Narrow Results

100 mol% activator orthorhombic Tb₂(MoO₄)₃ green phosphors were prepared using a solid-state reaction method. The impact of sintering temperature on the crystalline phase structures, the compositions, the sizes and morphologies of particles, the values of energy bandgap ($E$${}_g$), the photoluminescence (PL) excitation and emission spectra, the fluorescence lifetimes, PL quantum yield (PLQY), and the luminescent thermal stabilities of the prepared material were comprehensively investigated. The particle size increased from 2.54 to 5.81 $\mu$m and the $E$${}_g$ decreased from 3.60 to 3.41 eV with the calcine temperature increased from $800^{\circ }\text{C}$ to $1100^{\circ }\text{C}$. The Tb₂(MoO₄)₃ green phosphor prepared at $1000^{\circ }\text{C}$ exhibited optimal PL intensity though it did not possess the highest PLQY with 380 nm excitation. Moreover, the sample prepared at $1000^{\circ }\text{C}$ showed better thermal stabilities than that prepared at $1100^{\circ }\text{C}$. The research proved the sintering temperature has great effects on the properties of Tb₂(MoO₄)₃ phosphors.

A novel class of copolyesters containing the metallophthalocyanine ring [M-Pc, M=Fe(III), Co(II)] in the chain was synthesized by polycondensation of (dicarboxyphthalocyaninato) metal [M-Dapc, M=Fe(III), Co(II)] diacid chloride, terephthalic acid chloride and aliphatic diols. The structures of the copolyesters were characterized by infrared, electronic as well as ESR spectra, and viscosity measurement. The thermal stabilities of the polymers were evaluated by dynamic thermogravimetric analyses. The polymers obtained thus were easily soluble in chloroform, dichloromethane, etc. The green or blue colored fiber was formed by melt spinning of the copolyesters containing below 1 mol % M-Pc component. The copolyester containing Co(II)-Pc in the chain obtained from 1,2-ethanediol as a diol component catalysed the autoxidation of 2-mercaptoethanol in the presence of oxygen.

A thermal stability analysis method of meta-aramid insulating paper based on computer molecular dynamics technology is designed in this paper. First, the raw materials and equipment for preparing meta-aramid insulating paper were determined to prepare meta-aramid insulating paper. Then, the internal structure and morphology of meta-aramid insulating paper are analyzed for the subsequent stability analysis. Finally, the basic principle of computer molecular dynamics technology is analyzed, which is used to analyze the thermal stability of meta-aramid insulating paper, mainly from the stability of its crystal region. The experimental results show that the proposed method is effective and feasible in analyzing the thermal stability of aramid insulating paper between samples.

This paper deals with general thermodynamics for the universe filled with a perfect fluid, obeying an equation of state p = ω(z)ρ where the varying equation of the state parameter is chosen as two-index parametrization models namely: (a) linear redshift parametrization: ω(z) = ω₀ + ω₁z or (b) Jassal–Bagla–Padmanabhan (JBP) parametrization: where ω₀, ω₁ are constants. The behavior of temperature and the thermodynamic stability have been discussed. The thermal equation of state depends on both temperature and volume. As the universe evolves the fluid cools down obeying third law of thermodynamics and there will be thermodynamic stability during the expansion process without any phase transition or passing through any critical point.

Criteria for thermal stability of charged rotating black holes of any dimension are derived for horizon areas that are large relative to the Planck area (in these dimensions). The derivation is based on generic assumptions of quantum geometry, supported by some results of loop quantum gravity, and equilibrium statistical mechanics of the Grand Canonical ensemble. There is no explicit use of classical spacetime geometry in this analysis. The only assumption is that the mass of the black hole is a function of its horizon area, charge and angular momentum. Our stability criteria are then tested in detail against specific classical black holes in spacetime dimensions 4 and 5, whose metrics provide us with explicit relations for the dependence of the mass on the charge and angular momentum of the black holes. This enables us to predict which of these black holes are expected to be thermally unstable under Hawking radiation.

