Abstract. We give a straightforward derivation of the string equation and Virasoro constraints on the τ function of the BKP hierarchy by means of some special additional symmetry flows. The explicit forms of the actions of these additional symmetry flows on the wave function and then the negative Virasoro generators L_-k are given, where k is a positive integer.

Abstract. We describe the time evolution of the quantum coherence in an open system consisting of two coupled bosonic modes embedded in a thermal reservoir. We discuss the influence of the environment in terms of the covariance matrix for initial squeezed thermal states. The coherence is quantified using the relative entropy as a measure, and its dynamics is studied in the framework of the theory of open systems based on completely positive quantum dynamical semigroups. We show that the evolution of the quantum coherence strongly depends on the initial state of the system (squeezing parameter and thermal photon numbers), frequencies of the modes, parameters characterizing the thermal reservoir (temperature and dissipation coefficient) and the intensity of the coupling between the two modes.

Abstract. In this paper, we investigate the dynamics of a nonlinear model responsible for the transition of turbulence phenomena and cellular instabilities to a chaos. The two-mode Kuramoto-Sivashinsky (TMKS) model is an example of such application. We study both integer and fractional time-derivative involved in this model. Solitary wave solutions and approximate analytical solutions will be derived to TMKS model by means of well-posed different techniques. The mechanism of the concepts of two-mode and time-fractional derivative will be discussed in this work. Finally, both 2-dimensional and 3-dimensional plots will be provided to support our findings.

Abstract. This paper addresses spectral collocation techniques to treat with the distributed-order fractional partial differential equation (DOFPDE). We introduce a new shifted fractional order Jacobi orthogonal function (SFOJOF) outputted by Jacobi polynomials. Also, we state some corollaries and theorems related to new SFOJOF. The shifted Jacobi-Gauss-Lobatto collocation (SJ-GL-C) and shifted fractional order Jacobi-Gauss-Radau collocation (SFJ-GR-C) methods are developed for approximating the DOFPDEs. The basis of the shifted Jacobi polynomial is adapted for spatial discretization and another basis of SFOJOF is investigated for temporal discretization. Through the selected basis functions, the related conditions are automatically accomplished. The principal target in our technique is to transform the DOFPDE to a system of algebraic equations. Some numerical examples are given to test the accuracy and applicability of our technique.

Abstract. The present paper aims to study the trajectory of a charged particle in Brownian Motion in a time variable magnetic field. The approach presented here builds on methods of statistical physics and produces an analytical general solution for the stochastic differential equation of motion. A numerical approach is also devised and example trajectories are presented for particular analytical shapes of the external magnetic field.

Abstract. The torque-free motion of a coin in gravitational field is analyzed for general initial conditions. After launch at the end of motion the coin lands on a soft surface that allows no bouncing. The model assumes the coin is a thin cylindrical rigid body and the air resistance is absent. The motion is described by numerical integration of the Euler equation of motion. Biased probabilities of heads and tails are obtained for various initial conditions accessible to a skilled person.

Abstract. Ternary fission into three equal fragments is studied within an adapted macroscopic-microscopic method. The Yukawa-plus-exponential potential is used to calculate the charged liquid drop part of the deformation energy. The particular feature is that one calculates the electrostatic and nuclear interaction two by two between the three fragments. For the microscopic part a three center shell model is developed in order to obtain the single particle levels for ternary configuration. The Strutinsky method is then employed to calculate the shell corrections. The ternary fission barriers are obtained by varying the total deformation energy along the distance between the three fragment centers. Calculations are performed for the splitting of ¹⁴⁴Nd and ²¹⁰Po.

