| 1. |
- Akhtar, Farid, et al.
(författare)
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TiB 2 and TiC stainless steel matrix composites
- 2007
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Ingår i: Materials letters (General ed.). - : Elsevier BV. - 0167-577X .- 1873-4979. ; 61:1, s. 189-191
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Tidskriftsartikel (refereegranskat)abstract
- Stainless steel matrix composites reinforced with TiB2 or TiC particulates have been in situ produced through the reactive sintering of Ti, C and FeB. X-ray diffraction analysis confirmed the completion of reaction. The TiB2, TiC and steel were detected by X-ray diffraction analysis. No other reaction product or boride was found, indicating the stability of TiB2 and TiC in steel matrix. The SEM micrographs revealed the morphology and distribution of in situ synthesized TiB2 and TiC reinforcements in steel matrix. During sintering the reinforcements TiB2 and TiC grew in different shapes. TiB2 grew in hexagonal prismatic and rectangular shape and TiC in spherical shape.
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| 2. |
- Clark, Andrew G., et al.
(författare)
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Evolution of genes and genomes on the Drosophila phylogeny
- 2007
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 450:7167, s. 203-218
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Tidskriftsartikel (refereegranskat)abstract
- Comparative analysis of multiple genomes in a phylogenetic framework dramatically improves the precision and sensitivity of evolutionary inference, producing more robust results than single-genome analyses can provide. The genomes of 12 Drosophila species, ten of which are presented here for the first time (sechellia, simulans, yakuba, erecta, ananassae, persimilis, willistoni, mojavensis, virilis and grimshawi), illustrate how rates and patterns of sequence divergence across taxa can illuminate evolutionary processes on a genomic scale. These genome sequences augment the formidable genetic tools that have made Drosophila melanogaster a pre-eminent model for animal genetics, and will further catalyse fundamental research on mechanisms of development, cell biology, genetics, disease, neurobiology, behaviour, physiology and evolution. Despite remarkable similarities among these Drosophila species, we identified many putatively non-neutral changes in protein-coding genes, non-coding RNA genes, and cis-regulatory regions. These may prove to underlie differences in the ecology and behaviour of these diverse species.
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| 3. |
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| 4. |
- Feng, Tao, et al.
(författare)
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Adaptive finite element methods for parameter estimation problems in linear elasticity
- 2009
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Ingår i: International Journal of Numerical Analysis & Modeling. - 1705-5105. ; 6:1, s. 17-32
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the Lame coefficients in the linear elasticity problem are estimated by using the measurements of displacement. Some a posteriori error estimators for the approximation error of the parameters are derived, and then adaptive finite element schemes are developed for the discretization of the parameter estimation problem, based on the error estimators. The Gauss-Newton method is employed to solve the discretized nonlinear least-squares problem. Some numerical results are presented.
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| 5. |
- Feng, Tao
(författare)
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Adaptive finite element methods for parameter estimation problems in partial differential equations
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Physical and chemical phenomena are often described by a system of partial di®erential equations. These equations usually involve unknown parameters, which cannot be measured directly but which can be adjusted to make the model predictions match the observed data. The process of ¯tting these para- meters to laboratory or plant data is called parameter estimation. In order to recover these parameters, the well-known output least squares formulation is of- ten utilized. To solve the optimization problem governed by partial di®erential equations, the in¯nite-dimensional problem must be approximated by introduc- ing discretizations such as a ¯nite elements or di®erences. It is clear that the e±ciency of the numerical methods dealt with here will be in°uenced by the discretization scheme. The goal of this thesis is to develop e±cient numerical methods for the parameter estimation problems governed by partial di®erential equations, based on adaptive ¯nite element methods. This work was initiated by an investigation into an a posteriori error esti- mator of residual type for parameter estimation problems with a ¯nite number of unknown parameters. It appears that an adaptive ¯nite element algorithm guided by the derived a posteriori error estimator produces a sequence of eco- nomical, locally re¯ned meshes. The methods are then applied to the identi¯ca- tion of elastic constants in paper from measured displacements. Further, some a posteriori error estimators of gradient recovery type are derived for the error in parameters due to the discretization. The main advantages of using error estimators of this type are the simplicity of their implementation and their cost e®ectiveness. Often, the unknown parameters are functions, which also need to be dis- cretized. Adaptive ¯nite element method is developed for the estimation of distributed parameters in elliptic equations with multi-mesh techniques. Finally, a goal-oriented adaptive method, dual weighted residual methods (DWR methods) are employed determining the elastic constants in paper from measured displacements.
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| 6. |
- Feng, Tao, et al.
