On the Divergence of Perturbation Theory: Steps Towards a Convergent Series

The mechanism underlying the divergence of perturbation theory is exposed. This is done through a detailed study of the violation of the hypothesis of the Dominated Convergence Theorem of Lebesgue using familiar techniques of Quantum Field Theory. That theorem governs the validity (or lack of it) of the formal manipulations done to generate the perturbative series in the functional integral formalism. The aspects of the perturbative series that need to be modified to obtain a convergent series are presented. Useful tools for a practical implementation of these modifications are developed. Some resummation methods are analyzed in the light of the above mentioned mechanism

Three-dimensional Ising critical behavior in R0.6Sr0.4MnO3(R=Pr,Nd) manganites

Magnetic as well as calorimetric measurements have been performed on single crystal samples of Pr0.6Sr0.4MnO3 and Nd0.6Sr0.4MnO3 to develop a complete critical behavior study of the paramagnetic to ferromagnetic transition in both manganites. The critical exponents α,β,γ , and δ have been independently obtained. For Pr0.6Sr0.4MnO3, these are α = 0.09, β = 0.312, γ = 1.106, and δ = 4.545, while for Nd0.6Sr0.4MnO3 they are α = 0.11, β = 0.308, γ = 1.172, and δ = 4.75. All these values agree with the three-dimensional (3D)-Ising universality class (α = 0.11, β = 0.3265, γ = 1.237, and δ = 4.79) and are very far away from any other known universality class. This suggests the presence of magnetocrystalline anisotropies in the system that must be taken into account to fully describe the magnetism of these manganites, which deviates from a simple double exchange model

Presurgical diagnosis of diffuse gliomas in adults:Post-WHO 2021 practical perspectives from radiologists in neuro-oncology units

The 2021 World Health Organization classification of CNS tumours was greeted with enthusiasm as well as an initial potential overwhelm. However, with time and experience, our understanding of its key aspects has notably improved. Using our collective expertise gained in neuro-oncology units in hospitals in different countries, we have compiled a practical guide for radiologists that clarifies the classification criteria for diffuse gliomas in adults. Its format is clear and concise to facilitate its incorporation into everyday clinical practice. The document includes a historical overview of the classifications and highlights the most important recent additions. It describes the main types in detail with an emphasis on their appearance on imaging. The authors also address the most debated issues in recent years. It will better prepare radiologists to conduct accurate presurgical diagnoses and collaborate effectively in clinical decision making, thus impacting decisions on treatment, prognosis, and overall patient care.</p

Presurgical diagnosis of diffuse gliomas in adults:Post-WHO 2021 practical perspectives from radiologists in neuro-oncology units

The 2021 World Health Organization classification of CNS tumours was greeted with enthusiasm as well as an initial potential overwhelm. However, with time and experience, our understanding of its key aspects has notably improved. Using our collective expertise gained in neuro-oncology units in hospitals in different countries, we have compiled a practical guide for radiologists that clarifies the classification criteria for diffuse gliomas in adults. Its format is clear and concise to facilitate its incorporation into everyday clinical practice. The document includes a historical overview of the classifications and highlights the most important recent additions. It describes the main types in detail with an emphasis on their appearance on imaging. The authors also address the most debated issues in recent years. It will better prepare radiologists to conduct accurate presurgical diagnoses and collaborate effectively in clinical decision making, thus impacting decisions on treatment, prognosis, and overall patient care.</p

Critical behavior study of the spin ordering transition in RVO3 (R = Ce, Pr, Nd, Sm, Gd, Er) by means of ac photopyroelectric calorimetry

The thermal diffusivity of RVO3 single crystals (R = Ce, Pr, Nd, Sm, Gd, and Er) has been measured with an ac photopyroelectric calorimetry in the region in which the G-type orbital ordering and C-type spin ordering take place. Detailed measurements in the close neighbourhood of the spin ordering temperature have allowed to extract the critical parameter α and the critical ratio A+/A− for this transition. While the samples containing Ce, Nd, Sm and Er belong to the 3D-XY universality class (showing that the spins have an easy plane anisotropy), the sample with Gd, which is known to present a clear easy axis, belongs to the 3D-Ising class. Finally, PrVO3 shows an effective isotropic behavior, as the critical parameters found agree with the 3D-Heisenberg class