Central limit theorems for Poisson hyperplane tessellations

We derive a central limit theorem for the number of vertices of convex polytopes induced by stationary Poisson hyperplane processes in $\mathbb{R}^d$. This result generalizes an earlier one proved by Paroux [Adv. in Appl. Probab. 30 (1998) 640--656] for intersection points of motion-invariant Poisson line processes in $\mathbb{R}^2$. Our proof is based on Hoeffding's decomposition of $U$-statistics which seems to be more efficient and adequate to tackle the higher-dimensional case than the ``method of moments'' used in [Adv. in Appl. Probab. 30 (1998) 640--656] to treat the case $d=2$. Moreover, we extend our central limit theorem in several directions. First we consider $k$-flat processes induced by Poisson hyperplane processes in $\mathbb{R}^d$ for $0\le k\le d-1$. Second we derive (asymptotic) confidence intervals for the intensities of these $k$-flat processes and, third, we prove multivariate central limit theorems for the $d$-dimensional joint vectors of numbers of $k$-flats and their $k$-volumes, respectively, in an increasing spherical region.Comment: Published at http://dx.doi.org/10.1214/105051606000000033 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

The new keynesian approach to dynamic general equilibrium modeling: models, methods, and macroeconomic policy evaluation

This chapter aims to provide a hands-on approach to New Keynesian models and their uses for macroeconomic policy analysis. It starts by reviewing the origins of the New Keynesian approach, the key model ingredients and representative models. Building blocks of current-generation dynamic stochastic general equilibrium (DSGE) models are discussed in detail. These models address the famous Lucas critique by deriving behavioral equations systematically from the optimizing and forward-looking decision-making of households and firms subject to well-defined constraints. State-of-the-art methods for solving and estimating such models are reviewed and presented in examples. The chapter goes beyond the mere presentation of the most popular benchmark model by providing a framework for model comparison along with a database that includes a wide variety of macroeconomic models. Thus, it offers a convenient approach for comparing new models to available benchmarks and for investigating whether particular policy recommendations are robust to model uncertainty. Such robustness analysis is illustrated by evaluating the performance of simple monetary policy rules across a range of recently-estimated models including some with financial market imperfections and by reviewing recent comparative findings regarding the magnitude of government spending multipliers. The chapter concludes with a discussion of important objectives for on-going and future research using the New Keynesian framework

Multiple modernities? The case against

"The paper rejects the notion of 'multiple modernities' as both conceptually flawed and empirically unfounded. In line with the sociological tradition, it will argue that we should speak of modernity only in the singular. Modernity, according to this view, denotesa peculiar epoch in the history of human kind, originating in Europe and spreading from there to the rest of the world. We may well be tempted to succumb too quickly to ill-conceived generalizations of what are in fact often only particular, locally based experiences. But we should also not lose sight of the truly revolutionary character of the historical 'breakthrough' to modernity. The protagonists of the multiple modernities paradigm appear to be doing precisely this: their very terminology impliesa trivialization of what is common to 'the' modern condition. At the same time, it suggests an overrating of which ever diversities (may) exist in different parts of the world. The paper will identify four main conceptual flaws in the pertinent literature: 1. The proclivity to equate modernity with its polity. The proposed conception of modernity is thus too thin for capturing the complex social structure of modern society as a whole. 2. To the extent that a theory of modernity is proposed at all, this theory is a self proclaimed cultural theory. Such a theory may shed light on some of the historical roots and self-perceptions of modernity, but it does so at the cost of excluding any thorough analysis of institutions. 3. The conceptualization of inter-societal difference in civilizational terms is misleading because it rules out, almost by definition, the possibility that countries belonging to different civilizations may in certain respects have more in common with ones from other civilizations than with some of the members of their 'own'. 4. The account's notion of diversity is exceedingly vague - the nature and profundity of the differences that are said to exist between different modernities are nowhere discussed at adequate length. But we need to know them to assess their social theoretic significance. In addition to these conceptual flaws, there are also various empirical phenomena and trends that challenge key premises of the multiple modernities approach. None of this is to say there are no differences between different regions, countries, civilizations. Nor is it to suggest their insignificance. It is, however, to suggest that we be more precise and that we extend our analyses beyond the confines of culture and politics - at least if we want to say something meaningful about modernity or modern society at large. Rather than speaking of multiple modernities, a better alternative to accommodate existing differences might be a yet to be developed concept of 'varieties of modernity' - akin to (but naturally pitched at a higher level of abstraction than) the notion of 'varieties of capitalism' which is beginning to crystallize in the new political economy literature." (author's abstract

