SUMMARYAccessions of four Saccharum spp. from the world collection of sugarcane germplasm maintained at the ICAR-Sugarcane Breeding Institute Research Center, Kannur, Kerala State, India, were screened against Chilo sacchariphagus indicus (Kapur) (Lepidoptera: Crambidae), commonly known as internode borer. Observations on the progression of borer attack in the most susceptible Saccharum officinarum indicated that the incidence began in the first fortnight of July, increased in the next 2 months and reached its peak in September. Thereafter, the incidence decreased in the next 2 months but reached its overall peak in December. Simple correlation coefficients between mean monthly weather parameters and borer incidence were not significant. Percent of canes attacked was significantly lower in 2011 than in 2012 for S. officinarum, Saccharum barberi and Saccharum sinense but did not differ between the years for Saccharum robustum. Amongst the four Saccharum spp., S. robustum showed the lowest borer incidence whereas S. officinarum recorded the lowest attack intensity. Whilst infestation index showed the same trend as percent canes attacked, percent deadhearts did not differ amongst the four Saccharum spp. Considering the 171 accessions evaluated, 29 (16.9%) accessions were resistant, 39 (22.8%) moderately resistant and 103 (60.2%) susceptible to internode borer. Out of the 39 accessions of S. officinarum, none occupied the resistant category whereas 17.9% were in the moderately resistant category. In S. robustum, whilst nearly half (44.5%) the accessions emerged as resistant, a considerable number occupied the moderately resistant category. In S. barberi, no accession was resistant to the borer. In S. sinense, only one accession each represented resistant and moderately resistant categories. Plant morphological characters, yield and quality parameters did not show clear-cut relationship with the three infestation parameters.

We investigate the onset of thermoacoustic instabilities in a turbulent combustor terminated with an area contraction. Flow speed is varied in a swirl-stabilized, partially premixed combustor and the system is observed to undergo a dynamical transition from combustion noise to instability via intermittency. We find that the frequency of thermoacoustic oscillations does not lock-on to any of the acoustic modes. Instead, we observe that the dominant mode in the dynamics of combustion noise, intermittency and thermoacoustic instability is a function of the flow speed. We also find that the observed mode is insensitive to the changes in acoustic field of the combustor, but it varies as a function of upstream flow time scale. This new kind of thermoacoustic instability was independently discovered in the recent theoretical analysis of premixed flames. They are known as intrinsic thermoacoustic modes. In this paper, we report the experimental observation and the route to flame intrinsic thermoacoustic instabilities in partially premixed flame combustors. A simplified low-order network model analysis is performed to examine the driving mechanism. Frequencies predicted by the network model analysis match well with the experimentally observed dominant frequencies. Intrinsic flame-acoustic coupling between the unsteady heat release rate and equivalence ratio fluctuations occurring at the location of fuel injection is found to play a key role. Further, we observe intrinsic thermoacoustic modes to occur only when the acoustic reflection coefficients at the exit are low. This result indicates that thermoacoustic systems with increased acoustic losses at the boundaries have to consider the possibility of flame intrinsic thermoacoustic oscillations.

The impact of woolly aphid Ceratovacuna lanigera Zehntner (Homoptera: Aphididae) attack in five / six month old sugarcane on growth, yield and quality parameters of the crop was assessed in two field trials (cv. Co 86032) in 2004-05 and one trial (cv. Co 7219) in 2006-07. The effect on linear growth was assessed by measuring the incremental growth of benchmarked canes with and without woolly aphid attack at fortnight intervals. The mean aphid intensity rating per leaf on individual canes was recorded alongside in one trial to relate it to cane growth. At harvest, the weight of marked canes were recorded and juice and jaggery analysis for various parameters was performed. In the first trial (cv. Co 86032) with aphid attack in fifth month, incremental growth in infested canes was on par with that in healthy canes. In the second trial (cv. Co 86032) with aphid attack in the sixth month, incremental growth was lower in infested canes in most fortnights. In the third trial (cv. Co 7219) with aphid attack in sixth month, incremental growth was significantly lower in infested canes in the initial stages whereas in the later stages the differences became nonsignificant. Aphid abundance in the early stage and its subsequent abrupt disappearance showed correspondence with the observed pattern in incremental growth. While differential effect on cane and juice weight in the first two trials suggested the role of crop age at the time of attack, the results of the second year study indicated the possible effect of aphid intensity. Higher brix and sucrose% in infested canes in the second trial suggested possible effect of sap feeding on their concentration. Inconsistently higher phenols in infested canes did not positively suggest their role as induced resistant factors. Jaggery analysis did not show definite trends in different trials.

Telescopes with unobstructed pupil are known to deliver clean point spread function (PSF) to their focal plane, in contrast to traditional telescopes with obstructed pupil. Recent progress in the manufacturing aspheric surfaces and mounting accuracy favors unobstructed telescopes over obstructed telescopes for science cases that demand stable and clean PSF over the entire field-of-view. In this paper we compare the image quality of an unobstructed Three-Mirror-Anastigmat (TMA) design with that of an obstructed TMA. Both the designs have the same primary mirror, effective focal length, field-of-view and detector characteristics. We demonstrate using simulated images of faint elliptical galaxies imaged through the two designs, that both the designs can measure morphological parameters with same precision, if the PSF is reconstructed within 12 arc-minutes of the source. We also demonstrate that, the unobstructed design delivers desirable precision even if the PSF is reconstructed 50 arc-minutes away from the source. Therefore the PSF of unobstructed design is uniform over a wider field-of-view compared to an obstructed design. The image quality is given by the 1σ error-bars (68% confidence level) in the fitted values of the axisratio and position-angle of the simulated galaxies.

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Vortex separation and breakdown are an important source of unsteady heat release rate fluctuations in thermoacoustic systems. The coupling between the acoustic field and the energy released by vortex breakdown can cause combustion instability. The objective of this work is to perform linear stability analyses and to quantify the stability of thermoacoustic interactions where vortex breakdown is the dominant cause of heat release rate fluctuations. The dynamics of the system is modelled as a kicked oscillator, where the energy released by vortex breakdown is represented as the kick. Assuming small fluctuations, periodic and low values of kick, a Poincaré map is derived analytically. The stability of the system is determined from the eigenvalues associated with the Poincaré map. The results allow us to identify the region where vortex shedding or the acoustic mode is dominant. Previous experimental investigations report the transition between the two modes for variation in the flow Mach number. Similar transitions are observed in the present study.

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