Miracle-dz/UniFAR-FTUs huggingface dataset:
Surface group representations in PU(p,q) and Higgs bundles

Using the L^2 norm of the Higgs field as a Morse function, we study the moduli spaces of U(p,q)-Higgs bundles over a Riemann surface. We require that the genus of the surface be at least two, but place no constraints on (p,q). A key step is the identification of the function's local minima as moduli spaces of holomorphic triples. In a companion paper "Moduli spaces of holomorphic triples over compact Riemann surfaces" (math.AG/0211428) we prove that these moduli spaces of triples are non-empty and irreducible. Because of the relation between flat bundles and fundamental group representations, we can interpret our conclusions as results about the number of connected components in the moduli space of semisimple PU(p,q)-representations. The topological invariants of the flat bundles are used to label subspaces. These invariants are bounded by a Milnor-Wood type inequality. For each allowed value of the invariants satisfying a certain coprimality condition, we prove that the corresponding subspace is non-empty and connected. If the coprimality condition does not hold, our results apply to the closure of the moduli space of irreducible representations. This paper, and its companion mentioned above, form a substantially revised version of math.AG/0206012.
The Elements of Climate Variability in the Tropical Atlantic Region

Abstract The tropical Atlantic region, unlike the tropical Pacific, is not dominated by any single mode of climate variability such as the El Nino–Southern Oscillation (ENSO). Rather, this region is subject to multiple competing influences of comparable importance. The nature and potential predictability of these various influences has been investigated by analysis of an ensemble of atmospheric GCM integrations forced with observed SST for the period December 1948–November 1993. The dominant modes of internal atmospheric and SST-forced variability are determined. Internal variability in the tropical Atlantic region is dominated by the equatorward extension of extratropical patterns, especially the North Atlantic oscillation. Three different SST-forced signals are identified. These are (a) a remote response to ENSO, (b) a response to the so-called Atlantic Dipole SST pattern, and (c) a response to equatorial Atlantic SST anomalies. The spatial structure and seasonality of these different elements of climat.
THE TECTONIC FRAMEWORK AND REGIONAL HYDROCARBON PROSPECTIVITY OF THE GULF OF ADEN

The Gulf of Aden rifting predates that in the Red Sea. Isolated sub-basins developed during the earliest Oligocene following a major emergent (erosional) period during the latest Eocene. Marine sedimentation began in the middle-to-late Oligocene and progressed upwards from marginal marine to bathyal environments with significant turbidite input (primarily on the Yemen side).
A 3H/3He Study of Ground Water Flow in a Fractured Bedrock Aquifer

The concentrations of tritium, helium isotopes, and neon have been measured in ground water from a fractured bedrock aquifer in a densely populated suburban area near New York City. Samples were obtained from heavily pumped production wells of a regional water supply company. Helium and neon concentrations exceed the values for air‐saturated water, which is explained by the addition of unfractionated atmospheric air, radiogenic helium, and tritiogenic 3He. The identification of the composition of these excess components allows reliable separation of the tritiogenic 3He concentration, and hence the calculation of the 3H/3He ages of the ground water. Comparison of the combined tritium plus tritiogenic 3He concentrations with the historical record of tritium input from precipitation confirms that the 3H/3He data are self‐consistent and provides constraints on the degree of mixing or helium loss. The distribution of 3H/3He ages is related to the large‐scale topography of the study area and the depth of the wells. Furthermore, correlations between the 3H/3He ages and concentrations of total dissolved solids and total CO2 show that the ages contain meaningful information related to the temporal changes of the ground water chemistry.
Rifting and magmatism in the northeastern South China Sea from wide‐angle tomography and seismic reflection imaging

