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Demonstracijski prototip Kibbleove vage izrađen je prilagodbom stare laboratorijske vage [1]. Za to su izrađeni odgovarajuće nosači te ugrađeni neodimijski magneti, zavojnice, laser i električni priključci. U odnosu na originalnu LEGO vagu [2] uvedena su poboljšanja tako da su zavojnice i laser fiksirani na postolju, a gibaju se magneti i zrcalo koje reflektira lasersku zraku. Na taj način dovodne žice nisu smještene na pokretnim dijelovima vage i ne ometaju njezin rad. Brzina gibanja magneta mjeri se praćenjem laserskog spota pomoću kamere. Posebnost vage je u tome što određuje masu isključivo na temelju kinematički i električni podataka: brzine magneta, induciranog napona i struje kroz zavojnicu, bez usporedbe s utegom poznate mase. To je ujedno i glavna prednost nove definicije kilograma, s tim da su električne mjerene veličine povezane s Planckovom konstantom. Povezivanje Planckove konstante s makroskopskim svijetom rezultiralo je dvjema Nobelovim nagradama i novom definicijom kilograma 2019. godine. Rad s vagom podrazumijeva poznavanje koncepata magnetske sile, elektromagnetske indukcije, harmonijskog titranja, rezonantne frekvencije te rada s generatorom signala, osciloskopom i programom za video analizu. Zbog toga Kibbleova vaga može poslužiti kao praktikumska vježba u kojoj se koncepti opće fizike izvrsno mogu nadovezati na složenije koncepte kvantne fizike. [1] S. Matko, Mjerenje mase Kibbleovom vagom: Nova definicija kilograma, diplomski rad, Prirodoslovno-matematički fakultet u Splitu, voditelj I. Aviani, Split 2020. https://www.bib.irb.hr/1106281 [2]. L. S. Chao et. al, A LEGO Watt balance: An apparatus to determine a mass based on the new SI, Am. J. Phys. 83, 913 (2015), https://doi.org/10.1119/1.4929898

Plasma technologies today are taking attention in the development of emerging advanced materials of new generation due of its unique properties, broadness of applications and effectiveness of treatment. Plasma processing of materials is increasingly used in industrial, technological and medical applications. This work is based on innovative laser synthesis of colloidal nanoparticle solutions and their applications. Laser synthesis of nanoparticles is based on a process of laser ablation of metallic or metal-oxide targets immersed in liquids and it is known as ‘green’ and versatile synthesis route (no chemicals involved in the synthesis) allowing synthesis of pure nanoparticles of wide variety of materials. Nanoparticle applications to be discussed: - Metal oxide nanoparticles as solid contact in ion-selective electrodes sensitive to potassium ions - Controlling the composition of plasma-activated water by Cu ions - Bacteria Exposed to Silver Nanoparticles Synthesized by Laser Ablation in Water: Modelling E. Coli Growth and Inactivation - Photodegradation of Methylene Blue and Rhodamine B Using Laser-Synthesized ZnO Nanoparticles

In nanoscience and nanotechnology, nanoparticles have a significant role due to their unique magnetic, electrical, mechanical, optical, and electronic properties with respect to the bulk materials [1]. Zinc oxide (ZnO) is one of the most widely used materials with unique physicochemical properties and direct band-gap energy of 3.37 eV [2]. Introducing a new element in the crystal structure of ZnO leads to enhancement of the electrical and optical properties and broadens the area of its application [3]. Pulsed laser ablation in liquid (PLAL) gained a lot of attention due to the simplicity, effectiveness, high purity, and fast production of nanoparticles [4], while a wide range of parameters can be optimized [5, 6]. In this work, a simple two-step method for the synthesis of silver (Ag), gold (Au), and platinum (Pt) doped ZnO nanoparticles have been developed. The method is based on the fabrication of targets using pulsed laser deposition (PLD) technique where thin layers of metals (Ag, Pt, Au) have been deposited on a ZnO substrate. Such formed two-layer structures were used as a target for the production of doped nanoparticles (ZnO: Ag, ZnO: Au, and ZnO: Pt) by pulsed laser ablation in water. The optical properties, crystalline structure, elemental composition, morphology, and nanoparticle size distribution were studied using UV-VIS spectrophotometer, Xray diffraction (XRD), X-ray spectroscopy (XPS), scanning electron microscope (SEM), and atomic force microscope (AFM), respectively.

Polymer surface modification has gained a lot of interest over the last few decades. The surface modification offers new physical and chemical properties to polymers by changing their surface properties or incorporating metal or metal oxide nanoparticles [1, 2]. Nanoparticles have a significant role due to their unique magnetic, electrical, mechanical, optical, and electronic properties with respect to the bulk materials. Zinc oxide (ZnO) is one of the most widely used materials with unique physicochemical properties and direct band-gap energy of 3.37 eV, making him a good UV absorber [3]. Polymer/nanoparticle composites gain attention due to their excellent properties for applications in the food industry, biomedicine, biotechnology, optoelectronics, etc. In this work, PVC (polyvinyl chloride) and HDPE (high-density polyethylene) polymers were treated with an atmospheric pressure plasma jet using helium as a working gas. The ZnO colloidal solution was synthesized using pulsed laser ablation in water. After plasma treatment, ZnO colloidal solution was dropped on the polymer surface, and, finally, the polymer was treated again with helium plasma. Optical emission spectroscopy (OES) was used to determine the elemental composition of plasma. All polymer samples (treated and untreated) were characterized using Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The ZnO optical properties, crystalline structure, elemental composition, morphology, and nanoparticle size distribution were studied using UV-VIS spectrophotometer, X-ray diffraction (XRD), X-ray spectroscopy (XPS), and scanning electron microscope (SEM), respectively.

This work is motivated by the possibilities of applying the bactericidal effect of silver nanoparticles to resistant bacterial strains, which represent one of the greatest scientific challenges of today. The goal of this research is to better understand the bactericidal effect of silver nanoparticles. For this research, it was necessary to synthesize pure colloidal nanoparticles, and to carefully control the growth of the untreated and treated bacteria to detect and understand changes that occur during treatment. The work resulted in a PhD thesis in biophysics.

In this paper a model for quantitative and calibration-free determination of colloidal metal nanoparticle diameter and concentration synthesized by laser ablation in water is developed. Model is valid under assumption that total ablated material is transferred into nanoparticles which is proved by Mie theory under dipole approximation and Beer Lambert law using experimentally determined ablated crater volumes, size distributions and photoabsorbances. The novelty of the model manifests in the possibility of determination of nanoparticle diameter and concentration using only volume (or mass) of ablated crater and UV-Vis photoabsorbance spectrum. It allows fast, accurate and simple colloidal metal nanoparticle quantitative analysis without use of electron microscopy, mass spectrometry or relevant experimental techniques.

Razumijevanje koncepata vezanih uz električnu vodljivost čvrstih tvari započinje već u osnovnoj školi putem makroskopskih modela te se razvija sve do kvantnomehaničkih modela u okviru specijaliziranih kolegija, poput Fizike čvrstog stanja. Unatoč tome, edukacijska istraživanja ukazuju na brojne konceptualne poteškoće o spomenutom fenomenu, posebice kada se sagledavaju s razine mikroskopskih modela. Poznavanje učeničkih konceptualnih poteškoća može nastavnicima poslužiti za poticanje učeničkih rasprava i kreiranje kurikulumskih materijala s ciljem efektivnijeg korištenja mikroskopskog fizikalnog modela električne vodljivosti čvrstih tvari.

Introduction Silver nanoparticles are one of the most commercialized types of nanoparticles, with a wide range of applications owing to their antimicrobial activity. However, there is a lack of data on cumulative toxicity of silver nanoparticles used with polymeric materials, especially polymer nanoparticles. In this study, toxicity of PVP-coated silver nanoparticles (AgNP) combined with polystyrene nanoparticles (PSNP) was tested on Jurkat cells. Results Silver and polystyrene nanoparticles reduced cell viability through generation of reactive oxygen species (ROS), depletion of cellular GSH, and damage to cellular structures and mitochondria. Nanoparticle treatment also reduced cell stiffness, measured by Atomic Force Microscope (AFM), which is indicative of changes in cytoskeletal structure. Cellular treatment with combinations of non-toxic AgNP and PSNP concentrations resulted in significant induction of oxidative stress and reduction of cell viability. Conclusions AgNP share the mechanism of toxicity with PSNP and results for combined AgNP/PSNP treatments can be understood as compounded effect of overloading cellular mechanisms for managing oxidative stress. These results have important implications for use of these materials in medical contexts, particularly for long-term medical implants.

