Nucleation-induced transition to collective motion in active systems

While the existence of polar ordered states in active systems is well established, the dynamics of the self-assembly processes are still elusive. We study a lattice gas model of self-propelled elongated particles interacting through excluded volume and alignment interactions, which shows a phase transition from an isotropic to a polar ordered state. By analyzing the ordering process we find that the transition is driven by the formation of a critical nucleation cluster and a subsequent coarsening process. Moreover, the time to establish a polar ordered state shows a power-law divergence

Bronze Age globalisation and Eurasian impacts on later Jōmon social change

From northern China, millet agriculture spread to Korea and the Maritime Russian Far East by 3500–2700 BC. While the expansion of agricultural societies across the Sea of Japan did not occur until around 900 BC, the intervening period saw major transformations in the Japanese archipelago. The cultural florescence of Middle Jōmon central Honshu underwent a collapse and reorganisation into more decentralised settlements. Mobility increased as Late Jōmon influences spread from eastern into western Japan, and populations expanded to offshore islands such as Okinawa and the Kurils. In Kyushu and other parts of western Japan, the eastern Jōmon expansion was associated with the cultivation of adzuki and soybeans but, contrary to earlier assessments, there is no evidence for the introduction of cereal crops at this time. Here, we analyse archaeological and historical linguistic evidence of connections between the Eurasian mainland and the Japanese Islands c. 3500 to 900 BC. A re-evaluation of archaeological material discussed since the 1920s concludes that the transformations in Jōmon society during this period were at least in part a response to contacts with Eurasian Bronze Age cultures. Evidence for linguistic contact between Koreanic and the Ainuic languages which are presumed to have been spoken by Jōmon populations is also consistent with new Bronze Age mobilities. Although prehistoric Japan was one of the most isolated regions of Eurasia, we conclude that the historical evolution of societies in the Japanese archipelago after the third millennium BC was linked with processes of Bronze Age globalisation.紀元前 3500–2700 年頃、アワ・キビ農耕が中国東北部から朝鮮半島と極東ロシアに広がった. 農耕社会が実際に日本海を渡るのは、時代をはるかに下る紀元前900年頃まで待たねばならない. しかし、この時期、日本列島の縄文社会にも大きな変化がみられる. 中部地方の縄文中期文化の輝きは失われ、大型集落は放棄され、分散型居住パターンへと社会の再編成が行われた. 縄文後期の文化要素が東から西日本へ広がり、琉球列島や千島列島等の離島への移動が多くなり、社会の流動性が増した. 九州等、列島西部では、東方からの縄文文化がダイズ・アズキ栽培と共に広がった. 一方、この時期には穀物栽培の証拠は認められていない. 本論では、考古学と言語学の分析により起源前 3500~900 年頃の間のユーラシア大陸と日本列島の交流について検討する. そのうえで、 1920 年代以来議論された考古資料の再評価の結果、縄文後晩期の社会変化は少なくても部分的には大陸の青銅器時代文化との接触に起因すると論じる. 縄文人が話したと推定されるアイヌ語族(Ainuic)と朝鮮語族 (Koreanic) との言語的交流も青銅器時代の新しい流動性と一致する. 先史時代の日本列島はユーラシアで最も孤立した地域の一つだったにも関わらず、紀元前3千年紀後の列島の歴史的展開は青銅器時代のグローバリゼーションのプロセスと関連していたと結論する.- Introduction - Social Change in the Middle to Final Jōmon: Overview - Middle–Final Jōmon Interactions Between Continental East Asia and Japan -- Cultivated Plants and Domesticated Animals -- Agricultural Tools -- Bronze and Bronze Skeuomorphs -- The Itoku Site -- Stone Axes -- Linguistic Interaction - Discussion - Conclusion

Critical aging of a ferromagnetic system from a completely ordered state

We adapt the non-linear $\sigma$ model to study the nonequilibrium critical dynamics of O(n) symmetric ferromagnetic system. Using the renormalization group analysis in $d=2+\epsilon$ dimensions we investigate the pure relaxation of the system starting from a completely ordered state. We find that the average magnetization obeys the long-time scaling behavior almost immediately after the system starts to evolve while the correlation and response functions demonstrate scaling behavior which is typical for aging phenomena. The corresponding fluctuation-dissipation ratio is computed to first order in $\epsilon$ and the relation between transverse and longitudinal fluctuations is discussed.Comment: 5 pages, revtex

Gravity of Monopole and String and Gravitational Constant in 3He-A

We discuss the effective metric produced in superfluid 3He-A by such topological objects as radial disgyration and monopole. In relativistic theories these metrics are similar to that of the local string and global monopole correspondingly. But in 3He-A they have the negative angle deficit, which corresponds to the negative mass of the topological objects. The effective gravitational constant G in superfluid 3He-A, derived from the comparison with relativistic theories, is inversely proportional to the square of the gap amplitude Delta, which plays the part of the Planck energy cut-off. G depends on temperature and increases with T, which corresponds to the vacuum screening of the Newton's constant.Comment: Latex file, 10 pages, no figure

