3,317 research outputs found
Movement-based Group Awareness with Wireless Sensor Networks
We propose a method through which dynamic sensor nodes
determine that they move together, by communicating and correlating their movement information. We describe two possible solutions, one using inexpensive tilt switches, and another one using low-cost MEMS accelerometers. We implement a fast, incremental correlation algorithm,
with an execution time of 6ms, which can run on resource constrained devices. The tests with the implementation on real sensor nodes show that the method is reliable and distinguishes between joint and separate movements. In addition, we analyze the scalability from four different
perspectives: communication, energy, memory and execution speed. The solution using tilt switches proves to be simpler, cheaper and more energy efficient, while the accelerometer-based solution is more reliable, more
robust to sensor alignment problems and, potentially, more accurate by using extended features, such as speed and distance
Online Movement Correlation of Wireless Sensor Nodes
Sensor nodes can autonomously form ad-hoc groups based on their common context. We propose a solution for grouping sensor nodes attached on the same vehicles on wheels. The nodes periodically receive the movement data from their neighbours and calculate the correlation coefficients over a time history. A high correlation coefficient implies that the nodes are moving together. We demonstrate the algorithm using two types of movement sensors: tilt switches and MEMS accelerometers. We place the nodes on two wirelessly controlled toy cars, and we observe in real-time the group membership via the LED colours of the nodes. In addition, a graphical user interface running on the base station shows the movement signals over a recent time history, the latest sampled data, the correlation between each two nodes and the group membership
Access Point Security Service for wireless ad-hoc communication
This paper describes the design and implementation of a security solution for ad-hoc peer-to-peer communication. The security solution is based on a scenario where two wireless devices require secure communication, but share no security relationship a priori. The necessary requirements for the security solution described here comprise topics such as energy efficiency, security standards and ad-hoc networks. The devised solution is called Access Point Security Service (APSS). APSS is able to provide security by delivering a symmetric key to two wireless devices that require ad-hoc peer-to-peer communication. The main principle of APSS is that it makes use of an existing security relationship between a network provider and its customers. The existing security relationship enables the network provider to deliver security to two or more communicating parties in the form of a shared key. An implementation of APSS is provided making use of the existing Wi-Fi security standards
Geographic Information Systems, Spatial Data Analysis and Spatial Modelling. - Problems and Possibilities -
This article is the position paper for the ESF-GISDATA Specialist Meeting on GIS &
Spatial Analysis, Amsterdam, 1-5December1993. The focus here is on the two major
themes of the meeting: Spatial Data Analysis and Spatial Modelling. Special emphasis
is laid on specific problems and possibilities for interfacing spatial analysis tools (i.e.
spatial data analysis techniques and spatial models) and GIS. Both GIS application
fields, the environmental sciences and the social sciences, are taken into
consideration. (authors' abstract)Series: Discussion Papers of the Institute for Economic Geography and GIScienc
Anharmonic Decay of Vibrational States in Amorphous Silicon
Anharmonic decay rates are calculated for a realistic atomic model of
amorphous silicon. The results show that the vibrational states decay on
picosecond timescales and follow the two-mode density of states, similar to
crystalline silicon, but somewhat faster. Surprisingly little change occurs for
localized states. These results disagree with a recent experiment.Comment: 10 pages, 4 Postscript figure
Single-Shot Electron Diffraction using a Cold Atom Electron Source
Cold atom electron sources are a promising alternative to traditional
photocathode sources for use in ultrafast electron diffraction due to greatly
reduced electron temperature at creation, and the potential for a corresponding
increase in brightness. Here we demonstrate single-shot, nanosecond electron
diffraction from monocrystalline gold using cold electron bunches generated in
a cold atom electron source. The diffraction patterns have sufficient signal to
allow registration of multiple single-shot images, generating an averaged image
with significantly higher signal-to-noise ratio than obtained with unregistered
averaging. Reflection high-energy electron diffraction (RHEED) was also
demonstrated, showing that cold atom electron sources may be useful in
resolving nanosecond dynamics of nanometre scale near-surface structures.Comment: This is an author-created, un-copyedited version of an article
published in Journal of Physics B: Atomic, Molecular and Optical Physics. IOP
Publishing Ltd is not responsible for any errors or omissions in this version
of the manuscript or any version derived from it. The Version of Record is
available online at http://dx.doi.org/10.1088/0953-4075/48/21/21400
Consequences of wall stiffness for a beta-soft potential
Modifications of the infinite square well E(5) and X(5) descriptions of
transitional nuclear structure are considered. The eigenproblem for a potential
with linear sloped walls is solved. The consequences of the introduction of
sloped walls and of a quadratic transition operator are investigated.Comment: RevTeX 4, 8 pages, as published in Phys. Rev.
Comparing phenomenological recipes with a microscopic model for the electric amplitude in strangeness photoproduction
Corrections to the Born approximation in photo-induced strangeness production
off a proton are calculated in a semi-realistic microscopic model. The vertex
corrections and internal contributions to the amplitude of the reaction are included on the one-loop level. Different
gauge-invariant phenomenological prescriptions for the modification of the Born
contribution via the introduction of form factors and contact terms are
discussed. In particular, it is shown that the popular minimal-substitution
method of Ohta corresponds to a special limit of the more realistic approach.Comment: 10 pages, 6 figures in the tex
Resource consumption analysis of online activity recognition on mobile phones and smartwatches
Most of the studies on human activity recognition using smartphones and smartwatches are performed in an offline manner. In such studies, collected data is analyzed in machine learning tools with less focus on the resource consumption of these devices for running an activity recognition system. In this paper, we analyze the resource consumption of human activity recognition on both smartphones and smartwatches, considering six different classifiers, three different sensors, different sampling rates and window sizes. We study the CPU, memory and battery usage with different parameters, where the smartphone is used to recognize seven physical activities and the smartwatch is used to recognize smoking activity. As a result of this analysis, we report that classification function takes a very small amount of CPU time out of total app’s CPU time while sensing and feature calculation consume most of it. When an additional sensor is used besides an accelerometer, such as gyroscope, CPU usage increases significantly. Analysis results also show that increasing the window size reduces the resource consumption more than reducing the sampling rate. As a final remark, we observe that a more complex model using only the accelerometer is a better option than using a simple model with both accelerometer and gyroscope when resource usage is to be reduced
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