Orbital magnetoelectric coupling in band insulators

Magnetoelectric responses are a fundamental characteristic of materials that break time-reversal and inversion symmetries (notably multiferroics) and, remarkably, of "topological insulators" in which those symmetries are unbroken. Previous work has shown how to compute spin and lattice contributions to the magnetoelectric tensor. Here we solve the problem of orbital contributions by computing the frozen-lattice electronic polarization induced by a magnetic field. One part of this response (the "Chern-Simons term") can appear even in time-reversal-symmetric materials and has been previously shown to be quantized in topological insulators. In general materials there are additional orbital contributions to all parts of the magnetoelectric tensor; these vanish in topological insulators by symmetry and also vanish in several simplified models without time-reversal and inversion those magnetoelectric couplings were studied before. We give two derivations of the response formula, one based on a uniform magnetic field and one based on extrapolation of a long-wavelength magnetic field, and discuss some of the consequences of this formula.Comment: 13 page

A Political Economy of Access: Infrastructure, Networks, Cities, and Institutions

Why should you read another book about transport and land use? This book differs in that we won’t focus on empirical arguments – we present political arguments. We argue the political aspects of transport policy shouldn’t be assumed away or treated as a nuisance. Political choices are the core reasons our cities look and function the way they do. There is no original sin that we can undo that will lead to utopian visions of urban life. The book begins by introducing and expanding on the idea of Accessibility. Then we proceed through several major parts: Infrastructure Preservation, Network Expansion, Cities, and Institutions. Infrastructure preservation concerns the relatively short-run issues of how to maintain and operate the existing surface transport system (roads and transit). Network expansion in contrast is a long-run problem, how to enlarge the network, or rather, why enlarging the network is now so difficult. Cities examines how we organize, regulate, and expand our cities to address the failures of transport policy, and falls into the time-frame of the very long-run, as property rights and land uses are often stickier than the concrete of the network is durable. In the part on Institutions we consider things that might at first blush appear to be short-run and malleable, are in fact very long-run. Institutions seem to outlast the infrastructure they manage. Many of the transport and land use problems we want to solve already have technical solutions. What these problems don’t have, and what we hope to contribute, are political solutions. We expect the audience for this book to be practitioners, planners, engineers, advocates, urbanists, students of transport, and fellow academics

Shading and Smothering of Gamma Ray Bursts

The gamma ray burst (GRB) 980425 is distinctive in that it seems to be associated with supernova (SN) 1998bw, has no X-ray afterglow, and has a single peak light curve and a soft spectrum. The supernova is itself unusual in that its expansion velocity exceeds c/6. We suggest that many of these features can be accounted for with the hypothesis that we observe the GRB along a penumbral line of sight that contains mainly photons that have scattered off ejected baryons. The hypothesis suggests a baryon poor jet (BPJ) existing within a baryon rich outflow. The sharp distinction can be attributed to whether or not the magnetic field lines thread an event horizon. Such a configuration suggests that there will be some non-thermal acceleration of pick-up ex-neutrons within the BPJ. This scenario might produce observable spallation products and neutrinos.Comment: 7 pages, 2 figures, submitted to ApJ

Estimating the Social Gap With a Game Theory Model of Lane Changing

Changing lanes is a commonly-used technique for drivers to either overtake slow-moving cars or enter/exit highway ramps. Optional lane changes may save drivers travel time but increase the risk of collision with others. Drivers make such decisions based on experience and emotion rather than analysis, and thus may fail to select the best solution while in a dynamic state of flux. Unlike human drivers, autonomous vehicles can systematically analyze their surroundings and make real-time decisions accordingly. This paper develops a game theory-based lane-changing model by comparing two types of optimization methods. To realize our expectations, we need to first investigate the payoff function of drivers in discretionary lane-changing maneuvers and then quantify it in an equation of costs that trades-off safety and time-saving. After the evaluation for each alternative strategy combination, the results show that there exists a social gap in the discretionary lane-changing game. To deal with that problem, we provide some suggestions for future policy as well as autonomous vehicle controller designs, offering solutions to reduce the impact of disturbances and crashes caused by inappropriate lane changes, and also, inspire further research about more complex cases

