1,720,995 research outputs found
A metrological and historical perspective on the stadion and its use in ancient geography
Full text linkThe stadion is the unit of length by which distances are reported in ancient Greek geographical sources. The itinerary indications in stadia can be found in several texts, but no specific unit values are given in the ancient geographers' surviving works. However, the notion of a vaguely quantified, non-metrological itinerary unit is contradicted by the presence, since Hellenistic times, of road marker stones bearing distance indications along major ancient roads. The key assumption in this study is that, whatever the unit involved, main roads were actually measured to the best of capabilities, and distance measurements in ancient works did refer to some specific metrological system. Some well-known Greek languagecxesst sources are analyzed with the support of archeologic information obtained from a small number of pre-Roman road markers, and from modern reports of investigations about ancient roads and sites. Based on the evidence, it is shown that two different stadion values were most often used as itinerary units in the Greek and Hellenistic world, namely 177 m and 210 m, that can be traced respectively to the so-called Attic foot and Philetaeric (Ionic/Samian) foot. Conversion among units did also occur, and this may offer explanations for supposed textual inconsistencies that have so far proved hard to understand
Waveform monitoring with LoRaWAN: Is it feasible?
No full textLoRaWAN is well suited for the transmission of small amounts of numeric data, while its technical features are not conceived for the continuous real-time monitoring of time-evolving signals. The aim of this paper is to discuss the usability of the Long Range Wide Area Network (LoRaWAN) technology for the continuous transmission of signals characterized by different scales of variability. At the purpose the so-called burst-mode acquisition is considered and analyzed for a LoraWAN infrastructure. Furthermore, a very simple messaging protocol is introduced to increase data throughput, by allowing application-level messages to be sent using the same data message, avoiding extra overload. To demonstrate this approach, the paper focuses on possible techniques to perform a long-term monitoring of the electrocardiographic (ECG) signal over a LoRaWAN communication infrastructure where duty cycle induced constraints are carefully considered. The analysis of real signals proves the feasibility of the proposed system, which can be easily generalized for other kind of signals
Accurate ECG monitoring by Gaussian feature streaming
No full textWearable cardiac monitors can usefully contribute to early detection of potential cardiovascular pathologies. However ECG trace data streaming over wireless links creates some significant challenges, due to the amount of data to be transmitted. We employ a signal analysis approach based on a Gaussian dictionary to model ECG traces in a compressed way. The algorithm operates on fixed-length segments, and achieves effective compression for wireless data transmission, associating just 6 bytes to each Gaussian feature. At the same time it enables accurate reconstruction of ECG traces from the reduced data set. We tested our method on a set of 46 ECG recordings taken from the Physionet MIT-BIH Arrhythmia Database, obtaining 90% data compression rates, while percent relative deviation of reconstructed traces is always below 5%
Internet Traffic Measurement: a Critical Study of Wavelet Analysis
No full textIn communication networks, traffic measurements serve two main purposes: the characterization of traffic load patterns and the monitoring of performances. This paper is a study of the applicability of traffic analysis methods as a mean to detect malfunctions and performance changes in packet data networks, through measurements of selected parameters. The main contribution is of a methodological nature and is motivated by the fact that wavelet analysis, which has come to be regarded as a standard approach, is by no means a straightforward method. Controversial results can be found, which are not always attributable to the complex nature of the measured object. Careful study of the uncertainty of traffic parameter estimates is also an important issue, which turns out to be somewhat neglected in the literature. The aim of the work is twofold: on the one hand, to enhance the model validation process; on the other, to provide for objective assessment of the feasibility of network monitoring procedures that rely on measurement and model-based diagnostic
Internet traffic measurement: A critical study of wavelet analysis
No full textIn communication networks, traffic measurements serve two main purposes: the characterization of traffic-load patterns and the monitoring of performances. This paper is a study of the applicability of traffic-analysis methods as a means of detecting malfunctions and performance changes in packet data networks through measurements of selected parameters. The main contribution is of a methodological nature and is motivated by the fact that wavelet analysis, which has come to be regarded as a standard approach, is by no means a straightforward method. Controversial results can be found that are not always attributable to the complex nature of the measured object. Careful study of the uncertainty of traffic-parameter estimates is also an important issue, which turns out to be somewhat neglected in the literature. The aim of this paper is twofold: on the one hand, to enhance the model validation process and, on the other hand, to provide for objective assessment of the feasibility of network-monitoring procedures that rely on measurement and model-based diagnostics
Smartphone-based IOT systems for personal health monitoring
No full textThe term "Internet of Things" (IoT) was first used in 2009 by Kevin Ashton to refer to networks of physical devices with the capability to acquire data and forward them to a data concentrator for processing. In the last decade, IoT systems have provided effective and valuable solutions for monitoring and control in a variety of fields such as transportation, smart agriculture, smart cities and smart health, as discussed here
Statistical analysis of local features in network traffic processes
No full textThis work presents an approach to the detection of local features in network traffic, based on the analysis of short-time maximal rate envelopes, also called statistical arrival curves. In the proposed method, the time series representing a traffic trace is divided into non-overlapping segments, which are further divided into smaller blocks. The maximal rate envelope is estimated for each block and histograms of rate parameters are built over each segment. When significant local features are present in a trace segment, values of the maximal rates may change, resulting in the appearance of peaks or long tails in the corresponding histograms. These effects can be detected with remarkable sensitivity, since they are often evidenced by positive or negative peaks in skewness values of rate parameters histograms. The algorithm can be employed to detect such features on a reasonably fine-grained scal
Passive measurement tool for monitoring mobile packet network performances
No full textContinuous monitoring of performances is necessary to detect critical situations in the radio interface of digital mobile telephone networks. This paper presents a measurement tool that analyzes Transmission Control-Protocol (TCP) level packet traffic and detects the effects of variations in the radio-channel conditions of a wireless network. The analysis algorithm considers the wavelet coefficients of the aggregated-traffic process at a suitably selected number of time scales. Variations in the energy of wavelet coefficients are detected by a statistical test, from which a score is calculated. This indicator reveals changes in the performances of the monitored network
A passive measurement tool for monitoring wireless packet network performances
No full textContinuous monitoring of performances becomes necessary to detect critical situations in the radio interface of digital wireless telephone networks. This paper presents a measurement tool that analyzes TCP-level packet traffic and detects the effects of variations in the radio channel conditions of a mobile network. The analysis algorithm considers the energies of wavelet coefficients of the aggregated traffic process at a suitably selected number of time scales. Wavelet energy variations are detected by a statistical test from which a score is calculated. This indicator reveals changes in the performances of the monitored network
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