6,910 research outputs found
Internal avalanches in models of granular media
We study the phenomenon of internal avalanching within the context of
recently introduced lattice models of granular media. The avalanche is produced
by pulling out a grain at the base of the packing and studying how many grains
have to rearrange before the packing is once more stable. We find that the
avalanches are long-ranged, decaying as a power-law. We study the distriution
of avalanches as a function of the density of the packing and find that the
avalanche distribution is a very sensitive structural probe of the system.Comment: 12 pages including 9 eps figures, LaTeX. To appear in Fractal
A case for adaptive sub-carrier level power allocation in OFDMA networks
In today's OFDMA networks, the transmission power is typically fixed and the same for all the sub-carriers that compose a channel. The sub-carriers though, experience different degrees of fading and thus, the received power is different for different sub-carriers; while some frequencies experience deep fades, others are relatively unaffected. In this paper, we make a case of redistributing the power across the sub-carriers (subject to a fixed power budget constraint) to better cope with this frequency selectivity. Specifically, we design a joint power and rate adaptation scheme (called JPRA for short) wherein power redistribution is combined with sub-carrier level rate adaptation to yield significant throughput benefits. We further consider two variants of JPRA: (a) JPRA-CR where, the power is redistributed across sub-carriers so as to support a maximum common rate (CR) across sub-carriers and (b) JPRA-MT where, the goal is to redistribute power such that the transmission time of a packet is minimized. While the first variant decreases transceiver complexity and is simpler, the second is geared towards achieving the maximum throughput possible. We implement both variants of JPRA on our WARP radio testbed. Our extensive experiments demonstrate that our scheme provides a 35% improvement in total network throughput in testbed experiments compared to FARA, a scheme where only sub-carrier level rate adaptation is used. We also perform simulations to demonstrate the efficacy of JPRA in larger scale networks. © 2012 ACM
Auralization of Amplitude Modulated Helicopter Flyover Noise
Rotorcraft noise is an active field of study as the sound produced by these vehicles is often found to be annoying. A means to auralize rotorcraft flyover noise is sought to help understand the factors leading to annoyance. Previous work by the authors auralized a complete flyover event in which the source noise synthesis traversed a range of emission angles. The source noise definition process for the synthesis used helicopter flyover recordings. Although this process yielded both periodic and aperiodic (modulation) components at a set of discrete emission angles, only the periodic components were used in the previous work to synthesize the sound of the flyover event. In the current work, aperiodic amplitude modulation is incorporated into the source noise synthesis to improve its fidelity toward assessing rotorcraft noise annoyance. The method is demonstrated using ground recordings from a flight test of the AS350 helicopter for the source noise definition
Serum protein profile in patients with pulmonary tuberculosis
A detailed study of the alterations in the serum protein fractions following commencement
of effective anti-tuberculosis treatment was undertaken in 511 patients with
pulmonary tuberculosis. The concentration of serum albumin was 20-30 per
cent higher (P<0.001) and that of a1, a2 and g -globulins significantly lower at
the end of treatment than on admission (P <0.01), the magnitude of decrease being
7-17 per cent for g -globulin, 19-30 per cent for a1- globulin and 35-38 per cent for
a2- globulin. In all, 481 patients had a favourable response to treatment, 46 of
whom had a bacteriological relapse within 18 months of stopping treatment. The
likelihood of a relapse was found to be greater with higher a2 -globulin concentrations
at the end of treatment, the proportions of patients who relapsed being 3, 9,
13 and 15 per cent with a2 -globulin concentrations of < 0.40, 0.40-0.59, 0.60-0.79
and > 0.80 g/dl (P=0.02)
Self-Structuring of Granular Media under Internal Avalanches
We study the phenomenon of internal avalanching within the context of
recently proposed ``Tetris'' lattice models for granular media. We define a
recycling dynamics under which the system reaches a steady state which is
self-structured, i.e. it shows a complex interplay between textured internal
structures and critical avalanche behavior. Furthermore we develop a general
mean-field theory for this class of systems and discuss possible scenarios for
the breakdown of universality.Comment: 4 pages RevTex, 3 eps figures, revised version to appear in Phys.
Rev. Let
Coarsening and Slow-Dynamics in Granular Compaction
We address the problem of the microscopic reorganization of a granular medium
under a compaction process in the framework of Tetris-like models. We point out
the existence of regions of spatial organization which we call domains, and
study their time evolution. It turns out that after an initial transient, most
of the activity of the system is concentrated on the boundaries between
domains. One can then describe the compaction phenomenon as a coarsening
process for the domains, and a progressive reduction of domain boundaries. We
discuss the link between the coarsening process and the slow dynamics in the
framework of a model of active walkers on active substrates.Comment: Revtex 4 pages, 4 figures, in press in PRL. More info
http://axtnt3.phys.uniroma1.it/Tetri
Seaweed culture in India-an appraisal
In recent years there has been a steady increase in the demand for naturally occuring seaweeds
as a result of many seaweed based industries coming up. In order to meet the raw material requirement
of these industries attempts have been made in this country to develop suitable seaweed farming techniques
by some Institutes notably the CMFRI at its Mandepam. Regional Centre and CSMCRI at its field
centre, Mandapam. Experimental culture of economically important seaweeds such as Gracllaria
edulis, Gelidiella acerosa and other species was undertaken since 1972 at Mandapam- in these
experiments production rates ranging from 3 to 8 times the initial wet weight were obtained. The
techniques of seaweed culture, the favourable seasons optimum duration of culture period and the
influence of environmental parameters are discussed in this account with notes on economics of
seaweed culture. General information on the seaweed resources slong our coasts, their potential for
exploitation and culture are also highlighted
Adsorption and diffusion of CO<sub>2</sub> in CPO-27–Ni beads
The present work involves the scale-up and characterization of CPO-27–Ni metal organic framework using a range of experimental techniques aimed at determining equilibrium and kinetic parameters to assess its potential for post-combustion carbon capture. CPO-27–Ni was prepared from its precursors by molecular gastronomy methods in kilogram scale. Adsorption of isotherms of pure CO2 and N2 were obtained for diferent temperatures on these beads, using a volumetric apparatus and the isotherms were ftted to a dual-site Langmuir model. A series of experiments were then carried out in the volumetric apparatus by dosing a known volume of CO2 and the pressure was monitored with time. The difusional time constants were then extracted by ftting the series of curves to an isothermal difusion model. From the time constants, the values of the difusivities were obtained and compared with the values obtained from frst principles correlations, which employed the pore size, and the porosity values from independent mercury porosimetry experiments. The results from the analysis showed that the transport of CO2 in the beads was well described by a combination of Knudsen and viscous difusion mechanisms. Experiments were also carried out using a zero-length column (ZLC) apparatus by preparing a 10% CO2–He and 10% CO2– N2 mixture. The analysis of the ZLC curves showed that the two diferent carrier gases had an efect of the long-time slope, indicating the presence of a macropore-controlled difusion mechanism.publishedVersio
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