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We give a new view on building content clusters from page pair models. We measure the heuristic importance within every two pages by computing the distance of their accessed positions in usage sessions. We also compare our page pair models with the classical pair models used in information theories and natural language processing, and give different evaluation methods to build the reasonable content communities. And we finally interpret the advantages and disadvantages of our models from detailed experiment results
Motivated by the successful Karlsruhe dynamo experiment, a relatively low-dimensional dynamo model is proposed. It is based on a strong truncation of the magnetohydrodynamic (MHD) equations with an external forcing of the Roberts type and the requirement that the model system satisfies the symmetries of the full MHD system, so that the first symmetry-breaking bifurcations can be captured. The backbone of the Roberts dynamo is formed by the Roberts flow, a helical mean magnetic field and another part of the magnetic field coupled to these two by triadic mode interactions. A minimum truncation model (MTM) containing only these energetically dominating primary mode triads is fully equivalent to the widely used first-order smoothing approximation. However, it is shown that this approach works only in the limit of small wave numbers of the excited magnetic field or small magnetic Reynolds numbers ($Rm ll 1$). To obtain dynamo action under more general conditions, secondary mode
There is strong observational evidence of shocks and clumping in radiation-driven stellar winds from hot, luminous stars. The resulting non nous monotonic velocity law allows for radiative coupling between distant locations, which is so far not accounted for in hydrodynamic wind simulations. In the present paper, we determine the Sobolev source function and radiative line force in the presence of radiative coupling in spherically symmetric flows, extending the geometry-free formalism of Rybicki & Hummer (1978, ApJ, 219, 654) to the case of three-point coupling, which can result from, e. g., corotating interaction regions, wind shocks, or mass overloading. For a simple model of an overloaded wind, we find that, surprisingly, the flow decelerates at all radii above a certain height when nonlocal radiative coupling is accounted for. We discuss whether radiation-driven winds might in general not be able to re- accelerate after a non monotonicity has occurred in the velocity law
Chlamydomonas acidophila, a unicellular green alga, is a dominant phytoplankton species in acidic water bodies, facing severe environmental conditions such as low pH and high heavy metal concentrations. We examined the pH-, and temperature-dependent accumulation of heat-shock proteins in this alga to determine whether heat-shock proteins play a role in adaptation to their environment. Our results show increased heat-shock proteins accumulation at suboptimal pHs, which were not connected with any change in intracellular pH. In comparison to the mesophilic Chlamydomonas reinhardtii, the acidophilic species exhibited significantly higher accumulations of heat-shock proteins under control conditions, indicating an environmental adaptation of increased basal levels of heat-shock proteins. The results suggest that heat- shock proteins might play a role in the adaptation of C. acidophila, and possibly other acidophilic algae, to their extreme environment
For the first time, site-selective distortion has been investigated for two different structural units in the ternary compound alpha-GaPO4 under the influence of a permanent external electric field. Based on 54 measured reflection intensities, the electric-field-induced distortion of PO4 and GaO4 tetrahedra in alpha-GaPO4 crystals is evaluated using a model of pseudoatomic displacements introduced recently [Gorfman, Tsirelson & Pietsch (2005). Acta Cryst. A61, 387- 396]. A stronger variation of the P-O bond lengths in the PO4 tetrahedron was found compared to the bonds in the GaO4 tetrahedron. The different distortions of the tetrahedra owing to the electric field were analysed in terms of the valence charge density of alpha-GaPO4 and its topological characteristics. The larger charge of the P pseudoatom compared to the Ga atom was recognized as the main reason for the higher sensitivity of the PO4 tetrahedron to a permanent external electric field
Genetic correlations between plant resistances to multiple natural enemies are important because they have the potential to determine the mode of selection that natural enemies impose on a host plant, the structure of herbivore and pathogen communities, and the success of plant breeding for resistance to multiple diseases and pests. We conducted a meta-analysis of 29 published studies of 16 different plant species reporting a total of 467 genetic correlations between resistances to multiple herbivores or pathogens. In general, genetic associations between resistances to multiple natural enemies tended to be positive regardless of the breeding design, type of attacker, and type of host plant. Positive genetic correlations between resistances were stronger when both attackers were pathogens or generalist herbivores and when resistance to different enemies was tested independently, suggesting that generalists may be affected by the same plant resistance traits and that interactions among natural enemies are common. Although the mean associations between resistances were positive, indicating the prevalence of diffuse selection and generalized defenses against multiple enemies, the large variation in both the strength and the direction of the associations suggests a continuum between pairwise and diffuse selection
Characterization of polarization attributes of seismic waves using continuous wavelet transforms
(2006)
