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Hydrodynamic Analysis of Binary Immiscible Metallurgical Flow in a Novel Mixing Process: Rheomixing
This paper presents a hydrodynamic analysis of binary immiscible metallurgical flow by a numerical simulation of the rheomixing process. The concept of multi-controll is proposed for classifying complex processes and identifying individual processes in an immiscible alloy system in order to perform simulations. A brief review of fabrication methods for immiscible alloys is given, and fluid flow aspects of a novel fabrication method – rheomixing by twin-screw extruder (TSE) are analysed. Fundamental hydrodynamic micro-mechanisms in a TSE are simulated by a piecewise linear (PLIC) volume-of-fluid (VOF) method coupled with the continuum surface force (CFS) algorithm. This revealed that continuous reorientation in the TSE process could produce fine droplets and the best mixing efficiency. It is verified that TSE is a better mixing device than single screw extruder (SSE) and can achieve finer droplets. Numerical results show good qualitative agreement with experimental results. It is concluded that rheomixing by a TSE can be successfully employed for casting immiscible engineering alloys due to its unique characteristics of reorientation and surface renewal
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Numerical analysis of the hydrodynamic behaviour of immiscible metallic alloys in twin-screw rheomixing process
A numerical analysis by a VOF method is presented for studying the hydrodynamic mechanisms of the rheomixing process by a twin-screw extruder (TSE). The simplified flow field is established based on a systematic analysis of flow features of immiscible alloys in TSE rheomixing process. The studies focus on the fundamental microstructure mechanisms of rheological behaviour in shear-induced turbulent flows. It is noted that the microstructure of immiscible alloys in the mixing process is strongly influenced by the interaction between droplets, which is controlled by shearing forces, viscosity ratio, turbulence, and shearing time. The numerical results show a good qualitative agreement with the experimental results, and are useful for further optimisation design of prototypical rheomixing processes
Properties of Resonating-Valence-Bond Spin Liquids and Critical Dimer Models
We use Monte Carlo simulations to study properties of Anderson's
resonating-valence-bond (RVB) spin-liquid state on the square lattice (i.e.,
the equal superposition of all pairing of spins into nearest-neighbor singlet
pairs) and compare with the classical dimer model (CDM). The latter system also
corresponds to the ground state of the Rokhsar-Kivelson quantum dimer model at
its critical point. We find that although spin-spin correlations decay
exponentially in the RVB, four-spin valence-bond-solid (VBS) correlations are
critical, qualitatively like the well-known dimer-dimer correlations of the
CDM, but decaying more slowly (as with , compared with
for the CDM). We also compute the distribution of monomer (defect) pair
separations, which decay by a larger exponent in the RVB than in the CDM. We
further study both models in their different winding number sectors and
evaluate the relative weights of different sectors. Like the CDM, all the
observed RVB behaviors can be understood in the framework of a mapping to a
"height" model characterized by a gradient-squared stiffness constant . Four
independent measurements consistently show a value , with the same kinds of numerical evaluations of give
results in agreement with the rigorously known value . The
background of a nonzero winding number gradient introduces spatial
anisotropies and an increase in the effective K, both of which can be
understood as a consequence of anharmonic terms in the height-model free
energy, which are of relevance to the recently proposed scenario of "Cantor
deconfinement" in extended quantum dimer models. We also study ensembles in
which fourth-neighbor (bipartite) bonds are allowed, at a density controlled by
a tunable fugacity, resulting (as expected) in a smooth reduction of K.Comment: 26 pages, 21 figures. v3: final versio
DC Spin Current Generation in a Rashba-type Quantum Channel
We propose and demonstrate theoretically that resonant inelastic scattering
(RIS) can play an important role in dc spin current generation. The RIS makes
it possible to generate dc spin current via a simple gate configuration: a
single finger-gate that locates atop and orients transversely to a quantum
channel in the presence of Rashba spin-orbit interaction. The ac biased
finger-gate gives rise to a time-variation in the Rashba coupling parameter,
which causes spin-resolved RIS, and subsequently contributes to the dc spin
current. The spin current depends on both the static and the dynamic parts in
the Rashba coupling parameter, and , respectively, and is
proportional to . The proposed gate configuration has the
added advantage that no dc charge current is generated. Our study also shows
that the spin current generation can be enhanced significantly in a double
finger-gate configuration.Comment: 4 pages,4 figure
Representation of SO(3) Group by a Maximally Entangled State
A representation of the SO(3) group is mapped into a maximally entangled two
qubit state according to literatures. To show the evolution of the entangled
state, a model is set up on an maximally entangled electron pair, two electrons
of which pass independently through a rotating magnetic field. It is found that
the evolution path of the entangled state in the SO(3) sphere breaks an odd or
even number of times, corresponding to the double connectedness of the SO(3)
group. An odd number of breaks leads to an additional phase to the
entangled state, but an even number of breaks does not. A scheme to trace the
evolution of the entangled state is proposed by means of entangled photon pairs
and Kerr medium, allowing observation of the additional phase.Comment: 4 pages, 3 figure
Optical properties of Si/Si0.87Ge0.13 multiple quantum well wires
Nanometer-scale wires cut into a Si/Si0.87Ge0.13 multiple quantum well structure were fabricated and characterized by using photoluminescence and photoreflectance at temperatures between 4 and 20 K. It was found that, in addition to a low-energy broadband emission at around 0.8 eV and other features normally observable in photoluminescence measurements, fabrication process induced strain relaxation and enhanced electron-hole droplets emission together with a new feature at 1.131 eV at 4 K were observed. The latter was further identified as a transition related to impurities located at the Si/Si0.87Ge0.13 heterointerfaces
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