In this paper, we compare the dynamics of the growth rates of the original Divisia monetary aggregates, the credit card-augmented Divisia monetary aggregates, and the credit card-augmented Divisia inside monetary aggregates. This analysis is based on the methods of recurrence plots, recurrence quantification analysis, and visual boundary recurrence plots which are phase space methods designed to depict the underlying dynamics of the system under study. We identify the events that affected Divisia money growth and point out the differences among the different Divisia monetary aggregates based on the recurrence and visual boundary recurrence plots. We argue that the broad Divisia monetary aggregates could be used for monetary policy and business cycle analysis as they are exhibiting less fluctuation compared to the narrow Divisia monetary aggregates. They could positively affect policy decisions regarding environmental choices and sustainability. We also point out the changes in the monetary dynamics locating the 2008 global financial crisis and the Covid-19 pandemic.

This study investigates the time-series behavior of vegetable prices in the Central Market of Thessaloniki, Greece, using Recurrence Plot (RP) analysis and Recurrence Quantification Analysis (RQA), which considers non-linearities and does not necessitate stationarity of time series. The period of study was 1999–2016 for practical and research reasons. In the present work, we focus on vegetables available throughout the year, exploring the dynamics and interrelationships between their prices to avoid missing data. The study applies RP visual inspection classification, a clustering based on RQA parameters, and a classification based on the RQA analysis graphs with epochs for the first time. The aim of the paper was to investigate the grouping of products based on their price dynamical behavior. The results show that the formed groups present similarities related to their use as dishes and their way of cultivation, which apparently affect the price dynamics. The results offer insights into market behaviors, helping to inform better management strategies and policymaking and offer a possibility to predict variability of prices. This information can interest government policies in various directions, such as what products to develop for greater stability, identity for fluctuating prices, etc. In future work, a larger dataset including missing data could be included, as well as a machine-learning algorithm to classify the products based on the RQA with epochs graphs.

We construct recurrence plots (RPs) and conduct recurrence quantification analysis (RQA) to investigate the dynamic properties of the new Center for Financial Stability (CFS) Divisia monetary aggregates for the United States. In this study, we use the latest vintage of Divisia aggregates, maintained within CFS. We use monthly data, from January 1967 to December 2020, which is a sample period that includes the extreme economic events of the 2007-2009 global financial crisis. We then make comparisons between narrow and broad Divisia money measures and find evidence of a nonlinear but reserved possible chaotic explanation of their origin. The application of RPs to broad Divisia monetary aggregates encompasses an additional drift structure around the global financial crisis in 2008. Applying the moving window RQA to the growth rates of narrow and broad Divisia monetary aggregates, we identify periods of changes in data-generating processes and associate such changes to monetary policy regimes and financial innovations that occurred during those times.

The visual boundary recurrence plot (VBRP) method is used in this analysis to study time series of fluctuating velocities in turbulent magnetohydrodynamic channel flow that were studied in our previous study using the theory of the recurrence plots. The VBRP is a new graphical tool, which visualizes each point of the recurrence plot with colors depending on whether the neighboring points are recurrent or not and enhances, thus, the study of the stability of the textures of the recurrence plots, viewing them as geometrical shapes. We calculate the VBRPs of the turbulent velocity time series of a simulated channel flow monitored at constant streamwise and spanwise positions and at a number of positions along the wall-normal direction. We further estimate the visual boundary recurrence plot rates to indicate the change of the dynamics of the flow. The results highlight the flow dynamics under the influence of the magnetic field and identify additional correlations/similarities between the flow point positions within the channel. In this study, we show that these areas correspond to perturbations due to strikes that are created close to the boundary and move toward the centerline. It also seems that we have more often creation of streaks in the case of absence of magnetic field.

Understanding the underlying processes and extracting detailed characteristics of rivers is critical and has not yet been fully developed. The purpose of this study was to examine the performance of non-linear time series methods on environmental data. Specifically, we performed an analysis of water level measurements, extracted from sensors, located on specified stations along the Nestos River (Greece), with Recurrence Plots (RP) and Recurrence Quantification Analysis (RQA) methods. A more detailed inspection with the sliding windows (epoqs) method was applied on the Recurrence Rate, Average Diagonal Line and Trapping Time parameters, with results showing phase transitions providing useful information about the dynamics of the system. The suggested method seems to be promising for the detection of the dynamical transitions that can characterize distinct time windows of the time series and reveals information about the changes in state within the whole time series. The results will be useful for designing the energy policy investments of producers and also will be helpful for dam management assessment as well as government energy policy.

