Congestion-aware fair rate control in wireless mesh networks

This paper presents a fair and efficient rate control mechanism, referred to as congestion-aware fair rate control (CFRC), for IEEE 802.11s-based wireless mesh networks. Existing mechanisms usually concentrate on achieving fairness and achieve a poor throughput. This mainly happens due to the synchronous rate reduction of neighboring links or nodes of a congested node without considering whether they actually share the same bottleneck or not. Furthermore, the achievable throughput depends on the network load, and an efficient fair rate is achievable when the network load is balanced. Therefore, existing mechanisms usually achieve a fair rate determined by the mostly loaded network region. CFRC uses an AIMD-based rate control mechanism which enforces a rate-bound to the links that use the same bottleneck. To achieve the maximum achievable rate, it balances the network load in conjunction with the routing mechanism. Furthermore, it allows the intra-mesh flows to utilize the network capacity, and the intra-mesh flows achieve a high throughput. Finally, we investigate the performance of CFRC using simulation in ns-2, and the results demonstrate that CFRC increases the throughput with the desired fairness.     

Effects of Sm<Superscript>3+</Superscript> Doping on Dielectric Properties of Anatase TiO<Subscript>2</Subscript> Nanoparticles Synthesized by a Low-Temperature Hydrothermal Method

Samarium-doped thermally stable TiO₂ nanoparticles in the anatase phase have been synthesized by a low-temperature hydrothermal method. The formation of the anatase phase has been investigated by x-ray diffraction. Thermogravimetry and differential thermal analysis have been used for thermal studies. The morphology and composition of synthesized powders have been studied using scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectroscopy. Surface areas were studied by the Brunauer–Emmett–Teller method. Dielectric properties were studied for dopant levels of 0.2 mol% and 0.5 mol% at 300 K in the frequency range of 42 Hz to 5 MHz. At low frequency, charge carriers at the grain boundary produce interfacial polarization giving rise to a high dielectric constant (ε′), which is significantly reduced by doping with samarium ions (Sm³⁺). Strong frequency dependence of the dielectric loss was also observed for each concentration. Conductivity studies showed that the reduction in conductivity is due to the decrease in particle size with the increase in Sm³⁺ dopant level.     

Modeling spatial variation in microbial degradation of pesticides in soil

Currently, no general guidance is available on suitable approaches for dealing with spatial variation in the first-order pesticide degradation rate constant k even though it is a very sensitive parameter and often highly variable at the field, catchment, and regional scales. Supported by some mechanistic reasoning, we propose a simple general modeling approach to predict k from the sorption constant, which reflects bioavailability, and easily measurable surrogate variables for microbial biomass/activity (organic carbon and clay contents). The soil depth was also explicitly included as an additional predictor variable. This approach was tested in a meta-analysis of available literature data using bootstrapped partial least-squares regression. It explained 73% of the variation in k for the 19 pesticide-study combinations (n = 212) in the database. When 4 of the 19 pesticide-study combinations were excluded (n = 169), the approach explained 80% of the variation in the degradation rate constant. We conclude that the approach shows promise as an effective way to account for the effects of bioavailability and microbial activity on microbial pesticide degradation in large-scale model applications.     

Constructal design of multiscale elliptic tubes in crossflow

The optimal configuration of two‐scale elliptic tubes in crossflow is found on the basis of the constructal design. The larger tubes are installed inside a domain of fixed length and height. In the same domain, smaller tubes are inserted between the larger tubes in the entrance region at the mid leading edge to leading edge distance of the larger tubes. The spacing between the larger tubes, the semiminor axis of the larger tubes, the major axis of the smaller tubes, and the semiminor axis of the smaller tubes are varied inside the domain freely to find the optimal configuration. There are two optimal configurations: one without the smaller tubes and the other with the presence of the smaller tubes. Both the larger and the smaller tubes are heated at a constant surface temperature. The flow is induced by a fixed pressure difference. The equations for steady, laminar, two‐dimensional, and incompressible flow are solved by finite volume method. In the absence of the smaller tubes, the range of Bejan number (dimensionless pressure drop) is ${10}^3<\mathit{Be}<{10}^5$, and in the presence of the smaller tubes, Bejan number is Be = 10⁵. The range of the dimensionless larger tubes semiminor axis is 0.1 ≤ B ≤ 0.4. Air is used to cool the row of the tubes with Prandtl number equal to 0.7. The results show that for different semiminor axes of the larger tubes, the heat transfer rate is enhanced when the smaller tubes are placed between the larger tubes.     

