Bifurcations of electron acoustic traveling waves in an unmagnetized quantum plasma with cold and hot electrons

Bifurcations of nonlinear electron acoustic solitary waves and periodic waves in an unmagnetized quantum plasma with cold and hot electrons and ions has been investigated. The one dimensional quantum hydrodynamic model is used to study electron acoustic waves (EAWs) in quantum plasma. Applying the well known reductive perturbation technique (RPT), we have derived a Korteweg-de Vries (KdV) equation for EAWs in an unmagnetized quantum plasma. By using the bifurcation theory and methods of planar dynamical systems to this KdV equation, we have presented the existence of two types of traveling wave solutions which are solitary wave solutions and periodic traveling wave solutions. Under different parametric conditions, some exact explicit solutions of the above waves are obtained.     

Dust ion acoustic travelling waves in the framework of a modified Kadomtsev-Petviashvili equation in a magnetized dusty plasma with superthermal electrons

For the critical values of the parameters q and V, the work (Samanta et al. in Phys. Plasma 20:022111, 2013b) is unable to describe the nonlinear wave features in magnetized dusty plasma with superthermal electrons. To describe the nonlinear wave features for critical values of the parameters q and V, we extend the work (Samanta et al. in Phys. Plasma 20:022111, 2013b). To extend the work, we derive the modified Kadomtsev-Petviashvili (MKP) equation for dust ion acoustic waves in a magnetized dusty plasma with q-nonextensive velocity distributed electrons by considering higher order coefficients of ?. By applying the bifurcation theory of planar dynamical systems to this MKP equation, the existence of solitary wave solutions of both types rarefactive and compressive, periodic travelling wave solutions and kink and anti-kink wave solutions is proved. Three exact solutions of these above waves are determined. The present study could be helpful for understanding the nonlinear travelling waves propagating in mercury, solar wind, Saturn and in magnetosphere of the Earth.     

Implications of rapid footpoint motions of photospheric flux tubes for coronal heating

Some recent observations at Pic-du-Midi (Mulleret al., 1992a) suggest that the photospheric footpoints of coronal magnetic field lines occasionally move rapidly with typical velocities of the order 3 km s^–1 for about 3 or 4 min. We argue that such occasional rapid footpoint motions could have a profound impact on the heating of the quiet corona. Qualitative estimates indicate that these occasional rapid motions can account for the entire energy flux needed to heat the quiet corona. We therefore carry out a mathematical analysis to study in detail the response of a vertical thin flux tube to photospheric footpoint motions in terms of a superposition of linear kink modes for an isothermal atmosphere. We find the resulting total energy that is asymptotically injected into an isothermal atmosphere (i.e., an atmosphere without any back reflection). By using typical parameter values for fast and slow footpoint motions, we show that, even if the footpoints spend only 2.5% of the time undergoing rapid motions, still these rapid motions could be more efficient in transporting energy to the corona than the slow motions that take place most of the time.     

Thermo-elastic interactions in an infinite elastic solid due to a concentrated transient heat source

Summary The present paper is concerned with the determination of thermo-elastic stress and temperature distribution in an infinite elastic solid when it is subjected to a concentrated transient heat source taking into account the effect of coupling. The fundamental partial differential equation for the thermo-elastic potential is solved by means of the operational method. The solutions are obtained for small values of time in terms of known functions such as complementary error functions and associated complementary error functions and have the form of power series with respect to the parameter of coupling . Since this parameter is generally very small for most of the metals, the expressions for stress and temperature distribution have been obtained by considering terms upto linear .     

Ancient urban water supply systems

Water supply systems were important components of early urban settlements. Because of frequent invasions, much thought was given to develop an enemy proof and reliable water supply system for a city. Sinnõrs, or water tunnels, were used in Palestine prior to 1200 BC. Qanãts were used in many areas for ground water utilization. A qanãt is an artificial underground channel which carried water over long distances, either from spring or from a water-bearing strata for irrigation and domestic consumption. Qanãts were probably used in Armenia, from where they rapidly spread to many Middle East countries.Fairly detailed information is available on urban water supply systems during the time of the Roman Civilization, a period which extended from about 100 BC to 200 AD, from the writings of Vitruvius and especially Frontinus, who was the curator aquarum of Rome. Frontinus made a state-of-the-art review of urban water supply systems, which is now the primary source of information on technology and practice prevalent at that time.     

