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61.
Let w be a finite word and n the least non-negative integer such that w has no right special factor of length and its right factor of length n is unrepeated. We prove that if all the factors of another word v up to the length n + 1 are also factors of w, thenv itself is a factor ofw. A similar result for ultimately periodic infinite words is established. As a consequence, some ‘uniqueness conditions’ for
ultimately periodic words are obtained as well as an upper bound for the rational exponents of the factors of uniformly recurrent
non-periodic infinite words. A general formula is derived for the ‘critical exponent’ of a power-free Sturmian word. In particular,
we effectively compute the ‘critical exponent’ of any Sturmian sequence whose slope has a periodic development in a continued
fraction.
Received: 6 May 1999 / 21 February 2000 相似文献
62.
Beyond the Web: Mobile WAP-Based Management 总被引:1,自引:0,他引:1
Luca Deri 《Journal of Network and Systems Management》2001,9(1):15-29
Mobility, tightening competition and changes in system administrator behavior present new challenges in the management world. In particular, the need to constantly monitor services and rapidly identify and fix problems is becoming increasingly important. The Internet has made it possible to offer a comprehensive range of management services and applications accessible over the web. Nevertheless, in the near future a new and improved way to manage systems will be done by means of mobile phones. This paper shows how existing web-based solutions can be enhanced to support the new generation of media phones based on WAP (Wireless Application Protocol) technology. Although the specific focus of this work is on management solutions, the rsults are general and applicable to many other types of existing web-based applications. Some implementation details and experiences drawn from adding a WAP interface to an existing web-based management application are described. 相似文献
63.
Interfacing human and computer with wireless body area sensor networks: the WiMoCA solution 总被引:1,自引:0,他引:1
Elisabetta Farella Augusto Pieracci Luca Benini Laura Rocchi Andrea Acquaviva 《Multimedia Tools and Applications》2008,38(3):337-363
Wireless Body Area Sensor Networks (WBASN) are an emerging technology enabling the design of natural human–computer interfaces
(HCI). Automatic recognition of human motion, gestures, and activities is studied in several contexts. For example, mobile
computing technology is being considered as a replacement of traditional input systems. Moreover, body posture and activity
monitoring can be used for entertainment and health-care applications. However, until now, little work has been done to develop
flexible and efficient WBASN solutions suitable for a wide range of applications. Their requirements pose new challenges for
sensor network designs, such as optimizing traditional solutions for use as environmental monitoring-like applications and
developing on-the-field stress tests. In this paper, we demonstrate the flexibility of a custom-designed WBASN called WiMoCA
with respect to a wide range of posture and activity recognition applications by means of practical implementation and on-the-field
testing. Nodes of the network mounted on different parts of the human body exploit tri-axial accelerometers to detect its
movements. The advanced digital Micro-electro-mechanical system (MEMS) based inertial sensor has been chosen for WiMoCA because
it demonstrated high flexibility of use in many different situations, providing the chance to exploit both static and dynamic
acceleration components for different purposes. Furthermore, the sensibility and accuracy of the sensing element is perfectly
adequate for monitoring human movement, while keeping cost low and size compact, thus meeting our requirements. We implemented
three types of applications, stressing the WBASN in many aspects. In fact, they are characterized by different requirements
in terms of accuracy, timeliness, and computation distributed on sensing nodes. For each application, we describe its implementation,
and we discuss results about performance and power consumption.
相似文献
Andrea AcquavivaEmail: |
64.
65.
Pechkova E Sartore M Giacomelli L Nicolini C 《The Review of scientific instruments》2007,78(9):093704
A customized atomic force microscopy (AFM) instrument optimized for imaging protein crystals in solution is described. The device was tested on crystals and Langmuir-Blodgett (LB) films of two proteins with quite different molecular weights. This approach enables the periodicity and morphology of crystals to be studied in their mother liquid, thereby preserving the native periodic protein crystal structure, which is typically destroyed by drying. Moreover, the instrument appears to distinguish protein crystals from salt crystals, which under the optical microscope are frequently quite similar, the difference between them often being revealed only during x-ray analysis. AFM estimates of the packing, order, and morphology of the given single proteins appear quite similar in the LB thin film and in the crystals, which means that routine crystal measurements can be performed at high resolution. The AFM consists of a custom-built measuring head and a homemade flexible SPM controller which can drive the head for contact, noncontact and spectroscopy modes, thus providing the user with a high degree of customization for crystal measurement. 相似文献
66.