Abstract. Cosmic rays have been a hot topic for the Astroparticle Physics community, since discovered in 1912. After over a century and many efforts from scientists worldwide we know now that the most energetic particles observed on Earth, the ultra-high energy cosmic rays (UHECRs), have an extragalactic source. Where, how and what exactly accelerates them? These questions remain still mysterious nowadays. The extensive air showers (EAS) developed by cosmic rays (CRs) in the Earth's atmosphere are at this moment the most resourceful subject of study for researchers who make efforts to better understand these fascinating particles. However, the detection and study of EAS is not at all an easy task. Because the Earth's atmosphere is being used as a giant detector of cosmic rays, EAS develop differently based on primary particle energy and mass, incoming direction and atmospheric environment at a given location. In this paper we look at the development of EAS from two different, but complementary perspectives. First, we show how the main parameters of the showers modify, as function of the primary properties, by multiple longitudinal profiles simulated with CONEX, for different sets of CR parameters (energy, mass, direction of propagation). Next, we look at the radio signals emitted by EAS, which develop at the Pierre Auger Observatory location, by using a simplified v✕B model to describe the geomagnetic emission, and sophisticated simulations with the CoREAS option in the CORSIKA Monte Carlo code, who treat the full radio emission released by an air shower. Some of the results presented in this paper are included in an open source graphical user interface (GUI) application, EAS Browser v2.0.

Abstract. A new approach for passive mode-locking, i.e. the nonlinear mirror applied to self-frequency-doubling materials, is proposed. The mode-locking threshold and its dependence on several parameters (nonlinear crystal length, beam focusing strength, effective second order nonlinear coefficient and dichroic mirror linear reflection coefficient at fundamental wave), for a nonlinear mirror consisting of Nd:GdCOB self-frequency doubling medium, are evaluated. A comparison with the data achieved for Nd:YVO₄, when is frequency doubled by LBO, is performed. The results are useful in developing efficient and compact ultrashort pulsed laser sources, operating at 1 micron, based on self-frequency doubling Nd:GdCOB medium or a similar one.

Abstract. The effects that determine the shift and damping of the surface plasmon resonance (SPR) band of colloidal gold nanoparticles due to the chemisorption of tetrahydroxyborate (B(OH)₄) anions are analyzed experimentally and theoretically. The contribution of chemical interface damping, change in refractive index and charge density variations to the experimentally observed shift of the SPR band are evaluated qualitatively by simulating the optical response of gold nanoparticles upon the chemisorption of B(OH)₄ anions. The results show that changing the refractive index of the medium and the charge density cannot account entirely for the shift of the SPR band. Thus, chemical interface damping should be considered when analyzing surface effects in the presence of strongly chemisorbed adsorbates.

Abstract. We studied theoretically and experimentally the interference pattern of a water droplet placed in the object arm of a Mach-Zehnder interferometer, and the influence of heating on it. It turns out that due to special circumstances, the diffraction pattern of the sphere in the shadow area is particularly insensitive to changes of the refractive index, because it is identical to the Fresnel diffraction of an opaque disc in the shadow area. However, this pattern is sensitive to changes of the droplet volume caused by dilation, which is another effect of the heating. More promising turns out to be the Mie back- and lateral-scattering. The scattering pattern in this case is sensitive to heating at certain angles. The most general and biggest problem turns out to be the fact that the two effects of heating, the refractive index and radius change, tend to cancel each other. Scanning the scattering angle for sensitivity provides measurement configurations where the two effects of heating do not cancel anymore.

Abstract. Tungsten films with various nitrogen content (WN_x with _I = 1.25, 2.00 and 2.47 at%), intended for use as hard coatings were deposited by Combined Magnetron Sputtering and Ion Implantation method. A study was performed to assess the correlations between the nitrogen flow rate and physical and mechanical properties of the films.

Abstract. We investigate the formation of optical extreme waves in a resonant two-level medium that entails the self-induced transparency (SIT) effect, within the framework of the sine-Gordon equation. By virtue of the exact breather solutions and numerical simulations, we reveal that the extreme waves may occur as a result of an intense interaction between individual breather components, by an optimal choice of the breathing periods and the propagation directions for each component. We expect that this work may stimulate the experimental study of the extreme wave formation in SIT media.

