Mircea Bardac, George Milescu, Răzvan Deaconescu,
This paper introduces a BitTorrent tracker monitoring architecture and implementation. The tracker monitoring architecture is designed with robustness, scalability and extensibility in mind, making it suitable for large scale BitTorrent tracker monitor analysis. The solution is implemented as part of a BitTorrent experiment for studying the behavior of a real-life swarm. The peer-to-peer network can be analyzed considering both statistic data variation and geographical distribution of data, leaving room for other analysis methods to be implemented if needed. The paper presents challenges and solutions found while designing, implementing and integrating the components of the tracker monitoring solution.
Tópico(s): Peer-to-Peer Network Technologies
2009 - Springer Nature | Studies in computational intelligence
... absolute terms (such as the absolute number of BitTorrent trackers and absolute dollar amount lost due to piracy). ...
Tópico(s): FinTech, Crowdfunding, Digital Finance
2013 - International Journal of Cyber Criminology | International journal of cyber criminology
Jiangchuan Liu, Haiyang Wang, Ke Xu,
... as a distributed probing platform to interact with BitTorrent trackers and peers in the global Internet. Our design ... and also shed new light on re-engineering trackers and reusing historically downloaded data to make BitTorrent a better storage system.
Tópico(s): Internet Traffic Analysis and Secure E-voting
2010 - Institute of Electrical and Electronics Engineers | IEEE Network
... a content management system called Gazelle and a bittorrent tracker called Ocelot—to demonstrate how largely invisible server- ...
Tópico(s): Digital and Traditional Archives Management
2015 - SAGE Publishing | Journal of Technical Writing and Communication
Matteo Varvello, Moritz Steiner,
... claim. We monitor during four consecutive days the BitTorrent traffic (both tracker-based and DHT-based) within a large ISP. The second contribution of this paper is the design, prototype, and preliminary evaluation of the first traffic localization mechanism for DHT-based BitTorrent networks.
Tópico(s): Internet Traffic Analysis and Secure E-voting
2011 - Springer Science+Business Media | Lecture notes in computer science
Jiaqi Gong, Lin Wu, Junbin Gong, Jie Ma, Jinwen Tian,
Using star tracker to perform space surveillance is a focal point of research in aerospace engineering. However, autonomous attitude determination with star trackers in missions is a challenging task, because of spacecraft attitude dynamics and false stars. We present a novel star pattern recognition algorithm to resolve these problems. The algorithm defines a star pattern, called a flower code, composed of angular distances and circular angles. Then, a three-step strategy is adopted to find the ...
Tópico(s): Space Satellite Systems and Control
2009 - SPIE | Optical Engineering
Benjamin B. Spratling, Daniele Mortari,
The author surveys algorithms used in star identification, commonly used in star trackers to determine the attitude of a spacecraft. Star trackers are a staple of attitude determination systems for most types of satellites. The paper covers: (a) lost-in-space algorithms (when no a priori attitude information is available), (b) recursive algorithms (when some a priori attitude information is available), and (c) non-dimensional algorithms (when the star tracker calibration is not well-known). The performance ...
Tópico(s): Space Satellite Systems and Control
2009 - Multidisciplinary Digital Publishing Institute | Algorithms
Hossein Mousazadeh, Alireza Keyhani, Arzhang Javadi, Hossein Mobli, Karen Abrinia, Ahmad Sharifi,
Finding energy sources to satisfy the world's growing demand is one of society's foremost challenges for the next half-century. The challenge in converting sunlight to electricity via photovoltaic solar cells is dramatically reducing $/watt of delivered solar electricity. In this context the sun trackers are such devices for efficiency improvement. The diurnal and seasonal movement of earth affects the radiation intensity on the solar systems. Sun-trackers move the solar systems to compensate for ...
