http://planet.livingreviews.org/ en Planet Livingreviews - http://planet.livingreviews.org/ http://solarphysics.livingreviews.org/Articles/lrsp-2010-1 http://www.livingreviews.org/lrsp-2010-1 The Solar Cycle is reviewed. The 11-year cycle of solar activity is characterized by the rise and fall in the numbers and surface area of sunspots. We examine a number of other solar activity indicators including the 10.7 cm radio flux, the total solar irradiance, the magnetic field, flares and coronal mass ejections, geomagnetic activity, galactic cosmic ray fluxes, and radioisotopes in tree rings and ice cores that vary in association with the sunspots. We examine the characteristics of individual solar cycles including their maxima and minima, cycle periods and amplitudes, cycle shape, and the nature of active latitudes, hemispheres, and longitudes. We examine long-term variability including the Maunder Minimum, the Gleissberg Cycle, and the Gnevyshev–Ohl Rule. Short-term variability includes the 154-day periodicity, quasi-biennial variations, and double peaked maxima. We conclude with an examination of prediction techniques for the solar cycle. Tue, 02 Mar 2010 11:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2010-1 http://www.livingreviews.org/lrr-2010-1 Several km-scale gravitational-wave detectors have been constructed world wide. These instruments combine a number of advanced technologies to push the limits of precision length measurement. The core devices are laser interferometers of a new kind; developed from the classical Michelson topology these interferometers integrate additional optical elements, which significantly change the properties of the optical system. Much of the design and analysis of these laser interferometers can be performed using well-known classical optical techniques, however, the complex optical layouts provide a new challenge. In this review we give a textbook-style introduction to the optical science required for the understanding of modern gravitational wave detectors, as well as other high-precision laser interferometers. In addition, we provide a number of examples for a freely available interferometer simulation software and encourage the reader to use these examples to gain hands-on experience with the discussed optical methods. Thu, 25 Feb 2010 11:00:00 +0000 http://europeangovernance.livingreviews.org/Articles/lreg-2009-3 http://www.livingreviews.org/lreg-2009-3 This article reviews the literature on Europeanization beyond the group of EU member, “quasi-member” and applicant states. It uses the analysis of Europeanization in applicant states as a theoretical starting point to ask if, how and under which conditions we can expect domestic effects of European integration beyond Europe. Focusing on Europeanization effects in the areas of regionalism, democracy and human rights, and the literature on the European Neighborhood Policy in particular, the article collects findings on the strategies and instruments as well as the impact and effectiveness of the EU. The general conclusion to be drawn from the theoretical and empirical literature reviewed is one of low consistency and impact. Thu, 17 Dec 2009 11:00:00 +0000 http://solarphysics.livingreviews.org/Articles/lrsp-2009-4 http://www.livingreviews.org/lrsp-2009-4 Active regions on the solar surface are generally thought to originate from a strong toroidal magnetic field generated by a deep seated solar dynamo mechanism operating at the base of the solar convection zone. Thus the magnetic fields need to traverse the entire convection zone before they reach the photosphere to form the observed solar active regions. Understanding this process of active region flux emergence is therefore a crucial component for the study of the solar cycle dynamo. This article reviews studies with regard to the formation and rise of active region scale magnetic flux tubes in the solar convection zone and their emergence into the solar atmosphere as active regions. Mon, 14 Dec 2009 11:00:00 +0000 http://solarphysics.livingreviews.org/Articles/lrsp-2009-3 http://www.livingreviews.org/lrsp-2009-3 Coronal holes are the darkest and least active regions of the Sun, as observed both on the solar disk and above the solar limb. Coronal holes are associated with rapidly expanding open magnetic fields and the acceleration of the high-speed solar wind. This paper reviews measurements of the plasma properties in coronal holes and how these measurements are used to reveal details about the physical processes that heat the solar corona and accelerate the solar wind. It is still unknown to what extent the solar wind is fed by flux tubes that remain open (and are energized by footpoint-driven wave-like fluctuations), and to what extent much of the mass and energy is input intermittently from closed loops into the open-field regions. Evidence for both paradigms is summarized in this paper. Special emphasis is also given to spectroscopic and coronagraphic measurements that allow the highly dynamic non-equilibrium evolution of the plasma to be followed as the asymptotic conditions in interplanetary space are established in the extended corona. For example, the importance of kinetic plasma physics and turbulence in coronal holes has been affirmed by surprising measurements from the UVCS instrument on SOHO that heavy ions are heated to hundreds of times the temperatures of protons and electrons. These observations point to specific kinds of collisionless Alfvén wave damping (i.e., ion cyclotron resonance), but complete theoretical models do not yet exist. Despite our incomplete knowledge of the complex multi-scale plasma physics, however, much progress has been made toward the goal of understanding the mechanisms ultimately responsible for producing the observed properties of coronal holes. Tue, 29 Sep 2009 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2009-6 http://www.livingreviews.org/lrr-2009-6 A priori, there is nothing very special about shear-free or asymptotically shear-free null geodesic congruences. Surprisingly, however, they turn out to possess a large number of fascinating geometric properties and to be closely related, in the context of general relativity, to a variety of physically significant effects. It is the purpose of this paper to try to fully develop these issues. This work starts with a detailed exposition of the theory of shear-free and asymptotically shear-free null geodesic congruences, i.e., congruences with shear that vanishes at future conformal null infinity. A major portion of the exposition lies in the analysis of the space of regular shear-free and asymptotically shear-free null geodesic congruences. This analysis leads to the space of complex analytic curves in complex Minkowski space. They in turn play a dominant role in the applications. The applications center around the problem of extracting interior physical properties of an asymptotically-flat spacetime directly from the asymptotic gravitational (and Maxwell) field itself, in analogy with the determination of total charge by an integral over the Maxwell field at infinity or the identification of the interior mass (and its loss) by (Bondi’s) integrals of the Weyl tensor, also at infinity. More specifically, we will see that the asymptotically shear-free congruences lead us to an asymptotic definition of the center-of-mass and its equations of motion. This includes a kinematic meaning, in terms of the center-of-mass motion, for the Bondi three-momentum. In addition, we obtain insights into intrinsic spin and, in general, angular momentum, including an angular-momentum–conservation law with well-defined flux terms. When a Maxwell field is present, the asymptotically shear-free congruences allow us to determine/define at infinity a center-of-charge world line and intrinsic magnetic dipole moment. Fri, 11 Sep 2009 10:00:00 +0000 http://landscaperesearch.livingreviews.org/Articles/lrlr-2009-3 http://www.livingreviews.org/lrlr-2009-3 This article aims to give an overview of how place meanings are created and how they influence people's sense of belonging. It should be noted that the current literature has various shortcomings which mostly result from the lack of interdisciplinary research. The studies in place attachment usually focus on personal sense of belonging leaving aside those extending over various scales -- such as, for instance, national identity. Also, place meanings and identity are primarily discussed as the very personal phenomena. On the contrary, place making and shaping is usually seen through more structural viewpoint by claiming that places mainly change in result of political or economic processes. Nowadays, there are even claims that due to the influx of globalization place no more matters and similar processes will happen everywhere. This notion does not take into account the special character of every place and the fact that outside forces come together in different ways in every place. Authors suggest that these different perspectives need to be united in order to fully grasp the character of place making and place meanings. In current articles, authors have adopted the multi-disciplinary approach and understood the place as uniting different processes starting from deeply personal meaning creation and ending with changes happening in global scale. Wed, 29 Jul 2009 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2009-5 http://www.livingreviews.org/lrr-2009-5 The sensitivity of present ground-based gravitational wave antennas is too low to detect many events per year. It has, therefore, been planned for years to build advanced detectors allowing actual astrophysical observations and investigations. In such advanced detectors, one major issue is to increase the laser power in order to reduce shot noise. However, this is useless if the thermal noise remains at the current level in the 100 Hz spectral region, where mirrors are the main contributors. Moreover, increasing the laser power gives rise to various spurious thermal effects in the same mirrors. The main goal of the present study is to discuss these issues versus the transverse structure of the readout beam, in order to allow comparison. A number of theoretical studies and experiments have been carried out, regarding thermal noise and thermal effects. We do not discuss experimental problems, but rather focus on some theoretical results in this context about arbitrary order Laguerre–Gauss beams, and other “exotic” beams. Fri, 17 Jul 2009 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2009-4 http://www.livingreviews.org/lrr-2009-4 The present status of the quasi-local mass, energy-momentum