Effect of thermal alkaline pretreatment on the anaerobic digestion of wasted activated sludge

The effect of alkaline pretreatment of waste-activated sludge, using two models to study the sequential hydrolysis rates of suspended (Sanders' surface model) and dissolved (Goel's saturation model) solids, on the mesophilic and thermophilic anaerobic digestion rate is evaluated. The pretreatment, which reduces the size of the solids, increases the reaction rate by increasing the surface area and the specific surface hydrolysis constant (K(SBK)); at thermophilic conditions from 0.45 x 10(-3) kg m(-2) d(-1) for the fresh sludge to 0.74 x 10(-3) kg m(-2) d(-1) for the pretreated sludge and at mesophilic conditions these values are 0.28 x 10(-3) kg m(-2) d(-1) and 0.47 x 10(-3) kg m(-2) d(-1) confirming the usefulness of a pretreatment for solids reduction. But for soluble solids, the thermoalkaline pretreatment decreases the reaction rates by inducing a competitive inhibition on the thermophilic anaerobic digestion rate while in the mesophilic range, a non-competitive inhibition is observed. A mathematical simulation of the consecutive reactions, suspended solids to dissolved solids and to methane in staged anaerobic thermophilic-mesophilic digestion, shows that with 4% suspended solids concentration it is better not to use a thermoalkaline pretreatment because overall solids reduction and total methane production are not as good as without pretreatment.     

Maintaining strong mutual visibility of an evader moving over the reduced visibility graph

In this paper, we address the problem of determining whether a mobile robot, called the pursuer, is able to maintain strong mutual visibility (a visibility notion between regions over a convex partition of the environment) of an antagonist agent, called the evader. We frame the problem as a non cooperative game. We consider the case in which the pursuer and the evader move at bounded speed, traveling in a known polygonal environment with or without holes, and in which there are no restrictions as to the distance that might separate the agents. Unlike our previous efforts (Murrieta-Cid et al. in Int J Robot Res 26:233–253, 2007), we give special attention to the combinatorial problem that arises when searching for a solution through visiting several locations in an environment with obstacles. In this paper we take a step further, namely, we assume an antagonistic evader who moves continuously and unpredictably, but with a constraint over its set of admissible motion policies, as the evader moves in the shortest-path roadmap, also called the reduced visibility graph (RVG). The pursuer does not know which among the possible paths over the RVG the evader will choose, but the pursuer is free to move within all the environment. We provide a constructive method to solve the decision problem of determining whether or not the pursuer is able to maintain strong mutual visibility of the evader. This method is based on an algorithm that computes the safe areas (areas that keep evader surveillance) at all times. We prove decidability of this problem, and provide a complexity measure to this evader surveillance game; both contributions hold for any general polygonal environment that might or not contain holes. All our algorithms have been implemented and we show simulation results.     

On intranode impairments and engineering rules for an optical label switching router supporting an FSK/IM labeling scheme

This paper presents a study on intranode impairments and engineering rules for a label switching router supporting intensity modulated (IM) optical payload data signals labeled by using frequency-shift key (FSK) modulation. Engineering rules and design guidelines are presented regarding the choice of system parameters such as IM extinction ratio, FSK frequency deviation, alignment of optical filtering stages, label swapping, and node cascadability. The presented rules are derived from insights obtained from computer simulations and experimental validation for a 10-Gb/s IM payload signal.     

Poly(sulphopropylbetaines): 1. Synthesis and characterization

The synthesis of aromatic and aliphatic poly(sulphopropylbetaines) is described within the series of vinylpyridines and tertiary amino-methacrylates. Two complementary strategies were used: (a) preparation and free radical polymerization in aqueous solution (60°C, 4,4'-azobiscyanovaleric acid) of the monomers; (b) heterogeneous quaternization of preformed poly(vinylpyridines) and poly(tertiary amino-methacrylates) by 1,3-propanesultone in propylene carbonate or tetramethylene sulphone solution (120°C). The high molecular weight poly (zwitterions) ($\text{10}{}^5\text{<}\text{M}\text{?}{}_{\mathrm{W}}\text{< 5 × 10}{}^6$) were characterized by ultra-violet and ¹H nuclear magnetic resonance spectroscopy, and their water affinity at 20°C was estimated by water vapour absorption measurements.     

