Statistical analysis of water quality parameters in the basin of the Nisava River (Serbia) in the period 2009-2018

This paper analyzes water quality from four hydrological stations in the Nisava river basin from 2009-2018 based on the following parameters: pH, conductivity, O-2 saturation, BOD5, suspended solids, total oxidized nitrogen, phosphates, turbidity and coliform bacteria. Authors have applied WQI (water quality index) as the most reliable indicator of the watercourses pollution for setting of surface water flow quality. Statistical analysis of variance (ANOVA) using t-test inferential statistical analysis and post-hoc Tukey test were applied to evaluate statistically significant differences between specific data groups. The results show that bad water quality was registered on all the profiles on an annual basis (WQI = 65-71). The river water pH decreases downstream, while values of BOD5, suspended solids, turbidity, TON, phosphates and coliform bacteria gradually increase. The waters of the Nisava at the station Nis belong to the third class of waters and they are mostly loaded with organic matter originating from waste sewage and industrial waters of both urban and rural areas

The impact of Mediterranean oscillations on periodicity and trend of temperature in the valley of the Nisava river - a fourier and wavelet approach

Periodicity of temperature on three stations in the Nisava River valley in period 1949-2014, has been analyzed by means of Fourier and wavelet transforms. Combined periodogram based on fast Fourier transform shows considerable similarity among individual series and identffies significant periods on 2.2, 2.7, 3.3, 5, 6-7, and 8.2 years in all datasets. Wavelet coherence analysis connects strongest 6-7 years spectral component to Mediterranean oscillation, starting in 1980s. Combined periodogram of Mediterranean oscillation index reveals 6-7 years spectral component as a dominant mode in period 1949-2014. Wavelet power spectra and partial combined periodograms show absence of 6-7 years component before 1975, after which this component becomes dominant in the spectrum. Consistency between alternation in temperature trend in the Nisava River valley and change in periodicity of Mediterranean oscillation was found

Statistical analysis of temperature regime change on the example of Sokobanja basin in eastern Serbia

The changes and oscillations in air temperature during the second half of the 20th and in the early 21st century, have become one of the major concerns of almost all scientific disciplines. Such changes are noticeable both at the local and global level. The objective of this paper is to point out that the changes of this climate element can also be detected at the local level. The research underlying this paper is, in terms of territory, limited to the Sokobanja basin in Eastern Serbia. The analysis relies on the data on air temperature for the period 1946-2012 taken from the Meteorological weather station located in Sokobanja. The obtained data were processed in line with the recommendations of the World Meteorological Organization. The evidenced statistically significant changes in air temperature were examined using the following statistical tests: Pettit test, Standard Normal Homogeneity test, Buishand range test, and von Neumann test

Breakdown probability and influence on breakdown delay

A method for determination of probability of electrical breakdown of gases is presented in this paper and results are compared with theory. The method is based on the measurements of breakdown time delay at different afterglow periods (relaxation times), where the secondary electron yield initiating breakdown is caused by residual active states reMayning from the preceding glow. Measurements are carried out at low pd (gas pressure times electrode spacing) of nitrogen and higher overvoltages up to 2.1Us (Us: the static breakdown voltage). The experimentally determined breakdown probability is fitted by theoretical expressions for both the Townsend and streamer model of electrical breakdown, with particular attention to the higher overvoltages. On the basis of our measurements and theoretical fit it can be concluded that the Townsend mechanism is applicable at low pd value over the whole range of overvoltage applied and a value of a secondary emission coefficient for gold-plated copper cathode is obtained. With the decrease of the breakdown probability and electron yield the distributions of delay times become broader and centered at larger delay times, and the positive asymmetry and roundness increase

Determination and modelling of the formative and statistical time delay in neon

In this paper the breakdown time delay td in neon was measured and the formative time delay tf determined in three different ways: (1) from the Laue diagrams, by taking the values where linear approximation of experimental data intersects the time axis; (2) from histograms, by taking the minimum values of delay times $t_{d\min}$ for the formative time; and (3) from a difference $t_f= \overline {t_d}- \overline {t_s}\approx \overline {t_d} - \sigma\,(t_d)$, where standard deviation $\sigma\,(t_d)$ is approximately equal to the mean of the statistical time delay $\overline {t_s}$. The dependency of the formative time delay on working voltages Uw was found and fitted by different approximate analytical models. The separation of the formative and statistical time delay distributions was discussed and the distribution of the formative time delay experimentally obtained. The nonstationary exponential distributions with time dependent parameters were introduced to describe the statistical time delay distributions under conditions of increased cathode sputtering

Determination of effective electron yield from swarm and time delay measurements

In this paper the dependence of the effective secondary emission coefficient-effective electron yield γeff in nitrogen on the reduced field (the ratio of the electric field and the gas density E/N) for various cathode surfaces is determined. Two different methods are applied: swarm measurements (from breakdown voltage) and time delay measurements. In the latter technique, first the breakdown probability is determined as a function of voltage and then γeff is derived from it. The results of applying both methods are in good agreement for the γeff versus E/N dependence. The measurements were made for copper cathode, untreated and treated by gas discharge and also several thousand electrical breakdowns, gold-plated copper and steel cathodes. Secondary electron yield γeff is of the order of a few percent at moderate and high E/N, and slightly increases with increasing E/N up to several kTd. At low E/N, a characteristic peak appears (at about 600 Td for copper). The γeff value increases when copper cathode is treated by gas discharges and becomes stable after several thousand breakdowns, agreeing well with other breakdown results in the literature. The chosen values for the Townsend primary ionization coefficient, obtained from best fits to available experimental data in the literature and the choice of the equilibration distance from the cathode significantly influence determination of γeff. Finally, our results are compared with the results of other authors for different cathode materials and a good agreement is found

Statistical analysis of temperature regime change on the example of Sokobanja basin in eastern Serbia

The changes and oscillations in air temperature during the second half of the 20th and in the early 21st century, have become one of the major concerns of almost all scientific disciplines. Such changes are noticeable both at the local and global level. The objective of this paper is to point out that the changes of this climate element can also be detected at the local level. The research underlying this paper is, in terms of territory, limited to the Sokobanja basin in Eastern Serbia. The analysis relies on the data on air temperature for the period 1946-2012 taken from the Meteorological weather station located in Sokobanja. The obtained data were processed in line with the recommendations of the World Meteorological Organization (WMO). The evidenced statistically significant changes in air temperature were examined using the following statistical tests: Pettit test, Standard Normal Homogeneity test, Buishand range test, and von Neumann test. [Projekat Ministarstva nauke Republike Srbije, br. ОI 176008