and angular-momentum constructions in general relativity is reviewed. First, the general ideas, concepts, and strategies, as well as the necessary tools to construct and analyze the quasi-local quantities, are recalled. Then, the various specific constructions and their properties (both successes and deficiencies are discussed. Finally, some of the (actual and potential) applications of the quasi-local concepts and specific constructions are briefly mentioned. This review is based on talks given at the Erwin Schrödinger Institute, Vienna in July 1997, at the Universität Tübingen in May 1998, and at the National Center for Theoretical Sciences in Hsinchu, Taiwan and at the National Central University, Chungli, Taiwan, in July 2000. Fri, 19 Jun 2009 10:00:00 +0000 http://europeangovernance.livingreviews.org/Articles/lreg-2009-2 http://www.livingreviews.org/lreg-2009-2 This Living Review presents an overview of the research on European identity in the context of EU governance by focussing on central debates in the political science literature. It departs from the problems of disagreement between European citizens and their elites as well as the lack of a European demos. Against this background, the article discusses the functions of collective identity including the legitimation function and solution of collective dilemmas. Here, two perspectives pertaining to these functions are depicted: first, the issue of European public space and second, the integrative workings of European citizenship. Next, the article explores the conceptual and methodological problems of the research on European collective identity. In particular, it focuses on the conceptual ambiguity of the collective identity term and problems of operationalization and measurement. Following this, the article discusses the literature on identity technologies of the EU and identifies the shortcomings of identity technologies with regard to EU governance. Tue, 19 May 2009 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2009-3 http://www.livingreviews.org/lrr-2009-3 I review the development of numerical evolution codes for general relativity based upon the characteristic initial value problem. Progress is traced from the early stage of 1D feasibility studies to 2D axisymmetric codes that accurately simulate the oscillations and gravitational collapse of relativistic stars and to current 3D codes that provide pieces of a binary black hole spacetime. Cauchy codes have now been successful at simulating all aspects of the binary black hole problem inside an artificially constructed outer boundary. A prime application of characteristic evolution is to eliminate the role of this artificial outer boundary via Cauchy-characteristic matching, by which the radiated waveform can be computed at null infinity. Progress in this direction is discussed. Thu, 16 Apr 2009 10:00:00 +0000 http://landscaperesearch.livingreviews.org/Articles/lrlr-2009-2 http://www.livingreviews.org/lrlr-2009-2 Urbanisation belongs to the most complex and dynamic processes of land use and landscape change. At present, we claim ``the millennium of the cities,'' since more than half of the currently 6.6 billion world population is living in urban areas. Due to the huge impact of urban land consumption on environment and landscape, this paper provides a review of existing urban land use models. The review analyses non-spatially explicit economic and system dynamics models, spatially explicit cellular automata and agent-based model approaches by addressing the respective conceptual approach, model components and causal relationships, including feedbacks. Based upon the review, conclusions are drawn regarding the future development of urban landscape models, as well as on indispensable causal relationships and their representation when modelling urban systems. Thu, 09 Apr 2009 10:00:00 +0000 http://solarphysics.livingreviews.org/Articles/lrsp-2009-2 http://www.livingreviews.org/lrsp-2009-2 We review the properties of solar convection that are directly observable at the solar surface, and discuss the relevant underlying physics, concentrating mostly on a range of depths from the temperature minimum down to about 20 Mm below the visible solar surface. The properties of convection at the main energy carrying (granular) scales are tightly constrained by observations, in particular by the detailed shapes of photospheric spectral lines and the topology (time- and length-scales, flow velocities, etc.) of the up- and downflows. Current supercomputer models match these constraints very closely, which lends credence to the models, and allows robust conclusions to be drawn from analysis of the model properties. At larger scales the properties of the convective velocity field at the solar surface are strongly influenced by constraints from mass conservation, with amplitudes of larger scale horizontal motions decreasing roughly in inverse proportion to the scale of the motion. To a large extent, the apparent presence of distinct (meso- and supergranulation) scales is a result of the folding of this spectrum with the effective "filters" corresponding to various observational techniques. Convective motions on successively larger scales advect patterns created by convection on smaller scales; this includes patterns of magnetic field, which thus have an approximately self-similar structure at scales larger than granulation. Radiative-hydrodynamical simulations of solar surface convection can be used as 2D/3D time-dependent models of the solar atmosphere to predict the emergent spectrum. In general, the resulting detailed spectral line profiles agree spectacularly well with observations without invoking any micro- and macroturbulence parameters due to the presence of convective velocities and atmosphere inhomogeneities. One of the most noteworthy results has been a significant reduction in recent years in the derived solar C, N, and O abundances with far-reaching consequences, not the least for helioseismology. Convection in the solar surface layers is also of great importance for helioseismology in other ways; excitation of the wave spectrum occurs primarily in these layers, and convection influences the size of global wave cavity and, hence, the mode frequencies. On local scales convection modulates wave propagation, and supercomputer convection simulations may thus be used to test and calibrate local helioseismic methods. We also discuss the importance of near solar surface convection for the structure and evolution of magnetic patterns: faculae, pores, and sunspots, and briefly address the question of the importance or not of local dynamo action near the solar surface. Finally, we discuss the importance of near solar surface convection as a driver for chromospheric and coronal heating. Sat, 04 Apr 2009 10:00:00 +0000 http://landscaperesearch.livingreviews.org/Articles/lrlr-2009-1 http://www.livingreviews.org/lrlr-2009-1 The aim of this overview paper is to analyze the use of various landscape metrics and landscape indices for the characterization of landscape structure and various processes at both landscape and ecosystem level. We analyzed the appearance of the terms landscape metrics/indexes/indices in combination with seven main categories in the field of landscape ecology [1) use/selection and misuse of metrics, 2) biodiversity and habitat analysis; 3) water quality; 4) evaluation of the landscape pattern and its change; 5) urban landscape pattern, road network; 6) aesthetics of landscape; 7) management, planning and monitoring] in the titles, abstracts and/or key words of research papers published in international peer-reviewed scientific journals indexed by the Institute of Science Information (ISI)\href{http://isiknowledge.com/wos}{Web of Science (WoS)} from 1994 to October 2008. Most of the landscape metrics and indices are used concerning biodiversity and habitat analysis, and also the evaluation of landscape pattern and its change (up to 25 articles per year). There are only a few articles on the relationships of landscape metrics/indices/indexes to social aspects and landscape perception. Tue, 17 Mar 2009 11:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2009-2 http://www.livingreviews.org/lrr-2009-2 Gravitational wave detectors are already operating at interesting sensitivity levels, and they have an upgrade path that should result in secure detections by 2014. We review the physics of gravitational waves, how they interact with detectors (bars and interferometers), and how these detectors operate. We study the most likely sources of gravitational waves and review the data analysis methods that are used to extract their signals from detector noise. Then we consider the consequences of gravitational wave detections and observations for physics, astrophysics, and cosmology. Wed, 04 Mar 2009 11:00:00 +0000 http://solarphysics.livingreviews.org/Articles/lrsp-2009-1 http://www.livingreviews.org/lrsp-2009-1 This article surveys the development of observational understanding of the interior rotation of the Sun and its temporal variation over approximately forty years, starting with the 1960s attempts to determine the solar core rotation from oblateness and proceeding through the development of helioseismology to the detailed modern picture of the internal rotation deduced from continuous helioseismic observations during solar cycle 23. After introducing some basic helioseismic concepts, it covers, in turn, the rotation of the core and radiative interior, the “tachocline” shear layer at the base of the convection zone, the differential rotation in the convection zone, the near-surface shear, the pattern of migrating zonal flows known as the torsional oscillation, and the possible temporal variations at the bottom of the convection zone. For each area, the article also briefly explores the relationship between observations and models. Mon, 23 Feb 2009 11:00:00 +0000 http://europeangovernance.livingreviews.org/Articles/lreg-2009-1 http://www.livingreviews.org/lreg-2009-1 This Living Review makes the case for the study of Europeanization and political parties as related but distinct from the study of political parties and European integration. It then presents the Europeanization approach to parties, noting that some of the components in this approach developed to study policy and institutional change may not lend themselves so well to the study of national parties. This argument distinguishes between direct and indirect effects of European Union influence on parties. Next, it briefly discusses the application of party Europeanization research to post-communist parties. This is followed by a