On the origin of exponential growth in induced earthquakes in Groningen

The Groningen gas field shows exponential growth in earthquakes event counts around a magnitude M1 with a doubling time of 6-9 years since 2001. This behavior is identified with dimensionless curvature in land subsidence, which has been evolving at a constant rate over the last few decades {essentially uncorrelated to gas production.} We demonstrate our mechanism by a tabletop crack formation experiment. The observed skewed distribution of event magnitudes is matched by that of maxima of event clusters with a normal distribution. It predicts about one event $<$\,M5 per day in 2025, pointing to increasing stress to human living conditions.Comment: 12 pages, 7 figures, to appear in Earthquakes and Structure

Numerical Integration of Nonlinear Wave Equations for General Relativity

A second-order numerical implementation is given for recently derived nonlinear wave equations for general relativity. The Gowdy T$^3$ cosmology is used as a test bed for studying the accuracy and convergence of simulations of one-dimensional nonlinear waves. The complete freedom in space-time slicing in the present formulation is exploited to compute in the Gowdy line-element. Second-order convergence is found by direct comparison of the results with either analytical solutions for polarized waves, or solutions obtained from Gowdy's reduced wave equations for the more general unpolarized waves. Some directions for extensions are discussed.Comment: 19 pages (LaTex), 3 figures (ps

Uniqueness in MHD in divergence form: right nullvectors and well-posedness

Magnetohydrodynamics in divergence form describes a hyperbolic system of covariant and constraint-free equations. It comprises a linear combination of an algebraic constraint and Faraday's equations. Here, we study the problem of well-posedness, and identify a preferred linear combination in this divergence formulation. The limit of weak magnetic fields shows the slow magnetosonic and Alfven waves to bifurcate from the contact discontinuity (entropy waves), while the fast magnetosonic wave is a regular perturbation of the hydrodynamical sound speed. These results are further reported as a starting point for characteristic based shock capturing schemes for simulations with ultra-relativistic shocks in magnetized relativistic fluids.Comment: To appear in J Math Phy

Carbon footprint bloembollen 2010

Voor exporteurs en handelaren van leverbare bollen is het in de toekomst mogelijk van belang om aan te kunnen geven wat de carbon footprint (kg CO2 –equivalenten per eenheid) van hun product is. Daarom is een rekenmodel ontwikkeld, waarmee met een minimum aan variabelen op eenvoudige wijze de directe en indirecte CO2 uitstoot per 1000 stuks van op de plaats van bestemming afgeleverde bloembollen kan worden berekend. Andere hierbij vrijgekomen broeikasgassen zoals N2O en CH4 worden omgerekend in CO2-equivalenten. De rekenmethodiek (wat wordt nog wel en wat wordt niet aan productie en transport van leverbare bloembollen toegerekend) en de gebruikte kengetallen voor CO2-equivalenten zijn afgestemd met het LEI/Hans Blonk Milieu Advies. Op de invoer- en resultaatpagina van dit model in Excel kunnen de meeste gegevens door het aanklikken van keuzemogelijkheden worden ingevoerd. Onderscheidende factoren in dit model zijn: het gewas, gewastype, het teeltgebied (Nederland of elders), de bewaarduur, de bewaarmethode (gangbaar of State-of-the-Art), de exportbestemming en het wel of niet terughalen van de exportkratten. Verdere differentiëring is in dit model geen optie. Het model laat zien dat bolgewassen en vaste planten een carbon footprint hebben die vergelijkbaar is met andere landbouwgewassen. Een uitzondering daarop zijn Irissen. Door de hoge temperaturen bij de bewaring is de Iristeelt niet alleen in vergelijking met andere bolgewassen, maar ook vergeleken met andere landbouwproducten zéér energie-intensief te noemen. Bij het transport van vaste planten wordt turf gebruikt. Vervanging van dit materiaal door een alternatief zou de relatief grote carbon footprint van tweejarige vaste planten met de helft kunnen terugbrengen. Van bijna alle bolgewassen bestaat de CO2-footprint voor het grootste gedeelte uit emissies in de verwerking en bewaringsfase. Het terugbrengen van de circulatie en ventilatie bij de bewaring, bijvoorbeeld door frequentieregelaars en/of ethyleen gestuurde ventilatie, kan de CO2-uitstoot resulterend uit de teelt van bolgewassen aanzienlijk verminderen. Het uitgebreide rekenmodel komt via internet beschikbaar voor exporteurs en handelaren

Gravitational wave frequencies and energies in hypernovae

A torus develops a state of suspended accretion against a magnetic wall around a rapidly rotating black hole formed in core-collapse hypernovae. It hereby emits about 10% of the black hole spin-energy in gravitational radiation from a finite number of multipole mass moments. We quantify the relation between the frequency of quadrupole gravitational radiation and the energy output $E_w$ in torus winds by $f_{gw}\simeq 470{Hz}(E_w/4\times 10^{52}{erg})^{1/2}(7M_\odot/M)^{3/2}$, where $M$ denotes the mass of the black hole. We propose that $E_w$ irradiates the remnant stellar envelope from within. We identify $E_w$ with energies $\sim 10^{52}$ erg inferred from X-ray observations on matter injecta; and the poloidal curvature in the magnetic wall with the horizon opening angle in baryon poor outflows that power true GRB energies of $E_\gamma\simeq 3\times 10^{51}$ erg.Comment: To appear in AP