Complex-trace analysis is the method of choice for analyzing polarized data. Because particle motion can be represented by instantaneous attributes that show distinct features for waves of different polarization characteristics, it can be used to separate and characterize these waves. Traditional methods of complex-trace analysis only give the instantaneous attributes as a function of time or frequency. However. for transient wave types or seismic events that overlap in time, an estimate of the polarization parameters requires analysis of the time-frequency dependence of these attributes. We propose a method to map instantaneous polarization attributes of seismic signals in the wavelet domain and explicitly relate these attributes with the wavelet-transform coefficients of the analyzed signal. We compare our method with traditional complex-trace analysis using numerical examples. An advantage of our method is its possibility of performing the complete wave-mode separation/ filtering process in the wavelet domain and its ability to provide the frequency dependence of ellipticity, which contains important information on the subsurface structure. Furthermore, using 2-C synthetic and real seismic shot gathers, we show how to use the method to separate different wave types and identify zones of interfering wave modes
Flagellates are important bacterial grazers in most planktonic food webs. The prey-size preference of the mixotrophic flagellate, Ochromonas sp. (Chrysophyceae), isolated from an extremely acidic lake, Lake 111 (pH 2.6), was determined using fluorescently labelled microspheres (beads). According to grazing experiments with cultured bacteria, also isolated from Lake 111, the potential grazing impact on Lake 111"s single-celled bacterial production was calculated. Ochromonas sp. ingested the smallest beads offered (0.5 µm diameter) at the highest rate. Ingestion rate declined with increasing bead size. The highest prey volume-specific ingestion was measured for Ochromonas sp. feeding on intermediate-sized beads (1.9 µm). Ingestion rates were low due in part to the large fraction of inactive flagellates observed. According to the bacterial ingestion rate, a mean of 88% (epilimnion) and 68% (hypolimnion) of in situ single- celled bacterial production is potentially grazed daily by Ochromonas sp. In the epilimnion of Lake 111, the heterotrophic carbon gain is three times higher than the autotrophic production. Alongside carbon uptake, Ochromonas sp. also benefits from ingesting bacteria through the uptake of phosphorus. A biovolume minimum corresponding to the prey size at which Ochromonas sp. feeds most efficiently occurred in the Lake 111 epilimnetic bacterial community, implying top-down control of the bacterial community by Ochromonas sp.
We present a theoretical framework for the analysis of the statistical properties of thermal fluctuations on a lossy transmission line. A quantization scheme of the electrical signals in the transmission line is formulated. We discuss two applications in detail. Noise spectra at finite temperature for voltage and current are shown to deviate significantly from the Johnson-Nyquist limit, and they depend on the position on the transmission line. We analyze the spontaneous emission, at low temperature, of a Rydberg atom and its resonant enhancement due to vacuum fluctuations in a capacitively coupled transmission line. The theory can also be applied to study the performance of microscale and nanoscale devices, including high-resolution sensors and quantum information processors
A 13.94-m-long sediment core, collected from a medium-sized lake in the Qilian Mountains (NE Tibetan Plateau, China), was analysed palynologically at 81 horizons. The interpretation of indicator taxa yielded various vertical shifts of the vegetation belts. These palaeovegetation results have been checked with lake surface pollen spectra from 8 takes representing different altitudinal vegetation belts. Our main findings are the following: A short period of the late Marine Isotope Stage 3 (around similar to 46,000 yr ago) was characterized by interglacial temperature conditions with a tree line above its present-day altitude. During the LGM, the vicinity of the lake was not covered by ice but by sparse alpine vegetation and alpine deserts, indicating that the climate was colder by similar to 4-7 degrees C than today Markedly higher temperatures were inferred from higher arboreal pollen frequencies between similar to 13,000 and similar to 7000 yr ago with a Holocene temperature optimum and a maximal Picea-Betula mixed-forest expansion between similar to 9000 and similar to 7000 yr ago, when temperatures exceeded the present-day conditions by at least 1-2 degrees C. Alpine steppes and meadows and sub-alpine shrub vegetation dominated around the lake since the middle Holocene, suggesting that vegetation and climate conditions were exceptionally stable in comparison to previous periods.
Two common data representations are mostly used in intelligent data analysis, namely the vectorial and the pairwise representation. Pairwise data which satisfy the restrictive conditions of Euclidean spaces can be faithfully translated into a Euclidean vectorial representation by embedding. Non-metric pairwise data with violations of symmetry, reflexivity or triangle inequality pose a substantial conceptual problem for pattern recognition since the amount of predictive structural information beyond what can be measured by embeddings is unclear. We show by systematic modeling of non-Euclidean pairwise data that there exists metric violations which can carry valuable problem specific information. Furthermore, Euclidean and non-metric data can be unified on the level of structural information contained in the data. Stable component analysis selects linear subspaces which are particularly insensitive to data fluctuations. Experimental results from different domains support our pattern recognition strategy.