We present a new travel time tomography velocity model and seismic reflection images that delineate the rift architecture and magmatic features of the rifted margin in the northeastern South China Sea. These data reveal moderately stretched crust ~25 km thick along the continental shelf and thin but laterally variable crustal thickness in the distal margin. Along the continental slope, crust rapidly thins to ~4 km in a basin characterized by tilted fault blocks that sole into a low-angle detachment. Strain was localized to a degree within the highly stretched basin but failed to progress to breakup and seafloor spreading. Crust in the distal margin is ~12–15 km thick. Few extensional structures are apparent in the distal margin, but seismic velocities are suggestive of highly thinned and magmatically intruded continental crust. The magmatic features we interpret include volcanic zones at the top of the basement that deform or disrupt overlying postrift strata, sills intruded into the postrift sedimentary section, and a high-velocity (~6.9–7.5 km/s) lower crustal layer that we take to be magmatic underplating or pervasive lower crustal intrusions. These features primarily occur in the distal margin and may have been emplaced during postrift seafloor spreading. The postrift magmatism may have been induced by convective removal of continental lithosphere following breakup and the onset of seafloor spreading in the South China Sea.
Optimal Preconditioners for Finite Element Approximations of Convection-Diffusion Equations on structured meshes

The paper is devoted to the spectral analysis of effective preconditioners for linear systems obtained via a Finite Element approximation to diffusion-dominated convection-diffusion equations. We consider a model setting in which the structured finite element partition is made by equi-lateral triangles. Under such assumptions, if the problem is coercive, and the diffusive and convective coefficients are regular enough, then the proposed preconditioned matrix sequences exhibit a strong clustering at unity, the preconditioning matrix sequence and the original matrix sequence are spectrally equivalent, and the eigenvector matrices have a mild conditioning. The obtained results allow to show the optimality of the related preconditioned Krylov methods. %It is important to stress that The interest of such a study relies on the observation that automatic grid generators tend to construct equi-lateral triangles when the mesh is fine enough. Numerical tests, both on the model setting and in the non-structured case, show the effectiveness of the proposal and the correctness of the theoretical findings.
Bayesian Modelling of Pattern Formation from One Snapshot of Pattern

Partial differential equations (PDE) have been widely used to reproduce patterns in nature and to give insight into the mechanism underlying pattern formation. Although many PDE models have been proposed, they rely on the pre-request knowledge of physical laws and symmetries, and developing a model to reproduce a given desired pattern remains difficult. We propose a novel method, referred to as Bayesian modelling of PDE (BM-PDE), to estimate the best PDE for one snapshot of a target pattern under the stationary state. We show the order parameters extracting symmetries of a pattern together with Bayesian modelling successfully estimate parameters as well as the best model to make the target pattern. We apply BM-PDE to nontrivial patterns, such as quasi-crystals, a double gyroid and Frank Kasper structures. Our method works for noisy patterns and the pattern synthesised without the ground truth parameters, which are required for the application toward experimental data.
The Measurement of Residual Strength in Triaxial Compression

Synopsis The triaxial compression of soil samples with preformed shear plances involves difficulties in the estimation of the effects of the change in the crosssectional area and effects of the change in the crosssecitional area and the restraint of the rubber membrane. Corrections for these two effects are developed and are shown to give acceptable stess-strain curves, enabling ‘multi-stage’ tests to be used. La compression triaxiale d'echantillons de sol avec des plans de cisaillement pre-formes cause des difficultes dans l'evaluation des effects du changement dans la region en coupe et la restriction de la membrane de caoutchouc. On a developpe pour ces deux effects des corrections montrant qu'elles donnent des courbes de contrainte et de deformation acceptables, ce qui permet d'utiliser les essais a stades multiples.
The Effects of Twitter Sentiment on Stock Price Returns

