Abstract. As part of the centennial celebrations that mark 100 years that have passed since 1918 when all Romanian historical provinces were united in a single nation state, we survey in this resource article the publication record of the Physics Section of Proceedings of the Romanian Academy - Series A. Following a series of historical information on the Romanian physics community and the appearance of Proceedings of the Romanian Academy - Series A, we outline the research topics covered by the journal and briefly sketch the scientific profiles of some of the scientists who published in the journal.

Abstract. We study the general relativity with an electromagnetic stress tensor, as source, and Maxwell's equations in curved space. We investigate the similarity solutions of field equations of these two areas by using the generalized symmetry method based on Fréchet derivative of the differential operators. Metrics and electromagnetic fields as functions of two independent variables are considered. The field equations are presented in a scientific form and certain exact solutions of these equations are systematically derived. The results are achieved by obtaining the infinitesimals of the group of transformations, which leave the system of field equations invariant. An optimal system of conjugacy inequivalent subgroups is then identified with the adjoint action of the symmetry group. This is further used to reduce the system of field equations into a system of ordinary differential equations with the aim of deriving certain exact solutions.

Abstract. In this paper, the problem of heat transfer of the boundary layer nanofluid flow over a stretching and a shrinking sheet has been investigated in the presence of the suction and the slip parameters. In the case of stretching sheet, the current exact results for the heat transfer rate (in the absence of some parameters) have been compared with the numerical ones in the literature, where some differences are found. In the presence of the slip parameter and no suction, the present results by using a few components of Adomian's series agree with those of the homotopy analysis method in the literature. In the case of shrinking sheet, the exact dual solution is obtained in a special case, while the approximate dual solution has been obtained in the general case by Adomian's method. In addition, the effects of the suction, the slip, the Brownian motion parameter, and the thermophoresis parameters on the dual velocity, the dual temperature, and the dual nano-particle concentration have been discussed through graphs.

Abstract. O-H stretching vibrations of the two formic acid rotamers were studied using a static approach, based on calculation of the corresponding 1D vibrational potential and subsequent solution of the vibrational Schrödinger equation, and with a dynamic approach, based on Born-Oppenheimer molecular dynamics simulations, followed by computation of partial autocorrelation functions and their subsequent Fourier transformation. All calculations were performed at second-order Møller-Plesset perturbation theory level, using the 6-311++G(3df,3pd) basis set for orbital expansion. Emphasis has been put on the usage of these results in the course of spectroscopic detection of this compound, with unique atmospheric chemistry significance, under realistic conditions.

Abstract. The effects of the electric, magnetic, non-resonant intense laser and control laser fields on the electronic and optical properties (absorption coefficient and refraction index) of a GaAs/Al_0.3Ga_0.7As semi-parabolic quantum well related to the occurrence of the electromagnetically induced transparency phenomenon are investigated. We found that the electromagnetically induced transparency occurs in the system in all cases but it is advantaged by a proper choice of the external fields. The increase of the non-resonant laser intensity strongly enlarges the transparency window width. Furthermore, the transparency window for absorption of the probe laser is blue-shifted by the augment of the electric or magnetic field strength.

Abstract. The field of microfluidic devices for real-time polymerase chain reaction analysis has seen significant advances during the last years. Our study of Ni thin films grown on polydimethylsiloxane (PDMS) substrates was triggered by the perspective of using and integrating such structures in future on-chip DNA amplification devices. The thin films were obtained by pulsed laser deposition from a Ni target onto Si and PDMS supports. The samples were characterized mainly from a structural, morphological, compositional, and optical point of view. Initial electrical measurements, at low currents, revealed that the stripes exhibit resistance values of the order of 100 ohms.

Abstract. The properties of thin film polymers such as low dielectric constant, high thermal and photo balance, high chemical resistance and high optical transmittance are widely used in optic and microelectronics. In this work, plasma poly(ethylene oxide) (pPEO) thin films in different thicknesses were deposited between Aluminum (Al) electrodes on glass substrates by plasma assisted physical vapor deposition (PAPVD) technique at Argon plasma under 10^-3 Torr. The plasma was produced at 5 W by magnetron connected to RF power supply. The ac measurements of the samples were made were in the frequency range 10^-1 Hz -10⁷ Hz and in temperatures from 193 to 353 K with increments of 10 K. Thickness dependent AC conductivity of pPEO thin films can be interpreted by empirical relation ς(ω)∝ωⁿ where ω is the angular frequency and n is the parameter. Frequency, temperature and thickness dependence of AC conductivity showed that there were oligomers and free radicals with different sizes produced by plasma polymerization of PEO. The thickness dependence of AC conductivity of plasma PEO samples can be evaluated to adjust AC conductivity and also to adjust the DC-like conductivity which is a results of drift of free charge carriers or the orientation polarization of long oligomers. Three different relaxation mechanisms depending on the film thickness were observed. The effect of the dead layer in the polarization region of long oligomers was determined.