Abstract. This paper reports a creative bottom-up eco-benign design of novel nanocomposites based on bio-inspired membranes, green nanosilver and chitosan, for biomedical purposes. Chlorophyll a was used as a sensor to monitor the nanomaterial biofabrication, by UV-Vis absorption and fluorescence emission spectroscopy. SEM analysis confirmed the phytosynthesis of AgNPs (from Eugenia caryophyllata aqueous extract), and the formation of silver-based materials. The developed nanomaterials presented hemocompatibility, high antioxidant activity (90.2÷99.1%, checked by chemiluminescence method), anti-proliferative effect against HT-29 cancer cells, and no toxicity to normal cells in a dose-dependent manner. Chitosan and biomimetic membranes induced biocompatibility and interesting bio-activities of the obtained materials.

Abstract. Commercially available zinc oxide nanoparticles (ZnO NPs) with different sizes (7-13 nm and < 100 nm) were selected for this study in order to analyze the interaction with serum albumin of bovine or human origin (BSA and HSA). The composition, morphology and surface of particles were characterized by transmission and scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. Further, the hydrodynamic size and zeta potential were assessed after their dispersion in ultrapure water. The proteins were incubated with ZnO NPs for 10, 30 or 60 min at 37° C. The secondary structure of albumin that were adsorbed on the particles surface was evaluated using Fourier transform infrared spectroscopy. The supernatant with unbound proteins was used for an indirect evaluation of protein corona by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Our study revealed that the features of nanoscale surface topographies created by ZnO NPs agglomeration in clusters can significantly influence the protein adsorption and secondary structure.

Abstract. The goal of the present study was to evaluate the genotoxic influence of iron oxide nanoparticles coated with aspartic acid (AIONPs) with 9.3 nm physical diameters on the root tip cells of Zea mays seeds. The seeds germination occurred under AIONPs presence by addition into the germination substrate of AIONPS aqueous solutions with different volume fractions (range between 20 and 400 μ/l). For all samples (control and treated samples) indexes of cytogenetic assays were established. The mitotic division of cells seems was stimulated under AIONPs influence (up to 68%) with a low rate of aberrant cells occurrence (up to 1.42%).

Abstract. Monthly time series of mean and maximum wind speed over the period 1961–2018 from 104 weather stations evenly distributed over Romania (spatially and elevation-wise) were tested for trends with the Mann-Kendall nonparametric test. The monthly mean wind speed is decreasing at about half of the stations, while increasing trends are between 5% (November) and 28% (September). The maximum wind speed presents decreasing trends in all months at the vast majority of stations - between 75% and 88.5%.

Abstract. The anthropogenic noise has become a major pollution source concern in the European seas. The Descriptor 11 of the Marine Strategy Framework Directive (MSFD) deals with the introduction of energy in the marine environment by human activities. The indicators that describe Descriptor 11, cover low and mid frequency impulsive sound (e.g. seismic airguns, sonars, pile driving and explosives) and the frequencies of ambient noise (that are dominated by shipping sound). This study is focused on some key aspects of the existing knowledge on the sound speed features in the Romanian Black Sea shelf. Information gathered for temporal and spatial record of activities that produced low to mid frequency (10 Hz to 10 kHz) impulsive noise in the North-Western Black Sea shelf are also described.

Abstract. In this paper, we have studied the seismic activity in relation with geology, and tectonics in order to highlight seismogenic processes recorded in Danubian area and Hateg-Strei Basin. The Danubian seismogene area presents a complex geological structure, being characterized by the following tectonic units: Median Dacides (Getic and Supra-Getic nappes), Marginal Dacides (Danubian Unit) and External Dacides (Severin nappe). The recent seismic activity in this area, starting from 1990 until present, is described by the seismic sequence from 2002, in the Moldova Noua area, in connection to Oravita-Moldova Noua fault and by the seismic sequence from 1991, in the Baile Herculane area, belonging to the Cerna-Jiu fault system. Also, the Teregova area is present with the seismic sequence from 2014 and another two smaller sequences. From a statistical point of view, the seismicity is mainly described by the b-value coefficients from the empirical relation between the frequencies and magnitudes. Determination of spatial and temporal variations of the b-value is thought to reflect the stress conditions in the crust.

