3,725 research outputs found
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 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
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 in torus winds by , where denotes the mass of the black
hole. We propose that irradiates the remnant stellar envelope from
within. We identify with energies 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 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 âstuffâ categories (e.g., grass, sky, sand, stone). Campbell et al. [1] use similar concepts to describe certain parts of an image, which they named âlabeled image regionsâ. 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 âtyped patchesâ) 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
Focusing Light through Random Photonic Media by Binary Amplitude Modulation
We study the focusing of light through random photonic materials using
wavefront shaping. We explore a novel approach namely binary amplitude
modulation. To this end, the light incident to a random photonic medium is
spatially divided into a number of segments. We identify the segments that give
rise to fields that are out of phase with the total field at the intended focus
and assign these a zero amplitude, whereas the remaining segments maintain
their original amplitude. Using 812 independently controlled segments of light,
we find the intensity at the target to be 75 +/- 6 times enhanced over the
average intensity behind the sample. We experimentally demonstrate focusing of
light through random photonic media using both an amplitude only mode liquid
crystal spatial light modulator and a MEMS-based spatial light modulator. Our
use of Micro Electro-Mechanical System (MEMS)-based digital micromirror devices
for the control of the incident light field opens an avenue to high speed
implementations of wavefront shaping
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 âequivalenten 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 differentiĂ«ring 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 zĂ©Ă©r 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
Scattering Lens Resolves sub-100 nm Structures with Visible Light
The smallest structures that conventional lenses are able to optically
resolve are of the order of 200 nm. We introduce a new type of lens that
exploits multiple scattering of light to generate a scanning nano-sized optical
focus. With an experimental realization of this lens in gallium phosphide we
have succeeded to image gold nanoparticles at 97 nm optical resolution. Our
work is the first lens that provides a resolution in the nanometer regime at
visible wavelengths.Comment: 4 pages, 3 figure
Entropic force in black hole binaries and its Newtonian limits
We give an exact solution for the static force between two black holes at the
turning points in their binary motion. The results are derived by Gibbs'
principle and the Bekenstein-Hawking entropy applied to the apparent horizon
surfaces in time-symmetric initial data. New power laws are derived for the
entropy jump in mergers, while Newton's law is shown to derive from a new
adiabatic variational principle for the Hilbert action in the presence of
apparent horizon surfaces. In this approach, entropy is strictly monotonic such
that gravity is attractive for all separations including mergers, and the
Bekenstein entropy bound is satisfied also at arbitrarily large separations,
where gravity reduces to Newton's law. The latter is generalized to point
particles in the Newtonian limit by application of Gibbs' principle to
world-lines crossing light cones.Comment: Accepted for publication in Phys. Rev.
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