We have derived the criteria for thermal stability of charged rotating black holes, for horizon areas that are large relative to the Planck area (in these dimensions). In this paper, we generalized it for black holes with arbitrary hairs. The derivation uses results of loop quantum gravity and equilibrium statistical mechanics of the grand canonical ensemble and there is no explicit use of classical spacetime geometry at all in this analysis. The assumption is that the mass of the black hole is a function of its horizon area and all the hairs. Our stability criteria are then tested in detail against some specific black holes, whose metrics provide us with explicit relations for the dependence of the mass on the area and other hairs of the black holes. This enables us to predict which of these black holes are expected to be thermally unstable under Hawking radiation.

We have already derived the criteria for thermal stability of charged rotating quantum black holes, for horizon areas that are large relative to the Planck area. The derivation is done by using results of loop quantum gravity and equilibrium statistical mechanics of the grand canonical ensemble. We have also showed that in four-dimensional spacetime, quantum AdS Kerr–Newman black hole and asymptotically AdS dyonic black hole with electric and magnetic charge are thermally stable within certain range of its parameters. In this paper, the expectation values of fluctuations and correlations among horizon area, electric charge and angular momentum (magnetic charge) of these black holes are calculated within their range of stability. Interestingly, it is found that leading order fluctuations of electric charge and angular momentum (magnetic charge), in large horizon area limit, are independent of the values of electric charge and angular momentum (magnetic charge) at equilibrium.

We are engaged in studying thermodynamics of black holes from quantum mechanical perspective and already have published a series of papers. We first showed, based on certain assumptions for quantum mechanical nature of black holes, that they can be thought to be immersed in a thermal bath, i.e. rest of the universe. Of course, this consideration is required to study the thermodynamics of the black holes. We were able to find out the conditions of thermal stability for a black hole with arbitrary number of hairs in arbitrary dimensional spacetime. They came in form of a series of inequalities, connecting second-order derivatives of black hole mass with respect to its area and all the hairs. We then introduced the concept of “Quasi stability”, based on partial fulfillment of stability criteria, for thermally decaying black holes. We had also calculated the fluctuations for different hairs of a stable black hole. In this paper, we extend this calculation for charged rotating quasi-stable black holes. These fluctuations are interestingly found to be similar to that of stable black holes in certain aspects.

A particular type of charged black holes is chosen, based on an action obtained from string theory. This theory predicts the existence of such black holes. Thermodynamic properties of such kinds of black holes are studied. As conjectured earlier, for the dilaton-Maxwell field coupling constant $a=0$, the behaviors of the thermodynamic parameters ($T$, $S$, $F$, $H$ and $G$) are found to resemble with those of the Reissner–Nordström black hole. The geometrothermodynamics of the aforesaid black hole is studied and the Ricci scalar of the Ruppeiner metric is graphically examined for different values of the parameter $a$. Finally, the parameters as well as the $P$-$V$ criticality with different equations for nonzero values of $a$ are analyzed. Their deviations from the case of Reissner–Nordström black hole are noted with care. Furthermore, the stability of the black hole is studied by computing the specific heat and analyzing it graphically.

The issues of holography and possible links with gauge theories in spacetime physics is discussed, in an approach quite distinct from the more restricted AdS-CFT correspondence. A particular notion of holography in the context of black hole thermodynamics is derived (rather than conjectured) from rather elementary considerations, which also leads to a criterion of thermal stability of radiant black holes, without resorting to specific classical metrics. For black holes that obey this criterion, the canonical entropy is expressed in terms of the microcanonical entropy of an Isolated Horizon which is essentially a local generalization of the very global event horizon and is a null inner boundary of spacetime, with marginal outer trapping. It is argued why degrees of freedom on this horizon must be described by a topological gauge theory. Quantizing this boundary theory leads to the microcanonical entropy of the horizon expressed in terms of an infinite series asymptotic in the cross-sectional area, with the leading 'area-law' term followed by finite, unambiguously calculable corrections arising from quantum spacetime fluctuations.

