arXiv subjects

Pai-Yi Hsiao

Publications and source records attributed to Pai-Yi Hsiao.

At least 19 recordsLinked to original sources

arXiv2024

Two types of quaking and shear unjamming: state diagram for soft granular particles under shear

Understanding intermittency, an ubiquitous behavior in flows of packed grains, is pivotal for establishing the rheology of granular matter. A straightforward explanation has been missing despite the long development of theories at various levels of abstraction. Here, we propose the use of a Stribeck-Hertz model that starts with the classic Coulomb friction but takes into account the inter-particle tribology, i.e. the reduction of friction coefficient with sliding speed as is commonly observed. Our numerical experiments reveal a state diagram that covers a wide range of packing fractions and show that incorporating the tribology enables the occurrence of quaking intermittency in the mid-range of a newly established dimensionless shear rate, in consistence with prior experimental observations. Further study of the discontinuities in the evolution of mean contact number leads to our discovery of two types of quaking, that are distinguished by the abrupt increase or decrease of neighboring contacts and reveal different pathways of microstructural change underlying these discrete events. In contrast to the prevailing paradigm in which shear is believed to promote jamming at intermediate densities, our study demonstrates that shear can also unjam a granular system, and this occurrence depends on the shear rate.

cond-mat.soft↗

arXiv2019

Scaling Behaviors of a Polymer Ejected from a Cavity through a Small Pore

Langevin dynamics simulations are performed to investigate ejection dynamics of spherically confined flexible polymers through a pore. By varying the chain length $N$ and the initial volume fraction $ϕ_0$ of the monomers, two scaling behaviors for the ejection velocity $v$ on the monomer number $m$ in the cavity are obtained: $v \sim m^{1.25}ϕ_0^{1.25}/N^{1.6}$ for large $m$ and $v \sim m^{-1.4}$ as $m$ is small. A robust scaling theory is developed by dividing the process into the confined and the non-confined stages, and the dynamical equation is derived via the study of energy dissipation. After trimming the prior stage related to the escape of the head monomer across the pore, the evolution of $m$ is shown to be well described by the scaling theory. The ejection time exhibits two proper scaling behaviors: $N^{2/(3ν)+y_1}ϕ_0^{-2/(3ν)}$ and $N^{2+y_2}$ under the large and small $ϕ_0$- or $N$-conditions, respectively, where $y_1=1/3$, $y_2=1-ν$, and $ν$ is the Flory exponent.

cond-mat.soft↗

arXiv2019

Crumple-Origami Transition for Twisting Cylindrical Shells

Origami and crumpling are two extreme tools to shrink a 3-D shell. In the shrink/expand process, the former is reversible due to its topological mechanism, while the latter is irreversible because of its random-generated creases. We observe a morphological transition between origami and crumple states in a twisted cylindrical shell. By studying the regularity of crease pattern, acoustic emission and energetics from experiments and simulations, we develop a model to explain this transition from frustration of geometry that causes breaking of rotational symmetry. In contrast to solving von Karman-Donnell equations numerically, our model allows derivations of analytic formula that successfully describe the origami state. When generalized to truncated cones and polygonal cylinders, we explain why multiple and/or reversed crumple-origami transitions can occur.

cond-mat.soft↗

arXiv2019

Crumpling an elasto-plastic thin sphere

The phenomenon of crumpling is common in our daily life and nature. It exhibits many interesting properties, such as ultra-tough resistance to pressure with less than 30$\%$ of volume density, power-law relation for pressure vs density, and crackling noises with occurrence frequency vs intensity mimicking that of earthquakes. These results are mainly obtained by using flat thin sheets. But, in reality the majority of crumpled objects exhibit nonzero intrinsic curvatures. Notable examples are crushed aluminum cans, car wreckage, and cells move in and out of blood vessels. In this work we concentrate on establishing the fact that they behave very differently from flat sheets by employing both experiments and molecular dynamics simulations.

cond-mat.mtrl-sci↗

arXiv2018

Size Scaling of Neutral Polymers and Charged Polymers in Nanochannels

We expand the blob theory for freely-jointed chains and perform molecular dynamics simulations to study the behavior of polymers confined in cylindrical channels. From weak to strong confinement, five scaling regimes, de Gennes, extended de Gennes, transition, backfolding, and Odijk regimes, are distinguished for neutral polymers.The size scalings in each regime are derived as a function of the channel width. The scaling exponents $-1$ and $-1/3$ are obtained for the transition and backfolding regimes, respectively, which result from the reduction of the excluded volume of the segments by restriction of the segment's orientation in the narrowed channels. For charged flexible chains, the de Gennes regime is split into Flory-de Gennes and electro-de Gennes regimes owing to strong Coulomb repulsion in electrostatic blobs. Nonetheless, the extended de Gennes and transition regimes are shrunken. The study of the fluctuations of the chain size shows consistent scaling demarcations for both the neutral and charged chain systems.

