Indoor Radio Propagation and Interference in 2.4 GHz Wireless Sensor Networks: Measurements and Analysis

In wireless sensor networks (WSNs), the performance and lifetime are significantly affected by the indoor propagation and the interference from other technologies using the 2.4 GHz band. Next to an overview of the propagation and coexistence issues in the literature, we present a model for analysing these effects in WSNs. We also present our measurements results on the indoor propagation, the interference of the microwave oven (MWO) and their impact on the performance of the WSN. The propagation measurements reveal significant influence of the multipath: changing a node position with a few centimetres or changing the communication channel can lead up to 30 dB difference in the received power. The power leakage of MWO has been observed around $-$ 20 dBm at 1 m distances to the oven. This leads to extra retries of the 802.15.4 messages which matches our simulation results: the packet success ratio at first try decreases to 30–40 %, which increases the average active time of the sensor, closely located to the MWO. We observe that the ON–OFF pattern of the MWO could be exploited by WSNs to improve the performance.     

Necklaces,Convolutions, and X+Y

We give subquadratic algorithms that, given two necklaces each with n beads at arbitrary positions, compute the optimal rotation of the necklaces to best align the beads. Here alignment is measured according to the ? _p norm of the vector of distances between pairs of beads from opposite necklaces in the best perfect matching. We show surprisingly different results for p=1, p even, and p=∞. For p even, we reduce the problem to standard convolution, while for p=∞ and p=1, we reduce the problem to (min,+) convolution and $(\operatorname {median},+)$ convolution. Then we solve the latter two convolution problems in subquadratic time, which are interesting results in their own right. These results shed some light on the classic sorting X+Y problem, because the convolutions can be viewed as computing order statistics on the antidiagonals of the X+Y matrix. All of our algorithms run in o(n ²) time, whereas the obvious algorithms for these problems run in Θ(n ²) time.     

One cannot not interact

As the digital becomes part of the underlying structure of human existence and activity (just as electricity was integrated in the infrastructure), human interaction will be less and less direct. Mediated through various interfaces, human interaction via all kinds of networks becomes increasingly an expression of the semiotic condition of the human being in the post-industrial age. Professionals dedicated to human–computer interaction (HCI, a more suitable acronym than CHI) and semioticians must realize that they would benefit mutually if they would collaborate better than they have until now. Therefore, this paper submits working hypotheses to HCI practioners and to semioticians dedicated to aspects of human interaction.     

Exact Cover with Light

We suggest a new optical solution for solving the YES/NO version of the Exact Cover problem by using the massive parallelism of light. The idea is to build an optical device which can generate all possible solutions of the problem and then to pick the correct one. In our case the device has a graph-like representation and the light is traversing it by following the routes given by the connections between nodes. The nodes are connected by arcs in a special way which lets us to generate all possible covers (exact or not) of the given set. For selecting the correct solution we assign to each item, from the set to be covered, a special integer number. These numbers will actually represent delays induced to light when it passes through arcs. The solution is represented as a subray arriving at a certain moment in the destination node. This will tell us if an exact cover does exist or not.

Solving the subset-sum problem with a light-based device

We propose an optical computational device which uses light rays for solving the subset-sum problem. The device has a graph-like representation and the light is traversing it by following the routes given by the connections between nodes. The nodes are connected by arcs in a special way which lets us to generate all possible subsets of the given set. To each arc we assign either a number from the given set or a predefined constant. When the light is passing through an arc it is delayed by the amount of time indicated by the number placed in that arc. At the destination node we will check if there is a ray whose total delay is equal to the target value of the subset sum problem (plus some constants). The proposed optical solution solves a NP-complete problem in time proportional with the target sum, but requires an exponential amount of energy.     

On Measuring Closed‐Loop Non‐Linearity: A Topological Approach

The focal point of this paper is to develop a measure of closed‐loop non‐linearity. In this work, the Vinnicombe metric and the Quasi‐Linear Parameter Varying representation of a non‐linear system are exploited for this purpose. It is expected that the proposed measure can serve as a decision making tool for control engineers when considering whether a linear or a non‐linear control strategy should be employed to close the loop for a non‐linear system operating in a prescribed range.     

A-Brain: a general system for solving data analysis problems

An intelligent system should be able to solve a wide range of problems from different domains. In this paper we propose a complex and adaptive system capable of solving various data analysis problems without needing human help for parameter settings. The system, called A-Brain, consists of several interconnected components (a decision-maker, a trainer, and several problem solvers) which provide a base for building complex problem solvers. The parameters of the trainer's algorithm are problem independent. This fact is a requirement for intelligent systems which cannot rely on human intervention while operating. The A-Brain system is used to solve some well-known problems in the field of symbolic regression and classification. Numerical experiments show that the A-Brain system is able to perform very well on the considered test problems.     

Analyzing motoric and physiological data in describing upper extremity movement in the aged

Cognitive functions, motoric expression, and changes in physiology are often studied separately, with little attention to the relationships or correlations among them. The study presented in this paper implements an integrated approach by combining motion capture (action) and EMG (physiological) parameters as synchronized data streams resulting from the action and associated physiological data. The reported experiments were designed to measure the preparatory movement capabilities of the upper extremities. In particular, measurement of changes in preparatory activity during the aging process is of interest in this context, as the attempt is to develop means to compensate for loss of adaptive capabilities that aging entails. To achieve this goal, it is necessary to quantify preparation phases (timing and intensity). Motion capture and EMG parameters were measured when subjects raised their arms without constraint (condition one) and raised their arms while holding a ball (second condition). Furthermore, on comparing aging and young participants, it was confirmed that with aging the temporal relationships between actual movement and the preceding EMG signal change.     

Adaptive backstepping flight control for a mini‐UAV

The paper presents the design of a mini‐unmanned aerial vehicle (UAV) attitude controller using the backstepping method. Starting from the nonlinear dynamic equations of the mini‐UAV, by using the backstepping method, the authors of this paper obtained the expressions of the elevator, rudder, and aileron deflections, which stabilize the UAV at each moment to the desired values of the attitude angles. The attitude controller controls the attitude angles, the angular rates, the angular accelerations, and other variables describing the UAV longitudinal and lateral motions. The designed controller has been implemented in Matlab/Simulink environment, and its effectiveness has been tested with a campaign of numerical simulations using data from the UAV flight tests. Copyright © 2012 John Wiley & Sons, Ltd.