Nonplanar ion-acoustic Gardner solitons in a pair-ion plasma with nonextensive electrons and positrons

The properties of nonplanar (cylindrical and spherical) ion-acoustic solitary waves (IA SWs) in an unmagnetized, collisionless electron-positron-ion (e-p-i) plasma, whose constituents are q-distributed electrons and positrons and inertial ions, are investigated by deriving the modified Gardner (MG) equation. The well known reductive perturbation method is employed to derive the MG equation. The basic features of nonplanar IA Gardner solitons (GSs) are discussed. It is found that the properties of nonplanar IA GSs (rarefactive and compressive) are significantly affected by the particle nonextensivity.     

On the application of information theory to the optimum state-space reconstruction of the short-term solar radio flux (10.7 cm), and its prediction via a neural network

The prediction of a time series using a neural network involves an optimum state-space reconstruction. The state space of the daily 10.7-cm solar radio flux is reconstructed using an information theory approach. A multi-layer feed-forward neural net is used for short-term prediction of the time series. The convergence of the synaptic weights is obtained partially by simulated annealing and partially by the 'quick prop' variation of back-propagation. The result gives a reasonably accurate short-term prediction.     

The formation of ring galaxies

The conditions under which a head-on collision between a disk galaxy and a spherical galaxy can lead to ring formation are investigated, using the impulsive approximation. The spherical galaxy is modeled as a polytrope of indexn=4 and radiusR _S and the disk galaxy as an exponential disk whose surface density is given by \(\sigma (r) = \sigma _c e^{ - 4r/R_D } \) , where σ _c is the central density andR _D is the radius of the disk. The formation and properties of the rings are closely related to the fractional change in binding energy of the disk galaxy, given by ΔU/?U?=γ _D β _D , where (GM _S ² R _D )/(V ² M _D R _S ² ),M _S andM _D being the masses of the spherical and disk galaxies, respectively, and β _D ≡β _D (n, σ, ?,i) is a function of the models of the two galaxies, the ratio of the radii of the two galaxies ?=R _S /R _D , and the angle of inclinationi, of the disk to the direction of relative motion of the two galaxies. Calculations are made for the caseR _S =R _D . Since practically the entire mass of the spherical galaxy, for the chosen model, lies within 1/3 of its radius, the radius of the spherical galaxy is effectively \(\tfrac{1}{3}\) that of the disk galaxy. It is found that as a result of the collision, the innermost and the outer parts of the disk galaxy are not much affected, but the intermediate region expands and gets evacuated, leading to the crowding of stars in a preferential region forming a ring structure. The rings are best formed for a normal, on-axis collision. For this case, rings form when ΔU/|U| lies between \(\tfrac{1}{2}\) and 2, while they are very sharp and bright when ΔU/|U| lies between \(\tfrac{1}{2}\) and 1. Within this range, as ΔU/|U| increases, the rings become sharper and their positions shift outwards with respect to the centre of the disk galaxy. The relationship $$\gamma _D = 0.0016 + 0.045s_{{\text{max}}}^2 ,$$ wheres _max is the radial distance of the density maximum of the ring from the centre of the disk galaxy (measured in terms of the radius of the disk galaxy as unit) enables us to finds _max from γ _D and vice versa, and interpret some prominent ring galaxies. The effect of introducing a bulge to the disk is to distribute the tidal disruptive effects more evenly and, hence, reduce the sharpness of the ring.     

The formation of faint ring structures

In a previous paper (Chatterjee, 1984), we studied the formation of ring galaxies due to head-on collisions between disk and spherical galaxies. The rings so formed are quite prominent and well defined. However, in the domain of rings, there are many faint rings which are ill defined and are so faint that they lie on the borderline of detectability. In this paper the formation of such rings is investigated.Using the impulsive approximation technique, in this paper we study an off-center collision between an exponential model disk galaxy and a polytropic (n=4) model spherical galaxy, in which the spherical galaxy moves normal to the plane of the disk galaxy and grazes its periphery. The radii of the two galaxies are taken to be equal, but due to the high central concentration of the spherical galaxy its radius is effectively one-third that of the disk galaxy. It is found that, as a result of the collision, the disk galaxy expands and attains an oblate shape. If the fractional change in binding energy of the disk galaxy, U/|U|, lies between 0.001 to 0.01, then a faint ring structure is formed which does not close on itself. If U/|U|0.01, then in addition to the faint ring a bridge and tail are formed. The ability of such low-energy collisions to affect even minor structural changes in the disk is due to the preferentially higher energy changes occurring in the side nearer to the perturbing galaxy than in the opposite side. Consequently, the structural changes produced are asymmetric.Such a faint ring may elude detection on photographs, but it will be revealed by sensitive photometric observations. There are several examples of such faint ring structures embedded in disks, which have been detected by observation.     

