Usporedba strukture sastojina gospodarenih i prašumskih bukovih šuma Srbije

This study presents results of the comparison of structural and production characteristics of managed and virgin European beech forests in Serbia. Five managed and three virgin European beech stands were studied. The aim of this research was to determine the impact of the previous forest management on the structural diversity and production characteristics of managed European beech high forests in Serbia. The observed stands are located in the mountainous range of 400 to 1200 meters above sea level in the areas with the most productive beech forests in Serbia. Structural characteristics were compared using the following parameters: Height curves, Diameter distribution, Gini index, Coefficient of variation, Slenderness coefficient and maximum dimensions of standing living and dead trees. Stand density and productive characteristics were studied using the following forest estimation elements: number of trees, basal area, volume, biomass, carbon stock, stand quadratic mean diameter, Lorey’s mean height and volume of dead wood. The greatest differences were found in the dimensions of the largest trees in managed and virgin beech forests (diameters at breast height and heights). Certain differences were found in the shape of Height curves and Diameter distribution and in the values of Slenderness coefficient. However, the Gini index and the Coefficient of variation show that these managed beech forests in Serbia substantially preserve the primeval structural diversity. The differences in the average value of most forest estimation elements of managed beech high forests in Serbia compared to virgin beech forests are statistically significant, which tells us that the previous management had a significant impact on the changes in the production characteristics of these forests in Serbia.U radu se prikazuju rezultati usporedbe strukturnih i proizvodnih karakteristika bukovih sastojina gospodarskog i  prašumskog tipa u Srbiji. Istraživano je pet sastojina gospodarskog  i tri sastojine prašumskog tipa. Cilj ovog istraži­va­nja bio je utvrditi utjecaj prethodnog gospodarenja šumama na strukturnu raznolikost i proizvodne osobine visokih bukovih šuma u Srbiji. Istraživane sastojine nalaze se u planinskom rasponu od 400 do 1200 metara nadmorske visine u područjima gdje se nalaze najproduktivnije bukove šume u Srbiji (slika 1 i tablica 1). Strukturne karakteristike uspore­đe­ne su pomoću sljedećih parametara: visinske krivulje, debljinska struktura, Gini indeks, koeficijent varijacije, koeficijent vitkosti i maksimalne dimenzije dubećih živih i mrtvih stabla. Sastojinsku gustoću i produktivne osobine  proučavane su pomoću sljedećih procijenenih taksacijskih elemenata: broj stabala, temeljnica, volumen, biomasa, zaliha ugljika, srednji promjer po temeljnici, Lorajeva srednja visina i volumen mrtvog drveta. Najveće razlike pronađene su u dimenzijama najvećih stabala u bukovim sasatojinama gospodarskog i prašumskog tipa (tablica 4). Određene razlike pro­na­đene su u obliku visinskih krivulja i debljinskoj strukturi, i vrijednostima koeficijenta vitkosti (slike 2, 3, 4 i 5, i tablica 3).  Međutim, Ginijev indeks i koeficijent varijacije pokazuju da su bukove sastojine gospodarskog tipa u Srbiji u velikoj mjeri sačuvale iskonsku strukturnu raznolikost (tablica 2 i slika 6). Razlike u prosječnim vrijednostima taksacijskih elemenata sastojina gospodarskog tipa visokih bukovih šumama u Srbiji u odnosu na sastojine prašumskog tipa su statistički značajne, što nam govori da je prethodno gospodarenje imalo značajan utjecaj na promjene u proizvodnim karakteristikama ovih šuma u Srbiji (tablica 5)

