An exact Bianchi type-V cosmological model in Saez-Ballester theory of gravitation

An exact Bianchi type-V cosmological model is obtained in a scalar-tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986) in case of perfect fluid distribution. Some physical properties of the model are also discussed.     

Characterization of Earthquake Dynamics in Northeastern India Regions: A Modern Nonlinear Forecasting Approach

— The Northeastern India (NEI) region, is seismotectonically one of the most active regions of the world. Earlier studies of NEI earthquake data have provided contrasting evidence for the presence of randomness and low-dimensional strange attractor. Here, in the present study, we assess the dimensionality of an earthquake-generating mechanism by nonlinear predictability analyses on phase portrait constructed by monthly frequency earthquake time series which was obtained from the NOAA catalogue. The result of nonlinear forecasting analyses suggests that the earthquake processes in the NEI region evolve on a non-random high-dimensional chaotic system. Such a complex high-dimensional earthquake behavior is indicative of heterogeneous geological structures in which weak fault zones and/or individual fault interactions might have strength fluctuations due to pore pressure variation. Further, K₂ entropy analysis was performed to isolate the non-random component from the data. The analysis reveals a quasi-coherent time structure, (K₂ 0.08/month) which corresponds to a seasonal time scale of about 12 months. We argue that stochastic resonance created by seasonality bias may have combined with noise to affect the pore pressure variation leading to subsequent earthquake triggering. It is interesting to note that most earthquakes and swarm activities occurred during or after the monsoon season. Geological and geophysical evidence also reconciles with the above view. Evidence for high-dimensional chaos associated with seasonal bias in the NEI region may provide useful constraints for testing models and criteria to assess earthquake hazards on a more rigorous and quantitative basis.Received: 1 September 2001     

A package for digital processing and automatic contouring of aeromagnetic data

Aeromagnetic data processing refers to the processing of magnetic data acquired through airborne surveys. The total magnetic field at various points along the predetermined flight path is recorded using the on board cesium magnetometer. At each of these points, the positional information in terms of latitude, longitude obtained from Inertial Navigation System (INS) and attitude, time and date are also recorded. The track flown by the aircraft while data acquisition is also recorded using video flight path camera. A software package has been developed to process this data and generate outputs in a form amenable to visual interpretation. It is developed on a VAX 11/780 system using VAX FORTRAN and PLOT 10 GKS software. This paper gives an outline of the various functions available in this package and also highlights the problems encountered in choosing the most appropriate techniques/methods to be used in the gridding and contouring of the data.     

Discovering points of interest from users’ map annotations

One of the potential problems of volunteered geographic information (VGI) is ensuring its quality. Innocent mistakes and intentional falsehoods can reduce not only the quality of the information, but also people’s confidence in VGI as a legitimate source of data. We present a case study in VGI that addresses the quality problem by aggregating input from many different people. Specifically, we present a technique to maintain a comprehensive list of points of interest (POI) for digital maps. This is traditionally difficult, because new POI are created, because some POI are known only locally, and because some POI have multiple names. We address this problem by exploiting map annotations contributed by regular, online map users. Our institution’s mapping Web site allows users to create arbitrary collections of geographically anchored pushpins that are annotated with text. Our data mining solution finds geometric clusters of these pushpins and examines the pushpins’ text and other features for likely POI names. For instance, if a given text phrase is mentioned frequently in a cluster, but infrequently elsewhere, this increases our confidence that this phrase names a POI. We tested the quality of our results by asking 100 local residents whether or not the POI we found were correct, and our user study told us we were generally successful. We also show how we can use the same user-annotated pushpins to assess the popularity of existing POI, which is a guide for which ones to display on a map.     

Decadal and interannual variability of the Indian Ocean SST

The variability of the Indian Ocean on interannual and decadal timescales is investigated in observations, coupled model simulation and model experiment. The Indian Ocean Dipole (IOD) mode was specifically analyzed using a data-adaptive method. This study reveals one decadal mode and two interannual modes in the sea surface temperature (SST) of the IOD. The decadal mode in the IOD is associated with the Pacific Decadal Oscillation (PDO) of the North Pacific SST. The two interannual modes are related to the biennial and canonical components of El Niño-Southern Oscillation (ENSO), consistent with previous studies. This study hypothesizes that the relation between the Indian Ocean and the North Pacific on decadal scale may be through the northerly winds from the western North Pacific. The long simulation of Community Climate System Model version 4 also indicates the presence of IOD modes associated with the decadal PDO and canonical ENSO modes. However, the model fails to simulate the biennial ENSO mode in the Indian Ocean. The relation between the Indian Ocean and North Pacific Ocean is further supported by the regionally de-coupled model experiment.