discussion of proposed normative consequences of party Europeanization. Finally, suggestions for further research focuses on the need for refining the analytic framework in order to better identify the causal mechanisms specific to party Europeanization. Tue, 27 Jan 2009 11:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2009-1 http://www.livingreviews.org/lrr-2009-1 Equations arising in general relativity are usually too complicated to be solved analytically and one must rely on numerical methods to solve sets of coupled partial differential equations. Among the possible choices, this paper focuses on a class called spectral methods in which, typically, the various functions are expanded in sets of orthogonal polynomials or functions. First, a theoretical introduction of spectral expansion is given with a particular emphasis on the fast convergence of the spectral approximation. We then present different approaches to solving partial differential equations, first limiting ourselves to the one-dimensional case, with one or more domains. Generalization to more dimensions is then discussed. In particular, the case of time evolutions is carefully studied and the stability of such evolutions investigated. We then present results obtained by various groups in the field of general relativity by means of spectral methods. Work, which does not involve explicit time-evolutions, is discussed, going from rapidly-rotating strange stars to the computation of black-hole–binary initial data. Finally, the evolution of various systems of astrophysical interest are presented, from supernovae core collapse to black-hole–binary mergers. Fri, 09 Jan 2009 11:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2008-10 http://www.livingreviews.org/lrr-2008-10 The physics of neutron star crusts is vast, involving many different research fields, from nuclear and condensed matter physics to general relativity. This review summarizes the progress, which has been achieved over the last few years, in modeling neutron star crusts, both at the microscopic and macroscopic levels. The confrontation of these theoretical models with observations is also briefly discussed. Fri, 12 Dec 2008 11:00:00 +0000 http://landscaperesearch.livingreviews.org/Articles/lrlr-2008-3 http://www.livingreviews.org/lrlr-2008-3 Urbanization is a well-known topic in sustainable development debates as it is known to have great impacts on landscape and environment. Low density, apparently random, scattered or fragmented and leap frogging forms of urban land use, not classified as core urban fabric (town, city, ...) nor classified as real ‘countryside’ are studied in this paper. With a thorough literature study of more than 200 publications, a number of interesting conclusions about this important environmental and socio-economical phenomenon can be made. At first, it is generally described as either a type of land use or land use dynamic functioning as ‘divide’ between city and countryside (the urban fringe theory), or it is very often described as the dynamic and fast transformation of rural land into urban land (the sprawl approach). In some cases it forms its own ‘landscape’ and it is called the peri-urban or more correctly semi-urban area. Generally, there seems to be a lack of good definitions and frameworks, although it is studied often and in various scientific disciplines. Prominently, there is an always present dichotomy between rural and urban in all concepts, theories and definitions proposed. Tue, 09 Dec 2008 11:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2008-9 http://www.livingreviews.org/lrr-2008-9 Neutron stars and black holes are the astrophysical systems with the strongest gravitational fields in the universe. In this article, I review the prospect of using observations of such compact objects to probe some of the most intriguing general relativistic predictions in the strong-field regime: the absence of stable circular orbits near a compact object and the presence of event horizons around black-hole singularities. I discuss the need for a theoretical framework, within which future experiments will provide detailed, quantitative tests of gravity theories. Finally, I summarize the constraints imposed by current observations of neutron stars on potential deviations from general relativity. Tue, 18 Nov 2008 11:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2008-8 http://www.livingreviews.org/lrr-2008-8 We review the main properties, demographics and applications of binary and millisecond radio pulsars. Our knowledge of these exciting objects has greatly increased in recent years, mainly due to successful surveys which have brought the known pulsar population to over 1800. There are now 83 binary and millisecond pulsars associated with the disk of our Galaxy, and a further 140 pulsars in 26 of the Galactic globular clusters. Recent highlights include the discovery of the young relativistic binary system PSR J1906+0746, a rejuvination in globular cluster pulsar research including growing numbers of pulsars with masses in excess of $1.5\,M_{\odot}$, a precise measurement of relativistic spin precession in the double pulsar system and a Galactic millisecond pulsar in an eccentric (e=0.44) orbit around an unevolved companion. Tue, 04 Nov 2008 11:00:00 +0000 http://solarphysics.livingreviews.org/Articles/lrsp-2008-3 http://www.livingreviews.org/lrsp-2008-3 Presented here is a review of present knowledge of the long-term behavior of solar activity on a multi-millennial timescale, as reconstructed using the indirect proxy method. The concept of solar activity is discussed along with an overview of the special indices used to quantify different aspects of variable solar activity, with special emphasis upon sunspot number. Over long timescales, quantitative information about past solar activity can only be obtained using a method based upon indirect proxy, such as the cosmogenic isotopes 14C and 10Be in natural stratified archives (e.g., tree rings or ice cores). We give an historical overview of the development of the proxy-based method for past solar-activity reconstruction over millennia, as well as a description of the modern state. Special attention is paid to the verification and cross-calibration of reconstructions. It is argued that this method of cosmogenic isotopes makes a solid basis for studies of solar variability in the past on a long timescale (centuries to millennia) during the Holocene. A separate section is devoted to reconstructions of strong solar–energetic-particle (SEP) events in the past, that suggest that the present-day average SEP flux is broadly consistent with estimates on longer timescales, and that the occurrence of extra-strong events is unlikely. Finally, the main features of the long-term evolution of solar magnetic activity, including the statistics of grand minima and maxima occurrence, are summarized and their possible implications, especially for solar/stellar dynamo theory, are discussed. Tue, 21 Oct 2008 10:00:00 +0000 http://europeangovernance.livingreviews.org/Articles/lreg-2008-5 http://www.livingreviews.org/lreg-2008-5 This essay takes stock of the literature on how European Union policies are being put into practice by the member states. It first provides an overview of the historical evolution of the field. After a relatively late start in the mid 1980s, the field has meanwhile developed into one of the growth industries within EU research. The paper identifies three different waves of EU implementation scholarship. The first wave considered implementation primarily a problem of institutional efficiency. In the second wave, the degree of compatibility between European demands and domestic policy legacies took centre stage. However, many second-wave scholars complemented the basic "misfit" argument with a set of additional explanatory factors to account for deviant cases. In the third wave, some researchers began to stress the role of domestic politics, while others re-discovered the importance of administrative capabilities. As an attempt to synthesise some of the partial explanations presented by earlier research, one group of scholars pointed to the existence of culturally-shaped country clusters, each with its own typical style of complying with EU legislation. After this historical overview, the paper summarises the most important theoretical, empirical and methodological lessons to be drawn from existing studies, and it discusses promising avenues for future research. First, most scholars seem to agree on the basic set of factors that may have an impact on transposition processes. The main task to be accomplished by future research is to establish under which conditions which configurations of factors prevail. While we already know that there are country-specific patterns, the importance of sector-specific patterns will need to be explored further. Second, greater research efforts will have to be devoted to the neglected area of enforcement and application. In theoretical terms, going back to the insights of traditional domestic implementation research seems to be most promising for this type of studies. Third, the paper cautions against the poor quality of the data employed by the growing number of quantitative compliance studies. Unless the problems with the data can be solved, scholars are well advised to rely on comparative case studies, at least in addition to statistical analyses. To increase the number of cases to be covered by qualitative research, the paper makes the case for crafting collaborative qualitative research projects as a viable alternative to quantitative research. Tue, 21 Oct 2008 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2008-7 http://www.livingreviews.org/lrr-2008-7 This article presents a comprehensive overview of numerical hydrodynamics and magnetohydrodynamics (MHD) in general relativity. Some significant additions have been incorporated with respect to the previous two versions of this review (2000, 2003), most notably the coverage of general-relativistic MHD, a field in which remarkable activity and progress has occurred in the last few years. Correspondingly, the discussion of astrophysical simulations in general-relativistic hydrodynamics is enlarged to account for recent relevant advances, while those dealing with general-relativistic MHD are amply covered in this review for the first time. The basic outline of this article is nevertheless similar to its earlier versions, save for the addition of MHD-related issues throughout. Hence, different formulations of both the hydrodynamics and MHD equations are presented, with special mention of conservative and