Evaluation,modification and comparison of two rapid assays for cyanogens in cassava

Two rapid semi-quantitative assays for total cyanogens in cassava were evaluated. These were the well-known rapid picrate paper test, and a recently proposed rapid paper test involving the reagent tetra base (TB, 4,4′- methylenebis-(N, N-dimethylaniline)). A precise colorimetric assay was used as a control in the evaluative work. After primary evaluation, both assay methods underwent some modification regarding the interpretation of sample scores. As a result, the reliability of the picrate assay was greatly improved. The TB assay was modified in the interests of safety. Evaluation of this assay over a range of temperatures between 20 and 35°C showed no significant temperature effects upon performance when the new scoring interpretation system was used. The level of endogenous linamarase activity in the sample was found to be an influential factor in rapid assay performance. In a series of comparative trials in three distinct ecosystems, the newly modified picrate assay produced correct results in 68% of cases. This compared with 66% of results correct in the TB assay. It was observed that the TB assay performed more reliably with low cyanogen samples, whilst the picrate assay was more reliable with intermediate cyanogen samples.     

High-Gain Chemically Gated Organic Electrochemical Transistor

Organic electrochemical transistors (OECTs) have exhibited promising performance as transducers and amplifiers of low potentials due to their exceptional transconductance, enabled by the volumetric charging of organic mixed ionic/electronic conductors (OMIECs) employed as the channel material. OECT performance in aqueous electrolytes as well as the OMIECs’ redox activity has spurred a myriad of studies employing OECTs as chemical transducers. However, the OECT's large (potentiometrically derived) transconductance is not fully leveraged in common approaches that directly conduct chemical reactions amperometrically within the OECT electrolyte with direct charge transfer between the analyte and the OMIEC, which results in sub-unity transduction of gate to drain current. Hence, amperometric OECTs do not truly display current gains in the traditional sense, falling short of the expected transistor performance. This study demonstrates an alternative device architecture that separates chemical transduction and amplification processes on two different electrochemical cells. This approach fully utilizes the OECT's large transconductance to achieve current gains of 10³ and current modulations of four orders of magnitude. This transduction mechanism represents a general approach enabling high-gain chemical OECT transducers.     

Managing logical channel configurations in complex satellite architectures

As a result of the increased switching complexity of many communications satellites, often transponders are available with a variety of configuration options offering flexibility in power, bandwidth, and coverage. Many of these configurations share resources that prevent them from being simultaneously active, making it a challenge to understand and manage the satellite capacity inventory. In this paper we define the logical channel configuration (LCC) as an unambiguous unit of the inventory and present a novel method of modelling the interdependencies between these LCCs using linear algebra. In particular, a projector matrix is defined which can be used to update the activation state of all LCCs when the state of one or more of these is changed. As a result, a number of valid LCC scenarios can be easily generated and evaluated for optimal use of the satellite resources. Copyright © 2005 John Wiley & Sons, Ltd.     

An altruistic cross‐layer recovering mechanism for ad hoc wireless networks

Video streaming services have restrictive delay and bandwidth constraints. Ad hoc networks represent a hostile environment for this kind of real‐time data transmission. Emerging mesh networks, where a backbone provides more topological stability, do not even assure a high quality of experience. In such scenario, mobility of terminal nodes causes link breakages until a new route is calculated. In the meanwhile, lost packets cause annoying video interruptions to the receiver. This paper proposes a new mechanism of recovering lost packets by means of caching overheard packets in neighbor nodes and retransmit them to destination. Moreover, an optimization is shown, which involves a video‐aware cache in order to recover full frames and prioritize more significant frames. Results show the improvement in reception, increasing the throughput as well as video quality, whereas larger video interruptions are considerably reduced. Copyright © 2014 John Wiley & Sons, Ltd.     

Least Squares Boundary Residual Method for the Analysis of Step Discontinuities in Open Chiral Waveguides

We analyse the reflection, transmission and radiation characteristics of a step discontinuity in a grounded chiral slab and we show that the step radiation can be enhanced due to the effect of the chirality. The analysis is performed using a mode matching technique. The fields are expressed in terms of the discrete modes and the continuous spectrum using two subsets of hybrid radiation modes: incident transverse electric (ITE) and incident transverse magnetic (ITM) modes. The scattering matrix of the step is determined by minimizing the boundary residual error in the sense of the least squares. The influence of chirality on the characterization of the step is demonstrated and we show that control of the radiation pattern is achieved, including angle and width of the radiation beam.     

