1,573 research outputs found
Microstructure modelling of hot deformation of Al–1%Mg alloy
This study presents the application of the finite elementmethod and intelligent systems techniques to the
prediction of microstructural mapping for aluminium alloys. Here, the material within each finite element
is defined using a hybrid model. The hybrid model is based on neuro-fuzzy and physically based components
and it has been combined with the finite element technique. The model simulates the evolution of
the internal state variables (i.e. dislocation density, subgrain size and subgrain boundary misorientation)
and their effect on the recrystallisation behaviour of the stock. This paper presents the theory behind
the model development, the integration between the numerical techniques, and the application of the
technique to a hot rolling operation using aluminium, 1 wt% magnesium alloy. Furthermore, experimental
data from plane strain compression (PSC) tests and rolling are used to validate the modelling outcome.
The results show that the recrystallisation kinetics agree well with the experimental results for different
annealing times. This hybrid approach has proved to be more accurate than conventional methods using empirical equations
Lattice Boltzmann modeling of dendritic growth in forced and natural convection
AbstractA two-dimensional (2D) coupled model is developed for the simulation of dendritic growth during alloy solidification in the presence of forced and natural convection. Instead of conventional continuum-based Navier–Stokes (NS) solvers, the present model adopts a kinetic-based lattice Boltzmann method (LBM), which describes flow dynamics by the evolution of distribution functions of moving pseudo-particles, for the numerical computations of flow dynamics as well as thermal and solutal transport. The dendritic growth is modeled using a solutal equilibrium approach previously proposed by Zhu and Stefanescu (ZS), in which the evolution of the solid/liquid interface is driven by the difference between the local equilibrium composition and the local actual liquid composition. The local equilibrium composition is calculated from the local temperature and curvature. The local temperature and actual liquid composition, controlled by both diffusion and convection, are obtained by solving the LB equations using the lattice Bhatnagar–Gross–Krook (LBGK) scheme. Detailed model validation is performed by comparing the simulations with analytical predictions, which demonstrates the quantitative capability of the proposed model. Furthermore, the convective dendritic growth features predicted by the present model are compared with those obtained from the Zhu–Stefanescu and Navier–Stokes (ZS–NS) model, in which the fluid flow is calculated using an NS solver. It is found that the evolution of the solid fraction of dendritic growth calculated by both models coincides well. However, the present model has the significant advantages of numerical stability and computational efficiency for the simulation of dendritic growth with melt convection
General Spectral Flow Formula for Fixed Maximal Domain
We consider a continuous curve of linear elliptic formally self-adjoint
differential operators of first order with smooth coefficients over a compact
Riemannian manifold with boundary together with a continuous curve of global
elliptic boundary value problems. We express the spectral flow of the resulting
continuous family of (unbounded) self-adjoint Fredholm operators in terms of
the Maslov index of two related curves of Lagrangian spaces. One curve is given
by the varying domains, the other by the Cauchy data spaces. We provide
rigorous definitions of the underlying concepts of spectral theory and
symplectic analysis and give a full (and surprisingly short) proof of our
General Spectral Flow Formula for the case of fixed maximal domain. As a side
result, we establish local stability of weak inner unique continuation property
(UCP) and explain its role for parameter dependent spectral theory.Comment: 22 page
A novel axial flux magnetically geared machine for power split application
This paper proposes an axial flux magnetically geared (AFMG) permanent magnet (PM) machine for power split application in hybrid electric vehicles. The proposed AFMG machine has the merits of simple structure and improved torque density by combining a magnetic gear with a PM machine. The machine can realize power split with the help of dual mechanical ports and one electrical port, i.e., the input mechanical power and/or electrical power produced by the machine can be split or integrated. The operation principle and two feasible stator slot/rotor pole combinations are analyzed. Moreover, the influence of the machine parameters on the output torque as well as the performance of both combinations are investigated and compared by using JMAG three-dimensional finite element analysis (FEA). In addition, the method of boosting the machine torque is described and experiment results of the proposed machine prototype are provided and compared with FEA results
Sheaves on fibered threefolds and quiver sheaves
