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Search Results: 1 - 10 of 312770 matches for " P. K. Shukla "
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Effec.t of casing soil thickness on crop duration and yield of milky mushroom (Calocybe indica P.&C.)
P.K. SHUKLA*
Indian Phytopathology , 2012,
Abstract:
How Entrepreneurial Firms Prosper while Larger Firms Crumble
P. K. Shukla
International Journal of Business and Management , 2009, DOI: 10.5539/ijbm.v4n3p3
Abstract: Many firms are facing great difficulty surviving the declining financial markets in Fall 2008. As larger firms take drastic measures to control and cut costs while forecasting declining revenue, entrepreneurial firms view the same marketplace in a more positive light. What separate these two types of firms is their differing levels of entrepreneurial intensity. An entrepreneurial grid positions firms upon two dimensions: Frequency of Entrepreneurship and Degree of Entrepreneurship (innovativeness, risk taking, and proactiveness). Just as managers select the placement of their firm on market dimensions such as quality and price, firms need to make a strategic position choice on where they wish their firm to be placed as related to entrepreneurial intensity. The firms listed in a recent article from BusinessWeek magazine titled “The World’s Most Innovative Companies” portrays a higher level of entrepreneurial efforts on both dimensions; firms that would be labeled as revolutionary on the entrepreneurial grid. It would be expected that as consumers expect new and improved products and services to emerge from innovative markets, firms labeled as periodic/incremental would have difficulties in sustaining continual growth. Additionally, firms labeled as continuous or incremental, dynamic, and periodic or discontinuous on the grid would be expected to have moderate success.
Alfvenic tornadoes
P. K. Shukla
Physics , 2012,
Abstract: It is shown that a three-dimensional (3D) modified-kinetic Alfv\'en waves (m-KAWs) can propagate in the form of Alfv\'enic tornadoes characterized by plasma density whirls or magnetic flux ropes carrying orbital angular momentum (OAM). By using the two fluid model, together with Amp\`ere's law, we derive the wave equation for a 3D m-KAWs in a magnetoplasma with $m_e/m_i \ll \beta \ll 1$, where $m_e$ $(m_i)$ is the electron (ion) mass, $\beta =4 \pi n_0 k_B (T_e + T_i)/B_0^2$, $n_0$ the unperturbed plasma number density, $k_B$ the Boltzmann constant, $T_e (T_e)$ the electron (ion) temperature, and $B_0$ the strength of the ambient magnetic field. The 3D m-KAW equation admits solutions in the form of a Laguerre-Gauss (LG) Alfv\'enic vortex beam or Alfv\'enic tornadoes with plasma density whirls that support the dynamics of Alfv\'en magnetic flux ropes.
Twisted Dust Acoustic Waves in Dusty Plasmas
P. K. Shukla
Physics , 2012, DOI: 10.1063/1.4746091
Abstract: We examine linear dust acoustic waves (DAWs) in a dusty plasma with strongly correlated dust grains, and discuss possibility of a twisted DA vortex beam carrying orbital angular momentum (OAM). For our purposes, we use the Boltzmann distributed electron and ion density perturbations, the dust continuity and generalized viscoelastic dust momentum equations, and Poisson's equation to obtain a dispersion relation for the modified DAWs. The effects of the polarization force, strong dust couplings, and dust charge fluctuations on the DAW spectrum are examined. Furthermore, we demonstrate that the DAW can propagate as a twisted vortex beam carrying OAM. A twisted DA vortex structure can trap and transport dust particles in dusty plasmas.
Effects of the synoptic scale variability on the thermohaline circulation
I. Kourakis,P. K. Shukla
Nonlinear Processes in Geophysics (NPG) , 2005,
Abstract: The parametric coupling between large amplitude magnetic field-aligned circularly polarized electromagnetic ion-cyclotron (EMIC) waves and ponderomotively driven ion-acoustic perturbations in magnetized space plasmas is considered. A cubic nonlinear Schr dinger equation for the modulated EMIC wave envelope is derived, and then solved analytically. The modulated EMIC waves are found to be stable (unstable) against ion-acoustic density perturbations, in the subsonic (supersonic, respectively) case, and they may propagate as "supersonic bright" (`"subsonic dark", i.e. "black" or "grey")type envelope solitons, i.e. electric field pulses (holes, voids),associated with (co-propagating) density humps. Explicit bright and dark (black/grey) envelope excitation profiles are presented, and the relevance of our investigation to space plasmas is discussed.
Exact theory for localized envelope modulated electrostatic wavepackets in space and dusty plasmas
I. Kourakis,P. K. Shukla
Nonlinear Processes in Geophysics (NPG) , 2005,
Abstract: Abundant evidence for the occurrence of modulated envelope plasma wave packets is provided by recent satellite missions. These excitations are characterized by a slowly varying localized envelope structure, embedding the fast carrier wave, which appears to be the result of strong modulation of the wave amplitude. This modulation may be due to parametric interactions between different modes or, simply, to the nonlinear (self-)interaction of the carrier wave. A generic exact theory is presented in this study, for the nonlinear self-modulation of known electrostatic plasma modes, by employing a collisionless fluid model. Both cold (zero-temperature) and warm fluid descriptions are discussed and the results are compared. The (moderately) nonlinear oscillation regime is investigated by applying a multiple scale technique. The calculation leads to a Nonlinear Schr dinger-type Equation (NLSE), which describes the evolution of the slowly varying wave amplitude in time and space. The NLSE admits localized envelope (solitary wave) solutions of bright-(pulses) or dark- (holes, voids) type, whose characteristics (maximum amplitude, width) depend on intrinsic plasma parameters. Effects like amplitude perturbation obliqueness (with respect to the propagation direction), finite temperature and defect (dust) concentration are explicitly considered. Relevance with similar highly localized modulated wave structures observed during recent satellite missions is discussed.