Tópico(s): Photovoltaic System Optimization Techniques
2009 - Elsevier BV | Renewable and Sustainable Energy Reviews
Bala Muralikrishnan, Christopher J. Blackburn, Daniel Sawyer, Steven Phillips, Robert L. Bridges,
We describe a method to estimate the scale errors in the horizontal angle encoder of a laser tracker in this paper. The method does not require expensive instrumentation such as a rotary stage or even a calibrated artifact. An uncalibrated but stable length is realized between two targets mounted on stands that are at tracker height. The tracker measures the distance between these two targets from different azimuthal positions (say, in intervals of 20° over 360°). Each target is measured in both ...
Tópico(s): Advanced Optical Sensing Technologies
2010 - The National Institute of Standards and Technology | Journal of Research of the National Institute of Standards and Technology
Juan Shen, Guangjun Zhang, Xinguo Wei,
The elongated imaging track pertaining to a star spot recorded in the image sensor of a star tracker will diffuse over several pixels at a high angular velocity, leading to an inaccurate, even false, attitude value. A computer simulation of the attitude determination from a dynamic star tracker is developed first, based on a dynamic mathematical model of the star-spot imaging and an efficiency validation of the star centroiding algorithm in the dynamic condition. Then major error sources affecting ...
Tópico(s): Geophysics and Sensor Technology
2010 - Optica Publishing Group | Journal of the Optical Society of America A
This paper describes a "maturing" class of attitude sensors used to determine spacecraft attitude with respect to the celestial sphere. During the past fifteen years, the design direction of attitude sensors has turned towards star field trackers and away from single-star trackers. The focus of this paper is on the description of the principles of operation and processes by which these star field trackers recognize and track a desired star field.
Tópico(s): Spacecraft Design and Technology
1996 - Elsevier BV | Acta Astronautica
Peter S. Jørgensen, John Leif Jørgensen, Troelz Denver, Maurizio Betto,
The German geo-observations satellite CHAMP carries highly accurate vector instruments. The orientation of these relative to the inertial reference frame is obtained using star trackers. These advanced stellar compasses (ASC) are fully autonomous units, which provide, in real time, the absolute attitude with accuracy in the arc second range. In order to investigate the in-flight accuracy of the ASC, the terminology to characterize noise and biases is introduced. Relative instrument accuracy (RIA) ...
Tópico(s): GNSS positioning and interference
2004 - Elsevier BV | Acta Astronautica
John P. Mitchell, Allan D. Spence, Manhtriet Hoang, Arnold Free,
Laser trackers are precision measurement devices often used to measure parts too large for conventional Coordinate Measuring Machines (CMMs). Multiple laser trackers can be used simultaneously to increase the number of part features viewable and therefore available for measurement. Each laser tracker has its own coordinate system that is linked to the others through the measurement of common points. The process of registration uses these common points to bring all measurement data into a Common Coordinate ...
Tópico(s): Astronomical Observations and Instrumentation
2004 - SPIE | Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE
Xinguo Wei, Wei Siang Tan, Jian Li, Guangjun Zhang,
Under highly dynamic conditions, the star-spots on the image sensor of a star tracker move across many pixels during the exposure time, which will reduce star detection sensitivity and increase star location errors. However, this kind of effect can be compensated well by setting an appropriate exposure time. This paper focuses on how exposure time affects the star tracker under highly dynamic conditions and how to determine the most appropriate exposure time for this case. Firstly, the effect of ...
Tópico(s): Astronomical Observations and Instrumentation
2014 - Multidisciplinary Digital Publishing Institute | Sensors
Jochen Meyer, Jutta Fortmann, Merlin Wasmann, Wilko Heuten,
Of all lifelogging tools, activity trackers are probably among the most widely used ones receiving most public attention. However, when used on a long-term basis e.g. for prevention and wellbeing, the devices' acceptance by the user and its usability become critical issues. In a user study we explored how activity trackers are used and experienced in daily life. We identified critical issues with regard not just to the HCI topics wearability, appearance of the device, and display and interaction, ...
