Abstract. We suggest that, instead of transforming a general quintic equation into the Bring - Jerrard form, to get the solution in terms of hypergeometric functions ₄F₃, it could be simpler to transform it into a principal, and to get the solution using the Passare - Tsikh formula. This approach is illustrated for the Euler equation of the three body problem and for the Landau equation of the phenomenological theory of phase transitions. Two equations with applications in magnetism, never studied previously in the context of quintic equation, are discussed.

Abstract. In this paper, the Jacobi elliptic function expansion approach is used to explore the Kundu-Mukherjee-Naskar equation, which describes the fiber pulse in optics, rogue waves in the seas, and light beam bending. As a consequence, many structures of solutions based on the parameter module m, such as optical dark-bright, dark, bright, singular, Jacobi elliptic function, and exponential solutions, have been effectively developed. In the solutions produced to analyze wave propagation, specific values for free parameters are presented. We also used computer tools to display 3D surfaces, 2D images, and contour plots of some of the created solutions. To our knowledge, all the obtained solutions verify the partial differential equation.

Abstract. Entangled photons are crucial for the development of quantum technologies and especially important in quantum communications. Hence it is paramount to have a reliable, high-fidelity source of entangled photons. Here we describe the construction and characterization of a polarization-entangled photon source. We generate maximally-entangled Bell states using a type-II PPKTP nonlinear crystal inside a Sagnac interferometer. We characterize the source in terms of brightness, visibility, Bell-CHSH test and we perform quantum-state tomography of the density matrix. Our source violates Bell-CHSH inequality |S|≦2 by n = 22 standard deviations. With visibilities up to V = 98.9% and fidelity F = 97%, our source is highly competitive, with state-of-the-art performance. To the best of our knowledge, this is the first source of entangled-photons designed and build in Romania and as such, represents an important step for the development of quantum technologies in our country. We envisage that our results will stimulate the progress of quantum technologies in Romania and will educate the future generation of quantum engineers.

Abstract. The current study deals with a new (3+1)-dimensional integrable extension of Boussinesq equation, for establishing some new analytic solutions. The concept of Hirota's bilinear operator and Bell polynomials are uniformly applied to derive the bilinear form of the considered equation. Further, quadratic and homoclinic test functions are utilized for extracting lump and homoclinic breather wave solutions with abundant free parameters, controlling the phase shifts, shapes and energy distributions, and propagation directions. The graphical demonstrations of extracted solutions are presented for obtaining information about the physical phenomenon.

Abstract. The deformed soliton solutions of the (2+1)-dimensional nonlinear Schrödinger equation are constructed based on the zero seed solutions q = r = 0 using the n-fold Darboux transformation. Without loss of generality, the order-1 and order-2 deformed soliton solutions are discussed in detail. Their dynamical properties, including trajectory and amplitudes, are analyzed. In addition, the order-n deformed positon solutions are investigated. Especially, two examples of the order-2 deformed positons are studied through formulas and figures.

Abstract. The aim of this manuscript is to study the dynamics of the motion of an accelerated mass-spring system within fractional calculus. To investigate the described system, firstly, we construct the corresponding Lagrangian and derive the classical equations of motion using the Euler-Lagrange equations of integer-order. Furthermore, the generalized Lagrangian is introduced by using non-integer, so-called fractional, derivative operators; then the resulting fractional Euler-Lagrange equations are generated and solved numerically. The obtained results are presented illustratively by using numerical simulations.

Abstract. The purpose of this paper is to present a generalized transformation for constructing analytic solutions to the b-equation. The proposed unified ansätze are used to obtain exact solutions that are general solutions to simpler equations that are integrable or have special solutions. The ansätze are built by selecting either an integrable differential operator or a basis set of functions. The method is used to generate families of new exact solutions, solitary solutions, and traveling wave solutions for the b-equation.

Abstract. The two-body motion for the gravitational and linear elastic central conservative force field is discussed by comparing the differential equations of motions. The inverse and direct square displacement dependency of the two force types is shown as emerging in the trajectories. The closed (for the gravitational field) and open (for the particular dumbbell elastic system considered) character of the trajectory is discussed.

Abstract. We propose a theoretical model describing the arising of a quadratic nonlinearity in the increasing electric field at low intensities in weakly nonlinear crystals. New modes of formation of nonlinear optical domain characterized by a positive nonlinear response near crystal surface covered by the screening thin film are described. The exact solutions to five formulated boundary-volume problems corresponding to the nonlinear surface waves with unique characteristics are found in explicit analytical form. Two types of surface waves propagate with a freely varying effective refractive index and three types of surface waves with specific values of the effective refractive index determined by the control parameters and optical properties of the crystal. The influence of the system parameters such as the effective refractive index, surface amplitude, and surface and domain field gradients on the peculiarities of the field localization is analyzed.

Abstract. In this work, a transverse spin-dependent shift (SDS) of the horizontal photonic spin Hall effect (PSHE) at a fixed wavelength (1557 nm) is simulated for detection of magnetic field applied to a honeycomb fiber without the first ring of air holes where the core air hole is filled with a magnetic fluid that is surrounded by a gold layer. The variation of the refractive index with the magnetic field for some values of the volume fractions c of Fe₃O₄ particles in a solution is given from the experimental values. The sensor is based on variation of the imaginary part of the effective index and transmission loss with the magnetic field. For small core diameter of D = 2 μm of the truncated optical fiber in the conventional weak measurements, a refractive index resolution (1.32 × 10 ^{− 8} RIU) and corresponding magnetic field resolution (0.0017 Oe) are obtained when the volume fraction of Fe₃O₄ particles in a solution is c = 1.48% and amplified angle is Δ = 0.1 deg. This value of magnetic field resolution is very good in comparison with the best published value (0.0023 Oe).