cond-mat.soft↗

arXiv2013

Effect of Ridge-Ridge Interactions in Crumpled Thin Sheets

We study whether and how the energy scalings based on the single-ridge approximation are revised in an actual crumpled sheet; namely, in the presence of ridge-ridge interactions. Molecular Dynamics Simulation is employed for this purpose. In order to improve the data quality, modifications are introduced to the common protocol. As crumpling proceeds, we find that the average storing energy changes from being proportional to one-third of the ridge length to a linear relation, while the ratio of bending and stretching energies decreases from 5 to 2. The discrepancy between previous simulations and experiments on the material-dependence for the power-law exponent is resolved. We further determine the averaged ridge length to scale linearly with the crumpled ball size $R$, the ridge number as $1/R^2$, and the average storing energy per unit ridge length as $1/R^{2.364\sim 2.487}$. These results are consistent with the mean-field predictions. Finally, we extend the existent simulations to the high-pressure region for completeness, and verify the existence of a new scaling relation that is more general than the familiar power law at covering the whole density range.

cond-mat.soft↗

arXiv2011

Polyelectrolytes in Multivalent Salt Solutions under the Action of DC Electric Fields

We study conformational and electrophoretic properties of polyelectrolytes (PEs) in tetravalent salt solutions under the action of electric fields by means of molecular dynamics simulations. Chain conformations are found to have a sensitive dependence on salt concentration $C_s$. As $C_s$ is increased, the chains first shrink to a globular structure and subsequently reexpand above a critical concentration $C_s^*$. An external electric field can further alter the chain conformation. If the field strength $E$ is larger than a critical value $E^*$, the chains are elongated. $E^*$ is shown to be a function of $C_s$ by using two estimators $E_{I}^*$ and $E_{II}^*$ through the study of the polarization energy and the onset point of chain unfolding, respectively. The electrophoretic mobility of the chains depends strongly on $C_s$, and the magnitude increases significantly, accompanying the chain unfolding, when $E> E_{II}^*$. We study the condensed ion distributions modified by electric fields and discuss the connection of the modification with the change of chain morphology and mobility. Finally, $E^*$ is studied by varying the chain length $N$. The inflection point is used as a third estimator $E_{III}^*$. $E_{III}^*$ scales as $N^{-0.63(4)}$ and $N^{-0.76(2)}$ at $C_s=0.0$ and $C_s^*$, respectively. $E_{II}^*$ follows a similar scaling law to $E_{III}^*$ but a crossover appears at $C_s=C_s^*$ when $N$ is small. The $E_{I}^*$ estimator fails to predict the critical field, which is due to oversimplifying the critical polarization energy to the thermal energy. Our results provide valuable information to understand the electrokinetics of PE solutions at the molecular level and could be helpful in micro/nano-fluidics applications.

cond-mat.soft↗

arXiv2011

Pore-Spanning Lipid Membrane under Indentation by a Probe Tip: a Molecular Dynamics Simulation Study

We study the indentation of a free-standing lipid membrane suspended over a nanopore on a hydrophobic substrate by means of molecular dynamics simulations. We find that in the course of indentation, the membrane bends at the point of contact, and the fringes of the membrane glide downward intermittently along the pore edges and stop gliding when the fringes reach the edge bottoms. The bending continues afterwards, and the large strain eventually induces a phase transition in the membrane, transformed from a bilayered structure to an interdigitated structure. The membrane is finally ruptured when the indentation goes deep enough. Several local physical quantities in the pore regions are calculated, which include the tilt angle of lipid molecules, the nematic order, the included angle and the distance between neighboring lipids. The variations of these quantities reveal many detailed, not-yet-specified local structural transitions of lipid molecules under indentation. The force-indentation curve is also studied and discussed. The results make connection between the microscopic structure and the macroscopic properties, and provide deep insight in the understanding of the stability of a lipid membrane spanning over a nanopore.

cond-mat.soft↗

arXiv2010

Unfolding Collapsed Polyelectrolytes in Alternating-Current Electric Fields

We investigate the unfolding of single polyelectrolyte (PE) chains collapsed by trivalent salt under the action of alternating-current (AC) electric fields through computer simulations and theoretical scaling. The results show that a collapsed chain can be unfolded by an AC field when the field strength exceeds the direct-current (DC) threshold and the frequency is below a critical value, corresponding to the inverse charge relaxation/dissociation time of condensed trivalent counterions at the interface of the collapsed electrolyte. This relaxation time is also shown to be identical to the DC chain fluctuation time, suggesting that the dissociation of condensed polyvalent counterion on the collapsed PE interface controls the polyelectrolyte dipole formation and unfolding dynamics under an AC electric field.