hyperbolic formulations well adapted to advanced numerical methods. A large sample of numerical approaches for solving such hyperbolic systems of equations is discussed, paying particular attention to solution procedures based on schemes exploiting the characteristic structure of the equations through linearized Riemann solvers. As previously stated, a comprehensive summary of astrophysical simulations in strong gravitational fields is also presented. These are detailed in three basic sections, namely gravitational collapse, black-hole accretion, and neutron-star evolutions; despite the boundaries, these sections may (and in fact do) overlap throughout the discussion. The material contained in these sections highlights the numerical challenges of various representative simulations. It also follows, to some extent, the chronological development of the field, concerning advances in the formulation of the gravitational field, hydrodynamics and MHD equations and the numerical methodology designed to solve them. To keep the length of this article reasonable, an effort has been made to focus on multidimensional studies, directing the interested reader to earlier versions of the review for discussions on one-dimensional works. Fri, 19 Sep 2008 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2008-6 http://www.livingreviews.org/lrr-2008-6 We review black-hole solutions of higher-dimensional vacuum gravity and higher-dimensional supergravity theories. The discussion of vacuum gravity is pedagogical, with detailed reviews of Myers–Perry solutions, black rings, and solution-generating techniques. We discuss black-hole solutions of maximal supergravity theories, including black holes in anti-de Sitter space. General results and open problems are discussed throughout. Mon, 08 Sep 2008 10:00:00 +0000 http://europeangovernance.livingreviews.org/Articles/lreg-2008-4 http://www.livingreviews.org/lreg-2008-4 There is a plethora of studies on interest groups in the European Union. While these studies have generated a wealth of insights, it is not actually clear what they have accomplished. This Living Review seeks to identify those areas of interest group studies in which our knowledge is fairly consolidated and in which major research gaps or major controversies can be noted. I argue that these research gaps and controversies stem from both the empirical variance in the interest group landscape and the theoretical segmentation of EU interest group studies. These have been shaped by influences from Comparative Politics, International Relations, Policy Analysis, and Democratic Theory. I suggest that future research should engage to a greater extent in cross-cutting theoretical debates in order to overcome the pronounced demarcation of research areas and in more rigorous theory testing than has sometimes been the case. The article starts by discussing the problem of conceptualizing interest groups before moving on to the fissured theoretical landscape. Thereafter, major research themes are discussed. First, I review the relation between EU institutions and interest groups. Here, I look both into multilevel governance and Europeanization studies that focus on the vertical interaction and into analyses that stress the horizontal segmentation of the EU system in different institutions and sectors. Second, I analyze core themes of EU and comparative interest group studies, namely the issue of collective action, the access of interest groups to policy-makers and their influence on EU policymaking. Tue, 02 Sep 2008 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2008-5 http://www.livingreviews.org/lrr-2008-5 The problem of describing the quantum behavior of gravity, and thus understanding quantum spacetime, is still open. Loop quantum gravity is a well-developed approach to this problem. It is a mathematically well-defined background-independent quantization of general relativity, with its conventional matter couplings. Today research in loop quantum gravity forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained so far are: (i) The computation of the spectra of geometrical quantities such as area and volume, which yield tentative quantitative predictions for Planck-scale physics. (ii) A physical picture of the microstructure of quantum spacetime, characterized by Planck-scale discreteness. Discreteness emerges as a standard quantum effect from the discrete spectra, and provides a mathematical realization of Wheeler’s “spacetime foam” intuition. (iii) Control of spacetime singularities, such as those in the interior of black holes and the cosmological one. This, in particular, has opened up the possibility of a theoretical investigation into the very early universe and the spacetime regions beyond the Big Bang. (iv) A derivation of the Bekenstein–Hawking black-hole entropy. (v) Low-energy calculations, yielding n-point functions well defined in a background-independent context. The theory is at the roots of, or strictly related to, a number of formalisms that have been developed for describing background-independent quantum field theory, such as spin foams, group field theory, causal spin networks, and others. I give here a general overview of ideas, techniques, results and open problems of this candidate theory of quantum gravity, and a guide to the relevant literature. Tue, 15 Jul 2008 10:00:00 +0000 http://landscaperesearch.livingreviews.org/Articles/lrlr-2008-2 http://www.livingreviews.org/lrlr-2008-2 It is increasingly expected from environmental research such as landscape research that science directly contributes to the solving of pressing societal problems. However, despite increased efforts to direct research towards societal problems, it is not obvious if science has become more effective in supporting environmental problem-solving. We present in this article a framework that facilitates the analysis and design of problem-orientation in research fields. We then apply the proposed framework to a concrete example of a problem-oriented landscape research field - namely research on biotic invasions. Invasion research addresses the problem that some organisms, that have been introduced by humans to a new geographic area where they were previously not present, spread in the landscape and pose negative impacts. We argue that problem-oriented research is more than applied research. Besides research on specific questions it also encompasses boundary management, i.e., deliberations among experts and stakeholders on the framing of adequate research questions about processes, values and practices for effective problem-solving. We postulate that such research may assist problem-solving in three ways, by analysing causal relationships (systems knowledge), clarifying conflicts of interests and values (target knowledge), or contributing to the development of appropriate means for action (transformation knowledge). We show that over the past decades a broad range of different research approaches has emerged in the young field of invasion research in order to produce systems, target and transformation knowledge for invasive species management. Early research in the field was dominated by the development of systems knowledge, but increasingly the three knowledge forms are treated more equally. The research field has also become more interdisciplinary and context-specific. Boundary management in invasion research is mainly restricted to informal networks (communities of practice), while formal processes such as transdisciplinary research are scarce. We suggest that the paucity of structured and explicit boundary management processes will limit the future development of a more effective science for invasive species management. In particular, we envisage three obstacles that can only be removed through explicit boundary management. First, the existing theoretical frameworks are currently only partly able to integrate natural and social sciences research on the processes underlying invasions. Second, a clarification of the normative thinking about alien plant invasions is needed. Third, research on transformation knowledge has so far not fundamentally challenged the existing conceptual framing and institutional setup of invasive species management. Tue, 15 Jul 2008 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2008-4 http://www.livingreviews.org/lrr-2008-4 Quantum gravity is expected to be necessary in order to understand situations in which classical general relativity breaks down. In particular in cosmology one has to deal with initial singularities, i.e., the fact that the backward evolution of a classical spacetime inevitably comes to an end after a finite amount of proper time. This presents a breakdown of the classical picture and requires an extended theory for a meaningful description. Since small length scales and high curvatures are involved, quantum effects must play a role. Not only the singularity itself but also the surrounding spacetime is then modified. One particular theory is loop quantum cosmology, an application of loop quantum gravity to homogeneous systems, which removes classical singularities. Its implications can be studied at different levels. The main effects are introduced into effective classical equations, which allow one to avoid the interpretational problems of quantum theory. They give rise to new kinds of early-universe phenomenology with applications to inflation and cyclic models. To resolve classical singularities and to understand the structure of geometry around them, the quantum description is necessary. Classical evolution is then replaced by a difference equation for a wave function, which allows an extension of quantum spacetime beyond classical singularities. One main question is how these homogeneous scenarios are related to full loop quantum gravity, which can be dealt with at the level of distributional symmetric states. Finally, the new structure of spacetime arising in loop quantum gravity and its application to cosmology sheds light on more general issues, such as the nature of time. Wed, 02 Jul 2008 10:00:00 +0000 http://europeangovernance.livingreviews.org/Articles/lreg-2008-3 http://www.livingreviews.org/lreg-2008-3 This Living Review deals with the division of competences between the EU and its member states in a multilevel political system. The article summarises research on the relations between the EU and the national and sub-national levels of the member states. It provides an overview on normative and theoretical concepts and empirical research. From the outset, European integration was about the transfer of powers from the national to the European level, which