32,363 research outputs found
First report on incidence of inflorescence blight and pod rot (Choanephora infundibulifera) on dolichos bean (Dolichos lablab, L.) and yard long beanin (Vignaunguiculata sub sp. sesquipedalis) India
Inflorescence blight and pod rot caused by Choanephorasp. were recorded in two major vegetable crops viz.dolichos bean and yard long bean at a very high degree of severity. Usually, the disease occurs in mild proportions without causing economic loss during rainy season in Kerala (June to September) affecting vegetable crops like cowpea and bhendi. However, during the year 2016, the disease was noticed with a very high severity of more than 90 per cent on two crops grown at two different locations in Thrissur district of Kerala during October to January. None of the commonly used fungicides could control the disease. The pathogen was found to be luxuriantly growing on the inflorescences of dolichos bean and on the fruits of yard long bean. The first incidence of the disease was recorded during the last week of October, 2016. The disease spread was almost cent per cent on susceptible genotypes of dolichos bean and more than 90 per cent in variety ‘Vaijayanthi’ of yard long bean. A study was conducted exploring the pre disposing factors leading to the occurrence of the disease in epidemic proportions.Meteorological factors affecting the disease were studied and it was found that there is positive correlation of the disease severity with increasing atmospheric temperature and rainfall.Atmospheric temperature more than 30oC along with high humidity and rain fall during the preceding week are found to be the major pre disposing factors lead to the epidemic in both the crops. The pathogen was isolated and based on morphological characters, identified as Choanephora sp. Pathogenicity was proved by inoculation on healthy inflorescence stalks.Molecular characterization of the pathogen confirmed the identity as Choanephora infundibulifera. This is the first report of the pathogen on dolichos bean and yard long bean in India
Brane Cosmology Solutions with Bulk Scalar Fields
Brane cosmologies with static, five-dimensional and Z_2 symmetric bulks are
analysed. A general solution generating mechanism is outlined. The qualatitive
cosmological behaviour of all such solutions is determined. Conditions for
avoiding naked bulk singularities are also discussed. The restrictions placed
on the solutions by the assumption of such a static bulk are investigated. In
particular the requirement of a non-standard energy-momentum conservation law.
The failure of such solutions to provide viable quintessence terms in the
Friedmann equations is also discussed.Comment: 15 pages, references added, minor change
Tele-operated high speed anthropomorphic dextrous hands with object shape and texture identification
This paper reports on the development of two number of robotic hands have been developed which focus on tele-operated high speed anthropomorphic dextrous robotic hands. The aim of developing these hands was to achieve a system that seamlessly interfaced between humans and robots. To provide sensory feedback, to a remote operator tactile sensors were developed to be mounted on the robotic hands. Two systems were developed, the first, being a skin sensor capable of shape reconstruction placed on the palm of the hand to feed back the shape of objects grasped and the second is a highly sensitive tactile array for surface texture identification
Collective excitations of a trapped Bose-condensed gas
By taking the hydrodynamic limit we derive, at , an explicit solution of
the linearized time dependent Gross-Pitaevskii equation for the order parameter
of a Bose gas confined in a harmonic trap and interacting with repulsive
forces. The dispersion law for the
elementary excitations is obtained, to be compared with the prediction
of the noninteracting harmonic oscillator model.
Here is the number of radial nodes and is the orbital angular
momentum. The effects of the kinetic energy pressure, neglected in the
hydrodynamic approximation, are estimated using a sum rule approach. Results
are also presented for deformed traps and attractive forces.Comment: uuencoded file including 12 pages REVTEX and 1 figur
Gravitational and electromagnetic fields of a charged tachyon
An axially symmetric exact solution of the Einstein-Maxwell equations is
obtained and is interpreted to give the gravitational and electromagnetic
fields of a charged tachyon. Switching off the charge parameter yields the
solution for the uncharged tachyon which was earlier obtained by Vaidya. The
null surfaces for the charged tachyon are discussed.Comment: 8 pages, LaTex, To appear in Pramana- J. Physic
The experimental observation of Beliaev damping in a Bose condensed gas
We report the first experimental observation of Beliaev damping of a
collective excitation in a Bose-condensed gas. Beliaev damping is not predicted
by the Gross-Pitaevskii equation and so this is one of the few experiments that
tests BEC theory beyond the mean field approximation. Measurements of the
amplitude of a high frequency scissors mode, show that the Beliaev process
transfers energy to a lower lying mode and then back and forth between these
modes. These characteristics are quite distinct from those of Landau damping,
which leads to a monotonic decrease in amplitude. To enhance the Beliaev
process we adjusted the geometry of the magnetic trapping potential to give a
frequency ratio of 2 to 1 between two of the scissors modes of the condensate.
