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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.