystal particles that did not aggregate. SEM was used to observe the effect of increasing gum arabic concentrations and EDX was used to confirm the elemental purity of the particles.
基金supported by the Helmholtz Portfolio "elektrochemische Speicher",particularly the work related to lithium-ion batteriespartially supported as part of the HeteroFoam Center,an Energy Frontier Research Center funded by the U.S.Department of Energy,Office of Science, Basic Energy Sciences(DE-SC0001061)+1 种基金support from the Center for Scientific Computing at the CNSI and MRL:an NSF MRSEC(DMR-1121053) and NSF (CNS-0960316)Australian Research Council Grant DE130101639
文摘Optimization of composition and microstructure is important to enhance performance of solid oxide fuel cells (SOFC) and lithium-ion batteries (LIB). For this, the porous electrode structures of both SOFC and LIB are modeled as a binary mixture of electronic and ionic conducting particles to estimate effective transport properties. Particle packings of 10000 spherical, binary sized and randomly positioned particles are created numerically and densified considering the different manufacturing processes in SOFC and LIB: the sintering of SOFC electrodes is approximated geometrically, whereas the calendering process and volume change due to intercalation in LIB are modeled physically by a discrete el- ement approach. A combination of a tracking algorithm and a resistor network approach is developed to predict the con- nectivity and effective conductivity for the various densified structures. For SOFC, a systematic study of the influence of morphology on connectivity and conductivity is performed on a large number of assemblies with different compositions and particle size ratios between 1 and 10. In comparison to percolation theory, an enlarged percolation area is found, es- pecially for large size ratios. It is shown that in contrast to former studies the percolation threshold correlates to varying coordination numbers. The effective conductivity shows not only an increase with volume fraction as expected but also with size ratio. For LIB, a general increase of conductivity during the intercalation process was observed in correlation with increasing contact forces. The positive influence of cal- endering on the percolation threshold and the effective conductivity of carbon black is shown. The anisotropy caused by the calendering process does not influence the carbon black phase.
文摘Energy storage technologies, which enable demand response, are being explored throughout the world as a component of strategies for switching to renewable intermittent energy sources and reducing peak loads. This study examines thermal storage refrigeration (TSR) technology as a case study for the potential value of demand response in California and Denmark. Using technical specifications from a TSR prototype developed at UC Davis and market data from California and Denmark, the analysis examines possible business models for the TSR refrigerators and highlights market characteristics that are important to its adoption. Results suggest that the TSR technology is not a viable option in the current market environment in Denmark, but could payback in less than 6 years in California if a part of a demand response based virtual power plant. In a hypothetical future scenario involving real-time pricing in the retail market, a high degree of price volatility would be needed to make TSR technology appealing to residential consumers. Based on this analysis, an interesting area of future work would focus on the market potential of TSR technology for commercial and industrial applications.
基金partially supported by Shenzhen Key Laboratory of Robotics Perception and Intelligence(Southern University of Science and Technology,China)(Grant No.ZDSYS20200810171800001).
文摘Biopsy is a method commonly used for early cancer diagnosis.However,bleeding complications of widely available biopsy are risky for patients.Safer biopsy will result in a more accurate cancer diagnosis and a decrease in the risk of complications.In this article,we propose a novel biopsy needle that can reduce bleeding during biopsy procedures and achieve stable hemostasis.The proposed biopsy needle features a compact structure and can be operated easily by left and right hands.A predictive model for puncture force and tip deflection based on coupled Eulerian–Lagrangian(CEL)method is developed.Experimental results show that the biopsy needle can smoothly deliver the gelatin sponge hemostatic plug into the tissue.Although the hemostatic plug bends,the overall delivery process is stable,and the hemostatic plug retains in the tissue without being affected by the withdrawal of the needle.Further experiments indicate that the specimens are well obtained and evenly distributed in the groove of the outer needle without scattering.Our proposed design of biopsy needle possesses strong ability of hemostasis,tissue cutting,and tissue retention.The CEL model accurately predicts the peak of puncture force and produces close estimation of the insertion force at the postpuncture stage and tip position.