Proof‐of‐Concept Studies Directed toward the Formation of Metallic Ag Nanostructures from Ag3PO4 Induced by Electron Beam and Femtosecond Laser

In this work, for the first time, the instantaneous nucleation and growth processes of Ag nanoparticles on Ag₃PO₄ mediated by femtosecond laser pulses are reported and analyzed. The investigated samples are pure Ag₃PO₄ sample, electron‐irradiated Ag₃PO₄ sample, and laser‐irradiated sample. Complete characterization of the samples is performed using X‐ray diffraction (XRD), Rietveld refinements, field emission scanning electron microscopy, and energy dispersive spectroscopy (EDS). XRD confirms that the irradiated surface layer remains crystalline, and according to EDS analysis, the surface particles are composed primarily of Ag nanoparticles. This method not only offers a one‐step route to synthesize Ag nanoparticles using laser‐assisted irradiation with particle size control, but also reports a complex process involving the formation and subsequent growth of Ag nanoparticles through an unexpected additive‐free in situ fabrication process.     

A Numerical Investigation of the Pinning Phenomenon in Quasi-Periodic Frenkel Kontrova Model Under an External Force

We derive the relativistic Vlasov equation from quantum Hartree dynamics for fermions with relativistic dispersion in the mean-field scaling, which is naturally linked with an effective semiclassic limit. Similar results in the non-relativistic setting have been recently obtained in Benedikter et al. (Arch Rat Mech Anal 221(1): 273–334, 2016). The new challenge that we have to face here, in the relativistic setting, consists in controlling the difference between the quantum kinetic energy and the relativistic transport term appearing in the Vlasov equation.     

Running vacuum in the Universe and the time variation of the fundamental constants of Nature

We compute the time variation of the fundamental constants (such as the ratio of the proton mass to the electron mass, the strong coupling constant, the fine-structure constant and Newton’s constant) within the context of the so-called running vacuum models (RVMs) of the cosmic evolution. Recently, compelling evidence has been provided that these models are able to fit the main cosmological data (SNIa+BAO+H(z)+LSS+BBN+CMB) significantly better than the concordance \(\Lambda \)CDM model. Specifically, the vacuum parameters of the RVM (i.e. those responsible for the dynamics of the vacuum energy) prove to be nonzero at a confidence level \({\gtrsim } 3\sigma \). Here we use such remarkable status of the RVMs to make definite predictions on the cosmic time variation of the fundamental constants. It turns out that the predicted variations are close to the present observational limits. Furthermore, we find that the time evolution of the dark matter particle masses should be crucially involved in the total mass variation of our Universe. A positive measurement of this kind of effects could be interpreted as strong support to the “micro–macro connection” (viz. the dynamical feedback between the evolution of the cosmological parameters and the time variation of the fundamental constants of the microscopic world), previously proposed by two of us (HF and JS).     

Nonautonomous Linear-Quadratic Dissipative Control Processes Without Uniform Null Controllability

In this paper the dissipativity of a family of linear-quadratic control processes is studied. The application of the Pontryagin Maximum Principle to this problem gives rise to a family of linear Hamiltonian systems for which the existence of an exponential dichotomy is assumed, but no condition of controllability is imposed. As a consequence, some of the systems of this family could be abnormal. Sufficient conditions for the dissipativity of the processes are provided assuming the existence of global positive solutions of the Riccati equation induced by the family of linear Hamiltonian systems or by a convenient disconjugate perturbation of it.     

Exclusion Process with Slow Boundary

We study the hydrodynamic and the hydrostatic behavior of the simple symmetric exclusion process with slow boundary. The term slow boundary means that particles can be born or die at the boundary sites, at a rate proportional to \(N^{-\theta }\), where \(\theta > 0\) and N is the scaling parameter. In the bulk, the particles exchange rate is equal to 1. In the hydrostatic scenario, we obtain three different linear profiles, depending on the value of the parameter \(\theta \); in the hydrodynamic scenario, we obtain that the time evolution of the spatial density of particles, in the diffusive scaling, is given by the weak solution of the heat equation, with boundary conditions that depend on \( \theta \). If \(\theta \in (0,1)\), we get Dirichlet boundary conditions, (which is the same behavior if \(\theta =0\), see Farfán in Hydrostatics, statical and dynamical large deviations of boundary driven gradient symmetric exclusion processes, 2008); if \(\theta =1\), we get Robin boundary conditions; and, if \(\theta \in (1,\infty )\), we get Neumann boundary conditions.     

