Sudden Fragmentation Research Articles

Shortest-Path Percolation on Random Networks.

We propose a bond-percolation model intended to describe the consumption, and eventual exhaustion, of resources in transport networks. Edges forming minimum-length paths connecting demanded origin-destination nodes are removed if below a certain budget. As pairs of nodes are demanded and edges are removed, the macroscopic connected component of the graph disappears, i.e., the graph undergoes a percolation transition. Here, we study such a shortest-path-percolation transition in homogeneous random graphs where pairs of demanded origin-destination nodes are randomly generated, and fully characterize it by means of finite-size scaling analysis. If budget is finite, the transition is identical to the one of ordinary percolation, where a single giant cluster shrinks as edges are removed from the graph; for infinite budget, the transition becomes more abrupt than the one of ordinary percolation, being characterized by the sudden fragmentation of the giant connected component into a multitude of clusters of similar size.

“There’s like no support system”: the life course stories of women with children about growing up, becoming mothers, and becoming homeless

ABSTRACT The current study reports on a narrative analysis of the stories of women (N = 20, 40% African American) with children who have been or are currently homeless with a focus on the women’s experiences during childhood, becoming homeless, and becoming mothers, and for some, exiting homelessness. We employed the life course theoretical framework to identify six themes across two developmental periods, pre-adulthood and adulthood: (1) constant fragmentation, (2) sudden fragmentation, (3) constrained agency, (4) learned substance abuse, (5) independence aborted, and (6) without a net. All reported childhoods characterized by disruption, although for some this only occurred after a lifechanging family event such as parental divorce or death. The majority described entering abusive relationships as adults and all became pregnant before the age of 20. Lacking family and friends able to help, they found themselves with limited economic options and often self-medicating through substance abuse that had been modeled in childhood and/or reinforced in adulthood. Findings underscore the need for rapid re-housing using a trauma-informed housing first model. Certain events in childhood, specifically parental divorce or death, are critical junctures for homeless prevention services. Further, evidence of reproductive coercion indicates that contraception, family planning, and economic supports may be critical targets for homeless prevention among women, as all of our participants reported an unplanned pregnancy by the age of 20 and poverty, often due to lack of education and job skills, rendering them dependent on male partners and abuse relationships.

Recent advances on failure and recovery in networks of networks

Until recently, network science has focused on the properties of single isolated networks that do not interact or depend on other networks. However it has now been recognized that many real-networks, such as power grids, transportation systems, and communication infrastructures interact and depend on other networks. Here, we will present a review of the framework developed in recent years for studying the vulnerability and recovery of networks composed of interdependent networks. In interdependent networks, when nodes in one network fail, they cause dependent nodes in other networks to also fail. This is also the case when some nodes, like for example certain people, play a role in two networks, i.e. in a multiplex. Dependency relations may act recursively and can lead to cascades of failures concluding in sudden fragmentation of the system. We review the analytical solutions for the critical threshold and the giant component of a network of n interdependent networks. The general theory and behavior of interdependent networks has many novel features that are not present in classical network theory. Interdependent networks embedded in space are significantly more vulnerable compared to non-embedded networks. In particular, small localized attacks may lead to cascading failures and catastrophic consequences. Finally, when recovery of components is possible, global spontaneous recovery of the networks and hysteresis phenomena occur. The theory developed for this process points to an optimal repairing strategy for a network of networks. Understanding realistic effects present in networks of networks is required in order to move towards determining system vulnerability.

Interferometric mapping of the 3.3-mm continuum emission of comet 17P/Holmes after its 2007 outburst

Comet 17P/Holmes underwent a dramatic outburst in October 2007, caused by the sudden fragmentation of its nucleus and the production of a large quantity of grains scattering sunlight. We report on 90 GHz continuum observations carried out with the IRAM Plateau de Bure interferometer on 27.1 and 28.2 October 2007 UT, i.e., 4-5 days after the outburst. These observations probed the thermal radiation of large dust particles, and therefore provide the best constraints on the mass in the ejecta debris. The thermal emission of the debris was modelled and coupled to a time-dependent description of their expansion after the outburst. The analysis was performed in the Fourier plane. Visibilities were computed for the two observing dates and compared to the data to measure their velocity and mass. Optical data and 250-GHz continuum measurements published in the literature were used to further constrain the dust kinematics and size distribution. Two distinct dust components in terms of kinematic properties are identified in the data. The large-velocity component, with typical velocities V0 of 50-100 m/s for 1 mm particles, displays a steep size distribution with a size index estimated to q = -3.7 (\pm0.1), assuming a minimum grain size of 0.1 \mum. It corresponds to the fast expanding shell observed in optical images. The slowly-moving "core" component (V0 = 7-9 m/s) detected near the nucleus has a size index |q| < 3.4 and contains a higher proportion of large particles than the shell. The dust mass in the core is in the range 0.1-1 that of the shell. Using optical constants pertaining to porous grains (50% porosity) made of astronomical silicates mixed with water ice (48% in mass), the total dust mass Mdust injected by the outburst is estimated to 4-14 x 10**11 kg, corresponding to 3-9% the nucleus mass.

