Distributed Optimization in Energy Harvesting Sensor Networks with Dynamic In-network Data Processing

Energy Harvesting Wireless Sensor Networks (EH- WSNs) have been attracting increasing interest in recent years. Most current EH-WSN approaches focus on sensing and net- working algorithm design, and therefore only consider the energy consumed by sensors and wireless transceivers for sensing and data transmissions respectively. In this paper, we incorporate CPU-intensive edge operations that constitute in-network data processing (e.g. data aggregation/fusion/compression) with sens- ing and networking; to jointly optimize their performance, while ensuring sustainable network operation (i.e. no sensor node runs out of energy). Based on realistic energy and network models, we formulate a stochastic optimization problem, and propose a lightweight on-line algorithm, namely Recycling Wasted Energy (RWE), to solve it. Through rigorous theoretical analysis, we prove that RWE achieves asymptotical optimality, bounded data queue size, and sustainable network operation. We implement RWE on a popular IoT operating system, Contiki OS, and eval- uate its performance using both real-world experiments based on the FIT IoT-LAB testbed, and extensive trace-driven simulations using Cooja. The evaluation results verify our theoretical analysis, and demonstrate that RWE can recycle more than 90% wasted energy caused by battery overflow, and achieve around 300% network utility gain in practical EH-WSNs

Development of a Cytochrome P450 Expression System with Biomass Scale-up, Streamlined Downstream Processing and Stability Modifications

Recombinant human P450s are important in preclinical studies to discover possible interactions between drugs when taking medicines. Drugs may be either inhibitors or substrates for P450s. Some P450s also play a major role in cancer and other diseases. Recombinant P450s offer better activity, availability and consistency than primary hepatocytes. In this thesis, a recombinant P450 expression system in yeast was developed with the aim of providing a cost-effective way of producing human P450 enzymes upon the yeast’s endoplasmic reticulum (ER). These ER-bound P450s are usually referred to as microsomal P450s. A yeast expression system was used to co-express several human P450s and their reductases, essential for P450 activities. Episomal and chromosomally integrating plasmids with auxotrophic markers were used to build the system. Gene expression was by either GAL1 promoter (galactose inducible) or ADH2 promoter (ethanol inducible). High level P450 expressions and activities were optimised by the effect of different growth media. It was found that by using different media conditions for recombinant protein expression, P450 activities could be improved. Efforts were made to produce P450 proteins in fermentors. For these larger-scale cultures, a cheaper, cost effective alternative to lyticase-mediated cell wall lysis was developed; it involves mechanical cell disruption- without degrading the microsomes. For large volumes, fractionation of microsomes by ultracentrifugation was unfeasible so a procedure was established that allows precipitation using polyethylene glycol (PEG). Recombinant P450s are extremely temperature-sensitive. They are stable only at minus 80°C and rapidly lose activity at room temperature. Lyophilisation is known to extend the shelf-life of recombinant proteins. Although lyophilisation is a harsh procedure which could shear the P450 proteins, from the microsomal membranes, it was found it could stabilise P450 activity so that the enzymes could be kept at room temperatures for weeks. The process was extensively optimised using a variety of different buffers and lyophilisation conditions and it was confirmed that: (a) Recombinant microsomal P450s produced from yeast, insect and bacterial cells could be stabilised using lyophilisation; (b) The lyophilised P450s could be plated out in 96-well microtitre plates and the plates could be kept at ambient temperature (+21°C) for weeks without losing activity, indicating that the process was robust; (c) The lyophilised enzymes and un-lyophilised samples behaved in the same way regarding their, potency towards known inhibitors, in fluorometric/ mass spectrometry assays and shipment to overseas destinations for P450 activity testing

EBS: decentralised slot synchronisation for broadcast messaging for low-power wireless embedded systems

In this paper, we present a decentralised scheme that facili- tates reliable network wide broadcast messaging without the requirement of strict time synchronisation, for duty-cycled low-power wireless embedded systems. In this emergent broadcast slot (EBS) scheme, devices coordinate their wake- up periods with their neighbours to exchange schedule infor- mation locally. This leads to the emergence of local slot syn- chronisation without the need for either network-wide syn- chronisation or a centralised time synchronisation element. We theoretically show that this scheme converges faster than similar emergent and gradient-based approaches, which we confirm by evaluation on real test-beds. We also show that our scheme exhibits lower overheads while being more tol- erant to disturbances caused by faulty nodes, wireless link failures, contention and interference in presence of deter- ministic propagation delays

Measurement of the energy dependence of phase relaxation by single electron tunneling

Single electron tunneling through a single impurity level is used to probe the fluctuations of the local density of states in the emitter. The energy dependence of quasi-particle relaxation in the emitter can be extracted from the damping of the fluctuations of the local density of states (LDOS). At larger magnetic fields Zeeman splitting is observed.Comment: 2 pages, 4 figures; 25th International Conference on the Physics of Semiconductors, Osaka, Japan, September 17-22, 200

Tunable graphene system with two decoupled monolayers

The use of two truly two-dimensional gapless semiconductors, monolayer and bilayer graphene, as current-carrying components in field-effect transistors (FET) gives access to new types of nanoelectronic devices. Here, we report on the development of graphene-based FETs containing two decoupled graphene monolayers manufactured from a single one folded during the exfoliation process. The transport characteristics of these newly-developed devices differ markedly from those manufactured from a single-crystal bilayer. By analyzing Shubnikov-de Haas oscillations, we demonstrate the possibility to independently control the carrier densities in both layers using top and bottom gates, despite there being only a nanometer scale separation between them

The regional and sectoral mobility of high-tech workers:insights from Finland

In this paper we employ data on 156,000 workers working within the Finnish high-tech industries in order to identify the extent to which labour mobility between sectors and regions is influenced by the characteristics of the locality in which the worker works. With these data we are able to estimate different types of binary, multinomial and ordered logit models to capture different types of inter- or intra-sector or region employment mobility. As we will see the different categories of employment mobility are influenced by different factors such that we cannot simply talk about 'labour mobility', but rather need to be specific regarding each particular form of employment mobility. Our results show that urbanisation and industrial diversity are not just associated with greater intra-regional mobility, as is emphasised by the agglomeration literature, but also greater inter-regional mobility