Prirast i vitalnost hrasta lužnjaka u Sremu sa aspekta promene vodostaja Save

The decline in vitality and dieback of oak forests is increasingly present Vojvodina. This is old challenge for forestry, which again became actual. The paper used dendrochronological methods with the intention to describe trends in growth of pedunculate oak forests in Srem and trends of the water level of the Sava River and air temperature, which are defined as critical to the vitality of these forests. Predicted were water levels of Sava River in the 21st century with overview of its implications on the oak forests growth. Samples were taken from three stands in Srem (Stara Vratična, Smogva and Blate). Flows of Sava river were taken according to five climate scenarios for the periods 2012-2040 and 2042-2070, and converted into the water levels. A trend of decrease in growth in all three stands in last 30 years was observed, together with decrease in water level and temperature rise. Predicted future water levels of the Sava River were in general lower than those in the period 1951-1981, and higher than in the period 1982-2012. The differences between the various scenarios, as well as the impossibility of adequate simulations of extreme events, leavs space for further considerations.Opadanje vitalnosti i sušenje šuma je sve više prisutno u šumama hrasta lužnjaka u Vojvodini. Stari izazov za šumarstvo koji ponovo postaje aktuelan. U radu su korišćene dendrohronološke metode sa namerom da se prikažu trendovi prirasta hrasta lužnjaka u Sremu i trendovi vodostaja reke Save i temperature koji su definisani kao kritični za vitalnost ovih šuma. Izvršeno je predviđanje vodostaja Save u 21. veku i dat osvrt na njen uticaj na šume lužnjaka. Uzorci su uzeti iz tri sastojine u Sremu (Stara Vratična, Smogva i Blate). Razmatrano je pet klimatskih scenarija budućih protoka reke Save za period 2012-2040 i 2042-2070, koji su preračunati u vodostaje. Uočen je trend smanjenje prirasta u sve tri istraživane sastojine u proteklih 30 godina, kao i trend smanjenja vodostaja i porasta temperature. Projekcije budućih vodostaja reke Save su u većini slučajeva bile niže od onih u periodu 1951-1981, a više od onih u period 1982-2012. Razlike između različitih scenarija, kao i nemogućnost verodostojne simulacije ekstremnih voda, ostavlja prostora za dalja razmatranja

Climate change impact on a mixed lowland oak stand in Serbia

Climatic changes and bad environmental conditions may lead to forests vitality loss and even mortality. This is the reason why increased sanitary felling operations were performed in mixed oak forests in northern Serbia in 2013 in order to solve the severe dieback which affected some Pedunculate oak (Quercus robur L.) and Turkey oak (Quercus cerris L.) stands, after the very dry years 2011 and 2012.Dendrochronological techniques were applied to both these oak species collected in a stand, to examine the impact of temperature, precipitation and ground water level on forest growth and investigate the potential causes of the dieback.Differences in tree-ring patterns between surviving and dead trees were not significant according to t-value (from 5.68 to 14.20) and Gleichläufigkeit coefficient (from 76% to 82%), this meaning no distinctive responses of the two ecologically different oak species. As for radial increment, pedunculate and Turkey oak trees showed a similar response to environmental variables in this mixed stand. The Simple Pearson’s correlation analysis, which was conducted, showed that among three basic environmental variables (the mean monthly air temperature, the monthly sum of precipitation and the mean monthly water level, proxy of ground water level), the water level of Danube river in May and the temperature in April were statistically related to the growth of the four tree groups: (i) pedunculate oak vital, (ii) pedunculate oak dead, (iii) Turkey oak vital and (iv) Turkey oak dead trees, for the period 1961-2010 (p<0.05, n=60). Similar phenomena had already been observed in the Sava River basin for the growth of pure pedunculate oak forests. The long-term decline of the Danube River water level may be related to climate variations and to the changes of water management, river bed, as well as land-use. Together with the increase of temperature, this decline of the water level, and its potential unavailability in the soil, represents a serious challenge for the mixed oak forests silviculture in the Danube basin

PREDICTION OF PASSENGER CAR FUEL CONSUMPTION USING ARTIFICIAL NEURAL NETWORK: A CASE STUDY IN THE CITY OF NIŠ

The reduction of CO2 emission which is in direct relationship with fuel consumption is of prime importance for the future sustainable use of passenger cars. For the given passenger car, the fuel consumption in urban areas is mostly affected by the conditions related to traffic and driving behavior. In this paper, an artificial neural network model for the prediction of passenger car fuel consumption in the City of Niš was developed based on experimentally measured data recorded through on-board diagnostics equipment. Fuel consumption was assumed to be a function of car speed, a city zone, an hour of day and a day of week. A comprehensive preliminary investigation revealed that single hidden layer artificial neural network model having ten neurons can be efficiently trained with Levenberg-Marquardt algorithm to provide satisfactory prediction accuracy. Finally, the analysis of effects of the selected independent variables on the fuel consumption was discussed based on twelve 3D surface plots