Predstavljamo primjer istraživački usmjerene online nastave kreirane na originalan način uz pomoć virtualnog laboratorija s internetske stranice GoLabz te Google obrasca koji omogućuje jednostavnu transakciju sadržaja, kao i statistički uvid u povratne informacije učenika. U radu je prikazana metoda samostalnog učenja učenika prvih razreda srednje škole na temu Elastična potencijalna energija. Učenje se sastoji od tri dijela. Prvi dio započinje opažanjem pojava unutar virtualnog laboratorija i postavljanjem hipoteza na temelju opaženog. Ispituje se ovisnost elastične potencijalne energije o pojedinim varijablama. Koristeći se analizom rezultata mjerenja, učenici provjeravaju ispravnost postavljenih hipoteza. Drugi dio posvećen je teorijskom razmatranju u kojem učenici trebaju pročitati i pogledati videozapise koji pobliže objašnjavaju navedenu nastavnu temu. U posljednjem dijelu nastavnik provjerava znanje učenika u vidu različitih konceptualnih i numeričkih zadataka koji predstavljaju problemske situacije iz svakidašnjeg života.

Iznosimo primjer istraživački usmjerene online nastave za učenike drugog razreda srednje škole na temu Rad i snaga električne struje. Lekcija je pripremljena uz pomoć virtualnih laboratorija na Go- Lab portalu te Google obrasca koji nam je, uz prenošenje sadržaja, dao uvid u statistiku uspješnosti nastave. Napravljeni su i odgovarajući web sadržaji koji uključuju pred-kviz za ponavljanje te tekst teorijskog objašnjenja lekcije. Istraživački pristup ostvaren je pomoću virtualnog laboratorija u kojemu se snaga grijača određivala mjerenjem brzine promjene temperature vode u kalorimetru. U drugom virtualnom laboratoriju mjerila se ovisnost snage žarulje o njezinom otporu uz konstantni napon i o naponu uz konstantni otpor. U istraživanju je sudjelovalo 19 učenika iz gimnazije u Splitu. Analizom i sintezom rezultata vlastitih mjerenja učenici su trebali formulirati matematički izraz za snagu električne struje. Na kraju su ispunjavali upitnik s konceptualnim pitanjima te zadacima vezanim uz svakodnevni život, koji provjeravaju sposobnost primjene usvojenog znanja. Rezultati istraživanja ukazuju na učeničke poteškoće, najčešće u crtanju i interpretaciji grafova. Učenici su prihvatili metodu rada te su je smatrali zanimljivom i korisnom.

Predstavljamo primjer nastavnog sata s temom Stefan- Boltzmannovog zakona kojeg započinjemo motivacijskim pitanjima: Koliko bi iznosila prosječna temperatura Zemlje kada ne bi postojala atmosfera? Koja je uloga atmosfere? Kako nastaje globalno zatopljenje? Kroz odgovore na postavljena pitanja dolazimo do Stefan- Boltzmannovog zakona i njegove primjene. U laboratorijskom eksperimentu, koji se zasniva na mjerenju I-V karakteristike žaruljice sa žarnom niti, pokazujemo proporcionalnost snage žaruljice i četvrte potencije temperature žarne niti. PHET simulacijom pokazujemo utjecaj atmosfere na temperaturu Zemlje te uspoređujemo temperaturu Zemlje iz simulacije s temperaturom Zemlje izračunatom u okviru jednostavnog modela zasnovanog na Stefan- Boltzmannovom zakonu. Staklenički učinak atmosfere objašnjavamo pomoću analognog modela temeljenog na punjenju i pražnjenju rezervoara s vodom, pri čemu je voda energija, a razina vode u rezervoaru temperatura Zemlje. Na kraju sata objašnjavamo primjene zakona zračenja u svakodnevnom životu.

Introduction: Tropaeolum majus L. altum is a plant that belongs to Tropaeolaceae family and is known for its ornamental and medicinal properties [1]. It contains benzyl glucosinolate (glucotropaeolin) whose degradation product benzyl isothiocyanate shows various biological activities such as anticancer, antimicrobial and anti-inflammatory [2, 3, 4]. Objectives: The aim of this study was to investigate the anticancer activity of T. majus essential oil against human bladder cancer cell line TCCSUP and to determine if membrane alterations are a part of the anticancer mechanism of T. majus essential oil. Materials & methods: The essential oil of T. majus seeds was obtained by microwave-assisted distillation. Gas chromatograph equipped with mass spectrometer was used to identify volatile compounds. The half maximal inhibitory concentration (IC50) of T. majus essential oil was determined against TCCSUP cell line via the MTT assay. Atomic force and optical microscopy were used to detect morphology and membrane changes of cells treated with sub-IC50 concentration. Results: T. majus essential oil has shown anticancer activity against TCCSUP cell line due to high amount of benzyl isothiocyanate. Bright-field microscopy of sub-IC50 concentration treated cells reveals the change in cell morphology and possible membrane blebbing of some cells. Atomic force microscopy analysis suggests notable cell surface alterations/membrane bleb formation as a part of the anticancer mechanism. Conclusion: The T. majus essential oil exhibits anticancer activity against TCCSUP cancer cells by altering cell morphology after exposure with sub-IC50 concentration.

Silver nanoparticles are one of the most commercialized types of nanoparticles, with a wide range of applications owing to their antimicrobial activity.[1] However, there is a lack of data on cumulative toxicity of silver nanoparticles used with polymeric materials, especially polymer nanoparticles. In this study, toxicity of PVP-coated silver nanoparticles (AgNP) combined with polystyrene nanoparticles (PSNP) was tested on Jurkat cells. Silver and polystyrene nanoparticles reduced cell viability through generation of reactive oxygen species (ROS), depletion of cellular GSH, and damage to cellular structures and mitochondria. Cellular treatment with combinations of non-toxic AgNP and PSNP concentrations resulted in significant induction of oxidative stress and reduction of cell viability. Results for combined AgNP/PSNP treatments can be understood as compounded effect of overloading cellular mechanisms for managing oxidative stress. These results have important implications for use of tested nanomaterials in medical contexts.

Interdisciplinarnost ima sve veći značaj u suvremenoj znanosti. Međutim, učenici i studenti fizike često nisu u stanju sagledati fiziku kao cjelinu, niti ju povezati sa srodnim poljima poput kemije i biologije. Jedan od razloga za to je način strukturiranja sadržaja iz fizike koji ne pruža jedinstven fizikalni pogled na svijet. Manjak kohezivnog i objedinjavajućeg pristupa je posebno vidljiv u poučavanju termodinamike. Tako većina učenika i studenata postaje svjesna čestične prirode tvari još u osnovnoj školi, a molekularno-kinetičku teoriju (MKT) proučava u okviru srednjoškolskih i sveučilišnih predmeta iz fizike. No edukacijska istraživanja pronalaze brojne miskoncepcije vezane uz MKT kao i uz njenu ulogu i primjenu u vezanim znanstvenim područjima. Miskoncepcije koje se odnose na molekularne sustave u međudjelovanju, općenito ukazuju na nerazumijevanje makroskopskih pojava na mikroskopskoj razini. Ciljano sagledavanje postojećih pogrešnih ideja uz usporednu izgradnju kvalitetnih fizičkih modela se preporuča kao važan dio konceptualnog okvira za ispravljanje učeničkih miskoncepcija i za kreiranje učinkovitije nastave. Na tragu navedenog, u okviru prve faze projekta „Istraživanje studentskog konceptualnog razumijevanja mikroskopskih modela u termodinamici i razvoj suvremenih metodičkih alata“ (uniri-pr-prirod-19-5 financiranog od strane Sveučilišta u Rijeci) ispituje se studentsko konceptualno razumijevanje MKT čvrstih tijela, nastavno na prethodno provedena istraživanja studentskog razumijevanja MKT plinova i tekućina. U okviru predavanja biti će izloženi najznačajniji rezultati prethodnih istraživanja kao i preliminarni rezultati dobiveni u okviru spomenutog projekta.