Predicting the breeding success of large raptors in arid southern Africa : a first assessment
(2006)
Raptors are often priorities for conservation efforts and breeding success is a target measure for assessing their conservation status. The breeding success of large raptors in and southern Africa is thought to be higher in years of high rainfall. While this correlation has been found in several studies, it has not yet been shown for data from a wider geographical area. In conservation research, it is important to explore the differences between spatially- separated populations to estimate and to compare their conservation status, and to deduce specific management strategies. Using a theoretical approach, we develop a simplistic model to explain the breeding success-rainfall relationship in large African raptors at larger spatial scales. Secondly, we validate this model and we show that the inclusion of field data leads to consistent predictions. In particular, we recommend that the average size of the 'effective territory' should be included in the relationship between annual rainfall and breeding success of raptors in and southern Africa. Accordingly, we suggest that breeding success is a function of precipitation and inter- nest distance. We present a new measure of territory quality depending on rainfall and territory size. We suggest that our model provides a useful first approach to assess breeding success in large raptors of and southern Africa. However, we strongly emphasise the need to gather more data to further verify our model. A general problem in conservation research is to compare the status of populations assessed in different study areas under changing environmental conditions. Our simplistic approach indicates that this problem can be overcome by using a weighted evaluation of a target measure (i.e. breeding success), taking regional differences into account
We investigate the relationship between the gap between the energy of the ground state and the first excited state and the decay of correlation functions in harmonic lattice systems. We prove that in gapped systems, the exponential decay of correlations follows for both the ground state and thermal states. Considering the converse direction, we show that an energy gap can follow from algebraic decay and always does for exponential decay. The underlying lattices are described as general graphs of not necessarily integer dimension, including translationally invariant instances of cubic lattices as special cases. Any local quadratic couplings in position and momentum coordinates are allowed for, leading to quasi-free ( Gaussian) ground states. We make use of methods of deriving bounds to matrix functions of banded matrices corresponding to local interactions on general graphs. Finally, we give an explicit entanglement-area relationship in terms of the energy gap for arbitrary, not necessarily contiguous regions on lattices characterized by general graphs
We study pseudo-differential operators on a cylinder R x B where B has conical singularities. Configurations of that kind are the local model of corner singularities with cross section B. Operators in our calculus are assumed to have symbols a which are meromorphic in the complex covariable with values in the algebra of all cone operators on B. We show an explicit formula for solutions of the homogeneous equation if a is independent of the axial variable t is an element of R. Each non-bijectivity point of the symbol in the complex plane corresponds to a finite-dimensional space of solutions. Moreover, we give a relative index formula
In an attempt to map the shallow geometry of the Maleme Fault Zone (North Island, New Zealand) and estimate vertical displacements of selected fault strands, we have collected 2D and 3D georadar data using 100 MHz antennae. The 2D data consisted of three parallel georadar lines recorded perpendicular to the axis of the well-defined graben of the Maleme Fault Zone. These similar to 160 in long lines, which were 7.5 m apart, crossed several fault strands on either side of the graben axis. The processed georadar sections revealed two prominent parallel reflections that originated from the boundaries of Late Pleistocene lacustrine and tephra deposits. Distinct vertical offsets of these reflections allowed us to estimate displacernents at individual fault strands across the entire inner graben. The total displacements represented by these offsets was similar to 10-20% greater than that inferred from geomorphological studies, thus demonstrating the limitations of surface observations for determining cumulative fault movements. The 3D georadar data set, recorded across an area of similar to 70x similar to 20 in to one side of the graben axis, provided key details on individual fault strands. For the 3D visualization of fault-related structures, various spatial attribute analyses based on the cosine of the instantaneous phase proved to be useful
We compared growth rates and efficiencies of pelagic bacteria from an extremely acidic mining lake (pH 2.6, mean depth 4.6m) supplied with different sources of carbon: (1) excreted by phytoplankton, (2) derived from benthic algae, (3) entering the lake via ground water, and (4) leached from leaf litter. Bacteria exhibited high growth rate and efficiency on exudates of pelagic and benthic algae. In contrast, they showed a lower growth rate and efficiency with organic carbon from ground water, and grew at a very high rate but a very low efficiency on leaf leachate. Results from stable isotope analyses indicate a greater importance of benthic exudates and leaf leachate for bacteria in the epilimnion, and a higher impact of ground water sources in the hypolimnion. Given the magnitude of differential source inputs into the lake, we suggest that benthic primary production was the most important carbon source for pelagic bacteria. The benthic-pelagic coupling seems to be more relevant in this shallow acidic lake with low pelagic carbon dioxide concentrations than in neutral lakes
The parameters of the nutations are now known with a good accuracy, and the theory accounts for most of their values. Dissipative friction at the core-mantle boundary (CMB) and at the inner core boundary is an important ingredient of the theory. Up to now, viscous coupling at a smooth interface and electromagnetic coupling have been considered. In some cases they appear hardly strong enough to account for the observations. We advocate here that the CMB has a small- scale roughness and estimate the dissipation resulting from the interaction of the fluid core motion with this topography. We conclude that it might be significant
In side pumped laser head geometries good extraction of energy has to be weighted against diffraction effects of the amplified beam. Beam clipping at the aperture of laser rods can be avoided by using an undoped cladding around the doped core. The wings of e. g. Gaussian beams can be accommodated in the cladding. Phase distortion by the refractive index step of the rod can be compensated by a phase conjugating mirror in double pass configuration. In our proof of principle experiment the brightness of the beam from core doped amplifier rods was shown to be doubled compared to a conventional rod of the same outer diameter. (c) 2006 Optical Society of America