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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.

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.

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.

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.

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)

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.

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.

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.

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.

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.

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.

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).

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.

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

We report the discovery of two consecutive, pressure driven magnetic instablities in Yb2Pd2Sn. They emerge in a non-Fermi liquid environment at the initial and the final point of a dome-like, single magnetic phase at pressures pc1 = 1 GPa and pc2 = 4 GPa. This singular behavior of Yb compounds is supposed to result from mutually competing, pressure modi ed energy scales, which in case of Yb2Pd2Sn cause a sign change of the pressure dependence of the Kondo temperature TK and magnetic ordering temperature TN.

The antiferromagnetic state of TbB6 has been investigated by means of magnetic susceptibility, magnetostriction and X-ray diffraction measurements on a single crystal. The anisotropy of the magnetic susceptibility and the magnetostriction data point to a tetragonal symmetry in the antiferromagnetic state. Below TN, the X-ray diffraction investigation shows charge satellites, related to the and h wave vectors stars, similar to those observed in GdB6. The satellites clearly result from the formation of static atomic displacements waves. The displacive phenomenon is described as a compromise between the exchange coupling and a single-ion elastic energy. This mechanism is shown to be responsible for the recurrence of the h i magnetic wave vectors in rare-earth hexaborides. A combined analysis of experimental and theoretical data points to only two stable tetragonal models for TbB6 antiferromagnetic structure. This study confirms the influence of exchange displacements in rare-earth hexaborides and highlights the need for a systematic investigation of the magnetic anisotropy of antiferromagnets

The phase diagram of 4f heavy fermions is obtained by the scaling solution of the Anderson model with the crystal field (CF) split states. The results explain the phase boundaries revealed by pressure and doping experiments on intermetallic compounds with Ce, Yb and Eu magnetic ions. The theoretical phase diagram is constructed by comparing the mean-field free energies of the local-moment and aniferromagnetic phases. The Kondo temperature TK(g) of the CF split multiplet of 4f ions, as function of coupling constant g, is calculated by the non-crossing approximation which replaces the lattice model with the single impurity Anderson model. This Kondo scale agrees with the scaling result of Hanzawa, and we use it to estimate the energy gain due to the singlet formation. The RKKY temperature TRKKY (g) is estimated from the 2nd-order expansion for interaction energy of two magnetic impurities. The mean-field phase diagram obtained in such a way captures the essential features of the experimental data. A comparison with the pressure experiments on CeRu2Ge2 and Yb2Pd2Sn, and doping experiments on EuCu2(SixGe1−x)2 is provided.

In intermetallic compounds with Ytterbium ions, the fluctuations between magnetic Yb 4f 13 and nonmagnetic 4f 14 electronic configuration (EC) with different ionic volumes, provide an additional degree of freedom for the pressuredriven competition among the electronic ground states. This can lead to novel features in the phase diagram, as observed in Yb2Pd2Sn, the first compound exhibiting the two consecutive, pressure-driven quantum critical points (QCP). The novel phase diagram is explained applying Doniach approach to the Anderson model with the crystal field (CF) split f states. Such a model is characterized by the position of the f level Ef , the conduction band density of states, the hybridization strength Γ, and the coupling constant g = Γ/π |Ef |. For the CF states, the f-f correlation is infinite, i.e., the total f occupancy is always less than one. Since the ionic radius of Yb is very small, we assume that pressure does not affect, initially, the hybridization with ligands, so that Γ does not change. The main effect of pressure is, then, to make the nonmagnetic 4f 14 EC energetically unfavorable, due to it’s large volume. This increases it’s separation from the small-volume magnetic 4f 13 EC, which makes Ef more negative and favors the magnetic ground state. For higher pressures Ef saturates, but as the lattice constant is now reduced, the hybridization Γ increases. In this pressure range, the magnetic moment of f ions is quenched and the non-magnetic ground state is restored. The theoretical phase diagram is constructed by comparing the mean-field free energies of the local moment (LM) and aniferromagnetic (AFM) phases. The Kondo temperature TK(g) of the CF split 4f-octet of Yb ions is calculated by the NCA approximation which replaces the lattice model with the single impurity Anderson model. This Kondo scale agrees very well with the scaling result of Hanzawa, and we use it to estimate the energy gain due to the singlet formation. The RKKY temperature TRKKY (g) is estimated from the 2nd-order expansion for interaction energy of two magnetic impurities. The mean-field phase diagram obtained in such a way captures the essential features of the experimental data. A more sophisticated approach should obtain both solutions, the non-magnetic and the magnetic one, directly from the free energy of the periodic Anderson model. The experimental data regarding this work can be found in the papers: E. Bauer et al., The magnetic instability of Yb2Pd2 (In ; Sn) in a non-Fermi liquid environment, J. Phys.: Condens. Matter 17, S999-1009 (2005). T. Muramatsu et al., Pressure induced magnetic ordering in Yb2Pd2 Sn with two quantum critical points, arXiv:0704.3307v2 [cond-mat.str-el] (2007).