evolved as explicit bargaining among governments or as an incremental drift. This process was reframed with the competence issue entering the agenda of constitutional policy. It now concerns the shape of the European multilevel polity as a whole, in particular the way in which powers are allocated, delimited and linked between the different levels. The article is structured as follows: First of all, normative theories of a European federation are discussed. The section deals with different concepts of federalism and presents approaches of the economic theory of federalism in the context of the European polity. The normative considerations conclude with a discussion of the subsidiarity principle and the constitutional allocation of competences in the European Treaties. The next section covers the empirical issue of how to explain the actual allocation of competences (scope and type) between levels. Integration theories are presented here only in so far as they explain the transfer of competence from the national to the European level or the limits of this centralistic dynamics. Normative and empirical theories indeed provide some general guidelines and conclusions on the allocation of competences in the EU, but they both contradict the assumption of a separation of competences. The article therefore concludes that politics and policy-making in the EU have to be regarded as multilevel governance. The main theoretical approaches and results from empirical research on European multilevel governance are presented before the article concludes with recommendations for further discussion and research in the field. Following Fritz Scharpf, it is recommended that research on the vertical allocation of competences and the application of shared competences in the European multilevel governance should stop searching for holistic approaches (grand theory) explaining unique features of the European political system; instead, research will best succeed when relying on a variety of simpler theories and models to describe European governance modes. Mon, 30 Jun 2008 10:00:00 +0000 http://europeangovernance.livingreviews.org/Articles/lreg-2008-2 http://www.livingreviews.org/lreg-2008-2 This article reviews the by now extensive literature on the Europeanisation of the political systems of the EU-15, with an emphasis on parliaments and executives (i.e., governments and ministerial administrations). The Living Review highlights apparently contradictory effects of integration: de-parlamentarisation re-parlamentarisation; bureaucratisation politicisation; and centralisation diffusion. These diverging assessments of the effects of integration do, in part, reflect diversity in the EU-15; in part, they are, however, also a result of differences in the specification of variables, research designs and theoretical approaches. Work that inquires into patterns of Europeanisation - across institutional domains, countries, regions and time - and which seeks to tackle the `methodological nationalism' of the Europeanisation literature promises a clearer picture of the institutional consequences of European integration than we possess at present. Mon, 30 Jun 2008 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2008-3 http://www.livingreviews.org/lrr-2008-3 Whereas semiclassical gravity is based on the semiclassical Einstein equation with sources given by the expectation value of the stress-energy tensor of quantum fields, stochastic semiclassical gravity is based on the Einstein–Langevin equation, which has, in addition, sources due to the noise kernel. The noise kernel is the vacuum expectation value of the (operator-valued) stress-energy bitensor, which describes the fluctuations of quantum-matter fields in curved spacetimes. A new improved criterion for the validity of semiclassical gravity may also be formulated from the viewpoint of this theory. In the first part of this review we describe the fundamentals of this new theory via two approaches: the axiomatic and the functional. The axiomatic approach is useful to see the structure of the theory from the framework of semiclassical gravity, showing the link from the mean value of the stress-energy tensor to the correlation functions. The functional approach uses the Feynman–Vernon influence functional and the Schwinger–Keldysh closed-time-path effective action methods. In the second part, we describe three applications of stochastic gravity. First, we consider metric perturbations in a Minkowski spacetime, compute the two-point correlation functions of these perturbations and prove that Minkowski spacetime is a stable solution of semiclassical gravity. Second, we discuss structure formation from the stochastic-gravity viewpoint, which can go beyond the standard treatment by incorporating the full quantum effect of the inflaton fluctuations. Third, using the Einstein–Langevin equation, we discuss the backreaction of Hawking radiation and the behavior of metric fluctuations for both the quasi-equilibrium condition of a black-hole in a box and the fully nonequilibrium condition of an evaporating black hole spacetime. Finally, we briefly discuss the theoretical structure of stochastic gravity in relation to quantum gravity and point out directions for further developments and applications. Thu, 29 May 2008 10:00:00 +0000 http://europeangovernance.livingreviews.org/Articles/lreg-2008-1 http://www.livingreviews.org/lreg-2008-1 Since its inception, the European Union has stimulated many vigorous debates. This Living Review provides a state of the field perspective on the academic work that has been done to address the question of the perceptions of the European Union as a system of governance. It takes a broad scope in assessing the efforts of scholars and highlights significant theoretical and empirical contributions as well as identifying potential avenues for research. In order to understand perceptions of the EU, scholars have employed national-level frameworks of popular support, particularly partisanship and instrumental self-interest. As the number of members has increased, further research has taken a broader scope to include national identity, institutions, and attitudes regarding the normative and empirical function of both national and EU institutions. Additional works address political intermediaries such as parties, media, and elites. Finally, all of the works are fundamentally concerned with the supportive popular sentiment that underpins the EU’s legitimacy as a political institution. While there are far more works that can be practically included in this Living Review, we have attempted to construct an overview based on the dimensions that define this research as set out by significant contributions at the core of this literature. Wed, 21 May 2008 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2008-2 http://www.livingreviews.org/lrr-2008-2 This article gives an outline of the historical events that led to the formation of contemporary astroparticle physics. As a starting point for analyzing the history of astroparticle physics this article will review the various, yet scattered pieces of historical work that have been done so far. To make the picture more complete it will then give a brief survey of the most important fields that have played a role in the development of astroparticle physics as we know it today. It will conclude with an overview of the historical questions that are still open and the rich philosophical implications that lie behind those questions. Wed, 07 May 2008 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2008-1 http://www.livingreviews.org/lrr-2008-1 We review the intimate connection between (super-)gravity close to a spacelike singularity (the “BKL-limit”) and the theory of Lorentzian Kac-Moody algebras. We show that in this limit the gravitational theory can be reformulated in terms of billiard motion in a region of hyperbolic space, revealing that the dynamics is completely determined by a (possibly infinite) sequence of reflections, which are elements of a Lorentzian Coxeter group. Such Coxeter groups are the Weyl groups of infinite-dimensional Kac-Moody algebras, suggesting that these algebras yield symmetries of gravitational theories. Our presentation is aimed to be a self-contained and comprehensive treatment of the subject, with all the relevant mathematical background material introduced and explained in detail. We also review attempts at making the infinite-dimensional symmetries manifest, through the construction of a geodesic sigma model based on a Lorentzian Kac-Moody algebra. An explicit example is provided for the case of the hyperbolic algebra E_10, which is conjectured to be an underlying symmetry of M-theory. Illustrations of this conjecture are also discussed in the context of cosmological solutions to eleven-dimensional supergravity. Thu, 24 Apr 2008 10:00:00 +0000 http://landscaperesearch.livingreviews.org/Articles/lrlr-2008-1 http://www.livingreviews.org/lrlr-2008-1 Land-use change has been identified as one the most important processes to understand and to model global change. It is the result of complex interactions between human and environmental driving factors. A key to capturing this complexity is the analytical framework of land systems as coupled human-environment systems, a concept that is a central component of the science plan of the Global Land Project. Based on this framework, this paper presents an overview of eight integrated models of the land system. The review concentrates on model approaches that include processes of both the human and the environment sub-system and which operate in a spatially explicit manner on a regional to global scale. Another criterion used to select models is that they take into account interplay and competition between different land-use activities, e.g. between agriculture and urban development. Each model is reviewed separately in detail with focus on the different aspects of the land system that are represented within the model and on the implemented modelling concepts. This is done by systematically addressing the following topics: model purpose and application, model concepts for the human sub-system and for the environment sub-system and linkages between the sub-systems (model integration). Based on these findings commonalities and differences between the models are discussed and further research needs are identified. Sat, 05 Apr 2008 10:00:00 +0000 http://solarphysics.livingreviews.org/Articles/lrsp-2008-2 http://www.livingreviews.org/lrsp-2008-2 The Sun, stars similar to it, and many rather dissimilar to it, have chromospheres, regions classically viewed as lying above the