Blocking nonorientability of a surface

AbstractLet S be a nonorientable surface. A collection of pairwise noncrossing simple closed curves in S is a blockage if every one-sided simple closed curve in S crosses at least one of them. Robertson and Thomas [9] conjectured that the orientable genus of any graph G embedded in S with sufficiently large face-width is “roughly” equal to one-half of the minimum number of intersections of a blockage with the graph. The conjecture was disproved by Mohar (Discrete Math. 182 (1998) 245) and replaced by a similar one. In this paper, it is proved that the conjectures in Mohar (1998) and Robertson and Thomas (J. Graph Theory 15 (1991) 407) hold up to a constant error term: For any graph G embedded in S, the orientable genus of G differs from the conjectured value at most by O(g2), where g is the genus of S

Die Architektur der neuen Weltordnung : 11. Internationales Bauhaus-Kolloquium

Eine neue, kopflose Gewalt hat den Imperialismus vergangener Zeiten abgelöst. Die neue Weltordnung, das »Empire«, überschreitet alle Grenzen unserer althergebrachten politischen Begriffe – Staat und Gesellschaft, Krieg und Frieden, Kontrolle und Freiheit. Das dezentralisierte und deterritorialisierte Empire beherrscht uns, indem es durch die Medien, die Technik und durch soziale Praktiken unmittelbaren Einfluss auf uns Menschen nimmt. Architektur und Raumplanung haben sich in den letzten Jahrzehnten radikal gewandelt. Die alten, modernistischen Bestrebungen nach erschwinglichen Wohnungen und einer rationalen Organisation der Städte sind ebenso in den Hintergrund gerückt wie die postmodernen Obsessionen der Kommunikation, der Nutzerbeteiligung und des öffentlichen Raumes. Stattdessen stehen nun ästhetische und entschieden unpolitischere Belange im Vordergrund: Diskussionen zwischen einer kritischen und einer projektiven Praxis, zwischen Blobs und Kisten, zwischen Atmosphäre und Ornament. Doch das ist noch lange nicht das Ende der Geschichte, wie im vorliegenden Band deutlich wird. Die Beiträge des 11. Bauhaus-Kolloquiums umspannen einen Zeitraum, der von der Gründung des Bauhauses in Weimar bis zur globalen Architektur unserer Zeit reicht, und verfolgen dabei die Entwicklung des Empires zurück, um gleichzeitig nach Konsequenzen und Alternativen zu fragen, denen die Architektur sich heute gegenübergestellt sieht

The Fifteenth Marcel Grossmann Meeting

The three volumes of the proceedings of MG15 give a broad view of all aspects of gravitational physics and astrophysics, from mathematical issues to recent observations and experiments. The scientific program of the meeting included 40 morning plenary talks over 6 days, 5 evening popular talks and nearly 100 parallel sessions on 71 topics spread over 4 afternoons. These proceedings are a representative sample of the very many oral and poster presentations made at the meeting.Part A contains plenary and review articles and the contributions from some parallel sessions, while Parts B and C consist of those from the remaining parallel sessions. The contents range from the mathematical foundations of classical and quantum gravitational theories including recent developments in string theory, to precision tests of general relativity including progress towards the detection of gravitational waves, and from supernova cosmology to relativistic astrophysics, including topics such as gamma ray bursts, black hole physics both in our galaxy and in active galactic nuclei in other galaxies, and neutron star, pulsar and white dwarf astrophysics. Parallel sessions touch on dark matter, neutrinos, X-ray sources, astrophysical black holes, neutron stars, white dwarfs, binary systems, radiative transfer, accretion disks, quasars, gamma ray bursts, supernovas, alternative gravitational theories, perturbations of collapsed objects, analog models, black hole thermodynamics, numerical relativity, gravitational lensing, large scale structure, observational cosmology, early universe models and cosmic microwave background anisotropies, inhomogeneous cosmology, inflation, global structure, singularities, chaos, Einstein-Maxwell systems, wormholes, exact solutions of Einstein's equations, gravitational waves, gravitational wave detectors and data analysis, precision gravitational measurements, quantum gravity and loop quantum gravity, quantum cosmology, strings and branes, self-gravitating systems, gamma ray astronomy, cosmic rays and the history of general relativity

