Scaling analysis of time series of stock market indices of transitional economies in the Western Balkans

In this paper we have analyzed scaling properties of time series of stock market indices (SMIs) of developing economies of Western Balkans, and have compared the results we have obtained with the results from more developed economies. We have used three different techniques of data analysis to obtain and verify our findings: Detrended Fluctuation Analysis (DFA) method, Detrended Moving Average (DMA) method, and Wavelet Transformation (WT) analysis. Following extensive research in the area of econophysics of national and international stock markets, we were interested to contribute to this body of knowledge by analyzing the dynamics of market behavior of transitional economies in the Western Balkans, and to compare data from these emerging economies with data from more economically developed countries. Analyzes of stock market behavior of the emerging economies of South America, or the developing Asian or African markets have shown that the values of scaling exponents, calculated from the time series of stock market indices, could be used to estimate the efficiency of markets in question. With that in mind, by applying the theoretical approach of statistical physics, we aim to offer a new perspective on stock market dynamics in the Western Balkans and contribute to better understanding of the development process in the region's economies. We have found scaling behavior in all SMI data sets that we have analyzed. Scaling of SMI series changes from long-range correlated to slightly anti-correlated behavior, i.e. the appropriate scaling exponents decrease in value with the increase in growth and/or maturity of the economy the stock market is embedded in. Scaling exponents α, H, and β, corresponding to the DFA, DMA, and WT technique, all cross the 0.5 (and zero) line, marking this alteration. We also report the presence of effects of potential periodic-like influences on the SMI data that we have analyzed. One such influence is visible in all our SMI series, and appears at a period Tp ≈ 90 days. We propose that the existence of various periodic-like influences on SMI data may partially explain the observed difference in types of correlated behavior of corresponding scaling functions. The application of time-dependent scaling analysis (tdDMA) proved that these influences are of a complex type, that is, they can not be easily distinguished from a local correlations profile

Prevalence and severity of TMD in orthodontic patients

Introduction Temporomandibular disorder (TMD) is a collective term for numerous symptoms, with the most common being masticatory muscle pain, pain in temporomandibular joints, limited mouth opening, irregular jaw movements, headaches and sound effects in TMJ. The aim was to determine the prevalence and severity of TMD in orthodontic patients determining whether the type of malocclusion affects the prevalence and severity of TMD. Material and Methods The study was conducted in the form of Fonseca Anamnestic Index, which classifies TMD severity among examinees (no TMD, mild, moderate and severe TMD). The experimental group consisted of orthodontic patients with confirmed malocclusions, while the control group consisted of dental students with a Class I occlusion and no need for orthodontic treatment. Orthodontic patients were classified into the three subgroups based on malocclusions. Results In the experimental group, 45.03% of orthodontic patients had some degree of TMD, while among students, that percentage was 56.41%. Compared to Class I, higher percentage of TMD was found among patients with distal and mesial occlusion in experimental group. In the experimental and control groups, the greatest percentage of participants showed mild TMD. The prevalence of TMD was greater in females than in males in the experimental group. Conclusion The high prevalence of TMD in the control group speaks in favor of its complex etiology, with stress having an important role. Malocclusion is one of many factors which can contribute to the occurrence and severity of TMD, but it cannot be considered the most significant

Interrelation between the beryllium-7 specific activity in the surface air and North Atlantic Oscillation based on their wavelet coherence