Proporcionalno zaključivanje prirodan je način na koji razmišljamo. Intuitivno nam je lako prihvatiti tzv. „jednostavno pravilo trojno“ i na temelju njega zaključiti, primjerice, da nam za dva kilograma jabuka treba 20 kuna, ako kilogram košta 10 kuna. Ova jednostavna logika ne ovisi ni o robi ni o valuti niti o cijeni, a ljudima omogućuje da nesmetano trguju i da argumentirano diskutiraju o najrazličitijim pojavama i odnosima, bez obzira na jezik i kulturu. Znanstvenicima je omogućila da opišu veliki broj prirodnih zakona i zakonitosti. U osnovnoj i srednjoj školi proporcionalnost je osnovni matematički izraz, veza između zavisne i nezavisne varijable, alat kojim se služimo da bi opisali fizičke pojave i logički povezali njihove uzroke i posljedice. I u školi nam se činila korisnom, a negodovali smo uglavnom zbog učenja logaritama, postavljajući pitanja poput: „Čemu služe takva znanja?“, „Imaju li logaritmi ikakve veze s našim svakodnevnim životom?“ i sl. Cilj ovog predavanja je da pokaže kako logaritmi itekako imaju smisla, štoviše, da je priroda same prirode zapravo logaritamska. Promjene u prirodi najčešće ovise o već postojećoj broju jedinki ili količini tvari pa njihov broj, odnosno količina, raste ili pada kao eksponencijalna funkcija vremena - logaritamski. Logaritamska je priroda naših osjetila, priroda energije, ali i struktura prirode. Iz tog razloga, koliko god mala ili velika bila prostorno- vremenska skala na kojoj promatramo objekte, ona će uvijek obuhvaćati približno jednak broj karakterističnih tvorevina. Fizičari su ustanovili da je i temperaturna ljestvica logaritamska te da između temperatura 100 K i 10 K ima jednako toliko „fizike“, kao između 10 i 1 K ili 1 i 0, 1 K pa u potrazi za novim pojavama dosežu sve niže temperature. O svemu navedenom bit će poneka riječ, a predavanje će biti popraćeno nizom primjera iz prirode.

Quaternary ammonium compounds (QACs) have long been praised for their powerful antimicrobial potential. With a wide range of application, from different industries to pharmacy and medicine, these compounds are omnipresent ingredients of many commercial products. However, recent studies show that as much as 83% of MRSA isolates are resistant toward most of the commonly used QACs. Therefore, elucidation of resistance mechanism(s) and development of new potent QACs are in the centre of further research in the field. Quinuclidine is a bicyclic part of alkaloids isolated from a bark of the Cinchona trees. Even though these alkaloids have long been used in a traditional medicine, the biological potential of quinuclidine derivatives is still underexplored. Apart from its anticholinergic, antiparasitic, antioxidative and antitumor activity, some quinuclidine derivatives have been shown to act on FitZ protein, known to be essential for bacterial cell division. All this motivated us to synthesize new quinuclidine containing QACs in order to further explore its antimicrobial potential and to develop new and powerful naturally derived QACs. Our studies have shown that quaternisation of substituted quinuclidine improves its antimicrobial activity by several hundred folds and that this activity depends on the type of substituent used for quaternisation. Aryl- quinuclidines typically had lower antimicrobial activity than their alkyl counterparts. Also, somewhat better antimicrobial activity was observed toward Gram-positive bacteria, suggesting that bacterial membrane might be involved in the mode of action mechanism. Therefore, the PI- uptake measurements were performed along with atomic force microscopy (AFM) and indeed, obtained results indicated bacterial membrane perforation. Moreover, alkyl-quinuclidines, more specifically an identified candidate with the longest alkyl chain, exhibited the best antimicrobial activity with the lowest MIC values across selected panel of the bacteria and good activity toward S. aureus biofilms. In addition, this compound had lower toxicity toward healthy human cell lines than the referent QACs, suggesting that quinuclidine could serve as a new possible core molecule for future QACs development.

Study of bactericidal effect of silver nanoparticles (AgNPs), free of chemical byproducts, could be of great importance in understanding the underlying antibacterial mechanism(s). In this work, we present the production and characterization of AgNPs, synthesized by laser ablation of silver in water, and optical density (OD) growth curves of E. coli cells treated at sub MIC (minimal inhibitory concentration) and MIC concentrations. Besides the increase of the baseline and reduction of the maximal OD, the main impact of the treatment is the increase of the lag time, which becomes infinitive for the MIC treatment. The obtained bacterial growth curves are described by a novel growth and inactivation model given by the set of three differential equations. Our model fits the OD data very well and explains the apparent lag phase, which we found to be a dynamic state in which the bacterial growth and death rates are close in value.

Demonstration experiments are performed by teachers individually or in cooperation with one or more students, at the teachers’ desk, in front of the whole class. It is usually less expensive and less time-consuming than student experiments. The advantage is also that all students have opportunity to observe and participate in an ongoing experiment, directly influencing its course. The teacher can direct student's attention and focus on important details that are essential for understanding the concepts to be adopted. He can discuss relevant questions with students, if necessary, repeat the key parts of the experiments, and carefully scaffold students to the conclusions. Demonstration experiments have an irreplaceable role in the demonstration of dangerous phenomena and materials such as chemicals, boiling water, electricity, fire, etc. It is also convenient for experiments that are expensive. difficult to perform or take a long time. The lecture will demonstrate the use of the demonstration experiment in research-based teaching throug the use of few important experiments from different parts of the high school physics program.

In order to study Kondo ferromagnetism, we have investigated the CexLa1-xPt, and CexY1-xPt alloy systems in the temperature range from 1.8 K to 320 K. While CexY1-xPt show considerable hybridization and, therewith, Kondo effect, in CexLa1-xPt hybridization very weak. By the resistivity measurements, we determined the energetic specter of the 4f level of the Ce3+ ion split by the crystal electrical field (CEF): a doublet and a quasiquartet at 120 K. The magnetic contribution to the resistivity, ρmag, of CexLa1-xPt is nicely scaled to concentration. The ρmag of CexY1-xPt is successfully described by Cornut – Coqblin theory. The minimum in the thermopower which one usually ascribes to Kondo minimum, does not correspond to Kondo effect ; rather to CEF. The dc susceptibility can be described by the Curie-Weiss law down to about 100 K and also above in the vicinity phase transition. The Curie-Weiss constant at high temperature θp, is negative indicating that the interaction between the spin of the Ce ion and conducting electron is antiferromagnetic one. At low temperatures, θC is positive indicating the transition into ferromagetic ordered state. The effective magnetic moment per Ce ion, µef, at the higher temperatures is the same for all alloys of CexLa1-xPt and is close to the theoretical value of the isolated Ce3+ ion, µ = 2.54µB, indicating the hybridization is very weak and, and, consequently, Kondo effects are weak. At low temperatures, µef ≈ 1.5 µB is also the same for all alloys. On contrary, µef of CexY1-xPt at high as well at low temperatures strongly depend on the Ce content, x. These observations confirm the main important conclusions inferred from the investigations of the transport properties of these alloy systems. Although La and Y are nonmagnetic, they have a strong influence on the different magnetic properties of these two systems, but, interestingly enough, they have no considerable effect on the Curie temperature, TC. The TC(x) linearly depends on x and it is about the same for both systems. We show that these systems cannot be considered within Doniach’s diagram. The ac susceptibility shows in CexY1-xPt (x < 1) double-peak structure in the vicinity of the phase transition, TC, which is determined by the resistivity measurements. The peak at lower temperatures corresponds to one- peak structure in CexLa1-xPt reflecting TC. The peak at high temperatures reveal the processes which may be treated as an entrance CexLa1-xPt in a new phase of CexY1-xPt. It is stretched within less than 1 K above TC and it is within the Griffiths phase but has quite different underlying physics. This phase is characterized with long range ordered ferromagnetic fluctuations which do not allow spin fluctuations. i.e., Kondo interaction and thus the Ce3+ is in the stable state just it is in CexLa1-xPt. This explains why TC(x) is the same for both systems and why RKKY interaction is not responsible for the ferromagnetism leading us to the conclusion that direct exchange interaction establishes ferromagnetism in these alloy systems. We believe that the same process takes place in all truly Kondo ferromagnetics. However, it is difficult to be noticed because it takes place in a very narrow temperature interval above TC. In addition, we noticed this process because we investigated two similar alloy systems where in one them, CexLa1-xPt, hybridization is very weak while in the other one, CexY1-xPt, is very strong.