What's wrong with the concept of multiple modernities?

The concept of multiple modernities has been developed with a view to highlighting the ways in which modern societies differ from each other. Other sociological approaches, by contrast, emphasize such societies' commonalities. But does the juxtaposition of convergence and divergence in the form of a mutually exclusive, binary opposition really make sense? Might it be that there is convergence in some respect, while diversity persists in other respects; that there are dimensions of social change that exhibit common trends across regions and cultural zones, while other aspects of social life show remarkable resilience against homogenization? The present paper argues that our observation of convergence or diversity might be less a matter of truth or falsity than an artifact of our chosen methodologies. Based on this premise, the concept of multiple modernities will be rejected as sociologically meaningless, conceptually flawed and empirically dubious. It is sociologically meaningless because its advocates fail to spell out sufficiently clearly what they mean by modern as against non-modern societies; it is conceptually flawed because it does not provide criteria for distinguishing theoretically significant from insignificant (or less significant) differences, and it is empirically dubious because it misrepresents the state of the world's development

Limits to growth? China's rise and its implications for Europe

"The paper outlines two future scenarios, one 'pessimistic', the other more 'optimistic'. The first assumes that definite limits to growth exist and that, to the extent that this is still possible, economic policies must be radically altered to prevent the collapse of our ecosystems ('global warming'). If this assessment were correct, then we would probably be doomed. For even if all understood the dangers, it would still seem to be extremely unlikely that the major world powers will exit the market economy, i.e. an economic system premised on perpetual growth, anytime soon. Because such a scenario, while possibly realistic, would be social scientifically sterile (why bother if the world is going bust anyway?), the second scenario construes a somewhat 'friendlier' outlook of the future, one in which technologies become available that render economic growth and ecological sustainability compatible. If this scenario came true, then where would the world be headed in the 21st century? This is the question I wish to pursue here, with special emphasis given to China's rise and its implications for Europe. During the past 27 years, China's economy exhibited an average annual growth of 9.6%. At this rate of growth, a country doubles its income every 7.5 years. That means a child born in China today grows up in a country that is 12 times richer than it was during the youth of his/ her parents. If this growth continues unabated, as economist believe it can for at least several more years, then China will overtake the US as the world's largest economy by 2020. At that point, China's per capita incomes would still be below the OECD average. But the world would already have witnessed the emergence of an economic giant of historically unprecedented proportions. And this giant would still have ample scope for further catching up. Given that China's population is more than double that of the whole West, a China that reached a level of development similar to that of an average OECD member would dwarf any single European economy and, eventually, surpass the economies of North America and Europe combined. This would not only shift the weights in the world economy, but sooner or later also those in world politics, in military strength, and, potentially, in the areas of science and (popular) culture as well. At the present point in time, nobody can say with certainty whether any of this will come true. But if it did, then it would mean nothing less than the end of an era that lasted for about 500 years: the era of uncontested European or, for that matter, Western supremacy. Since China is not the only newly emerging power (as is well known, India and Brazil are rapidly rising too now), such a development would seem to be all the more likely. Thus far, however, Europeans appear to be largely oblivious to it. Remarkably, this is true even of the continent's leading intellectual circles. They had better attend to the matter and prepare their publics." (author's abstract

