Facultatea de Fizică şi Inginerie / Faculty of Physics and Engineering
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Item Peculiarities of Seebeck coefficient of semi-metallic bismuth wires in high magnetic field [Articol](2019) Condrea, E.; Muntyanu, F.; Nicorici, ValentinaThe effect of high magnetic field on the transport properties of semi-metallic bismuth has been a subject of increasing interest in the last years because a lot of unexpected findings detected far above the quantum limit of the electrons[1-3]. The presented investigations of the magnetotransport measurements of Bi wires complement the series of recently published experimental results on bulk Bi in high magnetic field. The design of measurements in magnetic field was diversified by using uniaxial deformation directed along the wire axis. By combining high magnetic field and uniaxial strain, the electronic structure of the bismuth wires was modified; as a result, the quantum limit for light and heavy electrons could be changed in different ways. Measurements of the thermoelectric response (Seebeck coefficient) in quantizing magnetic field have revealed some oscillating instabilities in the magnetothermopower dependence in a magnetic field of 15 - 20 T. Observed correlation between a simultaneous shift in a magnetic field of the position of the anomalies and of the quantum limit of electrons, when modifying of the electronic structure under strain, allows us to attribute of unidentified peaks to the complex structure of the lowest Landau level of electrons when one of the lowest spinpolarized Landau sublevel of heavy electrons approaches and crosses the Fermi energy level. It should also be noted that a decrease in the resistance in higher fields with the apparent metallization of bismuth indicates possible changes in the mechanism of carrier scattering associated also with the Lifshitz Transition and with the substructure of the last Landau level of electrons.Item Obtaining highly conductive oxide single crystals for manufacturing nanotemplates [Articol](2019) Colibaba, Gleb; Monaico, E.; Rusnac, D.The present investigation is devoted to obtaining ZnO, In2O3 and Ga2O3 single crystals by chemical vapor transport (CVT). The thermodynamic analysis of the composition of CVT systems with ZnO, In2O3, Ga2O3 and various transport agents (TAs) is carried out for wide temperature range and for various density/composition of TA. The influence of the growth temperature and of the TA density/composition on the mass transport rate is investigated theoretically and experimentally. The possibility of increase in mass transport rate by several orders of magnitude at the presence of compound TAs is demonstrated. The application prospects of obtained single crystals as substrates for manufacturing nanoporous matrices (nanotemplates) by the electrochemical etching are analyzed. The fabrication of nanopore arrays with various morphology, which depends on the crystallographic orientation of substrates, is demonstrated for ZnOItem Phonons in twisted graphene [Articol](2019) Nika, DenisWhen two graphene layers are placed on top of each other, they can form a moire pattern – twisted graphene. In this case, one layer of carbon atoms is rotated relative to another layer by an arbitrary angle. In the talk, a brief review of recent theoretical and experimental results [1-3] on the engineering of phonon properties of twisted graphene by atomic plane rotations are provided. Angle-dependent specific heat and thermal conductivity of twisted graphene are discussed.Item Quantum nanostructures for terahertz devices and applications [Articol](2019) Sirkeli, Vadimerahertz (THz) waves refer to the electromagnetic radiation in the frequency range from 0.1 to 10 THz, which corresponds to the wavelengths from 3 mm to 30 μm, respectively. This spectral region, called also as “T-gap”, is important for many practical applications, including THz imaging, chemical and biological sensing, high-speed telecommunication, security and medical applications. Here we report the results of a numerical study of quantum transport in ZnO-based resonant-tunneling diodes (RTDs) and quantum cascade lasers (QCLs) with different design schemes. We found that by varying and optimizing constituent layer widths and doping level these quantum structures, high power performance of THz RTDs and QCLs can be achieved at room temperature. Moreover, it was established also that