Spectral properties of electromagnetic turbulence in plasmas
D. Shaikh,P. K. Shukla
Nonlinear Processes in Geophysics (NPG) , 2009,
Abstract: We report on the nonlinear turbulent processes associated with electromagnetic waves in plasmas. We focus on low-frequency (in comparison with the electron gyrofrequency) nonlinearly interacting electron whistlers and nonlinearly interacting Hall-magnetohydrodynamic (H-MHD) fluctuations in a magnetized plasma. Nonlinear whistler mode turbulence study in a magnetized plasma involves incompressible electrons and immobile ions. Two-dimensional turbulent interactions and subsequent energy cascades are critically influenced by the electron whisters that behave distinctly for scales smaller and larger than the electron skin depth. It is found that in whistler mode turbulence there results a dual cascade primarily due to the forward spectral migration of energy that coexists with a backward spectral transfer of mean squared magnetic potential. Finally, inclusion of the ion dynamics, resulting from a two fluid description of the H-MHD plasma, leads to several interesting results that are typically observed in the solar wind plasma. Particularly in the solar wind, the high-time-resolution databases identify a spectral break at the end of the MHD inertial range spectrum that corresponds to a high-frequency regime. In the latter, turbulent cascades cannot be explained by the usual MHD model and a finite frequency effect (in comparison with the ion gyrofrequency) arising from the ion inertia is essentially included to discern the dynamics of the smaller length scales (in comparison with the ion skin depth). This leads to a nonlinear H-MHD model, which is presented in this paper. With the help of our 3-D H-MHD code, we find that the characteristic turbulent interactions in the high-frequency regime evolve typically on kinetic-Alfvén time-scales. The turbulent fluctuation associated with kinetic-Alfvén interactions are compressive and anisotropic and possess equipartition of the kinetic and magnetic energies.
Effect of supplemented nutrition on yield of oyster mushroom, Hypsizygus ulmarius
RUCHITA DIXIT and P. K. SHUKLA*
Indian Phytopathology , 2012,
Abstract: Effect of three chemical compounds on growth and yield of Blue Oyster mushroom, Hypsizygus ulmarius was studied in three separate experiments on soaking of substrate, spray on growing beds and soaking followed by spray. Soaking with Ferrous sulphate (FeSO4) resulted maximum yield of sporocarps (726.2g per kg dry substrate) followed by Magnesium sulphate (MgSO4), Potassium nitrate (KNO3) and untreated (620g) respectively. In spray treatment, maximum yield of 792.8 g per kg dry substrate was recorded in FeSO4 followed by MgSO4, KNO3 and untreated (595.0 g) respectively. Maximum yield of sporocarps (931.4 g per kg dry substrate) was recorded with T-3 (soaking in MgSO4 solution followed by spray with FeSO4) followed by T-6 (KNO3 followed by FeSO4), T-2 (MgSO4 followed by KNO3), T-4 (KNO3 followed by MgSO4), T-1 (soaking and spray with MgSO4), T-5 (soaking and spray with KNO3 solution), T-9 (soaking and spray with FeSO4), T-10 (untreated), T-8 (FeSO4 followed by KNO3) and T-7 (FeSO4 followed by MgSO4) (591.2 g) respectively.
Letter to the Editor: Interpretations of new features of time domain electric-field structures in the auroral acceleration region
P. K. Shukla,L. Stenflo
Annales Geophysicae (ANGEO) , 2003,
Abstract: Possible theoretical interpretations of the various nonlinear electric-field structures in the auroral acceleration region are provided.
The dynamics of electron and ion holes in a collisionless plasma
B. Eliasson,P. K. Shukla
Nonlinear Processes in Geophysics (NPG) , 2005,
Abstract: We present a review of recent analytical and numerical studies of the dynamics of electron and ion holes in a collisionless plasma. The new results are based on the class of analytic solutions which were found by Schamel more than three decades ago, and which here work as initial conditions to numerical simulations of the dynamics of ion and electron holes and their interaction with radiation and the background plasma. Our analytic and numerical studies reveal that ion holes in an electron-ion plasma can trap Langmuir waves, due the local electron density depletion associated with the negative ion hole potential. Since the scale-length of the ion holes are on a relatively small Debye scale, the trapped Langmuir waves are Landau damped. We also find that colliding ion holes accelerate electron streams by the negative ion hole potentials, and that these streams of electrons excite Langmuir waves due to a streaming instability. In our Vlasov simulation of two colliding ion holes, the holes survive the collision and after the collision, the electron distribution becomes flat-topped between the two ion holes due to the ion hole potentials which work as potential barriers for low-energy electrons. Our study of the dynamics between electron holes and the ion background reveals that standing electron holes can be accelerated by the self-created ion cavity owing to the positive electron hole potential. Vlasov simulations show that electron holes are repelled by ion density minima and attracted by ion density maxima. We also present an extension of Schamel's theory to relativistically hot plasmas, where the relativistic mass increase of the accelerated electrons have a dramatic effect on the electron hole, with an increase in the electron hole potential and in the width of the electron hole. A study of the interaction between electromagnetic waves with relativistic electron holes shows that electromagnetic waves can be both linearly and nonlinearly trapped in the electron hole, which widens further due to the relativistic mass increase and ponderomotive force in the oscillating electromagnetic field. The results of our simulations could be helpful to understand the nonlinear dynamics of electron and ion holes in space and laboratory plasmas.
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