403 research outputs found
Seasonal march of surface pressure gradients across India and the southwest monsoon
No full textIt is well known that the seasonal weather features of Indian sub-continent are associated with corresponding changes in the pressure gradients across the country
Concentration in Knowledge Output: A case of Economics Journals
No full textThis paper assesses the degree of author concentration in seven economics journals, which were published in India during 1990-2002. To measure the degree of author concentration, Lotka's Law was used. Moreover, we also make an exploratory analysis of the geographic, economics subfield and institutional concentration in 704 economics journals. An important finding of this paper is that specialized journals in the sample report the highest degree of author concentration. This result is quite similar to the findings by Cox and Chung (1991). Furthermore, there are several instances showing that the journals lean towards certain norms; this may affect the flow of innovative ideas into economics. We conclude that a knowledge activity, involving the high degree of concentration and a biased publication process, may affect the flow of new ideas into the discipline.Concentration, Lotka's Law
Pollination in Wedelia chinensis (Osbeck) Merr and Tridax procumbens L. (Compositae) by Thrips (Thysanoptera: Insecta)
No full textAvailable information on the role of thrips as pollinators of various species of Chenopodiaceae, Sterculiaceae, Ericaceae, Verbenaceae and Palmae pertains to the works of Muller (1883), Shaw (1914), Annand (1926), Hilles (1941), Hagerup (1950), Hagerup and Hagerup (1953), Ananthakrishnan (1973), Mathur and Mohan Ram (1978) and Syed (1978). Although Bailey (1937), Raizada (1961), and Bullock (1964) have provided some basic information on the thrips-Compositae association, their specific role as pollinators has not received any particular attention. Sufficient evidence exists suggesting the role of thrips as pollinators in Compositae, and an attempt has been made to study the role of Microcephalothrips abdominalis (Crawford), Frankliniella schultzei (Trybom), Haplothrips tardus Priesner, and Haplothrips gowdeyi (Franklin), frequenting the floral heads of Wedelta chinensis and Tridax procumbens
Density-dependent prophylaxis in insects.
No full textParasites and pathogens are a ubiquitous threat facing all organisms. Life history theory predicts that if investment in parasite resistance mechanisms is costly (as suggested by numerous studies), then organisms should tailor their investment in them to match their perceived risk of infection. Because most parasites are transmitted in a positively density-dependent manner, the threat from parasites tends to increase as population density increases. As a result, it is predicted that organisms should use population density as a cue to the risk of becoming infected and should increase investment in disease resistance mechanisms as the degree of crowding increases—this is known as density-dependent prophylaxis (DDP). This phenomenon has been experimentally tested in a number of insect species, and in most cases support for the DDP hypothesis has been forthcoming. DDP is likely to be particularly prevalent in species exhibiting density-dependent phase polyphenism (i.e. the phenotype adopted by the insect is plastic and dependent on the population density it experiences during its early development). We discuss the hormonal and genetic mechanisms underlying phase polyphenism and DDP, and speculate on the circumstances leading to their evolution. We end by discussing how future research into DDP might develop
Optimization of Solar Sailcraft Trajectory for a Comet Sample Return Mission
No full textComets, the sporadic visitors from the outer edges of the Solar System, are considered to hold the key for understanding the formation of planets and the origin of life on Earth. Having spent the majority of time away from the radiative environment of the inner Solar System, the chemistry of the comets has remained unaltered, making them the pristine samples of the matter from the ancient Solar nebula. A mission to bring cometary particles back to Earth enables the examination of the materials in well equipped laboratories and saves the mass of the instruments to be carried on board. As conventional propulsion methods require a large quantity of propellant for this type of mission, the feasibility of using the novel propulsion technique of solar sailing is explored in this thesis. In order to return the comet samples to Earth within a reasonable time period, the orbit transfer is considered as an optimal control problem with constraints placed on the sailcraft’s position and velocity. The Differential Evolution (DE) algorithm was used to search for time-optimal trajectories that minimize the approach distance and the relative velocity with respect to the comet during sample collection. The optimal trajectory obtained predicts the solar sailcraft to reach the comet, collect the samples and return back to Earth in 6.8 years. The time of arrival at the comet was found to match with the comet's perihelion passage, enabling effective sample collection. The outcome of the trajectory analysis, thus successfully demonstrates the applicability of solar sailing to comet sample return missions in the near future.Aerospace Engineering | Astrodynamics & Space Mission
Ultrafast laser inscription: perspectives on future integrated applications
No full textThis paper reviews the recent advancements achieved using ultrafast laser inscription (ULI) that highlight the cross-disciplinary potential of the technology. An overview of waveguide fabrication is provided and the three distinct types of waveguide cross-section architectures that have so far been fabricated in transparent dielectric materials are discussed. The paper focuses on two key emergent technologies driven by ULI processes. First, the recently developed photonic devices, such as compact mode-locked waveguide sources and novel mid-infrared waveguide lasers are discussed. Secondly, the phenomenon and applications of selective etching in developing ultrafast laser inscribed structures for compact lab-on-chip devices are elaborated. The review further discusses the conceivable future of ULI in impacting the aforementioned fields.</p
Distribution of heights of prominences
No full textStudy of the frequency distribution of heights of nearly 50000 prominences observed on K Spectro-heliograms during a complete solar cycle shows a nearly exponential decrease of frequency with increasing height between 20″ and 220″ of height above the chromosphere
Distribution of heights of prominences
No full textStudy of the frequency distribution of heights of nearly 50000 prominences observed on K Spectro-heliograms during a complete solar cycle shows a nearly exponential decrease of frequency with increasing height between 20″ and 220″ of height above the chromosphere
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