Temporal Variations in Activity Network Using Smart Card Data

This study explores temporal variations in activity networks for four million passengers, differentiated as workers and non-workers, using public transport based on a large-scale smart card dataset generated over 105 days in Beijing. We aim to capture their day-to-day transition and cumulative temporal expansion in activity network using transit over days, weeks, and months. Particularly, workers and non-workers are automatically identified based on their different daily routines, whose activity networks are characterized by six features concerning space coverage, distance coverage, and frequency coverage in two ways, namely, on a per-day transition and with an accumulation of days. The transition features of the networks are statistically analyzed and compared by time, while how the expansion features evolve with time are modeled. Results show that, on weekdays, workers are more likely to travel longer (have larger distance coverage), but cover less area (have smaller space coverage) than non- workers. While opposite patterns occur on weekends. Traveling in the ‘North-South’ direction is weakly correlated with traveling in the ‘East-West’ direction. Workers on weekdays, as well as non-workers on weekends, make longer ‘North-South’ trips. Manhattan distance, trip count, and perimeter present a ∩ shape in their probability density functions, while the remaining features decline dramatically, with probability density functions fit by the exponential distribution. The distance coverage expands faster than that of space coverage. Most passengers increase coverage of space and distance when time expands (obviously no one decreases coverage over time, but some don’t change). The research enables findings on temporal load-balancing, long-term cumulative expansion in travel demands of workers and non-workers, re-balancing the distribution of existing workplace and residential location opportunities, and constructing transit-oriented developments with mixed functions over time.Chinese Scholarship Council TransportLa

A Schematic for Focusing on Youth in Investigations of Community Design and Physical Activity

This paper provides a first step in addressing special considerations for youth in a relatively new area of physical activity research. After reviewing the urgent need for novel approaches to increasing physical activity, the growing interest in the effects of community design are discussed. Although most discussion on this topic has focused on adults, there are important differences between youth and adults that warrant a special focus on youth and need to be accounted for. This article presents a schematic that accounts for how and where youth spend their time, decomposing the day into time spent in travel and time spent at destinations, and identifying portions of those times that are spent engaged in physical activity. By focusing on both spatial and behavioral dimensions of youth time, the schematic may help organize and advance scientific inquiry into the relationships between community design and physical activity specifically for youth

Review of The Economics of Urban Transportation by Kenneth Small and Erik Verhoef David Levinson June 26, 2008

Review of The Economics of Urban Transportation by Kenneth Small and Erik Verhoef Routledge $59.95 ISBN 978-0-415-28515-5 The Economics of Urban Transportation by Kenneth Small and Erik Verhoef is the latest book in the emerging area of transportation economics, and updates and extends Small’s earlier Urban Transportation Economics published in 1992. The book comprises five chapters: Demand, Costs, Pricing, Investment, and Industrial Organization of Transportation Providers. These five chapters cover many of the important transportation economic issues that have emerged in the academic liter- ature over the past three decades, including deregulation, privatization, and road pricing. The book provides the underlying theory that is leading economists, and increasingly policy-makers to examine alternative formulations of transportation sys- tems. It is perhaps most pertinent in the area of road pricing, where a confluence of events, including the opportunities presented by electronic toll collection, continuing congestion, and the coming switch away from gasoline (and thus the gas tax) are making this an issue all transportation professionals will confront in one form or another over the coming decade. The text provides a mainstream treatment of demand, including both aggregate and disaggregate (discrete choice) approaches in an intensively mathematical way (though not to the level of theoretical derivations). The econometrics is also covered in some detail. Helpfully, a list of variables used in the book is provided, though this is four full pages, and is only “selected” variables. The discussion of costs includes accounting, engineering, and economic methods of cost estimating, and consideration of congestion and other externalities, which are important for understanding and developing welfare-maximizing prices. More 1 discussion could have been given to collection costs, the costs of collecting revenue, which are surprisingly large for many toll roads, and could help shape the design of alternative strategies. The chapter does include discussion of economies of scale, which are especially important in public transport economics. Significant attention is also paid to getting the correct technical (engineering) model for underlying economic congestion cost functions. Choosing unrealistic technological functions for use in models of road pricing has historically been a major weakness of transportation economics, and the attempts to rectify it are moving in the correct direction. The chapter on pricing considers the idea of first-best and second-best (how to optimize when dealing with a suboptimal world), which is conceptually important for making economics relevant to policy. There are several qualifications about the use of the book, that may suggest for which classes it is most appropriate, depending on the abilities of the students and the nature of the course. First, the book is math heavy: Chapter 2 numbers 61 equations and Chapter 3 has 44. Nevertheless, the equations are clearly supplemented with graphics that suggest the main idea. Second, the book only peripherally treats game theory, agent-based models, or network structure. It also glosses over the land use - transportation interaction (which of course could consume another book). Finally, for geographers, despite being about transportation economics, the book is not formulated with space and time comprising the structure over which economic transactions take place. Transportation economists have had a major effect on policy, and the trend to- ward modal deregulation and privatization is due to lessons from transportation economics. Yet, given what is known about transportation economics, it may seem surprising that such basic issues like road pricing, which in congested circumstances if efficiently implemented can provide enormous gains, have barely emerged as a policy consideration outside a few central cities, while investment decisions are still so misguided. The problem of course is politics, on which this text says little, but whose absence suggests a fundamental topic: why are political systems at odds with economic efficiency and equity, and how can they be aligned? This text should appear on the shelf of everyone practicing transportation eco- nomics, and is likely to become the standard in the field. I plan to use this for the transportation economics course I teach to civil engineering and planning students, and I think it provides a strong technical supplement for a more policy-oriented work like Essays in Transport Economics and Policy by Gomez-Ibanez, Tye, and Winston. – David Levinson, RP Braun/CTS Chair in Transportation, University of Minnesota [email protected], David M. (2008). Review of The Economics of Urban Transportation by Kenneth Small and Erik Verhoef David Levinson June 26, 2008. Retrieved from the University Digital Conservancy, http://dx.doi.org/DOI:10.1016/j.jtrangeo.2008.07.001