SCADA SYSTEMS IN DISTRICT HEATING – THE IMPACT ON INCREASING ENERGY EFFICIENCY AND THE REDUCTION OF CO2 EMISSION

Improving energy efficiency of district heating systems as a whole is closely related to the application of computer technologies for visualization and control of heat production and distribution. Control in district heating enables fast adjustability of all sub-systems to variations in heat demand. At the same time it enables solving optimal control problems in transition periods like system start and system stop. A district heating system supplies heat to different end-users which can differ in both the quantity of supplied heat and the character of their heat demand. Heat demand of end-users varies with change in outside conditions (outside dry bulb temperature, solar radiation, wind speed and direction etc.), so it is crucial to be able to adjust heat carrier parameters in order to meet the heat demand. This can be achieved only with proper control. In addition, the quality of heat supply can be improved and heat losses reduced, which leads to the reduction in primary energy consumption, the improvement of energy efficiency of the system and, finally, the reduction in green house gasses (GHG) emissions. It is considered that the largest potential of reducing GHG emissions lies in increasing energy efficiency, especially in the district heating sector. Special attention is paid to CO2 emission, since this gas is substantially emitted through anthropogenic activities

Analiza znanja i stavova studenata zdravstvenih studija o upotrebi stimulativnih supstanci u sportu

Background/Aim. Since the beginning of competitive sports, athletes have been trying to improve their abilities by taking various substances. The problem of using prohibited substances is not strictly tied to elite athletes; it is also present in the general population. The aim of this study was to test the knowledge and attitudes of the students regarding the use of stimulative substances and dietary supplements in sports. Methods. A cross-sectional study was performed among students at the College of Health and Professional Studies in Belgrade, Serbia. The data was collected by filling in an especially designed questionnaire. Results. Knowledge of prohibited substances and methods was characterized as 'good' with 24.2% of respondents, namely 8.09% of males and 16.1% of females; knowledge of the adverse effects of prohibited substances and methods on health was demonstrated by 17.7% (9.03% of male respondents and 8.72% of female respondents). Conclusion. Student population is not knowledgeable enough about the problems of prohibited substances use and their negative effects on one's health. The comparative analysis of our and European researches on knowledge, attitudes and uses of prohibited substances show a rather uniform prevalence rate. Not being aware of the adverse effects shows the need to further educate students.Uvod/Cilj. Sportisti oduvek u takmičarskom sportu pokušavaju da poprave svoje sposobnosti uzimanjem različitih supstanci. Problem korišćenja nedozvoljenih supstanci nije vezan isključivo za elitne sportiste, već je prisutan i u opštoj populaciji. Cilj rada bio je ispitivanje znanja i stavova studenata u vezi sa upotrebom stimulativnih supstanci i dijetetskih suplemenata u sportu. Metode. Istraživanje je srovedeno kao studija preseka kod studentske populacije u Visokoj zdravstvenoj školi strukovnih studija u Beogradu. Podaci su prikupljani popunjavanjem posebno dizajniranog upitnika. Rezultati. Dobro znanje o nedozvoljenim supstancama i metodama, pokazalo je 24,2% ispitanika (8,09% muškog pola i 16,1% ženskog pola), a o neželjenim efektima zabranjenih supstanci i metoda na zdravlje, znanje je pokazalo 17,7% ispitanika (9,03% muškog pola i 8,72% ženskog pola). Zaključak. Populacija studenata nema dovoljno znanja o problemu upotrebe nedozvoljenih supstanci i njihovim negativnim posledicama po zdravlje. Komparativna analiza našeg i evropskih istraživanja znanja, stavova i upotrebe nedozvoljenih supstanci ukazuje na približno ujednačene stope prevalencije. Nepoznavanje neželjenih efekata ukazuje na potrebu za dodatnom edukacijom studenata

Future of the Main Important Forest Tree Species in Serbia from the Climate Change Perspective

Background and Purpose: Climate change is possibly the biggest 21st century challenge for the European forestry. Serbia is also under pressure, since the regions of South Europe and Mediterranean are expected to suffer the most. Main purpose of this study was to predict how distribution of several tree species in Serbia may change in the future. Materials and Methods: Our study integrates climate change scenarios for the region of Serbia together with the current distribution of forest tree species. Evaluation was performed using forest aridity index which takes into account mean temperatures and sums of precipitation of the critical months during the growing season. Distribution data of the nine most abundant tree species in Serbia (European beech, Turkey oak, Sessile oak, Hungarian oak, Pedunculate oak, Norway spruce, Silver fir, Black and Scots pine) were taken from the National Forest Inventory. Results: Significant change of bioclimatic niches is expected for the majority of the studied tree species. The most endangered will be Pedunculate oak due to the extreme change of its habitats, while drought prone species (like pines and Hungarian oak) will be less endangered. Sessile oak, Turkey oak, Silver fir, Norway spruce and European beech will be out of their 20th century bioclimatic niches before the end of 21st century according to A2 scenario. Conclusion: Our results suggest that some of the most important tree species in Serbia (Sessile oak, Turkey oak, Silver fir, Norway spruce and European beech) will be endangered by the end of 21st century. General adaption options and specific measurements for forestry sector have to be made for the region of southeast Europe due to the expected extreme change in climate