The natural radionuclide beryllium-7 (Be-7) is produced in the upper levels of the atmosphere and is transported to the surface on carrier aerosols. Therefore, among other factors, the abundance of Be-7 in the surface air is governed by the rate of its production and large-scale air transport. The North Atlantic Oscillation (NAO) index, which quantifies the surface sea-level pressure difference between the Subtropical (Azores) High and Subpolar low, exerts large effects on precipitation and circulation patterns in Europe. With an aim to look closely into the interrelations between the Be-7 specific activity in the surface air, sunspot number (as a proxy for the production signal), and NAO index, this paper investigates their long-term time series over 28 years, between February 1987 and December 2014. The Be-7 specific activity was recorded in Vienna (48.22 ºN; 16.35 ºE; 193 m a.s.l.), Austria, and stored in the Radioactivity Environmental Monitoring databank (REMdb) that is created and supported by the European Commission-Joint Research Centre in Ispra, Italy. The sunspot number (SN) data were downloaded from SILSO (Royal Observatory of Belgium, Brussels, Belgium), while the NAO records were retrieved from the Climate Prediction Centre of the National Oceanic and Atmospheric Administration, USA. Since the temporal resolution of the Be-7 measurements varied between six and eight days, they were first linearly interpolated into an array of weekly data, and then, the daily SN and NAO data were averaged into weekly records to match the Be-7 data. Next, Pearson’s correlation analysis and wavelet transform were used to analyse the time series. The low Pearson’s correlation coefficients between the Be-7 specific activity in the surface air and SN (-0.15207) on one hand, and the NAO index and SN (0.13512) on the other hand, imply a lack of direct linear interrelations between these variables. The Pearson’s correlation coefficient between the Be-7 specific activity in the surface air and NAO index is even lower (-0.05904). However, the Be-7 specific activity wavelet spectrum shows a pronounced annual period, and looking further into the link between the Be-7 specific activity and NAO index at this characteristic periodicity, reveals a prominent pattern. Specifically, the wavelet coherence levels between these two parameters show variations that seem to be in agreement with the 11-year solar cycle: the coherence increases as the sunspot number transitions between its extremes, and it decreases around the maxima and minima in sunspot number. Further, phase difference shows that at the one-year periodicity, the Be-7 specific activity always lags behind the NAO index. The phase difference ranges between 2 and 6 months; it reaches the minimum around the solar activity extremes, and the maximum in-between. These findings imply that, although weak, the signature of sunspot number can be seen in the wavelet coherence level between the Be-7 specific activity and NAO index

Analysis of the Fractal Nature of the Specific Activity of Beryllium-7 in the Near-Surface Layer of the Atmosphere Measured in Belgrade, Serbia (1991–2022)

U ovom istraživanju analizirana je fraktalna priroda vremenske serije specifične aktivnosti berilijuma-7 u površinskom sloju atmosfere u Beogradu, Srbija, sa ciljem da se prouči dinamika njene samosličnosti, a s posebnim fokusom na godišnji ciklus. Korišćene su metode vejvlet analize i vremenski zavisne detrendovane pokretne srednje vrednosti radi identifikacije karakterističnih intervala i procene Hurstovih eksponenata. Podaci o specifičnoj aktivnosti berilijuma-7 preuzeti su iz GRAMON baze podataka, za lokaciju Beograd (44,88 °N; 20,58 °E; 95 m nadmorske visine). Vremenska serija obuhvata 362 mesečna merenja od 1991. do 2022. godine. Rezultati ukazuju na postojanje izraženog godišnjeg ciklusa u ovoj vremenskoj seriji. Takođe, promene u lokalnom Hurstovom eksponentu otkrivaju varijacije u ponašanju vremenske serije – ona iz umereno korelisanog prelazi u izrazito antikorelisan proces između 2015. i 2020. godine. Ovaj rezultat biće predmet šire analize koja uključuje i druge lokacije iz GRAMON baze podataka.This research analyzes the fractal nature of the beryllium-7 specific activity time series in the near-surface layer of the atmosphere in Belgrade, Serbia. The aim was to study the dynamics of self-similarity in this series, with a particular focus on the annual cycle. Wavelet analysis and time-dependent detrended moving averages were used to identify characteristic intervals and estimate Hurst exponents. The data on specific activity of beryllium-7 were obtained from the GRAMON database for the location of Belgrade (44.88 °N; 20.58 °E; 95 m a.s.l.). The time series comprises 362 monthly measurements between February 1991 and December 2022. The results indicate a pronounced annual cycle in this time series. Moreover, changes in the local Hurst exponent reveal variations in the behavior of the time series, transitioning from moderately correlated to highly anti-correlated process between 2015. and 2020. This finding will be a subject of a further analysis including other locations from the GRAMON database.XXXII Simpozijum Društva za zaštitu od zračenja Srbije i Crne Gore, 4-6. oktobar 2023; Budva, Crna GoraProceedings: [https://vinar.vin.bg.ac.rs/handle/123456789/11602

