Spatial CSMA: A Distributed Scheduling Algorithm for the SIR Model with Time-varying Channels

Recent work has shown that adaptive CSMA algorithms can achieve throughput optimality. However, these adaptive CSMA algorithms assume a rather simplistic model for the wireless medium. Specifically, the interference is typically modelled by a conflict graph, and the channels are assumed to be static. In this work, we propose a distributed and adaptive CSMA algorithm under a more realistic signal-to-interference ratio (SIR) based interference model, with time-varying channels. We prove that our algorithm is throughput optimal under this generalized model. Further, we augment our proposed algorithm by using a parallel update technique. Numerical results show that our algorithm outperforms the conflict graph based algorithms, in terms of supportable throughput and the rate of convergence to steady-state.Comment: This work has been presented at National Conference on Communication, 2015, held at IIT Bombay, Mumbai, Indi

Evaluating mode of loading effect and laboratory fatigue performance of asphalt concrete using viscoelastic continuum damage mechanics

In this research, an existing uniaxial constitutive model has been extended to flexural loading mode and a new approach to predict fatigue behavior is proposed. The proposed methodology involves dynamic modulus testing to obtain viscoelastic properties and subsequent fatigue testing. Several asphalt concrete beams were tested according to the proposed methodology. The analysis of data indicates that there exists a unique relationship between the flexural pseudostiffness and amount of damage in the specimen. To verify the accuracy of the fatigue prediction model, fatigue tests were conducted on specimens that were not part of preliminary analysis. The fatigue life predictions made were comparable to actual measurements. The proposed methodology offers advantages like considerable savings in testing time and materials when compared to the existing AASHTO protocol. An alternative approach for the determination of the fatigue endurance limit of asphalt concrete using the elastic-viscoelastic correspondence principle is proposed. The proposed testing procedure consists of applying stress or strain blocks of loading starting from low to high amplitude. The development of loops and changes in stress-pseudostrain loops is used to detect damage in the specimen. To verify the proposed methodology, tests were conducted under different modes (stress and strain controlled, uniaxial and flexure). When compared to strain controlled mode, the stress controlled mode required shorter testing time, had less noise and offered better control during testing. The third part of this research is to study the effect of mode of loading on viscoelastic properties and damage characteristics. Several specimens were tested under uniaxial, biaxial and flexure mode to obtain fingerprints of viscoelastic and damage properties. It was found that viscoelastic and damage properties are dependent on loading mode and testing frequency. A systematic variation of viscoelastic properties was found between different loading modes. Several frequency dependent modular ratios are proposed which, in principle, can be used as modal correction factors. It was observed that the specimen undergoes damage at a faster rate under uniaxial mode when compared to flexure loading mode. At a given value of normalized pseudostiffness, the damage parameter ratio remained approximately same and is a function of material properties

Online semantic mapping strategies for augmenting retention of lexical fields: applying theory to online practices

Vocabulary learning is a prominent aspect of attaining mastery in a language. At the same time, it is a complex cognitive process (Cook, 2001), that leaves the learners, especially the weak vocabulary learners, with learning difficulties. Enabling such learners to use strategies such as semantic mapping would help them navigate this complex process more effectively. Integrating the use of certain online learning tools available with the advent of web 2.0 technology could help this process further and lead to better retention of the lexical fields. This paper attempts to analyse these possibilities by drawing a link between vocabulary learning difficulties, use of semantic mapping strategy and the use of an online tool, MindMup 2.0. The paper begins by introducing the challenges in vocabulary learning and then brings in the prominence of semantic mapping strategy in addressing them. This is followed by a discussion on the multidisciplinary perspectives of the strategy and from this an outline of its theoretical framework has been critically drawn. Finally, the paper argues in favour of implementing the essence of the theoretical underpinnings of the strategy using online tools for better lexical retention