(författare)
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Adaptive finite element methods for the identification of distributed parameters in elliptic equation
- 2008
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Ingår i: Advances in Computational Mathematics. - : Springer Science and Business Media LLC. - 1019-7168 .- 1572-9044. ; 29:1, s. 27-53
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, adaptive finite element method is developed for the estimation of distributed parameter in elliptic equation. Both upper and lower error bound are derived and used to improve the accuracy by appropriate mesh refinement. An efficient preconditioned project gradient algorithm is employed to solve the nonlinear least-squares problem arising in the context of parameter identification problem. The efficiency of our error estimators is demonstrated by some numerical experiments
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| 7. |
- Feng, Tao, et al.
(författare)
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Adaptive finite element methods for the identification of elastic constants
- 2006
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Ingår i: Journal of Scientific Computing. - : Springer Science and Business Media LLC. - 0885-7474 .- 1573-7691. ; 26:2, s. 217-235
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the elastic constants of a material are recovered from measured displacements where the model is the equilibrium equations for the orthotropic case. The finite element method is used for the discretization of the state equation and the Gauss–Newton method is used to solve the nonlinear least squares problem attained from the parameter estimation problem. A posteriori error estimators are derived and used to improve the accuracy by an appropriate mesh refinement. A numerical experiment is presented to show the applicability of the approach.
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| 8. |
- Feng, Tao, et al.
(författare)
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Levenberg-Marquardt Methods for Parameter Estimation Problems in the Radiative Transfer Equation
- 2007
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Ingår i: Inverse Problems. - : IOP Publishing. - 0266-5611 .- 1361-6420. ; 23:3, s. 879-891
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Tidskriftsartikel (refereegranskat)abstract
- A discrete ordinate method is developed for solving the radiative transfer equation, and the corresponding parameter estimation problem is given a least-squares formulation. Two Levenberg-Marquardt methods, a feasible-path approach and an SQP type method, are analyzed and compared. A sensitivity analysis is given, and it is shown how it can be used for designing measurements with minimal impact of measurement noise. Numerical experiments are performed to exemplify the usefulness of the theory.
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| 9. |
- Gao, Feng, et al.
(författare)
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Visible-light photocatalytic properties of weak magnetic BiFeO3 nanoparticles
- 2007
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Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 19:19, s. 2889-2892
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Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline BiFeO3 nanoparticles (size 80-120 nm) are prepared by a simple sol-gel technique. Such nanoparticles are very efficient for photocatalytic decomposition of organic contaminants under irradiation from ultraviolet to visible frequencies. The BiFeO3 nanoparticles also demonstrate weak ferromagnetism of about 0.06 mu(B)/Fe at room temperature, in good agreement with theoretical calculations.
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| 10. |
- Kärrholm Peng, Fabian, 1980, et al.
(författare)
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On Performance of Advection Schemes in the Prediction of Diesel Spray and Fuel Vapour Distributions
- 2008
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Ingår i: ILASS 2008, Como Lake.
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Konferensbidrag (refereegranskat)abstract
- We have investigated the performance of advection schemes (focusing mainlyon Total Variation Diminishing, TVD, schemes)applied in modelling diesel sprays, and assessed their influence on liquidspray penetration and fuel vapour distribution. Here,we compare sprays simulated using several types of TVD schemes (Superbee,MUSCL, limited Linear, and UMIST) – andstandard upwind and linear schemes as references – in conjunction withthree different turbulence models (standard, RNG andLaunder-Sharma k-ε models), to non-reacting diesel sprays observed inthe Sandia high-pressure, high-temperature constant-volume vessel. The OpenFOAM CFD code was used for all of the simulationsdescribed. In addition to comparing thesimulations to experimental data, we provide overall assessments of theperformance and utility of the TVD schemes in multi-dimensional diesel modelling.
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| 11. |
- Kärrholm Peng, Fabian, 1980, et al.