Tópico(s): Technology Use by Older Adults
2014 - Springer Science+Business Media | Lecture notes in computer science
Óscar Altuzarra, Erik Macho, Jokin Aginaga, V. Petuya,
Solar trackers are devices that improve the efficiency of photovoltaic collectors increasing the area exposed to direct radiation of the sun. The main drawback of these kinds of devices is that they have to consume certain energy in order to move the collectors following the sun trajectory. This work presents the detailed design of a mechanism with parallel kinematics architecture able to accurately follow the sun motion, which has been designed with the aim of minimizing the energy consumption ...
Tópico(s): Solar Thermal and Photovoltaic Systems
2014 - SAGE Publishing | Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science
The dual threats of energy depletion and global warming place the development of methods for harnessing renewable energy resources at the center of public interest. Solar energy is one of the most promising renewable energy resources. Sun trackers can substantially improve the electricity production of a photovoltaic (PV) system. This paper proposes a novel design of a dual-axis solar tracking PV system which utilizes the feedback control theory along with a four-quadrant light dependent resistor ( ...
Tópico(s): Solar Thermal and Photovoltaic Systems
2013 - Multidisciplinary Digital Publishing Institute | Sensors
A. I. Zakharov, М. Е. Прохоров, M. S. Tuchin, A O Zhukov,
Tópico(s): Adaptive optics and wavefront sensing
2013 - Pleiades Publishing | Astrophysical Bulletin
Zhao Zhao, S. Ali Etemad, Ali Arya,
Wearable technologies are a growing industry with significant potential in different aspects of health and fitness. Gamification of health and fitness, on the other hand, has recently become a popular field of research. Accordingly, we believe that wearable devices have the potential to be utilized towards gamification of fitness and exercise. In this paper, we first review several popular activity tracking wearable devices, their characteristics and specifications, and their application programming ...
Tópico(s): Mobile Health and mHealth Applications
2015 - Springer Nature | Advances in intelligent systems and computing
Fabienne Sallaberry, Ramón Pujol-Nadal, Marco Larcher, Mercedes Hannelore Rittmann-Frank,
The solar trackers are devices used to orientate solar concentrating systems in order to increase the focusing of the solar radiation on a receiver. A solar concentrator with a medium or high concentration ratio needs to be orientated correctly by an accurate solar tracking mechanism to avoid losing the sunrays out from the receiver. Hence, to obtain an appropriate operation, it is important to know the accuracy of a solar tracker in regard to the required precision of the concentrator in order ...
Tópico(s): solar cell performance optimization
2015 - Elsevier BV | Energy Conversion and Management
Tara O’Brien, Meredith Troutman‐Jordan, Donna Hathaway, S. Beth Armstrong, Michael S. Moore,
Wristband activity trackers have become widely used among young adults. However, few studies have explored their use for monitoring and improving health outcomes among older adults. The purpose of this study was to evaluate the feasibility and utility of activity tracker use among older adults for monitoring activity, improving self-efficacy, and health outcomes. A 12-week pilot study was conducted to evaluate the feasibility and utility of mobile wristband activity trackers. The sample (N = 34) was ...
Tópico(s): Obesity, Physical Activity, Diet
2015 - Elsevier BV | Geriatric Nursing
Manon L. Dontje, Martijn de Groot, Remko R. Lengton, Cees P. van der Schans, Wim P. Krijnen,
Activity trackers like Fitbit are used for self-tracking of physical activity by an increasing number of individuals. Comparing physical activity scores with peers can contribute to the desired behavioural change. However, for meaningful social comparison a high inter-device reliability is paramount. This study aimed to determine the inter-device reliability of Fitbit activity trackers in measuring steps. Ten activity trackers (Fitbit Ultra) were worn by a single person (male, 46 years) during eight ...
Tópico(s): Mobile Health and mHealth Applications
2015 - Taylor & Francis | Journal of Medical Engineering & Technology
Walter Dempsey, Peng Liao, Pedja Klasnja, Inbal Nahum‐Shani, Susan A. Murphy,
Data from activity trackers and mobile phones can be used to craft personalised health interventions. But measuring the efficacy of these "treatments" requires a rethink of the traditional randomised trial.