cond-mat.soft↗

arXiv2009

Effect of chain stiffness on ion distributions around a polyelectrolyte in multivalent salt solutions

Ion distributions in dilute polyelectrolyte solutions are studied by means of Langevin dynamics simulations. We show that the distributions depend on the conformation of a chain while the conformation is determined by the chain stiffness and the salt concentration. We observe that the monovalent counterions originally condensed on a chain can be replaced by the multivalent ones dissociated from the added salt due to strong electrostatic interaction. These newly condensed ions give an important impact on the chain structure. At low and at high salt concentrations, the conformation of a semiflexible chain is rodlike. The ion distributions show similarity to those for a rigid chain, but difference to those for a flexible chain whose conformation is a coil. In the mid-salt region, the flexible chain and the semiflexible chain collapse but the collapsed chain structures are, respectively, disordered and ordered structures. The ion distributions hence show different profiles for these three chain stiffness with the curves for the semiflexible chain lying between those for the flexible and the rigid chains. The number of the condensed multivalent counterions, as well as the effective chain charge, also shows similar behavior, demonstrating a direct connection with the chain morphology. Moreover, we find that the condensed multivalent counterions form triplets with two adjacent monomers and are localized on the chain axis at intermediate salt concentration when the chain stiffness is semiflexible or rigid. The microscopic information obtained here provides valuable insight to the phenomena of DNA condensation and is very useful for researchers to develop new models.

cond-mat.soft↗

arXiv2009

An ac field probe for the magnetic ordering of magnets with random anisotropy

A Monte Carlo simulation is carried out to investigate the magnetic ordering in magnets with random anisotropy (RA). Our results show peculiar similarities to recent experiments that the real part of ac susceptibility presents two peaks for weak RA and only one for strong RA regardless of glassy critical dynamics manifested for them. We demonstrate that the thermodynamic nature of the low-temperature peak is a ferromagnetic-like dynamic phase transition to quasi-long range order (QLRO) for the former. Our simulation, therefore, is able to be incorporated with the experiments to help clarify the existence of the QLRO theoretically predicted so far.

cond-mat.mtrl-sci↗

arXiv2009

Unfolding Polyelectrolytes in Trivalent Salt Solutions Using DC Electric Fields: A Study by Langevin Dynamics Simulations

We study the behavior of single linear polyelectrolytes condensed by trivalent salt under the action of electric fields through computer simulations. The chain is unfolded when the strength of the electric field is stronger than a critical value. This critical electric field follows a scaling law against chain length and the exponent of the scaling law is $-0.77(1)$, smaller than the theoretical prediction, $-3ν/2$ [Netz, Phys. Rev. Lett. 90 (2003) 128104], and the one obtained by simulations in tetravalent salt solutions, $-0.453(3)$ [Hsiao and Wu, J. Phys. Chem. B 112 (2008) 13179]. It demonstrates that the scaling exponent depends sensitively on the salt valence. Hence, it is easier to unfold chains condensed by multivalent salt of smaller valence. Moreover, the absolute value of chain electrophoretic mobility increases drastically when the chain is unfolded in an electric field. The dependence of the mobility on electric field and chain length provides a plausible way to impart chain-length dependence in free-solution electrophoresis via chain unfolding transition induced by electric fields. Finally, we show that, in addition to an elongated structure, a condensed chain can be unfolded into an U-shaped structure. The formation of this structure in our study is purely a result of the electric polarization, but not of the elasto-hydrodynamics dominated in sedimentation of polymers.

cond-mat.soft↗

arXiv2009

Comment on "Critical and slow dynamics in a bulk metallic glass exhibiting strong random magnetic anisotropy" [Appl. Phys. Lett. 92, 011923 (2008)]

In this comment, by using Monte Carlo simulation, we show that the perpendicular shift of hysteresis loops reported in the commented work is nothing special but simply due to the fact that the range of field does not surpass the reversible field beyond which the two branches of the loop merge. If the reversible field is exceeded, the shift is no longer observed. Moreover, we point out that even using a small range of field, the shift will not be observed if the observation time is long enough for the reversible field to drop within the range.

