arXiv subjects

B. Kahng

Publications and source records attributed to B. Kahng.

141 records · Page 8Linked to original sources

arXiv2001

Spectra and eigenvectors of scale-free networks

We study the spectra and eigenvectors of the adjacency matrices of scale-free networks when bi-directional interaction is allowed, so that the adjacency matrix is real and symmetric. The spectral density shows an exponential decay around the center, followed by power-law long tails at both spectrum edges. The largest eigenvalue λ_1 depends on system size N as λ_1 \sim N^{1/4} for large N, and the corresponding eigenfunction is strongly localized at the hub, the vertex with largest degree. The component of the normalized eigenfunction at the hub is of order unity. We also find that the mass gap scales as N^{-0.68}.

cond-mat.stat-mech↗

arXiv2000

Modeling relaxation and jamming in granular media

We introduce a stochastic microscopic model to investigate the jamming and reorganization of grains induced by an object moving through a granular medium. The model reproduces the experimentally observed periodic sawtooth fluctuations in the jamming force and predicts the period and the power spectrum in terms of the controllable physical parameters. It also predicts that the avalanche sizes, defined as the number of displaced grains during a single advance of the object, follow a power-law, $P(s)\sim s^{-τ}$, where the exponent is independent of the physical parameters.

cond-mat.soft↗

arXiv2000

Depinning of an anisotropic interface in random media: The tilt effect

We study the tilt dependence of the pinning-depinning transition for an interface described by the anisotropic quenched Kardar-Parisi-Zhang equation in 2+1 dimensions, where the two signs of the nonlinear terms are different from each other. When the substrate is tilted by m along the positive sign direction, the critical force F_c(m) depends on m as F_c(m)-F_c(0) \sim -|m|^{1.9(1)}. The interface velocity v near the critical force follows the scaling form v \sim |f|^θΨ_{\pm}(m^2 /|f|^{θ+ϕ}) with θ= 0.9(1) and ϕ= 0.2(1), where f \equiv F-F_c(0) and F is the driving force.

cond-mat.stat-mech↗

arXiv2000

Quantum Dot and Hole Formation in Sputter Erosion

Recently it was experimentally demonstrated that sputtering under normal incidence leads to the formation of spatially ordered uniform nanoscale islands or holes. Here we show that these nanostructures have inherently nonlinear origin, first appearing when the nonlinear terms start to dominate the surface dynamics. Depending on the sign of the nonlinear terms, determined by the shape of the collision cascade, the surface can develop regular islands or holes with identical dynamical features, and while the size of these nanostructures is independent of flux and temperature, it can be modified by tuning the ion energy.

cond-mat↗

arXiv1999

Jamming and Fluctuations in Granular Drag

We investigate the dynamic evolution of jamming in granular media through fluctuations in the granular drag force. The successive collapse and formation of jammed states give a stick-slip nature to the fluctuations which is independent of the contact surface between the grains and the dragged object -- thus implying that the stress-induced collapse is nucleated in the bulk of the granular sample. We also find that while the fluctuations are periodic at small depths, they become "stepped" at large depths, a transition which we interpret as a consequence of the long-range nature of the force chains.

cond-mat.dis-nn↗

arXiv1999

Nonequilibrium phase transition by directed Potts particles

We introduce an interface model with q-fold symmetry to study the nonequilibrium phase transition (NPT) from an active to an inactive state at the bottom layer. In the model, q different species of particles are deposited or are evaporated according to a dynamic rule, which includes the interaction between neighboring particles within the same layer. The NPT is classified according to the number of species q. For q=1 and 2, the NPT is characterized by directed percolation, and the directed Ising class, respectively. For $q \ge 3$, the NPT occurs at finite critical probability p_c, and appears to be independent of q; the $q=\infty$ case is related to the Edwards-Wilkinson interface dynamics.

cond-mat.stat-mech↗

arXiv1999

Dynamics of ripple formation in sputter erosion: nonlinear phenomena

Many morphological features of sputter eroded surfaces are determined by the balance between ion induced linear instability and surface diffusion. However, the impact of the nonlinear terms on the morphology is less understood. We demonstrate that while at short times ripple formation is described by the linear theory, after a characteristic time the nonlinear terms determine the surface morphology by either destroying the ripples, or generating a new rotated ripple structure. We show that the morphological transitions induced by the nonlinear effects can be detected by monitoring the surface width and the erosion velocity.

cond-mat↗

arXiv1998

Nonequilibrium roughening transition by two-species particles

We introduce an interface growth model exhibiting a nonequilibrium roughening transition (NRT). In the model, particles consist of two species, and deposit or evaporate on one dimensional substrate according to a given dynamic rule. When the dynamics is limited to occur on monolayer, this model has two absorbing states, belonging to the directed Ising (DI) universality class. At criticality, the density of vacant sites at the bottom layer in the growth model decays faster than the DI behavior, however, the dynamic exponent is close to the DI value, suggesting that the dynamics is related to the DI universality class. We also consider an asymmetric version of the growth dynamics, which is according to the directed percolation behavior.