In this paper, we introduce a new graphical tool, the visual boundary recurrence plot, in order to provide a more detailed visualization of the well-established method of recurrence plots. In this approach, we are coloring each point of the recurrence plot depending on whether the neighboring points in the vertical and horizontal directions are recurrent or not. We use this plot to study the stability of the textures of the recurrence plots viewing them as geometrical shapes under horizontal and vertical changes. In order to compare two recurrence plots, we define the visual boundary recurrence plot rate distance between their visual boundary recurrence plots to study their closeness/similarity. Finally, we introduce a topological criterion to select an optimal threshold for constructing a recurrence plot. A threshold is optimal when the recurrence plot associated with it remains similar to the ones that are constructed for consecutive values of backwards and forwards thresholds. The results are applied to recurrence plots of time series emanating from different sources: molecular dynamics simulations, Lorenz dynamical system, random noise and daily water level measurements of a river.

Non-recurrent congestion disrupts normal traffic operations and lowers travel time (TT) reliability, which leads to many negative consequences such as difficulties in trip planning, missed appointments, loss in productivity, and driver frustration. Traffic incidents are one of the six causes of non-recurrent congestion. Early and accurate detection helps reduce incident duration, but it remains a challenge due to the limitation of current sensor technologies. In this paper, we employ a recurrence-based technique, the Quadrant Scan, to analyse time series traffic volume data for incident detection. The data is recorded by multiple sensors along a section of urban highway. The results show that the proposed method can detect incidents better by integrating data from the multiple sensors in each direction, compared to using them individually. It can also distinguish non-recurrent traffic congestion caused by incidents from recurrent congestion. The results show that the Quadrant Scan is a promising algorithm for real-time traffic incident detection with a short delay. It could also be extended to other non-recurrent congestion types.

In this work, a topological criterion is proposed for selecting a recurrence threshold for constructing a recurrence plot of a time series. It is based on a metric structure of the set of the recurrence plots that is defined by the recurrence plot deviation distance among recurrence plots, introduced in a previous paper by the authors. In this process for a range of threshold values, the corresponding recurrence plots are constructed. Then, a value of the threshold is considered to be optimal when the image of its recurrence plot remains close to images of the other recurrence plots constructed for close values of thresholds based on the topological criterion introduced in the present work. The results are applied both to time series emanating from the Lorenz dynamical system and to Molecular Dynamic simulations.

We present Recurrence Plots (RPs) and Recurrence Quantification Analysis (RQA) of time series of velocities in a low-Reynolds-number magnetohydrodynamic turbulent channel flow. The flow was simulated using a fully spectral code with Fourier and Chebyshev decomposition in the periodic and wall bounded directions, respectively. Direct numerical simulations of the flow were performed for Reτ=180, based on the friction velocity and the channel half-height, for the hydrodynamic flow and in the case of a streamwise magnetic field with magnetic interaction number 0.1. The turbulent velocity time series of both cases of the flow were recorded at several positions in the wall-normal direction at fixed spanwise and streamwise positions and analyzed along all directions using RPs and RQA. Using this approach, a number of different flow regions were identified depending on the distance from the channel walls in accordance to the turbulent boundary-layer theory. Different characteristic times were extracted for the various velocity components and related to the dynamics of the flow. Moreover, with the use of Recurrence Plots several distinct system regimes were identified and the effect of the magnetic field was localized.

In the present paper, a topological classification of recurrence plots of time series that are constructed with equal embedding dimension and delay time is proposed by defining a metric structure in the set of those recurrence plots. To achieve this, the Recurrence Plot deviation distance and the Recurrence deviation plot are introduced along with qualitative and quantitative indices, which allows for a detailed comparison of the recurrence plots of two time series and their corresponding dynamical systems. In the range of values studied, the application of additive noise on the thermostat results in a less deterministic system behavior, quite close to that of the system with the unperturbed thermostat. On the other hand, multiplicative noise of small strength results in a less deterministic system quite close to the unperturbed system behavior. For a larger strength, the system presents a behavior which is significantly different from that of the unperturbed system. The new methodology introduced here provides detailed quantitative and graphical insights for the way that noise, additive and multiplicative, influences on the morphology of recurrence plots of the unperturbed and noise perturbed time series. The results are encouraging for potential future applications on the analysis of complex dynamical systems.

In this study, we present results of the application of nonlinear time series analysis on traffic data for incident detection. More specifically, we analyze daily volume records of Attica Tollway (Greece) collected from sensors located at various locations. The analysis was performed using the Recurrence Plot (RP) and Recurrence Quantification Analysis (RQA) method of the volume data of the lane closest to the median. The results show that it is possible to identify, through the abrupt change of the dynamics of the system revealed by RPs and RQA, the occurrence of incidents on the freeway and differentiate from recurrent traffic congestion. The proposed methodology could be of interest for big data traffic analysis.

In the present study, the direct numerical simulation of the turbulent flow of an electrically conductive fluid in a channel is performed and time series are recorded at a range of locations along the y-direction between the parallel plates of the channel. An external streamwise magnetic field is applied and the correlations between pairs of time series of the fluctuating velocities from the magnetohydrodynamic and the hydrodynamic cases measured at the same probing location of the channel are analyzed. We compare the situation with and without magnetic field using the nonlinear method of Cross Recurrence Plots and Cross Recurrence Quantification Analysis (CRQA). The results of CRQA indicate very well the spatiotemporal extension of the effect of the applied magnetic field on the flow and are in very good agreement with the detailed analysis obtained with other methods.

