Oscillatory instability and fluid patterns in low-Prandtl-number Rayleigh-B\'{e}nard convection with uniform rotation

We present the results of direct numerical simulations of flow patterns in a low-Prandtl-number ($Pr = 0.1$) fluid above the onset of oscillatory convection in a Rayleigh-B\'{e}nard system rotating uniformly about a vertical axis. Simulations were carried out in a periodic box with thermally conducting and stress-free top and bottom surfaces. We considered a rectangular box ($L_x \times L_y \times 1$) and a wide range of Taylor numbers ($750 \le Ta \le 5000$) for the purpose. The horizontal aspect ratio $\eta = L_y/L_x$ of the box was varied from $0.5$ to $10$. The primary instability appeared in the form of two-dimensional standing waves for shorter boxes ($0.5 \le \eta < 1$ and $1 < \eta < 2$). The flow patterns observed in boxes with $\eta = 1$ and $\eta = 2$ were different from those with $\eta < 1$ and $1 < \eta < 2$. We observed a competition between two sets of mutually perpendicular rolls at the primary instability in a square cell ($\eta = 1$) for $Ta < 2700$, but observed a set of parallel rolls in the form of standing waves for $Ta \geq 2700$. The three-dimensional convection was quasiperiodic or chaotic for $750 \le Ta < 2700$, and then bifurcated into a two-dimensional periodic flow for $Ta \ge 2700$. The convective structures consisted of the appearance and disappearance of straight rolls, rhombic patterns, and wavy rolls inclined at an angle $\phi = \frac{\pi}{2} - \arctan{(\eta^{-1})}$ with the straight rolls.Comment: 32 pages, 14 figures, 1 tabl

On the propagation of gravity waves in the lower solar atmosphere in different magnetic configurations

Gravity waves are generated by turbulent subsurface convection overshooting or penetrating locally into a stably stratified medium. While propagating energy upwards, their characteristic negative phase shift over height is a well-recognized observational signature. Since their first detailed observational detection and estimates of energy content, a number of studies have explored their propagation characteristics and interaction with magnetic fields and other wave modes in the solar atmosphere. Here, we present a study of the atmospheric gravity wave dispersion diagrams utilizing intensity observations that cover photospheric to chromospheric heights over different magnetic configurations of quiet-Sun (magnetic network regions), a plage, and a sunspot as well as velocity observations within the photospheric layer over a quiet and a sunspot region. In order to investigate the propagation characteristics, we construct two-height intensity - intensity and velocity-velocity cross-spectra and study phase and coherence signals in the wavenumber-frequency dispersion diagrams and their association with background magnetic fields. We find signatures of association between magnetic fields and much reduced coherence and phase shifts over height from intensity-intensity and velocity-velocity phase and coherence diagrams, both indicating suppression/scattering of gravity waves by the magnetic fields. Our results are consistent with the earlier numerical simulations, which indicate that gravity waves are suppressed or scattered and reflected back into the lower solar atmosphere in the presence of magnetic fields.Comment: 19 pages, 19 Figures, Accepted for publication in Advances in Space Research journa

An Energy Constraint Approach to Improve Lifetime and Reduce Routing Overhead in Heterogeneous MANET

Heterogeneous Mobile Ad-hoc Networks (H-MANET) contain different configuration nodes, each of which communicates over a wireless channel and is capable of movement. Heterogeneous wireless networking has attracted lot of interest from consumers in the previous few years for its applications in mobile and personal communications. One of the main constraints in MANET is the high probability of failure due to energy-exhausted nodes. So if the path selected for communication has low battery life then the path breaks prematurely and the re-discovery phase starts, which costs more overhead in the network. Therefore, there is unequal consumption of node energy, which must be prevented. The energy expenditure of the nodes should be balanced in order to minimize path breakage. This can be done by finding the communication path that is the most energy-efficient among alternative disjoint paths. This approach reduces path breakage and routing overhead caused by nodes with low battery life dying in the communication path, thus increasing the network's lifetime

