Homogeneous spin Riemannian manifolds with the simplest Dirac operator

We show the existence of nonsymmetric homogeneous spin Riemannian manifolds whose Dirac operator is like that on a Riemannian symmetric spin space. Such manifolds are exactly the homogeneous spin Riemannian manifolds $(M,g)$ which are traceless cyclic with respect to some quotient expression $M=G/K$ and reductive decomposition $\mathfrak{g} = \mathfrak{k} \oplus \mathfrak{m}$. Using transversally symmetric fibrations of noncompact type, we give a list of them

Más allá de la tipología. Herramientas para un enfoque funcional de la cerámica protohistórica

La necessitat de superar les tipologies tradicionals s'ha posat de manifest en els últims anys arran del plantejament de noves problemàtiques arqueològiques que requereixen analitzar la ceràmica com una eina. L'estudi funcional dels conjunts ceràmics, no obstant això, ha de resoldre el problema de la relació entre formes ceràmiques concretes, mides, mòduls i funcions precises, i avaluar la possibilitat de determinar aquestes a través de l'arqueologia. Fins ara, la falta d'una metodologia sistemàtica i de pautes per a la seva aplicació a conjunts reals han estat els principals esculls. L'objectiu d'aquest treball és respondre a aquest desafiament proposant una seqüència metodològica que implica un enfocament global de la funcionalitat de la ceràmica protohistòrica, capaç d'oferir una alta potencialitat interpretativa. Lluny de constituir un exercici teòric, aquesta proposta inclou un esquema d'aplicació a diferents conjunts procedents del Castro de Capote (Higuera la Real, Badajoz), aixi com una perspectiva sobre les implicacions d'aquest tipus d’anàlisis en l’ investigació arqueològica.The need to overcome traditional typologies has become evident in the last few years due to the rising of new archaeological issues that require analyzing pottery as a tool. The study of function in pottery assemblages, however, must solve the problem regarding the relationship between specific forms, sizes, modules and precise functions; and evaluate the possibility of determining such functions through archaeological studies. Until now, the lack of a systematic method and guidelines to apply it have been the main obstacles. The aim of this paper is to respond to this challenge by proposing a methodological sequence that implies a global approach to the function of protohistorical pottery, offering a high interpretative potential. Far from being a theoretical exercise, this proposal includes a scheme of application on different pottery assemblages from Castro de Capote (Higuera la Real, Badajoz), as well as a perspective of the implication of this kind of analysis in archaeological research.La necesidad de superar las tipologías tradicionales se ha puesto de manifiesto en los últimos años a raíz del planteamiento de nuevas problemáticas arqueológicas que requieren analizar la cerámica como una herramienta. El estudio funcional de los conjuntos cerámicos, no obstante, debe resolver el problema de la relación entre formas cerámicas concretas, tamaños, módulos y funciones precisas, y evaluar la posibilidad de determinar éstas a través de la arqueología. Hasta ahora, la falta de una metodología sistemática y de pautas para su aplicación a conjuntos reales han sido los principales escollos. El objetivo de este trabajo es responder a este desafío proponiendo una secuencia metodológica que implica un enfoque global de la funcionalidad de la cerámica protohistórica, capaz de ofrecer una alta potencialidad interpretativa. Lejos de constituir un ejercicio teórico, esta propuesta incluye un esquema de aplicación a diferentes conjuntos procedentes del Castro de Capote (Higuera la Real, Badajoz), así como una perspectiva sobre las implicaciones de este tipo de análisis en la investigación arqueológica

Improved thermal isolation of silicon suspended platforms for an all-silicon thermoelectric microgenerator based on large scale integration of Si nanowires as thermoelectric material

Special suspended micro-platforms have been designed as a part of silicon compatible planar thermoelectric microgenerators. Bottom-up grown silicon nanowires are going to bridge in the future such platforms to the surrounding silicon bulk rim. They will act as thermoelectric material thus configuring an all-silicon thermoelectric device. In the new platform design other additional bridging elements (usually auxiliary support silicon beams) are substituted by low conductance thin film dielectric membranes in order to maximize the temperature difference developed between both areas. These membranes follow a sieve-like design that allows fabricating them with a short additional wet anisotropic etch step. © Published under licence by IOP Publishing Ltd.Peer ReviewedPostprint (published version