Novel approach to analysing large data sets of personal sun exposure measurements

Personal sun exposure measurements provide important information to guide the development of sun awareness and disease prevention campaigns. We assess the scaling properties of personal ultraviolet radiation (pUVR) sun exposure measurements using the wavelet transform (WT) spectral analysis to process long-range, high-frequency personal recordings collected by electronic UVR dosimeters designed to measure erythemal UVR exposure. We analysed the sun exposure recordings of school children, farmers, marathon runners and outdoor workers in South Africa, and construction workers and work site supervisors in New Zealand. We found scaling behaviour in all the analysed pUVR data sets. We found that the observed scaling changes from uncorrelated to long-range correlated with increasing duration of sun exposure. Peaks in the WT spectra that we found suggest the existence of characteristic times in sun exposure behaviour that were to some extent universal across our data set. Our study also showed that WT measures enable group classification, as well as distinction between individual UVR exposures, otherwise unattainable by conventional statistical methods

Linear and nonlinear analysis of dental pulp blood flow oscillations in ageing

Aim To investigate the effect of ageing on control mechanisms of pulpal microcirculation using wavelet analysis and to calculate linear and nonlinear parameters of blood flow oscillations, in a healthy general population. Methodology Pulpal blood flow (PBF) oscillations were recorded on right maxillary central incisors using laser Doppler Flowmeter (PeriFlux PF 5001, Perimed, Jarfalla, Sweden) on a group of 10 young participants (20-25 years) and a group of 10 older adults (60-70 years). In total, 20 recordings were obtained for at least 20 min (one recording on one tooth per subject). Using wavelet spectral analysis, the amplitude and power were calculated as a linear and Hurst exponent as a nonlinear parameter of PBF oscillations. Differences between the two groups were assessed with the independent Student t-test. Results Mean PBF levels were significantly lower (P = 0.024) in older adults than in young participants. Relative amplitudes and powers corresponding to the myogenic (P = 0.046, P lt 0.001, respectively) and neurogenic activity (P = 0.04, P = 0.01, respectively) were significantly higher, whereas values corresponding to the endothelial function (P = 0.04, P = 0.01, respectively) were significantly lower in older adults than in young participants. Hurst exponents of the total spectrum, myogenic and endothelial component (P lt 0.001, P = 0.02, P lt 0.001, respectively) of PBF oscillations were significantly lower in older adults in comparison to young participants. Conclusions At the level of pulpal microcirculation, ageing was associated with altered blood flow levels, the contribution of different control mechanisms to blood flow oscillations as well as the interaction of vascular smooth muscle and endothelium. Described changes of pulpal haemodynamics contribute to a better understanding of physiological behaviour and decreased adaptability of aged dental pulp to pathological stimuli

Wavelet transform analysis of time series generated by the stimulated neuronal activity

We have studied the stimulated discharge dynamics of fusimotor neurons by applying the wavelet transform technique and by adopting that the neuronal discharge dynamics is manifested by the random time series of interspike intervals. We found two different power-law type behaviors along interspike intervals (ISI) time scale (which implies existence of two different types of neuronal noise), which are separated by a crossover region. Our results reveal that complex neuronal dynamics, in the presence of external stimulation, is manifested with long-range correlated noise in the region before the crossover, on the ISI time scale

Effect of Aging and Carotid Atherosclerosis on Multifractality of Dental Pulp Blood Flow Oscillations

