An Application-Tailored MAC Protocol for Wireless Sensor Networks

We describe a data management framework suitable for wireless sensor networks that can be used to adapt the performance of a medium access control (MAC) protocol depending on the query injected into the network. The framework has a\ud completely distributed architecture and only makes use of information available locally to capture information about network traffic patterns. It allows\ud nodes not servicing a query to enter a dormant mode which minimizes transmissions and yet maintain an updated view of the network. We then introduce an Adaptive, Information-centric and Lightweight MAC\ud (AI-LMAC) protocol that adapts its operation depending on the information presented by the framework. Our results demonstrate how transmissions are greatly reduced during the dormant mode. During the active mode, the MAC\ud protocol adjusts fairness to match the expected requirements of the query thus reducing latency. Thus such a data management framework allows the MAC to operate more efficiently by tailoring its needs to suit the requirements of the application

A new wireless underground network system for continuous monitoring of soil water contents

A new stand-alone wireless embedded network system has been developed recently for continuous monitoring of soil water contents at multiple depths. This paper presents information on the technical aspects of the system, including the applied sensor technology, the wireless communication protocols, the gateway station for data collection, and data transfer to an end user Web page for disseminating results to targeted audiences. Results from the first test of the network system are presented and discussed, including lessons learned so far and actions to be undertaken in the near future to improve and enhance the operability of this innovative measurement approac

Inline control of a strip bending process in mass production

The accuracy of a metal forming process is highly influenced by the variation of the process input, such as variation of friction and material properties. Therefore it may be required to decrease the input variation to meet the desired accuracy. However, this may increase the production costs, since stricter requirements generally come with a higher price tag. Other solutions may be to design the process in such a way that it becomes less sensitive to the input variation, or to implement a control scheme in the production line. Adding sensors to measure the state of the production process and actuators to change the process settings during production allows for a drastic increase of the production accuracy.\ud In this study a numerical comparison is made between different methods to control a thin strip bending process with an over-bending and a back-bending stage. The aim is to implement the method in a mass production line with a production speed of 100 products per minute, which demands for fast measurement, processing and actuation. A discrete control scheme is used, meaning that the process settings can only be adapted in between the process stages. The adaptable control parameter is the amount of back-bending. In the case of the strip bending process, the angle of the measured strip may be used to adapt the angle of the following strip. However, the accuracy of such a control scheme is limited by product-to-product variation. Therefore the force of the over-bending stage is measured and used to construct a predictive model of the process based on measured process data. Hence, the final angle of the flap can be predicted by measuring the force at the first stage of the process. Different factors influence the effectiveness of the control methods: the size and autocorrelation of the input variation, the noise of the measurement system and the predictive ability of the predictive model. A qualitative study on the influence of these factors on different control methods is given in this paper

On the design of an energy-efficient low-latency integrated protocol for distributed mobile sensor networks

Self organizing, wireless sensors networks are an emergent and challenging technology that is attracting large attention in the sensing and monitoring community. Impressive progress has been done in recent years even if we need to assume that an optimal protocol for every kind of sensor network applications can not exist. As a result it is necessary to optimize the protocol for certain scenarios. In many applications for instance latency is a crucial factor in addition to energy consumption. MERLIN performs its best in such WSNs where there is the need to reduce the latency while ensuring that energy consumption is kept to a minimum. By means of that, the low latency characteristic of MERLIN can be used as a trade off to extend node lifetimes. The performance in terms of energy consumption and latency is optimized by acting on the slot length. MERLIN is designed specifically to integrate routing, MAC and localization protocols together. Furthermore it can support data queries which is a typical application for WSNs. The MERLIN protocol eliminates the necessity to have any explicit handshake mechanism among nodes. Furthermore, the reliability is improved using multiple path message propagation in combination with an overhearing mechanism. The protocol divides the network into subsets where nodes are grouped in time zones. As a result MERLIN also shows a good scalability by utilizing an appropriate scheduling mechanism in combination with a contention period

Protocol assessment issues in low duty cycle sensor networks: The switching energy

