http://dspace.univ-jijel.dz:8080/xmlui/handle/123456789/28 Mon, 28 Sep 2026 13:15:52 GMT 2026-09-28T13:15:52Z http://dspace.univ-jijel.dz:8080/xmlui/handle/123456789/16590 Systèmes Dépendant du Temps et Création de Particules CHERIET, Loubna; Haouat, S(directeur de thesse) This thesis deals with the problem of scalar particle creation in time-dependent systems using the Ermakov-Lewis invariant method. We begin by reviewing di erent formulations of quantum mechanics, with an emphasis on those that can be extended to quantum eld theory. We then study particle creation in time-dependent electric elds, making use of solutions of the Ermakov{Milne equation, and discuss several exactly solvable cases. We next turn to the cosmological setting and consider the dynamics of quantum elds in an expanding universe, both isotropic and anisotropic. In this context, we show that the time-dependent particle number can be interpreted as a measure of the deviation between the adiabatic vacuum and the invariant vacuum. We also point out that a suitable rede nition of the elds, together with a reparameterization of time, is often necessary to recover an adiabatic evolution in the asymptotic regimes, and hence to give a consistent de nition of particles. Finally, we introduce a uniform semiclassical approximation to deal with more complicated situations where exact analytical solutions are not available, such as transitions between di erent cosmological eras or models involving a generalized uncertainty principle with a minimal length. This work shows that the Ermakov-Lewis approach provides a general and useful framework for describing non-stationary quantum systems, and o ers a coherent way to analyze particle creation in various physical contexts. Wed, 01 Jan 2025 00:00:00 GMT http://dspace.univ-jijel.dz:8080/xmlui/handle/123456789/16590 2025-01-01T00:00:00Z http://dspace.univ-jijel.dz:8080/xmlui/handle/123456789/16585 Optimisation de la production de métabolites secondaires à intérêt thérapeutique par Penicillium sp. CHEMMAM, Dounya Achwak This research provides new insights into the thin-layer quantization method for both spinless and spin-1/2 particles, particularly regarding the impact of the induced geometric potential on a system's energy levels. For the spinless case, we have correctly applied the thin-layer quantization scheme to a particle constrained to a cone. The bound states for this system occur only when the quantum number is equal to zero, and we demonstrate that the Gaussian curvature reduces the binding energy. For the spin-1/2 particle case, we have considered the non-relativistic limit of the Schrödinger-Dirac equation defined in a curved space-time. This was achieved by introducing a squeezing potential through a minimal coupling procedure. As a result, we obtained a new scalar geometric potential composed of three additive terms. These new potentials can alter the nature of the usual da Costa potential. Furthermore, we have demonstrated, through examples, the important role of the coupling between the geometry of the curved surface and the particle's spin in creating bound states. Wed, 01 Jan 2025 00:00:00 GMT http://dspace.univ-jijel.dz:8080/xmlui/handle/123456789/16585 2025-01-01T00:00:00Z http://dspace.univ-jijel.dz:8080/xmlui/handle/123456789/14810 Study of the effect of doping and processing conditions on the temperature coefficient of resistivity of perovskite manganite doped at A-site: A1-xRxMnO3 Belal, Ibtihal; Meriche, Faiza (Encadreur) Manganite based perovskite materials are extremely intriguing from both a technological and fundamental standpoint due to the substantial correlations observed among their structural, magnetic, and transport properties. The primary aim of this thesis is to synthesize La0.7Ca0.18Ba0.12Mn0.95Sn0.05O3 (serie 1) and La0.7Ca0.18-xSrxBa0.12Mn0.95Sn0.05O3(0.00≤x≤0.06) (serie 2) perovskite manganite compounds with different quenching processes and strontium content and to investigate their structural, electrical, magneto-transport and magnetic properties. These two sets of samples were prepared by the well-known solid-state method and characterized by using X-ray diffraction, SEM, 4- Point probe method and SQUID magnetometer. The detailed structural study of the both series confirmed that all samples crystallized in the orthorhombic system with Pnma , Pbnmspace-groups and in the rhombohedral system with R3 ̅c space-group. The micrometric granular nature of the samples with distinct grain boundariesare revealed by a scanning electron microscope. The magnetic measurements carried out for all the samples showed a Ferromagnetic-paramagnetic transition at TC temperature and demonstrated the existence of Griffiths phase in the nitrogen quenched sample (serie 1). Doping with Sr ions (serie 2) conducted to an increase in the TC temperature. Moreover, the electrical and magneto-transport findings indicated that all samples undergo a transition from metal to insulator at TMI temperature and demonstrated a magnetoresistive character when