Evolution of clusters in dynamic point patterns: with a case study of Ants' simulation

Recent developments in sensing and tracking technologies have enabled large geographical databases to be established that represent spatial dynamics of ‘behavioral entities’. Within this type of dynamics there are several levels and modes of organization that need to be revealed. Clusters are high‐level groupings of entities, where change in their location and form, including split and merge events, represents self‐organization and functioning patterns. Such information may contribute for better understanding spatially complex dynamic patterns. The main objective of this article is to develop an adaptable methodology that facilitates exploration of spatial order and processes in point pattern dynamics. The approach presented here utilizes data‐clustering at each snapshot of the moving pattern, and then involves pairwise linking between the clusters identified at each snapshot and those identified in the following snapshot. Such linking is based on a new methodology that defines well globally optimized solutions for numerous possible linking combinations based on Linear Programming. A preliminary assessment of the approach was conducted with an existing Ants' simulation tool, capable of creating data sets covering in detail a substantial portion of the nest's life cycle.     

Radio and X-ray signatures of merging neutron stars

We describe the possible electromagnetic signals expected from the magnetospheric interactions of a neutron star binary prior to merger. We find that both radio and X-ray signals of detectable strength are possible. We discuss possible links with the phenomenon of gamma-ray bursts (GRBs) and describe the prospects for direct detection of these signals in searches for radio and X-ray transients.     

Percolation in the Crust

Considering the Earth's Crust as a heterogeneous medium, we show here that the general features of the seismic, electrical, and mechanical properties of the Crust can be conveniently described with a unified model derived from percolation theory. The basic assumption is that fracture density is a variable parameter which decreases with depth and as a result there exists a critical threshold below which fractures are only connected within finite clusters. This threshold corresponds to a critical fracture density and to a critical depth. Fluids circulate through a connected network of fractures down to the critical depth Z_c. Below Z_c, anisotropic fracture clusters result in seismic reflectors and high electrical conductivity. Earthquakes are restricted to depths shallower than Z_c, where friction controls the mechanical resistance to fluid infiltrated pre-existing fractures.     

Local stability and estimation of uncertainty for solutions to inverse problems

 We present a method for studying local stability of a solution to an inverse problem and evaluate the uncertainty in determining true values of particular observables. The investigation is done under the assumption that only the Gaussian part of fluctuations about the local minimum of the cost (likelihood) function is essential. Our approach is based on the spectral analysis of the Hessian operator associated with the cost function at its extremal point, and we put forward an effective iterative algorithm suitable for numerical implementation in the case of a computationally large problem. Received: 16 May 2001 / Accepted: 22 October 2001     

Paleomagnetism of Cretaceous units of the Mametchinskiy Peninsula, Kuyul Region, Northeastern Russia: implications for development and evolution of the Northwest Pacific Basin

The northernmost part of the Kamchatka Peninsula of northeastern Russia, located along the northwestern margin of the Bering Sea, consists of zones of complexly deformed accreted terranes. Progressing from the northwestern Bering Sea inland are the Olyutorskiy, Ukelayat, and Koryak superterranes, which were accreted to the Okhotsk–Chukotsk volcanic–plutonic belt (OChVB) during the Campanian–Maastrichtian (Koryak) to Middle Eocene (Olyutorskiy), respectively. To constrain the accretion paleolatitude of the Koryak superterrane, we paleomagnetically sampled a sedimentary series on the Mametchinskiy Peninsula. At the Mametchinskiy Peninsula, in the northeastern Penzhinskaya Guba (61.45° N, 163.75° E), a gently deformed, well-bedded section of fine-grained Lower to lower Upper Cretaceous turbidites, the Mametchinskaya and Tylakrylskaya Formations are exposed. These strata, which represent the lower part of the sedimentary cover of the terranes in this region and the forearc of OChVB, were sampled at 39 sites (three to seven samples per site). Within the Ainyn terrane, more than 1000 m of section of Cenomanian–Turonian age was sampled at a basal locality (sample groups I and II, sites 1–18, 19–29) and at an upper locality of Valanginian–Barremian age (sample group III, sites 30–39) along the western shore of the Peninsula. Thermal demagnetization and principal component analysis of the demagnetization data show lower-temperature (A) and higher-temperature (B) magnetic components. Although group III samples did not display a coherent A component, the A component of group I and II samples was observed as a single-polarity lower-unblocking temperature component generally removed by 100–400 °C. This component failed the fold test at the 95% confidence level. With respect to direction, the A component is similar to both the present-day field and axial–geocentric dipole directions expected at this site. The B component was observed during thermal demagnetization steps up to 580 °C and was always of downward-directed inclination. Coherence of bedding corrections within each section do not allow statistically meaningful fold tests within groups I, II or III. Assuming the B component represents a Cretaceous magnetization, two overall models are proposed. In the first model (preferred), with the highest clustering of directions (k-value=36.7, N (sites)=36), indicates significant poleward motion of the Ainyn terrane (observed paleolatitude λ_M1=61.0±6.5°; expected North America plate reference site paleolatitude λ_E=74.0±3.5°). In the second model, no significant poleward displacement is implied (λ_M2=72.0±9.6).     