Real time automatic scene classification

This work has been done as part of the EU VICAR (IST) project and the EU SCOFI project (IAP). The aim of the first project was to develop a real time video indexing classification annotation and retrieval system. For our systems, we have adapted the approach of Picard and Minka [3], who categorized elements of a scene automatically with so-called ’stuff’ categories (e.g., grass, sky, sand, stone). Campbell et al. [1] use similar concepts to describe certain parts of an image, which they named “labeled image regions”. However, they did not use these elements to classify the topic of the scene. Subsequently, we developed a generic approach for the recognition of visual scenes, where an alphabet of basic visual elements (or “typed patches”) is used to classify the topic of a scene. We define a new image element: a patch, which is a group of adjacent pixels within an image, described by a specific local pixel distribution, brightness, and color. In contrast with pixels, a patch as a whole can incorporate semantics. A patch is described by a HSI color histogram with 16 bins and by three texture features (i.e., the variance and two values based on the two eigen values of the covariance matrix of the Intensity values of a mask ran over the image. For more details on the features used we refer to Israel et al. [2]. We aimed at describing each image as a vector with a fixed size and with information about the position of patches that is not strict (strict position would limit generalization). Therefore, a fixed grid is placed over the image and each grid cell is segmented into patches, which are then categorized by a patch classifier. For each grid cell a frequency vector of its classified patches is calculated. These vectors are concate- nated. The resulting vector describes the complete image. Several grids were applied and several patch sizes with the grid cells were tested. Grid size of 3x2 combined with patches of size 16x16 provided the best system performance. For the two classification phases of our system, back-propagation networks were trained: (i) classification of the patches and (ii) classification of the image vector, as a whole. The system was tested on the classification of eight categories of scenes from the Corel database: interiors, city/street, forest, agriculture/countryside, desert, sea, portrait, and crowds. Each of these categories were relevant for the VICAR project. Based upon their relevance for these eight categories of scenes, we choose nine categories for the classification of the patches: building, crowd, grass, road, sand, skin, sky, tree, and water. This approach was found to be successful (for classification of the patches 87.5% correct, and classification of the scenes 73.8% correct). An advantage of our method is its low computational complexity. Moreover, the classified patches themselves are intermediate image representations and can be used for image classification, image segmentation as well as for image matching. A disadvantage is that the patches with which the classifiers were trained had to be manually classified. To solve this drawback, we currently develop algorithms for automatic extraction of relevant patch types. Within the IST project VICAR, a video indexing system was built for the Netherlands Institute for Sound and Vision1, consisting of four independent mod- ules: car recognition, face recognition, movement recognition (of people) and scene recognition. The latter module was based upon the afore mentioned approach. Within the IAP project SCOFI, a real time Internet pornography filter was built, based upon this approach. The system is currently running on several schools in Europe. Within the SCOFI filtering system, our image classification system (with a performance of 92% correct) works together with a text classi- fication system that includes a proxy server (FilterX, developed by Demokritos, Greece) to classify web-pages. Its total performance is 0% overblocking and 1% underblocking

An Evolving Understanding of Sense of Place in Social-Ecological Systems Research and the Barriers and Enablers to its Measurement

Social-ecological systems (SES) are changing more in the Anthropocene than ever before. With this also comes a change in Sense of Place (SoP), that is, the emotional bond that a person (or group of people) has with a place. This impacts how individuals and groups interact with a place (i.e., their behaviours) and respond to disturbance or change (i.e., their adaptive capacity). To understand how SoP is changing across space and time and to be able to compare this across social-ecological contexts, we must first take stock of how SoP is conceptualised so as to understand how to capture and measure the phenomena in a meaningful way (e.g., to inform policy). Based on in-depth qualitative interviews with leading SoP researchers (n = 17 from 8 countries) this paper aims to identify: (1) the current breadth of theoretical conceptualisations for SoP; (2) the methodologies that have been used to measure SoP in different contexts and settings; and (3) the barriers and (4) enablers to the use of different methodologies. Results show that there has been a change in how SoP has been conceptualised over time, whereby it was traditionally considered as something singular and limited, towards something much more dynamic. Results also show that diverse methods (both quantitative and qualitative) have been used to measure SoP, but the choice of method is often a result of resource constraints that limit research design. These findings suggest that broader collaboration among stakeholders and increased interdisciplinarity would undoubtedly lead to improved outcomes in our understanding of SoP, specifically how it is changing in response to anthropogenic pressures, and how the results can be integrated into policy and practice to support environment conservation and management. It is hoped these findings can help establish a community of practice around how we conceptualise SoP, and hence understand it, to create space for methodological integration and shared learnings as a field