7,581 research outputs found
Driving dynamic colloidal assembly using eccentric self-propelled colloids
Designing protocols to dynamically direct the self-assembly of colloidal
particles has become an important direction in soft matter physics because of
the promising applications in fabrication of dynamic responsive functional
materials. Here using computer simulations, we found that in the mixture of
passive colloids and eccentric self-propelled active particles, when the
eccentricity and self-propulsion of active particles are high enough, the
eccentric active particles can push passive colloids to form a large dense
dynamic cluster, and the system undergoes a novel dynamic demixing transition.
Our simulations show that the dynamic demixing occurs when the eccentric active
particles move much faster than the passive particles such that the dynamic
trajectories of different active particles can overlap with each other while
passive particles are depleted from the dynamic trajectories of active
particles. Our results suggest that this is in analogy to the entropy driven
demixing in colloid-polymer mixtures, in which polymer random coils can overlap
with each other while deplete the colloids. More interestingly, we find that by
fixing the passive colloid composition at certain value, with increasing the
density, the system undergoes an intriguing re-entrant mixing, and the demixing
only occurs within certain intermediate density range. This suggests a new way
of designing active matter to drive the self-assembly of passive colloids and
fabricate dynamic responsive materials.Comment: Accepted in Soft Matter. Supplementary information can found at
https://www.dropbox.com/sh/xb3u5iaoucc2ild/AABFUyqjXips7ewaie2rFbj_a?dl=
Investigating the evolution of microtextured region in Ti-6242 using FE-FFT multiscale modeling method
Titanium alloy Ti-6242 (Ti-6Al-2Sn-4Zr-2Mo) is frequently used in the high-pressure compressor of aero engines due to its excellent resistance to fatigue and creep failure at high temperature. While exhibiting high strength at elevated temperatures, it is susceptible to dwell fatigue at temperatures below 473 K due in part to the presence of microtextured regions (MTRs), also known as macrozones. MTRs are clusters of similarly orientated alpha particles, which form during alpha/beta processing and remain stable even after large deformation. The major objective of this dissertation is to quantify the evolution of MTRs under different thermomechanical processing parameters, and predict the optimal processing parameters to eliminate the MTRs.Idealized MTRs with pure initial orientation are first employed as the benchmark case to investigate the loading direction effect on its breakdown efficiency. Three high-temperature compression processes are simulated with different loading directions using crystal plasticity finite element method, and the results are validated against high-temperature compression experiments and EBSD measurement. The evolution of equivalent plastic strain, accumulated shear strain, and misorientation distribution is analyzed in detail to reveal the relationship between loading direction and MTR breakdown efficiency. Lastly, the reorientation velocity divergence of arbitrary loading direction is expressed in the Rodrigues\u27 space in order to predict the optimal processing parameters for MTR elimination. The MTR breakdown efficiency also depends on the morphology and its position within the specimen. Two different length scales have to be analyzed in order to consider both factors, which present great challenge to the numerical simulation. In this dissertation, a high-efficient FE-FFT multiscale modeling framework is derived and developed to overcome this challenge. The Fourier-Galerkin method is utilized to solve the microscale unit cell problem, while total Lagrangian nite element is used to solve the macroscopic boundary value problems. Several numerical improvements are derived and implemented to further improve its numerical efficiency, including consistent linearization, consistent homogenized tangent stiffness, and inexact Newton method. A series of numerical studies is conducted to investigate the accuracy, efficiency, and robustness of this algorithm
Self-Assembled Chiral Photonic Crystals From Colloidal Helices Racemate
Chiral crystals consisting of micro-helices have many optical properties
while presently available fabrication processes limit their large-scale
applications in photonic devices. Here, by using a simplified simulation
method, we investigate a bottom-up self-assembly route to build up helical
crystals from the smectic monolayer of colloidal helices racemate. With
increasing the density, the system undergoes an entropy-driven
co-crystallization by forming crystals of various symmetries with different
helical shapes. In particular, we identify two crystals of helices arranged in
the binary honeycomb and square lattices, which are essentially composed by two
sets of opposite-handed chiral crystal. Photonic calculations show that these
chiral structures can have large complete photonic bandgaps. In addition, in
the self-assembled chiral square crystal, we also find dual polarization
bandgaps that selectively forbid the propagation of circularly polarized lights
of a specific handedness along the helical axis direction. The self-assembly
process in our proposed system is robust, suggesting possibilities of using
chiral colloids to assemble photonic metamaterials.Comment: Accepted in ACS Nan
Interpretation of 750 GeV Diphoton Excess at LHC in Singlet Extension of Color-octet Neutrino Mass Model
We propose that the possible 750 GeV diphoton excess can be explained in the
color-octet neutrino mass model extended with a scalar singlet . The
model generally contains species of color-octet, electroweak doublet
scalars and species of color-octet, electroweak triplet or
singlet fermions. While both scalars and fermions contribute to the
production of through gluon fusion, only the charged members induce the
diphoton decay of . The diphoton rate can be significantly enhanced due
to interference between the scalar and fermion loops. We show that the diphoton
cross section can be from 3 to 10 fb for O(TeV) color-octet particles while
evading all current LHC limits.Comment: 12 pages, 4 figures; v2: 13 pages, 4 figures, version to appear in
EPJC, clarified a few things, updated numerical analysis using the most
recent bound on color-octet fermions but without changing conclusions,
corrected a mistake when quoting the branching ratio to Z gamma, added some
references missed in v
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