Detection of chloride in reinforced concrete using a dualpulsed laser-induced breakdown spectrometer system: comparative study of the atomic transition lines of Cl I at 594.85 and 837.59 nm

The presence of chloride in reinforced concrete can cause severe damage to the strength and durability of buildings and bridges. The detection of chloride in concrete structures at early stages of the corrosion buildup process is, therefore, very important. However, detection of chlorine in trace amounts in concrete is not a simple matter. A dual-pulsed laser-induced breakdown spectrometer (LIBS) has been developed at our laboratory for the detection of chloride contents in reinforced concrete by using two atomic transition lines of neutral chlorine (Cl I) at 594.8 and 837.5 nm. A calibration curve was also established by using standard samples containing chloride in known concentration in the concrete. Our dual-pulsed LIBS system demonstrated a substantial improvement in the signal level at both wavelengths (594.8 and 837.5 nm). However, the new atomic transition line at 594.8 nm shows a significant improvement compared to the line at 837.5 nm in spite of the fact that the relative intensity of the former is 0.1% of the latter. This weak signal level of the 837.5 nm transition line of chlorine can be attributed to some kind of self-absorption process taking place in the case of the concrete sample.     

Practical data mining and machine learning for optics applications: introduction to the feature issue

Data mining algorithms utilize search techniques to explore hidden patterns and correlations in the data, which otherwise require a tremendous amount of human time to explore. This feature issue explores the use of such techniques to help understand the data, build better simulators, explain outlier behavior, and build better predictive models. We hope that this issue will spur discussions and expose a set of tools that can be useful to the optics community.     

Synthesis and characterization of nanostructured SnO<Subscript>2</Subscript> film

Nanostructured tin dioxide (SnO₂) film was deposited on glass substrate by thermal evaporation of tin metal followed by thermal oxidation at 600 °C for 2 h. XRD investigation confirms that grown film is crystalline tetragonal rutile. The average optical transmittance of the film was as high as 90%. The optical band gap of the nanostructured SnO₂ was estimated from transmittance data and found to be 3.4 eV. The variation of electrical conductivity with temperature was investigated. The root mean square (RMS) roughness and topography of the film were investigated by atomic force microscopy and found to be 2 nm with grain size of 17 nm.     

Synthesis of indium-catalyzed Si nanowires by hot-wire chemical vapor deposition

Indium (In) catalyzed silicon nanowires (SiNWs) were synthesized by using hot-wire chemical vapor deposition (HWCVD) technique. Indium droplets were deposited on Si substrates by hot-wire evaporation of In wire, which was immediately followed by the growth of SiNWs from the droplets. Three sets of samples were prepared by varying the length of In wires, l, as 3, 1 and 0.5 mm. The sizes of In catalyst droplets decreased from 271.4 ± 66.8 to 67.4 ± 16.6 nm when the l was reduced from 3 to 0.5 mm. Larger size of In droplets (271.4 ± 66.8 nm) was found to induce the growth of worm-like NWs. The decrease in size of In catalyst droplets induced the formation of aligned and tapered NWs with smaller tips. The smallest value of tapering parameter, T_p of 40.5 nm/μm is correlated to the SiNWs induced by the smallest size of In droplets (67.4 ± 16.6 nm). The as-grown SiNWs showed high purity and good crystalline structure.     

Exploring isolated lignin material from oil palm biomass waste in green composites

Lignin obtained from oil palm biomass empty fruit bunches (EFB) fibers, has been used as curing agent in green epoxy composites. Epoxy–lignin composites, with varying lignin content (15%, 20%, 25% and 30%), reinforced with EFB fiber were prepared. The effect of EFB-based lignin on the mechanical, thermal and morphology properties of the composites were investigated and compared with the composites cured with isophorone diamine curing agent. The improved thermal stability and the observed microstructure of the fractured surface of the composites were attributed to good fiber–matrix interaction, induced by the curing agent. The epoxy composites cured with 25% lignin content proved to be a better matrix and gave optimum value compared with other formulations which was confirmed by its mechanical, thermal and morphological properties.