In some cases, simple metallic alloys, whose magnetic behaviour is supposed to be wellknown and, thus, they are not subject of further studies, might surprise us revealing anomalous behaviours that point towards a more complicated magnetic ground state. This is the case of CeGe, a binary Ce-based alloy that was already studied in the 60’ s, and reported as a simple antiferromagnet [1], being this consideration accepted until recent times [2]. However, a careful study of this alloy has evinced that the magnetic ground state of this alloy must be more complex. In the present work we will show experimental results that clearly prove that the magnetic structure of CeGe at low temperatures must be incommensurate. These results include microscopic probes, such as neutron diffraction or muon spectroscopy, and macroscopic measurements, among which the transport properties (electrical resistivity and thermoelectric power) are specially relevant, as they exhibit an anomalous behaviour at the Néel temperature that is indicative of a gap opening at the magnetic superzone. [1] K.H.J. Buschow and J.F. Fast, Phys. Stat. Sol. 16, 467 (1966). [2] P. Schobinger-Papamantellos, M. Kenzelmann, A. Schenck, F.N. Gygax, K.H.J. Buschow and C. Ritter, Physica B 349, (2004) 100. 22

U cilju proučavanja intermetalnog spoja CePt, za koji se smatra da je Kondo feromagnet (TC, TK < TC) izvršena su opsežna istraživanja karakteristika Ce3+ iona u slitina: CexLa1-xPt i CexY1-xPt. Određene su kristalne strukture slitina i parametri kristalne rešetke slitina, izmjereni su električni otpor, termostruje, dc i ac susceptibilnosti od 1.5 K do 320 K, te magnetizacija do 5 T. Naši rezultati dovode u sumnju da se intermetalni spoj CePt može smatrati kao Kondo feromagnet. U CexLa1-xPt sistemu slitina električni otpor ne pokazuje kondo značajke, a dc susceptibilnost ne pokazuju postojanjehibridizacije. Kondo značajke javljaju se u CexY1-xPt sistemu, ali dc susceptibilnost pokazuje da je sistem valentno-fluktuirajući. Smatramo da se smanjenje magnetskog momenta u feromagnetskoj fazi može objasniti utjecajem kristalnog električnog polja a ne hibridizacijom. Ac susceptibilnost pokazuje da je formiranje feromagnetske faze u sistemu CexY1-xPt slitina mnogo kompleksnije nego u CexY1-xPt sistemu.

We report Vickers microhardness measurements on flux grown single crystals of the YbAgxIn1-xCu4 alloy system. Although sample dependent, the microhardness exhibits clear concentration dependence: in general, it decreases with x. The lattice parameter as a function of x exhibits a similar behavior. For x < 0.5, where the lattice parameter is almost constant, the microhardness exhibits a weak enhancement. Similar concentration dependence of the lattice parameter, resistivity and microhardness allows us to conclude that the microhardness reflects the evolution of the YbAgxIn1-xCu4 alloy system towards more metallic character with increasing x.