The Fifteenth Marcel Grossmann Meeting

The three volumes of the proceedings of MG15 give a broad view of all aspects of gravitational physics and astrophysics, from mathematical issues to recent observations and experiments. The scientific program of the meeting included 40 morning plenary talks over 6 days, 5 evening popular talks and nearly 100 parallel sessions on 71 topics spread over 4 afternoons. These proceedings are a representative sample of the very many oral and poster presentations made at the meeting.Part A contains plenary and review articles and the contributions from some parallel sessions, while Parts B and C consist of those from the remaining parallel sessions. The contents range from the mathematical foundations of classical and quantum gravitational theories including recent developments in string theory, to precision tests of general relativity including progress towards the detection of gravitational waves, and from supernova cosmology to relativistic astrophysics, including topics such as gamma ray bursts, black hole physics both in our galaxy and in active galactic nuclei in other galaxies, and neutron star, pulsar and white dwarf astrophysics. Parallel sessions touch on dark matter, neutrinos, X-ray sources, astrophysical black holes, neutron stars, white dwarfs, binary systems, radiative transfer, accretion disks, quasars, gamma ray bursts, supernovas, alternative gravitational theories, perturbations of collapsed objects, analog models, black hole thermodynamics, numerical relativity, gravitational lensing, large scale structure, observational cosmology, early universe models and cosmic microwave background anisotropies, inhomogeneous cosmology, inflation, global structure, singularities, chaos, Einstein-Maxwell systems, wormholes, exact solutions of Einstein's equations, gravitational waves, gravitational wave detectors and data analysis, precision gravitational measurements, quantum gravity and loop quantum gravity, quantum cosmology, strings and branes, self-gravitating systems, gamma ray astronomy, cosmic rays and the history of general relativity

Delivering Justice: Food Delivery Cyclists in New York City

In New York City (NYC), food delivery cyclists ride the streets all day and night long to provide convenient, affordable, hot food to New Yorkers. These working cyclists are often Latino or Asian male immigrants who are situated within intersectional and interlocking systems of global migration and capital flows, intense time pressures by restaurants and customers, precarious tip-based livelihoods, an e-bike ban and broken windows policing, and unsafe streets designed for drivers. I approach this research through participatory action research (PAR) and han, an indigenous Korean word that describes collective transgenerational traumas that are rooted in systems and structures of oppression. A han-based PAR approach seeks to use participatory research methods with delivery workers to create communities of resistance and healing that name structural oppressions, to gain societal acknowledgement of these named oppressions, and to change structures and systems to undo oppressions and heal collective traumas. As a rationale for this work, I examine how echo chambers of whiteness craft demonizing public narratives about immigrant delivery workers by excluding their voices. This exclusion signals a need to listen to delivery worker voices to characterize and name their conditions and experiences. Intermingled systems of transnational migration, restaurant business, and labor conditions coerce competition, isolation, exploitation, and tactics for transnational survival that speed up the bodies of delivery workers to meet the demands of food delivery while also disposing of worker bodies that are too slow, old, or injured. Exacerbating this disposability of worker bodies, unsafe streets are based upon a system of cumulative irresponsibility where mass harm accrues from the inability to address this harm through individual responsibility. This system undermines the right to the street for immigrant delivery workers by creating harmful conditions and criminalizing worker tactics for survival such as riding electric bikes (e-bikes), which are perceived to disrupt social order. By being unable to address systematic and structural labor and street conditions that compel the speeding up of worker bodies, NYC has responded to “disorderly” immigrant delivery workers by excluding immigrant workers from the boundaries of legality and enacting broken windows policing. Accordingly, the City and NYPD have created a regime of Vision Zero Apartheid by racially weaponizing a public policy to reduce traffic fatalities by exerting punitive disciplinary measures against immigrant delivery workers in the name of public safety. The transgressive, intersectional, and agentic movements of delivery workers expose the porosity of boundaries and trace out desire paths in the shifting cracks and crevices within oppressive systems. Traveling along desire paths involves risk, but doing so opens up possibilities of communities of resistance and healing that strive toward liberation as collective projects of delivering more just cities

Die Architektur der neuen Weltordnung : 11. Internationales Bauhaus-Kolloquium

Eine neue, kopflose Gewalt hat den Imperialismus vergangener Zeiten abgelöst. Die neue Weltordnung, das »Empire«, überschreitet alle Grenzen unserer althergebrachten politischen Begriffe – Staat und Gesellschaft, Krieg und Frieden, Kontrolle und Freiheit. Das dezentralisierte und deterritorialisierte Empire beherrscht uns, indem es durch die Medien, die Technik und durch soziale Praktiken unmittelbaren Einfluss auf uns Menschen nimmt. Architektur und Raumplanung haben sich in den letzten Jahrzehnten radikal gewandelt. Die alten, modernistischen Bestrebungen nach erschwinglichen Wohnungen und einer rationalen Organisation der Städte sind ebenso in den Hintergrund gerückt wie die postmodernen Obsessionen der Kommunikation, der Nutzerbeteiligung und des öffentlichen Raumes. Stattdessen stehen nun ästhetische und entschieden unpolitischere Belange im Vordergrund: Diskussionen zwischen einer kritischen und einer projektiven Praxis, zwischen Blobs und Kisten, zwischen Atmosphäre und Ornament. Doch das ist noch lange nicht das Ende der Geschichte, wie im vorliegenden Band deutlich wird. Die Beiträge des 11. Bauhaus-Kolloquiums umspannen einen Zeitraum, der von der Gründung des Bauhauses in Weimar bis zur globalen Architektur unserer Zeit reicht, und verfolgen dabei die Entwicklung des Empires zurück, um gleichzeitig nach Konsequenzen und Alternativen zu fragen, denen die Architektur sich heute gegenübergestellt sieht