Subsonic investigations of vortex interaction control for enhanced high-alpha aerodynamics of a chine forebody/Delta wing configuration

A proposed concept to alleviate high alpha asymmetry and lateral/directional instability by decoupling of forebody and wing vortices was studied on a generic chine forebody/ 60 deg. delta configuration in the NASA Langley 7 by 10 foot High Speed Tunnel. The decoupling technique involved inboard leading edge flaps of varying span and deflection angle. Six component force/moment characteristics, surface pressure distributions and vapor-screen flow visualizations were acquired, on the basic wing-body configuration and with both single and twin vertical tails at M sub infinity = 0.1 and 0.4, and in the range alpha = 0 to 50 deg and beta = -10 to +10 degs. Results are presented which highlight the potential of vortex decoupling via leading edge flaps for enhanced high alpha lateral/directional characteristics

A New Upperbound for the Oblivious Transfer Capacity of Discrete Memoryless Channels

We derive a new upper bound on the string oblivious transfer capacity of discrete memoryless channels. The main tool we use is the tension region of a pair of random variables introduced in Prabhakaran and Prabhakaran (2014) where it was used to derive upper bounds on rates of secure sampling in the source model. In this paper, we consider secure computation of string oblivious transfer in the channel model. Our bound is based on a monotonicity property of the tension region in the channel model. We show that our bound strictly improves upon the upper bound of Ahlswede and Csisz\'ar (2013).Comment: 7 pages, 3 figures, extended version of submission to IEEE Information Theory Workshop, 201

Wind tunnel tests on a tail-less swept wing span-distributed cargo aircraft configuration

The configuration consisted of a 30 deg -swept, untapered, untwisted wing utilizing a low-moment cambered airfoil of 20 percent streamwise thickness designed for low wave drag at M = 0.6, C sub L = 0.4. The tests covered a range of Mach numbers 0.3 to 0.725 and chord Reynolds number 1,100,000 to 2,040,000, angles of attack up to model buffet and sideslip angles + or - 4 deg. Configuration build up, wing pod filleting, airfoil modification and trailing edge control deflection effects were briefly investigated. Three wing tip vertical tail designs were also tested. Wing body filleting and a simple airfoil modification both produced increments to maximum lift/drag ratio. Addition of pods eliminated pitch instability of the basic wing. While the magnitude of these benefits probably was Reynolds number sensitive, they underline the potential for improving the aerodynamics of the present configuration. The cruise parameter (product of Mach number and lift/drag ratio) attained a maximum close to the airfoil design point. The configuration was found to be positively stable with normal control effectiveness about all three axes in the Mach number and C sub L range of interest

Federalism and fiscal reform in India.

This paper attempts to analyse the experience of incentivising economic reforms at the state level through central transfers to states. It reviews the experiences of the central government introducing incentives for reform directly through various specific purpose transfers as well as the incentive schemes recommended by various Finance Commissions. The incentive schemes directly introduced by the central government include, accelerated irrigation benefit programme, accelerated power development and reform programme, Jawaharlal Nehru Urban Renewal Mission, education and health sector reforms. The reforms recommended by the Finance Commissions include incentivising tax reforms and fiscal restructuring and consolidation. The review of the experiences of Indian fiscal federalism shows that the incentivising reforms have neither been an unqualified success nor have they been a total failure. There are interesting lessons to be learnt from the experiences for both designing the incentive schemes and implementing them. The paper summarises the lessons of experience. While incorporating these in designing and implementing incentive schemes can be useful in the short and medium term, what matters in the long run is the political incentive for reforms.

Basic studies on delta wing flow modifications by means of apex fences

The effectiveness of apex fences on a 60-deg delta wing at low speeds was experimentally investigated. Resembling highly swept spoilers in appearance, the fences are designed to fold out of the wing apex region upper surface near the leading edges, where they generate a powerful vortex pair. The intense suction of the fence vortices augments lift in the apex region, the resulting positive pitching moment being utilized to trim trailing edge flaps for lift augmentation during approach and landing at relatively low angles of attack. The fences reduce the apex lift at high angles of attack, leading to a desirable nose-down moment. The above projected functions of the apex fence device were validated and quantified through low speed tunnel tests, comprising upper surface pressure surveys on a semispan model and balance measurements on a geometrically similar fully span wing/body configuration. Fence parameters such as area, shape, hinge position and deflection angle were investigated. Typical results are presented indicating the apex fence potential in controlling the longitudinal characteristics of a tail-less delta