A new model of nonlinear electrodynamics with two parameters is proposed. We study the phenomenon of vacuum birefringence, the causality and unitarity in this model. There is no singularity of the electric field in the center of pointlike charges and the total electrostatic energy is finite. We obtain corrections to the Coulomb law at $r\to \infty$. The weak, dominant and strong energy conditions are investigated. Magnetized charged black hole is considered and we evaluate the mass, metric function and their asymptotic at $r\to \infty$ and $r\to 0$. The magnetic mass of the black hole is calculated. The thermodynamic properties and thermal stability of regular black holes are discussed. We calculate the Hawking temperature of black holes and show that there are first-order and second-order phase transitions. The parameters of the model when the black hole is stable are found.

Making use of a model of nonlinear electrodynamics (NED), whose action remains invariant under conformal transformations, a new class of charged higher-dimensional black holes (BHs) has been introduced in the massive gravity theory. Our exact solutions, with A(dS) asymptotic behavior, in addition to the BHs with one, two and three horizons, show the extreme and horizon-less ones. The conserved and thermodynamic quantities have been calculated in the presence of massive gravitons and NED. By use of a Smarr mass formula, it has been found that the standard form of the first law of BH thermodynamics (FLT) remains valid for our new massive BHs. Thermal stability of the BHs has been studied comparatively, by use of the geometrical and thermodynamical methods. The size of those BHs which undergo first- or second-order phase transition, as well as those of which are locally stable has been determined. The results of geometrical and thermodynamical approaches have been compared, for bout of dS and AdS cases, by use of the plots. It has been shown that both of the aforementioned methods produce the same results provided that HPEM or Quevedo type-two (QII) metrics are used. Critical behavior of the BHs has been studied by taking thermodynamic pressure proportional to the cosmological constant. It has been found that in addition to the Van der Waals (VdW) like phase transition, the so-called reentrant phase transition (RPT) can occur as well.

The influence of noncommutativity on the local stability of the accelerating (un)charged Schwarzschild black hole is what we aim to investigate. It results in the C-metric description of accelerating Schwarzschild black hole. Such a notion describes a pair of separated black holes that accelerate in opposite directions under the action of forces represented by conical singularities. However, the impact of spatial noncommutativity on the thermodynamic properties of an accelerating (un)charged Schwarzschild black hole is explored by analyzing the Gaussian distribution of mass and charge densities, reflecting the smearing effects due to noncommutative geometry. We begin the study with the uncharged case, examining the influence of noncommutativity and acceleration. This approach highlights how these parameters jointly modify the temperature, entropy, and heat capacity of the black hole, deviating from classical thermodynamics. Next, the charged case is considered, introducing additional complexity as charge density now interacts with both noncommutativity and acceleration. This scenario reveals further modifications in the black hole’s thermodynamic behavior. The effects of noncommutativity and acceleration are reexamined, revealing further interactions and modifications of the black hole’s thermodynamic properties. By addressing these two cases sequentially, the paper offers new insights into black holes in noncommutative and accelerated geometries.

The dynamic behaviors of the new soliton in the improved Davydov model in the protein molecules at biological temperature have been numerically simulated by utilizing the dynamic equations for the bio-energy transport and the Runge–Kutta way. In this simulation the influences of the temperature and structure disorders of the protein molecules on the soliton transporting the bio-energy have been completely considered. We find that the new soliton is quite stable in the cases of motion of a long time of 300 ps and of disorders of the structures of the proteins at biological temperatures of 300 K–320 K. The disorders of the structures contain the disorder of mass sequence of amino acids and the fluctuations of the coupling constant, force constant and dipole- dipole interaction constant and ground state energy of the proteins, designating the features of its structure and interactions between the particles in it. However, the soliton disperses in the cases of higher temperature of 325 K and larger structure disorders. The numerical results show that the new soliton is very robust against the influences of the thermal perturbation and structure disorders at biological temperature 300 K, its lifetime and critical temperature are at least 300 ps at 300 K and 320 K, respectively. These results are also consistent with analytical data.