A study of the propagation of magnetoacoustic waves in small-scale magnetic fields using solar photospheric and chromospheric Dopplergrams: HMI/SDO and MAST observations

In this work, we present a study of the propagation of low-frequency magneto-acoustic waves into the solar chromosphere within small-scale inclined magnetic fields over a quiet-magnetic network region utilizing near-simultaneous photospheric and chromospheric Dopplergrams obtained from the HMI instrument onboard SDO spacecraft and the Multi-Application Solar Telescope (MAST) operational at the Udaipur Solar Observatory, respectively. Acoustic waves are stochastically excited inside the convection zone of the Sun and intermittently interact with the background magnetic fields resulting into episodic signals. In order to detect these episodic signals, we apply the wavelet transform technique to the photospheric and chromospheric velocity oscillations in magnetic network regions. The wavelet power spectrum over photospheric and chromospheric velocity signals show a one-to-one correspondence between the presence of power in the 2.5-4 mHz band. Further, we notice that power in the 2.5-4 mHz band is not consistently present in the chromospheric wavelet power spectrum despite its presence in the photospheric wavelet power spectrum. This indicates that leakage of photospheric oscillations (2.5-4 mHz band) into the higher atmosphere is not a continuous process. The average phase and coherence spectra estimated from these photospheric and chromospheric velocity oscillations illustrate the propagation of photospheric oscillations (2.5-4 mHz) into the solar chromosphere along the inclined magnetic fields. Additionally, chromospheric power maps estimated from the MAST Dopplergrams also show the presence of high-frequency acoustic halos around relatively high magnetic concentrations, depicting the refraction of high-frequency fast mode waves around vA ~ vs layer in the solar atmosphere.Comment: 16 pages, 7 figures, Accepted for Publication in Journal of Atmospheric and Solar-Terrestrial Physics (Special Issue of STP-15

Heterosis study in Okra [Abelmoschus esculentus (L.) Moench] genotypes for pod yield attributes

A study was conducted at Vegetable Research Farm, Department of Horticulture, Institute of Agriculture Sciences, Banaras Hindu University, Varanasi during Spring-Summer and Rainy season of 2012 and 2013 using 12 diverse parental lines of okra and their 66 F1 hybrids (through diallel cross-excluding reciprocals) with the objective to measure the extent of heterosis over better parent and standard commercial check varieties for the purpose of judging the extent up to which heterosis can be exploited in commercial okra breeding. The extent of heterosis for five best crosses over better parent and check (48.32 % to 82.42 % and 7.13 % to 35.66 %, respectively) for yield per hectare suggested the great scope of realizing higher yield in okra through heterosis breeding. Other economic traits also recorded moderate to high level of heterosis over the better parents. The cross combination IC -282280×EC – 329380showed high heterosis over better parent and standard check for pod yield (82.42 % and 35.66 %), number of pods per plant (62.82 % and 48.54 %) and respectively. This particular cross combination eventually resulted the height magnitude of heterobeltiosis and standard heterosis for the most of the desirable growth parameters as well as yield attributing characters which may be taken for further breeding programme

Short-range structure and thermal properties of lead tellurite glasses

PbO-TeO2 glasses having composition: xPbO–(100 - x)TeO2 (x = 10, 15 and 20 mol%) were prepared by melt quenching and characterized by X-ray diffraction,density measurements, differential scanning calorimetry and Raman spectroscopy. Glass density increases from 5.89 to 6.22 g cm-3 with increase in PbO concentration from 10 to 20 mol%, due to the replacement of TeO2 by heavier PbO. DSC studies found that glass transition temperature (Tg) decreases from a value of 295°C to 281°C. Raman studies found that glass short-range structure consists of TeO4 and TeO3 structural units and that PbO modifies the network by the structural transformation: TeO4 to TeO3