287 research outputs found
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Least expected time paths in stochastic, time-varying transportation networks
The authors consider stochastic, time-varying transportation networks, where the arc weights (arc travel times) are random variables with probability distribution functions that vary with time. Efficient procedures are widely available for determining least time paths in deterministic networks. In stochastic but time-invariant networks, least expected time paths can be determined by setting each random arc weight to its expected value and solving an equivalent deterministic problem. This paper addresses the problem of determining least expected time paths in stochastic, time-varying networks. Two procedures are presented. The first procedure determines the a priori least expected time paths from all origins to a single destination for each departure time in the peak period. The second procedure determines lower bounds on the expected times of these a priori least expected time paths. This procedure determines an exact solution for the problem where the driver is permitted to react to revealed travel times on traveled links en route, i.e. in a time-adaptive route choice framework. Modifications to each of these procedures for determining least expected cost (where cost is not necessarily travel time) paths and lower bounds on the expected costs of these paths are given. Extensive numerical tests are conducted to illustrate the algorithms` computational performance as well as the properties of the solution
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Mothers behaving badly: chaotic hedonism and the crisis of neoliberal social reproduction
This article focuses on the significance of the plethora of representations of mothers âbehaving badlyâ in contemporary anglophone media texts, including the films Bad Moms, Fun Mom Dinner and Bad Momâs Christmas, the book and online cartoons Hurrah for Gin and the recent TV comedy dramas Motherland, The Let Down and Catastrophe. All these media texts include representations of, first, mothers in the midst of highly chaotic everyday spaces where any smooth routine of domesticity is conspicuous by its absence; and second, mothers behaving hedonistically, usually through drinking and partying, behaviour that is more conventionally associated with men or women without children. After identifying the social type of the mother behaving badly (MBB), the article locates and analyses it in relation to several different social and cultural contexts. These contexts are: a neoliberal crisis in social reproduction marked by inequality and overwork; the continual if contested role of women as âfoundation parentsâ; and the negotiation of longer-term discourses of female hedonism. The title gestures towards a popular British sitcom of the 1990s, Men Behaving Badly, which popularized the idea of the ânew ladâ; and this article suggests that the new ladâs counterpart, the ladette, is mutating into the mother behaving badly, or the âlad momâ. Asking what work this figure does now, in a later neoliberal context, it argues that the mother behaving badly is simultaneously indicative of a widening and liberating range of maternal subject positions and symptomatic of a profound contemporary crisis in social reproduction. By focusing on the classed and racialised dynamics of the MBB â by examining who exactly is permitted to be hedonistic, and how â and by considering the MBBâs limited and partial imagining of progressive social change, the article concludes by emphasizing the urgency of creating more connections between such discourses and âparents behaving politicallyâ
Racism, anti-racist practice and social work: articulating the teaching and learning experiences of Black social workers
In the mid 1990s a Black practice teacher programme was established in Manchester and Merseyside with the primary aim to increase the number of Black practice teachers in social work organisations, and in turn provide a supportive and encouraging learning environment for Black student social workers whilst on placement. In the northâwest of England research has been undertaken, to establish the quality of the practice teaching and student learning taking place with Black practice teachers and students. This paper is an exploration of the ideas generated within the placement process that particularly focused on the discourse of racism and antâracist practice. Black students and practice teachers explain their understanding of racism and antiâracist practice within social work. From the research, the paper will critique some of the ideas concerning antiâracism. In particular, it will question whether antiâracist social work practice needs to be reâevaluated in the light of a context with new migrants, asylum seekers and refugees. It will concluded, by arguing that whilst the terms antiâracism, Black and Minority Ethnic have resonance as a form of political strategic essentialism, it is important to develop more positive representations in the future
Increasing the simulation performance of large-scale evacuations using parallel computing techniques based on domain decomposition
Evacuation simulation has the potential to be used as part of a decision support system during large-scale incidents to provide advice to incident commanders. To be viable in these applications, it is essential that the simulation can run many times faster than real time. Parallel processing is a method of reducing run times for very large computational simulations by distributing the workload amongst a number of processors. This paper presents the development of a parallel version of the rule based evacuation simulation software buildingEXODUS using domain decomposition. Four Case Studies (CS) were tested using a cluster, consisting of 10 Intel Core 2 Duo (dual core) 3.16 GHz CPUs. CS-1 involved an idealised large geometry, with 20 exits, intended to illustrate the peak computational speed up performance of the parallel implementation, the population consisted of 100,000 agents; the peak computational speedup (PCS) was 14.6 and the peak real-time speedup (PRTS) was 4.0. CS-2 was a long area with a single exit area with a population of 100,000 agents; the PCS was 13.2 and the PRTS was 17.2. CS-3 was a 50 storey high rise building with a population of 8000/16,000 agents; the PCS was 2.48/4.49 and the PRTS was 17.9/12.9. CS-4 is a large realistic urban area with 60,000/120,000 agents; the PCS was 5.3/6.89 and the PRTS was 5.31/3.0. This type of computational performance opens evacuation simulation to a range of new innovative application areas such as real-time incident support, dynamic signage in smart buildings and virtual training environments