brilliant photosphere and characterized by a positive temperature gradient and a marked departure from radiative equilibrium. Stellar chromospheres exhibit a wide range of phenomena collectively called activity, stemming largely from the time evolution of their magnetic fields and the mass flux and transfer of radiation through the complex magnetic topology and the increasingly optically thin plasma of the outer stellar atmosphere. In this review, I will (1) outline the development of our understanding of chromospheric structure from 1960 to the present, (2) discuss the major observational programs and theoretical lines of inquiry, (3) review the origin and nature of both solar and stellar chromospheric activity and its relationship to, and effect on, stellar parameters including total energy output, and (4) summarize the outstanding problems today. Mon, 10 Mar 2008 11:00:00 +0000 http://solarphysics.livingreviews.org/Articles/lrsp-2008-1 http://www.livingreviews.org/lrsp-2008-1 Solar flares are observed at all wavelengths from decameter radio waves to gamma-rays at 100 MeV. This review focuses on recent observations in EUV, soft and hard X-rays, white light, and radio waves. Space missions such as RHESSI, Yohkoh, TRACE, and SOHO have enlarged widely the observational base. They have revealed a number of surprises: Coronal sources appear before the hard X-ray emission in chromospheric footpoints, major flare acceleration sites appear to be independent of coronal mass ejections (CMEs), electrons, and ions may be accelerated at different sites, there are at least 3 different magnetic topologies, and basic characteristics vary from small to large flares. Recent progress also includes improved insights into the flare energy partition, on the location(s) of energy release, tests of energy release scenarios and particle acceleration. The interplay of observations with theory is important to deduce the geometry and to disentangle the various processes involved. There is increasing evidence supporting reconnection of magnetic field lines as the basic cause. While this process has become generally accepted as the trigger, it is still controversial how it converts a considerable fraction of the energy into non-thermal particles. Flare-like processes may be responsible for large-scale restructuring of the magnetic field in the corona as well as for its heating. Large flares influence interplanetary space and substantially affect the Earth’s lower ionosphere. While flare scenarios have slowly converged over the past decades, every new observation still reveals major unexpected results, demonstrating that solar flares, after 150 years since their discovery, remain a complex problem of astrophysics including major unsolved questions. Tue, 26 Feb 2008 11:00:00 +0000 http://europeangovernance.livingreviews.org/Articles/lreg-2007-3 http://www.livingreviews.org/lreg-2007-3 This Living Review takes stock of our current theoretical and empirical knowledge with respect to a European public sphere. It first provides a discussion of the notion of a public sphere and the virtual incompatibility between the notion of a public sphere in the nation state and the current state of European integration. It is then argued why a notion of a (Europeanized national) public space for debate between citizens and with power-holders is important for the legitimacy and accountability of the EU. A three-fold typology is proposed that organizes previous research on the European public sphere: the Utopian, the Elitist and the Realist perspective. The diverging conclusions stemming from extant research are reviewed in the light of the methodological pluralism in the studies. It is demonstrated that most signs of Europeanization of national public spheres stem from studies focusing on the quality broadsheet press, whereas studies focusing on the popular press, television and new media provide little evidence (yet) of a Europeanization trend. The review looks ahead in both theoretical and methodological terms and also assesses the consequences of the (absence of) a European public sphere and current policy initiatives in this area. Fri, 21 Dec 2007 11:00:00 +0000 http://europeangovernance.livingreviews.org/Articles/lreg-2007-2 http://www.livingreviews.org/lreg-2007-2 The debate on the European Union's legitimacy crisis led to the discovery of civil society in EU governance. With the waning of the permissive consensus, politicians, bureaucrats, and academics shifted their attention towards the input-oriented dimension of democratic legitimacy which results from authentic participation and governance `by the people'. Participatory democracy via civil society involvement came to be considered as a promising supplement to representative democracy and entered EU documents such as the White Paper on European Governance and the draft Constitutional Treaty around the turn of the millennium. However, the origins of the current debate on civil society in EU governance can also be traced back to interest group research which has flourished since the early 1980s and the debate on `participatory governance' that unfolded in the 1990s. These approaches are more concerned with effective political problem-solving and the output-dimension of democratic legitimacy which can, from this point of view, be improved by stakeholder participation and civil society engagement. In fact, two scholars who refer to `civil society' do not necessarily mean the same thing and this is even less obvious if journalists, politicians or public officials allude to civil society. In order to enhance the basis of the discussion, we should seek to identify the conceptions they rely on. This will help us to understand where different arguments come from. Hence, this essay seeks to identify the different layers of the current debate on civil society participation in EU governance by unfolding the traditions of thought academic and political advocates of civil society in EU affairs currently draw on. This essay will basically distinguish between output-oriented approaches which explore the contribution of civil society groups to effective governance and problem-solving on the one hand and research that is interested in input-oriented legitimacy and participatory democracy on the other. Fri, 21 Dec 2007 11:00:00 +0000 http://solarphysics.livingreviews.org/Articles/lrsp-2007-3 http://www.livingreviews.org/lrsp-2007-3 The Sun’s magnetic activity has steadily declined during its main-sequence life. While the solar photospheric luminosity was about 30% lower 4.6 Gyr ago when the Sun arrived on the main sequence compared to present-day levels, its faster rotation generated enhanced magnetic activity; magnetic heating processes in the chromosphere, the transition region, and the corona induced ultraviolet, extreme-ultraviolet, and X-ray emission about 10, 100, and 1000 times, respectively, the present-day levels, as inferred from young solar-analog stars. Also, the production rate of accelerated, high-energy particles was orders of magnitude higher than in present-day solar flares, and a much stronger wind escaped from the Sun, permeating the entire solar system. The consequences of the enhanced radiation and particle fluxes from the young Sun were potentially severe for the evolution of solar-system planets and moons. Interactions of high-energy radiation and the solar wind with upper planetary atmospheres may have led to the escape of important amounts of atmospheric constituents. The present dry atmosphere of Venus and the thin atmosphere of Mars may be a product of early irradiation and heating by solar high-energy radiation. High levels of magnetic activity are also inferred for the pre-main sequence Sun. At those stages, interactions of high-energy radiation and particles with the circumsolar disk in which planets eventually formed were important. Traces left in meteorites by energetic particles and anomalous isotopic abundance ratios in meteoritic inclusions may provide evidence for a highly active pre-main sequence Sun. The present article reviews these various issues related to the magnetic activity of the young Sun and the consequent interactions with its environment. The emphasis is on the phenomenology related to the production of high-energy photons and particles. Apart from the activity on the young Sun, systematic trends applicable to the entire main-sequence life of a solar analog are discussed. Thu, 20 Dec 2007 11:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2007-5 http://www.livingreviews.org/lrr-2007-5 As first discovered by Choptuik, the black hole threshold in the space of initial data for general relativity shows both surprising structure and surprising simplicity. Universality, power-law scaling of the black hole mass, and scale echoing have given rise to the term “critical phenomena”. They are explained by the existence of exact solutions which are attractors within the black hole threshold, that is, attractors of codimension one in phase space, and which are typically self-similar. Critical phenomena give a natural route from smooth initial data to arbitrarily large curvatures visible from infinity, and are therefore likely to be relevant for cosmic censorship, quantum gravity, astrophysics, and our general understanding of the dynamics of general relativity. Tue, 11 Dec 2007 11:00:00 +0000 http://solarphysics.livingreviews.org/Articles/lrsp-2007-2 http://www.livingreviews.org/lrsp-2007-2 Variations in solar activity, at least as observed in numbers of sunspots, have been apparent since ancient times but to what extent solar variability may affect global climate has been far more controversial. The subject had been in and out of fashion for at least two centuries but the current need to distinguish between natural and anthropogenic causes of climate change has brought it again to the forefront of meteorological research. The absolute radiometers carried by satellites since the late 1970s have produced indisputable evidence that total solar irradiance varies systematically over the 11-year sunspot cycle, relegating to history the term “solar constant”, but it is difficult to explain how the apparent response to the Sun, seen in many climate records, can be brought about by these rather small changes in radiation. This article reviews some of the evidence for a solar influence on the lower atmosphere and discusses some of the mechanisms whereby the Sun may produce more significant impacts than might be surmised from a consideration only of variations in total solar irradiance. Tue, 02 Oct 2007 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2007-4 