Thermal network theory for switchgear under continuous current

All electrical equipments generate heat through I2R loss within a specified volume resulting in temperature rise. The regulating bodies define the temperature rise limits for all equipments for safe operation. So during the design phase of any electrical equipment thermal analysis is mandatory to predict the temperature rise. The objective is to develop an analytical tool based on thermal networking method by exploiting the similarity between thermal and electrical analogy to calculate steady state temperatures in less time along current carrying path in electrical equipments. As a later part, the tool developed is used to predict change in temperatures for change in geometry of the components in the electrical equipment. The problem is considered as two parts. As first part, an Excel tool is developed with Visual Basic backend, based on thermal networking method to calculate steady state temperatures in electrical equipments. Here the numerical method used is Elementary Balance Method, in which every element is represented by a node and relevant energy balance equations are formulated for it. Temperatures are calculated using the Excel tool for frame 1 and 3. Test (Thermal Run) is conducted on AKD-12 switch gear (frame 1 and frame 3) under continuous current to find out temperatures. Analytical results from the tool are then validated against the test data. As second part, dimensions of components in the switch gear are varied and variation in temperatures of components, particularly at moving contact (highest temperature point) with respect to original temperatures is observed. Good matching is observed in temperature profile between analytical and experimental results. The maximum percentage error is 15%.By analyzing the results, it can be concluded that thermal network theory helps engineers to predict temperatures easily for changes in design reducing design cycle time and it is flexible as to expand its application to any heat generating equipment

Green revolution vaccines, edible vaccines

Edible vaccines are sub-unit vaccines where the selected genes are introduced into the plants and the transgenic plant is then induced to manufacture the encoded protein. Edible vaccines are mucosal-targeted vaccines where stimulation of both systematic and mucosal immune network takes place. Foods under study include potatoes, bananas, lettuce, rice, wheat, soybean, corn and legumes. Edible vaccines for various diseases such as measles, cholera, hepatitis-B, and many more are in the process of development. Food vaccines may also help to suppress autoimmunity disorders such as Type-1 Diabetes. Key words: Edible vaccines, oral vaccines, antigen expression, food vaccines. African Journal of Biotechnology Vol. 2 (12), pp. 679-683, December 200

A multicomponent model of the infrared emission from Comet Halley

A model based on a mixture of coated silicates and amorphous carbon grains produces a good spectral match to the available Halley data and is consistent with the compositional and morphological information derived from interplanetary dust particle studies and Halley flyby data. The dark appearance of comets may be due to carbonaceous coatings on the dominant (by mass) silicates. The lack of a 10 micrometer feature may be due to the presence of large silicate grains. The optical properties of pure materials apparently are not representative of cometary materials. The determination of the optical properties of additional silicates and carbonaceous materials would clearly be of use

Cumulative theoretical uncertainties in lithium depletion boundary age

We performed a detailed analysis of the main theoretical uncertainties affecting the age at the lithium depletion boundary (LDB). To do that we computed almost 12000 pre-main sequence models with mass in the range [0.06, 0.4] M_sun by varying input physics (nuclear reaction cross-sections, plasma electron screening, outer boundary conditions, equation of state, and radiative opacity), initial chemical elements abundances (total metallicity, helium and deuterium abundances, and heavy elements mixture), and convection efficiency (mixing length parameter, alpha_ML). As a first step, we studied the effect of varying these quantities individually within their extreme values. Then, we analysed the impact of simultaneously perturbing the main input/parameters without an a priori assumption of independence. Such an approach allowed us to build for the first time the cumulative error stripe, which defines the edges of the maximum uncertainty region in the theoretical LDB age. We found that the cumulative error stripe is asymmetric and dependent on the adopted mixing length value. For alpha_ML = 1.00, the positive relative age error ranges from 5 to 15 per cent, while for solar-calibrated mixing length, the uncertainty reduces to 5-10 per cent. A large fraction of such an error (about 40 per cent) is due to the uncertainty in the adopted initial chemical elements abundances.Comment: LDB tables for several [Fe/H] values are available at the url: http://astro.df.unipi.it/stellar-models/ld