Abstract. Many scientific disciplines contribute with their specific methods of investigation, to the formation of a real image of different ancient objects. For ceramic materials, the use of analytical methods (especially those based on physical phenomena) presents a great importance: they can offer information regarding the raw materials, human traditions and regional history. The study presents the archaeometrical characterization of ceramic artifacts with a high historical value. The artifacts were collected from A1_1 Sagu site (Arad county), being dated to approx. 1600–1250 BC, belonging to an unfortified Late Bronze Age (LBA) settlement. Due to the impressive amount of ceramic material found and the large area the settlement covered, the mentioned site represents a LBA landmark of the region. The artifacts were analyzed using X-ray diffraction, X-ray fluorescence, thermal analysis, FTIR spectroscopy and optical microscopy. The analytical results obtained confirmed a common origin for the three analyzed samples, similar to other Late Bronze Age pottery discovered in Transylvania. The ceramic artefacts are of low-calcium nature, with a high iron content; the presence of hematite in all the samples, can define the technique used for firing: most probably, the process was ended in oxidizing atmosphere and it can also be correlated with an increased firing temperature. The elemental and mineralogical composition can be further used for the development of provenance maps of Romanian ceramic artefacts.

Abstract. The paper describes the use of two lab tools of Inquiry-Based Learning (IBL) and Science Technology Engineering and Mathematics (STEM) for the study of the Kater pendulum. The first tool is based on Arduino microcontrollers and compatible sensors while the second one uses Tracker Video Analysis (Tracker) software. The laboratory experiment involves measurements of the oscillation period of the Kater pendulum, finalized with for now classical calculation of the gravitational acceleration. We compare the results obtained with both tools, finding a very good agreement between them. Our aim is to motivate students on the study of STEM fields in their future educational pathway by applying inquiry-based learning using these lab tools.

Abstract. Augmented Reality (AR) allows students to overlap the reality with additional information or indirect observation through a technological device of the physics of reality. The aim of this paper is to present the use of Tracker for learning a classical study in the coupled oscillations of two coupled pendula. We show the study of the symmetric normal mode, antisymmetric normal mode and the beats phenomena for the oscillations of coupled pendula. Measurements are made by recording the experiment with a digital camera and using Tracker software, video analysis and video modeling tool to process and get information from recorded videos. With this set-up detailed comparisons can be established between theoretical calculations and measurements, focusing on several relevant concepts such as the oscillation period for the symmetrical and antisymmetrical mode, the elastic coupling spring constant and the beats period dependence on the position of the spring coupling. Consequently, the experiment based on video analysis of the experiment is used to emphasize key physical concepts, to motivate students in their exploratory work and also to stimulate autonomous investigations.

Abstract. The aim of the current research is to determine the internal structure of the Physics items present in the 6th grade Romanian National Evaluation Tests. The study also focuses on the efficiency of the Physics item group in the evaluation of logical-scientific thinking competence which represents the construct evaluated by these tests. The analysis of the items includes the 2016–2019 tests. The inclusion of the items at the different levels of the construct scale measured by each test is statistically supported by the Categorical Principal Components Analysis and the "Wright Map" tools. The items calibration is performed within the framework of the Item Response Theory. The results show that the items have content validity and have a high discriminatory power. The small number of Physics items in the National Evaluation Tests, as well as the fact that the internal structure of these items is almost identical in all the tests applied over the four years covered by the analysis, determined their low effectiveness in the competence’s evaluation. This study proposes a useful tool for Physics teachers to interpret the results obtained by their students in the National Evaluation Tests, as it complements the image of these items, given by the National Centre for Assessment and Examination in Evaluator's Guidebook, with their strengths, but also their limitations.