Search

International audience; Agriculture is responsible for supplying food, feed, fibres, and an increasing fraction of fuel and raw chemicals for industry. Fulfilling such demands sustainably is one of the major challenges of our time. In this metadata analysis, we offer a quantitative overview of how scientists have been addressing the effects of nanomaterials on plants between 2009 and 2022. The analysis showed that cultivated crops (55%) and plant nutrients (52%) are mostly employed in the studies, pointing to the relevance of these aspects to agriculture. Nevertheless, it also revealed that the concentration of elements as nanomaterials is, generally, more than 2-fold higher than the elemental concentration applied as traditionally formulated fertilisers or those naturally found in soil. Furthermore, the median time span of most studies, i.e., 49 days for plants cultivated in soil, is still quite short compared to annual crop life cycles (90-120 days), and little attention (19% of treatments) has been devoted to soil microorganisms. Also, only a small fraction of experiments (6%) has been carried out under field conditions. Therefore, the data did not allow establishing correlations between effects and experimental parameters, such as concentration range, soil pH, or time of exposure. These observations point to the intricate relationship between our ability to infer conclusions and the experimental design employed. Finally, this comprehensive and up-to-date overview of the effects of nanomaterials in plant systems raises the question of whether nanomaterials will lead to incremental yield gains by replacing current inputs with nanotechnology-based ones, such as the controlled release of fertilizers and pesticides, or it will disrupt agriculture by attacking problems so far not practically addressed, such as hacking plant stress and defence mechanisms or modulating metabolism and photosystems.

In this paper, we study the transport properties (percolation and conductivity) of a two-dimensional structure created by depositing dimers on a one-dimensional substrate where multilayer deposition is allowed. Specifically, we are interested in studying how the mentioned properties vary as a function of the height of the multilayer. The critical parameters of the percolation transition are calculated using finite-size scaling analysis, obtaining the scaling laws for the probability of percolation and the conductivity of the system. To calculate the electrical conductivity of the multilayer, we use the Frank-Lobb algorithm.

Crumpled thin sheets are complex fractal structures whose physical properties are influenced by a hierarchy of ridges. In this paper, we report experiments that measure the stress-strain relation and show the coexistence of phases in the stretching of crumpled surfaces. The pull stress showed a change from a linear Hookean regime to a sublinear scaling with an exponent of 0.65±0.03, which is identified with the Hurst exponent of the crumpled sheets. The stress fluctuations are studied. The statistical distribution of force peaks is analyzed. It is shown that the unpacking of crumpled sheets is guided by a hierarchical order of ridges.

This paper describes an experiment with two touching rotating disks, whose movement is followed by video analysis. Within the disks’ movements, there are intervals with sliding and intervals without sliding, that is, intervals with frictional forces between the touching surfaces and intervals without it. This system configuration allows for measurement of the changeable magnitudes and directions of frictional forces (much more difficult to set up with translational motion). This activity may be used to combat students misconceptions of “frictional force always opposes the motion” and “between the same two bodies, one gets the same frictional force,” commonly found in the classroom, or just to reinforce the rotational dynamics relationships.

The mass-extinction events caused by human-driven habitat loss are a current concern in conservation science. However, the observed number of extinctions is considerably smaller than predicted. The overestimation of extinction rates comes from the time-delay which depends on the species sensitivity to habitat changes. The standard method of predicting the effect of habitat loss on biodiversity is to use the species–area relationship and progressively following it backwards to smaller areas. The difference between the actual number of species and the one provided by the backwards species–area relationship is dubbed extinction debt. Previous studies in general adopt a static view for the spatial distribution of species. Nonetheless, a precise understanding of the problem urges us to adopt a dynamic framework to this issue since the time between disturbances of the landscape plays an active role in influencing the strength of the extinction debt. In this context, here we address two distinct approaches for this question: a static and a dynamic view of fragmentation. In the former we quantify the extinction debt in a quenched spatial distribution of species, whereas in the latter the community is let to evolve between disturbance events of the landscape. Here we show that the size of the extinction debt depends on the pattern of the fragmentation. It is found that random distributions of destroyed habitats provide larger extinction debts than those obtained for contiguous areas of fragmentation. Furthermore, in the dynamic approach it is observed that dispersal can lead to unexpected outcomes such as lower biodiversity levels than ones inferred from the backwards species–area relationship.