Effect of sudden flow reduction on the decomposition of alder leaves (Alnus glutinosa [L.] Gaertn.) in a temperate lowland stream: a mesocosm study

Climate change leads to summer low flow conditions and premature litter input in lowland streams in Central Europe. This may cause a sudden reduction of flow and fragmentation into isolated pools of permanently flowing streams, with a simultaneous increase in the food supply for detrivores during summer months. We performed a mesocosm study to investigate shredder and microbial mediated litter decomposition under these conditions. Leaf litter was placed in a lowland stream with a natural flow regime (reference) and in a stream mesocosm with significant flow reduction (FR) and a representative density of macroinvertebrates and detritus. Physicochemical parameters, leaf mass loss, macroinvertebrate abundance and biomass, leaf-associated respiration, fungal sporulation, and biomass were measured at regular intervals for 6 weeks. Coarse and fine-mesh bags were used to include or exclude macroinvertebrate shredders. In the coarse-mesh bags, leaf mass loss was significantly lower in the FR system than in the reference regime. In the fine-mesh bags, leaf respiration, fungal sporulation, and biomass but not leaf mass losses were substantially lower with flow reduction. Chironomid larvae (Micropsectra spp.) appeared to effectively fragment leaf litter in fine-mesh bags. In the FR system, leaf respiration was higher in the coarse-than in the fine-mesh bags. Our results suggest that, in temperate lowland streams, premature litter input during or after a sudden fragmentation into isolated pools and a reduction of stream flow reduces direct shredder-mediated litter decomposition, but shredders may indirectly influence the decomposition process.

Probing the liquid–gas coexistence in p+Xe reactions from 200 to 1400 MeV

The nuclear equation of state (EOS) is probed from statistical parameters, determined in an excitation function experiment on p + Xe-nat reactions at 200-1400 MeV. Total charge (Z) distributions follow a cascade-[multi]fragmentation-evaporation (CFEM) model well. The caloric curve in regions supposedly dominated by fast processes is compatible with a pure statistical multifragmentation (SMM) process, where the temperature (T)-excitation energy (epsilon*) relation starts in the Fermi liquid phase and progresses into a liquid/gas coexistence region, where it remains up to 1400 MeV. A local peak in T at epsilon* = 2.1 MeV agrees with the idea of sudden fragmentation. (c) 2006 Elsevier B.V. All rights reserved.

Meteoroid Properties from Photographic Records of Meteors and Fireballs

Statistical criteria based on the single-body theory enabled the distinction of different composition groups of meteoroids in the past. The new single-body model proposed by Pecina and Ceplecha (1983, 1984) is capable of determining the individual values of ablation coefficients, which has proved to be a better tool for separating meteoroids of different ablation properties. However, a significant fraction of fireballs exhibit a time-dependence of residuals, when the single-body model is applied to their photographic observations. This was recently explained by assuming sudden fragmentation at a point (gross-fragmentation). The proposed gross-fragmentation model was checked in exceptional cases, when splitting of a fireball was directly visible on the photographs. The new fragmentation model was then applied to the best photographic records of Prairie Network fireballs (PN). Least-squares fit of computed to observed distances along a meteoroid trajectory determines uniquely the ablation coefficient, the shape-density coefficient, the position of the gross-fragmentation point and the amount of fragmented material relative to the main body mass. This enabled not only a better classification according to ablation coefficient (composition groups), but also a recognition of different strength categories according to dynamic pressure at the fragmentation point. Except for composition groups (types) I, II, IIIA, IIIB, each meteoroid with precise photographic data on its fireball can be classified as NF (no-fragmenting), 1F (with one point of fragmentation) and MF (with many points of fragmentation). The fragmenting meteoroids (1F and MF) can moreover be sorted into several categories (a, b, c, d, e) according to dynamic pressure at the fragmentation point. Thus the classification became two dimensional, separating meteoroid composition from structure. Values of ablation coefficients and bulk-densities were revised using this model. The amount of fragmented mass relatively to the main body was also determined. Typical sudden fragmentation for almost half of all fragmenting meteoroids is equivalent to stripping away slightly more than half of the mass.

Size-distribution in sudden breakage by the use of entropy maximization

We derive the number and weight distributions of fragment pieces (of linear size a) that are obtained in a sudden fragmentation process. The information-entropic derivation is based on a fragment energy e(a) which incorporates the physical mechanisms and material properties responsible for breakage. For not too large fragments the number distribution follows a power law a−Θ, where Θ is between 2 and 5, depending on the size range and circumstances of the breakage. Our results are compared with other theories of size distributions.

Cable Penetration and Competition among Belgian and Foreign Stations

The effects of programme abundance as a result of cable should be observable in the most densely cabled country in Europe — Belgium — where most viewers have a choice of 11 to 15 channels. Time series data on audience behaviour in the Flemish-speaking part of the country demonstrate the strength of pre-existing patterns of TV utilization, slowness of change, the dominant influence of linguistic barriers and community divisions in channel choice; there is no sudden fragmentation. The implications for programming policy and the future strategy of public service broadcasting in a densely cabled country are discussed.