Validation of ERS-1 and High-Resolution Satellite Gravity with in-situ Shipborne Gravity over the Indian Offshore Regions: Accuracies and Implications to Subsurface Modeling

Geoid and gravity anomalies derived from satellite altimetry are gradually gaining importance in marine geoscientific investigations. Keeping this in mind, we have validated ERS-1 (168 day repeat) altimeter data and very high-resolution free-air gravity data sets generated from Seasat, Geosat GM, ERS-1 and TOPEX/POSEIDON altimeters data with in-situ shipborne gravity data of both the Bay of Bengal and the Arabian Sea regions for the purpose of determining the consistencies and deviations. The RMS errors between high resolution satellite and ship gravity data vary from 2.7 to 6.0 mGal, while with ERS-1 data base the errors are as high as 16.5 mGal. We also have generated high resolution satellite gravity maps of different regions over the Indian offshore, which eventually have become much more accurate in extracting finer geological structures like 85° E Ridge, Swatch of no ground, Bombay High in comparison with ERS-1satellite-derived gravity maps. Results from the signal processing related studies over two specific profiles in the eastern and western offshore also clearly show the advantage of high resolution satellite gravity compared to the ERS-1 derived gravity with reference to ship gravity data.     

Magnetic field induced metal-insulator transition in a one-dimensional chain: Application to neutron star atmospheres

It is shown that, in the non-interacting limit, a one-dimensional metallic system has a transition to an insulating phase, in presence of external magnetic fieldH, if _B H>E _B where _B is the Bohr magneton andE _Bis the energy band width of the electronic states. Possible realization of this effect in the atmosphere of neutron stars is pointed out.     

A Bootstrap Test Using Maximum Likelihood Ratio Statistics to Check the Similarity of Two 3-Dimensionally Oriented Data Samples

Comparing three-dimensionally oriented datasets is a problem encountered in various branches of earth science. A simple statistical tool for the comparison of two 3-dimensionally oriented datasets using the bootstrap method in line with the usual nonparametric permutation test is described here. This bootstrap test involves the estimation of maximum likelihood ratio statistic for properly constructed joint frequency tables of the datasets to be compared. This test does not use asymptotic result and will work well even for small sample sizes. Also this test does not make any specific distributional assumptions.     

Optimization of spread configuration for seismic data acquisition through numerical modeling in tectonically complex areas: a case study from Badarpur anticline, Cachar, India

Cachar area, a part of the Assam–Arakan frontal fold belt in the eastern part of India is characterized by a series of narrow anticlines which are dissected by a number of faults including thrusts, and broad synclines. Out of several exposed structures, Badarpur anticline is most important because of its major share of hydrocarbon strikes in Cachar. However, the seismic image of this area so far has been extremely poor for deciding locations for exploratory drilling. The problems in obtaining a good seismic image in this area include proper spread configuration including far and near offsets to capture reflected signals from the complex subsurface, variation of charge-sizes and depths along a line, large variation in statics due to rapid changes in elevation and near surface properties. The presence of coherent noise due to scattering and proper migration are major processing problems. This paper deals with the problem of spread configuration. For areas of complex subsurface, spread configuration obtained through field experiment at one spot may be quite different from other spots, requiring a large number of costly experiments. In this work, therefore, we used numerical modeling to derive an optimum spread configuration. For this, we chose a line passing through four wells on Badarpur anticline, and prepared a depth model using available seismic, surface geological and well data. Continuous synthetic common shot records were generated through oblique incidence ray tracing and were processed to obtain stacks with various spread configurations. Comparison of these stacks of synthetic data shows that end-on shooting configuration is inadequate for acquiring a good seismic image of the complex subsurface. From the present study it is evident that a split–spread configuration with near and far offsets of 50 m and 2400 m, respectively, can bring out optimum seismic images in Badarpur and other anticlines in this area.     

Patterns of deformed early lineations over later folds formed by buckling and flattening

The patterns of deformed early lineations (L₁) over later folds (F₂) can be classified into several morphological types depending on the nature of variation of L₁ F₂ over the folds. The field relations indicate that the folds under consideration are neither shear folds nor parallel folds modified by flattening. The lineation patterns are therefore interpreted in terms of an empirical model of simultaneous buckling and flattening in which it is assumed that (i) the central surface of the folded layer remains a sine curve in transverse profile, (ii) the ratio of rates of buckle shortening to homogeneous strain is proportional to sin 2a, with a as the dip angle and (iii) the progressive deformation is coaxial with the Z-axis of bulk strain parallel to the planar segments of the early folds. The model gives an insight into the relative importance of different physical factors which control the development of dissimilar lineation patterns. Not all lineation patterns are explicable by this simplified model. Thus complex patterns with variable L₁ F₂ along the fold axis may develop by a progressive rotation of the geometrically defined fold hinge through successive material lines. The theoretical results have been applied to interpret the lineation patterns in Central Rajasthan, India. It is concluded that L₁ was initially very close to the E-ESE trending subhorizontal Z-axis of bulk deformation during F₂-folding and that the X-axis was subhorizontal or gently plunging with a N-NNE trend.