Crumpled thin foils as exemplified by crumpled paper balls are complex fractal structures that belong to the class of auxetic materials, i.e. materials with negative Poisson coefficient. Here we report evidence that the unpacking of a crumpled surface is controlled asymptotically by a strain-strain relation similar in form to the Richardson scaling which describes the diffusion of particles in a turbulent fluid. This relationship was found using several photographs that recorded the expansion of the transverse deformation of the crumpled paper balls. Through an image analysis program we show that the average transversal expansion ? (or the maximum transverse distance ??' ) exhibits an asymptotic power law scaling with the pull strain ?x. The analysis of the photographs of transverse dilatation also showed some aspects similar to those found in L?vy's walking statistics.

Aim The aim of this study was to design, develop and compare ultrasound tips with different angulations on time required for cast post removal. Materials and methods To test and compare the ultrasonic tips developed, 36 metal patterns were fabricated from tin bars, on a mechanical precision lathe. Each metal pattern simulated an endodontically treated tooth, without coronal remaining, prepared to receive a cast post with 10 mm long. The cast posts were cemented with zinc phosphate cement. The metal patterns with their respective intraradicular posts cemented were stored at 37°C, at relative humidity 100%, for a period of 48 hours. After this period, the specimens were randomly divided into three groups, and each group was submitted to the action of one of the ultrasonic tips (n = 12): G1—tip with 30° angulation; G2—tip with 45° angulation and G3—tip without angulation (straight tip). Each ultrasonic tip was used on the surfaces of the cast posts (mesial, distal, buccal, lingual and incisal) for 5 seconds, at maximum power, until the cast post removal using an ultrasound device (Jet Sonic, Satelec System, Gnatus, Ribeirão Preto, SP, Brazil). The time required for cast posts removal was recorded and the data statistically analyzed by the ANOVA and Tukey tests (p < 0.05). Results The means of time evaluated for cast posts removal were G1: 59.25s; G2: 119.0s and G3: 48.4s. Group 2 presented the highest mean value in seconds, differing statistically from G1 and G3. No significant differences were observed between G1 and G3. Conclusion It may be concluded that the ultrasonic tip angulation had a direct influence on the time required for cast posts removal by ultrasound. When the different ultrasonic tips were compared, the 30° angulation and the straight tips required a shorter ultrasonic vibration time. All cast posts luted with zinc phosphate were successfully removed in a relatively short time by the different ultrasonic tips analyzed. How to cite this article da Silva EG, Xavier ACC, Kamozaki MBB, Gomes APM, Torres CRG, Pagani C. Comparison of Different Ultrasonic Tip Angulations on Time Required for Cast Post Removal. World J Dent 2014;5(3):147-151.

The continuous packing of a flexible rod in two-dimensional cavities yields a countable set of interacting domains that resembles non-equilibrium cellular systems and belongs to a new class of light-weight material. However, the link between the length of the rod and the number of domains requires investigation especially in the case of non-simply connected cavities, where the number of avoided regions emulates an effective topological temperature. In the present article we report the results of an experiment of injection of a single flexible rod into annular cavities in order to find the total length needed to insert a given number of loops (domains of one vertex). Using an exponential model to describe the experimental data we quite minutely analyze the initial conditions, the intermediary behavior, and the tight-packing limit. This method allows the observation of a new fluctuation phenomenon associated with instabilities in the dynamic evolution of the packing process. Furthermore, the fractal dimension of the global pattern enters the discussion under a novel point of view. A comparison with the classical problems of the random close packing of disks, and jammed disk packings is made., Comment: 19 pages, 14 equations, 8 figures

The present work deals with the injection and packing of a flexible polymeric rod of length $L$ into a simply connected rectangular domain of area $XY$. As the injection proceeds, the rod bends over itself and it stores elastic energy in closed loops. In a typical experiment $N$ of these loops can be identified inside the cavity in the jammed state. We have performed an extensive experimental analysis of the total length $L(N, X, Y)$ in the tight packing limit, and have obtained robust power laws relating these variables. Additionally, we have examined a version of this packing problem when the simply connected domain is partially occupied with free discs of fixed size. The experimental results were obtained with 27 types of cavities and obey a single equation of state valid for the tight packing of rods in domains of different topologies. Besides its intrinsic theoretical interest and generality, the problem examined here could be of interest in a number of studies including packing models of DNA and polymers in several complex environments., Comment: 13 pages, 2 equations, and 8 figures (24 images)

