Mitigating the gateway bottleneck via transparent cooperative caching in wireless mesh networks

Wireless mesh networks (WMNs) have been proposed to provide cheap, easily deployable and robust Internet access. The dominant Internet-access traffic from clients causes a congestion bottleneck around the gateway, which can significantly limit the throughput of the WMN clients in accessing the Internet. In this paper, we present MeshCache, a transparent caching system for WMNs that exploits the locality in client Internet-access traffic to mitigate the bottleneck effect at the gateway, thereby improving client-perceived performance. MeshCache leverages the fact that a WMN typically spans a small geographic area and hence mesh routers are easily over-provisioned with CPU, memory, and disk storage, and extends the individual wireless mesh routers in a WMN with built-in content caching functionality. It then performs cooperative caching among the wireless mesh routers.We explore two architecture designs for MeshCache: (1) caching at every client access mesh router upon file download, and (2) caching at each mesh router along the route the Internet-access traffic travels, which requires breaking a single end-to-end transport connection into multiple single-hop transport connections along the route. We also leverage the abundant research results from cooperative web caching in the Internet in designing cache selection protocols for efficiently locating caches containing data objects for these two architectures. We further compare these two MeshCache designs with caching at the gateway router only.Through extensive simulations and evaluations using a prototype implementation on a testbed, we find that MeshCache can significantly improve the performance of client nodes in WMNs. In particular, our experiments with a Squid-based MeshCache implementation deployed on the MAP mesh network testbed with 15 routers show that compared to caching at the gateway only, the MeshCache architecture with hop-by-hop caching reduces the load at the gateway by 38%, improves the average client throughput by 170%, and increases the number of transfers that achieve a throughput greater than 1 Mbps by a factor of 3.     

Biological hydrogen production from probiotic wastewater as substrate by selectively enriched anaerobic mixed microflora

Biohydrogen production from probiotic wastewater using mixed anaerobic consortia is reported in this paper. Batch tests are carried out in a 5.0 L batch reactor under constant mesophillic temperature (37 °C). The maximum hydrogen yield 1.8 mol-hydrogen/mol-carbohydrate is obtained at an optimum pH of 5.5 and substrate concentration 5 g/L. The maximum hydrogen production rate is 168 ml/h. The hydrogen content in the biogas is more than 65% and no significant methane is observed throughout the study. In addition to hydrogen, acetate, propionate, butyrate and ethanol are found to be the main by-products in the metabolism of hydrogen fermentation.     

Homogenization technique of discrete atoms into smeared continuum

A homogenization technique was developed and presented to replace a discrete atomic domain by an equivalent continuum domain that could be discretized into finite elements. Equivalent material properties of the smeared continuum domain were computed from the atomic model. Using the developed technique, a computationally efficient analysis could be performed for a large size of domain by proper mixture of a discrete atomic region and a smeared continuum region. In addition, this technique provided a means for multi-scale analysis. Examples for static and dynamic analyses were provided to demonstrate the technique.     

Vibrational characteristics of carbon nanotubes as nanomechanical resonators

Using eigenvalue analysis of mass and stiffness matrices directly computed from atomistic simulations, natural frequencies and mode shapes of various carbon nanotubes are studied. The stiffness matrix was developed from the Tersoff-Brenner potential for carbon-carbon interactions. The computed frequencies of the radial breathing modes of a variety of armchair (n, n) nanotubes agree well with results obtained by others using different techniques. In addition, the study reveals diverse mode shapes such as accordion-like axial modes, lateral bending modes, torsional modes, axial shear modes, and radial breathing modes for a variety of single-wall, multi-wall, and bamboo-type carbon nanotubes. The effects of different constraints on the carbon nanotube ends on the computed frequencies and mode shapes have been investigated for possible applications in vibration sensors or electromechanical resonators.     

Engineering, characterization and directional self-assembly of anisotropically modified nanocolloids

Along with traditional attributes such as the size, shape, and chemical structure of polymeric micro-objects, control over material distribution, or selective compartmentalization, appears to be increasingly important for maximizing the functionality and efficacy of biomaterials. The fabrication of tri- and tetracompartmental colloids made from biodegradable poly(lactide-co-glycolide) polymers via electrohydrodynamic co-jetting is demonstrated. The presence of three compartments is confirmed via flow cytometry. Additional chemical functionality is introduced via the incorporation of acetylene-functionalized polymers into individual compartments of the particles. Direct visualization of the spatioselective distribution of acetylene groups is demonstrated by confocal Raman microscopy as well as by reaction of the acetylene groups with azide-biotin via 'click chemistry'. Biotin-streptavidin binding is then utilized for the controlled assembly and orientation of bicompartmental particles onto functionalized, micropatterned substrates prepared via chemical vapor deposition polymerization.     

Comparison of various advanced oxidation processes for the degradation of 4-chloro-2 nitrophenol

In the present study an attempt is made efficiently to degrade USEPA listed 4-chloro-2-nitrophenol (4C-2-NP), widely available in bulk drug and pesticide wastes using various advanced oxidation processes (AOPs). A comparative assessment using various AOPs (UV, H(2)O(2,) UV/H(2)O(2), Fenton, UV/Fenton and UV/TiO(2)) was attempted after initial optimization studies, viz., varying pH, peroxide concentration, iron concentration, and TiO(2) loading. The degradation of the study compound was estimated using chemical oxygen demand (COD) reduction and compound reduction using spectrophotometric methods and further validated with high performance liquid chromatography (HPLC). The degradation trends followed the order: UV/Fenton > UV/TiO(2) > UV/H(2)O(2) > Fenton > H(2)O(2) > UV(.) It can be inferred from the studies that UV/Fenton was the most effective in partial mineralization of 4C-2-NP. However, lower costs were obtained with H(2)O(2). Kinetic constants were evaluated using first order equations to determine the rate constant K.     

