Self-assembly of carbon based nanoparticles films by Langmuir-Blodgett method

Carbon nanoparticles are a class of materials with extraordinary properties. In the past three decades, four major types of carbon nanoparticles were synthesized and investigated: fullerenes, carbon nanotubes, graphene and carbon quantum dots. One of the main properties of such materials is their hydrophobic nature. At the same time, Langmuir–Blodgett (LB) method the for deposition of thin films of hydrophobic materials provides the possibility to design thin films of different carbon-based nanoparticles with special architectures and features enabling their usage in various fields, particularly in electronics and biomedicine. In this review, the state of art of LB thin films of four types of carbon-based nanoparticles and their application in electronics and biomedicine are presented. The breakthrough in this field was finally achieved by application of carbon quantum dots soluble in solvents optimized for LB deposition

Stability of zirconia sol in the presence of various inorganic electrolytes

Zirconia sol was prepared from zirconium oxychloride solutions by forced hydrolysis at 102ºC. The prepared sol consisted of almost spherical, monoclinic, hydrated zirconia particles 61 nm in diameter. The stability of zirconia sol in the presence of various inorganic electrolytes (LiCl, NaCl, KCl, CsCl, KBr, KI, KNO3, and K2SO4) was studied by potentiometric titration method. Dependence of the critical concentration of coagulation (CCC) on the dispersion pH was determined for all studied electrolytes. The critical coagulation concentration values, for all investigated electrolytes, are lower at higher pH. These values for all 1:1 electrolytes are equal in the range of experimental error. For a given pH value, CCCs of K2SO4 are 3-4 orders of magnitude lower than the corresponding values for 1:1 electrolytes. [Projekat Ministarstva nauke republike Srbije, br. III 45012

Classical stability and quantum instability of black-hole Cauchy horizons

For a certain region of the parameter space $\{M,e,\Lambda\}$, the Cauchy horizon of a (charged) black hole residing in de Sitter space is classically stable to gravitational perturbations. This implies that, when left to its own devices, classical theory is unable to retain full predictive power: the evolution of physical fields beyond the Cauchy horizon is not uniquely determined by the initial conditions. In this paper we argue that the Cauchy horizon of a Reissner-Nordstr\"om-de Sitter black hole must always be unstable quantum mechanically.Comment: 4 pages; uses ReVTeX; figure available upon request to [email protected]

Synthesis and characterization of Cu-ZrB2 alloy produced by PM techniques

The copper alloy with 7vol.% ZrB2 examined in this study was consolidated via powder metallurgy processing (PM) by combining mechanical alloying and hot pressing process. Structural changes, morphological properties and elemental analysis of the hotpressed samples were studied as a function of milling time with the use of X-ray diffraction, scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometry (EDS). Also, mechanical properties of the Cu-7vol.%ZrB2 alloy was investigated. Distribution of ZrB2 particles and presence of agglomerates in the Cu matrix directly depend on the milling time and show strong influence on hardness, compressive and electrical properties of Cu-ZrB2 alloys. [Projekat Ministarstva nauke Republike Srbije, br. 172005

