Effect of electron temperature on small-amplitude electron acoustic solitary waves in non-planar geometry

Effects of electron temperature on the propagation of electron acoustic solitary waves in plasma with stationary ions, cold and superthermal hot electrons is investigated in non-planar geometry employing reductive perturbation method. Modified Korteweg–de Vries equation is derived in the small amplitude approximation limit. The analytical and numerical calculations of the KdV equation reveal that the phase velocity of the electron acoustic waves increases as one goes from planar to non planar geometry. It is shown that the electron temperature ratio changes the width and amplitude of the solitary waves and when electron temperature is not taken into account,our results completely agree with the results of Javidan & Pakzad (2012). It is found that at small values of \(\tau \), solitary wave structures behave differently in cylindrical (\(\text {m} = 1\)), spherical (\(\text {m} = 2\)) and planar geometry (\(\text {m} = 0\)) but looks similar at large values of \(\tau \). These results may be useful to understand the solitary wave characteristics in laboratory and space environments where the plasma have multiple temperature electrons.     

Seasonal changes of antioxidant and oxidative parameters in the coral Pocillopora capitata on the Pacific coast of Mexico

The physiological responses of the coral Pocillopora capitata to environmental conditions common in winter and summer were studied in 2007 during February–March (winter) and June–July (summer) at La Boquita reef (Manzanillo, Colima, Mexico). Shallow and deep sampling stations were established at different distances from a small jetty built next to the Juluapan Lagoon. We analyzed superoxide radicals () and lipid peroxidants (TBARS); the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione‐S‐transferase (GST); chlorophyll a (Chl a), zooxanthellae density (ZD); and mycosporine‐like amino acids (MAAs). Our results showed that the , TBARS, CAT, GST, MAAs, and Chl a, levels were significantly higher in summer (P < 0.05); no seasonal difference was found for GPx, GR or ZD. We found significant differences (P < 0.05) in winter only for Chl a and ZD at shallow sites and, in contrast, for at deeper sites. The results of this study indicate that increasing temperature and radiation associated with seasonal changes (from winter to summer), the efficiency of the enzymes GST, CR and GPX, and the production of MAAs together form a powerful mechanism for P. capitata to offset the detrimental effects of environmental change.     

Global stability of disk-bulge systems: Spiral structure of disk galaxies

The spiral arms of disk galaxies are very sensitive to various morphological properties, such as, the gas content, the disk-to-bulge ratioetc. Here, the stability of self-gravitating annular disks surrounding the central rigid bulge component has been studied in order to explain the transition from the tight spiral arms in Sa galaxies to rather open patterns in Sc galaxies as the central amorphous component diminishes. Smooth spiral patterns are found associated with the dominant (or the fastest growing) modes of the system. When the disk-to-bulge mass ratio is small, a tight pattern results restricted to the inner regions of the disk. This pattern opens up and occupies larger disk areas as the disk component becomes comparable to the bulge. It is found here that the ‘explosive’ instabilities of the global density waves do not occur in the presence of a massive bulge. The growth-rates of the eigen-modes decrease as the disk-to-bulge mass ratio decreases. It is also found that unstable modes of the annular disk can be suppressed by increasing the thermal pressure sufficiently.     

The effect of Main-Sequence stars on age estimates of open clusters

Existing methods for age estimation of open clusters are discussed. Most of the observed open clusters (except extremely young and old) contain 50–90% unevolved Main-Sequence stars. Possible difficulties encountered in estimating the actual age of an unevolved Main-Sequence star are discussed. For a relatively reliable cluster age estimation only a small percentage of cluster members are suitable. The effect of unevolved Main-Sequence stars on open cluster age estimates using the modified method of isochromes is analyzed.On leave of absence from the Department of Physics, Kumaon University, Naini Tal, India.     

Radial clastic dykes formed by a salt diapir in the Dead Sea Rift, Israel

ABSTRACT Fanning structures radiating from a central perturbation are known in various geological environments, where different processes have produced similar geometry. The present contribution describes and analyses fanning clastic dykes in the Dead Sea Rift, a new example of diapir-related deformation. The dykes are opening-mode fractures exposed in lacustrine varved marl of the Lisan Formation, deposited 70–15 ka. They are arranged mainly in a radial and tangential geometry. The radial traces converge at the 'Black Hill' structural dome. The geometry of the fractures is consistent with stresses exerted by the rise of a salt diapir located underneath the Black Hill. The estimated extension of the radial fractures is in good agreement with the present topographic elevation of the hill. The absence of fractures in the overlying Holocene alluvium probably indicates that either the rise of the Black Hill salt diapir paused or is associated now with a different style of deformation.     

Unsteady MHD free-convective flow through a porous medium with hall currents

The two-dimensional unsteady free-convective flow through a porous medium bounded by an infinite vertical plate for an incompressible viscous and electrically conducting fluid is considered, when a strong magnetic field is imposed in a direction which is perpendicular to the free stream and makes an angle to the vertical direction. The effects of Hall currents on the flows are studied for various values of .     

Effect of oblateness on the non-linear stability of L 4 in the restricted three-body problem

Non-linear stability of the libration point L ₄ of the restricted three-body problem is studied when the more massive primary is an oblate spheroid with its equatorial plane coincident with the plane of motion, Moser's conditions are utilised in this study by employing the iterative scheme of Henrard for transforming the Hamiltonian to the Birkhoff's normal form with the help of double D'Alembert's series. It is found that L ₄ is stable for all mass ratios in the range of linear stability except for the three mass ratios: $$\begin{gathered} \mu _{c1} = 0.0242{\text{ }}...{\text{ }}{}^{{\text{\_\_}}}0.1790{\text{ }}...{\text{ }}A_1 , \hfill \\ \mu _{c2} = 0.0135{\text{ }}...{\text{ }}{}^{{\text{\_\_}}}0.0993{\text{ }}...{\text{ }}A_1 , \hfill \\ \mu _{c3} = 0.0109{\text{ }}...{\text{ }}{}^{{\text{\_\_}}}0.0294{\text{ }}...{\text{ }}A_1 . \hfill \\ \end{gathered} $$      

Finite-difference analysis of the MHD stokes problem for a vertical plate with Hall and ion-slip currents

An explicit finite-difference method is employed to study the MHD free convection heat generating fluid past an impulsively started vertical infinite plate when a strong magnetic field is applied perpendicular to the plate. The velocity and temperature profiles are shown on graphs and the results are discussed in terms of the non-dimensional parameters _e (Hall parameter), _i (ionslip parameter), (heat source parameter), and Gr (Grashof number).     

Survey of antibodies to Mycoplasma agalactiae and Mycoplasma mycoides subsp. mycoides (large colony type) in dromedaries (Camelus dromedarius) in close contact with an infected goat population

Given recent evidence of a possible role of camelids in the epidemiology of diseases caused by mycoplasma species in other ruminants, we examined the prevalence of the mycoplasmas most commonly responsible for contagious agalactia (CA) in small ruminants among the dromedaries (Camelus dromedarius) of Lanzarote. On this island, one of the most arid regions of Spain in which CA is considered endemic, dromedaries and infected small ruminants such as goats and sheep, live in close contact. Specific IgG antibodies against Mycoplasma agalactiae and Mycoplasma mycoides subsp. mycoides (large colony biotype) were determined using two indirect enzyme immunoassays in 28% of the island's dromedary population. None of the serum samples tested were found to have antibodies against the two mycoplasma species, suggesting that the camels are not potential carriers of the main causative agents of CA.