Aggregation in sensor networks: an energy–accuracy trade-off

Wireless ad hoc sensor networks (WASNs) are in need of the study of useful applications that will help the researchers view them as distributed physically coupled systems, a collective that estimates the physical environment, and not just energy-limited ad hoc networks. We develop this perspective using a large and interesting class of WASN applications called aggregation applications. In particular, we consider the challenging periodic aggregation problem where the WASN provides the user with periodic estimates of the environment, as opposed to simpler and previously studied snapshot aggregation problems. In periodic aggregation our approach allows the spatial–temporal correlation among values sensed at the various nodes to be exploited towards energy-efficient estimation of the aggregated value of interest. Our approach also creates a system level energy vs. accuracy knob whereby the more the estimation error that the user can tolerate, the less is the energy consumed. We present a distributed estimation algorithm that can be applied to explore the energy–accuracy subspace for a subclass of periodic aggregation problems, and present extensive simulation results that validate our approach. The resulting algorithm, apart from being more flexible in the energy–accuracy subspace and more robust, can also bring considerable energy savings for a typical accuracy requirement (fivefold decrease in energy consumption for 5% estimation error) compared to repeated snapshot aggregations.     

Lithographic patterning of superconducting YBCO films

Microbridges of YBa₂Cu₃O₇ thin films have been fabricated by conventional photolithography and wet chemical etching using EDTA, and by the lift-off lithography technique. The variation of etch rate with etch time, etchant temperature, and post-deposition sintering temperature has been studied. It has been shown that both techniques are useful for film patterning. However, an additional sintering step is necessary for the chemically etched sample to regain the original film properties. An order of increase in critical current density is observed for the patterned film.     

Parameterized algorithms for feedback set problems and their duals in tournaments

The parameterized feedback vertex (arc) set problem is to find whether there are k vertices (arcs) in a given graph whose removal makes the graph acyclic. The parameterized complexity of this problem in general directed graphs is a long standing open problem. We investigate the problems on tournaments, a well studied class of directed graphs. We consider both weighted and unweighted versions.     

Nanosuspension of efavirenz for improved oral bioavailability: formulation optimization,in vitro,in situ and in vivo evaluation

Context: Nanosuspensions (NSs) of poorly water-soluble drugs are known to increase the oral bioavailability.

Objectives: The purpose of this study was to develop NS of efavirenz (EFV) and to investigate its potential in enhancing the oral bioavailability of EFV.

Materials and methods: EFV NS was prepared using the media milling technique. The Box–Behnken design was used for optimization of the factors affecting EFV NS. Sodium lauryl sulfate and PVP K30 were used to stabilize the NS. Freeze-dried NS was completely re-dispersed with double-distilled filtered water.

Results: Mean particle size and zeta potential of the optimized NS were found to be 320.4?±?3.62?nm and –32.8?±?0.4 mV, respectively. X-ray diffraction and differential scanning calorimetric analysis indicated no phase transitions. Rate and extent of drug dissolution in the dissolution medium for NS was significantly higher compared to marketed formulation. The parallel artificial membrane permeability assay revealed that NS successfully enhanced the permeation of EFV. Results of in situ absorption studies showed a significant difference in absorption parameters such as K_a, t_1/2 and uptake percentages between lyophilized NS and marketed formulation of EFV. Oral bioavailability of EFV in rabbits resulting from NS was increased by 2.19-fold compared to the marketed formulation.

Conclusion: Thus, it can be concluded that NS formulation of EFV can provide improved oral bioavailability due to enhanced solubility, dissolution velocity, permeability and hence absorption.     

Growth and characterizations of dual ion beam sputtered CIGS thin films for photovoltaic applications

The growth of CIGS thin films on soda-lime glass substrates at different substrate temperatures by dual ion beam sputtering system in a single-step route from a single quaternary sputtering target with the composition of Cu (In_0.70 Ga_0.30) Se₂ was reported. The effects of the substrate temperature on structural, optical, morphological and electrical properties of CIGS films were investigated. Stoichiometry of one such film was investigated by X-ray photoelectron spectroscopy. All CIGS films had demonstrated a strong (112) orientation located at 2θ ~26.70^o, which indicated the chalcopyrite structure of films. The value of full-width at half-maximum of (112) peak was reduced from 0.58° to 0.19° and crystallite size was enlarged from 14.98 to 43.05 nm as growth temperature was increased from 100 to 400 °C. However, atomic force microscope results showed a smooth and uniform surface at lower growth temperature and the surface roughness was observed to increase with increasing growth temperature. Hall measurements exhibited the minimum film resistivity of 0.09 Ω cm with a hole concentration of 2.42 × 10¹⁸ cm^?3 and mobility of 28.60 cm² V^?1 s^?1 for CIGS film grown at 100 °C. Film absorption coefficient was found to enhance nominally from 1 × 10⁵ to 2.3 × 10⁵ cm^?1 with increasing growth temperature from 100 to 400 °C.     

