Diffusion coefficients for multi-step persistent random walks on lattices

We calculate the diffusion coefficients of persistent random walks on lattices, where the direction of a walker at a given step depends on the memory of a certain number of previous steps. In particular, we describe a simple method which enables us to obtain explicit expressions for the diffusion coefficients of walks with two-step memory on different classes of one-, two- and higher-dimensional lattices.Comment: 27 pages, 2 figure

Despite the recent crises in Syria and Ukraine, reforming UN Security Council decision-making remains a pipe dream

The decision-making procedures used in the UN Security Council – chiefly the veto granted to its five permanent members – have frequently been criticised on the basis that they prevent agreements being reached on key issues. This criticism has been particularly acute with respect to the failure of the Security Council to agree joint positions on the ongoing crises in Syria and Ukraine. Thomas G. Weiss argues that while such arguments have been made for decades, there remain no easy answers. Nevertheless, despite the recent criticism, the Security Council is likely to remain as relevant to international peace and security as it ever was

A stable range description of the space of link maps

We study the space of link maps, which are smooth maps from the disjoint union of manifolds P and Q to a manifold N such that the images of P and Q are disjoint. We give a range of dimensions, interpreted as the connectivity of a certain map, in which the cobordism class of the "linking manifold" is enough to distinguish the homotopy class of one link map from another.Comment: 10 page

The 'Third' UN: imagining post-COVID-19 multilateralism

If the United Nations system is to remain relevant, or even survive, the thinking to re‐imagine and redesign contemporary global governance will come from the Third UN. This article focuses on the ecology of supportive non‐state actors – intellectuals, scholars, consultants, think tanks, NGOs, the for‐profit private sector, and the media – that interacts with the intergovernmental machinery of the First UN and international civil servants of the Second UN to formulate and refine ideas and decision‐making in policy processes. Despite the growth in analyses of non‐state actors in global governance, the ‘other’ or ‘Third’ UN is poorly understood, often ignored, and normally discounted. Some advocate for particular ideas, others help analyze or operationalize their testing and implementation; in any case, many help the UN ‘think’ and have an impact on how we think about the United Nations

Change and continuity in global governance

Why, despite well-established and well-publicized intergovernmental processes that date back to the early 1970s, have we been unable to put in place effective mechanisms to combat climate change? Why, despite the existence of extensive global human rights machinery, do we live in a world where mass kidnapping, rape, torture, and murder continue to blight the lives of so many? Why, despite a great deal of effort on the part of intergovernmental organizations (IGOs) and nonstate actors, have we been unable to make much of a difference to the lives of the ultra-poor and attenuate the very worst aspects of growing global inequalities? Most fundamentally, why have the current international system and the outcomes that it has produced remained so inadequate in the postwar period

1945’s Forgotten Insight: Multilateralism as Realist Necessity

The 70th anniversary of the signing and entry into force of the UN Charter provided an occasion to explore the historical underpinnings of contemporary global governance. This article redresses the neglect of the United Nations as a multilateral structure before the conference that drafted the Charter in 1945. It rehabilitates an underappreciated aspect of the period that began on January 1, 1942, with the “Declaration by United Nations,” namely, the combination of multilateral strategies for military and human security to achieve victory in war and peace. The wide substantive and geographic resonance suggests the extent to which the pressures of the second war to end all wars helped states to overcome their disinclination to collaborate. Today’s fashionable calls for “good enough” global governance abandon the strategy of constructing robust intergovernmental organizations; they are not good enough, especially, because our forebears did much better. Many insights and operational approaches from 1942 to 1945 remain valid for addressing twenty-first-century global challenges

Optimizing Higher-Order Lagrangian Perturbation Theory for Standard CDM and BSI models

We investigate the performance of Lagrangian perturbation theory up to the second order for two scenarios of cosmological large-scale structure formation, SCDM (standard cold dark matter) and BSI (broken scale invariance). The latter model we study as a representative of COBE-normalized CDM models which fit the small-scale power of galaxy surveys. In this context we optimize the performance of the Lagrangian perturbation schemes by smoothing the small-scale fluctuations in the initial data. The results of the so obtained Lagrangian mappings are computed for a set of COBE-normalized SCDM and BSI initial data of different sizes and at different times. We compare these results against those obtained with a numerical PM-code. We find an excellent performance of the optimized Lagrangian schemes down to scales close to the correlation length. This is explained by the counterintuitive fact that nonlinearities in the model can produce more small-scale power, if initially such power is removed. The optimization scheme can be expressed in a way which is independent of the type of fluctuation spectrum and of the size of the simulations.Comment: 19 pages uuencoded compressed postscript file (including 7 figures). Figure 8 (greyscale and color postcript files) are available by anonymous ftp from ftp://ibm-3.mpa-garching.mpg.de/pub/aow . See the directory with this preprint numbe

Humanitarianism's Contested Culture in War Zones

Humanitarians are no longer simply seen as selfless angels. Their motivations and mastery, their principles and products are questioned from within and from without. Understanding the ongoing transformations in contemporary humanitarianism requires examining the nature and evolution of humanitarian culture away from an agreed culture of cooperation to a contested one of competition. The latter reflects militarization, politicization, and marketization. What is required is a learning culture for practitioners and a consequentialist ethics more oriented to responsible reflection than rapid reaction