Social media are increasingly reflecting and influencing behavior of other complex systems. In this paper we investigate the relations between a well-known micro-blogging platform Twitter and financial markets. In particular, we consider, in a period of 15 months, the Twitter volume and sentiment about the 30 stock companies that form the Dow Jones Industrial Average (DJIA) index. We find a relatively low Pearson correlation and Granger causality between the corresponding time series over the entire time period. However, we find a significant dependence between the Twitter sentiment and abnormal returns during the peaks of Twitter volume. This is valid not only for the expected Twitter volume peaks (e.g., quarterly announcements), but also for peaks corresponding to less obvious events. We formalize the procedure by adapting the well-known “event study” from economics and finance to the analysis of Twitter data. The procedure allows to automatically identify events as Twitter volume peaks, to compute the prevailing sentiment (positive or negative) expressed in tweets at these peaks, and finally to apply the “event study” methodology to relate them to stock returns. We show that sentiment polarity of Twitter peaks implies the direction of cumulative abnormal returns. The amount of cumulative abnormal returns is relatively low (about 1–2%), but the dependence is statistically significant for several days after the events.
The movement of septic tank effluent through sandy soils near perth. Ii movement of phosphorus

The potential of seven septic tank installations in the Perth (Western Australia) metropolitan area to contribute phosphate to the groundwater was investigated. The phosphate concentration in the soil solution below the soak wells and leach drains was measured using immiscible displacement and compared with the phosphate concentration of the water flowing into the systems. The phosphate sorbing properties of the subsoils were measured, and these were found to vary up to 100-fold within the same profile. A very strong correlation was established between a laboratory measure of the ability of the soil to sorb phosphate and the phosphate sorbed in the soil profile below leach drains and soak wells. The correlation held only for those systems for which little further phosphate was removed by reaction with the soil, and the phosphate in the soil solution was at or near the same concentration as the phosphate in the effluent. For a system receiving water from the bathroom, laundry and kitchen the phosphate concentration was as low as 8 µg P/ml. For a system receiving water from a toilet only, the concentration was as high as 29 µg P/ml. In systems receiving water from both sources the values were intermediate. For systems that had been installed for more than a few years, the concentration of phosphorus in the soil water down to 6 m below the soak well and leach drain was similar to that in the effluent being discharged into the soil.
Geometric interpretation of quantitative instability

Given a real algebraic group $G$ acting on a linear space $V$, a vector $v\in V$ is called unstable if $0\in \overline{Gv}-Gv$. A fundamental theorem of Kempf in geometric invariant theory states that $v$ is unstable if and only if there is a one-parameter subgroup $A$ of $G$ such that $Av$ is unstable. Assuming $G$ is a semisimple real algebraic $\mathbb{Q}$-group, we give a new proof to this result using a geometric interpretation of the setting. In the process, we also give a new proof of an effective version of this result by Shah and Yang. Our interpretation involves relating the length of vectors under a linear action to convex functions on certain $\cat$-spaces, and bound the later from below by Busemann functions.
Decadal variations in equatorial Pacific ecosystems and ferrocline/pycnocline decoupling

The equatorial Pacific Ocean is known for its large interannual to decadal variability in circulation. In particular, the changes that occurred in 1976/1977 have received considerable attention in the climate dynamics literature, and recently there has been much attention focused on changes that may have occurred there in 1997/1998. Unfortunately, because of data sparsity, the impact of these changes or shifts on ocean biogeochemistry and ecosystems remains largely unknown. Here a three‐dimensional ocean circulation model (the ORCA2 configuration of OPA) which has a food web/biogeochemistry model (PISCES) embedded in it, and which has been forced with both NCEP‐1 and ERA‐40 reanalysis fluxes over multiple decades, is used as a tool to investigate decadal changes and their associated mechanisms. Our main finding with the model is that a decrease in the amplitude of the surface zonal wind stress in the tropical Pacific in the mid‐to‐late‐1970s leads to a decrease in Fe and Chl concentrations in the upwelling regions of the eastern equatorial Pacific after 1976/1977. These changes find expression predominantly during the upwelling season (the seasonal maximum for Fe and Chl concentrations), when surface Fe and Chl concentrations tend to be significantly higher pre‐1976/1977 than post‐1976/1977. The changes in Chl concentrations need to be understood as modulations of the amplitude of the seasonal cycle, rather than as a “biological regime shift” (an abrupt transition from one mean state to another). In contrast to what is found for Fe and Chl, for NO3 the decadal changes in surface concentrations in the upwelling region about 1976/1977 can be described as a shift in the mean state. It is shown that the response in surface Fe and Chl in the upwelling region about 1976/1977 is proportionally larger than the decadal changes in surface wind stress forcing, and it is also larger than the previously reported change in the strength of the meridional overturning strength of the subtropical cells (STCs). Importantly, this amplified response reflects a decoupling of the ferrocline and pycnocline within the equatorial Pacific. In this way, the presence of a time‐invariant sediment source for Fe can substantially amplify the ecosystem response to decadal variability in ocean circulation.
Natural Computing