Većina studenata susreće se s čestičnim opisom građe tvari još u osnovnoj školi, a molekularno- kinetičku teoriju proučava u okviru mnogih uvodnih kolegija fizike i kemije te kasnije kroz specijalizirane kolegije, poput termodinamike i statističke fizike. Unatoč tome, edukacijska istraživanja ukazuju na brojne učeničke i studentske miskoncepcije te na slabo razumijevanje mikroskopskog modela tvari. Za kreiranje učinkovitije nastave, preporuča se sagledati postojeće pogrešne ideje kao važan dio učeničkog/studentskog konceptualnog okvira te kvalitetan fizički model izgrađivati uz ispravljanje njihovih miskoncepcija. Konceptualni testovi predstavljaju jedan od suvremenih metodičkih alata za procjenu znanja i detekciju miskoncepcija. Saznavši da ne postoje takvi testovi za procjenu učeničkog/studentskog razumijevanja molekularno-kinetičke teorije, radom [1] nastojali smo dati originalan doprinos području edukacijske fizike. Važan korak u našem pristupu bila je radna pretpostavka da uzrok velikom broju studentskih miskoncepcija mogu biti upravo nelogičnosti i slabosti modela idealnog plina. Osmislili smo konceptualni test s pitanjima višestrukog izbora iz molekularno- kinetičke teorije plina (MKTP). Kao distraktori su nam poslužili odgovori studenata koje smo prethodno intervjuirali, postavljajući im jednaka pitanja otvorenog tipa. Neki od njihovih odgovora potvrdili su već poznate miskoncepcije, dok su drugi (posebice oni koji su se odnosili na međumolekularnu potencijalnu energiju) otkrili neke nove pogrešne ideje. Uz pomoć tako dobivenog testa, ispitali smo studente s različitih Sveučilišta u Republici Hrvatskoj. Ustanovili smo veliku zastupljenost miskoncepcija, nekonzistentnih odgovora te, što je posebno indikativno, sličnu raspodjelu odgovora na većinu pitanja kod svih grupa ispitanika, neovisno o različitim pristupima nastavi s obzirom na nastavni program i godinu studija. [1] Erceg, N., Aviani, I., Mešić, V., Glunčić, M. and Žauhar G. (2016), Development of the kinetic molecular theory of gases concept inventory: Preliminary results on university students' misconceptions, Phys. Rev. Phys. Educ. Res., 12, 020139

There are many growth and inactivation models in the literature which are purely empirical and do not poster a mechanistic insight [1, 2]. Here, we present a novel, intuitive and mathematically relatively simple model for bacterial growth and inactivation. The proposed model well describes E. coli batch culture growth curves obtained for different inoculum sizes and different initial nutrients concentration. The model is, furthermore, expanded in order to fit and explain growth curves obtained for E. coli treated with different concentrations of laser produced silver nanoparticles. The model is described by three nonlinear mutually dependent di erential equations that give time evolution of bacterial, nutrients and nanoparticle concentrations. These equations are of general nature and can be used to predict growth of different bacteria in batch culture since the equations do not include a parameter that is characteristic for E. coli. As our model can be linked to the logistic model, it is possible that the equations could be applicable to any single species growth. [1] M. Peleg and M. G. Corradini, Crit. Rev. Food Sci. Nutr. 51, 917 (2011) [2] K. D. Dolan and D. K. Mishra, Annu. Rev. Food Sci. Technol. 4, 401 (2013)

research based teaching, physical law, physical rule, curriculum

Antimicrobial peptides (AMPs) are endogenous antibiotics present in all organisms acting directly towards pathogens and also showing immunomodulatory properties. Skin secretions of many tested anuran species have been shown to contain a variety of bioactive peptides that often exhibit antibacterial activity, also against multidrug resistant isolates. We have selectively amplified transcripts likely to encode for AMPs, thus providing their sequences. After RNA extraction from frog skin tissue samples, cDNA synthesis followed by PCR amplification was performed. For this purpose, forward degenerate primers were designed based on highly conserved signal peptide regions from Ranidae, Hylidae and Bombinatoridae together with a reverse primer designed on the poly-A tail of mRNA. Signal peptide regions themselves were derived from sequences already available in DADP database and transcriptome data in SRA database. Resulting amplicons were size-selected and processed by ion semiconductor sequencing, obtaining several thousand sequencing reads which were then assembled into contigs representing nearly full-length AMP-encoding transcripts. Analysis of the assembled sequencing output allowed to identify more than a hundred full-length mature peptides from 5 different specimens belonging to 5 different frog species, mostly from Ranidae species. Based on appropriate biophysical properties (e.g. charge, hydrophobicity, amphipathicity) six of the most promising candidates were chosen for chemical synthesis and extensive characterization. All peptides were tested against a panel of Gram-negative and Gram-positive bacteria, as well on tumour cell lines. One peptide, identified in Rana arvalis, proved to be active against both reference ATCC strains and cancer cells, while non-toxic for human MEC-1 cells in a range of concentrations several folds higher then minimal inhibitory concentration (MIC) and IC50 values. Furthermore, the peptide was found to disrupt the bacterial membrane even at sub-MIC concentrations, as observed by flow cytometry and visualised by atomic force microscopy (AFM).

Skin secretions of many tested anuran species have been shown to contain a variety of antimicrobial peptides (AMPs) acting directly towards pathogens, including multidrug resistant isolates, and also showing immunomodulatory properties [1]. We have selectively amplified transcripts likely to encode for AMPs, thus providing their sequences. After RNA extraction from frog skin tissue samples, cDNA synthesis followed by PCR amplification was performed. For this purpose, forward degenerate primers were designed based on highly conserved signal peptide regions [2], together with a reverse primer designed on the poly-A tail of mRNA. Signal peptide regions were derived from sequences deposited in DADP database [3] and transcriptome data in SRA database [4]. Resulting amplicons were size-selected and processed by ion semiconductor sequencing, obtaining several thousand sequencing reads. Those were then assembled into contigs representing nearly full-length AMP-encoding transcripts. Analysis of the assembled sequencing output allowed to identify more than a hundred full-length mature peptides from 5 different specimens belonging to 5 different frog species, mostly from Ranidae species. Based on appropriate biophysical properties (e.g. charge, hydrophobicity, amphipathicity) six of the most promising candidates were chosen for chemical synthesis and extensive characterization. All peptides were tested against a panel of Gram-negative and Gram-positive bacteria, as well on tumour cell lines. One peptide, identified in Rana arvalis, proved to be active against both reference ATCC strains and epithelial cancer cell lines, while less toxic for circulating MEC-1 cells in a range of concentrations several fold higher then minimal inhibitory concentration (MIC) and IC50 values. Furthermore, the peptide was found to disrupt the bacterial membrane even at sub-MIC concentrations, as observed by flow cytometry and visualised by atomic force microscopy (AFM). [1] A. Nijnik and R. Hancock, Emerg. Health Threats J. 2, (2009). [2] V. Tessera, F. Guida, D. Juretić, and A. Tossi, FEBS J. 279, 724 (2012). [3] M. Novković, J. Simunić, V. Bojović, A. Tossi, and D. Juretić, Bioinformatics 28, 1406 (2012). [4] Y. Kodama, M. Shumway, and R. Leinonen, Nucleic Acids Res. 40, D54 (2012).

There are numerous reports of antibacterial activity of the silver nanoparticles (AgNPs) produced by chemical methods [1, 2], but the laser ablation in liquid has been proven to be the most convenient technique for the production of nanoparticles free of chemical byproducts. Here we present the study of AgNPs and the influence these nanoparticles have on the bacteria and their growth kinetics. AgNPs were produced by laser ablation in water and characterized by different experimental methods. In the present literature, there are only few reports on attempts to model the bacterial growth in the presence of nanoparticles [3]. To explain the obtained growth curves of untreated and treated bacterial cells, we have designed the novel microscopic growth model described by three differential equations. Our model gives a good description of the experimentally obtained data.

Na početku sata u kojem se obrađuje nova nastavna cjelina poželjno je odabrati pokus koji će proizvesti neočekivani ishod, nešto što se protivi učeničkom iskustvu. To će zainteresirati učenike i razviti njihovu potrebu za objašnjenjem, odnosno učenjem. Treba ih zamoliti da opišu što su točno vidjeli i čemu se zapravo čude. Poželjno je da pokus i svoja opažanja prikažu crtežom i tekstom u svojoj bilježnici. Budući da su učenici subjektivni promatrači i da događaj vide na različite načine, pokus treba ponavljati i nekoliko puta sve dok se svi učenici ne slože o tome što se sve u pokusu zaista može opaziti. Pravilno opažanje je izuzetno važno jer omogućuje objektivno istraživanje. Sada se može prijeći na istraživanje. Zajednički treba utvrditi što se sve i kako u eksperimentu može mijenjati, odnosno što su varijable. Potom pretpostaviti što će se događati ako se jedna od varijabli mijenja, a druge drže konstantnima te zatim mijenjati tu varijablu i bilježiti promjene. Na temelju takvih opažanja i mjerenja treba ustanoviti na koji način jedna varijabla ovisi o drugoj te pronaći zakonitost. Ona se najčešće svodi na proporcionalnost ili obrnutu proporcionalnost. Prilikom izvođenja pokusa učeničko kognitivno opterećene može se znatno umanjiti ako se na katedri postave isključivo predmeti koji su potrebni za planirani pokus. Nepotrebni predmeti stvaraju samo zbrku i otežavaju zaključivanje. Zbog istog razloga ostale pokuse vezane uz lekciju poželjno je izvoditi na kraju sata, nakon teorijske obrade. Tada će učenici oboružani znanjem i većom mogućnošću predviđanja sa zanimanjem ispratiti preostale pokuse. Prilikom izvođenja istraživački usmjerene nastave pomoću demonstracijskog pokusa poželjno je formativno vrednovanje učenika temeljem njihovih opažanja, razmišljanja, predviđanja, zaključivanja, crteža, grafičkih prikaza itd. Ovakav oblik nastave sadrži u sebi nekoliko osnovnih ciljeva: (i) efikasno učenje fizičkih koncepata i principa temeljem neposrednog vlastitog iskustva, (ii) razvijanje učeničkih sposobnosti istraživanja prirodnih pojava kao generičke vještine, (iii) razvijanje prirodoznanstvenog pristupa, (iv) razvijanje kritičkog mišljenja. Na predavanju će biti prikazana uporaba demonstracijskog pokusa u istraživački usmjerenoj nastavi na primjeru nekoliko važnih pokusa iz različitih cjelina programa fizike za osnovne škole.