cond-mat.stat-mech↗

arXiv1998

Numerical test of the damping time of layer-by-layer growth on stochastic models

We perform Monte Carlo simulations on stochastic models such as the Wolf-Villain (WV) model and the Family model in a modified version to measure mean separation $\ell$ between islands in submonolayer regime and damping time $\tilde t$ of layer-by-layer growth oscillations on one dimension. The stochastic models are modified, allowing diffusion within interval $r$ upon deposited. It is found numerically that the mean separation and the damping time depend on the diffusion interval $r$, leading to that the damping time is related to the mean separation as ${\tilde t} \sim \ell^{4/3}$ for the WV model and ${\tilde t} \sim \ell^2$ for the Family model. The numerical results are in excellent agreement with recent theoretical predictions.

cond-mat.stat-mech↗

arXiv1998

Facet Formation in the Negative Quenched Kardar-Parisi-Zhang Equation

The quenched Kardar-Parisi-Zhang (QKPZ) equation with negative non-linear term shows a first order pinning-depinning (PD) transition as the driving force $F$ is varied. We study the substrate-tilt dependence of the dynamic transition properties in 1+1 dimensions. At the PD transition, the pinned surfaces form a facet with a characteristic slope $s_c$ as long as the substrate-tilt $m$ is less than $s_c$. When $m s_c$. We explain these features from a pinning mechanism involving a localized pinning center and the self-organized facet formation.

cond-mat.stat-mech↗

arXiv1997

Island Density in Homoepitaxial Growth:Improved Monte Carlo Results

We reexamine the density of two dimensional islands in the submonolayer regime of a homoepitaxially growing surface using the coarse grained Monte Carlo simulation with random sequential updating rather than parallel updating. It turns out that the power law dependence of the density of islands on the deposition rate agrees much better with the theoretical prediction than previous data obtained by other methods if random sequential instead of parallel updating is used.

cond-mat.stat-mech↗

arXiv1996

Anomalous Height Fluctuation Width in Crossover from Random to Coherent Surface Growths

We study an anomalous behavior of the height fluctuation width in the crossover from random to coherent growths of surface for a stochastic model. In the model, random numbers are assigned on perimeter sites of surface, representing pinning strengths of disordered media. At each time, surface is advanced at the site having minimum pinning strength in a random subset of system rather than having global minimum. The subset is composed of a randomly selected site and its $(\ell-1)$ neighbors. The height fluctuation width $W^2(L;\ell)$ exhibits the non-monotonic behavior with $\ell$ and it has a minimum at $\ell^*$. It is found numerically that $\ell^*$ scales as $\ell^*\sim L^{0.59}$, and the height fluctuation width at that minimum, $W^2(L;\ell^*)$, scales as $\sim L^{0.85}$ in 1+1 dimensions. It is found that the subset-size $\ell^*(L)$ is the characteristic size of the crossover from the random surface growth in the KPZ universality, to the coherent surface growth in the directed percolation universality.

cond-mat.stat-mech↗

arXiv1995

Renormalization group analysis of the anisotropic Kardar-Parasi-Zhang equation with spatially correlated noise

We analyze the anisotropic Kardar-Parisi-Zhang equation in general substrate dimensions $d'$ with spatially correlated noise, $\langle\tilde η({\bf{k}},ω)\rangle=0$ and $\langle\tilde η({\bf{k}},ω) \tilde η({\bf{k}}',ω')\rangle$ $=2D(k)δ^{d'}({\bf{k}}+{\bf{k}}')δ(ω+ω')$ where $D(k)=D_0+D_ρk^{-2ρ}$, using the dynamic renormalization group (RG) method. When the signs of the nonlinear terms in parallel and perpendicular directions are opposite, a novel finite stable fixed point is found for $d'< d'_c \equiv 2+2ρ$ within one-loop order. The roughening exponent $α$ and the dynamic exponent $z$ associated with the stable fixed point are determined as $α={2 \over 3}\big(ρ-{{d'-2}\over 2}\big)$, and $z=2-α$. For $d' > d'_c$, the RG transformations flow to the fixed point of the weak-coupling limit, so that the dynamic exponent becomes $z=2$.

cond-mat↗

arXiv1993

Avalanche size distribution in the Toom interface

We present numerical data of the height-height correlation function and of the avalanche size distribution for the three dimensional Toom interface. The height-height correlation function behaves samely as the interfacial fluctuation width, which diverges logarithmically with space and time for both unbiased and biased cases. The avalanche size defined by the number of changing sites caused by a single noise process, exhibits an exponentially decaying distribution, which is in contrast to power-law distributions appearing in typical self-organized critical phenomena. We also generalize the Toom model into arbitrary dimensions.

cond-mat↗

arXiv1993

Dynamics of Toom interface in three dimensions

We introduce a novel three dimensional Toom model on bcc lattice, and study its physical properties. In low-noise limit, the model leads to an effective solid-on-solid-type model, which exhibits a stationary interface via depositions and evaporations with avalanche process. We find that the model is described by the Edwards-Wilkinson equation for unbiased case and the anisotropic-Kardar-Parisi-Zhang equation in the weak-coupling limit for biased case. Thus the square of the surface width diverges logarithmically with space and time for both unbiased and biased cases.

cond-mat↗