Energy assessment of MAC protocols for wireless sensor networks is generally based on the times of transmit, receive and sleep modes. The switching energy between two consecutive states is generally considered negligible with respect to them. Although such an assumption is valid for traditional wireless ad hoc networks, is this assumption valid also for low duty cycle wireless sensor networks? The primary objective of this work is to shed some light on relationships between node switching energy and node duty cycle over the total energy consumption. In order to achieve the target, initially, we revisit the energy spent in each state and transitions of three widespread hardware platforms for wireless sensor networks by direct measurements on the EYES node. Successively, we apply the values obtained to the SMAC protocol by using the OmNet++ simulator

Interfacial separation between elastic solids with randomly rough surfaces: comparison of experiment with theory

We study the average separation between an elastic solid and a hard solid with a nominal flat but randomly rough surface, as a function of the squeezing pressure. We present experimental results for a silicon rubber (PDMS) block with a flat surface squeezed against an asphalt road surface. The theory shows that an effective repulse pressure act between the surfaces of the form p proportional to exp(-u/u0), where u is the average separation between the surfaces and u0 a constant of order the root-mean-square roughness, in good agreement with the experimental results.Comment: 6 pages, 10 figure

Adaptive process control strategy for a two-step bending process

A robust production is an important goal in sheet metal forming in order to make the process outcome insensitive to variations in input and process conditions. This would guarantee a minimum number of defects and reduced press downtime. However, for com-plex parts it is difficult to achieve robust settings. Parts without defects can only be real-ized if the process parameters are adapted to the changed conditions.\ud In this paper, an approach for adaptive process control is presented, taking the uncertain-ties and tolerances of the process and material into consideration. The proposed control approach combines feedback and feed-forward control strategies. The most significant improvement is to incorporate feed-forward control with knowledge about the system (also known as predictive models). To create these models high fidelity numerical models have been created. Furthermore, a procedure is presented to update the coefficients of the predictive model to adapt it to the actual process state.\ud To evaluate the control strategy prior to its implementation, a testing environment has been developed. Different test scenarios for common states of the process have been generated to evaluate the improvement of the proposed control strategy

Electronic structure, phase stability and chemical bonding in Th2_2Al and Th2_2AlH4_4

We present the results of theoretical investigation on the electronic structure, bonding nature and ground state properties of Th$_2$Al and Th$_2$AlH$_4$ using generalized-gradient-corrected first-principles full-potential density-functional calculations. Th$_2$AlH$_4$ has been reported to violate the "2 \AA rule" of H-H separation in hydrides. From our total energy as well as force-minimization calculations, we found a shortest H-H separation of 1.95 {\AA} in accordance with recent high resolution powder neutron diffraction experiments. When the Th$_2$Al matrix is hydrogenated, the volume expansion is highly anisotropic, which is quite opposite to other hydrides having the same crystal structure. The bonding nature of these materials are analyzed from the density of states, crystal-orbital Hamiltonian population and valence-charge-density analyses. Our calculation predicts different nature of bonding for the H atoms along $a$ and $c$. The strongest bonding in Th$_2$AlH$_4$ is between Th and H along $c$ which form dumb-bell shaped H-Th-H subunits. Due to this strong covalent interaction there is very small amount of electrons present between H atoms along $c$ which makes repulsive interaction between the H atoms smaller and this is the precise reason why the 2 {\AA} rule is violated. The large difference in the interatomic distances between the interstitial region where one can accommodate H in the $ac$ and $ab$ planes along with the strong covalent interaction between Th and H are the main reasons for highly anisotropic volume expansion on hydrogenation of Th$_2$Al.Comment: 14 pages, 9 figure

On the thermoelectricity of correlated electrons in the zero-temperature limit

The Seebeck coefficient of a metal is expected to display a linear temperature-dependence in the zero-temperature limit. To attain this regime, it is often necessary to cool the system well below 1K. We put under scrutiny the magnitude of this term in different families of strongly-interacting electronic systems. For a wide range of compounds (including heavy-fermion, organic and various oxide families) a remarkable correlation between this term and the electronic specific heat is found. We argue that a dimensionless ratio relating these two signatures of mass renormalisation contains interesting information about the ground state of each system. The absolute value of this ratio remains close to unity in a wide range of strongly-correlated electron systems.Comment: 15 pages, including two figure