Critical neural networks with short and long term plasticity

In recent years self organised critical neuronal models have provided insights regarding the origin of the experimentally observed avalanching behaviour of neuronal systems. It has been shown that dynamical synapses, as a form of short-term plasticity, can cause critical neuronal dynamics. Whereas long-term plasticity, such as hebbian or activity dependent plasticity, have a crucial role in shaping the network structure and endowing neural systems with learning abilities. In this work we provide a model which combines both plasticity mechanisms, acting on two different time-scales. The measured avalanche statistics are compatible with experimental results for both the avalanche size and duration distribution with biologically observed percentages of inhibitory neurons. The time-series of neuronal activity exhibits temporal bursts leading to 1/f decay in the power spectrum. The presence of long-term plasticity gives the system the ability to learn binary rules such as XOR, providing the foundation of future research on more complicated tasks such as pattern recognition.Comment: 8 pages, 7 figure

Achievement tests in school practice

У раду се разматрају могућности примене тестова знања у школској пракси, карактеристике примењених тестова и начини на које се могу користити резултати добијени тестовима знања. Иако тестови знања нису нов истраживачки проблем, последњих деценија дошло је до промена на плану теорија тестирања и приступа конструкцији теста. Намера истраживача је била да се постојећа сазнања у вези са тестовима допуне испитивањем методолошких карактеристика тестова знања који се користе у нашој школској пракси. У истраживању је коришћена дескриптивно-аналитичка метода, технике анкетирања, скалирања, анализе садржаја и интервјуисања. Испитивање је реализовано на узорку од 362 наставника предметне наставе. Истраживањем је утврђено да су могућности за примену тестова релативно повољне, али се могу унапређивати, изменама у сфери иницијалног професионалног образовања и стручног усавршавања наставника. Резултати тестова знања користе се превасходно у сврхе сумативне евалуације, уз извесно препознавање потенцијала који примена тестова може имати и у домену формативне евалуације. Када је реч о могућностима примене тестова знања и начинима коришћења резултата добијених тестирањем, године радног стажа у већој мери објашњавају разлику у одговорима испитаника у односу на предмет који наставници предају. Анализом чији циљ је био да се опишу методолошке карактеристике тестова обухваћено је 80 тестова знања израђених за потребе наставе српског језика и математике. Овог пута, регистроване су значајне разлике у појединим карактеристикама тестова. Методолошка знања наставника разликују се у доменима препознавања фаза конструкције теста, карактеристика различитих типова задатака, нивоа знања који се тестом могу мерити и стандардизације услова тестирања.This paper concerns potentials for applying achievement tests in school practice, characteristics of applied tests and ways in which testing results can be used. Although achievement tests are not a new research topic, over the past decades changes have occurred in testing theory and construction of achievement tests. Our intention was to complement relevant scientific findings with new findings about the characteristics of tests applied in our school practice. The research was implemented using the descriptive method, techniques of survey, scaling, content analysis and interviews. Field research was conducted on a sample of 362 elementary school teachers. Results show that potentials for applying achievement tests are good, but they can be promoted according to changes in initial professional education and vocational training of teachers. Testing results are commonly used for the purpose of summative evaluation, with some tendency toward using results for the purpose of formative evaluation. Referring to potentials for applying tests and ways in which testing results are used, differences between teachers’ opinions are better explained considering years of teachers’ practice service than considering subject domains that they teach. Aiming to describe methodological characteristics of applied tests, we analyzed 80 achievement tests applied in courses of Serbian language and mathematics. This time, significant differences were found between the characteristics of the tests. Methodological knowledge of teachers differs in domains of identifying phases in test construction, characteristics of some types of questions, levels of knowledge that can be measured by a test and standardization of testing requirements

Anatomical characteristics of two Ornithogalum L. (Hyacinthaceae) taxa from Serbia and Hungary and their taxonomic implication

Anatomical characters of two morphologically similar Ornithogalum taxa, O. umbellatum and O. divergens, were investigated. An analysis of leaf and scapus cross-sections was performed on plants from ten populations from Serbia and Hungary, using light microscopy. The aim of this research was to give data about the qualitative and quantitative anatomical characteristics of these taxa, in order to evaluate their taxonomic significance and single out distinctive anatomical features, as well as to contribute to the knowledge of the genus Ornithogalum in the studied region. On the basis of the variability of anatomical characters, similar populations formed two clusters, joining the plants previously determined as O. divergens and O. umbellatum. The two taxa significantly differed for most of the quantitative leaf and scapus characters. Since only quantitative differences were recorded in this research, anatomical characters could not be solely used to separate these two taxa. However, the results of anatomical investigations are consistent with the results of previous morphological and genetic analyses; therefore anatomical parameters could be useful as additional taxonomic characters

"Thermal diffusivity and electron transport properties of NTC samples obtained by photoacoustic method

Poster presented at the Seventh Yugoslav Materials Research Society Conference - YUCOMAT 2005, Herceg Novi, Crna Gora, September 12-16, 2005

Photoacoustic properties of single crystal PbTe(Ni)

