2,313 research outputs found
Adaptive and coupled continuum-molecular mechanics simulations of amorphous materials
A method to reduce the degrees freedom in molecular mechanics simulation is presented. Although the approach is formulated for amorphous materials in mind, it is equally applicable to crystalline materials. The method can be selectively applied to regions where molecular displacements are expected to be small while simultaneously using classical molecular mechanics (MM) for regions undergoing large deformation. The accuracy and computational efficiency of the approach is demonstrated through the simulation of a polymer-like substrate being indented by a rigid hemispherical indentor. The region directly below the indentor is modelled by classical molecular mechanics while the region further away has the degrees of freedom (DOFs) reduced by about 50 times. The results of automatically reverting regions of reduced DOFs back to classical MM also demonstrate the capability of performing adaptive simulations
A Floating Node Method for the Modelling of Discontinuities Within a Finite Element
This paper focuses on the accurate numerical representation of complex networks of evolving discontinuities in solids, with particular emphasis on cracks. The limitation of the standard finite element method (FEM) in approximating discontinuous solutions has motivated the development of re-meshing, smeared crack models, the eXtended Finite Element Method (XFEM) and the Phantom Node Method (PNM). We propose a new method which has some similarities to the PNM, but crucially: (i) does not introduce an error on the crack geometry when mapping to natural coordinates; (ii) does not require numerical integration over only part of a domain; (iii) can incorporate weak discontinuities and cohesive cracks more readily; (iv) is ideally suited for the representation of multiple and complex networks of (weak, strong and cohesive) discontinuities; (v) leads to the same solution as a finite element mesh where the discontinuity is represented explicitly; and (vi) is conceptually simpler than the PNM
Floating Node Method and Virtual Crack Closure Technique for Modeling Matrix Cracking-Delamination Interaction
A novel approach is proposed for high-fidelity modeling of progressive damage and failure in composite materials that combines the Floating Node Method (FNM) and the Virtual Crack Closure Technique (VCCT) to represent multiple interacting failure mechanisms in a mesh-independent fashion. In this study, the approach is applied to the modeling of delamination migration in cross-ply tape laminates. Delamination, matrix cracking, and migration are all modeled using fracture mechanics based failure and migration criteria. The methodology proposed shows very good qualitative and quantitative agreement with experiments
Floating Node Method and Virtual Crack Closure Technique for Modeling Matrix Cracking-Delamination Migration
A novel approach is proposed for high-fidelity modeling of progressive damage and failure in composite materials that combines the Floating Node Method (FNM) and the Virtual Crack Closure Technique (VCCT) to represent multiple interacting failure mechanisms in a mesh-independent fashion. In this study, the approach is applied to the modeling of delamination migration in cross-ply tape laminates. Delamination, matrix cracking, and migration are all modeled using fracture mechanics based failure and migration criteria. The methodology proposed shows very good qualitative and quantitative agreement with experiments
On the Thermal Symmetry of the Markovian Master Equation
The quantum Markovian master equation of the reduced dynamics of a harmonic
oscillator coupled to a thermal reservoir is shown to possess thermal symmetry.
This symmetry is revealed by a Bogoliubov transformation that can be
represented by a hyperbolic rotation acting on the Liouville space of the
reduced dynamics. The Liouville space is obtained as an extension of the
Hilbert space through the introduction of tilde variables used in the
thermofield dynamics formalism. The angle of rotation depends on the
temperature of the reservoir, as well as the value of Planck's constant. This
symmetry relates the thermal states of the system at any two temperatures. This
includes absolute zero, at which purely quantum effects are revealed. The
Caldeira-Leggett equation and the classical Fokker-Planck equation also possess
thermal symmetry. We compare the thermal symmetry obtained from the Bogoliubov
transformation in related fields and discuss the effects of the symmetry on the
shape of a Gaussian wave packet.Comment: Eqs.(64a), (65a)-(68) are correcte
Modeling Quasi-Static and Fatigue-Driven Delamination Migration
An approach was proposed and assessed for the high-fidelity modeling of progressive damage and failure in composite materials. It combines the Floating Node Method (FNM) and the Virtual Crack Closure Technique (VCCT) to represent multiple interacting failure mechanisms in a mesh-independent fashion. Delamination, matrix cracking, and migration were captured failure and migration criteria based on fracture mechanics. Quasi-static and fatigue loading were modeled within the same overall framework. The methodology proposed was illustrated by simulating the delamination migration test, showing good agreement with the available experimental data
Isostatic phase transition and instability in stiff granular materials
In this letter, structural rigidity concepts are used to understand the
origin of instabilities in granular aggregates. It is shown that: a) The
contact network of a noncohesive granular aggregate becomes exactly isostatic
in the limit of large stiffness-to-load ratio. b) Isostaticity is responsible
for the anomalously large susceptibility to perturbation of these systems, and
c) The load-stress response function of granular materials is critical
(power-law distributed) in the isostatic limit. Thus there is a phase
transition in the limit of intinitely large stiffness, and the resulting
isostatic phase is characterized by huge instability to perturbation.Comment: RevTeX, 4 pages w/eps figures [psfig]. To appear in Phys. Rev. Let
Quantum Magnetization Plateau in Spin-1 Triangular-Lattice Antiferromagnet BaNiSbO
We report the results of magnetization and specific heat measurements on
BaNiSbO, which is a quasi-two-dimensional spin-1 triangular-lattice
antiferromagnet. We observed a nonclassical magnetization plateau at one-third
of the saturation magnetization that is driven by spin frustration and quantum
fluctuation. Exact diagonalization for a 21-site rhombic cluster was performed
to analyze the magnetization process. Experimental and calculated results agree
well.Comment: published in Journal of the Physical Society of Japan 80 (2011)
09370
Highly multimode memory in a crystal
We experimentally demonstrate the storage of 1060 temporal modes onto a
thulium-doped crystal using an atomic frequency comb (AFC). The comb covers
0.93 GHz defining the storage bandwidth. As compared to previous AFC
preparation methods (pulse sequences i.e. amplitude modulation), we only use
frequency modulation to produce the desired optical pumping spectrum. To ensure
an accurate spectrally selective optical pumping, the frequency modulated laser
is self-locked on the atomic comb. Our approach is general and should be
applicable to a wide range of rare-earth doped material in the context of
multimode quantum memory
Overcoming the penetration depth limit in optical microscopy: Adaptive optics and wavefront shaping
Despite the unique advantages of optical microscopy for molecular specific high resolution imaging of living structure in both space and time, current applications are mostly limited to research settings. This is due to the aberrations and multiple scattering that is induced by the inhomogeneous refractive boundaries that are inherent to biological systems. However, recent developments in adaptive optics and wavefront shaping have shown that high resolution optical imaging is not fundamentally limited only to the observation of single cells, but can be significantly enhanced to realize deep tissue imaging. To provide insight into how these two closely related fields can expand the limits of bio imaging, we review the recent progresses in their performance and applicable range of studies as well as potential future research directions to push the limits of deep tissue imaging
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