http://www.livingreviews.org/lrr-2007-4 I review the current state of determinations of the Hubble constant, which gives the length scale of the Universe by relating the expansion velocity of objects to their distance. In the last 20 years, much progress has been made and estimates now range between 60 and 75 km s^-1 Mpc^-1, with most now between 70 and 75 km s^-1 Mpc^-1, a huge improvement over the factor-of-2 uncertainty which used to prevail. Further improvements which gave a generally agreed margin of error of a few percent rather than the current 10% would be vital input to much other interesting cosmology. There are several programmes which are likely to lead us to this point in the next 10 years. Mon, 24 Sep 2007 10:00:00 +0000 http://landscaperesearch.livingreviews.org/Articles/lrlr-2007-3 http://www.livingreviews.org/lrlr-2007-3 In this contribution we try to look at the new role for agriculture in rural areas by reviewing the concept of multifunctional agriculture as well as the analytical frameworks used. Next, we review the existing evidence about the multifunctional role of farming. Although not overwhelming, the existing literature shows that agriculture contributes to the rural wealth not only through the production of commodities, but also by the delivery of non-tradable goods. This contribution can be both direct through increased values for properties or economic benefits in the tourism sector, but also indirect through conservation of rural heritage or agri-ecological systems. Next we focus on how this role of agriculture can be stimulated. It is argued that multifunctionality can be a unifying principle to bring the productive and non-productive functions into harmony. This requires the development of new institutional arrangements and a major change in policy incentives. Mon, 25 Jun 2007 10:00:00 +0000 http://landscaperesearch.livingreviews.org/Articles/lrlr-2007-2 http://www.livingreviews.org/lrlr-2007-2 Recreation and nature tourism are increasingly important activities with many implications both economic and environmental. As society changes so the demands and trends for recreation and nature tourism change and develop. This poses many challenges for planners and managers of recreational areas and providers of services. This review article focuses on the situation in Europe but does not ignore some major trends and issues arising elsewhere, while much of the research can be traced back to ideas and methods developed elsewhere, such as the U.S.A. To set the scene the main social and environmental trends are presented that show how the changing nature of society feeds through in expectations and demands for recreation and nature tourism. Demographic changes, consumer behaviour and the increasingly mobile and connected lifestyles of European citizens have produced trends for outdoor recreation preferences and for broadening travel horizons. Knowing about these trends enables planners and entrepreneurs to change their recreation or tourism offer to meet these demands. However, these demands have to be seen in the context of changing pressures and sensitivities of the environments, frequently natural, in which recreation and nature tourism activities are located. Climate change is a prime example of these pressures. Many countries have developed sophisticated survey and other monitoring tools and instruments to identify demand, to monitor levels and types of activity, changing preferences and pressures on the environment. While recreation is often led by demand from people who wish to participate in certain activities there are also increasingly well recognised benefits to health and well-being from closer contact with nature. Policy makers in the health sphere are taking a keen interest in this and in the means for encouraging sedentary populations to engage with physical activity in natural environments. The evidence base for this is improving and is reviewed in this paper. Management of environments and visitors produces many conflicts which must be resolved. Recent surveys of forest recreation have enabled a European-wide pattern to be identified which will help planners and managers identify issues to be considered. The paper draws on work being undertaken as part of two EU funded Cost Actions: ``Cost E33: Forest Recreation and Nature Tourism'' and ``Cost E39: Forests, Trees and Human Health and Well-being''. These allow experts from around Europe to network and to pool research and practice. Mon, 25 Jun 2007 10:00:00 +0000 http://landscaperesearch.livingreviews.org/Articles/lrlr-2007-1 http://www.livingreviews.org/lrlr-2007-1 In the absence of drainage systems, runoff is a major transport pathway of pesticides from agricultural areas to aquatic systems. We provide an overview of existing runoff models eligible to describe the transport and fate of pesticides in the terrestrial environment. We distinguish between leaching, erosion, and hydrological models. Recent developments in runoff modelling include the evolution of complex deterministic models, combinations of models and probabilistic approaches on a GIS-platform. The latter enable users to make geo-referenced predictions of diffuse pesticide emissions from small to large scales. Simulated loads mostly correlate well with measured pesticide loads and concentrations on a catchment scale, but often overestimate measured concentrations, because the edge-to-field approach applied does not consider any attenuation by degradation or sorption between the location of pesticide application and surface waters. Therefore, future developments of horizontal pesticide transport models should focus on detention and retention mechanisms during transport on highly resolved temporal and spatial scales. Additionally, for the simulation of realistic scenarios of pesticide emissions on a catchment scale, the evaluation and standardization of probabilistic approaches can be helpful. Mon, 25 Jun 2007 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2007-3 http://www.livingreviews.org/lrr-2007-3 Event and apparent horizons are key diagnostics for the presence and properties of black holes. In this article I review numerical algorithms and codes for finding event and apparent horizons in numerically-computed spacetimes, focusing on calculations done using the 3+1 ADM formalism. The event horizon of an asymptotically-flat spacetime is the boundary between those events from which a future-pointing null geodesic can reach future null infinity and those events from which no such geodesic exists. The event horizon is a (continuous) null surface in spacetime. The event horizon is defined nonlocally in time: it is a global property of the entire spacetime and must be found in a separate post-processing phase after all (or at least the nonstationary part) of spacetime has been numerically computed. There are three basic algorithms for finding event horizons, based on integrating null geodesics forwards in time, integrating null geodesics backwards in time, and integrating null surfaces backwards in time. The last of these is generally the most efficient and accurate. In contrast to an event horizon, an apparent horizon is defined locally in time in a spacelike slice and depends only on data in that slice, so it can be (and usually is) found during the numerical computation of a spacetime. A marginally outer trapped surface (MOTS) in a slice is a smooth closed 2-surface whose future-pointing outgoing null geodesics have zero expansion Theta. An apparent horizon is then defined as a MOTS not contained in any other MOTS. The MOTS condition is a nonlinear elliptic partial differential equation (PDE) for the surface shape, containing the ADM 3-metric, its spatial derivatives, and the extrinsic curvature as coefficients. Most “apparent horizon” finders actually find MOTSs. There are a large number of apparent horizon finding algorithms, with differing trade-offs between speed, robustness, accuracy, and ease of programming. In axisymmetry, shooting algorithms work well and are fairly easy to program. In slices with no continuous symmetries, spectral integral-iteration algorithms and elliptic-PDE algorithms are fast and accurate, but require good initial guesses to converge. In many cases, Schnetter’s “pretracking” algorithm can greatly improve an elliptic-PDE algorithm’s robustness. Flow algorithms are generally quite slow but can be very robust in their convergence. Minimization methods are slow and relatively inaccurate in the context of a finite differencing simulation, but in a spectral code they can be relatively faster and more robust. Fri, 01 Jun 2007 10:00:00 +0000 http://solarphysics.livingreviews.org/Articles/lrsp-2007-1 http://www.livingreviews.org/lrsp-2007-1 Space weather effects arise from the dynamic conditions in the Earth’s space environment driven by processes on the Sun. While some effects are influenced neither by the properties of nor the processes within the Earth’s magnetosphere, others are critically dependent on the interaction of the impinging solar wind with the terrestrial magnetic field and plasma environment. As the utilization of space has become part of our everyday lives, and as our lives have become increasingly dependent on technological systems vulnerable to space weather influences, understanding and predicting hazards posed by the active solar events has grown in importance. This review introduces key dynamic processes within the magnetosphere and discusses their relationship to space weather hazards. Wed, 23 May 2007 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2007-2 http://www.livingreviews.org/lrr-2007-2 We discuss various aspects of the post-Newtonian approximation in general relativity. After presenting the foundation based on the Newtonian limit, we show a method to derive post-Newtonian equations of motion for relativistic compact binaries based on a surface integral approach and the strong field point particle limit. As an application we derive third post-Newtonian equations of motion for relativistic compact binaries which respect the Lorentz invariance in the post-Newtonian perturbative sense, admit a conserved energy, and are free from any ambiguity. Mon, 12 Mar 2007 11:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2007-1 http://www.livingreviews.org/lrr-2007-1 The relativistic fluid is a highly successful model used to describe the dynamics of many-particle, relativistic systems. It takes as input basic physics from microscopic scales and yields as output predictions of bulk, macroscopic motion. By inverting the process, an understanding of bulk features can lead to insight into physics on the microscopic