The physics of tightly packed structures of a wire and other threadlike materials confined in cavities has been explored in recent years in connection with crumpled systems and a number of topics ranging from applications to DNA packing in viral capsids and surgical interventions with catheter to analogies with the electron gas at finite temperature and with theories of two-dimensional quantum gravity. When a long piece of wire is injected into two-dimensional cavities, it bends and originates in the jammed limit a series of closed structures that we call loops. In this work we study the extraction of a crumpled tightly packed wire from a circular cavity aiming to remove loops individually. The size of each removed loop, the maximum value of the force needed to unpack each loop, and the total length of the extracted wire were measured and related to an exponential growth and a mean field model consistent with the literature of crumpled wires. Scaling laws for this process are reported and the relationship between the processes of packing and unpacking of wire is commented upon., Comment: 18 pages, 11 equations, 7 figures

The packing of a genome in virions is a topic of intense current interest in biology and biological physics. The area is dominated by allometric scaling relations that connect, e.g., the length of the encapsulated genome and the size of the corresponding virion capsid. Here we report scaling laws obtained from extensive experiments of packing of a macroscopic wire within rigid three-dimensional spherical and nonspherical cavities that can shed light on the details of the genome packing in virions. We show that these results obtained with crumpled wires are comparable to those from a large compilation of biological data from several classes of virions.

Habitat fragmentation displays a crucial role in conservation biology. Despite this, little is known about the detailed ecological consequences of habitat fragmentation due to the scarce number of controlled experimental surveys. The species–area relationship, a fundamental concept in ecology, requires the understanding of the fragmentation effects in a long term perspective, which turns this task even harder. Here we address the spatial patterns of species distribution in fragmented landscapes, assuming a neutral community model. We study the species area relationship and how its shape changes as the landscape becomes more fragmented. Recent investigations, based on extensive computer simulation, have contributed to establish some definite conclusions in the study of non-fragmented landscapes: the existence of a three-regime or two-regime scenario for the species–area relationship, the emergence of a power-law regime at intermediate scales and the augment of the species–area exponent z with the speciation rate. Despite the recent efforts, some other questions remain, such as the dependence of z in the whole range of the speciation rate. Questions like these are currently debated but generalizations cannot be drawn. This is the first paper, to our knowledge, that uses the coalescence method and neutral theory to examine biodiversity on more complex spatial structures. Our simulation results corroborate that the fragmentation plays a crucial role in shaping the species–area relationship, by determining the existence and extension of the power-law regime associated with small and intermediate areas. On the other hand, when individuals are allowed to disperse over longer distances the species–area relationship now displays the classic triphasic pattern, and the intermediate regime, which is well described by a power-law, is established even for highly fragmented landscapes.

This study evaluated the microhardness of restorative materials after the use of self-etching and acid-etching adhesives. Specimens were divided into four groups: Group 1 (CR): Composite resin, Group 2 (GIC): Glass ionomer cement chemically activated, Group 3 (EC): Dual resinous cement, Group 4 (E): Dual resinous cement. Each group was divided into three subgroups, according to the type of adhesive system applied on the surface: Subgroup 1 (C): Control subgroup, Subgroup 2 (XE): Xeno III self-etching adhesive, Subgroup 3 (SB): Single bond acid-etching adhesive. Vickers microhardness analysis was performed on the surfaces and the data were submitted to the two-way ANOVA and the Tukey's test. The means for the material factor: GIC: (35.61)a; CR: (43.54)b; E: (44.65)b; EC: (50.13)c. The means for the adhesive factor: SB: (36.35)a; XE: (38.44)a; C: (55.65)b. All materials tested showed a decrease in surface hardness after application of the adhesive systems, irrespective of the system. The lowest microhardness was shown by GIC and the highest by Enforce Core.

The cream layer is a complex heterogeneous material of biological origin which forms spontaneously at the air-milk interface. Here, it is studied the crumpling of a single cream layer packing under its own weight at room temperature in three-dimensional space. The structure obtained in these circumstances has low volume fraction and anomalous fractal dimensions. Direct means and noninvasive NMR imaging technique are used to investigate the internal and external structure of these systems., 9 pages, 4 figures, accepted in J. Phys. D: Appl. Phys

A simple spatial computer simulation model was recently introduced to study the evolution of the linguistic diversity. The model considers processes of selective geographic colonization, linguistic anomalous diffusion and mutation. In the approach, we ascribe to each language a fitness function which depends on the number of people that speak that language. Here we extend the aforementioned model to examine the role of saturation of the fitness on the language dynamics. We found that the dependence of the linguistic diversity on the area after colonization displays a power law regime with a nontrivial exponent in very good agreement with the measured exponent associated with the actual distribution of languages on the Earth., Comment: 10 pages, 3 figures