The canonical 8-form on manifolds with holonomy group Spin(9)

An explicit expression of the canonical 8-form on a Riemannian manifold with a Spin(9)-structure, in terms of the nine local symmetric involutions involved, is given. The list of explicit expressions of all the canonical forms related to Berger's list of holonomy groups is thus completed. Moreover, some results on Spin(9)-structures as G-structures defined by a tensor and on the curvature tensor of the Cayley planes, are obtained

Fluorescence in quantum dynamics: accurate spectra require post-mean-field approaches

Real time modeling of fluorescence with vibronic resolution entails the representation of the light–matter interaction coupled to a quantum-mechanical description of the phonons and is therefore a challenging problem. In this work, taking advantage of the difference in timescales characterizing internal conversion and radiative relaxation—which allows us to decouple these two phenomena by sequentially modeling one after the other—we simulate the electron dynamics of fluorescence through a master equation derived from the Redfield formalism. Moreover, we explore the use of a recent semiclassical dissipative equation of motion [C. M. Bustamante et al., Phys. Rev. Lett. 126, 087401 (2021)], termed coherent electron electric-field dynamics (CEED), to describe the radiative stage. By comparing the results with those from the full quantum-electrodynamics treatment, we find that the semiclassical model does not reproduce the right amplitudes in the emission spectra when the radiative process involves the de-excitation to a manifold of closely lying states. We argue that this flaw is inherent to any mean-field approach and is the case with CEED. This effect is critical for the study of light–matter interaction, and this work is, to our knowledge, the first one to report this problem. We note that CEED reproduces the correct frequencies in agreement with quantum electrodynamics. This is a major asset of the semiclassical model, since the emission peak positions will be predicted correctly without any prior assumption about the nature of the molecular Hamiltonian. This is not so for the quantum electrodynamics approach, where access to the spectral information relies on knowledge of the Hamiltonian eigenvalues

The population of deformed bands in 48^{48}Cr by emission of 8^{8}Be from the 32^{32}S + 24^{24}Mg reaction

Using particle-$\gamma$ coincidences we have studied the population of final states after the emission of 2 $\alpha$-particles and of $^{8}$Be in nuclei formed in $^{32}$S+$^{24}$Mg reactions at an energy of $\textrm{E}_{\rm L}(^{32}\textrm{S}) = 130 {\rm MeV}$. The data were obtained in a setup consisting of the GASP $\gamma$-ray detection array and the multidetector array ISIS. Particle identification is obtained from the $\Delta$E and E signals of the ISIS silicon detector telescopes, the $^{8}$Be being identified by the instantaneous pile up of the $\Delta$E and E pulses. $\gamma$-ray decays of the $^{48}$Cr nucleus are identified with coincidences set on 2 $\alpha$-particles and on $^{8}$Be. Some transitions of the side-band with $K^\pi=4^{-}$ show stronger population for $^{8}$Be emission relative to that of 2 $\alpha$-particles (by a factor $1.5-1.8$). This observation is interpreted as due to an enhanced emission of $^{8}$Be into a more deformed nucleus. Calculations based on the extended Hauser-Feshbach compound decay formalism confirm this observation quantitatively.Comment: 17 pages, 9 figures accepted for publication in J. Phys.

Dissipative equation of motion for electromagnetic radiation in quantum dynamics

The dynamical description of the radiative decay of an electronically excited state in realistic many-particle systems is an unresolved challenge. In the present investigation electromagnetic radiation of the charge density is approximated as the power dissipated by a classical dipole, to cast the emission in closed form as a unitary single-electron theory. This results in a formalism of unprecedented efficiency, critical for ab initio modeling, which exhibits at the same time remarkable properties: it quantitatively predicts decay rates, natural broadening, and absorption intensities. Exquisitely accurate excitation lifetimes are obtained from time-dependent DFT simulations for C2+, B+, and Be, of 0.565, 0.831, and 1.97 ns, respectively, in accord with experimental values of 0.57±0.02, 0.86±0.07, and 1.77–2.5 ns. Hence, the present development expands the frontiers of quantum dynamics, bringing within reach first-principles simulations of a wealth of photophysical phenomena, from fluorescence to time-resolved spectroscopies