Geochemistry of cold seeps - Fluid sources and systematics

Emanation of fluids at cold seeps, mud volcanoes, and other types of submarine seepage structures is a typical phenomenon occurring at continental margins worldwide. They represent pathways along which volatiles and solutes are recycled from deeply buried sediments into the global ocean, and hence they may be considered as a potentially important link in global geochemical cycles. In this contribution we present geochemical data from various geological and tectonic settings such as the Gulf of Cadiz, the convergent margin off Central America, and/or the Black Sea and provide approaches how to systemize available data sets. Clay-mineral dewatering plays a central role in terms of fluid-mobilization from greater depth, however, resulting cold seep fluids are typically very different from each other and cover a large range of geochemical signatures. This is is due to variations in control parameters such as the type and thickness of the sediment cover, thermal conditions, extension of fluid pathways, and the potential for secondary overprinting. For example, freshened fluids emanating at cold seeps off Costa Rica indicate dewatering and related geochemical reactions in subducting sediments, while fluids sampled at mud volcanoes in the Gulf of Cadiz provide evidence for a high-temperature fluid source originating in the underlying oceanic basement. The latter finding provides evidence for a hydrological connection between buried oceanic crust and the water column even at old crustal ages. Varius geochemical tracers were proposed in the past to decipher relevant processes in the subsurface. In a recent systematic study, Scholz et al. [1] demonstrated the general use of Li, reflecting the temperature-dependent isotope fractionation during early diagenetic Li uptake and burial diagenetic Li release from sediments. However, additional approaches are required in order to provide robust geochmical interpretations of cold seep fluids

Anaerobic oxidation of methane in the Concepcion Methane Seep Area, Chilean continental margin

Within subduction zones of active continental margins, large amounts of methane can be mobilized by dewatering processes and transported to the seafloor along migration pathways. A recently discovered seep area located off Concepción (Chile) at water depth between 600 to 1100 mbsl is characterized by active methane vent sites as well as massive carbonates boulders and plates which probably are related to methane seepage in the past. During the SO210 research expedition “Chiflux” (Sept-Oct 2010), sediment from the Concepción Methane Seep Area (CSMA) at the fore arc of the Chilean margin was sampled to study microbial activity related to methane seepage. We sampled surface sediments (0-30cm) from sulfur bacteria mats, as well as clam, pogonophoran, and tubeworm fields with push cores and a TV-guided multicorer system. Anaerobic oxidation of methane (AOM) and sulfate reduction rates were determined using ex-situ radioisotope tracer techniques. Additionally, porewater chemistry of retrieved cores as well as isotopic composition and age record of surrounding authigenic carbonates were analyzed. The shallowest sulfate-methane-transition zone (SMTZ) was identified at 4 cm sediment depth hinting to locally strong fluid fluxes. However, a lack of Cl- anomalies in porewater profiles indicates a shallow source of these fluids, which is supported by the biogenic origin of the methane (�13C -70h PDB). Sulfide and alkalinity was relatively high (up to 20 mM and 40 mEq, respectively). Rates of AOM and sulfate reduction within this area reached magnitudes typical for seeps with variation between different habitat types, indicating a diverse methane supply, which is affecting the depths of the SMTZ. Rates were highest at sulfur a bacteria mats (20 mmol m-2 d-1) followed by a large field of dead clams, a pogonophoran field, a black sediment spot, and a carbonate rich clam field. Lowest rates (0.2 mmol m-2 d-1) were measured in close vicinity to these hot spots. Abundant massive carbonate blocks and plates hint to a very old seep system with a probably much higher activity in the past. The U-Th age record of these authigenic carbonates reach back to periods of venting activity with more than 150 ka ago. Carbon isotopic signatures of authigenic carbonates (�13C -50 to -40hPDB) suggest a biogenic carbon source (i.e. methane), also in the past. We found several indications for the impact of recent earthquakes within the seep area (cracks, shifted seafloor), which could be an important mechanism for the triggering of new seepage activity, change in fluid expulsion rates and colonization patterns of the cold seep fauna