It is investigated the statistical properties of random walks evolving on real configurations of a crumpled wire rigidly jammed in two dimensions. These crumpled hierarchical structures with complex topology are obtained from a metallic wire injected at a constant rate into a transparent planar cell of 20cm of diameter. The observed diffusion is anomalous with an exponent very close to that obtained at the threshold of two dimensional percolation. A comparison of the system studied in this paper with other systems of physical interest is also made, and an experimental consequence of our results is discussed., Comment: 10 pages including 4 figures. Physica A (2006). Preprint

Basic statistical properties of monolayer packing configurations of a string of beads of diameter D in a planar cavity of size L×L×D are extensively investigated from experiments. The observed packing density p of the beads within the cavity is examined as a function of the packing fraction δ along the string. In particular, we have examined the dependence of p(δ) with the ratio D/L. The relationship of the maximum packing density, pmax, with D/L is found, and the thermodynamic limit of pmax as D/L goes to zero is also obtained.

The stress relaxation in crumpled surfaces maintained at a fixed compressive strain is investigated. The experiments indicate a slow relaxation of the mechanical stress in these non-equilibrium disordered systems. The experimental data indicate an anomalous stretched exponential decay with exponent β=0.28±0.03 along six decades in the rescaled variable t/τ, for a wide interval of strain. The results are compared with the similar behaviour of glassy materials, among others.

Long sequences of slidings of solid blocks on an inclined rough surface submitted to small controlled perturbations are examined and scaling relations are found for the time distribution of slidings between pairs of large events as well as after and before the largest events. These scaling laws are similar to the Omori law in seismology but the scaling exponents observed are different. Log-periodicity correction to the Omori scaling is also found. It is shown that the scaling behaviors are dependent on the angle that the incline forms with the horizontal., Comment: 10 pages including 4 figures

Reproductive endocrine patterns were characterized in female ocelots (Leopardus pardalis; n = 3), tigrinas (Leopardus tigrinus; n = 2), and margays (Leopardus wiedii; n = 2) housed in captivity in southern Brazil. Females were maintained as singletons and exposed to natural fluctuations in photoperiod. Cyclic changes in ovarian steroids were monitored by analyzing estrogen and progestogen metabolites in fecal samples collected five times weekly for 14 to 18 months. Based on intervals between fecal estrogen peaks, mean (+/- SEM) duration of the estrous cycle was 18.4 +/- 1.6 days for the ocelots (range, 7-31 days; n = 75 cycles), 16.7 +/- 1.3 days for the tigrinas (range, 11-27 days; n = 23 cycles), and 17.6 +/- 1.5 days for the margays (range, 11-25 days; n = 32 cycles). Fecal progestogen analyses combined with two laparoscopic observations of the ovaries confirmed that ocelots and tigrinas did not ovulate spontaneously. In contrast, non-mating-induced luteal phases of 40.1 +/- 6.3 days in duration (range, 30-60 days) were observed frequently in both margays. There was no evidence of gonadal seasonality in margays in either follicular or luteal activity. In ocelots, cyclic changes in estrogen excretion were observed during each month of the year; however, only one female cycled continuously. In the other two ocelots, periods of acyclicity of several months' duration were observed. It was not possible to conclude whether tigrinas were aseasonal because estrous cyclicity was observed in only one of two individuals. In the female that cycled, a 3-month period of acyclicity was observed in the late fall/early winter. These data demonstrate similarities among three felid species of the genus Leopardus, including evidence they are polyestrous but experience unexplained periods of ovarian inactivity. Only the margays differed by exhibiting occasional spontaneous, non-mating-induced ovulations. Historically, these species have not bred well in captivity. However, it is hoped that understanding the biological similarities and differences among them could lead to improved management strategies that may one day result in increased reproductive success. Zoo Biol 20:103-116, 2001. Copyright 2001 Wiley-Liss, Inc.

Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-27T11:19:59Z No. of bitstreams: 0Bitstream added on 2014-05-27T14:45:07Z : No. of bitstreams: 1 2-s2.0-0034207355.pdf: 149291 bytes, checksum: b402b628f6cd57af18851a24e80416db (MD5) Made available in DSpace on 2014-05-27T11:19:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2000-12-01 A nonthermal quantum mechanical statistical fragmentation model based on tunneling of particles through potential barriers is studied in compact two- and three-dimensional systems. It is shown that this fragmentation dynamics gives origin to several static and dynamic scaling relations. The critical exponents are found and compared with those obtained in classical statistical models of fragmentation of general interest, in particular with thermal fragmentation involving classical processes over potential barriers. Besides its general theoretical interest, the fragmentation dynamics discussed here is complementary to classical fragmentation dynamics of interest in chemical kinetics and can be useful in the study of a number of other dynamic processes such as nuclear fragmentation. ©2000 The American Physical Society. Departamento de Física Universidade Federal de Pernambuco, 50670-901 Recife-PE Inst. de Fis. Teórica Universidade Estadual Paulista, 01405-900 São Paulo, SP Laboratory for Theoretical Physics Inst. for Nucl. Sci. Vinča, P. O. Box 522, YU-11001 Belgrade Inst. de Fis. Teórica Universidade Estadual Paulista, 01405-900 São Paulo, SP

The classical problem of the random packing of spheres is restudied by introducing a new type of constraint among the spheres. This is done by examining the three-dimensional packing density of an open string of spherical beads as a function of the corresponding one-dimensional density along the string. The discussion stresses the peculiar behaviour of the problem as well as connections with some results in random packing of spheres and other systems.

The distribution of living languages is investigated and scaling relations are found for the diversity of languages as a function of the country area and population. These results are compared with data from Ecology and from computer simulations of fragmentation dynamics where similar scalings appear. The language size distribution is also studied and shown to display two scaling regions: (i) one for the largest (in population) languages and (ii) another one for intermediate-size languages. It is then argued that these two classes of languages may have distinct growth dynamics, being distributed on the sets of different fractal dimensions., 10 pages, 4 figures

An extensive Hurst analysis to quantify long-term statistical dependence is performed on time series associated with sliding of blocks on an inclined plane induced by small perturbations. The analysis reveals the existence of a fluctuation phenomenon exhibiting two phases, depending on the angle of inclination, both obeying a Hurst scaling . The first (second) phase has H = 0.70 (0.50) and refers to large (small) inclinations irrespective of the material of the block. These results indicate that sliding of blocks in the first regime exhibits persistence and indicate that there are long-term memory effects on the storage of shear stress at the block-plane interface. In the second regime, the long-term memory effects disappear and the sliding activity is intermittent; that is, it is distributed in bursts separated by variable periods of stasis.

The persistence of scaling laws in the evolution of the automaton Game of Life from a correlated configuration is investigated. It is found that even for a highly correlated initial state, the temporal evolution is able to preserve scaling relations as observed for uncorrelated states, although with possibly discordant critical exponents. The difference can be accounted for by introducing a stochastic component in the transition rules, which at the same time establishes a connection with the possible convergence of Life to a self-organized critical state.

An experimental study of fragmentation of brittle solids under the application of repeated impulsive force is made, emphasizing the behavior of the diversity of fragments. Several scaling relations involving diversity and number of fragments are obtained from experiments and the results are compared with computer simulations.

The packing density of a crumpled wire and a crumpled surface submitted to axial compression is investigated. The geometrical, topological and mechanical aspects of both problems are reported and connected with classical results in sphere packing and percolation theory.

An algebraic reformulation of the Bohr - Sommerfeld (BS) quantization rule is suggested and applied to the study of bound states in one-dimensional quantum wells. The energies obtained with the present quantization rule are compared to those obtained with the usual BS and WKB quantization rules and with the exact solution of the Schrodinger equation. We find that, in diverse cases of physical interest in molecular physics, the present quantization rule not only yields a good approximation to the exact solution of the Schrodinger equation, but yields more precise energies than those obtained with the usual BS and/or WKB quantization rules. Among the examples considered numerically are the Poeschl - Teller potential and several anharmonic oscillator potentials, which simulate molecular vibrational spectra and the problem of an isolated quantum well structure subject to an external electric field.

A simple method based on the enumeration of all random walk configurations for a very reduced number of steps is used to obtain the critical exponent ν for self‐avoiding random walks in two and three dimensions.