Governing for Access

The only reason to locate anywhere is to be near some people, places, and things (opportunities) and be far from others. Access quantifies the ability to reach, or be reached by, people, places, and things. It explains much of the variation in real estate prices and development density. It does so in large part because real estate capitalises into land value the ease of travel to desired opportunities. Physical infrastructure networks like roads and rails exist to connect within and between places faster than travel without them. Transport agencies often plan networks as if the land use is given, and regulators plan and zone development as if the network were unchangeable. Since the efficiency of a transport network depends on the land use pattern and the efficiency of the land use pattern depends on the network configuration, systems which coordinate these may be more efficient than those where transport and land use are planned independently. This is especially pertinent for long-term capital investments which are largely irreversible. While compared to some peer cities, Sydney has done a good job coordinating transport services and land development, it can do much better. This would lead to shorter commutes lengths, greater public and active transport mode shares, higher employment and incomes, and greater productivity. Overall Sydney would be a more desirable and convenient city. This is also important as better coordinating transport with land development while better balancing jobs and housing will thereby reduce motor vehicle travel. Reducing private vehicle travel will remain critical to addressing environmental problems such as CO2 emissions and air and water pollution, and increasing traveler safety. Modern urban planning confronts the challenge of coordinating policies in transport investment, land use and development regulation, budgets and taxation, and capital spending so that they reinforce instead of undermine each other.1 Several inter-related problems with transport - land use planning processes in New South Wales are apparent: 1. Mobility-centric transport planning and density-centric land use planning. 2. The uncoordinated and disjointed nature of decision making, wherein transport and land use decisions made by different organisations assume the other is unchanged. 3. Lack of systematic feedback in the infrastructure/land development cycle, so the gains in land value from new transport facilities don’t generate revenue could have helped fund the infrastructure in the first place. 4. The political cycle reversing long-term strategic planning decisions. 5. Lack of institutional knowledge caused by lack of long-term stability in senior staff and organisational structure. 6. Lack of domain expertise within operating agencies leading to: • Very high costs (and unexpectedly high costs) for infrastructure, reducing the capacity for investment. • Under-utilisation (over-forecast of demand) of many major new infrastructure projects. 7. Lack of transparency and authentic public participation in decision processes. This report contains several major parts. The next part, The Value of Access to Opportunity (chapter 2) discusses the framework of the Fundamental Model of Access. Then chapter 3 of the report, Operationalising Access describes formally how access is measured. This is followed be an examination of how Infill Stations Expand Access (chapter 4), including an example that illustrates how access might change between two public transport service scenarios when an infill station is added, and a sample of some potential sites for Infill Stations on the Sydney network are provided. Access-Oriented Planning Globally: Case Studies (chapter 5), discusses how integrated transport and land use planning is conducted in several key metropolitan regions globally. It looks at the governance structures in the Randstad (Amsterdam, Rotterdam, Utrecht, and The Hague) in the Netherlands, Singapore, Hong Kong, and Tokyo. The subsequent section, Governing for Access in New South Wales: A Future Sydney Commission (chapter 6), describes how long-term strategic transport - land use planning might be conducted in Greater Sydney, with an aim to address several of those inter-related problems. The final section (chapter 7) concludes the report, showing how the proposed strategy addresses the key problems identified above

Network Neutrality: Lessons from Transportation

The politically-charged notion of network neutrality came to the fore in 2005 and 2006, using analogy from transportation as one of the key tools in motivating arguments. This paper examines how the various notions around network neutrality (common carriage, regulation, price discrimination) have played out in the transportation sector, and suggests many of the current arguments fail to understand the nuances of how complex networks actually operate to serve the many demands placed on them.Levinson, David M. (2009). Network Neutrality: Lessons from Transportation. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/179989

Road network circuity in metropolitan areas

Because people seek to minimize their time and travel distance (or cost) when commuting, the circuity–the ratio of network distance traveled to the Euclidean distance between two points–plays an intricate role in the metropolitan economy. This paper seeks to measure the circuity of the United States’ 51 most populated Metropolitan Statistical Areas and identify trends in those circuities over the time period from 1990- 2010. With many factors playing a role such as suburban development and varying economic trends in metropolitan areas over this timeframe, much is to consider when calculating results. In general, circuity is increasing over time.Giacomin, David J; Levinson, David M. (2015). Road network circuity in metropolitan areas. Retrieved from the University Digital Conservancy, http://dx.doi.org/10.1068/b130131p