cond-mat.mtrl-sci↗

arXiv2009

Exchange-driven Collective Behavior in a 3D Array of Nanoparticles

A Monte Carlo simulation is performed in a cubic lattice of interacting identical Stoner-Woldfarth nanoparticles. The model system is a randomly-anisotropic Heisenberg spin system with a small anisotropy-to-exchange ratio D/J = 3.5. The dc susceptibility, chi(dc)(T), shows a Curie-Weiss-like transition at a temperature T-C/J approximate to 1.5, followed by a low-temperature glassy behavior manifested by cusps in both the zero-field-cooled and the field-cooled curves. The ac susceptibility, chi(ac) (T, omega), at various frequencies, w, shows that with decreasing temperature, a non-Arrhenius dispersive peak occurs at T-b(omega), succeeded by another dispersionless peak at T-g/J approximate to 1.20 in the in-phase part, chi'(T, omega), of chi (T, omega) while the out-of-phase part, chi '' (T, omega), shows only one peak. A dynamic scaling analysis shows that the system exhibits a critical slowing-down at T-g with a quite small exponent zv approximate to 1.65. However, no universal collapse is seen for the fully-scaled data of chi '' (T, omega). These observed behaviors are interpreted under the droplet-like hypothesis that the formation and development of exchange-induced correlated clusters drive ensembles of nanoparticles undergoing a transition from a paramagnetic order to a short-range order (SRO) at T-C, followed by a transition at T-g to the magnetic state in which a magnetic glassy order and a magnetic quasi-long-range order (QLRO) coexist. In addition, our simulation shows that the onset of the latter transition, which is peculiarly manifested by the dispersionless peak, occurs only for those ensembles possessing the anisotropy strength in the region 1.0 <= D/J <= 5.0.....

cond-mat.stat-mech↗

arXiv2009

Mangetic phase transition for three-dimensional Heisenberg weak random anisotropy model: Monte Carlo study

Magnetic phase transition (MPT) to magnetic quasi-long-range order (QLRO) phase in a three-dimensional Heisenberg weak (D/J=4) random anisotropy (RA) model is investigated by Monte Carlo simulation. The isotropic and cubic distributions of RA axes are considered for simple-cubic-lattice systems. Finite-size scaling analysis shows that the critical couplings for the former and latter are K_c= 0.70435(2) and K_c=0.70998(4), respectively. While the critical exponent 1/ν=1.40824(0) is the same for both cases. A second-order MPT to the QLRO phase is therefore evidenced to be possible in favor with the existence of the QLRO predicted by recent functional renormalization group theories.

cond-mat.stat-mech↗

arXiv2009

Strong Asymmetric Effect of Lattice Mismatch on Epilayer Structure in Metal Thin Film Deposition

We investigate the hetero-epitaxial growth of thin film deposited on a (001) substrate via molecular dynamics simulations, using six fcc transition metals as our modeling systems. By studying the radial distribution function in the film layers, we demonstrate the importance of the sign of lattice mismatch on the layer structure. For positive lattice mismatches, the film favors pseudomorphic growth, whereas for negative mismatches, a sharp transition happens within the first few monolayers of adatoms and the film layers are transformed into the close-packed (111) structure. We propose a way to quantify the compositional percentage of different planar structures in an epilayer, and demonstrate the strong asymmetric effect between the tensile and compressive cases of deposition. How temperature affects the asymmetry is also discussed.

cond-mat.mtrl-sci↗

arXiv2009

Stick-release pattern in stretching single condensed polyelectrolyte toroids

Using Langevin dynamics simulations, we study elastic response of single semiflexible polyelectrolytes to an external force pulling on the chain ends, to mimic the stretching of DNA molecules by optical tweezers. The linear chains are condensed by multivalent counterions into toroids. The force-extension curve shows a series of sawtooth-like structure, known as the stick-release patterns in experiments. We demonstrate that these patterns are a consequence of the loop-by-loop unfolding of the toroidal structure. Moreover, the dynamics, how the internal structure of chain varies under tension, is examined. At the first stage of the stretching, the toroidal condensate decreases its size until the loss of the first loop in the toroid and then, oscillates around this size for the rest of the unfolding process. The normal vector of the toroid is pulled toward the pulling-force direction and swings back to its early direction repeatedly when the toroidal chain looses a loop. The results provide new and valuable information concerning the elasticity and the microscopic structure and dynamic pathway of salt-condensed DNA molecules being stretched.

cond-mat.soft↗

arXiv2008

Free Solution Electrophoresis of Homopolyelectrolytes

We investigate the behavior of single polyelectrolytes in multivalent salt solutions under the action of electric fields through computer simulations. The chain is unfolded in a strong electric field and aligned parallel to the field direction, and the chain size shows a sigmoidal transition. The unfolding electric field $E^*$ depends on the salt concentration and scales as $V^{-1/2}$ with $V$ being the ellipsoidal volume occupied by the chain. The magnitude of the electrophoretic mobility of chain drastically increases during the unfolding. The fact that $E^*$ depends on the chain length provides a plausible mechanism to separate long charged homopolymers by size in free solution electrophoresis via the unfolding transition of globule polyelectrolytes condensed by multivalent salt.

cond-mat.soft↗