There are numerous reports of antimicrobial activity of the silver nanoparticles (AgNPs) produced by different methods (1-2), but the laser ablation in liquid has been proven to be the most convenient technique for the production of nanoparticles free of chemical byproducts. Here we present the study of AgNPs and the influence these nanoparticles have on the bacteria and their growth kinetics. AgNPs were produced by laser ablation in water and characterized by different experimental methods. Their antibacterial activity was observed by different microscopic techniques. In the present literature, there are only few reports on attempts to model the bacterial growth in the presence of nanoparticles. The reported model (3) is just a modification of the empirical Gompertz model. To explain the obtained growth curves of treated and untreated bacterial cells, we have designed the novel microscopic model described by three differential equations. Our model gives a good description of the experimentally obtained data. References: 1. I. Sondi and B. Salopek- Sondi, J. Colloid Interface Sci. 275 (2004) 177-182. 2. G. A. Martinez-Castanon et al., J Nanopart Res 10 (2008) 1343–1348. 3. T. Chatterjee, et al., Biochim. Biophys. Acta 1850 (2014) 299–306.

Površina vode, građena tek od nekoliko desetaka slojeva molekula, sasvim je drugačijih svojstava od ostatka tekućine. Razmatrat ćemo uzroke pojave površinske napetosti vode na molekularnoj skali i učinak sila koje se, zbog toga, pojavljuju na makroskopskoj skali. Bit će riječi o uzrocima pojave supervodoodbojnosti, koji su s jedne strane posljedica strukture površine tijela na mikro- i nano- ljestvici, a s druge strane posljedica površinske napetosti tekućine. Predavanje će biti popraćeno radionicom s pokusima u kojima se demonstriraju mehanička i električna i magnetska svojstva površine vode te pokusima u kojima se prikazuje pojava supervodoodbojnosti.

Koristeći iskustva stečena u radu s nastavnicima i učenicima te najnovija dostignuća magnetizma, razvili smo niz jednostavnih pokusa s neodimijskim magnetima. Dio pokusa direktno prati nastavne programe u osnovnim i srednjim školama, dok ostatak služi kao temelj za dodatnu nastavu i projektne zadatke. Mnoge fizikalne fenomene moguće je prikazati na dojmljiv način, gotovo kao mađioničarski trik. Tako možemo zainteresirati učenike, a jednom kad ih zainteresiramo, pažljivo će slušati naša objašnjenja. Dakako, uz pokus potrebno je ispričati i zanimljivu priču. Zato sam u ovom tekstu opisao nekoliko osnovnih ideja iz povijesti magnetizma te dao i neka temeljna objašnjenja pojave magnetizma. Iako ću na predavanju predstaviti pokuse iz raznih područja fizike ovaj tekst prvenstveno je posvećen magnetizmu tvari koji nije značajnije zastupljen u kurikulumu.

Teaching by analogy is not yet sufficiently used within our practice. This could be partially because of the fear of introducing additional misconceptions to students but also because the teacher could be "accused" of trivializing the important physical concepts. Physics, especially quantum mechanics, mostly relying on an abstract language of mathematics, as such remains difficult to understand or unclear. We are aware that our comprehension of physical phenomena comes from the world accessible to our senses. This is a world of interaction and motion - the world of classical mechanics. Through the use of analogy of our macro world to describe the micro world and noticing similarities among seemingly different processes at different spatial and temporal scales, we set a natural way of thinking, teaching and learning. Analogy, although not completely accurate, can help us to perceive, model and predict the behavior of systems that are invisible to the human eye. This can be illustrated by the examples from history. It is well known that thermodynamics have been developed on the incorrect assumption that heat is a kind of fluid. Regardless of such an assumption, Carnot derived the correct expression for the maximum possible efficiency for any heat- engine. Likewise, although Tesla did not fully master the language of mathematics, his notion of electricity as a fluid enabled him to "see" and to perceive things invisible to the human eye and led him to important discoveries. In fact, it is worth asking is it even possible to understand the world without analogue ideas? The goal of the talk is to discuss the analogies that describe the separation and transport of charge carriers in different materials. The original model of electricity based on the analogy with cars and highway traffic will be introduced. It will be shown that the model easily introduces quantum mechanical description of the electronic bands in solids with both electrons and holes as charge carriers. Note that quantum-mechanical description is necessary for proper understanding of conductivity in metals, semiconductors and insulators as well as operating principles of devices such as transistors, photocells and thermoelectrics.

Predstavljamo projekt izgradnje istraživačkih kapaciteta u MEMS tehnologiji u Hrvatskoj kroz nedavno odobreni projekt financiran iz Europskih strukturnih fondova, zasnovan na suradnji između Sveučilišta i tvrtke u kategoriji malog i srednjeg poduzetništva.

Koristeći iskustva stečena u radu s nastavnicima i učenicima te najnovija dostignuća magnetizma, razvili smo niz jednostavnih pokusa s neodimijskim magnetima. Dio pokusa direktno prati nastavne programe u osnovnim i srednjim školama, dok ostatak služi kao temelj za dodatnu nastavu i projektne zadatke. Mnoge fizikalne fenomene moguće je prikazati na dojmljiv način, gotovo kao mađioničarski trik. Tako možemo zainteresirati učenike, a jednom kad ih zainteresiramo, pažljivo će slušati naša objašnjenja. Dakako, uz pokus potrebno je ispričati i zanimljivu priču. Zato sam u ovom tekstu opisao nekoliko osnovnih ideja iz povijesti magnetizma te dao i neka temeljna objašnjenja pojave magnetizma. Iako ću na predavanju predstaviti pokuse iz raznih područja fizike ovaj tekst prvenstveno je posvećen magnetizmu tvari koji nije značajnije zastupljen u kurikulumu.

Koristeći iskustva stečena u radu s nastavnicima i učenicima te najnovija dostignuća magnetizma, razvili smo niz jednostavnih pokusa s neodimijskim magnetima. Dio pokusa direktno prati nastavne programe u osnovnim i srednjim školama, dok ostatak služi kao temelj za dodatnu nastavu i projektne zadatke. Mnoge fizikalne fenomene moguće je prikazati na dojmljiv način, gotovo kao mađioničarski trik. Tako možemo zainteresirati učenike, a jednom kad ih zainteresiramo, pažljivo će slušati naša objašnjenja. Dakako, uz pokus potrebno je ispričati i zanimljivu priču. Zato ću na predavanju dati nekoliko osnovnih ideja iz povijesti magnetizma te neka temeljna objašnjenja pojave magnetizma. Na predavanju predstaviti pokuse iz raznih područja fizike, koji se mogu izvoditi pomoću neodimjskih magneta.

Laser ablation in liquids is a very convenient technique for production of nanoparticles free of chemical byproducts. Silver nanoparticles made in this way could show antimicrobial activity. For the purpose of this work we produced colloidal silver nanoparticles in water using a 1064 nm ns Nd:YAG laser at 100 mJ output energy and 5 Hz repetition rate. Size- distribution of nanoparticles was obtained from atomic force microscopy (AFM) images. We found the average diameter of silver nanoparticles to be around 10 nm with a relatively narrow size distribution. Obtained colloidal solution is stable on a scale of few months, which implies that nanoparticles are well dispersed and/or charged. We use this colloidal solution to investigate antimicrobial effects of silver nanoparticles on different strains of E. coli bacteria where the changes on bacterial membrane are monitored by AFM. Here we present our preliminary results.