This paper classifies a class of holomorphic D-branes, closely related to
framed torsion-free sheaves, on threefolds fibered in resolved ADE surfaces
over a general curve C, in terms of representations with relations of a twisted
Kronheimer--Nakajima-type quiver in the category Coh(C) of coherent sheaves on
C. For the local Calabi--Yau case C\cong\A^1 and special choice of framing, one
recovers the N=1 ADE quiver studied by Cachazo--Katz--Vafa.Comment: 13 pages, 2 figures, minor change
Conductance of a Quantum Point Contact in the presence of a Scanning Probe Microscope Tip
Using the recursive Green's function technique, we study the coherent
electron conductance of a quantum point contact in the presence of a scanning
probe microscope tip. Images of the coherent fringe inside a quantum point
contact for different widths are obtained. It is found that the conductance of
a specific channel is reduced while other channels are not affected as long as
the tip is located at the positions correspending to that channel. Moreover,
the coherent fringe is smoothed out by increasing the temperature or the
voltage across the device. Our results are consistent with the experiments
reported by Topinka et al.[Science 289, 2323 (2000)].Comment: 5 page
Comments on Noncommutative ADHM Construction
We extend the method of matrix partition to obtain explicitly the gauge field
for noncommutative ADHM construction in some general cases. As an application
of this method we apply it to the U(2) 2-instanton and get explicit result for
the gauge fields in the coincident instanton limit. We also easily apply it to
the noncommutative 't Hooft instantons in the appendix.Comment: 17 pages, LaTeX; an appendix added, typos corrected, refs adde
Continuous-distribution puddle model for conduction in trilayer graphene
An insulator-to-metal transition is observed in trilayer graphene based on
the temperature dependence of the resistance under different applied gate
voltages. At small gate voltages the resistance decreases with increasing
temperature due to the increase in carrier concentration resulting from thermal
excitation of electron-hole pairs. At large gate voltages excitation of
electron-hole pairs is suppressed, and the resistance increases with increasing
temperature because of the enhanced electron-phonon scattering. We find that
the simple model with overlapping conduction and valence bands, each with
quadratic dispersion relations, is unsatisfactory. Instead, we conclude that
impurities in the substrate that create local puddles of higher electron or
hole densities are responsible for the residual conductivity at low
temperatures. The best fit is obtained using a continuous distribution of
puddles. From the fit the average of the electron and hole effective masses can
be determined.Comment: 18 pages, 5 figure
Quasiparticle Scattering Interference in High Temperature Superconductors
We propose that the energy-dependent spatial modulation of the local density
of states seen by Hoffman, et al [hoff2] is due to the scattering interference
of quasiparticles. In this paper we present the general theoretical basis for
such an interpretation and lay out the underlying assumptions. As an example,
we perform exact T-matrix calculation for the scattering due to a single
impurity. The results of this calculation is used to check the assumptions, and
demonstrate that quasiparticle scattering interference can indeed produce
patterns similar to those observed in Ref. [hoff2].Comment: RevTex4 twocolumn, 4 pages, 3 figures. Figs.2-3 virtually embedded
(bacause of too big size) while jpg files available in the postscript/source
package. Further polishe
Effect of recent R_p and R_n measurements on extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
The Gari-Krumpelmann (GK) models of nucleon electromagnetic form factors, in
which the rho, omega, and phi vector meson pole contributions evolve at high
momentum transfer to conform to the predictions of perturbative QCD (pQCD), was
recently extended to include the width of the rho meson by substituting the
result of dispersion relations for the pole and the addition of rho' (1450)
isovector vector meson pole. This extended model was shown to produce a good
overall fit to all the available nucleon electromagnetic form factor (emff)
data. Since then new polarization data shows that the electric to magnetic
ratios R_p and R_n obtained are not consistent with the older G_{Ep} and G_{En}
data in their range of momentum transfer. The model is further extended to
include the omega' (1419) isoscalar vector meson pole. It is found that while
this GKex cannot simultaneously fit the new R_p and the old G_{En} data, it can
fit the new R_p and R_n well simultaneously. An excellent fit to all the
remaining data is obtained when the inconsistent G_{Ep} and G_{En} is omitted.
The model predictions are shown up to momentum transfer squared, Q^2, of 8
GeV^2/c^2.Comment: 14 pages, 8 figures, using RevTeX4; email correspondence to
[email protected] ; minor typos corrected, figures added, conclusions
extende
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