Global processes of anthropogenesis characterise the early Anthropocene in the Japanese Islands

Although many scholars date the onset of the Anthropocene to the Industrial Revolution or the post-1945 ‘Great Acceleration’, there is growing interest in understanding earlier human impacts on the earth system. Research on the ‘Palaeoanthropocene’ has investigated the role of fire, agriculture, trade, urbanisation and other anthropogenic impacts. While there is increasing consensus that such impacts were more important than previously realised, geographical variation during the Palaeoanthropocene remains poorly understood. Here, we present a preliminary comparative analysis of claims that pre-industrial anthropogenic impacts in Japan were significantly reduced by four factors: the late arrival of agriculture, an emphasis on wet-rice farming limited to alluvial plains, a reliance on seafood rather than domesticated animals as a primary source of dietary protein, and cultural ideologies of environmental stewardship. We find that none of these claims of Japanese exceptionalism can be supported by the archaeological and historical records. We make some suggestions for further research but conclude that the Japanese sequence appears consistent with global trends towards increased anthropogenic impacts over the course of the Palaeoanthropocene.Introduction Claims for Japanese environmental exceptionalism - Claim 1: late arrival of agriculture. - Claim 2: the sustainability of rice. - Claim 3: domesticated animals versus marine foods. - Claim 4: cultural ideologies of stewardship. Conclusion

Topological defects and shape of aromatic self-assembled vesicles

We show that the stacking of flat aromatic molecules on a curved surface results in topological defects. We consider, as an example, spherical vesicles, self-assembled from molecules with 5- and 6-thiophene cores. We predict that the symmetry of the molecules influences the number of topological defects and the resulting equilibrium shape.Comment: accepted as a Letter in the J. Phys. Chem.

Power laws and stretched exponentials in a noisy finite-time-singularity model

We discuss the influence of white noise on a generic dynamical finite-time-singularity model for a single degree of freedom. We find that the noise effectively resolves the finite-time-singularity and replaces it by a first-passage-time or absorbing state distribution with a peak at the singularity and a long time tail exhibiting power law or stretched exponential behavior. The study might be of relevance in the context of hydrodynamics on a nanometer scale, in material physics, and in biophysics.Comment: 10 pages revtex file, including 4 postscript-figures. References added and a few typos correcte

Classical self-forces in a space with a dispiration

We derive the gravitational and electrostatic self-energies of a particle at rest in the background of a cosmic dispiration (topological defect), finding that the particle may experience potential steps, well potentials or potential barriers depending on the nature of the interaction and also on certain properties of the defect. The results may turn out to be useful in cosmology and condensed matter physics.Comment: 5 pages, 4 figures, revtex4 fil

Logarithmic Corrections in Dynamic Isotropic Percolation

Based on the field theoretic formulation of the general epidemic process we study logarithmic corrections to scaling in dynamic isotropic percolation at the upper critical dimension d=6. Employing renormalization group methods we determine these corrections for some of the most interesting time dependent observables in dynamic percolation at the critical point up to and including the next to leading correction. For clusters emanating from a local seed at the origin we calculate the number of active sites, the survival probability as well as the radius of gyration.Comment: 9 pages, 3 figures, version to appear in Phys. Rev.

Crossover from Isotropic to Directed Percolation

Percolation clusters are probably the simplest example for scale--invariant structures which either are governed by isotropic scaling--laws (``self--similarity'') or --- as in the case of directed percolation --- may display anisotropic scaling behavior (``self--affinity''). Taking advantage of the fact that both isotropic and directed bond percolation (with one preferred direction) may be mapped onto corresponding variants of (Reggeon) field theory, we discuss the crossover between self--similar and self--affine scaling. This has been a long--standing and yet unsolved problem because it is accompanied by different upper critical dimensions: $d_c^{\rm I} = 6$ for isotropic, and $d_c^{\rm D} = 5$ for directed percolation, respectively. Using a generalized subtraction scheme we show that this crossover may nevertheless be treated consistently within the framework of renormalization group theory. We identify the corresponding crossover exponent, and calculate effective exponents for different length scales and the pair correlation function to one--loop order. Thus we are able to predict at which characteristic anisotropy scale the crossover should occur. The results are subject to direct tests by both computer simulations and experiment. We emphasize the broad range of applicability of the proposed method.Comment: 19 pages, written in RevTeX, 12 figures available upon request (from [email protected] or [email protected]), EF/UCT--94/2, to be published in Phys. Rev. E (May 1994