Uticaj pripreme površine aluminijuma na površinsku refleksiju

Aluminum samples were electrochemically polished in one of three solutions for electrochemical polishing. On those samples the surface reflection was measured. The effect of the anode treatment as the interface between the chemical preparation and electrochemical polishing on the surface reflection was shown. Based on the results it can be concluded that among all the solutions investigated, the most efficient solution for electrochemical polishing is the solution number II. Aluminum samples treated with this solution have the greatest reflection. The effects of temperature change and stirring on the aluminum reflection were also investigated. It was shown that mirror brightness of metal surfaces can be associated with the high degree of mirror reflection which approaches very nearly the ideal reflectance of the same metal, with the small degree of diffuse reflection.Uzorci aluminijuma su podvrgavani elektrohemijskom glačanju u jednom od tri rastvora za elektrohemijsko glačanje. Na tako pripremljenim uzorcima merena je površinska refleksija svetlosti. Pokazan je i uticaj anadne obrade kao među faze između hemijske pripreme i elektrohemijskog glačanja na refleksiju aluminijuma. Na osnovu dobijenih rezultata može se zaključiti da je od ispitivanih rastvora za elektrohemijsko glačanje, najefikasniji rastvor II. Uzorci aluminijuma tretirani u ovom rastvoru imaju najveću refleksiju. Takođe je ispitivan i uticaj promene temperature i mešanja rastvora na refleksiju aluminijuma. Pokazano je da se ogledalski sjaj metalnih površina može povezati sa visokim stepenom ogledalske refleksije svetlosti, koji se približava idealnoj refleksivnosti istog metala, uz što manji stepen difuzne refleksije

Uticaj pripreme površine aluminijuma na površinsku refleksiju

Aluminum samples were electrochemically polished in one of three solutions for electrochemical polishing. On those samples the surface reflection was measured. The effect of the anode treatment as the interface between the chemical preparation and electrochemical polishing on the surface reflection was shown. Based on the results it can be concluded that among all the solutions investigated, the most efficient solution for electrochemical polishing is the solution number II. Aluminum samples treated with this solution have the greatest reflection. The effects of temperature change and stirring on the aluminum reflection were also investigated. It was shown that mirror brightness of metal surfaces can be associated with the high degree of mirror reflection which approaches very nearly the ideal reflectance of the same metal, with the small degree of diffuse reflection.Uzorci aluminijuma su podvrgavani elektrohemijskom glačanju u jednom od tri rastvora za elektrohemijsko glačanje. Na tako pripremljenim uzorcima merena je površinska refleksija svetlosti. Pokazan je i uticaj anadne obrade kao među faze između hemijske pripreme i elektrohemijskog glačanja na refleksiju aluminijuma. Na osnovu dobijenih rezultata može se zaključiti da je od ispitivanih rastvora za elektrohemijsko glačanje, najefikasniji rastvor II. Uzorci aluminijuma tretirani u ovom rastvoru imaju najveću refleksiju. Takođe je ispitivan i uticaj promene temperature i mešanja rastvora na refleksiju aluminijuma. Pokazano je da se ogledalski sjaj metalnih površina može povezati sa visokim stepenom ogledalske refleksije svetlosti, koji se približava idealnoj refleksivnosti istog metala, uz što manji stepen difuzne refleksije

Analysis of the frequency and characteristics of the most common predictors of anxiety in adolescents

Anxiety represents the behavioral, emotional and cognitive response of the person on experience if potential or future danger. Pathological anxiety occurs when this reaction is unreasonable, that is it is not proportionate to the stress or challenge, and it leads to intense fear, nervousness and impaired functioning. Anxiety can occur in any period of life. Adolescence is a turbulent developmental period that increases the risk of young people to develop numerous mental disorders. Numerous predictors determinate the development of anxiety in adolescents. Prevention of anxiety disorders in adolescents is a public health priority, therefore it is necessary to identify risk factors and implement activities to suppress these factors