Environmental systems and time series emanating from such systems present a particular interest. System state transitions can occur in time and/or in space and the detection of such transitions can be particularly useful in the design related to such systems. Since the majority of physical systems present non linear behavior the use of appropriate tools is necessary. Recurrence Plots (RPs) and Recurrence Quantitative Analysis (RQA) along with Cross Recurrence Plots (CRPs) are some tools that permit to extract the underlying system dynamics [1-3]. In the present work we analyze time series from two different environmental systems. In the first case we study records of daily values of the Nestos river (Greece) water level at various measurement stations. Transitions from “periodicity” to “chaos” and “chaos” to “laminarity” are identified in time. In the second part we analyze temperature fluctuations in a horizontal round heated turbulent jet where instantaneous temperature time series were recorded at several points on the jet cross section. The temperature time series are analyzed in a first place using RQA. The variation of RQA measures is related with and interpreted via the transitions of the physical state of the fluid from the fully-turbulent flow near the jet centerline to the transitional flow near the boundary of the jet [9]. In a second phase the CRP analysis reveals correlations between the various parts of the jet.

We present an analysis of temperature fluctuations in a horizontal round heated turbulent jet. Instantaneous temperature time series were recorded at several points along a horizontal line in the plane of symmetry of the jet. The time series are analyzed using Recurrence Quantification Analysis (RQA). The variation of characteristic RQA measures is associated with and interpreted via the transitions of the physical state of the fluid from the fully-turbulent flow near the jet centerline to the transitional flow near the boundary of the jet.

Until recently, academic libraries were viewed as a supportive factor in the learning process and their role was restricted to material provision. Over the last few years, though, the role of libraries in the learning process is being re-evaluated. One area in which libraries are expected to play an active teaching role is information literacy skills. The main purpose of information literacy programs is to enable students to evaluate information and its sources critically and incorporate selected information into his or her knowledge base and value system. During the last few years, the world has also witnessed major changes in teaching and learning paradigms. In particular, asynchronous e-learning has emerged as the learning method of choice in many education scenarios. The widespread adoption of this teaching technique is fueled by the global connectivity provided by the Internet which allows students to access material and tutors virtually anytime and from any location. Combining the trends and requirements described above the Library and Information Center of the University of Macedonia (UOM) created a virtual learning environment called Telemathea (http://telemathea.uom.gr) using Moodle, a freely available open source course management system. In the context of the 3rd Community Support Framework and the PLOEGIS project in particular, the UOM Library embarked on the development of online courses with the help of University Professors. The topic of the administered courses was selected to be computer usage with free and open source software. This choice was motivated on one hand by the importance of basic computer skills as a component of information literacy and on the other hand by the intention of both the Library and the University to promote free and open source software. Separate courses were created for both Linux and Microsoft Windows users with different content depending on the operating system. All teaching and learning was performed asynchronously via the Telemathea virtual learning environment and did not require the presence of students in a classroom at any point. The selected audience was not restricted to Library users but instead encompassed people of various ages and occupations located in several Greek cities. The course content was based on material granted by the ICDL (International Computer Driving License) Foundation. The audience was selected after a public call. Course design and preparation was handled by Library personnel in cooperation with University of Macedonia Professors. This paper describes the e-learning seminar conducted by the UOM Library during the first semester of 2007 which included the courses on web browsing and e-mail. During a period of 2 months, 47 people (30 Windows users and 17 Linux users) “attended” the online courses. Among the issues covered in this paper is the design and construction of online courses, the supervision of courses while they were offered to students, the statistics of student activity and the conclusions of the evaluation of both the courses and the learning environment from the viewpoint of students. Several interesting conclusions that were drawn during the evaluation process are presented, including the creation of a virtual classroom, the social interaction between learners, and the communication of learners with teachers.

The present work examines the applicability and efficacy of recurrence plots and recurrence quantification analysis in interpreting statistical-mechanics-based simulations of classical fluids and solids. We analyze temperature time series obtained from molecular dynamics simulations of a Lennard-Jones system at various fluid and solid states. It turns out that the structure of the recurrence plots reflects the different regimes of atomic motion as well as the degree of atomic diffusivity as the system density and temperature are varied. Recurrence plots (RPs) can help to localize a region where a phase transition occurs, while recurrence quantitative analysis descriptors confirm in a more clear way the results of RPs. The trends identified in our results are in qualitative agreement with direct computation of Lyapunov exponents for liquid Lennard-Jones systems reported in the literature.

This paper describes the e-learning seminar conducted by the Library and Information Center of the University of Macedonia during the first semester of 2007. The courses offered included web browsing and e-mail using open source software, namely Mozilla Firefox and Mozilla Thunderbird. Separate courses were created for Windows and Linux users. Among the issues covered is the design and construction of online courses, the supervision of courses while they were offered to students, the reports on student activity and the evaluation of both the courses and the learning environment from the viewpoint of students.