1,721,371 research outputs found
Book Review: Shankar Kumar Bhaumik, Principles of Econometrics: A Modern Approach Using EViews
No full text Shankar Kumar Bhaumik, Principles of Econometrics: A Modern Approach Using EViews, 2015, New Delhi: Oxford University Press, 496 pp., ₹795. ISBN: 978-0-19-809853-9 </jats:p
Effects of the extrusion process parameter
No full textRetraction of: Effects of the Extrusion Process Parameter by Prashant Baredar, Jitendra Kumar, Anil Kumar, Shankar Kumar and Ajeet Kumar Giri as it was republished due to oversite.</jats:p
Silicon-photonic-assisted on-chip RF signal processing
No full textWe present a Silicon-photonic-assisted RF signal processing, in particular, frequency up conversion and RF pulse generation. For frequency up-conversion, we use compact silicon PN micro-ring modulator to frequency double the input RF signal. Experimentally we report an up-conversion of the baseband to a maximum of 12 GHz covering L, S, C and X band. We achieve a maximum suppression of 30 dB of the baseband at the output. The extinction could be improved by operating the ring modulator at the critical coupling. We present a detailed study on the effect of the optical carrier offset from the resonance wavelength and its effect on the suppression and the upconverted RF linewidth. Using the same platform, we also demonstrate RF-pulse generation using a PN Mach-Zehnder modulator. An RF modulated optical carrier, and an RF signal can be fed to the MZM to create pulsed RF of desired pulse width and rate. As a demonstrator, we show that RF-signal of frequency between L-X band could be fed and pulsed at various rates from 100-0.1 millisecond. The two examples demonstrate the feasibility of the Silicon Photonics Platform for building photonic assisted RF technology
Precise modelling of spacecraft relative motion for formation flying spacecraft
No full textRelative spacecraft motion has long been a problem for mission analysts who plan rendezvous maneuvers. These planners look to the solution devised by Clohessy and Wiltshire as their primary analysis tool. The Clohessy-Wiltshire (CW) equations are usually sufficient for the rendezvous problem that is of short duration and has frequent thruster firings. Consequently, the long-term accuracy of the equations of motion is not as important in the rendezvous problem as in the formation-flying problem. The errors resulting from the assumptions made in the CW equations such as circular reference orbit, very close target orbit are unacceptable for the long-term prediction of relative motion needed for formation flying satellites. A precise analytic solution for the relative motion of and formation flying
satellites is needed to minimize fuel consumption and maximize lifetime. In this paper, we derive the relative coordinates of a deputy satellite with respect to a master satellite by a series of transformations and translations from the Earth-centered inertial frame to the spacecraftcentered rotating frame. The equations of relative coordinates derived in this paper are very precise and
can be used to analyze orbits of any eccentricity and of any initial separation with or without the inclusion of orbit perturbations
A numerical study of some vortex ring phenomena using direct numerical simulation (DNS)
No full textDirect numerical simulation (DNS) is used to study some aspects of the dynamics of vortex rings in viscous, incompressible flow at Reynolds numbers (defined as the ratio of the initial circulation to the kinematic viscosity) in the range of 103 to 104. Firstly, the effect of the particular initial core azimuthal vorticity profile of a vortex ring on its subsequent evolution in unbounded flow is studied. Vortex rings with a wide range of initial core vorticity profiles are shown to relax to a common equilibrium state. Additionally the behaviour of the equilibrium vortex ring at large times is studied. When the slenderness ratio of the vortex rings increases beyond a particular limit, the vortex rings diverge from the common equilibrium state and follow paths determined by the viscosity of the fluid. Secondly, the interaction of a laminar vortex ring with a non-deformable, free-slip surface at an oblique angle of incidence leading to the phenomenon of vortex reconnection is investigated. Specifically the effect of Reynolds number on the dynamics of the reconnection process is studied. The scaling of the reconnection timescale with the Reynolds number is obtained. At high Reynolds numbers the reconnection process leads to a breakdown of the entire vortex ring structure to a turbulent-like flow. This phenomenon is shown to be related to the mechanics of the reconnection process. Finally, the dynamics of vortex rings with swirl in unbounded flow is studied. Two different types of vortex rings with swirl were considered: i) Vortex rings with Gaussian distributions of core azimuthal vorticity and core azimuthal velocity and ii) Steady state solutions of the Euler equations for vortex rings with swirl. Both types of vortex rings develop an elongated axial vortex after initialisation. The existence of a maximum limit for the swirl on a vortex ring is shown above which the vortex rings undergo a rapid de-swirling readjustment. A helical instability occurring in vortex rings due to swirl at high Reynolds numbers is presented. A relation is shown to exist between one of the modes of the helical instability and the geometric parameters of the vortex ring
System design issues of small formation-flying spacecraft
No full textThis paper deals with the analysis of the relative trajectory of small formation flying spacecraft and shows how the orbit control requirements of the formation impose particular constraints on the overall spacecraft design. The relative trajectory is simulated in the presence of perturbative forces like drag, solar radiation and J2. The fuel requirements for different formation flying patterns are studied and the feasibility of using either passive or active control methods is discussed. The effects of small differences in drag-area on cluster stability and spacecraft design are addressed. The assessment of the relative trajectory is imperative for selecting the actuators for station keeping, designing control laws and deciding the configuration of the spacecraft
Dynamics of spacecraft formation flight
No full textEThOS - Electronic Theses Online ServiceGBUnited Kingdo
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Contextual bitext-derived paraphrases in automatic MT evaluation
Full text linkIn this paper we present a novel method for deriving paraphrases during automatic MT evaluation using only the source and reference texts, which are necessary for
the evaluation, and word and phrase alignment software. Using target language paraphrases produced through word and
phrase alignment a number of alternative reference sentences are constructed automatically for each candidate translation. The method produces lexical and lowlevel
syntactic paraphrases that are relevant to the domain in hand, does not use external knowledge resources, and can be
combined with a variety of automatic MT evaluation system
- …