Single crystals of PbTe(Ni) were investigated by the photoacoustic method. They were produced using the Bridgeman method. These crystals have a sodium chloride cubic lattice and could be cleaved paralel to the plane orientation (200). They were of the n-type. Phase and amplitude photoacoustic spectra were measured using a transmision detection configuration set-up. Photoacoustic (PA) spectra (single and normalized) were numerically analyzed using the Rosencwaig-Gersho model. Thermal diffusivity and some electron-transport parameters were determined. These results were compared with existing results for pure single crystal PbTe. Thermal difusivity of PbTe(Ni) is a bit higher than the thermal difusivity of pure PbTe. This is the consequence of a decreasing concentration of the majority free carriers in the doped alloy

Structural adaptation of Salsola soda L. (Chenopodiaceae) from inland and maritime saline area

The microscopic analysis of leaf and stem in two populations of Salsola soda was carried out in order to examine mechanism of anatomical adaptations to environmental condition on saline habitats and to determine if there exists a morpho-anatomical differentiation between populations from maritime and inland saline area. Analysis included 26 quantitative characters of leaf and stem. The results showed that both populations exhibited halomorphic and xeromorphic adaptations, which refered to ecological plasticity and adaptations of plants to their habitats. Our research also showed that S. soda had quite a stable morphoanatomical structure, since only quantitative changes were recorded. [Projekat Ministarstva nauke Republike Srbije, br. 173002

Thermal diffusivity of sintered 12CaO×7AI2O3

Poster presented at the 14th International Conference on Photoacoustic and Photothermal Phenomena, Cairo, Egypt, January 6-9, 2007Paper: [http://dx.doi.org/10.1140/epjst/e2008-00423-7

Far infrared properties of iron doped single crystal PbTe

Far infrared reflectivity spectra of single crystal PbTe samples doped with 0.2 at% Fe were measured in the temperature range between 10 K and 300 K. These spectra show very sharp and narrow dips below 120 cm-1. The experimental data were numerically analyzed using a fitting procedure based on the plasmon-phonon interaction model. Two local modes were observed. The first one was noted between 130 cm-1 and 170 cm-1 depending on the temperature and the second more frequency stable one was noted at about 230 cm-1

Mikromorfološke karakteristike ahenije populacija divljih, jednogodišnjih vrsta suncokreta

The aim of this research is to characterize wild annual sunflowers on the basis of achene micro-morphology. Plant material was grown up on an experimental field of the Institute of Field and Vegetable Crops in Novi Sad during 2015. Achene samples were hand-collected at the time of physiological maturity. Morphological measurements of achenes were performed using stereoscopic microscope Leica MZ16 with Leica DFC 320 Camera. The micro-morphological diversity of achenes was assessed using scanning electron microscopy (SEM). Obtained results indicated the presence of some quantitative and qualitative differences in achene characteristics among analyzed species, such as in their size, color, carpopodium and stylopodium shape, and distribution of trichomes on the achene surface. The carpopodium of examined species was asymmetrical at the maturity. Differences in the cuticle and wax ornamentation in different parts of the achenes, on the anticlinal walls of epidermal cells, were identified. The SEM analysis revealed the presence of non-glandular, multicellular bi-seriate trichomes (twin hairs) on the achene surface. This trichome type consisted of two elongated, parallel cells of different length. Considering the distribution of trichomes among the apical, median and basal regions of the fruit, most of the species demonstrated greater trichome density in the apical part.Cilj istraživanja u ovom radu je karakterizacija jednogodišnjih vrsta suncokreta na osnovu mikromorfoloških parametara ahenije. Biljni materijal uzgajan je na eksperimentalnom polju Instituta za ratarstvo i povrtarstvo u Novom Sadu. Uzorci ahenija sakupljani su ručno tokom 2015. godine, u vreme fiziološke zrelosti. Morfološka merenja izvršena su primenom stereoskopskog mikroskopa Leica MZ16 sa Leica DFC 320 kamerom. Mikromorfološke karakteristike analizirane su pomoću skening elektronskog mikroskopa (SEM). Dobijeni rezultati ukazuju na prisustvo kvalitativnih i kvantitaivnih razlika između analiziranih vrsta, u parametrima kao što su veličina i boja ahenije, karakteristike karpopodijuma i stilopodijuma, kao i distribucija trihoma. Pronađena je razlika u ornamentici kutikule i voska antiklinih zidova epidermalnih ćelija na različitim delovima ahenije. SEM analiza ukazala je na prisustvo nežlezdanih, višećelijskih, biserijatnih trihoma (twin hairs). Navedeni tip trihoma sastoji se od dve izdužene, paralelne ćelije različite dužine. Imajući u vidu različitu raspodelu trihoma na apikalnom, medijalnom i bazalnom delu, većina vrsta se karakteriše najvećom gustinom trihoma u apikalnom delu ahenije

Thermal Diffusivity of Sintered 12CaOx7Al2O3

Poster presented at the 14th International Conference on Photoacoustic and Photothermal Phenomena, Cairo, Egypt, January 6-9, 200