(författare)
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Three-Dimensional Simulation of Diesel Spray Ignition and Flame Lift-Off Using OpenFOAM and KIVA-3V CFD Codes
- 2008
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional simulations of ignition and combustion of a dieselspray were conducted. The primary goal of the work was to compare twodifferent CFD codes: OpenFOAM, an object-oriented C++ based code, andKIVA-3V. The spray is modelled by the Eulerian-Lagrangian approach inboth codes, with several common submodels. Some important sub-modelsimplemented include \emph{inter alia} aKelvin-Helmholtz/Rayleigh-Taylor (KH/RT) model for spray break-up, animproved spray collision model, and a Partially Stirred Reactor (PaSR)model for turbulence-chemistry interaction. Both CFD codes solve thechemical reaction equations in a fully coupled manner. A cubic-shaped Cartesianmesh was used in the KIVA-3V simulations, while a polyhedral meshincluding a combination of hexagonal and prism-shaped cells wasconstructed for the OpenFOAM computations.The effects of high EGR and ambient temperature on the ignition and flamelift-off processes of a diesel spray were investigated. Sandia experimentsconducted in a high-pressure and high-temperature constant-volume vessel werechosen for the simulations and validations. A single spray was injected intothe vessel, and EGR was mimicked by reducing the oxygen concentration. Thediesel reference fuel (n-heptane) was considered. For the study, a medium-sizemechanism involving 83 species and 338 reactions was employed. The mechanismwas validated using the CHEMKIN II package and the reaction rate constantswere adjusted on the basis of measurements of auto-ignition delays ofn-heptane/air mixtures in shock-tube experiments (with equivalence ratiosranging from 0.2 to 0.4 at 50 bar, and from 0.5 to 2.0 at 13.5 bar and 41.0bar), laminar flame speeds (1 atm and 3 atm), and flame structure inburner-stabilized premixed flames (1 atm).The simulations demonstrate that both CFD codes are capable of spray ignitionand combustion studies, though both show stronggrid-dependence. The numerical results show that the ignition delay,flame lift-off and combustion temperature of the spray are stronglyinfluenced by EGR and ambient gas temperature. These predictions arein agreement with measurements. Nevertheless, differences are observedbetween the results predicted by OpenFOAM and those from KIVA-3V, forexample, the flame predicted by the former is thinner and longer than that by thelatter, which requires further investigation.
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| 12. |
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| 13. |
- Tao, Feng, 1964, et al.
(författare)
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Effect of ultra-high injection pressure on diesel ignition and flame under high-boost conditions
- 2008
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Ingår i: SAE Technical Papers: 2008 SAE International Powertrains, Fuels and Lubricants Congress; Shanghai; China; 23 June 2008 through 25 June 2008. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
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Konferensbidrag (refereegranskat)abstract
- In this work, we conducted three-dimensional numerical simulations to investigate the effect of ultra-high injection pressure on diesel ignition and flame under high-boost and medium-load conditions. Three injection cases employed in experiments with a multi-cylinder Volvo D12 engine were applied for validation. The simulations were performed using the KIVA-3V code, with a Kelvin-Helmholz/Rayleigh-Taylor (KH/RT) spray breakup model and a diesel surrogate mechanism involving 83 species and 445 reactions. A range of higher injection pressure levels were projected and the injection rates estimated for the current study. Three different rate shapes of injection were projected and investigated as well. All the projected injection events start at top dead center (TDC). Computations demonstrate that high-pressure injection strongly affects engine ignition and combustion. An increase in injection pressure leads to reduced ignition delay time, higher in-cylinder pressure peak, advanced combustion phasing, and faster flame propagation. The study found that the ultra-high pressure injection does not cause the flame lift-off length in the engine to increase, the trend of which seems to be contradictory to the observations obtained from the studies in high-pressure, high-temperature constant-volume vessels. While the burn durations reduced with an increase in injection pressure, the simulations of three different injection rate shapes suggest that the rate-falling injection leads to a shorter, early (10-30%) burn duration angle but a longer, late (70-90%) burn angle. The prediction indicates that the engine has a relatively larger flame area of higher temperature in the late cycle for the rate-rising injection than for the rate-falling one. The existence of higher temperature in the late engine cycle may be beneficial to soot oxidation. On the other hand, the simulations show that higher injection pressure results in a faster NO production rate in the early phase of combustion but leads to a lower NO peak level. The rate-rising injection lowers NO production compared with the other two injection strategies.
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| 14. |
- Zhang, Xuanjun, et al.
(författare)
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Self-assembly of Organic Chromophore with Cd-S Nanoclusters: Supramolecular Structures and Enhanced Emissions
- 2005
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 5:2, s. 565-570
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Tidskriftsartikel (refereegranskat)abstract
- By combination of the large organic cation [trans-4-(4-dimethylanilino-styryl)-N-methyl-pyridinium with nanocluster anions ([Cd4(SC6H5)10]2- for compound 1 and [Cd4(SC6H5)6I4]2- for compound 2), two new hybrids were obtained and the structure of the [Cd4(SC6H5)6I4]2- cluster was first characterized by single-crystal X-ray diffraction. A novel supramolecular dimer {[Cd4(SC6H5)10]2-}2, connected via strong π−π interactions, was observed in 1, whereas every two [Cd4(SC6H5)6I4]2- clusters in 2 were linked by multiple C−H···I hydrogen bonds forming dimers, which, as building blocks, were further connected to each other via C−H···I hydrogen bonds and weak I···I interactions to form novel 1D helical chains. The UV−visible−near-IR spectra, one-photon excited photoluminescence, and two-photon pumped lasing were measured. The organic chromophore exhibits enhanced PL and two-photon pumped lasing in the two hybrids
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| 15. |
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| 16. |
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