Vacuum system of SST-1 Tokamak

Vacuum chambers of Steady State Superconducting (SST-1) Tokamak comprises of the vacuum vessel and the cryostat. The plasma will be confined inside the vacuum vessel while the cryostat houses the superconducting magnet systems (TF and PF coils), LN₂ cooled thermal shields and hydraulics for these circuits. The vacuum vessel is an ultra-high (UHV) vacuum chamber while the cryostat is a high-vacuum (HV) chamber. In order to achieve UHV inside the vacuum vessel, it would be baked at 150 °C for longer duration. For this purpose, U-shaped baking channels are welded inside the vacuum vessel. The baking will be carried out by flowing hot nitrogen gas through these channels at 250 °C at 4.5 bar gauge pressure. During plasma operation, the pressure inside the vacuum vessel will be raised between 1.0 × 10^?4 mbar and 1.0 × 10^?5 mbar using piezoelectric valves and control system. An ultimate pressure of 4.78 × 10^?6 mbar is achieved inside the vacuum vessel after 100 h of pumping. The limitation is due to the development of few leaks of the order of 10^?5 mbar l/s at the critical locations of the vacuum vessel during baking which was confirmed with the presence of nitrogen gas and oxygen gas with the ratio of ～3.81:1 indicating air leak. Similarly an ultimate vacuum of 2.24 × 10^?5 mbar is achieved inside the cryostat. Baking of the vacuum vessel up to 110 °C with ±10 °C deviation was achieved with a net mass flow rate of 0.8 kg/s at 1.5 bar gauge inlet pressure and supply temperature of 230 °C at the heater end. Also during gas feed system installation, the pressure inside the VV was raised from 3.01 × 10^?5 mbar to 1.72 × 10^?4 mbar by triggering a pulse of lower amplitude of 25 voltage direct current (VDC) for 100 s to piezoelectric valve. This paper describes in detail the design and implementation of the various vacuum subsystems including relevant experimental results.     

Usability study of digital libraries: ACM, IEEE-CS, NCSTRL, NDLTD

If digital libraries are to be used effectively, their user interfaces should be tested and enhanced. We observed 48 participants as they worked with the following digital libraries: ACM, IEEE-CS, NCSTRL, and NDLTD. We discuss how the features of these digital libraries influence the subjects’ efforts to perform search and retrieval tasks. Data analysis indicates that the IEEE-CS digital library was rated the best overall and NDLTD had the best search time. We present user recommendations and propose a taxonomy of features that we believe are essential for the design of future digital libraries. Noteworthy is the observation that users’ judgements on the importance of different features varied widely between the beginning and end of their test sessions. Received: 15 December 1997 / Revised: June 1999     

Adsorption Characteristics of Atrazine on Granulated Activated Carbon and Carbon Nanotubes

Adsorption of atrazine (ATZ) from aqueous solutions by granular activated carbon (GAC) and carbon nanotubes (CNT) was studied in a batch‐mode adsorption system at different initial concentrations of ATZ (1.0–30.0 mg L^–1) and at three temperatures of 288, 296 and 304 K. The adsorption isotherms of Langmuir, Freundlich, Polanyi–Manes, and Brunauer–Emmett–Teller (modified) were used to model the process. The adsorption kinetics followed a pseudo‐second‐order kinetic model. The thermodynamic parameters ΔH⁰, ΔS⁰, and ΔG⁰ of the adsorption were estimated. The thermodynamic parameters indicate that the adsorption process is spontaneous and exothermic.     

Bioavailability of iron and zinc from multiple micronutrient fortified beverage premixes in Caco-2 cell model

Abstract: Iron and zinc deficiencies are the most prevalent nutrient deficiencies worldwide. They often coexist as the dietary factors, especially phytate, which impairs iron absorption also affects zinc absorption. Therefore, suitable strategies are required to control multiple micronutrient deficiencies in populations that subsist on high‐phytate foods such as the whole wheat flour based Indian bread (chapatti). The objective of the study, therefore, was to test the bioavailability of iron and zinc in 2 multiple micronutrient beverage premixes in the absence and presence of chapatti. The premix‐1 contained iron, zinc, and vitamin A while premix‐2 contained all micronutrients in premix‐1, plus folic acid and ascorbic acid. Ferritin induction and ⁶⁵Zn uptake were assessed using coupled in vitro digestion/Caco‐2 cell line model as the surrogate markers of iron and zinc bioavailability, respectively. The results show that iron bioavailability from premixes‐1 and 2 was similar in the absence of chapatti. However, premix‐2 showed significantly higher iron bioavailability compared to premix‐1 in the presence of chapatti. In contrast, the zinc uptake was similar from both premixes‐1 and 2 in the absence or presence of chapatti. These results suggest that both the premixes provide bioavailable minerals, but premix‐2 appears to be promising in the presence of foods that have high phytate.