Intrinsic selectivities and yields in the catalytic hydrogenation of polyenoic fatty acid methyl esters

Precise values of the intrinsic selectivities and yields for the hydrogenation products of methyl linolenate (Ln) and methyl linoleate (L) obtained under carefully controlled conditions using a commercial Ni catalyst are presented and analyzed in detail. The existence of a preferential adsorption of Ln and a significant co-hydrogenation of its double bonds are confirmed as being the dominant features under typical vegetable oil processing conditions. It is shown that the values of the selectivities that are obtained from the classical consecutive reactions network account for the intrinsic selectivity of the catalyst only while hydrogenating feedstocks with moderate to low (<10%) contents of Ln. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad Nacional del Lltoral (U.N.L.)     

Molds and Resists Studies for Nanoimprint Lithography of Electrodes in Low-Voltage Polymer Thin-Film Transistors

A low-cost patterning of electrodes was investigated looking forward to replacing conventional photolithography for the processing of low-operating voltage polymeric thin-film transistors. Hard silicon, etched by sulfur hexafluoride and oxygen gas mixture, and flexible polydimethylsiloxane imprinting molds were studied through atomic force microscopy (AFM) and field emission gun scanning electron microscopy. The higher the concentration of oxygen in reactive ion etching, the lower the etch rate, sidewall angle, and surface roughness. A concentration around 30 % at 100 mTorr, 65 W and 70 sccm was demonstrated as adequate for submicrometric channels, presenting a reduced etch rate of 176 nm/min. Imprinting with positive photoresist AZ1518 was compared to negative SU-8 2002 by optical microscopy and AFM. Conformal results were obtained only with the last resist by hot embossing at 120 °C and 1 kgf/cm² for 2 min, followed by a 10 min post-baking at 100 °C. The patterning procedure was applied to define gold source and drain electrodes on oxide-covered substrates to produce bottom-gate bottom-contact transistors. Poly(3-hexylthiophene) (P3HT) devices were processed on high-κ titanium oxynitride (TiO _x N _y ) deposited by radiofrequency magnetron sputtering over indium tin oxide-covered glass to achieve low-voltage operation. Hole mobility on micrometric imprinted channels may approach amorphous silicon (～0.01 cm²/V s) and, since these devices operated at less than 5 V, they are not only suitable for electronic applications but also as sensors in aqueous media.     

Disaster-survivable cloud-network mapping

Cloud-computing services are provided to consumers through a network of servers and network equipment. Cloud-network (CN) providers virtualize resources [e.g., virtual machine (VM) and virtual network (VN)] for efficient and secure resource allocation. Disasters are one of the worst threats for CNs as they can cause massive disruptions and CN disconnection. A disaster may also induce post-disaster correlated, cascading failures which can disconnect more CNs. Survivable virtual-network embedding (SVNE) approaches have been studied to protect VNs against single physical-link/-node and dual physical-link failures in communication infrastructure, but massive disruptions due to a disaster and their consequences can make SVNE approaches insufficient to guarantee cloud-computing survivability. In this work, we study the problem of survivable CN mapping from disaster. We consider risk assessment, VM backup location, and post-disaster survivability to reduce the risk of failure and probability of CN disconnection and the penalty paid by operators due to loss of capacity. We formulate the proposed approach as an integer linear program and study two scenarios: a natural disaster, e.g., earthquake and a human-made disaster, e.g., weapons-of-mass-destruction attack. Our illustrative examples show that our approach reduces the risk of CN disconnection and penalty up to 90 % compared with a baseline CN mapping approach and increases the CN survivability up to 100 % in both scenarios.     

Analysis of network function sharing in Content Delivery Network-as-a-service slicing scenarios

Video content consumption is currently dominating the mix of traffic observed in Internet service provider (ISP) networks. The distribution of that content is usually performed by means of content delivery network (CDN) caches storing and delivering multimedia. The advent of virtualization is calling attention to the CDN providers as a use case for virtualizing the cache function. In parallel, there is a trend for sharing network infrastructures as a way of reducing deployment costs by ISPs. Then, an interesting scenario emerges when considering the possibility of sharing virtualized cache functions among ISPs which are sharing a common physical infrastructure, mostly considering that those ISPs offer similar video content catalogs to end users. Furthermore, when deciding to share the caches among ISPs, it is interesting to understand the impacts due to limiting the storage capacity at the edge sites. This paper investigates through simulations the potential efficiencies that can be achieved when sharing a virtual cache function if compared with the classical approach of independent virtual caches operated per ISP, as well as the implications of limiting the storage capacity of the caches at the edge.