Natural Computing refers to computational processes observed in nature, and humandesigned computing inspired by nature. When complex natural phenomena are analyzed in terms of computational processes, our understanding of both nature and the essence of computation is enhanced. Characteristic for human-designed computing inspired by nature is the metaphorical use of concepts, principles and mechanisms underlying natural systems. Natural computing includes evolutionary algorithms, neural networks, molecular computing and quantum computing. The journal Natural Computing provides a forum for discovery in natural computing, offering links among researchers and insight into trends in an emerging specialty. The journal reports on theory, experiments, and applications, and covers natural computing from a very broad perspective, including use of algorithms to consider evolution as a computational process, and neural networks in light of computational trends in brain research. Now indexed in ISI.
LREE distribution patterns in zoned alkali feldspar megacrysts from the Karkonosze pluton, Bohemian Massif - implications for parental magma composition

Abstract The elemental compositions of zoned alkali feldspar megacrysts from the Karkonosze pluton have been analysed and Pb isotope ratios determined using LA-ICP-MS, EMPA and TIMS. The results are used to interpret the magmatic environments within which they crystallized. Growth zones in the megacrysts show fluctuating trace element patterns that reflect a systematic relationship between incompatible LREE and compatible Ba. Chemical gradients between zones in the cores and rims of the megacrysts are not accompanied by significant variation in initial Pb isotope composition. The nucleation and crystallization of the megacrysts is interpreted as having occurred in an environment of magmatic hybridization caused by mixing of mantle and crustal components in which effective homogenization of the Pb isotope composition preceded the onset of megacryst growth. The concentrations of LREE in alkali feldspar zones were used to reconstruct hypothetical melt compositions. Some of the zones appear to have crystallized in an homogenous magmatic environment having clear geochemical affinities with end-member magmas in the Karkonosze pluton, whereas others crystallized in heterogeneous domains of magma hybridization. With the exception of Nd, zones crystallized in more homogeneous magma show LREE fractionation under near-equilibrium conditions. Trace element abundances of megacrysts grown in dynamic, homogeneous magmatic environments of the Karkonosze pluton occasionally deviate from the predicted patterns and show LREE impoverishment.
A comparison of satellite‐derived carbon dioxide transfer velocities from a physically based model with GasEx cruise observations

[1] A method has been developed to use satellite observations with the physically based National Oceanic and Atmospheric Administration–Coupled Ocean Atmosphere Response Experiment (NOAA-COARE) gas transfer model (COAREG) to determine global estimates of carbon dioxide (CO2) transfer velocities. Ship observations from three Gas Exchange (GasEx) experiments conducted in 1998 (GasEx-98), 2001 (GasEx-01), and 2008 (SO GasEx) were used to validate the satellite estimates. Satellite retrievals of near-surface temperature, humidity, and wind speed along with observations of sea surface temperature, longwave and shortwave radiative fluxes at the surface were used to execute the gas transfer model. These satellite products exhibited good agreement with collocated in situ measurements even in higher-latitude environments where the retrieval techniques had not yet been extensively validated. Transfer velocities computed with COAREG using both the satellite- and ship-derived inputs further showed good agreement with an overall bias of −1.01 cm/h and a root mean square (RMS) difference of 7.43 cm/h. These results imply that COAREG can be applied with satellite inputs with accuracy comparable to that achieved with ship-based observations. COAREG transfer velocities were found to have a bias of 6.32 cm/h and RMS difference of 14.02 cm/h when compared with covariance-derived transfer velocities. Comparison of satellite-derived COAREG transfer velocities with empirical-derived wind-only models shows generally higher transfer velocities for wind speeds exceeding 7 m/s. However, these higher transfer velocities show good agreement with covariance-derived observations from both GasEx-98 and SO GasEx.
A New Robust Low-Scatter X-Ray Mass Indicator for Clusters of Galaxies

