物理最新文献

A study of the dynamical and thermodynamical stability of a charged thin-shell wormhole built by gluing two Reissner–Nordström geometries is presented. The charge on the shell is linearly related to the matter content. For the dynamical stability, a concise inequality is obtained, valid for any barotropic equation of state that relates the pressure with the energy density at the throat. A thermodynamical description of the system is introduced, which leads to the temperature and the electric potentials. Adopting a linear equation of state for the pressure and a definite form for the entropy function, the set of equilibrium configurations that are both dynamically and thermodynamically stable is found.

Porosity of materials, understood as an overall averaged parameter or as the pore-size distribution related data is an important quality of numerous functional materials including proton conductive glasses. While most of the existing techniques applied for its assessment cannot be used to monitor the behaviour of ‘live’ systems in operando conditions, it is possible to use Electrochemical Immittance Spectroscopy (EIS) for this purpose. Nevertheless, analysis of these systems still requires an approximation made using transmission lines based models, which can be equated to specific diffusion elements parameters, which can in turn be related to qualities of the porous material investigated. The changes of these parameters can be correlated with various processes– such as dehydration and phase transitions or to the material’s processing history. In this part of the material we present a case study of highly grinded, mechanochemically processed powder-pressed proton conductors: phosphate-silicate glass and two uranyl based compounds– hydroxy phosphate (HUP) and hydroxy arsenate, delivering proof that the dispersive properties of proton transporting materials can be correlated with their dehydration processes, which were followed by means of FT-IR and terahertz time domain spectroscopies.

We obtained the metric of the Schwarzschild-like black hole with loop quantum gravity (LQG) corrections in anti-de Sitter (AdS) space-time, under the assumption that the cosmological constant is decoupled in LQG. We investigated its thermodynamics, including the equation of state, criticality, heat capacity, and Gibbs free energy. The (P-v) graph was plotted, and the critical behavior was calculated. It was found that, due to the LQG effect, the quantum-corrected Schwarzschild-AdS black hole exhibits a critical point and a critical ratio of 7/18, which differs from the Reissner–Nordstr(ddot{textrm{o}})m-AdS black hole’s ratio of 3/8 (the same as that of the Van der Waals system) slightly. However, there are still some similarities compared to the Van der Waals system, such as the same critical exponents and a similar (P-v) graph. Moreover, it is concluded that the energy-momentum tensor related to the black hole’s mass could violate the conventional first law of thermodynamics. This modified first law may violate the conservation of Gibbs free energy during the small black hole-large black hole phase transitions, potentially indicating the occurrence of the zeroth-order phase transition. The Joule–Thomson expansion was also studied. Interestingly, compared to the Schwarzschild-AdS black hole, the LQG effect leads to inversion points. The inversion curve divides the (left( P,Tright) ) coordinate system into two regions: a heating region and a cooling region, as shown in detail by the inversion curves and isenthalpic curves. The results indicated that there is a minimum inversion mass, below which any black hole will not possess an inversion point.

Polycrystalline YBa₂Cu₃O_7−δ (Y-123) samples with different varying weight percentages (x = 0.0, 0.1, 0.3, 0.5, 1.0, and 5.0 wt.%) of neodymium oxide (Nd₂O₃) addition have been successfully synthesized using a modified thermal decomposition method (DM) under ambient conditions. X-ray diffraction (XRD) analysis revealed favorable orthorhombicity values (~ 0.008) for the Y-123 crystal structure, and an estimated oxygen content close to the theoretical value (~ 6.8), along with the presence of light secondary phases such as Y₂BaCuO₅ (Y-211) and BaCuO₂. For FESEM analysis, it was found that 5.0 wt.% Nd₂O₃ increased porosity and reduced grain size, negatively impacting superconductivity. Conversely, 0.5 wt.% Nd₂O₃ promoted significant grain growth, leading to enhanced grain contact and a denser microstructure. Electrical resistivity measurements confirmed superconducting transitions in all samples. Notably, the 0.5 wt.% Nd₂O₃ sample exhibited an optimal T_c-onset of 94.14 K with a narrow transition width ΔT_c of 4.04 K. In contrast, the higher 5.0 wt.% Nd₂O₃ concentration resulted in a broader ΔT_c of 7.47 K, suggesting the lower doping provided more optimal superconducting performance. AC susceptibility measurements corroborated these findings. This DM method offers a cost-effective approach for Y-123 synthesis, with potential for further optimization through alkali metal doping to reduce costs and environmental impact.

We studied the impact of Ge-doping on material properties of polycrystalline GaN layers with different Ge percentages of 2%, 5% and 10%. The carrier concentration for the undoped polycrystalline GaN layer is ~ 6 × 10¹⁹ cm^− 3, and the value increases up to ~ 1.1 × 10²¹ cm^− 3 by the Ge-doping with 5% of Ge. Meanwhile, the electron mobility is the lowest at 98.6 cm²/Vs with 5% of Ge. The result is comparable to some reported Ge-doped single crystal GaN layers with the carrier concentration of above 10²⁰ cm^− 3. Additionally, the surface of the polycrystalline GaN layer changes significantly with the Ge percentage above 5%. In particular, GaN grain protrusions and GaN grain-like rods are observed. It is found that Ge-N related compounds can form on the GaN grain-like rods. The grain protrusions and grain-like rods lead to the broadening of the Raman E₂ peak, indicating that the crystalline properties can be degraded by excessive Ge-doping.

In the context of General Relativity (GR), violation of the null energy condition (NEC) is necessary for existence of static spherically symmetric wormhole solutions. Also, it is a well-known fact that the energy conditions are violated by certain quantum fields, such as the Casimir effect. The magnitude and sign of the Casimir energy depend on Dirichlet or Neumann boundary conditions and geometrical configuration of the objects involved in a Casimir setup. The Casimir energy may act as an ideal candidate for the matter that supports the wormhole geometry. In the present work, we firstly find traversable wormhole solutions supported by a general form for the Casimir energy density assuming a constant redshift function. As well, in this framework, assuming that the radial pressure and energy density obey a linear equation of state, we derive for the first time Casimir traversable wormhole solutions admitting suitable shape function. Then, we consider three geometric configurations of the Casimir effect such as (i) two parallel plates, (ii) two parallel cylindrical shells, and (iii) two spheres. We study wormhole solutions for each case and their property in detail. We also check the weak and strong energy conditions in the spacetime for the obtained wormhole solutions. The stability of the Casimir traversable wormhole solutions are investigated using the Tolman-Oppenheimer-Volkoff (TOV) equation. Finally, we study trajectory of null as well as timelike particles along with quasi-normal modes (QNMs) of a scalar field in the wormhole spacetime.