Tópico(s): Digital Mental Health Interventions
2015 - Oxford University Press | Significance
Xusheng Zhu, Lianyu Zheng, Xiaojun Tang,
The laser trackers play an important role in fabrication and assembly of aircraft, spacecraft and other large-scale products, and optimization of laser tracker configuration station is one of the core issues. When laser trackers are used on the shop floor, environment factors, especially non-uniform temperature can induce considerable measurement uncertainty. Aiming to reduce measurement uncertainty of laser tracker, optimization of laser tracker configuration station for large-scale components ...
Tópico(s): Manufacturing Process and Optimization
2016 - Elsevier BV | Procedia CIRP
Muhammad Burhan, Seung Jin Oh, K.J. Chua, Kim Choon Ng,
The conventional CPV systems, as big unit design, are only suitable to be installed in the open regions, like desert areas. This gigantic system design restricts their use on the rooftop of commercial and residential buildings, unlike the conventional PV systems. This paper proposes a compact but highly accurate and cheap two axis solar tracking system, designed for CPV system field operation. The proposed system is designed and verified for tracking accuracy requirement of 0.3°, and has maximum ...
Tópico(s): Solar Radiation and Photovoltaics
2016 - Elsevier BV | Solar Energy
In this study, a novel high accurate offline sensorless dual-axis solar tracker is proposed that can be widely used in photovoltaic systems and solar concentrators. The offline estimated data extracted from solar map equations are used by the tracker to find the sun direction where the maximum value of solar energy is captured. The solar tracker has been built, and it is experimentally verified that 19.1%–30.2% more solar energy can be captured depending on the seasons by utilizing the tracker. ...
Tópico(s): Solar Thermal and Photovoltaic Systems
2016 - Elsevier BV | Renewable Energy
Sjaan R. Gomersall, Norman Ng, Nicola W. Burton, Toby Pavey, Nicholas D. Gilson, Wendy J. Brown,
Background: Activity trackers are increasingly popular with both consumers and researchers for monitoring activity and for promoting positive behavior change. However, there is a lack of research investigating the performance of these devices in free-living contexts, for which findings are likely to vary from studies conducted in well-controlled laboratory settings. Objective: The aim was to compare Fitbit One and Jawbone UP estimates of steps, moderate-to-vigorous physical activity (MVPA), and sedentary ...
Tópico(s): Obesity, Physical Activity, Diet
2016 - JMIR Publications | Journal of Medical Internet Research
Lisa Gualtieri, Sandra Rosenbluth, Jeffrey Phillips,
Background: Wearable activity trackers (trackers) are increasingly popular devices used to track step count and other health indicators. Trackers have the potential to benefit those in need of increased physical activity, such as adults who are older and face significant health challenges. These populations are least likely to purchase trackers and most likely to face challenges in using them, yet may derive educational, motivational, and health benefits from their use once these barriers are removed.
Tópico(s): Behavioral Health and Interventions
2016 - JMIR Publications | JMIR Research Protocols
Personal activity trackers are an inexpensive and easy way for people to record their physical activity and simple biometric data. As these devices have increased in availability and sophistication, their use in daily life and in medicine has grown. This column will briefly explore what these devices are, what types of data they can track, and how that data can be used. It will also discuss potential problems with trackers and how librarians can help patients and physicians manage and protect activity ...
Tópico(s): Innovative Human-Technology Interaction
2016 - Taylor & Francis | Medical Reference Services Quarterly
Kimberly C. Preusse, Tracy L. Mitzner, Cara Bailey Fausset, Wendy A. Rogers,
To assess the usability and acceptance of activity tracking technologies by older adults.
Tópico(s): Mobile Health and mHealth Applications
2016 - SAGE Publishing | Journal of Applied Gerontology