An analysis of the lifetime of OLSR networks

The Optimized Link State Routing (OLSR) protocol is a well-known route discovery protocol for ad-hoc networks. OLSR optimizes the flooding of link state information through the network using multipoint relays (MPRs). Only nodes selected as MPRs are responsible for forwarding control traffic. Many research papers aim to optimize the selection of MPRs with a specific purpose in mind: e.g., to minimize their number, to keep paths with high Quality of Service or to maximize the network lifetime (the time until the first node runs out of energy). In such analyzes often the effects of the network structure on the MPR selection are not taken into account. In this paper we show that the structure of the network can have a large impact on the MPR selection. In highly regular structures (such as grids) there is even no variation in the MPR sets that result from various MPR selection mechanisms. Furthermore, we study the influence of the network structure on the network lifetime problem in a setting where at regular intervals messages are broadcasted using MPRs. We introduce the ’maximum forcedness ratio’, as a key parameter of the network to describe how much variation there is in the lifetime results of various MPR selection heuristics. Although we focus our attention to OLSR, being a widely implemented protocol, on a more abstract level our results describe the structure of connected sets dominating the 2-hop neighborhood of a node

Increasing network lifetime by battery-aware master selection in radio networks

Mobile wireless communication systems often need to maximize their network lifetime (defined as the time until the first node runs out of energy). In the broadcast network lifetime problem, all nodes are sending broadcast traffic, and one asks for an assignment of transmit powers to nodes, and for sets of relay nodes so that the network lifetime is maximized. The selection of a relay set consisting of a single node (the ‘master’), can be regarded as a special case of this problem. We provide a mean value analysis of algorithms controlling the selection of a master node with the objective of maximizing the network lifetime. The results show that already for small networks simple algorithms can extend the average network lifetime considerably

Routing versus energy optimization in a linear network

In wireless networks, devices (or nodes) often have a limited battery supply to use for the sending and reception of transmissions. By allowing nodes to relay messages for other nodes, the distance that needs to be bridged can be reduced, thus limiting the energy needed for a transmission. However, the number of transmissions a node needs to perform increases, costing more energy. Defining the lifetime of the network as the time until the first node depletes its battery, we investigate the impact of routing choices on the lifetime. In particular we focus on a linear network with nodes sending messages directly to all other nodes, or using full routing where transmissions are only sent to neighbouring nodes. We distinguish between networks with nodes on a grid or uniformly distributed and with full or random battery supply. Using simulation we validate our analytical results and discuss intermediate options for relaying of transmissions

Economics, scientific doubt and history

Subjects such as public finance, corporate finance, banking theory, risk management and management accounting are all largely based on the neoclassical approach. Most recent appointed professors have started their work with ideas based on a neoclassical fundament and its methodological preferences. Neoclassical economic thinking is not bad in itself. It has brought much good, even. However, now the downside of neoclassical theory has occurred. Failing financial markets have plunged the global economy into crisis. It is, therefore, high time for a debate on economic concepts as taught in universities and business schools. Are students really trained to think critically about economic theory and the consequences when economic theories are put into practice

Reintroducing ethics to economics and development theories

Frank Jan de Graaf argues that the domination of neoclassical economic thinking in academia has contributed to the economic crisis and hindered thinking about sustainable development. Currently, ethics is re-entering the debate about how to develop prosperous open societies. A group of NGOs recently came up with an interesting alternative perspective on economics and social development. Their thinking could enrich mainstream economics. Verschenen in de Working papers series

Cultuurwijziging bank niet te meten:nodig is debat over waarden en normen, benoemen sociaal-ethische vragen en daar beleid op voeren

De monitoringcommissie Code-Banken maakt met haar pleidooi voor meetbaarheid dezelfde fouten die de bankencrisis veroorzaakten. Ze neigt naar overwaardering van één groep belanghebbenden en toont een onjuiste verwachting van meetsystemen, terwijl sociaal-ethische vragen niet aan de orde komen. Wanneer de monitoringcommissie werkelijk verschil wil maken, dan zal zij een sociaal-ethisch gesprek binnen de bankensector moeten stimuleren, plus zorgen dat in controlesystemen deze ethische vragen aan de orde komen

The demand for mortgage debt, increases in house prices and the elderly home equity puzzle