In most physics courses vector calculus is carried out by resolving the forces into components and then summing up the components of the same direction. Although this procedure facilitates the calculation, it potentially leads to the misconception that the components are also some real forces. In addition, the procedure is not entirely in accord with the concepts of the Newton’s laws which state that the motion of the body is determined by the vector sum of the forces. The question arises: is the direct vector method or application of the polygon rule for vector addition more successful in teaching mechanics? In this study, we have developed an instrument to measure students’ ability to identify real forces in different diagrams. Using this instrument we made an initial study of the effectiveness of the two different problem solving methods. Our test, consisting of 12 items, was administered to two groups of first-year physics students at Rijeka (RG) (n = 27) and Split (SG) (n = 25) university, after the “concept of force” had been covered in class. Afterwards, both groups exercised additional force diagrams tasks for a period of two class hours. The only difference was that RG used the polygon rule and SG the vector components method. Post test showed a shift in the average rate of correct responses which was significantly larger for RG. Based on these initial results we formulate the working hypothesis for the future investigation: If we apply the teaching method where the force diagrams are solved by using the polygon rule, we foster the students' ability to identify real forces and we improve their understanding of Newton's laws.

Laserska ablacija u tekućini je jedinstvena tehnika za proizvodnju nanočestica bez kemijskih nusprodukata koji mogu utjecati na rezultate istraživanja. Srebrne nano- čestice, dobivene na ovaj način, trebale bi također pokazati antimikrobnu aktivnost. U našem laboratoriju proizveli smo srebrne koloidne nanočestice u vodi koristeći nanosekundni Nd:YAG laser valne duljine 1064 nanometara, izlazne energije 100 mJ te frekvencije 5 Hz. Distribuciju promjera nanočestica dobili smo iz snimaka napravljenih pretražnikom atomskih sila (AFM). Prosječni promjer srebrnih nanočestica iznosio je oko 10 nanometara uz relativno usku distribuciju. Stabilnost koloida ispitivali smo analizom apsorbcijskog spektra. Dobiveni koloid pokazao se stabilnim tokom nekoliko mjeseci iz čega možemo zaključiti da su dobivene nanočestice dobro raspršene. Koristeći ovaj koloid istraživali smo antimikrobne efekte srebrnih nanočestica na sojevima E. coli bakterija promatrajući promjene bakterijske membrane također pomoću AFM-a. U ovom radu predstavljamo inicijalne rezultate istraživanja.

Regardless of wide use of satellites they are still often considered as “mysterious” objects, mostly because they travel in space where most of us have never been. So that developing an intuitive understanding of satellite motion remains out of our scope. That's probably why the dynamics of orbital motion proved to be conceptually difficult for students. Being aware of these conceptual difficulties, many years after he published Principia, Newton wrote a popular text to explain the orbital motion of the Moon. In this paper he demonstrated the significance of the velocity of the satellite as equally responsible for the orbital motion as the attractive gravitational force of the Earth [1]. He discussed the trajectory of a cannon ball which was launched horizontally from the top of a high mountain and, which was attracted by the Earth gravity. If the launch speed was increased enough, the ball would start orbiting the Earth. Besides, the gravitational force is directed toward the center of the Earth so that the center of the circular satellite orbit and the center of Earth should match. Two and half centuries later, students enter and leave the physics instruction with a wide variety of misconcepts about satellite motion. Many physics education researchers were aware of the importance of studying this topic which resulted in identification of many students’ misconceptions. In our study [2], we investigated students’ ideas about possible satellite orbits. And we have concluded following: 1) Students tend to use the p-prim [3] "closer is stronger" instead of applying physics knowledge ; 2) Regardless of their educational level and curricula, students in Croatia lack deep understanding of circular motion, gravitational force and first cosmic velocity. 3) The teachers considerably overestimate students’ abilities. References [1] I. Newton, A treatise of the system of the world (printed for F. Fayram, London, 1731). [2] N. Erceg, I.Aviani, V.Mešić, Z. Kaliman and D. Kotnik-Karuza, Rev. Mex. Fis. E 60 (2014) 75. [3] A. A. DiSessa, Cogn. Instr. 10 (1993) 105.

Energija je nužna za naš razvoj i opstanak, ali njeno pretjerano i neprikladno korištenje zagađuje i uništava prirodu čiji smo i sami nerazdvojni dio. Kako uskladiti očite suprotnosti? Na sreću, velikom potrošnjom energije omogućili smo i snažan napredak znanosti, pa sada energiju poznajemo i možemo koristiti znatno bolje. Što je to energija i kako je pretvaramo u razne oblike. Kako možemo stvoriti osjećaj o količini energije pojedinih izvora te o našim potrebama i potrošnji. Koji su izvori energije obnovljivi i kako ih možemo koristiti a da ne ugrozimo sebe. Kako znanost i novi materijali otvaraju nove mogućnosti pohrane i korištenja energije.

Nanoparticles of various materials are today implemented in wide variety of industrial, scientific and medical applications. Biocompatible nanoparticles are used for cell treatment ; as nano-biomarkers, for therapy and diagnostics. Nanoparticles can be synthesized conventionally either using wet chemistry methods or gas phase processes. Such nanoparticles are often characterized by impurities which are reaction products of additives and precursors. Laser ablation in liquids appeared to be a solution for that drawback. It is recognised as simple and versatile technique and there are almost no limitations in a selection of materials for the nanoparticle synthesis. The remarkable advantages of this technique over other techniques are absence of impurities in the final product (free of contaminating processes, chemical precursors not required), possibility of preparation of multicomponent nanoparticles, weak agglomeration, narrow size distribution of nanoparticles, etc. In our work we studied laser synthesized silver nanoparticles produced in water by ns Nd:YAG laser operating at 1064 nm with 100 mJ of output energy and 5 Hz of repetition rate. From AFM figures size- distribution of nanoparticles is obtained. Laser ablation is monitored by optical emission spectroscopy while colloidal solution is characterized by photospectrometry and photoluminescence. Our results show that average diameter of laser synthesized silver nanoparticles is around 10 nm and size distribution is relatively narrow. Our colloidal solution is very stable in time (few months) implying that nanoparticles are well dispersed and/or charged.

Energija je nužna za naš razvoj i opstanak, ali njeno pretjerano i neprikladno korištenje zagađuje i uništava prirodu čiji smo i sami nerazdvojni dio. Kako uskladiti očite suprotnosti? Na sreću, velikom potrošnjom energije omogućili smo i snažan napredak znanosti, pa sada energiju poznajemo i možemo koristiti znatno bolje. Što je to energija i kako je pretvaramo u razne oblike. Kako možemo stvoriti osjećaj o količini energije pojedinih izvora te o našim potrebama i potrošnji. Koji su izvori energije obnovljivi i kako ih možemo koristiti a da ne ugrozimo sebe. Kako znanost i novi materijali otvaraju nove mogućnosti pohrane i korištenja energije.

We investigated the students' ability to translate the velocity-time graph into a real physical situation and the possible sources of conceptual difficulties. The study involved the sample of n = 324 high-school/university students, and physics teachers in Croatia. The students were presented the original non- traditional open-ended graph problem. Their written answers were classified and used to form a closed-ended prediction questionnaire for teachers. Comparing the teachers’ expectations with the actual students' responses, we found that teachers significantly overestimate students' understanding. Our results also show that the observed difficulties are common to all groups of participants and not much dependent on the educational level and curriculum. We also found that the physics textbooks are also possible sources of difficulties, giving understated or incomplete statements regarding the sign of physical quantities in kinematic expressions. We feel that non-traditional graph problems of this kind could help teachers in establishing active-learning process in the classroom to become aware of students' thinking and to overcome the difficulties. / Ispitivali smo učeničke i studentske sposobnosti prevođenja grafičkog prikaza vremenske promjene brzine u realnu fizikalnu situaciju te moguće izvore konceptualnih poteškoća. Istraživanjem je obuhvaćen uzorak od n = 324 srednjoškolskih učenika, studenata fizike i srednjoškolskih nastavnika fizike iz Republike Hrvatske. Učenicima i studentima smo zadali originalni netradicionalni grafički problem s pitanjima otvorenog tipa. Njihove pisane odgovore smo klasificirali te na tom temelju sastavili upitnik predviđanja zatvorenog tipa za nastavnike. Uspoređujući odgovore koje nastavnici unaprijed očekuju od učenika, sa stvarnim odgovorima učenika, uočili smo da nastavnici značajno precjenjuju učeničko razumijevanje. Naši rezultati također pokazuju da su opažene poteškoće zajedničke za sve skupine ispitanika te da ne ovise u značajnijoj mjeri o stupnju obrazovanja i kurikulumu. Ustanovili smo da hrvatski udžbenici također predstavljaju mogući izvor poteškoća jer sadrže nedorečene i necjelovite tvrdnje koje se odnose na predznake fizičkih veličina u kinematičkim jednadžbama. Smatramo da netradicionalni grafički problemi ovog tipa potiču aktivni proces učenja te nastavnicima omogućuju prilagodbu učeničkom načinu razmišljanja s ciljem svladavanja opaženih poteškoća.