Temporary feeding shocks increase the productivity in a continuous biohydrogen-producing reactor

Continuous hydrogen production stability and robustness by dark fermentation were comprehensively studied at laboratory scale. Continuous bioreactors were operated at two different hydraulic retention times (HRT) of 6 and 10 h. The reactors were subjected to feeding shocks given by decreases in the HRT, and therefore the organic loading increases, during 6 and 24 h. Results indicated that the H₂ productivity was significantly improved by the temporary organic shock loads, increasing the hydrogen production rate up to 40%, compared to the rate obtained at the steady-state condition. Besides, it was observed that after the shock load, the stability of the reactor (measured as the hydrogen production rate) was recovered attaining the values observed before the feeding shocks. The bioreactor operated at shorter HRT (6 h) showed better H₂ productivity (17.3?±?1.1 L H₂/L-d) in comparison with the other one operated at 10-h HRT (12.4?±?1.6 L H₂/L-d).     

Hybrid RSOA and fibre Raman amplified long reach feeder link for WiMAX-on-fibre

A distributed fibre Raman amplified long reach optical access feeder link using a reflective semiconductor optical amplifier in the remote base station is experimentally demonstrated for supporting WiMAX-over-fibre transmission. The measured values for the error vector magnitude for quadrature phase shift keying and 16-ary quadrature amplitude modulation after 40 km of fibre transmission meet the IEEE 820.16 standard requirements.     

Predicate Synthesis for Correcting Faulty Conjectures: The Proof Planning Paradigm

The synthesis of programs as well as other synthetic tasks often end up with an unprovable, partially false conjecture. A successful subsequent synthesis attempt depends on determining why the conjecture is faulty and how it can be corrected. Hence, it is highly desirable to have an automated means for detecting and correcting faulty conjectures.We introduce a method for patching faulty conjectures. The method is based on abduction and performs its task during an attempt to prove a given conjecture. On input X. G(X), the method builds a definition for a corrective predicate, P(X), such that X. P(X) G(X) is a theorem. The synthesis of a corrective predicate is guided by the constructive principle of formulae as types, relating inference with computation.We take the construction of a corrective predicate as a program transformation task. The method consists of a collection of construction commands. A construction command is a small program that makes use of one or more program editing commands, geared towards building recursive, equational procedures.A synthesised corrective predicate is guaranteed to be correct, turning a faulty conjecture into a theorem. Whether conditional or not, it will be well-defined. If recursive, it will also be terminating.Our method is amenable to mechanisation, but careful search guidance is required for making a productive use of the failure of a proof. A failed proof attempt quickly yields a huge, possibly infinite, deduction tree, giving rise to exponentially many abductive explanations. We suggest that a proof planning approach can structure the task of correcting a formula in such a way as to allow significant automation, while dramatically restricting the search space.     

All-Optical Data Vortex Node Using an MZI-SOA Switch Array

We propose and demonstrate a new structure of a Data Vortex switch node for all-optical routing of wavelength-division-multiplexing (WDM) 10-Gb/s optical packets. The proposed node consists of two Mach-Zehnder interferometers with integrated semiconductor optical amplifier: an optical and gate and a high-speed optical switch. In the experiment, WDM 10-Gb/s data packets are successfully routed with 1-dB power penalty at a bit-error rate of 10^-9.     

Passivity-based control for variable speed constant frequency operation of a DFIG wind turbine

A standard passivity based control for a double fed induction generator of a wind turbine is presented. The control problem is posed as a variable speed constant frequency operation with the aim to maximise the generated electric power. The controller is designed in such a way that the dual control objective, unity power factor in the stator side and speed tracking in the mechanical port, are satisfied guaranteeing internal stability. The proposed scheme is the first attempt to approach the speed tracking operation from the energy dissipation (passivity) perspective. Simulation results show good performance of the control scheme for wind speeds in different operating regimes.