scale. Relativistic fluids have been used to model systems as ``small'' as heavy ions in collisions, and as large as the Universe itself, with ``intermediate'' sized objects like neutron stars being considered along the way. The purpose of this review is to discuss the mathematical and theoretical physics underpinnings of the relativistic (multiple) fluid model. We focus on the variational principle approach championed by Brandon Carter and his collaborators, in which a crucial element is to distinguish the momenta that are conjugate to the particle number density currents. This approach differs from the ``standard'' text-book derivation of the equations of motion from the divergence of the stress-energy tensor in that one explicitly obtains the relativistic Euler equation as an ``integrability'' condition on the relativistic vorticity. We discuss the conservation laws and the equations of motion in detail, and provide a number of (in our opinion) interesting and relevant applications of the general theory. Tue, 30 Jan 2007 11:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2006-6 http://www.livingreviews.org/lrr-2006-6 We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs) within the frequency band of ground-based detectors, while compact binaries of WDs are important sources of GWs at lower frequencies to be covered by space interferometers (LISA). Major uncertainties in the current understanding of properties of NSs and BHs most relevant to the GW studies are discussed, including the treatment of the natal kicks which compact stellar remnants acquire during the core collapse of massive stars and the common envelope phase of binary evolution. We discuss the coalescence rates of binary NSs and BHs and prospects for their detections, the formation and evolution of binary WDs and their observational manifestations. Special attention is given to AM CVn-stars -- compact binaries in which the Roche lobe is filled by another WD or a low-mass partially degenerate helium-star, as these stars are thought to be the best LISA verification binary GW sources. Tue, 19 Dec 2006 11:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2006-5 http://www.livingreviews.org/lrr-2006-5 The asymptotic safety scenario in quantum gravity is reviewed, according to which a renormalizable quantum theory of the gravitational field is feasible which reconciles asymptotically safe couplings with unitarity. The evidence from symmetry truncations and from the truncated flow of the effective average action is presented in detail. A dimensional reduction phenomenon for the residual interactions in the extreme ultraviolet links both results. For practical reasons the background effective action is used as the central object in the quantum theory. In terms of it criteria for a continuum limit are formulated and the notion of a background geometry self-consistently determined by the quantum dynamics is presented. Self-Contained appendices provide prerequisites on the background effective action, the effective average action, and their respective renormalization flows. Fri, 01 Dec 2006 11:00:00 +0000 http://europeangovernance.livingreviews.org/Articles/lreg-2006-2 http://www.livingreviews.org/lreg-2006-2 This Living Review uses concepts of aggregation to analyse what we do and do not know about the contribution of political parties to the politics and democratic performance of the European Union. It suggests that present representative structures are better at aggregating `choices of policies' than `choices of leaders'. Much more, however, needs to be done to analyse the causal contribution of party actors to those patterns of aggregation, and to understand why European Union parties do not develop further where aggregation seems to be deficient in the EU arena. Thu, 09 Nov 2006 11:00:00 +0000 http://europeangovernance.livingreviews.org/Articles/lreg-2006-3 http://www.livingreviews.org/lreg-2006-3 The Europeanisation of candidate countries and new members is a rather recent and still comparatively small, but - particularly since 2003 -- a fast-growing research area. Research in this area has developed primarily in the context of the EU's eastern enlargement. More recently, a small number of theoretically informed, book-length studies of the EU's influence on the East Central European candidate countries have established the Europeanisation of applicant states as a distinctive research area. These studies fit within a common conceptual framework, which draws on the debate between rationalist and constructivist institutionalist theories in International Relations and Comparative Politics. This framework makes these studies highly compatible with analyses of the Europeanisation of member states, with which they share one key empirical finding, namely that the impact of the EU on candidate countries is differential across countries and issue areas. On the other hand, the theoretical implications of these findings appear more clear-cut than in the case of the Europeanisation of member states: rationalist institutionalism, with its focus on the external incentives underpinning EU conditionality, and on the material costs incurred by domestic veto players, appears well suited to explaining variation in the patterns of Europeanisation in candidate countries. The next stage of this research agenda concerns the impact of accession on the dynamics of pre-accession Europeanisation and how durable the patterns of candidate Europeanisation are in the post-accession stage. Thu, 09 Nov 2006 11:00:00 +0000 http://solarphysics.livingreviews.org/Articles/lrsp-2006-2 http://www.livingreviews.org/lrsp-2006-2 The term space weather refers to conditions on the Sun and in the solar wind, magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and that can affect human life and health. Our modern hi-tech society has become increasingly vulnerable to disturbances from outside the Earth system, in particular to those initiated by explosive events on the Sun: Flares release flashes of radiation that can heat up the terrestrial atmosphere such that satellites are slowed down and drop into lower orbits, solar energetic particles accelerated to near-relativistic energies may endanger astronauts traveling through interplanetary space, and coronal mass ejections are gigantic clouds of ionized gas ejected into interplanetary space that after a few hours or days may hit the Earth and cause geomagnetic storms. In this review, I describe the several chains of actions originating in our parent star, the Sun, that affect Earth, with particular attention to the solar phenomena and the subsequent effects in interplanetary space. Wed, 09 Aug 2006 10:00:00 +0000 http://solarphysics.livingreviews.org/Articles/lrsp-2006-1 http://www.livingreviews.org/lrsp-2006-1 Kinetic plasma physics of the solar corona and solar wind are reviewed with emphasis on the theoretical understanding of the in situ measurements of solar wind particles and waves, as well as on the remote-sensing observations of the solar corona made by means of ultraviolet spectroscopy and imaging. In order to explain coronal and interplanetary heating, the microphysics of the dissipation of various forms of mechanical, electric and magnetic energy at small scales (e.g., contained in plasma waves, turbulences or non-uniform flows) must be addressed. We therefore scrutinise the basic assumptions underlying the classical transport theory and the related collisional heating rates, and also describe alternatives associated with wave-particle interactions. We elucidate the kinetic aspects of heating the solar corona and interplanetary plasma through Landau- and cyclotron-resonant damping of plasma waves, and analyse in detail wave absorption and micro instabilities. Important aspects (virtues and limitations) of fluid models, either single- and multi-species or magnetohydrodynamic and multi-moment models, for coronal heating and solar wind acceleration are critically discussed. Also, kinetic model results which were recently obtained by numerically solving the Vlasov–Boltzmann equation in a coronal funnel and hole are presented. Promising areas and perspectives for future research are outlined finally. Thu, 27 Jul 2006 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2006-4 http://www.livingreviews.org/lrr-2006-4 The article reviews the current status of a theoretical approach to the problem of the emission of gravitational waves by isolated systems in the context of general relativity. Part A of the article deals with general post-Newtonian sources. The exterior field of the source is investigated by means of a combination of analytic post-Minkowskian and multipolar approximations. The physical observables in the far-zone of the source are described by a specific set of radiative multipole moments. By matching the exterior solution to the metric of the post-Newtonian source in the near-zone we obtain the explicit expressions of the source multipole moments. The relationships between the radiative and source moments involve many non-linear multipole interactions, among them those associated with the tails (and tails-of-tails) of gravitational waves. Part B of the article is devoted to the application to compact binary systems. We present the equations of binary motion, and the associated Lagrangian and Hamiltonian, at the third post-Newtonian (3PN) order beyond the Newtonian acceleration. The gravitational-wave energy flux, taking consistently into account the relativistic corrections in the binary moments as well as the various tail effects, is derived through 3.5PN order with respect to the quadrupole formalism. The binary's orbital phase, whose prior knowledge is crucial for searching and analyzing the signals from inspiralling compact binaries, is deduced from an energy balance argument. Thu, 01 Jun 2006 10:00:00 +0000 http://relativity.livingreviews.org/Articles/lrr-2006-3 http://www.livingreviews.org/lrr-2006-3 The status of experimental tests of general relativity and of theoretical frameworks for analyzing them is reviewed. Einstein’s equivalence principle (EEP) is well supported by experiments such as the Eötvös experiment, tests of special relativity, and the gravitational redshift experiment. Ongoing tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, and the Nordtvedt effect in lunar motion. Gravitational wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and other binary pulsar systems have yielded other tests, especially of strong-field effects. When direct observation of gravitational radiation from astrophysical sources begins, new tests of general relativity will be possible. Mon, 27 Mar 2006 10:00:00 +0000