Regardless of nowadays widespread use of satellites in navigation, communication and earth observation, they are still often considered as “mysterious” objects, mostly because they travel in space where most of us have never been, so that developing an intuitive understanding of satellite motion remains out of our scope. That's probably why the dynamics of orbital motion, although being central to proper understanding of many aspects of physics, proved to be conceptually difficult for students. Being aware of conceptual difficulties of this kind, Newton wrote a popular text to explain the orbital motion of the Moon, that was published a year after his death. In this paper he demonstrated the significance of the velocity of the satellite as equally responsible for the orbital motion as the attractive gravitational force of the Earth [1]. Besides, the gravitational force is directed to the center of the Earth so that the center of the circular satellite orbit and the center of Earth should match. In this paper we present students’ ideas about these important issues. For this purpose, we surveyed 276 high-school and university students from Croatia. Students were presented a nontraditional problem [2] with a diagram of the motion of the Earth satellite in different orbits and were asked to choose the one which is the best to receive satellite TV channels in Croatia. Implicitly students were expected to recognize the only possible orbit, for which the gravitational force is directed toward the center. The students were also asked several questions to explain their choice. In order to gain insight into teachers' awareness of student's knowledge, we asked 48 physics teachers to predict how their students would answer the given problems. The results of our study suggest that most students have difficulties with providing physically based explanations. They tend to use phenomenological primitives [3]. Specifically, they tend to use the “closer is stronger” p-prim when attempting to identify the satellite orbit which would ensure the receipt of satellite television signal at a certain location, paying no attention to the direction of the gravitational force. Our results also show that students across different educational levels and curricula in Croatia lack deep understanding and functional knowledge related to the concepts of circular motion, gravitational force and first cosmic velocity. This conclusion is supported by the fact that only 4 % of students provided complete answers regarding the causes of satellite’s motion. Moreover, the teachers considerably overestimate students’ abilities. Based on this study we believe that the use of diagrams could facilitate designing an interactive classroom environment, especially when it comes to promoting of a creative classroom discussion. However, further experimental studies are necessary in order to additionally reinforce the effectiveness of the proposed approach. References: [1] I. Newton, A treatise of the system of the world (printed for F. Fayram, London, 1731). [2] A. A. DiSessa, Cogn. Instr. 10 (1993) 105. [3] N. Erceg, I. Aviani and V. Mešić, Can. J. Phys. 92 (2014) 9.

When solving physics problems, students often fail to identify real forces acting on the body under consideration [1]. This problem is mainly due to the abstract nature of the force concept, but it can also result from the traditional teaching methods. Typically, the mathematical approach to physics problem solving is characterized by introducing additional, nonexistent forces, thus leading to a loss of physical clarity. Vector calculus, in most physics courses, is carried out by the traditional algebraic methods, i.e. by resolving the forces into components and then summing up the components of the same direction. In this procedure the number of the vectors appearing in the force diagram is significantly increased. Although this procedure facilitates the calculation, it potentially leads to the misconception that the components are also some real forces. In addition, the procedure is not entirely in accord with the concepts of the Newton’s laws which state that the motion of the body is determined by the vector sum of the forces, usually not considering the components. The question arises: is the direct vector method [2] or application of the polygon rule for vector addition more successful in teaching mechanics? In this study, we have developed an instrument that aims to measure the extent to which students can identify the real forces in different diagrams. Unlike the FCI test, which mainly checks for preconceived notions, our test checks for didactogenic misconceptions. In addition, our multiple choice questionnaire is based on the visual representation, where the students have to choose the diagram that correctly presents only the real forces. Using this instrument we made an initial study of the effectiveness of the two different problem solving methods. Our test, consisting of 12 items, was administered to the two groups of first-year physics students at Rijeka (RG) (n = 27) and Split (SG) (n = 25) University, after the “concept of force” had been covered in class. We found the pretest item difficulty index ranging from 0.12 to 0.83, with the discrimination values from 0.21 to 0.93 and the KR-20 reliability estimate 0.72. Afterwards, both groups exercised additional force diagrams tasks for a period of two class hours. The only difference was that RG used the polygon rule and SG the vector components method. Posttest showed a shift in the average rate of correct responses which was larger for RG. The normalized average gain in RG was 0.46 compared with 0.24 in the SG. The ANCOVA showed a statistically significant difference (p=0.009) in favor of RG. Based on these initial results we formulate the working hypothesis for the future investigation: If we apply the teaching method where the force diagrams are solved, not by separating force vectors into the components, but by adding them by using the polygon rule, we foster students' ability to identify real forces and we improve their understanding of Newton's laws. Further tests of this hypothesis are the subject of our future work. References [1] For a recent review of literature see e.g. A. Savinainen et al., Phys. Rev. ST Phys. Educ. Res. 9, 010104 (2013). [2] A.S. Kondratyev, W. Sperrym, Phys. Teach. 32, 417 (1994).

Mada se od svih sila najviše družimo s težinom postoje brojne nejasnoće, kako oko njene definicije i značenja, tako oko njene uloge i djelovanja. Primjerice, svi „znamo koliko smo teški“ samo ako težinu izrazimo u jedinicama mase. Većina udžbenika engleskog govornog područja težinu poistovjećuje s gravitacijskom silom, eventualno umanjenom za iznos centrifugalne sile Zemljine rotacije. U našim udžbenicima težina je sila kojom tijelo djeluje na podlogu ili ovjes te ovisi i o drugim čimbenicima kao što su uzgon i ubrzanje. Zato možemo slobodno tvrditi da smo u vodi lakši a da smo pri slobodnom padu bez težine. Mi ćemo se držati upravo toga, operativnog značenja težine. Razlikovat ćemo gravitacijsku silu, koja djeluje na svaku molekulu tijela, i težinu kojom molekule na dodirnoj površini tijela djeluju na podlogu. Tako definirana težina javlja se u ravnoteži gravitacijske i elektromagnetske sile, pri čemu elektromagnetska sila svijet gradi a gravitacijska sila ga razgrađuje i razara. Bit će riječi o utjecaju težine na živa bića i njene važnosti za život na Zemlji. Pokušat ćemo odgovoriti na pitanja: zašto ne osjećamo gravitacijsku silu, kako zadobivamo osjećaj težine i što je to bestežinsko stanje. Diskutirat ćemo kako su se živa bića svojom građom i načinom života prilagodila težini i mogu li preživjeti u bestežinskom stanju. Pritom, poslužit ćemo se rezultatima eksperimenata i iskustvima astronauta s Međunarodne svemirske stanice te zanimljivim demonstracijskim pokusima.

Tijekom proteklih 400 godina prešli smo dug put prema ovladavanju i razumijevanju hladnoće. Naučili smo kako je opisati i mjeriti. Slijedili smo je prema sve nižim temperaturama, gdje se ukapljuju dušik, kisik, vodik, helij te pojavljuju nova, čudesna stanja materije kao što su supervodljivost, superfluidnost i supersolidnost. Na temperaturama blizu apsolutne nule malo je energije za termičke oscilacije atoma. Tu glavnu ulogu preuzimaju kvantne oscilacije i nulta energija gibanja. Kvantne fluktuacije održavaju tvar u pokretu čak i na apsolutnoj nuli.