This paper studies the demand for mortgage debt in the Netherlands. Currently the size of this debt exceeds that of GDP, which makes is interesting to look at its determinants. We argue that the absence of a downpayment constraint is important and focus on two other issue. The first is the impact of the prolonged boom in house prices in the period 1985-2005, which makes it interesting to investigate how much of this increase in housing wealth has been ‘cashed' by households. The second is the elderly home equity puzzle,' or the habit of elderly people to leave their housing wealth untouched when aging. Recent analyses for the US have suggested that this behavior may be caused by the combination of a strong precautionary savings motive and a high risk of large health care costs. However, in the Netherlands long term care is publicly financed, which makes this explanation unlikely to be valid. It is therefore interesting to see if Dutch households liquefy substantial parts of their housing wealth by increasing the size of the mortgage loan

Effective Scheduling for Coded Distributed Storage in Wireless Sensor Networks

A distributed storage approach is proposed to access data reliably and to cope with node failures in wireless sensor networks. This approach is based on random linear network coding in combination with a scheduling algorithm based on backpressure. Upper bounds are provided on the maximum rate at which data can be reliably stored. Moreover, it is shown that the backpressure algorithm allows to operate the network in a decentralized fashion for any rate below this maximum

Influence of the bulk and surface morphology on adhesion of polystyrene-inter-poly-cross-2-ethylhexyl-methacrylate films and particles

The adhesion behavior of semi-interpenetrating polymer networks (semi-IPNs) of linear polystyrene (PS) in crosslinked poly-2-ethylhexylmethacrylate (EHMA) was studied by variation of the bulk and surface morphology, i.e., domain size, continuity, and concentration in the domains. Semi-IPNs were prepared by liquid-liquid demixing upon cooling of a homogeneous solution of PS in methacrylate monomer, followed by gelation of the PS-rich phase and UV polymerization of the methacrylate resin. Welding of films allowed the preparation of larger objects provided that (1) the samples were phase separated to a high degree and contained domains with a high PS concentration (>90%) and (2) polystyrene was present at the interface. For semi-IPN films, a linear dependence of the adhesion strength on the (crack healing time)1/4 was obtained. Based on these considerations, a process was developed to obtain melt-processable semi-IPN particles, by quenching droplets of the polymer solution into a cold liquid. These particles obtained a PS-rich skin layer and showed good adhesion after blending with a thermoplast

Dynamics of quantized vortices in applied flow in superfluid 3He-B

This thesis is mostly focussed on studies of dynamics of superfluid ³He-B at temperatures below 0.4Tc where the flow of quantized vortex lines was expected to be generally turbulent. The damping in vortex motion changes many orders of magnitude in a small temperature interval making vortices in superfluids an ideal tool to study turbulence. The quantum nature of vortices in superfluids allows for exotic hydrodynamics that does not exist in classical fluids. Earlier research had showed that vortices become unstable and lead to turbulence when the superfluid Reynolds number exceeds unity. The question remained open whether vortical flow is inherently unstable at lower temperatures. This thesis addresses issues surrounding the instability of quantized vortices in applied flow in the zero-temperature limit. Using the non-invasive nuclear magnetic resonance measurement technique, we have studied the dynamics of vortices in transient states during spin-up experiments where the rotation velocity of the system changes in a step-like manner. We found transition temperatures where the vortices connected to the cylindrical container become unstable and, ultimately, start a turbulent burst of vortex formation. This is in contrast to the laminar motion at higher temperatures, where the vortex ends smoothly slide in helical motion on the cylindrical surface. The exact conditions for this onset temperature to turbulence are established in terms of the applied flow, and the perturbation of the superfluid state by so-called seed vortices. The spin-up and spin-down experiments in the zero-temperature limit show different vortex dynamics. The vortex motion in applied flow is laminar for a cylindrical container, while in a cubical geometry the motion is expected to be partly turbulent. Our experiments on turbulent front propagation after injection of seed vortices from the AB-phase boundary (via the Kelvin-Helmholtz instability) into the rotating Landau state show a change over from quasi-classical turbulence at high temperatures, to quantum turbulence in the low temperature regime where the energy cascade of Kelvin wave excitations starts to contribute to the dissipative process. The effect of a bottleneck in this energy cascade is expressed in the front propagation velocity. The contribution of the density anisotropy to the textural energy of the superfluid in rotation is measured from the high to the zero-temperature limit. Comparison with theory allows determination of the superfluid energy gap. We have mapped the superfluid order parameter flare out textures in terms of applied flow and temperature. A quartz tuning fork with a high quality factor has been studied in superfluid ³He-B. The device is found to be an excellent tool to measure temperature, pressure and viscosity. In the zero-temperature limit, where other temperature measurement devices start to saturate, the fork's sensitivity increases due to the exponential dependence on the quasiparticle density