The effects of habitat fragmentation and their implications for biodiversity is a central issue in conservation biology which still lacks an overall comprehension. There is not yet a clear consensus on how to quantify fragmentation even though it is quite common to couple the effects of habitat loss with habitat fragmentation on biodiversity. Here we address the spatial patterns of species distribution in fragmented landscapes, assuming a neutral community model. To build up the fragmented landscapes, we employ the fractional Brownian motion approach, which in turn permits us to tune the amount of habitat loss and degree of clumping of the landscape independently. The coupling between the neutral community model, here simulated by means of the coalescent method, and fractal neutral landscape models enables us to address how the species-area relationship changes as the spatial patterns of a landscape is varied. The species-area relationship is one of the most fundamental laws in ecology, considered as a central tool in conservation biology, and is used to predict species loss following habitat disturbances. Our simulation results indicate that the level of clumping has a major role in shaping the species-area relationship. For instance, more compact landscapes are more sensitive to the effects of habitat loss and speciation rate. Besides, the level of clumping determines the existence and extension of the power-law regime which is expected to hold at intermediate scales. The distributions of species abundance are strongly influenced by the degree of fragmentation. We also show that the first and second commonest species have approximately self-similar spatial distributions across scales, with the fractal dimensions of the support of the first and second commonest species being very robust to changes in the spatial patterns of the landscape.

A complex system is often identified by the absence of a characteristic length, e.g. as in a fractal. A very large system subject to a fragmentation and/or aggregation dynamics passes through such complex configurations. We study statistically creation and maintenance of such configurations in space dimensions d=1 to 5 and find that they are easily created (maintained) for small (large) d. An intermediate d such as d=3 seems to be ideal for the creation and maintenance of complex systems. This has consequences in a statistical description of the universe.

In this letter we study the crumpled state observed in metallic closed surfaces submitted to a rapid variation in temperature. Scaling laws for the crumpled volume and the average size are obtained and critical exponents are found. The results are compared with those obtained for crumpled structures at equilibrium.

In this paper, we study experimentally the configurations of a plastic wire injected into a cubic cavity containing periodic obstacles placed along a fixed direction. The wire moves in a wormlike manner within the cavity until it becomes jammed in a crumpled state. The maximum packing fraction of the wire depends on the topology of the cavity, which in turn depends on the number of obstacles. The experimental results exhibit scaling laws and display similarities as well as differences with a recently reported two-dimensional version of this complex packing problem. We discuss in detail several aspects of this problem that seem as intricate as the problem of a self-avoiding random walk. Analogies between the experiment reported and some statistical aspects of the bond-percolation problem, as well as of the interacting electron gas at finite temperature, and other physical issues are also discussed.

The dynamics of a fragmentation model is examined from the point of view of numerical simulation and rate equations. The model includes effects of temperature. The number n(s,t) of fragments of size s at time t is obtained and is found to obey the scaling form n(s,t)∼ s−τtwsγe−ρtf(s/tz) where f(x) is a crossover function satisfying f(x)≂1 for x≪1 and f(x)≪1 for x≫1. The dependence of the critical exponents τ, w, γ, and z on space dimensionality d is studied from d=1 to 5. The result of the dynamics on fractal and nonfractal objects as well as on square and triangular lattices is also examined.

In this letter we compare the plastic properties of crumpled surfaces, crumpled wires and massive spheres of pastes deformed between parallel platens. All these systems have a spherical shape but different topological dimensions. Power laws are obtained from experiments and the dependence of the critical exponents on topology is examined. A comparison is made with the plastic deformation of solid (metallic) spheres.

One of the most important features of biological life in all levels is its astounding diversity. In this work we study the well-known game “Life” due to Conway analysing the statistics of cluster population, N ( t ), and cluster diversity, D ( t ). We have performed simulations on “Life” for dimensions d = 1 and 2 starting with an uncorrelated distribution of live and dead sites at t = 0. For d = 2 we study the effect of different neighbourhood relations in identifying and counting clusters. An interesting scaling relation connecting the maxima of N ( t ) and D ( t ) is found.

In this paper, we report an extensive experimental study of the configurations of a plastic wire injected into a two-dimensional planar cavity populated with fixed pins. The wire is not allowed to cross any pin, but it can move in a wormlike manner within the cavity until to become jammed in a crumpled state. The jammed packing fraction depends heavily on the topology of the cavity, which depends on the number of pins. The experiment reveals nontrivial entanglement effects and scaling laws which are largely independent of the details of the distribution of pins, the symmetry of the cavity or the type of the wire. A mean-field model for the process is presented and analogies with some basic aspects of statistical thermodynamics are discussed.