The grain growth kinetics of nanocrystalline copper thin film samples was investigated. The grain size of nanocrystalline copper samples was determined from the broadening of X-ray spectra. It was found that the grain size increased linearly with isothermal annealing time within the first 10 minutes, beyond which power-law growth kinetics is applied. The activation energy for grain growth was determined by constructing an Arrhenius plot, which shows an activation energy of about 21 – 30 kJ/mol. The low activation energy is attributed to the second phase particle drag and the porosity drag, which act as the pinning force for grain growth in nanocrystalline copper.

The thermal stability of low dose Ga⁺ ion-irradiated IrMn/CoFe/AlO_x/CoFe magnetic tunnel junction (MTJ) was investigated using a vibrating sample magnetometer at room temperature and compared with that of the non-irradiated one. The results show that not only does the loop become broad both in the pinned FM layer and in the free FM layer but also there is an obvious larger shift in the pinned FM layer after irradiated at a dose of 1×10¹³ions/cm²Ga⁺ ions. The training effect becomes more legible after performing a low dose irradiation. In both the non-irradiated and the low dose Ga⁺ irradiated MTJs the thermal activation has been observed and holding the films at negative saturation of the pinned FM layer for up to 28 h results in a decrease of the exchange bias field (H_ex). However, the absolute value of H_ex of the irradiated MTJ is always larger than that of the non-irradiated one in the experimental period of time, although the H_ex of the irradiated MTJ decreases a little faster.

In this paper, the effect of minor element addition on the initial structural evolution during crystallization in a simple binary Cu–Zr bulk metallic glass (BMG) forming liquid has been investigated by using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Despite no changes in the completely crystallized products, the remarkable opposite impacts on the supercooled liquid region (SLR) and crystallization reaction rate constant $K_{\mathrm{\text{cr}}}$ are observed as a result of minor selective additions of an affine element, i.e., Sn and an immiscible element, i.e., Nb into the Cu–Zr BMG alloy, respectively. Furthermore, it is demonstrated that the primary devitrification pathway and crystalline phases are simultaneously modified, which leads to significant changes in kinetics of atomic rearrangement and thus thermal stability of this material. Such a finding offers a promising way to control the type of primary crystalline phases of BMG-forming metallic supercooled liquids to synthesize novel BMGs or BMG matrix composites for structural or functional applications.

The effect of compressive deformation on thermal stability and corrosive property of Zr${}_{61.7}$Al₈Ni${}_{13}$Cu${}_{17}$Sn${}_{0.3}$ bulk metallic glass with a strain of 80% was investigated in this work. The corresponding thermal stability is found to decrease after deformation and this can probably be attributed to the reduction of the viscosity and the increase of the Gibbs free energy after compressive deformation. In addition, the corrosion current density increases and this suggests that the corrosion resistance decreases for the deformed sample in comparison with the as-cast sample.

The effect of long-term room temperature ageing on structure and thermal stability of as-cast and inhomogeneously deformed Pd${}_{40}$Ni${}_{40}$P${}_{20}$ metallic glass has been investigated. It is found that the first crystallization peak temperature decreases and this indicates that the thermal stability decreases after ageing for these as-cast and inhomogeneously deformed metallic glass samples. The high density of shear bands formed after deformation disappears and nanocrystallization has been observed after ageing for the inhomogeneously deformed Pd${}_{40}$Ni${}_{40}$P${}_{20}$ metallic glass.

In this paper, NaYGeO₄:$x$Bi${}^{3+}$ phosphors were successfully prepared by high-temperature solid-state reaction. XRD patterns and refinement results show that Bi${}^{3+}$ ions are successfully incorporated into the matrix material and replaced by Y${}^{3+}$. The emission spectrum shows that the optimal doping concentration of the sample is 0.25%, and it is theoretically studied that the concentration quenching is caused by the nearest neighbor ions. The fluorescence lifetime curve showed that with the increase of Bi${}^{3+}$ concentration, the fluorescence lifetime first increased and then decreased. The thermal stability of the sample was studied, and it was found that when the temperature increased to 523 K, the luminescence intensity of the phosphor was still 70% of the initial intensity, and the activation energy was calculated to be 0.306 eV. Finally, the CIE color coordinates of the sample with the best luminous intensity were calculated as (0.1595, 0.0342), and the color coordinates are located in the blue light region.