Introduction: Age-related changes of dental pulp tissue and atherosclerosis of carotid arteries as its feeding arteries could influence the functionality of pulpal circulation. The objective of our study was to evaluate the effect of aging (physiological process) and carotid bifurcation atherosclerosis (pathologic process) on the pulpal microcirculatory system using multifractal analysis of the laser Doppler flowmetry signal. Methods: Three groups of 10 subjects were enrolled in the study: the young group (healthy subjects, 20-25 years), the middle-aged group (healthy subjects, 50-60 years), and the clinical group (subjects with carotid bifurcation atherosclerosis, 50-60 years). Pulpal blood flow (PBF) signals recorded by laser Doppler flowmetry were assessed by multifractal analysis that estimates Holder exponents of the signal. PBF levels, the average mean values, and the range of Holder exponents were obtained. Results: PBF levels were significantly higher in the young group compared with the middle-aged and clinical groups, and the difference between the middle-aged and clinical groups was not statistically significant. The range of the Holder exponents was narrower in the middle-aged and clinical groups than in the young group and narrower in the clinical group than in the middle-aged group. The average mean value of Holder exponents was significantly higher in the young group than in the middle-aged and clinical groups, whereas there was no significant difference between the middle-aged and clinical groups. Conclusions: Our study investigating the multifractality of the PBF signal showed that the aging process and carotid atherosclerosis could affect the complex structure of PBF oscillations and contribute to a better understanding of pulpal hemodynamics

Analysis of cyclical behavior and quantification of the level of development from time series of stock market returns

We have analyzed cyclical behavior of the three types of stock market indexes (SMI) time series: data belonging to stock markets of developed economies, emerging economies, and of the underdeveloped or transitional economies. We have used two techniques of data analysis to obtain and verify our findings: the wavelet transformation (WT) spectral analysis to study SMI returns data, and the Hurst exponent formalism to study local behavior around market cycles and trends. We calculated WT power spectra for all our SMI series, and have searched for characteristic peaks (local maxima) that point to existence of cycles in our data. We found cyclical behavior in all SMI data sets that we have analyzed. Moreover, the positions and the boundaries of cyclical intervals that we found seem to be common for all markets in our dataset. We differentiated nine such periods in our SMI data. Our results show that measures like the relative WT energy content and the relative WT amplitude for the peaks in the small scales region could be used to partially differentiate levels of growth and/or maturity of market economies in our dataset. Finally, we propose a way to quantify and compare the level of development of a stock market, based on the Hurst scaling exponent approach. From the local scaling exponents calculated for our nine peak regions we have defined what we named the Development Index (HDI), which proved, at least in the case of our dataset, to be suitable to rank the SMI series that we have analyzed in three distinct groups. Further verification of this method remains open for future research

Changes in long-term properties and natural cycles of the Danube river level and flow induced by damming

In this paper we assessed changes in scaling properties of the river Danube level and flow data, associated with building of Djerdap/Iron Gates hydrological power plants positioned on the border of Romania and Serbia. We used detrended fluctuation analysis (DFA), wavelet transform spectral analysis (WTS) and wavelet modulus maxima method (WTMM) to investigate time series of measurements from hydrological stations in the vicinity of dams and in the area of up to 480 km upstream from dams, and time series of simulated NOAA-CIRES 20th Century Global Reanalysis precipitation data for the Djerdap/Iron Gates region. By comparing river dynamics during the periods before and after construction of dams, we were able to register changes in scaling that are different for recordings from upstream and from downstream (from dams) areas. We found that damming caused appearance of human-made or enhancement of natural cycles in the small time scales region, which largely influenced the change in temporal scaling in downstream recording stations. We additionally found disappearance or decline in the amplitude of large-time-scale cycles as a result of damming, which changed the dynamics of upstream data. The most prominent finding of our paper is a demonstration of a complete or partial loss of annual cycles in the upstream stations' data that stems from the operation of the artificial water reservoir and extends as far as 220 km from dams. We discussed probable sources of such found changes in scaling, aiming to provide explanations that could be of use in future environmental assessments