Yonathan Shapir

Bio: Yonathan Shapir is an academic researcher from University of Rochester. The author has contributed to research in topics: Scaling & Diffusion-limited aggregation. The author has an hindex of 15, co-authored 37 publications receiving 809 citations. Previous affiliations of Yonathan Shapir include Technion – Israel Institute of Technology & Brookhaven National Laboratory.

Interface pinning and dynamics in random systems.

Abstract: A detailed low-temperature treatment of the domain wall or interface pinning by imperfections in disordered systems with discrete symmetry of the order parameter is presented. Crossover behavior as well as analogies between pinning mechanisms in different systems is analyzed. Pinning may arise from random bonds, when the disordering agents do not break the local symmetry of the order parameter, or from random fields, when the disordering agents do break this symmetry. The interface roughness and response to an external driving force are discussed. The model is explained for dilute magnetic systems in a uniform field where the magnetic domain walls are pinned by random fields and/or random bonds. The results are, however, more general and apply also to interfaces in other systems, e.g., in fluid-fluid interfaces, (anti)ferroelectrics, solitons in incommensurate systems, etc. The interface roughness and pinning pressure (force per unit area) are estimated for weak and strong pinning and their scaling relations to length scale, temperature, frequency, and disorder strength (concentration) are given. The interface contribution to the static and dynamic susceptibility at low temperatures is evaluated. Because of pinning, the low-temperature dynamical susceptibility of disordered ferromagnets in or out of equilibrium carries a [ln(1/\ensuremath{\omega})${]}^{2/\mathrm{\ensuremath{\theta}}}$ frequency dependence in addition to the Debye relaxation behavior. In particular, \ensuremath{\theta}=(d+1)/3 for random-field systems, and \ensuremath{\theta}(d=2)=1/3 and \ensuremath{\theta}(d=3)\ensuremath{\approxeq}0.83 for random-bond systems.

Improved kinetic renormalisation group approach to diffusion-limited aggregation

Abstract: An improved kinetic renormalisation group approach to diffusion-limited aggregation is presented. This approach is based on the growth process itself and accounts for the dispersity in the growth probabilities. It yields the multifractal spectrum D(q) with better values at smaller q. On the 2D square lattice the authors find Df=1.694 for the fractal dimensions of the cluster and that of its interface, and D(1)=1.01 for the information dimension. The former agrees with the simulation results (Df approximately=1.70) and the latter compares very well with the exact value D(1)=1.

Maximal height scaling of kinetically growing surfaces.

Abstract: The scaling properties of the maximal height of a growing self-affine surface with a lateral extent L are considered. In the late-time regime its value measured relative to the evolving average height scales like the roughness: h*(L) approximately L alpha. For large values its distribution obeys logP(h*(L)) approximately (-)A(h*(L)/L(alpha))(a). In the early-time regime where the roughness grows as t(beta), we find h*(L) approximately t(beta)[lnL-(beta/alpha)lnt+C](1/b), where either b = a or b is the corresponding exponent of the velocity distribution. These properties are derived from scaling and extreme-value arguments. They are corroborated by numerical simulations and supported by exact results for surfaces in 1D with the asymptotic behavior of a Brownian path.

Interference of directed paths in disordered systems.

Abstract: We consider sums over directed paths, interfering due to quenched random elements controlling either the phase or the sign of each term. The former enter the determination of electronic transport in the localized regime, and the latter that of correlations in the high-temperature phase of the Ising spin-glass. Numerical computations in two dimensions indicate anomalous fluctuations dominated by untypical paths, with scaling behavior similar to that of random but positive impurities. This is argued to follow from a bound state, due to a subtle attraction between pairs, in replica space.

Fractal-mound growth of pentacene thin films

Abstract: The growth mechanism of pentacene film formation on $\mathrm{Si}{\mathrm{O}}_{2}$ substrate was investigated with a combination of atomic force microscopy measurements and numerical modeling. In addition to the diffusion-limited aggregation (DLA) that has already been shown to govern the growth of the ordered pentacene thin films, it is shown here that the Schwoebel barrier effect steps in and disrupts the desired epitaxial growth for the subsequent layers, leading to mound growth. The terraces of the growing mounds have a fractal dimension of 1.6, indicating a lateral DLA shape. This growth morphology thus combines horizontal DLA-like growth with vertical mound growth.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Localization: theory and experiment

Abstract: The transport properties of disordered solids have been the subject of much work since at least the 1950s, but with a new burst of activity during the 1980s which has survived up to the present day. There have been numerous reviews of a more or less specialized nature. The present review aims to fill the niche for a non-specialized review of this very active area of research. The basic concepts behind the theory are introduced with more detailed sections covering experimental results, one-dimensional localization, scaling theory, weak localization, magnetic field effects and fluctuations.