Abstract. Yttria Stabilized Zirconia thin films are of great technological interest, mainly as high-k dielectric materials, having potential applications as electrolytes for ionic devices. In this work, we explore the influence of growth parameters, such as target-substrate distance and number of ablation pulses, on the properties of YSZ thin films with variable thicknesses, which are of interest for the fabrication of micro-sized solid oxide fuel cells (μSOFC) and lambda sensor operating at low temperatures. Yttria Stabilized Zirconia (8YSZ) thin films with crystalline cubic structures were grown by pulsed laser deposition (PLD) on Si (100) substrates at a temperature of 600^oC, in oxygen atmosphere. The structural and optical properties of the target and thin films were investigated through different techniques.

Abstract. The effect of gamma irradiation on three antibiotics (Nalidixic acid, Spectinomycin, and Rifampicin) were studied. The drugs were exposed to different doses of radiation emitted by ⁶⁰Co source, up to 205 kGy. The degradation induced on the above antibiotics by ionizing radiation was discussed based on their UV-VIS and FTIR absorption spectra.

Abstract. Dose distributions in different models of inhomogeneous phantoms irradiated with 3-19 MeV electron beams have been calculated using DOSXYZnrc/EGSnrc Monte Carlo code. The rectilinear 3D voxel phantoms, relevant for radiotherapy and clinical dosimetry, were built from ICRU soft tissue equivalent material in which was inserted a single layer of bone, lung, air or Titanium. Significant interface effects have been found and qualitatively discussed.

Abstract. The presented study is part of a research project that has as main purpose recycling of coarse and fine aggregates from radioactive concrete, as rubble pre-placed and mortar for filling containers and the stabilization of the radioactive waste. The leaching behaviour of ¹³⁷Cs, ⁶⁰Co and ¹⁵²Eu radionuclides was studied in aqueous medium, for the radioactive mortar samples made from recycled aggregates compared to samples made of natural aggregates. Recycling of the radioactive concrete allows the minimization of the low level radioactive concrete volume that should be disposed, in accordance with all the applied legal requirements.

Abstract. On April 25, 2009, at 20:18:48 (local hour) the Romanian territory was shaken by a moderate size earthquake centred beneath the bending area of the south-eastern Carpathians, in the Vrancea seismogenic region (Romania). In the present paper we present intensity map, macroseismic intensities, and community observations of effects for the M_W=5.4 Vrancea subcrustal earthquake of 25 April, 2009. For many locations, for the estimation of the macroseismic intensities besides questionnaires other type of sources such as press reports, internet were used. The highest intensity assigned for this Vrancea earthquake was VI MSK, estimated for eleven locations, situated in the north-eastern part of Vrancea seismogenic zone, which include parts from Vrancea, Bacau, and Galati counties. At the lowest intensities, the 2009 earthquake was felt to a distance of 500 km from the epicenter, in Rep. of Moldova, Bulgaria, Ukraine, and Serbia. A non-uniform distribution of intensity resulted for locations on different directions from the epicenter. A scatter of as much as one-two intensity units were observed for places situated very close. The comparison of the intensity areas for the October 27, 2004 and April 25, 2009 moderate subcrustal earthquakes of the Vrancea seismogenic zone was performed.

Abstract. Earthquake mechanism information is fundamental to determine the stress field and to define seismogenic zones. At the same time, it is a basic input to compute seismic hazard by deterministic approach. The present paper extends the catalogue of the fault plane solutions for the earthquakes in Romania, previously completed until 1997, for 1998-2012 time interval. The catalogue is limited geographically to the Carpathians Orogeny and extra-Carpathians area located in the south-eastern part of Romania because similar investigations cover the rest of the country. The catalogue comprises 259 intermediate-depth seismic events and 90 crustal seismic events, recorded in the considered time interval with acceptably constrained fault plane solutions. We use specific graphical tools in order to emphasize statistically representative features of the stress field as coming out from our results. The fault plane solutions of the Vrancea earthquakes generated in a confined sinking plate in the mantle reflect the dominant geodynamic process in the study region. The typical features revealed by all the previous studies on the subcrustal seismic activity (predominant dip-slip, reverse faulting, characterizing both the weak and strong earthquakes) are reproduced as well by our investigation. As concerns the earthquake activity in the crust, a few new refined aspects are highlighted in the present work: (1) a deficit of the strike-slip component over the entire Carpathians foredeep area, (2) different stress field pattern in the Fagaras-Campulung zone as compared with the Moesian Platform and Pre-Dobrogean and Barlad Depressions, (3) a larger range for the dip angle of the nodal planes in the Vrancea subcrustal source, ∼ 40^o-70^o against ∼ 70^o, as commonly considered.

Abstract. In this article we investigate how students can build and use, in high-school Physics lessons, various interactive simulations aiming to a better understanding of the phenomenon of multiple reflections in two intersected plane mirrors. The applets achieved with GeoGebra allow changing the angle between the mirrors, the position of the source object and the position of the first reflexion point of a successively reflected ray of light. The applets provide a dynamic representation of the images of a movable object and also a representation of a reflected ray, highlighting the relation between the positions of the images and the extensions of a reflected ray. After discussing the positioning of the images of the point-like objects, we will address the same problem for some colourful polygonal shapes, resulting in kaleidoscopic figures. Finally, using GeoGebra, the students can simulate the movement of a point-like body that collides elastically against two walls forming an arbitrary angle, based on the analogy between the trajectory of the body and the path of a successively reflected ray in two plane mirrors. By building and using simulations students have the opportunity to make connections between their Math and Science knowledge, developing their skills in solving interdisciplinary problems.