subjected to a 1 Tesla external magnetic field. Quenching in nitrogen showed a decrease in the electrical resistivity of the sample, an increase in the TMI, and an increase in the magnetoresistance value (best magnetoresistance value 33.31%), while the maximum value of the temperature coefficient of resistivity (TCR) is recorded for the sample quenched in air. The Sr doped samples displayed a decrease in the electrical resistivity, which affected the magnetoresistive properties. The maximum temperature coefficient of resistivity value 1.63% was obtained for the sample with x=0.02. According to the resistivity fitting results, the ρ (T)curves for all samples in the metallic state are governed by a combination of various interactions: weak localization, residual resistivity, electron-phonon, electron-electron and electron-magnon interactions. Additionally, the fitting indicated that within the insulating state, the conduction process is regulated by variable range hopping mechanism above the half Debye's temperature 〖(θ〗_D/2) and by polaronic mechanism below it. The mean hopping distance (R_h) and the mean hopping energy (E_h) expended by the electron during its hops were calculated within the suitable temperature range and discussed in the light of the theory of VRH. Mon, 01 Jan 2024 00:00:00 GMT http://dspace.univ-jijel.dz:8080/xmlui/handle/123456789/14810 2024-01-01T00:00:00Z http://dspace.univ-jijel.dz:8080/xmlui/handle/123456789/14770 Elaboration and study of the physical properties of a chromite with perovskite structure and/or derivatives Bouasla, Fatima Zohra; Mahamdioua, N. (Encadreur) In this thesis, we prepared and examined in depth the structural, microstructural, optical, and magnetic properties of some lanthanum-based perovskite chromites. We are interested in the effect of rare earth substitution in the 𝐿𝑎0.8𝐶𝑎0.2𝐶𝑟𝑂3 and 𝐿𝑎0.8𝐵𝑎0.2𝐶𝑟𝑂3, in which the RE are Nd, Sm, and Eu, so that we got the series: 𝐿𝑎0.7𝑅𝐸0.1𝐶𝑎0.2𝐶𝑟𝑂3, as well as 𝐿𝑎0.7𝑅𝐸0.1𝐵𝑎0.2𝐶𝑟𝑂3. We have prepared the samples by the solid-state reaction technique under identical conditions. The structural investigation revealed that the samples crystallized in an orthorhombic perovskite structure with the Pbnm or Pnma space group with slight differences in the structural parameters values. The FTIR analysis confirms the perovskite structure, while EDS checks and confirms the purity of our components. The SEM images revealed the granular and the porous characters of the samples surfaces. The grains have a micrometer size which appears to be influenced by the RE substitution. The optical absorption of the samples is found to be influenced by the A-site composition, where the LCCO sample exhibits a higher optical absorption than the LBCO. The reduction in the RE ionic radius improves the optical absorption in the 𝐿𝑎0.7𝑅𝐸0.1𝐶𝑎0.2𝐶𝑟𝑂3 samples; however, it has no significant effect on the 𝐿𝑎0.7𝑅𝐸0.1𝐵𝑎0.2𝐶𝑟𝑂3 ones. In the 𝐿𝑎0.7𝑅𝐸0.1𝐶𝑎0.2𝐶𝑟𝑂3 system, the estimated Eg values show an increase by decreasing the RE ionic radii from 2.96 to 3.27 eV, while the inversion trend is obtained for 𝐿𝑎0.7𝑅𝐸0.1𝐵𝑎0.2𝐶𝑟𝑂3. For pristine samples, the lowest value of Eg=3.2 eV is achieved for LBCO sample. The structural parameters: Cr- O band distance, Cr-O-Cr average bond angles, and octahedral tilting, present an obvious effect on the magnetic properties of the samples. The magnetic investigation of samples showed a reduction of the antiferromagnetic transition temperature (TN), except in the case of 𝐿𝑎0.7𝑅𝐸0.1𝐵𝑎0.2𝐶𝑟𝑂3 system, where it presents a slight rise which could be consider as stable. By the cooling below TN, the samples exhibit a weak ferromagnetic explained via the Cr3+ ions antiferromagnetic canting behavior. A particular magnetic signature is seen in the samples substituted with 𝑁𝑑 and 𝑆𝑚, traduced by the occurrence of a spin reorientation transition. The samples doped with Nd exhibit negative magnetization in their FC curves, which is may be caused by the formation of an opposite internal field to an applied one and confirmed by the fitting of M(T). In its ZFC curve, the sample 𝐿𝐶𝐸𝑢𝑂 exhibits spin glasses-like behavior at low temperatures. The hysteresis loops of all compounds indicate the presence of AFM and Weak FM states. It is found to be varied with the selected temperature measurement and with the RE elements. The interaction of these two states in the interface gives rise to the exchange bias effect. This effect is most noticeable at low temperatures (T=1.8), and its field takes opposite sign in some samples. According to the finding values of 𝐸𝑔, we can suggest that our materials can be used in optoelectronic devices. In thermomagnetic switch and spin-valve devices, Nd-doped samples can be a useful material. Because of the EB effect, the samples are suitable for magnetic sensors, magnetic recording devices, nonvolatile magnetic random-access memory (NMRAMs), and other spintronics devices. Mon, 01 Jan 2024 00:00:00 GMT http://dspace.univ-jijel.dz:8080/xmlui/handle/123456789/14770 2024-01-01T00:00:00Z