Stick–slip friction of gecko-mimetic flaps on smooth and rough surfaces

The discovery and understanding of gecko ‘frictional-adhesion’ adhering and climbing mechanism has allowed researchers to mimic and create gecko-inspired adhesives. A few experimental and theoretical approaches have been taken to understand the effect of surface roughness on synthetic adhesive performance, and the implications of stick–slip friction during shearing. This work extends previous studies by using a modified surface forces apparatus to quantitatively measure and model frictional forces between arrays of polydimethylsiloxane gecko footpad-mimetic tilted microflaps against smooth and rough glass surfaces. Constant attachments and detachments occur between the surfaces during shearing, as described by an avalanche model. These detachments ultimately result in failure of the adhesion interface and have been characterized in this study. Stick–slip friction disappears with increasing velocity when the flaps are sheared against a smooth silica surface; however, stick–slip was always present at all velocities and loads tested when shearing the flaps against rough glass surfaces. These results demonstrate the significance of pre-load, shearing velocity, shearing distances, commensurability and shearing direction of gecko-mimetic adhesives and provide us a simple model for analysing and/or designing such systems.     

Design and development of nanoemulsion drug delivery system of amlodipine besilate for improvement of oral bioavailability

Nanoemulsion (NE) of amlodipine besilate (AB) was developed by spontaneous emulsification method with the aim to enhance the solubility and oral bioavailability of AB and to achieve localized delivery of drug at target site. Pseudoternary phase diagrams were constructed to identify the NE region. The selected formulations from NE region were subjected to droplet size analysis, partitioning study and in vitro drug release. The partition coefficient was calculated and correlated with percent dissolution efficiency as a tool to predict in vitro drug release from NEs. The release of drug from NEs was significantly higher (p < 0.01) than the marketed tablet formulation. The optimal formulation contained 15% Labrafil M, 35% [Tween 80: ethanol (2:1)], and 50% by weight aqueous phase (NE3) was characterized by transmission electron microscopy (TEM) and for thermodynamic stability. The pharmacokinetics and biodistribution studies of the optimized radiolabeled formulation (99mTc-labeled) in mice (p.o.) demonstrated a relative bioavailability of 475% against AB suspension. In almost all the tested organs, the uptake of AB from NE was significantly higher (p < 0.05) than AB suspension especially in heart with a drug targeting index of 44.1%, also confirming the efficacy of nanosized formulation at therapeutic site. A three times increase in the overall residence time of NE further signifies the advantage of NEs as drug carriers for enhancing bioavailability of AB.     

Heavy oil and bitumen recovery by hot solvent injection

Thermal and miscible methods are commonly used for in situ recovery of heavy oil and bitumen. Both techniques have their own limitations and benefits. However, these methods can be combined by co-injecting solvent with steam or injecting solvent into a pre-heated reservoir. The current work was undertaken to study the performance of solvents at higher temperatures for heavy oil/bitumen recovery. Glass bead packs and Berea sandstone cores were used in the experiments to represent different types of pore structures, porosity and permeability. After saturating with heavy oil, the samples were exposed to the vapor of paraffinic solvents (propane and butane) at a temperature above the boiling point of the solvent, and a constant pressure of 1500 kPa. A mechanical convection oven was used to maintain constant temperature across the setup. The setup was designed in such a way that a reasonably long sample (up to 30 cm) can be tested to analyze the gravity effect. The oil recovered from each of these experiments was collected using a specifically designed collection system and analyzed for composition, viscosity and asphaltene content.The final amount of oil recovered in each case (recovery factor but not extraction rate) was also analyzed and the quantity and nature of asphaltene precipitated with each of the tested solvents under the prevailing temperature and pressure of the experiment was reported. Optimal conditions for each solvent type were identified for the highest ultimate recovery. It was observed that recovery decreased with increasing temperature and pressure of the system for both solvents, and that the best results were found when experimental temperature is only slightly higher than the saturation temperature of the solvent used. It was also noticed that butane diluted the oil more than propane which resulted in lower asphaltene content and viscosity of oil produced with butane as a solvent.     

Spatial distribution of biomass consumption as energy in rural areas of the Indo-Gangetic plain

Biomass is widely used as energy source in rural households in India. Biomass samples and socio-economic data have been collected at district level in the rural areas of Indo-Gangetic plain (IGP), India to determine the emissions of trace gases and aerosols from domestic fuels. Dung cake, fuelwood and crop residue are main sources of energy in rural areas of the IGP. Dung cake is the major domestic fuel (80-90%) in the rural areas of Delhi, Punjab, Haryana, Uttar Pradesh, Bihar and West Bengal, whereas, 99% of rural households in Uttarakhand use wood as the main energy source. Using crop production data and usage of crop residues as energy, new consumption values have been estimated (21.13 Mt). Present information on the domestic fuel usage would be helpful in determining budgets estimates of trace gases and aerosols for India.