the ZnO-based terahertz sources can cover the spectral region of 5-12 THz, which is very important for THz imaging and detection of explosive materials, and which could be not covered by conventional GaAs-based terahertz devices.Item The interaction between Endothelial Cells and Gallium Nitride nanoparticles [Articol](2019) Braniste, Tudor; Andree, Birgit; Benecke, Nils; Raevschi, Simion; Plesco, Irina; Cebotari, Serghei; Haverich, Axel; Tighineanu, Ion; Hilfiker, AndresIn this study, human umbilical vein endothelial cells (HUVECs) were investigated in direct contact with Gallium Nitride (GaN/Fe) based nanoparticles. GaN is a compound semiconduc- tor material, with remarkable characteristics including piezoelectric properties, high thermal stability, radiation hardness and excellent chemical inertness, which make it promising for biomedical applications. There is, however, limited knowledge about the biocompatibility of nanostructured GaN and the impact of GaN nanoparticles on living cells. We report on growth and characterization of GaN/ZnFe2O4 multifunctional piezoelectric and magnetic nanoparticles as well as on their assimilation and interaction with HUVECs. Thin GaN layers were grown on ZnFe2O4 nanoparticles with sizes up to 100 nm, using Hydride Vapor Phase Epitaxy (HVPE). After GaN growth, the sacrificial core of nanoparticles was decomposed at high temperatures in hydrogen flow, the final composition of nanoparticles corresponding to GaN:Fe. The resulted nanoparticles were incubated with human umbilical vein endothelial cells in order to remotely influence the cells activity through nanoparticles. By cultivating cells in medium supplemented with different concentrations of nanoparticles, we show that HUVECs tolerate GaN nanoparticles. The obtained results show that, being uptaken by the cells, the GaN nanoparticles are deposited into vesicles and thus can be used as guiding elements for controlled transportation or designed spatial distribution of cells in a magnetic field, which represent a step forward towards application in cellular therapy.Item Educaţie pentru Drone : Suport de curs(CEP USM, 2019) Nedeoglo, Natalia; Rotaru, Corneliu; Sprincean, Veaceslav; Danici, Anton; Seinic, Valeriu; Vozian, Constantin; Cazan, Valeriu; Corcimari, Ion; Cebotaru, EugeniaItem Разработка программно-аппаратного комплекса для удаленного управления системами освещения [Articol](CEP USM, 2019) Чукля, НикитаThe article focuses on sketch-based 3D-modeling. While drawings are easy for humans to create, they are very challenging for computers to interpret due to their ambiguity. My approach is to use neural networks to solve image recognition problems. Neural network is able to recognize a sketch and return parameters to generate a polygonal model. The result of practical work is an application written in JavaScript that combines a neural network and a visualizer of three-dimensional models.Item Применение нейронных сетей в компьютерной графике [Articol](CEP USM, 2019) Гаврищук, ВладиславThe article focuses on sketch-based 3D-modeling. While drawings are easy for humans to create, they are very challenging for computers to interpret due to their ambiguity. My approach is to use neural networks to solve image recognition problems. Neural network is able to recognize a sketch and return parameters to generate a polygonal model. The result of practical work is an application written in JavaScript that combines a neural network and a visualizer of three-dimensional models.Item Developing an expert system [Articol](CEP USM, 2019) Stratan, CristinaLanguage is important to communicate with another human being in any way that they both can understand each other. Being tolerant does not only mean that you have to accept others but also give a chance to interact with minorities in a society. We all know a few phrases from foreign languages that we don’t speak, just imagine learning a few expressions from the sign language. Mika chatbot is exactly designed for that, it teaches you fingerspelling for a basic communication with a disabled person.Item Proprietațile galvanomagnetice ale cristalelor Pb0,9Cd0,1Te:Ga<0,5> [Articol](CEP USM, 2019) Oprea, IrinaRecently, narrow band Pb1-xCdxTe semiconductors have gained a special interest, because they are used to construct IR detectors. In this work is presented a complex study of the transport phenomena in Pb1-xCdxTe:Ga crystals and the analysis of their parameters.