New Olivine Reference Material for In Situ Microanalysis

A new olivine reference material – MongOL Sh11‐2 – for in situ analysis has been prepared from the central portion of a large (20 × 20 × 10 cm) mantle peridotite xenolith from a ~ 0.5 My old basaltic breccia at Shavaryn‐Tsaram, Tariat region, central Mongolia. The xenolith is a fertile mantle lherzolite with minimal signs of alteration. Approximately 10 g of 0.5–2 mm gem quality olivine fragments were separated under binocular microscope and analysed by EPMA, LA‐ICP‐MS, SIMS and bulk analytical methods (ID‐ICP‐MS for Mg and Fe, XRF, ICP‐MS) for major, minor and trace elements at six institutions world‐wide. The results show that the olivine fragments are sufficiently homogeneous with respect to major (Mg, Fe, Si), minor and trace elements. Significant inhomogeneity was revealed only for phosphorus (homogeneity index of 12.4), whereas Li, Na, Al, Sc, Ti and Cr show minor inhomogeneity (homogeneity index of 1–2). The presence of some mineral and fluid‐melt micro‐inclusions may be responsible for the inconsistency in mass fractions obtained by in situ and bulk analytical methods for Al, Cu, Sr, Zr, Ga, Dy and Ho. Here we report reference and information values for twenty‐seven major, minor and trace elements.     

Synthetic fluid inclusions. XV. TEM investigation of plastic flow associated with reequilibration of fluid inclusions in natural quartz

The nature and abundance of dislocations in quartz surrounding fluid inclusions were studied to obtain a better understanding of processes associated with fluid inclusion reequilibration. Synthetic fluid inclusions containing 10 wt% NaCl aqueous solution were formed in three samples at 700 °C and 5 kbar. One of the samples was quenched along an isochore to serve as a reference sample. The other two samples were quenched along a P-T path that generated internal pressures in excess of the confining pressure. The two samples were held at the final reequilibration P-T conditions of 625 °C and 2 kbar for 30 and 180 days, respectively. Following the experiments, microstructures associated with fluid inclusions were examined with the TEM. Quartz in healed fractures in the reference sample that was quenched isochorically shows a moderate dislocation activity. Quartz adjacent to reequilibrated fluid inclusions in the other two samples, however, showed a marked increase in dislocation activity compared to the un-reequilibrated sample. Deformation of the inclusion walls occurred anisotropically by expansion of mobile dislocations in their slip systems. Dislocation expansion was controlled by glide in the rhombohedral planes {1 0 1 1} that was restricted to narrow zones (≤3 μm) in the immediate vicinity of the fluid inclusion walls outside of the healed fracture plane. These plastic zones were observed after both short term (30 days) and long term (180 days) experiments and are attributed to hydrolytic weakening of quartz around fluid inclusions owing to diffusion of water into the quartz matrix during the experiment. The close spatial association of submicroscopic water bubbles with dislocations, and the rarity of water bubbles in the reference sample, show clearly that in both the 30 and 180 day experiments reequilibration involves water loss from the fluid inclusions. Our results indicate that synthetic fluid inclusions in this study recover (chemically and volumetrically), even at relatively fast experimental loading rates, such that internal stresses never reach the point of brittle failure. The driving force for fluid inclusion deformation involves two related mechanisms: plastic deformation of hydrolytically weakened wet quartz in the healed fracture, and water leakage associated with preexisting and strain-induced dislocations. Received: 5 May 1998 / Accepted: 10 February 2000