The ratios of the trap oscillation frequencies and
were changed independently, so that we could investigate
the resonant coupling over a range of conditions.Comment: 4 pages including 5 fig
Simulations of thermal Bose fields in the classical limit
We demonstrate that the time-dependent projected Gross-Pitaevskii equation
derived earlier [Davis, et al., J. Phys. B 34, 4487 (2001)] can represent the
highly occupied modes of a homogeneous, partially-condensed Bose gas. We find
that this equation will evolve randomised initial wave functions to
equilibrium, and compare our numerical data to the predictions of a gapless,
second-order theory of Bose-Einstein condensation [S. A. Morgan, J. Phys. B 33,
3847 (2000)]. We find that we can determine the temperature of the equilibrium
state when this theory is valid.
Outside the range of perturbation theory we describe how to measure the
temperature of our simulations. We also determine the dependence of the
condensate fraction and specific heat on temperature for several interaction
strengths, and observe the appearance of vortex networks. As the
Gross-Pitaevskii equation is non-perturbative, we expect that it can describe
the correct thermal behaviour of a Bose gas as long as all relevant modes are
highly occupied.Comment: 15 pages, 12 figures, revtex4, follow up to Phys. Rev. Lett. 87
160402 (2001). v2: Modified after referee comments. Extra data added to two
figures, section on temperature determination expande
Observation of harmonic generation and nonlinear coupling in the collective dynamics of a Bose condensate
We report the observation of harmonic generation and strong nonlinear
coupling of two collective modes of a condensed gas of rubidium atoms. Using a
modified TOP trap we changed the trap anisotropy to a value where the frequency
of the m=0 high-lying mode corresponds to twice the frequency of the m=0
low-lying mode, thus leading to strong nonlinear coupling between these modes.
By changing the anisotropy of the trap and exciting the low-lying mode we
observed significant frequency shifts of this fundamental mode and also the
generation of its second harmonic.Comment: 4 pages,3 figure
Probing the classical field approximation - thermodynamics and decaying vortices
We review our version of the classical field approximation to the dynamics of
a finite temperature Bose gas. In the case of a periodic box potential, we
investigate the role of the high momentum cut-off, essential in the method. In
particular, we show that the cut-off going to infinity limit decribes the
particle number going to infinity with the scattering length going to zero. In
this weak interaction limit, the relative population of the condensate tends to
unity. We also show that the cross-over energy, at which the probability
distribution of the condensate occupation changes its character, grows with a
growing scattering length. In the more physical case of the condensate in the
harmonic trap we investigate the dissipative dynamics of a vortex. We compare
the decay time and the velocities of the vortex with the available analytic
estimates.Comment: 7 pages, 8 eps figures, submitted to J. Optics B for the proceedings
of the "Atom Optics and Interferometry" Lunteren 2002 worksho
Ultrasonic propagation in finite-length granular chains
A narrowband ultrasound source has been used to generate solitary wave impulses in finite-length chains of spheres. Once the input signal is of sufficient amplitude, both harmonics and sub-harmonics of the input frequency can be generated as non-linear normal modes of the system, allowing a train of impulses to be established from a sinusoidal input. The characteristics of the response have been studied as a function of the physical properties of the chain, the input waveform and the level of static pre-compression. The results agree with the predictions of a theoretical model, based on a set of discrete dynamic equations for the spheres for finite-length chains. Impulses are only created for very small pre-compression forces of the order of 0.01 N, where strongly non-linear behaviour is expected
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