Elliptic supersonic jet morphology manipulation using sharp-tipped lobes

Elliptic nozzle geometry is attractive for mixing enhancement of supersonic jets. However, jet dynamics, such as flapping, gives rise to high-intensity tonal sound. We experimentally manipulate the supersonic elliptic jet morphology by using two sharp-tipped lobes. The lobes are placed on either end of the minor axis in an elliptic nozzle. The design Mach number and the aspect ratio of the elliptic nozzle and the lobed nozzle are 2.0 and 1.65. The supersonic jet is exhausted into ambient at almost perfectly expanded conditions. Time-resolved schlieren imaging, longitudinal and cross-sectional planar laser Mie-scattering imaging, planar Particle Image Velocimetry, and near-field microphone measurements are performed to assess the fluidic behavior of the two nozzles. Dynamic Mode and Proper Orthogonal Decomposition (DMD and POD) analysis are carried out on the schlieren and the Mie-scattering images. Mixing characteristics are extracted from the Mie-scattering images through the image processing routines. The flapping elliptic jet consists of two dominant DMD modes, while the lobed nozzle has only one dominant mode, and the flapping is suppressed. Microphone measurements show the associated noise reduction. The jet column bifurcates in the lobed nozzle enabling a larger surface contact area with the ambient fluid and higher mixing rates in the near-field of the nozzle exit. The jet width growth rate of the two-lobed nozzle is about twice as that of the elliptic jet in the near-field, and there is a 40\% reduction in the potential core length. Particle Image Velocimetry (PIV) contours substantiate the results.Comment: 19 pages, 16 figures. Revised version submitted to Physics of Fluids for peer review. URL of the Video files (Fig. 6 & Fig. 14) are given in the text files (see in '/anc/*.txt'

Detection of anti-correlated hard X-ray time lag in Cygnus X-3

The wide-band X-ray spectra of the high mass X-ray binary Cygnus X-3 exhibits a pivoting behavior in the `low' (as well as `hard') state, correlated to the radio emission. The time scale of the soft and hard X-rays' anti-correlation, which gave rise to the pivoting feature, was found to be less than a day from the monitoring observations by RXTE--ASM and CGRO--BATSE. In this Letter we report the detection of a lag of $\lesssim$ 1000s in the anti-correlation of the hard X-ray emission (20--50 keV) to that of the soft X-ray emission (2--7 keV), which may be attributed to the viscous time scale of flow of matter in the accretion disk. This suggests the geometrical picture of a truncated accretion disc with a Compton cloud inside the disc, the relative sizes of which determine the spectral shape. Any change in the disc structure will take place in a viscous time scale, with corresponding anti-correlated change in the Compton cloud. We also report the pivoting in the spectra in one span of a pointed observation when an episode of the rearranging of the accretion system is serendipitously observed. This is the first such observation of hard X-ray delay seen in the persistent Galactic microquasars, within the precincts of the hard state.Comment: Accepted in The Astrophysical Journal (Letters): in pres

Dynamic Response of Ising System to a Pulsed Field

The dynamical response to a pulsed magnetic field has been studied here both using Monte Carlo simulation and by solving numerically the meanfield dynamical equation of motion for the Ising model. The ratio R_p of the response magnetisation half-width to the width of the external field pulse has been observed to diverge and pulse susceptibility \chi_p (ratio of the response magnetisation peak height and the pulse height) gives a peak near the order-disorder transition temperature T_c (for the unperturbed system). The Monte Carlo results for Ising system on square lattice show that R_p diverges at T_c, with the exponent $\nu z \cong 2.0$, while \chi_p shows a peak at $T_c^e$, which is a function of the field pulse width $\delta t$. A finite size (in time) scaling analysis shows that $T_c^e = T_c + C (\delta t)^{-1/x}$, with $x = \nu z \cong 2.0$. The meanfield results show that both the divergence of R and the peak in \chi_p occur at the meanfield transition temperature, while the peak height in $\chi_p \sim (\delta t)^y$, $y \cong 1$ for small values of $\delta t$. These results also compare well with an approximate analytical solution of the meanfield equation of motion.Comment: Revtex, Eight encapsulated postscript figures, submitted to Phys. Rev.