Burst-Time-Dependent Plasticity Robustly Guides ON/OFF Segregation in the Lateral Geniculate Nucleus
Spontaneous retinal activity (known as âwavesâ) remodels synaptic connectivity to the lateral geniculate nucleus (LGN) during development. Analysis of retinal waves recorded with multielectrode arrays in mouse suggested that a cue for the segregation of functionally distinct (ON and OFF) retinal ganglion cells (RGCs) in the LGN may be a desynchronization in their firing, where ON cells precede OFF cells by one second. Using the recorded retinal waves as input, with two different modeling approaches we explore timing-based plasticity rules for the evolution of synaptic weights to identify key features underlying ON/OFF segregation. First, we analytically derive a linear model for the evolution of ON and OFF weights, to understand how synaptic plasticity rules extract input firing properties to guide segregation. Second, we simulate postsynaptic activity with a nonlinear integrate-and-fire model to compare findings with the linear model. We find that spike-time-dependent plasticity, which modifies synaptic weights based on millisecond-long timing and order of pre- and postsynaptic spikes, fails to segregate ON and OFF retinal inputs in the absence of normalization. Implementing homeostatic mechanisms results in segregation, but only with carefully-tuned parameters. Furthermore, extending spike integration timescales to match the second-long input correlation timescales always leads to ON segregation because ON cells fire before OFF cells. We show that burst-time-dependent plasticity can robustly guide ON/OFF segregation in the LGN without normalization, by integrating pre- and postsynaptic bursts irrespective of their firing order and over second-long timescales. We predict that an LGN neuron will become ON- or OFF-responsive based on a local competition of the firing patterns of neighboring RGCs connecting to it. Finally, we demonstrate consistency with ON/OFF segregation in ferret, despite differences in the firing properties of retinal waves. Our model suggests that diverse input statistics of retinal waves can be robustly interpreted by a burst-based rule, which underlies retinogeniculate plasticity across different species
Weird exoskeletons: propositional politics and the making of home in underground Bucharest
The article explores the politics of life underground in Bucharest, Romania. It focuses on a tunnel passing under Bucharest's central train station, where a community of drug users and soâcalled âhomelessâ have made a longâstanding home, using a space that many others considered uninhabitable. Relying on extensive ethnographic observations and interviews undertaken within the tunnels, the article traces and illustrates the socioâmaterial entanglements characterizing life underground. It frames this assemblage of bodies, veins, syringes, substances and various relationships of power and affect, as a âpropositional politicsâ of home and life at the margins. Such a politics speaks of drug addiction and extreme marginalization, but also of a sense of belonging, reciprocal trust and care. In tracing such a politics, the article does not aim to romanticize the status of home in the underground or to treat it as the marginal antithesis of normative homeliness, but to reveal the ways in which an affirmative, selfâgrounding politics of home emerges from the immanence of tunnel life within the fabric of the city. As such, the article contributes to debates around homing practices in conditions of uninhabitability and proposes a radical approach to the politics of life at the margins in the contemporary urban
Track D Social Science, Human Rights and Political Science
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138414/1/jia218442.pd
Reversals of fortune: path dependency, problem solving, and temporal cases
Historical reversals highlight a basic methodological problem: is it possible to treat two successive periods both as independent cases to compare for causal analysis and as parts of a single historical sequence? I argue that one strategy for doing so, using models of path dependency, imposes serious limits on explanation. An alternative model which treats successive periods as contrasting solutions for recurrent problems offers two advantages. First, it more effectively combines analytical comparisons of different periods with narratives of causal sequences spanning two or more periods. Second, it better integrates scholarly accounts of historical reversals with actorsâ own narratives of the past
LEAST EXPECTED TIME HYPERPATHS IN STOCHASTIC, TIME-VARYING MULTIMODAL NETWORKS
The adaptive multimodal least expected time (AMLET) algorithm is presented for determining the adaptive least expected time (LET) hyperpaths from all origins to a specified destination for all departure times in a period of interest in stochastic, time-varying multimodal networks, when the fastest path can be appropriately selected depending on the arrival time at each node en route. Mode transfer delays are incorporated into the algorithm to represent waiting times required in transferring modes, such as between driving and boarding a transit vehicle. Both mode transfer delays and arc travel times may be stochastic and time varying. By considering stochastic, time-varying networks, the proposed algorithm can more realistically represent conditions in transportation networks than can exist in deterministic approaches. The resulting solutions provide not only the adaptive LET hyperpaths but also the travel mode to choose from along each path segment for completing a trip. Travelers are not restricted to traveling on only one path and one mode found to be best before they depart from the origin. Instead, they can choose their paths and travel modes en route in accordance to the knowledge of their arrival time at intermediate nodes. Hence, the solution is a set of hyperpaths instead of a single path to the destination. The AMLET algorithm is tested on a real-world transportation network, with several possible traffic scenarios to illustrate the nature of the solution paths
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