U cilju pronalaženja učinkovitih metoda za nastavu fizike istraživali smo kakve su učeničke i studentske sposobnosti rješavanja netradicionalnog problema iz kinematike. U istraživanju je sudjelovalo ukupno 276 srednjoškolskih učenika i studenata fizike. Radi stjecanja uvida u okružje u kojem učenici stječu svoja znanja, analizirali smo 16 nastavnih materijala iz fizike s ciljem utvrđivanja zastupljenosti netradicionalnih problema u njima, a 48 srednjoškolskih nastavnika smo pitali kako očekuju da bi na postavljena pitanja u zadatku odgovorila većina njihovih učenika. Pred učenike i studente postavili smo problem s pitanjima otvorenog tipa, a nastavnicima smo dali upitnik zatvorenog tipa sastavljen iz odgovora učenika i studenata. Rezultati pokazuju postojanje povezanosti kurikuluma i stupnja obrazovanja s rješivosti zadatka. Međutim, pojedini ispitanici daju netočne odgovore na jednostavna konceptualna pitanja iako točno odgovaraju na pitanje koje zahtijeva matematičke vještine. Nastavnici značajno precjenjuju točnost učeničkih odgovora. Analiza udžbenika i ostalih nastavnih sredstava iz fizike pokazuje da su tradicionalni problemi većinski zastupljeni s tim da nismo našli probleme tipa kojeg smo koristili u istraživanju. To dijelom objašnjava rezultate ispitivanja. Pretpostavljamo da bi se uvođenjem netradicionalnih problema u nastavu fizike sposobnosti matematičkog korištenja i konceptualnog razumijevanja fizičkih jednadžbi mogle razvijati usporedno. U tom smislu planiramo buduća istraživanja koja će se temeljiti na provedenoj studiji.

S dugoročnim ciljem razumijevanja načina na koji učenici i studenti shvaćaju i koriste pojmove iz fizike te pronalaženja metoda za što učinkovitije poučavanje, po prvi puta su opsežnije istraživane učeničke i studentske strategije rješavanja netradicionalnih problema iz fizike. To su problemi koji se odlikuju, primjerice, nedosljednim, nebitnim ili nepotpunim podacima te nerealnim ili višestrukim rješenjima, čime se potiču značajke znanstvenog procesa kao što su planiranje i analiza. Istraživanjem je obuhvaćeno 303 srednjoškolca i 55 studenata te 48 nastavnika fizike Republike Hrvatske. Rezultati istraživanja pokazali su da standardna nastava u dovoljnoj mjeri ne razvija sposobnost kritičnog razmišljanja potrebnu za rješavanje netradicionalnih problema, uz niz specifičnih poteškoća prilikom povezivanja pojedinih reprezentacija s odgovarajućim fizikalnim konceptima, pri čemu praktična i konceptualna znanja nisu u znatnoj mjeri povezana sa stupnjem obrazovanja i tradicionalnim kurikulumom. Nastavnici u pravilu precjenjuju učeničko razumijevanje koncepata dok analiza udžbenika i pripadajućih dopunskih nastavnih sredstava pokazuje prevladavajuću zastupljenost tradicionalnih problema.

Antiferomagnetsko stanje kubiˇcnog TbB6, ispod temperature prijelaza TN = 21 K i u magnetskim poljima do 6 T, istraživano je na monokristalu pomo´cu magnetske susceptibilnosti, magnetostrikcije i difrakcije x-zraka. Magnetska susceptibilnost i magnetostrikcija pokazuju tetragonalnu simetriju antiferomagnetske faze [1]. U njoj nastaju statiˇcki pomaci atoma u obliku valova, kao kompromis med¯udjelovanja izmjene i elasticˇnih sila [2]. Postoje tri ekvivalentne domene koje nastaju uz tetragonalnu deformaciju jediniˇcne ´celije duž jedne od triju glavnih osi kubiˇcnog kristala. U magnetskom polju domene poprimaju razli ˇcite energije. To omogu´cuje da primjenom magnetskog polja duž jedne od glavnih osi odaberemo domenu s najmanjom energijom ˇcime kristal postaje jednodomenski. Potrebna jakost polja ovisi o temperaturi što daje liniju selekcije domena u magnetskom faznom dijagramu. Naglom promjenom smjera polja u drugu os zapoˇcinje nukleacija i rast druge domene. Brzina ovog procesa ovisi o jakosti polja i o temperaturi. U ovom radu istražujemo dinamiku rasta antiferomagnetske domene promatranjem vremenske promjene magnetostrikcije. Prikazani su rezultati mjerenja magnetostrikcije kao funkcije vremena nakon nagle promjene smjera magnetskog polja, za razne jakosti polja i temperature. Diskutiran je oblik linije selekcije domene u magnetskom faznom dijagramu i vremenska ovisnost magnetostrikcije. [1] R. M. Galéra, M. Amara, I. Aviani, F. Givord, F. Zontone, and S. Kunii, Phys. Stat. Sol. (c) 3 (2006) 3184 [2] M. Amara, R.-M. Galéra, I. Aviani, and F. Givord, Phys. Rev. B 82 (2010) 214414

Godine 1911., točno prije sto godina, na Sveučilištu u Leidenu nizozemski fizičar Heike Kamerlingh Onnes mjerio je električni otpor žive na niskim temperaturama tekućeg helija. To je mogao zahvaljujući tehnologiji ukapljivanja helija koju je sam pronašao još 1908. godine. Sasvim neočekivano, na temperaturi od 4, 2 K električni otpor žive skokovito je pao na nulu. Pojava je bila zapanjujuća jer, iako se snižavanjem temperature i slabljenjem termičkog gibanja otpor metala smanjuje, on ne može iščeznuti čak ni kod najboljih vodiča (bakra i srebra). Nečistoće i defekti u materijalu ometaju gibanje elektrona čak i na temperaturi apsolutne nule. Pojavu je nazvao je supravodljivost. Godine 1933. njemački istraživači Walther Meissner i Robert Ochsenfeld otkrili su da prijelazom u supravodljivo stanje vodič potpuno izbacuje magnetsko polje iz svoje unutrašnjosti, što ne može idealan vodič (vodič kojemu je električni otpor jednak nuli). Supravodič nije idealan vodič, nego nešto sasvim drugo i neobično: makroskopski kvantnomehanički objekt! Tijekom godina supravodljivost se razvila u modernu znanost i tehnologiju koja je omogućila niz specijaliziranih primjena: npr. u akceleratorima i detektorima velikog hadronskog sudarivača u CERN-u, u projektu nuklearne fuzije ITER u Cadarachu te za dijagnostičke uređaje magnetske rezonancije i magnetoencefalografije u medicini. Nadu za masovniju primjenu i novi poticaj istraživanjima dalo je otkriće visokotemperaturne supravodljivosti 1986. godine. Ovo otkriće je ujedno potpuno uzdrmalo postojeća teorijska objašnjenja. Tijekom godina, otkrića i napreci u razumijevanju supravodljivosti honorirani su čak sa sedam Nobelovih nagrada, ali ni danas nakon 100 godina istraživanja ovu pojavu ne razumijemo dovoljno. Supravodljivost ostaje zagonetka na rubu spoznaje, baš kao i istraživanja u čijim uređajima je našla primjenu. Na predavanju ćemo pokušati odgovoriti na pitanja: Što je to supravodljivost? Koji su materijali supravodiči? Kako se supravodljivost može iskoristiti? Što to još ne razumijemo? Koliko je supravodljivost zastupljena u nastavi fizike? Predavanje će biti popraćeno nizom zanimljivih pokusa

The antiferromagnetic (AFM) ground state of cubic TbB6 is characterized by multiaxial ordering and a complex magnetic phase diagram. Magnetic susceptibility and magnetostriction show a tetragonal symmetry of AFM phase [1]. The x-ray diffraction shows the charge reflections resulting from the formation of static atomic displacement waves which can be described as a compromise between the exchange and a single-ion elastic couplings [2]. The single crystal of TbB6 is studied at the first order AFM phase transition and within the ordered phase by means of magnetostriction and anisotropic magnetic susceptibility in magnetic fields up to 6 T. The tetragonal AFM phase below TN = 21 K is a mixture of three equivalent AFMdomains. Based on the symmetry of spontaneous deformation and the magnetostriction data we conclude that Tb magnetic moments lay in the tetragonal plane. If we apply magnetic field of about 5 T along one of the fourfold axes, the energetically most favorable domain is selected, and the whole crystal tunes into a single-domain state. This state is stable even in zero magnetic field. The observed behaviors are consistent with the tetragonal symmetry of the AFM state. In this work we discuss the the domain selection line observed in the magnetic phase diagram. We relate this line to the measured anisotropic magnetic susceptibilities and the magnetic energy difference for the magnetic field applied along the two characteristic directions of AFM domain. For a sudden change of the field direction to another fourfold axis the nucleation and the growth of another domain emerge. We attain to explain the temperature and field dependent time evolution of this process. We use the time dependence of magnetostriction to study the domain nucleation and growth dynamics. [1] R. M. Galéra, M. Amara, I. Aviani, F. Givord, F. Zontone, and S. Kunii, Phys. Stat. Sol. (c) 3 (2006) 3184 [2] M. Amara, R.-M. Galéra, I. Aviani, and F. Givord, Phys. Rev. B 82 (2010) 214414