We present a comparison of X-ray proxies for the total cluster mass, M500, including the spectral temperature (TX), gas mass measured within r500 (Mg,500), and the new proxy, YX, which is a simple product of TX and Mg,500 and is related to the total thermal energy of the ICM. We use mock Chandra images constructed for a sample of clusters simulated with the Eulerian N-body+gasdynamics adaptive mesh refinement ART code in the concordance ΛCDM cosmology. The simulations achieve high spatial and mass resolution and include radiative cooling, star formation, and other processes accompanying galaxy formation. Our analysis shows that simulated clusters exhibit a high degree of regularity and tight correlations between the considered observables and total mass. The normalizations of the M500-TX, Mg,500-TX, and M500-YX relations agree to better than ≈10%-15% with the current observational measurements of these relations. Our results show that YX is the best mass proxy with a remarkably low scatter of only ≈5%-7% in M500 for a fixed YX, at both low and high redshifts and regardless of whether clusters are relaxed or not. In addition, we show that redshift evolution of the YX-M500 relation is close to the self-similar prediction, which makes YX a very attractive mass indicator for measurements of the cluster mass function from X-ray-selected samples.
On Strong Cosmic Censorship

For almost half of the one hundred year history of Einstein's theory of general relativity, Strong Cosmic Censorship has been one of its most intriguing conjectures. The SCC conjecture addresses the issue of the nature of the singularities found in most solutions of Einstein's gravitational field equations: Are such singularities generically characterized by unbounded curvature? Is the existence of a Cauchy horizon (and the accompanying extensions into spacetime regions in which determinism fails) an unstable feature of solutions of Einstein's equations? In this short review article, after briefly commenting on the history of the SCC conjecture, we survey some of the progress made in research directed either toward supporting SCC or toward uncovering some of its weaknesses. We focus in particular on model versions of SCC which have been proven for restricted families of spacetimes (e.g., the Gowdy spacetimes), and the role played by the generic presence of Asymptotically Velocity Term Dominated behavior in these solutions. We also note recent work on spacetimes containing weak null singularities, and their relevance for the SCC conjecture.
Summertime measurements of selected nonmethane hydrocarbons in the Arctic and Subarctic during the 1988 Arctic Boundary Layer Expedition (ABLE 3A)

Approximately 1000 whole air samples were collected and assayed for selected C2-C5 hydrocarbons during the 6-week Arctic Boundary Layer Expedition (ABLE 3A). Transit flights enabled latitudinal (40°N to 83°N) and longitudinal (70°W to 155°W) profiles to be obtained for altitudes between 4000 and 6000 m yielding summertime background mixing ratios for ethane, ethyne, propane and n-butane of 1050±200, 100±40, 120±80 and 10±8 pptv, respectively. Drilling associated with oil exploration in the Alaskan North Slope area is suggested to be a probable source of the enhanced levels of alkanes observed in the Arctic region within a radius in excess of 300 km from Prudhoe Bay, Alaska. A significant number of pollution plumes were encountered which could be attributed to wildfires. Factors describing the emissions caused by biomass burning relative to ethane for ethyne (0.40) and propane (0.08) were determined. An increase of hydrocarbon mixing ratios with altitude was observed during all but two of the missions. Therefore, the Arctic and sub-Arctic are significantly influenced by the long-range transport of pollutants from nonlocal sources. A single vertical profile made in the vicinity of Wallops Island, Virginia, revealed elevated levels of isoprene, numerous hydrocarbons of the types associated with the leakage of natural gas and fossil fuel combustion, and substantial concentrations of nitrogen oxides and ozone. This implies that long-range transport of various gases from urban areas, combined with local biogenic emissions of isoprene, are significant sources of regional tropospheric ozone.