The effect of Kelvin-Helmholtz instability on rising flux tubes in the convection zone

If the solar dynamo operates at the bottom of the convection zone, then the magnetic flux created there has to rise to the surface. When the convection zone is regarded as passive, the rising flux is deflected by the Coriolis force to emerge at rather high latitudes, poleward of typical sunspot zones (Choudhuri and Gilman, 1987; Choudhuri, 1989). Choudhuri and D'Silva (1990) included the effects of convective turbulence on the rising flux through (a) giant cell drag and (b) momentum exchange by small-scale turbulence. The momentum exchange mechanism could enable flux tubes of radii not more than a few hundred km to emerge radially at low latitudes, but the giant cell drag mechanism required unrealistically small flux tube radii (a few meters for a reasonable giant cell upflow) to counteract the Coriolis force. We now include the additional effect of Kelvin-Helmholtz instability in a symmetrical flux ring caused by the azimuthal flow induced during its rise. The azimuthal flow crosses the threshold for the instability only if there is a giant cell upflow to drag the flux tubes appreciably. In the absence of such a drag, as in the case of a passive convection zone or in the case of momentum exchange by small-scale turbulence, the azimuthal velocity never becomes large enough to cause the instability, leaving the results of the previous calculations unaltered. The giant cell drag, aided by Kelvin-Helmholtz instability, however, becomes now a viable mechanism for curbing the Coriolis force - 10⁴ G flux tubes with radii of a few hundred km being dragged radially by upflows of 70 m s^-1.     

A New Explanation for the Origin of Trans-equatorial Loops based on a Dynamo Model

Trans-equatorial loops (TLs) are one of the distinct magnetic structures in the solar corona and have a close relationship to solar activity. We present a systematic study of the origin of TLs linking with the Babcock?–?Leighton dynamo process based on the model of Chatterjee, Nandy, and Choudhuri (Astron. Astrophys. 427, 1019, 2004). We propose that TLs are visible signatures of poloidal field lines across the equator. The cycle variation of TL lengths obtained by the connectivities of poloidal field lines happens to be roughly in agreement with what one gets by considering the positions of sunspots. This explains why this cycle variation of TL lengths was found to be in conformity with Spörer’s law. The active regions always make the poloidal field configuration favorable to form TLs, which causes the conformity. The formation of TLs is a three-dimensional problem, which will require three-dimensional dynamo models for full investigation.     

Deciphering the Seasonal Cycle of Copepod Trophic Dynamics in the Strait of Georgia,Canada, Using Stable Isotopes and Fatty Acids

Characterizing trophic flows is central to our understanding of energy transfer in marine ecosystems. The food webs of coastal systems are difficult to study because the proportion of autochthonous to allochthonous sources often varies seasonally and is often overlaid on a seasonal cycle of zooplankton composition. Here, we use a combination of fatty acids and stable isotopes to disentangle the trophic pathways in a productive coastal system (the Strait of Georgia (SoG), Canada). Over the span of a year, Metridia pacifica, a ubiquitous omnivorous copepod, can utilize a wide range of dietary items including diatoms, flagellates, bacteria, detritus, and microzooplankton. M. pacifica can switch from herbivory to carnivory in response to declining chlorophyll concentrations after the spring bloom and can occasionally utilize detrital sources. These findings are discussed in the context of previous knowledge of the SoG ecosystem, the current state of ecosystem modeling in the region, and the use of stable isotopes and fatty acids to assess trophic dynamics.     

Pelagic food web interactions and hypolimnetic oxygen depletion: Results from experimental enclosures and lakes

Large lakes enclosures were used to examine the influence of nutrient (P, N) enrichment and planktivorous fish (1 + yellow perch) predation on hypolimnetic oxygen depletion. Results were compared to similar data for lakes with high (Lake St. George) and low (Haynes Lake) abundances of planktivorous fish. In both the unfertilized and fertilized enclosures, fish predation on large cladocerans increased the biomasses of pico- and nanoplankton (0.2–20 µm), phytoplankton (chlorophyll a) and total phosphorus (TP), reduced sedimentation, water clarity, and hypolimnetic oxygen concentrations (AHO). Fertilized enclosures without fish had highest TP and sedimentation rates, but the AHO were low. The high planktivore lake had higher pico- and nanoplankton, higher chlorophyll a, reduced water clarity, and lower AHO than the low planktivore lake. Areal hypolimnetic oxygen depletion (AHOD) rates were strongly related with Secchi depth and plankton size-distribution (r ² = 0.77, and 0.79, respectively), but not as strongly with TP, chlorophyll a, and sedimentation rates (r ² = 0.25, 0.53, and 0.02, respectively). Such observations are useful in forming a generalized hypothesis that lakes with low planktivory and high water clarity have lower oxygen depletion because 1) plankton that are settling are larger and spend less time in the hypolimnetic water column before reaching the sediment, and therefore undergo less decomposition, and 2) the euphotic depth extends into the hypolimnion and production of oxygen can take place.