A model of integrated practice in initial education of pre-school teachers

Već se duži niz godina govori o važnosti i značaju prakse studenata u osposobljavanju za poslove i zadatke koji se od njih očekuju. Uloga prakse (praktikuma) unutar institucijskog konteksta središnje je područje u kome se ostvaruje pripremanje studenata za budući profesionalni život. Međutim, iako se stalno ukazuje na neophodnost efikasnijeg i kvalitetnijeg pripremanja, dakle, obrazovanja i osposobljavanja studenata budućih vaspitača kao refleksivnih praktičara, do značajnih pomaka još uvek nije došlo. I dalje je prisutno izvesno nerazumevanje i nepoverenje u metodičke koncepcije iskustvene, problemske, grupne i saradničke nastave koje integrativni i refleksivni pristup učenju uzimaju kao načela delovanja. Predmet istraživanja koje će biti predstavljeno je razvijanje i provera novog nastavnog predmeta Integrativna praksa i utvrđivanje njegovog doprinosa u profesionalizaciji budućih vaspitača. Reč je o nastavnom predmetu organizovanom u trajanju od jednog semestra (VI semestar), koji u najkraćem možemo opisati kao pokušaj realizacije integrativnog procesa u nastavi kroz praktičnu obuku studenata. Istraživanje čini deo napora da se, s jedne strane, razviju savremeni strateški pristupi nastavi koji se odnose na integrativno učenje i obrazovanje studenata kao kreatora integrativnog pristupa u radu sa decom predškolskog uzrasta, kao istraživača realnih procesa učenja i stvaranja znanja kroz projekatski pristup u radu sa decom, i da se, sa druge strane, otkriju i istraže odlike obrazovanja budućih vaspitača za refleksivnu praksu i doprinese njihovom razvijanju kao budućih refleksivnih praktičara. Posebno nas je zanimalo da, na uzorku od 60 studenata, polaznika nastavnog predmeta Integrativna praksa, ispitamo koliko sadržaj ovog nastavnog predmeta i način organizovanja nastave doprinose razvoju studenata, budućih vaspitača kao refleksivnih praktičara. Rezultati istraživanja upućuju na nekoliko opštih zaključaka vezanih za implicitne teorije studenata - shvatanje deteta, vaspitača, nastavnika, učenja i podučavanja: Prvi - postoje dva različita viđenja (ispitivanih problema), dve različite slike – eksplicitna i implicitna, i njihovo „mešanje“, nadjačavanje u zavisnosti od korišćene tehnike. Naime, odgovori u upitniku govore o uverenjima koja su bliža savremenim naučnim saznanjima (usmerenost prema detetu i učenju, viđenje vaspitača/nastavnika kao partnera i saradnika, učenja kao razmene), dok su odgovori dati putem crteža bliži tradicionalnom pristupu (dete je najveća vrednost, objekat ljubavi, ali bespomoćno i zavisno od odraslih; vaspitač je uzor, prenosilac znanja, neko ko brine o deci, drugi roditelj; nastavnik je model, autoritet). Odgovori o učenju i podučavanju u visokom procentu imaju konstruktivističku orijenataciju i transakcijski model podučavanja. Analiza uverenja o učenju i podučavanju pokazala je da studenti visoko procenjuju važnost usmerenosti prema detetu i učenju, što ukazuje na odmak od njihovih uverenja o ulozi vaspitača, nastavnika, deteta identifikovanih u analizi crteža...The importance and relevance of students´ practice the purpose of which is to enable them to perform the activities and tasks expected of them has been a topic for discussion for many years. The role of practice (a practicum) within an institutional context is a central point at which the preparation of students for their future careers takes place. However, although the necessity for a more efficient and quality preparation, i.e. for the education of future reflexive practitioners, has been constantly emphasised, no significant progress has been achieved so far. Even now, there still exist a misunderstanding about and mistrust of methodical concepts of experiential, problem, group and collaborative teaching upon which the integrated and reflexive approach to education is based. The subject of the research which is presented here is the development and testing of the new course Integrative practice and determining its contribution to professionalisation of future pre-school teachers. It is a one-semester course (taking place during the sixth semester) which can briefly be described as an attpempt at realisation of an integrated teaching process by means of practical training of students. On the one hand, the research is a part of an effort to develop modern strategic approaches to teaching relating to integrated learning and education of students as creators of an integrated approach in a pre-school institution, as well as the researchers of real learning processes and knowledge construction through a project-based approach to working with pre-school children. On the other hand, the research aims at discovering and exploring the characteristics of education of future pre-school teachers with respect to a reflexive practice, which is to contribute to their development as future reflexive practitioners. Starting from the sample comprising sixty students – attendees of the course Integrated practice, the main aim was to explore to which extent the course contents and the manner of its organisation contribute to the development of students, i.e. to future pre-school teachers as reflexive practitioners. The results of the research point to several general conclusions relating to implicit theories of students reflecting their understanding of children, pre-school teachers, teachers, and teaching and learning processes. The first conclusion shows that there are two different viewpoints (of the examined issues), two different images – the explicit and the implicit which mix and build upon each other, depending on the applied technique. Namely, the answers in the questionnaire suggest the beliefs which are closer to modern scientific findings (which focus on children and learning, on the idea of a pre-school teacher/teacher as a partner and a collaborator, on learning as a process of exchange), while those answers which have been given in a form of drawings are closer to traditional approaches (according to which a child is the greatest value, the object of love, a helpless creature depending on the care od the adults; the pre-school teacher is a role model, a provider of knowledge, someone who takes care of children, a second parent; a teacher is a model, an authority). The answers on teaching and learning are mostly constructivist-oriented and point to a transactional model of teaching. The analysis of the standpoints regarding teaching and learning revealed that students have high regard for the importance of the orientation towards a child, which testifies to the departure from their beliefs regarding the role of a pre-school teacher and a child depicted in the analysed drawings. However, the behaviour of students is more closer to the answers given in a form of drawings (to their implicit theories)..

Thermal ageing and γ-radiation resistance of polyisoprene /chlorosulphonated polyethylene rubber blends

The effect of carbon black (average particle size 26nm) and wood flour (particle size from 300 to 400 μm) on thermal ageing and γ-radiation resistance of polyisoprene /chlorosulphonated polyethylene rubber blend (NR/CSM) was studied. The tensile strength of the aged samples was determined, after conditioning at 70°C during 72h. The radiation exposure of samples was performed at two doses: 212 and 400 kGy.Physical chemistry 2008 : 9th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 200