Line energy,line tension and drop size

The relation between drop radius, r, the force to move the three phase contact line and the advancing and receding contact angles θ_A and θ_R is studied. To keep the line energy (energy per 2πr, also named line tension) independent of r, the modified Young equation predicts that the advancing and receding contact angles, θ_A and θ_R, change considerably with r. As shown by many investigators, θ_A and θ_R change negligibly, if at all, with r. We quantify recent evidences showing that the line energy is a function of the Laplace pressure and show that this way the modified Young equation is correct and still θ_A and θ_R should hardly change with r. According to our model, the small surface deformation associated with the unsatisfied normal component of the Young equation results in higher intermolecular interactions at the three phase contact line which corresponds to a higher retention force. This time increasing effect is supported by recent experiments.     

Oxygen adsorption and surface segregation in (2 1 1) surfaces of Pt(shell)/M(core) and Pt3M (M = Co,Ir) alloys

Density functional theory is used to study oxygen adsorption and its effect on surface segregation in (2 1 1) surfaces of Pt(shell)/M(core) and Pt₃M (M = Co, Ir) alloys. It is found that the most energetically favorable oxygen adsorption site is the bridge site over and parallel to the (1 0 0) step. Surface segregation phenomena is observed in Pt₃Co, Pt₃Ir and Pt/Co(core) systems. The Pt/Ir(core) structure was the only one, among the studied systems, that showed antisegregation behavior even in presence of oxygen adsorbed.     

The QCD spin chain S matrix

Beisert et al. have identified an integrable SU(2,2)$\mathit{SU}(2,2)$ quantum spin chain which gives the one-loop anomalous dimensions of certain operators in large Nc$N_c$ QCD. We derive a set of nonlinear integral equations (NLIEs) for this model, and compute the scattering matrix of the various (in particular, magnon) excitations.     

The Influence of Propolis on Dental Plaque Reduction and the Correlation between Dental Plaque and Severity of COVID-19 Complications—A Literature Review

Current studies suggest that cariogenic bacteria in dental plaque influence the severity of COVID-19 complications since the oral cavity is a reservoir for respiratory pathogens potentially responsible for the development of hospital-acquired pneumonia. This article focuses on the association between dental plaque and COVID-19 concerning the influence of altered oral biofilm on the risk of increased severity of SARS-CoV-2 infection. Moreover, it concentrates on the usefulness of propolis, with its apitherapeutic antibacterial properties, for treating oral bacterial infections co-occurring with SARS-CoV-2 infection. A review of the literature on PubMed, Cochrane Library and Medline between 2000 and 2021 revealed 56 published articles indicating that a link between dental plaque and COVID-19 complications was probable. Furthermore, they indicated that propolis may minimize COVID-19 severity by reducing dental plaque accumulation. The possibility that improved oral health could reduce the risk of COVID-19 complications should be of interest to scientists.     

On the importance of thermo-elastic cooling in the fracture of glassy polymers at high rates

In a previous thermo-mechanical analysis [Estevez, R., Basu, S., van der Giessen, E., 2005. Analysis of temperature effects near mode I cracks in glassy polymers. Int. J. Fract. 132, 249–273] in which shear yielding of the bulk and failure by crazing were accounted for, we examined which of these two viscoplastic processes contributed to heat in mode I fracture. The present study completes this work by investigating the conditions for thermo-elastic cooling prior to crack propagation as reported experimentally by Rittel [Rittel, D., 1998. Experimental investigation of transient thermo-elastic effects in dynamic fracture. Int. J. Solids Struct. 35, 2959–2973] and Bougaut and Rittel [Bougaut, O., Rittel, D., 2001. On crack tip cooling during dynamic crack propagation. Int. J. Solids Struct. 38, 2517–2532] on high strain rate loading of PMMA. To this end, coupled thermo-mechanical finite element simulations are carried out by accounting for the thermo-elastic source, in addition to the heat sources related to shear yielding and crazing. The bulk as well as cohesive zone parameters for crazing realistically describe PMMA as they are obtained from detailed calibration experiments. Our results show that if significant thermo-elastic cooling has to be observed in the vicinity of the crack tip of a polymeric material, suppression of shear yielding as well as suppression of crazing is necessary. It seems that at these high strain rates a brittle fracture mechanism activated at very high stresses takes over from crazing, or at least that craze initiation occurs for stress levels very different to those for quasi-static conditions.