Placidi G Franchi D Marsili L Gallo P 《Computer methods and programs in biomedicine》2007,88(2):144-151
Vascular catheterization is a common procedure in clinical medicine. It is normally performed by a specialist using an X-ray fluoroscopic guide and contrast-media. In the present paper, an image-guided navigation system which indicates a path providing guidance to the desired target inside the vascular tree is described with the aim of reducing the exposure of personnel and patients to X-rays during the catheterization procedure. A 3D model of the patient vascular tree, reconstructed with data collected by an angiography before starting the intervention, is used as a guide map instead of fluoroscopic scans. An accurate spatial correspondence between the body of the patient and the 3D reconstructed vascular model is established and, by means of a position indicator installed over the catheter tip, the real-time position/orientation of the tip is indicated correctly. This paper describes the system and the operational procedures necessary to use the proposed method efficiently during a catheter intervention. Preliminary experimental results on a phantom are also reported. 相似文献
67.
Real-time scheduling for energy harvesting sensor nodes 总被引:1,自引:1,他引:0
Energy harvesting has recently emerged as a feasible option to increase the operating time of sensor networks. If each node
of the network, however, is powered by a fluctuating energy source, common power management solutions have to be reconceived.
This holds in particular if real-time responsiveness of a given application has to be guaranteed. Task scheduling at the single
nodes should account for the properties of the energy source, capacity of the energy storage as well as deadlines of the single
tasks. We show that conventional scheduling algorithms (like e.g. EDF) are not suitable for this scenario. Based on this motivation,
we have constructed optimal scheduling algorithms that jointly handle constraints from both energy and time domain. Further
we present an admittance test that decides for arbitrary task sets, whether they can be scheduled without deadline violations.
To this end, we introduce the concept of energy variability characterization curves (EVCC) which nicely captures the dynamics
of various energy sources. Simulation results show that our algorithms allow significant reductions of the battery size compared
to Earliest Deadline First scheduling.
相似文献
Clemens MoserEmail: |
68.
69.
We analyze generalization in XCSF and introduce three improvements. We begin by showing that the types of generalizations evolved by XCSF can be influenced by the input range. To explain these results we present a theoretical analysis of the convergence of classifier weights in XCSF which highlights a broader issue. In XCSF, because of the mathematical properties of the Widrow-Hoff update, the convergence of classifier weights in a given subspace can be slow when the spread of the eigenvalues of the autocorrelation matrix associated with each classifier is large. As a major consequence, the system's accuracy pressure may act before classifier weights are adequately updated, so that XCSF may evolve piecewise constant approximations, instead of the intended, and more efficient, piecewise linear ones. We propose three different ways to update classifier weights in XCSF so as to increase the generalization capabilities of XCSF: one based on a condition-based normalization of the inputs, one based on linear least squares, and one based on the recursive version of linear least squares. Through a series of experiments we show that while all three approaches significantly improve XCSF, least squares approaches appear to be best performing and most robust. Finally we show how XCSF can be extended to include polynomial approximations. 相似文献
70.
Matteo Casadei Luca Gardelli Mirko Viroli 《Electronic Notes in Theoretical Computer Science》2007,175(2):59
Recent coordination languages and models are moving towards the application of techniques coming from the research context of complex systems: adaptivity and self-organization are exploited in order to tackle the openness, dynamism and unpredictability of today's distributed systems. In this area, systems are to be described using stochastic models, and simulation is a valuable tool both for analysis and design. Accordingly, in this work we focused on modelling and simulating emergent properties of coordination techniques.We first develop a framework acting as a general-purpose engine for simulating stochastic transition systems, built as a library for the Maude term rewriting system. We then evaluate this tool to a coordination problem called collective sort, where autonomous agents move tuples across different tuple spaces according to local criteria, and resulting in the emergence of the complete clustering property. 相似文献