Abstract. Cobalt is a heavy metal that has a key role in various human physiological metabolism processes. However, the excess consumption of cobalt ions (above 40 μg/L) affects the human health, causing cardiomyopathy, asthma and cancer. Herein, a polyaniline/platinum (PANI/Pt) bilayer fiber optic sensor based on surface plasmon resonance phenomenon (FO-SPR) was fabricated, characterized and used to detect cobalt ions (Co²⁺) in an aqueous solution. The obtained results showed that the sensor's sensitivity is 37.62 nm/μM, exhibiting a limit of detection for Co²⁺ of 0.14 μM. Therefore, this portable and simple sensor has a remarkable potential for environmental water quality control, and can be successfully extended to other applications.

Abstract. Recent progress in “Green” Nanotechnology is trying to fight against many diseases, a special interest being given to silver-based nanoparticles biogenerated from plants. In this study, phytogenic silver chloride nanoparticles (m-AgClNPs) were “green” synthesized by using an aqueous extract of Mentha piperita L. leaves, and then examined against urease activity. Urease, a nickel-containing enzyme, has been reported to contribute to the pathogenesis of many diseases (hepatic coma, encephalopathy, gastritis, gastric ulcer, and others). The obtained m-AgClNPs presented good physical stability (checked by zeta potential measurements) and high antioxidant activity (evaluated by chemiluminescence technique). Their size was estimated by Dynamic Light Scattering (DLS) measurements. UV-Vis absorption and fluorescence emission spectroscopy were used to study the impact of bio-AgNPs on urease. Our bio-developed m-AgClNPs exhibited good urease inhibitory activity and no destabilization of urease structure against thermal denaturation. These findings could be exploited in the development of novel inhibitors of urease for agronomic and biomedical applications.

Abstract. Radiocesium content in wild boar meat, originating from Serbia, was determined. It ranged from 0.01 to 1.11 Bq/kg and 0.09 to 5.18 Bq/kg, for ¹³⁴Cs and ¹³⁷Cs, respectively. The corresponding average effective dose equivalents ranged from 0.003 to 0.337 μSv, thus do not represent a health risk for humans.

Abstract. This paper presents an efficient method of knowledge evaluation in the field of radiation protection and of dissemination of basic concepts in the field, by the operation of a freely accessible web platform. The motivation of the study is presented, aimed for the improvement of the radiation protection culture of interested public, consisting mainly in professionals working in the radiation or nuclear technology applications, and for the informed acceptance of the risks associated to nuclear medical and industrial technologies. The method is described in detail and the results are discussed, explained and compared with other similar literature reported studies.

Abstract. Amazing technological advancement has been made in the aria of communications. Modern communication technology has brought about an evolution in the access to knowledge, in globalization and also in the new ways of shaping education. Therefore, this period, called Knowledge Age or Information Age, opens up new possibilities in the field of formal and informal education, in the ways of delivering education, either in class or online, and also in the role of the teacher. Smartphones, due to their high speed internet access capabilities, large storage capacities, embedded multi-functional sensors, and integrated modern smart applications, are in fact mobile computers that can be integrated into learning environments. This article presents two physics experiments performed using smartphones, experiments that are meaningful because they relate reality to physics laws, creating theory-practice linkage, and that can be performed outside the classic physics laboratory. The cost-free application employed is called Phyphox. Following the experiments described in this paper, acceleration of a non-inertial frame of reference was calculated, respectively, Malus law was verified. Students were able to follow the real-time obtained graphs just by accessing a link (URL).

Abstract. In this paper problems that arose with the introduction of distance learning in physics at the Technical University of Sofia due to the COVID-19 pandemic and the imposition of video recording of laboratory exercises are indicated. It was found that the video for the Damped Mechanical Oscillations exercise provides enough information for a more detailed and in-depth analysis of the studied phenomenon compared to the standard way of capturing the data. The Video Editor program was used to view the video frame by frame and statistical processing - non-linear regression - was performed with the recorded data. The laboratory results are compared with the theoretical function, the parameters of which are optimized as a result of the specified processing. A theoretical model of the damped oscillation is described and the dependence of the damping coefficient on the current through the electromagnetic brake is theoretically investigated.

Abstract. In the framework of the Romanian Educational Seismic Network project (ROEDUSEIS, 2012 ̶ 2016), the National Institute for Earth Physics introduced in Romania the globally validated concept of using seismology as a tool for teaching geosciences by installing educational recording instruments in schools. The ROEDUSEIS network has been upgraded in the last year by installing new Raspberry Shake educational seismometers. This type of seismometer is very similar to the professional ones, in terms of performance, data acquisition and technical characteristics, the main difference being the low cost of the educational seismometers. In addition to the development of the ROEDUSEIS network, which allowed the recording of a larger number of earthquakes, several online tools have been implemented for the visualization and analysis of the recorded data. They are available for download and can be run online by teachers and students to improve their programming skills using real seismic data and learn more about Earth Sciences. These developments capitalize on and at the same time ensure the sustainability of the successful ROEDUSEIS projects results.

Abstract. Research in physics education shows that for an efficient learning, it is necessary to combine traditional and eLearning methods. In this paper, we present means of employing virtual experiments in introductory physics laboratory for the second year of the middle school. We used Articulate Storyline 2 software to create two simple interactive virtual experiments for determination of length and duration physical quantities. The interaction with the proposed virtual systems creates a more constructive and active learning environment and enhances the quality of instruction.